Below is a comprehensive overview of human anatomy (structure) and physiology (function), organized from the most fundamental levels of organization through each major organ system, and concluding with integrative and clinical correlations.
1. Levels of Organization
- Chemical Level
- Atoms (carbon, hydrogen, oxygen,
nitrogen) combine into
- Molecules (water, proteins, lipids,
carbohydrates, nucleic acids), which form
- Macromolecules (DNA, RNA, enzymes).
- Cellular Level
- Cells are the smallest living
units.
- Organelles: nucleus
(genetic control), mitochondria (ATP production), endoplasmic reticulum
(protein/lipid synthesis), Golgi apparatus (sorting/packaging), lysosomes
(digestion), cytoskeleton (shape/movement).
- Tissue Level
- Epithelial: lining/protection (skin,
mucosa).
- Connective: support (bone, cartilage,
adipose, blood).
- Muscle: contraction (skeletal,
cardiac, smooth).
- Nervous: signaling (neurons,
glia).
- Organ Level
- Structures composed of ≥2
tissue types, e.g., heart (muscle + connective + nervous + epithelial),
kidney, lung, liver.
- System Level
- Organs working together
toward a common function (e.g., respiratory, digestive, cardiovascular).
- Organism Level
- All systems integrated to
form the complete human being.
2. The Integumentary System
- Anatomy
- Skin: Epidermis (keratinocytes,
melanocytes), Dermis (connective tissue, blood vessels, nerves),
Hypodermis (adipose).
- Accessories: Hair follicles, sebaceous
glands (oil), sweat glands, nails.
- Physiology
- Barrier: Physical/chemical defense
against microbes, UV damage.
- Thermoregulation: Sweating,
vasodilation/constriction.
- Sensory: Touch, pressure,
temperature, pain receptors.
- Metabolism: Vitamin D synthesis (UV →
cholecalciferol).
3. The Skeletal System
- Anatomy
- Bones: 206 in adults, classified
by shape (long, short, flat, irregular).
- Cartilage: Hyaline (articular
surfaces), fibrocartilage (intervertebral discs), elastic (ear).
- Joints: Fibrous (skull sutures),
cartilaginous (pubic symphysis), synovial (knee, shoulder).
- Ligaments & Tendons: Connect bone–bone and
muscle–bone, respectively.
- Physiology
- Support & Protection: Framework for body,
protects brain (skull), heart/lungs (rib cage).
- Movement: Levers for muscle
attachment.
- Mineral Storage: Calcium, phosphate
reservoir.
- Hematopoiesis: Red marrow produces blood
cells.
- Energy Storage: Yellow marrow (fat).
4. The Muscular System
- Anatomy
- Skeletal Muscle: Striated, multinucleated,
under voluntary control.
- Cardiac Muscle: Striated, branched,
intercalated discs, involuntary.
- Smooth Muscle: Non-striated, in walls of
viscera/vessels, involuntary.
- Physiology
- Contraction: Actin–myosin cross-bridge
cycling powered by ATP.
- Functions:
- Movement: Body and limb motion.
- Posture & Stability.
- Heat Production: Shivering thermogenesis.
- Propulsion: Peristalsis in gut,
vasomotion in vessels, cardiac pumping.
5. The Nervous System
- Anatomy
- Central Nervous System
(CNS):
Brain (cerebrum, diencephalon, brainstem, cerebellum) and spinal cord.
- Peripheral Nervous System (PNS): Cranial/spinal nerves,
ganglia.
- Somatic Division: Voluntary—innervates
skeletal muscle.
- Autonomic Division: Involuntary—sympathetic,
parasympathetic, enteric.
- Physiology
- Signal Transmission:
- Resting Potential: ~–70 mV maintained by
Na⁺/K⁺-ATPase.
- Action Potential: Voltage-gated Na⁺
influx, K⁺ efflux, refractory period.
- Synaptic Transmission:
- Chemical synapses:
Ca²⁺-dependent neurotransmitter release (e.g., glutamate, GABA,
acetylcholine).
- Functional Roles:
- Sensory Input, Integration, Motor
Output, Homeostatic Regulation, Cognition, Emotion,
Memory.
6. The Endocrine System
- Anatomy
- Glands: Pituitary (master),
thyroid, parathyroids, adrenals, pancreas (islets), pineal, gonads
(ovaries/testes).
- Physiology
- Hormone Secretion: Chemical messengers into
bloodstream.
- Peptide/Protein hormones (insulin, growth
hormone).
- Steroid hormones (cortisol,
estrogens, androgens).
- Amino Acid–Derived (thyroid hormones,
catecholamines).
- Functions:
- Metabolism (insulin/glucagon,
thyroid).
- Growth & Development (GH, thyroid).
- Reproduction (gonadotropins, sex
steroids).
- Stress Response (cortisol,
catecholamines).
- Fluid/Electrolyte Balance (ADH, aldosterone).
7. The Cardiovascular System
- Anatomy
- Heart: Four chambers, valves
(AV, semilunar), myocardium.
- Vessels: Arteries (elastic,
muscular), arterioles, capillaries, venules, veins (with valves).
- Blood: Plasma (water, proteins,
nutrients), cells (RBCs, WBCs, platelets).
- Physiology
- Hemodynamics: Cardiac output = stroke
volume × heart rate; pressure gradients drive flow.
- Gas & Nutrient Exchange: At capillary level (via
diffusion, filtration, reabsorption).
- Hemostasis: Platelet plug,
coagulation cascade, fibrinolysis.
- Transport: Hormones, immune cells,
heat distribution.
8. The Lymphatic & Immune System
- Anatomy
- Lymphatic Vessels: Blind‐ended capillaries,
trunks, ducts (thoracic duct).
- Lymphoid Organs: Lymph nodes, spleen,
thymus, tonsils, Peyer’s patches.
- Physiology
- Fluid Balance: Returns interstitial
fluid to circulation.
- Fat Absorption: Lacteals in small
intestine absorb chylomicrons.
- Immunity:
- Innate: Physical barriers,
phagocytes (macrophages, neutrophils), NK cells, complement.
- Adaptive: T and B lymphocytes,
antigen presentation, antibody production, immunologic memory.
9. The Respiratory System
- Anatomy
- Upper Airway: Nose, pharynx, larynx.
- Lower Airway: Trachea → bronchi →
bronchioles → alveolar ducts → alveoli.
- Accessory: Diaphragm, intercostal
muscles.
- Physiology
- Ventilation: Negative‐pressure
breathing—diaphragm contraction lowers intrapulmonary pressure.
- Diffusion: O₂ into blood, CO₂ out,
across alveolar–capillary membrane.
- Gas Transport:
- O₂ bound to hemoglobin
(~98%) + dissolved.
- CO₂ transported as
bicarbonate (~70%), carbaminohemoglobin, dissolved.
- Acid–Base Balance: CO₂ ↔ H₂CO₃ (carbonic
anhydrase).
10. The Digestive System
- Anatomy
- Alimentary Canal: Mouth, pharynx,
esophagus, stomach, small intestine (duodenum, jejunum, ileum), large
intestine (cecum, colon, rectum), anus.
- Accessory Organs: Salivary glands, liver,
gallbladder, pancreas.
- Physiology
- Ingestion & Propulsion: Mastication, deglutition,
peristalsis.
- Secretion: Enzymes (salivary
amylase, pepsin, pancreatic lipase), bile (emulsifies fats), mucus.
- Digestion: Carbohydrates →
monosaccharides; proteins → amino acids; fats → fatty
acids/monoglycerides.
- Absorption:
- Small Intestine: Nutrients via villi and
microvilli.
- Large Intestine: Water, electrolytes,
vitamin K.
- Elimination: Formation and defecation
of feces.
11. The Urinary System
- Anatomy
- Kidneys: Cortex (glomeruli),
medulla (loops of Henle, collecting ducts).
- Ureters, Urinary Bladder, Urethra.
- Physiology
- Filtration: Glomerular capillary
pressure filters plasma into Bowman’s capsule.
- Reabsorption &
Secretion:
- Proximal tubule: bulk
reabsorption of water, electrolytes, nutrients.
- Loop of Henle:
countercurrent multiplier concentrates urine.
- Distal tubule &
collecting duct: fine-tuning (aldosterone, ADH).
- Homeostasis: Fluid volume, electrolyte
balance (Na⁺, K⁺, Ca²⁺), acid–base (H⁺, HCO₃⁻).
- Excretion: Urea, creatinine, drugs,
toxins.
12. The Reproductive System
- Anatomy
- Male: Testes (spermatogenesis),
epididymis, vas deferens, seminal vesicles, prostate, penis.
- Female: Ovaries (oogenesis),
fallopian tubes, uterus, vagina, external genitalia, mammary glands.
- Physiology
- Gamete Production: Spermatogenesis
(continuous post‐puberty), oogenesis (cyclical with finite pool).
- Hormonal Regulation:
- Hypothalamus (GnRH) →
pituitary (LH, FSH) → gonads (testosterone, estrogen, progesterone).
- Female Cycle: Follicular phase,
ovulation, luteal phase, menstruation.
- Fertilization &
Pregnancy:
Implantation, placental hormone secretion (hCG, progesterone).
- Lactation: Prolactin,
oxytocin–mediated milk ejection.
13. Integration & Homeostasis
- Cross‐Talk
- Neural, endocrine, immune,
metabolic systems coordinate via feedback loops.
- Examples
- Thermoregulation: Hypothalamus senses temperature
→ sweat/vasomotion (skin) + shivering (muscle).
- Blood Pressure: Baroreceptor reflex
(nervous) + renin–angiotensin–aldosterone (endocrine) + renal volume
control (kidneys).
14. Clinical Correlations & Applications
- Trauma & Repair
- Wound healing: Inflammation
→ proliferation → remodeling.
- Bone fracture healing:
Hematoma → callus → ossification.
- Infection & Immunity
- Sepsis: Dysregulated
systemic inflammation.
- Autoimmunity: Loss of
self‐tolerance (e.g., type 1 diabetes, rheumatoid arthritis).
- Genetic Disorders
- Cystic fibrosis (CFTR
mutation → thick mucous, lung disease).
- Sickle cell disease
(hemoglobin mutation → vaso‐occlusion).
- Neurodegeneration
- Alzheimer’s disease
(β-amyloid, tau pathology).
- Parkinson’s disease (dopaminergic
neuron loss in substantia nigra).
- Cardiovascular Disease
- Atherosclerosis →
myocardial infarction, stroke.
- Heart failure: Pump
failure, volume overload, neurohormonal activation.
- Endocrine Disorders
- Diabetes mellitus: Type 1
(autoimmune β‐cell destruction), Type 2 (insulin resistance).
- Thyroid disorders:
Hypothyroidism, hyperthyroidism (Graves’ disease).
15. Summary
Human
anatomy and physiology span scales from molecules and cells to organ systems
and the whole organism. Structural form at each level underpins specific
functions, and integration across systems maintains internal stability.
Clinical practice and biomedical research continually deepen our understanding
of how disruptions at any level can lead to disease, and how targeted therapies
can restore health.
