Download Digestive System Functions

Digestive System Functions
Ch 14
Digestive System Major Functions
• Digestion of food
• Absorption of nutrients
6 major activities
1.
Ingestion
–
2.
Food placed in mouth
Propulsion
–
Food is moved from one organ to the next
•
3.
Mechanical digestion
–
4.
Breaking down of large food molecules by enzymes
Absorption
–
6.
Mixing food in mouth and stomach
Chemical digestion
–
5.
Peristalsis- smooth muscle pushes food through digestive tract
Digested product absorbed in blood
Defecation
–
Elimination of indigestible substances in the form of feces
Mouth
• Ingestion
• Mechanical digestion
– Teeth and tongue
• Chemical digestion
– Saliva
• Amylase breaks down starches
• Food propulsion- 1st phase: buccal phase
(voluntary)
– Bolus (food mass) forced into pharynx by tongue
• No absorption occurs
Pharynx and Esophagus
• Passageways to the
stomach
• Food propulsion
– Peristalsis
– 2nd phase
• Pharyngeal-esophageal
phase (involuntary)
– Soft palate closes off nasal
cavity
– Tongue blocks off mouth
Stomach
• Food opens cardioesophageal sphincter and
enters stomach
• Food breakdown
– Hormone gastrin stimulates production of gastric
juices
• HCl, protein digesting enzymes (pepsinogen) and
mucus
– Mechanical digestion
– Produces chyme
Stomach continued…
• Food propulsion
– Peristalsis in lower half of stomach pushes small
amounts of chyme into small intestines
• Little to no absorption
Small Intestines
• Food breakdown and absorption
– Chemical digestion
• Sugars are broken down into simple sugars
• Pancreatic juice breaks down starch, proteins, fats
(lipase) and nucleic acids
• Bile from gall bladder and liver emulsifies fats
• Chyme is neutralized
• Food propulsion- peristalsis
Large Intestines
• Food Breakdown and absorption
– Bacteria metabolize some of the remaining
nutrients make vitamins K and B
• Absorption of only the vitamins and water
• Propulsion of feces
– Peristalsis and mass movements (slow, powerful
contractions) that move feces toward rectum