Anterior Pituitary Gland Hormones

Releasing and Inhibiting Hormones

The hypothalamusA small but vital brain region controlling hormones, temperature, and autonomic functions. controlsVariables that remain constant to ensure a fair test. the anteriorThe front of the body or toward the front when standing in the anatomical position. pituitary by releasing hormonesHypothalamic hormones that regulate pituitary gland secretions. into the hypophyseal portal systemBlood vessel network connecting hypothalamus to anterior pituitary.. These hormones, such as releasing hormones like thyroid-releasing hormone(TRH): Stimulates TSH and PRL release. or inhibiting hormones, regulate the anterior pituitary. For example, the hypothalamus releases growth hormone-releasing hormone(GHRH): Stimulates GH secretion.. It also releases growthAn increase in size and number of cells. hormone-inhibiting hormone. These hormones regulate growth hormone(GH): Stimulates growth and metabolism. secretionThe process of moving substances from the blood into the nephron tubule to be excreted in urine. by the anterior pituitary. The anterior pituitary produces hormones like ACTH (adrenocorticotropic hormone(ACTH): Stimulates adrenal cortex to release corticosteroids.) and TSH (thyroid-stimulating hormone (TSH): Stimulates thyroid hormone production.). It also produces reproductive hormones FSH (follicle-stimulating hormone) and LH (luteinizing hormone(LH): Triggers ovulation and testosterone production.). These hormones act on the gonads.

TSH Thyroid-stimulating Hormone

Thyroid-stimulating hormone (TSH), also known as thyrotropin, is produced by the anterior pituitary glandEndocrine gland at the brain’s base controlling many hormones.. It acts upon the follicular cellsCells surrounding the oocyte that support its development. in the thyroid gland Endocrine gland regulating metabolism through thyroid hormones.. It is released in response to thyrotropin-releasing hormone (TRH) from the hypothalamus. TSH stimulates the follicular cellsThe basic structural and functional units of life. of the thyroid gland to secrete T3 and T4 into the colloidA mixture where small particles are dispersed but not dissolved in a liquid.. At the same time, it releases T3 and T4 from the colloid.  TSH also promotes the growth of the thyroid gland. It ensures there are enough follicular cells to generate the T4 and T3 that the systemic tissues require.  T3 and T4 are collectively known as the thyroid hormone (TH): Includes T3 and T4, regulating metabolism. (TH).  This hormone affects all cells in your body with nucleiClusters of neurons in the CNS responsible for processing information. and mitochondria.  Sooo…all your cells except red blood cells.  The thyroid hormone and its effects on these items here are discussed in another minilecture.

The secretion of TSH is tightly controlled by a feedback loop involving thyroid hormones. When T3 and T4 levels are sufficient, they inhibit the release of TRH and TSH, maintaining a balance. Low levels of thyroid hormones, however, stimulate increased TSH production to restore normal function.

PRL
Prolactin

Prolactin is a hormone produced by the anterior pituitary gland. Its primary role is to stimulate milk production in the mammary glands after childbirth. During pregnancy, prolactin(PRL): Promotes milk production. contributes to the growth and developmentThe process of growth and differentiation. of mammary glands in preparation for lactation.

Prolactin helps regulate reproductive health by suppressing ovulationThe release of a mature oocyte from the ovary. in nursing mothers.

The hypothalamus secretes dopamineA catecholamine neurotransmitter involved in motor control, motivation, and reward., which suppresses prolactin release. This keeps prolactin levels low under normal conditions. During pregnancy and nursing, higher levels of estrogen decrease dopamine levels. Additionally, the baby’s suckling reflex further reduces dopamine. These changes lead to increased prolactin secretion. Milk production itself doesn’t directly inhibit prolactin, but if milk isn’t removed (e.g., the baby stops nursing), prolactin secretion decreases over time.

ACTH
Adreno
Cortico
Tropic
Hormone

ACTH is released by the anterior pituitary gland in response to corticotropin-releasing hormone(CRH): Stimulates ACTH release. (CRH), from the hypothalamus.  Long-term, low level physical or emotional stress increases CRH secretion. The primary target of ACTH is the adrenal cortexOuter portion of the adrenal glands producing corticosteroids.. It specifically targets the zona fasciculataMiddle adrenal cortex layer, secreting glucocorticoids. and zona reticularisInner adrenal cortex layer, producing androgens. layers. These layers are discussed in more detail in the minilecture for the adrenal cortex.

Negative feedback from cortisolA glucocorticoid involved in stress response, metabolism, and immune regulation. regulates ACTH release; low cortisol triggers more ACTH, while high cortisol suppresses it.  We find that people have a natural fluctuation of ACTH, not necessarily a set set-point.  ACTH levels peak in the morning and decrease throughout the day, kinda like melatoninRegulates sleep-wake cycles..

LH and FSH
Luteinizing
Follicle-Stimulating

Reproductive hormones FSH and LH are also controlled by the hypothalamus.  The hypothalamus releases gonadotropin-releasing hormoneGnRH   A hormone from the hypothalamus that stimulates the release of FSH and LH. (GnRH) into the hypophyseal portal system to stimulate the anterior pituitary. These hormones act on the gonads to regulate reproductive functions. FSH influences folliclesStructures in the ovaries that contain developing oocytes. in the ovariesThe female gonads that produce eggs and hormones.. It also affects sperm production in the testes. LH is crucial for ovulation. It plays a key role in testosterone production.

GH Growth Hormone Release

Growth hormone (GH) can also be known as somatotropin. This word reflects its ability to promote growth in somatic tissues. Growth hormone secretion is regulated by the hypothalamus in the same way that the other anterior pituitary hormones are regulated.  The hypothalamus senses that GH levels are low and releases growth hormone releasing hormone into the hypophyseal portal system.  GHRH then travels to the anterior pituitary gland to stimulate the release of GH into systemic circulation.  When GH levels in the blood are high, the hypothalamus releases growth hormone inhibiting hormone or GHIH. This stops the release of GH into the blood.

An interesting note about GH is its unique interaction with IGF. This interaction is not shared with the other hormones of the APG.  GH can make your liverA large organ that produces bile, detoxifies blood, and stores nutrients. do many of the same things that insulin makes your liver do.  This makes GH a powerful anabolic steroid. GH stimulates the release of IGF from the liver. IGF increases the half-lifeTime for hormone levels to reduce by half. of GH, preventing it from being cleared from your blood.

Disorders of growth hormone include gigantism. It is caused by excess GH. Andre the Giant was a great wrestling icon of the 1980s. It was thought he was afflicted with this condition. However, he never sought treatment.  Pituitary dwarfism, characterized by insufficient GH is unlike endochondral dwarfism, which affects long bones. Pituitary dwarfism results in a proportionately small stature. It is much like the stature of the actor Vern Troyer. He played MiniMe in the Austin Powers franchise in the 1990s. 

GH Growth Hormone Effects

This hormone affects the liver, cartilageA flexible connective tissue found in joints, the ear, nose, and rib cage. Cartilage can be of three, and adipose tissue. In adipose tissue, it releases fatty acids. This increases energyThe capacity to do work or cause change. availability for cellular respirationThe process of gas exchange, including ventilation, external and internal respiration. and muscle growth. This process is called gluconeogenesis. In the liver, it stimulates glycogenA storage form of glucose found in animals. breakdown, called glycogenolysisBreakdown of glycogen into glucose., releasing glucoseA simple sugar that is the main source of energy for cells. into the blood. It also promotes skeletal muscle and cartilage growth by increasing myofibrils and supportive structures

To increase energy intake, ghrelinHunger hormone from the stomach. is released, often called the “hunger hormone,” encouraging food consumption. Meanwhile, a glucose-sparing effectGH and cortisol reducing glucose usage to save it for the brain. redirects the use of energy. The body taps into fatty acids stored in adipose tissue. This serves as an alternative fuel source. It conserves glucose for critical organs like the brain.  This is called gluconeogenesis.

In the liver, there is glycogenolysis where glycogen is broken down into glucose and released into the bloodstream. This helps maintain stable blood sugar levels, especially during periods of high energy demand.