Hormonal coordination

All animals are made up of chemical components formed by exocrine or endocrine glands. Exocrine glands discharge their chemicals into ducts. The endocrine glands discharge their secretions, the hormones, openly into the blood-stream.

These hormones are afterward carried to other parts of the body known as target organs, where in very minute quantities, they bring out cellular responses.
Hormones are specifically-acting organic compounds with changeable chemical compositions, frequently steroids, proteins, peptides or amino acids. Based on their common roles, hormones are metabolic.
They either stimulate or retard metabolic activities. They are trophic-they regulate rate and secretion of other endocrine glands and morphogenetic –they influence rate and development of assorted parts.
Hormones are an additional means of coordination and communication. Together with the nervous system, the endocrine system forms a combined neuro-endocrine system. The hormone pathway is by the blood stream, while nervous pathway is by the neuron-reflex arc.

Glands are classified into two:

•Exocrine glands
•Endocrine glands
The diagram of Exocrine and Endocrine Gland Showing Release of Secretion
Exocrine glands are those glands which pour their secretions into a duct. For instance, sweat glands, tear glands, and so on.
Endocrine glands are those glands which are abundantly filled with blood vessels and discharge their secretions directly into the blood vessels. The secretions get to their target through blood. These glands are known as the ductless glands as they do not possess ducts. Examples of ductless glands are: thyroid, adrenal, etc.
The control and coordination of the various bodily functions is as well done with the assistance of the endocrine system. The endocrine system exerts chemical power over the activities. These chemicals are secreted from organs known as endocrine glands.
The secretions of the endocrine glands are known as hormones. Hormones possess the following characteristics:
•they may be proteinaceous or non-proteinaceous -amino acids or steroids
•they are secreted as per requirement and not stored, only excreted
•their secretion may be controlled by nerves or by feedback effect
•they are transported through the blood
•they mainly give rise to long-term effects like growth, alteration in behaviour, etc.
•they do not catalyze or speed up any reactions
•they function by motivating or inhibiting the target organs.
Hormones can be defined as secretions that are discharged into blood in order to get to a particular target organ.

The human endocrine system is composed of the following glands:

•Ovary in female
•Testes in male

Position of Various Endocrine glands in the Human Body

Pituitary Gland

The pituitary gland also known as hypophysis is about the size of a large pea, situated beneath the brain, at the back the nasal cavity on the floor of the cranium. It is affixed by a stalk to the hypothalamus part of the brain on the undersurface of the cerebrum.
It is positioned in the sphenoid bone of the skull and is strictly invested by a connective tissue capsule.

The location of Pituitary gland

The pituitary gland is referred to as the master endocrine gland due to its control over quite a few other endocrine glands.
Nevertheless, the body’s actual master gland is the hypothalamus of the brain which takes charge of the secretions of the anterior pituitary by discharging and inhibiting hormones. Also, the pituitary itself is as well regulated by feedback from other glands.
The anterior lobe of the pituitary gland manufactures six dissimilar hormones. Among them, two function directly on body tissue (somatotrophic) and the other four controls the action of other endocrine organs.
The middle lobe known as pars intermedia discharges only one hormone known as intermedin. This hormone is in charge of the control of skin colors in lower vertebrates, but is vestigial in mammals, and has no function in humans.
The posterior lobe purpose is for storage and discharge point for two hormones secreted by the hypothalamus-neurosecretory cells and carried to the lobe via a linking duct referred to as the neurohypophysis).

The hormones of the Pituitary gland

The anterior lobe of the pituitary gland secretes six hormones. They are:
1. Thyroid stimulating hormone (TSH) or thyrotropin:
This hormone stimulates the secretion of thyroxin from the thyroid glands.
2. Somototropic or growth hormone:
This hormone controls growth of tissue, bone, muscles and internal organs, and as well influences metabolic processes. Hyper secretion in early on of life gives rise to a condition known as gigantism, and after the growth period in adult life it leads to acromegaly.
In acromegaly, excess secretion becomes visible after long bones have become hardened and the growth continues alone in certain bones, leading to lengthening of forelimbs, hindlimbs, and enlarged jaw and face.
Hypo secretion during growth years leads to pituitary infantilism, a kind of dwarfism, in which an adult is not above three or four feet tall, and is typically sexually immature.
3. Follicle stimulating hormone (FSH):
The follicle stimulating hormone excites the ovaries and testes. In females, it controls the development of grafian follicles or ova. In males, FSH influences spermatogenesis. That is the production of sperm by the seminiferous tubules of the testes.
4. Adrenocorticotropic hormone (ACTH):
This hormone motivates the adrenal cortex and controls the secretion from the adrenal glands.
5. Luteinizing hormone (LH) along with FSH:
This hormone in addition to FSH is responsible for the growth of ovarian follicles, release of mature ova or egg, development of the corpus luteum, production of progesterone and regulation of menstrual cycle in females. In males, LH stirs the testes to secrete testosterone or ICSH- interestitial cell stimulating hormone.
6. Prolactin kicks off the secretion of milk by the mammary glands after the birth of a baby. In the nonexistence of prolactin, milk secretion is put to a stop.

Relationship between the pituitary and other endocrine glands

(———In charge of feed back or inhibition)
(———Pituitary Hormones that stimulate other glands)
The intermediate lobe of the pituitary gland:
The intermediate lobe secretes only one hormone, Melanophore Stimulating Hormone (MSH), or intermedin, which regulates the pigmentation of the skin in varieties of vertebrates. It darkens the color of the skin. Nevertheless it is of no significant purpose in humans.

The posterior lobe of the pituitary gland

The posterior lobe secretes the following hormones:
1. Oxytocin: This hormone is responsible for the contraction of the uterus in females during childbirth and also controls lactation or the release of milk.
2. Antidiuretic hormone (ADH) or Vasopressin: This hormone stimulates the kidneys to reabsorb more water, preventing too much water loss by urination. Chronic deficiency of ADH causes diabetes insipidus (polyuria), in which the patient feels extremely thirsty and passes a large amount of dilute urine.

The Thyroid Gland

Position and Structure of thyroid gland:
All vertebrates have a pair of thyroid glands, situated in the neck just beneath the larynx or Adams apple. In human being, the thyroid gland is made up of two lobes-H-shaped that is positioned on either side of the trachea.
The two lobes are linked by a narrow isthmus that passes in front of the trachea. The gland differs in size with the variation in sexual development, diet and age.

The histology of the thyroid gland:

The thyroid gland is made up of a large number of round or oval follicles enclosed by connective tissue with a large number of blood vessels. Every one of the follicle is lined by one-cell thickcuboidal epithelial cells.
The cavities of the follicles are packed with viscous protein material known as colloid. The thyroid hormone, thyroxine contains iodine atoms. It is not stored in the cells of the thyroid, but in the colloid enriching the follicles.
The function of thyroid cells is to pull iodine out of the blood. This is then integrated into the protein thyroglobulin, which is subsequently hydrolyzed into the energetic hormone thyroxine.

The hormones of the Thyroid Hormones

Thyroid glands manufacture a hormone known as thyroxine. The secretion of thyroxin is restricted by TSH which is manufactured in the the pituitary. The hypo secretion or under secretion of thyroxine in a child leads to a condition known as cretinism.
This condition exhibits itself by retarded growth and development (dwarfism), a overhanging abdomen, mental retardation, puffy skin and stumpy metabolic rate.
In adults hypo function results in myxedema; the symptoms are a low metabolic rate, reduction in mental and physical activity, and increase in weight, puffy skin, a decrease in heart beat and body temperature, and loss of hair.
When hypofunction or under secretion leads to a deficiency of iodine in diet, swelling of the thyroid which leads to a condition known as simple goiter.
In a bid to grab more iodine from the blood, the gland enlarges follicles and grows excessively. Hypofunction can be cured with a supply of iodized salt, sea food, and by surgery foods with the aim of getting rid of excess thyroid tissue.
In amphibians, thyroxine plays a vital role during metamorphosis. If thyroid function of an embryo or young tadpole is repressed for instance by removing the thyroid gland, then the animal remains a tadpole permanently.
On the contrary, if a young tadpole is offered an excess of thyroxin, the larva metamorphoses ahead of time into a miniature froglet.
Hyperfunction leads to a boost on the rate of metabolism of about 40%, abundant sweating, augmented food intake but loss of weight, high blood pressure, nervous tension and muscular weakness.
Some patients with hyperthyroidism possess protruding eyeballs, a condition known as exophthalmos. The swelling of thyroid gland as a result of hypersecretion gives rise to exophthalmic goiter.
Another hormone manufactured by the thyroid gland is calcitonin. It regulates the level of blood calcium. Calcitonin is discharged by the thyroid when there is an elevated level of calcium in the blood. The surplus Calcium is next reduced and dropped in bones.
To summarize all we have discussed:
•The chemicals controlling the majority systems of vertebrates are made up of secretory cells, which are structured into exocrine and endocrine glands. Endocrine glands function is to secrete hormone into the blood. A hormone is a biological molecule (chemical transmitter) which works on target organs and elicits a lot of cellular activities.
•The key endocrine organs are the hypothalamus, pituitary gland, thyroid gland, parathyroids, adrenal glands, islets of Langerhans, testis and ovary.
•The pituitary gland is referred to as the master endocrine gland. It is positioned beneath the brain, and posseses three divisions-the anterior lobe, middle lobe and posterior lobe.
•The anterior lobe secretes six hormones-the TSH, somatotrophic hormone, FSH, ACTH, LH and prolactin, whereas the posterior lobe secretes oxytocin and antidiuretic hormone (ADH). Middle lobe has no function in humans.
•The malfunctions of the pituitary cause various conditions like gigantism, acromegaly, pituitary infantilism, and diabetes insipidus and so on
•The thyroid gland is situated in the neck and is made up of thyroid follicles which contain colloid.
•The Thyroid gland secretes the hormone thyroxin; hypofunctin Hyperthyroidism leads to exophthalmos and exophthalmic goiter.
•The hormone calcitonin regulates the blood calcium level.
•The majority of biological or chemical control systems function on feed back

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