1. Animal Nutrition
Human Digestion

2. Human digestive system
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Human digestive system
After chewing and swallowing, it takes 5 to 10 seconds for food to pass down the esophagus to the stomach, where it spends 2 to 6 hours being partially digested.
Final digestion and nutrient absorption occur in the small intestine over a period of 5 to 6 hours.
In 12 to 24 hours, any undigested material passes through the large intestine, and feces are expelled through the anus.

3. What do animals need to live?
Animals make energy using:
food
oxygen
food
ATP O2
mitochondria

4. Animals build bodies using:
food for raw materials
amino acids, sugars, fats, nucleotides
ATP energy for synthesis

5. Mouth Functions mechanical digestion teeth break up food
chemical digestion (saliva)
amylase enzyme
digests starch
All that in spit!

6. Swallowing (& not choking)
ESOPHAGUS
Peristalsis
involuntary muscle contractions
to move food along

7. Stomach Functions disinfect food hydrochloric acid = pH 2
But the stomach is made out of protein!
What stops the stomach from digesting itself?
Functions
disinfect food
hydrochloric acid = pH 2
kills bacteria
food storage
can stretch to fit ~2L food
digests protein
pepsin enzyme
mucus secreted by stomach cells protects stomach lining
Still, the epithelium is continually eroded, and the epithelium is completely replaced by mitosis every three days.
Gastric ulcers, lesions in the stomach lining, are caused by the acid-tolerant bacterium Heliobacter pylori.
Ulcers are often treated with antibiotics.
Pepsin is secreted in an inactive form, called pepsinogen by specialized chief cells in gastric pits.
Parietal cells, also in the pits, secrete hydrochloric acid which converts pepsinogen to the active pepsin only when both reach the lumen of the stomach, minimizing self-digestion.
Also, in a positive-feedback system, activated pepsin can activate more pepsinogen molecules.

8. Small intestine Functions digestion absorption
nutrients move into body cells by:
diffusion
active transport
About every 20 seconds, the stomach contents are mixed by the churning action of smooth muscles.
As a result of mixing and enzyme action, what begins in the stomach as a recently swallowed meal becomes a nutrient-rich broth known as acid chyme.
At the opening from the stomach to the small intestine is the pyloric sphincter, which helps regulate the passage of chyme into the intestine.
A squirt at a time, it takes about 2 to 6 hours after a meal for the stomach to empty.

9. Absorption in Small Intestines
Absorption through villi & microvilli
finger-like projections
increases surface area for absorption
SMALL INTESTINES 6 meters long, but can stretch to cover a tennis court

10. Pancreas Produces digestive enzymes Buffers
neutralizes acid from stomach
pancreas
small intestine

11. Balancing Blood Sugar levels
Homeostasis
Balancing Blood Sugar levels
insulin
body cells take up sugar from blood
liver stores sugar
reduces appetite
pancreas
liver
high
blood sugar level
low
liver releases sugar
triggers hunger
pancreas
liver
Feedback
glucagon

12. Liver & Gall Bladder Produces bile breaks up fats
gallbladder only stores bile
(that’s why you can have your gall bladder removed)
bile contains colors from old red blood cells collected in liver =
iron in RBC rusts & makes feces brown

13. Large intestines (colon)
Function
re-absorbs water
use ~9 liters of water every day in digestive juices
if don’t reabsorb water would die of dehydration
> 90% of water re-absorbed
not enough water re-absorbed
diarrhea
can be fatal!
too much water re-absorbed
constipation

14. Appendix
Vestigial organ

15. So don’t forget to wash your hands!
Rectum
Last section of large intestines
eliminate feces
what’s left over?
undigested materials
mainly cellulose from plants
called roughage or fiber
keeps everything moving & cleans out intestines
masses of bacteria
So don’t forget to wash your hands!

16. DIGESTIVE HOMEOSTATIC DISORDERS
1. Ulcer: open sores in the lining of the stomach.
Used to think ulcers were caused by stress
tried to control with antacids
Now know ulcers caused by bacterial infection of stomach
H. pylori bacteria
now cure with antibiotics

17. 2. Gallstones: small hard stones made of cholesterol that collect in the gallbladder.
3. Constipation: too much water taken out of the feces resulting in difficulty evacuating the feces.

18. 4. Diarrhea: too little water taken out of feces; prolonged diarrhea can cause dehydration of body tissues.
5. Appendicitis: infection and inflammation of the appendix.