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Transcript
GROWTH HORMONE
Dr. Shaikh Mujeeb Ahmed
Objectives
 Factors influence growth beside growth
hormone
 Metabolic effect of GH
 Relation between GH & insulin-like growth
factors
 Functions of GH
 Factors influencing GH secretion
 GH abnormalities
 Hormones affecting growth beside GH
Endocrine Control of Growth
 Growth depends on growth hormone
but is influenced by other factors as
well
 Genetic determination of an individual’s
maximum growth capacity
 An adequate diet
 Freedom from chronic disease and
stressful environmental conditions
 Normal levels of growth-influencing
hormones
Hormones regulating growth





Thyroid Hormone
Insulin: Stimulates IGF-1
Prolactin: Stimulates IGF-1
Testosterone
Estrogen
Growth
 Other hormones besides growth hormone
are essential for normal growth
 Thyroid hormone
 Growth severely stunted in hypothyroid children
 Hypersecretion does not cause excessive
growth
 Insulin
 Deficiency often blocks growth
 Hyperinsulinism often spurs excessive growth
 Androgens
 Play role in pubertal growth spurt, stimulate
protein synthesis in many organs
 Effects depend on presence of GH
 Estrogens
 Effects of estrogen on growth prior to bone
maturation are not well understood poorly
Growth Stages - Regulation
 Prenatal – Maternal factors, Fetal
Insulin, & IGF
 Growth in infancy – Genetic factors,
GH production, Thyroid hormone, IGF
 Adolescence- GH, Insulin, IGF & Sex
hormone surge
Growth hormone (GH)
 A peptide hormone (~200 amino
acids)
 Also known as somatotropin:
 tropic hormone that affects somatic cells
Growth Hormone
GH Function: Direct Effect
 GH binds directly to its target cells:
 bones & muscles
 Stimulates growth
 Hypertrophy: increase in size/volume of cells
 Example: increase in bone thickness
 Stimulates cell reproduction
 Increased rate of mitosis
 Hyperplasia: increase in the number of cells,
proliferation rate
 Example: increase in bone length
 Stimulates cell metabolism
 Increase protein synthesis
 Increase fat breakdown for energy
 Increase glycogen breakdown so that there is an
increase in blood glucose levels to fuel cell growth
Bone growth at the epiphyseal plate
GH function on metabolism
 Stimulates cell metabolism
 Increase protein synthesis
 amino acid transport through cell membrane
  catabolism of protein
 Increase fat breakdown for energy
 Carbohydrate metabolism








use of glucose for energy
glycogen deposition in the cell
blood glucose levels
insulin secretion
GH Function: Indirect Effect
 Most growth occurs through the
indirect method
 GH acts as a tropic hormone
 Signals the liver to produce Insulinlike Growth Factors (IGF)
Growth Regulation: Neuroendocrine
pathway
Location
Hypothalamus
Hormone
Growth hormone release
hormone (GHRH)
Growth hormone inhibiting
hormone (GHIH) aka
somatostatin (SS)
Anterior Pituitary Growth hormone (GH)
Liver & other
Insulin-like growth factor
tissues
(IGF)
IGF-1: Insulin-like Growth Factor 1
targets almost every cell in the body
including the muscle, cartilage, bone,
and skin cells
Stimulates hypertrophy and
hyperplasia of the cells
Growth Hormone Regulation
hypothalamus
growth hormone
releasing hormone
(GHRH)
growth hormone
inhibiting hormone
Somatostatin (GHIH)
anterior pituitary
growth hormone (GH)
GH half-life is
20 – 30 min
liver
Insulin-like growth
factor 1 (IGF-1)
Negative Feedback
 High levels of IGF-1
 Stimulates GHIH/SS
 decreased secretion
of GH
 High levels of GH
 inhibits GHRH
GH Secretion
 Secreted in bursts
(not continuous)
 GH his released
most during sleep
 optimal at night time
 Changing sleeping
pattern affects GH
release
 GH production
declines with age
Increasing GH Production




Exercise regularly
8 hours of sleep
Protein-rich diet
Avoid Stress
GH Associated Disorders
 Dwarfism
 Gigantism
 Acromegaly
Dwarfism
 Deficiency in GH
 Short stature
 Adult 4'10" or
shorter
 Proportional body
 Affects 1/10 000
 Occurs in children
 GH absent during
child’s development
Gigantism – Vertical Growth
 Excessive growth and
height
 Continuous secretion
of GH
 Open epiphyseal plate
 Affects bone growth
length
 Occurs during
childhood
World’s Tallest Man:
Robert Wadlow (1918-1940)
8 feet 11 inches and 439 pounds when
he died
Tallest person alive
 Sultan Kosen
 born in Turkey
 8 feet 1 inch
http://www.youtube.com/watch?v=ODFHC2XCtjU
http://www.youtube.com/watch?v=Rf-lcBzZwC4
Gigantism Cause
 Pituitary Adenoma
 Tumour formed by
pituitary gland
 Secretes excessive GH /
IGF-1
 Non cancerous
 Average brain size
 Skull grows but brain
size stays the same,
thus the brain function
is unchanged
Gigantism Problems
 Poor blood flow due to large body
 Increased muscle mass but weaker
muscle
 Excess GH produces salt in muscle
tissues
 Muscles swell with water
 Results in disproportional muscle growth
 weaker muscles
Comparing Growths
Acromegaly – Lateral Growth
 Increased GH
secretion in adults
 Closed epiphyseal
plate
 Bone lengthening
stopped
 Bone width increases
 Slow progression
Acromegaly: Physical Effects
 Bone thickens




Forehead expands
Eyebrow ridges bulge outwards
Cheekbones more prominent
Mandible enlarges and pushes lower
teeth outwards and become widely
space
Acromegaly: Physical Effects
 Soft tissue harden
 Deeper voice because larynx enlarges
 Bigger tongue and lips that affects
breathing
 Cartilage in nose enlarges making nose
broader
Acromegaly: Effect on Muscles
 Impaired Movements
 Enlargement of bones
crushes peroneal nerve
in knee
 Nerve carries messages
to move foot and lower
leg
 Nerve cannot send
messages to leg to
trigger walking motion
 Also cause muscle
numbness
 Leads to early death
Acromegaly: Heart Defects
 Heart tissue stiffen
 heart cannot contract and relax
 Ventricle harder to fill up
 Heart grows bigger in order to pump
out sufficient blood
Acromegaly: Lung Defect
 As bones grow,
rib cage expands
 Diaphragm is
stretched thin
and loses
elasticity
 Breathing is
reduced
The Pineal Gland
The pineal gland is a
small, cone – shaped
structure located in
the center of the
brain, diencephalon.
The pineal gland is
composed of
pinealocytes & glial
cells.
Connects endocrine
with nervous system
Functions
 Secretion of the Hormone Melatonin
 Regulation of Endocrine Functions
 Conversion of Nervous System
Signals to Endocrine Signals
 Causes Feeling of Sleepiness
 Influences Sexual Development
 Precursor of melatonin is serotonin.
 Synthesis and secretion of melatonin
is affected by light exposure to the
eyes.
Biological Effects of Melatonin
 Helps keep body’s circadian rhythms in
synchrony with light-dark cycle
 Effects on Reproductive Function
 Anti-gonadotropic
 Effects on Sleep and Activity
 Acts as antioxidant to remove free
radicals
 Alterations in melanin pigment
distribution