Circulatory System

Question 1

Why is the circulatory system necessary?

Answer 1

• mammals are relatively large and highly organised; the interdependence of our specialised regions requires an efficient transport system
• mammals are too large to rely solely on diffusion for transport of substances

Question 2

Mass flow

Answer 2

• bulk movement of substances from one area to another due to differences in pressure
• more efficient transport over long distances

Question 3

Blood vascular system

Answer 3

Provides most important means of mass flow in mammals

Question 4

Open circulatory system

Answer 4

• blood is not confined to vessels
• blood flow is slow, at a low pressure, and there is little control over its distribution
• e.g. through the haemocoel of arthropods

Question 5

Closed circulatory system

Answer 5

• heart, arteries, artérioles, capillaires, venules, veins
• blood can be at much higher pressures
• much more control over distribution
• allows vasodilation and vasoconstriction by contraction of smooth muscle

Question 6

Artérioles

Answer 6

Narrow, thin-walled arteries

Question 7

Venules

Answer 7

Small veins

Question 8

Double circulatory system

Answer 8

• in each complete circuit of the body, blood flows through the heart twice
• pulmonary + systemic circulation
• each organ has a major artery (supplies it with blood) and a major vein

Question 9

Pulmonary circulation

Answer 9

Transports blood between the heart and the lungs

Question 10

Systemic circulation

Answer 10

Transports blood between the heart and the rest of the body

Question 11

Why don’t the stomach and small intestine have major veins?

Answer 11

• carried by hepatic portal veins to the liver, for digested food molecules to be processed
• blood is then transported back to the heart via hepatic vein

Question 12

Single circulatory system in fish

Answer 12

• in each complete circuit of the body, blood flows through the heart once
• blood is pumped from the heart to the gills, then to the rest of the body
• pressure drops dramatically as blood leaves the gills- it reaches the body slower
• does not work for mammals, as the kidneys cannot function efficiently at low pressures

Question 13

Pressure gradients

Answer 13

• blood is pumped from a high pressure to a low pressure through

i) the heart pumping
ii) contractions of skeletal muscles squeezing blood through veins
iii) inspiration reduces thoracic cavity pressure, helping to draw blood back to the heart

• valves prevent backflow and ensure unidirectional blood flow

Question 14

Heart tissue under a microscope

Answer 14

• pink -> muscle tissue

* purple -> elastic tissue

Question 15

Arteries

Answer 15

• thick muscular wall
• lots of smooth muscle
• more elastic than fibrous tissue
• relatively small lumen
• blood under high pressure
• no valves (except aorta and pulmonary artery)
• layers of endothelium + collagen fibres
• e.g. aorta

Question 16

Smooth muscle

Answer 16

Elastic and fibrous tissue

Question 17

Why does arteries have more elastic rather than fibrous tissue?

Answer 17

Allows distension and recoil for he artery, and development of a pulse wave

Question 18

Veins

Answer 18

• thinner muscular wall
• less smooth muscle
• more fibrous than elastic tissue
• relatively large lumen
• blood under low pressure
• semi-lunar valves maintain unidirectional flow; upward pressure of blood forces valves to open

Question 19

Why do veins have more fibrous tissue than elastic?

Answer 19

For protection

Question 20

Capillaries

Answer 20

• microscopic thin-walled structures made of squamous endothelium
• forms networks in various parts of the body
• no muscle
• no elastic or fibrous tissue
• relatively large lumen
• blood under low pressure
• no valves
• transport oxygenated blood through organs; appear at exchange surfaces
• involved in tissue fluid formation

Question 21

Squamous endothelium

Answer 21

A layer of flattened epithelial cells one cell thick

Question 22

Exchange surfaces

Answer 22

Alveoli, villi, placenta

Question 23

Circulatory system order

Answer 23

Arteries -> artérioles -> capillaries -> venules -> veins

Question 24

What is the relationship between pressure and blood vessel thickness?

Answer 24

• blood vessels lose thickness as pressure decreases
• pressure is dissipated by increasing cross-sectional area
• vasoconstriction and vasodilation

Question 25

Cross-sectional area

Answer 25

Number of branches