CVS S1 - Introduction and histology of cardiovascular system

Question 1

What 3 factors affect diffusion?

Answer 1

• Area available for exchange
• Diffusion resistance
• Concentration gradient

Question 2

How is the area available for exchange determined?

Answer 2

Capillary density - how many capillaries per unit volume

Question 3

How is diffusion resistance determined?

Answer 3

Nature of the barrier and nature of the molecule diffusing

Path length

Question 4

Why is adequate blood flow so important for maintenance of capillary exchange?

Answer 4

Unless blood is supplied at an appropriate rate, the gradients between capillary content and nearby cells will dissipate and nutrients will not be supplied at the the right rate for the prevailing metabolic activity

Question 5

What are the main components of the CVS?

Answer 5

Pump - Heart

Distribution vessels - Arteries

Flow control - Arterioles and pre-capillary sphincters

Capacitance - ability to cope with changes in cardiac output via storage of blood in veins

Question 6

How is blood volume distributed throughout the body in percentages?

Answer 6

Veins - 67%

Heart + lungs - 17%

Arteries and arterioles - 11%

Capillaries - 5%

Question 7

What are the three main purposes of the cvs ?

Answer 7

• Deliver between 5 and 25 litres per min of blood to the body
• Maintain a blood flow of 0.75 litres per min to the brain
• Maintain blood flow to heart and kidneys at all times

Question 8

What is the mediastinum?

Answer 8

Intervening region in the thoracic cavity between the right and left pleural cavities which are occupied by the lungs

Question 9

What makes up the middle mediastinum?

Answer 9

Pericardial sac containing the heart, its coronary vessels and the roots of the aorta, superior and inferior vena cava and the pulmonary vessels

Question 10

Describe the structure of the pericardium?

Answer 10

Two layers

Fibrous outer layer of connective tissue

Inner serous layer for lubrication that is split into two layers: the visceral (touching heart) and the parietal (attache to inside of the fibrous layer)

Question 11

Where are the visceral and parietal layers of the serosa found?

Answer 11

Visceral - Outer lining of the heart

Parietal - Attached to inside of fibrous layer of pericardium

Question 12

Describe the structure of elastic arteries

Answer 12

Tunica Intima - endothelium cells with long axes parallel to the long axes of the artery, narrow sub endothelium of connective tissue, discontinuous elastic lamina

Tunica Media - 40-70 fenestrated elastic membranes, smooth muscle and collagen between lamellae

Tunica Adventitia - Fibroelastic connective tissue containing vasa vasorum, nerve and lymph vessels

Question 13

Describe the structure of muscular arteries

Answer 13

Tunica Intima - Endothelium and internal elastic lamina

Tunica media - 40 layers of smooth muscle connected via gap junctions, external elastic lamina

Tunica Adventitia - Fibroelastic connective tissue containing vasa vasorum, nerve lymph vessels and nerves

Question 14

What is the function of the unmylinated nerve endings in the tunica adventitia of muscular arteries?

Answer 14

Noradrenaline is released from unmyelinated nerve endings and travels through fenestrations in the external elastic lamina to depolarise smooth muscle cells in the tunica media causing vasoconstriction

Question 15

Describe the structure of arterioles

Answer 15

• No internal or external elastic lamina
• Diameter of less than 0.1mm
• 1-3 layers of smooth muscle cells
• Tunica adventitia is scant

Question 16

What is the function of meta-arterioles?

Answer 16

Supply blood to the capillary bed

Question 17

How is the structure of meta-arterioles related to their function?

Answer 17

Discontinuous smooth muscle which form pre-capillary sphincters around endothelial cells enabling control of blood flow into the capillary bed

Question 18

Describe the structure of a capillary

Answer 18

• Single layer of endothelium with adjacent basement membrane
• Diameter of 7-10 micrometers and 1mm in length

Question 19

How is the structure of capillaries adapted to their function?

Answer 19

• Slowest velocity of blood flow through capillaries as velocity is inversely proportional to cross sectional area means that there is maximum time for gas and nutrient exchange.
• Narrow diameter means that a red blood cell occupies the entire lumen so diffusion path length is short

Question 20

What are the three types of capillaries?

Answer 20

• Continous
• Fenestrated
• Sinusoid

Question 21

Describe the structure of continuous capillaries

Answer 21

Pericytes form branching network on outer surface of endothelium

Question 22

What are pericytes?

Answer 22

Cells capable of forming smooth muscle cells or fibroblasts in angiogenesis, tumour growth and wound healing

Question 23

Describe the structure of fenestrated capillaries

Answer 23

Pericytes still present yet there are pores in the endothelium

Question 24

Describe the structure of sinusoids

Answer 24

Discontinuous basal lamina creates large openings in the endothelium enabling WBC and RBC to move in and out

Question 25

What are discontinuous sinusoids?

Answer 25

Sinusoids with no tight junctions found in the liver and spleen

Question 26

Describe the structure of post-capillary venuoles

Answer 26

• Diameter of 10-30 micrometers

- More permeable than capillaries and decreasing pressure

Question 27

How does the structure of post-capillary venues relate to their function?

Answer 27

Site of most fluid and leukocyte emigration in inflammation due to increased permeability

Question 28

Describe the structure of veins

Answer 28

• Wide diameter and thin wall

- More connective tissue in tunica media and less elastic lamina and smooth muscle cells

Question 29

How does the structure of small to medium veins differ to large veins?

Answer 29

Small/medium - well developed tunica adventitia

Large - longitudinal smooth muscle in tunica adventitia and circular smooth muscle in tunica media

Question 30

What is different about superficial veins of the leg?

Answer 30

Well defined muscle layer to aid transport of blood back to the heart overcoming gravity