1. Human Digestion
This part of the life process of NUTRITION-> process by which an organism obtains and utilizes food

2. Digestive System

3. Food processing occurs in four stages
Ingestion: taking in food
Digestion: mechanical and chemical breakdown of food so that it can be absorbed by the cells
Absorption: cells lining the digestive tract take up (absorb) small nutrient molecules
Elimination: undigested material passes out of the digestive tract

4. Two Types of Digestion
1. Mechanical digestion – physical breakdown of large pieces of food into smaller ones
2. Chemical digestion – hydrolysis – the splitting of large insoluble molecules in small, soluble molecules with the use of water and enzymes ( in other words; breaking complex molecules into simple ones). Chemical digestion is regulated by enzymes.

5. Examples of chemical Digestion:
1. Carbohydrates+ water -> simple sugars (glucose for instance)
2. Proteins+ water -> amino acids
3. Lipids+ water -> 3 fatty acids +gylcerol

6. HUMAN DIGESTIVE SYSTEM
Human digestive tract = GI (gastrointestinal) Consists of a continuous one way food tube (mouth to anus).

7. 1. Mouth Functions mechanical digestion chemical digestion (saliva)
teeth
break up food
chemical digestion (saliva)
amylase enzyme
digests starch
mucus
protects soft lining of digestive system
lubricates food for easier swallowing
buffers
neutralizes acid to prevent tooth decay
anti-bacterial chemicals
kill bacteria that enter mouth with food
All that in spit!

8. HUMAN DIGESTIVE SYSTEM
2. Esophagus: muscular tube that moves food from mouth to the stomach by process of peristalsis: wave of muscular contractions that moves chewed food to stomach

9. Swallowing (& not choking)
Epiglottis
flap of cartilage
closes trachea (windpipe) when swallowing
food travels down esophagus
Peristalsis
involuntary muscle contractions to move food along

10. Ulcers

11. 3. Stomach Functions disinfect food food storage digests protein
hydrochloric acid = pH 2
kills bacteria
food storage
can stretch to fit ~2L food
digests protein
pepsin enzyme
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.
But the stomach is made out of protein!
What stops the stomach from digesting itself?
mucus secreted by stomach cells protects stomach lining

12.   Ulcers Used to think ulcers were caused by stress
Free of H. pylori
Colonized by H. pylori
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
inflammation of stomach
inflammation of esophagus
H. pylori
cell damaging proteins
(VacA)
inflammatory proteins
(CagA)  
cytokines
helper T cells
neutrophil cells
white blood cells

13. Small intestine Functions digestion absorption digest carbohydrates
amylase from pancreas
digest proteins
trypsin & chymotrypsin from pancreas
digest lipids (fats)
bile from liver & lipase from pancreas
absorption
nutrients move into body cells by:
diffusion
active transport
This is where all the work is done!
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.

14. 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

15. Pancreas ~ accessory organ
Produces digestive enzymes
digest proteins
trypsin, chymotrypsin
digest starch
amylase
digest lipids
lipase
Buffers
neutralizes acid from stomach
small intestine
pancreas

16. Liver & Gall Bladder ~accessory organs
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

17. 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
reabsorb by diffusion

18. You’ve got company!
Living in the large intestine is a community of helpful bacteria
Escherichia coli: E. coli
digest cellulose
digests fruits & vegetables
produce vitamins
vitamin K & B vitamins
BUT generate gases
by-product of bacterial metabolism
methane, hydrogen sulfide
STINKY!
PEE-YOO!

19. Rectum Last section of large intestines eliminate feces through anus
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!

20. Appendix
Vestigial organ

21. Some Digestive Homeostasis Disorders
1.Constipation– person has uncomfortable or infrequent bowel movements results from sluggish peristalsis that allows excess water to be removed from feces (fecal matter hardens)- may result from insufficient fiber in diet
2. Diarrhea– opposite of constipation– associated with intestinal disturbances caused by infections or stress– prolonged diarrhea may result in severe dehydration
3. Gall stones– small hard particles made of cholesterol which form & collect in gall bladder- may block the bile duct and cause pain
4. acid reflux -backflow of stomach contents upward into esophagus
5. appendicitis- inflammation of appendix