Endocrine Control of Growth and Disorders of Growth Flashcards
Name the three factors which regulate growth.
Genetics
Nutrition
Hormones
List the hormones have a role in growth.
Growth hormone
IGF-1
Thyroid hormones
Insulin
Sex steroids
Cortisol
Which hormone is particularly important from growth on puberty?
Sex steroids
Which hormone does growth hormone need in order to work through?
IGF-1
(Insulin-like growth factor 1)
Growth hormone does not work on it’s own. Which two other hormones must be present to allow growth hormone to work?
Insulin
Thyroid hormones
Which hormone in antagonistic and actually counteracts the function of growth hormone?
Cortisol
Which hormone mediates the direct effects of growth hormone?
Growth hormone
Which hormone mediates the indirect effects of grwoth hormone?
IGF-1
What are the two stages of rapid growth in humans?
Infancy
Puberty
What is the infancy growth period controlled by?
Nutritional intake
Thyroid hormones
Insulin
Growth hormone is pretty insignificant during infancy. At what age does growth hormone become significant?
10 months
What is growth in puberty dependant on?
Androgens and oestrogens which produce spikes in growth hormone
How are sex steroids also linked to terminating growth relating to height?
They cause the epiphyses of long bones to fuse
In normal puberty, before the epiphyseal plates fuse, what do growth hormone and IGF-1 do?
Promote bone elongation and increased height, weight an body mass.
Which hormones act the close the epiphyses and stop bone elongation?
Sex steroids
Which hormones dominate intra-uterine grwoth?
Thyroid hormones, insulin and IGF-II
If a child is deficient in growth hormone, how do they develop?
Normal cognitive function, short stature
If a child is deficient in thyroid hormone, how do they develop?
Cognitively impaired, short stature
->thyroid hormone is required for normal brain development
When is IGF-II important in term of grwoth?
Only in uterine development, after birth, it has no effect
What is congenital hypothyroidism?
Condition in which babies are born of normal size but are unable to produce their own thyroid hormones.
What happens to those with congenital hypothyroidism if they are left untreated?
They have retarded growth and development.
They retain infantile facial features
Maternal deficiency of what can result in severely retarded intra-uterine growth?
Maternal iodine defiency
What is iodine essential for?
Thyroid hormone production
Thyroid hormones have a permissible effect on growth hormones. What does this mean?
Growth hormones only reach their full potential if there is also thyroid hormone present
If a child had normal levels of GH and low levels of TH, what would they look like, at the age of approx. 8?
Stunted growth and infantile features due to low TH
If a child had normal levels of TH and low levels of GH, what would they look like, at the age of approx. 8?
Stunted growth but otherwise look like a normal child
Where is GH released from?
Anterior pituitary
What is another name for GH?
Somatotropin
Which cells in the anterior pituitary release GH?
Somatotroph cells
Release of GH is controlled via the release of which two hypothalamic neurohormones?
Growth hormone inhibiting hormone (aka somatostatin)
Growth hormone releasing hormone
->these two hormones have opposing actions
RECAP- what is meant by tropic regarding hormones?
A tropic hormones stimulates the release of another hormone
RECAP- GH requires the permissive action of which other hormones before it stimulates grwoth?
Insulin and thyroid hormones
Even though growth in terms of height stops during puberty, GH is still produced throughout adult life. What role does it play?
Maintenance and repair of tissue
->GH promotes an increase in hypertrophy and hyperplasia in many target tissues.
Hypertrophy=increased cell size
Hyperplasia=increased cell division
Which type of receptor does GH act on?
Tyrosine kinase receptors
What are the indirect actions of GH mediated by and what o they bring about?
Mediated by IGF-1 and bring about growth of long bones
What is the direct action of growth hormone directly binding to the tyrosine kinase receptors?
Regulation of metabolism
IGF-1 has insulin like qualities. Give an example.
Stimulates the uptake of glucose in muscle, and in bone
Where is IGF-1 primarily released from?
Liver
What does IGF-1 control the release of?
GH via a negative feedback loop
What type of hormones are GH and IGF-1?
Peptide hormones
->however, like steroid and thyroid hormones they are transported in the blood bound to carrier proteins
There is also an autocrine action of GH, describe this.
Autocrine negative feedback loop. There’s an autocrine inhibitory effect within the anterior pituitary itself and it inhibits the somatotrophs in the pituitary
As previously mentioned, the direct effect of GH regulates metabolism. How does it do this?
- Increases gluconeogenesis in the liver
- Reduces the ability of insulin to stimulate glucose uptake by muscle and adipose tissue
- Makes adipocytes more sensitive to lipolytic stimuli
- Increases amino acid uptake and protein synthesis in most cells
All of these actions release energy to support growth.
RECAP- which tissues require insulin for the uptake of glucose?
Muscle and adipose tissue
Why is GH said to be diabetogenic?
Increases blood glucose by releasing energy stores
Is GH anabolic or catabolic?
Anabolic
->maybe think of it as building up bone and muscle for growth
Compare the actions of insulin and GH.
Both anabolic hormones.
Both increase amino acid uptake.
Both increase protein synthesis.
Only insulin increased glucose uptake
->this feels a wee bit like a higher bio essay question hahaha
At which stage of life is the secretion of GH the highest?
Puberty
When is the majority of GH released in all people?
First 2 hours of sleep during deep delta sleep
If you increase the secretion of growth hormone releasing hormone, what effect does that have on the amount of GH secreted?
Increases
If there is a decrease to energy supply to cells, what happens?
Increased release of GHRH which increases GH
GH required for maintenance of tissues and their energy supply.
->maybe think of GH like a caretaker/janitor for the cells, trying to maintain the tissues
If you are cold, exercising or fasting, there is an increase in energy demand. How is this solved?
Increases the secretion of GHRH which then increases the release of GH
If eating a high protein meal, with little carbs, there is increased GHRH secretion (which in turn increases GH release….hope you’re getting the picture now). Why is this?
There is increased amount of amino acids in the plasma.
GH promotes amino acid transport and protein synthesis by muscle and liver
Physical stress of illness can also cause an increase in the secretion of GHRH (which increases etc.). Why is this?
There is an increase in energy demand so GH required to help
What happens to physical growth in times of illness of physical stress?
Growth is stunted
Why is growth often stunted in illness?
Because of antagonistic effects of cortisol which is a stress hormone and is released during illness.
Is cortisol anabolic or catabolic?
Catabolic- breaks down protein
->AHHH THIS IS WHY IF YOU’RE ILL YOU CAN LOSE MUSCLE MASS MAYBE IDK
In which period of sleep is there an increased secretion of GH thanks to GHRH?
Delta sleep
Which hormones are responsible for the release of GH in puberty which causes a growth spurt?
Testosterone and oestrogen
If there is an increase in GHIH (growth hormone inhibiting hormone), what effect does this have on the secretion of GH?
Decreases
List some stimuli which increase the release of GHIH and in turn decrease the release of GH.
- Glucose
- Free fatty acids
- Ageing
- Cortisol
Why do both glucose and FFA’s lead to an increase in GHIH?
GH is a hyperglycaemic hormone which increases blood glucose levels.
If blood glucose levels are already high, no more blood glucose is needed so GH supply is switched off via GHIH.
->same for FFA’s
What is the most common cause of hypersecretion of GH?
Endocrine tumours
What causes gigntaism?
Excess GH due to a pituitary tumour before the epiphyseal plates of long bones close
What does gigantism cause to happen?
Excessive growth, individual may be more than 7ft tall.
Excess secretion of GH from the pituitary can be classed of one of two disorders. Name them.
Gigantism
Acromegaly
What is the most classic sign of acromegaly?
Bigger feet- adult feet should NOT get bigger
What happens in someone with acromegaly?
Long bones cannot increase so no increase in height. However, bones increases in width. Characteristic features are enlarged hands and feet
What causes acromegaly?
Excess GH due to a pituitary tumour after the epiphyseal plates have fused.
Okay, lets check you were paying attention :)
Which condition would occur if there was an endocrine tumour AFTER epiphyseal plates fused?
Acromegaly
Okay, lets check you were paying attention :)
Which condition would occur if there was an endocrine tumour BEFORE epiphyseal plates fused?
Gigantism
As well bones of the hands and feet increasing in acromegaly, which other bone can change shape and be quite noticabe?
Jaw- patient may have a very prominent jaw.
->this is because the skull is an intramembranous bone and grows due to intramembranous ossification
How is acromegaly tretaed?
Surgery to remove the tumour or somatostatin analogues to treat
RECAP- if there was a tumour pressing on the pituitary gland, what would this cause?
Bitemporal hemianopia
Hyposecretion of GH can lead to small stature.
List some of the causes of hyposecretion of GH.
- GHRH deficiency
- GH deficiency
- Genetic mutations
- Precocious puberty
- Hypothyroid dwarfism
If there was a deficiency in GH, where is the origin of the problem?
Pituitary gland
Individuals with genetic mutations being responsible for their short stature often have high levels of GH circulating. Why does this not work?
The problem is at the level of the receptors o no matter the level of GH, it has nothing to act on
What is precocious puberty?
When a child’s body begins to change into an adult’s body too soon
What causes precocious puberty?
Excess gonadotrophin releasing hormones which then increases release of testosterone and oestrogen, and these sex steroids promote puberty
How can precocious puberty stunt growth?
During puberty, the epiphyseal plates of bones fuse and in this case, will occur prematurely before growing, in terms of height, has finished.
What happens in hypothyroid dwarfism?
Reduction in the release of thyroid hormone
->therefore, there is loss of the permissive effect of TH on GH
RECAP- those with hypothyroid dwarfism also experience what?
Impaired cognitive function because TH is critical for brain development
How the impact of hypothyroid dwarfism be reduced?
TH supplementation
RECAP- why do injury and disease stunt growth?
Increased protein catabolism by cortisol
During pregnancy, which condition can lead to very big babies?
Gestational diabetes
Why do babies get so big during pregnancy if there mother has gestational diabetes?
Increased BG levels in mother, glucose transmitted to foetus.
Foetus is not diabetic so produces insulin to take up glucose into cells.
Foetus undergoes an increase of anabolic processes hence a big baby
