Download Functions of the Digestive System

Functions of the
Digestive System
Ingestion
Active, voluntary
process
Food is placed into
the mouth
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Propulsion
Food is moved from one organ to
another
Peristalsis – alternating waves of
contraction and relaxation of the organ
walls (GI tract)
Segmentation – food is moved back and
forth across the internal wall of the
organ.
a) Peristalsis
b) Segmentation
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Food Breakdown:
Mechanical Digestion
Prepares food for further degradation
–Mixing food in the mouth by tongue
–Churning food in stomach
–Segmentation in small intestine
Food Breakdown:
Chemical Digestion
Sequence of steps where large food
molecules are broken down to their
building blocks by enzymes
– Proteins to amino acids
– Lipids to fatty acids and glycerol
– Carbohydrates to galactose, glucose, and
fructose
Absorption
Transport of digested end products to the
blood or lymph
Occurs mainly in the small intestine
Defecation
Elimination of undigested substances from
the body via the anus in the form of feces.
Mouth
Ingestion
Mechanical digestion – teeth breaks down
food into smaller pieces
Chemical digestion – food is mixed with
salivary amylase to begin breaking down
starches into maltose
Pharynx & Esophagus
No digestion occurs
Deglutition (swallowing)
– Buccal phase – voluntary; mouth to pharynx
– Pharyngeal-esophageal phase – involuntary;
pharynx to esophagus; peristalsis
Stomach – chemical digestion
Gastric juices is produced
– Protein digesting enzymes (pepsin)
– Hydrochloric acid (very low pH)
– mucus
No absorption except for aspirin and
alcohol
Stomach - Propulsion
Rippling peristalsis occurs in lower half of
stomach
As the stomach contracts, chyme (partially
digested food) is squirted through the
pyloric sphincter in small amounts into the
duodenum.
Small Intestine – Chemical Digestion
Proteins and starches are partially
digested
Fats begins to be digested
Brush border enzymes
Pancreatic juices – contains many
enzymes
Pancreatic Juices
Complete the digestion of starches
Carry out half protein digestion
Responsible for fat digestion
Digest nucleic acids
Contains bicarbonate which neutralizes
the acid chyme
Small Intestine - Absorption
Most substances are absorbed through
intestinal cell plasma membrane via active
transport.
Lipids are absorbed via diffusion
Water is also absorbed
Small Intestine - Propulsion
Peristalsis – waves of contraction moves
substances through the intestine
Segmentation – mixes chyme with
digestive juices and propels food
Large Intestines – chemical digestion
No digestive enzymes
Bacterial metabolizes remaining nutrients
releasing methane gas
Bacteria makes vitamine K and B
Large Intestine - Absorption
Some ions
Vitamin K and B
More water
Large Intestine - Propulsion
Peristalsis
Mass movements – long, slow-moving but
powerful contractile waves
Defecation reflex – initiated when the
rectum’s wall is stretched