Mammalian Nutrition

Requirement for food

To maintain good health, human beings consume a balanced diet from the main food groups.

The main food groups are; carbohydrates, fats, proteins, vitamins and minerals.

Energy requirements vary from person to person.

Someone who leads an active lifestyle will need more energy than someone who is inactive.

CHEMICAL STRUCTURE

• Carbohydrates, fats and proteins all contain the chemical elements carbon (C);hydrogen (H) and oxygen (O).

• Proteins contain all the above elements but also nitrogen (N).

CARBOHYDRATESCARBOHYDRATES

• Energy rich compounds• E.g. sugars, starch, glycogen, and

cellulose.

CARBOHYDRATESCARBOHYDRATES

Glucose is the most common simple sugar.

Excess glucose is stored as starch in plants and glycogen in the liver in humans

A maltose molecule has 2 molecules of glucose stuck together.

Starch is made up of lots of repeating units

CARBOHYDRATESCARBOHYDRATES

Glycogen

CARBOHYDRATESCARBOHYDRATES

Cellulose

Cellulose is a complex carbohydrate made up of thousands of glucose molecules arranged into long chains. (Cell walls are made of cellulose)

People are unable to digest cellulose but it is good ‘roughage’ and gives bulk to faeces!

FATSFATS

• Release twice as much energy as carbohydrates and proteins.

• A molecule of fat is made up of 1 glycerol and 3 fatty acids.

GLYCEROL

FATTY ACID

FATTY ACID

FATTY ACID

PROTEINSPROTEINS

• Each molecule of protein is made up of many different sub-units called amino acids.

• There are about 20 different types of amino acids.

VITAMINSVITAMINS

• Are complex chemical compounds required for good health. E.g. Vitamins A,B, C and D.

• They do not provide energy but are essential.

• Stick in table of importance of vitamins.

Vitamin

Function If deficient, what happens?

Rich sources

A Component of visual pigment in retina; needed to maintain epithelial tissues

Night blindness; dry skin

Carrots and other yellow vegetables

B1 Plays essential role in removal of CO2 made during tissue respiration

Weakening of heart; beri-beri (paralysis of limbs)

Liver, yeast and un-refined cereal grains

B12 Essential for development of new red blood cells

Anaemia Meat, eggs and milk

C Needed for growth and repair of the skin and mucous membranes

Scurvy (poor healing of wounds; soft bleeding gums)

Citrus fruits and green vegetables

D Required for absorption of calcium and phosphate from small intestine

Rickets (soft bones that become deformed easily)

Fish liver oil, butter, milk and egg yolk

MINERALSMINERALS

• Refers to certain chemical elements essential in small quantities for a wide range of functions.

• E.g. Calcium for strong bones and teeth.

• Stick in the importance of minerals table

Mineral Function Rich sources

Calcium Needed for hardening of bones and teeth, clotting of blood and contraction of muscles

Milk, cheese and green vegetables

Iron Acts as a structural component of haemoglobin and some enzymes.

Meat, eggs, cereals and green vegetables

Phosphorous

Needed for the formation of bones and teeth, and synthesis of DNA and ATP

Milk, fish, meat, nuts and cereals

Iodine Required for formation of hormones produced by thyroid gland

Sea foods and iodised salt

Sodium Essential for contraction of muscles and transmission of nerve impulses

Fish, meat, milk and salt

Potassium Essential for contraction of muscles and transmission of nerve impulses

Present in almost all foods

FOOD TESTS FOR STARCH, GLUCOSE, PROTEIN AND FAT

• You need to know the food tests for starch, glucose, protein and fats.

FOOD TYPE 

TEST OUTCOME

  

Starch

  

Iodine

  

Brown to blue-black if starch present

 

  

Glucose

  

Benedict’s

  

Blue to orange brick-red if glucose present

(heat required) 

  

Protein  

  

Biuret

  

Blue to lilac if protein is present

  

Fat  

  

Translucent spot

  

Drop of fat on filter paper makes a

translucent spot

Energy Content of FoodEnergy Content of Food

• Different food groups have different energy contents.

• Fat contains twice as much energy (kJ) than protein and carbohydrate.

-> Read pg 225 and complete Q1.

The Need for DigestionThe Need for Digestion

• Digestion involves the breakdown of large, insoluble food molecules into smaller soluble food molecules in the gut.

• This allows absorption of the food molecules into the bloodstream through the lining of the small intestine.

Large particles of insoluble food

Insoluble food digested to soluble state

Small soluble molecules of food absorbed into bloodstream

Undigested waste passed out

ExperimentExperiment

The purpose of digestion and absorption using Visking tubing as

a model gut

• Food passing along the alimentary canal is a mixture of large particles of carbohydrates, protein and fat.

• Every cell in the human body needs a supply of food from a nearby blood vessel. The food must first gain access to the bloodstream from the gut.

In this experiment:-• The visking tubing acts as the wall of the gut.

• Starch and glucose acts as the food in the gut.

• Water in the boiling tube acts as the blood surrounding the gut.

Starch + glucose

Visking tubing

Water

Method

1) Mix starch and glucose solution together.2) Knot 1 end of Visking tubing3) Pour in starch and glucose solution4) Tie other end of visking tubing5) Rinse the Visking tubing sausage under the

tap.6) Put into boiling tube and top up with water.7) Place in water bath (37ºC – body temperature)8) Start clock – take sample of water and test for

glucose and starch.9) Test again at 10, 20 and 30 minutes.10) Record your results in a table

Results

Time (mins)

Starch present (x or )

Glucose present (x or )

0    

10    

20    

30    

1) Which food was unable to pass out of the Visking tube ‘sausage’ through tiny pores in the membrane because its molecules are too large?

2) Which food was able to pass out of the Visking tube ‘sausage’ because its molecules are too small?

Think Questions??

Conclusion

Starch molecules are large and insoluble

and so are unable to pass through the gut

wall.

Glucose molecules are small and soluble

and so are able to pass through the gut wall.

Alimentary Canal and Associated Alimentary Canal and Associated OrgansOrgans

The alimentary canal is a long tube running

from the mouth to the anus.

The salivary glands, liver and pancreas are

connected to the alimentary by ducts.

Label your diagram

A

C

B

D

J

H

K

G

F

I

E

L

The passage of food along the alimentary canal

• Food is broken down mechanically in the mouth by the action of the teeth.

• The salivary glands secrete saliva which mixes with

food. • The saliva contains the enzyme amylase which digests

the starch into maltose sugar.

Starch Maltose

• Mucus in the saliva keeps the mouth moist and lubricates the food, making the food easier to swallow.

AMYLASE

• Once chewed, the food is swallowed. It moves along the oesophagus (gullet). This is a muscular tube that connects the back of the mouth to the stomach.

• It moves along the oesophagus by a mechanism called peristalsis.

• Note that peristalsis occurs throughout the length of the alimentary canal not just down the oesophagus.

• Label your diagram of what happens

Muscular gut wall

Circular muscles form a ring that contracts and squeezes

the food from behind

Circular muscles in front relax and allow the food to

pass

Direction of foodFoodFood

• Peristalsis will happen even if you are standing on your head!

• It is a wave-like motion since the gut wall muscles contract and relax alternately along the entire length of the alimentary canal.

• It ensures that food once swallowed is actively carried to the stomach and once in the large intestine, keeps unwanted wastes on the move to exit the body.

• The food then reaches the stomach.

• The stomach is a muscular bag whose wall contains longitudinal and circular muscles.

• These muscles contract and relax to bring about churning of the contents of the stomach.

• The contents of the stomach are mixed with gastric juices inside the stomach.

You do not need to know the parts of the stomach in this detail. Just realise that the churning happens as a result of the contraction and relaxation of the longitudinal and circular muscles.

• The inner lining of the stomach is folded and contains gastric glands which posses 3 types of cells.

• 1) Mucus-secreting cells

• 2) Acid-secreting cells

• 3) Enzyme-secreting cells

• (Stick in diagram 11.4)

• The slimy mucus sticks to the stomach lining and protects it from being damaged by digestive enzymes.

• Hydrochloric acid is secreted by the acid-secreting cells which creates acidic conditions inside the stomach.

• The enzyme-secreting cells secrete inactive pepsinogen. The acidic conditions then convert it to active pepsin.

• The pepsin then breaks down insoluble protein into soluble peptides.

Protein peptidespepsin

• The partially digested food will then pass from the stomach to the small intestine by the action of peristalsis.

• Fat is digested by the enzyme lipase and protein is further digested by the enzyme trypsin.

• Once the food is digested into small, soluble molecules the food can then be absorbed by the process of diffusion from the small intestine into the bloodstream.

• Structure of the small intestine

The structure of the small intestine is suited to its function in 3 ways:-

1) It is long and has a folded inner lining with many finger-like villi. A large surface area is provided for absorbing digested food.

2) The lining of each villus (epithelium) is only 1 cell thick allowing nutrient molecules to pass through easily.

3) A blood capillary network and a central lacteal are present in each villus to allow efficient transport of substances.

                                                  

Thin epithelium

Absorption of substances from Absorption of substances from the small intestinethe small intestine

• Glucose and amino acids are absorbed into the epithelial cells and then pass directly into the blood capillaries.

• The products of fat digestion are also absorbed into the epithelial cells but do not pass into the blood capillary. They pass into the lacteal instead.

• (the lacteal is part of the lymphatic system which will drain into the blood circulation through ducts in the upper chest region.)

Fate of Absorbed Materials

• Blood rich in amino acids and glucose from the small intestine is transported in the hepatic portal vein to the liver.

• Enough glucose is is released into the blood circulation for use as an energy source.

• Excess glucose is converted in the liver to glycogen and is stored there until needed.

• Enough amino acids is released into the blood circulation to be used in protein synthesis during growth and tissue repair.

• Excess amino acids are broken down in the liver to urea. (The kidneys deal with this later)

• The process of breaking down amino acids is called deamination. This happens in the liver

• Some of the products of fat digestion (fatty acids and glycerol) are used as an energy source.

• Excess fatty acids and glycerol are converted to fat and stored in the body’s fatty tissue until required.

The role of the pancreasThe role of the pancreas

• The pancreas produces pancreatic juices which contains lipase, trypsin and amylase all being digestive enzymes.

Fat fatty acids + glycerol

Peptides amino acids

Starch maltose

lipase

trypsin

amylase

The role of the gall bladderThe role of the gall bladder

• The gall bladder stores bile which emulsifies* fats to aid digestion.

• * just means to disperse fat into tiny globules, this allows the enzyme to get close enough to break down the fat.

The role of the large intestineThe role of the large intestine

• Material that passes into the large intestine consists of undigested material, bacteria and dead cells.

• The large intestine absorbs water from this leaving behind faeces.

• The faeces are passed into the rectum and are later expelled through the anus.