Physiology Of Growth Flashcards
Intrauterine growth phase is dependent on three factors….
Genetics
Nutrition
Placenta
What drives the infancy phase of growth
Nutritional factors in the first 2-3 years of postnatal life
Early childhood phase of growth is dependent on…
Growth hormones s
What regulates the pubertal growth spurt
Combination of GH and sex hormones
Growth is characterised by an increase in …..
Hypertrophy
Hyperplasia
Volume of intracellular material
Examples of when apoptosis occurs during foetal development
Webs between fingers are removed
Hollow organs such as the heart begin off as solid structures
Apoptosis normal event in fully developed tissues with sites of high cell turnover
Replacement and regeneration of cells in the skin, respiratory and GI tract
What cellular changes are observed with a cell undergoing apoptosis
Condensation of the chromatin
Formation of membrane blebs that go on to form apoptotic bodies (cellular fragmentation)
Phagocytosis of bodies and fragments
What triggers the intrinsic and extrinsic pathways of apoptosis
Extrinsic = mainly by adjacent cells and immune cells via superfamily of caspases
Intrinsic = stimuli which is lethal such as DNA damage or ER stress, hypoxia and metabolic stress
When is foetal growth at its peak
16- 20 weeks
By cell division
When does foetal weight gain peak
34 weeks
Due to deposition of fat
Senescent changes occur when
Sex hormones decline eg menopause
Reduces capability to initiate homeostatic mechanisms in response to internal or external environmental stresses
What change occurs to the cardiovascular system in senescence
Reduced blood flow
Arteriosclerosis
Respiratory system senescence change:
Reduced elasticity of lungs
Decreased lung function
Urinary system changes in ageing
Decreased muscle tone and decreased GFR
Changes to the skin in senescence
Loss of elasticity —> sagging and wrinkling
Immune system senescent changes
Reduced sensitivity and responsiveness
What happens to brain in senescence
Impaired coordination, memory and intellectual function
Senescent changes to the GI system
Decreased GI muscle tone and less peristalsis
Senescent changes to endocrine function
Decreased in hormone production and sensitivity
What happens to bones as a person ages
Decline in rate of Bone deposition
Decrease in mobility
What happens to muscular system as a person ages
Reduction in muscle mass, strength and ability
Why does growth not occur after puberty
Epiphysis and diaphysis of bones fuse so no further increase in length is possible
4 zones of bone growth at the epiphyseal plate
Proliferation zone = chondroblasts divide quickly and push the epiphysis away from the diaphysis lengthening the bone
Hypertrophic zone = chondrocytes enlarge and signal surrounding matrix to calcify
Calcification zone (not bone yet) matrix calcifies and chondrocytes die
Ossification zone
Which types of hormones required in combination to result in growth
Growth hormones
Thyroid hormones
Sex hormones
Effects of growth hormones
Produced by anterior pituitary
Direct = fat metabolism
Indirect = stimulates liver to produce IGFs which indirectly affect bones
Which 5 tissues make IGF-1 and IGF-II
Liver
Kidney
Bone
Muscle
Cartilage
Which IGF is stimulated by growth factor after birth and which plays a role in foetal development
IGF-I stimulated by GF after birth and is independent previous to birth. Rises during childhood and peaks at puberty and declines to low levels at old age
IGF-II = largely independent of GF and role in foetal development
Overexpression of IGF-II in foetuses leads to
Disproportionate growth of tongue, other muscles, kidneys, heart and liver
Role of thyroid hormones in growth
T3 - triiodothyronine
T4 - thyroxine
Secretion commences at 15-20 wks of gestation
Essential for protein synthesis in brain of foetus and young children
Normal differnetaotn and maturation of skeletal and nervous tissue
Promotes linear growth of bone until puberty and ossification of bones and maturation of epiphyseal growth regions
Deficiencies in thyroid hormones lead to
Mental retardation
Insufficient bone and height growth
What is cretinism
Inadequate levels of thyroid hormones during foetal period lead to severe mental retardation
Due to:
- decrease in size and number of cerebral cortical neurons
- reduction in degree of branching of dendrites
- deficiencies in myelination of nerve fibres
- reduced blood supply to the brain
Hypothyroidism detected at birth if left untreated leads to what
Permanent neurological and intellectual damage (cretinism)
In relation thyroid function what does the Guthrie blood spot detect
High TSH levels in case of hypothyroidism
How do corticosteroids affect growth
Cortisol if in excess has inhibitory actions on growth
Interfere with cartilage and bone synthesis at growth plates = increased rate of skeletal maturation so potential for further growth is reduced
How do sex steroids influence growth
Androgens have anabolic effects
Oestradiol and testosterone (leydig cells) positive effect on secretion of GH
Results in increase in long bone growth and height
Somatotropin/ growth hormone is what kind of hormone
Peptide hormone
What is the diurnal variation in secretion of GH
Most secretions occur with slow wave deep sleep
(Pursatile bursts)
How does GH secretion change over lifetime
Continues to increase from birth until puberty where it peaks. Slight decline in adulthood which remains constant until senescent age (significant reduction but still constant in this period)
How does IGF-1 inhibit secretion of GH to regulate levels of growth
1) direct inhibition by suppressing somatotrophs
2) indirectly reducing gnRH release from arcuate nucleus in hypothalamus
3) indirectly via increasing secretion of somatostatin from periventricular region
What is achondroplasia
- dwarfism
- autosomal dominant inheritance pattern
- mutation in gene on C. Four that code for fibroblast growth factor receptor 3 FGFR3
Avg male height 125cm
Avg female height 120cm
Mutation of gene that produces FGFR3 results in what
Increased function of gene which:
Decreased endochondral ossification
Inhibited proliferation of chondrocytes in growth plate cartilages
Decreased cellular hypertrophy and decreased cartilage matrix production
Earlier closure of epiphyseal plates
Presentation of achondroplasia
Large forehead
Proportionate trunk but limbs are v small compared to rest of body
What causes acromegaly
Hypersecretion of GH
Adenoma of pituitary somatotroph cells
Affects all organs and tissues. Leads to gigantism
Those with acromegaly at higher risk of
T2 DM
CVD
Hypertension
Arthritis
How is GH secretion pattern diurnally different in those with acromegaly
Constant elevated levels throughout day and night
A way to test for acromegaly
Administer glucose
Glucose normally suppresses GH secretion but in those with acromegaly there is no change
What is pituitary dwarfism
GH deficiency may be accompanied by under secretion of other pituitary hormones. As a result skeleton fails to grow and 120cm height achieved with normal proportions
Causes of pituitary dwarfism
Pituitary or hypothalamic tumours
Infections such as meningitis or syphilis
Pituitary infarction and vascular malformations
Head trauma
What is panhypopituitarism
Absence of all pituitary hormones
What is Laron dwarfism
Mimics GH deficiency but GH levels are high
Levels of IGF-I and IGFbinding protein3 are low
Caused by mutation in GH receptor - becomes unresponsive —> growth retardation
Treated with recombinant IGF-1
What is the most common cause of growth failure worldwide
Malnutrition
Mainly due to lack of protein and other basic nutrients
Shows sign of weakness, frailty and muscle wasting
