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| Major endocrine glands |
The
body secretes chemical messengers called HORMONE that directly enters the blood
stream without passing through ducts and goes on to acts on specific target
organs, the secretion of these chemicals in the body has profound effects on
many body processes, for instance, they regulate growth, secondary sexual
characters, mood swing, sleep and even appetite. The over production or under production of
these substances can be detrimental to health, they can cause retarded growth
and many other health condition.
Hormone
By
definition, hormones are chemicals release by cells or glands in one part of
the body that exert their effect in another part of the body.
Some
of these synthetic substances exert their effects at the cellular level with
the help of a second messenger or intermediate after activating the appropriate
receptors called Prolein.
Prolein
are specific for each receptor, examples of receptors are vasopressin,
Catecholamine, Glucagon, polypeptide, glycoprotein and hypothalamic releasing
hormone found on the cell membrane, they acts on the enzyme Adenyl cyclase to form Adenosine Monophosphate = Cyclic AMP
or CAMP, the second messenger from
ATP.CAMP convert inactive protein Kinases
to active protein kinases which causes cell phosphorylation which
finally leads to the expression of the desired hormonal action. Calcium ion (Ca2+)
which regulates body function also acts as a third messenger.
Hormones
can also have receptor on the cytoplasm and nucleus, those with receptor on
cytoplasm for example steroidal, glucocorticoid, mineralocorticoid, progestin,
androgen and estrogen acts by activations of gene.
Hormone
having receptor in the nucleus interacts with DNA
to bring about the synthesis of MRNA
leading to the production of protein that
brings about hormonal action.
Properties of hormone
1. They are controlled by gene
2. Enters directly into the blood
stream by diffusion and bind to cellular receptors which give out signals to
change cellular activities.
3. Acts on target organ.
What is endocrine gland?
Endocrine
glands are ductless glands that produce hormone that are secreted directly into
the blood stream without passing through ducts, they act on specific target
organ and are distributed around the body by the circulatory system. In other
words, the glands do not require duct (ductless) in other to exact their effect
but needs nearness to blood vessels.
Characteristics of endocrine gland
1. Are specialized for secretion and
their appearance depends on the nature of their secretary products and on the
cellular mechanism needed to produce and store their end products.
2. They are secreted into interstitial
fluid from where they diffuse into the blood stream.
3. Are arranged into cords or small
clumps with each cell closely linked to adjacent vessels.
4. Have perforated endothelium to
facilitate diffusion of hormone into blood vessels.
5. Employs messengers called hormone.
6. Their secretions are directed
towards specific organs known as “Target organ”.
Endocrine includes the followings,
1.
Thyroid gland
2.
Pituitary gland
3.
Pancreases
4.
Gonad gland
Thyroid Gland
Thyroid
gland is located in the cervical region anterior to the larynx and consist of two lobe united by an isthmus,, its emerges
from early embryonic life from the endoderm of initial portion of primitive
gut.
Function
of Thyroid Gland
1. It synthesizes thyroxine hormone (T4)
and triiodothyronine (T3) which are needed for growth, cell differentiation,
control of oxygen consumption and basal body metabolism rate. T3, in
particular affect almost all physiological processes in the body.
2.Carbohydrate
metabolism: it enhances glucose absorption from the G.I.T and may cause
hyerglucemia.
3. It enhances the action of
catecholamine on the heart through beta adrenergic receptor causing increase in
cardiac output and mental rate.
4. It facilitates mental process and
enhance reflexes particularly stretch reflex.
5. Lipid metabolism: hypothyroidism
increases the level of serum cholesterol while hyperthyroidism decreases the
level of cholesterol.
6. Caroligenic
effect: speeds up the rate of metabolic
processes and maintain body metabolism level leading to increase oxygen
consumption and heat production with an added increase in Na+ - K-
ATPase pump activity.
7. Growth and maturation:
it is important in growth, deficiency causes critinism (Dwarfism),
enlarge tongue and mental retardation,
over secretion leads to gigantism. It is also known to cause hyperplastic goiter and mexoedema coma.
Thyroid gland secretes three
hormones,
a. Triiodothyronine
(T3): this is the active form of thyroxine
hormone; thyroid gland secretes about 20% of this chemical substance directly
into the blood stream while the remaining 80% is produced in the liver and
kidney by conversions of thyroxine.
b. Calciton:
this is a polypeptide hormone produce by the parafollicular cells of the
thyroid in man but by the ultimopharyngeal in other animals.
c. Thyroxine
Hyperthyroidism
Thyroid
gland sometimes over produce it’s hormone resulting in increase in body processes, usually, there
is weight loss, increase heart rate, nervousness and mood swing, sometimes the
condition remain asymptomatic.
In
essence, hyperthyroidism is the over production of thyroxine leading to increase
in body mechanisms.
The
condition is associated with Gravis disease, the immune system attack thyroid
gland, while the gland retaliate by producing too much of the hormone.
Thyroid
noodles (swollen thyroid) are another common cause of hyperthyroidism.
Hyperthyroidism
is a hereditary disease, it runs in the family.
It can be treated surgically by removal of affected part of the gland or
with pills. Anti-thyroid drugs and iodine solution are also used to slow down
the rate of the hormone production.
Parathyroid gland
Parathyroid
glands are two pairs of glands positioned behind the thyroid gland, one on each
end of the upper and lower pole usually in the capsule that covers the gland,
sometimes, they occur embedded in the mother thyroid gland.
Parathyroid
gland produces parathormone which is
important in regulating calcium serum level. it decreases the concentration of
phosphate in the blood, this leads to reduction in phosphate absorption causing an increase in phosphate excretion in
the urine.
PITUITARY GLAND
This
is a pear shape gland located at the base of the mid brain between the optic
lobe. It is regarded as the master endocrine gland because it controls the
activities of other endocrine gland secretions (hormone). Pituitary gland controls other hormone
functions such as thyroid activities, growth during childhood, testosterone
production, and urine production.
It
is made up of both posterior and anterior glands which secretes different type
of hormones, each anterior pituitary gland is produced by a separate group of
cells which according to their staining characteristics are either acidophilic
or baseophilic.
Anterior
part of the gland produces
1- Growth
hormone somatotrophin (GH/STH): It is the only hormone that does
not require target organ in other to produce its effect.
a- It stimulates growth in children
and control metabolism in adult.
b- It enhances lipolysis in adipose
tissue causing liberation of free fatty acid (FTA) into the blood.
c- It causes
elevation of blood sugar level by antagonizing the actions of in female and
spermatogenesis in male.
d- It is the fountain of
youthfulness in terms of positive feedback mind and energy.
Prolactin: it stimulates mammary growth and milk production or lactation.
- Prevent ovulation in lactating women.
- Stimulates corpus liteum to produce progesterone.
- Controls prolactin inhibitory hormone called DOPAMINE.
3. Follicle stimulating hormones (FSH)
- stimulates growth in female
and spermatogenesis in male.
- stimulates Estrogen
production and induce the release of ovary.
4. Luteinizing
hormone (LH/SCH)
- Induces ovulation
- Stimulates progesterone
secretion by Corpus luteum
- Stimulates testosterone
production.
5. Thyroid
stimulating hormone (TSH)
- Stimulates production of thyroxine by thyroid gland.
6. Adrenocorticotrophic
hormone (ACTH)
- Stimulates production of
adrenocorticoid by the adrenal cortex.
- It has MSH property
responsible for ADDISON disease.
ADRENAL
GLAND
Adrenal
gland are tiny structures located on top
of each kidney, it js made up of two parts, the adrenal cortex which produces
cortisol and Aldosterone hormone and the
adrenal medulla which produces
adrenalin and noradrenalin.
Functions of Cortisol and Aldosterone
a - promotes gluconeogenesis and
glycogenolysis
b - Reduces gastric mucus predisposing to
ulcer
c - It helps to combat stress
d - It performs anti immune and anti
allergic function by reducing eosinophiles and lymphocyte circulation. It also
reduces the size of lymphoid tissue.
Adrenalin on the other hand, causes
stress condition which results from harmful stimuli, for example, emotional or
physical strain, pain and anger,
stressors stimulates the hypothalamus
to release Corticotropin- releasing
hormone(CRH), which in turn causes the production of Adrenocorticotropic hormone (ACTH)
which stimulates cortisol production. Cortisol then effects its action on energy
metabolism and vascular effects.
In
addition to ACTH response, stress can also lead to an increase Sympatho -
adrenal response resulting in increase heart rate , cardiac output, increase blood pressure and blood flow to muscles in response to
danger or defence reaction.
Noradrenalin
is a vasoconstrictor; it normalizes the body after stress thereby countering
the effect of adrenalin.
Posterior
part of the gland produces
1. Antidiuretic
hormone (ADH): also known as Pitressin or Vesopressin
causes re-absorption of water (fluid) in the renal tubule thereby reducing
urination, it also causes rise in blood pressure.
2. Oxytocin:
it stimulates uterine contraction, contraction of myoepithelial cells of
mammary gland during milk ejection reflex.
PANCREAS
Pancreas
is a whitish gland made up of many diffused lobe located between the lower part
of the stomach and duodenum (small intestine).
It
secretes pancreatic juice which contains three digestive enzymes, the Amylopesin, trypsin and lipase, about 1 to 1.5 litres of
pancreatic juice is secreted daily by an average man and they are released into
the duodenum through duct.
The
enzyme Amylase converts starch to maltose sugar; lipase converts
fats and oil to fatty acid and glycerol, trypsin converts proteins to peptones and amino acid.
The
pancreas also secretes Insulin which
is produced in the islets of Langerhans.
Insuline was discovered by Banting and Best who demonstrated the hypoglycemic action of Pancreas extract.
Insulin
is synthesized in the (β) of the Pancreas Islets
Langerhans.
Function of Pancreas
1. Regulates the amount of glucose in the blood
stream
2.
Increase the amount of glucose entering into the cells
3.
Converts glucose to glycogen
4.
Increase synthesis of triglycerides in the liver
5.
Reduce lipases in adipose tissue.
6.
Enhance protein synthesis by increasing transport of amino acid into the
cells.
7.
Facilitate entry of potassium into the cell.
GONAD GLAND
Gonad
gland produces sex hormone Gonadotrophi SEE DIAGRAM.
Physiological
Importance Of Gonadotrophin
1 – Stimulation of follicular growth
2 – Produces luteinizing hormone
3 - Stimulates production of Progesterone, Testosterone, Estrogen and Androgen
PINEAL GLAND
Pineal gland also
known as conarium or epiphysis
cerebri is located in the epithalamus near the center of the
brain, it secrete melantonin which regulate sleep circle.
HYPOTHALAMUS
Hypothalamus is not a gland but produces a hormone that
controls the action of pituitary gland, it’s
found above the pituitary and optic chasma and below the hypothalamus sulcus, and is delineated into
prominent nuclei and area SEE MORE.
It secretes the followings
-
Thyriotropin releasing hormone ( TRH)
-
Corticotrophin releasing hormone (
CRH)
-
Prolactin releasing hormone (PRH)
-
Growth releasing hormone (GRH)
-
Follicle stimulating hormone (FSH)
-
Luteinizing hormone( LH)
Function of hypothalamus
- Secretes many chemical substances
that controls different cells and organs
- Regulate sleep, thirst, hunger, temperature
and sex drive
- Controls involuntary (unconscious
actions) actions such as metabolism.
- Regulates fluid and electrolyte
balance of the body.
DEFINITION OF TERMS
Prolein
– Amino acid with alpha amino acid group, alpha carboxylic acid group and a
pyrolydine side chain used in biosynthesis of protein.
Basophilic
– used in histology to describe cell that is readily stained with basic dye.
Estrogen
– primary female sex hormone and pill responsible for developments of secondary
sex characters in female.
Gluconeogenolysis
– is a metabolic pathway that leads to generation of glucose from non
carbohydrate carbon substrate such as glucogenic amino acid, glycerol and
lactate.
Duodenum
– small intestine.
Corticotropin- releasing hormone (CRH)
– Peptide hormone involve in stress response.
Hyperglucemia
– this is the abnormal high level of glucose n the blood stream.
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