Introduction to the CVS

Question 1

Why do we need a cardiovascular system?

Answer 1

• Temperature regulation.
• Pump blood through lungs to collect + carry oxygen.
• Transport nutrients to muscles and organs.
• Circulate hormones and immune mediators.
• Connection to the lymphatic system.
• Reproduction.

Question 2

Passive diffusion

The random and undirected thermal movement of molecules.

Answer 2

• The time needed to diffuse a given distance = proportional to square of the distance.
• t ∝ d^2.
• Diffusion and fast and adequate over distances in the μm, but distances over 1mm are too time consuming and not efficient for transport.

Time to diffuse a given distance down a conc. gradient.

Question 3

Circulation in humans

Answer 3

1. Blood returns to heart from veins via the right atrium and is pumped to the lungs by the right ventricle.
2. Blood returns to the heart from the lungs via the left atrium and is pumped to the rest of the body by the left ventricle.

Circulation

Question 4

The heart

Answer 4

• Systole = contraction.
• Diastole = relaxation.

Pressure difference is what drives blood flow –> Aorta = 100mmHg, Large veins = 5-10 mmHg.

Typical resting blood pressure = 120/80mmHg.
( 120 - Systolic pressure) (80 - diastolic pressure)

Question 5

Cardiac output

Cardiac output = Heart rate X Stroke volume.

Answer 5

• CO = HR x SV.

Typical maximum heart rate: 220 - age.

Question 6

What controls blood flow and determines blood pressure?

Answer 6

Blod flow is:
1. Proportional to pressure across blood vessel.
2. Inversely proportional to resistance of blood vessel.

Blood flow = (Pa - Pv) / resistance.
This means increase in resistance = decrease in blood flow.

• High pressure is needed to pump blood around body.
• Low pressure is needed for gaseous exchange.

Question 7

4 Main functional groups of blood vessels

Answer 7

1. Arteries - elastic vessels:
   Accomodate stroke volume, convert ejection into continuous flow.
2. Arterioles - resistance vessels:
   Control artetial BP and regulate local blood flow.
3. Venules and veins - capacitance vessels:
   Control filling pressure of heart and provide a reservoir of blood.
4. Capillaries - exchange vessels:
   Nutrient delivery to tissue and lymph formation, also removal of metabolic waste.

Question 8

Where does cardiac output go?

Answer 8

Question 9

Pressure profile of the circulation

Order of bloodflow:
Heart > aorta > arteries > arterioles > capillaries > venules > veins > venae cavae

Answer 9

Question 10

Why does blood slow down in capillaries>

Answer 10

Blood velocity = Blood flow / TOTAL cross - sectional area.

• Capillaries are made of many small vessels, resulting in a large cross-sectional area.
• It is important for reduced velocity - so that gaseous and nutrient exchanges occur.

Question 11

Distribution of blood volume

Answer 11

Systemic veins and venules act as reservoir : 65% of volume.

Question 12

Structure of blood vesel walls

Answer 12

1. Sympathetic nerves in Tunica Adventitia = release noradrenaline which stimulates α1 receports and triggers vasoconstriction.
2. Endothelium releases nitric oxide = relaxes vessels leading to vasodilation.

Question 13

Structure of vessels

Answer 13

• Tunica intima - endothelial layer:
  Controls vascular permeability, modulates vasoconstriction, site of angiogenesis, regulates coagulation.
• Tunica media - smooth muscle:
  Embedded in extracellular matrix regulates vasoconstriction and vasodilation.
• Tunica adventitia - collagenous material:
  Fibroblasts, innervated layer.