Endocrine System - Notes, Biology | IBPS PO Prelims & Mains Preparation - Bank Exams PDF Download

Endocrine System

• Formed by endocrine glands ( or Ductless Glands ) and their secretion.
• They secrete hormones directly into the blood stream in response to instructions from the brain.
• The blood then carries them around the body.

Endocrine System

Hypothalamus

• Forms a part of fore – brain, secretes neurohormones, which effect the release of hormones from pituitary.
• Acts as the thermostat.

Pituitary Gland

• Also called Master Gland.
• It is the smallest endocrine gland.
• It secretes:
• 1. Somatotrophic Hormone ( Growth stimulating Hormone ): Controls the general growth of the body.
  • Its hypersecretion leads to acromegaly in adults and gigantism in children. Its hyposecretion leads to dwarfness in children.
• 2. Gonadotrophic Hormone ( GTH ): Stimulates the primary sex hormones, i.e. ovaries and testes.
• 3. Lactogenic Hormone: Initiates milk production in the pregnant females.
• 4. Thyrotrophic Hormone: Aids in the regulation of thyroid secretion.
• 5. Adrenocorticotrophic Hormone ( ACTH ): Influences the secretion from the cortex of adrenal glands.
• 6. Diabetogenic or Metabolic hormone: influences metabolism of carbohydrates, fats and proteins.
• 7. Oxytocin or Pitocin: Stimulates smooth muscle contractions, especially of the uterus during child birth. Also helps in the secretion of milk in females.
• 8. Vasopressin or ADH (Anti–Diuretic Hormone ): Regulates reabsorption of water from the kidney tubules.
  • Its Hypoactivity leads to Diabetes insipidus in which patients excrete large amount of urine.
  • Also causes contraction of small arteries, causing increase in Blood Pressure.

Thyroid Gland               

• It is the largest endocrine gland located in the neck between the trachea and larynx.
• Controls BMR ( Basal Metabolic Rate ).
• BMR is minimum energy requirement for maintenance of body during rest or sleep.
• For normal human adult, it is 1600 Kcal / day.

Thyroid Gland Secretes :

1. Thyroxine : 

• Hypoactivity in children leads to cretinism. Hypoactivity in adults leads to Myxoedema ( sluggish appearance, feeble mindedness, low body temperature ).
• A diet, poor in iodine, which is insufficient for the synthesis of thyroxin, leads to simple goitre.
• Its hyperactivity leads to increased metabolic activities (highly nervous, overactive and irritated person).

2. Pancreas

• It is an exocrine as well as an endocrine gland. Its endocrine part is known as Islets of Langerhans. Its 3 types of cells secrete 3 different hormones.
• Beta cells secrete Insulin which controls the amount of sugar in the blood. Its hyposecretion leads to Diabetes Mellitus.
• Alpha cells secretes Glucagon which increases blood sugar level.
• Gamma cells secrete Somatostatin which controls the functioning of alpha and beta cells.

3. Adrenal Glands

• 2, on each kidney.
• Adrenal gland is also known as 4S gland. ( 4S stands for: Sugar metabolism, Salt retention, Sex hormone and Source of energy ).
• Consists of 2 Distinct Parts : Outer cortex and inner medulla.
• 1. Adrenal Medulla secretes Adrenaline or epinephrine which effects liberation of glucose from glycogen stored in liver and increases the rate of metabolism.
• Its over – secretion leads to increased saliva flow, tears, bile and sweat, quickens heart beat, speeds up respiratory activities.
• It is also known as 3F Gland because of these ( fear, fight, flight ).
• Nor – epinephrine or Nor – adrenaline is also secreted from medulla (20%) which is opposite to adrenaline.

Adrenal Cortex secretes two types of Hormones :

• Mineralo Corticoids : Maintain electrolyte balance in the body and distribution of water to the tissues.
• It. is also known as salt retaining hormone.
• Its hyposecretion results in Addison’s disease. In this disease, excessive loss of Na, Cl ions takes place and level of K ions increases in blood.
• Its hypersecretion leads to retension of Na, Cl ions and more absorption of water.
• Gluco Corticoids : It influences carbohydrate metabolism and also effect protein and fat metabolism.
• Its hyposecretion leads to fall in glucose level due to which body temperature decreases.
• Its hypersecretion leads to Cushing Disease in which irregular deposition of fat takes place and glucose level increases in blood

Gonads

• Both testes and ovaries, in addition to producing sperms and ova, also produce hormones.

Testes

• Its interstitial cells (Leydig’s cells) secrete testosterone which is responsible for male secondary sexual characters (beard, body hair, deep voice, muscles, formation of sperms, sexual urge, etc).
• Deficiency leads to sterility (eunuchoidism).

Ovaries

• In females, the follicular cells and corpus luteum secretes the following hormones :
• Follicular Cells produces Oestrogen which controls the female secondary sexual characters (Broadening of pelvis, development of breasts, growth of uterus and vagina, pubic hair, onset of menstrual cycle, etc).
• Corpus luteum secretes Progesterone which is essential for the completion of each menstrual cycle.
• It controls the final changes in the uterine wall and brings about the attachment of embryo and causes development of breasts in the later months of pregnancy.
• Corpus Luteum also secretes Relaxin at the end of gestation period, and helps in easy birth by relaxing the uterus and ligaments of the pelvic girdle.