BIOLOGY
SS 2 &SS 3
IMPORTANT HORMONES
AND THEIR FUNCTIONS
The
pituitary gland,found just below the hypothalamus consist of an interior part
and a posterior part. Both parts release hormones, which are either
polypeptides or proteins.
A. ANTERIOR PITUITARY HORMONES.
These hormones
consist of several tropic hormones that regulate the activities of other
endocrine glands (through homeostatic mechanisms) growth hormone and prolactin.
1.Thyroid stimulating
hormone(TSH) which stimulates the
thyroid glands to produce its hormones, for instance, thyroxine.
2.Follicle stimulating
hormone(FSH)which causes follicles in the ovary to ripen and mature testes
to initrate sperm formation.
3. Luteinizing hormone(LH) which causes the release of mature eggs (ovulation)
into the fallopian tube and the secretion of testosterone in the testes.
4. The growth hormone:
It stimulates the growth of long bones, increases the metabolic rate and
promote synthesis. When there is over secretion, it causes giantism and under
secretion causes dwarfism.
5. prolactin:This
induces milk production in pregnant women.
B.POSTERIOR PITUITARY HORMONES.
Two hormones are
produced here: Anti-duretic hormone and the Oxytocin.
Anti-duretichormone(ADH)raises
the blood pressure by constricting arterioles and increases reabsorption of water
by kidney tubules.
Oxytocin: It induces milk secretion from
nipples and the contraction of the uterine wall during child birth.
THYROID HORMONE
The glands is found in the region close to the laryrix.
Three main hormones are produced from these glands, the most important being
thyroxine which is formed from an amino acid and iodine. It regulates the
growth and development of all body cells by increasing the basal metabolic
rate.
ABNORMALITIES DUE TO THYROXINE
The abnormalities
are;
1.
It leads to hypothyroidism, that is low
metabolic rate.
2.
It leads to sluggishness.
3.
In infants, it results in a condition known as
CRETINISM. A cretin, which is a dwarf, is physically, mentally and sexually
under developed. The condition can be prevented by detecting the problem and
following up with treatment of thyroxine supplements.
4.
It may result in goiter (swelling of the neck).
Under secretion of thyroxine may be due to;
1.
A diet that is low in iodine.
2.
A defective thyroid gland and
3.
An insufficient TSH production by the pituitary
gland.
PARATHYROID HORMONE
This is secreted by four tiny glands (parathyroid glands) attached to
the thyroid gland. The parathyroid hormone raises the level of calcium ions in
the blood by;
1.
Increasing the calcium absorption in the gut.
2.
Releasing calcium from bones and
3.
Reducing calcium secretion by the kidney.
The
thyroid hormone, calcitonin lowers the level of calcium ions in the blood by
counteracting the effect of the parathyroid hormone.
PANCREATIC HORMONES
The pancreas produces both digestive enzymes and hormones.
Group of cells which are scattered throughout the pancreas are called islets of
longer bans which secretes the hormones, insulin from the B cells and glucagon
from the A cells. Both hormones are polypetides, they maintain a normal glucose
level by;
1.
Causing the conversion of excess glucose to
glycogen for storage in the liver.
2.
Stimulating the absorption of glucose by the
tissue cells.
When blood glucose falls below normal, glucagors raises it by reversing
the action of insulin, by promoting the breakdown of glycogen in the liver to
glucose.
DEFICIENCY OF INSULIN PRODUCTION
The
deficiency of insulin production by the pancreas brings about the disorder
described as DIABETES MELLITUS. In the absence of insulin;
1.
Excess glucose cannot be converted to glycogen
and
2.
The body cells cannot absorb glucose.
Diabetes having an elevated blood sugar so that some glucose is excreted
in urine.
The urine leaves the body with plenty of water so that the body tends to
dehydrate.
As diabetes cannot utilize blood sugar to provide energy, other energy resources
such as fats and proteins are broken down. The diabetic therefore tends to lose
weight and suffer from muscular weakness.
ADRENAL HORMONES
These
glands can be found above the kidney. There are two hormones produced from
these glands. The other region of the adrenal cortex produces corticoids while
the adrenal medulla (inner region produces adrenaline noradrenaline). Both are
made up of amino acid.
The adrenal cortex hormones. The corticoid or
corticosteroids are grouped into:
ü
glucocorticoid and mineralocorticoids.
FUNCTIONS
ü
The glucocorticoids raise the blood glucose
level by promoting the conversion of non-carbohydrate, like amino acids to
glucose, then producing is during stressful situations like shock, pain,
injury, extreme cold.
ü
Mineral corticoids (e.g aldosterone)- They
regulate the level of sodium and potassium ions in the body fluids.
Adrenaline and non-adrenaline are the energy hormones. They are released
when we are faced with a dangerous situation. They prepare the body for
intermediate action by affecting many organs at once. They are referred to as
the fight and flight hormone. They make one respond quick and energetically to
situations. Once the danger is order, they are inactivated in the liver.
THE SEX HORMONE
The reproduction organs produce
sex hormones which are:
ü
The testis produces testosterone, the male sex
hormones and
ü
The ovaries produce oestrogen and progesterone,
the female sex hormones.
Their production begins at puberty and continues into old age. They are
steroids.
The stimulation of sex hormones is brought about by the gonad otropins
(tropic hormones of the pituitary gland) whose production is induced by
chemicals released by the hypothalamus.
1.
THE MALE SEX HORMONES: At puberty,
testosterone stimulates;
a.
The growth and maturity of the penis, testes and
accessary sex structures and
b.
The development of secondary male sex characters
such as growth of hair in the public regions, armpit, chest and face and the
deepening of the voice.
Testosterone influences sexual
behavior and together with FSH, regulates sperm production in the seminiferous
tubules of the testes in a sexually matured male.
2. THE FEMALE
SEX HORMONES:Also at puberty, the ovaries produce and release the female
sex hormones. The primary female sex hormone is the oestrogen, which;
a.
Enlarges the uterus and vagina
b.
Imitates the development of secondary female
sexual characteristics such as growth of the hair in the public region and
armpits, enlargement of the breasts and the widening of the hips and
distribution of fat typical of the female body, and
c.
Regulates the female reproductive cycle female
in which these changes have taken place are said to be sexually mature female
under goes a 28-day reproductive cycle called MENSTRUAL CYCLE that is regulated
by oestrogen and progesterone. During each cycle, a mature egg is released to
be fertilized by a sperm of it is present. This monthly release of egg
[OVULATION] is inhibited during pregnancy by progesterone which also brings
about the development of the placentas. In most of 45 to 55, a change known as
MENOPAUSE. When this happens they are
unable to reproduce anymore.
PLANT HORMONES
These are also chemicals involved in the co-ordination of
the internal environment in plants. They are needed in small quantities to
bring their effects and are produce in one part of the plant and are
transported to other part where the effect is required.
TYPES OF PLANT HORMONES
These include auxins, gibberellin, cytokinin, floregens,
abscisic acid, ethene(ethylene), traumatindormin, formin etc.
AUXINS
Among the
naturally occurring auxins that are known, the indole acetic acid[IAA] is the
most important. This auxin is found in the actirely growing and developing
parts of the plant such as the apices of shoot, from it is transported downward
for short distances by diffusion and long distances through the phloem tissues.
It affect the rate of division, a longation and differentiation of newly
produced cells.
FUNCTIONS OF AUXINS
1.
Auxin causes the shoot of plants to grow fast.
2.
Auxin stimulate the development of fruits,
ensures the fruits are retained and promote on induce the ripening of fruits in
plants.
3.
It induces the flowering of plants.
4.
It stimulate the growth of stems towards the source
of light and the roots towards the source of light and the roots towards
gravity.
5.
It causes opical dominance in plants.
6.
Auxin in petiole of fruits and leaves delays
absicsion or leaf fall.
7.
It also induce root formation in plants.
GIBBERELLINS
ASSIGNMENT
1.
What is homeostasis?
2.
What are hormones and give examples and their
functions.
3.
List 4 applications of plant hormones.
4.
Give 3 diseases each of the liver and the
kidney.
5.
List 5 functions of the skin and explain them.
6.
Define nervous system and explain the
components.
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