Biology: Organ Systems
Free MCAT study guide — Biological and Biochemical Foundations of Living Systems
Cardiovascular System
CO = SV × HR | MAP ≈ DBP + ⅓(SBP − DBP)
Respiratory System
Key Point: Right shift (↓ affinity): ↑CO₂, ↑H⁺, ↑temp, ↑2,3-BPG. Left shift: opposite + fetal Hb, CO.
Renal System
| Segment | Function | Regulation |
|---|---|---|
| Glomerulus | Filtration (size + charge barrier) | GFR = ~125 mL/min |
| PCT | Reabsorbs 65% (glucose, AAs, Na⁺, HCO₃⁻) | Obligatory water reabsorption |
| Descending LoH | Water out (permeable) | Concentrates filtrate |
| Ascending LoH | NaCl out (impermeable to H₂O) | Dilutes filtrate, NKCC2 |
| DCT | Na⁺ reabsorption, Ca²⁺ | Aldosterone, PTH |
| Collecting duct | Water (ADH), K⁺ secretion | ADH → aquaporin-2 |
Immune System
Key Point: MHC I: all nucleated cells → CD8⁺ (cytotoxic). MHC II: APCs only → CD4⁺ (helper). Rule of 8.
Endocrine System
Key Point: Anterior pituitary (FLAT PiG): FSH, LH, ACTH, TSH, Prolactin, GH. Posterior: ADH, Oxytocin.
Nervous System
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