3.4.1 Mass transport in animals

Question 1

Why do large, multicellular organisms need mass transport systems?

Answer 1

Needed to carry substances between exchange surfaces and rest of body and between parts of body

• Most cells too far away from exchange surfaces / each other for diffusion alone to maintain composition of tissue fluid within suitable metabolic range
• Mass transport maintains final diffusion gradients bringing substances to and from cells
• Mass transport helps maintain relatively stable immediate environment of cells that is tissue fluid

Question 2

How does the closed double circulatory system work?

Answer 2

Blood passes through heart twice for each complete circulation of body

Pulmonary circulation - Deoxygenated blood in right side of heart pumped to lungs→oxygenated blood returns to left side of heart

Systemic circulation - Oxygenated blood in left side of heart pumped to tissues / organs of body → deoxygenated blood returns to right side

Question 3

Why is the double circulatory system important?

Answer 3

• Prevents mixing of oxygenated and deoxygenated blood → so blood pumped to body is fully saturated with oxygen→efficient delivery of oxygen and glucose for respiration
• Blood can be pumped at a higher pressure (after being lower from lings) → substances taken to and removed from body cells quicker and more efficiently

Question 4

What do the coronary arteries do?

Answer 4

Deliver oxygenated blood to cardiac muscle

Question 5

What is the aorta?

Answer 5

Carry oxygenated blood to the organs and tissues of the body

Contraction of the left ventricle pumps blood into the aorta

Question 6

What are the pulmonary arteries?

Answer 6

Carries deoxygenated blood from the heart to the lungs

Contraction of the right ventricle pumps blood into the pulmonary arteries

Question 7

Wha are the pulmonary veins?

Answer 7

Carries oxygenated blood to heart from the lungs

Question 8

What is the superior vena cava?

Answer 8

Carries deoxygenated blood from the rest of the body to the right atrium

Question 9

What is the inferior vena cava?

Answer 9

Vena cava carries deoxygenated blood from the rest of the body to the right atrium

Question 10

What are the blood vessels entering and leaving kidneys:

Answer 10

• Renal arteries – take deoxygenated blood→kidneys
• Renal veins – take deoxygenated blood to the vena cava from the kidneys

Question 11

How does the structure of the heart relate to its function?

Answer 11

Atrioventricular valves
- Prevent backflow of blood from ventricles to atria

Semi lunar valves
- Prevent backflow of blood from arteries to ventricles

Left has a thicker muscular wall
- Generates higher blood pressure
- For oxygenated blood has to travel greater distance around the body

Right has thinner muscular wall
- Generates lower blood pressure
- For deoxygenated blood to travel a small distance to the lungs where high pressure would damage alveoli

Question 11

How does the structure of the heart relate to its function?

Answer 11

Atrioventricular valves
- Prevent backflow of blood from ventricles to atria

Semi lunar valves
- Prevent backflow of blood from arteries to ventricles

Left has a thicker muscular wall
- Generates higher blood pressure
- For oxygenated blood has to travel greater distance around the body

Right has thinner muscular wall
- Generates lower blood pressure
- For deoxygenated blood to travel a small distance to the lungs where high pressure would damage alveoli

Question 12

What is the structure of the arteries in relation to their function:

Answer 12

Arteries – carry blood from heart to rest of body at high pressure

Thick smooth muscle layer:
- Stretch as ventricle contracts and recoil as ventricle relaxes
- Reduces pressure surges, maintain high pressure

Thick wall: withstands high pressure and prevents artery bursting

Smooth (and thin) endothelium - reduces friction

Narrow lumen - increases and maintains high blood pressure

Question 13

What is the structure of the arterioles in relation to their function:

Answer 13

Arterioles – division of arteries to smaller vessels which can direct blood to different capillaries / areas

Note: their structure in relation to their function is similar to that of arteries, but…
Thicker muscle layer than arteries:
- Constricts (contracts) to reduce blood flow by narrowing lumen
- Dilates (relaxes) to increase blood flow by enlarging lumen

Thinner elastic later as lower pressure surges

Question 14

What is the structure of the veins in relation to their function:

Answer 14

Veins – carry blood back to heart under lower pressure

• Wider lumen than arteries
• Very little elastic and muscle tissue
• Valves
• Prevent backflow of blood
• Contraction of skeletal muscles squeezes veins, maintaining blood flow

Question 15

What is the structure of the capillaries and why is important?

Answer 15

• Allows efficient exchange of gases and nutrients between blood and tissue fluid
• Wall is one cell thick - short diffusion pathway
• Large network of capillaries - increases surface area
• Narrow lumen - reduces flow rate so more time for diffusion
• Capillaries permeate tissues - short diffusion pathway
• Pores in walls between cells - allows substances to escape

Question 16

What is tissue fluid?

Answer 16

Tissue fluid – the fluid surrounding cells / tissues
- Provides respiring cells with e.g. water / oxygen / glucose / amino acids
- Enables (waste) substances to move back into the blood e.g. urea, lactic acid, carbon dioxide

Question 17

Describe the formation of tissue fluid:

Answer 17

The formation of tissue fluid – at / nearest arteriole end of capillaries (start)…
- Higher blood / hydrostatic pressure inside capillaries (due to contraction of left ventricle) than tissue fluid (net outward pressure/force)
- Forces fluid / water out of capillaries (into spaces around cells)
- Large plasma proteins remain in capillary (too large to leave capillaries)

Question 18

Describe the process of the return of tissue fluid to the circulatory system:

Answer 18

The return of tissue fluid to the circulatory system - towards venule end of capillaries (end) …
- Hydrostatic pressure reduces as fluid leaves capillary (also due to friction)
- (Due to water loss,) an increasing concentration of plasma proteins (too large to leave capillaries) lowers the water potential in the capillary below the water potential of the tissue fluid
- Water (re-)enters the capillaries from the tissue fluid by osmosis down a water potential gradient
- Excess water taken up by lymph system (lymph capillaries) and is returned to the circulatory system (through superior vena cava)

Question 18

Describe the process of the return of tissue fluid to the circulatory system:

Answer 18

The return of tissue fluid to the circulatory system - towards venule end of capillaries (end) …
- Hydrostatic pressure reduces as fluid leaves capillary (also due to friction)
- (Due to water loss,) an increasing concentration of plasma proteins (too large to leave capillaries) lowers the water potential in the capillary below the water potential of the tissue fluid
- Water (re-)enters the capillaries from the tissue fluid by osmosis down a water potential gradient
- Excess water taken up by lymph system (lymph capillaries) and is returned to the circulatory system (through veins in the neck)

Question 19

What are the causes of accumulation of tissue fluid?

Answer 19

Low concentration of protein in blood plasma can lead to an accumulation of tissue fluid
- Water potential in capillary not as low so water potential gradient is reduced
- More tissue fluid formed at arteriole end
- Less / no water absorbed into blood capillary by osmosis

High blood pressure can lead to an accumulation of tissue fluid
- High blood pressure = high hydrostatic pressure
- Increases outward pressure from arterial end of capillary / reduces inward pressure at venule end of capillary
- So more tissue fluid formed / less tissue fluid is reabsorbed
- And the lymph system is not able to drain tissues fast enough

Question 19

What are the causes of accumulation of tissue fluid?

Answer 19

Low concentration of protein in blood plasma can lead to an accumulation of tissue fluid
- Water potential in capillary not as low so water potential gradient is reduced
- More tissue fluid formed at arteriole end
- Less / no water absorbed into blood capillary by osmosis

High blood pressure can lead to an accumulation of tissue fluid
- High blood pressure = high hydrostatic pressure
- Increases outward pressure from arterial end of capillary / reduces inward pressure at venule end of capillary
- So more tissue fluid formed / less tissue fluid is reabsorbed
- And the lymph system is not able to drain tissues fast enough

Question 20

Describe atrial systole:

Answer 20

• When pressure inside atria > pressure inside ventricles, atrioventricular valves open
• Atrial contract→decreasing volume and increasing pressure inside atria
• Atrioventricular valves forced open

Blood pushed into ventricles
(note: semilunar valves are shut)

Question 21

Describe ventricular systole:

Answer 21

• Ventricles contract from the bottom up → decreasing volume and increasing pressure inside ventricles
• Semilunar valves forced open
• When pressure inside ventricles > pressure inside arteries
• Atrioventricular valves shut
• When pressure inside ventricles > pressure inside atria
• Blood pushed out of heart through arteries

Question 22

Describe diastole:

Answer 22

• Atria and ventricles relax→increasing volume and decreasing pressure inside chambers
• Blood from veins fills atria (increasing pressure inside atria slightly) and flows passively to ventricles
• Atrioventricular valves open
• When pressure inside atria > pressure inside ventricles blood flows passively to ventricles
• Semilunar valves shut
• When pressure inside arteries > pressure inside ventricles
• Note: the purpose of valves shutting is to prevent back flow into (named chamber / vein) to maintain unidirectional flow of blood through the heart

Question 23

Equation for cardiac output:

Answer 23

Cardiac output = stroke volume x heart rate

Cardiac output = amount of blood pumped out of the heart per minute
Stroke volume = volume of blood pumped by the ventricles in each heart beat
Heart rate = number of beats per minute

Question 24

What is coronary heart disease associated with?

Answer 24

Atherosclerosis and atheroma formation

Question 25

How can atheroma result in a heart attack:

Answer 25

• Atheroma causes narrowing of coronary arteries
• Restricts blood flow to heart muscle supplying glucose, oxygen etc.
• Heart anaerobically respires → less ATP produced → not enough energy for heart to contract→lactate produced→damages heart tissue / muscle

Question 26

What are the risk factors that could increase probability of getting cardiovascular disease:

Answer 26

• Age
• Diet high in salt or saturated fat
• High consumption of alcohol
• Stressful lifestyle
• Smoking cigarettes
• Genetic factors
• High blood pressure increases risk of damage to endothelium of artery wall which increases risk of atheroma which can cause blood clots (thrombus)

Question 27

What is haemoglobin:

Answer 27

The haemoglobins are a group of chemically similar molecules found in many different organisms

Question 28

Where are haemoglobin found?

Answer 28

Found in red blood cells (erythrocytes)
- No nucleus – contain more haemoglobin
- Biconcave shape – increase surface area for rapid diffusion/absorption of oxygen

Question 29

What is the structure of a haemoglobin:

Answer 29

• Quaternary structured protein – made of 4 polypeptide chains
• Each polypeptide chain contains a Haem group containing an iron ion (Fe2+) which combines with oxygen

Question 30

What happens at high pO2?

Answer 30

Haemoglobin is saturated with O2

Question 31

What happens at low pO2?

Answer 31

Haemoglobin is less saturated with O2

Question 32

Why is the oxygen dissociation graph S shaped?

Answer 32

Haemoglobin has a low affinity for oxygen as the 1st oxygen molecule binds

• So from 0% saturation, an increase in pO2 results in a slow increase in saturation (shallow gradient)
• After the 1st oxygen molecule binds, the shape of haemoglobin changes in a way that makes it easier for the 2nd and 3rd oxygen molecules to bind too i.e. haemoglobin has a higher affinity for oxygen
• The rate of increase in % saturation increases (between approximately 25-75% saturation) as pO2 further increases (steep gradient)
• After the 3rd molecule binds, and haemoglobin starts to become saturated, the shape of haemoglobin changes in a way that makes it harder for other molecules to bind too
• At a high pO2, the rate increase in % saturation decreases

Question 33

What are the effects of carbon dioxide concentration on the dissociation of oxyhaemoglobin?

Answer 33

When rate of respiration is high e.g. during exercise → releases CO2
- High pCO2 lowers pH and reduces haemoglobin’s affinity for oxygen as haemoglobin changes
shape
- Increases rate of oxygen unloading

Advantageous because provides more oxygen for muscles/tissues for aerobic respiration
Oxygen dissociation curve for haemoglobin shifts to the right

Question 34

What does it mean when the curve shifts to the left?

Answer 34

Curve shifted left→haemoglobin has a higher affinity for oxygen
- More oxygen associates with haemoglobin more readily (in the lungs) at the lower pO2
BUT dissociates less readily

Advantageous to organisms such as those living in high altitudes, underground, or foetuses