Growth Hormone

where are red blood cells produced

bone marrow

what substance is important for RBC production

erythropoietin

parts of long bones

shaft, ends (epiphysis)

where is the epiphyseal growth plate

between epiphysis and shaft

Hyperplasia

increase in number of cells

hypertrophy

increase in cell size

process of bone growth

1. hyperplasia: chondrocytes undergo cell division (mitosis)

2. hypertrophy: older chondrocytes enlarge and move down toward the shaft

3. osteoblasts in the shaft convert cartilage to bone

processes involved in bone growth are influenced by

local paracrine agents and circulating hormones

chondrocytes

cartilage cells

osteoblasts

convert cartilage to bone

BUILDERS

brain growth

rapid growth in first year of life

eventually stops when the skull fuses (nowhere for brain to expand)

total body height growth

two growth spurts (early in life and then again during puberty)

reproductive organ growth

do not start growing until puberty

environmental factors that influence growth

-adequate nutrition (esp. protein)

-freedom of chronic illness/disease

-freedom from chronic psychological stress (high cortisol = stunted growth)

-sleep

**also hormones

Hormones that influence growth

1. GH

2. IGF

3. insulin

4. thyroid hormone

5. testosterone

6. estrogen/ DHEA

7. cortisol

how does insulin effect growth

stimulates glucose and amino acid uptake into cells, favoring protein synthesis and growth; stimulates IGF-1 secretion

thyroid hormone effect on growth

permissive--> stimulates GH synthesis and directly affects bone by stimulating growth factors, chondrocytes, and blood vessels

important for CNS development

testosterone effect on growth

stimulates GH and IGF-1 secretion, esp. during puberty

prolonged exposure can cause closure of epiphyseal plates, stimulates protein synthesis

estrogen/DHEA effect on growth

stimulates GH and IGF-1 secretion esp. in puberty

prolonged exposure usually causes closure of epiphyseal plate

Cortisol effect on growth

exerts anti-growth effects such as protein catabolism, decalcification of bone, and it inhibits IGF-1 and GH

high GH + low cortisol =

growth

High GH + High Cortisol =

fuel mobilization, no growth

pathways controlling GH and IGF-1

hypothalamus--> GHRH --> AP --> increase GH --> liver and other cells--> increase IGF-1

hypothalamus --> SST --> AP --> decrease GH --> liver and other cells --> decrease IGF-1

GHRH

growth hormone regulating hormone

positive tropic effect on GH

released by hypothalamus

SST

somatostatin

negative tropic effect on GH

released by hypothalamus

IGF-1 negative feedback on SST and GHRH

SST: negative feedback tells SST to increase secretion to decrease GH and IGF-1

GHRH: negative feedback tells GHRH to decrease secretion to decrease GH and IGF-1

long loop negative feedback IGF-1

IGF-1 singles for hypothalamus and anterior pituitary to reduce secretions

short loop negative feedback GH

GH tells SST to increase secretion and GHRH to decrease secretion

Functions of GH

promotes postnatal growth

metabolic effects

functions of GH: promote postnatal growth

-stimulate cell differentiation and division (bone and other tissue)

-stimulate protein synthesis (muscle)

-stimulate secretion of IGF-1

functions of GH: metabolic effects

-mobilize glucose for energy (prevent storage)

-mobilize fatty acids for energy (fat breakdown)

Functions of IGF-1

promote postnatal growth

-stimulates cell division (hyperplasia)

-stimulates protein synthesis (hypertrophy)

end results of GH and IGF-1

enhances body protein

burns fat

prevents glucose storage

promotes bone and organ growth

Hormone abnormalities: GH and IGF-1

-genetic mutations

-destructive tumors

-hypersecreting tumors

-receptor insensitivity

-mimic antibodies

growth abnormalities may lead to

short stature

most common cause of excess growth hormone

hyper-secreting tumor of the anterior pituitary

acromegaly

too much GH after epiphyseal plates close

thickening bones in hands, feet, and face

other organs also enlarge (heart)

Gigantism

too much GH before growth plate closes