Homeostasis PDF

 What is homeostasis? 0 Maintenance of a constant internal environment. 0 It ensures that the composition of the body fluids is kept within narrow limits. 0 It allows an organism to be independent from the changes in the external environment.  Maintenance of the body temperature...

 What is homeostasis? 0 Maintenance of a constant internal environment. 0 It ensures that the composition of the body fluids is kept within narrow limits. 0 It allows an organism to be independent from the changes in the external environment.  Maintenance of the body temperature 0 Why? 0 Enzymes in the body only can work within a certain range of temperatures. Maintenance of the pH and water potential of tissue fluid 0 Why? 0 Enzymes only can work in certain range of pH values. 0 Cells will be affected if water potential in the plasma and tissue fluids change drastically.  Negative feedback 0 A process that acts on the changes detected to restore the system to its original state. 0 Components involved: 0 Receptors (sense organs) 0 Stimulus  Negative feedback 0 A negative feedback control loop consists of: 0 A norm (set-point) 0 A stimulus 0 A receptor 0 A corrective mechanism 0 A feedback Regulation of blood glucose concentration Blood glucose concentration 0 Normal blood glucose concentration 0 70-90 mg/ cm3 0 Glucose levels in blood rise after a sugary meal. 0 It falls during physical exercise or starvation  Normal set point Blood glucose Blood glucose concentration concentration Stimulus drops. Insulin rises above production is normal decreased Blood glucose concentration rises above normal level Islets of Excess glucose Langerhans in is converted to the pancreas Receptor glycogen are stimulated Islets of Blood Langerhans transports secrete insulin insulin to liver into and muscles bloodstream  Function of insulin 0 It increases the permeability of the plasma membrane to glucose. 0 Glucose is absorbed more quickly by the cells. 0 It causes liver and muscles to convert excess glucose to glycogen. 0 Glycogen is stored in liver and muscles.  Normal set point Blood glucose concentration Blood glucose rises. concentration Stimulus Glucagon falls below production is normal decreased Blood glucose concentration falls below Glycogen is normal level Islets of converted Langerhans in back to the pancreas Receptor glucose are stimulated Blood Islets of transports Langerhans glucagon to secrete liver and glucagon into muscles bloodstream  Function of glucagon 0 It stimulates liver and muscle cells to convert stored glycogen to glucose 0 The glucose is released into the bloodstream Regulation of blood water potential  Regulating body water potential Stimulus Water potential of blood returns to Water potential of Water potential of blood normal blood decreases increases above the norm Negative feedback More water is Receptor excreted and urine Hypothalamus in brain produced is more dilute detects stimulus Corrective Mechanism Pituitary gland releases less Less water is anti-diuretic hormone (ADH) reabsorbed by kidney tubules brain  Regulating body water potential Stimulus Water potential of blood returns to Water potential of Water potential of blood normal blood increases decreases below the norm Negative feedback Less water is Receptor excreted and urine Hypothalamus in brain produced is more concentrated detects stimulus Corrective Mechanism Pituitary gland releases More water is more anti-diuretic hormone reabsorbed by (ADH) kidney tubules brain Structure of Human Skin  Hair Sweat pore Cornified layer Blood capillaries Sebaceous Skin papilla gland epidermis Granular layer Malphigian layer Nerve ending Dermis Sweat duct Hair erector Subcutaneous muscle fat Sweat gland Hair papilla Adipose tissues  Structures involved in temperature regulation Blood vessels in dermis layer 0 Capillaries and arterioles 0 Vasodilation – dilation of the arterioles 0 Skin arterioles dilate → more blood is sent to blood capillaries in the skin 0 Skin becomes blushed 0 Vasoconstriction – constriction of the arterioles 0 Skin arterioles constrict → less blood flow through the blood capillaries in the skin 0 Skin becomes pale  Hair hair erector 0 Hairs are embedded in the dermis. hair papilla 0 They are produced by the epidermis. 0 Each hair grows inside the hair follicle. 0 Blood capillaries and nerves are found in hair papilla. 0 Hair erector muscles are attached to the hair follicles. 0 Contraction of these muscles lead to: 0 Hairs stand on their ends 0 Skin around the hair is raised  Sweat gland 0 Secreted sweat flows through a sweat duct to a sweat pore. sweat duct 0 Sweat consists sweat gland mainly of water , dissolved salts blood capillaries and urea.  Sensory receptor 0 Stimuli are detected by the nerve endings. 0 They detect pain, pressure and temperature changes.  Subcutaneous fat 0 Layers of adipose cells 0 Place for fat storage 0 It also serves as an insulating layer Gaining and losing heat Production and gaining of heat 0 Heat is produced from metabolic activities like cellular respiration. 0 Large amount of heat is released in muscles and liver. 0 Heat is distributed to the rest of the body via bloodstream. 0 Heat can be gained from: 0 Vigorous exercise 0 Consumption of hot food 0 In warm environment  Losing heat 0 Heat is lost through: 0 From the skin surface via radiation, convection and conduction 0 Evaporation of water in sweat from the surface of skin 0 In faeces and urine 0 Exhalation of air  How the body temperature is regulated Body temperature rises Reduce heat production (heat gain greater than Increase heat loss to heat loss) surroundings Normal body temperature (37°C) Body temperature falls Increase heat production (heat loss greater than Decrease heat loss to heat gain) surroundings  Regulation of body temperature 0 Hypothalamus 0 It monitors and regulates body temperature 0 It receives info about temperature changes from 0 Thermoreceptors in skins 0 Detects temperature of environment 0 Thermoreceptors in hypothalamus 0 Detects temperature of blood Body temperature rises above norm Rise in body temperature is detected by hypothalamus, nerve impulses are sent to the relevant parts Skin arterioles dilate (vasodilation) and shunt vessels constrict to allow more blood flow through blood capillaries in skin – more heat is lost Sweat glands produces more sweat. More water is evaporated from skin surface, more latent heat of vaporisation is lost Metabolic rate decreases to reduce the amount of heat produced.  Vasodilation 4 Greater heat loss When shunt vessels constrict, more blood skin surface flows to capillaries. 1 capillaries More heat is lost from skin by radiation, Arterioles in skin 3 convection and dilate Shunt vessel conduction. constricts arteriole shunt 2 vessel More blood flows to capillaries in skin  Relaxation of hair erector muscles Hair erector muscles relax when body temperature increases. Hairs lie flat, allowing air to circulate over skin. This removes heat. hairs lie flat  Reduced metabolic rate Rate of metabolic activities slow down. Less heat is produced within body. Body temperature drops below norm Drop in body temperature rise is detected by hypothalamus, nerve impulses are sent to the relevant parts Skin arterioles constrict (vasoconstriction) and shunt vessels dilate to allow less blood flow through blood capillaries in skin – less heat is lost Sweat glands produces less sweat. Less water is evaporated from skin surface, less latent heat of vaporisation is lost Metabolic rate increases to increase the amount of heat produced. Shivering may occur to increase the amount of heat produced and helps to raise the body temperature to normal.  Vasoconstriction 4 Less heat loss When shunt vessels skin surface dilate, less blood flows to capillaries. capillaries 1 Less heat is lost from Arterioles skin by radiation, 3 in skin constrict Shunt vessel convection and dilates conduction. arteriole shunt 2 vessel Less blood flows to capillaries in skin  Contraction of hair erector muscles Hair erector muscles contract when body temperature decreases. Hairs “stand up”, trapping an insulating layer of warm air over skin. hairs “stand up”  Increased metabolic rate Rate of metabolic activities increase. More heat is produced within body. Shivering Occurs when more heat production is needed to prevent drop in temperature. Reflex contraction of the body muscles generates heat which increases body temperature to normal. Test Yourself 12.2 Structure of the Human Skin Test Yourself 2. (a) In extremely cold conditions people may get frostbite. This causes the cells in the toes and fingers to die. Explain why this takes place even if thick gloves, socks and shoes are worn. (b) Cold environments cause the body to shiver. Explain why shivering takes place in cold conditions. (c) Explain how the mechanisms for controlling body temperature are coordinated.  Test Yourself 2. (a) In extremely cold conditions people may get frostbite. This causes the cells in the toes and fingers to die. Explain why this takes place even if thick gloves, socks and shoes are worn. - Vasoconstriction – arterioles near the skin constrict, shunt vessels dilate; - To reduce heat loss near skin surface due to conduction, convection, radiation; - Resulting in less blood flow to the skin capillaries, and to the cells of the extremities (toes and fingers); - Less/lower rate of oxygen and glucose transportation to the cells near skin surface; - Decreasing the rate of rate of respiration / metabolism in cells of toes / fingers, causing them to die  Test Yourself (b) Cold environments cause the body to shiver. Explain why shivering takes place in cold conditions. Shivering is a reflex contraction of the muscles of the body Muscle cells undergo respiration which generates heat (thermal energy) transported via blood to the rest of the body and increases body temperature to normal.  Test Yourself (c) Explain how the mechanisms for controlling body temperature are coordinated. - Stimulus: Increase or decrease of blood temperature of the body - Detector: Monitored by the hypothalamus of the brain - Stimulation of corrective mechanisms for negative feedback to occur for the restoration of the norm