l12 food and digestion

8/6/2019 L12 Food and Digestion

1/32

FOOD AND NUTRITION


2/32

Food

Food is any edible material that supportsgrowth, repair and maintenance of the body.

Classification of foods:A. According to the source of origin

1. Animal foods2. Plant foodsB. According to the calorigenicity

1. Calorigenic foods2. Non- Calorigenic foods

C. According to the main function1. Energy yielding foods2. Body building foods3. Protective foods


3/32

Food

Foods are substances containing nutrients

They are needed for:

Cell repair Cell growth

Energy

Protection


4/32

Factors in relation to Food

The important factors in relation to Food are:

1. Energy Value

2. Quality and Quantity of Primary Foods

3. Variation in the diet4. Digestibility

5. Cooking

6. Psychological factors

7. Cost


5/32

NutrientsNutrients are specific dietary constituents. They can

be classified into:

Macronutrients

Carbohydrate

ProteinFat

Trace elements

Dietary fibre

Water

Micronutrients

Vitamins

Minerals


6/32

Role of Proteins in the Diet

Replacement of cells

Growth

Large molecules

Smaller molecules called Amino Acids

Source: meats, eggs, beans


7/32

Role of Carbohydrates

Primary energy source

Molecules of C, H, O

Sugars ~ simple carbohydrates

Starches ~ complex carbohydrates Fiber

Sources: Rice, potatoes, sugar etc.


8/32

Role of Fats

Provide energy / stores energy

Absorb vitamins

Make up cell membranes

Sources: oil, cheese, butter and other milkproduct.


9/32

Vitamins

Organic (contain carbon)

Growth

Regulate body functions

Prevent disease

No food has all vitamins

Water soluble

Fat soluble

Sources: Vitamins are organic molecules. Theyare water and fat soluble and found invegetables, fruits, egg, milk etc.


10/32

Minerals

Inorganic (no carbon)

Control chemical reactions

Build cells Conduct nerve impulses

Carry oxygen


11/32


12/32

Water

Nutrients carried in water

Used in chemical reactions


13/32

DIGESTIVE SYSTEM


14/32

Digestion

Digestion is a catabolic process in whichcomplex food molecules are broken down intosimpler molecules. It can be divided into:

Mechanical digestion

Chemical digestion

The structure of the alimentary canal isspecialized to facilitate digestion and absorptionin heterotrophic organisms.


15/32


16/32

Parts of the Digestive System

Mouth

Esophagus

Stomach

Small intestine (consists of duodenum, jejunum andileum)

Large intestine (consists of caecum, ascendingcolon, transverse colon and descending colon)

Rectum Anus


17/32

Accessory Glands involved in Digestion

Liver- Produces bile which helps in the emulsificationof fats

Gall bladder- Temporarily stores the bile producedby the liver

Pancreas- Secretes pancreatic juice containingenzymes involved in digestion


18/32


19/32

The Mouth

Crush foods into smallerpieces.

Saliva of mouth containswater, salt and starch

digesting enzyme- Amylase. Fluids in mouth blend to ease

swallowing.

Fluids dissolves food that

gives Taste. Amylase begins the digestion

of starch.


20/32

20

Esophagus

Passes food from mouth to stomach. Sphincter muscles at each end

prevent backflow.

The wall of the digestive tube iscomposed of 4 basic layers.

1. Mucosa, innermost layer2. Submucosa, a layer of connective

tissue

3. Muscularis externa, composed ofcircular and longitudinal smoothmuscle fibres

4. Serosa, outermost layer made up ofloose connective tissue


21/32

Stomach

Stomach volume varies between 0.5 dl1 liter.

Mucus protects the stomach wall.

Gastric juice (water, enzymes, hydrochloric acid: HCl)secreted by stomach cells.

Food is mixed into a liquid mass: chyme.

Protein digestion is initiated.


22/32

Small intestine

Most digestion occurs here

Enzymes excreted from pancreas digest the energy-yielding nutrients.

Cells of the ileum wall absorb nutrients into blood andlymph.


23/32

Small intestine


24/32

Large intestine (colon or bowel)

Absorbs water and minerals

Forms faeces

Rectum ~ stores faeces

Anus ~ strong round muscles No enzymes are excreted.

Very little nourishment is absorbed.

If colon not emptied every day, too much water is

absorbed, can lead to constipation.


25/32

Large intestine


26/32

CHEMICAL DIGESTION


27/32

Chemical Digestion

Chemical digestion involves the action of hydrolases (hydrolytic enzymes) on the food

constituents. there are three major groups of digestiveenzymes involved:

Carbohydrases hydrolyze thegycosidic bonds incarbohydrates converting them to simple sugars

Proteases hydrolyze the peptidebonds in proteinsconverting them to amino acids

Lipases hydrolyze the esterbonds in triglycerides (fat)converting them into fatty acids and glycerol


28/32

Carbohydrate Digestion

Begins in mouth - salivary amylase breaks down starch Stalled in the stomach Mostly occurs in small intestine aided by the following

enzymes:

a. Pancreatic amylase - breaks starch into maltoseb. Maltase - breaks maltose into 2 glucosesc. Sucrase - breaks sucrose into 1 glucose and 1 fructose

d. Lactase - breaks lactose into 1 glucose + 1 galactose

Last 3 enzymes produced by small intestine. Followingabsorbtion, glucose, fructose, & galactose transported tothe liver where they are converted to glycogen.


29/32

Fat Digestion

Gastric lipase of stomach breaks down some fats.

Most fat digestion occurs in small intestine. bile emulsifies fat, exposing more fat to enzymes.

Bile salts link fat molecules to water molecules;(normally fats are hydrophobic).

Pancreatic lipases continues fat digestion subunits now cross into microvilli

subunits are reassembled into triglycerides, combinedwith cholesterol, and transported to the circulatorysystem.


30/32

Protein Digestion

1. Stomach - pepsinogen converted to pepsin in thepresence of HCL. Pepsin breaks some of the peptidebonds of some proteins.

2. Small intestine - Pancreatic enzymes trypsin &chymotrypsin break proteins into smaller units. Thepancreatic enzyme carboxypeptidase breaks peptidesinto free amino acids. Several enzymes produced by

the small intestine further break peptides into aminoacids.


31/32

Nucleic Acid Digestion

Enzymes called nucleases break down nucleic acids suchas RNA (ribonucleic acid) and DNA (deoxyribonucleicacid) into nucleotide chains.

1. The pancreas produces ribonuclease anddeoxyribonuclease

2. Small intestine produces nucleases that break downnucleotides into smaller subunits.


32/32

Thank you

l12 food and digestion

Documents