Digestion

I. Nutrition

A. Humans are heterotrophs, ingest nutrients they need. (carbohydrates, proteins, lipids, vitamins, minerals, and water)

B. Large molecules must be digested (carbs, protein, lipids)

C. Small molecules can be absorbed w/o being digested (vitamins, minerals and water)

II. Human Digestive SystemA. One-way digestive tube called

gastrointestinal (GI) tract and accessory organs

B. Food is moved through by rhythmic muscular contractions called peristalsis

II. Human Digestive System

C. Food is broken down physically and chemically as it moves through

D. Accessory organs secrete enzymes and other substances to help digestion

II. Human Digestive System

III. Structures of Dig Sys

A. Oral Cavity 1. contains teeth, tongue and salivary

glands

2. food is ingested into mouth

3. teeth mechanically break down food to inc surface area for enzymes

4. salivary glands secrete saliva that begins to break down starch (carbohydrates)

5. tongue mixes saliva and food together

III. Structures of Dig Sys

B. Esophagus 1. food is swallowed into esophagus and peristalsis

(wave action) moves the food to stomach

2. digestion of starch continues

C. Stomach 1. muscular sac mixes and liquefies food

(mechanical digestion)

2. gastric glands secrete HCl (hydrochloric acid) to make stomach acidic and enzyme, gastric protease (digests proteins)

3. gastric protease NEEDS acid env to work

III. Structures of Dig Sys

D. Small Intestine 1. long wrapped tube where most digestion

takes place

2. intestinal glands secrete enzymes to digest proteins, lipids, and carbs

III. Structures of Dig Sys

3. accessory organs secrete their liquids into SI a. Liver – makes bile which passes to gall

bladder (stored). Gall bladder secretes into SI. Bile acts on fats, breaking them into tiny droplets (emulsification). This inc surface area for digestion. Bile also helps neutralize acidic food mass from stomach.

b. Pancreas – produces and secretes juice into SI, has protease, lipase and amylase to finish chem digestion

III. Structures of Dig Sys

4. End products of digestion are absorbed through the lining of SI (hydrolysis – enzymes and water break apart molecules) a. proteins = amino acids, by proteases

b. lipids (fats) = fatty acids & glycerol, by lipases

c. carbohydrates = glucose

III. Structures of Dig Sys

5. surface area of SI is inc by many folds and fingerlike projections called villi

6. each villi has capillaries and a lacteal (lymphatic vessel) a. glucose and amino acids = capillaries (goes

into blood)

b. fatty acids & glycerol = lacteal (goes into lymph then blood)

III. Structures of Dig Sys

III. Structures of Dig Sys

7. extra glucose in blood is converted by liver into glycogen and stored. When glucose dec in blood, liver breaks down glycogen and returns glucose to blood. This keeps constant levels of sugar in blood (homeostasis)

III. Structures of Dig Sys

E. Large Intestine 1. undigested and indigestible foods and

water move to LI

2. shorter and wider than SI

3. water reabsorbed into capillaries in wall of LI

4. remaining wastes, feces, are pushed to rectum, by peristalsis, where stored until body passes it through anus (egestion)

IV. Nutrient Requirements

A. Carbohydrates – major source of energy, glucose

1. Extra carbs are stored as glycogen or fat

2. Cellulose, carb found in cell walls of plants, CANNOT be digested (roughage) and helps move food mass through intestines

IV. Nutrient Requirements

B. Proteins 1. broken down to amino acids (a.a.), used

to build human proteins

2. 20 different a.a. needed to make human proteins. 12 can be made by body, 8 must be taken in by diet (essential a.a.)

3. get from meat or eating variety of veg @ one time

IV. Nutrient Requirements

C. Fats 1. used for energy storage and building cell

membranes

2. two types a. saturated – all hydrogen atoms can hold (too

much can cause cardiovasular disease)

b. unsaturated – not full of H atoms (healthier)

V. DisordersA. Ulcer

1. open sore in lining of stomach/intestines

2. caused by excess HCl, breaks down lining of digestive tract

3. causes bleeding and pain

V. DisordersB. Constipation

1. difficulty eliminating feces from LI

2. too much water is removed from feces, reduces peristalsis, slows down movement of waste

3. can be caused by not eating enough roughage

V. DisordersC. Diarrhea

1. frequent elimination of watery feces

2. dec water absorption and inc peristaltic activity

3. can cause severe dehydration

V. DisordersD. Appendicitis

1. inflammation of appendix, small pouch at beginning of LI