Anatomy & Physiology

Anatomy & Physiology for the MCAT

Part 1 of 7 — Musculoskeletal System

Muscle Contraction: Sliding Filament Theory

1. Ca$^{2+}$ released from sarcoplasmic reticulum (SR)
2. Ca$^{2+}$ binds troponin → tropomyosin moves → exposes actin binding sites
3. Myosin heads bind actin (cross-bridge formation)
4. Power stroke: myosin pulls actin toward center (uses ATP)
5. ATP binds myosin → detachment → cycle repeats

Sarcomere Structure

Mnemonic: "Happy I Shrink" — H zone and I band shrink during contraction. A band stays the same.

Bone Structure

• Osteoblasts: BUILD bone (deposit calcium)
• Osteoclasts: Break down (CLAST = break) bone (resorb calcium)
• Osteocytes: Mature bone cells (maintenance)

Bone remodeling regulated by PTH (stimulates osteoclasts → Ca$^{2+}$ into blood) and calcitonin (stimulates osteoblasts → Ca$^{2+}$ into bone).

Muscle & Bone 🎯

Key Takeaways — Part 1

• Sliding filament: Ca$^{2+}$ → troponin → tropomyosin moves → cross-bridge cycling
• A band = constant. H zone and I band shrink during contraction.
• Osteoblasts build. Osteoclasts break. PTH raises blood Ca$^{2+}$.
• ATP needed for both contraction AND relaxation (rigor mortis!)

Anatomy & Physiology for the MCAT

Part 2 of 7 — Reproductive System

Male Reproductive System

• Testes: Spermatogenesis (Sertoli cells support; Leydig cells produce testosterone)
• Epididymis: Sperm maturation and storage
• Vas deferens: Transports sperm
• Seminal vesicles: Fructose (energy for sperm)
• Prostate: Alkaline fluid (neutralizes vaginal acidity)

Female Reproductive System

• Ovaries: Oogenesis, estrogen, progesterone
• Fallopian tubes (oviduct): Fertilization site
• Uterus: Implantation and fetal development
• Endometrium: Uterine lining (shed during menstruation)

Menstrual Cycle (28 days)

Anatomy & Physiology for the MCAT

Part 3 of 7 — Embryology & Development

Early Development

Three Germ Layers (ULTRA HIGH YIELD)

Anatomy & Physiology for the MCAT

Part 4 of 7 — Skin & Integumentary System

Skin Layers

From outside to inside:

1. Epidermis (epithelial): Keratinocytes, melanocytes, no blood vessels
2. Dermis: Connective tissue, blood vessels, hair follicles, nerve endings, sweat glands
3. Hypodermis (subcutaneous): Fat storage, insulation

Skin Functions

Thermoregulation

Hot environment:

• Vasodilation (increased blood flow to skin → heat loss)
• Sweating (evaporative cooling)

Cold environment:

• Vasoconstriction (reduced blood flow to skin → conserves heat)
• Shivering (muscle contraction generates heat)
• Piloerection (goosebumps — minimal effect in humans)

Anatomy & Physiology for the MCAT

Part 5 of 7 — Special Senses

Vision

Hearing

Sound waves → Pinna → Ear canal → Tympanic membrane (vibrates) → Ossicles (malleus, incus, stapes) → Oval window → Cochlea → Hair cells → Auditory nerve → Brain

• Cochlea: Tonotopic organization (base = high frequency, apex = low frequency)
• Hair cells: Stereocilia bend → mechanotransduction → neural signal

Taste & Smell

• Taste: 5 basic modalities (sweet, salty, sour, bitter, umami)
• Smell: Olfactory receptors in nasal epithelium → olfactory bulb → limbic system
• Smell is the ONLY sense that bypasses the thalamus (connects directly to limbic system → emotional memories)

Senses 🎯

Key Takeaways — Part 5

Anatomy & Physiology for the MCAT

Part 6 of 7 — Blood & Lymphatic System

Blood Components

Hemostasis (Blood Clotting)

1. Vascular spasm: Blood vessel constricts
2. : Platelets adhere to collagen, aggregate

Anatomy & Physiology for the MCAT

Part 7 of 7 — Homeostasis & Integration

Homeostasis

Maintenance of a stable internal environment despite external changes.

Negative feedback (most common):

• Response opposes the stimulus
• Example: Blood glucose rises → insulin secreted → glucose drops → insulin stops

Positive feedback (amplifying):

• Response AMPLIFIES the stimulus
• Examples: Oxytocin during labor, LH surge, blood clotting cascade

Acid-Base Balance

$\text{pH} = -\log[\text{H}^+]$