Human Digestive System
Need to know
Ø The functions of the main parts of the alimentary canal and the associated glands
Ø Function of teeth . The human dental formula
Ø Role of mechanical digestion and peristalsis
Ø Details of chemical digestion by one amylase,
one protease and one lipase . Role of bile salts
Ø Symbiotic bacteria functions in the large intestine
Ø Benefits of fibre
Ø The functions of the main parts of the alimentary canal and the associated glands
Ø Function of teeth . The human dental formula
Ø Role of mechanical digestion and peristalsis
Ø Details of chemical digestion by one amylase,
one protease and one lipase . Role of bile salts
Ø Symbiotic bacteria functions in the large intestine
Ø Benefits of fibre
Mechanical breakdown of food: physical breakdown of food. (Chemical breakdown: Enzyme/molecular breakdown of food)
1.Teeth
2.Contractions in stomach wall
3.Peristalsis
Rhythmic muscular contraction and relaxation in the wall of the alimentary canal causing the food to move along the canal
1.Teeth
2.Contractions in stomach wall
3.Peristalsis
Rhythmic muscular contraction and relaxation in the wall of the alimentary canal causing the food to move along the canal
Human Teeth
Incisors:Cutting
Canines:Tearing
Pre molars and Molars:Crushing and grinding
Canines:Tearing
Pre molars and Molars:Crushing and grinding
Human Dental Formula
![Picture](/uploads/2/6/9/0/26900109/1318666.png)
The number of each type of tooth in the upper jaw one side of the mouth
Oesophagus
A muscular tube
25 cm long
Connects Pharynx to stomach
Food moves down the Oesophagus by Peristalsis
25 cm long
Connects Pharynx to stomach
Food moves down the Oesophagus by Peristalsis
Stomach
J shaped muscular bag
Stores food for about 4 hours
Churns and mixes food with gastric juice forming Chyme
Digests food
Stores food for about 4 hours
Churns and mixes food with gastric juice forming Chyme
Digests food
Digestion in the Stomach
1. Mechanical Digestion
Peristalsis physically breaks up food particles
2. Chemical Digestion
using Gastric Juice containing
a. Mucus
b. HCl
c. Pepsinogen
1. Mucus:Lines and protects the stomach wall
2. HCl:
a. Kills bacteria
b. Activates pepsinogen
3. Pepsinogen:Converted to the active enzyme Pepsin by HCL.Pepsin digests protein to peptides
Peristalsis physically breaks up food particles
2. Chemical Digestion
using Gastric Juice containing
a. Mucus
b. HCl
c. Pepsinogen
1. Mucus:Lines and protects the stomach wall
2. HCl:
a. Kills bacteria
b. Activates pepsinogen
3. Pepsinogen:Converted to the active enzyme Pepsin by HCL.Pepsin digests protein to peptides
Sphincter Muscle
![Picture](/uploads/2/6/9/0/26900109/6297282.png)
Cardiac Sphincter Muscle:
Circular muscle which contracts to close entry from oesophagus to stomach
Pyloric Sphincter Muscle
Circular muscle which contracts to close the entry to duodenum from the stomach.
(Open when relaxed )
Circular muscle which contracts to close entry from oesophagus to stomach
Pyloric Sphincter Muscle
Circular muscle which contracts to close the entry to duodenum from the stomach.
(Open when relaxed )
Small Intestine
![Picture](/uploads/2/6/9/0/26900109/9052267.png)
Muscular tube 5-6m long
Functions
Digestion
Absorption
Two parts
1.duodenum
2. ileum
Duodenum
25cm muscular tube
Function :Most Digestion takes place in the duodenum
Functions
Digestion
Absorption
Two parts
1.duodenum
2. ileum
Duodenum
25cm muscular tube
Function :Most Digestion takes place in the duodenum
Ileum
![Picture](/uploads/2/6/9/0/26900109/6605718.png)
Function: Absorb nutrients
Adaptations for absorption
1. Long tube.
This gives time for absorption
2. Villi.
Infoldings which increase the
surface area available for the absorption of food
Villi: Infolding in the lining of the small intestine
Function: Increase surface area for absorption of digested food
A single Villus
Fatty acids and Glycerol and fat soluble vitamins are absorbed into the Lacteal
All other digested food are absorbed into the blood vessels
Food is absorbed by diffusion/passive transport
Route of food following absorption:
The hepatic portal vein carriers blood from the alimentary canal to the live.
Adaptations for absorption
1. Long tube.
This gives time for absorption
2. Villi.
Infoldings which increase the
surface area available for the absorption of food
Villi: Infolding in the lining of the small intestine
Function: Increase surface area for absorption of digested food
A single Villus
Fatty acids and Glycerol and fat soluble vitamins are absorbed into the Lacteal
All other digested food are absorbed into the blood vessels
Food is absorbed by diffusion/passive transport
Route of food following absorption:
The hepatic portal vein carriers blood from the alimentary canal to the live.
Large Intestine
![Picture](/uploads/2/6/9/0/26900109/9273067.png)
Large Intestine Functions:
Colon
1.Reabsorb water
2.Produce B group vitamins
3.Digest cellulose
Functions 2 & 3 are carried out by symbiotic bacteria
Symbiotic bacteria are bacteria that live in (or on) another organism involving benefit.
Caecum and Appendix
Function unknown in humans
Rectum
Stores Faeces
Colon
1.Reabsorb water
2.Produce B group vitamins
3.Digest cellulose
Functions 2 & 3 are carried out by symbiotic bacteria
Symbiotic bacteria are bacteria that live in (or on) another organism involving benefit.
Caecum and Appendix
Function unknown in humans
Rectum
Stores Faeces
Role of the Liver in digestion
Ø The liver produces bile
Ø Bile is a yellow-green liquid
Ø Bile is stored in the gall bladder
Ø Bile enters the duodenum through the bile duct
Bile consists of
1.Water
2.Bile salts
3.Bile pigments
Function of bile
1.Emulsifies fat : This increases the surface area of the fat droplets
2.Neutralises the acidic chyme from stomach
Ø Bile is a yellow-green liquid
Ø Bile is stored in the gall bladder
Ø Bile enters the duodenum through the bile duct
Bile consists of
1.Water
2.Bile salts
3.Bile pigments
Function of bile
1.Emulsifies fat : This increases the surface area of the fat droplets
2.Neutralises the acidic chyme from stomach
Benefits of dietry fibre
Ø Fibre stimulates peristalsis in the colon
Ø Helps prevent constipation
Ø Constipation results when undigested material passes through the colon too slowly.
This leads to too much water being reabsorbed
Ø Helps prevent constipation
Ø Constipation results when undigested material passes through the colon too slowly.
This leads to too much water being reabsorbed
Three enzymes involved in digestion
![Picture](/uploads/2/6/9/0/26900109/1140629.png)
Enzymes are biological catalysts
1Amylase
2Pepsin
3Lipase
Salivary amylase
Role: Digest starch
Production site : Salivary glands
Where it acts: Mouth
pH in mouth : Alkaline, pH =8
Digestion product : Maltose
Pepsin
Role: Digest protein
Production site : Gastric glands in Stomach wall
Where it acts : Stomach
pH in Stomach : Acid, pH =2
Digestion product : Peptides
Lipase
Role: Digest fat
Production site : Pancreas
Where it acts : Dudenum
pH in mouth : Alkaline, pH =8
Digestion product : Fatty acids + Glycerol
1Amylase
2Pepsin
3Lipase
Salivary amylase
Role: Digest starch
Production site : Salivary glands
Where it acts: Mouth
pH in mouth : Alkaline, pH =8
Digestion product : Maltose
Pepsin
Role: Digest protein
Production site : Gastric glands in Stomach wall
Where it acts : Stomach
pH in Stomach : Acid, pH =2
Digestion product : Peptides
Lipase
Role: Digest fat
Production site : Pancreas
Where it acts : Dudenum
pH in mouth : Alkaline, pH =8
Digestion product : Fatty acids + Glycerol