Lecture 4 - Growth and disorders Flashcards
Which factors affect growth?
Genetics
Nutrition
Hormones
What factor influences growth the most?
Hormones (even if genetics and nutrition are good)
Which hormones have a permissive effect on growth hormone?
Growth hormone releasing hormone
Thyroid hormone
Insulin
Sex hormones (oestrogen + testosterone).
Which hormone has an antagonistic effect on growth hormone?
Growth hormone inhibiting hormone (Somatostatin)
Cortisol
Which hormone does growth hormone use to act indirectly on the body?
IGF-1
insulin like growth factor 1.
What two hypothalamic hormones dictate growth hormone release?
Somatostatin (GHIH) and GHRH.
What periods of life are rapid growth periods?
Infancy (in utero and the first 10 months post utero).
Puberty.
When does growth hormone play a role in growth?
After 10 months - for the rest of your life.
What type of growth do sex hormones promote?
Elongation of long bones (from the epiphyseal plate).
What hormones terminate growth?
The same sex hormones at the end of puberty. (late teens/early 20s).
What causes growth in puberty?
The sex hormones - these promote the release of more GH and IGF-1
Which hormones are responsible for infancy growth?
Nutrition from mother
Thyroid hormone
Insulin
What type of bone growth still happens after puberty?
Remodelling of bones - like membranous bones (skull, jaw etc)
Who usually hits their puberty growth spurt first?
Girls
Which hormones are responsible for the increase in GH in puberty?
The sex hormones - testosterone and oestrogen
What is seen in babies who lack GH and IGF-1?
They are born normal size (these hormones don’t become important in growth until later)
What is seen in babies who lack GH and IGF-1?
They are born normal size (these hormones don’t become important in growth until later)
They fail to grow normally after 10 months
Which hormone is critical for brain development?
Thyroid hormone
What is seen in hypothyroid babies?
Often nothing at first (they get their thyroid from the mother)
After birth, they fail to develop cognitively and growth
What happens in children deficient in growth hormone?
They are short, but normal cognitively and in proportion.
What happens in children with a thyroid deficiency?
Normal at birth - due to getting thyroid in utero from mother
They are short (thyroid has a permissive effect on growth hormone)
They have poor cognitive development
They retain infantile features (struggle to move fat deposits)
When is IGF-II used?
In utero
Where is IGF-I used?
After birth
What is iodine needed for?
The production of thyroid hormone
What occurs in maternal iodine deficiency?
This is very rare. Causes severe growth retardation intra-uterine because thyroid cannot be made (mum can’t pass on to baby).
What happens with a lack of GH?
They appear normal at birth.
Stunted growth - but still proportionate
don’t retain infantile features
normal cognitive function
What is another name for Growth Hormone?
Somatotropin
What is another name for growth hormone inhibiting hormone?
Somatostatin
Where is somatotropin released from?
Somatotroph cells in the anterior pituitary.
What controls the ratio of GHIH and GHRH?
Factors which influence the hypothalamus
Can growth hormone act on its own?
It will produce stunted growth, even if there’s lots of it. If there is no thyroid hormone or insulin.
What is GH used for after puberty?
Remodelling and maintenance/repair of bones.
It promotes an increase in cell size and cell division.
What receptors does growth hormone act on?
Tyrosine kinase
What direct effects does GH have?
- Increases blood glucose
- increasing lipolysis (fatty acids made into ketone bodies)
- increases amino acid uptake
- antagonistic effect against insulin to prevent muscle and adipose taking up all glucose
What is another name for IGF-1?
somatomedin C
What type of hormones are GH and IGF-1?
Peptides BUT they are carried through the plasma bound to carrier proteins
Why is Gh and IGF-1 bound to carrier proteins?
To provide a reservoir and stop erratic spikes in the blood of secretion.
Extends the half life - protects against excretion from the urine.
What is IGF-1 responsible for?
promotion of cartilage growth and the elongation of long bones
When is most GH secreted?
In puberty
During the first 2 hours of sleep (deep delta sleep)
because general energy levels are low, so the glucose in the blood can be used almost entirely for growth
When is IGF-1 released?
IGF-1 levels are constant because it binds tightly to the carrier protein. - less vulnerable to degradation - long half-life.
gives a constant increase in growth and not just in the first 2 hours of sleep.
there’s not big spikes like seen in GH.
What is the half life of GH?
20 mins
What is the half life of IGF-1?
20 hours
Stimuli causing an increase in GHRH - so increase in GH?
- decrease in energy supply to cells
- increased amino acid levels in plasma
- physical stress and illness (due to increase in energy supply BUT growth might be stunted because cortisol is also there)
- increase in delta sleep
- sex hormones (oestrogen and testosterone - they increase GH directly not GHRH first)
Stimuli causing increase in GRIH - so decrease in GH?
- hyperglycaemia
- high levels of free fatty acids
- ageing (this is why tissue repair is less efficient in older people)
- cortisol
What is gigantism?
Increase in GH from a pituitary tumour BEFORE the epiphyseal plate closes.
Extra elongation of long bones.
What is acromegaly?
Increase in GH from a pituitary tumour AFTER the epiphyseal plate closes.
No longitudinal growth and no increase in height BUT increase in width.
What is the common sign of acromegaly?
Increase in feet size of adults.
What is treatment for gigantism or acromegaly?
Remove the pituitary tumour by surgery or use GHIH.
What is a common symptom of a pituitary tumour?
Bitemporal hemianopia (pressure on optic chiasm).
What is hypo secretion or hyporesponsiveness caused by?
gives abnormally small stature.
- GHRH deficiency (hypothalamus problem)
- GH deficiency (pituitary problem)
- under expression of GH receptor
- precocious puberty (sex hormones released too early and growth stopped too soon)
- reduce in thyroid (loss of permissive effect)
Whatis precocious puberty?
excess release of gonadotropin releasing hormone. - increase in sex hormone - earlier closure of epiphyseal growth plate.
What is gestational diabetes?
women gets diabetes when pregnant.
High blood glucose levels travel to baby.
Baby uses the extra glucose and is born very large.
