Nutrition In Humans

Nutrition in Humans

Sites for food digestion mouth cavity

duodenum

stomach

ileum

Types of Digestion

Mechanical

Chemical

Mechanical digestion bread

Increases the surface area for chemical digestion

Digestion in mouth cavity

Mechanical

Chemical

Bread Saliva

2 Mastication

Teeth 1

Saliva 3 Increase the S.A. for chemical digestion

Bolus + Saliva

Starch + H2O

contains

Amylase

Maltose

Saliva Amylase Starch

Maltose Lubricates the food, so it can be swallowed easily

Water Moistens dry food

Swallowing Nasal cavity Soft palate bolu

s

Epiglottis Trachea

Oesophagus

Position of different structures during swallowing

2

Soft palate is prevent food raised from going up

3 Trachea is 1 Tongue is raised

closed by epiglottis Bolus enters 4 oesophagus

Peristalsis

Wave action

X

Circular muscle contracts

Longitudinal muscle Circular muscle These two muscles contract & relax alternately

Digestion in stomach

Closed during physical digestion Circular muscle Longitudinal muscle Closed during physical digestion

The churning movement of the stomach

sphincters open

Digestion in stomach

Mechanical Feature Strong muscle contraction

Adaptation

Food is churned up to form chyme to increase surface area for enzyme to act on

Chemical Feature

1. Protease

Adaptation

Protein

Peptides

Wall of Stomach Mucus-secreting gland Feature Mucus

Adaptation

Gastric gland Feature

• Protects the wall 1. Protease from being • Lubrication digested

2. Acid

Adaptation

Protein

Peptides

* Provides an acidic medium for enzymes * Kills germs

Digestion in Duodenum

1

2

Digestion in Duodenum contains three juices

Bile Pancreatic juice Intestinal juice from gall bladder

Bile

from pancreas

Duodenum Pancreatic juice

Intestinal juice

Ileum

Liver, bile and gall bladder

Bile

which is stored in the gall bladder

Produces

Liver

Gall bladder

the bile is then discharged into the duodenum

Bile

Composition

Bile salt

Bile pigment (green in colour)

emulsified

Oil

Oil droplets

Increase S.A. for latter chemical digestion

NaHCO3

Products of breakdown of haemoglobins

Emulsification

No enzyme in bile

Mechanical digestion

Bile is an alkaline fluid

Pancreas The pancreatic juice is discharged into the duodenum

Pancreatic juice Produces

Pancreas

Pancreatic juice

Composition

Pancreatic amylase Starch

Maltose

Protease

NaHCO3

Lipase

Protein

Peptides

Peptides

Amino acids

Oil droplets

Fatty acids

+

Glycerol

Pancreatic juice is an alkaline fluid

intestine

Duodenum

small

3

4

Ileum

from gall bladder

from pancreas Duodenum

Intestinal juice Ileum

3

Duodenum

4

Ileum

Intestinal juice

Composition Intestinal protease Peptides

Amino acids

Intestinal carbohydrases Disaccharides Maltose

Monosaccharides Glucose

Bile

which neutralises the acid in chyme 1

Pancreatic juice

Contains hydrogencarbonate

Intestinal juice

which provides an alkaline medium for the enzymes

2

Summary Starch

Salivary Gland Amylase

Pancreas

Maltose Carbohydrase Glucose

Intestinal Gland

Protein Proteases

Gastric Gland Pancreas

Peptides Pancreas Proteases Amino Acids

Intestinal Gland

Oil Bile salt

Liver

Oil droplets Lipase Fatty Acids + Glycerol

Pancreas

Summary Process Mechanical Digestion

Structure involved

Chewing :Large

food is broken into smaller pieces

ChurningLarge :

food is broken into smaller pieces

Emulsification : Oil

is broken into oil droplets

Chemical Digestion

By enzymes

By teeth

By strong muscle

By bile salt

All digested food will be absorbed in the small intestine

Undigested remains

Large intestine

Large intestine 3

No function in human

Reduced in size

2

Caecum 1

Appendix

Colon But in herbivores, caecum & appendix are longer. 4 They play an important roleRectum in digestion of cellulose.

Digestion – completed in small intestine Before digestion Protein Fat Starch

After digestion Amino Acids Fatty Acids & glycerol Glucose

Absorption

Absorption 1. Stomach e.g. water, alcohol 2. Ileum (most important site for food absorption)

Absorption in ileum

Wall of ileum

ileum

Absorption in ileum

Wall of ileum Finger-like structure called

villus

Villus / villi Increases the surface area for absorption

Finger-like structure called

villus

Villus 1 Epithelium 2 Blood capillaries 3 Lacteal

Villus 1 Epithelium (very thin) Digested food

is one-cell thick

shorten the distance for diffusion of digested food

Villus Blood 2 capillaries Transport the absorbed food Maintain a steep conc. gradient to enhance the rate of diffusion

Villus Absorb & transport fat molecules in digested food 3 Lacteal

Absorption in villus Blood capillary

Epithelial cell

Lacteal

Absorption in villus Blood capillary

By diffusion & active transport

Pass into the capillaries

Epithelial cell

Lacteal

ileum blood vessel

100 units glucose

0

90 … 50

40

0

10 … 50

60

100

Movement of molecules from high conc. to low conc.

Diffusion

Movement of molecules from low conc. to high conc. using energy from respiration

Active Transport

Absorption in villus Blood capillary

By diffusion & active transport

2 1

2

Enter the lacteal & recombine to fat molecules

Epithelial cell

Lacteal

Summary Structural features

Adaptation of ileum

Wall of ileum is highly folded & has numerous villi

To increase surface area for food absorption

One-cell thick epithelium Lacteal is surrounded by a network of blood capillaries

To shorten distance for diffusion

To transport absorbed food

heart hepatic vein

cells

lym to ph fat tran ves sp se ort l the

aorta

liver hep atic

um e il

por t

al v

ein

Glucose, amino acids, fat etc. carried by aorta to all tissue cells

Assimilation

- the used up of digested food by cells

Amino acids

protein (for growth & repair)

Glucose

energy source

Fat

energy source

cell

heart

Blood glucose = 100 units Blood amino acid =90 units

hepatic vein

aorta

1. Excess glucose converted to glycogen 2. Excess amino acids deaminated to form urea

el he s s tt e v or h p nsp lym tra to t fa

liver hep atic

por t

um e il

al v

ein

After a diet Blood glucose = 200 units Blood amino acid =120 units

Excess fat molecules are stored around internal organs & under the skin

Large intestine 3

Colon

2

Caecum 1

Appendix

4

Rectum Anus

5

3

Colon absorbs water & minerals but most of the water in the gut is absorbed in the small intestine

3

Colon If

absorbs water & minerals leads to

diarrhoea & results in dehydration & excessive loss of ions

Egestion Undigested food Dead bacteria

semisolid

Living bacteria

faeces

Bile pigment Water Dead cells from digestive system

Secretions of the alimentary canal

temporarily stored in

9

Rectum

Removal of undigested or unabsorbed food

Egestion Constipation difficult to remove the faeces become harder excess water is absorbed

semisolid faeces faeces stay longer in the large intestine

Removal of undigested or unabsorbed food If you do not have dietary fibers

which would stimulate peristalsis

Functions of liver 4. Storage of vitamin A & D, iron & glycogen

3. Bile secretion

2. Deamination 6. Detoxification 1. Blood glucose 5. Production level regulation of heat, plasma protein