Cardiovascular Microanatomy

Question 1

distinguish between the three major layers of the heart

Answer 1

1. endocardium/tunica intima
   -inner layer; comprised of endothelial lining, subendothelial CT, vessels, and nerves; subendothelial region contains impulse-conducting purkinje fibers
2. myocardium/tunica media
   -filled with cardiac muscle and some CT conducting elements
3. epicardium/tunica externa
   -made up of serosal surface epithelium and the underlying CT (visceral pericardium); often the region where fat accumulates

Question 2

distinguish between endothelium and mesothelium; know where these tissues are located in the heart

Answer 2

mesothelium is simple squamous epithelium, lines the external surface of the heart, and together with the underlying connective tissue makes up the epicardium

endothelium/endocardium is a single layer of endothelial that lines the inner surface of the heart, is continuous with the tunica interna, and makes up the heart valves

Question 3

list and describe the 3 layers of vessels

Answer 3

tunica interna/intima: composed of simple squamous endothelium and its basement membrane, a subendothelial region of CT, and an internal elastic membrane/lamina of elastic fibers and related CT matrix that changes during vascular diseases; smooth layer ensures laminar, not turbulent blood flow

tunica media: smooth muscle arranged in a circular pattern; contains collagen, elastic fibers, and a CT matrix, plus fibroblasts and an external elastic membrane (not always visible)

tunica externa/adventitia: varies from dense fibroelastic to loose irregular CT, blends into the surrounding CT and may or may nor contain smooth muscle depending on vessel type; contains vaso vasorum/nervi vasorum because t. media sometimes so thick that central endothelial blood/nerve supply can’t reach t. externa, so makes its own supply

Question 4

explain why purkinje (myoconducting) fibers are not present in the atria

Answer 4

i got no idea other than that they branch from left and right bundle branches, not SA node??? atria don’t need such rapid conduction??? who’s to say or potentially because the atria don’t need the contractile force because we want them to remain a low pressure sink to keep blood flow

Question 5

from which layer of the heart are the valves formed?

Answer 5

heart valves are folds of endocardium

Question 6

distinguish between elastic (conducting), muscular (distributing) and arterioles (resistance) arteries

Answer 6

1. elastic/conducting arteries: large volume-handling conduits with large amounts of elastic fibers in tunica media (like rubber band) to maintain even flow and maintenance of constant blood pressure
2. muscular/distributing arteries: highly convoluted internal elastic membrane (artifactual); t. media contains large amounts of smooth muscle and some elastic fibers to regulate volume of blood sent to organs in response to functional demand
3. arterioles/resistance arteries: 1-5 complete layers of smooth muscle in media (thiccc af); thin t. adventitia with NO definitive external elastic membrane; function is principal control of systemic blood pressure and distribution of blood to capillaries via vasoconstriction and vasodilation in response to neurotransmitters and hormones

Question 7

is there identifiable smooth muscle in the tunica media of an elastic artery?

Answer 7

(from looking at histo pic); can see smooth muscle somewhat under elastic fibers but mainly just see a shit ton of elastic fibers = elastic artery

Question 8

are there identifiable elastic laminae in the tunica media of a muscular artery?

Answer 8

histo slide says they are still present, but not rly obvious on the slide

Question 9

distinguish between arteries, veins, and lymphatic vessels

Answer 9

1. see other question about types of arteries
2. large veins: may have an internal elastic membrane; smooth muscle in T. media, but always less than companion artery; prominent adventitia; considerable elastic fiber component
3. small/medium veins: smooth muscle in T. media, but always less than companion artery, make up most of the named veins; adventitia contains collagen and elastic fibers
4. venules: postcapillary; similar size but larger diameter than capillaries; very thin t. media
5. lymphatic vessels: irregular lumen with no red blood cells, poorly organized t. media and t. adventitia; extremely thin walls (thinner than similar sized veins

Question 10

list the basic types of vessels that have valves (excluding the heart)

Answer 10

small, medium, and large veins have valves; so do lymphatic vessels

Question 11

list the 3 basic types of capillaries

Answer 11

1. continuous
2. fenestrated
3. sinusoidal

Question 12

what 2 layers make up the wall of a capillary?

Answer 12

endothelium and thin basement membrane

Question 13

how do the layers of a capillary wall differ between the 3 capillary types?

Answer 13

1. continuous:
   -endothelium is uninterrupted and typically has pinocytotic vesicles for two-way transport; basement membrane lacks pores; most common type in body
2. fenestrated:
   -fluid transport function; endothelium has thinner regions where the plasmalemma of opposite surfaces of the cell come in close contact and fuse to form a window one unit membrane thick; found in the choroid plexus of CNS and glomerulus of kidney
3. sinusoidal:
   -marked expansion of capillary lumen; discontinuities in the basement membrane between adjacent endothelial cells; present in parenchyma of liver

Question 14

understand the generalized patter on vessel structure by sketching/labeling a generic blood vessel in transverse section; including endothelium, subendothelial CT, internal elastic membrane, external elastic membrane, and all the tunics

Answer 14

look at histo slides!!