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Human Body

Understand the human body — hardware, systems, and repair.

Genetics​

Understand the biological hardware.

DNA is a molecule shaped like a twisted ladder that contains genetic instructions.

Chromosomes are tightly packed bundles of DNA. Humans have 46 total:

  • 44 autosomes (regular chromosomes)
  • 2 sex chromosomes (X and Y)

Genes are segments of DNA that code for specific traits. Each chromosome contains many genes. Humans can produce ~70 trillion possible genetic combinations.

Biological sex is determined by the father's sperm:

ChromosomesTypical Sex
XXFemale
XYMale
  • Mother always contributes an X chromosome.
  • Father contributes either X (→ XX female) or Y (→ XY male).

Mitochondrial DNA (mtDNA) are inherited only from your mother. Used to trace maternal ancestry.

Dominant genes show up if you have one copy (e.g., brown eyes) while recessive genes only show up if you have two copies (e.g., blue eyes).

Epigenetics: Controls which genes are turned on or off based on environment and life experiences. Think of DNA as hardware and epigenetics as software settings. You = Genes + Environment.

Systems​

Know what each body system does.

Skeletal System​

Bones, cartilage, ligaments:

  • Support: Framework for the body.
  • Protection: Shields vital organs (skull protects brain, ribs protect heart/lungs).
  • Movement: Muscles attach to bones via tendons. Joints allow motion.
  • Mineral storage: Stores calcium and phosphorus.
  • Blood cell production: Bone marrow produces red (oxygen transport) and white (immune defense) blood cells, and platelets (clotting).

Muscular System​

Muscles:

  • Movement: Contract to move bones and body parts.
  • Posture: Maintain body position and stability.
  • Heat production: Generate warmth through muscle activity.

Circulatory System​

Heart, blood vessels, blood:

  • Transport: Arteries deliver oxygen and nutrients to cells.
  • Waste removal: Veins carry carbon dioxide and metabolic waste away from tissues. Contain valves that prevent backflow and thinner walls than arteries because blood pressure is lower.
  • Temperature regulation: Distributes heat throughout the body.
  • Immune function: Transports white blood cells and antibodies.
  • Hormone distribution: Carries hormones from glands to target organs.

See circulatory_system.png.

Respiratory System​

Lungs, airways:

  • Gas exchange: Oxygen enters the bloodstream. Carbon dioxide is expelled.
  • Breathing: Diaphragm and intercostal muscles control inhalation/exhalation.
  • pH regulation: Maintains blood pH by controlling CO₂ levels.
  • Voice production: Air passing through vocal cords in voice box (Larynx) enables speech.

Nervous System​

Brain, spinal cord, nerves:

  • Control center: Brain processes information and coordinates responses.
  • Communication: Nerves transmit electrical signals throughout the body.
  • Sensory processing: Receives and interprets sensory information.
  • Motor control: Controls voluntary and involuntary movements.
  • Regulation: Manages heart rate, breathing, digestion, and other autonomic functions.

Digestive System​

Mouth, stomach, intestines, gallbladder, pancreas:

  • Digestion: Breaks down food into nutrients. Gallbladder stores and concentrates bile produced by the liver to break down fatty foods. Pancreas produces digestive enzymes.
  • Absorption: Nutrients pass through intestinal walls into bloodstream.
  • Waste elimination: Removes undigested material from the body.

Urinary System​

Kidneys, bladder:

  • Filtration: Kidneys filter waste from blood.
  • Fluid balance: Regulates water and electrolyte levels.
  • Waste removal: Excretes urine containing metabolic waste.

Endocrine System​

Hormone-producing glands (thyroid, pancreas, adrenal glands):

  • Hormone production: Releases chemical messengers into bloodstream.
  • Metabolism regulation: Controls energy use and storage.
  • Growth and development: Regulates physical growth and maturation.
  • Homeostasis: Maintains internal balance (blood sugar, body temperature, sleep cycles).

Important hormones:

  • Insulin: Regulates blood sugar by helping cells absorb glucose (produced by pancreas)
  • Cortisol: Stress hormone. Increases blood sugar and suppresses immune system (produced by adrenal glands)
  • Thyroid hormones: Control metabolism, heart rate, and body temperature (produced by thyroid gland)
  • Adrenaline (Epinephrine): "Fight or flight" hormone. Increases heart rate and energy (produced by adrenal glands)
  • Growth hormone (GH): Stimulates growth and cell reproduction (produced by pituitary gland)
  • Melatonin: Regulates sleep-wake cycles (produced by pineal gland)
  • Estrogen: Female sex hormone. Regulates reproductive system and menstrual cycle (produced by ovaries)
  • Progesterone: Prepares uterus for pregnancy and maintains early pregnancy (produced by ovaries/corpus luteum)
  • Testosterone: Male sex hormone. Promotes muscle mass, bone density, and sperm production (produced by testes)
  • Dopamine: "Reward" hormone. Motivation, pleasure, and learning (produced by brain)
  • Serotonin: Regulates mood, appetite, and sleep (produced by brain and gut)
  • Oxytocin: "Bonding" hormone. Promotes social connection, trust, and childbirth/lactation (produced by pituitary gland)

Immune/Lymphatic System​

Lymph nodes, spleen, white blood cells:

  • Infection defense: Fights bacteria, viruses, and pathogens.
  • Fluid drainage: Returns excess tissue fluid to bloodstream.
  • Toxin removal: Spleen filters harmful substances from lymph fluid.
  • Immune response: Produces antibodies and immune cells.

Infection Types:

Viruses: Smallest infectious agents. Require host cells to reproduce. Not affected by antibiotics (e.g., influenza, common cold).

Bacteria: Larger single-celled organisms. Reproduce independently. Treatable with antibiotics (e.g., strep throat, urinary tract infections).

Fungi: Eukaryotic organisms. Cause infections in skin, nails, or mucous membranes (e.g., yeast infections, athlete's foot, ringworm).

Parasites: Organisms that live on or inside a host. Include protozoa, helminths (worms), and ectoparasites (e.g., malaria, tapeworms, lice).

Vaccines prevent infection by preparing the immune system, mainly against viruses and some bacteria.

Reproductive System​

Male and female organs:

  • Reproduction: Produces offspring.

  • Hormone production: Produces sex hormones (testosterone, estrogen, progesterone).

  • Sexual development: Controls development of sexual characteristics.

  • Vulva refers to external parts of the female genitalia, while vagina is the tube between the vulva and the cervix. See vulva_and_vagina.png.

  • Menstrual cycle (21-35 days, typically 28). See menstrual_cycle.png.

    • Menstrual Phase (Days 1-5): Uterine lining sheds. Low estrogen/progesterone.
    • Follicular Phase (Days 1-13): FSH stimulates follicle maturation. Estrogen rises, thickening uterine lining.
    • Ovulation (Day 14): LH surge releases egg. Peak fertility.
    • Luteal Phase (Days 15-28): Corpus luteum produces progesterone. If no fertilization, hormone levels drop and cycle repeats.

Integumentary System​

Skin, hair, nails:

  • Protection: Barrier against pathogens and physical injury.
  • Temperature regulation: Controls body heat through sweating and blood flow.
  • Sensation: Detects touch, pressure, pain, and temperature.
  • Vitamin D synthesis: Produces vitamin D from sunlight.

Sensory System​

Eyes, ears, nose, tongue, skin:

  • Vision: Eyes detect light and color.
  • Hearing: Ears detect sound waves.
  • Balance: Inner ear maintains equilibrium.
  • Smell: Nose detects chemical molecules in air.
  • Taste: Tongue identifies flavors.
  • Touch: Skin senses pressure, texture, and temperature.

Treatment​

Treat common conditions.

Emergency​

ABCDE First Responder protocol:

  • Airway: If airway is blocked (e.g. person cannot make noise), tilt head backwards and remove visible obstructions.

  • Breathing:

    • If not breathing but has a pulse, give rescue breaths.
    • If no pulse, begin CPR.

  • Circulation: If trauma is obvious or suspected, start here.

    • If there's bleeding:
      • If embedded object, do not remove.
      • If minor, apply direct pressure.
      • If major:
        • If extremity, apply tourniquet.
        • If core, pack wound.

  • Disability: If neurological problems are detected with suspected spinal injury, do not move the patient.

  • Exposure: If exposed to harsh weather conditions, address with heat/cold.

LU-SOAP Note protocol (start with location and request for evacuation if life threatening):

  • Location: Where are you?
  • Urgency: Do you need evacuation?
  • Subjective: What happened (timeline), what patient feels, start with chief complaints (provides fast anchor)
  • Objective: Your findings: vitals, CTM, AVPU, etc.
  • Assessment: Your best impression, state certainty level (e.g. "suspected...")
  • Plan: What you're doing: treatment or evac decision.
L: Ridge Trail mile 2, north gate access.
U: Immediate evac – life threatening.
S: Chest pain, started suddenly 30 min ago, worsening, feels like pressure.
O: A: clear. B: labored 28/min. C: HR 128 weak. Skin pale/cool/clammy. AVPU A but slow responses.
A: Concern for cardiac event; unstable.
P: Gave aspirin (per protocol). Patient resting, airway supported. Request immediate evac with ALS capability.

Cold​

  • 8:00 AM

    • Hydration: 16 oz
    • Vitamin C: 1000 mg
    • Quercetin: 500 mg (optional)
    • Zinc lozenge (~15–20 mg, dissolve slowly)

  • 11:00 AM

    • Hydration: 16 oz
    • Zinc lozenge (~15–20 mg)

  • 2:00 PM

    • Hydration: 16 oz
    • Zinc lozenge (~15–20 mg)

  • 5:00 PM

    • Hydration: 12–16 oz
    • Zinc lozenge (~15–20 mg)

  • 8:00 PM

    • Hydration: 12–16 oz (or warm tea)
    • Vitamin C: 500–1000 mg
    • Quercetin: 500 mg (optional)
    • Zinc lozenge (~15–20 mg)

If you still have symptoms, you are contagious.

Headaches​

  • Hydrate with Oral Rehydration Solution (ORS). Main number is baseline and number in parens is for therapeutic hydration needs (e.g. vomiting).
  • Rest in dark room.
  • Apply cold or warm compress.
  • Red flags:
    • Sudden severe headache ("worst of your life")
    • Headache with fever, stiff neck, or confusion
    • Vision changes or difficulty speaking
    • Headache after head injury
    • Persistent headache lasting > 72 hours

Burns​

  • Run under cool water for 20 minutes.
  • Dress with clear non-stick dressing.
  • Red flags:
    • Burn is bigger than your palm
    • Located on face, hands, feet, groin, or joints
    • Signs of infection (pus, fever, worsening redness)
    • Charred/white skin - DO NOT apply ointments

Cuts​

  • Sanitize: Use rubbing alcohol to sanitize hands (don't use on wound as it kills cells).

  • Pressure: If bleeding, apply firm pressure 5–10 min (standard window to allow a clot to form).

    • If still bleeding, add more gauze (don't lift old one).

  • Clean: Once bleeding has stopped, washing the skin around the cut with mild soap and use clear running water to irrigate the wound itself.

  • Protect: Protect the wound with antibiotics or even plain petroleum jelly keeps the wound moist.

  • Dress: Apply clean gauze.

  • Red flags:

    • Deep wound (needs stitches)
    • Won't close on its own
    • Edges far apart
    • Caused by a dirty/rusty object
    • Bleeding > 10 min despite pressure

Allergies​

  • If skin irritating:
    • Avoid scratching, which can cause infection.
    • Wash area gently.
    • Apply cold compress.
    • Use hydrocortisone cream.
  • Use OTC antihistamine (cetirizine, loratadine).
  • Red flags:
    • Trouble breathing (medical emergency)
    • Rash spreading rapidly
    • Fever + rash
    • Suspected infection (pus, warmth, severe pain)

Fever​

  • Hydrate.
  • Rest.
  • Red flags:
    • Fever > 40°C (104°F)
    • Fever lasting > 3 days
    • Confusion or stiff neck
    • Trouble breathing
    • In infants < 3 months, any fever is urgent

Diarrhea​

  • Oral rehydration solution. Avoid drinks with excess sugar and dairy.
  • BRAT diet (Bananas, Rice, Applesauce, Toast). Avoid greasy, spicy, or high-fat foods.
  • Red flags:
    • Blood in stool
    • Persistent fever
    • Signs of dehydration (dark urine, dizziness)
    • Diarrhea lasting > 48 hours
    • Severe abdominal pain

Nausea​

  • Avoid greasy, spicy, or strong-smelling foods.
  • Ginger or peppermint may help.
  • Try bland foods (crackers, toast) once nausea improves.
  • Take tiny sips of fluid every 15 minutes (set a timer - "hydration timer").
  • Use oral rehydration solution (Pedialyte, diluted sports drink).
  • Avoid solid foods until vomiting stops.
  • Red flags:
    • Severe abdominal pain
    • Vomiting lasting > 24–48 hours
    • Inability to keep liquids down
    • Signs of dehydration (dark urine, dizziness)
    • Blood in vomit
    • Head injury before nausea began
    • Chest pain with nausea (possible heart issue)
    • Fever + stiff neck (possible meningitis)

Sprains​

PEACE & LOVE protocol. RICE is outdated.

  • PEACE (first 48–72 hours):

    • P – Protect the injury (limit movement but avoid total immobilization).
    • E – Elevate the limb to reduce swelling.
    • A – Avoid anti-inflammatories early on if possible (they may slow tissue healing).
    • C – Compress with a wrap.
    • E – Educate the patient on safe movement & recovery.

  • LOVE (after 48–72 hours):

    • L – Load: Begin gentle movement to promote healing.
    • O – Optimism: Positive mindset improves outcomes (yes—studies support this).
    • V – Vascularization: Light exercise to increase blood flow.
    • E – Exercise: Gradual strengthening to restore function.

  • Red flags:

    • Inability to bear weight
    • Visible deformity
    • Suspected fracture
    • Severe pain or swelling

Nosebleeds​

  • Lean forward NOT backward (keeps airway clear).
  • Pinch soft part of nose 10–15 minutes.
  • Apply ice to bridge of nose.
  • Red flags:
    • Bleeding > 20 minutes
    • Caused by significant trauma
    • Frequent nosebleeds

Choking​

  • Encourage coughing if person can still cough or speak.
  • If unable to cough/speak:
    • Alternate 5 back blows and 5 abdominal thrusts (Heimlich maneuver) if trained. See choking_protocol.png.
  • For infants: alternate 5 back blows + 5 chest thrusts.
  • Red flags:
    • Person becomes unconscious (begin CPR)
    • Inability to breathe or make sound
    • Blue/gray skin color

Panic​

  • Reassure the person.
  • Encourage slow breathing (e.g., 4–7–8 method: breathe in 4 seconds, hold 7 seconds, exhale 8 seconds).
  • Avoid bag breathing (no longer recommended).
  • Red flags:
    • Chest pain or pressure
    • Difficulty breathing that doesn't improve
    • Confusion or loss of consciousness
    • First-time occurrence with no known anxiety history

Constipation​

  • Hydrate.
  • Increase fiber intake.
  • Light exercise.
  • OTC stool softener if needed.
  • Red flags:
    • Severe abdominal pain
    • Vomiting
    • No stool for > 5–7 days
    • Blood in stool

Muscle Cramps​

  • Stretch gently.
  • Massage the affected area.
  • Hydrate.
  • Electrolyte solution (sports drink, coconut water).
  • Apply warm compress.
  • Red flags:
    • Severe pain or swelling
    • Cramps that don't improve with stretching
    • Frequent cramping without clear cause
    • Muscle weakness or numbness
    • Cramps with signs of dehydration

Splinter​

  • Don't squeeze the area (can break the splinter or push it deeper).
  • Gently clean the foot with soap and water.
  • If there's visible blood or dirt, rinse thoroughly.
  • If you can see the splinter, use sterilized tweezers to remove (soak foot to encourage splinter to rise).