Lecture 7 Normal Growth and Clinical Aspects Flashcards
Name factors that regulate growth
- Growth hormone release from anterior pituitary – which in turn is regulated by the balance of GHRH vs GHIH release from the hypothalamus
- Thyroid hormones
- Insulin
- Sex steroids (esp. at puberty)
- Availability of nutrients
- Stress
- Genetics
What is Growth Hormone
a peptide hormone released from the anterior pituitary. Aka somatotropin. Released from somatotroph cells (“troph” relating to growth).
What is the GHIH
Growth Hormone Inhibiting Hormone (GHIH) (aka Somatostatin (“statin” relating to stasis = static/stopped)
What are the 2 categories of biological activity of Growth Hormone
- Growth and development (indirect action)
2. Regulation of metabolism (direct action)
Growth in the foetal period and first 8-10 months is largely controlled by what
Nutritional intake
What hormone mediates the action of GH
IGF-1 (somatomedin C)
How does IGF-1 mediate GH
IGF-1 has structure very similar to pro-insulin, binds to receptors very similar to the insulin receptor and has hypoglycaemic qualities (hence “insulin-like”) although latter action is limited to glucose uptake in muscle. Liver and adipose tissue have few IGF receptors
How are IGF-1 and GH transported in the blood
Blood bound carrier proteins
How does IGF-1 exhibit negative feedback on GH
via inhibiting GHRH and stimulating GHIH
How does GH/IGF-1 effect bone growth
- GH stimulates chondrocyte precursor cells (prechondrocytes) in the epiphyseal plates to differentiate into chondrocytes.
- During the differentiation, the cells begin to secrete IGF-I and to become responsive to IGF-I
- IGF-I then acts as an autocrine or paracrine agent to stimulate the differentiating chondrocytes to undergo cell division and produce cartilage, the foundation for bone growth
Why is there no longer longitudinal growth after puberty
• Epiphyseal plates close during adolescence under the influence of sex steroid hormones then no further longitudinal growth is possible.
How does GH directly regulate metabolsim
Directly
• Increases gluconeogenesis by the liver.
• Reduces the ability of insulin to stimulate glucose uptake by muscle and adipose tissue.
• Makes adipocytes more sensitive to lipolytic stimuli.
• Releasing energy stores to support growth
Increases amino acid uptake and protein synthesis unlike cortisol and just like insulin
Anabolic hormones that increase amino acid uptake
Insulin and GH
Anabolic hormones that increase protein synthesis
Insulin and GH
Anabolic hormones that increase glucose uptake
Insulin
