The circulatory system

Question 1

What are the functions of the circulatory system?

Answer 1

-primary function - distribute gases + molecules
-secondary functions:
fast chemical signalling, dissipation of heat, mediated inflammatory + host defence

Question 2

How is the circulatory system organised?

Answer 2

-pump (heart)
-fluid (blood)
-containers (blood vessels - arteries, capillaries, veins)

Question 3

What circulation is the left side of the heart involved in?

Answer 3

Systemic circulation:
-usually flows through a single capillary bed
-some have 2 capillary beds in series (e.g kidney)
-capillary beds in parallel + series

Question 4

What circulation is the right side of the heart involved in?

Answer 4

Pulmonary circulation:
-single pathway from left to right

Question 5

What are the 4 building blocks in vascular walls?

Answer 5

-endothelial cells
-elastic fibres
-collagen fibres
-smooth muscle cells (VSMC)

Question 6

What are the layers that blood vessels are made up of?

Answer 6

-Intima (Tunica Interna) - internal
-Media (Tunica Media) - middle
-Adventitia (Tunica Externa) - external

Question 7

What determines the compliance and distensibility of blood vessels?

Answer 7

Varying elastic + collagen fibres

Question 8

Describe elastic arteries

Answer 8

-large arteries
-high compliance - enables vessels to cope with peak ejection pressures
-recoil of elastic fibres force blood to move even when ventricles are relaxed

Question 9

Describe muscular arteries

Answer 9

-medium sized arteries
-VSMC arranged circumferentially, so circle around the blood vessels
-capable of greater vasoconstriction/dilation to adjust blood flow
-vascular tone - partially contracted at all times to maintain vessel pressure + efficient flow

Question 10

Describe aterioles

Answer 10

-smooth muscle enables blood flow regulation to capillary networks
-terminal regions (metarterioles) provide a network shortcut
-precapillary sphincters monitor blood flow to capillary

Question 11

Describe venules

Answer 11

-postcapillary venules are por0us, so act as exchange sites for nutrients + waste
-muscular venules hace a thin smooth muscle cell layer
-thin walls allow for expansion, creating reservoirs for blood

Question 12

Describe veins

Answer 12

-less muscular + elastic, but distensible, so adapt to variations in blood volume + pressure
-“store” blood

Question 13

Describe capillaries

Answer 13

-small vessels
-composed of only endothelial cells + basement membrane
-exchange of substances between blood + interstitial fluid

Question 14

What are the 3 groups of capillary and what are they based on?

Answer 14

-continuous capillary
-fenestrated capillary
-sinusoidal (discontinuous) capillary
-based on their degree of ‘leakiness’

Question 15

What is fluid transfer across capillary walls driven by?

Answer 15

Sum of:
-hydrostatic pressure (blood pressure against wall)
-osmotic pressure (substances dissolved within blood plasma)

Question 16

What is colloid osmotic pressure?

Answer 16

Oncotic pressure due to serum proteins (albumin)

Question 17

How do you calculate fluid movement?

Answer 17

Hydrolic conductance x ((capillary hydrostatic pressure - interstitial hydrostatic pressure) - (capillary oncotic pressure - interstitial oncotic pressure))

Question 18

What is the lymphatic system?

Answer 18

-drains excess interstitial fluid
-runs alongside blood vessels
-interstitial tissue fluid drained from capillaries into lymphatic system
Other functions:
-transport of dietary lipids
-lymph nodes/organs involved in immunology

Question 19

How does the lymphatic system maintain blood volume?

Answer 19

Returns fluid from lymphatic system to CVS via subclavian vein