The Digestive System:
By Naomi Keddy
Nutrition: The way organism obtain and use their food.
Ingestion: Is the taking of the food into the digestive system.
Digestion: The physical and chemical breakdown of food.
Absorption: Is when the digested food passes from the digestive system and enters into the blood stream.
Egestion: Is the removal of waste from the digestive system.
Why is Digestion important?
To breakdown food particles until they are small enough to pass in body cells. It is a good use for metabolism.
Mechanical breakdown of food:
-Teeth
-Contractions in the stomach wall
-Peristalsis
Oesophagus:
-A Muscular tube 25cm long.
-Connects the pharynx to the stomach.
-Food moves down the oesophagus by peristalsis.
Stomach:
-J-shaped muscular bag.
-Stores food for about 4 hours.
-Churns and mixes the food with gastric juice forming chime.
-Digests food.
Digestion in the stomach:
-Mechanical digestion: peristalsis physically breaks up the food.
-Chemical digestion: Using gastric juice (Containing mucus, HCL and pepsinogen)
Functions of gastric juice:
Mucus: Lines and protects the stomach wall.
HCL: Kills bacteria and activates pepsinogen.
Pepsinogen: Converted to the active enzyme pepsin by HCL. Pepsin digests protein to peptides.
Sphincter muscle location:
Cardiac sphincter muscle: Circular muscle which contracts to close entry from oesophagus to the stomach.
Pyloric sphincter muscle: Circular muscle which contracts to close the entry to duodenum from the stomach
Small intestine:
-Muscular tube 5-6cm long
-Functions are digestion and absorption
-Made up of three part:
· Duodenum
· Ileum
· Jejunum
Duodenum:
-25cm long muscular tube.
-Most digestion takes place in the duodenum
Jejunum/ Ileum:
Functions:
Absorb nutrients
Adaptions for absorption:
-Long tube: This gives time for absorption.
-Villi: Infolding’s which increase the surface area for absorption.
Villi: Infolding’s in the lining of the small intestine. Its function is to increase surface area.
A single villus:
-Fatty acid and glycerol are absorbed into the lacteal.
-All other digested food are absorbed into the blood vessel.
Large intestine:
Colon: Contains symbiotic bacteria, which help prevents disease causing organisms.
Functions of the colon:
-Reabsorbs water
-Produce B group of vitamins
-Digests cellulose
Functions of caecum and appendix:
-Functions are unknown in Humans
Functions of the rectum:
-To store faeces
Role of the liver in digestion:
-The Liver produces bile
-Bile is yellow-green liquid
-Bile is stored in the gall bladder
-Bile enters the duodenum through the bile duct
Functions of the liver:
-Makes bile
-Stores glycogen
-Breaks down toxins
-Store vitamins A, D and K
-Makes plasma proteins
-Make urea from excess protein
-Produces heat
-Stores Iron
-Transport waste products to the kidney for filtration and excretion
Bile: Is made from the remains of dead red blood cells. It makes pigments bilverdin and bilirubin. It contains sodium hydrogen carbonate, this helps neutralise chime from the stomach. Gall stones can be formed in the bile duct and prevent the release of bile.
Bile Consists of:
1. Water
2. Bile salts
3. Bile pigment
Functions of bile:
1. Emulsifies fats- This increase the surface area of the fat droplets.
2. Neutralises the acidic chime from the stomach
Benefits of fibre in the diet:
-Fibre stimulates peristalsis in the colon
-Help prevent constipation.
-Constipation results when undigested material passes through the colon slowly.
-This leads too much water being absorbed.
Three enzymes involved in digestion:
-Amylase
-Pepsin
-Lipase
Amylase:
-Role is the digestion of starch
-Produced in salivary glands
-Acts in the mouth
-Produces maltose
Pepsin:
-Role is the digestion of protein
-Produces in gastric glands in the stomach
-Acts in the stomach
-Optimum pH 2-3
-Produces peptides
Lipase:
-Role is the digestion of fats
-Produced in the pancreas
-Acts in the duodenum
-Produces fatty acids and glycerol
Blood transport of nutrients:
Absorption of nutrients:
Fatty acids and glycerol are absorbed from the small intestine into the lymphatic system for transport to the liver.
Glucose, Amino acids, vitamins and minerals pass through the blood capillaries.
The hepatic portal vein transports nutrients and waste urea from the liver to the heart.
From the heart, the nutrients are transported away from the heart through the aorta to the body cells dissolved in the plasma.
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