Download Note 13

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.