Notes
Respiratory system
- Air flows through the nasal cavity, pharynx, larynx, trachea, bronchi and bronchioles to the alveoli, where gas exchange occurs. Surfactant keeps alveoli open.
- Inspiration: the diaphragm contracts and the chest volume increases, so pressure falls (Boyle's law) and air flows in. Quiet expiration is passive.
- Gases diffuse down partial pressure gradients. Hemoglobin carries oxygen; most CO2 travels as bicarbonate. Rising CO2 and falling pH are the main stimuli for breathing, detected by chemoreceptors and processed in the medulla.
Digestive system
- Alimentary canal: mouth, pharynx, esophagus, stomach, small intestine, large intestine. Accessory organs: salivary glands, liver, gallbladder and pancreas.
- Enzymes: amylase (carbohydrates), pepsin and trypsin (proteins), lipase (fats). Bile emulsifies fat.
- The small intestine absorbs nutrients through villi. Fats enter lacteals; sugars and amino acids enter capillaries and go to the liver via the hepatic portal vein.
Topics in this unit
Each topic has its own short notes and practice.
Practice
Rising CO2 lowers pH, stimulating chemoreceptors and faster breathing.
Diaphragm contraction enlarges the thoracic cavity.
Pepsin is active in acidic conditions and digests protein.
Bile helps break fat into droplets.
Chylomicrons are too large for capillaries and enter lacteals.
Lactase digests lactose into glucose and galactose.
Free response
Write your answer first, then open the scoring guide.
Free-response question
Dan eats a cheeseburger with a bun, then runs up several flights of stairs.
(a) Name the main enzyme for each of the three nutrient groups in his meal (starch in the bun, protein in the meat, fat in the cheese) and the organ that makes it.
Show the answer and scoring guide
Starch: amylase (salivary glands and pancreas). Protein: pepsin (stomach) and trypsin (pancreas). Fat: lipase (pancreas), with help from bile (liver).
Check off the points you earned:
(b) Describe how the fat is absorbed and how this differs from the absorption of glucose.
Show the answer and scoring guide
Bile emulsifies fat, lipase digests it, and the products form micelles and enter intestinal cells. They are repackaged as chylomicrons and enter the lacteals (lymph). Glucose enters the capillaries in the villus and travels to the liver by the hepatic portal vein.
Check off the points you earned:
(c) Explain how breathing changes as Dan climbs the stairs and why.
Show the answer and scoring guide
His muscles make more CO2, which lowers blood pH. Chemoreceptors signal the medulla to increase breathing rate and depth, which supplies more oxygen and removes the extra CO2.
Check off the points you earned: