What is the endocrine system? — A network of glands and organs that secrete hormones directly into the bloodstream. Hormones travel to target cells/organs that have specific receptors. Regulates metabolism, growth, reproduction, blood chemistry, and stress response.

What is the difference between endocrine and exocrine glands? — Endocrine (ductless) glands: Secrete hormones directly into the blood. Examples: thyroid, adrenal, pancreas (islets of Langerhans). Exocrine glands: Secrete substances through ducts to a surface. Examples: sweat glands, salivary glands, pancreas (digestive enzymes). The pancreas is both.

What is a hormone and how does it work? — A chemical messenger produced by an endocrine gland, transported in the blood, and acting on target cells that possess specific receptors. Hormone-receptor binding triggers a response. Key principle: only target cells with the matching receptor respond.

What is the hypothalamus and why is it the "master controller"? — A region of the brain that links the nervous and endocrine systems. It produces releasing hormones that control the pituitary gland — the body's main hormonal control centre. Also controls body temperature, hunger, thirst, sleep, and autonomic functions.

What is the pituitary gland and its two lobes? — The "master gland" — a pea-sized gland below the hypothalamus. Anterior pituitary: Produces and releases TSH, FSH, LH, GH, ACTH, prolactin — controlled by hypothalamic releasing hormones. Posterior pituitary: Stores and releases ADH and oxytocin (made in hypothalamus).

What is negative feedback in the endocrine system? — When the output of a system inhibits further production of the hormone, keeping levels within a narrow normal range. Example: high blood glucose → insulin released → glucose falls → insulin secretion stops. Maintains homeostasis.

What does the thyroid gland produce and what do thyroid hormones do? — Located in the neck. Produces thyroxine (T4) and triiodothyronine (T3) which regulate basal metabolic rate (BMR), growth, and development. Also produces calcitonin (lowers blood calcium). Controlled by TSH from the pituitary.

What is hypothyroidism vs hyperthyroidism? — Hypothyroidism (underactive): Low T3/T4 → slowed metabolism, weight gain, fatigue, cold intolerance. Common cause: Hashimoto's disease (autoimmune). Hyperthyroidism (overactive): High T3/T4 → rapid metabolism, weight loss, heat intolerance, rapid heart rate. Common cause: Graves' disease.

What do the adrenal glands produce? — Located on top of the kidneys. Adrenal medulla (inner): Produces adrenaline (epinephrine) and noradrenaline — the "fight-or-flight" response. Adrenal cortex (outer): Produces cortisol (stress response, metabolism), aldosterone (kidney — regulates Na⁺/K⁺/blood pressure), and androgens (sex hormones).

What is the "fight-or-flight" response and what triggers it? — An acute stress response triggered by the sympathetic nervous system and adrenaline from the adrenal medulla. Effects: increased heart rate and blood pressure, dilated pupils, bronchodilation, redirected blood to muscles, glucose released from liver, reduced digestive activity.

What is the role of cortisol and what is Cushing's syndrome? — Cortisol (released under chronic stress): Raises blood glucose (gluconeogenesis), suppresses the immune system, reduces inflammation. Cushing's syndrome: Excess cortisol → weight gain (especially abdominal), muscle weakness, moon face, hyperglycemia, immunosuppression.

How does the body regulate blood glucose? — Rising blood glucose: Beta cells of pancreatic islets of Langerhans release insulin → cells take up glucose → glycogen synthesis in liver/muscles → glucose falls. Falling blood glucose: Alpha cells release glucagon → glycogen breakdown (glycogenolysis) + gluconeogenesis in liver → glucose rises.

What is insulin and how does it lower blood glucose? — A peptide hormone from beta cells of the pancreatic islets. Actions: (1) Increases glucose uptake by cells (via GLUT transporters). (2) Stimulates glycogenesis (glucose → glycogen) in liver and muscle. (3) Promotes lipogenesis (glucose → fat). (4) Inhibits gluconeogenesis.

What is glucagon and how does it raise blood glucose? — A peptide hormone from alpha cells of the pancreatic islets. Actions: (1) Stimulates glycogenolysis (glycogen → glucose) in the liver. (2) Stimulates gluconeogenesis (amino acids/glycerol → glucose). (3) Promotes lipolysis (fat → fatty acids). Opposes insulin.

What is Type 1 diabetes mellitus? — An autoimmune condition where the immune system destroys pancreatic beta cells → no insulin produced. Without insulin, cells cannot take up glucose → hyperglycemia. Glucose spills into urine (glycosuria). Treatment: lifelong insulin injections. Onset usually in childhood.

What is Type 2 diabetes mellitus? — Either insufficient insulin production or insulin resistance (target cells no longer respond normally to insulin). Associated with obesity, inactivity, and genetics. Blood glucose remains high. Treatment: diet and exercise, metformin, other drugs; sometimes insulin. Most common form (~90% of cases).

What are the symptoms and complications of uncontrolled diabetes? — Symptoms: Polydipsia (thirst), polyuria (frequent urination), fatigue, blurred vision, slow wound healing. Long-term complications: Neuropathy, retinopathy (blindness), nephropathy (kidney failure), cardiovascular disease, foot ulcers. All caused by chronic hyperglycemia damaging blood vessels and nerves.

What hormones control the menstrual cycle? — FSH (pituitary): Stimulates follicle development and oestrogen secretion. Oestrogen (ovary): Thickens uterine lining, triggers LH surge. LH (pituitary): Triggers ovulation (~day 14). Progesterone (corpus luteum): Maintains uterine lining. If no pregnancy: progesterone falls → menstruation.

What is ADH (Antidiuretic Hormone / Vasopressin)? — Made in the hypothalamus, stored in the posterior pituitary. Released when blood is too concentrated (high osmolarity) or blood pressure is low. Acts on kidney collecting ducts → increases water reabsorption → more concentrated urine → blood water level restored.

What is aldosterone and where is it produced? — Produced by the adrenal cortex (zona glomerulosa). Part of the renin-angiotensin-aldosterone system (RAAS). Increases Na⁺ and water reabsorption and K⁺ excretion in kidney tubules → raises blood pressure and blood volume.

What is the thyroid-stimulating hormone (TSH) feedback loop? — Hypothalamus → TRH → anterior pituitary → TSH → thyroid gland → T3/T4. High T3/T4 → negative feedback inhibits TRH and TSH → T3/T4 production decreases. Low T3/T4 → releases inhibition → more TSH released. Classic negative feedback loop.

What is the parathyroid gland and what does PTH do? — Four small glands embedded in the thyroid. Produce Parathyroid Hormone (PTH) which raises blood calcium: (1) Stimulates osteoclasts to break down bone. (2) Increases Ca²⁺ reabsorption in kidneys. (3) Stimulates vitamin D activation → more Ca²⁺ absorbed from gut. Antagonist of calcitonin.

What is the pancreas and its endocrine function? — A mixed exocrine/endocrine gland. Exocrine: Secretes digestive enzymes (amylase, lipase, proteases) via pancreatic duct. Endocrine: Islets of Langerhans contain alpha cells (glucagon), beta cells (insulin), and delta cells (somatostatin — inhibits both).

What is melatonin and what controls its release? — Produced by the pineal gland in response to darkness. Regulates circadian rhythm (sleep-wake cycle). Levels rise at night → promotes sleep. Suppressed by light (especially blue light). Disrupted by jet lag, shift work, and excessive screen use at night.

What are the sex hormones and where are they produced? — Testosterone (mainly testes; small amount in adrenal cortex): male secondary sexual characteristics, sperm production, muscle mass. Oestrogen (mainly ovaries): female secondary sexual characteristics, uterine lining, bone density. Progesterone (corpus luteum): maintains pregnancy. All are steroid hormones.