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.
Geat information about digestive health
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