3 Organisms exchange substances: 7 Mass Transport Flashcards
What are haemoglobins?
A group of chemically similar molecules found in many different organisms.
Haemoglobin is a protein with a quaternary structure.
What is the role of haemoglobin and red blood cells in the transport of oxygen? When does it associate and dissociate with oxygen?
Haemoglobin has a high affinity for oxygen in the lungs so oxygen associates.
It has a low affinity for oxygen near respiring tissues, so oxygen dissociates.
Oxygen loads onto haemoglobin when there’s a high pO2 (high partial pressure of O2) - alveoli have high pO2.
Oxygen unloads when there’s a lower pO2 - tissues respire so there’s a low pO2.
How do oxyhaemoglobin dissociation curves show how affinity for oxygen varies?
- The haemoglobin shape makes it difficult for the first oxygen to bind to a site. Therefore, at low pO2, little oxygen binds so the gradient is shallow.
- The binding of the first O2 changes the quaternary structure of the haemoglobin, making it easier to bind a second O2. The binding of the first O2 induces the other subunits to an O2 molecule.
- Positive cooperativity - binding of the first O2 makes it easier to bind others. It takes a smaller increase in pO2. Gradient steepens.
- After the third O2 binds, the binding of the fourth is harder as it’s less likely for an O2 to find an empty site. Gradient reduces and curve flattens off.
What are the effects of carbon dioxide concentration on the dissociation of oxyhaemoglobin?
The Bohr Effect:
- the greater the concentration of CO2, the more readily haemoglobin releases its oxygen.
At gas-exchange surface:
- CO2 concentration is low
- affinity for oxygen increases so oxygen is readily loaded
- oxygen dissociation curve shifts left
At respiring tissues:
- CO2 concentration is high
- affinity for oxygen decreases so oxygen is readily unloaded
- oxygen dissociation curve shifts right
Dissolved CO2 is acidic and the low pH causes haemoglobin to change shape to either a high affinity or low affinity one.
How are animals adapted to their environment in relation to haemoglobin?
Different animals possess different types of haemoglobin with different oxygen transport properties.
Organisms that live in low O2 environments have higher affinity for oxygen haemoglobin - dissociation curve is to the left of a human’s.
Organisms that are very active (so have a high oxygen demand) have lower affinity for oxygen haemoglobin - curve is to the right.
What is the general pattern of blood circulation in a mammal?
Deoxygenated blood:
Right ventricle -> pulmonary artery -> lungs
Oxygenated blood:
Lungs -> pulmonary vein -> left atrium -> left ventricle -> aorta -> arteries -> renal artery -> kidneys
Deoxygenated blood:
Kidneys -> renal vein -> veins -> vena cava -> right atrium - > right ventricle
What is the gross structure of the human heart?
What are the stages of the cardiac cycle?
- Diastole
- Atrial systole
- Ventricular systole
What happens in diastole?
- ventricles and atria are relaxed
- the semi-lunar valves close due to higher pressure in the pulmonary artery and aorta (prevents backflow into ventricles)
- atria fill due to higher pressure in vena cava and pulmonary vein
- atria pressure increases
- ventricle pressure is lower so atrioventricular valves open and blood flows into the ventricles
What happens in atrial systole?
- ventricles are relaxed
- atria contract, decreasing chamber volume and increasing its pressure
- blood is pushed into the ventricles
- ventricular pressure and chamber volume increases
What happens in ventricular systole?
- atria are relaxed
- ventricles contract, decreasing chamber volume and increasing its pressure
- ventricle pressure is higher than in the atria so atrioventricular valves shut to prevent backflow
- ventricle pressure is higher than in the aorta and pulmonary artery
- semi-lunar valves open and blood is forced out into the arteries.
What is the structure of arteries related to their function?
Thick muscle tissue
- arteries can be constricted to control the volume of blood passing through and the flow of it
Thick elastic tissue
- stretching and recoil helps maintain high pressure and evens out pressure surges
Thick wall
- resists high pressure
Smooth endothelium
- reduces friction
No valves
- blood is under constant high pressure so tends not to flow backwards
What is the structure of the arterioles related to their function?
Thick muscle layer
- contraction constricts the lumen, restricts the flow of blood
Thin elastic layer
- blood pressure is lower
What is the structure of the veins related to their function?
Thin muscle layer
- their contraction can’t control the flow of blood to tissue since they are carrying blood away from tissues
- instead, the contraction of the tissues helps blood flow
Thin elastic layer
- blood pressure is low
Thinner wall
- pressure is low so no need for thick wall
- allows them to be flattened easily, aiding blood flow
Valves
- ensures blood doesn’t flow backwards
What is the structure of the capillaries related to their function?
Thin walls
- short diffusion distance for substance exchange
Capillary beds (networks of capillaries in tissues)
- large surface area for exchange
Found near cells in exchange tissues
- short diffusion pathway
Narrow lumen
- red blood cells are flattened against the walls, reducing diffusion distance
Spaces between endothelial cells
- allows white blood cells to escape to deal with infections
How is tissue fluid formed?
Ultrafiltration
1. At the arterial end, the hydrostatic pressure inside the capillaries is greater than in the tissue fluid.
2. Difference in hydrostatic pressure forces water out of the capillaries, forming tissue fluid.
- water potential is higher outside which would cause water to move back into the capillaries but pressure difference is greater.
How does tissue fluid return to the circulatory system?
- As water left and plasma proteins remained, the hydrostatic pressure and water potential in the capillaries at the venule end is much lower.
- Water re-enters the capillaries via osmosis down the water potential gradient.
- Excess tissue fluid is drained by the lymphatic system.
What is the equation for cardiac output?
cardiac output = stroke volume x heart rate
What are the most common risk factors for cardiovascular disease?
High blood cholesterol and poor diet.
Cigarette smoking.
High blood pressure.
Why is high blood cholesterol and a poor diet a risk factor for cardiovascular disease?
Cholesterol forms atheromas which can lead to increased blood pressure and clots.
Could block flow of blood to coronary arteries which could cause a myocardial infarction.
Why is cigarette smoking a risk factor for cardiovascular disease?
Nicotine increases risk of high blood pressure.
CO combines with haemoglobin which reduces the amount of oxygen going to the heart which can lead to a heart attack.
Why is high blood pressure a risk factor for cardiovascular disease?
High blood pressure increases the risk of damage to artery walls, increasing the risk of atheroma formation.
Blood clots can form, blocking flow of blood which can lead to a myocardial infarction.
What is xylem?
The tissue that transports water in the stem and leaves of plants.
What is the cohesion-tension theory of water transport in the xylem?
- Water evaporates from the leaves (transpiration).
- This creates tension which pulls more water up.
- Cohesion between water molecules means a column of water moves up the xylem.
