Introduction to Circulation

Question 1

What is the function of the heart and blood vessels?

Answer 1

Heart and blood vessels evolved to transport oxygen, nutrients, waste products and heat around the body quickly

Question 2

Diffusion vs the cardiovascular system

Answer 2

Diffusion is sufficient for small, primitive organisms

It is vital for transport over short distances

Cardiovascular system is in place due to the limitations of diffusion

Question 3

What is diffusion?

Answer 3

Diffusion is a passive process driven by the random thermal motion of molecules

Metabolic energy does not play a part

Question 4

How do particles move in diffusion?

Answer 4

The path is known as a random walk (example of brownian motion)

When a concentration gradient is present, the random walk leads to a net movement of solute down its concentration gradient.

Question 5

Why is rate of diffusion important?

Answer 5

It needs to keep up with cellular demand

Question 6

What formulas relate diffusion time?

Answer 6

x^2 is directly proportional to t where x is the distance of the particle from starting position and t is time

t = x^2/D where D is the diffusion coefficient

Hence diffusion is faster over small distances (eg. 0.1um neuromuscular junction) but slow over larger ones (eg. O2 over 1m of tissue takes 7 years)

Question 7

What factors affect the diffusion coefficient?

Answer 7

• Size of the molecule
• Temperature
• Viscosity of medium

Question 8

Describe how convection (bulk flow) in the body works

Answer 8

The cardiovascular system dissolves substances in a fluid and flows it to where it is needed

The energy for this is provided by the contraction of the heart.

Question 9

What is the primary function of the cardiovascular system?

Answer 9

The primary function of the CV system is rapid convective transports of nutrients and waste

Question 10

What are the two circulation circuits called?

Answer 10

Systemic and Pulmonary Circulation

Question 11

Give one similarity between the two circuits of the heart

Answer 11

They both originate and terminate at the heart

Question 12

Name the chambers of the heart

Answer 12

Upper chambers: right and left atria

Pumps: right and left ventricles

Blood in the two halves do not mix

Question 13

Is the heart connected in series or in parallel? Comment on the volume and pressures of blood pumped

Answer 13

They are connected in series so the same volume of blood is pumped through both sides but the pressures differ

Question 14

How do the right and left side of the heart differ?

Answer 14

The right side

• Pumps deoxygenated blood through the pulmonary artery to the lungs
• Low pressure

The left side

• Pumps oxygenated blood through the aorta to the body
• High pressure

Question 15

Is systemic circulation parallel or series?

Answer 15

Parallel

Heart directly connects to organs such as brain, heart wall etc.

Ensures good perfusion

Question 16

Name type of system connected in series and some of the disadvantages

Answer 16

Portal systems eg. liver and kidney

Secondary organs receive partially deoxygenated blood under lower pressure

Downstream tissue vulnerable to damage during hypotension (low arterial pressure)

Question 17

Name the 3 layers of blood vessels (except capillaries)

Answer 17

• Tunica intima (innermost)
• Tunica media (middle)
• Tunica adventitia (outermost)

Question 18

Describe the tunica intima

Answer 18

• Endothelial cells on basal lamina
• Main barrier to escape of plasma
• Secretes vasoactive agents such as the vasodilator NA

Question 19

Describe the tunica media

Answer 19

• Smooth muscle allows contraction
• Collagen fibers provide strength
• Elastin fibers allows stretchiness

Question 20

Describe the tunica adventitia

Answer 20

• Maintains large arteries by having a blood supply
• Tethers vessel to surrounding tissue
• Few mechanical advantages

Question 21

What are the adaptations of the aorta and other large arteries?

Answer 21

• Elastic as they contain a lot of elastin
• Allows expansion by 10% each heart beat to accommodate ejected blood
• Recoil during diastole smoothes out flow downstream
• Collagen prevents over distension

Question 22

What are the adaptations of arteries?

Answer 22

• Tunica media thicker and contains more smooth muscle
• Can contract and relax (rich autonomic innervation)
• Spasm and contract to close in injury

Question 23

What are the functions and adaptations of terminal arteries and arterioles (resistance vessels)?

Answer 23

• Regulate BP and control blood flow
  (Vasodilation: resistance falls, blood flow increases)
  (Vasoconstriction: resistance rises, blood flow decreases)
• Large drop in pressure due to large increase in resistance
  (Small lumen and few vessels)
• Sympathetic innervation do so by contracting posses lots of smooth muscle

Question 24

What are the adaptations of capillaries?

Answer 24

• Large network of vessels (most tissue cells are within 10-20um of a capillary)
• Wall is a single endothelial cell thick (allows fast diffusion)
• Capillary bed has low resistance despite narrow vessels due to large parallel array

Question 25

What do most capillary venules do (15 - 50um)

Answer 25

• Some exchange also occurs here

- Lacks a smooth muscle coat

Question 26

What are the adaptations of capacitance vessels?

Answer 26

Veins ( 50 - 200um)

• Thin walls contain a thin layer of smooth muscle and collagen (intima of limb veins contain semilunar valves )
• Net resistance is low
• Contains 2/3 of circulating blood at one instant
• Easily distended or collapsed (act as a variable store, many are innervated by vasoconstrictor fibers, can constrict and displace blood into heart and arteries)

Question 27

What is laplace’s law?

Answer 27

• Larger vessels must have thicker walls are they are under greater tension for the same internal fluid pressure
• T = Pr
• T = tension of vessel per unit length
• P = pressure
• r = radius of vessel