What is Pituitary Gland?
What is Pituitary Gland?The pituitary gland is an endocrine gland that serves to maintain cellular homeostasis in the body by releasing various hormones.
- The pituitary gland is also known as the master gland because it controls the work and secretion of other endocrine glands.
- Although the main endocrine gland, the pituitary gland is controlled by secretions from the hypothalamus. The pituitary gland is connected to the hypothalamus of the brain by a single stalk called the infundibulum.
- The word “pituitary gland” is derived from the Latin word “pituta”, which means slime or mud.
- This gland is located behind and above the sphenoid sinus in a depression called the sella turchisia.
- Structurally, the pituitary gland is divided into two distinct parts; Anterior and posterior pituitary lobes. The anterior pituitary lobe is the part of the gland called the adenohypophysis, while the posterior pituitary lobe is made up of nerve tissue called the neurohypophysis.
- Between the two pituitary lobes is a small avascular region called the pars intermedia that is functional in some animals but underdeveloped in humans.
- The two lobes of the gland have different embryonic origins; The anterior pituitary lobe comes from the Rathke’s sac present in the Rathke epithelium, while the posterior pituitary lobe comes from the outgrowth of nerve tissue in the hypothalamus.
- The anterior lobe of the pituitary makes up most of the pituitary gland and releases about six different peptide hormones. The posterior lobe of the pituitary takes in a small amount and releases two peptide hormones.
- The anterior pituitary hormones are secreted within the lobe because it is made up of glandular tissue. The posterior lobe of the pituitary hormones comes from the hypothalamus, and the lobe acts as a hormone store.
- The pituitary gland is in close association with the hypothalamus, and the organs interact with each other through the pituitary portal system. The portal system is essential for the release and transport of even small amounts of hormones from the hypothalamus to the pituitary gland.
Structure of the pituitary gland
- The pituitary is a small pea-sized gland at the base of the skull that is usually located in a bony structure below the hypothalamus.
- The gland is also called the pituitary gland to indicate that the gland is under the brain.
- This nerve is connected to the hypothalamus by a short stalk made of axons and veins. The weight of the gland is around 500-900, depending on the age and physical condition of the individual.
- Typically, the pituitary gland consists of three different lobes; Anterior lobes, posterior lobes, and intermediate lobes.
- As in humans, the intermediate lobe does not exist as an independent anatomical structure but remains as part of the anterior pituitary lobe.
- The two glandular lobes differ in their functions, anatomical structures, and their embryonic origin.
- The anterior pituitary lobe consists of epithelium in which cells perform secretory functions.
- The posterior lobe of the pituitary gland consists of neurons that do not secrete their hormones, but rather serve as hormone stores.
- The anterior pituitary contains five different types of cells, each of which secretes a different hormone. Most of the space in the anterior pituitary is covered by somatotrophs.
- Although the posterior pituitary lobe has no secretory units, hormones are brought into this region for activation.
- In the posterior lobe of the pituitary gland, hormone precursor proteins are broken down to make hormones.
The anterior pituitary secretes six different hormones, the posterior pituitary two hormones.
1. Growth Hormone
- Growth hormone is produced by the somatotropic cells of the anterior lobe. Thus growth hormone is also called somatotropin.
- The hormone is an anabolic or tissue-building hormone that has metabolic and growth-inducing functions.
- Growth hormones exert a wide range of direct and indirect effects on metabolism and other cellular functions.
- Growth hormone is responsible for the deposition of fat in the body by increasing the level of fatty acids. Growth hormone from the pituitary also affects the breakdown of glycogen and the release of glucose into the blood.
- The hormone is also involved in growth-promoting effects by forming a group of growth-promoting proteins called insulin-like growth factors.
- These proteins affect cell division and differentiation in organs such as the liver, skeletal muscle, bones and connective tissues.
- The secretion of growth hormone by the anterior pituitary is controlled by two hypothalamic hormones; Growth hormone-releasing hormone and growth hormone-inhibiting hormone.
2. Thyroid Stimulating Hormone
- Thyroid-stimulating hormone is a hormone that stimulates the development of the thyroid gland and the secretion of thyroid hormones. The hormone is tropic and is also called thyrotropin.
- As in the case of growth hormone, the activity and secretion of the thyroid-stimulating hormone are influenced by a thyrotropin-releasing hormone from the hypothalamus.
- In addition, the growth hormone-inhibiting hormone of the hypothalamus also affects the activity of this hormone.
- The release of regulatory hormones, in turn, is controlled by thyroid hormone levels in the blood.
3. Adrenocorticotropic Hormone
- Adrenocorticotropic hormone or ACTH secreted by the anterior pituitary controls the release of adrenocortical hormone by the adrenal gland.
- The hormone is secreted by corticotropic cells as a prohormone or precursor molecule.
- The most important function of the hormone is the activation of the adrenal cortex for the release of glucocorticoids.
- The release of ACTH is controlled by the hypothalamic corticotrophin-releasing hormone. The hormone is released in a diurnal rhythm where levels are highest in the morning and decrease during the night.
- The gonadotropin hormones secreted by the anterior pituitary include two important hormones; Luteinizing hormone and follicle-stimulating hormone.
- Both hormones are essential for stimulating the gonads in both men and women.
- The follicle-stimulating hormone (FSH) is responsible for the production of gametes, while the luteinizing hormone (LH) controls the production of gonadal hormones.
- The role of FSH and LH in women is extended to regulate the ovarian cycle and release ovarian hormones.
- In men, LH also stimulates the testes to produce the male sex hormone testosterone.
- Gonadotropins are released in small amounts before puberty; However, the concentration of these hormones in the blood increases during puberty.
- During puberty, the gonadotropic cells of the anterior pituitary mature to increase gonadotropin levels in the blood.
- The release of these hormones is controlled by the gonadotropin-releasing hormone released by the hypothalamus. In addition, increased levels of gonadal hormones suppress the release of these hormones.
- Prolactin is secreted by the prolactin cells of the anterior pituitary gland and is responsible for stimulating the mammary glands to produce milk.
- The hormone is also produced in men, but its role in men is not yet understood.
- The release of prolactin, unlike other pituitary hormones, is controlled by a prolactin-inhibiting hormone, also known as dopamine.
- Oxytocin is one of two hormones secreted by the hypothalamus and the posterior pituitary gland.
- The main function of oxytocin is to stimulate uterine contractions during childbirth. The end of pregnancy increases the number of oxytocin receptors on the uterine wall, making the smooth muscles of the uterine wall sensitive.
- In addition, oxytocin, also known as the milk expectoration hormone, is produced in women who produce milk in response to prolactin.
- Sucking on the nipples triggers a reflex-induced release of oxytocin that targets specialized myoepithelial cells of the mammary glands.
- Oxytocin is produced in the hypothalamus as a neurotransmitter that is involved in sexual and loving behaviors such as cuddling, caring, and bonding.
- Oxytocin drugs, both natural and synthetic, are given during labor or delivery to speed up the process.
7.Antidiuretic hormone (ADH)
- Antidiuretic hormone is the second hormone found in the posterior lobe of the pituitary gland that controls urine production.
- The hormone is responsible for maintaining the water balance and prevents dehydration and water overload in the body.
- The hormone is released from the hypothalamus under the influence of osmoreceptors, which monitor the level of solutes in the blood.
- When solute levels increase in the blood, osmoreceptors send excitatory signals to the hypothalamus to release ADH.
- ADH targets the collecting and collecting ducts of the nephron in the kidney, which causes them to reabsorb water and release more solutes into the urine.
Diseases and Disorders of Pituitary Gland
The disorders and diseases associated with the pituitary gland are usually due to the hypersecretion or hyposecretion of the hormones.
The following are some of the disorders associated with the pituitary gland and its secretions;
- Gigantism is observed in children due to the excess of the growth hormone, causing the epiphyseal cartilages of long bonds to keep growing.
- Gigantism is the most prominent in the bones of the limbs and extremities, where an individual can grow up to 2.1 to 2.4 m in height.
- The increased secretion of growth hormone from the anterior pituitary is due to the excess release of growth hormone-releasing hormone by the hypothalamus.
- It might even cause enlargement of the internal organs and the formation of excess connective tissue mass in the body.
- Even though gigantism results in abnormally large limbs, the body proportions remain normal.
- Acromegaly is similar to gigantism except that the increased secretion of growth hormone takes place after bone ossification.
- The condition is characterized by abnormally thick bones along with the thickening of soft tissues.
- Acromegaly is most prominent on the facial bones in the form of excessive growth of the lower jaw and enlarged tongue.
- Unlike gigantism, the body of the individual doesn’t remain proportional.
- 3. Ischemic necrosis
- Ischemic necrosis is a condition caused due to the hypofunction of the anterior pituitary and the deficiency of hormones.
- Usually, intense hypotensive shock results in ischemic necrosis, which can be characterized by effects like deficient stimulation of the target glands and deficiency of the respective hormones.
- The overall effect of the condition depends on the degree of pituitary necrosis and the extent of hormone deficiency in different glands.
4. Pituitary dwarfism
- Pituitary dwarfism is caused by a deficiency in growth hormone and other hormones of the anterior pituitary gland during childhood.
- A person’s body is smaller than normal, but the body is usually proportionate. The cognitive and behavioral development of the individual remains unaffected.
- If the deficiency is followed by a gonadotropin hormone deficiency, puberty is delayed, which affects the reproductive health of the individual.
- The condition arises from a lack of growth-stimulating hormone from the hypothalamus.
5. Frölich syndrome
- This condition is caused by the pituitary gland, which is characterized by a decreased release of all pituitary hormones.
- Boo status is most commonly seen with a deficiency in growth hormone, follicle-stimulating hormone, and luteinizing hormone.
- Some common traits are low growth, delayed sexual development, and obesity in women. Some people may also develop learning difficulties.
- The main cause of the disease is often associated with tumor formation in the anterior pituitary gland or hypothalamus, but in many cases, the cause is known.
6. Diabetes insipidus
- Diabetes insipidus is a rare condition caused by hyposecretion of antidiuretic hormone by the posterior lobe of the pituitary gland.
- The most common cause of this condition is the failure of the kidney tubules to respond to hormones.
- The lack of hormones prevents water from being absorbed in the renal tubules, resulting in diluted urine.
- The condition can lead to severe dehydration if not ingested the correct amount of water to maintain water balance.
7. Pituitary adenoma
- One of the most common diseases of the pituitary gland is pituitary adenoma. In this condition, tumors are seen in the vein area of the gland.
- Tumors are divided into microadenomas (size under 10 mm) and macroadenomas (size over 10 mm).
- Large tumors can compress other organs in the area and cause other serious diseases.
- These are usually asymptomatic or have a mild headache.
What is Pituitary Gland? Structure, Pituitary hormones