Somatic capillaries. Capillaries: continuous, fenestrated, sinusoidal. Venules are divided into

Instructions for studying microslides

A. Vessels of the MCR. Arterioles, capillaries, venules.

Staining: hematoxylin-eosin.

In order to determine the relationship between the links of the microvasculature, it is necessary to color and examine a total, film preparation, where the vessels are visible not in a section, but as a whole. We select an area with small vessels on the preparation so that their connection with the capillaries is visible.

Arterioles, as the first link of the microvasculature, are recognizable by the characteristic arrangement of smooth myocytes. Light elongated oval nuclei of endothelial cells are visible through the wall of the arteriole. Their long axis coincides with the course of the arteriole.

Venules have a thinner wall, darker endothelial cell nuclei, and several rows of red red blood cells in the lumen.

Capillaries – thin vessels, have the smallest diameter and the thinnest wall, which includes one layer of endothelial cells. Red blood cells are located in the lumen of the capillary in one row. You can also see where capillaries depart from arterioles and where capillaries flow into venules. Between the vessels there is loose fibrous connective tissue of a typical structure.

1. On the electron diffraction pattern of the capillary, fenestrae in the endothelium and pores in the basement membrane are clearly visible. Name the type of capillary.

A. Sine wave.

B. Somatic.

C. Visceral.

D. Atypical.

E. Shunt.

2. I.M. Sechenov called arterioles the “faucets” of the cardiovascular system. What structural elements provide this function of arterioles?

A. Circular myocytes.

B. Longitudinal myocytes.

C. Elastic fibers.

D. Longitudinal muscle fibers.

E. Circular muscle fibers.

3. An electron micrograph of a capillary with a wide lumen clearly shows fenestrae in the endothelium and pores in the basement membrane. Determine the type of capillary.

A. Sine wave.

B. Somatic.

C. Atypical.

D. Shunt.

E. Visceral.

4. The presence of what type of capillaries is characteristic of the microvasculature of human hematopoietic organs?

A. Perforated.

B. Fenestrated.

C. Somatic.

D. Sinusoidal.

5. B histological specimen Vessels are found that begin blindly, have the appearance of flattened endothelial tubes, do not contain a basement membrane and pericytes, the endothelium of these vessels is fixed by tropic philants to the collagen fibers of the connective tissue. What vessels are these?

A. Lymphocapillaries.

B. Hemocapillaries.

C. Arterioles.

D. Venules.

E. Arteriolo-venular anastomoses.

6. The capillary is characterized by the presence of fenestrated epithelium and a porous basement membrane. Type of this capillary:

A. Sine wave.

B. Somatic.

C. Visceral.

D. Lacunar.

E. Lymphatic.

7. Name a vessel of the microvasculature in which the subendothelial layer in the inner lining is weakly expressed and the internal elastic membrane is very thin. The middle membrane is formed by 1-2 layers of spirally directed smooth myocytes.

A. Arteriole.

B. Venula.

C. Capillary of somatic type.

D. Fenestrated capillary.

E. Sinusoidal type capillary.

8. Which vessels have the largest total surface area, which creates optimal conditions for two-way exchange of substances between tissues and blood?

A. Capillaries.

B. Arteries.

D. Arterioles.

E. Venulach.

9. An electron micrograph of a capillary with a wide lumen clearly shows fenestrae in the endothelium and pores in the basement membrane. Determine the type of capillary.

A. Sinusoidal.

B. Somatic.

C. Atypical.

D. Shunt.

E. Visceral.

Appendix P

(required)

Histofunctional features of MCR vessels

in questions and answers

1. What functional units of the ICR are distinguished?

A. The link in which the regulation of blood flow to the organs occurs. It is represented by arterioles, metarterioles, and precapillaries. All of these vessels contain sphincters, the main components of which are circularly located SMCs.

B. Another link is the vessels, which are responsible for the metabolism of substances and gases in the tissues. Such vessels are capillaries. The third link is the vessels that provide the drainage and storage function of the MCR. These include venules.

2. What are the structural features of arterioles?

Each membrane consists of one layer of cells. Myocytes in the tunica media form an inclined spiral, located at an angle of more than 45 degrees. Myoendothelial contacts are formed between myocytes and the endothelium. Arterioles do not have an elastic membrane.

3. What are the histofunctional features of precapillaries?

Myocytes along the precapillary are located at a considerable distance. Where precapillaries depart from arterioles and where precapillaries branch into capillaries, there are sphincters in which SMCs are located circularly. Sphincters provide selective distribution of blood between the exchange links of the MCR. It should also be noted that the lumen of open precapillaries is smaller than capillaries, which can be compared to the bottleneck effect.

4. What are the histofunctional features of arteriolo-venular anastomoses? (addition 7 drawing 3)

There are two groups of anastomoses:

1) true (shunts);

2) atypical (half shunts).

Flows through true shunts arterial blood. According to their structure, true shunts are:

1) simple, where there are no additional contractile apparatuses, that is, regulation of blood flow is carried out by the SMC of the middle tunic of the arteriole;

2) with special contractile apparatuses in the form of rolls or pads in the subendothelial layer, which protrude into the lumen of the vessel.

Mixed blood flows through atypical (half shunts). In structure, they are a connection of an arteriole and a venule through a short capillary, the diameter of which is up to 30 microns.

Arteriolo-venular anastomoses take part in the regulation of blood supply to organs, local and general blood pressure, and in the mobilization of blood deposited in venules.

A significant role of ABA in the body’s compensatory reactions during circulatory disorders and the development of pathological processes.

5. What are the structural basis of hemato-tissue interaction?

The main component of hemato-tissue interaction is the endothelium, which is a selective barrier and is also adapted to metabolism. In addition, control of transcellular and intracellular transport is ensured by the multimembrane principle of cell organization and the dynamic properties of cell membranes.

Appendix 2. Table 1– Types of capillaries

Types of capillaries	Structure	Localization
1. Somatic	d = 4.5 – 7 µm The endothelium is continuous (ordinary), the basement membrane is continuous	Muscles, lungs, skin, central nervous system, exocrine glands, thymus.
2. Fenestrated (visceral)	d = 7 – 20 µm Fenestrated endothelium and continuous basement membrane	Renal glomeruli, endocrine organs, gastrointestinal mucosa, choroid plexus of the brain
3. Sinusoidal	d = 20 -40 µm Vendothelia have gaps between cells and the basement membrane is perforated	Liver, hematopoietic organs and adrenal cortex

Appendix 3. Table 2 - Types of venules

Types of venules	Structure
Post-capillary	d =12 – 30 µm. More pericytes than in capillaries. Vorganakh immune system have high endothelium	1. Return of blood cells from tissues. 2. Drainage. 3. Removal of poisons and metabolites. 4. Blood deposition. 5. Immunological (recirculation of lymphocytes). 6. Participation in the implementation of nervous and endocrine influences on metabolism and blood flow
Collective	d = 30 – 50 µm.
Muscular	d › 50 µm, up to 100 µm.

Appendix 4

Picture 1–Types of capillaries (scheme according to Yu.I. Afanasyev):

I – hemocapillary with a continuous endothelial lining and basement membrane; II—hemocapillary with fenestrated endothelium and continuous basement membrane; III—hemocapillary with slit-like openings in the endothelium and a discontinuous basement membrane; 1–endotheliocyte; 2–basal membrane; 3–fenestrae; 4–slits (pores); 5–pericyte; 6–adventitial cell; 7–contact between endotheliocyte and pericyte; 8–nerve ending

Appendix 5

Precapillary sphincters

Figure 2–Components of the ICR (according to V. Zweifach):

diagram of blood vessels different types, which form the terminal vascular bed and regulate microcirculation in it.

Appendix 6

Figure 3–Arteriolo-venular anastomoses (ABA) (scheme according to Yu.I. Afanasyev):

I–ABA without a special locking device: I–arteriole; 2–venule; 3–anastomosis; 4-smooth myocytes of anastomosis; II–ABA with a special locking device: A–anastomosis of the locking artery type; B – simple anastomosis of epithelioid type; B – complex anastomosis of epithelioid type (glomerular): G – endothelium; 2–longitudinally arranged bundles of smooth myocytes; 3–internal elastic membrane; 4-arteriole; 5-venule; 6–anastomosis; 7–epithelial cells of the anastomosis; 8-capillaries in the connective tissue membrane; III—atypical anastomosis: 1—arteriole; 2-short hemocapillary; 3-venule

Appendix 8

Figure 4

Appendix 9

Figure 5

Module 3. Special histology.

"Special histology of sensory and regulatory systems"

Lesson topic

"Heart"

Relevance of the topic. Detailed Study morphofunctional characteristics of the heart normally predetermine the possibilities of prevention, early diagnosis structural and functional heart disorders. Knowledge histological features cardiac muscle helps to understand and explain the pathogenesis of heart disease.

General purpose of the lesson. Be able to:

1. Diagnose the structural elements of the heart muscle on microscopic specimens.

Specific goals. Know:

1. Features of the structural and functional organization of the heart.

2. Morphofunctional organization of the conduction system of the heart.

3. Microscopic, ultramicroscopic structure and histophysiology of the heart muscle.

4. The course of embryonic development processes, age-related changes and heart regeneration.

Initial level of knowledge and skills. Know:

1. Macroscopic structure of the heart, its membranes, valves.

2. Morphofunctional organization of the heart muscle (Department of Human Anatomy).

After mastering the necessary basic knowledge, proceed to study the material that you can find in the following sources of information.

A. Basic literature

1. Histology /ed. Yu.I.Afanasyeva, N.A.Yurina. – Moscow: Medicine, 2002. – P. 410–424.

2. Histology /ed. V.G.Eliseeva, Yu.I.Afanasyeva, N.A.Yurinoy - Moscow: Medicine, 1983. - P. 336–345.

3. Atlas of histology and embryology / ed. I.V. Almazova, L.S. Sutulova. – M.: Medicine, 1978.

4. Histology, cytology and embryology (atlas for independent work of students) /ed. Y.B.Chaikovsky, L.M.Sokurenko - Lutsk, 2006.

5. Methodological developments for practical classes: in 2 parts. – Chernivtsi, 1985.

B. Further reading

1. Histology (introduction to pathology) / ed. E.G. Ulumbekova, prof. Yu.A. Chelysheva. – M., 1997. – P. 504–515.

2. Histology, cytology and embryology (atlas) / ed. O.V.Volkova, Yu.K.Eletsky - Moscow: Medicine, 1996. - P. 170–176.

3. Particular human histology /ed. V.L. Bykova. – SOTIS: St. Petersburg, 1997. – pp. 16–19.

B. Lectures on this topic.

Theoretical issues

1. Sources of heart development.

2. general characteristics structure of the heart wall.

3. Micro- and submicroscopic structure of the endocardium and heart valves.

4. Myocardium, micro- and ultrastructures of typical cardiomyocytes. The leading system of the heart.

5. Morphofunctional characteristics of atypical myocytes.

6. The structure of the epicardium.

7. Innervation, blood supply and age-related changes in the heart.

8. Modern ideas about heart regeneration and transplantation.

Brief guidelines for work

during a practical lesson

At the beginning of the lesson, homework will be checked. Then, on your own, you must study a microscopic specimen such as the wall of a bull’s heart. You perform this work according to the algorithm for studying microslides. During independent work You can consult with your teacher regarding any questions regarding microslides.

Technological map of the lesson

	Duration	Means of education	Equipment	Location
Checking and correcting the initial level of knowledge and homework		Tables, drawings, diagrams	Computers	Computer class, training room
Independent work on studying micropreparations, electron diffraction patterns		Instructions for studying micro-preparations of tables, microphotograms, electron-grams	Microscopes, microslides, albums for sketches of microslides	Study room
Analysis of the results of independent work		Microphoto-grams, electron-grams, test set	Computers	Computer class
Summing up the lesson				Study room

To consolidate the material, complete the following tasks:

For the structures indicated by numbers, select descriptions that correspond to them in terms of morphology and function. Name the cell and the designated structures:

a) these structures are located along the muscle fiber and have anisotropic and isotropic stripes (or A and I discs);

b) general-purpose membrane organelles that form and accumulate energy in the form of ATP;

c) a system of components of different shapes that ensures the transport of calcium ions;

d) a system of narrow tubules that branches in the muscle fiber and ensures the transmission of nerve impulses;

e) general-purpose membrane organelles that provide cellular digestion;

f) dark stripes running across the fiber contain three types of intercellular contacts: g) desmosomal; h) nexus; i) adhesive.

Questions for test control

1. What is the main function of the heart?

2. When does the formation of the heart occur?

3. What is the source of endocardial development?

4. What is the source of myocardial development?

5. What is the source of development of the epicardium?

6. When does the formation of the conduction system of the heart begin?

7. What is the name of the inner lining of the heart?

8. Which of the following layers is not part of the endocardium?

9. Which layer of the endocardium contains vessels?

10. How is the endocardium nourished?

11. What cells are there in the subendothelial layer of the endocardium?

12. What tissue forms the basis of the structure of heart valves?

13. What are the heart valves covered with?

14. What does the myocardium consist of?

15. The heart muscle consists of...

16. Myocardium in structure belongs to...

17. How are myocardial muscle fibers formed?

18. What is not characteristic of cardiomyocytes?

19. What is characteristic of the heart muscle?

20. Which lining of the heart consists of cardiomyocytes?

21. What is the source of development of cardiomyocytes?

22. What types are cardiomyocytes divided into?

23. What is not typical for the structure of cardiomyocytes?

24. How do T-tubules of the heart muscle differ from T-tubules skeletal muscles?

25. Why is there no typical pattern of triads in contractile cardiomyocytes?

26. What function do T-tubules of the heart muscle perform?

27. What is not characteristic of atrial cardiomyocytes?

28. Where is natriuretic factor synthesized?

29. What is the significance of atrial natriuretic factor?

30. What is the significance of insertion disks?

31. What intercellular connections are located in the areas of intercalary discs?

32. What function do desmosomal contacts perform?

33. What is the function of gap contacts?

34. What cells form the second type of myocardial myocytes?

35. What is not part of the conduction system of the heart?

36. Which cells are not included in the conductive cardiac myocytes?

37. What function do pacemaker cells perform?

38. Where are pacemaker cells located?

39.What is not typical for the structure of pacemaker cells?

40. What function do transition cells perform?

41. What function do Purkinje fibers perform?

42. What is not typical for the structure of transitional cells of the conduction system of the heart?

43. What is not typical for the structure of Purkinje fibers?

44. What is the structure of the epicardium?

45. What is the epicardium covered with?

46. ​​Which layer is missing in the epicardium?

47. How does heart muscle regenerate in childhood?

48. How does heart muscle regenerate in adults?

49. What tissue does the pericardium consist of?

50. Epicardium is...

Instructions for studying micropreparations

A. Wall of the heart of a bull

Staining with hematoxylin-eosin.

At low magnification, it is necessary to navigate the membranes of the heart. The endocardium appears as a pink strip covered with endothelium with large purple nuclei. Below it is the subendothelial layer - loose connective tissue, deeper - the muscular-elastic and outer connective tissue layers.

The bulk of the heart is the myocardium. In the myocardium we observe strips of cardiomyocytes, the nuclei of which are located in the center. Anastomoses are distinguished between strips (chains) of cardiomyocytes. Inside the strips (these are functional muscle “fibers”), the cardiomyocytes are connected by intercalary discs. Cardiomyocytes have transverse striations due to the presence of isotropic (light) and anisotropic (dark) disks in the composition of the myofibrils themselves. Between the chains of cardiomyocytes there are light spaces filled with loose fibrous connective tissue.

Directly under the endocardium there are clusters of conducting (atypical) cardiomyocytes. In cross section they have the appearance of large oxyphilic cells. Their sarcoplasm contains fewer myofibrils than contractile cardiomyocytes.

Tasks for the licensing exam "Krok-1"

1. Microscopic specimen shows the wall of the heart. One of the membranes contains contractile and secretory myocytes, endomysium with blood vessels. Which lining of the heart corresponds to these structures?

A. Atrial myocardium.

B. Pericardium.

C. Adventitial membrane.

D. Ventricular endocardium.

2. The laboratory mixed up the labeling of histological preparations of myocardium and skeletal muscles. What structural feature allowed us to identify the myocardial preparation?

A. Peripheral position of the nuclei.

B. Presence of an insertion disk.

C. Absence of myofibrils.

D. Presence of transverse striations.

3. As a result of myocardial infarction, damage to a section of the heart muscle occurs, which is accompanied by massive death of cardiomyocytes. What cellular elements will ensure replacement of the resulting defect in the myocardial structure?

A. Fibroblasts.

B. Cardiomyocytes.

C. Myosatellite cells.

D. Epitheliocytes.

E. Unstriated myocytes.

4. On the histological specimen of the “heart wall”, the main part of the myocardium is formed by cardiomyocytes, which form muscle fibers with the help of intercalary discs. What type of connection provides electrical communication between neighboring cells?

A. Gap contact (Nexus).

B. Desmosome.

C. Hemidesmosoma.

D. Tight contact.

E. Simple contact.

5. The histological specimen shows an organ of the cardiovascular system. One of its shells is formed by fibers that anastomose with each other, consist of cells, and form intercalary discs at the point of contact. The membrane of which organ is represented on the preparation?

A. Hearts.

B. Muscular type arteries.

D. Muscular type veins.

E. Arteries mixed type.

6. There are several membranes in the wall of blood vessels and the wall of the heart. Which of the membranes of the heart is similar in histogenesis and tissue composition to the wall of blood vessels?

A. Endocardium.

B. Myocardium.

S. Pericardium.

D. Epicardium.

E Epicardium and myocardium.

7. On the histological specimen of the “heart wall” under the endocardium, one can see elongated cells with a nucleus at the periphery with a small number of organelles and myofibrils, which are located chaotically. What kind of cells are these?

A. Striated myocytes.

B. Contractile cardiomyocytes.

C. Secretory cardiomyocytes.

D. Smooth myocytes.

E. Conducting cardiomyocytes.

8. As a result of myocardial infarction, heart block occurs: the atria and ventricles contract asynchronously. Damage to which structures causes this phenomenon?

A. Conducting cardiomyocytes of the Hiss bundle.

B. Pacemaker cells of the sinoatrial node.

C. Contractile myocytes of the ventricles.

D. Nerve fibers of the n.vagus.

E. Sympathetic nerve fibers.

9. A patient with endocarditis has a pathology of the valve apparatus. inner shell hearts. What tissues form the heart valves?

A. Dense connective tissue, endothelium.

B. Loose connective tissue, endothelium.

C. Cardiac muscle tissue, endothelium.

D. Hyaline cartilage tissue, endothelium.

E. Elastic cartilage tissue, endothelium.

10. In a patient with pericarditis, serous fluid accumulates in the pericardial cavity. This process is associated with disruption of the activity of which pericardial cells?

A. Mesothelial cells.

B. Endothelial cells.

C. Smooth myocytes.

D. Fibroblasts.

E. Macrophagov

Appendix V

(required)

Conduction system of the heart. Systema conducens cardiacum

The heart is distinguished by an atypical (“conducting”) muscular system. The microanatomy of the cardiac conduction system is shown in Diagram 1. This system is represented by: the sinoatrial node (sinoatrial); atrioventricular node (AV); atrioventricular bundle of Hiss.

There are three types muscle cells, which are found in different proportions in different departments of this system.

The sinus-atrial node is located almost in the wall of the superior vena cava in the area of ​​the venous sinus; in this node, an impulse is formed that determines the automaticity of the heart; its central part is occupied by cells of the first type—pacemakers, or pacemaker cells (P-cells). These cells differ from typical cardiomyocytes in large sizes, polygonal shape, a small number of myofibrils, the sarcoplasmic reticulum is poorly developed, the T-system is absent, there are many pinocytotic vesicles and caveolae. Their cytoplasm has the ability for spontaneous rhythmic polarization and depolarization. The atrioventricular node consists mainly of transitional cells (cells of the second type).

They perform the function of conducting excitation and its transformation (inhibition of rhythm) from P-cells to bundle and contractile cells, but with pathology of the sinoatrial node, its function passes to the atrioventricular one. Their cross section is smaller than the cross section of typical cardiomyocytes. Myofibrils are more developed, oriented parallel to each other, but not always. Individual cells may contain T-tubules. Transitional cells contact each other using both simple contacts and intercalary disks.

The atrioventricular bundle of His consists of a trunk, right and left legs (Purkinje fibers), left leg splits into anterior and posterior branches. The Hiss bundle and Purkinje fibers are represented by cells of the third type, which transmit excitation from transitional cells to contractile cardiomyocytes of the ventricles. In terms of structure, the cells of the bundle are distinguished by their large diameter, almost complete absence of T-systems, thin myofibrils, which are randomly located mainly along the periphery of the cell. The nuclei are located eccentrically.

Purkinje cells are the largest not only in the leading system, but in the entire myocardium. They have a lot of glycogen, a sparse network of myofibrils, and no T-tubules. The cells are connected by nexuses and desmosomes.

Educational edition

Vasko Lyudmila Vitalievna, Kiptenko Lyudmila Ivanovna,

Budko Anna Yurievna, Zhukova Svetlana Vyacheslavovna

Special histology of sensory and

regulatory systems

In two parts

Responsible for the release is Vasko L.V.

Editor T.G. Chernyshova

Computer layout A.A. Kachanova

Signed for publication on July 7, 2010.

Format 60x84/16. Conditional oven l. . Uch. - ed. l. . Circulation

Deputy No. Cost of publication

Publisher and manufacturer Sumy State University

st. Rimsky-Korsakov, 2, Sumy, 40007.

Certificate of the subject of the publishing business DK 3062 dated December 17, 2007.

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Structure of blood vessels Cordially- vascular system(CVS) consists of the heart, blood and lymphatic vessels. Vessels in embryogenesis are formed from mesenchyme. They are formed from the mesenchyme of the marginal zones of the vascular strip of the yolk sac or the mesenchyme of the embryo. In late embryonic development and after birth, vessels are formed by budding from capillaries and post-capillary structures (venules and veins). Blood vessels are divided into great vessels (arteries, veins) and microvasculature vessels (arterioles, precapillaries, capillaries, postcapillaries and venules). In the main vessels, blood flows at high speed and there is no exchange of blood with tissues; in the vessels of the microvasculature, blood flows slowly for better exchange blood with tissues. All organs of the cardiovascular system are hollow and, in addition to the vessels of the microcirculatory system, contain three membranes: 1. The inner membrane (intima) is represented by the internal endothelial layer. Behind it is the subendothelial layer (PBST). The subendothelial layer contains a large number of poorly differentiated cells migrating into the tunica media and delicate reticular and elastic fibers. In muscular-type arteries, the inner tunica is separated from the middle tunica by an internal elastic membrane, which is a collection of elastic fibers. 2. The middle membrane (media) in arteries consists of smooth myocytes arranged in a gentle spiral (almost circular), elastic fibers or elastic membranes (in elastic-type arteries); In the veins, it may contain smooth myocytes (in veins of the muscular type) or predominate connective tissue (veins of the non-muscular type). In veins, unlike arteries, the middle membrane (media) is much thinner compared to the outer membrane (adventitia).

3. Outer shell(adventitia) is formed by RVST. In arteries of the muscular type there is an outer elastic membrane that is thinner than the internal one.

Arteries Arteries have 3 membranes in their wall structure: intima, media, adventitia. Arteries are classified depending on the predominance of elastic or muscular elements on the artery: 1) elastic, 2) muscular and 3) mixed type.

In arteries of elastic and mixed types, in comparison with arteries of muscular type, the subendothelial layer is much thicker. The middle shell in elastic arteries is formed by fenestrated elastic membranes - an accumulation of elastic fibers with zones of their sparse distribution (“windows”). Between them there are layers of PBST with single smooth myocytes and fibroblastic cells. Muscular-type arteries contain many smooth muscle cells. The farther from the heart, the located are the arteries with a predominance of the muscular component: the aorta is of the elastic type, the subclavian artery is of the mixed type, and the brachial artery is of the muscular type. An example of a muscular type is also the femoral artery.

Veins Veins have 3 membranes in their structure: intima, media, adventitia. Veins are divided into 1) non-muscular and 2) muscular (with weak, medium or strong development of the muscular elements of the middle shell). Veins of a muscleless type are located at the level of the head, and vice versa - veins with a strong development of the muscular membrane at lower limbs. Veins with a well-developed muscular layer have valves. Valves are formed by the inner lining of the veins. This distribution of muscle elements is associated with the action of gravity: it is more difficult to lift blood from the legs to the heart than from the head, therefore in the head there is a muscleless type, in the legs there is a highly developed muscle layer(example - femoral vein). The blood supply to the vessels is limited to the outer layers of the tunica media and the adventitia, while in the veins the capillaries reach the inner tunica. Innervation of blood vessels is provided by autonomic afferent and efferent nerve fibers. They form the adventitial plexus. Efferent nerve endings reach mainly the outer regions of the tunica media and are predominantly adrenergic. Afferent nerve endings of baroreceptors that respond to pressure form local subendothelial accumulations in the great vessels.

An important role in the regulation of vascular muscle tone, along with the autonomic nervous system, is played by biologically active substances, including hormones (adrenaline, norepinephrine, acetylcholine, etc.).

Blood capillaries Blood capillaries contain endothelial cells lying on the basement membrane. The endothelium has a metabolic apparatus capable of producing a large number of biologically active factors, including endothelins, nitric oxide, anticoagulant factors, etc., which control vascular tone and vascular permeability. Adventitial cells are closely adjacent to the vessels. Pericytes, which may be involved in membrane cleavage, take part in the formation of capillary basement membranes. Capillaries are distinguished: 1. Somatic type. The lumen diameter is 4-8 microns. The endothelium is continuous, not fenestrated (i.e. not thinned, the fenestra is a window in translation). The basement membrane is continuous and well defined. The pericyte layer is well developed. There are adventitial cells. Such capillaries are located in the skin, muscles, bones (what is referred to as the soma), as well as in organs where cells need to be protected - as part of histohematic barriers (brain, gonads, etc.) 2. Visceral type. Clearance up to 8-12 microns. The endothelium is continuous, fenestrated (in the area of ​​the windows there is practically no cytoplasm of the endothelial cell and its membrane is adjacent directly to the basement membrane). All types of contacts predominate between endothelial cells. The basement membrane is thinned. There are fewer pericytes and adventitial cells. Such capillaries are found in internal organs, such as the kidneys, where urine must be filtered.

3. Sinusoidal type. The lumen diameter is more than 12 microns. The endothelial layer is discontinuous. Endotheliocytes form pores, hatches, fenestrae. The basement membrane is discontinuous or absent. There are no pericytes. Such capillaries are necessary where not only the exchange of substances between blood and tissues occurs, but also “cell exchange”, i.e. in some blood-forming organs (red bone marrow, spleen), or large substances - in the liver.

Arterioles and precapillaries. Arterioles have a lumen diameter of up to 50 microns. Their wall contains 1-2 layers of smooth myocytes. The endothelium is elongated along the vessel. Its surface is smooth. The cells are characterized by a well-developed cytoskeleton, an abundance of desmosomal, hinge, and imbricated contacts. In front of the capillaries, the arteriole narrows and becomes a precapillary. Precapillaries have a thinner wall. The muscular layer is represented by individual smooth myocytes. Postcapillaries and venules. Postcapillaries have a lumen of smaller diameter than that of venules. The structure of the wall is similar to the structure of the venule. Venules have a diameter of up to 100 µm. The inner surface is uneven. The cytoskeleton is less developed. The contacts are mostly simple, butt-to-end. Often the endothelium is higher than in other vessels of the microvasculature. Cells of the leukocyte series penetrate through the wall of the venule, mainly in the areas of intercellular contacts. The outer layers are similar in structure to capillaries. Arteriolo-venular anastomoses.

Blood can flow from the arterial systems to the venous system, bypassing the capillaries, through arteriole-venular anastomoses (AVA). There are true AVA (shunts) and atypical AVA (half-shunts). In half-shunts, the afferent and efferent vessels are connected through a short, wide capillary. As a result, mixed blood enters the venule. In true shunts, there is no exchange between the vessel and the organ, and arterial blood enters the vein. True shunts are divided into simple (one anastomosis) and complex (several anastomoses). It is possible to distinguish shunts without special locking devices (the role of the sphincter is played by smooth myocytes) and with a special contractile apparatus (epithelioid cells, which, when swollen, compress the anastomosis, closing the shunt).

Lymphatic vessels. Lymphatic vessels are represented by microvessels lymphatic system(capillaries and postcapillaries), intraorgan and extraorgan lymphatic vessels. Lymphatic capillaries begin blindly in tissues, contain thin endothelium and a thinned basement membrane.

The wall of medium and large lymphatic vessels contains endothelium, subendothelial layer, muscular layer and adventitia. According to the structure of the membranes, the lymphatic vessel resembles a muscular vein. The inner lining of the lymphatic vessels forms valves, which are an integral attribute of all lymphatic vessels after the capillary section.

Clinical significance. 1. In the body, arteries, especially elastic and muscular-elastic types, are most sensitive to atherosclerosis. This is due to hemodynamics and the diffuse nature of the trophic supply of the inner membrane, its significant development in these arteries. 2. In the veins, the valve apparatus is most developed in the lower extremities. This greatly facilitates the movement of blood against the hydrostatic pressure gradient. Violation of the structure of the valve apparatus leads to gross disruption of hemodynamics, edema and varicose veins of the lower extremities. 3. Hypoxia and low molecular weight products of cell destruction and anaerobic glycolysis are among the most powerful factors stimulating the formation of new blood vessels. Thus, areas of inflammation, hypoxia, etc., are characterized by subsequent rapid growth of microvessels (angiogenesis), which ensures the restoration of the trophic supply of the damaged organ and its regeneration.

4. Antiangiogenic factors that prevent the growth of new vessels, according to a number of modern authors, could become one of the effective antitumor groups of drugs. By blocking the growth of blood vessels into rapidly growing tumors, doctors could thereby cause hypoxia and death of cancer cells.

cytohistology.ru

Particular histology of the cardiovascular system

Vascular development.

The first vessels appear in the second - third week of embryogenesis in yolk sac and chorion. A cluster is formed from the mesenchyme - blood islands. The central cells of the islets round off and become blood stem cells. Peripheral islet cells differentiate into the vascular endothelium. Vessels in the body of the embryo are formed a little later; blood stem cells do not differentiate in these vessels. Primary vessels are similar to capillaries, their further differentiation is determined by hemodynamic factors - pressure and blood flow speed. Initially, a very large part is deposited in the vessels, which is reduced.

Structure of blood vessels.

In the wall of all vessels, 3 membranes can be distinguished:

1. internal

2. average

3. external

Arteries

Depending on the ratio of muscle elastic components, arteries of the following types are distinguished:

Elastic

Large main vessels are the aorta. Pressure – 120-130 mm/Hg/st, blood flow speed – 0.5 1.3 m/sec. The function is transport.

Inner shell:

A) endothelium

flattened polygonal cells

B) subendothelial layer (subendothelial)

It is represented by loose connective tissue and contains stellate-shaped cells that perform combial functions.

Middle shell:

It is represented by fenestrated elastic membranes. Between them a small amount of muscle cells.

Outer shell:

It is represented by loose connective tissue and contains blood vessels and nerve trunks.

Muscular

Arteries of small and medium caliber.

Inner shell:

A) endothelium

B) subendothelial layer

B) internal elastic membrane

Middle shell:

Smooth muscle cells predominate, arranged in a gentle spiral. Between the middle and outer shells is the outer elastic membrane.

Outer shell:

Represented by loose connective tissue

Mixed

Arterioles

Similar to arteries. Function: regulation of blood flow. Sechenov called these vessels the taps of the vascular system.

The middle shell is represented by 1-2 layers of smooth muscle cells.

Capillaries

Classification:

Depending on the diameter:

narrow 4.5-7 microns - muscles, nerves, musculoskeletal tissue

average 8-11 microns – skin, mucous membranes

sinusoidal up to 20-30 microns – endocrine glands, kidneys

lacunae up to 100 microns – found in the corpora cavernosa

Depending on the structure:

Somatic – continuous endothelium and continuous basement membrane – muscles, lungs, central nervous system

Capillary structure:

3 layers, which are analogues of 3 shells:

A) endothelium

B) pericytes enclosed in a basement membrane

B) adventitial cells

2. Finished - have thinning or windows in the endothelium - endocrine organs, kidneys, intestines.

3. perforated - there are through holes in the endothelium and in the basement membrane - hematopoietic organs.

similar to capillaries, but have more pericytes

Classification:

● fibrous (muscleless) type

Found in the spleen, placenta, liver, bones, and meninges. In these veins, the subendothelial layer continues into the surrounding connective tissue

● muscular type

There are three subtypes:

● Depending on the muscle component

A) veins with weak development of muscle elements are located above the level of the heart, blood flows passively due to its heaviness.

B) veins with average development of muscle elements - brachial vein

C) veins with strong development of muscle elements, large veins lying below the level of the heart.

Muscular elements are found in all three membranes

Structure

Inner shell:

Endothelium

The subendothelial layer is a longitudinally directed bundle of muscle cells. A valve is formed behind the inner shell.

Middle shell:

Circularly arranged bundles of muscle cells.

Outer shell:

Loose connective tissue and longitudinally arranged muscle cells.

DEVELOPMENT

The heart is formed at the end of the 3rd week of embryogenesis. Under the visceral leaf of the splanchnotome, an accumulation of mesenchymal cells is formed, which turn into elongated tubes. These mesenchymal accumulations protrude into the cilomic cavity, bending the visceral layers of the splanchnotome. And the areas are myoepicardial plates. Subsequently, the endocardium, myoepicardial plates, myocardium and epicardium are formed from the mesenchyme. The valves develop as a duplicate of the endocardium.

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BSMU

Discipline: Histology | Comment

The importance of the cardiovascular system (CVS) in the life of the body, and therefore the knowledge of all aspects of this area for practical medicine, is so great that the study of this system has been separated into two independent areas, cardiology and angiology. The heart and blood vessels are systems that function not periodically, but constantly, therefore more often than other systems they are susceptible to pathological processes. Currently, cardiovascular diseases, along with oncological diseases, occupies a leading place in mortality. The cardiovascular system ensures the movement of blood throughout the body and regulates the flow of nutrients and oxygen into tissues and removal of metabolic products, blood deposition.

Classification: I. The central organ is the heart. II. Peripheral department: A. Blood vessels: 1. Arterial link: a) arteries of elastic type; b) arteries of the muscular type; c) arteries of mixed type. 2. Microcirculatory bed: a) arterioles; b) hemocapillaries; c) venules; d) arteriole-venular anastomoses 3. Venous link: a) veins of the muscular type (with weak, medium, strong development of muscle elements; b) veins of the non-muscular type. B. Lymphatic vessels: 1. Lymphatic capillaries. 2. Intraorgan lymphatic vessels. 3. Extraorgan lymphatic vessels. In the embryonic period, the first blood vessels are formed in the 2nd week in the wall of the yolk sac from the mesenchyme (see the stage of megaloblastic hematopoiesis on the topic “Hematopoiesis”) - blood islands appear, the peripheral cells of the islet flatten and differentiate into the endothelial lining, and form from the surrounding mesenchyme connective tissue and smooth muscle elements of the vascular wall. Soon, blood vessels are formed from the mesenchyme in the body of the embryo, which connect with the vessels of the yolk sac. Arterial link - represented by vessels through which blood is delivered from the heart to the organs. The term “artery” is translated as “air-containing”, since during autopsy, researchers often found these vessels empty (not containing blood) and thought that vital “pneuma” or air was distributed through them throughout the body. Arteries of elastic, muscular and mixed types have a common principle of structure: there are 3 membranes in the wall - inner, middle and outer adventitia. The inner shell consists of layers: 1. Endothelium on the basement membrane. 2. The subendothelial layer is a snout fibrous tissue with a high content of poorly differentiated cells. 3. Internal elastic membrane - a plexus of elastic fibers. The middle layer contains smooth muscle cells, fibroblasts, elastic and collagen fibers. At the border of the middle and outer adventitia there is an outer elastic membrane - a plexus of elastic fibers. The outer adventitia of the arteries is histologically represented by loose fibrous vascular tissue with vascular vessels and vascular nerves. Features in the structure of types of arteries are due to differences in the hemadynamic conditions of their functioning. Differences in structure mainly concern the middle shell (different ratios of the constituent elements of the shell): 1. Arteries of the elastic type - these include the aortic arch, pulmonary trunk, thoracic and abdominal aorta. Blood enters these vessels in spurts under high pressure and moves at high speed; There is a large pressure drop during the transition from systole to diastole. The main difference from arteries of other types is in the structure of the tunica media: in the tunica media, elastic fibers predominate from the above components (myocytes, fibroblasts, collagen and elastic fibers). Elastic fibers are located not only in the form of individual fibers and plexuses, but also form elastic fenestrated membranes (in adults, the number of elastic membranes reaches up to 50-70 words). Thanks to their increased elasticity, the wall of these arteries not only withstands high pressure, but also smoothes out large differences (jumps) in pressure during the systole-diastole transition. 2. Arteries of the muscular type - these include all arteries of medium and small caliber. A feature of the hemodynamic conditions in these vessels is a drop in pressure and a decrease in blood flow velocity. Arteries of the muscular type differ from arteries of other types by the predominance of myocytes in the middle shell over others structural components; The inner and outer elastic membranes are clearly defined. Myocytes are oriented spirally in relation to the lumen of the vessel and are found even in the outer lining of these arteries. Thanks to the powerful muscular component of the tunica media, these arteries control the intensity of blood flow individual organs, maintain the falling pressure and push blood further, which is why muscular-type arteries are also called the “peripheral heart.”

3. Arteries of mixed type - these include large arteries extending from the aorta (carotid and subclavian arteries). In structure and function they occupy an intermediate position. The main structural feature: in the tunica media, myocytes and elastic fibers are represented approximately equally (1: 1), there is a small amount of collagen fibers and fibroblasts.

The microcirculatory bed is a link located between the arterial and venous links; provides regulation of blood supply to the organ, metabolism between blood and tissues, deposition of blood in organs. Composition: 1. Arterioles (including precapillary). 2. Hemocapillaries. 3. Venules (including postcapillary). 4. Arteriolo-venular anastomoses. Arterioles are vessels connecting arteries with hemocapillaries. They retain the principle of the structure of arteries: they have 3 membranes, but the membranes are weakly expressed - the subendothelial layer of the inner membrane is very thin; the middle shell is represented by one layer of myocytes, and closer to the capillaries - single myocytes. As the diameter in the tunica media increases, the number of myocytes increases; first one, then two or more layers of myocytes are formed. Due to the presence of myocytes in the wall (in the precapillary arterioles in the form of a sphincter), the arterioles regulate the blood supply to the hemocapillaries, thereby the intensity of exchange between the blood and the tissues of the organ. Hemocapillaries. The wall of hemocapillaries has the smallest thickness and consists of 3 components - endothelial cells, basement membrane, pericytes in the thickness of the basement membrane. There are no muscle elements in the capillary wall, however, the diameter of the internal lumen may change somewhat as a result of changes in blood pressure, the ability of the nuclei of pericytes and endothelial cells to swell and contract. The following types of capillaries are distinguished: 1. Type I hemocapillaries (somatic type) - capillaries with continuous endothelium and a continuous basement membrane, diameter 4-7 µm. They are present in skeletal muscles, in the skin and mucous membranes.. 2. Type II hemocapillaries (fenestrated or visceral type) - the basement membrane is solid, the endothelium has fenestrae - thinned areas in the cytoplasm of endothelial cells. Diameter 8-12 microns. They are found in the capillary glomeruli of the kidneys, in the intestines, and in the endocrine glands. 3. Type III hemocapillaries (sinusoidal type) - the basement membrane is not continuous, is absent in places, and gaps remain between the endothelial cells; diameter 20-30 microns or more, not constant throughout - there are expanded and narrowed areas. The blood flow in these capillaries is slowed down. Found in the liver, hematopoietic organs, and endocrine glands. Around the hemocapillaries there is a thin layer of loose fibrous tissue with a large content of poorly differentiated cells, the state of which determines the intensity of exchange between the blood and the working tissues of the organ. The barrier between the blood in the hemocapillaries and the surrounding working tissue of the organ is called the histohematic barrier, which consists of endothelial cells and the basement membrane. Capillaries can change structure, transform into vessels of a different type and caliber; New branches can form from existing hemocapillaries. Precapillaries differ from hemocapillaries in that in the wall, in addition to endothelial cells, basement membrane, and pericytes, there are single or groups of myocytes.

Venules begin with postcapillary venules, which differ from capillaries by the large content of pericytes in the wall and the presence of valve-like folds of endothelial cells. As the diameter of the venules increases, the content of myocytes in the wall increases - first single cells, then groups and finally continuous layers.

Arteriolo-venular anastomoses (AVA) are shunts (or anastomoses) between arterioles and venules, i.e. carry out direct communication and participate in the regulation of regional peripheral blood flow. They are especially abundant in the skin and kidneys. ABA - short vessels, also have 3 membranes; There are myocytes, especially many in the middle shell, which act as a sphincter.

VEINS. A feature of the hemodynamic conditions in the veins is low pressure (15-20 mmHg) and low speed blood flow, which causes a lower content of elastic fibers in these vessels. The veins have valves - a duplication of the inner lining. The number of muscle elements in the wall of these vessels depends on whether the blood moves with or against gravity. Veins of the muscleless type are found in the dura mater, bones, retina, placenta, and red bone marrow. The wall of muscleless veins is lined internally with endothelial cells on the basement membrane, followed by a layer of fibrous SDT; there are no smooth muscle cells. Veins of the muscular type with weakly expressed muscular elements are located in the upper half of the body - in the system of the superior vena cava. These veins are usually in a collapsed state. The tunica media contains a small number of myocytes.

Veins with highly developed muscular elements make up the vein system of the lower half of the body. A feature of these veins is well-defined valves and the presence of myocytes in all three membranes - in the outer and inner membrane in the longitudinal direction, in the middle - circular direction.

LYMPHATIC VESSELS begin with lymphatic capillaries (LC). LCs, unlike hemocapillaries, begin blindly and have a larger diameter. The inner surface is lined with endothelium; there is no basement membrane. Under the endothelium there is a loose fibrous tissue with a high content of reticular fibers. The diameter of the LC is not constant - there are narrowings and expansions. Lymphatic capillaries merge to form intraorgan lymphatic vessels - their structure is close to veins, because are under the same hemodynamic conditions. They have 3 shells, the inner shell forms valves; Unlike veins, there is no basement membrane under the endothelium. The diameter is not constant throughout - there are expansions at the level of the valves. Extraorgan lymphatic vessels are also similar in structure to veins, but the basal endothelial membrane is poorly defined and absent in places. The internal elastic membrane is clearly visible in the wall of these vessels. The middle shell receives special development in the lower extremities.

HEART. The heart is formed at the beginning of the 3rd week of embryonic development in the form of a paired rudiment in the cervical region from the mesenchyme under the visceral layer of splanchnotomes. Paired cords are formed from the mesenchyme, which soon turn into tubes, from which the inner lining of the heart is ultimately formed - the endocardium. The areas of the visceral layer of splanchnotomes that encircle these tubes are called myoepicardial plates, which subsequently differentiate into the myocardium and epicardium. As the embryo develops, with the appearance of the trunk fold, the flat embryo folds into a tube - the body, while the 2 heart buds end up in the chest cavity, come closer and finally merge into one tube. Next, this heart tube begins to quickly grow in length and does not fit into chest forms several bends. Neighboring loops of the bending tube grow together and a 4-chambered heart is formed from a simple tube. HEART is the central organ of the cardiovascular system, has 3 membranes: internal - endocardium, middle (muscular) - myocardium, external (serous) - epicardium. The endocardium consists of 5 layers: 1. Endothelium on the basement membrane. 2. Subendothelial layer of loose fibrous tissue with a large number of poorly differentiated cells. 3. Muscle-elastic layer (myocytes, elastic fibers). 4. Elastic-muscular layer (myocyte-elastic fibers). 5. Outer SDT layer (loose fibrous SDT). In general, the structure of the endocardium resembles the structure of the wall of a blood vessel. The muscular layer (myocardium) consists of 3 types of cardiomyocytes: contractile, conductive and secretory (for structural features and functions, see the topic “ Muscle tissue"). The endocardium is a typical serous membrane and consists of layers: 1. Mesothelium on the basement membrane. 2. Superficial collagen layer. 3. Layer of elastic fibers. 4. Deep collagen layer. 5. Deep collagen-elastic layer (50% of the total thickness of the epicardium). Under the mesothelium, in all layers between the fibers there are fibroblasts. Regeneration of the cardiovascular system. Vessels, endocardium and epicardium regenerate well. Reparative regeneration of the heart is poor, the defect is replaced by a scar; physiological regeneration - well expressed, due to intracellular regeneration (renewal of worn-out organelles). Age-related changes SSS. In the vessels of elderly and senile age, a thickening of the inner lining is observed, and deposits of cholesterol and calcium salts (atherosclerotic plaques) are possible. In the middle layer of blood vessels, the content of myocytes and elastic fibers decreases, the amount of collagen fibers and acidic mucopolysaccharides increases.

27. Cardiovascular system

Arteriovenular anastomoses are connections of vessels carrying arterial and venous blood bypassing the capillary bed. Their presence is noted in almost all organs.

There are two groups of anastomoses:

1) true arteriovenular anastomoses (shunts), through which pure arterial blood is discharged;

2) atypical arteriovenular anastomosis (half-shunts), through which mixed blood flows.

The external shape of the first group of anastomoses can be different: in the form of straight short anastomoses, loop-shaped, sometimes in the form of branching connections.

Histostructurally, they are divided into two subgroups:

a) vessels that do not have special closure devices;

b) vessels equipped with special contractile structures.

In the second subgroup, the anastomoses have special contractile sphincters in the form of longitudinal ridges or cushions in the subendothelial layer. Contraction of the muscle cushions protruding into the lumen of the anastomosis leads to cessation of blood flow. Simple anastomoses of the epithelioid type are characterized by the presence in the middle shell of the inner longitudinal and outer circular layers of smooth muscle cells, which, as they approach the venous end, are replaced by short oval light cells, similar to epithelial ones, capable of swelling and swelling, due to which the lumen of the anastomosis changes. In the venous segment of the arteriovenular anastomosis, its wall becomes sharply thinner. The outer shell consists of dense connective tissue. Arteriovenular anastomoses, especially of the glomerular type, are richly innervated.

The structure of veins is closely related to the hemodynamic conditions of their functioning. The number of smooth muscle cells in the wall of the veins is not the same and depends on whether the blood in them moves towards the heart under the influence of gravity or against it. According to the degree of development of the muscular elements in the wall of the veins, they can be divided into two groups: veins of the non-muscular type and veins of the muscular type. Veins of the muscular type, in turn, are divided into veins with weak development of muscle elements and veins with medium and strong development of muscle elements. In veins (as well as in arteries), there are three membranes: internal, middle and outer, and the degree of expression of these membranes in the veins differs significantly. Veins of the non-muscular type are the veins of the dura and soft meninges, the veins of the retina, bones, spleen and placenta. Under the influence of blood, these veins are capable of stretching, but the blood accumulated in them flows relatively easily under the influence of its own gravity into larger venous trunks. Veins of the muscular type are distinguished by the development of muscle elements in them. These veins include the veins of the lower torso. Also, some types of veins have a large number of valves, which prevents the blood from flowing back under its own gravity.

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The structure of arterioles

Topic: Microcirculatory bed: arterioles, capillaries, venules and arteriolo-venular anastomoses. Features of the structure of the walls of blood vessels. Types of capillaries, structure, localization. Heart. Sources of development. The structure of the membranes of the heart. Age characteristics.

The vessels of the microvasculature include: arterioles, capillaries, venules and arteriolo-venular anastomoses.

The functions of the vessels of the microvasculature are:

1. Exchange of substances and gases between blood and tissues.

2. Regulation of blood flow.

3. Blood deposition.

4. Drainage of tissue fluid.

The microcirculatory bed begins with arterioles, into which arteries become as the lumen diameter and wall thickness decrease.

Arterioles– these are small vessels with a diameter of 100 to 50 microns. They are similar in structure to muscular arteries.

The arteriole wall consists of three membranes:

1. The inner lining is represented by endothelium located on the basement membrane. Underneath it are single cells of the subendothelial layer and a thin internal elastic membrane that has holes (perforations) through which endothelial cells contact the smooth myocytes of the middle layer to transmit signals from endothelial cells about changes in the concentration of biologically active substances that regulate arteriolar tone.

2. The middle membrane is represented by 1 – 2 layers of smooth myocytes.

3. The outer shell is thin and merges with the surrounding connective tissue.

The smallest arterioles with a diameter of less than 50 microns are called precapillary arterioles or precapillaries. Their wall consists of endothelium lying on the basement membrane, individual smooth myocytes and outer adventitial cells.

At the site where precapillaries branch into capillaries, there are sphincters, which are several layers of smooth myocytes that regulate blood flow into the capillaries.

Functions of arterioles:

· Regulation of blood flow in organs and tissues.

· Regulation of blood pressure.

Capillaries- these are the thinnest-walled vessels of the microcirculatory bed, through which blood is transported from the arterial bed to the venous bed.

The capillary wall consists of three layers of cells:

1. The endothelial layer consists of polygonal cells of various sizes. There are villi on the luminal (facing the lumen of the vessel) surface, covered with glycocalyx, which adsorbs and absorbs metabolic products and metabolites from the blood.

Endothelial functions:

Atrombogenic (synthesize prostaglandins that prevent platelet aggregation).

Participation in the formation of the basement membrane.

Barrier (it is carried out by the cytoskeleton and receptors).

Participation in the regulation of vascular tone.

Vascular (synthesize factors that accelerate the proliferation and migration of endothelial cells).

Synthesis of lipoprotein lipase.

1. A layer of pericytes (process-shaped cells containing contractile filaments and regulating the lumen of capillaries), which are located in the fissures of the basement membrane.

2. A layer of adventitial cells embedded in an amorphous matrix, in which thin collagen and elastic fibers pass.

Classification of capillaries

1. By lumen diameter

Narrow ones (4-7 microns) are found in transversely striated muscles, lungs, and nerves.

Wide (8-12 microns) are found in the skin and mucous membranes.

Sinusoidal (up to 30 microns) are found in the hematopoietic organs, endocrine glands, and liver.

Lacunae (more than 30 microns) are located in the columnar zone of the rectum and the cavernous bodies of the penis.

2. According to the structure of the wall

Somatic, characterized by the absence of fenestrae (local thinning of the endothelium) and holes in the basement membrane (perforations). Located in the brain, skin, muscles.

Fenestrated (visceral type), characterized by the presence of fenestrae and the absence of perforations. They are located where molecular transfer processes occur especially intensively: glomeruli of the kidneys, intestinal villi, endocrine glands).

Perforated, characterized by the presence of fenestrae in the endothelium and perforations in the basement membrane. This structure facilitates the passage through the wall of the capillary cells: sinusoidal capillaries of the liver and hematopoietic organs.

Capillary function– the exchange of substances and gases between the lumen of the capillaries and surrounding tissues is carried out due to the following factors:

1. Thin wall of capillaries.

2. Slow blood flow.

3. Large area of ​​contact with surrounding tissues.

4. Low intracapillary pressure.

The number of capillaries per unit volume varies in different tissues, but in each tissue there are 50% non-functioning capillaries that are in a collapsed state and only blood plasma passes through them. When the load on the organ increases, they begin to function.

There is a capillary network, which is enclosed between two vessels of the same name (between two arterioles in the kidneys or between two venules in portal system pituitary gland), such capillaries are called the “miraculous network”.

When several capillaries merge, they form postcapillary venules or postcapillaries, with a diameter of 12 -13 microns, in the wall of which there is fenestrated endothelium, more pericytes. When postcapillaries merge, they form collecting venules, in the middle membrane of which smooth myocytes appear, the adventitial membrane is better expressed. Collecting venules continue into muscle venules, the middle shell of which contains 1-2 layers of smooth myocytes.

Function of venules:

· Drainage (receipt of metabolic products from the connective tissue into the lumen of the venules).

· Blood cells migrate from the venules into the surrounding tissue.

The microvasculature consists of arteriolo-venular anastomoses (AVA)- these are vessels through which blood from arterioles enters venules bypassing capillaries. Their length is up to 4 mm, diameter more than 30 microns. AVAs open and close 4 – 12 times per minute.

ABAs are classified into true (shunts), through which arterial blood flows, and atypical (half shunts) through which mixed blood is discharged, because When moving along the half-shunt, a partial exchange of substances and gases occurs with the surrounding tissues.

Functions of true anastomoses:

· Regulation of blood flow in capillaries.

· Arterialization of venous blood.

· Increased intravenular pressure.

Functions of atypical anastomoses:

· Drainage.

· Partially exchangeable.

Vascular development.

The first vessels appear in the second – third week of embryogenesis in the yolk sac and chorion. A cluster is formed from the mesenchyme - blood islands. The central cells of the islets round off and become blood stem cells. Peripheral islet cells differentiate into the vascular endothelium. Vessels in the body of the embryo are formed a little later; blood stem cells do not differentiate in these vessels. Primary vessels are similar to capillaries, their further differentiation is determined by hemodynamic factors - pressure and blood flow speed. Initially, a very large part is deposited in the vessels, which is reduced.

Structure of blood vessels.

In the wall of all vessels, 3 membranes can be distinguished:

1. internal

2. average

3. external

Arteries

Depending on the ratio of muscle elastic components, arteries of the following types are distinguished:

Elastic

Large main vessels are the aorta. Pressure – 120-130 mm/Hg/st, blood flow speed – 0.5 1.3 m/sec. The function is transport.

Inner shell:

A) endothelium

flattened polygonal cells

B) subendothelial layer (subendothelial)

It is represented by loose connective tissue and contains stellate-shaped cells that perform combial functions.

Middle shell:

It is represented by fenestrated elastic membranes. Between them there is a small number of muscle cells.

Outer shell:

It is represented by loose connective tissue and contains blood vessels and nerve trunks.

Muscular

Arteries of small and medium caliber.

Inner shell:

A) endothelium

B) subendothelial layer

B) internal elastic membrane

Middle shell:

Smooth muscle cells predominate, arranged in a gentle spiral. Between the middle and outer shells is the outer elastic membrane.

Outer shell:

Represented by loose connective tissue

Mixed

Arterioles

Similar to arteries. Function: regulation of blood flow. Sechenov called these vessels the taps of the vascular system.

The middle shell is represented by 1-2 layers of smooth muscle cells.

Capillaries

Classification:

Depending on the diameter:

narrow 4.5-7 microns - muscles, nerves, musculoskeletal tissue

average 8-11 microns – skin, mucous membranes

sinusoidal up to 20-30 microns – endocrine glands, kidneys

lacunae up to 100 microns – found in the corpora cavernosa

Depending on the structure:

Somatic – continuous endothelium and continuous basement membrane – muscles, lungs, central nervous system

Capillary structure:

3 layers, which are analogues of 3 shells:

A) endothelium

B) pericytes enclosed in a basement membrane

B) adventitial cells

2. Finished - have thinning or windows in the endothelium - endocrine organs, kidneys, intestines.

3. perforated - there are through holes in the endothelium and in the basement membrane - hematopoietic organs.

Venules

postcapillary venules

similar to capillaries, but have more pericytes

collecting venules

muscle venules

Vienna

Classification:

● fibrous (muscleless) type

Found in the spleen, placenta, liver, bones, and meninges. In these veins, the subendothelial layer continues into the surrounding connective tissue

● muscular type

There are three subtypes:

● Depending on the muscle component

A) veins with weak development of muscle elements are located above the level of the heart, blood flows passively due to its heaviness.

B) veins with average development of muscle elements - brachial vein

C) veins with strong development of muscle elements, large veins lying below the level of the heart.

Muscular elements are found in all three membranes

Structure

Inner shell:

Endothelium

The subendothelial layer is a longitudinally directed bundle of muscle cells. A valve is formed behind the inner shell.

Middle shell:

Circularly arranged bundles of muscle cells.

Outer shell:

Loose connective tissue and longitudinally arranged muscle cells.

HEART

DEVELOPMENT

The heart is formed at the end of the 3rd week of embryogenesis. Under the visceral leaf of the splanchnotome, an accumulation of mesenchymal cells is formed, which turn into elongated tubes. These mesenchymal accumulations protrude into the cilomic cavity, bending the visceral layers of the splanchnotome. And the areas are myoepicardial plates. Subsequently, the endocardium, myoepicardial plates, myocardium and epicardium are formed from the mesenchyme. The valves develop as a duplicate of the endocardium.