HUMAN NUTRITION

DIGESTIVE SYSTEM

THE ALIMENTARY CANAL• INGESTION: taking substances (e.g. food, drink) into the body

through the mouth.

• DIGESTION: the break-down of large, insoluble foodmolecules into small, water-soluble molecules usingmechanical and chemical processes.

• ABSORPTION: the movement of digestive foodmoleculesthrough the wall of the intestine into the blood orlymph.

• ASSIMILATION: the movement of digestive food moleculesinto the cells of the body where they are used, becoming partof the cells.

• EGESTION: the ´passing out of food that has not been digeste, as faeces, through the anus.

Name the layers of tissue that makeup the alimentary canal, starting

from the inside

PERISTALSISA contraction in one region of the alimentary canal is followed by another contractionjust below it so that a wave of contraction passes along the canal pushing food in front

of it.

DIGESTION:

Physical: teethChemical: enzymes

Chemical digestion

FOOD ENZYMES PRODUCTS

Starch amylase glucose

Proteins protease Amino acids

Fats lipase Fatty acids + glycerol

MOUTH-Ingestion-Digestion

Food is chewed and mixed withsaliva.

How to reduce the risk of toothdecay

-Eating food with a low sugar content.

- Regular and effective brushing of teeth at least twice a day to prevent the build up of

plaque.

- Use a fluoride toothpaste regularly. Itmakes your teeth more resistant to decay

Chemical digestion (mouth)

• Saliva: contains salivary amylase

starch → maltose

SWALLOWING

• Ensures that food does not enter the windpipe(trachea) and cause choking.

• Beginning: voluntary

• Then: involuntary

STOMACH

STOMACH

• Functions:

- stores food from a meal.

- turns food into a liquid (peristalticmovements)

- releases food in small quantities at a time tothe rest of the alimentary canal (pyloricsphincter)

Chemical digestion:

• Production of gastric juice (glands in thelining)

- Enzyme: pepsin (protease)

Proteins → peptides

- Hydrochloric acid: provides the best degree of

acidity for pepsin to work in and kills many bacteria

of food.

THE SMALL INTESTINE

Duodenum Ileum

• Chemical digestion

Enzymes from:

1. Pancreatic juices

2. Bile

3. Intestinal juices

Liver, gall bladder, duodenum and pancreas

PANCREAS• Secretion of pancreatic juice:delivered to the

duodenum by the pancreatic duct.

i) Enzymes:-Proteases:

Proteins → peptides → aa- Pancreatic amylase:

Starch → maltose- Lipase:

Fats → fatty acids + glycerol

ii) Sodium hydrogencarbonate: neutralizes the acid liquid from

the stomach so that pancreatic enzymes work correctly. (alkaline conditions)

BILE

• Produced by the liver.

• Stored in the gall bladder.

• Delivered to the duodenum by the bile duct.

• No enzymes

• Bile pigment:from the break down of haemoglobin in the

liver.

• Bile salts: Emulsify the fats: they break them up into

small drops which are more easily digested by lipase.

INTESTINAL JUICES

• The epithelial cells of the villi produce enzymes which complete the breakdown of:

- Maltose

- Peptides

before they are absorbed.

Maltose → glucose

Peptides → aa

FINAL PRODUCTS OF DIGESTION

FOOD FINAL PRODUCTS

Starch Glucose

Proteins Amino acids

Fats Fatty acids + glycerol

ABSORPTION: ILEUM

VILLI: Hystology

Structure of a villus

Molecules

Epithelial cells → a large proportion of

↓ fatty acid + glycerolcapillaries (bloodstream ) ↓

↓ form fats againveins veins ↓

↓ pass to lactealsHepatic Portal Vein

↓ ↓ lymphatic systemLIVER

↓General circulation (vena cava)

LARGE INTESTINEColon and rectum

• Material that reaches it contains:

i) water with undigested matter

ii) cellulose

iii) fibre: digested partly by bacteria

iv) mucus

v) dead cells from the lining of the alimentary canal

• Function: absorption of water.

semisolid waste → faeces → rectum → anus (EGESTION)

ASSIMILATION

• Glucose

Respiration energy

• Fats

-Are built into cell membranes and other cell structures

- Source of energy

• Amino acids- Built up into proteins. Functions??

STORAGE OF DIGESTED FOOD

• Glucose

- Changed in the liver to glycogen

- Some of the glycogen is stored in liver(short- term store) and muscles.

- LIVER: If ↓ blood sugars Glycogen → glucose → circulation

- MUSCLES: glucose: for muscular activity

- Excess of glucose: converted to fat and stored in fats depots

STORAGE OF DIGESTED FOOD

• Fats

- There is no limit to storage of fats

- Long- term store as fat depots in:

-abdomen

- round the kidneys (adipose tissue)

- under the skin

STORAGE OF DIGESTED FOOD

• Amino acids

- They are not stored in the body

- Those not used in protein formation are deaminated (in the liver)

LIVERFunctions

• Regulation of blood sugars.

• Production of bile.

• Deamination

• Storage of iron.

• Manufacture of plasma proteins.

• Detoxication.

• Storage of vitamins