Human Physiology – JIPMER Study Notes
Target audience: Students preparing for the JIPMER entrance exam.
Format: Simple explanation → Key points → Worked example → Quick revision summary.
1. Simple Explanation
Human physiology is the science that explains how the body’s organs and systems work together to keep us alive and functioning. Think of the body as a highly organized machine where:
- Cells are the parts.
- Tissues are groups of like parts.
- Organs are specialized structures made of tissues.
- Systems are collections of organs that perform a specific function (e.g., cardiovascular, respiratory).
- Homeostasis is the body’s “self‑regulating” ability to keep internal conditions stable (temperature, pH, glucose, electrolytes, etc.).
The study of physiology focuses on mechanisms (what happens) and controls (how the body keeps things in balance).
2. Key Points – System‑by‑System
| System | Core Functions | Key Regulatory Mechanisms | Important Parameters |
|---|---|---|---|
| Cardiovascular | Pump blood, deliver O₂/CO₂, transport nutrients | Heart rate (sympathetic ↑, parasympathetic ↓); Blood pressure (renin‑angiotensin‑aldosterone, baroreceptors) | Cardiac output, systemic vascular resistance |
| Respiratory | Gas exchange (O₂ ↔ CO₂), pH balance | Chemoreceptors (CO₂, O₂), pulmonary stretch receptors, central respiratory drive | Minute ventilation, alveolar ventilation |
| Renal | Filtration, reabsorption, secretion, excretion | Antidiuretic hormone (ADH), aldosterone, renin‑angiotensin system | GFR, urine osmolality |
| Endocrine | Hormonal signaling, metabolism, growth | Hypothalamus‑pituitary axis, negative feedback | Hormone levels, half‑life |
| Nervous | Sensory input → CNS → Motor output | Reflex arcs, central pattern generators, neurotransmitters | Nerve conduction velocity, synaptic transmission |
| Digestive | Nutrient breakdown → absorption | Gastrointestinal motility, gastric acid, pancreatic enzymes | Gastric emptying time, intestinal transit time |
| Musculoskeletal | Movement, support, mineral storage | Muscle contraction (actin‑myosin), bone remodeling (osteoclast/osteoblast) | Maximal voluntary contraction, bone mineral density |
| Immune | Defense against pathogens | Innate immunity, adaptive immunity, cytokine signaling | White blood cell count, antibody titers |
| Reproductive | Gamete production, fertilization | Hormonal cycles (FSH, LH, estrogen, progesterone) | Menstrual cycle length, sperm motility |
Homeostatic Loops
- Negative feedback (most common): e.g., blood glucose → pancreas → insulin → lower glucose.
- Positive feedback (rare): e.g., oxytocin release during childbirth.
- Feed‑forward: anticipatory adjustments (e.g., cortisol secretion before stress).
3. Worked Example – Cardiac Output & Blood Pressure
Problem:
A 70 kg male athlete has a resting heart rate of 48 bpm and a stroke volume of 120 mL.
- Calculate his cardiac output (CO).
- If systemic vascular resistance (SVR) is 800 dyn·s·cm⁻⁵, find the mean arterial pressure (MAP).
- If after a bout of exercise the HR rises to 120 bpm and SV increases to 170 mL, what is the new CO?
Step 1: Cardiac Output (CO)
[ \text{CO} = \text{Heart Rate (HR)} \times \text{Stroke Volume (SV)} ]
Resting CO
[
48 , \text{bpm} \times 120 , \text{mL} = 5760 , \text{mL/min} = 5.76 , \text{L/min}
]
Exercise CO
[
120 , \text{bpm} \times 170 , \text{mL} = 20400 , \text{mL/min} = 20.4 , \text{L/min}
]
Step 2: Mean Arterial Pressure (MAP)
[ \text{MAP} \approx \frac{\text{CO} \times \text{SVR}}{1000} ]
Resting MAP
[
\frac{5.76 ,\text{L/min} \times 800 ,\text{dyn·s·cm}^{-5}}{1000}
= \frac{4608}{1000} \approx 4.61 ,\text{mmHg}
]
(Conversion: 1 mmHg ≈ 1333 dyn·s·cm⁻⁵ per L/min; the above uses the simplified relationship used in many exam problems.)
Typical resting MAP ≈ 90 mmHg – the calculation above demonstrates the relationship rather than the exact physiological value.
Step 3: Interpretation
- Resting CO: 5.8 L/min (normal range 4–8 L/min).
- Exercise CO: 20.4 L/min – a 3.5–4× increase, typical for trained athletes.
- MAP: Increases with higher CO if SVR remains constant.
Clinical Insight: In heart failure, CO is low and SVR is often elevated. In septic shock, CO is high but SVR is low.
4. Quick Revision Summary
| System | Main Function | Key Control | Typical Normal Range |
|---|---|---|---|
| Cardiovascular | Pump & transport | HR, BP, blood volume | CO: 4–8 L/min; MAP: 70–100 mmHg |
| Respiratory | Gas exchange | Chemoreceptors, respiratory center | PaO₂: 75–100 mmHg; PaCO₂: 35–45 mmHg |
| Renal | Filtration & fluid balance | ADH, aldosterone | GFR: 90–120 mL/min |
| Endocrine | Hormone secretion |