Endocrine System Notes with PDF
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Overview of the Endocrine System
- Definition: The endocrine system is a network of ductless glands that secrete hormones directly into the bloodstream.
- Function: Hormones act as chemical messengers to regulate various bodily functions, including growth, metabolism, reproduction, and mood.
Major Endocrine Glands and Their Hormones
The following table summarizes the primary glands, their key hormones, and essential functions.
| Gland | Location / Key Features | Hormone(s) Produced | Primary Function(s) of Hormone |
|---|---|---|---|
| Pituitary Gland | Base of the brain; smallest gland (pea-sized). Known as the “master gland”. | • Growth Hormone (Somatotropin) • ADH (Antidiuretic Hormone) • Oxytocin • TSH (Thyroid-Stimulating Hormone) |
• Stimulates growth. • Controls urine output from kidneys. • Social bonding; uterine contractions; milk ejection. • Stimulates the thyroid gland. |
| Thyroid Gland | Front of the neck, near the voice box. | • Thyroxine (T4) • Triiodothyronine (T3) |
• Regulates metabolism, heart function, digestion, brain development, bone health. |
| Parathyroid Glands | Located on the thyroid gland. | • Parathyroid Hormone (PTH) | • Regulates blood calcium and phosphate levels. (Can function independently of the pituitary). |
| Adrenal Glands | On top of the kidneys. | • Cortisol • Adrenaline (Epinephrine) |
• Stress response; metabolism. • “Fight or flight” response: increases heart rate, blood pressure; prepares body for sudden action. |
| Pancreas | Mixed gland (has both endocrine and exocrine functions). | • Insulin • Glucagon |
• Endocrine: Secretes hormones into blood to control blood sugar. • Exocrine: Produces pancreatic juice (sent to duodenum via duct). |
| Gonads: Ovaries | Female reproductive glands. | • Estrogen (e.g., Estrone) • Progesterone |
• Estrogen: Female secondary sexual characteristics; regulates menstrual cycle. (Secreted by follicles & corpus luteum). • Progesterone: Prepares uterus for pregnancy. (Secreted by the Corpus Luteum). Production decreases after menopause. |
| Gonads: Testes | Male reproductive glands. | • Testosterone | • Testosterone: Primary male sex hormone; produced by Leydig cells. (Also produced in small amounts by female ovaries/adrenals). Progesterone is also produced in small amounts here. |
| Pineal Gland | In the brain. | • Melatonin | • Regulates sleep-wake cycle (circadian rhythm). Production increases in darkness. |
| Thymus | In the upper chest. | – | – |
Detailed Focus on Key Hormones
Insulin
- Source: Pancreas, specifically the beta (β) cells of the Islets of Langerhans. Can also be sourced from dahlia plant roots.
- Chemical Nature: A peptide hormone (composed of 51 amino acids), not an enzyme, vitamin, or salt. Contains Zinc. Excipients can include disodium hydrogen phosphate, m-cresol, etc.
- Function: Regulates blood glucose levels. Allows cells to use glucose for energy. It is the body’s main anabolic (building-up) hormone, crucial for metabolizing carbohydrates, fats, and proteins.
- Dysfunction:
- Deficiency causes diabetes.
- Excess causes hypoglycemia (low blood sugar).
- Stimulation: Its production is stimulated by the hormone Secretin (from the duodenum).
Oxytocin
- Source: Produced in the brain and secreted by the pituitary gland.
- Chemical Nature: A peptide hormone, but not a protein (unlike keratin or collagen).
- Function:
- Often called the ‘love hormone’ or ‘cuddle hormone’ due to its role in social bonding (e.g., mother-baby attachment).
- Stimulates uterine contractions during childbirth.
- Responsible for milk ejection from mammary glands (let-down reflex); injected into livestock for this purpose.
Thyroxine (T4) & Triiodothyronine (T3)
- Source: Thyroid gland.
- Composition: Iodine-containing hormones synthesized from the amino acid Tyrosine and Iodine. T4 has four iodine atoms; T3 has three.
- Regulation: Production is stimulated by TSH from the pituitary gland.
- Function: Essential for metabolism, heart function, digestion, brain development, and muscle control.
- Deficiency: Lack of iodine leads to Goitre (enlarged thyroid), common in hilly areas with iodine-poor soil. Prevented by consuming iodised salt.
Adrenaline (Epinephrine)
- Source: Adrenal glands.
- Function: The primary ‘fight or flight’ hormone.
- Effects: Increases heart rate and blood pressure; widens blood vessels to key organs; produces a feeling of excitement in response to danger, anger, or fear.
Estrogen and Progesterone
- Source: Mainly the ovaries (follicles and corpus luteum); also the placenta during pregnancy.
- Function (Estrogen): Main female sex hormone; responsible for secondary sexual characteristics and regulating the menstrual cycle.
- Post-Menopause: Production of estrogen and progesterone by the ovaries significantly decreases or stops.
Additional Hormones and Facts
- Gastrin: Stimulates acid secretion in the stomach. Not involved in blood pressure regulation.
- Pheromones: Chemical substances produced by insects (and other animals) to attract partners via smell.
- Somatotropin (Growth Hormone): Production increases during exercise.
- Hormone Classification: Thyroxine is an example of an amino acid-derived hormone.
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