Introduction to CVS

Question 1

general properties of CV

Answer 1

Structure of heart & circulatory system Blood volume distribution Properties of vessels
Pressure distribution & dissipation Measurement of Blood Pressure

Question 2

Why is the cardiovascular system so important?

Answer 2

• it transports O2 and nutrients to tissues
• it helps remove waste products (e.g. CO2)
from the body
• it spreads hormones around the body
• it helps maintain body temperature by shifting heat around the body

Question 3

The heart is a ‘dual’ pump:

Answer 3

• The heart is divided into right and left halves which act as separate pumps, but pump simultaneously
• Each side has two chambers and two valves
• Each side pumps same volume of blood
• Septum prevents mixture of blood between two sides
• Heart muscle on the left side is thicker than the muscle on the right side, right side pumps with lower pressure than the left side

Question 4

Left ventricular wall is much thicker than the right:

Answer 4

Pressure generated in left ventricle during contraction (systole) ~120mmHg
Pressure generated in right ventricle during contraction ~30mmHg

Question 5

Two blood flow circuits:

Pulmonary circulation

Answer 5

Sends deoxygenated blood from right side of heart

to lungs

Question 6

Two blood flow circuits:

Systemic circulation

Answer 6

Receives oxygenated blood from lungs, sends it from heart to rest of the body

Question 7

Measuring what the heart is doing: ‘Cardiac output’

Answer 7

• volume of blood pumped by each ventricle per minute
• indicates blood flow through peripheral tissues
- Each ventricle, at rest: 72 bpm x 70 ml = 5040 ml/min

Question 8

How else could we control blood flow around the body?

Answer 8

Heart rate (beats/min) x stroke volume (ml/beat) = Cardiac output (CO)
- By controlling resistance in the blood vessels (e.g. make them bigger or smaller)
* body needs different amount of blood for different bits and acitivities
eg exercise, large meal

Question 9

Blood flow

Answer 9

Therefore, the rate at which blood flows through the circulatory system is dependent on:
The activity of the heart (cardiac output)
The resistance to blood blow (vessel diameter)

• The heart has to generate enough pressure to overcome resistance to blood flow

Question 10

Arterioles determine blood flow to tissues

- Vasoconstriction

Answer 10

increased contraction of circular

smooth muscle in wall, increased resistance and decreased flow

Question 11

Arterioles determine blood flow to tissues

- Vasodilation

Answer 11

decreased contraction of circular smooth muscle in wall, decreased resistance and increased flow

Question 12

total blood volume

Answer 12

Total blood volume = 5 litres
~7% of bodyweight in women, ~8% in men
450ml 350ml

Question 13

compliance

Answer 13

veins most compliant tissue in body = thin walls so can stretch a lot
- Compliance: The ability to stretch and hold a greater volume

Question 14

Arteries

Answer 14

several hundred, thick, highly elastic walls, large radius
- Low resistance, High pressure, Low volume
F: Passage to tissues, pressure
reservoir

Question 15

Arterioles

Answer 15

0.5 million
Highly muscular, well-innervated walls, small radius
Function: Resistance vessels, determine blood flow to tissues
“Microcirculation” High/variable resistance Large drop in pressure Low volume

Question 16

Capillaries

Answer 16

10 billion
Very thin walls, large total cross- sectional area, very small radius
Function: Site of exchange, balance ECF between plasma and interstitial fluid
“Microcirculation” High/variable resistance Large drop in pressure Low volume

Question 17

Veins

Answer 17

several hundred
Thin walled, highly distensible, large radius
Functions: Passage from tissues to heart, blood reservoir
Site of exchange, balance ECF between plasma and interstitial fluid
* Low resistance Low pressure High volume

Question 18

Systemic blood vessels

Answer 18

Endothelium = the same in large artery, Arteriole, capillary, large vein
Elastin fibers = large artery, smaller amount in large vein
Smooth muscle = most in large artery, then arteriole > large vein
Collagen fibers = large vein > large artery > arteriole

Question 19

Blood flow across the systemic circulation

Answer 19

Velocity of flow is inversely related to total cross-sectional area
Where cross-sectional area is higher, velocity is slower
- But the volume passing each spot is exactly the same!