Download Histology Study Questions: “Cardiovascular System” 9/15/97

Histology Study Questions: “Cardiovascular System” 9/15/97
1. The cardiac skeleton is a “fibrous” skeleton, composed of dense connective tissue. It serves as the
attachment and core of the valves of the heart. It also serves as the attachment for cardiac muscle.
It consists of two rings which encircle the base of the two arteries leaving the heart and the
right/left atrioventricular orifices. It also extends into the interventricular septum. Apart from this
structural function, the cardiac skeleton is also important because it does not conduct impulses,
providing an electrical barrier between atria and ventricles. That is how the impulse at the SA node
can spread across the atria and then collect at one point (the AV node), spreading downward via the
purkinje fibers where the impulse reaches the apex.
2. The three layers of the heart are:
a. Epicardium: single layer of simple sqamous epithelium called mesothelium that rests on
connective tissue bed; also contains coronary arteries and veins, autonomic nerves, and fat.
b. Myocardium: cardiac muscle
c. Endocardium: thin inner lining of simple squamous epithelium called endothelium. It is
continuous with endothelium of blood vessels; a deeper subendocardial layer of connective
tissue contains the impulse-conducting system of the heart.
3. I can’t draw. But there are good pictures of intercalated discs in Wheater’s pp107-110 as well as
Ross p228, 245, 246. Intercalated discs are specialized transverse junctions between cardiac
muscle cells which consist of three types of membrane to membrane contact:
a. fascia adherens: resembles zonula adherens but is less regular and more extensive
b. desmosomes
c. gap junctions
4. An electrical impulse at the SA node in the right atrium spreads across the atrium and ends at the
cardiac skeleton, where it all collects at the AV node, which is at the fibrous skeleton at the
beginning of the interventricular septum. It spreads down through the purkinje fibers located in the
subendocardial layer. It reaches the apex, where the ventricles begin contracting and the
contraction moves upward through the ventricles.
5. Mesenchymal cells (angioblasts) form blood islands on the yolk sac wall. The cells flatten out as
cavities form and the cells become endothelial cells. These cells eventually connect with other
blood islands, forming vessels. Other mesenchymal cells invade the wall and become smooth
muscle cells and fibroblasts.
6. A blood vessel wall contains:
a. Tunica intima: innermost layer of simple sqamous endothelium resting on loose connective
tissue. Smooth muscle cells are scattered in the subendothelium
b. Tunica media: concentric layers of smooth muscles with some elastic fibers, collagen, ground
substance
c. Tunica Adventitia: connective tissue layer on outer surface . In large vessels, the adventitia
contains blood vessels called vasa vasorum that supply blood to the tunica media. This layer
also contains sympathetic nerve fibers for vasoconstriction.
7. Nutrients move by pinocytosis.
8. a. Von Willebrand factor: responds to injuries in endothelium by promoting platelet clot
b. nitric oxide: endothelium derived released factor (EDRF) that causes vasodilation; half life of 6
seconds
d. endothelin: vasoconstrictor
9. Elastic arteries contain a lot of elastic fibers in the tunica media, which consists of 40-70 layers of
smooth muscle. The internal and external elastic membrane is not well developed. The tunica
adventitia is thin. In muscular arteries, the tunica intima has a prominent internal elastic
membrane. The tunica media contains less than 40 layers of smooth muscle cells and much less
elastin. There is a prominent external elastic membrane with fenestrations to allow free diffusion
of substances into the tunica media. The tunica adventitia is thicker than the tunica media.
10. The wall of the arteriole contains a tunica media that is only 1 or 2 smooth muscle layers thick.
There is neither a defined internal elastic membrane nor an external elastic membrane. The tunica
adventitia blends with stroma of the organ. Peripheral resistance is determined by the arteriole
diameter. Therefore, small changes in the diameter of the arteriole lumen changes the blood flow
and peripheral resistance.
11. Metarteriole: the transition between arteriole and capillary bed where smooth muscle layer
becomes discontinuous
Precapillary sphincter: beginning point of a capillary that is wrapped by a smooth muscle cell
that forms a sphincter regulating the blood that goes into the capillary. Low oxygen causes
vasodilator substance release that causes relaxation of smooth muscle in metarteriole and
precapillary sphincter to increase blood flow. Metabolic changes in the tissues will also cause
release of vasoactive substances.
12. Ateriovenous shunt: bypasses the capillary bed and provides direct communication between
arterial and venous circulation. Between the arteriole and venule is a thickened tunica media,
which controls the shunt. There are AV shunts in the skin, which control temperature. There are
also AV shunts in the penis and clitoris.
13. Capillaries: allow for exchange between circulatory system and tissues.
Pericytes: are cells that are in the basal lamina which have myosin, actin, and tropomysin and have
contractile function. They can become smooth muscle cells during growth.
14. continuous capillaries: uninterrupted endothelium with cells attached by tight junctions and gap
junctions; found in muscle, lung, nervous system, and CT. The blood-brain barrier consists of very
tight junctions
fenestrated capillaries: endothelial wall is interrupted by 60-80 nm pores which allow passage of
larger substances; found in pancreas, intestine, kidneys, endocrine glands, basically tissues where
there is a rapid exchange between blood and tissues.
Discontinuous capillaries: sinusoids that are irregular blood pools that conform to shape of
structure they’re found in; large fenestrae; endothelial wall and basal lamina may be discontinuous;
found in bone marrow, liver, spleen, lymphoid and endocrine.
15. Venules slowly accumulate smooth muscle in the tunica media. Veins have more smooth muscle
cells and they contain valves which prevent backflow of blood.
16. Angiogenesis: new blood vessels that sprout from existing capillaries and postcapillary venules,
usually during healing or in tumor growth. Endothelial cells respond to signals produced by the
tissues and produce proteases that eat through the basal lamina. They move toward the signal and
proliferate and form a lumen, eventually anastomosing with other capillaries.
17. If subendothelial tissue is exposed, von Willebrand’s factor is released causing binding of platelets
to collagen in the subendothelial tissue. This forms a plus in the damaged wall. If it is a small
injur, the endothelial cells will just divide and cover the part.
18. Atherosclerosis: Lesions develop in the intima. Monocytes migrate there and become
macrophages as well as smooth muscle cells migrate into the tunica intima. They accumulate lipid,
which eventually forms a thick fibrous capsule and necrotic mass of lipid. The endothelium loses
its integrity and eventually the clotting associated with the capsule may occlude the vessel.
19. Lymphatic capillaries contain no tight junctions and have a discontinuous basal lamina. Lymphatic
capillaries are not found in the CNS, cartilage, one, Bone marrow, thymus ,teeth and placenta.
Lymphatic vessels are larger with more smooth muscle and elastin. They eventually drain into
lymph nodes.