Chapter 5 (Growth Hormone) Flashcards
1
Q
Characteristics of Fetal Growth
A
- placental GH plays no role in fetal growth before birth
- fetal growth is promoted by certain hormones from the placenta
- after birth, non-placental GH plays a role in growth
- genetic and nutritional factors also affect fetal growth
2
Q
Post-natal and Pubertal Growth
A
- spurts for the first 2 years and again during adolescence
- a marked acceleration in linear growth is due to the lengthening of the long bones
- an increased secretion of androgen during growth increases protein synthesis and bone growth
- both testosterone and estrogen act on bones to achieve full adult height by the end of adolescence
3
Q
Diet
A
an adequate diet:
- protein and amino acids-rich diet
- inadequate diet in infancy and childhood stunt growth and brain development
- 70% of total brain growth occurs during the first 2 years of birth
- growth is genetically determined
4
Q
Stress
A
- prolonged stress-induced cortisol can have adverse effects on growth
- cortisol acts as an anti-growth hormone by breaking down protein, inhibiting the growth of long bones and blocking the secretion of GH
- thyroid, sex hormones and insulin also affect GH secretions and growth
5
Q
Bone Thickness and Growth
A
Thickness:
- achieved by adding new bone cells by osteoblasts to an outer surface of an existing bone
- thickness is produced by osteoblasts within periosteum
- osteoblast activity deposits new bone cells on exterior bone
Growth:
- proliferation of cartilage cells in epiphyseal plate
- division of multiplication of chondrocytes on the outer edge of the epiphyseal plate
6
Q
GH Actions on Soft Tissue
A
- increases the number of cells (hyperplasia)
- increasing the size of the cells (hypertrophy)
- prevents apoptosis (programmed cell death)
- increases protein synthesis by uptake of amino acids
7
Q
Negative Feedback
A
hypothalamus hypophysiotropic hormones anterior pituitary GH target tissue/endocrine glands
8
Q
Somatomedin
A
- it’s an insulin-like growth factor (IGF-1) produced by the liver
- acts directly on bone and soft tissues to elicit growth-promoting actions
- stimulates protein synthesis, cell division, lengthening and thickening of bones
exerts metabolic effects not related to growth
- increases fatty acid levels in the blood by enhancing breakdown of triglyceride/fat storage in adipose tissue
- increases blood glucose levels by decreasing glucose uptake by muscles
- acts as a paracrine - locally
9
Q
IGF-II
A
- does not depend on GH level
- important in fetal development
- role in adult in unclear
10
Q
Factors that Control IGF-1 Production
A
- nutrition
- inadequate food intake decreases IGF-1 level through sensitivity to GH
- fasting decreases IGF-1 level, but increases GH secretion - age
- a dramatic increase in circulating IGF-1 levels accompanies the moderate increase of GH at puberty - various tissues-specific stimulating factors
- can increase IGF-1 production in a particular tissue
- eg. gonadotropin and sex organ stimulate IGF-1 in the testes, ovaries and uterus
11
Q
Factors that Influence GH Secretion
A
- GHRH/GHIH (hypothalamus)
- antagonistic factors that elevate GH secretion
- negative feedback loop
- somatomedins (liver) influences the anterior pituitary to inhibit the effects of GHRH on GH release - Diurnal Rhythms
- GH levels tend to be low and constant most of the day
- 5 times higher one hour after deep sleep and drops over the next several hours - Exercise, stress and hypoglycemia
- increase GH secretion
- GH utilizes fat storage and promotes body protein synthesis during stress
- decreases body fat during exercise may partly increase GH secretion during exercise - Amino acids
- increased amino acid levels after high protein meal increases GH secretion
- decreased fatty acids in the blood stimulate GH release
- GH has fat-mobilizing ability to maintain constant blood fatty acid levels
12
Q
Dwarfism
A
causes
- lack of GH from anterior pituitary in a child
- lack of growth hormone releasing hormones (GHRH)
symptoms
- short stature causes by delayed skeletal growth
- poorly developed musculatrue
- excess subcutaneous fat (less fat mobilization)
13
Q
Laron Dwarfism
A
- caused by the failure of tissue to respond to GH
- GH receptors are unresponsive to GH
- reduced skeletal muscle mass and decreased bone density in adults
- increased risk of developing heart failure
14
Q
Gigantism
A
- causes by tumour of the GH producing cells in the anterior pituitary
- overproduction of GH in childhood before epiphyseal plate closes
- height could exceed 8 feet or higher
15
Q
Acromegaly
A
- hypersecretion of GH after adolescentes when further growth is prevented
symptoms:
- excessive GH secretion causes thickening of soft tissues such as skin, and thickening of bone in the extremities and face
- jaw and cheekbones thicken and fuse, giving ape like appearance
- hands and feet enlarge, fingers and toes become thick
- overgrown connective tissue trap nerve giving peripheral nerve disorder
- may result in visual disturbances
