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•Mechanical Digestion (mouth, stomach)
•Chemical Digestion (mouth, stomach, intestines)
•Absorption (intestines)
•Assimilation (at each cell in the body)
Sphincters divide the alimentary canal
Into separate compartments.
Cardiac sphincter
Pyloric sphincter
Ileocecal sphincter
Anal sphinters
1. Saliva:
Mucous - lubricates food, easier to swallow.
Amylase – initiates hydrolysis of starch
Lysozyme – bacteriostatic enzyme
2. Mastication:
3. Epiglottis: cartilage flap that covers the top of the larynx
Muscular tube that propels food to stomach using peristalsis
B – Esophagus
D – Cardiac Sphincter
(esophageal reflux)
F – Stomach
Muscular, mechanical digestion,
also produces bacteriostatic acid,
and digestive enzymes
H – Pyloric Sphincter
(controls flow of food into duodenum)
Internal Structure of Stomach
Chief Cells Secrete
Digestive Enzymes
Parietal Cells Secrete
Hydrochloric Acid
Pepsinogen – Most Important of
the Stomach Enzymes
When first secreted, pepsinogen is inactive.
When pepsinogen is exposed to HCl, it reacts and converts to Pepsin.
Pepsin is the active form of the enzyme. It is a protease.
Intrinsic Factor
Produced by parietal cells. Essential for absorption of vitamin B12 in the
Control of Gastric Secretions
1. Smell, sight or taste of
food stimulates the
vagus nerve to stimulate
the stomach.
2. Increased motility and
increased gastric
3. Increased release of a
hormone called gastrin.
4. Gastrin stimulates the
stomach to produce
even more secretions.
Peptic Ulcer: a sore in the mucosal lining of the stomach.
90% caused by a bacterial infection.
Liver, Gall Bladder and Exocrine Pancreas
Liver produces bile. The bile is stored in the gall bladder, and is delivered to the
duodenum by the bile duct.
Exocrine portion of the pancreas produces digestive enzymes that are carried
to the duodenum by the pancreatic duct.
Pancreatic Enzymes
• Amylase: hydrolyzes starch to maltose
• Protease: hydrolyzes proteins to peptides and
amino acids
• Lipase: hydrolyzes triglycerides (fats and oils)
to fatty acids and glycerol
• Nucleotidases: hydrolyzes DNA and RNA to
form nucleotides
Digestion at Duodenum
Role of gastric motility
Role of Bile
Role of pancreatic enzymes
Chemical changes in duodenum
(decreased pH)
Control of Pancreas and Gall
For Absorption to
occur, chemically
digested nutrients must
move through the wall
of the intestine and enter
the blood circulation
or the lymph (lacteal).
The inner wall of the
intestinal lumen is folded
to form villi. Each villus
has blood capillaries and
lymph vessels.
Mesentery has blood and
lymph supply
Lymph vessel (lacteal)
Blood capillaries
Serosa (serous membrane)
- outermost layer
(blood vessels, lymph
and nerves)
(mucous membrane)
Cells with microvilli
and goblet cells
(smooth muscle layer)
Absorption of Lipids
1. In the duodenum, lipids mix with
Bile, become emulsified and
forms “micelles.”
2. Micelles are taken up
by endocytosis and
moved through the
mucosal cell.
3. While in the mucosal
cell proteins are added
to the micelle to make
them more soluble.
4. The new mixture of bile,
lipids and protein is called a
5. The chylomicron enters
the lymph and is carried away.
8. Chlymycra are
carried in the blood
to the liver where the
liver converts them
into HDL’s and LDL’s
that are returned to
the blood.
7. Lymph vessels empty into
the blood circulation at the
subclavian vein.
6. Chylomicra pass through
lymph nodes and are
carried up the torso to the
lymph duct.
HDL’s and LDL’s
• Lipoproteins
- formed by the liver from chylomicra
- contain both lipids and proteins
• High Density Lipoproteins - “Good Cholesterol”
- contain more protein
- more soluble in water
- tend to remove fatty deposits from blood vessels.
• Low Density Lipoproteins – “Bad Cholesterol”
- contain less protein, more lipid
- tend to add fatty deposits to walls of blood vessels
Sugar, Nucleotide and Amino Acid Absorption
Active transport
processes move
these nutrients
through the mucosal
cells and into the
Sugars, amino acids and
nucleotides move into the
mesentery and are carried
to the liver via the hepatic
portal vessel.
Liver may store nutrients.
Liver may remove toxins.
The Amazing Liver
Stores and Releases Glucose
Produces bile
Stores Lipids and Converts Chylomicra
to HDL’s and LDL’s
Removes toxins from blood
Produces blood proteins
The Large Intestine
The ileum is the last segment of the small intestine. It joins the large intestine at
the ileocecal sphincter (valve). Below the junction is a small pouch called the
cecum, and hanging from that is the appendix. The appendix is believed to be a
vestigial organ because some animals have a very large, functional cecum.
Digestive Tract of the Pig
In the pig the cecum houses micro-organisms that are essential
for the digestion of cellulose (plant fibers). Humans can not digest plant
Large Intestine Function
• Each day a typical person swallows about two
liters of liquid.
• The salivary glands, stomach, pancreas, gall
bladder, and intestines add another 6-7 liters
of liquid per day.
• The large intestines reabsorb that liquid, form
a more compact feces, and reabsorb salt.
• In diarrhea, bacteria have infected the large
intestine and it is no longer able to reabsorb
fluids - risk of dehydration.
• Rectum: stores feces
• Anal Sphincters: control defecation