Powerpoint digestive system

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 food molecules

into small, water-soluble molecules using mechanical and chemical processes.

• ABSORPTION: the movement of digestive food moleculesthrough the wall of the intestine into the blood or lymph.

• ASSIMILATION: the movement of digestive food molecules into the cells of the body where they are used, becoming part of the cells.

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

Name the layers of tissue that make up the alimentary canal, starting from the

inside

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

of it.

DIGESTION: -Physical: teeth and churning

movements of the alimentary canal-Chemical: enzymes

Chemical digestion

FOOD ENZYMES FINAL PRODUCTS

Starch amylase glucose

Proteins protease Amino acids

Fats lipase Fatty acids + glycerol

MOUTH -Ingestion -Digestion

Food is chewed and mixed with saliva.

How to reduce the risk of tooth decay-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. It makes 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 (peristaltic

movements) - releases food in small quantities at a time to

the rest of the alimentary canal (pyloric sphincter)

Chemical digestion:

• Production of gastric juice (glands in the lining)

- 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 juices2. Bile3. 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 → glucose - Peptides → aa - Fats → fatty acid and glycerol before they are absorbed. By -Maltase -Peptidase

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 + glycerol capillaries (bloodstream ) ↓ ↓ form fats again

pass to lacteals Hepatic Portal Vein ↓

↓ lymphatic system

LIVER↓

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)

DEAMINATION (in the liver)

aa non nitrogen compound nitrogen compound glucose UREA

respiration excreted by the kidneys

urine

LIVERFunctions

• Regulation of blood sugars.• Production of bile.• Deamination• Storage of iron.• Manufacture of plasma proteins.• Detoxication.• Storage of vitamins