Blood glucose regulation is a very important variable within the human body. When food is digested, it is broken down into its components, one of which is Glucose. This causes the blood glucose levels to rise. The optimum amount of glucose in the blood is approximately 800mg per dm3, if this raises by about 200mg per dm3 this will cause the alpha and beta cells in the pancreas to detect the change. Insulin is released from the pancreatic beta cells located in the Islets of Langerhans and has four metabolic affects which cause the blood glucose levels to drop. It enhances entry of glucose into cells and the storage of glucose as glycogen, or conversion to fatty acids. Insulin also enhances the synthesis of fatty acids and proteins and supresses the breakdown of proteins into amino acids. This is an example of negative feedback. If the adverse effect happens to the blood glucose level and it starts to drop then two hormones released from the Islets of Langerhans, Glucagon from the alpha cells and Somatostatin from the delta cells. Glucagon enhances the release of glucose from glycogen and the synthesis of glucose from amino acids or fatty acids. Somatostatin supresses the release of insulin, which is important when the blood glucose level is low, as the insulin would cause it to go even lower.
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Negative feedback is the process that occurs during the regulation of an internal environment, which is called homeostasis. A good example of this is the regulation of glucose levels in the blood. The concentration of glucose in the blood is maintained around 800mg per dm3. If the blood glucose concentration is very low, this means that the person is suffering from hypoglycaemia and if the concentrations are very high then the person is suffering from hyperglycaemia. The two major hormones involved in the control of blood glucose levels are insulin and glucagon, which are both secreted by the pancreas. If the blood glucose levels rise then the alpha and beta cells in the Islets of Langerhans detect this and the alpha cells stop secreting glucagon and the beta cells start secreting insulin. This causes the liver to stop breaking down glycogen due to the drop in glucagon, and most body cells increase uptake and use of glucose due to rise of insulin. This brings the blood glucose level back down to the optimum level. If the blood glucose levels drop then the alpha and beta cells detect the change and the alpha cells secrete glucagon and the beta cells stop secreting insulin. This causes the liver to break down glycogen into glucose due to the rise in glucagon. This causes the blood glucose level to stabilize. In both cases negative feedback causes a rectification in the change of the blood glucose levels, returning them back to the norm.
Another example is thermoregulation, this is the regulation of the core temperature of the body, which is around 37oC. If the core temperature drops below 35oC it can cause hypothermia and if the temperature rises above 38oC it can cause hyperthermia, both of these can be fatal. If the body temperature drops then messages are sent from the hypothalamus to the blood vessels in the skin making then contract reducing blood flow and heat loss, this is called vasoconstriction. At the same time hairs become erect to attempt to trap a layer of air around the skin. Heat production increases causing shivering and respiration in brown fat, maximizing heat production. This brings the temperature back to the norm. If the temperature rises then messages are sent from the hypothalamus to the skin making the blood vessels dilate increasing blood flow and heat loss, this is called vasodilation. Also the body starts sweating and hairs become relaxed, there is also less respiration in brown fat. These processes bring the temperature back to the norm.
C) Passive Transport. Passive transport is the movement of biochemical and other atomic or molecular substances across membranes. The four kinds of passive transport are diffusion, facilitated diffusion, filtration and osmosis.
Diffusion is the net movement of substance from a high concentration to a low concentration. The diffusion of a solute across a membrane is a function within passive transport because it is the movement of a substance across a membrane. Facilitated diffusion is the movement of large molecules across a membrane, although due to the size of the molecules they canâ€™t just pass through. They have to use transport proteins to pass across the membrane. Facilitated diffusion is part of passive transport because molecules move across a membrane. Filtration is the movement of solutes across a membrane via hydrostatic pressure created by the cardio-vascular system. Whether a molecule can pass through or not is down to the membrane pores and only a certain size can pass through. As this is molecules passing across a membrane it is part of passive transport. Osmosis is the movement of water molecules across a permeable membrane from a high water potential to a low water potential. As this is again molecules crossing a membrane without chemical energy, it means that the process is part of passive transport. The transport of an ion down an electrochemical gradient involves both diffusion and active transport. An electrochemical gradient has two components, the first is a chemical component caused by a differential concentration of ions across a membrane. The second is the electrical component which is caused by a charge difference across a lipid membrane. Due to the diffusion occurring in this process, it means that an ion moving down an electrochemical gradient is passive transport as substances move across a membrane through diffusion.
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In the process of fracture healing, several phases of recovery facilitate the proliferation and protection of the areas surrounding fractures and dislocations. The length of the process depends on the extent of the injury, and usual margins of two to three weeks are given for the reparation of most upper bodily fractures; anywhere above four weeks given for lower bodily injury.
The process of the entire regeneration of the bone can depend on the angle of dislocation or fracture. While the bone formation usually spans the entire duration of the healing process, in some instances, bone marrow within the fracture has healed two or fewer weeks before the final remodeling phase.
While immobilization and surgery may facilitate healing, a fracture ultimately heals through physiological processes. The healing process is mainly determined by the periosteum (the connective tissue membrane covering the bone). The periosteum is one source of precursor cells which develop into chondroblasts and osteoblasts that are essential to the healing of bone. The bone marrow (when present), endosteum, small blood vessels, and fibroblasts are other sources of precursor cells.