1. Human Health & Physiology Digestion 6.1

2. Digestion Why do we digest food?
We digest so our cells are provided with the nutrients they need.
Basic Format:
Ingestion – you eat the food
Digestion – a series of chemical reactions that convert the ingested food into smaller and smaller molecular forms
Absorption – small molecular forms are absorbed through cells of your digestive system and pass into nearby blood or lymphatic vessels
Transport – circulatory system delivers small molecular nutrients to body cells

3. Molecular Form Ingested Molecular form after Digestion
Digestion Solves a Problem of Molecular Size
All foods we eat must be chemically digested to suitable size that allows for nutrients to enter the blood stream
Molecule Type
Molecular Form Ingested
Molecular form after Digestion
Protein
Amino Acids
Lipids
Triglycerides
Glycerol & Fatty Acids
Carbohydrates
Mono, Di, Poly Saccharides
Monosaccharides
Nucleic Acids
DNA / RNA
Nucleotides

4. Digestion All foods contain either plant or animal cells
Plants store carbohydrates as Starch
Animals store carbohydrates as Glycogen
Each living organism has its own set of proteins
Each organism protein has a unique sequence of amino acids
DNA and RNA also has a unique sequence
Hydrolyse – to undergo a change;
become different in essence
This is why we digest

5. Enzymes increase the rate of digestion at body temperature.
Enzymes in Digestion
As foods enter the alimentary canal digestive enzymes are added to the food
Remember:
Enzymes are proteins that catalyze reactions
Enzymes lower activation energy
Which reduces the amount of energy needed in a reaction which is usually heat
Enzymes increase the rate of digestion at body temperature.

6. Enzymes in Digestion
We have specific enzymes that break up different types of carbohydrates and proteins
Protease – general name for enzymes that break up proteins
Remember proteins are large so enzymes digest proteins by individual amino acids starting on the ends
Book says 3

7. Know this!!!!
Be able to Diagram this!!

8. The Role of the Stomach
Food is brought to the stomach via the esophagus
Peristalsis – a series of smooth muscle contractions that force
food down to the stomach.
Gastric Juice – a mixture of 3 secretions from cell in the
stomach lining
Pepsin – a protease enzyme most active in acidic pH
Hydrochloric Acid – degrade and breaks down foods and
creates the acidic pH necessary for pepsin to
be active
Mucus – lines the inside of the stomach wall to prevent
stomach damage from hydrochloric acid

9. The Role of the Stomach
The stomach wall of the stomach creates a churning motion to mix the food and the gastric juices
Then a valve opens and food enters the small intestine

10. The Role of the Small Intestine
Duodenum – first part of the small intestine
3 different organs secrete juices into the small intestine
Bile from the liver
Bile from the gall bladder
Trypsin – ( a protease), lipase, amylase, and bicarbonates from
the pancreas

11. The Role of the Small Intestine
Pancreas
A multipurpose organ
Produces insulin and glucagon (glucose metabolism)
Produces three enzymes:
Lipase
Amylase
Protein digesting enzyme known as endopeptidase
These are known as Pancreatic Juice
All these fluids are released in the beginning of the lumen of the small intestine

12. The Role of the Small Intestine
As digestion continues in the small intestine food is continually broken down into molecules
Now they can be absorbed
Villi – the inner wall of the small intestines
Each villus contains a capillary bed and a lacteal
Lacteal – a small vessel of your of your lymphatic system
just like a capillary
Small intestine lining is smooth
Villi increases the surface area to increase absorption rate of molecules

13. The Role of the Small Intestine
The contraction of circular and longitudinal muscle of the small intestine mixes the food with enzymes and moves it along the gut.
Need to know

14. Assimilation Assimilation follows digestion
Nutrients that are absorbed into the blood stream are transported to cells throughout the body to perform various functions.
Villi absorb monomers formed by digestion as well as mineral ions and vitamins
These nutrients are incorporated into the tissues and organs.
Starch, glycogen, lipids, and nucleic acids are digested into monomers, cellulose remain undigested

15. The Role of the Small Intestine
Inner lining of the small intestine make up what is called the mucosa.
The mucosa has many folds or projections called villi (villus singular)
Each villus is composed of may cells whose primary job is selectively absorbing molecules found in the lumen of the small intestine.
Absorption occurs through the cells in an epithelial layer that is in direct contact with the nutrients.

16. The Role of the Small Intestine
Epithelial cells have tiny membrane projections called microvilli that extend into the lumen.
This greatly increases the surface area
The interior of each villus contains a capillary bed for nutrient absorption and transport of digested monomers
Small vessel of the lymphatic system, called the lacteal, absorbs some of the nutrients.
Monomers are absorbed into the inner capillary bed
Larger monomers such as fatty acids are absorbed first into the lacteal

17. The Role of the Small Intestine
Substances Absorbed through the villi:
Water
Glucose
Amino acids
Glycerol
Fatty acids
Mineral ions
Vitamins

18. The Role of the Small Intestine

19. The Role of the Small Intestine
Most of the molecules absorbed are taken into the capillary bed
Fatty acids are absorbed by the lacteal
Undigested nutrients cannot pass through the villus epithelium

20. The Role of the Large Intestine
Most food is absorbed in the small intestine
Enzymes digest most macromolecules in food into monomers in the small intestine
Undigested food plus water is passed into the large intestine
Primary function of the large intestine is water absorption
Water allows food to travel easier through the alimentary canal
This is why it is absorbed last
Mutualistic bacteria Escherichia coli synthesis vitamin K and maintain a healthy environment in the large intestine
Any foods not digested are eliminated

21. The Role of the Large Intestine

22. Transport Mechanisms
Different methods of membrane transport are required to absorb different nutrients
Passive Transport (Mechanisms)
Simple diffusion – Direct movement through the cell following the concentration gradient
High concentrations to low concentrations
Facilitated Diffusion - movement through the cell following the concentration gradient, but the molecule must travel through a protein channel
Happens because of polarity
Glucose and amino acids

23. Transport Mechanisms Active Transport (Mechanism)
When a cell expends energy to move molecules or ions across a membrane
Protein “pumps” a solute across a membrane, usually in the opposite direction to the way it travels in diffusion
Requires chemical energy supplied by the mitochondria
Active Transport play a vital role in maintaining the cells chemical environment.

24. Transport Mechanisms
Endocytosis – takes in material into the cell within
vesicles that bud inward from the plasma membrane.