Transcript GROWTH HORMONE

GROWTH HORMONE
ENDO BLOCK 412
Dr. Shaikh Mujeeb Ahmed
Assistant Professor
AlMaarefa College
Objectives
The student should be able to:
 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.
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
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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
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 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 Insulin-like 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
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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
• In one type of dwarfism (the African pygmy
and the Lévi-Lorain dwarf), the rate of growth
hormone secretion is normal or high, but
there is a hereditary inability to form
somatomedin C, which is a key step for the
promotion of growth by growth hormone.
Gigantism – Vertical Growth
• Excessive growth and
height
• Continuous secretion of GH
• Hyperglycemia or full
blown diabetes mellitus
• 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
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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