Category: 12th Zoology

Errors of refraction

In a normal eye focused for distant objects, parallel rays of light come
to a sharp focus exactly on the retina. It can accommodate for clear vision of
objects from infinity (far point) down to 25 cm (near point). This ideal
refractive state is called emmetropia. A deviation from emmetropia is called
ametropia. The important forms of ametropia are myopia,
hypermetropia, astigmatism, presbiopia. Ametropia results from an
imbalance between the length of the eye ball and its refractive power. (Errors of refraction)

Myopia (Short Sightedness)

Myopia results if the lens curvature is too great or the entire eyeball
becomes elongated. Light rays entering the eye are refracted more than is
necessary. Consequently light is focused in front of the retina. The image
perceived is thus blurred. The condition is called short-sightedness as
objects near the eye are clearer than those further away. Myopia can be
corrected by placing a concave lens in front of the eye. The surface of the
concave lens refracts light rays in such a way that the rays diverge slightly
from their original path. The lens of the myopic eye now refracts the
diverged light rays in to focus on the retina. (Errors of refraction)

Hypermetropia (Long Sightedness)

Hypermetropia results when the curvature of the eye lens is not great
enough. Light rays are not refracted enough and would thus be focused
behind the retina. The condition is called long-sightedness because distant
objects are clearer than near ones. This happens because light rays from
distant objects require less refraction than rays from near objects.
Correction of hypermetropia requires placing a convex lens in front of the
eye. The lens converges light rays before they enter the eye so that the eye’s
focuses the light correctly on the retina. (Errors of refraction)

Astigmatism

Astigmatism occurs if either the cornea or lens is distorted. One part
of the focusing mechanism then refracts light rays too much, or too less.
Usually most of the images perceived is out of focus. Light rays from part of
the object are focused in front of the retina, as in myopia. Rays from other
parts would be focused behind the retina, as in hypermetropia. Astigmatism
can be corrected by placing a lens in front of the eye. The curvature of this
lens varies from one part to another to compensate for the eye’s
deficiencies. (Errors of refraction)

Presbiopia

This is the result of a reduction in the amplitude of accommodation
with age due to hardening and loss of plasticity of the lens. Hence it becomes
less capable of being moulded into a more complex form. Presbiopia begins
at about 40 years of age. The remedy is convex lenses for reading. Any
defect in the eye should be consulted immediately with the optometrist. (Errors of refraction)

Photochemistry of Retinal visual Pigments

Post author By Mr. Padeepz
Post date September 25, 2018
No Comments on Photochemistry of Retinal visual Pigments

Photochemistry of Retinal visual Pigments

Rhodopsin or Visual Purple is a puplish red photosensitive pigment
present in the outer segment of the rods (120 million rods). It is made up of protein portion, an opsin (scotopsin) combined with an aldehyde of vitamin
A called Retinene 1, which is referred to as a retino. On exposure to light,
rhodopsin is bleached, ie., broken down to retinene and opsin, but is
resynthesised in the dark. Some of the retinene recombines with scotopsin to
form rhodopsin while some are reduced to vitamin A. The rods are extremely
sensitive to light and are responsible for vision in dim light. This is called
SCOTOPIC VISION. (Retinal visual Pigments)

Cones also contain visual pigments made up of retinene, combined
with a protein opsin (photopsin). Three pigments each responding to
different wavelength are found in man. There are three primary colors namely
red, green and blue. Color vision is a function of bright light vision and cones
are responsible for color perceptions. (Retinal visual Pigments)

In bright light maximum perception of colors is at the fovea region of the retina where rods are absent and only cones are present. In dim light when the rods in the extra foveal retina function, colors are not perceived and the various colors appear as shades of grey. Cones function in bright light and the system has more acuity and can perceive colors (PHOTOPIC VISION).

Photochemical basis of retinal function is a basis of conversion of
light energy into nerve impulses. It is this process that excites the nerve fibres
and sets up nerve impulses.

The impulses generated in the receptor neurons in response to
generator potentials in the cones are interpreted by the brain as the
appropriate intermediate colour. The interpretation or perception of colour
pictures seen by our eyes is a complex function of the brain. It is located in
the occipital lobe of the cerebral cortex. (Retinal visual Pigments)

The visual pathway – Retinal visual Pigments

The axons of ganglion cells pass through the eyeball at the posterior
end and form the optic nerve which enters the cranial cavity. Therefore this
region of the retina lacks receptors and is unable to perceive images which
fall on it. This region is called optic disc and when charting the field of vision
it is referred to as the blind spot. (Retinal visual Pigments)

Receptor Organs – Eye

Receptor Organs

The survival of animals depends on their ability to compute all the
information flowing from the environment and integrate them into meaningful
instructions to the effector organs. Information relating to the external and
internal environment can be gained only through the sensory receptor
organs.

These organs have specialized cells that can transform the stimuli
falling on them, whether it is chemical, radiant, electrical or mechanical, into
electrical signals and convey the same to the central nervous system. In the
CNS the integration and coordination of the data happens.

This ability of the sensory cells is known as transduction and the receptors are sometimes referred to as transducers. (Receptor Organs)

Eye – Receptor Organs

The visual system gives information about size, shape, color,
luminosity and movements of object in the external world. (a) Focusing Mechanism in the Human Eye Light rays entering the eye are redirected or refracted. Refraction occurs through three surface of the eye before the light reaches the retina.

The first of the refracting surfaces is the cornea, then the front surface of the
lens and finally the rear surface of the lens. Between the cornea and the lens is a colourless, watery fluid called aqueous humour. At the back of the eye between the lens and the retina is the vitreous humour made of a gelatinus mucoprotein.

The humours are transparent so that transmissions of light through the cavities of the eye to the retina is not normally impeded. Human eye has a lens apparatus whose convexity can be adjusted for focusing near and distant objects. This ability of the eyes to focus objects at varying distances is called ACCOMMODATION. (Receptor Organs)

The accommodation is achieved due to suspensory ligament, ciliary muscle and ciliary body. When a normal eye is looking at a distant object, the ciliary muscles is fully relaxed and parallel rays from the object come to focus on the retina.

Hence a clear image is seen. When the object is brought close to the eye the
refractive power of the eye is increased by the process of accommodation.
The increase in refractive power is the result of an increase in the curvature
of the anterior surface of the lens. This avoids the blurred image for a closer
object. (Receptor Organs)

Similar accommodation happens for viewing a distant object by stretching the suspensory ligament attached to the lens. This act alters the contour of the lens.

Gonads

Both testes and ovaries, in addition to their role as reproductive
gamete producing organs, function as endocrine structures also.

Testis

The testis in males, in addition to the germinal epithelial cells,
contains groups of epithelioid cells called the interstitial or leydig cells. These
cells constitute the endocrine tissue of the testis. The leydig cells secrete the androgenic hormone testosterone. The androgens are C19 steroids. In the
normal post pubertal males, the rate of secretion of testosterone ranges from
4-9 mg per day. (Gonads)

Action of testosterone

1. Testosterone causes embryonic development of male reproductive
organs,
2. It promotes the development of the secondary sexual characters of males,
including physical development, hair distribution, masculine voice and male
behaviour at puberty. (Gonads)

Ovary

The ovaries are paired, oblong in shape and situated in the pelvic
portion of the abdominal cavity. It releases hormones such as oestrogen
and progesterone. (Gonads)

1. Oestrogen

Under the influence of the FSH from the adenohypophysis, the ovum
grows and becomes enclosed in the Graffian follicle. Associated cells of the
follicle produce a steroid hormone called estrogen. The oestrogens are C18
steroid compounds. It is responsible for the growth of female reproductive
organs and for the appearance of secondary sexual characters.

2. Progesterone

After the discharge of the ovum from the Graafian follicle and after
fertilisation, the ruptured follicle cells form a new structure called corpus
luteum. It produces the pregnancy hormone progesterone. Progesterone is
also synthesized and secreted by the placenta during the later part of
gestation. This hormone is a C-21 steroid compound.
Progesterone is responsible for the premenstrual growth in the
non-pregnant woman’s uterus. The development of the placenta during
pregnancy and the embedding of the fertilized ovum in the uterus
(implantation). (Gonads)

3. Relaxin

The corpus luteum of the pregnant woman secretes another hormone,
relaxin in addition to progesterone. Relaxin helps in relaxing the muscles and
ligaments of pelvic organs during childbirth (parturition). (Gonads)

Adrenal gland

The adrenal gland or supra renal gland is composed of an outer
cortex and an inner medulla. The adrenal cortex forms the major portion of
the total mass of tissue of adrenal gland. In adults three concentric zones are
discernible within the cortex. 1. A thin outer most layer, the Zona
glomerulosa, 2. A thick middle region, Zona fasciculata and 3. A
relatively thick inner layer, the Zona reticularis.

In man, the cells of zona fasciculata and zona reticularis act as a single unit, the main function of which is to form glucocorticoids and to a lesser extent androgens and possibly oestrogens. The mineralocorticoid hormone, aldosterone is secreted by the cells of the zona glomerulosa. The enzymes necessary for its synthesis reside in the cells of the zona glomerulosa. All the adreno corticoid hormones are
steroids. (adrenal gland)

Action of glucocorticoids

The major glucocorticoids are cortisone and certain closely related
steroids. These hormones stimulate the production of glucose from
non-carbohydrate sources such as fats and amino acids. Glucocorticoids
also decrease glucose utilization by tissues in general. All these effects lead
to increased blood glucose level. Cortisone also acts as an anti-inflammatory
agent. (adrenal gland)

Action of mineralocorticoids

The major effect is on the metabolism of sodium ions and indirectly
potassium ions. The major mineralocorticoid hormone is Aldosterone. Its
most important effect is to promote the resorption of sodium ions from the
renal glomerular filtrate. Secondary effects of sodium retention are an
increased chloride retention and a decreased potassium retention by the
kidneys. The most important function of the adrenal cortex is its role in stress
tolerance. (adrenal gland)

Adrenal medulla

The medulla of adrenal gland differs both in morphology and
physiology from the cortex portion. Both cortex and medulla are derived
independently and from totally different tissues in the embryo. The adrenal
medulla in the adult humans and other mammals is invested closely by the
cortical tissue.

The cells of the adrenal medulla are large ovoid and columnar
in type and are grouped into clumps around the blood vessels. The
hormones produced by adrenal medulla are 1. Adrenalin or epinephrine
and 2. Nor adrenalin or nor epinephrine. The two hormones belong to a
group called catecholamines. The various physiological and biochemical
actions of adrenalin or epinephrine are the following: (adrenal gland)

1. Adrenalin stimulates constriction of blood vessels supplying the intestine,
kidneys, viscera and skin and causes dilation of blood vessels supplying
skeletal and heart muscle.

2. It increases the rate, amplitude and frequency of the heart beat.
3. It causes relaxation of the smooth muscles of the digestive tract and brings
peristalsis to a halt
4. It causes relaxation of the bronchi, dilation of the pupil, closure of
sphincters and increases sweating
5. It causes contraction of muscles associated with hair follicles and makes
the hair “stand on end” and causes goose flesh
6. It accelerates respiration and stimulates mental alertness
7. It stimulates the breakdown of glycogen to glucose, thereby increasing
oxygen consumption and heat production.
8. Biochemically it releases the free fatty acids and increases blood glucose
level.
9. Adrenalin prepares an individual during emergency or stress situations.
Hence it is called the fight, flight and fright hormone.

Action of Nor adrenalin or Nor epinephrine

Nor adrenalin has certain effects similar to that of adrenalin. For
example, both the hormones dilate the coronary vessels. However, nor
epinephrine cause vaso constriction in most organs other than heart.

It increases both the systolic and diastolic blood pressures. It exerts a weakly
inhibitory action upon the contractile activity of smooth muscle in the gastro
intestinal tract. However, it does not relax the smooth musculature of the
pulmonary bronchioles. Nor epinephrine exerts very little effect upon
carbohydrate metabolism and oxygen consumption. (adrenal gland)

Pancreas

The endocrine part of the pancreas consists of specialized groups of
cells known as Islets of Langerhans. These cells synthesize, store and
secrete two hormones namely insulin and glucagon. There are two kinds of
cells namely, alpha and beta cells. The alpha cells produce glucagon while the beta cells secrete insulin. In addition to alpha and beta cells another type
of cells called delta cells are present in human pancreas. According to some
investigators the delta cells represent the transitional forms of the two cell
types alpha and beta.

Insulin (Pancreas)

Insulin is a protein hormone or a polypeptide hormone with 51 amino
acid residues. Human insulin has a molecular weight of 5,734 daltons. It
consists of two chains A and B, which are linked together by disulphide bridges
formed between two cystine residues.

Physiological effects of Insulin

It decreases glucose level in the blood in three ways:
a. It increases conversion of glucose into glycogen and deposition of it in
liver and muscles.
b. It increases the rate of oxidation of glucose in the tissues.
c. It increases the rate of conversion of glucose into fat and facilitates its
storage in adipose tissue.
d. It also regulates the rate at which amino acids are catabolised into water
and CO2.
e. Moderately, it also regulates the gluconeogenesis in the liver.

Thus, insulin reduces the glucose level in the blood (Hypoglycemia).
If the insulin is not secreted sufficiently, the liver and the muscles are unable
to convert the glucose into glycogen. As a result more glucose enters into the
bloodstream raising the blood sugar level. This condition is called
Hyperglycemia. The excess of glucose is eliminated along with the urine
resulting in a disease called diabetes mellitus. A diabetic patient excretes
large amount of urine (polyurea) and consumes excessive fluid
(polydipsia). He always feels hungry and eats excessively (polyphagia).
When insulin levels are low, fat catabolism is increased and fats are
converted into glucose. This further increases blood glucose levels and
results in the accumulation of ketone bodies (Ketosis). (Pancreas)

Hyperglycemia

The normal fasting blood glucose level is 70 to 110 mg/dl
(dl = deciliter). This range is maintained under varying conditions of food
intake, fasting or body exercise. After a carbohydrate meal the blood sugar
may reach a peak level of about 140mg/dl. If such a high level is maintained
for a prolonged time, the condition may be termed as hyperglycemia.
Hyperglycemia over a long period may cause degenerative changes in several
organs and systems leading to malfunctions and mortality. Elevated blood
sugar level of 400 mg/dl or more, in a few days causes dehydration leading
to coma and death. (Pancreas)

Hypoglycemia

It means a low plasma glucose concentration. This concentration can
drop to very low values during fasting. It is termed as fasting hypoglycemia.
It may result due to excess of insulin or other physiological factors. There is
no fixed level of blood sugar at which hypoglycemia occurs.
Fasting hypoglycemia may show symptoms such as hunger, increased
heart rate, tremulousness, weakness, nervousness and sweating. These are
caused due to activities of the sympathetic nervous system. Other symptoms
such as headache, confusion, uncoordination and slurred speech are due to
availability of too little glucans to the brain. Serious brain defects such as
convulsions (epilepsy) and coma can occur if the plasma glucose
concentration goes low. (Pancreas)

Diabetes Mellitus

The name ‘diabetes’ in Greek means ‘syphon’ or ‘running through’.
This term describes the enormity of urinary volume excreted by people suffering
from this disease. A persistant hyperglycemia leads to
diabetes mellitus. This disease can be due to a deficiency of insulin or to a
hypo responsiveness to insulin.
In type I (insulin dependent) diabetes, the hormone is completely
or almost completely absent from the islets of Langerhans and the plasma. In
type II (insulin-independent) diabetes, the hormone is often present in plasma
at near normal or even above normal levels. (Pancreas)

The type I is less common. It is due to the total or near total destruction
of the pancreatic b cells.

The type II is due to insulin resistance. The insulin target cells do not
respond normally to the circulating insulin. This may result due to obesity,
over-eating and lack of exercise. The insulin hyporesponsiveness can be
corrected if the person reduces his or her caloric intake. Thus dietary control
without any other therapy is frequently sufficient to eliminate the elevated
blood glucose level of type II diabetics. An exercise programme is also
useful, since it will help to increase the number of insulin receptors.

Glucagon

Glucagon, secreted by the alpha cells of the pancreas is a polypeptide
hormone with 29 amino acids residues.

Physiological actions of glucagon

The major function of glucagon in the body is to elevate the blood
glucose level by glycogenolysis in the liver. As it raises the blood sugar level
it is also called as Hyperglycemic hormone. A second important function of
glucagon is the gluconeogenesis in the liver in which amino acids are used as
substrates. It promotes lipolysis and the release of fatty acids in the adipose
tissues. The increased fatty acid oxidation leads to ketogenesis. Glucagon
also stimulates the myocardial contractility. Glucagon exerts a direct effect
upon the kidneys and accelerates the renal plasma flow and glomerular
filtration rate. A proper balance between insulin and glucagon production is
necessary to maintain proper blood glucose level. (Pancreas)

Parathyroid gland

In man the parathyroid gland are small oval yellow-brown bodies
found attached to the posterior surface of the thyroid gland. The parathyroid
gland secrete two hormones namely, 1. Parathormone and 2. Calcitonin.

Parathormone

Purified parathormone is a simple polypeptide chain. It has short
duration of biological activity. The half-life of the hormone is of about 20-30
minutes only.

Physiological effects of Parathormone

Parathormone manifests its regulatory effects at three different loci in
the body namely the skeleton, kidneys and the gastro intestinal tract. In
skeleton, the hormone directly acts upon the bone tissue to stimulate the
activity of osteoclast cells (bone destroying cells). Under the influence of this
hormone calcium is released from the bone matrix into the circulation. As a
result plasma calcium level increases. Thus it helps in the skeletal
remodelling. (parathyroid gland)

In kidney, parathormone induces a marked increase in phosphate
excretion. In the gastro intestinal tract, parathormone stimulates the
absorption of calcium and phosphate from the gut by enhancing the
vitamin D synthesis. As a result, more phosphate and calcium are
transported into the blood stream. Its other physiological effects include its
inhibitory action over the osteoblasts or bone forming cells, bicarbonate
reabsorption and reduction of urine pH, etc.

Calcitonin

It is a calcium-lowering hormone secreted by the parafollicular cells
of the parathyroid gland. It is a protein. Its physiological effects are antagonistic
to that of parathormone. It inhibits bone resorption. In kidney, it inhibits the
reabsorption of calcium, phosphorus, sodium, potassium, magnesium and
other ions. It decreases gastric HCl secretion. It also decreases the insulin
and glucagon secretion. (parathyroid gland)

Hyperparathyroidism

It is a condition where there is an increased amount of parathyroid
hormone in circulation. Excess secretion of parathormone brings about
demineralization of the bones.

The protein matrix of the bone is also absorbed. These changes result in bone cyst and the elevation of the calcium level in the blood. The latter causes calcification of kidneys, arteries, stomach and lungs. (parathyroid gland)

Hypoparathyroidism

Removal of parathyroids causes the blood calcium levels to fall and
results in tetany. Tetany is characterized by low serum calcium
(Hypocalcemea), reduced urinary excretion of calcium and phosphate,
neuromuscular hyperexcitability, spasms of muscles and cramps etc. (parathyroid gland)

Thyroid gland

Thyroid gland and thyroxine

Thyroid gland consists of a pair of lobes, which lie one on either side
of larynx in the neck region. The paired lobes are joined by a narrow anterior
bridge of glandular tissue called Isthmus of the thyroid. The lobes of
thyroid in turn are divided into many lobules. The lobules consist of follicles.
The follicles are called acini (acinus – singular). Each acinus is lined with
glandular cubical epithelial cells. The cavity of acinus is filled with a
gelatinous material called colloid, which contains the thyroxine. The hormone
thyroxine is an iodinated hormone. It contains 65% iodine. The amino acid
residue in thyroxine is tyrosine.

Functions of thyroid (Thyroid gland)

Thyroxine stimulates normal growth and development, especially the
skeletal and nervous systems. It controls the rate of cellular oxidation and
increases the basal metabolic rate. The basal metabolic rate (BMR) is
defined as the amount of heat produced in the body in a given time, in
complete state of physical and mental rest at 20oC room temperature.

Actions of thyroxine (Thyroid gland)

(i) This hormone is very essential for the development of nervous
system particularly at the time of birth and during the first year, (ii) This
hormone increases the metabolism of all tissues except brain, gonads and
accessory sex organs, lymph nodes, spleen and lungs, (iii) The most
important function is to increase the absorption of glucose from the small
intestine. (iv) This hormone reduces serum cholesterol level, (v) It promotes
protein anabolism, and helps in growth, (vi) It increases heart beat rate, force
of contraction and pulse pressure, (vii) Presence of optimum level of
thyroxine in the blood maintains efficient muscle functions and (viii) The
optimum level of thyroxine in the blood is also necessary for normal gonadal
function.

Hypothyroidism (Thyroid gland)

The physiological effect due to deficiency of thyroid hormone is
referred to as hypothyroidism. It is manifested by iodine deficiency and simple
goiter, cretinism and myxoedema. If the dietary intake of iodine becomes
inadequate (below 10 micro grams per day) the synthesis of thyroxine is
impaired. As a result, the thyroxine level falls in circulation and secretion of
TSH increases, causing the hypertrophy of thyroid gland as a consequence.
The thyroid enlarges to enormous proportions. This is called simple goiter.
This condition is also called endemic goiter. It is caused due to lack of iodine
in the soils of different regions of the world.

Cretinism (Thyroid gland)

Cretinism is found in children who are deficient of thyroxine hormone
from the time of birth. The characteristics of cretinism are, retardation of
mental growth to extreme degree, dwarf stature, protruding tongue and abdomen, low basal metabolic rate, subnormal body temperature,
retardation in skeletal growth and arrest of pubertal sexual maturity etc.

Myxoedema (Thyroid gland)

Myxoedema in adults, is a syndrome with the following
characteristics viz., low BMR, dry, coarse, scaly skin, puffy and bloated
face, coarse and sparse hair, hoarse voice, slow speech, slow thought
processes, poor memory, etc. Other symptoms are muscular weakness and
fatigue, low blood pressure, anaemia with increased serum cholesterol, etc.

Hyperthyroidism or thyrotoxicosis (Grave’s disease or exophthalmic goiter) (Thyroid gland)

The hyper function of thyroid gland results in Grave’s disease. Grave’s
disease is characterized by increased BMR with increased pulmonary
ventilation, protrusion of eye balls from the sockets (exophthalmas), increased
heart beat rate, nervousness, emotional instability, weight loss, increased blood
glucose and decreased serum cholesterol, derangement of sexual function
etc.

Hormones of Neurohypophysis – vasopressin

Post author By Mr. Padeepz
Post date September 24, 2018
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Hormones of Neurohypophysis

The neurohypophysis or the posterior pituitary secretes oxytocin and
vasopressin. Oxytocin contains a sequence of amino acid residues. The term
oxytocin refers to rapid birth. This hormone directly stimulates the smooth
muscles of uterus and causes the contraction, and helps in the delivery of
foetus. Another major physiological role of oxytocin is the secretion of milk
from the lactating breast. Oxytocin stimulates the myoepithelial cells, which

surround the alveoli and ducts of mammary gland. The contraction of
myoepithelial elements in turn expels the milk from the alveoli of the breast
into the larger ducts or sinuses. From the sinuses, the milk is ejected out.

The vasopressin

It is otherwise called as the antidiuretic hormone(ADH). Its main
function is the retention of water inside the body by acting on the renal
tubules. ADH increases the permeability of the distal tubules and collecting
ducts and promotes the reabsorption of water from the renal filtrate. It causes
the constriction of all blood vessels and increases the blood pressure. It also
helps in the retention of urea. ADH deficiency leads to Diabetes insipidus.
The symptoms of Diabetes insipidus are excretion of large volumes of dilute
urine (polyurea), combined with an intense thirst leading to the consumption
of large quantities of liquids (polydipsia).

Pituitary gland hormone

Pituitary gland

The Pituitary gland is otherwise called the hypophysis. It is located at
the base of the brain. It is approximately 1 cm long, 1-1.5 cm wide and 0.5 cm thick. It weighs about 500 mg. Anatomically the pituitary gland is divisible
into anterior adenohypophysis and posterior neurohypophysis.

The adenohypophysis consists of three lobes or zones namely, Pars intermedia,
Pars distalis and Pars tuberalis. The anterior lobe or adenohypophysis is
embryologically derived from the roof of the mouth as a dorsal pouch. The
neurohypophysis on the other hand, originates from the floor of
diencephalon, as a downward growth.

The hormones of anterior pituitary

The adenohypophysis is responsible for the secretion of six trophic
hormones or tropins. They are growth hormone or somatotropic
hormone (GH/STH), thyrotropic hormone or thyroid stimulating
hormone (TSH), Adrenocortico tropic hormone (ACTH), Follicle
Stimulating Hormone (FSH), Leutinizing hormone (LH) and Prolactin
or Leuteotropic hormone (LTH). (Pituitary gland)

Metabolic functions of the growth hormone

Growth hormone is responsible for various general metabolic
functions. It affects the diverse spectrum of integrated metabolic reactions,
which participate in the overall process of growth. Growth hormone
influences carbohydrate, protein and lipid metabolism.

Growth hormone stimulates both the formation of cartilage (Chondrogenesis) as well as bone (Osteogenesis). It causes the retention of minerals such as nitrogen,
potassium, phosphorus, sodium, etc useful for growth.

Deficiency of growth hormone or hyposecretion in children results in
retarded growth. The premature arrest of skeletal development causes
dwarfism. The adult dwarfs will grow to a height of only 0.9 to 1.2 meter.

They never attain puberty or do not develop secondary sexual characters.
Excessive secretion of GH results in over growth of the skeletal
structures and the person may reach a height of 7 to 9 feet
(gigantism).

The excessive GH in adults also results in the increase in thickness of lower jaw and disproportionate over growth of bones of the face, hands and feet. The above condition is known as acromegaly. (Pituitary gland)

Thyrotrophic hormone or thyroid stimulating hormone (TSH)

TSH is a glycoprotein with a molecular weight of 28,000 daltons. It
is made up of 211 amino acids. The specific target organ for the TSH is the
thyroid gland. It stimulates the thyroid to secrete the thyroxine.

There exists a negative feedback mechanism between the circulating level of thyroxine and the hypothalamic releasing factor. When the thyroxione is less in blood, the hypothalamus produces more TSH releasing factor which on reaching
the pituitary stimulates secretion of TSH. TSH on reaching the thyroid,
stimulates the thyroid to secrete more hormone.

Conversely, when there is excess thyroxine in the blood, the production of thyroxine is controlled by non-secretion of releasing factor from the hypothalamus. (Pituitary gland)

Adreno cortico trophic hormone (ACTH)

It is a protein hormone. ACTH also functions by the negative feed
back mechanism and stimulates the adrenal cortex and its secretion. Its other functions include the stimulation of formation of melanin pigments in the
melanocytes of the skin, stimulation of insulin secretion and mobilization of
fats from adipose tissue.

Follicle stimulating hormone (FSH)

It is a gonadotropic hormone that directly stimulates the gonadal functions
in both males and females. The human FSH is a small glyco
protein.

The target organs for FSH in the females are the ovaries. It
promotes the growth of graffian follicles and thereby increases the total weight
of the ovary. It also promotes the secretion of oestrogen.

In males, the target organs for FSH are the testes. It directly stimulates the germinal epithelium of the seminiferous tubules and augment the rate of spermatogenesis. (Pituitary gland)

Leutinizing hormone or Interstitial cells stimulating hormone (LH or
ICSH)

Human ICSH or LH is a glycoprotein. In females, the LH stimulates
the ripening of ovarian follicles and induces ovulation. In males, the LH or
ICSH, specifically affects the leydig cells or interstitial cells of the testes and
stimulates the synthesis and secretion of the male hormone (Androgen)
testosterone.

Prolactin or Luteotropic hormone (LTH)

Prolactin is called by several names such as luteotropin, luteotrophic
hormone, lactogenic hormone, mammotropin etc. It is a protein hormone. Its
main function is stimulation of milk formation or initiation of lactation
following parturition in mammals.

It also stimulates the corpus luteum to secrete the progesterone. Prolactin together with estrogen stimulates the growth of mammary glands and makes it ready for milk secretion. (Pituitary gland)

Errors of refraction

Myopia (Short Sightedness)

Hypermetropia (Long Sightedness)

Astigmatism

Presbiopia

Related Topics in Zoology:

Photochemistry of Retinal visual Pigments

The visual pathway – Retinal visual Pigments

Related Topics in Zoology:

Receptor Organs

Eye – Receptor Organs

Related Topics in Zoology:

Gonads

Testis

Action of testosterone

Ovary

1. Oestrogen

2. Progesterone

3. Relaxin

Related Topics in Zoology:

Adrenal gland

Action of glucocorticoids

Action of mineralocorticoids

Adrenal medulla

Action of Nor adrenalin or Nor epinephrine

Related Topics in Zoology:

Pancreas

Insulin (Pancreas)

Physiological effects of Insulin

Hyperglycemia

Hypoglycemia

Diabetes Mellitus

Glucagon

Physiological actions of glucagon

Related Topics in Zoology:

Parathyroid gland

Parathormone

Physiological effects of Parathormone

Calcitonin

Hyperparathyroidism

Hypoparathyroidism

Related Topics in Zoology:

Thyroid gland and thyroxine

Functions of thyroid (Thyroid gland)

Actions of thyroxine (Thyroid gland)

Hypothyroidism (Thyroid gland)

Cretinism (Thyroid gland)

Myxoedema (Thyroid gland)

Hyperthyroidism or thyrotoxicosis (Grave’s disease or exophthalmic goiter) (Thyroid gland)

Related Topics in Zoology:

Hormones of Neurohypophysis

The vasopressin

Related Topics in Zoology:

Pituitary gland

The hormones of anterior pituitary

Metabolic functions of the growth hormone

Thyrotrophic hormone or thyroid stimulating hormone (TSH)

Adreno cortico trophic hormone (ACTH)

Follicle stimulating hormone (FSH)

Leutinizing hormone or Interstitial cells stimulating hormone (LH or ICSH)

Prolactin or Luteotropic hormone (LTH)

Related Topics in Zoology:

Leutinizing hormone or Interstitial cells stimulating hormone (LH or
ICSH)