65. Question - Diagram the microvasculature naming the vessels traversed in passing from arteries to veins. Use the diagram to explain the origin and fate of lymph.
Not all the fluid that leaves capillaries at their arterial end returns at the venous end. The excess is taken up by lymph lacteals and capillaries. It follows lymph vessels and trunks to empty into the venous system near the heart.
66. Question - Diagram the morphology of 3 types of microvessels and give one location of each type.
Microvessels are the nutrient vessels that consist only of endothelium and its basement membrane. Continuous types are found in muscle, lung and brain; fenestrated types are found in intestines and kidneys; sinusoids are found in spleen and liver.
67. Question - Explain the function of each type of microvessel. Give two mechanisms for fluid movement across capillaries.
Continuous capillaries have the most control over what substances cross the endothelium. This is especially true in the brain where there are very tight occluding junctions between the endothelial cells. Where this occurs membrane pumps move ions across and water follows. A vesicular route is also operational for larger molecules. It is called transcytosis.
Fenestrated capillaries are freely permeable to components of plasma except where the basal lamina selectively excludes molecules greater than 70,000 MW, i.e. renal glomerulus.
Sinusoids are more tenuous than fenestrated capillaries and blood cells readily cross this epithelium.
Besides pumps that facilitate fluid crossing some capillary walls in most capillaries the forces of hydrostatic and osmotic pressure determine the direction of fluid flow. Fluid leaves capillaries at their arterial end and returns at their venous end.
68. Question - Diagram the morphology of a muscular artery.
69. Question - How do elastic arteries differ from muscular arteries? Explain how large blood vessels are nourished. How do veins differ from arteries?
Elastic arteries differ from muscular arteries in that the tunica media consists of alternating layers of elastic lamellae and smooth muscle. The smooth muscle is responsible for making and maintaining the elastic elements. In muscular arteries the tunica media is almost entirely smooth muscle. Large blood vessels, especially arteries, are nourished both by diffusion from within and through nutrient vessels (vasa vasorum) supplying the outer half of the wall. The muscular wall of veins has less apparent organization than in arteries. Longitudinal bundles are frequently found in the adventitia which is typically thicker than the media which has loosely organized circular fibers.
70. Question - Use diagrams to compare and contrast the histology of the walls of the atria and ventricles of the heart.
Both have epicardium covered by mesothelium. Both have three layers - epicardium, myocardium and endocardium. Atrial myocardium is thinner and endocardium is thicker than the ventricle. Atrial endocardium contains smooth muscle. Purkinje fibers are found between the endocardium and myocardium of the ventricle. Endothelium lines both atria and ventricles.
71. Question - Describe the histology of the heart valves. What is the role and composition of the tissue that surrounds the base of the valves? Diagram and label the components of the pericardial sac and the epicardium. Show them in relationship to each other.
Heart valves are a fold of endocardium. They are covered on both sides by endothelium and are supported by collagenic and elastic connective tissue. These fibers tie into a dense collagenic connective tissue (portions of this may be similar to fibrocartilage) that surrounds the base of the valves. This "annulus fibrosa" is part of the cardiac skeleton and prevents the base from spreading under pressure.
72. Question - Diagram the impulse generating and conducting system of the heart. Describe the histology of each component.
The sinoatrial (S-A) node is the pacemaker. It consists of small cardiac muscle cells intermingled with elements of both the parasympathetic (including ganglion cells) and sympathetic nervous systems. The contraction impulse travels over atrial musculature to the atrioventricular (A-V) node which has a similar morphology to the S-A node. A bundle of small cardiac muscle fibers (the bundle of His) arises from the A-V node and passes through the cardiac skeleton to form the right and left bundles on either side of the interventricular septum. These bundles and their branches consist of Purkinje fibers - large cardiac muscle fibers containing accumulations of glycogen.
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Last Revised: Thu, Jan 25, 2007
