Lesson 1 — The Cardiovascular System
The cardiovascular system — heart, blood, and blood vessels — circulates oxygen and nutrients to every cell while removing carbon dioxide and waste products.
Heart4-chambered pump; right side pumps blood to lungs; left side pumps to body
ArteriesCarry oxygenated blood away from heart; thick muscular walls
VeinsReturn deoxygenated blood to heart; contain valves to prevent backflow
CapillariesTiny vessels where gas and nutrient exchange occurs between blood and cells
Heart Rate Facts
Resting heart rate for teens: 60–100 bpm. Athletes can have resting HR as low as 40 bpm — a sign of a strong, efficient heart. Regular aerobic exercise lowers resting heart rate over time.
Resting heart rate for teens: 60–100 bpm. Athletes can have resting HR as low as 40 bpm — a sign of a strong, efficient heart. Regular aerobic exercise lowers resting heart rate over time.
Quick Check: What is the difference between arteries and veins?
Lesson 2 — The Respiratory System
The respiratory system brings oxygen into the body and expels carbon dioxide. Every breath moves air through a series of structures that filter, warm, and deliver it to the lungs.
- Nose/mouth → pharynx → larynx → trachea → bronchi → bronchioles → alveoli
- Alveoli are tiny air sacs where gas exchange occurs — O₂ in, CO₂ out
- Diaphragm — dome-shaped muscle that powers breathing
Smoking & Lung Damage
Tobacco smoke destroys cilia (tiny hairs that trap debris), damages alveoli, and causes chronic inflammation. This leads to COPD, emphysema, and lung cancer — often irreversible.
Tobacco smoke destroys cilia (tiny hairs that trap debris), damages alveoli, and causes chronic inflammation. This leads to COPD, emphysema, and lung cancer — often irreversible.
Quick Check: Where does gas exchange occur in the lungs?
Lesson 3 — The Digestive System
The digestive system breaks food into nutrients the body can absorb. This involves mechanical (physical) and chemical (enzyme-based) digestion across ~30 feet of digestive tract.
MouthMechanical digestion begins; salivary amylase starts breaking down starch
StomachChurns food; HCl kills bacteria; pepsin digests proteins
Small IntestineMost nutrient absorption; 20 ft long; villi increase surface area
Large IntestineWater absorption; houses gut microbiome; forms waste
Quick Check: What is the difference between mechanical and chemical digestion?
Lesson 4 — Keeping These Systems Healthy
Lifestyle choices profoundly affect cardiovascular, respiratory, and digestive health. Small daily habits compound into major differences over a lifetime.
- Aerobic exercise strengthens the heart and improves circulation
- Never smoke — tobacco is the leading cause of preventable cardiovascular and lung disease
- Eat fiber-rich foods to support healthy digestion and gut microbiome
- Stay hydrated — water is essential for blood volume and digestion
- Limit saturated fat and sodium — both elevate cardiovascular disease risk
- Know warning signs: chest pain, shortness of breath, persistent heartburn
Quick Check: Name two lifestyle choices that protect cardiovascular health.
Chapter Vocabulary
Cardiovascular systemThe organ system of the heart and blood vessels that circulates blood throughout the body.
ArteryA blood vessel that carries oxygenated blood away from the heart.
VeinA blood vessel that returns deoxygenated blood back to the heart.
CapillaryThe smallest blood vessels where gas and nutrient exchange occurs between blood and cells.
AlveoliTiny air sacs in the lungs where oxygen and carbon dioxide are exchanged.
DiaphragmThe dome-shaped muscle below the lungs that controls breathing.
PeristalsisThe wave-like muscle contractions that move food through the digestive tract.
VilliTiny finger-like projections in the small intestine that absorb nutrients.
CholesterolA fatty substance in the blood; high levels increase risk of heart disease.
HypertensionPersistently high blood pressure; a major risk factor for heart attack and stroke.
