Physiological Homeostasis Chapter 33. Internal Environment Millions of cells in a body make up a community Different parts of the body dependent on.
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Internal Environment Millions of cells in a body make up a community Different parts of the body dependent on each other All the cells and the fluid around them makes the internal environment This environment must be controlled E.g. water and solute concentrations, blood sugar, & temperature
Homeostasis Maintaining the internal environment within limits Changes from the norm are detected by receptors These send out a nerve/hormone signal to effectors Effectors then cause a response Response counteracts the original change from the norm This is negative feedback control
Homeostasis in the human body Osmoregulation - maintaining water, salt and ion concentrations - kidneys act as effectors - Water levels detected by osmoreceptors in the hypothalamus - Triggers the release of Anti Diuretic Hormone (ADH) by the pituitary - Low water conc.= lots of ADH - ADH increases tubule and collecting duct permeability to water - increased water reabsorption - opposite occurs with high water conc.
Homeostasis in the human body Blood sugar level - Cells constantly use blood sugar - Glucose only supplied when food is eaten - glucose supply has to be closely regulated - Glucose stored as glycogen in the liver - Blood sugar level detected by the Islets of Langerhans (in the pancreas) - If level is high, insulin is produced - Insulin activates an enzyme (glucose converted to glycogen) - If level is low, glucagon is produced - Activates a different enzyme (glycogen converted to glucose) - In an emergency, adrenaline released by the adrenal glands - It inhibits insulin secretion, promotes glucagon secretion
Diabetes Mellitus When insulin secreting cells are non-functional Insufficient (or no) insulin produced Blood glucose levels can rise (2-6 times more) Glucose often excreted in the urine (unable to be reabsorbed) Cells use glucose inefficiently Fat stores depleted to produce more sugar Can lead to weight loss and tissue wasting Now successfully treated by controlled diet and insulin injections/implants
Control of body temperature Ectotherm - animal unable to regulate own body temperature - ‘cold blooded’ Endotherm - animal that can regulate it’s own body temperature - high metabolic rate generates lots of heat - Role of hypothalamus Acts as a thermostat Receives impulses from thermoreceptors Also has central thermoreceptors –senses blood temp. - this reflects core temp. Sends nerve impulses to effectors
Control of body temperature Role of skin Correcting overheating: - arterioles near skin dilate - more blood flow to surface - heat lost by radiation through the skin - water in sweat converted to water vapour Correcting overcooling: - arterioles constrict near skin - less blood flow, less heat radiated - sweating rate reduced - erector muscles contracted - hairs (or feathers) raised to trap a layer of air – insulation - shivering & increased metabolic rate also occur
Voluntary Control If body temp changes, message sent to cerebrum Makes person ‘feel cold’ or ‘hot’ Appropriate action taken e.g. extra or less clothing, hot or cold drink
Importance of homeostasis Maintains internal environment at steady optimum state Body can function even if environment changes Can only work up to a point In extreme situations homeostasis cannot keep up Can lead to death