Human Glands and Hormones (Endocrine System): Detailed Notes + Functions
The endocrine system is a network of ductless glands that secrete hormones into the bloodstream. These chemical messengers coordinate growth, metabolism, reproduction, stress response, immunity, and fluid-electrolyte balance.
What Are Glands?
Glands are specialized organs that produce and release substances required by the body. They are classified into:
1) Endocrine Glands
- Ductless glands
- Secrete hormones directly into blood
- Effects are often slower but long-lasting
2) Exocrine Glands
- Have ducts
- Secrete products onto surfaces or into cavities
- Examples: salivary glands, sweat glands, gastric glands, pancreas (exocrine part)
What Are Hormones?
Hormones are chemical messengers produced by endocrine glands. They travel via blood to specific target organs, where they regulate body functions such as:
- Growth and development
- Metabolism and energy balance
- Reproduction and puberty
- Stress response
- Water, electrolytes, and blood pressure control
Major Endocrine Glands & Hormones
1) Hypothalamus
Location: Base of brain • Role: Links nervous and endocrine systems; controls pituitary.
Key hormones (releasing/inhibiting):
- TRH (thyrotropin-releasing hormone)
- CRH (corticotropin-releasing hormone)
- GnRH (gonadotropin-releasing hormone)
- GHRH (growth hormone-releasing hormone)
- Somatostatin (inhibits GH and TSH)
- Dopamine (inhibits prolactin)
2) Pituitary Gland (Master Gland)
Location: Below hypothalamus • Parts: Anterior and Posterior pituitary.
Anterior Pituitary Hormones
- GH (growth hormone): growth, tissue repair, metabolism
- TSH: stimulates thyroid to release T3/T4
- ACTH: stimulates adrenal cortex (cortisol production)
- FSH: follicle development (female), spermatogenesis (male)
- LH: ovulation/corpus luteum (female), testosterone synthesis (male)
- Prolactin: milk production
Posterior Pituitary Hormones (released; produced in hypothalamus)
- ADH (vasopressin): kidney water reabsorption, supports BP
- Oxytocin: uterine contraction, milk ejection reflex
3) Pineal Gland
Hormone: Melatonin
- Regulates sleep-wake (circadian) rhythm
- Influenced by light exposure
4) Thyroid Gland
Location: Front of neck
Hormones:
- T3 (triiodothyronine) and T4 (thyroxine): regulate metabolism, heat production, growth
- Calcitonin: lowers blood calcium (antagonist to PTH)
5) Parathyroid Glands
Location: 4 small glands behind thyroid • Hormone: PTH
- Increases blood calcium (bone resorption, kidney calcium reabsorption, vitamin D activation)
- Supports neuromuscular function and cardiac stability via calcium regulation
6) Adrenal Glands
Location: Above kidneys • Parts: Cortex and Medulla
Adrenal Cortex
- Cortisol: stress response, anti-inflammatory effects, raises glucose availability
- Aldosterone: sodium and water retention; potassium excretion → BP control
- Androgens: contribute to secondary sex traits (especially in females)
Adrenal Medulla
- Adrenaline (epinephrine) and Noradrenaline (norepinephrine): fight-or-flight response
7) Pancreas (Islets of Langerhans)
Type: Both endocrine and exocrine gland
Hormones:
- Insulin: lowers blood glucose (uptake/storage)
- Glucagon: raises blood glucose (glycogenolysis/gluconeogenesis)
- Somatostatin: inhibits insulin and glucagon release (regulatory)
8) Gonads (Reproductive Glands)
Testes (Male)
- Testosterone: spermatogenesis, muscle mass, libido, male secondary sexual characteristics
Ovaries (Female)
- Estrogen: female secondary sexual characteristics, endometrial growth
- Progesterone: maintains endometrium, supports pregnancy
9) Thymus
Hormone: Thymosin
- Promotes T-lymphocyte maturation
- Most active in childhood (immune development)
10) Placenta (Temporary Endocrine Organ in Pregnancy)
- hCG: supports corpus luteum early pregnancy
- Estrogen and Progesterone: maintain pregnancy
- Human placental lactogen (hPL): supports fetal nutrition; alters maternal metabolism
Quick Revision Table (Endocrine Glands & Key Hormones)
| Gland | Main Hormone(s) | Primary Function |
|---|---|---|
| Hypothalamus | TRH, CRH, GnRH, GHRH, Somatostatin, Dopamine | Controls pituitary (releasing/inhibiting hormones) |
| Pituitary | GH, TSH, ACTH, FSH, LH, Prolactin; ADH, Oxytocin | Regulates growth + controls major endocrine glands |
| Thyroid | T3, T4, Calcitonin | Metabolism; calcitonin lowers calcium |
| Parathyroid | PTH | Raises blood calcium |
| Adrenal | Cortisol, Aldosterone, Androgens; Adrenaline/Noradrenaline | Stress + BP/electrolytes + fight/flight |
| Pancreas | Insulin, Glucagon, Somatostatin | Blood glucose regulation |
| Gonads | Testosterone; Estrogen/Progesterone | Reproduction + secondary sexual traits |
| Pineal | Melatonin | Sleep-wake rhythm |
| Thymus | Thymosin | T-cell maturation (immunity) |
| Placenta | hCG, Estrogen, Progesterone, hPL | Maintains pregnancy + supports fetal growth |
Clinical Correlation (Nursing Focus)
- Monitor vitals and labs: glucose, electrolytes (Na+, K+, Ca2+), thyroid profile, cortisol as indicated.
- Recognize red flags: hypoglycaemia symptoms, thyroid storm/myxoedema signs, adrenal crisis features.
- Medication adherence education: insulin timing, thyroid meds (often morning), steroid tapering safety.
- Patient teaching: lifestyle support (diet, exercise), follow-up testing, when to seek urgent help.
FAQs (SEO)
What is the difference between endocrine and exocrine glands?
Endocrine glands are ductless and secrete hormones into the blood. Exocrine glands use ducts to deliver secretions (like sweat, saliva, or digestive enzymes) onto surfaces or into cavities.
Why is the pituitary called the master gland?
The pituitary releases hormones that control other endocrine glands—e.g., TSH controls the thyroid, ACTH controls the adrenal cortex, and FSH/LH control the gonads.
Which hormones regulate blood glucose?
Insulin lowers blood glucose by increasing cellular uptake and storage. Glucagon raises blood glucose by stimulating glycogen breakdown and gluconeogenesis.
Which hormone regulates water balance?
ADH (vasopressin) increases water reabsorption in the kidneys, supporting fluid balance and blood pressure.
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