Page 77 - Biology_Form_3

Biology for Secondary Schools

brain. Deficiency of this hormone during liver. It also facilitates the uptake of glucose
infancy causes a condition called cretinism in muscle cells and the liver. Apart from
which is accompanied by thickened facial that, insulin promotes the rate of protein
features, retarded and stunted growth, synthesis in the cell. When pancreas fails
abnormal bone development and mental to produce sufficient amount of insulin in
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retardation. Undersecretion of thyroxine the blood, it results into a disorder called
in adulthood leads to a condition called diabetes mellitus. This is the condition
myxoedema. This condition is characterised caused by the increase in amount of sugar
by low metabolic rate, increase in body in the blood. Excess blood sugar is excreted
fluid and fatigue. through urine. It is characterized by frequent

Calcitonin is another hormone secreted urination and excretion of sugar in urine.
by thyroid gland, it regulates the level of Glucagon hormone is secreted when there
Calcium in the blood by decreasing the is a fall in blood sugar. It converts glycogen
level of Calcium in blood. in the liver cells to glucose, resulting into an
increase of the level of glucose in the blood.
Parathyroid: This gland is found within
the thyroid gland, it secretes the hormone Gonadal hormones
called Parathyroid hormone (PTH). Like These are hormones produced by gonads
calcitonin, this hormone increases the level which are the ovaries and testes. Gonads
of calcium in the blood. are also called sex glands. They produce
both hormones and gametes. The testes
Pancreatic hormones produce testosterone hormone which
These are the hormones produced by facilitates the development of secondary
pancreas. Pancreas gland contains a cluster sexual characteristics and the production
of cells called islets of Langerhans. The of sperms. Testosterone is one of the
gland is located in the abdominal cavity. important androgen hormones secreted
This gland is surrounded by different organs in males. It controls the development of
such as small intestine, liver and spleen. secondary sexual characteristics in males
The pancreas performs two main functions such as deepening of voice, growth of beard
which are exocrine and endocrine functions. and growth of pubic hair. On the other
Through exocrine function, pancreas hand, the ovary produces oestrogens and
produces different enzymes that are used progesterone hormones. These hormones
in the digestion of food. As an endocrine control the development of secondary
gland the pancreas produces two important sexual characteristics in females such as
hormones called insulin and glucagon. development of mammary gland, pubic
These hormones are directly released hair, high pitched voice and broadening
into the bloodstream. Insulin hormone is of the hips. It also causes thickening of the
released when there is increase in blood lining of the uterus. Apart from that, the
sugar. It accelerates the rate through which progesterone hormone prepares the lining
glucose is converted to glycogen in the of the uterus for implantation. Table 3.1

70 Student’s Book - Form Three

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BIOLOGY FORM 3 FINAL EDITED 16.09.2025.indd 70
BIOLOGY FORM 3 FINAL EDITED 16.09.2025.indd 70 KAMISHNA 23/10/2025 11:52:41 KAMISHNA