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
Consists of 2 “parts”
1. Alimentary canal
(gastrointestinal - GItract) – path that food
travels
2. Accessory organs
Digestive processes
(disassembly)
1.
2.
Ingestion
Propulsion
a. Swallowing
b. peristalsis
3.
4.
5.
6.
Mechanical digestion
Chemical digestion
Absorption
Defecation
MOUTH (oral cavity)

Palate:


hard
Soft


uvula
Tongue
Salivary glands
1.
2.
3.
4.
Cleanses mouth
Important for taste
Moistens food
Contains enzymes
Major salivary glands
Parotid gland
 Submandibular
gland
 Sublingual
gland

The average person
produces 1000-1500
ml a day
Teeth

Masticate = to chew

Baby teeth (deciduous)


Full set = 20 teeth
Permanent teeth = 32 teeth



Incisors
Canines
Premolars/molars
pharynx

Longitudinal & circular layers of muscle 
peristalsis
esophagus

Propels food using muscles (peristalsis)
stomach





Mostly protein digestion
No absorption**
Mechanically and
chemically digested into
chyme
Gastric glands produce
gastric juice: acidic
Walls of stomach lined
with mucus so the acid
doesn’t “digest itself”
Problems of the stomach

Ulcers: a hole
in the mucus
lining of the
stomach

Heartburn
(acid reflux):
contents of
stomach move
into
esophagus
Small Intestine
Small intestine
 Chemical
digestion of
carbohydrates, proteins, nucleic
acids, and fats

Done with enzymes from pancreas
and bile (formed in liver).
 Pancreatic
duct and bile duct empty
into duodenum
Absorption by small intestine
Increased surface area: villi, microvilli



Almost all food absorption
All structures increase surface area;
decrease in # toward the end.
What’s left at end: some water, indigestible
food material and large amounts of bacteria
DON’T WRITE:

Appendix C (A-5,6) – vitamins and minerals
(DON’T WRITE) 5 basic food groups
and their major nutrients





FRUITS: carbohydrate, water (vitamins A, C, folic
acid, iron, potassium, fiber)
VEGETABLES: carbohydrate, water (Vitamins A,
C, E, K, B calcium, magnesium, iodine,
manganese, phosphorus)
GRAINS: carbohydrate, protein, thiamin, niacin
(water, fiber, iron, magnesium, selenium)
MILK PRODUCTS: protein, fat, riboflavin, B12,
calcium, phosphorus, water
MEATS/MEAT ALTERNATIVES (eggs, seeds,
nuts, soybeans, legumes): protein, niacin, B6,
iron, zinc (carbohydrate, fat, B12, B1, water, fiber)
Large Intestine

Function of large
intestine:




to absorb water
eliminate residue as
feces
Absorb vitamins
produced by bacteria
Role of bacteria:



Digest some nutrients
Produce vitamins
Produce gas

Action of L. intestine:



Peristalsis
Mass peristalsis: a
strong wave that
pushes contents
towards rectum
Problems: diarrhea
and constipation
PANCREAS

Releases enzymes into
duodenum

has an endocrine function
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; leaves
through common
hepatic duct
Bile: part waste
product, part
digestive secretion
(mechanical digestion
of lipids)
Other liver functions



Metabolism of carbs, lipids, and proteins
Processing of drugs and hormones
Excretion of bilirubin (from heme of old
RBCs)
Gallbladder



Releases bile in response to fatty food
entering duodenum
Location: underside of liver
gallstones
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.