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Biology - Chapter 6-9 - Coggle Diagram
Biology - Chapter 6-9
Transport in mammals
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8.1.7 Blood, Tissue Fluid and Lymph
- Plasma is a straw-coloured liquid that constitutes around 55% of the blood.
- Plasma is largely composed of water (95%) and because water is a good solvent, many substances can dissolve in it, allowing them to be transported around the body.
- As blood passes through capillaries, some plasma leaks out through gaps in the walls of the capillary to surround the cells of the body.
- The composition of plasma and tissue fluid are virtually the same, although tissue fluid contains far fewer proteins. Proteins are too large to fit through gaps in the capillary walls and so remain in the blood.
- Tissue fluid bathes almost all the cells and the blood occurs via the tissue fluid.
Tissue fluid formation:
- How much liquid leaves the plasma to form issue fluid depends on two opposing forces.
- When blood is at the arterial end of the capillary, the hydrostatic pressure is great enough to push molecules out of the capillary.
- Proteins remain in the blood; the increased protein content creates a water potential between the capillary and the tissue fluid. However, overall movement of water is out form the capillaries into the tissue fluid.
- At the venous end of the capillary, less fluid is pushed out of the capillary as pressure within the capillary is reduced.
- The water potential gradient between the capillary and the tissue fluid remains the same as at the arterial end, so water begins to flow back into the capillary from the tissue fluid.
- If blood pressure is high then the pressure at the arterial end is even greater. This pushes more fluid out of the capillary and fluid begins to accumulate around the tissues. This is oedema.
Formation of lymph:
- Some tissue fluid reenters the capillaries while some enters the lymph capillaries. The lymph capillaries are seperate from the circulatory system and they have closed ends and large pores that allow large molecules to pass through.
- Larger molecules that are not able to pass through the capillary wall enter the lymphatic system as lymph. Small valves in the vessel walls are the entry point to the lymphatic system.
- The liquid moves along the larger vessels of this system by compression caused by body movement. Any back flow is prevented by valves.
- The lymph eventually reenters the bloodstream through veins located close to the heart.
- Any plasma proteins that have escaped from the blood are returned to the blood via the lymph capillaries.
8.2.1 Red blood cells, haemoglobin and oxygen:
Transport of oxygen:
- Majority of oxygen transported around the body is bound to the protein haemoglobin in red blood cells. Red blood cells are known as erythrocytes.
- Each molecule of haemoglobin contains four ham groups, each able to bond with one molecule of haemoglobin can carry four oxygen molecules, or right oxygen atoms in total.
- When oxygen binds to haemoglobin, oxygyhaemoglobin is formed.
- The binding of the first oxygen molecule results in a conformational change in the structure of the haemoglobin molecule, making it easier for each successive oxygen molecule to bind; this is cooperative binding.
8.2.2 The Chloride Shift
The chloride shift is the movement of chloride ions into red blood cells that occurs when hydrogen carbonate ions are formed.
- Hydrogen carbonate ions are formed by the following process.
- Carbon dioxide diffuses into red blood cells and the enzyme carbonic anhydrase catalyses the combining of carbon dioxide and water to form carbonic acid.
- Negatively charged hydrogen carbonate ions formed from the dissociation of carbonic acid are transported out of red blood cells via a transport protein in the membrane.
- To prevent an electrical imbalance, negatively charged chloride ions are transported into the red blood ells via the same transport protein.
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8.3.3 The Cardiac Cycle
- The series of events that take place in one heart beat, including muscle contraction and relaxation.
The contraction of the heart is called systole, while the relaxation of the heart is called diastole.
Volume and pressure changes:
- Contraction of the heart muscle causes a decrease in volume in the corresponding chamber of the heart, which then increases again when the muscle relaxes.
- Volume changes lead to corresponding pressure changes. When volume decreases, pressure increases and when volume increases, pressure decreases.
- Throughout the cardiac cycle, heart valves open and close as a result of pressure changes in different regions of the heart.
Valves open when the pressure of blood behind them is greater than the pressure in front of them.
They close when the pressure of blood in front of them is greater than the pressure behind them.
Atrial systole:
- Walls of the atria contract. Atrial volume decreases and atrial pressure increases. The pressure in the atria rises above that in the ventricles, forcing the atrioventricular valves open.
- Blood is forced into the ventricles and there is a slight increase in ventricular pressure and chamber volume as the ventricles receive the blood from the atria.
Ventricular systole:
- Ventricular volume decreases and ventricular pressure increases.
- The pressure in the ventricles rises above that in the atria. This forces the AV valves to close, preventing back flow of blood.
- The pressure in the ventricles rises above that in the aorta and pulmonary artery. This forces the semilunar valves open so blood is forced into the arteries and out of the heart.
- During this period, the atria are relaxing; atrial diastole coincides with ventricular systole.
Diastole:
- Ventricles and atria are both relaxed.
- The pressure in the ventricles drops below that in the aorta and pulmonary artery, forcing the SL valves to close.
- The atria continue to fill with blood. Blood returns to the heart via the vena cava and pulmonary vein and the pressure in the atria rises above that in the ventricles, forcing the AV valves open.
- Blood flows passively into the ventricles without need of atrial systole and the cycle begins again.
8.3.4 Heart Action
Control of the basic heartbeat is myogenic, which means the heart will beat without any external stimulus.
This intrinsic rhythm means the heart beats at around 60 times per minute.
The sinoatrial node (SAN) is a group of cells in the wall of the right atrium. The SAN initiates a wave of depolarisation that causes the atria to contract.
Instead, the depolarisation is carried to the atrioventricular node (AVN).
This is a region of conducting tissue between atria and ventricles.
After a slight delay, the AVN is stimulated and passes the stimulation along the bundle of His.
This delay means that the ventricles contract after the atria.
The bundle of His is a collection of conducting tissue in the septum (middle) of the heart. The bundle of His divides into two conducting fibres, called Purkyne tissue, and carries the wave of excitation along them.
The Purkyne fibres spread around the ventricles and initiate the depolarization of the ventricles from the apex (bottom) of the heart.
This makes the ventricles contract and blood is forced out of the pulmonary artery and aorta.
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