Transcript The Digestive System

The Digestive System
Digestive System
• Also known as the gastrointestinal
(GI) tract or alimentary canal
• Long tube open at both ends
– Also has accessory organs
• Nutrients absorbed, waste
eliminated
– Converts food into useable form
Mouth
Salivary Glands
Esophagus
Liver
Stomach
Gallbladder
Pancreas
Small Intestine
Large Intestine
Appendix
Anus
4 Steps to Nutrient Intake
1. Ingestion
2. Digestion
- Prepares food for absorption
- Mechanical and chemical breakdown of food
3. Absorption
- Small intestine
4. Elimination
Two Types of Digestion
1. Mechanical
2. Chemical
Mechanical Digestion
• Physical breakdown
of food
– Mouth (chewing) and
stomach (churning)
• Movement of food
– Peristalsis - wavelike
involuntary muscle
contractions
Chemical Digestion
• In mouth, stomach, small intestine
• Chemicals (e.g., HCl) and enzymes
break down complex molecules
– e.g., Amylase in saliva - enzyme that
breaks down starch (a carbohydrate)
Enzymes
• Break down
substances
• Protein catalysts
• Specific to
substrates
Oral Cavity
(Mouth)
• Mechanical digestion (teeth)
and chemical digestion (saliva
with enzymes)
Bolus
• Bolus of food forms and
passes through pharynx into
esophagus
• Epiglottis prevents food from
entering trachea
Esophagus
• Muscular tube that
connects pharynx to
stomach
• Peristaltic contractions
move food to stomach
• Cardiac sphincter at
junction prevents food in
stomach from going
back into esophagus
Stomach
•
•
•
•
J-shaped muscular organ to churn and squeeze
Acts as a reservoir for food (1.5 L)
Rugae (folds) allow for expansion
Movement of food controlled by two sphincters:
– Cardiac sphincter: Between the stomach & the
esophagus
Cardiac sphincter
– Pyloric sphincter: Between
the stomach & the small
intestine
Stomach
• Digestion turns bolus into
chyme – paste-like partially
digested food
• Secretes HCl (pH of 2)
– Destroys microbes and
breaks down food
• Primarily digests protein
– Pepsin, an enzyme only
active at low pH
Small Intestine
• Major site of digestion
and absorption
• 80% of nutrient
absorption occurs here –
diffusion
• About 6 m long,
SMALLER diameter than
large intestine, 3 sections
• Bile produced by liver breaks down fats
• Enzymes secreted by pancreas break down carbs,
fats and proteins
Structure of Small Intestine
Microvilli
Villus
Villi and microvilli - increase surface area, maximize absorption
Duodenum
• First section of small
intestine
• Receives pancreatic
secretions for further
chemical digestion
• Basic pH
– Bile from gall bladder
and bicarbonate ions
from pancreas
neutralize acidic chyme
from stomach
Jejunum and Ileum
• Make up the other two
sections of the small
intestine.
• Where most nutrient
absorption takes place.
• Peristaltic contractions
continue to propel
chyme through tract.
Large Intestine
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About 1.5 m long and has a LARGER diameter
than the small intestine.
Consists of four sections:
1.
2.
3.
4.
Caecum
Colon
Rectum
Anus.
Large Intestine
• Main function is to
reabsorb water
• Bacteria produce
vitamins which are
absorbed
• Compacts unabsorbed
material into feces
• Defecation:
- Rectal sphincter passes feces into rectum for temporary
storage
- Anal sphincter passes feces from rectum out anus
Animated Digestion Video!
Graphic Digestion Video!