7247485 Chapter 6 Digestion

Chapter 7

Chapter 7

Digestion & Nutrition

Digestion & Nutrition

You will learn...• the concept of a balanced diet• the factors that affect energy intake• the problems of world food supply• the effects of malnutrition• the digestive system• the structure and function of a villus• the function of the hepatic portal vein• fats function as storage substances• the role of the liver

Contents

Diet

fats-sweets group

protein-rich group

dairy products group

fruits group

vegetables group

grain products group

Diet

Food Food GroupGroup Foods in the GroupFoods in the Group NutrientsNutrients

Grain Grain productsproducts

Products made with whole grains or enriched flour.

Mostly carbohydrates and fibres, Vitamin B, iron and protein.

Fruits and Fruits and vegetablesvegetables

Dark green vegetables (broccoli, spinach) and deep yellow vegetables (carrots).

Most carbohydrates and fibre. Various vitamins and minerals

Protein-rich Protein-rich foodfood

Poultry, eggs, fish, red meat, organ meat such as

kidneys and liver. Legumes, nuts and seeds.

Rich in proteins, Vitamin B and minerals such as magnesium and zinc.

Dairy Dairy productsproducts

Milk and milk products such as yoghurt and cheese.

Protein, Vitamins A, B and B2. Main source of calcium.

Fats-sweets Fats-sweets foodfood

Candy, pastries, salad dressing, coffee and

cooking oil.

Supplies fats and sugar. Low in nutrient value.

• A balanced diet is a diet which supplies all the essential nutrients in the correct proportions.

• A balanced diet must contain enough: Protein to provide all the essential amino acids for growth and

repair for the body Energy-food to meet the energy requirements of the individual Minerals and vitamins to maintain good health Roughage or dietary fibre to stimulate peristalsis Water to aid the chemical reactions in the body

DietBalanced Diet

• Basal metabolic rate and physical activity determine energy needs.

• Basal metabolic rate varies with sex, age and state of health of a person.

Diet

Malnutrition

In the underdeveloped nations, malnutrition takes many forms:

• Starvation – Insufficient quantity of food to supply the daily energy needs of an individual.

• Eating disorders – Genetic or environmental in origin, prevent the digestion of food or the absorption of digested food.

• Overweight – due to excessive feeding. The excess food is stored as fats.

• Obesity – the state in which a person weighs at least 20% more than his ideal weight.

• Over-consumption of cholesterol and saturated fats.

• Constipation due to a lack of dietary fibre in the diet.

Problems of World Food Supplies

Marasmus

• Marasmus is the wasting of the body from general starvation.

• It develops when both energy food and protein are insufficient.

• Most victims are children less than 1 year old who have been weaned too early or have been given a poor substitute for mother’s milk.


Kwashiorkor

• Kwashiorkor causes over half of infant deaths in underdeveloped countries.

• Children who survive has retarded brain development and their bodies are dwarfed.

• Protein deficiency during infancy is irreversible.


• Increases the level of cholesterol in the blood.

• Cholesterol deposited on arterial walls harden and eventually lead to heart disease.

Problems of World Food SuppliesOvereating Saturated Fats

• Formation of blood clots.

• This can strain the cardio-vascular system leading to heart attack and high blood pressure.

Problems of World Food SuppliesOvereating Saturated Fats

• Bowel movements are difficult and do not occur often enough.

• It is caused by a lack of exercise, emotional distress or misuse of laxatives, and/or a diet low in dietary fibres.

• Due to constipation, abdominal pressure causes blood vessels in the rectum to enlarge, producing haemorrhoids.

Problems of World Food SuppliesConstipation

• Anorexia nervosa is characterised by constant dieting, rapid weight loss and feeling too fat in spite of the weight loss.

• Bulimia is characterised by eating too much food through vomiting or the use of laxatives; tend to gain weight easily and live in constant fear of becoming obese. Bulimics often have mouth and throat problems due to repeating vomiting.

Both anorexics and bulimics have a constant fear of being fat and fear rejection

Problems of World Food SuppliesEating Disorders

The Population Explosion

• The world population today is 6 billion and is on the rise.

• Poverty, starvation and depletion of natural resources is on the increase

Famine

• Industrialised nations have agricultural surplus due to their advances in technology and their high yielding crops.

• This results in unequal distribution of food.

Floods

• Heavy rainfalls during monsoon season, tidal waves and collapsed dams, all cause widespread destruction of the agricultural land and the crops themselves.

Drought

• Droughts bring about extreme crop damage and the destruction of farm animals.

Causes of World Food Supply ShortageProblems of World Food Supplies

• Green revolution – enhanced food yields can be obtained using new strains of wheat, maize and rice.

• Culture fish, lobsters, prawns and crabs by farming the sea. Seaweed and algae could be grown and harvested as well.

• Genetically modified food – Plants and animals have their genes altered to improve quality. It is the potential solution to a growing world population and dwindling food supplies.

• Improve the distribution of food from countries with surplus to overpopulated third world countries. Surplus wheat from USA has been distributed to famine stricken nations.

Solutions to World Food Supply ShortageProblems of World Food Supplies

• Developing farming technology has helped farmers increase output.

• Enriched food, such as bread have nutrients added to them to improve the quality of food and help prevent malnutrition.

• Using better methods of pest control can reduce the quantity of food lost during storage

• Increasing the land under cultivation can increase food production.

Solutions to World Food Supply ShortageProblems of World Food Supplies

salivary glandsepiglottisglottis

stomach

cardiac sphincter

large intestine

pancreas

pyloric sphincter

descending colon

rectum

anus

mouthteeth

trachea

oesophagus

liver

gallbladder

duodenum

ileumascending colon

caecum

appendix

The Digestive System


StructureStructure FunctionsFunctions

Mouth

Teeth • Teeth grind and break down food, exposing a large surface area for enzyme action

Tongue • Rolls food into bolus before swallowing

Salivary glands

• Produce saliva• Saliva dilutes and moistens food• Mucus sticks food together• Lubricates bolus for swallowing

Pharynx • Bolus is pushed into the pharynx voluntarily• Involuntary action pushes bolus out of the pharynx

into the oesophagus during swallowing

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Oesophagus • Connects pharynx to stomach• Waves of muscular contractiond during peristalsis

push food into the stomach

Cardiac sphincter

• Controls the entry of food into the stomach from the oesophagus

Stomach • Muscular wall churns and breaks up food• Secretes gastric juice which mixes with the food to

form chyme• Stores food for 2 to 6 hours

Pyloric sphincter

• Controls the exit of chyme from the stomach into the duodenum



Small intestine

• Keeps chyme in motion by churning movements• Glands secrete mucus, water and digestive juices

Duodenum • Allows pancreatic juice to digest food in it

Jejunum • Absorption of digestion food occurs

Ileum • Absorption of digestion food occurs

Pancreas • Secretes pancreatic juice• Enzymes of the pancreatic juice hasten hydrolysis

of food in the small intestine

Liver and gall bladder

• Liver produces dark green bile• Gall bladder stores bile• Bile flows into the duodenum through the bile duct• Bile emulsifies fats, providing a greater surface

area for the action of lipase



Large intestine

Caecum and appendix

• Vestigial organs with no particular function• Forms junction of small and large intestine

Colon • Secrete mucus• Contains large number of bacteria which produce

vitamins, methane and hydrogen sulphide• Absorbs water from chyme• Peristalsis compact undigested food to form faeces

by muscular contraction of the wall of the rectum• Mucus lubricates faeces and protects the walls

from digestive juices

Rectum • Stores faeces before defaecation

Anus • Regulate emptying of rectum

What is Digestion?

Digestion is the process by which the body breaks down carbohydrates, fats

and proteins into simpler substances that cells can absorb and use.

Mechanical digestion is the process of chewing, mashing and

breaking food into smaller particles. This increases surface

area for enzyme action.

Chemical digestion is the process of changing food into smaller

particles through the actions of enzymes.


Mechanical DigestionThe Digestive System

ring of muscles contract

bolus

oesophagus

cardiac sphincter

stomach

The bolus is being pushed towards the stomach. The waves of muscular contraction are called peristalsis.

The passage of food along the alimentary canal is accomplished by rhythmic muscular contraction called peristalsis.

• Large molecules such as starch has to be digested to form smaller molecules which can be absorbed through the walls of the villi.

• Enzymatic breakdown involves hydrolysis, which splits large molecule by the addition of water.

• Enzymes which hasten the breakdown of carbohydrates, fats and proteins into soluble and simple products can be classified into three groups: amylases, proteases and lipases.

Amylases: act on carbohydrates and convert them into

simple sugars

Proteases: act on proteins and convert

them into various amino acids

Lipases: act on fats and convert them into glycerol and

fatty acids

The Digestive SystemChemical Digestion

• Saliva: starch maltose.

• Saliva: bicarbonate ions (HCO3-) to buffer the saliva

maintain optimum pH 6.5 ~ 7.5 for starch digestion.

salivary gland

palatesalivary duct

pharynx

glottis

nosenasal passage

buccal cavitytongue

epiglottis

salivary glands

The Digestive SystemDigestion in the Mouth

amylase

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• Gastric juices are secreted into the stomach by gastric glands in the walls of the stomach.

• Gastric juices contain water, hydrochloric acid and enzymes.

• The hydrochloric acid lowers the pH of the stomach contents to a pH of 2.0.

• Protein digestion begins with action of proteases – pepsin and rennin.

• Pepsin catalyses the hydrolysis of protein to form polypeptides.

• Rennin catalyses the hydrolysis of milk caseinogen to form milk curds (casein).


oesophagus

cardiac sphincter

stomach

pyloric sphincter

duodenum

Digestion in the Stomach

OrganOrgan GlandGland SecretionSecretion EnzymeEnzymeEnzyme ActionEnzyme Action

SubstrateSubstrate ProductProduct

Duodenum(pH 8.5)

Pancreas Pancreaticjuice

Trypsin Protein PolypeptidesPeptones

Amylase Starch Maltose

Lipase Emulsifiedfats

Fatty acids andglycerol

Intestinalglands

Intestinaljuice

(succusentericus)

Maltase Maltose Glucose

Sucrase Sucrose Glucose and fructose

Lactase Lactose Glucose andGalactose

Peptidases Peptones andpolypeptides

Amino acids

The Digestive SystemDigestion in the Small Intestine

Bile

• Is a thick, yellow-green fluid produced by the liver.

• Helps to digest fats in the body.

• Is either secreted directly into the duodenum through the bile duct or stored in the gall bladder.

• Contains sodium hydrogencarbonate, bile salts and bile pigments.


Absorption of Digested Food

About 90% of the digested food is absorbed in the small intestine.


duodenum

bile duct

hepatic portal vein

pancreas

pancreatic duct

liver

gall bladder

The small intestine and accesssory digestive organs.


Features of the intestine:

• It is the longest part of the alimentary canal, consisting of the duodenum, jejunum, ileum.

• The internal surface of its wall is folded to increase the surface area for absorption.

• Its surface is covered with villi to increase the absorptive surface.

• Each villus is covered with epithelial cells. The plasma membrane of each cell has minute fingerlike projections called microvilli to increase surface area.

• The villi move back and forth independently of each other. Motion is fast after a meal and absorption proceeds faster.

• Absorption of nutrients across the membrane occurs by diffusion and active transport.


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microvilli

microvilli nutrients enter villus

villi

blood capillaries

lacteal

epithelial lining of the villus

lymphatic vessel

blood vessel

lymph to the neck before entering the heart

blood from heart

blood carries non-fatty nutrients to the liver

The Digestive SystemAbsorption of Digested Food

Structure of the villus.

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Blood is carried directly from the stomach and the intestine to the liver via the hepatic portal vein. Hepatic veins then convey it to the heart via the posterior vena cava.


posterior vena cava

stomach

gastric vein

small intestine

to heart

intestinal vein

hepatic portal vein

liver

hepatic vein


• Is the uptake and use of digested food products by the cells.

• oxidised water + CO2

• excess glucose glycogen

• glycogen stored in liver cells and muscle tissues

• a portion of absorbed fats are stored in adipose tissues as fat droplets

• some are use in the synthesis of cell membrane and the rest for energy

The Digestive SystemAssimilation

fat droplet

nucleus large fat globule formed

• for synthesis of proteins for growth and development; enzymes and hormones

• excess amino acids ammonia + glycogen

• food residues that cannot be digested leave the small intestine large intestine

• waste material compacted into faeces

• faeces propelled along colon and rectum, then expelled


• Is the uptake and use of digested food products by the cells.

Assimilation

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Functions of the Liver• Metabolism of glucose

• Metabolism of amino acids

• Production of bile

• Storage of iron

• Excretion of bile pigments

• Synthesis of plasma proteins

• Detoxification

• Storage of vitamins

• Reservoir for blood

• Source of heat energy


Inquiry-based learning

• Divide class into 3 groups

• Each group to brainstorm questions related to one of the following facts on chemical digestion in– Mouth

– Stomach

– Small intestine

– Large intestin

7247485 Chapter 6 Digestion

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