1. Human Digestion

2. Nutrition Process by which organisms obtain and utilize their food.
There are two parts to Nutrition:
1. Ingestion- process of taking food into the digestive system so that it may be hydrolized or digested.
2. Digestion- the breakdown of food (either chemically or mechanically) in order to utilize nutrients

3. Types of Nutrients Micronutrients vitamins, minerals
Macronutrients proteins, lipids, carbohydrates
Not nutrients, but essential for health:
Water & fibre to prevent constipations

4. GI (gastrointestinal) tract = alimentary canal

5. Ingestion Mouth mechanical digestion chemical digestion teeth saliva
breaking up food
Chewing
grinding
chemical digestion
saliva
Amylase enzyme digests starch
Lubricates food for easier swallowing

6. Mouth Chemical and mechanical digestion.
Food is chewed (masticated) mechanically.
A bolus (lump) is formed with saliva and the tongue.

7. Peristalsis
series of wave-like muscle contractions move food along the digestive tract

8. Stomach Food is temporarily stored here. Gastric juices are secreted.
Has layers of muscle that line the inside.
Mechanically and chemically breaks down food.

9. Stomach Functions disinfect food chemical digestion
Hydrochloric acid = pH 2
kills bacteria
chemical digestion
Hydrochloric acid also starts the digestion of protein
pepsin
enzyme breaks down proteins
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.

10. Accessory Organs
Pancreas
Gall Bladder
Spleen

11. Gall bladder
Pouch located near the liver which concentrates and stores bile
Bile duct – a long tube that carries BILE.

12. BILE Bile emulsifies lipids (physically breaks apart into droplets)
This increases the surface area for the enzyme lipase to break down the lipids
It also neutralizes the contents of the stomach when they are emptied into the duodenum

13. Pancreas
An organ which secretes both digestive enzymes (exocrine) and hormones (endocrine).
Pancreatic juice digests all major nutrient types.
Digestion occurs in the small intestine.

14. Pancreas Digestive enzymes digest proteins digest starch digest lipids
trypsin, chymotrypsin
digest starch
Amylase
digest lipids
Lipase

15. Liver Function produces bile bile stored in gallbladder until needed
breaks up fats
act like detergents to breakup fats
bile contains colors from old red blood cells collected in liver =
iron in RBC rusts & makes feces brown

16. Small Intestine Most chemical digestion takes place here.
Simple sugars and amino acids are absorbed into the blood
Fatty acids and glycerol go to lymphatic system.
Lined with villi, which increase surface area for absorption, one cell thick.

17. Absorption by Small Intestines
Absorption through villi & microvilli
finger-like projections
increase surface area for absorption

18. VILLI

19. Large intestines (colon)
Function
re-absorb water
use ~9 liters of water every day in digestive juices
> 90% of water reabsorbed
not enough water absorbed
diarrhea
too much water absorbed
constipation

20. Rectum Last section of colon (large intestines) store faeces
undigested materials
extracellular waste
mainly cellulose from plants
roughage or fiber
masses of bacteria