Microanatomy

Question 1

Organization of blood vessels

Answer 1

• From lumen out: tunica intima, tunica media, tunica adventitia, vasa vasorum (part of adventitia)
• Arteries have large tunica media and veins have large tunica adventitia
• Internal elastic lamina (IEL) separates intima and media (part of intima)
• External elastic lamina (EEL) separates media and adventitia (part of media)

Question 2

Tunica intima

Answer 2

• Inner most layer consisting of endothelium and its basal lamina, sub endothelial CT (may contain smooth muscle), and IEL (arteries only)
• Smallest layer

Question 3

Tunica media

Answer 3

• Middle layer composed of circumferential smooth muscle (major site for SM), which secrete elastin and collagen, and there may be EEL
• Largest layer in arteries, mostly SM

Question 4

Tunica adventitia

Answer 4

• Outer layer composed of collagen (T1) and elastic fibers to anchor to surrounding CT
• Contains vasa vasorum (small arteries that supply blood to the vessel itself)
• Largest layer in veins, mostly CT

Question 5

Layers of the heart 1

Answer 5

• From in-> out: Endocardium, myocardium, epicardium (AKA visceral pericardium), parietal pericardium, fibrous pericardium
• Endocardium: inside of the heart (where blood is) lined by endothelium (w/ BL) and subendothelial CT. Contains purkinje fibers (modified cardiac muscle) and valves (core of DCT surrounded by endothelium)
• Myocardium: very abundant cardiac muscle cells, inserting in the fibrous cardiac skeleton (part of myocardium, separates atria from ventricles)

Question 6

Layers of the heart 2

Answer 6

• Epicardium: outer most layer (synonymous w/ visceral pericardium) composed of mesothelium (simple squamous epithelial layer w/ BL) and LCT
• The LCT of epicardium contains coronary vessels, nerves, ganglia, and fat
• Outside of the visceral pericardium is the parietal pericardium, together w/ the visceral pericardium forms the serous pericardium (w/ serous fluid btwn them)
• The entire structure is enclosed in the fibrous pericardium

Question 7

Conducting arteries

Answer 7

• Conducting (largest) arteries: aorta and its large branches responsible for maintaining a constant BP
• Thin IEL and EEL, but thick tunica media consisting of SM and elastic fibers
• Have thin adventitia w/ vasa vasorum (+ lymphatic vessels and nerves)

Question 8

Muscular arteries

Answer 8

• Muscular (distributing) arteries display thick tunica media and adventitia w/ scalloped (crescent) lumen
• Contain thick IEL and thin EEL, with the size of media (SM) and adventitia (fibroelastic CT) being about equal
• Adventitia may or may not have vasa vasorum

Question 9

Arterioles

Answer 9

• Arterioles: Smallest arterial vessels, control BP
• Walls are as thick as the diameter of lumen
• Intima shows endothelial nuclei bulging into lumen, may or may not have IEL (larger ones do)
• One to several layers of SM in media, +/- EEL
• Adventitia is very thin

Question 10

Capillaries

Answer 10

• Continuous: nonporous endothelial cells w/ tight junction btwn them and complete BL (no leakage)
• Form BBB and BNB
• Fenestrated: capillaries w/ opening to facilitate transport (may be covered by diaphragm to monitor the permeability of pores), w/ continuous BL (some leakage)
• Discontinuous: have wide lumens and large spaces within the capillary (btwn endothelial cells) for most rapid transportation
• Have discontinuous BL and and fenestrated endothelial cells (found in BM)

Question 11

Venules

Answer 11

• Post-capillary venules: principal site of action of vasoactive agents (?), no tunica media or adventitia (highly permeable)
• Site of lymphocyte homing
• Musclular venules: similar to post-capillary venues but contain very thin media and adventitia
• Site of lymphocyte diapedesis/extravasation

Question 12

Veins

Answer 12

• Small veins: tunica intima contains few valves +/- IEL, thin media and thick adventitia +/- vasa vasorum
• Large veins: thick intima w/ IEL, vlaves, and subendothelial CT, thin media w/ little EEL, thick adventitia w/ vasa vasorum and some SMCs
• Compared to arteries, veins have larger lumen, thinner walls and are often collapsed in histological sections

Question 13

Lymphatic vessels

Answer 13

• Blind-ended tubes lined w/ endothelium w/ large spaces and discontinuous BL
• Allows for transport of larger solutes into lymphatics
• No tunica media or adventitia for lymphatic capillaries
• Lymphatic vessels have thin media (some SMCs) and adventitia (vasa vasorum)
• Vessels empty into ducts (thoracic duct on L or R lymphatic duct) where subclavian + IJV meet