Lecture 10   ESS_2nd semester <ul><li>Microscopic anatomy and embryology  of the cardiovascular system </li></ul><ul><li>M...
<ul><li>CV  system distributes nutritive materials, oxygen, and hormones to all parts of the body and </li></ul><ul><li>re...
Blood  circulation systemic pulmonary the heart  arteries  veins capillaries
pulmonary circulation systemic circulation portal circulation =  2 capillary beds link up each other
The heart functions as a pump the right and the left half an atrium + a ventricle valves -  atrioventricular semilunar the...
<ul><li>Endocardium </li></ul><ul><li>is continuous with the tunica intima of the large vessels entering and leaving the h...
<ul><li>Epicardium  </li></ul><ul><li>is a smooth serous covering of the heart corresponding to the visceral layer of  </l...
<ul><li>The  conducting system  of the heart  </li></ul><ul><li>consists of non- contracting cardiomyocytes  in the subend...
<ul><li>Microscopic structure of blood vessels </li></ul><ul><li>Arteries </li></ul><ul><li>arteries  conduct blood from t...
<ul><li>arteries  are  sub classified into three  typ es: </li></ul><ul><li>conducting  or  large-sized arteries  - with w...
distributing artery    conducting  artery
<ul><li>Notice:  In cross-sections of fixed preparations (in which smooth muscle cells are contracted), the arteries  </li...
Conducting artery (aorta)
Conducting artery (aorta)
<ul><li>Distributing arteries   or arteries of muscular type  </li></ul><ul><li>the  all  medium-sized   arteries   </li><...
Distributing artery
 
<ul><li>Arterioles </li></ul><ul><li>Function:  they regulate the flow of blood through capillary bed </li></ul><ul><li>Tu...
 
<ul><li>Variations in  the structure of  arteries </li></ul><ul><li>-  c erebral arteries  resemble veins in having a thin...
an artery a  vein
<ul><li>t he wall of veins is similar to arteries 3-layered  </li></ul><ul><li>t unica intima   - consists of the  endothe...
 
<ul><li>Capillaries </li></ul><ul><li>c apillaries are the smallest branches of the CVS  that  are  distributed  in organs...
<ul><li>the  capillary wall is very simple in structure and consists of </li></ul><ul><li>the endothelium   -  endothelial...
<ul><li>b y electron microscopy, the capillaries are grouped into  3 t ypes :  </li></ul><ul><li>continuous, or somatic ca...
<ul><li>fenestrated   capillaries   </li></ul><ul><li>their wall consists of  the same  layers  as  that  in continuous on...
 
f enestrated capillaries  occur  in organs  with  rapid interchange of substances between cells and blood , i.e.  intestin...
conduct lymph to the bloodstream they begin in the organs as blind  lymphatic capillaries they are  usually  collapsed in ...
Lymphatic capillaries   very simple structure : their wall is composed of endothelial cells and fine reticular fibres of c...
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Lecture10 microscopic anatomy and embryology of the cardiovascular system

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Lecture10 microscopic anatomy and embryology of the cardiovascular system

  1. 1. Lecture 10 ESS_2nd semester <ul><li>Microscopic anatomy and embryology of the cardiovascular system </li></ul><ul><li>Microscopic structure of the heart, excitomotoric system - </li></ul><ul><li>its structural peculiarities </li></ul><ul><li>Blood vessels - arteries and veins - structural differences </li></ul><ul><li>Capillary bed </li></ul><ul><li>Lymph vessels and capillaries </li></ul>
  2. 2. <ul><li>CV system distributes nutritive materials, oxygen, and hormones to all parts of the body and </li></ul><ul><li>removes waste products of the metabolism </li></ul><ul><li>i t consists of the heart and a series of tubular vessels : </li></ul><ul><li>arteries </li></ul><ul><li>capillaries </li></ul><ul><li>veins </li></ul><ul><li>Remember: the CVS system derives from the mesenchyma and is lined by simple </li></ul><ul><li>squamous epithelium called the endothelium </li></ul><ul><li>Layers of the CVS : three </li></ul><ul><li>t he tunica intima / endocardium - the layer found nearest to the lumen </li></ul><ul><li>is composed of an endothelium with basement membrane and thin sheet of connective </li></ul><ul><li>tissue </li></ul><ul><li>t he tunica media / myocardium - the next layer outward from the lumen </li></ul><ul><li>consists primarily of smooth muscle cells (or cardiomyocytes) and elastic and collagen </li></ul><ul><li>fib res </li></ul><ul><li>t he tunica adventitia / epicardium - the outermost layer , in blood vessels the layer is </li></ul><ul><li>composed of areolar connective tissue that connects the wall with the surrounding, the </li></ul><ul><li>layer is smooth in the heart </li></ul><ul><li>local differences in the occurrence, thickness and composition of individual layers ( e.g. there is </li></ul><ul><li>no tunica media in capillaries and “arteriols”, tunica media of elastic arteries contains elastic laminae) </li></ul>
  3. 3. Blood circulation systemic pulmonary the heart arteries veins capillaries
  4. 4. pulmonary circulation systemic circulation portal circulation = 2 capillary beds link up each other
  5. 5. The heart functions as a pump the right and the left half an atrium + a ventricle valves - atrioventricular semilunar the wall of the heart - three layers : the endocardium ( tunica interna ) - is in contact with blood the myocardium ( tunica media ) - intermediate solid layer of cardiac muscle tissue the epicardium ( tunica externa) - smooth external covering layer = visceral layer of pericardium
  6. 6. <ul><li>Endocardium </li></ul><ul><li>is continuous with the tunica intima of the large vessels entering and leaving the heart </li></ul><ul><li>the endocardium of the left half of the heart is not continuous with the one on the right half as </li></ul><ul><li>it is separated by a heart septum </li></ul><ul><li>the endothelium and thin but continuous basement membrane </li></ul><ul><li>subendothelial connective tissue composed of collagen, elastic fibres, solitary smooth muscle cells, small blood vessels, and nerves </li></ul><ul><li>subendocardial layer containing the Purkinje fibres of the excitomotoric or conducting system </li></ul><ul><li>Cardiac valves are duplicatures of the endocardium, especially subendothelial layer </li></ul><ul><li>v alves lack blood vessels and nerves </li></ul><ul><li>Myocardium </li></ul><ul><li>varies in thickness in different parts, being thickest in the left ventricle and thinnest in the atria </li></ul><ul><li>has rich blood supply (many capillaries are seen in histological sections) </li></ul><ul><li>cardiomyocytes have no regenerative capacity - if they were damaged, then degenerate </li></ul><ul><li>and are substituted with connective tissue </li></ul><ul><li>a connective tissue mass in the myocardium that serves as insertion site for the fibres in valves </li></ul><ul><li>as well as for the myocardial cells themselves - c ardiac skeleton . It is also functioning as an electrical insulator with an foramen for the artrioventricular bundle. </li></ul><ul><li>/ involves the annuli fibrosi, trigona fibros i , and the septum membranaceum / </li></ul>
  7. 7. <ul><li>Epicardium </li></ul><ul><li>is a smooth serous covering of the heart corresponding to the visceral layer of </li></ul><ul><li>serous pericardium – </li></ul><ul><li>mesothelium and very thin submesothelial connective tissue layer </li></ul><ul><li>(in obese patients, it may contain an adipose tissue in considerable amount+ cornary arteries!) </li></ul><ul><li>It contains two layers, both of which function in lubricating the heart to prevent friction from occurring during heart activity: </li></ul><ul><li>The layer adherent to the fibrous pericardium is the parietal layer. </li></ul><ul><li>The layer deep to the fibrous pericardium is the visceral layer. [1] When this layer comes into contact with the heart (not the great vessels ), it is known as the epicardium . </li></ul><ul><li>Together these two layers form a continuous uninterrupted membrane. Between these two layers exists a small cavity called the pericardial cavity, which contains a supply of serous fluid . The serous fluid that is found in this space is known as the pericardial fluid . </li></ul>
  8. 8. <ul><li>The conducting system of the heart </li></ul><ul><li>consists of non- contracting cardiomyocytes in the subendocard.layer </li></ul><ul><li>the sinoatrial node (node of Keith-Flack ) </li></ul><ul><li>it lies o n the medial wall of the right atrium near the entrance of the superior vena cava </li></ul><ul><li>the atrioventricular node (node of Tawara ) </li></ul><ul><li>it runs on the right side of the interatrial septum </li></ul><ul><li>the atrioventricular (AV) bundle ( bundle of Hiss ) </li></ul><ul><li>it divides into 2 branches (for the left and right ventricles) </li></ul><ul><li>the Purkinje fibres - terminal ramifications of the AV bundle </li></ul>
  9. 9. <ul><li>Microscopic structure of blood vessels </li></ul><ul><li>Arteries </li></ul><ul><li>arteries conduct blood from the heart to the periphery </li></ul><ul><li>The wall of any artery is three - layer ed : </li></ul><ul><li>the t unica intima ( internal layer ) - is composed of the endothelium and subendothelial connective tissue, whose elements are predominantly oriented in a direction longitudinal to the vesse l </li></ul><ul><li>the internal elastic lamina separates the intima from the middle coat </li></ul><ul><li>the t unica media ( middle layer ) - the thickest layer and its structural elements run circular ly to the long axis of vessels </li></ul><ul><li>consists of elastic fibres & smooth muscle cells - the type of the artery depends on their mutual proportions </li></ul><ul><li>It is separated from the outer coat by the external elastic lamina </li></ul><ul><li>the t unica adventitia (external layer ) - of loose connective tissue with small blood vessels ( vasa vasorum ) and nerve bundles </li></ul><ul><li>elements of the external tunic run for the most part longitudinally </li></ul>
  10. 10. <ul><li>arteries are sub classified into three typ es: </li></ul><ul><li>conducting or large-sized arteries - with wall in which elastic elements predominate </li></ul><ul><li>distributing or medium-sized arteries - </li></ul><ul><li>with a predominance of smooth muscle cells in the media </li></ul><ul><li>arterioles - small arteries that immediately control the </li></ul><ul><li>supply of blood to the capillary bed </li></ul>
  11. 11. distributing artery conducting artery
  12. 12. <ul><li>Notice: In cross-sections of fixed preparations (in which smooth muscle cells are contracted), the arteries </li></ul><ul><li>show the distinct scalloped line of the internal elastic lamina with the characteristic corrugation of the intima </li></ul><ul><li>coat, as the elastic membranes are unable to contract and are thrown into longitudinal folds </li></ul><ul><li>the endothelial nuclei consequently tend to bulge into lumen </li></ul><ul><li>Conducting arteries = arteries of elastic type </li></ul><ul><li>have resistant, elastic and not thick wall (relative to the size of the lumen) </li></ul><ul><li>the aorta, brachiocephalic trunk, carotids, subclavian, axillary and iliacs </li></ul><ul><li>Function: elastic arteries absorb and store the contractile energy of the left ventricle and </li></ul><ul><li>transform the pulsatile flow of blood in smooth out </li></ul><ul><li>Tunica intima : </li></ul><ul><li>- endothelium (its cells are elongated in the direction of the long axis), </li></ul><ul><li>- subendothelial layer consists of loose connective tissue containing many fine longitudinal </li></ul><ul><li>elastic fibres; these gradually merge into the internal elastic lamina, which is not marked off </li></ul><ul><li>sharply from the elastic membranes of the middle coat </li></ul><ul><li>n ear the boundary of two coats the longitudinally running smooth muscle cells are found </li></ul><ul><li>Tunica media: </li></ul><ul><li>- elastic fibres arranged circularly as discontinuous fenestrated membranes about 2.5  m thick (about 50), </li></ul><ul><li>- circularly oriented smooth muscle interspersed between elastic membranes </li></ul><ul><li>Tunica adventitia: </li></ul><ul><li>consists of loose connective tissue containing next to the media longitudinally arranged elastic </li></ul><ul><li>fibres and vasa vasorum, nourish a portion of the media </li></ul>
  13. 13. Conducting artery (aorta)
  14. 14. Conducting artery (aorta)
  15. 15. <ul><li>Distributing arteries or arteries of muscular type </li></ul><ul><li>the all medium-sized arteries </li></ul><ul><li>they have thicker wall relative to the size of the lumen compared with elastic arteries </li></ul><ul><li>Function: t he contraction and relaxation of smooth muscle cells in muscular arteries regulate blood pressure </li></ul><ul><li>they also regulate the perfusion of different parts of the body under physiologic conditions </li></ul><ul><li>Tunica intima: </li></ul><ul><li>- endothelium </li></ul><ul><li>- subendothelial layer diminishes in thickness with decreasing size of the artery </li></ul><ul><li>it c onsists of cellular connective tissue with very fine elastic fibres and a few smooth muscle cells </li></ul><ul><li>t he internal elastic membrane is well-developed (in later life it tends to split into several layers ) </li></ul><ul><li>Tunica media: </li></ul><ul><li>- smooth muscle cells are prevalent; they are arranged circularly and form 3 to 40 layers, </li></ul><ul><li>- elastic network is fine and interlaced between leiomyocytes ( muscle cells ) </li></ul><ul><li>the external elastic lamina is always present and sharply demarcates this layer from the external coat </li></ul><ul><li>Tunica adventitia: </li></ul><ul><li>is composed of the loose connective tissue, in which elastic fibres are abundant and run longitudinally </li></ul>
  16. 16. Distributing artery
  17. 18. <ul><li>Arterioles </li></ul><ul><li>Function: they regulate the flow of blood through capillary bed </li></ul><ul><li>Tunica intima - consists of the endothelium and the internal </li></ul><ul><li>elastic membrane </li></ul><ul><li>(the subendothelial layer is mostly missing) </li></ul><ul><li>Tunica media - thin </li></ul><ul><li>consists of 2- 4 layers of smooth muscle cells wrapped </li></ul><ul><li>round the intima </li></ul><ul><li>Tunica adventitia - is reduced to a thin sheath of collagen </li></ul><ul><li>fibres </li></ul>
  18. 20. <ul><li>Variations in the structure of arteries </li></ul><ul><li>- c erebral arteries resemble veins in having a thin wall but contain a prominent internal </li></ul><ul><li>elastic membrane </li></ul><ul><li>- c oronary arteries have thick wall with considerable elastic component </li></ul><ul><li>- arteries of the penis contain longitudinal muscle fibres in the thickened intima (cushion s ) </li></ul><ul><li>- u mbilical arteries have an inner longitudinal and an outer circular layer of smooth muscle in </li></ul><ul><li>the media </li></ul>Veins vessels conducting blood to the heart f unction: veins serve as a blood reservoir the wall of veins shows 3-layered organization but is much thinner in proportion to the size of the lumen than is that of the arteries t he wall, although thin, is however very strong because the connective tissue components are greatly developed (elastic and muscular elements are inconspicuous) a fter death the wall of the veins tends to collapse i n some body regions , in particular the lower limbs, the veins over 2 mm in a diameter are provided with vein valves that prevent the blood in flowing back from the heart v alves are usually arranged in pairs opposite to one another histologically, they are duplicatures of the tunica intima
  19. 21. an artery a vein
  20. 22. <ul><li>t he wall of veins is similar to arteries 3-layered </li></ul><ul><li>t unica intima - consists of the endothelium and very thin subendothelial </li></ul><ul><li>layer of connective tissue ; the internal elastic membrane is delicate or missing </li></ul><ul><li>t unica media - is relatively thin with except ion of veins of lower </li></ul><ul><li>extremities </li></ul><ul><li>i t contains a considerably amount of collagen fibres and a little elastic </li></ul><ul><li>fibres and smooth muscle cells </li></ul><ul><li>t unica adventitia - is well-developed, being much thicker than the middle coat </li></ul><ul><li>i t contains collagen and elastic fibres and smooth muscle cells grouped into </li></ul><ul><li>small bundles that run chiefly longitudinal </li></ul><ul><li>robust vasa vasorum sometimes penetrat e even the intima </li></ul><ul><li>Variations of structure in veins </li></ul><ul><li>v eins of the brain and meninges lack valves and have no media </li></ul><ul><li>veins of bones, retina, placenta and trabecular veins of the s pleen show similar structure </li></ul><ul><li>ve ins of the pampiniform plexus of the spermatic cord and umbilical veins have an unusually thick media </li></ul><ul><li>the media is absent i n the inferior vena cava and it is replaced with an abundance of longitudinal muscle bundles in the thick ened adventitia </li></ul>
  21. 24. <ul><li>Capillaries </li></ul><ul><li>c apillaries are the smallest branches of the CVS that are distributed in organs, being </li></ul><ul><li>interposed between the terminal ramifications of the small arterioles and venules </li></ul><ul><li>a density of capillary network depends on the metabolic activity of the organ </li></ul><ul><li>- the highest density is found in the cerebral cortex, myocardium, kidney etc. </li></ul><ul><li>function of capillaries : metabolic exchange between </li></ul><ul><li>blood and surrounding tissues </li></ul><ul><li>t he average d . of capillaries is about 8  m </li></ul><ul><li>allowing the passage of the blood </li></ul><ul><li>corpuscles in single file </li></ul><ul><li>total length of capillaries in the human - 90 km </li></ul><ul><li>the surface area of capillary bed - </li></ul><ul><li>6 300 - 12 000 m 2 </li></ul>
  22. 25. <ul><li>the capillary wall is very simple in structure and consists of </li></ul><ul><li>the endothelium - endothelial cells are held together by zonulae occludentes, and an occasional desmosome s and gap junctions </li></ul><ul><li>the basal lamina </li></ul><ul><li>a delicate envelope of reticular fibres , in which fibroblasts, macrophages and pericytes occur </li></ul><ul><li>pericytes are non-differentiated mesenchymal cells hav íng long processes that may partly surround the endothelial cells </li></ul><ul><li>cells are suggested to have a contractile function because contain contractile proteins: actin, myosin and tropomyosin (called MESANGLIAL CELLS in nephron </li></ul>
  23. 26. <ul><li>b y electron microscopy, the capillaries are grouped into 3 t ypes : </li></ul><ul><li>continuous, or somatic capillaries </li></ul><ul><li>fenestrated, or visceral capillaries </li></ul><ul><li>sinusoidal capillaries , or sinusoids ( discontinuous capillaries ) </li></ul>continuous capillaries have all layers good developed c apillaries of this type occur in the central nerv ous system (cortex of the telen-cephalon, cerebellar cortex ), in all kinds of muscle tissue, the connective tissue, and exocrine glands
  24. 27. <ul><li>fenestrated capillaries </li></ul><ul><li>their wall consists of the same layers as that in continuous ones but endothelial cells </li></ul><ul><li>are provided by circular pores (fenestrae) </li></ul><ul><li>the fenestrae are 60 - 80 nm in d . and are closed by a diaphragm that is thinner </li></ul><ul><li>than a cell membrane and does not show trilaminar structure of a bio membrane </li></ul>
  25. 29. f enestrated capillaries occur in organs with rapid interchange of substances between cells and blood , i.e. intestinal villi, pancreas, choroid plexus, ciliary body Remember: modified fenestrated capillaries are contained in the renal glomeruli t he fenestrae are larger (70 - 90 nm) and more numerous than in the fenestrated capillaries of other organs, no diaphragms are present in the fenestrae sinusoidal capillaries , or sinusoids ( discontinuous capillaries ) are characterized by a tortuous path greatly enlarged diameter (30 - 40  m) and discontinuous basal lamina and absence of pericytes the endothelial cells are separated each other by numerous and large gaps that facilitate the transport of substances between blood and cells s inusoids occur mainly in the liver , some hematopoietic organs ( such as the bone marrow ), some endocrine glands (adenohypophysis, islets of Langerhans)
  26. 30. conduct lymph to the bloodstream they begin in the organs as blind lymphatic capillaries they are usually collapsed in histological sections capillaries collect tissue (interstitial) fluid from the organs . They are called lacteals in the intestine. small and medium-sized lymphatic vessels (lymphatics) c ontain the lymph and have valves in their lumina main ducts: ductus thoracicus - thoracic duct; right lympatic duct - truncus lymphaceus dx . both empty the lymph into the bloodstream at the junction of the left internal jugular and left subclavian veins (angulus venosus) Lymph vessels
  27. 31. Lymphatic capillaries very simple structure : their wall is composed of endothelial cells and fine reticular fibres of circular orientation the basal lamina is not developed Lymphatic vessels and ducts are thin walled tubes their wall s resemble the wall s of veins it consists of 3 layers: an intima, a media and an adventitia
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