Mass transport in animals

Question 1

Mass transport what is it

Answer 1

In large multicellular organisms, mass transport systems are needed to carry substances between exchange surfaces and the rest of the body and between parts of the body.

Most cells are too far away from the exchange surface/each other for diffusion alone to maintain the composition of tissue fluid within suitable metabolic range.

Mass transport maintains final diffusion gradients bringing substances to and from cells. It also helps to maintain relatively stable immediate environment of cells that is tissue fluid.

Question 2

The circulatory system

Answer 2

Closed double circulatory system - there are two circuits where blood passes through twice

Question 3

Pulmonary circulation

Answer 3

Deoxygenated blood in right side pumped to lungs

Oxygenated blood returns to the left side of the heart

Question 4

Systemic circulation

Answer 4

Oxygenated blood in left side pumped to tissues/organs of the body

Deoxygenated blood returns to the right side

Question 5

Why is circulation important for mammals

Answer 5

Prevents mixing of oxygenated and deoxygenated blood so that the blood pumped to the body is fully saturated with oxygen and is efficiently delivered for respiration

Blood can be pumped at a higher pressure (after being lowered from lungs) so that substances can be taken to and removed from body cells more quickly and efficiently

Question 6

Coronary arteries

Answer 6

Deliver oxygenated blood to cardiac muscles

Question 7

Blood vessels entering and leaving heart

Answer 7

Aorta - takes oxygenated blood from the heart to respiring tissues

Vena cava - takes deoxygenated blood from respiring tissues back to the heart

Question 8

Blood vessels entering and leaving lungs

Answer 8

Pulmonary artery - takes deoxygenated blood from the heart to the lungs

Pulmonary vein - takes oxygenated blood from the lungs to the heart

Question 9

Blood vessels entering and leaving kidneys

Answer 9

Renal arteries - takes deoxygenated blood to the kidneys

Renal veins - takes deoxygenated blood to the vena cava from the kidneys

Question 10

Structure of the heart related to its function

Answer 10

Atrioventricular valves that prevent backflow of blood from the ventricles to the atria.

Semi lunar valves that prevent backflow of blood from arteries to ventricles

Left has a thicker muscle wall which generates a higher blood pressure as oxygenated blood has to travel a greater distance around the body

Right has a thinner muscle wall which generates a lower blood pressure as deoxygenated blood has to travel a shorter distance to the lungs where high pressure would damage alveoli.

Question 11

Structure of arteries related to its function

Answer 11

Carry blood from the heart to the rest of the body at a high pressure.

Thick smooth muscle layer that contracts, pushing blood flow along and maintains the blood flow/pressure

Elastic tissue layer that stretches as the ventricle contracts (when under high pressure) and recoils when the ventricle relaxes (when under low pressure). It also reduces pressure surges.

Thick wall that can withstand high pressure and prevents the artery from bursting

Smooth, thin endothelium reduces friction

Narrow lumen increases and maintains the high blood pressure.

Question 12

Structure of arterioles related to its function

Answer 12

Division of arteries to smaller vessels which can direct blood to different capillaries/areas.

Thicker muscle layer than arteries - constricts to reduce blood flow by narrowing the lumen, dilates to increase blood flow by enlarging the lumen.

Thinner elastic layer as there are lower pressure surges

Question 13

Structure of veins related to its function

Answer 13

Carry blood back to the heart under lower pressure

Wider lumen than arteries

Very little elastic and muscle tissue

Valves to prevent backflow of blood

Contraction of skeletal muscles squeezes veins, maintaining blood flow

Question 14

Structure of capillaries related to function

Answer 14

Thin walls (one cell thick) that provide a short diffusion pathway

Capillary bed is made of a large network of branched capillaries for an increased SA:V, rapid diffusion

Narrow lumen which reduces flow rate so more time for diffusion to occur

Capillaries permeate tissues (short diffusion pathway)

Pores in walls between cells which allows substances to escape

Question 15

Importance of capillaries

Answer 15

Provides important exchange surfaces within the circulatory system as capillaries branch between cells

Capillaries allow the efficient exchange of gases and nutrients between blood and tissue fluid

Question 16

Tissue fluid what is it

Answer 16

Tissue fluid is the fluid surrounding cells/tissues

It provides respiring cells with substances such as water, glucose, amino acids and oxygen.

It enables waste substances to move back into the blood such as urea, lactic acid and carbon dioxide

Question 17

The formation of tissue fluid

Answer 17

At the arterial end of the capillaries, fluid is forced out of capillaries as there is a higher hydrostatic pressure inside capillaries (due to contraction of the left ventricle) than tissue fluid (net outward pressure)

Large plasma proteins remain in the capillary as they are too large to leave

Question 18

Return of tissue fluid to circulatory system

Answer 18

Towards the venule ends of capillaries hydrostatic pressure reduces as fluid leaves capillary

Due to water loss, an increasing concentration of plasma proteins lowers the water potential in the capillary below the water potential of the tissue fluid.

As a result, water reenters the capillaries from the tissue fluid by osmosis down a water potential gradient

Excess water is taken up by the lymphatic system and is returned to the circulatory system.

Question 19

Contraction of the atria (atrial systole)

Answer 19

Atria contract, decreasing volume and increasing pressure inside the atria.

Semilunar valves are shut

Atrioventricular valves are forced open

Blood is pushed into ventricles

Question 20

Contraction of the ventricles (ventricular systole)

Answer 20

Ventricles contract from bottom up, decreasing volume and increasing pressure inside ventricles

Semilunar valves forced open

Atrioventricular valves shut

Blood is pushed out of heart through arteries.

Question 21

Relaxation of heart (diastole)

Answer 21

Atria and ventricles relax, increasing volume and decreasing pressure inside chambers

Blood from veins fill atria (slightly increasing the pressure inside atria) and flows passively to ventricles

Atrioventricular valves open

Semilunar valves shut

Question 22

Cardiac output formula

Answer 22

Cardiac output = stroke volume (dm3) x heart rate (min-1)

Question 23

Coronary heart disease

Answer 23

Often associated with atherosclerosis and atheroma formation

Atheroma’s cause narrowing of coronary arteries which restricts blood flow to heart muscle supplying glucose, oxygen etc

Heart respires anaerobically, less ATP is produced, not enough energy for heart to contract, lactate is produced which damages heart tissues

Question 24

Risk factors that increase probability of getting disease

Answer 24

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 25

Haemoglobin what is it

Answer 25

The haemoglobin’s are a group of chemically similar molecules found in many different organisms (chemical structure may differ between organisms)

Found in red blood cells (have no nucleus so it can contain more haemoglobin, biconcave shape for rapid diffusion)

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 26

How oxygen is transported in the blood

Answer 26

Haemoglobin in red blood cells transports oxygen (as oxyhaemoglobin)

Haemoglobin can carry 4 oxygen molecules - one at each haem group

In the lungs, at a high partial pressure of oxygen, haemoglobin has a high affinity for oxygen and so oxygen readily loads/associates with haemoglobin

At respiring tissues, at a low partial pressure of oxygen, oxygen readily unloads/disassociates from haemoglobin. Also, concentration of CO2 is high, increasing the rate of unloading

Question 27

Oxyhaemoglobin disassociation curves

Answer 27

At high partial pressure of oxygen, haemoglobin is saturated with oxygen

At low partial pressure of oxygen, haemoglobin is less saturated with oxygen

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

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.

Question 28

The Bohr effect - effect of carbon dioxide concentration

Answer 28

When rate of respiration is high eg during exercise, more carbon dioxide is released

High partial pressure of CO2 lowers pH and reduces haemoglobins affinity for oxygen as haemoglobin changes shape, so the rate of oxygen unloading increases

This is advantageous because it provides more oxygen to muscles/tissue for aerobic respiration. Oxygen haemoglobin curve shifts to the right.

Question 29

Curve shifts

Answer 29

Curve shifts left: haemoglobin has a higher affinity for oxygen (so loads oxygen readily but unloads it less easily). More oxygen associates with haemoglobin more readily (in the lungs) but dissociates less easily.

Curve shifts right: haemoglobin has a lower affinity for oxygen (so loads oxygen less readily but unloads it more easily). Oxygen dissociates from haemoglobin more readily to respiring cells, associates less easily. Advantageous to organisms such as those with a high rate of respiration.