Chemical Coordination and Integration | Plus 1 Zoology | Exam Capsule Notes (Web and PDF)

Chapter at a glance

Endocrine Glands:
1. Hypothalamus

Neurosecretory cells (nuclei) secretes the following hormones:
  • Releasing hormones (E.g. GnRH): Stimulate secretion of pituitary hormones.
  • Inhibiting hormones: Inhibit secretion of pituitary hormones. E.g. Somatostatin inhibits release of GH from pituitary.
  • Oxytocin: Contracts smooth muscles. For contraction of uterus during child birth. Milk ejection.
  • Vasopressin or Anti-diuretic hormone (ADH): Reabsorption of water & ions by DCT. 
        Deficiency: Diabetes insipidus.
2. Pituitary

It has 2 parts: Adenohypophysis (Pars distalis + Pars intermedia) & Neurohypohysis. 

Adenohypophysis secretes the following hormones:
  • Somatotropin (Growth hormone, GH): For body growth. Over-secretion: Gigantism (abnormal growth). Hyposecretion: Dwarfism (stunted growth). Over-secretion in adults: Acromegaly.
  • Prolactin (PRL): Growth of mammary glands and milk production.
  • Thyroid stimulating hormone (TSH): Stimulates secretion of thyroid hormones from thyroid.
  • Adrenocorticotrophic hormone (ACTH): Stimulates the synthesis and secretion of steroid hormones (glucocorticoids) from the adrenal cortex.
  • Luteinizing hormone (LH): In males: stimulates synthesis of androgens from testis. 
        In females: induces ovulation. Maintains corpus luteum.
  • Follicle stimulating hormone (FSH): Stimulates gonadal activity. In males, FSH & androgens regulate spermatogenesis. In females, FSH stimulates development of the ovarian follicles.
  • Melanocyte stimulating hormone (MSH): From Pars intermedia. Acts on melanocytes to regulate skin pigmentation.
Neuro-hypophysis stores Oxytocin & Vasopressin from hypothalamus.

3. Pineal 
  • Hormone: Melatonin.
  • Function: Regulates diurnal (24-hour) rhythm, metabolism, pigmentation & menstrual cycle.
4. Thyroid

Largest endocrine gland. It releases the following hormones:

a. Thyroxin (tetraiodothyronine, T4) & Triiodothyronine (T3): 
  • Regulation of basal metabolic rate (BMR).
  • Physical, mental and sexual development.
  • Support RBC formation.
  • Control metabolism of carbohydrates, proteins & fats
    Hypothyroidism (Goiter): Deficiency of iodine.
    Hyperthyroidism: Exophthalmic goiter (Grave’s disease).

b. Thyrocalcitonin (TCT): Lowers blood calcium.

5. Parathyroid 

Secretes Parathyroid hormone (PTH).

Function: Increases Ca2+ level in blood (hypercalcaemic hormone).

6. Thymus 

Secretes Thymosins. 

Function: Gives immunity. 

Thymus is degenerated in old people. So, thymosin production decreases and immunity become weak.

7. Adrenals

It has outer Adrenal cortex and inner Adrenal medulla.

Adrenal cortex: Secretes the following hormones:

a. Glucocorticoids (mainly cortisol): 
  • For carbohydrate metabolism.
  • Stimulate gluconeogenesis, lipolysis and proteolysis.
    Deficiency: Addison’s disease.

b. Mineralocorticoids (mainly aldosterone):

    Regulate water & ionic balance, osmotic pressure and BP.

c. Androgenic corticoids: 

    For growth of axial hair, pubic hair and facial hair.

Adrenal medulla: 

Hormones: Adrenaline & Noradrenaline.

Functions: Secreted during stress emergency situations so called emergency hormones (hormones of Fight or Flight).

8. Pancreas (Islets of Langerhans) 

Glucagon (from α cells): Hyperglycemic factor.
  • For glycogenolysis to increase blood sugar (hyperglycemia).
  • Stimulates gluconeogenesis.
  • Reduces the cellular glucose uptake.
Insulin (from β cells): Hypoglycemic factor.
  • Decreases blood glucose level (hypoglycemia).
  • Glycogenesis.
    Deficiency: Diabetes mellitus.

9. Testis (male gonad) 

Hormone: Androgens (mainly testosterone).

  • Maturation of accessory sex organs & sex characters.
  • For spermatogenesis.
10. Ovary (female gonad) 

Hormones: Estrogen and Progesterone. 

Functions of Estrogen: 
  • Development of secondary sex organs & sex characters.
  • Development of ovarian follicles & mammary glands.
Functions of Progesterone:
  • Supports pregnancy.
  • Development of mammary alveoli & milk secretion.


Atrial wall of Heart:
  • Hormone: Atrial natriuretic factor (ANF).
  • Function: Dilation of blood vessels to reduce the BP.
JGA of kidney:
  • Hormone: Erythropoietin.
  • Function: Stimulates erythropoiesis.
Gastro-intestinal tract: Secretes the following hormones:
  • Gastrin: Stimulates secretion of HCl & pepsinogen from gastric glands.
  • Secretin: For secretion of water & bicarbonate ions from exocrine pancreas.
  • Cholecystokinin (CCK): For secretion of bile from gall bladder and pancreatic enzymes.
  • Gastric inhibitory peptide (GIP): Inhibits gastric secretion.


A hormone binds to its specific receptor in target tissue to form hormone-receptor complex.

It leads to biochemical changes in target tissue and thereby regulates metabolism and physiological functions.
Interaction of hormones (e.g. protein hormone, FSH) with Membrane-bound receptors.

Interaction of hormones (e.g. steroid hormones, iodothyronines) with Intracellular receptors 

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