S2 L3 Physio

Anterior Pituitary Hormones

• Anterior pituitary hormones are crucial for various bodily functions
• Thyrotropin stimulates the thyroid gland
• Growth hormone (GH) increases blood glucose and promotes insulin secretion
• Corticotropin stimulates the adrenal cortex
• Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) affect the ovaries and testes
• Prolactin stimulates the mammary glands

Growth Hormone

• Growth hormone (GH), also known as somatotropin, is a peptide hormone
• Essential for bone growth
• Produced by somatotrophs in the anterior pituitary gland
• Structurally similar to prolactin
• Acts with insulin-like growth factor 1 (IGF-1) to stimulate bone and muscle growth
• Stimulates amino acid uptake, protein synthesis, DNA/RNA synthesis, and chondroitin sulfate/collagen production to increase cell size and number

Growth Hormone Regulation

• GHRH (growth hormone releasing hormone) stimulates GH release
• Somatostatin inhibits GH release
• Hypoglycemia, sleep, and stress stimulate GH release
• IGF-1 levels regulate GH release
• Aging and obesity inhibit GH release

Clinical Correlation Growth Hormone

• Clinically, IGF-1 is measured when evaluating GH deficiency or excess
• IGF-1 levels are more stable than GH fluctuations
• GH is released in pulses

Growth Hormone Action on Bones

• GH and IGF-1 stimulate linear bone growth at the epiphyseal plates
• Epiphyseal plates fuse by ages 18 (females) and 20 (males), ceasing linear bone growth

Growth Hormone Action on Muscles

• GH and IGF-1 stimulate skeletal muscle growth
• This occurs through myocyte hypertrophy (muscle cell enlargement) and increased protein synthesis

Increasing Serum Glucose

• GH and IGF-1 increase serum glucose concentration
• This is due to hepatic gluconeogenesis, lipolysis and lipid oxidation, and antagonism of insulin action.
• GH is believed to optimize the body for athletics by increasing blood sugar for muscle and bone building and increasing lipolysis for fat reduction.

Prolactin

• Prolactin is a peptide hormone produced by lactotrophs in the anterior pituitary
• Structurally similar to growth hormone
• Produced in the anterior pituitary
• Can also be produced by extra-pituitary tissue

Prolactin Function

• Known as the "milk hormone" due to its role in stimulating and enlarging the mammary glands for milk production
• Plays regulatory roles in reproduction, nerve formation, and fetal development.
• It affects tissues by binding to prolactin receptors.
• Acts indirectly on the gonads, influencing estrogen and testosterone production

Prolactin Regulation

• Dopamine is a key negative regulator of prolactin secretion
• Prolactin inhibits GnRH and thus FSH and LH production
• Nipple stimulation, estrogen, and thyrotropin-releasing hormone stimulate prolactin production
• Progesterone inhibits prolactin at the peripheral receptor levels

Clinical Correlation Prolactin

• Dopamine-increasing drugs, and antipsychotics and mood stabilizers affect prolactin levels
• Elevated prolactin levels are linked to amenorrhea (absence of menstruation) and infertility in women.

Prolactin in Pregnancy

• Prolactin is present at high, steady levels during pregnancy and breastfeeding
• Continuous elevated levels and inhibition by dopamine create a "reservoir" for prolactin release when needed

Dwarfism

• Results from a generalized deficiency of anterior pituitary hormone secretion before puberty, causing stunted growth
• Individuals may appear much younger than their actual age
• Some types have deficiency in gonadotropin and may not reach puberty
• One subtype has normal or high GH but lacks somatomedin C production

Gigantism

• Resulting from excess GH secretion before puberty
• Characterized by extreme height growth (exceeding 8 feet)
• Often associated with hyperglycemia and diabetes

Acromegaly

• Excess GH secretion after puberty
• Leads to enlarged features like hands, feet, jaw, and nose (cranial and supra-orbital bone growth).
• Can cause kyphosis (humped back)
• Increased organ size (e.g., kidney, liver, heart, tongue).

Learning Objectives (Growth Hormone)

• Identify GH synthesis and production sites
• Describe GH cellular binding and physiological actions
• Explain GH release regulation by anterior pituitary
• Describe prolactin cellular binding and physiological actions -Describe prolactin release regulation

Learning Objectives (Prolactin)

• Describe prolactin synthesis and production sites
• Identify prolactin cellular binding and physiological actions
• Describe prolactin release regulation