Organ Systems - Complete Interactive Lesson
Part 1: Cardiovascular System
Organ Systems for the MCAT
Part 1 of 7 — Cardiovascular System
Heart Structure
- 4 chambers: RA → RV → Lungs → LA → LV → Body
- Right side: deoxygenated blood to lungs (pulmonary circulation)
- Left side: oxygenated blood to body (systemic circulation)
- LV has thickest walls (pumps against systemic resistance)
Cardiac Cycle
| Phase | AV Valves | Semilunar Valves | What happens |
|---|---|---|---|
| Atrial systole | Open | Closed | Atria contract, blood into ventricles |
| Ventricular systole | Closed (S1) | Open | Ventricles contract, blood into arteries |
| Diastole | Open | Closed (S2) | Ventricles relax, fill with blood |
Key Equations
Blood Vessel Types
- Arteries: Thick walls, elastic, carry blood FROM heart
- Veins: Thin walls, valves, carry blood TO heart
- Capillaries: Single cell thick, site of exchange
Cardiovascular 🎯
Key Takeaways — Part 1
- CO = HR SV; BP = CO TPR
- Left ventricle = thickest (systemic pressure)
- S1 = AV valves close (lub); S2 = semilunar valves close (dub)
- Capillaries = site of gas/nutrient exchange (largest total cross-sectional area)
Part 2: Respiratory System
Organ Systems for the MCAT
Part 2 of 7 — Respiratory System
Gas Exchange
Part 3: Renal & Excretory System
Organ Systems for the MCAT
Part 4 of 7 — Renal System (Kidneys)
Nephron Structure
Key Functions by Segment
| Segment | Function | Key Details |
|---|---|---|
| Glomerulus |
Part 4: Digestive System
Organ Systems for the MCAT
Part 3 of 7 — Digestive System
GI Tract Order
Mouth → Esophagus → Stomach → Small intestine (duodenum → jejunum → ileum) → Large intestine → Rectum
Digestive Enzymes
| Enzyme | Source | Substrate | Product |
|---|---|---|---|
| Salivary amylase | Mouth | Starch | Maltose |
| Pepsin | Stomach (chief cells) | Protein | Peptides |
| Trypsin, chymotrypsin | Pancreas | Protein | Peptides |
| Pancreatic lipase | Pancreas | Triglycerides | Monoglycerides + fatty acids |
| Pancreatic amylase | Pancreas | Starch | Maltose |
| Lactase, maltase | Small intestine brush border | Disaccharides | Monosaccharides |
Stomach
- Parietal cells: HCl (acidic pH ~2) + intrinsic factor (for B absorption)
Part 5: Endocrine System
Organ Systems for the MCAT
Part 5 of 7 — Endocrine System
Major Endocrine Glands & Hormones
| Gland | Hormone(s) | Function |
|---|---|---|
| Hypothalamus | Releasing/inhibiting hormones | Controls anterior pituitary |
| Anterior pituitary | GH, TSH, ACTH, FSH, LH, Prolactin | Master gland |
| Posterior pituitary | ADH, Oxytocin | Stores/releases hypothalamic hormones |
| Thyroid | T3/T4, Calcitonin | Metabolism, lowers Ca |
| Parathyroid |
Part 6: Nervous System
Organ Systems for the MCAT
Part 6 of 7 — Nervous System
Organization
- CNS: Brain + Spinal cord
- PNS: Everything else
- Somatic: Voluntary (skeletal muscle)
- Autonomic: Involuntary
- Sympathetic: Fight-or-flight (increases HR, dilates pupils, inhibits digestion)
- Parasympathetic: Rest-and-digest (decreases HR, constricts pupils, promotes digestion)
Neuron Structure & Action Potential
- Resting potential: ~ mV (Na/K ATPase maintains gradient)
Part 7: Review & MCAT Practice
Organ Systems for the MCAT
Part 7 of 7 — Immune System
Innate vs. Adaptive Immunity
| Feature | Innate | Adaptive |
|---|---|---|
| Speed | Immediate (0-12 hours) | Slow (days to weeks) |
| Specificity | Broad | Highly specific (antigen-specific) |
| Memory | No | Yes |
| Components | Neutrophils, macrophages, NK cells, complement | T cells, B cells, antibodies |
Adaptive Immunity
Humoral (B cells):
- B cells → Plasma cells → Antibodies (immunoglobulins)
- Antibodies neutralize, opsonize, activate complement
- IgG: Most abundant, crosses placenta
- IgM: First responder, pentamer
- IgA: Mucosal surfaces (saliva, breast milk)
- IgE: Allergies, parasites
Cell-mediated (T cells):
- CD4+ (Helper T): Activate B cells and CD8+ cells
- CD8+ (Cytotoxic T): Kill infected/cancer cells directly
- T regulatory: Suppress immune responses (prevent autoimmunity)