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.
2.
Ingestion
Propulsion
a. swallowing
b. peristalsis
3.
4.
5.
6.
Mechanical digestion
Chemical digestion
Absorption
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 acidreflux,
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:



Chemical digestion:


Peristalsis
Mass peristalsis
Bacteria
Absorption:


Water
Some vitamins
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.
2.
3.
4.
5.
6.
What mainly happens in the small intestine?
Where is bile made?
What organ stores bile?
In which organ is water mainly absorbed?
What is the circular muscle contraction
called that involuntarily moves food through
the GI tract?
Where is chyme produced?