transport in mammals

• The mammalian circulatory system is a closed double circulation. This is because blood passes through the heart twice in one circulation of the body (pulmonary circuit and systemic circuit), contained inside blood vessels
• The circulatory system also includes a heart and blood vessels (arteries, capillaries and veins).
• Arteries and veins contain three layers of tissues known as the tunica intima, tunica media, and tunica externa.
• Tunica interna: endothelium, containing squamous epithelial cells
• Tunica media: containing mainly smooth muscle and elastic fibres with some collagen
• Tunica externa: containing mainly collagen, with some elastin fibres.
• Arteries: These blood vessels transport oxygenated blood swiftly to the tissues at high pressures. They have thick walls to withstand this high pressure. The exception to this is the pulmonary artery, carrying deoxygenated blood to the lungs. As arteries reach tissues, they branch into smaller vessels called arterioles.
• Elastin fibres: recoil and contract, squeezing the blood and so moving it along in a continuous flow. They allow the walls to stretch, as pulses of blood surge through.
• Smooth muscles: contracts, reducing blood flow in arterioles. This controls volume of blood flowing into a tissue.
• Capillaries: Arterioles continue to branch into capillaries. These are the smallest blood vessels and they take the blood as close as possible to the cells. This allows for rapid transfer of substances between cells and the blood. Due to the very small diameter of these blood vessels, blood travels very slowly. This increases the opportunity for diffusion to occur.
• Walls of capillaries are made of a single layer of endothelial cells with pores between individual cells present to allow some components of blood to pass through into the cells and tissues of the body
• Veins: Many capillaries join to form venules which then join to form veins. These blood vessels carry deoxygenated blood back to the heart. The exception is pulmonary vein, carrying oxygenated blood from the lungs to the heart
• Tunica media is thinner in veins when compared to arteries, as the blood in veins is at a lower pressure. Valves are also present to prevent backflow of blood. To keep blood flowing upwards from legs, veins are usually near muscles, so pressure is increased when muscles contract. Veins also have a much larger lumen than arteries.
• blood is composed of plasma, leukocytes, platelets and erythrocytes
• what is plasma?


  liquid part of blood which is a dilute solution of salts, glucose, amino acids, vitamins, urea, protein and fats.
• Leukocytes (white blood cells): Involved in the immune system
• Platelets: Involved in blood clotting.
• Erythrocytes (red blood cells): Involved in carrying oxygen.
• Tissue fluid: This fluid surrounds all the cells. Substances move from the blood to the tissue fluid where they diffuse into the cells. Tissue fluid has almost the same components as plasma, but lacks large plasma proteins which are too large to diffuse through pores in capillaries. Osmotic pressure causes tissue fluid to move into and out of capillaries
• Lymph: About 90% of fluid that leaks from capillaries at the arterial end into tissue spaces eventually returns to the capillaries at the venous end. The remaining 10% is returned to the lymphatic system. Fluid inside the lymphatic vessels is called lymph. Lymph is very similar to tissue fluid but has a different name as it is in a different place. Lymph contains more large proteins and white blood cells than tissue fluid.
• how does Hb transport O2 and Co2 in respiring tissues?

  CO2 from the cells diffuses into the plasma. CO2 combines with -NH2 terminal of Hb to form carbaminohaemoglobin. (10% carried this way) Most CO2 combines with water (catalysed by carbonic anhydrase) to form carbonic acid which then dissociates into H+ and HCO3- ions. H+ ions combine with Hb to form Haemoglobinic acid (HHb).
• how does Hb carry O2 and Co2 in the lungs?

  CO2 in plasma diffuses from the blood into the alveoli and oxygen diffuses into the blood from the alveoli. Carbaminohaemoglobin dissociates to form CO2 and Hb Hb then picks up O2, and HHb (haemoglobinic acid) dissociates to form H+ and Hb. The H+ ions combine with HCO3- to form carbonic acid, which dissociates to form CO2 and water (catalysed by carbonic anhydrase). CO2 diffuses into alveoli.
• what is Bohr's effect?

  the presences of high pCO2 causes Hb to release oxygen
• where is high pCO2 found?


  most in actively respiring tissues which need oxygen which causes Hb to release oxygen even more readily than it would otherwise
• what is pco2?

  partial pressure of carbon dioxide
• how does Hb transport O2 and Co2 in high altitudes?

  the p02 is low at higher altitudes which can cause altitude sickness and in order to increase oxygen intake, populations that live in high-altitude areas have adapted by developing higher red blood cell count and greater number of mitochondria to increase the efficiency of oxygen transport from lung to tissue. the muscular wall of the right ventricle also thickens, more blood can be oxygenated
• people who live in high altitudes have adapted to the low partial pressure of oxygen by having increased red blood cell count and greater number of miotchondria which increase the efficiency of oxygen transport and have bigger right ventricle, bigger heart and can transport more blood
• Biconcave shape increases surface area: volume ratio, for more efficient diffusion of oxygen
• Contain haemoglobin to transport oxygen
• Nucleus, mitochondrion, ER absent: more room for Hb, thus more o2 carrying capacity.
• Thin outer membrane to allow oxygen to diffuse easily
• Very small (7μm): no haemoglobin molecule within the cell is very far from the cell surface membrane, thus oxygen is exchanged quickly with outer fluid. Capillaries are 7μm allowing RBC to squeeze through
• Flexible: capillaries narrow than 7μm cause RBC to deform (as they have a specialized cytoskeleton) and return back to shape in venules
• External structure of the heart: Blood vessels that leave the heart are the Aortic arch and pulmonary artery. Blood vessels that enter the heart are the superior vena cava, the inferior vena cava and the pulmonary vein. The left and right side of the heart are separated by the septum.
• Atria: 2 upper chamber are known as atria. They are thin walled and receive blood at low pressure.
• Ventricles: 2 lower chambers are known as ventricles. They are thick walled, receive blood from atria and pump it out through arterie
• The left ventricle has a thicker muscular wall, as it has to pump blood into the systemic circuit which has a higher resistance to blood flow than the pulmonary circuit. The systemic circuit is also longer and requires more pressure.
• Atrial systole: This occurs when muscles in the atrial walls contract and blood passes on to the ventricles. 70% of the blood flows passively down to the ventricles. The bicuspid and tricuspid valves open while the semilunar valves are closed.
• Ventricular systole: 0.1 seconds after the atria contracts, the ventricle walls contract as well increasing the blood pressure and pushing it out of the heart. The blood passes through the aorta and pulmonary arteries. The semilunar valves open and the bicuspid and tricuspid valves are closed
• Ventricular diastole: This lasts for about 0.3 seconds; the ventricles relax and the pressure falls below that in the arteries. The higher pressure in the arteries pushes against the semilunar valves, shutting them