ENDOCRINE SYSTEM

Endocrine system means the endocrine system of the body. Which keeps the internal environment of the body stable by secreting a special type of hormone through different glands and performs many vital functions.

Glands in the body which are made up of secretory epithelium cells and are mainly divided into two parts.

Endocrine Glands (Endocrine Glandus).

These type of glands in the body are ductal glands. These types of glands secrete their secretions directly into the blood or lymph. So it is called endocrine glands.

The secretions of these glands are called hormones. Any endocrine gland secretes one or more hormones.

Exocrine Glands (Exocrine Glands).

This type of gland sheds its secretion directly on the surface of any organ or tissue. The secretions of these glands are pushed to the surface through the ducts in the gland, do not mix directly with the blood, hence they are called exocrine glands.

The secretion of these glands can be known as juice, liquid or chyme. The size and shape of these glands are different. Mainly these type of glands are connected with the digestive track in the function of digestion.

Here in this unit we will study endocrine glands. In which the study of the structure, function and related disorders of these glands is known as Endocraniology.

Endocrine glands do not have ducts. Hence it is also known as ductless glands. With the help of all these glands, majority of body functions are controlled.

• List out the endocrine glands in the body.

The following endocrine glands are located in the body. Here the glands and their classification can be given as follows.

• Pituitary gland

The pituitary gland is known as the master gland of the body because the functions of other glands are regulated by the hormones of this gland.

The pituitary gland is located in the hypophysial fossa of the sphenoid bone of the cranium cvt. Pituitary gland is also known as hypophysis. The pituitary gland is strongly connected to the hypothalamus, so many functions are regulated due to this inter-connectivity.

The size of the pituitary gland is 1.2 to 1.5 cm long. It weighs approximately 0.5 grams. It is a peanut shaped gland.

Pituitary gland mainly consists of 3 lobes. Different hormones are secreted from each lobe which can be described as follows. Hormones secreted from each lobe are influenced by releasing and inhibiting hormones secreted from the hypothalamus. Releasing hormones secreted from the hypothalamus increase the secretion of the pituitary gland while inhibiting hormones decrease the secretion of the pituitary gland.

Anterior Lobe (Anterior Lobe).

This lobe is also known as adenohypophysis. There are fibers of connective tissue in its structure.

Due to the releasing and inhibiting hormones secreted from the hypothalamus, the following hormones are secreted from the anterior lobe of the pituitary gland.

The hypothalamus is connected by blood to the anterior lobe of the pituitary gland and the hormones secreted from the anterior lobe are controlled by the hypothalamus.

The following hormones are secreted from the anterior lobe.

A. Growth Hormone

Growth hormone is also called another somatotrophic hormone. The main function of this hormone in the body is to maintain the growth of the body. If this hormone is secreted normally, then the normal growth of the body is maintained. If the amount of this hormone is secreted more, then over growth is seen in the body which is called giantism and if the amount of hormone of this gland decreases then growth in the body is less than normal which is also called dwarfism. The secretion of this hormone is based on growth hormone releasing and inhibiting hormone secreted from the hypothalamus.

B. Thyroid Stimulating Hormone (TSH)

This hormone is secreted from the lobe of the anterior pituitary gland. Which stimulates the thyroid gland and the thyroid gland does its normal hormone production.

Ç. Adreno Corticotropic Hormone ACTH

Corticotrophic releasing hormone and inhibitory hormone are secreted by the hypothalamus. Through which a hormone called ACTH is secreted from the anterior lobe of the pituitary gland.

This hormone increases the production of hormones secreted from the cortex of the adrenal gland. The adrenal gland is associated with the secretion of steroid hormones.

D. Prolactin Hormone

This hormone is secreted by the anterior lobe. Which is the hormone responsible for the production of breast milk. Releasing and inhibiting hormone from the hypothalamus leads to the secretion of prolacting hormone from the anterior lobe after childbirth, which leads to milk production.

Especially after child birth, this hormone is very useful for the production of breast milk.

E. Gonadotropic Hormone

This hormone is also called sex hormone. Which secrete gonad trophin hormone in male and female.

The secretion of this hormone is also affected by the releasing and inhibiting hormones of the hypothalamus.

This hormone is secreted in two main ways

1. Follicle Stimulating Hormone (FSH)

This hormone produces estrogen and progesterone. Which works for ovum production in female and spermatozoa in male.

2. Luteinizing Hormone (LH)

This hormone produces the progesterone hormone that is responsible for the characteristic menstruation in females and helps the testes to produce testosterone for male.

Intermediate Lobe

An intermediate lobe lies between the anterior lobe and the posterior lobe of the pituitary gland. The function of this lobe in the human body is not yet known with certainty.

Posterior Lobe

This is a lobe of the posterior pituitary gland.

It is known as neurohypophysis.

This lobe of the pituitary gland is connected to the hypothalamus by nerves and nerve fibers.Due to which it is known as neurohypophysis. The following hormones are secreted by this lobe.

A. Oxytocin

It is a hormone secreted by the posterior lobe. It is the hormone responsible for initiating normal labor pain during delivery and the contraction of the myometrium muscles in the uterus. By which the process of child birth can be done well.

Oxytocin hormone also acts to eject the milk from the breast when the baby sucks the mother’s breast milk.

This hormone is also responsible for smooth muscle contractions during sexual intercourse that allow sperm to travel from the vaginal cavity and uterus to the fallopian tubes.

B. Anti Diuretic Hormone (ADH)

This hormone is also known by another name of vasopressin. This hormone prevents the body from releasing large amounts of urine, which leads to the absorption of water in the renal tubules, thereby controlling urine excretion.

It plays a very important role in maintaining body water content and fluid balance.

It causes the contraction of smooth muscles which is important for increasing blood pressure.

Functions of the pituitary gland

The pituitary gland acts as the body’s master gland. Due to which many other glands help to maintain normal function.

The growth hormone of the pituitary gland maintains the normal growth of the body.

The pituitary gland regulates steroid hormones in the body.

The prolactin hormone of the pituitary gland plays an important role in milk production.

Hormones of the pituitary gland play an important role in maintaining fertility.

Hormones of the pituitary gland play an important role in maintaining normal delivery, breast development and breast feeding.

Hormones from the pituitary gland play an important role in maintaining body water balance and blood pressure.

• Relationship of hypothalamus and pituitary gland

The Pituitary Gland is located below the Hypothalamus. It is connected to a structure called infundibulum.

Releasing and inhibitory hormones secreted from the hypothalamus affect the pituitary gland. It stimulates the pituitary gland to secrete its own hormones.

The anterior lobe of the pituitary gland is connected to the hypothalamus by a blood connection. It is called Hypophyseal Portal System. Due to the effect of which the hormones of the anterior lobe are secreted.

The posterior lobe of the pituitary gland is connected to the hypothalamus by nerve connections. Due to the effect of which

• Thyroid Gland

The thyroid gland is an important gland of the endocrine system. It is located in the soft tissue of the neck. This gland is a butterfly shaped gland.

The weight of this gland is approximately 30 grams. Its length is 5 cm and width is 3 cm.

This gland is located from the level of the fifth cervical vertebra to the level of the first thoracic vertebra.

Thyroid gland has one lobe on both sides. Which is covered with fibrous tissue around it. The middle part connecting the two lobes is called the isthmus. The lobes of the thyroid gland have a pyramidal shape.

The tissue in the thyroid gland is made up of tiny structures called follicles. Each follicle is composed of simple cuboidal glandular epithelium tissue. which is connected with secretion.

Thyroid stimulating hormone is a hormone released from the pituitary gland that regulates the function of the thyroid gland.

The thyroid gland secretes the following hormones.

1. Triiodothyronine (triiodo thyronine) T3

The main function of this hormone is to maintain normal physical growth and development in the body. This hormone also plays a useful role in maintaining heart rate and certain metabolic activities.

2. Thyroxin T4…

This hormone also performs the same function as the T3 hormone. That is, the body maintains metabolic activity and functions to maintain normal physical growth and development. This hormone increases the basal metabolic rate.

3. Calcitonin

This hormone is secreted by the parafollicular cells of the thyroid gland. Which affects the metabolism of calcium in the blood.

• Parathyroid glands.

The parathyroid glands are located behind the thyroid gland in the body. It is in the number of 4.

These parathyroid glands are arranged in numbers of superior and inferior two.
The effect of the hormone of these glands is opposite to that of the calcitonin hormone of the thyroid gland. Which reduces the level of calcium in the blood. This gland works to maintain the balance of calcium.

Parathyroid hormone stimulates the kidneys to release a hormone called calcitriol from the kidneys. Which allows the absorption of calcium in food from the gastrointestinal tract. This increases the amount of calcium in the blood.

The hormone of this gland releases the calcium deposited in the bones into the blood. Along with calcium, this gland also functions in maintaining the balance of phosphorus and magnesium.

• Adrenal glands (adrenal glands).

This gland is also called suprarenal gland as it is located above the kidneys on both sides. It is found in the number of 2. Its size is 3 to 5 cm long, 2 to 3 cm wide and 1 cm thick. Its weight is approximately 3 to 5 grams.

The outer part of the adrenal gland is called the adrenal cortex and the inner part is called the adrenal medulla.

Adrenal cortex (adrenal cortex).

This part lies on the outer side of the adrenal gland. Cells in this part secrete steroid hormones.

The following steroid hormones are secreted by the cortex portion of the adrenal gland.

A. Glucocorticoids.

This hormone is secreted by the Zona Fasciculata cells in the adrenal gland.

ACTH secreted from the anterior lobe of the pituitary gland stimulates the adrenal cortex to secrete glucocorticoid hormone.

This hormone helps in the metabolism of protein, glucose and fat in the body.

It provides resistance to stress in the body. So heart beat and blood pressure increases during stress. An increase in blood sugar is also seen.

The effect of this hormone is seen in every cell of the body. Its highest amount in blood is seen in the morning and its amount gradually decreases till night.

In Bodima, this hormone also provides an anti-inflammatory effect. It also depresses the immune system of our body. So our immune response decreases.

It includes cortisol and cortisone hormones.

B. Mineralocorticoid.

This hormone is secreted by Zona Glomerulosa cells in the adrenal gland.

Aldosterone hormone is mainly included in this hormone secreted from the adrenal cortex. This hormone works to maintain the amount of mineral salts in the body. Due to which fluid and electrolyte balance is maintained in the body.

Aldosterone hormone promotes reabsorption of sodium and excretion of potassium through urine. So retention of water in the body takes place and blood pressure is maintained due to maintaining body fluid.

This mechanism is maintained by the renin angiotensin aldosterone system (RAAS).

C. Androgens.

This hormone is secreted by the zona reticularis cells in the adrenal gland.

It is also known as sex hormone. Testosterone in males and estrogen in females are considered as androgens steroid hormones.

It plays an important role in developing male and female sex characteristics, hair growth and muscular structure.

Adrenal Medulla (Adrenal Medulla).

The part between the adrenal gland is known as the adrenal medulla. This part secretes catecholamine hormones. Which mainly secretes adrenaline and noradrenaline i.e. epinephrine and norepinephrine.

These hormones maintain the fight and flight response of the autonomic nervous system to the sympathetic nervous system during stress.

These hormones perform the following functions in the body.

Blood pressure increases and heart rate increases
Contraction in the diameter of blood vessels
Blood sugar is high and the rate of cellular metabolism is also high
The pupil dilates
Dilates the airways of the lungs, etc. functions are seen by these hormones.

Response to stress

• Thymus gland

This gland is located in the mediastinum below the sternum in the thoracic cavity. This gland is large in size in children and after puberty it becomes smaller in size with age. It weighs approximately 10 to 15 grams at birth.
This gland secretes a hormone called thymosin.

Structure : It has two lobes. It has a capsule. The outside of each lobe is divided into lobules with the outer part called the cortex and the inner part called the medulla.

• Functions:

Bone marrow-derived B-lymphocytes are activated as T-lymphocytes after entering the thymus gland.

Thymosin stimulates maturation of the thymus gland and other lymphoid tissues. Which hormone is secreted through the epithelial cells of the gland.

• Pineal gland

This gland is attached to the roof of the ventricle in the cranium cavity. Its shape is of pine cone shape.

It is about 10 mm long and reddish brown in colour.

This gland secretes a hormone called melatonin. The secretion of the hormone is seen at the time of dark light. Sunlight or light reduces the secretion of melatonin hormone. This results in decreased sleep.

In the absence of light, norepinephrine stimulates the secretion of melatonin. This causes sleep.

• Pancreas (Pancreas).

Pancreas functions as both an endocrine and an exocrine gland. The cells of the part of the pancreas that secrete hormones are endocrine and some cells of the same pancreas that produce digestive juices act as exocrine pancreas.

The pancreas is an organ 12 to 15 cm long. Its weight is approximately 100 grams.
Pancreas is divided into three parts, head, body and tail.

Pancreatic cells in this pancreas are arranged like jumkha. These millions of small pancreatic endocrine tissues are known as pancreatic islets or islets of Langerhans.

The following specific cells in this pancreatic islet are associated with the secretion of specific hormones.

Alpha cells secrete glucagon.
Beta cells secrete insulin.
Delta cells secrete somatostatin.

Blood glucose levels in the human body are controlled by the hormones insulin and glucagon.

Insulin

Insulin is secreted by beta cells in the pancreas. It works to reduce the blood glucose level in the body.

It works by converting excess glucose in the blood into glycogen. This process is known as Glycogenesis.

This hormone synthesizes proteins and also helps in the synthesis of fatty acids.

Glucagon (Glucagon).

It is a hormone secreted by alpha cells in the pancreas. It works opposite to insulin i.e. when the blood sugar level falls below normal, the alpha cells of the pancreas release glucagon and it converts sugar from glycogen into glucose.

In this way it maintains the blood glucose level. It prevents hypoglycemia in the body.

Somatostatin (Somatostatin).

This hormone is secreted by delta cells in the pancreas.
It reduces the secretion of insulin and glucagon and reduces the absorption of nutrient material through the gastrointestinal tract.

Other hormones of the human body.

Many tissues in the body function like endocrine glands and secrete local hormones. These locally secreted hormones are as follows.

Erythropoietin (Erythropoietin).

Erythropoietin is a hormone secreted by the kidneys. which help in the formation and production of RBC. Erythropoiesis is done by this hormone.

Histamine (histamine).

It is a local hormone secreted by the mast cells of the connective tissue in the body. Infection is prevented by this hormone i.e. it acts as an anti-inflammatory.

Prostaglandins (prostaglandigs).

It is a hormone that acts as a lipid substance found in many tissues of the body. It has many physiological functions.

It causes pain
is liable to fever
It is a blood pressure regulator
Also important for inflammatory response
Contracts the muscles of the uterus during labor pains
It plays an important role in the blood clotting mechanism.