Hormones are chemicals produced by endocrine glands that are transported via blood to target organs and regulate physiological processes by binding to specific receptors. There are two types of glands - endocrine glands that secrete hormones directly into the bloodstream and exocrine glands that secrete through ducts. The hypothalamus regulates hormone release from the pituitary gland which controls other glands like the thyroid, adrenals, ovaries and testes to maintain homeostasis. Hormones can be lipid soluble which bind intracellular receptors and control gene expression, or water soluble which signal through second messengers and phosphorylation to modify enzyme activity. Hormonal imbalances can cause diseases like Addison's, Cushing's, acromegal

1. HORMONES AND SIGNAL TRANSDUCTION
 Hormones are chemicals produced by the cell and transported via
the blood to their respective target organs, binding to which cognate
receptors leads to the regulation of certain physiological processes.
 Receptors are specific for each type of signal (hormone).
 Each cell has different kinds of receptors.
 Hormones are secreted by two glands in animals, namely:
• Endocrine glands- These glands lack ducts and pass their secretion directly to the sites
of action through the blood stream e.g. adrenal gland, pituitary, thyroid, parathyroid,
ovaries, testes, etc.
• Exocrine glands: These glands have ducts through which they pass their secretions e.g.
sweat, liver, etc.
 The endocrine system and the nervous system work together to
maintain homeostasis (balance) and are regulated by the
hypothalamus in the brain.
 The hypothalamus secret chemicals that either stimulate or suppress
the release of hormones by the pituitary gland.

2. Hormones, their secretary glands and functions
Antidiuretic hormone Hypothalamus gland Regulate fluid balance in the
kidneys
Growth hormone Pituitary gland Regulates body growth and
development
Thyroxine Thyroid gland Regulates body metabolism
Insulin and Glucagon Pancrease gland Regulates blood sugar level
Epinephrine and
Norepinephrine
Adrenal gland Regulates heart rate and blood
pressure
Testosterone Testes gland Development of sperms and male
characteristics
Oestrogen and progesterone Ovaries gland Development of eggs and female
characteristics

3. CLASSIFICATION OF HORMONES
Water soluble (Hydrophilic) Lipid soluble (Hydrophobic)
Receptor in cell membrane Receptor inside the cell
Second messenger often involved
Protein kinases activated
Hormone-receptor complex binds
hormone response elements (HRE of
enhancer regions) in DNA.
Protein phosphorylation to modify
activity of enzymes (requires minutes)
-
Control of gene expression through
proteins like cAMP response element
binding (CREB) protein (requires hours)
Control of gene expression (requires
hours)
Examples:
• Insulin
• Glucagon
• Catecholamines
Examples:
• Steroids
• Calcitriol
• Thyroxines
• Retinoic acid

5. MECHANISM OF ACTIONS OF HORMONES
Hormones Act by Binding to Receptors

9. Lipid soluble (Hydrophobic) Water soluble (Hydrophilic)
MECHANISM OF ACTIONS OF HORMONES

10. HORMONAL IMBALANCES
 Hormonal imbalances result in some abnormal conditions in the body, few among which
are:
• Addison’s disease- This occur as a result of insufficient secretion of adrenalin by the adrenal
gland. Symptoms include fatigue, dehydration and skin changes
• Cushing’s disease: This result from hypersecretion of hormones by the pituitary gland and
may result in an overactive adrenal gland. This condition is similar to Cushing’s syndrome,
which occur in people with high corticosteroid levels.
• Acromegaly ( Gigantism): This occur in hypersecretion of growth hormones by the pituitary
gland in children resulting in an abnormally large body.
• Hyperthyroidism: Over secretion of thyroxine by the thyroid hormone. Symptoms include
fast heart rate, sweating, increase metabolism etc.
• Hypothyroidism: Low secretion of thyroxine by the thyroid gland. Symptoms include fatigue,
constipation, dry skin etc.