Module three - The Circulatory System

Question 1

What is the overall purpose of the cardiovascular system?

Answer 1

To provide adequate blood flow to all tissues/ organs according to their immediate needs.

Question 2

What are the three tunics called?

Answer 2

intima, media and externa

Question 3

Vessels with specific structures for specific functions

Answer 3

Elastic arteries: conducting vessels
Muscular arteries: distributing vessels
Arterioles: resistance vessels
Capillaries: exchange vessels
Venules and veins: capacitance vessel

Question 4

What determines the dynamics of circulation?

Answer 4

Blood flow, blood pressure and resistance

Question 5

What is bood flow?

Answer 5

The volume of blood flowing through a vessel, organ or the entire circulation in a given time period. It is determined by blood pressure and resistance

Question 6

What is blood pressure?

Answer 6

The force exerted on a vessel wall by the blood in that vessel. expressed in mmHg. It is the force generated by the pumping of the heart that keeps blood moving (maintains blood flow)

Question 7

What is resistance?

Answer 7

Opposite to blood flow. A measure of the amount of friction blood encounters as it flows through a vessel. There are three types of resistance.

Question 8

What are the three types of resistance?

Answer 8

Blood viscosity, total blood vessel length and blood vessel diametre.

Question 9

What does viscosity refer to?

Answer 9

The thickness or stickiness of a fluid, due to formed elements (cells) and plasma proteins.

Question 10

How does vessel length change resistance?

Answer 10

resistance to flow increases as the vessel length increases.

Question 11

How does vessel diametre affect resistance?

Answer 11

The amount of contact between two surfaces determines the amount of friction - friction determines ease of movement.
The more contact the blood has with the walls of the vessel, the more friction between the blood and the vessel wall = more resistance.
As diametre changes, the degree of resistance to blood flow changes, depending on how much of the blood is contacting the vessel walls

Question 12

What is the primary means of altering local blood flow?

Answer 12

Changes in arteriole diametre.
vasoconstriction: decreased diametre - increased resistance - decrease blood flow.
Vasodialation: increase diametre - decrease resistance - increase blood flow.

Question 13

How is blood flow determined? (equation)

Answer 13

F= P/R

Question 14

What is sytemic blood pressure?

Answer 14

the pumping action of the heart generates pressure, which in turn drives blood. Highest in the aorta, lowest i venae cavae/ veins

Question 15

What is arterial blood pressure?

Answer 15

Reflects two factors;
1. how much elastic arteries can be stretched
2. the volume of blood forced into the elastic arteries by ventricular contraction i.e. stroke volume
Two types of arterial BP (systolic and diastolic)

Question 16

What are the two types of arterial blood pressure?

Answer 16

Systolic pressure: peak pressure generated in large arteries when the ventricles contract (average 120mmHg)
Diastolic pressure: pressure in large arteries during ventricular relaxation (average 80mmHg)

Question 17

What is pulse pressure?

Answer 17

PP= systolic pressure- diastolic pressure. i.e. 120-80 = 40mmHg. Felt as throbbing sensation in the artery, declines with increasing distance from heart

Question 18

What is mean arterial pressure?

Answer 18

MAP = the pressure that propels blood through the vessels.
MAP = diastolic pressure + (1/3 X pulse pressure)
= 80+ (1/3 X 40)
= 93mmHg

Question 19

What is hypotension?

Answer 19

Systolic pressure is below 100mmHg. May result in dizziness and fainting

Question 20

What is hypertension?

Answer 20

transient elevation due to exercise, illness, or emotional states. Chronis hypertension is sustained systolic pressure above 140mmHg: major cause of heart failure, vascular disease and stroke.

Question 21

What is capillary blood pressure

Answer 21

Blood pressure in capillaries. ranges from 35mmHg in the arterial end of capillary bed to 15mmHg at venous end.
** Low capillary pressure is required due to fragile capillary walls and the permeability of capillaries, so low pressure is adequate for fluid exchange

Question 22

What is venous return?

Answer 22

involves numerous factors:

1. valves (compartmentalise blood to move it and prevent backflow)
2. muscular pump (muscle contraction squeezes veins = pushes blood)
3. respiratory pump (squeezing of abdominal veins as thoracic veins expand… helps blood move toward heart due to pressure changes)
4. Pulsation (in nearby arteries)
5. Venoconstriction (tunic media)

Question 23

What are the factors that influence blood pressure?

Answer 23

1. cardiac output (rapid, short term regulation)
2. Peripheral resistance (rapid, short term regulation)
3. Blood volume (slower, long term regulation)

Question 24

How is blood pressure regulated?

Answer 24

1. autoregulation: occurs within tissues and is dependent on local conditions
2. neural regualtion: involves cardiovascular centres and ANS
3. renal mechanisms
4. endocrine regulation

Question 25

How does local regulation (autoregulation) of blood flow occur?

Answer 25

tissues can regulate their own blood flow and pressure in response to local conditions by:

1. altering arteriole diametre
2. opening or closing pre-capillary sphincters (alters blood flow into capillary beds)

Question 26

What is neural regulation?

Answer 26

the brains control of cardiovascular activity. three centres:
1. cardioinhibitory centre
2. cardioaccelatory centre
3. vasomotor centre 
Located in medulla oblongata. 
Input from hypothalamus includes:
- regularion of blood flow by maintaining temp. 
- fight or flight initiation.

Question 27

What is the vasomotor centre?

Answer 27

in medulla oblongata and involved in neural regulation.

sympathetic vasomotor fibres to the smooth muscle of arterioles - changes in vasomotor tone - changes in vessel diametre

Question 28

What are the two types of renal mechanisms?

Answer 28

1. direct mechanisms: rate of urine formation is determined by blood pressure
2. indirect mechanisms: involves hormones