Endocrine System - Full Notes
Introduction
The endocrine system is a system of glands that release hormones directly into the bloodstream.
Hormones are chemical messengers that regulate various functions of the body.
Works in coordination with the nervous system, but its action is slower and long-lasting.
Functions: growth, metabolism, reproduction, stress response, and maintaining homeostasis.
Characteristics of Endocrine Glands
Ductless glands (secrete directly into blood).
Secrete hormones in small amounts .
Specific in action (act on target organs/cells with receptors).
Maintain balance of body functions (internal environment).
Major Endocrine Glands & Hormones
1. Pituitary Gland
Location: Base of the brain, below hypothalamus.
Called the “Master gland” as it controls other glands.
Divisions:
Anterior Pituitary
Growth Hormone (GH): Body growth, protein synthesis, bone development.
Thyroid Stimulating Hormone (TSH): Stimulates thyroid to release thyroxine.
Adrenocorticotropic Hormone (ACTH): Stimulates adrenal cortex.
Follicle Stimulating Hormone (FSH): Development of eggs in ovaries, sperm in testes.
Luteinizing Hormone (LH): Ovulation in females, testosterone secretion in males.
Prolactin: Milk production.
Posterior Pituitary
Oxytocin: Contraction of uterus during childbirth, milk ejection.
Antidiuretic Hormone (ADH / Vasopressin): Regulates water balance by acting on kidneys.
2. Thyroid Gland
Location: Neck, around trachea.
Hormones:
Thyroxine (T₄) and Triiodothyronine (T₃) : Control metabolism, growth, and energy.
Calcitonin: Lowers blood calcium by depositing calcium in bones.
Disorders:
Hypothyroidism: Goitre, cretinism, myxedema.
Hyperthyroidism: Exophthalmic goitre.
3. Parathyroid Glands
Four small glands behind thyroid.
Hormone:
Parathormone (PTH): Increases calcium levels in blood by dissolving bone calcium.
Works opposite to calcitonin.
4. Adrenal Glands
Two glands on top of kidneys.
Two parts:
Adrenal Cortex:
Cortisol: Stress hormone, regulates metabolism.
Aldosterone: Regulates sodium and water balance (blood pressure).
Sex hormones (small amount).
Adrenal Medulla :
Adrenaline (Epinephrine): “Fight or flight” hormone, increases heartbeat, breathing, glucose.
Noradrenaline (Norepinephrine): Works with adrenaline.
5. Pancreas (Islets of Langerhans)
Mixed gland (exocrine + endocrine).
Endocrine part secretes:
Insulin: Lowers blood sugar (converts glucose → glycogen).
Glucagon : Raises blood sugar (converts glycogen → glucose).
Disorders:
Insulin deficiency → Diabetes Mellitus.
6. Gonads (Sex Glands)
Testes (male) :
Hormone: Testosterone
Functions: Male sexual traits, sperm production, muscle development.
Ovaries (female):
Hormones: Estrogen and Progesterone
Functions: Female sexual traits, menstrual cycle regulation, pregnancy maintenance.
7. Pineal Gland
Location: Brain
Hormone: Melatonin
Function: Regulates sleep-wake cycle, biological rhythms.
8. Thymus Gland
Location: Behind sternum (in chest).
Hormone: Thymosin
Function: Helps in development of T-lymphocytes (immunity in children).
Shrinks after puberty.
Functions of Endocrine System
Controls growth and development.
Regulates metabolism and energy use.
Maintains homeostasis (water, salts, temperature).
Controls reproduction and sexual development .
Helps body respond to stress (fight or flight).
Influences mood and behavior .
Differences: Nervous System vs Endocrine System
Feature Nervous System Endocrine System
Electrical Chemical
Mode of action
impulses messengers
Speed Very fast Slow
Duration Short-term Long-lasting
Pathway Nerves Bloodstream
Common Disorders of Endocrine System
Diabetes Mellitus: Low insulin, high blood sugar.
Goitre: Thyroid enlargement due to iodine deficiency.
Gigantism/Dwarfism : Excess/deficiency of GH.
Cushing’s Syndrome: Excess cortisol.
Addison’s Disease: Adrenal insufficiency.
Summary
The endocrine system is a vital control system of the body.
Works with the nervous system but with long-term regulation.
Hormones act as messengers to maintain stability, growth, metabolism, and reproduction.
Disorders of hormones can lead to serious health issues.
Remember: The endocrine system maintains the internal environment of the body and ensures proper growth, balance, and survival.
