The digestive system

The digestive system

“ The digestive system takes in food, breaks it down into nutrient molecules

and absorbs them into the bloodstream, and then rids the body of

the indigestible remains.”-E. Marieb

PARTS

1. Gastrointestinal (GI) tract

2. Accessory organs

Digestive processes(disassembly)

1. Ingestion2. Propulsion

a. swallowingb. peristalsis

3. Mechanical digestion4. Chemical digestion5. Absorption6. Defecation

1. MOUTH (oral cavity) Mechanical digestion -

teeth/tongue Chemical digestion -

salivary glands: Contains enzymes

2. pharynx Skeletal muscle

3. esophagus Propels food using muscles (peristalsis)

4. stomach Mechanically and chemically

digested into chyme Limited absorption Neural control

Stretch receptors activated. Impulse to neurons in stomach wall. Continued gastric gland production and causes peristalsis

Hormonal control: Food triggers release of gastrin

(hormone). Goes in blood. Triggers: gastric gland juices constricts sphincter to prevent acid-

reflux, relaxes lower stomach sphincter.

What food type is chemically digested in the mouth?

What is the function of the esophagus?

5. Small Intestine

Mechanical digestion Chemical digestion

(all) Done with enzymes

from pancreas and bile (formed in liver).

Pancreatic duct and bile duct empty into superior small intestine

Absorption (nutrients)

6. Large Intestine Mechanical digestion:

Peristalsis Mass peristalsis

Chemical digestion: Bacteria

Absorption: Water Some vitamins

ACCESSORY ORGANS

Don’t write:What is bile?

Bile is a yellow, brown, or green, watery solution containing bile salts, bile pigments, cholesterol, phospholipids and a variety of electrolytes. pH of 7.6 – 8.6

Liver Produces bile Bile: part waste

product, part digestive secretion (mechanical digestion of lipids)

Metabolism of carbs, lipids, and proteins

Processing of drugs and hormones

Excretion of bilirubin (from heme of old RBCs)

liver summary…

Blood from stomach and intestines passes through liver. When the liver has broken down harmful substances, they are excreted into the bile or blood. Bile by-products enter the intestine and ultimately leave the body in the feces. Blood by-products are filtered out by the kidneys and leave the body in the form of urine.

gallbladder Stores bile releases in response

to fatty food

PANCREAS

Releases enzymes into

duodenum (s. intestine)

has an endocrine function

Summary questions

1. What mainly happens in the small intestine?

2. Where is bile made?

3. What organ stores bile?

4. In which organ is water mainly absorbed?

5. What is the circular muscle contraction called that involuntarily moves food through the GI tract?

6. Where is chyme produced?