Quiz
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1. Where in the body is almost all of your food absorbed?
The small intestine, through millions of villi (Figure 3).
2. Why does the liver get first pick of glucose and amino acids?
Blood from the gut drains into the portal vein, which runs straight to the liver before the rest of the body (Figures 1 and 4).
3. Which nutrients skip the liver at first, and how?
Fats and vitamins A, D, E and K: they are packed into chylomicrons and travel up the lymph, joining the blood near the left collarbone (Figure 4).
4. What is a lacteal?
The lymph vessel in the middle of each villus, which takes in fat in chylomicrons (Figure 3).
5. What does bile do, and where is it made and stored?
It breaks fat into tiny droplets so enzymes can reach it. The liver makes it and the gallbladder stores it (Figure 3).
6. What happens to amino acids your body doesn’t need for building?
The liver strips off their nitrogen as urea, which the kidneys pass out in urine, and the rest is burned or stored as glucose or fat (Figure 4).
7. About how much of your resting energy does the brain use, and what is its main fuel?
About a fifth, mostly glucose (Figures 2 and 4).
8. How can a breath test measure the alcohol in your blood?
A few percent of alcohol leaves the blood unchanged through the lungs, so breath alcohol tracks blood alcohol (Figure 4).
9. What happens to fiber in your body?
Your enzymes can’t break it down. In the large intestine, gut bacteria ferment much of it into short-chain fatty acids; the rest adds bulk to stool (Figure 4).
10. Why is vitamin B12 absorbed differently from the other B vitamins?
It needs intrinsic factor from the stomach and is absorbed only at the end of the small intestine; the liver stores years of it (Figure 5).
11. Where does most of the iron for new red blood cells come from each day?
Recycled from old red cells broken down in the spleen. Only 1 to 2 mg a day is absorbed from food (Figure 5).
12. Where is 99% of your calcium, and what raises blood calcium when it dips?
In bones and teeth. Parathyroid hormone tells the kidneys to keep more and the bones to release some (Figure 5).