Lab 8: Digestive System
Announcements

Exams

Lab notes will be on reserve in library and
on the web
Goals of the Digestive System
1.
Extract nutrients from food
2.
Transform nutrients into useful forms
Ex- oreo= glucose
3. Absorb nutrients and distribute them
where they are needed
Functions of the Digestive
System

Ingestion: intake of nutrients

Digestion: breakdown of large particles into
smaller ones

Absorption: uptake of nutrient molecules

Defecation: elimination of undigested residues
Actions of the Digestive
System
1. Motility
-
2.
Secretion
-
3.
Breaks up food
Moves food through the GI tract (Peristalsis)
Mixes with digestive enzymes
Release of enzymes and hormones for chemical
digestion and regulation
Membrane Transport
- Absorption of nutrients from the tissues by the
blood and lymph for transport
Stages of Digestion

Mechanical: physical breakdown of food

Chemical: digestive enzymes hydrolyze food
particles to break larger molecules into smaller
ones

Some nutrients are absorbed with out digestion
– Vitamins, minerals, cholesterol, water
Anatomy of the Digestive
System







Oral Cavity
Pharynx
Esophagus
Stomach
Pyloric Sphincter
Small Intestine
Large Intestine
Accessory Organs

Teeth
 Tongue
 Salivary Glands

Liver
 Gall Bladder
 Pancreas
Oral Cavity

Functions:
– A.
Ingestion: cheeks lips
and tongue mobilize food
– B.


Digestion:
Mechanical
– Mastication
Chemical
– 3 salivary glands
– Digests some
starches and fat
Pharynx
Motility: pharyngeal
constrictors force food
down during
swallowing
Esophagus


Straight muscular tube
about 1 foot long
 Motility: muscular
contraction moves
food towards stomach
www.mywebmd.ca.com
Heartburn and the Esophagus
Heartburn, “ acid reflux”, is caused by acid and food
going from the stomach into the esophagus
The diaphragm normally prevents acid reflux, in
conjunction with the lower esophageal sphincter.
When this fails, the burning sensation felt is known
as “heartburn”
May be linked to a rare type of cancer,
adenocarcinoma
Stomach

Muscular sac on the left
side of the peritoneal
cavity

Functions:
– Food storage
– Mechanical digestion
– Chemical digestion
Rugae in the Stomach

Rugae- folds in the
stomach lining that
allow it to expand with
more food

How do we vomit?

http://arbl.cvmbs.colostate.edu/hbooks/pathphys/digestion
Pyloric Sphincter

Ring of smooth
muscle

Regulates the passage
of material from the
stomach into the
duodenum
http://arbl.cvmbs.colostate.edu/hbooks/pathphys/digestion
Digestion in the Stomach

Mechanical Digestion:
– Muscular contraction

Chemical Digestion:
– Secretes digestive enzymes and HCl
Small Intestine

http://www.afns.ualberta.ca/bbo/1/ANATOMY/SI1.asp

2 meters long, 1 inch
in diameter, 5-6 meters
in cadaver

Functions:
– Chemical Digestion
– Nutrient Absorption
– Motility
Anatomy of the Small Intestine

Duodenum (25 cm):
1. Receives stomach
contents, pancreatic
juice and bile
2. Neutralizes stomach
acid and pepsin
3. Pancreatic enzymes
and bile take over
chemical digestion

Fig 25.22
Anatomy of the Small Intestine

Jejunum (2.5m)

Ileum (3.6 m)
– Reabsorbs bile acids
Functions of the Small
Intestine

Motility: smooth muscle
contract

Digestion: chemical
enzymes received from
the pancreas, liver and gall
bladder

Nutrient reabsorption:
microvilli increase surface
area
Microvilli
Dynamic Human: Microvilli
Large Intestine

Functions
– Motility
– Reabsorbtion of Water and Electrolytes

Symbiotic bacteria
– Synthesis Vitamins B & K
Anatomy of the Large
Intestine
Transverse Colon: right to left
Ascending Colon:
up the right side
Descending Colon:
down the left side
Cecum: sac on
lower right side
Sigmoid Colon:
S-shaped
Anatomy of the Large
Intestine

Rectum: straight down
 Anal Canal: out the
body
 Appendix: hangs off
cecum
– Important in Immunity
Enzymes Involved in
Chemical Digestion

Saliva:
– Amylase: breaks down starch
– Lipase: breaks down fats when it enters the
stomach

Low pH of the stomach activates the enzyme
Enzymes Involved in
Chemical Digestion
• Stomach:
• Digestive chemicals• HCL: activates enzymes, breaks up foods
• Pepsin: digests proteins
• Renin: digests milk
Pepsin Formation
• Interactions between Cells
• Chief Cells make pepsinogen
• Parietal Cells make HCl
• Pepsinogen is cleaved by HCl into Pepsin
Dynamic Human: Pepsin
Formation
Enzymes Involved in
Chemical Digestion
• Small Intestine
• Two sources of
enzymes
• Liver and Gall bladder
• Pancreas
Enzymes Involved in
Chemical Digestion in the
Small Intestine
• Liver secretes bile that is active in the small
intestine
• Bile: aids in fat digestion and absorption
•Activates pancreatic enzymes
•Synthesized from cholesterol
•Bacteria in the small intestine use bilirubin to
make your feces brown
• Gall bladder stores and concentrates bile
Gall Stones

What is a gall stone?

How do they treat gall stones?

How is the gall bladder removed?
Enzymes Involved in
Chemical Digestion in the
Small Intestine

Pancreas: secretes pancreatic juice
1. Amylase: breaks down starch
2. Lipase: breaks down fats
3. Ribonuclease (RNAase): breaks down RNA
4. Deoxyribonuclease (DNAase): breaks down
DNA
5. Zymogens: inactive enzymes that activate in the
small intestine
Mechanism of Absorption

Membrane Transport:
– Nutrients pass through membrane surface
– The greater the membrane surface area, the
greater the amount of nutrients that can be
transported

Surface Area
– Rugae
– Microvilli
Final Destinations of Digestion
Products

Starches  bloodstream

Fats  lymph vessels (lacteals)

Proteins  bloodstream
Dynamic Human:
Visualization
Cat Dissection

Be able to locate and
identify

Also know accessory
organs
– Esophagus
– Tongue
– Stomach
– Teeth
– Small Intestine
– Gall Bladder
– Large Intestine
– Liver



Ascending colon
Transverse colon
Descending colon
Conclusion

Review today’s material
– Dynamic Human Overview

Know cat anatomy

Lab Practical II returned – well done!

Next week – Endocrine!!!