The pituitary gland is a pea-sized structure located in the base of the brain responsible for secreting a variety of hormones.
These hormones are either directly or indirectly controlling the metabolic activities of the body and other functions.
Anatomy and physiology of the pituitary gland
The pituitary gland has two distinct structures. Anterior pituitary and the posterior pituitary. The posterior pituitary is basically an extension of the hypothalamus.
The anterior pituitary is anatomically and functionally different from the posterior pituitary gland. The anterior pituitary produces different hormones.
The most important hormones produced by the anterior pituitary are adrenocorticotropic (ACTH) hormone, Thyroid stimulating hormone, growth hormone, luteinizing hormone, follicle stimulating hormone, and prolactin.
The posterior pituitary produces Oxytocin and ADH or anti-diuretic hormone.
What are the functions of each of these Pituitary gland hormones?
ACTH or Adrenocorticotropic hormone
ACTH or adrenocorticotropic hormone is responsible for activating the adrenal gland to produce cortisol.
The adrenal gland which is located at the superior pole of the Kidneys has an outer and an inner part called the cortex and medulla respectively.
The adrenal medulla produces hormones which are specifically activated during times of stress (the fight, fright or flight response). The cortex produces aldosterone primarily responsible for salt retention and maintaining blood pressure, cortisol and sex steroids.
To produce cortisol, ACTH stimulates the adrenal gland. The absence of ACTH has minimal direct effects on the body. Cortisol mediates most of the effects of ACTH.
An absence of cortisol leads to a lowering of blood pressure since cortisol has salt-retaining properties. This is initially manifested by dizziness (postural hypotension) and at times the patient may present with shock.
Low cortisol also causes hypoglycemia (low blood sugars), hyponatremia (low salt in the body), anorexia (loss of appetite) vomiting and abdominal pain.
The patients may not manifest these features normally but in situations of stress where cortisol production needs to be high in the body, these symptoms may then be manifested.
Thyroid stimulating hormone
The thyroid stimulating hormone is responsible for stimulating the thyroid gland which produces thyroxine.
When thyroid stimulating hormone is absent thyroid gland is no more stimulated and thyroxine levels in the body decline. This is called as Central hypothyroidism or secondary hypothyroidism.
Manifestations of primary and secondary hypothyroidism are almost the same since both the conditions have low thyroxine in the body.
Thyroxine is the main metabolic hormone in the body. Low thyroxine in the body will cause all the metabolic processes to slow down and patient main present with fatigue, lethargy, weight gain, accumulation of excess fluid in the body, hypothermia or decrease body basal body temperature.
Stunted growth and low IQ is especially worrisome in children. The hair may become coarse and dry, the voice becomes husky, the tongue enlarges and may cause obstructive sleep apnea and snoring may be present.
Other manifestations include pericardial effusion which is the accumulation of fluid around the heart, pleural effusion (accumulation of fluid in the pleural cavity or around the lungs) and ascites is the accumulation of fluid in the abdominal cavity.
Patients may present with infertility and loss of libido. Female patients may have menorrhagia or heavy and frequent menstrual cycles.
Other manifestations include anemia and carotenemia which is the yellowish discoloration of the sclera in the absence of Jaundice.
Patients may also present with weakness of the muscles called as proximal myopathy which is manifested by difficulty in getting up from squatting position or climbing up stairs.
Growth hormone as the name suggests is responsible for physical growth. This is especially important in patients less than 18 years of age when growth hormone levels in the body are the highest.
So a deficiency of growth hormone will lead to short stature in patients less than 18 years of age. In elderly and adult patients, deficiency of growth hormone causes a reduction in lean body mass, makes the person vulnerable to cardiovascular diseases and increases cholesterol in the body.
Elderly patients may also present with fatigue, low mood, lethargy, and obesity.
Gonadotropins, LH, and FSH.
The pituitary gland also produces Gonadotropins. These hormones include the LH (luteinizing hormone) and FSH (follicle stimulating hormone).
The LH is responsible for secreting testosterone in males and estradiol in females why the FSH is responsible for spermatogenesis and follicle maturation.
The absence of LH and FSH can cause secondary hypogonadism also called hypogonadotropic hypogonadism. Patients with secondary hypogonadism may present similarly to patients with primary hypogonadism.
In females, these features include amenorrhea (absent menstrual cycles), oligomenorrhea (infrequent menstrual cycles) and infertility.
Males may present with erectile dysfunction, loss of libido and infertility. Both genders may have absent secondary sexual characteristics if gonadotropins are deficient before puberty.
Sex steroids are also responsible for epiphyseal closure in patients who are less than 18 years of age so patience with testosterone or estradiol deficiency is tall.
These hormones also cause the bones to strengthen so the deficiency of these hormones can indirectly lead to osteoporosis. Low testosterone also reduces muscle strength and energy in both genders.
Prolactin is responsible for milk production in pregnant and lactating females. A patient with low prolactin levels may present with an inability to lactate her baby after delivery.
The posterior pituitary hormones:
ADH on anti-diuretic hormone:
ADH is responsible for maintaining fluid and sodium balance in the body. The absence of ADH will lead to diabetes insipidus.
The word “diabetes” means excessive urination while “insipidus” means tasteless. This is a condition in which the patient has normal blood sugars but passes a lot of urine. The twenty-four-hour urine usually exceeds three liters.
Diabetes insipidus can be central or nephrogenic. Central diabetes insipidus is due to a deficiency of anti-diuretic hormone while nephrogenic diabetes insipidus develops when the kidneys do not respond to ADH action.
Patients with diabetes insipidus may develop dehydration and hypernatremia owing to loss of free water from the body.
Oxytocin is responsible for the contractile activity of the uterus during labor. It also acts on the uterine muscles after delivery to minimize bleeding and keep the uterus back in its normal pre-pregnant state. Oxytocin also mediates smooth muscle contraction of the breasts during lactation.
These are functions of the major hormones of the pituitary gland. Disorders of these hormones will be discussed later.
Pituitary gland hormones are the primary controller hormones that indirectly influence body metabolism by increasing or decreasing the production of other hormones.