Histology

Question 1

What are the 3 layers of every macroscopic vessel?

Answer 1

tunica adventitia
tunica media
tunica intima

Question 2

What’s tunica adventitia?

Answer 2

Collagenous connective tissue, loose to dense

Question 3

Role of tunica adventitia?

Answer 3

Anchorage, support (transgenic mice deficient in type I collagen gene prematurely die with ruptured arteries), elasticity
Carries nerve + blood supply to vessel (vasa vasorum in larger vessels)

Question 4

What’s tunica media?

Answer 4

smooth muscle

Question 5

Role of tunica media?

Answer 5

Support, elasticity, contractility (tone).
Physical regulation of blood flow.
Smoothing of blood flow of elastic arteries

Question 6

What’s tunica intima?

Answer 6

Endothelium, over a little dense connective tissue

Question 7

Role of tunica intima?

Answer 7

Selectively permeable barrier to blood.
Regulated adhesion of platelets + leukocytes
Makes mediators controlling vessel tone (maintained by tunica media), eg NO, endothelins
Makes mediators of inflammation

Question 8

Diff between 3 layers in artery vs vein?

Answer 8

Artery: thick T.media>T.adventitia, round, wall>internal diameter
Vein: thin T.media, oval, internal diameter>wall

Question 9

Diff types of arteries?

Answer 9

elastic (conducting arteries)
muscular
arterioles

Question 10

eg of elastic (conducting arteries)?

Answer 10

aorta, pul arteries + their largest branches: brachiocephalic, common iliac

Question 11

Features of elastic (conducting arteries)?

Answer 11

Thick T.media with many elastic laminae (sheets of elastin/lamellae)

Question 12

Role of elastic (conducting arteries)?

Answer 12

Absorb systolic flow by stretching + continue blood flow in diastole by elastic recoil

Question 13

How do elastic arteries look with H/E stain?

Answer 13

Smooth muscle cells: purple nuclei, pink cytoplasm

Elastic laminae: darker pink

Question 14

How do elastic arteries look with EVG (elastic-Van Gieson) stain?

Answer 14

collagen: red
cytoplasm: yellow
elastin: brown/black
elastic laminae: brown

Question 15

What damage happens in AAA?

Answer 15

Partial rupture of arterial wall, with blood entering T.media, fatal if T.adventitia also ruptures.

Question 16

Features of muscular (distributing) arteries?

Answer 16

0.3mm diameter (40 🔴 wide)

Contractile - regulate blood flow + BP

Question 17

How diff types of arteries merge into another?

Answer 17

Elastic -> muscular -> arterioles

Question 18

How do muscular (distributing) arteries look with EVG (elastic-Van Gieson) stain?

Answer 18

collagen: red
cytoplasm: yellow
elastin: brown/black
Prominent internal elastic lamina, single, between intima and media
Thick T.media with some elastic fibres but no elastic laminae
External elastic lamina, several thin, discontinuous laminae, in adventitia at inner edge
Adventitia: red collagen

Question 19

Main diff between elastic vs muscular arteries?

Answer 19

ELASTIC: many elastic laminae in T.media
MUSCULAR: single internal + external elastic laminae at edges of T. media.

Question 20

Where are atheromas?

Answer 20

in T.media

Question 21

Role of muscular (distributing) arteries?

Answer 21

Contractile to regulate BP + flow

Question 22

Features of arterioles?

Answer 22

Microscopic, < 0.3 mm wide.

Difference from small arteries is arbitrary, there’s a continuum of sizes.

Question 23

Role of arterioles?

Answer 23

Regulating BP + flow, globally + locally

Question 24

How do arterioles look with H/E stain?

Answer 24

More T.media , for contractility against high BP
Smooth muscle of T.media runs circularly
Smallest arterioles have 1-2 layers of smooth muscle

Question 25

Features of capillaries?

Answer 25

Endothelium only, with scattered pericytes

Question 26

What are pericytes?

Answer 26

spindly cells, suggested to be stem cells for repair and/or contractile

Question 27

Diameter of capillaries?

Answer 27

3-(20-40) µm

Question 28

Diameter of 🔴?

Answer 28

7-8 µm

Question 29

What's the capillary diameter made of?

Answer 29

thin cytoplasm of 1-2 endothelial cells

Question 30

Role of layer of endothelial cytoplasm?

Answer 30

limits exchange + allows regulation

Question 31

Features of continuous capillaries?

Answer 31

no holes in walls

Question 32

Features of fenestrated capillaries?

Answer 32

many tiny pores in wall (right through cytoplasm)

Question 33

Role of fenestrated capillaries?

Answer 33

permeable, although limited by molecular diaphragm.

Question 34

What are sinusoids?

Answer 34

subgroup of fenestrated capillaries

Question 35

Features of sinusoids?

Answer 35

wider fenestrated capillaries (20-40 µm)

Question 36

Where are sinusoids located + why?

Answer 36

liver, spleen, allowing slow blood flow + highest rates of exchange

Question 37

How do typical capillaries in loose connective tissue look with H/E stain?

Answer 37

endothelial cell + pericyte (purple flat)

Question 38

How to see fenestrations?

Answer 38

SEM

Question 39

How big are fenestrations?

Answer 39

~70 nm pores

Question 40

Features of veins + venules?

Answer 40

Thin, flexible wall Adventitia: prominent Media: thin, but still controls BP + flow No Media in smallest Major veins have longitudinal smooth muscle in wall to assist flow against gravity Valves

Question 41

Role of veins + venules?

Answer 41

return low-pressure blood to heart

Question 42

Why does the saphenous vein have valves?

Answer 42

help with the flow against gravity

Question 43

Diff between venule vs arteriole?

Answer 43

larger diameter thinner wall less smooth muscle less rounded

Question 44

Role of heart?

Answer 44

Pumping blood | Regulation of BP: atria secretes atrial natriuretic peptide (ANP)

Question 45

What would you see in a TEM of part of atrial cardiac muscle cell?

Answer 45

dense (secretory) granules of ANP | myofibril

Question 46

What happens when the atria fills with blood?

Answer 46

- atria stretches after being filled with blood - release atrial natriuretic peptide (ANP) - increases secretion of water + Na into urine - reduction of BP

Question 47

What are the 3 layers of the heart?

Answer 47

epicardium (visceral pericardium) myocardium ENDOcardium

Question 48

Features of epicardium?

Answer 48

Outer layer Smooth lubricated epithelial covering = mesothelium Fatty (adipose) loose connective tissue with nerves, blood vessels (coronary arteries) sparse collagen

Question 49

Features of myocardium?

Answer 49

Middle layer | bundles of cardiac muscle running in diff directions, with septa of dense connective tissue

Question 50

Role of myocardium?

Answer 50

Contracts to give heartbeat

Question 51

Features of endocardium?

Answer 51

Thin layer of connective tissue Some collagen Endothelial lining Rich in Purkinje fibres

Question 52

What's mesothelium made of?

Answer 52

simple cuboidal epithelium

Question 53

Role of Purkinje fibres?

Answer 53

impulse-conducting system

Question 54

How does the aortic valve look with EVG (elastic-Van Gieson) stain?

Answer 54

elastic fibres along aortic face | collagen fibrous supporting tissue (underneath elastic fibres)

Question 55

How does an infected valve look with H/E stain?

Answer 55

thrombus | bacteria: purple