Endocrine Control of Growth Flashcards
<p>what factors affect the physiology of growth?</p>
<p>1. Genetics</p>
<p>2. Nutrition</p>
<p>3. Hormones</p>
<p>what hormones are involved in regulating growth?</p>
- thyroid hormones
- insulin
- growth hormones
- IGF-I/II
- cortisol (anatagnostic)
- sex hormones
<p>what are the periods of rapid growth in humans?</p>
<p>- Infancy (foetal/first 8-10 months of life)</p>
<p>-Puberty</p>
<p>Where is GH released from?</p>
<p>Anterior pituitary</p>
<p>What does GH do?</p>
<p>Promotes growth</p>
<p>What is another name for GH?</p>
<p>Somatotropin</p>
<p>What is somatostatin?</p>
<p>Growth hormone inhibiting hormone, a neurohormone released from the hypothalamus</p>
<p>What does GH require to stimulate growth?</p>
<p>Permissive action of thyroid hormones and insulin</p>
<p>Children with untreated hypothyroidism, or poorly controlled diabetes, have stunted growth despite normal GH levels.</p>
<p>GH is a peptide hormone, but what is unusual about it?</p>
<p>About 50% of GH circulates bound to carrier proteins</p>
<p>What largely controls in the foetal period and the first 8-10 months of life?</p>
<p>Nutritional intake</p>
<p>- thyroid hormones and insulin</p>
<p>What is the predominant influence on the rate children grow?</p>
<p>GH</p>
<p>What types of effect does GH have on adults?</p>
<p>Maintenance of tissues and their energy supply.</p>
<p>What is the growth-promoting effect of GH mediated through?</p>
<p>Stimulation of both</p>
<p>- cell size (hypertrophy)</p>
<p>- cell division (hyperplasia)</p>
<p>Why is GH effect on growth indirect?</p>
it is achieved through the action of an intermediate known as IGF-I (insulin-like growth factor-I)aka somatomedin C as it mediates the action of GH
<p>Why is IGF-1 said to be insulin-like?</p>
stimulates glucose uptake in muscles and bone (hypoglycaemic qualities)
<p>What secretes IGF-1?</p>
<p>Liver and many other cell types</p>
<p>What is IGF-1 secreted in response to?</p>
<p>GH release from the anterior pituitary</p>
<p>How does IGF-1 control GH release?</p>
<p>Through a negative feedback loop</p>
<p>Who is the functional effects of IGF-II limited to?</p>
<p>- Foetus</p>
<p>- Neonate</p>
<p>How does IGF exhibit a negative feedback on GH release?</p>
<p>both via</p>
<p>- inhibiting GHRH</p>
<p>- stimulating GHIH/somatostatin.</p>
<p>What are the effects of GH/IGF-1 on bone?</p>
<p>- GH stimulates chondrocyte precursor cells (prechondrocytes) in the epiphyseal plates to differentiate into chondrocytes</p>
<p>- During differentiation, cells begin to secrete IGF-I andbecome responsive to IGF-I</p>
<p>- 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.</p>
<p></p>
<p>What influences the closure of epiphyseal plates in adolescence?</p>
<p>Sex steroids</p>
<p>What does closure of the epiphyseal plates prevent?</p>
<p>Longitudinal growth</p>
<p>What are the direct effects of GH?</p>
GH releases energy stores to support growth - it has an anti-insulin effect (synergises with cortisol)
- 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
- increasesamino acid uptake and protein synthesis in almost all cells= anabolic effect (cortisol stimulates protein catabolism)
Why is GH said to be diabetogenic?
What anabolic effects does insulin have?
- Increased aa uptake
- Protein synthesis
- Increased glucose uptake
What anabolic effects does GH have?
- Increased aa uptake
- Protein synthesis
What is GH secretion controlled by?
Hypothalamus
How does the hypothalamus control GH secretion?
Its secretes GHRH and somatostatin (GHIH)
Where are large quantities of GH found?
Pituitaries of both adults and children
What happens to the rate of GH secretion?
undergoes rapid spontaneous fluctuations
increases or decreases in response to specific stimuli.
What is the basal [GH] plasma level in children and adults?
0-3ng/ml
Why does one value of [GH]plasma level not give an overall picture?
Spikes of secretion
24 hour mean [GH] is 2-4ng/ml in adults and 5-8ng/ml in children and puberty.
What happens to the levels of GH when children are in delta sleep?
Approximately 20X increase in GH secretion
Why does growth increase during sleep?
General energy requirements low so energy diverted to growth
When GH spikes, plasma levels of IGF-1 remain relatively constant suggesting...
IGF-1 buffers the pulsatile variance in GH levels.
What type of hormone are GH and IGF-1?
Peptide hormones
How are GH and IGF-1 transported?
Like steroid and thyroid hormones, they are transported in the blood associated with binding protein
How is a reservoir of GH provided in the blood?
Give 5 stimuli that increase GHRH secretion.
Why does an actual or potential decrease in energy supply to cells increase GHRH secretion?
Why is GHRH secretion stimulated by increased amino acids in the blood?
GH promotes amino acid transport and protein synthesis by muscle and liver
Give examples of stressful stimuli
Give 4 examples of stimuli that increase GHIH.
What 3 factors affect growth?
When are sex hormones important in growth?
During puberty when they dominate the growth spurt
What may dominate intrauterine growth?
What size are babies born deficient in GH and IGF-1?
Normal size
What are thyroid hormones particularly important for in terms of growth?
For development of the nervous system in utero and early childhood
What hormones do thyroid hormones have a permissive effect on?
What is cretinism?
What do thyroid hormones have a widespread effect on in terms of growth?
What is important in terms of diet in utero and development?
Adequate diet in terms of protein content and essential vitamins and minerals is just as important as enough calories.
Why do injury and disease stunt growth?
Increase protein catabolism (glucocorticoid effects
What do genetic factors help determine in terms of growth?
Maximum growth
What terminates growth in puberty?
Androgens and oestrogens by causing the epiphyses of the long bones to fuse
What do GH/IGF-1 promote during puberty?
What is usually the cause of hypersecretion of GH?
Endocrine tumours
What causes gigantism?
What causes acromegaly?
What is a classic sign of acromegaly?
Growth of feet
How is acromegaly treated?
Surgery to remove tumour or somatostatin analogues to treat
How do hypothyroid children and GH deficient children differ in appearance?
Hypothyroid children retain infantile proportions, whereas children deficient in GH are proportionally normal, just small.
What can cause dwarfism?
Why does precocious puberty lead to dwarfism?
Excess GnRH release stimulates puberty via promoting sex hormone release. These children have stunted growth because long bones fuse early under influence of sex hormones
Why do hypothyroid children have stunted growth?
Hypothyroid children retain infantile features with stunted growth due to loss of permissive effect of TH on GH. Limits bone growth and promotes fat storage. Also severely impacts on neurological development.
