Hormones in Animals, Biology tutorial


The hormones are organic compounds generated in minute quantities by cells of one portion of the body and transported to all and certain other parts of the body by the blood system of animals to generate a response. Such response results in the promotion of fine body growth, sexual adulthood, response to fight, fear of flight. When a hormone is under growth or overproduced, serious consequences can occur.

The Glandular Systems:

The body consists of two kinds of glandular systems: the Endocrine that generally secretes hormones via the bloodstream, and the Exocrine that secrete fluids to the external surfaces of the body, like sweating.

Endocrine glands:

The Endocrine System unites neural and glandular methods that control physiological functions or behavior through the secretion of hormones. Hormones are the chemical signaling molecules that play an essential role throughout growth (that is, organizational effects) and everyday functioning (that is, activation effects) of target tissues at vital times. The Secretory cells of a specific kind are frequently clumped altogether into a well defined gland (example: pituitary, adrenal, thyroid, testes and ovaries). Secreted at that site they allocate all through the body through the blood stream and cause physiological modifications at any other sites.

In the human body, the Endocrine glands comprise:

1) The pituitary gland: It is situated just beneath the hypothalamus, at the base of the brain.

2) The thyroid and parathyroid glands: Found in the neck, beneath the larynx.

3) Adrenal glands: These are located over the kidneys.

4) Pancreas: This is found beneath and at the back of the stomach.

5) Gonads: These are the ovaries found in pelvis, of the female reproductive organ and the testes situated in the scrotum of the male organ.

Important Hormones and their functions:

Hormones are basically organic (chemical) compounds secreted through endocrine glands in response to the internal and external stimuli. Hormones are transported in the blood streams to target organs. They thus act as chemical messengers. In target organs, they (i) speed up (motivate) the rate of reaction, (ii) slow down (restrain) the reactions or (iii) Change the activities.

You can then describe a hormone as a chemical messenger which is generated in one portion of an organism transported to the other portion where it brings around a particular effect on the target organ(s). Hormones are generated through endocrine glands. They as well are included in the homeostatic methods.

The Hypothalamus gland:

The hypothalamus is located at the base of the forebrain, over the pituitary gland. However it is not illustrated as a gland, it regulates some activities in the body like thirst, temperature, heart beat rate, ventilation rate, blood pressure, peristalsis, hunger and sleep. The hypothalamus is joined to and controls, the pituitary gland. This association is significant as it is the main link among the nervous system and the endocrine system and its hormones.

The hypothalamuses pass information to the pituitary gland which then regulates the activity directly or indirectly to the other glands.

The Pituitary gland:

The pituitary gland, situated at the base of the brain just below the hypothalamus, is considered the most significant portion of the endocrine system. It is often termed as the 'master gland' as it makes hormones which control some other endocrine glands. The secretion and production of pituitary hormones can be affected by factors like emotions and seasonal transforms. To achieve this, the hypothalamus transmits information sensed by the brain (like ecological temperature, light exposure patterns and feelings) to the pituitary.

The small pituitary is classified into two parts: the anterior lobe Adenohypophysis and the posterior lobe Neurohypophysis.

The pituitary as well secretes endorphins, chemicals which act on the nervous system to decrease the sensitivity to pain. Moreover, the pituitary secretes hormones which signal the ovaries and testes. The pituitary gland as well controls ovulation and the menstrual cycle in females.

Thyroid gland:

The gland is positioned in the neck. It secretes the hormone thyroxine that includes iodine. The secretion of thyroxine is triggered by the thyrotropic hormone, from the anterior lobe of the pituitary gland. Its secretion based on the level of thyroxine in the thyroid gland. In follicles of the thyroid gland is a precursor thyroglobulin (that is, thyroxine and protein). A proteolytic enzyme from follicle separates the thyroxine from protein prior to it passes into the blood stream.

Thyroxine regulates basal metabolic rate and is thus significant in growth. The deficiency or underproduction results in arrested physical and mental growth (that is, cretinism). Though, in adults a condition termed as myxoedema takes place. Signs comprise reduced metabolic rate, rise in subcutaneous fat, coarsening of skin and physical, sexual & mental retardation. If there is lack of iodine in the diet, the thyroid gland expands to compensate for the lack. This outcome in hyperplastic goitre that is observed as swelling in the frontal portion of the neck.

Over-production (that is, hyperthyroidism) leads to the exophthalmic goitre (that is, swelling of thyroid and protrusion of eyes), raised metabolic rate, loss of weight, raised heart beat and physical and mental restlessness. A person having these conditions is hyperactive, short-tempered, nervous and thin having bulging eyes.

The parathyroid glands:

There are basically four tiny glands joined to the thyroid gland. They secrete parathyroid hormone. The parathyroid and thyroid glands secrete calcitonin that regulates blood calcium levels. Parathyroid hormone increases level of calcium ions in the blood through:

a) Releasing calcium from bones into the blood.

b) Raising calcium absorption in the intestines.

c) Decreasing the calcium excretion from kidneys.

The Gonads:

The gonads are the reproductive organs of the male (that is, testis) and the female (that is, ovaries) animals. They generate hormones usually termed as gonadotropic hormones that are sex hormones.

The interstitial cells of the ovary and testes generate sex hormones. The testes generate the male hormone testosterone, whereas the ovary generates the female hormones termed as estrogen and progesterone. They are generated at maturity and thus, stimulate growth of sexual organs from the time of puberty. Gonadotrophic hormones in both sexes are accountable for secondary sexual appearance characters like enlargement of the breasts, appearance of hair in the pubic area and armpits and beginning of menstruation in females. In males, the organ rises in size, hair appears on the face, armpit and pubis and the voice get deeper.

Estrogen makes the uterus for reception of fertilized egg; it as well turns some animals on in heat period (that is, oestrus). Progesterone generated by corpus lutcum and placenta maintains pregnancy, restrains ovulation and prevents the uterus from contracting.

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