Overview
This lecture revises the endocrine system and homeostatic mechanisms, explaining their interaction and focusing on key hormones, negative feedback, and main homeostatic examples important for exams.
Endocrine and Homeostasis Systems Overview
- The endocrine and homeostatic systems work closely together to maintain the body's internal stability.
- Endocrine glands secrete hormones (chemical messengers) directly into the bloodstream, affecting processes like pH, water, salt, and glucose balance.
- Hormones act slowly over time, in contrast to the fast-acting nervous system.
- Homeostasis involves keeping the internal environment stable (e.g. pH, water, glucose).
Endocrine Glands and Hormones
- Endocrine glands (no ducts): hypothalamus, pituitary, thyroid, pancreas, adrenal, ovaries, and testes.
- Exocrine glands (have ducts): e.g. salivary glands.
- Pancreas is both exocrine and endocrine.
- Key hormones:
- Hypothalamus: ADH (water balance)
- Pituitary: TSH, LH, FSH, GH, ICSH (various functions)
- Thyroid: thyroxine (metabolism)
- Pancreas: insulin & glucagon (blood sugar)
- Adrenal: adrenaline & aldosterone (stress & salt)
- Ovaries: estrogen; Testes: testosterone (reproduction)
Homeostatic Feedback Loops (Template)
- Stepwise process: Stimulus → Receptor → Control Center → Corrective Measure → Effector → Response (return to norm).
- Stimulus: change detected (e.g. low hormone, temperature).
- Receptor: detects change (e.g. gland, arteriole, skin receptor).
- Control center: decides response (e.g. brain, gland).
- Corrective measure: hormone secreted to restore balance.
- Effector: tissue (muscle/gland) acts on corrective measure.
- Response: restores normal state, described specifically.
Examples of Homeostatic Regulation
- Thyroxine (Metabolism):
- Low thyroxine detected by pituitary, which releases TSH to stimulate thyroid → more thyroxine → metabolism normalizes.
- Negative feedback: increased thyroxine inhibits TSH.
- Disorders: hyperthyroidism (too much), hypothyroidism (too little).
- Salt Balance (Aldosterone):
- Low salt detected by afferent arterioles in kidney, which secrete renin → triggers angiotensin → stimulates adrenal cortex to release aldosterone → increases salt absorption in kidneys.
- Negative feedback maintains salt/water balance.
- Thermoregulation (Cold):
- Cold detected by skin receptors → hypothalamus signals dermal arterioles to constrict via circular muscles; shunt vessels relax so blood stays in subcutaneous layer → reduces heat loss.
Key Terms & Definitions
- Endocrine gland — Secretes hormones directly into the bloodstream.
- Exocrine gland — Secretes substances via ducts to specific locations.
- Homeostasis — Maintenance of a stable internal environment.
- Negative feedback — Process where the body reverses a change to restore balance.
- Stimulus — Change in environment (internal or external) triggering a response.
- Effector — Organ/muscle/gland that carries out the corrective response.
- Osmolarity — Ratio of water to solutes (like salt) in body fluids.
- Subcutaneous layer — Fat layer beneath the skin.
Action Items / Next Steps
- Review and memorize the functions and hormones of each endocrine gland.
- Practice explaining homeostatic feedback loops using the template (stimulus to response).
- Use the study guide and flashcards for efficient revision.
- Attempt past paper questions, checking your answers with memos.
- Prepare for next week’s live revision session.