L3-Anterior Pituitary Hormones

Anterior Pituitary Hormones

Growth hormone (GH)

Thyroid-stimulating hormone (TSH)

Adrenocorticotropic hormone (ACTH)

Follicle-stimulating hormone (FSH)

Luteinizing hormone (LH)

Prolactin (PRL)

Growth Hormone (GH)

Synthesized by somatotrophs (somatotropic cells), regulates the growth of bone, muscle, and other body tissues.

It is structurally similar to prolactin

Growth hormone receptor

The growth hormone receptor (GHR) is a transmembrane protein.

When GH binds to GHR, this activates Janus kinase 2 (JAK2), triggering a cascade.

this stimulates the liver to synthesize and release insulin-like growth factor 1 (IGF-1)

Insulin-like Growth Factor 1 (IGF-1)

Acts as the mediator of growth hormone, promoting bone growth, cartilage maturation, and muscle protein synthesis.

Inhibits muscle protein breakdown and limits certain catabolic processes

rises steeply during puberty

Growth hormons and bones

GH acts directly on bone cells (osteoblasts).

and indirectly by triggering the production of IGF-1

GH stimulates cartilage cells (chondrocytes) in the growth plates (epiphyseal plates) of long bones, lengthening the bones.

At puberty the remaining cartilage is completely replaced by bone, forming a thin epiphyseal line. Once this closure happens, longitudinal bone growth stops and appositional growth starts.

Growth hormons and muscles

GH strengthens tendons, ligaments, and skeletal muscle collagen synthesis, which helps protect against injuries during heavy exercise.

It shifts the body toward burning fats (lipolysis) and regulating glucose

Growth hormons and serum glucose

counterregulatory (diabetogenic) hormone that generally raises serum glucose levels.

GH signals the liver to increase gluconeogenesis and glycogenolysis, promoting lipolysis

growth hormone regulations

1. Ghrelin: A peptide released by the stomach ,during starvation that binds to growth hormone secretagogue receptors (in the hypothalamus) to potently boost GHRH and GH secretion

2. Growth Hormone-Releasing Hormone (GHRH): A hypothalamic hormone that stimulates the anterior pituitary to synthesize and release GH

3. Autocrine Feedback: GH acts directly on the pituitary to help regulate its own secretion

4. Somatostatin (Growth Hormone-Inhibiting Hormone / SRIF): A hypothalamic hormone that suppresses and inhibits the release of GH

Dwarfism

Generalized deficiency of anterior pituitary hormone secretion

In one type of dwarfism (Lévi-Lorain dwarf), GH secretion is normal or high, but inability to form somatomedin C

Gigantism

Excess GH secretion.

Hyperglycemia

Acromegaly

occurs in adults after growth plates have fused. Instead of lengthening bones, it thickens bones and enlarges soft tissues and organs

Prolactin (PRL)

secreted by the anterior lobe of the pituitary gland; promotes milk secretion.

by specialized cells called lactotrophs.

It is structurally similar to growth hormone

Prolactin receptor

binding to Prolactin Receptors (PRLR), triggering signaling cascades like JAK/STAT.

STAT moves into the cell nucleus, turning on target genes responsible for milk protein synthesis

Prolactin physiological effects

-induce and maintain lactation

-decrease reproductive function

-suppress sexual drive

-enlarges and stimulates the mammary

-Enhances maternal nurturing behavior

Prolactin and sex hormons

High levels of prolactin suppress the release of gonadotropin-releasing hormone (GnRH).

This in turn lowers luteinizing hormone (LH) and follicle-stimulating hormone (FSH)

Suppressed LH and FSH lead to lower estradiol levels

Excess prolactin inhibits testosterone production

prolactin and Immune Effects

Promotes T cell activation

Prolactin suppresses the negative selection of B cells, making the immune system more likely to attack native cells (autoimmunity)

Prolactin regulation

1. Dopamine: Dopamine travels to the anterior pituitary via the portal system and binds to D2 receptors on lactotroph cells to shut down prolactin synthesis

2. Progesterone inhibits prolactin at the level of the peripheral receptor

3. Thyrotropin-Releasing Hormone (TRH): stimulates lactotrophs to secrete prolactin

4. Breastfeeding (Suckling Reflex)

5. Estrogen: High levels of estrogen upregulate lactotroph sensitivity and

Adrenocorticotropic hormone (ACTH)

Stimulates adrenal cortex to release cortisol.

Thyroid-stimulating hormone (TSH)

Stimulates thyroid gland to produce thyroid hormones

Follicle-stimulating hormone (FSH)

secreted by the pituitary gland to stimulate maturation of the egg cell (ovum)

Luteinizing hormone (LH)

causes ovulation; stimulates the secretion of progesterone; causes the secretion of testosterone