Blood Vessel Histology

Question 1

What are the main 3 layers of blood vessels?

Answer 1

Tunica intima - endothelium (simple squamous) Tunica media - mixture of smooth muscle and some elastic fibres Tunica adventitia - collagen, reinforcement, prevents overexpansion

Question 2

Which arteries are muscular and which are elastic?

Answer 2

Elastic - aorta and its major branches Muscular - rest

Question 3

What is the function and histological features of the aorta?

Answer 3

• Function - conduct blood at high pressures and as a shock absorber to dampen the pulsatory blood flow
• Fenestrated lamellae
• Vasa vasorum - small blood vessels in the adventitia which nourish the outer 2/3 of the media and adventitia

Question 4

What are the functions of muscular arteries?

Answer 4

• Alter the direction of cardiac output due to changes in activity
• Divert blood from other organs e.g. GIT to muscles during exercise
• Due to the combined action of constriction o f muscular distributing arteries and arterioles to change the diameter and hence direction of blood flow. And dilation of vessels supplying muscles.

Question 5

What are the histological characteristics of a muscular artery?

Answer 5

• Prominent internal elastic lamina between the intima and media (in larger vessels there is also an external elastic lamina)
• Media is mainly smooth muscle under sympathetic control. Also contains elastic fibres
• Adventitia consists of CT and vasa vasorum

Question 6

What are the histological features and function of arterioles?

Answer 6

• Components of the wall - intima, internal elastic lamina (fenestrated), media (<5 layers), adventitia (blends with surrounding CT)
• Regulates amount of blood entering capillary beds

Question 7

What is microcirculation?

Answer 7

Blood flow through a capillary bed that can be altered by the action of precapillary sphincters (constricting and relaxing)

Question 8

What are the types of microcirculation?

Answer 8

1. Precapillary anastomosis - e.g. skin, SI. Allows blood to bypass the capillary bed without undergoing gas exchange. Arterial-venous shunt.
2. Arterial portal system - kidney glomerulus
3. Venous portal system - hepatic portal system

Question 9

What is a pericyte?

Answer 9

An undifferentiated cell which has the potential to differentiate into a smooth muscle cell.

Question 10

What types of capillaries can be found in the body?

Answer 10

1. Continuous - found in most areas of the body, have varying permeability
2. Fenestrated/porous - can have open fenestrae (kidney) or closed fenestrae (SI). More permeable than continuous
3. Sinusoids - discontinuous endothelium, absent basal lamina e.g. liver, spleen

Question 11

How are veins classified and what is their function?

Answer 11

• Function - capacitance/storage >60% of blood volume
• Classified as venules (post capillary and muscular) or sm, med, or large veins

Question 12

How can veins be distinguished from arteries?

Answer 12

• designed for capacitance
• have a thin wall with respect to the lumen
• have no internal elastic laminae
• have a thin media
• have valves (endothelium, outpockets of the intima)

Question 13

Describe the structure of large veins, e.g. caudal vena cava

Answer 13

• adventitia - longitudinal bundles of smooth muscle, spiral network of collagen bundles interwoven with elastic fibres to prevent overexpansion
• media - cardiac muscle is found here close to the heart

Question 14

Describe the structure of lymphatic vessels

Answer 14

• begin as lymphatic capillaries
• lined with endothelium
• lack a basal lamina
• thin walled veins
• contain valves
• main vessels are thoracic duct, tracheal duct and R lymphatic duct