GROWTH HORMONE
Dr. Amel Eassawi
OBJECTIVES
The student should be able to:
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Identify the factors that affect growth beside the growth hormone.
Identify the hormones that affect growth beside the growth hormone.
Describe the metabolic effect of growth hormone.
Identify the relationship between growth hormone and insulin-like
growth factors.
Explain the functions of the growth hormone.
Define the factors that influence the growth hormone secretion.
Describe the growth hormone abnormalities.
Describe the functions of melatonin hormone.
Explain the biological effect of melatonin hormone.
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FACTORS AFFECT 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
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HORMONES REGULATING GROWTH
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Thyroid Hormone
Insulin: Stimulates IGF-1 (Somatomedin)
Prolactin: Stimulates IGF-1
Testosterone
Estrogen
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HORMONES REGULATING 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 stimulate excessive growth
– Androgens
• Play role in pubertal growth surge, stimulate protein
synthesis in many organs
– Estrogens
• Effects of estrogen on growth prior to bone maturation are
not well understood.
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GROWTH RATE
• Not continuous
• Factors responsible for promoting growth are not the
same throughout growth period
• Fetal growth
– Promoted largely by hormones from placenta
– GH plays no role in fetal development
• Postnatal growth spurt
– Displayed during first two years of life
• Pubertal growth spurt
– Occurs during adolescence
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Growth Hormone
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GROWTH HORMONE FUNCTIONS
DIRECT EFFECT
• Growth hormone 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
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BONE GROWTH AT THE EPIPHYSEAL PLATE
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GROWTH HORMONE FUNCTIONS
INDIRECT EFFECT
• Most growth occurs through the indirect method.
• GH acts as a tropic hormone.
• stimulating liver’s production of somatomedins
– Primary somatomedin is insulin-like growth factor (IGF-1)
• Acts directly on bone and soft tissues to bring about
most growth-promoting actions
• Stimulates protein synthesis, cell division, and
lengthening and thickening of bones
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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)
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GROWTH HORMONE SECRETION
• Secreted in bursts (not continuous)
• GH released mostly during sleep
– optimal at night time
– Changing sleeping pattern affects GH release
• GH production declines with age
Increased Growth Hormone Secretion:
• Exercise regularly
• 8 hours of sleep
• Protein-rich diet
• Avoid Stress
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GH ASSOCIATED DISORDERS
• Dwarfism
• Gigantism
• Acromegaly
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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
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GIGANTISM
• Excessive growth and height
• Continuous secretion of GH
• Open epiphyseal plate
– Affects bone growth
length
• Occurs during childhood
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Robert Wadlow the world’s Tallest Man
(1918-1940)
8 feet 11 inches and 439 pounds when he died
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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
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COMPARING GROWTHS
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GIGANTISM
• 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
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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
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ACROMEGALY
• Increased GH secretion in adults
• Closed epiphyseal plate
– Bone lengthening stopped
• Bone width increases
• Slow progression
Effect of Acromegaly:
Soft tissue harden
– Deeper voice because larynx enlarges
– Bigger tongue and lips that affects breathing
– Cartilage in nose enlarges making nose broader
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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
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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
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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
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ACROMEGALY: LUNG DEFECT
• As bones grow, rib
cage expands
• Diaphragm is
stretched thin and
loses elasticity
• Breathing is
reduced
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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 and glial
cells.
• Connects endocrine with
nervous system
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PINEAL GLAND
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.
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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
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REFERENCES
 Human physiology, Lauralee Sherwood, seventh
edition.
 Text book physiology by Guyton &Hall,11th
edition.
 Physiology by Berne and Levy, sixth edition.
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