Human Anatomy & Physiology – Complete Atlas
Level: School to Pre-Medical | Approach: System-by-system anatomical study Detailed descriptions of every major body system — bones, muscles, organs, nerves, and vessels — with origin, insertion, innervation, and clinical notes.
3D Video Presentations
Interactive 3D animated videos to help visualize each body system. Watch these alongside the text content below for deeper understanding.
Complete Human Anatomy – Full 3D Overview
Complete Human Anatomy – All organ systems in 1 hour (3D Animation)
Human Body 101 – National Geographic overview of body systems
Skeletal & Muscular System
Skeletal System – Bones, joints, and structure (3D Animation)
Muscular System – Muscles, contraction, and movement (3D Animation)
Cardiovascular System (Heart & Blood)
Heart Anatomy – Chambers, valves, and blood flow (3D Animation)
Circulatory System – How blood flows through the body
Nervous System (Brain & Nerves)
Nervous System – Brain, spinal cord, and neurons (3D Animation)
Neurons – Structure, types, and nerve impulse (3D Animation)
Respiratory System (Lungs & Breathing)
Respiratory System – Lungs, alveoli, and gas exchange (3D Animation)
Mechanism of Breathing – Inhalation and exhalation (3D Animation)
Digestive System
Digestive System – Complete journey of food through the body (3D Animation)
Liver Anatomy – Structure and function (3D Animation)
Urinary & Reproductive System
Kidney & Nephron – Excretory system and urine formation (3D Animation)
Reproductive System – Male and female anatomy (3D Animation)
Eye, Ear & Special Senses
Eye Anatomy – Structure of the human eye (3D Animation)
Ear Anatomy – Outer, middle, inner ear and hearing (3D Animation)
CrashCourse – Anatomy & Physiology Series
CrashCourse A&P – Complete 47-episode series covering all body systems
Introduction to Anatomy – CrashCourse Episode 1
Musculoskeletal System
Skeletal System Overview
The adult human skeleton has 206 bones providing support, protection, movement, mineral storage, and blood cell production (hematopoiesis).
Axial Skeleton (80 bones)
Skull (22 bones)
| Bone | Type | Key Features |
|---|---|---|
| Frontal | Cranial | Forms forehead; contains frontal sinuses |
| Parietal (×2) | Cranial | Form sides and roof of cranium |
| Temporal (×2) | Cranial | House middle and inner ear; zygomatic process |
| Occipital | Cranial | Foramen magnum (spinal cord passage) |
| Sphenoid | Cranial | Butterfly-shaped; sella turcica holds pituitary |
| Ethmoid | Cranial | Forms nasal septum; cribriform plate (olfactory nerves) |
| Maxilla (×2) | Facial | Upper jaw; holds upper teeth |
| Mandible | Facial | Lower jaw; only movable skull bone |
| Zygomatic (×2) | Facial | Cheekbones |
| Nasal (×2) | Facial | Bridge of nose |
Vertebral Column (33 vertebrae)
| Region | Count | Features |
|---|---|---|
| Cervical | 7 | C1 (Atlas) – supports skull; C2 (Axis) – pivot for rotation |
| Thoracic | 12 | Articulate with ribs; limited mobility |
| Lumbar | 5 | Largest; weight-bearing; low back |
| Sacral | 5 (fused) | Forms posterior pelvis |
| Coccygeal | 4 (fused) | Tailbone; vestigial |
Rib Cage (25 bones) - True ribs (1–7): Attach directly to sternum via costal cartilage - False ribs (8–10): Attach indirectly to sternum - Floating ribs (11–12): No anterior attachment - Sternum: Manubrium + Body + Xiphoid process
Appendicular Skeleton (126 bones)
Upper Limb (per side: 30 bones)
| Bone | Location | Articulations |
|---|---|---|
| Clavicle | Collar bone | Sternum (medial), Acromion (lateral) |
| Scapula | Shoulder blade | Humerus (glenoid cavity), Clavicle |
| Humerus | Upper arm | Scapula (shoulder), Radius/Ulna (elbow) |
| Radius | Lateral forearm | Humerus, Ulna, Carpals |
| Ulna | Medial forearm | Humerus (olecranon), Radius |
| Carpals | Wrist (8 bones) | Scaphoid, Lunate, Triquetrum, Pisiform, Trapezium, Trapezoid, Capitate, Hamate |
| Metacarpals | Palm (5) | Carpals, Phalanges |
| Phalanges | Fingers (14) | 2 in thumb, 3 in each finger |
Lower Limb (per side: 30 bones)
| Bone | Location | Key Features |
|---|---|---|
| Hip bone | Pelvis | Ilium + Ischium + Pubis (fused); Acetabulum |
| Femur | Thigh | Longest bone; head fits acetabulum |
| Patella | Kneecap | Sesamoid bone; protects knee joint |
| Tibia | Medial leg (shin) | Weight-bearing; medial malleolus |
| Fibula | Lateral leg | Non-weight-bearing; lateral malleolus |
| Tarsals | Ankle (7) | Calcaneus (heel), Talus, Navicular, Cuboid, 3 Cuneiforms |
| Metatarsals | Foot (5) | Form arch of foot |
| Phalanges | Toes (14) | 2 in big toe, 3 in others |
Joints (Articulations)
| Type | Structure | Movement | Examples |
|---|---|---|---|
| Fibrous (Synarthrosis) | Dense connective tissue | None/minimal | Skull sutures, Gomphoses (teeth) |
| Cartilaginous (Amphiarthrosis) | Cartilage connects | Slight | Intervertebral discs, Pubic symphysis |
| Synovial (Diarthrosis) | Joint cavity with fluid | Free | Knee, Hip, Shoulder, Elbow |
Synovial Joint Subtypes
| Type | Axes | Movement | Example |
|---|---|---|---|
| Hinge | 1 (uniaxial) | Flexion/Extension | Elbow, Knee, Ankle |
| Pivot | 1 (uniaxial) | Rotation | Atlas-Axis (C1-C2), Radioulnar |
| Saddle | 2 (biaxial) | Flexion/Extension + Abduction/Adduction | Thumb (CMC joint) |
| Condyloid | 2 (biaxial) | Flexion/Extension + Abduction/Adduction | Wrist, MCP joints |
| Ball-and-socket | 3 (multiaxial) | All directions + Rotation | Shoulder, Hip |
| Gliding (Plane) | Multi-planar | Sliding | Intercarpal, Intertarsal, Acromioclavicular |
Muscular System
The body has approximately 600+ skeletal muscles responsible for movement, posture, heat generation, and joint stabilization.
Muscles of the Head and Neck
| Muscle | Origin | Insertion | Innervation | Action |
|---|---|---|---|---|
| Frontalis | Galea aponeurotica | Skin of eyebrows | Facial nerve (CN VII) | Raises eyebrows |
| Orbicularis oculi | Medial orbit | Skin around eye | Facial nerve (CN VII) | Closes eyelids |
| Orbicularis oris | Maxilla and mandible | Lips | Facial nerve (CN VII) | Closes and protrudes lips |
| Masseter | Zygomatic arch | Mandible (angle, ramus) | Trigeminal nerve (CN V₃) | Elevates mandible (chewing) |
| Temporalis | Temporal fossa | Coronoid process of mandible | Trigeminal nerve (CN V₃) | Elevates and retracts mandible |
| Sternocleidomastoid | Sternum + Clavicle | Mastoid process | Accessory nerve (CN XI) | Flexes neck; rotates head |
| Trapezius | Occipital bone, spinous processes | Clavicle, acromion, scapular spine | Accessory nerve (CN XI) | Elevates/retracts/depresses scapula |
Muscles of the Upper Limb
| Muscle | Origin | Insertion | Innervation | Action |
|---|---|---|---|---|
| Deltoid | Clavicle, Acromion, Scapular spine | Deltoid tuberosity (humerus) | Axillary nerve (C5, C6) | Abducts arm; flexes/extends |
| Pectoralis major | Clavicle, Sternum, Ribs 1-6 | Intertubercular groove (humerus) | Medial & Lateral pectoral nerves | Flexes, adducts, medially rotates arm |
| Latissimus dorsi | T7–L5 spinous processes, Iliac crest | Intertubercular groove (humerus) | Thoracodorsal nerve (C6-C8) | Extends, adducts, medially rotates arm |
| Biceps brachii | Short head: Coracoid process; Long head: Supraglenoid tubercle | Radial tuberosity | Musculocutaneous nerve (C5, C6) | Flexes elbow; supinates forearm |
| Triceps brachii | Long head: Infraglenoid; Lateral/Medial heads: Humerus | Olecranon process (ulna) | Radial nerve (C6-C8) | Extends elbow |
| Brachialis | Anterior humerus (distal half) | Coronoid process (ulna) | Musculocutaneous nerve (C5, C6) | Flexes elbow (primary flexor) |
| Pronator teres | Medial epicondyle + Coronoid process | Mid-lateral radius | Median nerve (C6, C7) | Pronates forearm |
| Supinator | Lateral epicondyle, Ulna | Proximal radius | Radial nerve (C6) | Supinates forearm |
Rotator Cuff Muscles (SITS)
| Muscle | Origin | Insertion | Action |
|---|---|---|---|
| Supraspinatus | Supraspinous fossa | Greater tubercle (superior) | Initiates abduction (first 15°) |
| Infraspinatus | Infraspinous fossa | Greater tubercle (middle) | External rotation |
| Teres minor | Lateral scapular border | Greater tubercle (inferior) | External rotation |
| Subscapularis | Subscapular fossa | Lesser tubercle | Internal rotation |
Muscles of the Lower Limb
| Muscle | Origin | Insertion | Innervation | Action |
|---|---|---|---|---|
| Iliopsoas (Psoas + Iliacus) | T12–L5 vertebrae + Iliac fossa | Lesser trochanter (femur) | Femoral nerve (L1-L3) | Flexes hip |
| Gluteus maximus | Ilium, Sacrum, Coccyx | IT band + Gluteal tuberosity | Inferior gluteal nerve (L5-S2) | Extends and laterally rotates hip |
| Gluteus medius | Outer ilium | Greater trochanter | Superior gluteal nerve (L4-S1) | Abducts hip; stabilizes pelvis |
| Quadriceps femoris | Rectus: AIIS; Vasti: Femur | Tibial tuberosity (via patellar ligament) | Femoral nerve (L2-L4) | Extends knee; Rectus flexes hip |
| Hamstrings (Biceps femoris, Semimembranosus, Semitendinosus) | Ischial tuberosity | Tibia/Fibula | Sciatic nerve (L5-S2) | Flexes knee; extends hip |
| Adductor group (Longus, Brevis, Magnus) | Pubis, Ischium | Linea aspera (femur) | Obturator nerve (L2-L4) | Adducts thigh |
| Gastrocnemius | Medial and lateral femoral condyles | Calcaneus (via Achilles tendon) | Tibial nerve (S1, S2) | Plantar flexes foot; flexes knee |
| Soleus | Posterior tibia and fibula | Calcaneus (via Achilles tendon) | Tibial nerve (S1, S2) | Plantar flexes foot |
| Tibialis anterior | Lateral tibia | Medial cuneiform, 1st metatarsal | Deep peroneal nerve (L4, L5) | Dorsiflexes and inverts foot |
Muscles of the Trunk
| Muscle | Origin | Insertion | Innervation | Action |
|---|---|---|---|---|
| Diaphragm | Xiphoid, Ribs 7-12, L1-L3 | Central tendon | Phrenic nerve (C3-C5) | Primary muscle of breathing |
| External oblique | Ribs 5-12 | Linea alba, Iliac crest | Intercostal nerves (T7-T12) | Flexes and rotates trunk |
| Internal oblique | Iliac crest, Inguinal ligament | Ribs 10-12, Linea alba | Intercostal nerves (T7-T12) | Flexes and rotates trunk |
| Rectus abdominis | Pubic crest | Xiphoid, Ribs 5-7 | Intercostal nerves (T7-T12) | Flexes trunk (sit-ups) |
| Transversus abdominis | Ribs 7-12, Iliac crest | Linea alba | Intercostal nerves (T7-T12) | Compresses abdomen |
| Erector spinae | Sacrum, Iliac crest, Vertebrae | Ribs, Vertebrae, Skull | Dorsal rami of spinal nerves | Extends and laterally flexes spine |
Mechanism of Muscle Contraction (Sliding Filament Theory)
- Motor neuron releases acetylcholine at neuromuscular junction
- Action potential spreads along sarcolemma and into T-tubules
- Ca²⁺ released from sarcoplasmic reticulum
- Ca²⁺ binds troponin → tropomyosin shifts → exposes binding sites on actin
- Myosin heads bind actin (cross-bridge formation)
- Power stroke — myosin pulls actin toward M-line
- ATP binds myosin → cross-bridge detaches
- Cycle repeats → sarcomere shortens → muscle contracts
- When stimulation stops → Ca²⁺ pumped back → muscle relaxes
Cardiovascular System
The Heart
- Location: Mediastinum, between lungs, slightly left of midline
- Size: ~12 cm long, 250–350 g
- Chambers: 4 (2 atria, 2 ventricles)
- Wall: Pericardium (outer sac) → Epicardium → Myocardium (muscle) → Endocardium (inner lining)
Heart Valves
| Valve | Location | Type | Function |
|---|---|---|---|
| Tricuspid | Right AV opening | Atrioventricular | Prevents backflow into right atrium |
| Bicuspid (Mitral) | Left AV opening | Atrioventricular | Prevents backflow into left atrium |
| Pulmonary | Right ventricle outlet | Semilunar | Prevents backflow from pulmonary artery |
| Aortic | Left ventricle outlet | Semilunar | Prevents backflow from aorta |
Blood Flow Pathway
Superior/Inferior Vena Cava (deoxygenated)
↓
Right Atrium
↓ (Tricuspid valve)
Right Ventricle
↓ (Pulmonary valve)
Pulmonary Arteries → LUNGS (gas exchange: CO₂ out, O₂ in)
↓
Pulmonary Veins (oxygenated)
↓
Left Atrium
↓ (Mitral valve)
Left Ventricle
↓ (Aortic valve)
Aorta → Systemic circulation → Body tissues
Cardiac Conduction System
SA Node (pacemaker, 60-100 bpm)
↓ (impulse spreads through atria)
AV Node (slight delay: 0.1 sec)
↓
Bundle of His
↓
Left and Right Bundle Branches
↓
Purkinje Fibers (ventricular contraction)
Cardiac Cycle (0.8 sec at 75 bpm)
| Phase | Events | Valves |
|---|---|---|
| Atrial systole (0.1s) | Atria contract → blood into ventricles | AV valves open |
| Ventricular systole (0.3s) | Ventricles contract → blood to lungs/body | Semilunar valves open; AV close |
| Diastole (0.4s) | All chambers relax → heart fills | Semilunar close; AV valves open |
- Cardiac output = Heart rate × Stroke volume = 72 × 70 mL ≈ 5 L/min
Major Blood Vessels
Arteries (carry blood away from heart)
| Artery | Supplies |
|---|---|
| Aorta | Largest artery; branches to entire body |
| Coronary arteries | Heart muscle itself |
| Carotid arteries | Head and brain |
| Subclavian → Axillary → Brachial | Upper limb |
| Celiac trunk | Stomach, Liver, Spleen |
| Superior/Inferior mesenteric | Intestines |
| Renal arteries | Kidneys |
| Femoral → Popliteal → Tibial | Lower limb |
Veins (return blood to heart)
| Vein | Drains |
|---|---|
| Superior vena cava | Head, neck, upper limbs |
| Inferior vena cava | Abdomen, pelvis, lower limbs |
| Jugular veins | Brain and head |
| Hepatic portal vein | GI tract → Liver |
| Great saphenous vein | Longest vein; medial leg |
Blood Composition
| Component | Percentage | Function |
|---|---|---|
| Plasma | 55% | Transport medium; contains proteins (albumin, globulins, fibrinogen) |
| Red Blood Cells | ~45% (hematocrit) | O₂ transport via hemoglobin; 120-day lifespan |
| White Blood Cells | <1% | Immune defense (Neutrophils, Lymphocytes, Monocytes, Eosinophils, Basophils) |
| Platelets | <1% | Clotting (hemostasis) |
Blood Groups
| System | Antigens | Antibodies | Clinical Significance |
|---|---|---|---|
| A | A antigen on RBC | Anti-B | Can donate to A, AB |
| B | B antigen on RBC | Anti-A | Can donate to B, AB |
| AB | Both A and B | None | Universal recipient |
| O | None | Anti-A and Anti-B | Universal donor |
| Rh+ | D antigen present | — | 85% of population |
| Rh− | D antigen absent | Anti-D (if sensitized) | Important in pregnancy |
Nervous System
Organization
Nervous System
├── Central Nervous System (CNS)
│ ├── Brain (1.4 kg, ~86 billion neurons)
│ └── Spinal Cord (45 cm, 31 segments)
└── Peripheral Nervous System (PNS)
├── Somatic (Voluntary) — 12 cranial + 31 spinal nerves
└── Autonomic (Involuntary)
├── Sympathetic — Fight or Flight
└── Parasympathetic — Rest and Digest
The Brain
| Structure | Location | Functions |
|---|---|---|
| Cerebrum | Largest part; 2 hemispheres | Consciousness, thought, memory, voluntary actions, sensory processing |
| Frontal lobe | Anterior | Motor control, personality, speech (Broca's area), decision-making |
| Parietal lobe | Superior-posterior | Somatosensory processing, spatial awareness |
| Temporal lobe | Lateral | Hearing, memory, language comprehension (Wernicke's area) |
| Occipital lobe | Posterior | Visual processing |
| Cerebellum | Inferior-posterior | Balance, coordination, fine motor control, posture |
| Brainstem | Connects brain to spinal cord | Vital functions (breathing, heart rate, consciousness) |
| Midbrain | Upper brainstem | Visual/auditory reflexes, motor pathways |
| Pons | Middle brainstem | Relay between cerebrum/cerebellum; breathing regulation |
| Medulla oblongata | Lower brainstem | Cardiac, respiratory, vasomotor centers; reflex centers (vomiting, coughing, sneezing) |
| Thalamus | Deep cerebrum (diencephalon) | Relay station for all sensory input (except smell) |
| Hypothalamus | Below thalamus | Temperature, hunger, thirst, sleep, hormones, ANS control |
| Limbic system | Deep cerebrum | Emotions, memory (hippocampus), fear (amygdala) |
Protection of CNS: - Skull and vertebral column (bone) - Meninges: Dura mater → Arachnoid mater → Pia mater - Cerebrospinal fluid (CSF): 150 mL; cushions, nourishes, removes waste
Cranial Nerves (12 pairs)
| Number | Name | Type | Function |
|---|---|---|---|
| CN I | Olfactory | Sensory | Smell |
| CN II | Optic | Sensory | Vision |
| CN III | Oculomotor | Motor | Eye movement (most), pupil constriction, eyelid |
| CN IV | Trochlear | Motor | Superior oblique muscle (eye) |
| CN V | Trigeminal | Both | Face sensation + Mastication (chewing) |
| CN VI | Abducens | Motor | Lateral rectus muscle (eye abduction) |
| CN VII | Facial | Both | Facial expression + Taste (anterior 2/3 tongue) |
| CN VIII | Vestibulocochlear | Sensory | Hearing and balance |
| CN IX | Glossopharyngeal | Both | Taste (posterior 1/3), swallowing, parotid gland |
| CN X | Vagus | Both | Heart, lungs, digestive tract; longest cranial nerve |
| CN XI | Accessory (Spinal) | Motor | Trapezius, Sternocleidomastoid (head/neck movement) |
| CN XII | Hypoglossal | Motor | Tongue movement |
Mnemonic: Oh Oh Oh To Touch And Feel Very Green Vegetables — AH!
Spinal Cord and Spinal Nerves
| Region | Segments | Key Nerves/Plexuses |
|---|---|---|
| Cervical | C1–C8 | Cervical plexus (C1-C4): Phrenic nerve (diaphragm); Brachial plexus (C5-T1): upper limb |
| Thoracic | T1–T12 | Intercostal nerves: chest wall and abdomen |
| Lumbar | L1–L5 | Lumbar plexus (L1-L4): Femoral nerve (anterior thigh) |
| Sacral | S1–S5 | Sacral plexus (L4-S3): Sciatic nerve (posterior thigh, leg) |
| Coccygeal | Co1 | Coccygeal plexus |
The Neuron
Structure: - Cell body (Soma) — Contains nucleus; integrates signals - Dendrites — Receive incoming signals (input) - Axon — Conducts impulse away from soma (output) - Myelin sheath — Insulating layer (Schwann cells in PNS, Oligodendrocytes in CNS) - Nodes of Ranvier — Gaps in myelin; allow saltatory conduction - Axon terminals — Release neurotransmitters at synapse
Nerve Impulse: - Resting potential: −70 mV (inside negative) - Depolarization: Na⁺ rushes in → +30 mV (action potential) - Repolarization: K⁺ rushes out → returns to −70 mV - Speed: 1–120 m/s (depends on myelination and diameter)
Key Neurotransmitters:
| Neurotransmitter | Function | Clinical Relevance |
|---|---|---|
| Acetylcholine | Muscle contraction, memory | Alzheimer's (deficiency) |
| Dopamine | Reward, movement, motivation | Parkinson's (deficiency); Schizophrenia (excess) |
| Serotonin | Mood, sleep, appetite | Depression (deficiency) |
| GABA | Inhibitory; calming | Anxiety (deficiency) |
| Norepinephrine | Alertness, fight-or-flight | Stress response |
| Glutamate | Excitatory; learning | Epilepsy (excess) |
Reflex Arc
Stimulus → Receptor → Sensory (afferent) neuron →
Integration center (spinal cord) →
Motor (efferent) neuron → Effector (muscle/gland) → Response
Example: Knee-jerk reflex (patellar) — monosynaptic stretch reflex
Respiratory System
Anatomy of the Respiratory Tract
| Structure | Description | Function |
|---|---|---|
| Nasal cavity | Lined with mucous membrane and cilia | Filters, warms, and humidifies air |
| Pharynx | Shared passage for air and food | Passageway; 3 parts: Naso-, Oro-, Laryngopharynx |
| Larynx | Voice box; contains vocal cords | Sound production; epiglottis prevents aspiration |
| Trachea | 10–12 cm; C-shaped cartilage rings | Conducts air; cilia move mucus upward |
| Primary bronchi | Right (wider, shorter, more vertical) and Left | Conduct air to each lung |
| Secondary bronchi | 3 right, 2 left (one per lobe) | Supply each lung lobe |
| Bronchioles | Smooth muscle walls; no cartilage | Air distribution; diameter regulated by ANS |
| Alveoli | ~300 million; 0.2 mm diameter each | Gas exchange; 70 m² total surface area |
The Lungs
| Feature | Right Lung | Left Lung |
|---|---|---|
| Lobes | 3 (superior, middle, inferior) | 2 (superior, inferior) |
| Fissures | Oblique + Horizontal | Oblique only |
| Special features | Wider, shorter | Cardiac notch; lingula |
| Weight | ~600 g | ~500 g |
Mechanics of Breathing
Inhalation (active process): 1. Diaphragm contracts (flattens) — phrenic nerve (C3-C5) 2. External intercostals contract — ribs elevate 3. Thoracic volume increases → intrapulmonary pressure drops 4. Air flows into lungs (Boyle's Law)
Exhalation (passive at rest): 1. Diaphragm relaxes (dome shape) 2. Elastic recoil of lungs 3. Thoracic volume decreases → intrapulmonary pressure rises 4. Air flows out
Gas Exchange
| Location | O₂ Direction | CO₂ Direction | Driving Force |
|---|---|---|---|
| Alveoli (External respiration) | Alveoli → Blood | Blood → Alveoli | Partial pressure gradient |
| Tissues (Internal respiration) | Blood → Cells | Cells → Blood | Partial pressure gradient |
Oxygen transport: - 98.5% bound to hemoglobin (oxyhemoglobin: HbO₂) - 1.5% dissolved in plasma
CO₂ transport: - 70% as bicarbonate ions (HCO₃⁻) in plasma - 23% bound to hemoglobin (carbaminohemoglobin) - 7% dissolved in plasma
Lung Volumes and Capacities
| Measurement | Definition | Value |
|---|---|---|
| Tidal Volume (TV) | Normal breath | 500 mL |
| Inspiratory Reserve (IRV) | Max extra inhalation | 3000 mL |
| Expiratory Reserve (ERV) | Max extra exhalation | 1100 mL |
| Residual Volume (RV) | Air left after max exhale | 1200 mL |
| Vital Capacity (VC) | TV + IRV + ERV | 4600 mL |
| Total Lung Capacity | VC + RV | 5800 mL |
| Respiratory rate | Breaths per minute | 12–20 |
Digestive System
Organs of the GI Tract
| Organ | Length/Size | Key Features | Function |
|---|---|---|---|
| Oral cavity | — | Teeth (32), Tongue, Salivary glands | Mechanical + chemical digestion begins |
| Pharynx | 12 cm | Oropharynx, Laryngopharynx | Swallowing (deglutition) |
| Esophagus | 25 cm | Muscular tube; peristalsis | Transports food to stomach |
| Stomach | 1.5 L capacity | Rugae, 3 muscle layers, Pyloric sphincter | Protein digestion; churning; HCl kills bacteria |
| Small intestine | 6 m total | Villi and microvilli (250 m² surface area) | Primary digestion and absorption |
| — Duodenum | 25 cm | Receives bile and pancreatic juice | Chemical digestion |
| — Jejunum | 2.5 m | Highly vascular; plicae circulares | Major absorption site |
| — Ileum | 3.5 m | Peyer's patches (lymphoid) | Absorbs B12, bile salts |
| Large intestine | 1.5 m | Haustra, Taeniae coli, No villi | Water absorption; feces formation |
| — Cecum | — | Appendix attached | Receives ileal contents |
| — Colon | — | Ascending → Transverse → Descending → Sigmoid | Water and electrolyte absorption |
| Rectum | 12 cm | Rectal valves | Feces storage |
| Anus | — | Internal (involuntary) + External (voluntary) sphincters | Defecation |
Accessory Digestive Organs
| Organ | Secretion | Key Components | Function |
|---|---|---|---|
| Salivary glands (Parotid, Submandibular, Sublingual) | Saliva (1–1.5 L/day) | Salivary amylase, Mucin, Lysozyme | Starch digestion; lubrication; antimicrobial |
| Liver | Bile (500–1000 mL/day) | Bile salts, Bilirubin, Cholesterol | Fat emulsification; detoxification; protein synthesis |
| Gallbladder | Stores/concentrates bile | — | Releases bile into duodenum |
| Pancreas | Pancreatic juice (1.5 L/day) | Trypsin, Lipase, Amylase, Bicarbonate | Digests proteins, fats, carbs; neutralizes stomach acid |
Enzymes and Digestion Summary
| Nutrient | Enzyme | Source | Product |
|---|---|---|---|
| Starch | Salivary amylase | Mouth | Maltose |
| Starch | Pancreatic amylase | Pancreas | Maltose |
| Maltose | Maltase | Small intestine | Glucose |
| Proteins | Pepsin (+ HCl) | Stomach | Polypeptides |
| Polypeptides | Trypsin, Chymotrypsin | Pancreas | Peptides |
| Peptides | Peptidase | Small intestine | Amino acids |
| Fats | Bile salts (emulsification) | Liver | Fat droplets |
| Fat droplets | Pancreatic lipase | Pancreas | Fatty acids + Glycerol |
| Lactose | Lactase | Small intestine | Glucose + Galactose |
| Sucrose | Sucrase | Small intestine | Glucose + Fructose |
Absorption
| Nutrient | Absorbed in | Pathway |
|---|---|---|
| Glucose, Amino acids | Small intestine (villi) | Blood capillaries → Portal vein → Liver |
| Fatty acids, Glycerol | Small intestine (villi) | Lacteals → Lymphatic system → Blood |
| Water, Electrolytes | Large intestine | Blood capillaries |
| Vitamin B12 | Ileum | Requires intrinsic factor from stomach |
| Iron | Duodenum | Active transport |
Urogenital System
Kidneys and Urinary Tract
| Structure | Description | Function |
|---|---|---|
| Kidneys (×2) | Bean-shaped; 11 cm; posterior abdominal wall | Filter blood; produce urine; regulate BP, pH, electrolytes |
| Renal cortex | Outer layer | Contains glomeruli and convoluted tubules |
| Renal medulla | Inner region; renal pyramids | Contains loops of Henle and collecting ducts |
| Nephron | Functional unit (~1 million/kidney) | Urine formation |
| Ureters (×2) | 25 cm muscular tubes | Transport urine to bladder via peristalsis |
| Urinary bladder | Hollow muscular organ; 500 mL capacity | Stores urine; detrusor muscle contracts during urination |
| Urethra | Female: 4 cm; Male: 20 cm | Urine exit; males share with reproductive tract |
Nephron Structure and Urine Formation
Afferent arteriole → Glomerulus (filtration under pressure)
↓
Bowman's capsule (collects filtrate)
↓
Proximal Convoluted Tubule (PCT) — reabsorbs 65% water, glucose, amino acids, Na⁺
↓
Descending Loop of Henle — permeable to water (concentrates filtrate)
↓
Ascending Loop of Henle — impermeable to water; pumps out Na⁺/Cl⁻
↓
Distal Convoluted Tubule (DCT) — regulated reabsorption/secretion (aldosterone, ADH)
↓
Collecting Duct — final water reabsorption (ADH dependent)
↓
Renal pelvis → Ureter → Bladder
| Process | Daily Volume | Key Points |
|---|---|---|
| Glomerular filtration | 180 L filtered | Only ~1.5 L becomes urine |
| Tubular reabsorption | 178.5 L reabsorbed | 99% of filtrate recovered |
| Tubular secretion | Variable | H⁺, K⁺, drugs, creatinine added to urine |
Reproductive System
Male Reproductive Organs
| Organ | Function | Key Details |
|---|---|---|
| Testes | Spermatogenesis + Testosterone production | Located in scrotum (2–3°C below body temp); Seminiferous tubules |
| Epididymis | Sperm maturation and storage | Coiled tube; 6 m uncoiled |
| Vas deferens | Sperm transport | Cut in vasectomy |
| Seminal vesicles | Produce 60% of semen volume | Fructose (energy), Prostaglandins |
| Prostate gland | Produces 30% of semen | Alkaline fluid; PSA (clinical marker) |
| Bulbourethral (Cowper's) glands | Pre-ejaculatory fluid | Lubrication; neutralizes urethral acidity |
| Penis | Copulation; urine passage | Erectile tissue (corpora cavernosa, corpus spongiosum) |
Female Reproductive Organs
| Organ | Function | Key Details |
|---|---|---|
| Ovaries (×2) | Oogenesis + Estrogen/Progesterone | Release one ovum per cycle (~400 in lifetime) |
| Fallopian tubes | Ovum transport; fertilization site | Fimbriae catch ovum; cilia move it toward uterus |
| Uterus | Embryo implantation and development | Endometrium (shed during menses); Myometrium (contractions) |
| Cervix | Lower uterus; opens to vagina | Produces mucus; dilates in labor |
| Vagina | Birth canal; receives sperm | Acidic pH (4.5) — protects against infection |
Menstrual Cycle (28 days)
| Phase | Days | Hormones | Events |
|---|---|---|---|
| Menstrual | 1–5 | Low estrogen/progesterone | Endometrium sheds |
| Follicular | 1–13 | FSH rises → Estrogen rises | Follicle develops in ovary |
| Ovulation | Day 14 | LH surge | Ovum released |
| Luteal | 15–28 | Progesterone (from corpus luteum) | Endometrium thickens for implantation |
Endocrine System
Major Glands and Hormones
| Gland | Hormone | Target | Function |
|---|---|---|---|
| Hypothalamus | Releasing/Inhibiting hormones | Anterior pituitary | Controls pituitary secretions |
| ADH (Vasopressin) | Kidneys (collecting ducts) | Water reabsorption; increases blood volume | |
| Oxytocin | Uterus, Mammary glands | Labor contractions; milk let-down | |
| Anterior Pituitary | Growth Hormone (GH) | Bones, muscles, liver | Growth; protein synthesis; fat metabolism |
| TSH | Thyroid | Stimulates T3/T4 production | |
| ACTH | Adrenal cortex | Stimulates cortisol release | |
| FSH | Ovaries/Testes | Follicle growth; Spermatogenesis | |
| LH | Ovaries/Testes | Ovulation; Testosterone production | |
| Prolactin | Mammary glands | Milk production | |
| Thyroid | T3 and T4 (Thyroxine) | Most cells | Basal metabolic rate; growth; development |
| Calcitonin | Bones | Lowers blood calcium (opposes PTH) | |
| Parathyroid | PTH (Parathormone) | Bones, Kidneys, GI tract | Raises blood calcium |
| Adrenal Cortex | Cortisol (glucocorticoid) | Most tissues | Stress response; anti-inflammatory; raises blood glucose |
| Aldosterone (mineralocorticoid) | Kidneys | Na⁺ reabsorption; K⁺ excretion; raises BP | |
| Adrenal Medulla | Epinephrine (Adrenaline) | Heart, Lungs, Blood vessels | Fight-or-flight: ↑HR, ↑BP, bronchodilation |
| Norepinephrine | Blood vessels | Vasoconstriction; raises BP | |
| Pancreas | Insulin (β-cells) | Liver, Muscle, Fat | Lowers blood glucose; promotes glycogen storage |
| Glucagon (α-cells) | Liver | Raises blood glucose; glycogenolysis | |
| Pineal | Melatonin | Brain | Circadian rhythm; sleep-wake cycle |
| Thymus | Thymosin | T-lymphocytes | T-cell maturation; immune development |
| Testes | Testosterone | Reproductive organs, Muscles | Male sex characteristics; spermatogenesis |
| Ovaries | Estrogen | Reproductive organs, Bones | Female sex characteristics; bone density |
| Progesterone | Uterus | Maintains endometrium; pregnancy support |
Lymphatic System
Components and Functions
| Component | Function |
|---|---|
| Lymph | Clear fluid; returns interstitial fluid to blood; transports fats, immune cells |
| Lymph vessels | One-way vessels with valves; collect excess tissue fluid |
| Lymph nodes | Filter lymph; contain lymphocytes and macrophages; immune surveillance |
| Spleen | Filters blood; recycles old RBCs; stores platelets; immune function |
| Thymus | T-cell maturation (most active before puberty) |
| Tonsils | First line of defense against inhaled/ingested pathogens |
| MALT | Mucosa-associated lymphoid tissue; protects GI and respiratory tracts |
Immune Response
| Type | Speed | Specificity | Memory | Components |
|---|---|---|---|---|
| Innate (Non-specific) | Immediate | None | No | Skin, Mucous membranes, Phagocytes, NK cells, Complement, Inflammation |
| Adaptive (Specific) | Days | Highly specific | Yes | B-cells (antibodies), T-cells (cell-mediated) |
Lymphocyte Types:
| Cell | Function |
|---|---|
| B-cells | Produce antibodies (humoral immunity); Plasma cells secrete Ig |
| Helper T-cells (CD4) | Activate B-cells and Killer T-cells; coordinate immune response |
| Killer T-cells (CD8) | Destroy virus-infected cells and cancer cells |
| Memory cells | Long-lived; rapid response on re-exposure (basis of vaccination) |
Special Senses – Eye and Ear
The Eye (Vision)
| Structure | Function |
|---|---|
| Cornea | Transparent anterior surface; refracts light (most bending) |
| Sclera | White outer coat; protects and maintains shape |
| Choroid | Middle vascular layer; nourishes retina |
| Iris | Colored part; controls pupil size (amount of light entering) |
| Pupil | Opening in iris; dilates in dark, constricts in light |
| Lens | Fine-focuses light on retina; accommodation (shape changes) |
| Ciliary body | Suspensory ligaments hold lens; ciliary muscle adjusts shape |
| Vitreous humor | Gel filling posterior chamber; maintains eye shape |
| Aqueous humor | Fluid in anterior chamber; nourishes cornea/lens; maintains intraocular pressure |
| Retina | Inner layer; contains photoreceptors |
| Rods | ~120 million; dim light; peripheral vision; black/white |
| Cones | ~6 million; bright light; color vision; visual acuity (fovea) |
| Optic nerve (CN II) | Transmits visual impulses to occipital lobe |
| Fovea centralis | Central retina; highest cone density; sharpest vision |
| Blind spot (Optic disc) | Where optic nerve exits; no photoreceptors |
Visual pathway: Light → Cornea → Aqueous humor → Pupil → Lens → Vitreous humor → Retina (rods/cones) → Optic nerve → Optic chiasm → Thalamus (LGN) → Visual cortex (occipital lobe)
Common defects: - Myopia (nearsightedness): Image forms before retina → concave lens - Hyperopia (farsightedness): Image forms behind retina → convex lens - Astigmatism: Irregular cornea curvature → cylindrical lens - Presbyopia: Age-related loss of lens elasticity → reading glasses - Cataracts: Clouding of lens - Glaucoma: Increased intraocular pressure → optic nerve damage
The Ear (Hearing and Balance)
| Region | Structure | Function |
|---|---|---|
| Outer ear | Pinna (auricle) | Collects sound waves |
| External acoustic meatus | Directs sound to tympanic membrane | |
| Tympanic membrane (eardrum) | Vibrates with sound waves | |
| Middle ear | Malleus (hammer) | Attached to tympanic membrane; receives vibrations |
| Incus (anvil) | Transmits vibrations from malleus to stapes | |
| Stapes (stirrup) | Smallest bone; transmits to oval window | |
| Eustachian tube | Equalizes pressure with atmosphere | |
| Inner ear | Cochlea | Hearing; contains Organ of Corti with hair cells |
| Vestibule (Utricle, Saccule) | Static balance (linear acceleration, head position) | |
| Semicircular canals (3) | Dynamic balance (rotational movement) |
Hearing pathway: Sound → Pinna → External meatus → Tympanic membrane → Ossicles (Malleus → Incus → Stapes) → Oval window → Cochlear fluid → Hair cells (Organ of Corti) → Cochlear nerve (CN VIII) → Temporal lobe (auditory cortex)
Integumentary System (Skin)
| Layer | Structure | Function |
|---|---|---|
| Epidermis | Stratified squamous epithelium; Keratinocytes, Melanocytes | Protection; waterproofing; UV protection |
| — Stratum corneum | Dead keratinized cells (outermost) | Barrier against pathogens and water loss |
| — Stratum basale | Dividing cells + Melanocytes | Cell renewal; melanin production |
| Dermis | Connective tissue; blood vessels, nerves, glands | Strength; sensation; temperature regulation |
| Hypodermis (Subcutaneous) | Adipose tissue | Insulation; energy storage; cushioning |
Skin appendages: - Hair: Protection, sensory; Hair follicle + arrector pili muscle (goosebumps) - Nails: Keratinized; protect fingertips - Sweat glands: Eccrine (thermoregulation) and Apocrine (odor; axilla/groin) - Sebaceous glands: Produce sebum (oils skin and hair)
Functions of skin: Protection, Temperature regulation, Sensation, Vitamin D synthesis, Excretion, Immune defense
Clinical Reference Values
| Parameter | Normal Range |
|---|---|
| Body temperature | 36.1–37.2°C (97–99°F) |
| Heart rate | 60–100 bpm |
| Blood pressure | 120/80 mmHg |
| Respiratory rate | 12–20 breaths/min |
| Blood pH | 7.35–7.45 |
| Blood glucose (fasting) | 70–100 mg/dL |
| Hemoglobin (Male) | 13.5–17.5 g/dL |
| Hemoglobin (Female) | 12–16 g/dL |
| WBC count | 4,000–11,000/mm³ |
| Platelet count | 150,000–400,000/mm³ |
| GFR (kidney filtration) | 90–120 mL/min |
| Cardiac output | 4–8 L/min |
| Tidal volume | 500 mL |
| Total blood volume | 5–6 L |
| CSF volume | 100–150 mL |
| Total body water | 60% of body weight |
Anatomical Terminology
Directional Terms
| Term | Meaning | Example |
|---|---|---|
| Superior (Cranial) | Toward the head/above | Heart is superior to diaphragm |
| Inferior (Caudal) | Toward the feet/below | Stomach is inferior to diaphragm |
| Anterior (Ventral) | Front | Sternum is anterior to spine |
| Posterior (Dorsal) | Back | Spine is posterior to sternum |
| Medial | Toward midline | Ulna is medial to radius |
| Lateral | Away from midline | Radius is lateral to ulna |
| Proximal | Closer to trunk/origin | Elbow is proximal to wrist |
| Distal | Farther from trunk/origin | Wrist is distal to elbow |
| Superficial | Closer to surface | Skin is superficial to muscle |
| Deep | Farther from surface | Bone is deep to muscle |
Body Planes
| Plane | Division | View |
|---|---|---|
| Sagittal (Median) | Left and Right | Side view |
| Frontal (Coronal) | Anterior and Posterior | Front/back view |
| Transverse (Horizontal) | Superior and Inferior | Cross-section |
Body Cavities
| Cavity | Contains |
|---|---|
| Cranial | Brain |
| Vertebral (Spinal) | Spinal cord |
| Thoracic | Heart, Lungs, Great vessels |
| Abdominal | Stomach, Intestines, Liver, Kidneys, Spleen |
| Pelvic | Bladder, Reproductive organs, Rectum |