Histo/Cell Bio Flashcards
What are the three layers of the blood vessel wall?
i. Tunica intima: simple squamous epithelial cells with basal lamina of collagen, proteoglycans, and glycoproteins, subendothelial layer of loose connective tissue with sheetlike layer or lamella of internal elastic membrane
ii. Tunica media: smooth muscle cells, thick in arteries, contains external elastic membrane on exterior
iii. Tunica adventitia: outermost layer, longitudinally arranged collagenous tissue and elastic fivers, thin in arteries and thick in veins; large arteries and veins have vasa vasorum to supply blood to vessel walls; also have network of autonomic nerves called nervi vascularis
How does the wall and diameter of arterial vessels change from the aorta to the capillary?
Decreases
How does the wall and diameter of venous vessels change from the post capillary venule to the large veins?
Increases
How do arterioles differ from small arteries in structure and function?
i. Arterioles have only one or two layers, and a small artery may have as many as eight layers of smooth muscle in the tunica media
ii. Tunica intima of small artery has an internal elastic membrane, whereas this layer may or may not be present in the arteriole
iii. Endothelium in both is essentially similar to endothelium in other arteries, except that at the electron microscope level, gap junctions may be found between endothelial cells and the smooth muscle cells of the tunica media.
iv. Tunica adventitia is a thin, ill defined sheath of connective tissue that blends with the connective tissue in which these vessels travel
What is the function of precapillary sphincters?
i. Slight thickening of the smooth muscle at the origin of a capillary bed from an arteriole
ii. Arterioles can dilate, therefore a large decrease or increase in vascular resistance has a direct effect on distribution of blood flow and systemic arterial pressure
iii. Directs blood to where it may be most needed (muscles in exercise, digestion after eating food).
What are the constituents of the capillary wall?
i. Endothelial cells (single layer) and their basal lamina, form a tube just large enough to allow the passage of RBCs
ii. Exchange gases
What are the three types of capillaries and where might they be found?
i. Continuous capillaries: muscle, lung and CNS.
1. Sometimes have pericytes
ii. Fenestrated capillaries: endocrine glands, sites of fluid and metabolite absorption such as the gallbladder, kidney, and intestinal tract
iii. Discontinuous capillaries (aka sinusoidal capillaries or sinusoids)
1. Larger in diameter and more irregularly shaped than other capillaries
2. Kupffer cells and Ito cells occur in association with the endothelial cells
What is the structure and function of a pericyte?
i. Surrounds capillary with branching cytoplasmic processes, are contractile and controlled by NO produced by endothelial cells, found in continuous and fenestrated capillaries
ii. Aka Rouget cells
iii. Enclosed by a basal lamina that is continuous with that of the endothelium
iv. Provide vascular support and promote stability of capillaries and post capillary venules through physical and chemical signaling with vascular endothelial cells.
How does the density of a capillary network impact extravascular fluid collection?
i. Determines the total surface area available for exchange between the blood and tissue.
ii. Related to metabolic activity of the tissue
iii. Liver, kidney, cardiac muscle, and skeletal muscle have rich capillary networks
iv. Dense connective tissue is less metabolically active and has less extensive capillary networks.
What are the structural and functional features of an arteriovenous shunt (AV Shunt)?
i. Aka AV anastomoses
ii. Different routes between the arteries and veins that divert blood from the capillaries
iii. Commonly found in skin of fingertips, nose, lips, and erectile tissue of penis and clitoris
iv. Coiled, have relatively thick smooth muscle layer, is enclosed in a connective tissue capsule, and is richly innervated
v. Contraction of arteriole smooth muscle of the AV shunt sends blood to a capillary bed; relaxation of the smooth muscle sends blood to a venule, bypassing the capillary bed
vi. Contrary to ordinary precapillary sphincter
What are the structural and functional features of a postcapillary venule?
i. Endothelial lining with basal lamina and pericytes
ii. Endothelium of postcapillary venules is the principal site of action of vasoactive agents, such as histamine and serotonin.
iii. Postcapillary venules in the lymph nodes are also called high endothelial venules (HEVs) because of the prominent cuboidal appearance of their endothelial cells and their ovoid nuclei.
How do lymphatic capillaries differ in structure and function from vascular capillaries?
i. Lymphatic capillaries < lymphatic vessels
ii. Lymphatic capillaries are blind ended in the microcapillary beds
iii. Lymphatic capillaries are more permeable than blood capillaries and collect excess protein rich tissue fluid
iv. Lymph vessels contain valves
v. Unidirectional flow
vi. No central pump
vii. Lymph fluid passes through lymph node
What are the variables that can activate endothelial cells?
i. Vasoconstrictors (endothelins, angiotensin-converting enzyme, prostaglandin H2, thromboxane A2) and vasodilators (NO, prostacyclin) modulate blood flow and vascular resistance
ii. Growth factors
What are the mechanisms by which endothelial cells move substances across the vessels wall?
i. Simple diffusion—O2, CO2
ii. Active transport—Glucose, AA, electrolytes
iii. Pinocytosis—H2O, small molecules, soluble proteins
iv. Receptor mediated endocytosis—LDL, cholesterol, transferrin, GF, antibodies, MHC complexes
How do endothelial cells prevent clotting?
i. Anticoagulants, anti-thrombogenetic agents – maintenance of a nonthrombogenic barrier
