Endocrine System:

A system formed by the collection of endocrine glands which produces hormone and functions in regulating the body's growth and development, metabolism, reproduction and other slow functions of our body.

    They work in sending signals to various parts of the body with hormones which acts as a chemical messenger.

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Endocrinology – The study of endocrine glands and their secretions with functions is known as endocrinology.

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[Thomas Addison is known as the father of Endocrinology.]

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Hormones

Hormones are the chemical messengers secreted by endocrine glands in a very little amount directly into the blood, from the blood they reach the target organ and perform their functions.

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CHARACTERISTICS OF HORMONES

• Hormones are highly specific for the target organ.

• They are produced in a very little quantity a little increase or decrease in quantity of hormones can cause diseases.

• They are very active and their functions are very rapid and after performing the function they are either destroyed or excreted out of the body hence they are not stored in our body

• They regulate the physiological process in our body and brings about the chemical changes that are irreversible.

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Categories of Hormones

There are two main categories of hormones:

1. Steroid hormones

2. Non steroidal hormone or protein hormone.

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Steroid hormones: These hormones are of steroid origin. There receptors are present inside the cell .They easily pass through the cell membrane and bind to their receptors. Eg. Oestrogen, progesterone, androgens, thyroid hormones, etc.

 

Protein or non steroidal hormones: These hormones are derived from amino acids . There receptors are present on surface of their target cells. They cannot pass through the cell membrane. Eg. Insulin, glucagon, prolactin, ADH, FSH ,etc.

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Thyroid Gland

Location:  In the neck just below the larynx (voice box) in front of trachea or windpipe.

Structure: Thyroid gland is a bilobed structure both the lobes are connected to each other by a narrow mass of tissues called isthmus. These glands has rich blood supply due to which large amounts of hormones are produced in a short period of time

Hormone secreted: Thyroxine and Calcitonin

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Functions:

1. Controls basic metabolic rate of body that results in energy production and maintenance of body temperature.

2. Regulates growth and development of a body and brain.

3. Regulates activities of Nervous system.

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*Secretion of thyroid gland is controlled by Thyroid Stimulating Hormone (TSH) secreted by pituitary gland.

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Diseases caused by hypo-secretion of thyroid gland:-

Hypothyroidism: Hyposecretion of thyroxine is known as hypothyroidism. In hypothyroidism basic metabolic rate decreases due to which patient gains weight.

Symptoms : Low blood pressure, obesity, slow heartbeat Person becomes lethargic and suffers lack of energy.

 

Goitre: Goitre is caused due to the deficiency of iodine which leads to the enlargement of thyroid glands.

 

Cretinism: Cretinism is caused due to under secretion of thyroxine in children. It causes abnormal development of brain and body. Child becomes mentally retarded and leads to dwarfism.

 

Myxoedema: It is caused in young people due to the under secretion of thyroxine. Its symptoms include swelling on hand and face and patience become lethargic due to slow metabolic rate.

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Diseases caused by hyper-secretion of thyroid gland:-

Hyperthyroidism: It is caused by the over secretion of thyroxine. The person suffering from hyperthyroidism faces high metabolic rate due to which patient becomes linger and thin/skinny.

Symptoms: High BMR, high blood pressure and heart beat rate, body remains hot due to excess liberation of energy and patient becomes hyperactive.

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Adrenal Gland

Location: One on the top of each kidney hence they are also known as suprarenal glands

Structure: Adrenal gland is divided into two part

1. Adrenal medulla

2. Adrenal cortex

 

Adrenal medulla (inner part) ➡️secretes ➡️adrenaline and non-adrenaline (emergency or stress hormone).

 

Adrenal cortex (outer part) ➡️ secretes ➡️ aldosterone (mineralocorticoids) and cortisol, cortisone and corticosterone (glucocorticoids)

 

Functions of adrenal hormone:-

Adrenaline and nor adrenaline – It is also known as emergency hormone and it prepares the body to cope up with an emergency or stress condition. When the stress condition is over nor-adrenaline is secreted to bring the body back to its normal condition.(Also known as fight and flight hormone)

Aldosterone – Regulates the salt-water balance  (Na and Cl ions) in the blood by controlling the absorption of Na and Cl ions by the kidneys.

​Cortisol – Controls the carbohydrate absorption by the kidney and thus maintains the blood sugar level.

 

Diseases caused by hypo-secretion of adrenal gland:-

Addison's disease – It is caused by hyposecretion of glucocorticoids. Its symptoms include weight loss, weakness, fatigue and low blood pressure. It also cause nervousness and hypertension.

 

Diseases caused by hyposecretion of adrenal gland:-

Cushing's syndrome – Its symptoms include obesity, increase in the accumulation of fat around the neck and the thinning of arms and legs.

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Pituitary Gland

Pituitary gland is known as master gland because it controls the secretion of other endocrine glands.

Location – It is located at the middle of the base of the the brain within a Bony structure called Sella turcica.

Pituitary gland is located just beneath the hypothalamus and it is connected to it by a stalk.

 

Structure – It is a pea sized gland it is divided into three lobes.

1. Anterior lobe: also known as adenohypophysis.

2. Intermediate (nonfunctional)

3. Posterior lobe: also known as neurohypophysis.

 

Hormone secreted by adenohypophysis :–

1. Growth hormone

2. Thyroid stimulating hormone

3. Adreno corticotrophic hormone

4. Follicle stimulating hormone

5. Luteinizing hormone

6. Prolactin hormone.

 

Hormones secreted by neurohypophysis :–

Hormones released by neurohypophysis are actually the hormones which are secreted by hypothalamus and are stored there and released by neurohypophysis of pituitary gland.

1. Oxytocin

2. Vasopressin

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Functions of Pituitary Hormones

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Hormones of anterior lobe:

Growth hormone (G.H)

Also known as Somatotropic hormone (STH) or somatotropin.

Controls the growth of a body by promoting the absorption of calcium by the bones and by increasing the rate of protein synthesis.

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Diseases caused by hypersecretion :–

Gigantism – In this disease person become very tall. It is caused by the over secretion of growth hormone during childhood or growth period. The growth of a body is proportionate in this gigantism.

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Acromegaly – Caused by the over secretion of growth hormone during adult stage after the growth period. In this condition the bones grow disproportionately which causes bent bones.

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Diseases caused by hyposecretion :–

Dwarfism – it is caused due to under secretion of growth hormone in children. Due to which growth is hindered and child becomes dwarf.

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TSH (Thyroid Stimulating Hormone)

Controls and stimulate the secretion of thyroxine from thyroid gland.

 

ACTH (Adreno Corticotrophic Hormone)

It controls and stimulate the secretion of adrenal hormones.

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FSH (Follicle Stimulating Hormone)

It stimulates the production of sperm and ovum in males and females.

It also stimulates follicle cells of ovary to secrete oestrogen hormone in females.

 

Luteinizing hormone (L.H)

​In males it stimulates the secretion of male hormone 'testosterone'.

In females, it stimulates the secretion of female hormones, estrogen and progesterone.

 

Prolactin hormone (PRL)

In females, it enhances yhe development of mammary glands and production of milk during lactation period

In males, it enhances the production of testosterone.

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Hormones of posterior lobe

Antidueretic Hormone (ADH) OR Vasopressin

It controls the re-absorption of water by the kidney tubules and helps kidney in retaining water and form more concentrated urine.

 

The deficiency of this hormone causes a disease named DIABETES INSIPIDUS in which patients urinate more frequently and large amount of urine is produced each time due to which patient suffers a loss of water from the body and feels thirsty .

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Oxytocin

It stimulates the contraction of uterus during labour and helps in child birth

It also promotes the release of milk in a nursing mother.

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Hormones of intermediate lobe

Melanocyte stimulating hormone (MSH)

It stimulates the production of melanin pigment from melanocyte cells of the skin and provide color to the skin.

 

PANCREAS (Mixed Gland)

​Location – behind the stomach.

Structure – long, flat in shape. It has both endocrine and exocrine.

• The endocrine part is known as “ISLETS OF LANGERHANS”. This part consist of two types of cells alpha cells and beta cells.

• The exocrine part is known as “PANCREATIC ACINI”. This part secretes pancreatic juice that contains enzymes which helps in digestion .

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Hormones secreted by pancreas

Insulin

It is secreted by the Beta cells of islets of langerhans. It controls and regulate the blood sugar level. It promotes the conversion of glucose into glycogen and this process is known as glycogenesis.

It is secreted when the level of blood glucose increases above normal level.

Diseases caused by hyposecretion :—

Diabetes Mellitus – It is a condition caused due to undersecretion of insulin. In this condition the blood sugar level is increased.

Insulin shock – Decrease in the blood sugar level due to overdose of insulin in diabetes mellitus.

 

Glucagon

Secreted when the level of glucose decreases below normal. It regulate the blood sugar level by converting glycogen into glucose and this conversion is known as glycogenolysis.

Insulin and glycogen works opposite to each other.