Download Digestion - biologyquest

Digestion:
Alimentary canal (digestive tract)
– food is passed through it
organs - mouth, pharynx, esophagus,
stomach, small intestine, large intestine,
rectum, and anus
Accessory glands
– lie outside the digestive tract
- food is never found in it
organs - salivary glands, liver, pancreas,
gallbladder
Ingestion – taking in of food
Digestion – breaking down food
Digestive System:
1. Mouth –
a. mechanical digestion
- food being chewed (physical change)
- mixing with mucus and forming a food mass called bolus
b. chemical digestion
- food mixing with salivary amylase found in
saliva (chemical change)
- breaks down starch
2. Pharynx
- back of the throat
3. Esophagus
- tube leading to the stomach
 epiglottis- flap of tissue that prevents
food and liquids from entering the larynx
(voice box)
 peristalsis – wavelike movements that
moves food down the esophagus
 sphincter – the ring of muscle (valve)
that controls the passage of food from
the esophagus to the stomach (called
the cardiac sphincter)
 ”heartburn” – when the sphincter muscle
relaxes and HCL from the stomach backs up into the esophagus
4. Stomach
- thick-walled, muscular, j-shaped sac
- can hold more than two liters of food or
liquid
- made up of mucus, pepsin, and HCL
- liquid passes through in 20 minutes or less
-solids pass as a thin, soupy liquid called
chyme through the pyloric sphincter –
takes 2 to 6 hours
- ulcer- when part of your stomach being
digested
a. Mechanical digestion
-food broken down by contractions of
the muscular stomach walls
b. Chemical digestion
- small pieces of food are mixed with
stomach juice (gastric juice) which
makes the food soft
- pepsin begins the digestion of proteins
(can only work in acidic environment)
- hydrochloric acid (HCL) kills bacteria
in the stomach and helps breaks
down food
- mucus protects the stomach lining
5. Small intestine
- coiled tube about 6.5 meters long and 2.5
centimeters in diameter
- food moves through by peristalsis
-most chemical digestion occurs here
- absorption– the movement of food from
the digestive system to the blood
through the villi - fingerlike projections
(p. 164 structure)
*digestion is completed in the
small intestine*
6. Accessory Organs
a) Liver
- largest organ in the body
- produces bile which aids in the
digestion of fats and oils by breaking
them up into tiny droplets
(emulsification)
- bile is stored in the gallbladder
(found under the liver) and goes into the
small intestine through a small tube
b) Pancreas
- small organ that lies below the stomach
- pancreatic juice neutralizes the acid in
the stomach
 enzymes
- amylase breaks down starch
- proteases break down protein
- lipase breaks down fats
c) Appendix
- found in the lower right side of the abdomen
- plays no part in the digestive system
- may become inflamed or infected
(appendicitis)
7. Large Intestine
- 1.5 meters long and 6 centimeters in
diameter
-no digestion occurs here
Three functions:
a. reabsorption of water from the food mass
through the capillaries
 normal condition-3/4 reabsorbed
 helps the body conserve water
 too little - diarrhea
 too much - constipation
b. absorption of vitamins
 vitamins K and B are produced by
bacteria that normally live in the large
intestine
 vitamins are absorbed with the water
from the food mass
c. elimination (egestion)
 removal of undigested and indigestible
material
 consists of cellulose, bacteria, bile,
mucus
 as it travels through the intestine, it
becomes feces or stool
8. Rectum
- fecal matter is stored here
9. Anus
- fecal matter eliminated
Summary of Digestion
Nutrient
Digestion Begins
Proteins
Digestion Completed
small intestine
stomach
small intestine
Carbohydrates
Fats
mouth
small intestine
small intestine