Endocrine control of growth and metabolism: Bridges

Question 1

List the hormones important for growth at key times in a person’s life.

Answer 1

Stage: Prenatal   Age: 9 months gestation 
Hormone Req: Insulin
--------------------------------------
Stage: Infant  Age: 0-1 yrs
Hormone Req'd: Insulin
--------------------------------------
Stage: Juvenile  Age: 1-12yrs
Hormone Req'd: GH, Insulin, T3, Vit. D
--------------------------------------
Stage: Adolescent  Age: 10-14 (F) 12-16 (M)
Hormone Req'd: GH, insulin, T3, Vitamin D
and Sex Steroids

Question 2

Describe the functions of human growth hormone on growth (bones and soft tissues), and on metabolism, and the regulation of its secretion. Explain what ’rhGH’ means.

Answer 2

Upon PKA action, GH is secreted from somatotrophs in the ant. pit.
GHRH—>GH release via Gs
Somatostatin —I GH release via Gi

The GH/IGF-1 axis functions to break down (catabolize) adipose for energy and build (anabolize) bone/muscle for bear combat.

Effects on metabolism: Increase liver glycogenolysis, gluconeogenesis, and adipose lipolysis. Inhibits glycogenesis.

rhGH is recombinant human growth hormone. It is the form of growth hormone that is administered to pts that have a GH deficiency. It is made by growing it in genetically modified yeast or bacteria.

Question 3

State the “dual effector hypothesis” for GH actions, and the relative roles of GH and IGF-1 in growth control.

Answer 3

Both GH and IGF-1 have peripheral actions on growth, but IGF-1 requires GH stimulation to be secreted and have action.
IGF-1 levels remain low during starvation, regardless of GH levels

Roles:
::GH- JAK/STAT –> new mRNA
::IGF-1- RTK –> rapid activation of enzymes —> distributing nutrients towards growing tissues such as muscle (via mTORC1) and bone.
IGF-1 also promotes glucose uptake, glycogenesis, and lipid storage in muscle cells. (mechanism same as insulin’s)

Question 4

Describe the interactions among all the key growth-regulating hormones at key times of a person’s life: in utero, neonatally, childhood, puberty, adulthood, and senescence.

Answer 4

::T3- req’d for GH synthesis in ant. pit. (hence, stunted growth in hypothyroidism)
::Cortisol- inhibits GHRH secretion. Promotes GH synthesis (so when stress passes, body can recoup). Antagonizes all actions of GH.

Hormone: Insulin
Effects: Fetal Growth, IGF-1 Secretion, Protein Synthesis
————————–
Hormone: T3
Effects: GH production, CNS development
————————–
Hormone: Testosterone and Estrogen
Effects: GH Secretion at puberty, Eventual epiphyseal closure, protein synthesis
————————–
Hormone: Cortisol
Effects: —I GH release, protein breakdown

Question 5

Describe the daily regulation of GH levels and the physiological relevance of these cycles.

Answer 5

GH levels highest during sleep, lowest during day.

Grow at night while nutrients not needed for other activities of day.

Question 6

Metabolic roles of epinephrine:

Answer 6

Don’t break down muscle protein.
Promote FA release, gluconeogenesis, glycogenolysis.
Provide skeletal muscle with fuel.