The Hypothalamus-Hypophysis Axis Flashcards

Question

Physiological Effects of the Growth Hormone: Indirect:

Answer 1

Mediated primarily by insulin-like growth factor (IGF-1). The majority of the growth promoting effects of GH is due to IGF-I acting on its target cells. The effect of GH on the liver is to produce a number of Somatomedins or growth factors , i.e., IGFs. The actions of GH are mediated mainly through IGF1→ stimulate growth in bone, protein synthesis in muscle and lipolysis of fat.

Answer 2

GH has important effects on protein, lipid and carbohydrate metabolism, as well as widespread effects on various body tissues. Examples: cartilage, bone, muscle, and adipocytes GH exerts much of its effect through intermediate substances called “Somatomedins” (also called “Insulin Like Growth Factors” (IGF)) → similar to the effects of insulin on growth . GH causes the liver to form several small proteins called somatomedins that have the potent effect of increasing all aspects of bone growth. Somatomedin C is also called insulin-like growth factor 1 (IGF-1)

Answer 3

1. Increase Protein synthesis and Deposition 2. Increase Lipolytic and Ketogenic effect 3. Decrease utilization of Carbohydrates for energy production

Answer 4

Adequate insulin and carbohydrates are necessary for GH to be effective. Increase amino acid transport inside cells →Increase protein accumulation in all cells. Increase DNA transcription to form mRNA → Increase protein synthesis. Increase RNA translation → Increase protein synthesis.

Answer 5

Increases mobilization and use of fatty acids for supplying energy. Excess GH → excessive mobilization of fat from the adipose tissue → ketosis (large quantities of aceto-acetic acid are formed by the liver and released into the body fluids - “Ketogenic Effect).

Answer 6

GH is one of the hormones that serves to maintain blood glucose within a normal range: Increase uptake of glucose by cells → Increase blood glucose (diabetogenic effect). Decrease use of glucose for energy production due to increased utilization of fatty acids for energy. It inhibits hexokinase enzyme → inhibits glucose uptake by muscles (opposite to insulin effect). Increase hepatic glucose output (stimulates glycogenolysis). Increase insulin output → burn out of beta cells of pancreas. The above GH effects contribute to hyperglycaemia → INCREASE insulin secretion (hyperinsulinemia).

Answer 7

In adolescents: (before union of epiphysis) GH stimulates chondrogenesis (proliferation of epiphyseal cartilage and widening of epiphyseal plates). Stimulation of osteoblasts → increase bone matrix → increase length of long bones. In adults: (after union of epiphysis) linear growth is impossible.

Answer 8

NB: Growth requires the coordinated action of several hormones. The major role of GH in stimulating body growth is to stimulate the liver and other tissues to secrete IGF-I. IGF-I stimulates proliferation of chondrocytes (cartilage cells), resulting in bone growth. Insulin-like growth factor I (somatomedin C) → Increase's growth promoting activities in many tissues and cartilage with a prolonged duration of action (20 hours). GH stimulates the liver and other tissues to secrete IGF-I. IGF-I stimulates differentiation and proliferation of chondrocytes (cartilage cells), resulting in bone growth. IGF-I is also a key player in muscle growth→ It stimulates both the differentiation and proliferation of myoblasts.

Answer 9

Growth Hormone Deficiency Growth Hormone Defect

Answer 10

Due to pituitary defect or hypothalamic dysfunction: - Hyposecretion of GH in child is one cause of dwarfism - Deficiency in adults produces relatively few symptoms

Answer 11

Most often caused by tumor of GH-producing cells of anterior pituitary Symptoms depend on age of individual when abnormal secretion begins Gigantism: Caused by overproduction of GH in childhood before epiphyseal plates close Acromegaly: Occurs when GH hypersecretion occurs after adolescence

Answer 12

Idiopathic GH deficienc: -Lacks hypothalamic GHRH Pituitary tumors -Cannot produce GH Dwarfism: -Inadequate secretion of GH during childhood. - Laron-type dwarfism: - Hereditary defect in IGF production

Answer 13

Gigantism: -Excess GH secretion in children-Maintain normal body proportions. Acromegaly: *Excess GH secretion in adults after the epiphyseal discs are sealed-No increase in height. *Growth of soft tissue-Elongation of jaw, deformities in hands, feet, and bones of face.

Answer 14

``` • Achondroplasia • Levi – Lorain dwarfism • Psychogenic Dwarfism • Spondyloepiphyseal dysplasia congenita • Diastrophic Dysplasia • Campomelic Dysplasia • dystrophia adiposogenitalis • Hypophosphatemia • Hallerman-Streiff Syndrome • Cartilage Hair Hypoplasia (CHH) • Robinow dwarfism/syndrome • Turner Syndrome • Panhypopituitarism ```