Ch 18 Pituitary Gland

What percentage of AP cells are somatotropic and release growth hormone?

~50% of total secretory cells in the AP are for growth hormone secretion

What is a tropic hormone?

A tropic hormone has another endocrine gland as its target. Most tropic hormones are released and produced by the AP gland. 

What is a trophic hormone?

A hormone with specific growth effects on their target tissues. If a hormone stimulates any aspect of growth in a tissue, it is trophic.

What do corticotropes release in the AP gland?

these hormones secrete adrenocorticotropic hormone (corticotropin; ACTH)

What do thyrotropes release in the AP gland?

Thyroid-stimulating hormone (thyrotropin; TSH)

What do gonadotropes release from the AP gland?

Follicle-stimulating hormone and Luteinizing Hormone (FSH and LH)

What do mammotropes/ lactotropes release from the AP gland?

Prolactin (PRL)

What do somatotropes release from the AP gland?

Growth hormone (Somatotropin; GH)

What is the function of Adrenocorticotropin (ACTH)?

stimulates the production of glucocorticoids and androgens in the adrenal cortex; maintains the size of the zona fasciculata and zona reticularis of the adrenal cortex

What is the function of TSH?

stimulates the production of thyroid hormones, T4 and T3, by thyroid follicular cells; maintains size of follicular cells

What is the role of FSH?

stimulates development of ovarian follicles and regulates spermatogenesis in the testis

What is the role of LH?

• causes ovulation and formation of corpus luteum

• stimulates production of estrogen and progesterone in the ovaries

• stimulates testosterone production in the testis

What is the function of PRL?

essential for milk production by lactating mammary glands

What is the function of growth hormone/ somatotropin?

Stimulates post-natal body growth

Stimulates secretion of IGF-1

stimulates triglyceride lipolysis

inhibits actions of insulin on carbohydrate and lipid metabolism

What is POMC?

Pro-opiomelanocortin is a large precursor protein that is cleaved to form various hormones. A signal peptide is cleaved, resulting in POMC. 

What hormones are produced from POMC hydrolysis?

ACTH (as well as small amounts of B-endorphin)

What percent of circulating growth hormone is in the bound/ inactive form?

~50%

What role does the JAK2-STAT pathway play in growth hormone responses?

Growth hormone binds to membrane receptors that are bound to JAK2 proteins. The JAK-STAT pathway results in increased gene transcription in triggered cells. 

What effect does growth hormone have on adipose tissue?

• decreased glucose uptake

• increased lipolysis

Results in an increase in FFAs and decreased adiposity

What effect does growth hormone have on the liver?

• increased RNA synthesis

• Increased protein synthesis

• Increased gluconeogenesis

• Increased release of somatomedin (IGF-1)

What effect does growth hormone have on muscle?

• decrease glucose uptake

• increased amino acid uptake

• increased protein synthesis

increase overall lean muscle mass

What effect do IGFs have on the heart, bone, and lungs?

• increased RNA synthesis

• increased protein synthesis

• increased DNA synthesis

• Increase in cell number and size

Overall increase in organ size and function

What effect do IGFs have on chondrocytes (joints)

• increased RNA/DNA synthesis

• increased amino acid uptake/ protein synthesis

• increased cell size and cell number

overall increase in linear bone growth in unfused bones.

What factors stimulate GH release?

• amino acid increase (arginine)

• Fasting or prolonged caloric deprivation

• Physical stress

• exercise

• puberty

• Sleep

• GHRH

Sleep is a major stimulatory factory of GH release

What factors inhibit GH release?

• somatostatin (GHIH)

• glucose increase

• cortisol

• FFA increase

• Somatomedins (IGFs)

• Growth Hormone (GH)

• Senescence 

Describe the growth hormone regulation pathway?

The hypothalamus releases Growth Hormone Releasing Factor, which stimulates GH release from the AP, which triggers release of IGF-1 from the liver.

IGF-1 inhibits further release of GH from the AP. GH also inhibits subsequent release of more GH. 

IGF-1 stimulates release of somatostatin from the hypothalamus, which inhibits GH release.

What are the two periods of rapid growth in humans?

• post-birth rapid growth occurs as a continuation of the fetal growth period

• During puberty due to growth hormone, androgens and estrogens increasing in concentration. 

What is the different between hypothyroid dwarfism and dwarfism?

• hypothyroid dwarfism displays infantile body proportions

• constitutional dwarfism displays body proportions more consistent with biological age

What is gigantism?

A condition diagnosed when a child displays high levels of growth hormone. The effects of this condition appear in early childhood and continue until the growth plates fuse.

What is acromegaly?

Occurs due to GH hypersecretion in adults, leads to large extremities and facial bones

can occur due to a tumor or growth hormone abuse

What is the function of prolactin?

• lactation, breast development

• causes milk secretion but only after estrogen and progesterone priming. 

• Prevents ovulation while lactating

What is the result of excess prolactin in males?

erectile dysfunction can occur as a result of excess prolactin

What increases secretion of prolactin?

• exercise

• surgical/physiological stress

• nipple stimulation

What is the primary regulator of prolactin?

Prolactin Inhibitory Hormone, released from the hypothalamus.