Human Digestion
“Who has the Guts?”
Digestion
There are 2 types of digestion:
Mechanical Digestion – breaks food into
smaller pieces to increase surface area
exposure to digestive enzymes
Chemical Digestion – breaks organic
compounds into their building blocks
Mechanical Digestion
Chewing
Salivary glands release saliva which moistens
the chewed food, now called a Bolus.
The tongue pushes the bolus to the back of the
throat, called the Pharynx.
A flap of skin called the Epiglottis flips down and
covers the entrance to the Trachea during
swallowing
Swallowing
Choking
Peristalsis/Alimentary Canal
The bolus passes through the esophagus by
peristalsis
Peristalsis
Food continues to pass through the Alimentary
Canal (any part that food passes through)
Mouth-Pharynx-Esophagus-Stomach-Small
Intestine-Large Intestine-Anus
Accessory organs play a role in digestion, but
food never enters them
Salivary glands-Pancreas-Gall Bladder-Liver
Anatomy of Digestion
Do you know your guts?
Try the quiz.
Chemical Digestion
Enzymes break down the organic
compounds (polymers) into their building
blocks (monomers) so they can be
absorbed into the blood stream and
transported to all cells
Carbohydrates – Simple sugars
Protein – Amino acids
Lipids – Glycerol and 3 Fatty acids
Nucleic acids - Nucleotides
Digestion of Carbohydrates
Mouth – Mechanical digestion breaks the carbs
into smaller pieces to increase the surface area
exposure to enzymes.
Saliva lubricates the bolus. It contains the enzyme
Amylase which begins the Chemical digestion of
Carbs.
Polysaccharides are broken into shorter chains.
Swallowing pushes the bolus into the esophagus
Carbs in the Stomach
Peristalsis moves the bolus to the stomach.
Cardiac sphincter opens and bolus enters the
stomach
Bolus now mixes with the gastric juices of the
stomach.
This acidic mixture is now called Chyme
Mechanical digestion (churning) continues
No chemical digestion of Carbs here because of
the acidity of the chyme
Protein is digested here
Carbs in the Duodenum
Pyloric sphincter opens and chyme moves
into the duodenum.
Pancreas secretes:


Alkaline secretion that neutralizes the acidic
chyme
Pancreatic amylase and disaccharase
continue the breakdown of carbs into simple
sugars
Absorption of Simple Sugars
Small intestine is about 6 meters long!
The lumen of the small intestine is lined
with Villi.
Absorption of Carbs
Each villi has microvilli on it’s surface
The infolds increase surface area contact so the
simple sugars can pass into the blood by
diffusion.
Small Intestine
Absorption is complete here.
Peristalsis moves the digested food mass
to the Large Intestine (Colon)
Large Intestine
Main function is to absorb water from the
unusable waste that remains.
Too much water absorption – constipation!
Not enough water absorption – diarrhea!
Bacteria in colon produce Vitamin K
Feces passes from descending colon to
rectum and then is excreted through the
anus (anal sphincter)
Accessory organs and their
Functions
Salivary glands – Amylase
Pancreas – Amylase
- Protease
- Lipase
Liver – produces bile which is stored in the
Gall Bladder and secreted into the
duodenum through the Common Bile Duct
- Bile emulsifies fats
Digestion
Human Digestion
Have another look
Digestion Animation
Digestive Problems
Heart burn – acidic gastric juice enters the
esophagus
Gastric ulcer – mucus lining of the
stomach deteriorates and the gastric juice
of the stomach begins to digest the
stomach wall
Pig Dissection