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PinkMonkey Online Study Guide-Biology

The intermediate lobe is poorly developed in man and contains smaller cells than the anterior lobe.

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Figure 22.4 Histology of pituitary

The cells in the posterior lobe show neurosecretory granules, prominent nuclei and polygonal supporting neuroglial cells. This is because the posterior lobe stores the hormones secreted by the neurosecretory cells of the hypothalamus.

(D) Pituitary Hormones

i.) Anterior lobe. The anterior lobe of the pituitary secretes six hormones.

a) Thyroid stimulating hormone (TSH), or thyrotropin, stimulates the secretion of thyroxin from the thyroid glands.

b) Somototropic or growth hormone controls growth of tissue, bone, muscles and internal organs, and also influences metabolic processes. Hypersecretion in early life gives rise to a condition called gigantism, and after the growth period in adult life it results in acromegaly. In acromegaly, excess secretion appears after long bones have ossified and the growth continues only in certain bones, resulting in lengthening of forelimbs, hindlimbs, and enlarged jaw and face. Hypofunction during growth years results in pituitary infantilism, a kind of dwarfism, in which an adult is not more than three or four feet tall, and is usually sexually immature.

c) Follicle stimulating hormone (FSH) stimulates the ovaries and testes. In females, it controls the development of grafian follicles (ova). In males, FSH influences spermatogenesis, i.e. production of sperm by the seminiferous tubules of the testes.

d) Adrenocorticotropic hormone (ACTH) stimulates the adrenal cortex and regulates the secretion from the adrenal glands.

e) Luteinizing hormone (LH) along with FSH, is responsible for the growth of ovarian follicles, release of mature ova, formation of the corpus luteum, production of progesterone and regulation of menstrual cycle in females. In males, LH stimulates the testes to secrete testosterone or ICSH- interestitial cell stimulating hormone.

f) Prolactin initiates the secretion of milk by the mammary glands after the birth of a baby. In the absence of prolactin, milk secretion stops.

Interaction among pituitary and other endocrine glands
(---------Responsible for feed back or inhibition)
(---------Pituitary Hormones that stimulate other glands)

ii)Intermediate lobe secretes only one hormone, Melanophore Stimulating Hormone (MSH), or intermedin, which controls skin pigmentation of many vertebrates. It makes the color of the skin dark. However, it has no function in humans.

iii) Posterior lobe

a) Oxytocin causes contraction of the uterus in females during childbirth and regulates lactation (release of milk).

b) Antidiuretic hormone (ADH) or Vasopressin stimulates the kidneys to reabsorb more water, preventing excessive water loss by urination. Chronic deficiency of ADH results in diabetes insipidus (polyuria), in which the patient feels extremely thirsty and passes a large amount of dilute urine.

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Table of Contents

22.0 Introduction
22.1 Pituitary gland
22.2 Thyroid gland

Chapter 23


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