CVS Session 1 (Lecture 1.1)

Question 1

Why does the body need a cardiovascular system (4 points)?

Answer 1

1) Most cells are too far from a source of O2 and nutrients therefore simple diffusion would not work.
2) System required to transport o2 and nutrients to cells around the body and waste out of the body.
3) The distribution system (vessels and blood), the pump (heart) and exchange mechanism (capillaries)
4) Two circulations (1) - Pulmonary circulation and (2) - Systemic circulation.

Question 2

By what method is exchange of substances between the blood and cells of the body take place?

Answer 2

Diffusion

Question 3

What does the CVS system do in relation to diffusion?

Answer 3

Provides the correct conditions for diffusion to take place at the tissues and lungs.

Question 4

What type of epithelium lines the wall of capillaries?

Answer 4

Endothelium - simple squamous

Question 5

Which molecules can directly diffuse through the bilayer of endothelial cells?

Answer 5

Oxygen and Carbon dioxide

Question 6

Which molecules can directly diffuse through small pores between endothelial cells?

Answer 6

Glucose, AAs and lactate (hydrophilic)

Question 7

Which way will molecules diffuse across an endothelium?

Answer 7

From an area of high concentration to an area of low concentration of substance. (down concentration gradient)

Question 8

Which factors affect diffusion?

Answer 8

1) Area available for exchange
2) Diffusion ‘resistance’ (difficulty of movement through the barrier)
3) Concentration gradient

Question 9

What influences the area for exchange?

Answer 9

Capillary density (more metabolically active tissues require more capillaries)

Question 10

What influences the resistance to diffusion?

Answer 10

1) Nature of molecule e.g. lipophilic, hydrophobicity or size
2) Nature of barrier e.g. pore size and no.
3) Path length (shortest in active tissues)

Mostly low!

Question 11

What is the rate limiting step in exchange of substances?

Answer 11

Concentration gradient.

Question 12

How is a concentration gradient affected and maintained?

Answer 12

Affected by usage of substances and rate of blood flow (perfusion rate). Maintained by blood flow through capillary bed.

Question 13

Why is it important to maintain a concentration gradient?

Answer 13

Perfusion rate must be high enough to maintain a sufficient concentration gradient for diffusion. Therefore an adequate supply of nutrients and oxygen can be delivered to tissues.

Question 14

State the blood flow to: body, brain, heart, kidneys and muscle in rest and in exercise.

Answer 14

1) Body - 5L to 24.5L per min
2) Brain - 0.75L per min
3) Heart - 0.3L - 1.2L per min
4) Kidneys - 1.2L per min
5) Muscle - 1.0L - 16L per min

Question 15

How is the perfusion rate controlled?

Answer 15

Arterioles and pre-capillary sphincters

Question 16

What are arterioles?

Answer 16

Resistance vessels

Question 17

Why is adding resistance necessary for good perfusion?

Answer 17

Makes it easier to perfuse hard to perfuse areas e.g. brain. Makes it harder to perfuse easy areas to perfuse e.g. feet. Allows blood to be directed to tissues that are harder to perfuse due to gravity.

Question 18

State the vessels of circulation to and from the heart.

Answer 18

Heart > Arteries > Arterioles > Metarterioles > Capillaries > Venules > Veins > Heart

Question 19

Where and why is a store of blood necessary?

Answer 19

Stored in veins as they have elastic walls which are thin so can easily distend and collapse (act as a reservoir). This allows the blood flow to match the cardiac output required at different states.

Question 20

What is capacitance?

Answer 20

Store of blood in veins

Question 21

At rest, what proportion of blood is in which vessels?

Answer 21

67% Veins
17% Heart & Lungs
11% Arteries & Arterioles
5% Capillaries