Human Body — Practice Quiz

A Biology cheat sheet for Human Body — every key formula with its symbols defined — plus a medium-level practice quiz to test recall.

Formulas & key concepts

Cells (basic unit) → Tissues (groups of similar cells): Epithelial (lining surfaces), Connective (support, collagen), Nervous (neurons + glia), Muscle (movement) → Organs (multiple tissues) → Organ Systems (related organs working together).
Body Organization Levels
Homeostasis: Maintaining relatively constant internal conditions (temperature, pH, glucose, water) despite external changes. Essential for survival.
Homeostasis
Negative Feedback: Response blocks further action (e.g., thermostat turns heat off when warm). Body uses this to maintain homeostasis. Positive Feedback: Amplifies response (e.g., oxytocin during labor).
Feedback Inhibition
Hypothalamus: Body's thermostat. When cold: speed up cell activity (generates heat), shivering. When hot: sweat (evaporation cools), slow cell activity. Ectotherms (rely on environment) vs. Endotherms (internal heat).
Thermoregulation
Detoxification: Breaks down toxins (ammonia → urea). Glucose Regulation: Stores excess glucose as glycogen, releases when blood sugar drops. Prevents dangerous glucose fluctuations.
Liver & Homeostasis
Calories (kcal): Energy measurement (1 Calorie = 1000 calories). Food provides energy for ATP production + raw materials for growth/repair. Body needs at least 45 substances it can't make.
Nutrients & Energy

Most important nutrient. Required for chemical reactions, blood, extracellular fluid. Lost via urine, sweat, breathing. Need ~1L/day minimum. <b>Dehydration</b>: Can be fatal.

Water
Simple (monosaccharides like glucose, disaccharides like sucrose). Complex (polysaccharides: starch, glycogen). Excess stored as glycogen (liver/muscles) or fat. Fiber (cellulose): Can't digest but needed for bulk/movement.
Carbohydrates
Saturated (all single bonds, solid at room temp). Unsaturated (double bonds, liquid). Trans fats (hydrogenated, linked to heart disease). Functions: cell membranes, hormone production, vitamin absorption, energy storage, insulation.
Fats (Lipids)

Made of <b>amino acids</b> (20 types; 8 essential from food). Functions: enzymes, structure (collagen), transport, regulation, sometimes energy. Animal sources provide all essential amino acids.

Proteins
Fat-soluble vitamins (A, D, E, K): Stored in body fat. Water-soluble (B, C): Can't be stored, needed daily. Minerals: Inorganic nutrients (calcium, iron, sodium, etc.) for various functions.
Vitamins & Minerals
Path: Mouth (ingestion) → Esophagus (peristalsis) → Stomach (acidic, churning) → Small Intestine (nutrient absorption) → Large Intestine/Colon (water reabsorption) → Rectum → Anus (elimination). Accessory: Salivary glands, liver, gallbladder, pancreas.
Digestive System Anatomy
Mechanical: Chewing, churning (breaks into smaller pieces). Chemical: Enzymes break bonds. Enzymes: Amylase (saliva/pancreas, breaks starch), Pepsin (stomach, breaks proteins), Bile (liver/gallbladder, emulsifies fats). Absorption: Villi/microvilli in small intestine increase surface area. Peristalsis: Wave-like muscle contractions move food.
Digestive Processes

Removes metabolic wastes (urea, CO₂), maintains <b>osmoregulation</b> (water/solute balance), regulates blood pH, blood pressure. Organs: skin, lungs, liver, kidneys.

Excretory System Functions
Nephron: Functional unit of kidney. Parts: Glomerulus (capillary cluster), Bowman's Capsule (surrounds glomerulus), Proximal tubule, Loop of Henle, Distal tubule, Collecting Duct.
Kidney Structure
Filtration: Blood pressure forces water/small molecules from glomerulus into Bowman's capsule. Reabsorption: Useful substances (glucose, water, ions) reclaimed into blood. Secretion: Additional wastes secreted into tubule. Result: concentrated urine.
Urine Formation
Kidneys (filter blood, produce urine) → Ureters (transport urine) → Bladder (stores urine) → Urethra (eliminates urine). Also includes: Renal artery (brings blood), Renal vein (removes filtered blood).
Urinary System
Central Nervous System (CNS): Brain + spinal cord (protected by meninges, cerebrospinal fluid). Peripheral Nervous System (PNS): Somatic (voluntary) + Autonomic (involuntary: sympathetic + parasympathetic).
Nervous System Organization
Cell body (nucleus, organelles) → Dendrites (receive signals) → Axon (transmits signal, long) → Myelin Sheath (glia cells, insulates, speeds transmission) → Synaptic terminals (release neurotransmitters).
Neuron Structure
Resting potential: -70mV (inside negative). Depolarization: Na⁺ channels open, inside becomes positive. Repolarization: K⁺ channels open, returns to negative. All-or-none: Either fires completely or not at all.
Action Potential
Synapse: Gap between neurons. Synaptic cleft: Space. Signal crosses via neurotransmitters (chemicals): Acetylcholine (muscle stimulation), Dopamine (reward/movement), Serotonin (mood), GABA (inhibitory), Glutamate (excitatory).
Synapse & Neurotransmitters
Cerebrum: Largest part, cerebral cortex (gray matter, higher functions), divided into lobes. Cerebellum: Coordination, balance, motor learning. Brainstem: Controls vital functions (breathing, heart rate, swallowing). Limbic system: Emotion, memory (hippocampus, amygdala).
Brain Structure
Frontal lobe: Motor cortex, planning, decision-making, language (Broca's area). Parietal lobe: Touch, temperature, spatial awareness. Temporal lobe: Hearing, memory (hippocampus), language (Wernicke's area). Occipital lobe: Visual processing.
Brain Functions by Lobe

Connects brain to peripheral nerves. <b>Gray matter</b> (inside, neuron cell bodies). <b>White matter</b> (outside, myelinated axons). <b>Reflex arc</b>: Sensory neuron → interneuron → motor neuron (bypasses brain for speed).

Spinal Cord
Sympathetic: 'Fight-or-flight' (accelerates heart, dilates pupils, inhibits digestion, releases epinephrine). Parasympathetic: 'Rest-and-digest' (slows heart, stimulates digestion, constricts pupils). Usually oppose each other.
Autonomic Nervous System
Sensory neurons: Transmit info from skin, muscles, sensory organs to CNS. Motor neurons: Transmit commands from CNS to muscles. Voluntary control (conscious movement). Usually one synapse.
Sensory-Somatic Nervous System
Hippocampus: Converts short-term to long-term memory. Amygdala: Processes fear/emotions. Synaptic plasticity: Connections strengthen with use (learning). Corpus callosum: Connects brain hemispheres.
Memory & Learning
Support (framework), Protection (skull protects brain, ribs protect organs), Movement (attachment for muscles), Mineral storage (calcium, phosphorus), Blood cell production (bone marrow).
Skeletal Functions
Compact bone: Dense, outer layer, contains osteons (concentric rings). Spongy bone: Inner, porous, lightweight. Bone marrow: Red (produces blood cells), Yellow (fat storage).
Bone Structure
Skull (cranium + facial bones), Hyoid bone (throat), Vertebral column (spine: cervical, thoracic, lumbar, sacrum, coccyx), Ribcage (ribs + sternum). Forms central axis, protects CNS and organs.
Axial Skeleton
Upper: Pectoral girdle (clavicle, scapula), arms (humerus, radius, ulna), hands. Lower: Pelvic girdle (hip bones), legs (femur, tibia, fibula, patella), feet. For movement and manipulation.
Appendicular Skeleton
Fibrous: Immovable (skull sutures). Cartilaginous: Slightly movable (vertebrae). Synovial: Freely movable, have synovial fluid for lubrication (shoulder, knee, elbow). Types: hinge, ball-and-socket, pivot.
Joints
Osteoblasts: Build bone. Osteoclasts: Break down bone. Continuous remodeling. Calcium regulation: Parathyroid hormone (PTH) increases blood Ca²⁺, calcitonin decreases it.
Bone Growth & Remodeling
Skeletal: Voluntary, striated, multinucleated, attached to bones. Smooth: Involuntary, non-striated, walls of organs/blood vessels. Cardiac: Involuntary, striated, branched, intercalated discs, only in heart.
Muscle Types
Sarcomere: Functional unit. Contains myofilaments: Actin (thin) + Myosin (thick, has heads). Sliding filament theory: Myosin heads pull actin, sarcomere shortens. Requires ATP + Ca²⁺.
Muscle Contraction

Synapse between motor neuron and muscle fiber. Neuron releases <b>acetylcholine</b> → binds to receptors on <b>sarcolemma</b> (muscle membrane) → triggers muscle contraction.

Neuromuscular Junction
Epidermis: Outer layer, constantly replaced, no blood vessels. Dermis: Inner layer, blood vessels, nerves, glands. Hair, Nails. Sweat glands (cooling), Sebaceous glands (oil).
Integumentary System
Protection: Barrier against pathogens, UV, injury. Temperature regulation: Sweat evaporation cools, blood flow adjusts heat loss. Sensation: Touch, pain, temperature receptors. Vitamin D synthesis: UV exposure converts precursors.
Skin Functions

Four chambers: <b>Right atrium</b> (receives deoxygenated blood) → <b>Right ventricle</b> (pumps to lungs) → <b>Left atrium</b> (receives oxygenated blood) → <b>Left ventricle</b> (pumps to body). <b>Valves</b>: <b>Tricuspid</b> (right), <b>Bicuspid/Mitral</b> (left), <b>Semilunar</b> (exits).

Heart Anatomy
Systole: Contraction (ventricles pump blood). Diastole: Relaxation (chambers fill). Pacemaker (SA node): Sets rhythm. Electrocardiogram (ECG): Records electrical activity.
Cardiac Cycle
Arteries: Carry blood away from heart, thick walls, high pressure. Veins: Carry blood to heart, thin walls, low pressure, valves prevent backflow. Capillaries: Tiny, one-cell thick, site of gas/nutrient exchange.
Blood Vessels
Plasma: Liquid (water, proteins, ions, nutrients). Red blood cells (RBCs): No nucleus, contain hemoglobin (carries O₂). White blood cells (WBCs): Immune defense. Platelets: Blood clotting.
Blood Components
Pulmonary: Right ventricle → pulmonary artery → lungs (gas exchange) → pulmonary vein → left atrium. Systemic: Left ventricle → aorta → body tissues → vena cava (superior/inferior) → right atrium. Closed system: Blood stays in vessels.
Circulation Pathways
Systolic: Pressure during ventricular contraction (higher, ~120 mmHg). Diastolic: Pressure during relaxation (lower, ~80 mmHg). Regulated by heart rate, blood volume, vessel diameter.
Blood Pressure
Nasal cavity (filters, warms air) → Pharynx (throat) → Larynx (voice box) → Trachea (windpipe) → Bronchi (left/right) → Bronchioles (smaller branches) → Alveoli (air sacs, gas exchange).
Respiratory System Anatomy
Alveoli: Tiny sacs with huge surface area, surrounded by capillaries. Diffusion: O₂ moves from alveoli → blood (high to low concentration), CO₂ moves blood → alveoli. Thin walls facilitate exchange.
Gas Exchange
Inspiration: Diaphragm contracts (flattens), intercostal muscles lift ribs, chest cavity expands, air rushes in. Expiration: Diaphragm relaxes (rises), ribs lower, chest cavity shrinks, air pushed out. Usually passive.
Breathing Mechanism
Chemical messengers: Travel in blood, affect distant target cells. Endocrine glands: Secrete into blood (no ducts). Exocrine glands: Secrete through ducts (e.g., sweat, digestive enzymes).
Hormones
Receptors: Cell membrane (protein hormones, trigger cascade) vs. Intracellular (steroid hormones, enter cell, affect transcription). Up-regulation: More receptors when hormone low. Down-regulation: Fewer receptors when hormone high.
Hormone Action
Hypothalamus: Controls hormone release, homeostasis, connects nervous + endocrine. Anterior pituitary: Releases FSH, LH, TSH, ACTH, GH, prolactin. Posterior pituitary: Stores/releases ADH (water retention), oxytocin (labor, bonding). 'Master gland.'
Hypothalamus & Pituitary
Thyroid: Thyroxine (T4) increases metabolism, growth. Requires iodine. Calcitonin lowers blood Ca²⁺. Parathyroid glands: PTH raises blood Ca²⁺ (stimulates bone breakdown, kidney reabsorption).
Thyroid & Parathyroid
Cortex (outer): Cortisol (stress response, raises blood sugar), Aldosterone (Na⁺/K⁺ balance, blood pressure). Medulla (inner): Epinephrine/Norepinephrine (adrenaline, 'fight-or-flight').
Adrenal Glands
Insulin: Lowers blood glucose (promotes uptake, storage as glycogen). Glucagon: Raises blood glucose (breaks down glycogen). Diabetes: Type I (no insulin production), Type II (insulin resistance).
Pancreas (Endocrine)
Testosterone: Testes produce (males), stimulates sperm production, secondary sex characteristics (deep voice, body hair, muscle). Estrogen: Ovaries produce (females), menstrual cycle, secondary sex characteristics (breast development, wider hips). Progesterone: Maintains uterine lining.
Sex Hormones
Testes (produce sperm + testosterone), Scrotum (holds testes outside body, cooler temp), Seminiferous tubules (sperm production), Epididymis (sperm maturation), Vas deferens (sperm transport), Urethra (sperm exit), Penis (copulation). Accessory glands: Seminal vesicles, prostate, bulbourethral.
Male Reproductive Anatomy

Occurs in <b>seminiferous tubules</b>. <b>Sertoli cells</b>: Nourish developing sperm. <b>Spermatogonium</b> (diploid) → meiosis I → <b>secondary spermatocyte</b> (haploid) → meiosis II → 4 <b>spermatids</b> → mature to <b>sperm</b> (flagellum, neck with mitochondria, head with DNA, acrosome).

Spermatogenesis

Hypothalamus releases <b>GnRH</b> → anterior pituitary releases <b>FSH</b> (stimulates Sertoli cells, sperm production) + <b>LH</b> (stimulates interstitial cells of Leydig to produce testosterone). <b>Negative feedback</b>: High testosterone inhibits GnRH/FSH/LH. <b>Inhibin</b> (from Sertoli): Inhibits FSH when sperm count high.

Male Hormones
Ovaries (produce eggs + hormones), Oviducts/Fallopian tubes (fimbriae capture egg, cilia move it, fertilization site), Uterus (muscular, endometrium lining), Cervix (opening to uterus), Vagina (birth canal, copulation). External: Clitoris, labia majora/minora.
Female Reproductive Anatomy
Oogonium → primary oocyte (meiosis I arrested in prophase I before birth). At puberty: FSH triggers development. Meiosis I completes → secondary oocyte (most cytoplasm) + polar body (dies). Arrested at metaphase II. Ovulation releases secondary oocyte. If fertilized, meiosis II completes → egg + 2nd polar body.
Oogenesis
GnRH → FSH + LH from pituitary. Estrogen: Follicle growth, endometrium thickening, secondary sex characteristics. Progesterone: Maintains endometrium. Feedback: Low estrogen inhibits GnRH, high estrogen stimulates LH surge.
Female Hormones
Follicular phase (days 1-14): FSH stimulates follicle growth, rising estrogen thickens endometrium. Ovulation (day 14): LH surge triggers egg release. Luteal phase (days 15-28): Corpus luteum secretes progesterone + estrogen, maintains endometrium. If no fertilization: corpus luteum degenerates, hormone drop, menstruation (shedding).
Menstrual & Ovarian Cycles
Fertilization: Sperm + egg fuse (usually in oviduct). Zygote → cleavage (rapid mitosis) → blastula. In mammals: blastocyst (inner cell mass + trophoblast). Gastrulation: Forms 3 germ layers: Ectoderm (skin, nervous), Mesoderm (muscle, connective, circulatory), Endoderm (digestive, respiratory lining).
Fertilization & Development
Trimesters: 1st (organ formation), 2nd (growth, movement), 3rd (rapid growth). Placenta: Nutrient/waste exchange, produces hCG (maintains corpus luteum), estrogen, progesterone. Labor: Oxytocin (posterior pituitary) causes uterine contractions. 3 stages: cervix dilation, baby delivery, placenta expulsion. Lactation: Prolactin (milk production), oxytocin (milk release).
Pregnancy & Birth
First line: Physical barriers (skin, mucus, stomach acid). Second line: Inflammatory response (redness, swelling, heat, pain from histamine + increased blood flow), Fever (inhibits pathogens), Phagocytes (WBCs engulf pathogens). Non-specific, immediate.
Innate Immunity

Specific to pathogen, has <b>memory</b> (faster response on re-exposure). <b>B cells</b>: Antibody-mediated (humoral). <b>T cells</b>: Cell-mediated. Takes days to develop but long-lasting protection.

Adaptive Immunity

Y-shaped proteins produced by B cells. <b>Antigen-binding sites</b>: Recognize specific antigens (pathogens). <b>Classes</b>: <b>IgG</b> (most common, crosses placenta), <b>IgM</b> (first response), <b>IgA</b> (secretions: saliva, tears), <b>IgE</b> (allergies, parasites), <b>IgD</b> (B cell activation).

Antibodies

Antigen binds to B cell → <b>clonal selection</b> (rapid division). Differentiate into: <b>Plasma cells</b> (produce antibodies, short-lived) + <b>Memory B cells</b> (long-lived, rapid response on re-exposure).

B Cell Response
Helper T cells (CD4+): Activate B cells + cytotoxic T cells, release cytokines. Cytotoxic T cells (CD8+): Kill infected cells. Require MHC presentation: Cells display antigens on MHC molecules for T cell recognition. Mature in thymus.
T Cell Response
Lymph: Fluid similar to plasma. Lymph vessels: Return fluid to circulatory system, one-way flow. Lymph nodes: Filter lymph, house lymphocytes. Spleen: Filters blood, removes old RBCs. Thymus: T cell maturation.
Lymphatic System
Allergies: Overreaction to harmless antigens (IgE, histamine release). Autoimmune diseases: Immune system attacks own cells (Type I diabetes, lupus, MS). Immunodeficiency: Weakened immune system (HIV/AIDS attacks helper T cells).
Immune Disorders

Practice quiz

  1. Which of the following represents the correct hierarchical organization of the human body from simplest to most complex?

    • Cells \rightarrow Organs \rightarrow Tissues \rightarrow Organ \ Systems
    • Tissues \rightarrow Cells \rightarrow Organs \rightarrow Organ \ Systems
    • Cells \rightarrow Tissues \rightarrow Organs \rightarrow Organ \ Systems
    • Organs \rightarrow Tissues \rightarrow Cells \rightarrow Organ \ Systems

    Answer: Cells \rightarrow Tissues \rightarrow Organs \rightarrow Organ \ Systems

  2. A person's body temperature rises above the normal range. The hypothalamus detects this change and initiates sweating to cool the body down. Once the temperature returns to normal, sweating stops. This is an example of:

    • Positive feedback maintaining homeostasis.
    • Negative feedback maintaining homeostasis.
    • Positive feedback disrupting homeostasis.
    • Negative feedback disrupting homeostasis.

    Answer: Negative feedback maintaining homeostasis.

  3. Which sequence correctly traces the path of food through the digestive system and identifies a key enzyme active in that region?

    • Mouth \ (Amylase) \rightarrow Stomach \ (Pepsin) \rightarrow Small \ Intestine \ (Bile \ emulsification)
    • Esophagus \ (Pepsin) \rightarrow Stomach \ (Amylase) \rightarrow Large \ Intestine \ (Bile \ emulsification)
    • Mouth \ (Bile) \rightarrow Stomach \ (Amylase) \rightarrow Small \ Intestine \ (Pepsin)
    • Stomach \ (Bile) \rightarrow Small \ Intestine \ (Amylase) \rightarrow Large \ Intestine \ (Pepsin)

    Answer: Mouth \ (Amylase) \rightarrow Stomach \ (Pepsin) \rightarrow Small \ Intestine \ (Bile \ emulsification)

  4. The functional unit of the kidney responsible for filtering blood and forming urine is the nephron. Which process involves blood pressure forcing water and small molecules from the glomerulus into Bowman's capsule?

    • Reabsorption
    • Secretion
    • Filtration
    • Osmoregulation

    Answer: Filtration

  5. During the depolarization phase of an action potential, what ion channels open, causing the inside of the neuron to become positive?

    • $K^+$ channels
    • $Cl^-$ channels
    • $Na^+$ channels
    • $Ca^{2+}$ channels

    Answer: $Na^+$ channels

  6. Which cells are primarily responsible for breaking down bone tissue during continuous bone remodeling, and what mineral is primarily stored in bones?

    • Osteoblasts; Sodium
    • Osteoclasts; Calcium
    • Osteocytes; Potassium
    • Chondrocytes; Iron

    Answer: Osteoclasts; Calcium

  7. According to the sliding filament theory, what two myofilaments interact, with one pulling the other, to shorten the sarcomere during muscle contraction?

    • Myosin and Collagen
    • Actin and Elastin
    • Actin and Myosin
    • Troponin and Tropomyosin

    Answer: Actin and Myosin

  8. Deoxygenated blood from the body first enters which chamber of the heart before being pumped to the lungs?

    • Left atrium
    • Left ventricle
    • Right atrium
    • Right ventricle

    Answer: Right atrium

  9. A patient is diagnosed with Type I diabetes. This condition is characterized by:

    • The body's cells becoming resistant to glucagon.
    • The pancreas producing too much insulin.
    • The pancreas failing to produce insulin.
    • The body's cells becoming resistant to insulin.

    Answer: The pancreas failing to produce insulin.

  10. Upon initial exposure to a specific pathogen, B cells undergo clonal selection and differentiate into two main types of cells. What are these two types, and what is their primary function?

    • Helper T cells (activate other immune cells) and Cytotoxic T cells (kill infected cells)
    • Plasma cells (produce antibodies) and Memory B cells (provide long-term immunity)
    • Macrophages (phagocytosis) and Neutrophils (first responders)
    • Mast cells (release histamine) and Natural Killer cells (destroy abnormal cells)

    Answer: Plasma cells (produce antibodies) and Memory B cells (provide long-term immunity)

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