Integumentary, Skeletal, and Muscular Systems
The three systems that give the body form, protection, and movement. These cards pair structural knowledge with the physiological mechanisms that underlie skin function, bone remodeling, and muscle contraction.
| Term | Meaning |
|---|---|
| Epidermis Layers | From deep to superficial: stratum basale (mitotic), stratum spinosum, stratum granulosum, stratum lucidum (thick skin only), stratum corneum (dead keratinized cells). Mnemonic: 'Come, Let's Get Sun Burned.' |
| Dermis | Below the epidermis; contains the papillary layer (loose connective tissue with capillaries and Meissner's corpuscles) and the reticular layer (dense irregular connective tissue with collagen and elastin fibers, hair follicles, sweat glands, and Pacinian corpuscles). |
| Skin Functions | Protection (mechanical, chemical, UV, microbial), thermoregulation (sweat glands, vasodilation/constriction), sensation (touch, pressure, temperature, pain receptors), vitamin D synthesis (7-dehydrocholesterol → cholecalciferol with UVB), and excretion of small amounts of urea and salts. |
| Bone Composition | Approximately 70% inorganic (hydroxyapatite: calcium phosphate) for compressive strength, and 30% organic (collagen fibers) for tensile strength. Osteoblasts build bone, osteoclasts resorb it, and osteocytes are mature cells in lacunae. |
| Compact vs. Spongy Bone | Compact (cortical) bone: dense outer layer, organized into osteons (Haversian systems) with concentric lamellae around central canals. Spongy (trabecular) bone: interior lattice of trabeculae containing red marrow; resists stress from multiple directions. |
| Bone Remodeling | Continuous cycle of resorption (osteoclasts) and deposition (osteoblasts). Regulated by mechanical stress (Wolff's law), calcitonin (lowers blood Ca2+, inhibits osteoclasts), parathyroid hormone (raises blood Ca2+, stimulates osteoclasts), and vitamin D. |
| Joint Types | Fibrous (sutures, syndesmoses): minimal to no movement. Cartilaginous (intervertebral discs, pubic symphysis): limited movement. Synovial (most limb joints): freely movable, with articular cartilage, synovial fluid, joint capsule, and often ligaments, menisci, and bursae. |
| Skeletal Muscle Structure | Hierarchy: muscle → fascicle → fiber (muscle cell) → myofibril → sarcomere. The sarcomere (Z-line to Z-line) contains thick (myosin) and thin (actin, troponin, tropomyosin) filaments. I-bands contain only actin; A-bands contain myosin. |
| Sliding Filament Theory | Contraction occurs as myosin heads bind actin, pivot (power stroke), release (ATP required), and rebind. Sarcomeres shorten as thin filaments slide past thick filaments. I-band and H-zone shrink; A-band width remains constant. |
| Neuromuscular Junction | Motor neuron releases acetylcholine (ACh) at the synaptic cleft. ACh binds nicotinic receptors on the motor end plate, depolarizing the sarcolemma. Action potential travels down T-tubules, triggering Ca2+ release from the sarcoplasmic reticulum, which initiates contraction. |
| Excitation-Contraction Coupling | Ca2+ binds troponin C, which moves tropomyosin off actin's myosin-binding sites. Myosin heads (pre-cocked by ATP hydrolysis) bind and execute the power stroke. Relaxation requires Ca2+ pumping back into the sarcoplasmic reticulum (SERCA pump). |
| Muscle Fiber Types | Type I (slow oxidative): red, fatigue-resistant, many mitochondria, used for posture and endurance. Type IIa (fast oxidative): pink, intermediate. Type IIx/b (fast glycolytic): white, powerful but fatigue quickly, used for sprinting and heavy lifts. |
| Smooth vs. Cardiac vs. Skeletal Muscle | Skeletal: striated, voluntary, multinucleated. Cardiac: striated, involuntary, uninucleated (usually), intercalated discs with gap junctions. Smooth: non-striated, involuntary, spindle-shaped, single-nucleated; found in viscera and blood vessels. |
| Origin vs. Insertion | Origin: the (usually) more stationary muscle attachment. Insertion: the more movable attachment; typically the bone that moves when the muscle contracts. Agonists (prime movers) oppose antagonists; synergists assist; fixators stabilize. |
| Muscle Metabolism | Immediate energy: stored ATP and creatine phosphate. Short-term: anaerobic glycolysis (lactate accumulation). Long-term: aerobic respiration in mitochondria (glucose and fatty acid oxidation). Oxygen debt is repaid after exercise to restore ATP and remove lactate. |
| Bone Fracture Healing | Four stages: hematoma formation, fibrocartilaginous callus formation (days to weeks), bony callus formation (weeks to months), and bone remodeling (months to years). Requires adequate calcium, vitamin D, protein, and mechanical loading. |
Nervous and Endocrine Systems
The body's two communication networks. These cards cover neural signaling, brain regions, and hormonal regulation, the machinery that coordinates every other system.
| Term | Meaning |
|---|---|
| Neuron Structure | Dendrites (receive signals), cell body (soma, contains nucleus), axon (conducts impulse), axon terminals (release neurotransmitters). Myelin sheath (oligodendrocytes in CNS, Schwann cells in PNS) speeds conduction via saltatory conduction between nodes of Ranvier. |
| Resting Membrane Potential | Approximately -70 mV, maintained by the Na+/K+ ATPase (pumps 3 Na+ out, 2 K+ in per ATP) and K+ leak channels. The inside is negative relative to the outside due to K+ diffusion out and organic anion retention. |
| Action Potential | Depolarization to threshold (-55 mV) opens voltage-gated Na+ channels, driving the potential to +30 mV. Na+ channels inactivate; voltage-gated K+ channels open, repolarizing the membrane, with a brief hyperpolarization (undershoot). Absolute and relative refractory periods follow. |
| Synaptic Transmission | Action potential reaches axon terminal → voltage-gated Ca2+ channels open → vesicles fuse with membrane and release neurotransmitter → neurotransmitter binds postsynaptic receptors → ion channels open, producing excitatory (EPSP) or inhibitory (IPSP) postsynaptic potentials. |
| Key Neurotransmitters | Acetylcholine (NMJ, parasympathetic, memory), glutamate (primary excitatory CNS), GABA (primary inhibitory CNS), dopamine (reward, motor control), serotonin (mood, sleep), norepinephrine (arousal, sympathetic), endorphins (pain modulation). |
| Central vs. Peripheral Nervous System | CNS: brain and spinal cord. PNS: cranial nerves, spinal nerves, ganglia. PNS divides into somatic (voluntary, skeletal muscle) and autonomic (involuntary), which further splits into sympathetic ('fight or flight') and parasympathetic ('rest and digest'). |
| Brain Regions | Cerebrum (higher cognition, four lobes), diencephalon (thalamus: sensory relay; hypothalamus: homeostasis), brainstem (midbrain, pons, medulla: vital functions), cerebellum (balance, coordination), limbic system (emotion, memory: amygdala and hippocampus). |
| Spinal Cord Tracts | Ascending (sensory): dorsal column-medial lemniscus (fine touch, proprioception), spinothalamic (pain, temperature, crude touch). Descending (motor): lateral corticospinal (voluntary motor), rubrospinal, reticulospinal, vestibulospinal. |
| Reflex Arc | Five components: receptor, sensory (afferent) neuron, integration center (CNS), motor (efferent) neuron, effector. Patellar (knee-jerk) reflex is monosynaptic; withdrawal reflex from a pain stimulus involves interneurons and is polysynaptic. |
| Autonomic Receptors | Parasympathetic uses ACh at both pre- and postganglionic synapses (nicotinic then muscarinic receptors). Sympathetic uses ACh preganglionic (nicotinic) and norepinephrine postganglionic (alpha and beta adrenergic receptors), with exceptions at sweat glands and adrenal medulla. |
| Hypothalamic-Pituitary Axis | Hypothalamus controls the anterior pituitary via releasing/inhibiting hormones carried through the hypophyseal portal system. Anterior pituitary secretes ACTH, TSH, LH, FSH, GH, and prolactin. Posterior pituitary stores and releases hypothalamic-made oxytocin and ADH. |
| Thyroid Hormones | T3 (triiodothyronine) and T4 (thyroxine) increase basal metabolic rate, heat production, and protein synthesis. Calcitonin (from parafollicular cells) lowers blood calcium. Regulated by TSH from the anterior pituitary via negative feedback. |
| Adrenal Hormones | Cortex: aldosterone (zona glomerulosa, raises Na+/water retention), cortisol (zona fasciculata, raises blood glucose, suppresses immunity), androgens (zona reticularis). Medulla: epinephrine and norepinephrine (fight-or-flight response). |
| Pancreatic Islet Hormones | Alpha cells: glucagon (raises blood glucose via glycogenolysis and gluconeogenesis). Beta cells: insulin (lowers blood glucose by promoting cellular uptake and glycogen synthesis). Delta cells: somatostatin (inhibits both). Type 1 diabetes: autoimmune beta-cell destruction. Type 2: insulin resistance. |
| Calcium Regulation | Parathyroid hormone (PTH) from the parathyroid glands raises blood Ca2+ by stimulating osteoclasts, increasing kidney reabsorption, and activating vitamin D. Calcitonin from thyroid parafollicular cells lowers it by inhibiting osteoclasts. PTH is the primary regulator. |
| Blood-Brain Barrier | Formed by tight junctions between brain capillary endothelial cells, supported by astrocyte foot processes. Selectively permeable: allows lipid-soluble molecules (O2, CO2, alcohol) and actively transports glucose and amino acids; excludes most pathogens and many drugs. |
Cardiovascular, Respiratory, and Lymphatic Systems
The transport and defense systems. These cards address the physics and physiology of circulation, gas exchange, and immune response.
| Term | Meaning |
|---|---|
| Cardiac Cycle | One complete heartbeat, approximately 0.8 seconds. Atrial systole (0.1 s) fills ventricles → ventricular systole (0.3 s) ejects blood → ventricular diastole (0.4 s) fills atria. Heart sounds: S1 ('lub,' AV valves close); S2 ('dub,' semilunar valves close). |
| Cardiac Conduction System | SA node (pacemaker, 60-100 bpm) → atrial contraction → AV node (brief delay) → Bundle of His → right and left bundle branches → Purkinje fibers → ventricular contraction from apex upward. ECG: P wave (atrial depolarization), QRS (ventricular depolarization), T wave (ventricular repolarization). |
| Cardiac Output | CO = Heart Rate × Stroke Volume. Average adult CO at rest is roughly 5 L/min. Stroke volume depends on preload (end-diastolic volume, Frank-Starling law), afterload (peripheral resistance), and contractility (sympathetic tone, calcium). |
| Blood Pressure Regulation | BP = CO × Total Peripheral Resistance. Regulated short-term by baroreceptors (carotid sinus, aortic arch) via the autonomic nervous system, and long-term by the renin-angiotensin-aldosterone system (RAAS) and ADH acting on kidneys. |
| Blood Vessels | Arteries: thick tunica media with elastic and smooth muscle; high-pressure. Arterioles: major resistance vessels, regulate blood flow. Capillaries: single endothelial layer; site of exchange. Venules and veins: thin walls, one-way valves (in veins), serve as capacitance vessels. |
| Hemoglobin and Oxygen Transport | Each hemoglobin molecule has four subunits (2 alpha, 2 beta) each with a heme group that binds one O2. Cooperative binding yields the sigmoidal O2-Hb dissociation curve. Right-shift (Bohr effect) with increased CO2, H+, temperature, or 2,3-BPG promotes unloading to tissues. |
| CO2 Transport | Dissolved in plasma (7%), bound to hemoglobin as carbaminohemoglobin (23%), and, most importantly, as bicarbonate (70%). In RBCs, carbonic anhydrase catalyzes CO2 + H2O ↔ H2CO3 ↔ HCO3- + H+. The chloride shift exchanges HCO3- for Cl-. |
| Respiratory Zones | Conducting zone: nose/mouth → pharynx → larynx → trachea → bronchi → bronchioles → terminal bronchioles (no gas exchange; 'anatomical dead space'). Respiratory zone: respiratory bronchioles → alveolar ducts → alveolar sacs (site of gas exchange). |
| Pulmonary Ventilation | Inspiration: diaphragm contracts/flattens and external intercostals contract, expanding the thorax; intrapulmonary pressure drops below atmospheric; air flows in. Expiration: passive elastic recoil at rest; active use of internal intercostals and abdominals during exercise. |
| Lung Volumes and Capacities | Tidal volume (TV): normal breath (~500 mL). Inspiratory reserve (IRV): ~3000 mL. Expiratory reserve (ERV): ~1100 mL. Residual volume (RV): ~1200 mL (cannot be exhaled). Vital capacity (VC) = TV + IRV + ERV. Total lung capacity (TLC) = VC + RV. |
| Alveolar Gas Exchange | Occurs across the respiratory membrane (alveolar epithelium + fused basement membranes + capillary endothelium), only about 0.5 μm thick. Driven by partial pressure gradients: O2 moves from alveoli (PO2 ~104 mmHg) into blood (~40 mmHg); CO2 moves the other way. |
| Control of Breathing | Medullary respiratory centers (dorsal and ventral) set basic rhythm. Pons fine-tunes the pattern (pneumotaxic and apneustic centers). Central chemoreceptors respond to CSF H+ (reflecting CO2); peripheral chemoreceptors (carotid, aortic bodies) respond to O2, CO2, and pH. |
| Innate vs. Adaptive Immunity | Innate: rapid, nonspecific. Includes physical barriers, phagocytes (neutrophils, macrophages), NK cells, complement, and inflammation. Adaptive: slower, specific, with memory. B cells produce antibodies (humoral); T cells coordinate and kill infected cells (cellular). |
| Lymphatic System | Network of vessels returning interstitial fluid to the blood (as lymph), absorbing dietary fats (via lacteals), and housing immune cells. Major structures: lymph nodes, tonsils, spleen, thymus, and Peyer's patches. Drains into the subclavian veins via the right lymphatic duct and thoracic duct. |
| Antibody Classes | IgG: most abundant, crosses placenta, secondary response. IgM: first produced in primary response, largest (pentamer). IgA: mucosal surfaces and breast milk. IgE: allergic and parasitic responses. IgD: B-cell surface receptor. |
| Hemostasis | Three phases: vascular spasm, platelet plug formation (von Willebrand factor bridges platelets to exposed collagen), and coagulation cascade (intrinsic and extrinsic pathways converge on factor Xa, producing thrombin and finally fibrin). Vitamin K required for factors II, VII, IX, X. |
Digestive, Urinary, and Reproductive Systems
The remaining major systems: how the body processes food, balances fluids and electrolytes, and perpetuates itself.
| Term | Meaning |
|---|---|
| GI Tract Layers | From lumen outward: mucosa (epithelium, lamina propria, muscularis mucosae), submucosa (connective tissue with Meissner's plexus), muscularis externa (inner circular and outer longitudinal smooth muscle with Auerbach's plexus), and serosa or adventitia. |
| Salivary Digestion | Saliva (produced by parotid, submandibular, and sublingual glands) contains salivary amylase (begins starch digestion), lingual lipase, lysozyme (antibacterial), mucus, and bicarbonate buffers. Approximately 1-1.5 L produced daily. |
| Stomach Cells and Secretions | Parietal cells: HCl (activates pepsin, kills pathogens) and intrinsic factor (required for B12 absorption in ileum). Chief cells: pepsinogen (activated to pepsin by acid). G cells: gastrin (stimulates HCl secretion). Mucous cells: alkaline mucus (protects the stomach lining). |
| Small Intestine Digestion | Site of most digestion and absorption. Brush border enzymes (peptidases, disaccharidases, enterokinase) complete chemical digestion. Pancreatic enzymes (amylase, lipase, trypsin, chymotrypsin) and bile (emulsifies fats) enter via the ampulla of Vater. |
| Bile and Liver Function | Bile is produced by hepatocytes, stored and concentrated in the gallbladder, and released into the duodenum via CCK stimulation. Emulsifies fats for lipase action. The liver also metabolizes drugs, synthesizes albumin and clotting factors, stores glycogen, and processes bilirubin. |
| Nutrient Absorption | Carbohydrates: absorbed as monosaccharides (glucose and galactose via SGLT1, fructose via GLUT5). Proteins: absorbed as amino acids and di/tripeptides via Na+-coupled transporters. Fats: absorbed as free fatty acids and monoglycerides, packaged into chylomicrons, enter lacteals. |
| Nephron Structure | Functional unit of the kidney: glomerulus and Bowman's capsule (filtration), proximal convoluted tubule (reabsorption of 65% of filtrate), loop of Henle (concentration gradient), distal convoluted tubule (fine-tuning), and collecting duct (final concentration under ADH control). |
| Glomerular Filtration | GFR averages ~125 mL/min (~180 L/day). Driven by net filtration pressure (glomerular hydrostatic pressure minus capsular hydrostatic and blood colloid osmotic pressures). Regulated by autoregulation (myogenic, tubuloglomerular feedback) and sympathetic/hormonal influences. |
| Renin-Angiotensin-Aldosterone System (RAAS) | Low BP or Na+ → juxtaglomerular cells release renin → converts angiotensinogen to angiotensin I → ACE converts to angiotensin II → potent vasoconstriction plus adrenal cortex release of aldosterone → Na+ and water retention in collecting duct → BP rises. |
| ADH (Vasopressin) | Released by the posterior pituitary in response to increased blood osmolarity (osmoreceptors in hypothalamus) or decreased blood volume. Inserts aquaporin-2 channels in collecting duct principal cells, increasing water reabsorption and producing concentrated urine. |
| Acid-Base Balance | Three buffering systems: bicarbonate (extracellular), phosphate (intracellular and urine), and protein (especially hemoglobin). Respiratory compensation adjusts ventilation (minutes); renal compensation adjusts H+/HCO3- handling (hours to days). Normal arterial pH: 7.35-7.45. |
| Male Reproductive Anatomy | Testes (seminiferous tubules for sperm, Leydig cells for testosterone) → epididymis → vas deferens → ejaculatory duct → urethra. Accessory glands: seminal vesicles (fructose), prostate (alkaline fluid), bulbourethral glands (lubricant). |
| Spermatogenesis | Occurs in seminiferous tubules under FSH and testosterone control. Spermatogonia (2n) → primary spermatocytes (2n, meiosis I) → secondary spermatocytes (n, meiosis II) → spermatids (n) → sperm. Sertoli cells support the process; takes ~64-72 days. |
| Female Reproductive Anatomy | Ovaries (oogenesis and estrogen/progesterone production) → fallopian tubes (site of fertilization) → uterus (implantation and gestation) → cervix → vagina. Ovaries contain follicles at various stages; all primary oocytes are present at birth. |
| Menstrual Cycle | 28-day cycle with two overlapping cycles. Ovarian: follicular phase (days 1-14, FSH → follicle growth → estrogen), ovulation (day 14, LH surge), luteal phase (days 15-28, corpus luteum → progesterone). Uterine: menses, proliferative, secretory phases. |
| Fertilization and Implantation | Sperm penetrates zona pellucida via acrosomal enzymes; cortical reaction prevents polyspermy. Zygote undergoes cleavage as it travels down the fallopian tube. Blastocyst (day 5-7) implants in endometrium; trophoblast forms placenta; hCG maintains corpus luteum. |
How to Study anatomy and physiology Effectively
Mastering anatomy and physiology requires the right study approach, not just more hours. Research in cognitive science consistently shows that three techniques produce the best learning outcomes: active recall (testing yourself rather than re-reading), spaced repetition (reviewing at scientifically-optimized intervals), and interleaving (mixing related topics rather than studying one in isolation). FluentFlash is built around all three. When you study anatomy and physiology with our FSRS algorithm, every term is scheduled for review at exactly the moment you're about to forget it, maximizing retention while minimizing study time.
The most common mistake students make is relying on passive review methods. Re-reading your notes, highlighting textbook passages, or watching lecture videos feels productive, but studies show these methods produce only 10-20% of the retention that active recall achieves. Flashcards force your brain to retrieve information, which strengthens memory pathways far more than recognition alone. Pair this with spaced repetition scheduling, and you can learn in 20 minutes a day what would take hours of passive review.
A practical study plan for anatomy and physiology: start by creating 15-25 flashcards covering the highest-priority concepts. Review them daily for the first week using our FSRS scheduling. As cards become easier, intervals automatically expand, from minutes to days to weeks, so you're always working on material at the edge of your knowledge. After 2-3 weeks of consistent practice, you'll find anatomy and physiology concepts become automatic rather than effortful to recall.
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Generate flashcards using FluentFlash AI or create them manually from your notes
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Study 15-20 new cards per day, plus scheduled reviews
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Use multiple study modes (flip, multiple choice, written) to strengthen recall
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Track your progress and identify weak topics for focused review
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Review consistently, daily practice beats marathon sessions
Why Flashcards Work Better Than Other Study Methods for anatomy and physiology
Flashcards aren't just for vocabulary, they're one of the most research-backed study tools for any subject, including anatomy and physiology. The reason comes down to how memory works. When you read a textbook passage, your brain stores that information in short-term memory, but without retrieval practice, it fades within hours. Flashcards force retrieval, which is the mechanism that transfers information from short-term to long-term memory.
The "testing effect," documented in hundreds of peer-reviewed studies, shows that students who study with flashcards consistently outperform those who re-read by 30-60% on delayed tests. This isn't because flashcards contain more information, it's because retrieval strengthens neural pathways in a way that passive exposure cannot. Every time you successfully recall a anatomy and physiology concept from a flashcard, you're making that concept easier to recall next time.
FluentFlash amplifies this effect with the FSRS algorithm, a modern spaced repetition system that schedules reviews at mathematically-optimal intervals based on your actual performance. Cards you find easy get pushed further into the future. Cards you struggle with come back sooner. Over time, this builds remarkable retention with minimal time investment. Students using FSRS-based systems typically retain 85-95% of material after 30 days, compared to roughly 20% retention from passive review alone.