- The alveolus wall is an efficient exchange surface as it is only one cell thick (squamous cell). It is moist and is highly folded for a large surface area.
- Alveoli are supplied with a rich network of capillaries (walls one cell thick) which carry blood close to the alveolus wall (the surface exchange).
- Intercostal muscles on the ribs :
- Contract to raise the ribs.
- Relax which makes the ribs fall
- Muscle fibres in alveolus wall contract/relax to move air in and out of the lungs (ventilation). Along with the blood supply, this keeps up a concentration gradient of oxygen and carbon dioxide.
- These features increase the rate of diffusion of oxygen into the blood from the alveolus and carbon dioxide out of the blood into the alveolus.
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Lung structure and function
- pressure in chest cavity drops blow atmospheric pressure
- Expiration :
- pressure in lung increases and rises above atmospheric pressure.
- The trachea and bronchi have rings of cartilage which keep them open for airflow during ventilation.
- Smooth muscle contracts and narrows the bronchi and bronchioles and elastic tissue opens these airways. This controls airflow.
- Goblet cells in the lining of the trachea, bronchi and bronchioles secrete mucus which traps particles (e.g. pollen and bacteria).
- Ciliated epithelial cells in the lining beat upwards. This removes any swallowed mucus or particles, keeping the lungs clean.
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Animal Transport systems
- Large multicellular animals have a small surface area for their volume, resulting in a large distance for diffusion of gases.
- They need a special transport (blood) system to suppy oxygen and remove carbon dioxide, especially if very active. (e.g. birds, mammals and fish).
- Single system (fish): heart - gills - body - heart.
- Double system (mammels): Left heart - body - right heart - lungs - left heart.
- Cosed circulatory system (fish, birds and mammals) :
- blood stays in blood vessels.
- Open system (insects):
- blood leaves vessels.
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- The left ventricle wall (thick/high pressure) pumps blood around the body. The right ventricle wall (thinner/low pressure) only have to pump blood to the lungs.
- Atrial wall are very thin since they only have to pump blood a short distance into the ventricles.
- Cardiac cycle:
- chambers fill (diastole) ; ventricles contract (ventricular systole)(Atrio-ventricular valves close, "lub" sound); atria contract (atrial systole)(semi-lunar valves close, "dub" sound).
- The Sino-artial node (in right atrium) maintains beat rhythm. The AtrioVentricular Node and Purkyne fibres pass the beat on to ventricles.
- Heart cells respire fatty acids so needs oxygen for aerobic respiration.
- Coronary Atrteries lie over the surface of the heart. They carry oxygenated blood to the heart itself.
- Veins carry blood to the heart.
- Arteries carry blood away from the heart.
- String-like tendinous cords attach valves to the walls of the venricles and prevent the flimsy valves turning inside out.
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- Why low pressure ?
- Blood from the right ventricle does not need to travel far
- The lungs contain a lot of very fine capillaries which are not supported and could easily burst.
- So pressure of blood must be kept low.
- Heart muscle is myogenic it can initiate its own contractions.
- P- shows the excitation of atria.
- QRS- indicates the excitation of ventricles.
- T- shows diastole.
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- Blood contains cells, plasma proteins and dissolved substances.
- Tissue fluid is blood minus cells and plasma protiens.
- Harmoglobin (Hb) in red blood cells (erythrocytes) picks up oxygen easily at the lungs where oxygen pressure is high (Hb dissociation curve is to the left and S-shaped) and releases it at tissues where oxygen pressure low. (down a diffusion gradient)
- Carbon dioxide from tissues combines with Hb, making it release oxygen ( Carbon dioxide makes the dissociation curve move to the right). This Bohr effect means more oxygen for active tissues. The carbon dioxide diffuses into plasma.
- Has a higher affinity for oxygen than adult haemoglobin.
- Can "pick up" oxygen from an environment that makes adult haemoglobin release oxygen.
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- carries blood away from the heart
- small lumen to maintain high pressure
- wall is relatively thick ; contains collagon, a fibrous protien to give it strength to withstand high pressure.
- contains elastic tissue thats allows wall to stretch and recoil. The recoil maintains the high pressure while heart is relaxed.
- contains smooth muscle which contract to reduce blood flow to certain organs.
- folded endothelium so can unfold when the artery is stretched.
- large lumen to ease the flow of blood
- thinner layers of collagon, smooth muscle and elastic tissue. They do not need to stretch and recoil and do not contrict blood flow.
- Main feature valves that prevent blood flowing in the wrong direction.
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- has very thin walls. This allows exchange of materials between the blood and cells of tissue via the tissue fluid.
- Lumen is very narrow. Red blood cells are squeezed this helps them gve up oxygen.
How tissue fluid is formed :
- At the arterial end of a capillary, the blood is under high pressure due to the contractions of the heart muscle.
- This is know as hydrostatic pressure
- The fluid can leave through tiny gaps in the capillary wall.
- The fluid that leaves the capillary is known as the tissue fluid.
- Fluid surrounds the body cells so exchange can occur by diffusion/ facilitated diffusion.
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- Main difference between tissue fluid and lymph is that it contains lymphocytes.
Formation of Lymph
- Some tissue fluid is drained away in the lymphatic system.
- It consists of a number of capillary like vessels.
- Fluid starts in the tissue and drains the excess in a large vessel which rejoins the blood system in the chest cavity.
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Carbon dioxide transport
- Carbon dioxide diffuses from body cells to red blood cells.
- Enzyme (carbonic anhydrase) in red blood cells combine carbon dioxide and water
CO2 + H2O > H2CO3
- Hydrogen carbonate ions diffuse out of red blood cell.
H+ + HCO3-
- H ions combine with Hb (in plasma) to form HHb ( Haemoglobinic acid )
- Chloride ions (Cl -) move from plasm into red blood cell to maintain charge (chloride shift)
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Carbon dioxide transport
- Oxyhaemoglobin dissociates under the influence of hydrogen ions
HbO8 -> Hb + 4O2
- Oxygen is released into the blood plasma
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