WEEK 3: Histology of Blood Vessels

Question 1

What do the walls of blood vessels surround

Answer 1

A central cavity known as the lumen

Question 2

Can wall complexity vary in large blood vessels?

Answer 2

Yes, it varies with vessel size (diameter) and proximity to heart

Question 3

What circuits do blood vessels form with the heart?

Answer 3

The systemic circuit and pulmonary circuit.

Question 4

What is the primary function of arteries?

Answer 4

deliver blood from the tissues to the heart

Question 5

What are the three types of artieries?

Answer 5

• Elastic (close to heart)
  -Muscular
  -Arterioles

Question 6

What is the primary function of the vein?

Answer 6

Return blood to heart

Question 7

What are the different types of veins?

Answer 7

• Venules
• Medium/large veins

Question 8

Similarities between veins and arteries?

Answer 8

• Both have 3 layers (Tunica shit)

Question 9

Which layer of wall is closest to the lumen

Answer 9

Tunica interna (thin layer)

Question 10

Which wall layer is the thickest of the three layers?

Answer 10

Tunica media

Question 11

What do the composition of these wall layers influence?

Answer 11

Blood flow & Blood pressure

Question 12

What is the tunica interna made up of?

Answer 12

Endothelium
- Thin- Simple squamous epithelium
- Smooth
- Antithrombogenic
-Basement membrane
-Subendothelial connective tissue
-Internal elastic lamina - IEL

Question 13

What is the tunica media made up of?

Answer 13

• variable quanitites of elastic tissue/smooth muscle
• smooth muscle has a concentric arrangement of fibres that participate in contraction and relaxation
• Elastic laminae

Question 14

What is the tunica externa made up of?

Answer 14

• thickest in veins
  made up of fibrous connective tissues
  abundant collagen fibres
  external elastic lamina (EEL)
  can contain smooth muscle in veins
  can contain a number of smaller blood vessels (vasa vasorum)
  Can contain adipose tissue

Question 15

What are elastic arteries responsible for?

Answer 15

They are conducting arteries and asssist with the propulsion in a forward direction of the blood as the heart beats. These vessels have a large diameter and a thick wall, and are located close to the heart

Question 16

Why do elastic arteries have thick walls?

Answer 16

so it can withstand very high pressures exerted on it from the blood

Question 17

Media has?

Answer 17

a high elastin content organised as numerous concentric elastic laminae sheets

Question 18

What does laminae stretching during systole and recoiling during diastole do?

Answer 18

Reduce the amplitude of fluctuations in blood pressure hence propelling blood forwards

Question 19

Why is there vasa vasorum in the adventitia?

Answer 19

To provide O2 and nutrients to outer wall regions.

Question 20

What are muscular arteries?

Answer 20

Distributing arteries that have a role in directing blood flow to particular organs/regions of the body as metabolic requirements change

Question 21

T or F: The tunica media has less smooth muscle than elastic/collagen fibres

Answer 21

F

Question 22

What are arterioles?

Answer 22

They are resistance vessels
- smaller diameter, thinner less complex wall structure than arteries
- less than 5 mm diameter

Question 23

What is the primary function of these vessels (arterioles)?

Answer 23

• by constricting/varying/relaxing, they can reduce blood pressure and enable flow through capillaries - hence allowing for microcirculation

Question 24

Define microcirculation

Answer 24

the circulation of blood in the smallest blood vessels -> arterioles, capillaries & venules
It’s primary role is maintaining tissue health & regulating blood pressure

Question 25

What is the function of venules?

Answer 25

collect blood from capillaries

Question 26

What occurs to the tunica intima layer in venules?

Answer 26

It is reduced to an endothelium

Question 27

What occurs to the tunica media in a venule

Answer 27

It becomes thinner - 1-2 layers of smooth muscle fibres/elastic fibres

Question 28

What is the function of pericytes

Answer 28

They surround small venules and control blood flow through the microvasculature

Question 29

Define microvasculature

Answer 29

the network consisting of the smallest blood vessels in the body (arterioles, capillaries and venules)

Question 30

What are the role of medium sized veins?

Answer 30

They are blood reservoirs, due to high capacitance

Question 31

what is a capacitance vessel?

Answer 31

One that is able to distend/stretch readily, even at low pressures

Question 32

what differentiates a medium vein from an artery

Answer 32

The lumen in a medium vein is thin-walled, large and irregular compared to the lumen in an artery

Question 33

what is the function of the thin folds of tunica intima valves

Answer 33

- prevent backflow of blood

Question 34

what distinguishes the tunica media in a medium vein?

Answer 34

It consists of a low muscle content that makes it patchy and discontinuous, 2-3 cell layers only

Question 35

what distinguishes the tunica adventitia in a medium vein?

Answer 35

- it is the broadest layer compared to the intima and media - it consists of longitudinal collagen fibres and vasa vasorum

Question 36

what is the primary function of the large vein ?

Answer 36

acts as a blood reservoir

Question 37

what distinguishes the large vein from other veins?

Answer 37

- contains no valves and no IEL - the intima is thinner than the same sized arteries - a very prominent tunica adventitia high collagen content - prevents overdistension - vasa vasorum is present

Question 38

Artery VS vein

Answer 38

artery is part of a high pressure system VS vein is a low pressure system artery = pressure reservoir VS vein is a blood reservoir vessels in the artery are at full blood capacity whereas the vessels in the vein are at 30-70% blood capacity no valves present in arteries VS valves present in veins well defined circumferential muscle layer in the media of an artery VS reduced muscle in media, less compact and patchy distribution in vein. Adventitia in artery is thinner whereas it is thicker in vein vessels have small lumens and thick walls in artery whereas in veins vessels have larger lumens and thin walls

Question 39

What is vasa vasorum?

Answer 39

small blood vessels that supply the walls of large blood vessels like arteries and veins

Question 40

What are capillaries?

Answer 40

they are the smallest vessels and are the sites of exchange between blood and tissues

Question 41

what are the 3 types of capillaries

Answer 41

continuous, fenestrated and sinusoidal/discontinuous

Question 42

What is the wall structure of capillaries?

Answer 42

- reduced complexity - consists of endothelium that could consist of fenestrations and tight junctions, as well as pinocytotic vesicles -Basal lamina - external to endothelial cell - could consist of pericytes

Question 43

In a blood vessel, the endothelial cell is always simple squamous : T or F

Answer 43

T

Question 44

Why are endothelial cells thin (attenuated)

Answer 44

To maximise the exchange between blood and tissues

Question 45

Endothelial cells breakdown lipoproteins to triglycerides and cholesterol: T or F

Answer 45

T

Question 46

Why are there intercellular tight junctions between endothelial cells?

Answer 46

To restrict passage of materials between endothelial cells

Question 47

What is a continuous capillary

Answer 47

- It is the most widespread type of capillary - Tight junctions - Many pinocytotic vesicles for exchange - No gaps between endothelial cells

Question 48

What is a fenestrated capillary

Answer 48

- characterised by interruptions in endothelium - endothelial cell cytoplasm is pierced by pores = fenestrations - extend through full thickness of wall -allow for extensive exchange between blood & tissue - thin diaphragm - diaphragm is thinner than the cell membrane

Question 49

What is a sinusoidal/discontinous capillary?

Answer 49

allow for the maximum exchange of blood and tissues, with gaps in walls allow transport of whole cells between blood/tissues

Question 50

What are some characteristics of a sinusoidal capillary

Answer 50

- numerous large fenestrations -large diameter -follow a tortuous/irregular pathway -incomplete endothelial lining -discontinous basal lamina

Question 51

what is the functional implication of continuous capillaries

Answer 51

tight capillaries that allow for selective exchange of molecules - slower exchange

Question 52

what is the functional implication of fenestrated capillaries - where you want a reasonable amount of exchange fairly rapidly

Answer 52

less selective, more rapid, but not to the same extent to sinusoidal capillaries - so not extremely leaky but in the middle of the continuum

Question 53

What kind of exchange can occur in capillaries?

Answer 53

either selective exchange or more rapid exchange