📌 Introduction & Lecturer Notes

🖇 Transport Across Cell Membrane

🟣 Passive Transport (Diffusion)

🟠 Active Transport

✅ Requires ATP.
Moves substances against gradient (Low → High).
Needs a carrier protein.
Features:
- Saturation (limited carriers).
- Limited transport rate → plateau in curve.

📌 Types of Active Transport

🟣 1. Primary Active Transport (PAT)

Pump Properties:

Mechanism:

Functions:

Other PAT examples:

🟠 2. Secondary Active Transport (SAT)

Uses indirect energy from Na⁺ gradient (made by Na⁺/K⁺ pump).
Na⁺ moves passively in, releasing energy to move another molecule against gradient.

Types:

Cotransport (Symport): Both move same direction.
- Example: Na⁺ + Glucose / Na⁺ + Amino acids.
Counter-transport (Antiport): Move opposite directions.
- Example:
- - Na⁺ in / H⁺ out (renal tubules).
  - Na⁺ in / Ca²⁺ out (cardiac muscle).

Uniporter: moves only one substance.

🖇 Vesicular (Bulk) Transport

1. Endocytosis (into cell):

2. Exocytosis (out of cell):

Vesicle → fuses with membrane → releases content (e.g., neurotransmitters like ACh).

📌 Osmosis & Tonicity

🟣 Osmosis

Osmotic Pressure (Pₒₛₘ):

Pressure required to stop osmosis.
Depends on number of solute particles (not weight).
Ionizing substances (NaCl → 2 particles) exert higher osmotic effect than non-ionizing (Glucose → 1 particle).
Measured in Osmoles / mOsm.

Osmolality vs. Osmolarity:

🟠 Tonicity & Cell Volume

Isotonic:
- Same osmolarity as plasma (e.g. 0.9% saline).
- No water movement → Cell volume constant.
Hypotonic:
- Lower osmolarity (e.g. 200 mOsm/L).
- Water enters cell → Swelling → Hemolysis.
Hypertonic:
- Higher osmolarity (e.g. 400 mOsm/L).
- Water leaves cell → Shrinkage (Crenation).

🚨 Clinical Importance

Failure of Na⁺/K⁺ pump → Na⁺ accumulation → water influx → cell swelling/rupture.
In cardiac muscle, Na⁺/Ca²⁺ exchange critical for relaxation.
Isotonic IV fluids prevent osmotic injury to RBCs.

Physiology