Chapter 7 - Mass Transport

Question 1

What is haemoglobin and what does it do?

Answer 1

It is a quarternary protein capable of loading and unloading oxygen

Question 2

Where is haemoglobin most densely located?

Answer 2

Red blood cells

Question 3

Why is the first oxygen loading the most difficult, and where does oxygen assosciate with haemoglobin in humans?

Answer 3

The first oxygen only tends to bind to the haemoglobin in more oxygen rich environments, however this first oxygen binding changes the shape of the haemoglobin making it easier for the successive oxygens to bind. This process however happens easily in the lungs due to their high concentrations of oxygen and low concentrations of CO2, which raises the pH slightly, increasing the Hg affinity for oxygen

Question 4

What is haemoglobin affinity?

Answer 4

Haemoglobin with high affinity easily binds to oxygen, however it releases it less easily, whereas lower affinities find it harder to initally bind to oxygen but easier to release it

Question 5

What is the oxyhaemoglobin dissosciation curve?

Answer 5

It is a curve which shows the different partial pressures of oxygen and the saturation of haemoglobin. At lower pressures it takes a while for saturation to increase (low gradient), however the gradient then increases before decreasing again at approximately the fourth oxygen, because stearically it is more difficult for the oxygen to dock because there is only one haem group left available

Question 6

Why does oxygen unload easily at resipiring cells?

Answer 6

Respiring cells are already absorbing lots of oxygen from their environment, resulting in low partial pressures of oxygen which encourages the oxygen to unload from the haem groups. Furthermore, the respiring cells are releasing lots of CO2 which makes the blood more acidic and changes the shape of haemoglobin, reducing its affinity for oxygen and therefore further encouraging it to unload from haemoglobin

Question 7

Why is fetal haemoglobin different from adult haemoglobin?

Answer 7

It has a higher affinity for oxygen. This is because the fetuses cannot breathe for themselves therefore must receive all of their oxygen from their mothers cells. This means that they need haemoglobin with a higher oxygen affinity than their mothers to encourage the oxygen on the adult haemoglobin to unload and load onto it instead. This increased affinity is not a problem for the fetuses either because their cells don’t respire very quickly

Question 8

Give the gross structure of the heart:

Answer 8

The heart itself is made up of four chambers. The atria at the top are smaller than the ventricles below them which they lead to. Each atrium is seperated from its assosciated ventricle by a valve, and the two halves of the heart are seperated by cardiac tissue. There are four main blood vessels in the heart - The vena cava which goes into the right atrium, the pulmonary artery which leaves the right ventricle, the pulmonary vein which enters theleft atrium and the aorta which leaves the left ventricle

Question 9

What is the purpose of each of the blood vessels, and what other blood vessels exist?

Answer 9

The vena cava is the culmination of all of the veins in the body, and therefore returns deoxygenated blood to the heart, which then is passed to the ventricle which uses the pulmoary artery to return it to the lungs to be oxygenated. This oxygenated blood returns to the heart into the left atrium via the pulmonary vein and then passes to the left ventricle. The left ventricle contains large amounts of muscular tissue which is used to pump blood to the entire body via the aorta. The heart itself has a high respiratory requirement, and is supplied by coronary arteries which branch off shortly after the aorta starts

Question 10

What are the valves in the heart and what is their function?

Answer 10

The bicuspid valve seperates the left atrium and ventricle and the tricuspid seperates the right atrium and ventricle. These valves collectively are the atrioventricular valves and prevent backflow into the atria during ventricular systole. There are also semi-lunar valves between the ventricles and their assosciated blood vessels (pulmonary artery and aorta) which prevents backflow into the ventricles during diastole and atrial systole

Question 11

What are the 3 states the heart can be in?

Answer 11

Atrial systole, where the atria contract
Ventricular systole, where the ventricles contract
Diastole, when the muscles in the heart are relaxing

Question 12

Describe the movement of blood during each state

Answer 12

In diastole the atrioventricular valves are open and the semilunar are closed so blood doesn’t flow back into the ventricles. During atrial systole the atria contract increasing pressure, so all remaining blood moves into the ventricles. During ventricular systole the bicuspid and tricuspid shut so blood doesn’t flow back into the atria, and the semi-lunar open because the ventricular pressure becomes greater than the pulmoary artery and aorta, so blood flows into them. The heart then goes back to systole

Question 13

What is the structure of an artery?

Answer 13

It contains large amount of muscular and elastic tissue, and relatively narrow lumen. It does not contain valves and has thick walls so that it does not burst under its pressure

Question 14

What is the structure of a vein?

Answer 14

Veins have very wide lumen and less elastic and muscular tissue than arteries. They also have pocket valves to prevent backflow back down the vein

Question 15

Why are the differences between veins and arteries adapted to their function?

Answer 15

Arteries have large muscles to stabilise pressure surges when the heart beats, and also lots of elastic tissue which recoils during diastole and repressurises the blood providing more force. It does not need valves due to its high pressure blood only goes one way. The narrow lumen further increases pressure. Veins however don’t have elastic tissue because there is not enough pressure to burst or to create a recoil effect. The same reason they have little muscular tissue. They do however have valves, because the majority of the movement back towards the heart comes from blood leaving the capillaries forcing the rest of the blood upwards, and this pressure comes from systole. Therefore during diastole the blood would backflow so the valves prevent this

Question 16

What is the structure of a capillary and why is this useful?

Answer 16

The capillary is only one cell thick and very narrow. This provides a very short diffusion distance into the cells, and a very large surface area : volume ratio. It also forces the red blood cells to go in one at a time and touch all of the capillary at once to maximise surface area, making it an incredibly efficient diffusion membrane. Furthermore they are highly branched therefore permeate as many cells as possible, reducing diffusion distance. There are holes across the epithelial tissue meaning white blood cells can leave and fight infection

Question 17

What is tissue fluid and what is its purpose?

Answer 17

Capillaries cannot quite reach every cell, so tissue fluid is required to reach all cells. Tissue fluid is essentially water containing amino acid, glucose, oxygen, fatty acids and ions - all essential nutrients for nearly all cell types. The waste products of cells, most notably carbon dioxide, will then enter the tissue fluid. Tissue fluid is therefore the immediate environment of almost all cells, and due to it being formed from blood plasma which is heavily homeostatically controlled, it is a very constant environment

Question 18

How is it formed, and how does it return to the circulatory system?

Answer 18

The hydrostatic pressure on the arteriole end of capillaries forces water and small solutes out into the tissue fluid, which bathes cells with nutrients. This therefore lowers water potential of the capillary plasma which allows the water, as well as the waste products of cells, to re-enter the capillaries or small veins at the end of capillaries. However, tissue fluid which can’t re-enter the blood vessels instead enters the lymphatic system which is moved by the hydrostatic pressure of the tissue fluid and the contraction of skeletal muscles. The lymphatic system drains into the circulatory system via 2 ducts towards the end of the vena cava

Question 19

How do you calculate cardiac output?

Answer 19

CO (cardiac output) = stroke volume X heart rate
stroke volume = the volume of blood pumped out during each beat
heart rate = the rate at which the heart beats

Question 20

Which theory explains the movement in water in the xylem of a plant?

Answer 20

The cohesion-tension model. It starts with water being transpired out of leaves due to a higher concentration of water in the leave than in the atmosphere. When this happens, the water is replaced by water being lost from the mesophyll cells. These cells then pull water from the xylem to replace the lost water (via osmosis). The cohesive nature of water allows it to then move up the xylem as it moves into the mesophyll cells, coming all the way from the root

Question 21

What is the structure of a xylem and phloem?

Answer 21

The xylem is a stack of dead cells on top of each other, with holes going between each cell allowing water to very easily pass through. The xylem however is made of cells which are alive and contain “sieve plates” at each of end of the cell which allow the movement of organic substances. Due to this constant movement phloem cells cannot produce their own nutrients and have no organelles. To solve this each phloem has a companion cell which provides all of the necessary nutrients in their organelles for both themselves and their phloem cells. The xylem and phloem networks are always found next to each other in stems, forming vascular bundles

Question 22

Which hypothesis exaplains the process of translocation?

Answer 22

The mass flow hypothesis. It starts with organic sugars entering the phloem cells of the “source”. They do this by entering the companion cells of the phloem via facilitated diffusion. They then move into the main sieve tube via cotransport, when hydrogen ions are actively transported which allows the movement of the sucrose molecules. This then lowers the water potential of the sieve tube, causing water molecules to enter it from the adjacent xylem. This causes a hydrostaic pressure to occur. In respiring cells (sinks) they are absorbing the sugars from the phloem and therefore the water as well, which reduces the hydostatic pressure in that area. This means that areas with higher hydrostatic pressure (sources) will diffuse to areas with lower hydrostatic pressures(sinks), and the sucrose molecules along with them