Control Of The Circulation

Question 1

Why do we need to control the circulation

Answer 1

To maintain blood flow
To maintain arterial pressure
To distribute blood flow
Auto-regulation/homeostasis
To function normally
To prevent catastrophe
To maladapt in disease

Question 2

Characteristics of arteries

Answer 2

Low resistance conduits
Elastic
Cushion systole
Maintain blood flow to organs during diastole

Question 3

Where is the principle site of resistance of vascular flow

Answer 3

Arterioles

Question 4

What is TPR

Answer 4

Total arteriolar resistance

Question 5

What is TPR determined by

Answer 5

Local, neural and hormonal factors

Question 6

What are 2 major roles of arterioles

Answer 6

Major role in determining arterial pressure
Major role in distributing flow to tissue/organs

Question 7

What determines the radius of the arterioles

Answer 7

Vascular smooth muscle

Question 8

What happens if the vascular smooth muscle contracts

Answer 8

The radius decrease so the resistance increases and the flow decreases

Question 9

What happens when vascular smooth muscle relaxes

Answer 9

When the vascular muscle relaxes the radius increases which causes the resistance to decrease and the flow to increase

Question 10

Why does vascular smooth muscle never completely relaxed

Answer 10

Myogenic tone

Question 11

What does the slow flow of capillaries allow

Answer 11

It allows time for nutrients and waste to be exchanged

Question 12

How is flow determined inside the capillaries

Answer 12

Arteriolar resistance
Number of open pre-capillary sphincters

Question 13

Characteristics of veins

Answer 13

Compliant
Low resistance conduits
Valves present to aid venous return against gravity
Skeletal muscle/respiratory pump aids venous return
Vasoconstriction maintains venous return/pressure

Question 14

How is cardiac output calculated

Answer 14

Heart rate X stroke volume

Question 15

How is blood pressure calculated

Answer 15

Cardiac output X Total peripheral resistance

Question 16

How is pulse pressure calculated

Answer 16

Systolic - diastolic pressure

Question 17

How is mean arterial pressure calculated

Answer 17

Diastolic pressure + 1/3 pulse pressure

Question 18

What governs flow

Answer 18

Ohms law and poiseuilles law

Question 19

What is ohms law

Answer 19

Flow = pressure gradient/resistance

Question 20

What is poiseuille’s equation

Answer 20

Flow = radius to the power of 4

Question 21

What is the frank starling mechanism

Answer 21

Stroke volume increases as end diastolic volume increases, due to the length-tension relationship of muscle the end diastolic volume would increase so the stretch would increase along with the increased force of contraction. At rest the cardiac muscle is not at its optimum length. Increased vascular resistance increases end diastolic volume which increases stroke volume and increased cardiac output even if heart rate is constant

Question 22

What is the goal of control of circulation

Answer 22

Maintain blood flow
CO = SV X HR
This needs pressure to bush blood through the peripheral resistance

Question 23

What is blood pressure

Answer 23

Blood pressure is the pressure of blood within and against the walls of the arteries

Question 24

When is systolic blood pressure the highest

Answer 24

It is highest when the ventricles contract

Question 25

When is diastolic blood pressure the lowest

Answer 25

It is lowest when the ventricles relax

Question 26

How is blood pressure measured

Answer 26

Using the brachial artery

Question 27

Why is the brachial artery used to measure blood pressure

Answer 27

Convenient to compress, and it is at the level of the heart

Question 28

In what ways can blood pressure be controlled

Answer 28

Auto regulation Local mediators Humoral factors Baroreceptors Central (neural) control

Question 29

What is myogenic auto regulation

Answer 29

Myogenic autoregulation of the blood vessels is when the smooth muscle of the blood vessel stretches under the pressure of the blood within the lumen, so when this decreases the vessel will contract until the diameter normalises or is slightly reduced in normal size

Question 30

Why does autoregulation vary

Answer 30

It is an intrinsic ability of an organ and so will have constant flow despite perfusion pressure changes

Question 31

Where has excellent autoregulation

Answer 31

Renal, cerebral and coronary

Question 32

Where has moderate levels of autoregulation

Answer 32

Skeletal muscle/splanchnic

Question 33

Where has poor autoregulation

Answer 33

Cutaneous vessels

Question 34

How is blood flow maintained to vital organs such as the brain and heart

Answer 34

Intrinsic control

Question 35

What is examples of a vasoconstrictor

Answer 35

Endothelin-1 Internal blood pressure/myogenic contraction

Question 36

What are examples of vasodilators

Answer 36

Hypoxia Bradykinin Tissue breakdown products

Question 37

What is essential for control of the circulation

Answer 37

Endothelium

Question 38

What are examples of circulating hormonal vasoconstrictors

Answer 38

Epinephrine - skin Angiotensin II Vasopressin

Question 39

What are examples of circulating hormonal vasodilators

Answer 39

Epinephrine- muscle Atrial natriuretic peptide

Question 40

Where are primary baroreceptors found

Answer 40

Carotid sinus and aortic arch

Question 41

Where are secondary baroreceptors found

Answer 41

Veins Myocardium Pulmonary vessels

Question 42

How do baroreceptors respond to increased blood pressure

Answer 42

Blood pressure increase is detected which results in increased firing which results in a decreases in cardiac output so reduces blood pressure

Question 43

What are the role of arterial baroreceptors in the short term

Answer 43

Key role in short term regulation of blood pressure is minute to minute control in response to exercise or haemorrhage

Question 44

What happens to baroreceptors if the arterial pressure deviates from norm for more than few days

Answer 44

The baroreceptors would adapt to a new baseline pressure which would be seen in hypertension

Question 45

What is a major factor in long-term blood pressure control

Answer 45

Blood volume

Question 46

What are the main neural influences on the medulla

Answer 46

Baroreceptors Chemoreceptors Hypothalamus Cerebral cortex Skin Changes in blood oxygen and carbon dioxide

Question 47

What does stimulation of the anterior hypothalamus causes on cardiovascular reflexes

Answer 47

Decreased blood pressure and heart rate

Question 48

What is important in the regulation of skin blood flow in the response to temperature

Answer 48

Hypothalamus

Question 49

How can the cerebral cortex affect blood flow and pressure

Answer 49

Stimulation of the cerebral cortex can usually cause increased vasoconstriction Emotion can increase vasodilation and depressor responses

Question 50

Where are central chemoreceptors found

Answer 50

In the medulla

Question 51

How is short term blood pressure changes controlled

Answer 51

Baroreceptors

Question 52

How is long term blood pressure change controlled

Answer 52

Volume of blood Na+ H2O Renin-angiotensin-aldosterone ADH

Question 53

What are the key central effectors

Answer 53

These are peripheral Blood vessel vasodilation and vasoconstriction Heart rate and contractility Kidneys fluid balance in longer term control