Flashcards in Transport in animals (Blood and lymph) Deck (20):
What is an open circulatory system?
- An open circulatory system is where the blood fills the body cavity and directly bathes all cells and tissue, as opposed to being restricted into vessels.
- All insects have open circulatory systems.
- Some rely on muscular movement to circulate the heart while others have a heart-like pumping organ just under the dorsal that directs blood flow towards important parts of the body such as the head and legs.
What is a closed circulatory system?
- A closed circulatory system is where the blood is restricted into vessels and is pumped always pumped around the body on a set path of vessels.
- Blood flow is restricted and therefore blood pressure is high.
- All fish, birds, mammals... big organisms have closed circulatory systems.
Why do large animals have closed circulatory systems?
- Blood in an open circulatory system is at very low pressure. Insects are small, so blood doesn't travel far. However, in larger organisms, this would mean blood being pumped around at a very slow rate.
- Insects have a separate transport system for oxygen and carbon dioxide whereas larger organisms rely on blood for this task.
- The slow rate would mean that an open circulatory system in larger animals would not deliver enough nutrients and oxygen to tissue cells at a rate which the cells require them. This may lead to the cells dying.
What are the structural features of arteries?
- Lumen is narrow to maintain high blood pressure.
- Thick collagen walls in order to withstand high blood pressure.
- Elastic tissue in walls allows expansion and recoil during systole and diastole.
- Smooth muscles that contract to restrict blood flow. These can limit blood flow to certain organs and direct blood flow to others.
- Endothelium can fold and unfold.
What are the structural features of veins?
- Lumen is wide to maximise blood flow.
- Thin layers of collagen, elastic tissue and smooth muscles as they don't need to withstand high pressure; stretch or recoil and restrict blood flow.
- Valves are present to prevent the back flow of blood.
- Veins can be easily flattened by surrounding muscles to squeeze blood along veins, back to heart.
What are the structural features of capillaries?
- One cell tick wall of squamous epithelial cells to reduce diffusion distance.
- Thin lumen wide enough to fit one red blood cell. This means that red blood cells are close to the capillary walls and diffusion distance is reduced for oxygen.
What does blood consist of?
- Erythrocytes (red blood cells), leucocytes (white blood cells) and thrombocytes (platelets).
- Hormones and plasma proteins.
- Some fats in the form of lipoproteins.
- 80-120 mg/100cm^3 glucose concentration.
- More amino acids and oxygen.
- Less carbon dioxide.
What does tissue fluid consist of?
- Some white blood cells.
- Hormones and proteins secreted by cells.
- Some glucose (most absorbed by cells).
- Some amino acids and oxygen (most absorbed by cells).
- Lots of carbon dioxide.
What does lymph consist of?
- Lymphocytes (white blood cells).
- Some proteins.
- More lipids than blood.
- Some glucose, amino acids and oxygen.
- Lots of carbon dioxide.
How is tissue fluid formed?
1. Blood initially enters the capillaries at high pressure from the arteries.
2. Hydrostatic pressure is high, so small molecules are forced out of capillaries by ultrafiltration.
3. Only water, ions, oxygen, glucose and amino acids are small enough to leave capillaries. Blood cells and plasma proteins remain in blood
4. Water potential is lower in capillaries, so water also enters by osmosis. However, ultrafiltration outweighs the effects of osmosis and net movement of water is out of capillaries.
5. Exchange of nutrients occur between tissue fluid and bathed cells.
6. Hydrostatic pressure decreases along the capillaries and blood water potential becomes lower. Osmosis into capillaries is greater and outweighs ultrafiltration. Net movement of water is into capillaries. Tissue fluid also has some hydrostatic pressure.
7. Waste materials enter capillaries by diffusion.
What is lymph?
- Lymph is very similar to tissue fluid in composition, but also contains lots of lymphocytes.
- Lymph is made from tissue fluid draining into the lymph vessels.
- Lymph is then circulated around the body past the lymph nodes where it is filtered for any bacteria/pathogens that are destroyed by the lymphocytes.
How is oxygen transported in blood?
- Oxygen is transported in erythrocytes in the blood.
- Erythrocytes are filled with proteins called haemoglobin that are made out of 4 subunit polypeptide chains that each have a prosthetic haem group attached.
- The haem group contains a iron (II) ion which bonds to the oxygen molecule.
- Each haemoglobin binds 4 oxygen molecules.
What are the features of the oxyhaemoglobin dissociation curve?
The curve is a sigmoid shape curve, which means that it is relatively difficult for haemoglobin to take up oxygen at low pressures, but is easier at high pressures.
What mechanism is responsible for the sigmoid shape of the oxyhaemoglobin dissociation curve?
When the haemoglobin is not saturated with any oxygen molecules at low oxygen concentrations, it has a very low affinity. However, as the oxygen level rises in the surroundings and the haemoglobin binds onto 1 oxygen molecule, its 3D structure slightly changes and increases its oxygen affinity. The haemoglobin then acquires more oxygen molecules which increases its oxygen affinity even further, this is called conformational change. However, once the haemoglobin is saturated with 3 oxygen molecules, its shape changes to decrease the oxygen affinity so the curve slowly levels out and it is difficult to achieve 100% oxygen saturation.
Why is the oxyhaemoglobin dissociation curve important?
The lungs have high oxygen levels which are sufficient for haemoglobin to achieve almost 100% oxygen saturation. However, the tissue environment has a low enough oxygen level for the haemoglobin to release the oxygen into the tissue fluid.
Why does foetal haemoglobin have a higher oxygen affinity?
The foetus needs to pick up oxygen in an environment where normal haemoglobin would release oxygen, the blood in tissue. In order for the foetal blood to obtain enough oxygen from the mother's blood, its haemoglobin needs to have a higher oxygen affinity than the mothers.
How is carbon dioxide transported in the blood?
- 5% dissolves into plasma fluid.
- 10% combines with haemoglobin to form carbaminohaeoglobin.
- 85% is transported as hydrogencarbonate ions.
How are hydrogen carbonate ions formed?
1. Carbon dioxide is released by cells into tissue fluid that eventually enter the plasma of erythrocytes.
2. Carbon dioxide combines with water to form carbonic acid, a reaction which is catalysed by the enzyme carbonic anhydrase.
3. The carbonic acid dissociates into H+ ions and hydrogen carbonate ions.
4. To maintain a constant pH, the H+ ions combine with haemoglobin to form haemoglobinic acid.
5. Hydrogen carbonate ion concentration increases in erythrocytes and a diffusion gradient is set up, hydrogen carbonate ions diffuse out of erythrocytes and into plasma.
6. Mass outflow of hydrogen carbonate ions changes the electric neutrality of erythrocytes. This effect is countered by the inward diffusion of Cl- ions. This is called the chloride shift.
How does carbon dioxide leave the blood?
At the lungs, there is a higher oxygen concentration, so oxygen competes with H+ ions to combine with haemoglobin. This results in H+ ions being released into erythrocytic cytoplasm and the whole hydrogen carbonate formation process being reversed, releasing carbon dioxide into plasma which diffuses into the alveoli.