Study guides › B/B › Biology
Digestive & Excretory Systems
The gut breaks food into absorbable pieces and the kidney tunes the blood. You will learn each digestive organ, enzyme, and hormone, then follow filtrate down the nephron, see how urine is concentrated, and read acid-base data.
Study this chapter in PrepMed (free)
What this chapter covers
- The Digestive Tract & Its Enzymes. Match every enzyme to its source, substrate, site, and pH. Zymogens and their activators are classic exam traps.
- GI Hormones, Liver, Pancreas & Absorption. Secretin, CCK, and gastrin each have a trigger and a target. Absorption routes (portal vein versus lymph) are a common test point.
- The Nephron: Filtration, Reabsorption & Secretion. Know what each segment reabsorbs and secretes. Glomerular pressure and glucose transport maximum are common questions.
- Concentrating Urine: the Countercurrent Multiplier & Hormones. The loop of Henle builds a salt gradient, and ADH and aldosterone decide how much water and sodium you keep.
- Acid-Base Balance. Read a blood gas by asking which value moved with the pH. Compensation always moves the other system in the same direction as the problem.
Key points to know
- Parietal cells: HCl and intrinsic factor; chief cells: pepsinogen
- Enteropeptidase activates trypsinogen, then trypsin activates the rest
- Secretin: acid in, bicarbonate out; CCK: fat in, bile and enzymes out
- Bile emulsifies fat but is not an enzyme
- GFR ≈ 125 mL/min; about 99% of the filtrate is reabsorbed
- PCT reabsorbs 65% of Na⁺/H₂O and all normal glucose and amino acids
- Descending limb: water out; thick ascending limb: salt out, no water
- ADH inserts aquaporin-2 channels in the collecting duct
Try a practice question
Which cells of the stomach secrete intrinsic factor?
- Chief cells
- G cells
- Parietal cells
- Mucous neck cells
Show the answer
C. Parietal cells make both HCl and intrinsic factor. Chief cells make pepsinogen and G cells make gastrin, so those are the tempting but wrong options.
Common questions
What does this chapter cover?
Digestive & Excretory Systems covers The Digestive Tract & Its Enzymes, GI Hormones, Liver, Pancreas & Absorption, The Nephron: Filtration, Reabsorption & Secretion, Concentrating Urine: the Countercurrent Multiplier & Hormones, Acid-Base Balance.
What should I know first?
Parietal cells: HCl and intrinsic factor; chief cells: pepsinogen Enteropeptidase activates trypsinogen, then trypsin activates the rest Secretin: acid in, bicarbonate out; CCK: fat in, bile and enzymes out
24 original practice questions accompany this chapter in the app. Spaced review brings missed ideas back at the right time; it helps memory but cannot promise you will not miss an idea again.