Cardiovascular System Histology

Question 1

What are the 3 layers of blood vessels?

Answer 1

Tunica intima, media and adventitia (or serosa)

Question 2

Outline the general composition of the tunica intima

Answer 2

Endothelium layer, layer of loose CT and internal elastic lamina (separates from tunica media)

Question 3

Outline the general composition of the tunica media

Answer 3

Circular layer of smooth muscle (contraction regulates blood flow), supporting ECM (collagen and elastic fibres) and external elastic lamina (separates from adventitia)

Question 4

Outline the general composition of the tunica adventitia

Answer 4

Loose CT, vasa vasorum (nutrient arteries) to supply outer portion of large vessels

Question 5

What are the 3 layers of the heart wall?

Answer 5

Endocardium, myocardium and epicardium

Question 6

Describe the composition of the endocardium

Answer 6

Endothelial lining supported by elastic fibrocollagenous tissue (allows stretch)

Question 7

Describe the composition of the myocardium

Answer 7

Cardiac myocytes (intercalated discs connect) supported by vascularised fibrocollagenous tissue

Question 8

Describe the composition of the epicardium

Answer 8

Fibrocollagenous tissue with adipose tissue, act to carry coronary arteries and autonomic nerves

Question 9

What is mesothelium?

Answer 9

Epithelia that lines the pericardium

Question 10

What are cardiac myoocytes?

Answer 10

Short, branching cells with round central nuclei which are connected by intercalated discs (muscle cells of heart)

Question 11

What is angina?

Answer 11

Chest pain at times of increased heart demand

Question 12

What is myocardial infarction?

Answer 12

Heart attack; tissue necrosis due to ischaemia

Question 13

What is the biggest cause of death in the UK?

Answer 13

IHD

Question 14

Describe what happens to necrotic cardiac muscle following myocardial infarction (heart attack)

Answer 14

Necrotic cardiac myoocytes are replaced by a fibrous scar tissue to an acute inflammation response where neutrophils invade the site and cause tissue granulation to form cellular and vascularised loose CT

Question 15

What are the two main types of artery?

Answer 15

Elastic and muscular

Question 16

How are elastic arteries characterised?

Answer 16

Predominance of elastin and little SM in tunica media

Question 17

Describe the histology of elastic arteries

Answer 17

Intima: endothelium, loose CT and internal elastic lamina
Media: concentric fenestrated elastic sheets (merge with int/ext lamina) with smooth muscle and collagen between sheets
Adventitia: loose CT with vasa vasorum

Question 18

How are muscular arteries characterised?

Answer 18

Predominance of smooth muscle in tunica media

Question 19

Describe the histology of muscular arteries

Answer 19

Intima: smaller CT layer than elastic artery
Media: circular SM layers
Adventitia: Thick for vessel size with collagen and thicker elastic fibres

Question 20

What is arteriosclerosis?

Answer 20

Thickening and loss of elasticity in arterial walls leading to increased PVR and BP, increasing the risk of rupture

Question 21

What is atherosclerosis?

Answer 21

Most common pathology of arteriosclerosis and involves formation of yellow, fatty plaques in larger arteries

Question 22

Outline the pathogenesis of atherosclerosis

Answer 22

Endothelial damage –> altered endothelial permeability –> LDL and cell adhesion factors present –> monocyte and T cell migration –> accumulation of T cells and lipid-laden foam cells (macrophages) and lipid-laden SM from tunica media –> fatty streak formed –> fibrous cap over plaque toped by endothelia

Question 23

Which cells accumulate lipid in the development of atheromas?

Answer 23

Smooth muscle cells and macrophages

Question 24

What type of cell cover atheromatous plaques?

Answer 24

Endothelial cells

Question 25

What is a precapillary sphincter?

Answer 25

Band of SM at start of capillary (from arteriole) where contraction determined the extent of the capillary bed involved in exchange

Question 26

What are thoroughfare channels?

Answer 26

A-V shunts, connects arterioles and venules and relaxation of SM causes the blood to shunt away from capillary bed to venules

Question 27

What are pericytes?

Answer 27

Contractile cells which can proliferate to become mesenchymal cells in repair, which can differentiate into new endothelial cells, fibroblasts or myofibroblasts

Question 28

Describe the histology of capillaries

Answer 28

Single layer of endothelial cells which don't have tunica media and have little/no adventitia

Question 29

What are sinusoids?

Answer 29

Large diameter capillaries

Question 30

What are the 3 types of capillary?

Answer 30

Continuous, fenestrated and discontinuous

Question 31

Describe the structure of continuous capillaries

Answer 31

Uninterrupted endothelium on continuous basement membrane (form BBB and are relatively impermeable)

Question 32

Describe the structure of fenestrated capillaries

Answer 32

Found at sites of great molecular exchange; have uninterrupted endothelium with circular pores (fenestrae)

Question 33

Describe the structure of discontinuous capillaries

Answer 33

Found where blood components interact directly with tissue/organ; endothelium and basement membrane are discontinuous and endothelium is supported by reticulin fibre meshwotk

Question 34

Describe the general structure of veins

Answer 34

Large lumen and thin walls

Question 35

What are the two types of venules?

Answer 35

Post-capillary and muscle venules

Question 36

Describe the structure of post-capillary venules

Answer 36

There are only pericytes surrounding epithelium

Question 37

Describe the structure of muscular venules

Answer 37

Continuous smooth muscle (media) and fibrocollagenous adventitia present

Question 38

What is the main role of venules?

Answer 38

Major site of leucocyte migration in tissues and venule endothelium is sensitive to histamine --> leakiness

Question 39

Describe the histology of veins

Answer 39

Intima: endothelium and CT (elastic fibres) Media: variable, more circular muscle in legs Adventitia: thick fibrocollagenous CT with vasa vasorum in larger veins

Question 40

What are valves?

Answer 40

Semi-lunar projections of tunica intima consisting of fibro-elastic tissue covered by endothelium

Question 41

What is vasa vasorum?

Answer 41

Network of arteries which supply the tunica adventitia of larger blood vessels

Question 42

What is the main type of connective tissue present in the heart walls?

Answer 42

Fibrocollageneous connective tissue

Question 43

What is the main difference between elastic and muscular arteries?

Answer 43

Muscular have much smooth muscle in tunica media, elastic arteries do not

Question 44

Where are pericytes found?

Answer 44

In tunica intima; form discontinuous layer external to the capillary endothelium