Week 1: CV microanatomy

Question 1

Name three layers (tunics) that comprise the wall of blood vessels and the basic tissue types characteristically found in each of the three tunics.

Answer 1

1. Tunica Intima:
   - Endothelium+basal lamina
   - subendothelial CT +/- smooth muscle
   - =/-internal elastic lamina
2. Tunica media
   - smooth muscle cells and elastic fibers
   - Type III and IV collagen
   - +/-external elastic lamina
3. Tunica adventitia:
   - Type I collagen
   - elastic fibers
   - +/- vasa vasorum

Question 2

List the layers of the heart, the tunics of blood vessels to which they correspond.

Answer 2

1. Endocardium: innermost layer
   - perkinje fibers located beneath this layer
   - tunica intima
2. Myocardium: middle, muscular layer
   - tunica media
   - cardiac muscle
3. Epicardium: outermost layer of heart composed of mesothelium and its basal lamina
   - is the visceral layer of serous pericardium (other layer is parietal)
   - tunica adventitia
   - coronary vessels, fat

Question 3

Describe the structure of Perkinje fibers, valves, and fibrous skeleton

Answer 3

1. Perkinje fibers
   - modified cardiac muscle cells, larger, with whitish cytoplasm due to glycogen on H&E
2. valves
   - central core of DCT, covered by endothelium
3. fibrous skeleton is made of dense connective tissue, provides scaffolding for cardiac muscles, valves, and insulates atrium from ventricle

Question 4

What are the two different types of arteries and how are they different? Compare their tunics.

Answer 4

1. Elastic: large, conducting arteries (e.g. aorta), maintain diastolic bp
   - tunica intima: endothelium w/ weibel palade bodies, b.l., tight jxns, pinocytotic vesicles, subendothelial layer, IEL hard to see
   - Tunica media: 40-70 layers, fenestrated elastic membranes, smooth muscle cells between Ems, indistinct EEL, vasa vasorum in outer half
   - Tunica Adventitia: thin, disorganized fibroelastic CT, vasa vasorum
2. Muscular: small, medium, distributing arteries
   - tunica intima: thin endothelium with Weibel-Palade bodies, b.l., sub endothelial CT layer, PROMINENT IEL, scalloped lumen
   - tunica media: up to 40 layers of smooth muscle cells with some elastic fibers, may or may not have EEL
   - tunica adventitia: thick layer of fibroelastic CT, may have asa vasorum

Question 5

Describe the three types of capillaries.

Answer 5

1. Continous
   - tight jxns, complete endothelial cells w/ basal lamina
   - muscles, lungs, brains, bone, peripheral nerves
2. Fenestrated
   - have openings that facilitate fast transport of materials across endothelium
   - have diaphragm (decreases permeability compared to discontinuous, which has no diaphragm covering pores)
   - wall of gut and glands
3. Discontinuous
   - 30-40 um compared to 8-10 for the other two capillaries
   - incomplete endothelium and basal lamina
   - gaps in endothelium
   - phagocytes in cells
   - liver, spleen, bone marrow

Question 6

Compare microanatomy of arteries and veins (of the similar sizes)

Answer 6

Arteries
-thicker tunica intima
-IEL present, EEL may be present
-thicker tunica media
-thinner tunica adventitia
-more elastic fibers
-thicker walls
-smaller lumen
-round in section
Veins
-thinner tunica intima
-no IEL or EEL
-thin tunica media
-thicker tunica adventitia
-may have valves
-less elastic fibers
-thinner vessel wall
-larger lumen
-frequently have blood in lumen
-collapsed or flattened in section

Question 7

Describe characteristics of lymphatic capillaries and vessels.

Answer 7

1. lymphatic capillaries
   - blind-ending tubes with large diameter lumen
   - endothelium with thin discontinuous basal lamina
   - no fenestrations, fewer tight jxns than blood capillaries
   - no tunica media or tunica adventitia
2. lymphatic vessels
   - thin endothelium, b.l. elastic fiber, valves present
   - thin smooth muscle

Question 8

Describe postcapillary venules.

Answer 8

• made of 1-2 capillaries
• intima: endothelium+b.l.
• fxn: highly permeable, sites of action of vasoactive agents, similar to capillaries

Question 9

Describe the micro anatomy of large veins

Answer 9

• intima: well developed endothelial cells, b.l., thick sub endothelial CT, IEL
• media: thin
• adventitia: thick and well developed. May have bundles of smooth muscle cell (or cardiac muscle in heart)

Question 10

Describe the histology of venules.

Answer 10

• intima: endothelium and b.l.
• media: 0-2 layers of SM
• adventitia: thin
• extravasation and diapedesis of blood cells

Question 11

Describe the histology of small&medium sized veins.

Answer 11

• intima: endothelial cell w/ b.l., occasionally sub endothelial CT
• few valves protruding into lumen
• no IEL
• media: 2-3 layers SM, few elastic fibers, thin
• adventitia: thin CT