1) The Core Idea: Homeostasis
The body constantly balances internal conditions (temperature, pH, blood glucose, blood pressure, oxygen, electrolytes). This stable internal balance is called homeostasis. When homeostasis fails, symptoms appear and disease risk increases. Think of homeostasis as the body’s “autopilot”.
1.1 Negative vs Positive Feedback
Most regulation uses negative feedback: change triggers a response that returns the system toward normal. Example: high blood glucose → insulin release → glucose decreases. Positive feedback amplifies change temporarily for a specific outcome, like childbirth contractions.
2) Cellular Physiology Essentials
Many clinical concepts begin at the cell membrane. Cells maintain different concentrations of ions inside vs outside. This difference produces membrane potential and supports nerve/muscle function.
2.1 Membrane Transport
- Diffusion: movement from high to low concentration
- Facilitated diffusion: via channels/carriers (no ATP)
- Osmosis: water movement based on solute concentration
- Active transport: uses ATP (e.g., sodium-potassium pump)
Clinical link: Dehydration, edema, IV fluids, and electrolyte imbalance all relate to osmosis and transport.
3) Nervous System Physiology (High Yield)
Nerves communicate using electrical signals (action potentials) and chemical messengers (neurotransmitters). Focus on: stimulus → depolarization → action potential → synapse → response.
- Receptors: detect change (pain, pressure, temperature)
- Reflex arcs: quick protective responses (knee jerk)
- Autonomic nervous system: sympathetic (fight/flight) vs parasympathetic (rest/digest)
4) Cardiovascular Physiology (Vitals + Perfusion)
The cardiovascular system delivers oxygen and nutrients and removes waste. AHS students should master: heart rate, blood pressure, cardiac output, and peripheral resistance.
- Cardiac output (CO) = heart rate × stroke volume
- Blood pressure depends on CO and resistance
- Perfusion means blood flow to tissues; poor perfusion → dizziness, shock, organ dysfunction
5) Respiratory Physiology (Oxygenation Basics)
Respiration includes ventilation (air movement) and gas exchange (oxygen/carbon dioxide transfer). Oxygen moves into blood across alveoli; CO₂ leaves blood similarly.
- Ventilation: airway patency + breathing mechanics
- Diffusion: depends on surface area and membrane thickness
- Hemoglobin: carries most oxygen; anemia reduces oxygen delivery
Clinical link: Asthma affects airflow; pneumonia affects diffusion; anemia affects oxygen-carrying capacity.
6) Renal Physiology (Fluid & Electrolytes)
Kidneys regulate fluid volume, electrolytes, and pH. Key processes: filtration, reabsorption, secretion, and excretion. Even a basic understanding helps interpret creatinine, urine output, dehydration, and edema.
7) Endocrine Physiology (Hormonal Control)
Hormones coordinate longer-term regulation: metabolism, growth, reproduction, stress. Examples: insulin/glucagon (glucose), thyroid hormones (metabolic rate), cortisol (stress response).
8) Study Strategy (Physiology)
- Start with homeostasis + feedback loops.
- Make flowcharts: stimulus → sensor → control center → effector.
- Use case questions: “What happens to BP if vessels dilate?”
- Revise with diagrams + short notes, then attempt MCQs.
9) Quick FAQs / MCQs
- Q: Most common type of regulation in body? A: Negative feedback.
- Q: CO formula? A: Heart rate × stroke volume.
- Q: Osmosis means? A: Water movement based on solute gradient.
- Q: Sympathetic system generally does? A: Increases heart rate, prepares for stress.
Next: Behavioral Science — because patient outcomes depend on human behavior and communication too.