Testes :
- A pair of testes is present in the scrotal sac of male.
- Leydig cells or interstitial cells are located in the intertubular spaces.
- These cells secrete a group of steroid called androgen, mainly testosterone.
Function of testosterone :
- Regulate development, maturation and functioning of male accessory sex organs like epididymis, vas deferens, seminal vesicles, prostate gland etc.
- Stimulates muscular growth.
- Plays a major role in spermatogenesis.
- Acts on central nervous system and influence the male sexual behaviour (libido).
- Stimulate protein anabolic effect.
- Stimulate development of secondary sexual characters –
- Growth of facial and axillary hair.
- Aggressiveness.
- Low pitch voice
Ovary :
- Female have a pair of ovaries located in the abdomen.
- Primarily it acts as female sex organ and produce female gamete (ovum).
- It also acts as endocrine gland producing two groups of steroid hormones –
- Oestrogen synthesized in the growing ovarian follicles.
- Progesterone is produced from the corpus luteum.
- Corpus luteum is formed from the remnant of ruptured Graafian follicle.
Role of oestrogen :
- Develop female secondary sexual organs.
- Development of growing ovarian follicles.
- Regulate female sexual behaviour.
- Development of female secondary sexual characters –
- High pitch voices.
- Development of breast or mammary glands.
- Deposition of fat all over the body, making feminine appearance.
Role of progesterone :
- Support pregnancy.
- Control the second half of menstrual cycle.
- Maintain uterus for implantation.
- Prevents further ovulation.
- Inhibit action of Oxytocin (uterine contraction).
- Stimulate growth of mammary gland.
- Stimulates the formation of alveoli in the mammary gland.
- Stimulate milk secretion.
Hormones of heart :
- Atrial wall of heart secretes a peptide hormone called atrial Natriuretic factor.
- It decreases the blood pressure, by dilating the blood vessels.
- It also stops the secretion of renin; in the other hand suppress RAAS.
Hormones of Kidneys :
- Juxta glomerular cells of kidney produce a peptide hormone called erythropoietin which stimulates erythropoiesis (formation of RBC in bone marrow)
Hormones of gastro-intestinal tract :
- Gastrin – stimulates gastric gland to produce gastric juice.
- Secretin – stimulate exocrine part of pancreas to produce pancreatic juice.
- Cholecystokinin – contraction of gall bladder for secretion of bile juice.
- Gastric inhibitory peptide (GIP) – inhibits gastric secretion and motility.
MECHANISM OF HORMONE ACTION :
- Hormones produce their effects on target tissues by binding to specific proteins called hormone receptors located in the target tissues only.
- There are two types of receptors –
- Located on the cell membrane called membrane bound receptors.
- Located inside the cell called intracellular receptors.
- On the basis of chemical nature hormones are classified into four groups –
- Peptide, polypeptide, protein hormone (insulin, glucagon, pituitary and hypothalamic hormone).
- Steroids (cortisol, estradiol and progesterone, testosterone).
- Iodothyronines (thyroid hormone)
- Amino-acid derivatives (adrenaline and nor adrenaline)
- Hormones which interacts with membrane-bound receptors normally do not enters into the cell but generates second messengers (cyclic AMP, IP3, Ca++etc).
- The second messengers in turn regulate cellular metabolism.
- The hormones which interact with intracellular receptors (steroid hormones, Iodothyronines) mostly regulate gene expression.
