Pituitary Gland
- The pituitary gland or hypophysis is a pea-shaped compact mass of cells located at the base of the midbrain attached to the hypothalamus by a pituitary stalk.
- The pituitary gland is anatomically composed of two lobes and performs different functions.
- They are the anterior lobe (adenohypophysis) and the posterior lobe (neurohypophysis). The intermediate lobe is non-existent in humans.
- The pituitary gland forms the major endocrine gland in most vertebrates. It regulates and controls other endocrine glands and so is called as the “Master gland”.
- Hormones secreted by the anterior lobe (Adenohypophysis) of pituitary
- The anterior pituitary is composed of different types of cells and secretes hormones which stimulate the production of hormones by other endocrine glands.
- The hormones secreted by the anterior pituitary are
- Growth Hormone
- Thyroid stimulating Hormone
- Adrenocorticotropic Hormone
- Gonadotropic Hormone which comprises the Follicle Stimulating Hormone and Luteinizing Hormone
Growth hormone (GH)
- GH promotes the development and enlargement of all tissues of the body.
- It stimulates the growth of muscles, cartilage and long bones. It controls cell metabolism.
- The improper secretion of this hormone leads to the following conditions.
Dwarfism:
- It is caused by decreased secretion of growth hormone in children. The characteristic features are stunted growth, delayed skeletal formation and mental disability.
Gigantism:
- Over secretion of growth hormone leads to gigantism in children.
- It is characterised by the overgrowth of all body tissues and organs. Individuals attain an abnormal increase in height.
Acromegaly:
- Excess secretion of growth hormone in adults may lead to abnormal enlargement of the head, face, hands and feet.
Thyroid-stimulating hormone (TSH)
- TSH controls the growth of the thyroid gland and coordinates its activities and hormone secretion.
Adrenocorticotropic hormone (ACTH)
- ACTH stimulates the adrenal cortex of the adrenal gland for the production of its hormones. It also influences protein synthesis in the adrenal cortex.
Gonadotropic hormones (GTH)
- The gonadotropic hormones are follicle stimulating hormone and luteinizing hormone which are essential for the normal development of gonads.
Follicle-stimulating hormone (FSH)
- In males, it stimulates the germinal epithelium of testes for the formation of sperms.
- In females, it initiates the growth of ovarian follicles and their development in the ovary.
Luteinizing hormone (LH)
- In males, it promotes the Leydig cells of the testes to secrete the male sex hormone testosterone.
- In females, it causes ovulation (rupture of mature Graafian follicle), responsible for the development of corpus luteum and production of female sex hormones estrogen and progesterone.
Prolactin (PRL)
- PRL is also called lactogenic hormone.
- This hormone initiates the development of mammary glands during pregnancy and stimulates the production of milk after childbirth.
- Hormones secreted by the posterior lobe (Neurohypophysis) of pituitary
- The hormones secreted by the posterior pituitary are
- Vasopressin or Antidiuretic hormone
- Oxytocin
Vasopressin or Antidiuretic hormone (ADH)
- In kidney tubules, it increases the reabsorption of water.
- It reduces the loss of water through urine and hence the name antidiuretic hormone.
- The deficiency of ADH reduces the reabsorption of water and causes an increase in urine output (polyuria). This deficiency disorder is called Diabetes insipidus.
Oxytocin
- It helps in the contraction of the smooth muscles of the uterus at the time of childbirth and milk ejection from the mammary gland after childbirth.
Melatonin
- Melatonin is a hormone produced by the pineal gland. It is known as a time messenger. It signals nighttime information throughout the body.
- Exposure to light at night, especially short-wavelength light, can decrease melatonin production interrupting sleep.
- Suppression of melatonin has been implicated in sleep disturbances and related metabolic disorders.
Thyroid Gland
- The thyroid gland is composed of two distinct lobes lying on either side of the trachea.
- The two lobes are connected by means of a narrow band of tissue known as the isthmus.
- This gland is composed of glandular follicles and lined by cuboidal epithelium.
- The follicles are filled with colloid material called thyroglobulin.
- An amino acid tyrosine and iodine are involved in the formation of thyroid hormone.
- The hormones secreted by the thyroid gland are
- Triiodothyronine (T,)
- Tetraiodothyronine or Thyroxine (T)
Functions of thyroid hormones
- Production of energy by maintaining the
- Basal Metabolic Rate (BMR) of the body.
- Helps to maintain normal body temperature.
- Influences the activity of the central nervous system.
- Controls growth of the body and bone formation.
- Essential for normal physical, mental and personality development.
- It is also known as the personality hormone.
- Regulates cell metabolism.
Thyroid Dysfunction
- When the thyroid gland fails to secrete the normal level of hormones, the condition is called thyroid dysfunction. It leads to the following conditions
Hypothyroidism
- It is caused due to the decreased secretion of thyroid hormones. The abnormal conditions are simple goitre, cretinism and myxoedema.
Goitre
- It is caused due to the inadequate supply of iodine in our diet.
- This is commonly prevalent in Himalayan regions due to the low levels of iodine content in the soil.
- It leads to the enlargement of the thyroid gland which protrudes as a marked swelling in the neck and is called a goitre.
Cretinism
- It is caused due to decreased secretion of the thyroid hormones in children.
- The conditions are stunted growth, mental defect, lack of skeletal development and deformed bones. They are called as cretins.
Myxoedema
- It is caused by deficiency of thyroid hormones in adults.
- They are mentally sluggish, increase in body weight, puffiness of the face and hand, oedematous appearance.
Hyperthyroidism
- It is caused due to the excess secretion of the thyroid hormones which leads to Grave’s disease.
- The symptoms are protrusion of the eyeballs (Exopthalmia), increased metabolic rate, high body temperature, profuse sweating, loss of body weight and nervousness.
Parathyroid Gland
- The parathyroid glands are four small oval bodies that are situated on the posterior surface of the thyroid lobes.
- The chief cells of the gland are mainly concerned with secretion of parathormone.
Functions of Parathormone
- The parathormone regulates calcium and phosphorus metabolism in the body.
- They act on bone, kidney and intestine to maintain blood calcium levels.
Parthyroid Dysfunction
- The secretion of parathyroid hormone can be altered due to the following conditions.
- Removal of parathyroid glands during thyroidectomy (removal of thyroid) causes decreased secretion of parathormone.
The conditions are
- Muscle spasm known as Tetany (sustained contraction of muscles in face, larynx, hands and feet).
- Painful cramps of the limb muscles.