The pituitary gland

A small gland with a large work

The pituitary gland lies in a bony cavity of the skull called the sella turcica. A stalk joins it to the hypothalamus. It is often called the master gland, because many of its hormones switch other glands on. But you saw in lesson 1 that the hypothalamus controls the pituitary, so the name is not quite fair.

The pituitary has two main parts.

• The adenohypophysis (the glandular part) has the pars distalis, also called the anterior pituitary, and the pars intermedia. In an adult human, the pars intermedia is almost merged with the pars distalis.
• The neurohypophysis has the pars nervosa, also called the posterior pituitary.

Hormones of the pars distalis

The pars distalis makes six hormones.

• Growth hormone (GH): acts on body tissues and bones. It makes the body grow.
• Prolactin (PRL): acts on the mammary glands. It makes the glands grow and form milk.
• Thyroid stimulating hormone (TSH): acts on the thyroid. It makes the thyroid release its hormones.
• Adrenocorticotropic hormone (ACTH): acts on the adrenal cortex. It makes the cortex release glucocorticoids.
• Luteinising hormone (LH): acts on the testis and the ovary. See below.
• Follicle stimulating hormone (FSH): acts on the testis and the ovary. See below.

TSH, ACTH, LH and FSH act on other endocrine glands. Books call them tropic hormones.

LH and FSH are called the gonadotropins, because they act on the gonads.

• In the male, LH stimulates the interstitial (Leydig) cells of the testis to make androgens. FSH and the androgens together regulate spermatogenesis, the making of sperm.
• In the female, LH induces ovulation, the release of the egg from a fully mature follicle. It also maintains the corpus luteum that forms from the remains of the follicle. FSH stimulates the growth and development of the ovarian follicles.

Hormones of the pars intermedia and the pars nervosa

• Melanocyte stimulating hormone (MSH) is made by the pars intermedia. It acts on the melanocytes, the pigment cells, and regulates the pigmentation of the skin.
• Oxytocin acts on the smooth muscles of the body and makes them contract vigorously. In a woman it acts on the muscles of the uterus during childbirth, and it causes the ejection of milk from the mammary glands.
• Vasopressin acts mainly on the kidney. It stimulates the reabsorption of water and electrolytes by the distal tubules, so less water is lost in the urine. Its other name is antidiuretic hormone (ADH). A diuretic makes you pass more urine, so an antidiuretic does the opposite.

When the pituitary goes wrong

A child with pituitary dwarfism has a small body, but the mind develops normally. A child with cretinism, which comes from the thyroid, has stunted growth and a mind that does not develop. Do not mix them up.

In diabetes insipidus the word diabetes comes from a Greek word for a siphon, a tube that passes fluid. "Insipidus" means tasteless: the urine is dilute and has no sugar. In diabetes mellitus the urine is sweet. You will meet it in the second course.

You should find that the urine volume is about 1.8 L when ADH is at its normal level and about 18 L when ADH is absent. This is why a person with diabetes insipidus is always thirsty. NCERT does not give these figures for the model. It says that the kidneys reabsorb most of the 180 L of filtrate. The model uses the share taken back by the last parts of the nephron to show the idea.

Try it in Python

The program looks up the hormones of the pituitary that act on one target.

Practise with new numbers

Common mistakes

• Saying that acromegaly is a disease of children. Too much growth hormone in a child gives gigantism. In an adult it gives acromegaly.
• Mixing up pituitary dwarfism and cretinism. The first comes from too little growth hormone, the second from too little thyroid hormone.
• Saying that vasopressin makes the body lose water. It does the opposite. It is the antidiuretic hormone.
• Putting MSH in the posterior pituitary. It comes from the pars intermedia.
• Saying that LH and FSH act only in women. They act in both sexes.

Remember these

• The pituitary has the pars distalis (GH, PRL, TSH, ACTH, LH, FSH), the pars intermedia (MSH) and the pars nervosa (oxytocin, vasopressin).
• TSH, ACTH, LH and FSH act on other endocrine glands.
• Excess GH: gigantism in a child, acromegaly in an adult. Too little GH in a child: pituitary dwarfism.
• Vasopressin (ADH) makes the distal tubules reabsorb water. Lack of ADH gives diabetes insipidus.

Check yourself

Try each one on your own first. If you are stuck, open a hint. Then check with Show the answer.

1. Name the six hormones of the pars distalis.

2. Which hormone makes the thyroid release its hormones, and which makes the adrenal cortex release its hormones?

3. What is the work of LH in a woman and of FSH in a man?

4. What is the other name of vasopressin, and what does it do?

5. A woman has an enlarged jaw and thick hands and feet. Which hormone is too high, and what is the disorder?

References

• Betts J. G. et al. (2022). Anatomy and Physiology 2e, OpenStax, chapter 17, The Endocrine System.
• Hall J. E. and Hall M. E. (2021). Guyton and Hall Textbook of Medical Physiology, 14th edition, Elsevier, the chapter on the pituitary hormones and their control by the hypothalamus.
• NCERT (2023). Biology, Textbook for Class XI, chapter 19.