6b: Haemoglobin + Tissue Fluid

Question 1

Is blood a tissue?
Why?

Answer 1

• yes
• group of cells

Question 2

What is plasma?

Answer 2

• solution of which plasma proteins, red/white blood cells and platelets are suspended

Question 3

What does blood plasma transport?

Answer 3

• CO2 from organs to lungs
• soluble products of digestion from small intestine to organs
• urea from liver to kidney

Question 3

What are platelets?
What are their function?
Do white blood cells contain a nucleus?

Answer 3

• small fragment of cells with no nucleus
• helps form blood clots
• yes

Question 4

What is red blood cells function?
How long can they live?

Answer 4

• contains haemoglobin, involved in the loading of oxygen in the lungs, transportation of oxygen around the body and the unloading at respiratory tissue
• 120 days

Question 5

Describe + Explain 3 structural features of red blood cells:

Answer 5

1. they are very small
   - this small size means the haemoglobin would be closer to the red blood cells cell membrane, which provides a short diffusion pathway
   - small also increases SA:Vol ratio
2. they are shaped like a biconcave disc
   - contains a “dent” in each side of red blood cell, increasing SA:Vol ratio which means O2 can diffuse in and out fast
   - “dent” provides a short diffusion pathway
3. they contain no organelles
   - lacks nucleus, mitochondria and endoplasmic reticulum, allowing more space for haemoglobin and oxygen as possible

Question 6

Why can’t red blood cells take part in protein synthesis?
Why can’t red blood cells divide (cell division)?
Why can’t active transport occur in red blood cells?

Answer 6

• no rough endoplasmic reticulum to modify, synthesise and transport proteins
• no DNA/nucleus
• no mitochondria, so not enough ATP can be produced to undergo active transport

Question 7

Why can’t oxygen be transferred in water?
What’s the alternative?

Answer 7

• solubility of oxygen in water is relatively low
• however, blood pigments in animals can increase the oxygen carrying capacity of blood
• haemoglobin is a blood pigment in animals

Question 8

What does Haemoglobin do?

Answer 8

• blood pigment that has a high affinity for oxygen and readily loads oxygen where oxygen concentrations are high (lungs), however they release oxygen where oxygen concentrations are low (respiring tissue)

Question 9

What type of protein is haemoglobin?
What structure does it contain?

Answer 9

• conjugated
• quaternary

Question 10

In each _______ chain of haemoglobin, there is one ____ group present?

Answer 10

1. polypeptide
2. haem

Question 11

What is the haem group?
What’s it purpose?

Answer 11

1. Fe2+ (binding site)
2. binds to oxygen (O2-)

Question 12

How many oxygen molecules can on haemoglobin molecule carry?

Answer 12

4

Question 13

What is the name when oxygen binds to haemoglobin?
What is percentage saturation?

Answer 13

• oxyhaemoglobin
• amount of oxygen carried by haemoglobin referred as a percentage of the maximum oxygen that can be carried

Question 14

Why does a “oxygen dissociation curve” have a sigmoidal shape?

Answer 14

Co-operative Binding occurs:
- each haemoglobin molecule combines with 4 molecules of oxygen in 4 separate reversible reactions
- the binding of oxygen to the first haem group changes the tertiary structure and shape of the haemoglobin molecule
- this uncovers the second haem group, making the haem group more accessible and easier for oxygen to bind to, therefore increasing the affinity
- this in turn increases the affinity for the 3rd haem group and so on

Question 15

For an “oxygen dissociation curve”, what happens at high PO2 values and at low PO2 values?

Answer 15

high:
- haemoglobin has a high affinity for oxygen
- binds oxygen more readily
- (lungs)
low:
- haemoglobin has a low affinity for oxygen
- releases O2 more readily
- (respiring tissues)

Question 16

What is the Bohr Shift?

Answer 16

• when an oxygen dissociation curve is shifted to the right
• this means that at any given PO2 value, the haemoglobin releases oxygen more readily, and has a reduced affinity

Question 17

What conditions occur causing the Bohr Shift?
How do these conditions arise?

Answer 17

• acidic pH, high temperature, higher carbon dioxide concentration
• when exercising, more heat + CO2 produced via respiration in muscle tissues, as well dissolved CO2 producing acid

Question 18

Give an example and explain conditions causing a shift of the oxygen dissociation curve to the left:

Answer 18

• when Oxygen concentrations are low (e.g mountains + fetal haemoglobin):
• the left shift means that oxygen is loaded more readily, and haemoglobin has an increased affinity for oxygen
• this means at all pO2 values, haemoglobin has a higher oxygen saturation, as it will only release oxygen when respiring tissues are “desperate for O2”

Question 19

Give an example and explain conditions causing a shift of the oxygen dissociation curve to the right (other than exercise):

Answer 19

• if an animal has a large SA:Vol
• a higher SA:Vol, means that the animal loses heat faster
• they have increased metabolic/respiration rates to release heat that is lost
• they therefore have a shift to the right, where oxygen is released more readily, and haemoglobin has a lower affinity of oxygen at all PO2 values

Question 20

Why is lower affinity when Bohr Shift occurs not a disadvantage for respiring tissues?

Answer 20

• lower affinity ensures oxygen is released more readily to muscle tissues that require it, however the haemoglobin would still have full saturation of oxygen at high PO2 values

Question 21

What is Tissue Fluid?

Answer 21

• fluid containing water, glucose, amino acids, fatty acids and oxygen which bathes the tissues

Question 22

Why is Tissue Fluid required?

Answer 22

• no exchange of materials can occur between arteries and veins directly into cells, because arteriole + vein walls are too thick + impermeable
• therefore, as substances are reaching the capillaries they diffuse from blood in capillary to the tissue fluid (bathing the cells), and then into the cells

Question 23

Explain the Formation of Tissue Fluid + the entry of substances into cells:

Answer 23

1. Formation:
   - at the arterial end of the capillary, blood is still at high hydrostatic pressure, therefore blood plasma containing (water, glucose + amino acids, ions, gases) would be forced out through permeable walls of capillaries via pressure filtration.
   - Tissue Fluid is formed.
   - hydrostatic pressure is greater than the osmotic pull of blood in capillary
2. Entry:
   - the tissue fluid formed now bathes the tissue and surrounds the cells, so materials are exchanged between tissue fluid + cells:
   • gases + lipid soluble substances are exchanged via lipid diffusion
   • ions are exchanged via facilitated diffusion
   • glucose + amino acids are exchanged via active transport
   • water by osmosis

Question 24

Explain the reabsorption of products from tissue fluid to capillary:

Answer 24

1. In the Capillary:
   
   • At the venule end of the capillary, the blood is at low hydrostatic pressure
   • this is due to the loss of plasma
   • water potential is also lower in blood than tissue fluid as water has been lost
2. Reabsorption:
   - waste solutes (carbon dioxide + urea) enter the blood by diffusion down their concentration gradients
   - water will return into the blood by osmosis since the blood has lost a lot of water, so has a low water potential
   - osmotic pull > hydrostatic pressure so tissue fluid also returns to capillary
3. Lymph Vessels:
   - not all fluid will return to the blood, so there is excess tissue fluid
   - this excess tissue fluid will drain into lymph vessels found in capillary beds, for return to vena cava
   - lymph vessels have very thin walls, like capillaries and tissue fluid can easily diffuse inside, forming lymph

Question 25

What is the structural advantage of lymph vessels?

Answer 25

• thin walls, allowing tissue fluid to easily diffuse into