GROWTH HORMONE ENDO BLOCK 412 Dr Shaikh Mujeeb

GROWTH HORMONE ENDO BLOCK 412 Dr. Shaikh Mujeeb Ahmed Assistant Professor Al. Maarefa College

Objectives The student should be able to: q Identify the factors that affect growth beside the growth hormone. q Identify the hormones that affect growth beside the growth hormone. q Describe the metabolic effect of growth hormone. q Identify the relationship between growth hormone and insulin-like growth factors. q Explain the functions of the growth hormone. q Define the factors that influence the growth hormone secretion. q Describe the growth hormone abnormalities. q Describe the functions of melatonin hormone. q 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 • • • 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 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 • • 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=ODFHC 2 XCtj. U http: //www. youtube. com/watch? v=Rf-lc. Bz. Zw. C 4

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 Ø Human physiology, Lauralee Sherwood, seventh edition. Ø Text book physiology by Guyton &Hall, 11 th edition. Ø Physiology by Berne and Levy, sixth edition. 38