3.1.2 Tranport in animals

Question 1

why the hydrostatic pressure of the blood drops as blood moves away from the heart ?

Answer 1

• divides into more, smaller vessels
• vessels have larger, total lumen / cross sectional area
• reduced resistance to blood flow
• arteries, stretch / expand
• loss of fluid/plasma, from capillaries

Question 2

During the electrical stimulation of the heart, there is a short delay between the excitation of the atria and excitation of the ventricles
why this this delay essential

Answer 2

• time for the atria to fully contract

- blood to flow into ventricles before they contract

Question 3

The Purkyne tissue carries the excitation wave down the septum to the apex of the heart.
Explain why the excitation wave is carried to the apex.

Answer 3

ventricle contraction starts at the bottom to push blood upwards

Question 4

cause of fluctuation of blow flow in aorta

Answer 4

• systole / contraction → increases pressure
• diastole / relaxation/ blood flowing onwards
  → decreases pressure
• contraction of left ventricle

Question 5

describe the pressure changes in the blood as it flows

through the circulatory system from the aorta to the veins.

Answer 5

• pressure drops as distance from heart increases
• greatest pressure drop while blood in arteries
• constant pressure in veins ;

Question 6

causes of the change in pressure as blood flows from

1. aorta → arteries ;
2. from arteries → capillaries.

Answer 6

• blood flows into larger number of vessels

- cross-sectional area : capillaries > arteries > aorta

Question 7

why pressure changes as blood flows from the aorta to the capillaries

Answer 7

• capillary wall is, thin, one cell thick , would burst under high pressure
• reduce chance of, tissue fluid build up / oedema

Question 8

pros of blood enclosed in vessels

Answer 8

• maintain higher pressure
• increase rate of flow
• flow can be directed

Question 9

how does artery

1. withstand pressure
2. maintain pressure

Answer 9

1. withstand pressure
   - thick wall
   - thick collagen layer
   →provides strength
   - endothelium folded
   idea of: no damage to, endothelium / artery as it stretches
2. maintain pressure
   - thick elastic tissue layer
   → stretch, recoil → return to original size ;
   - thick smooth muscle layer
   → constricts lumen

Question 10

why wall of left ventricle is thicker than right ventricle

Answer 10

• more muscle to create more force
• higher pressure ;
• push blood against greater resistance, friction
• pumps blood further to all parts of body
• supplies systemic circulation ;

Question 11

Explain how pressure changes in the heart bring about the closure of the atrioventricular
(bicuspid) valve

Answer 11

ventricular systole
 or
 ventricle , wall / muscle , contracts ;
2 (ventricular contraction) raises ventricular pressure ;
3 (ventricular pressure) higher than atrial pressure ;
4 idea of (pressure / movement of blood,
generated by ventricular contraction)
 pushes valve shut ;
5 chordae tendinae prevent inversion ;

Question 12

Outline the benefits of the Bohr shift to actively respiring tissue.

Answer 12

• (actively respiring tissue) needs more oxygen for aerobic respiration to release more energy
• (actively respiring tissue produces) more CO2
• Hb involved in transport of CO2 ;
• less Hb available to combine with O2
• (Bohr shift) causes more oxygen to be
  released

Question 13

Explain why the curve for fetal oxyhaemoglobin is to the left of the curve for adult
oxyhaemoglobin.

Answer 13

• fetal Hb has a higher affinity for oxygen
• fetal Hb takes up oxygen in lower partial pressure of oxygen
• placenta has low partial pressure of oxygen
• at low partial pressure of oxygen in placenta, adult (oxy)Hb will dissociate /

Question 14

Distinguish lymph from tissue fluid.

Answer 14

• lymph is the fluid formed from the arterial end of the capillaries/that drains back into the venous end of the capillaries;
• when lymph is bathing the cells/exchanging metabolites with the cells it is called tissue fluid;

Question 15

Outline the process by which lymph is formed.

Answer 15

• high blood pressure at arterial end of capillary bed forces lymph out through capillary walls;
• solute potential/osmotic pressure exerted by plasma proteins tends to draw water back into the blood;
• but blood pressure is higher than osmotic pressure and so more fluid leaves blood than returns;
• water/glucose/amino acids can leave the capillaries but proteins cannot/ref to differentially permeable capillary wall;

Question 16

Outline the processes by which lymph is returned to the blood.

Answer 16

• blood pressure at venous end of capillary bed has fallen;
• now less than the osmotic pressure of the plasma proteins/solute potential;
• thus osmotic pressure now draws back lymph into the capillaries/venous end;
• some lymph drained back via lymph ducts/thoracic duct

Question 17

Explain how pressure changes in the heart bring about the closure of the atrioventricular
(bicuspid) valve.

Answer 17

• ventricular systole/ ventricle contracts raises ventricular pressure ;
• ventricular pressure higher than atrial pressure ;
• pressure / movement of blood,
  generated by ventricular contraction pushes valve shut ;
• chordae tendinae prevent inversion