Physiology: The Peripheral Circulation

Question 1

What is the function of capillaries?

Answer 1

For exchange

Question 2

What are the features of capillaries?

Answer 2

Thin walled - 1 cell thick

Small Diameter - bug surface area: volume ratio

Question 3

What are the different types of capillaries?

Answer 3

Continuous
Fenestrated
Discontinuous

Question 4

What are the features of continuous capillaries?

Answer 4

No clefts or pores

Clefts only in muscles

Question 5

Where are continuous capillaries found in the body?

Answer 5

Brain and Muscle

Question 6

What are features of fenestrated capillaries?

Answer 6

Clefts and pores

Question 7

Where are fenestrated capillaries found in the body?

Answer 7

Intestine

Question 8

What are the features of discontinuous capillaries?

Answer 8

Massive clefts and pores

Question 9

Where are discontinuous capillaries found in the body?

Answer 9

Liver

Question 10

What factors effect diffusion from the capillaries to the cells?

Answer 10

Self regulating
Non-saturable
Non-polar substances across the membrane
Polar substances through clefts/ channels

Question 11

Where is carrier mediated transport observed in capillaries?

Answer 11

The brain with glucose transporters

Question 12

What effect does starlings forces have on gas exchange entering and leaving the capillaries?

Answer 12

Hydrostatic Pressure is strong nearer the arterioles and decreases towards the venules - nutrients leaving the capillaries
Osmotic Pressure increases going towards the venules - nutrients entering the capillaries

Question 13

How much blood is lost and regained through the capillaries?

Answer 13

~ 20L is lost and ~17L is regained

Question 14

What are the functions of the lymphatic system?

Answer 14

Excess fluid is drained and filtered

Question 15

What is an oedema?

Answer 15

Accumulation of excess fluid in interstitial area

Question 16

Name causes of oedema

Answer 16

Lymphatic Obstruction
Raised Central Venous Pressure due to Ventricular failure
Hypoproteinaemia
Increased capillary permeability

Question 17

How is peripheral blood flow controlled?

Answer 17

Controlled by resistance of arterioles which is controlled by the radius of the vessel

Question 18

What is the formula of Mean Arterial Pressure?

Answer 18

MAP= CO x TPR

Question 19

What effect does intrinsic mechanisms have on control of the peripheral circulation?

Answer 19

Concerned with meeting the selfish needs of the tissue

Question 20

What are the effects of extrinsic mechanisms on the control of the peripheral circulation?

Answer 20

Concerned with controlling the TPR and therefore controlling MAP

Question 21

What extrinsic control neurally?

Answer 21

Sympathetic - release noradrenaline which bind to alpha 1 receptors causing constriction of arterioles and therefore increase TPR
Parasympathetic - no effect

Question 22

What effect does adrenaline have on the peripheral circulation?

Answer 22

Act on alpha 1 receptors and cause arteriolar constriction

However in some tissues the hormone binds to Beta 2 receptors and cause arteriolar dilation and decreases TPR

Question 23

What are the extrinsic controls of peripheral circulation?

Answer 23

Hormonal

Neural

Question 24

What are some of the hormones that effect on the peripheral circulation?

Answer 24

Adrenaline
Angiotensin II
Vasopressin
Atrial Natriuretic Factor

Question 25

What types of tissue have arteriolar dilation when adrenaline is secreted into the blood?

Answer 25

Skeletal muscle and cardiac muscle

Question 26

When is angiotensin II secreted into the blood?

Answer 26

When there is low blood volume

Question 27

What effect does angiotensin II have on TPR?

Answer 27

Causes arteriolar constriction which increases TPR

Question 28

When is Vasopressin (antidiuretic hormone) secreted into the blood?

Answer 28

When there is low blood volume

Question 29

What effect does vasopressin have on TPR?

Answer 29

Causes arteriolar constriction causing TPR

Question 30

When is Atrial Natriuretic Factor secreted into the blood?

Answer 30

When there is a high blood volume

Question 31

What effect does atrial natriuretic factor have on TPR?

Answer 31

Causes arteriolar dilation which causes a decrease in TPR

Question 32

What are the local controls of local tissue flow in peripheral circulation?

Answer 32

Active (metabolic) hyperaemia Pressure (flow) autoregulation Reactive Hyperaemia Injury Response

Question 33

What events occur when there is increased metabolic activity in the local tissue?

Answer 33

The increases conc of metabolites triggers the release of endothelial dependant relaxing factor (EDRF) causing arteriolar dilation This allows the wash out of the metabolites

Question 34

What events occur in local tissue when there is a decrease in arterial pressure? (Pressure auto-regulation)

Answer 34

The decrease in flow causes an accumulation of metabolites in the cerain tissue allowing EDRF to be released. This causes arterioles to dilate allowing blood flow to be normalised Can allow maintenance of blood supply even with changes of MAP

Question 35

What does an occlusion of blood supply cause to local arterioles in a tissue? (Reactive Hyperaemia)

Answer 35

There is an increase in blood flow due to arteriolar dilation

Question 36

What are the events the occur in arterioles when there is an injury to the local tissue?

Answer 36

Mast cells produce histamine which cause arteriolar dilation (increasing flow) and an increase in permeability

Question 37

When is there blood flow highest in the aorta?

Answer 37

During systole

Question 38

When is the blood flow highest in the coronary arteries?

Answer 38

During diastole

Question 39

What is special about the coronary circulation?

Answer 39

Blood supply interrupted by systole Able to cope with increased demand during exercise Active Hyperaemia Expresses B2 receptors Swamps sympathetic arteriolar constriction

Question 40

What is special about the cerebral circulation?

Answer 40

Need to be kept stable | Shows excellent pressure auto regulation

Question 41

What is special about the pulmonary circulation?

Answer 41

Decrease in O2 causes arteriolar constriction which is opposite other tissue Allows blood to be directed to highly ventilated parts of the lung

Question 42

What is special about the renal circulation?

Answer 42

Main function is filtration Dependant on pressure Changes in MAP have big effect on blood volume Excellent pressure auto-regulation