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South Tuen Mun Government Secondary School Biology Revision Note 13 Osmoregulation The functions of kidney : (i) to remove urea; (ii) to regulate the salt concentration / water potential / osmotic potential / water concentration (for osmoregulation). Production of urine by nephron kidney tubule (i) Ultrafiltration: The afferent arteriole is wider than the efferent arteriole and the capillary in the glomerulus increases the resistance to blood flow, this makes a big hydrostatic pressure at glomerulus, there are pores at glomerulus and blood capillary, thus small molecules in plasma are forced into the Bowman’s capsule. (ii) Reabsorption: Glucose is completely absorbed by diffusion and active transport. Water is absorbed by osmosis, mineral salt is absorbed by diffusion. Therefore urine is made up of urea, water and salt. Thermoregulation: Structure of the skin: Regulation of body temperature : When heat gain = heat loss, the body temperature is unchanged. If the external temperature is lower than 37oC, the lower the temperature, the heat loss by the body increases. When external temperature is higher than 37oC, the body gain heat. External temperature Strategy (方法) higher than 37oC Body regulatory activities decrease heat gain By decrease metabolism e.g. respiration (呼吸作用). increase heat loss By increase sweating → evaporation (蒸發) of water in sweat takes away body heat. o hot (less than 37 C) decrease heat gain By decrease metabolism. increase heat loss By increase sweating, arteriole dilation (vasodilation) → more blood flow to skin surface → more heat loss by conduction, convection and radiation. cold (much less than 37oC increase heat gain decrease heat loss By increase metabolism : skeletal muscles contract in shivering. By arteriole constriction (vasoconstriction) → less blood flow to skin surface → less heat loss by conduction, convection and radiation; erector muscle contracts → trap a thicker layer of air → air is an insulator and air is still → less heat loss by conduction and convection Regulation of gas content in the blood To calculate the rate of breathing and depth of breathing Breathing rate = 6 x 60/20 = 18 breaths per minute Depth of breathing = 500 cm3 Volume of air entering the lung in 1 min Breathing rate = 9 x 60/20 = 27 breaths per minute Depth of breathing = 2000 cm3 Volume of air entering the lung in 1 min = 500 x 18 = 9000 cm3 = 2000 x 27 = 54000 cm3 In exercise, the rate of breathing and depth of breathing increases to supply more oxygen to the skeletal muscle for the release of energy by respiration, and to remove more carbon dioxide from the skeletal muscle. Note : the respiratory centre is inside the medulla oblongata of the brain To calculate the cardiac output: Rate of heart beat = number of heart beat per minute Stroke volume = volume of blood pumping out of the heart in one beat Cardiac output = volume of blood pumping out of the heart in one minute = rate of heart beat x stroke volume The pacemaker can initiate nerve impulse to the atrial muscles so that the muscles contract. At the same time, the impulse stimulates the AV node that produces nerve impulse along the ventricular muscles so that the muscles contract. Hormonal control of the menstrual cycle Application of female sex hormones: (i) contraception Contraceptive pills have a high dose of progesterone and oestrogen to inhibit the secretion of FSH and LH. Thus a low level of FSH cannot lead to the maturation of the egg and a low level of LH prevents ovulation Morning after pills have a very high dose of progesterone / both oestrogen and progesterone to inhibit implantation. (ii) to treat infertility FSH is used to increase the development and maturation of eggs, so that more eggs can be collected for in vitro fertilization. LH is used to promote ovulation so that mature eggs can be released out of the ovary. Oestrogen and progesterone are used as drugs to stimulate the thickening of uterine lining so that the uterine lining is ready for implantation.