Download What is digestion?

The Digestive System
The Digestive System
Types of nutrition
Autotrophic: an organism that can make its own
food (plants)
Heterotrophic: an organism that cannot make its
own food (all animals)
Types of nutrition
Herbivores: animals that only eat plants.
Carnivores: animals that eat other animals
Omnivores: animals that eat plants and animals
What is digestion?
• Digestion is the break down of food into
smaller particles, This allows the food to be
absorbed into the bloodstream.
Two types of digestion:
1) Mechanical digestion
2) Chemical digestion
What is the alimentary canal?
• Starts at the mouth and ends at the anus.
Events in human digestion:
1)
2)
3)
4)
Ingestion: food enters mouth
Digestion: Breakdown of food
Absorption: food absorbed into the blood
Egestion: removal of unwanted waste
The digestion process - What happens to your
food as it travels through your body until it
exits? - YouTube
Mouth
Mechanical digestion in the mouth
Types of teeth
•
•
•
•
Incisors: cut, slice and bite
Canines: Tear and grip food
Premolars: crush and chew food
Molars: crush and chew food
Human dental formula
2 (I - C - PM - M - )
Digestion in the mouth
Mechanical digestion = food broken down into
smaller pieces by your teeth.
Chemical digestion: the enzyme amylase breaks
down the food in the mouth.
Chemical digestion in the mouth
Saliva: softens and dissolves the food. Saliva
consists of water, salts, and enzymes (amylase).
Lysozyme: destroys any harmful micro
organisms.
Amylase (pH 7)
Starch
Maltose
Oesophagus
• Carries food from the mouth to the stomach.
• Food is moved along the alimentary by the muscular action
called peristalsis.
• Peristalsis helps break down food mechanical.
Peristalsis... not for those with a weak stomach...lol –
YouTube
Peristaltic Wave in the Gastric Antrum - YouTube
Peristalsis in the Oesophagus
Role of fibre
• Plant cell walls contain cellulose, which provides
us with fibre.
• Sources of fibre: cereals, vegetables.
• Fibre helps us to absorb water from large
intestine.
• Fibre helps stimulate peristalsis.
Role of Fibre
• Fibre is believed to help
reduced the risk of cancer,
as waste produces will
leave your system faster.
Stomach
• Muscular bag that stores food and digests
food.
• Churns food causing mechanical digestion.
• Creates a mixture known as chyme.
Stomach
• Food enters and leaves the stomach through the
sphincter muscle.
• Stomach lining (mucosa) releases gastric juices.
What is in gastric juices:
• Mucous: prevents self digestion of the
stomach.
• Pepsinogen: inactive enzyme when released
(does not digest cells in stomach).
• Pepsinogen is converted to active pepsin
when reacting with acid.
Videos on the stomach
• Stomach Digestion – YouTube
• A Gastric Prepyloric Benign Ulcer – YouTube
• Parasites - Round Worm Found in Human
Colon - YouTube
Stomach
• Hydrochloric acid in the stomach has a pH of 1-2.
• This acid can kill any bacteria that may cause
harm to the body.
• HCl activates Pepsinogen to form pepsin.
• Pepsin (protease) is an enzyme that digests
proteins.
Protection from self digestion
• Mucous lines the stomach
• Mucous is alkaline which reduces acidity near
the cell wall.
• Pepsin is released as inactive pepsinogen.
• Cells that line the stomach are tightly packed
and are replaced rapidly.
Stomach Wall
Glands associated with small intestine
Pancreas
• Secretes pancreatic juice containing sodium
bicarbonate (sodium hydrogen carbonate)
• Sodium bicarbonate neutralises the chyme from the
stomach in the duodenum.
Dual Role of Pancreas - YouTube
Pancreatic Juice
• Also contains the enzymes amylase and lipase which
are secreted into the duodenum to aid digestion.
• Both these enzymes work best at the pH of 7.
Amylase
Starch
Maltose
Lipase
Lipids
Fatty acids and glycerol
Liver
Functions
• Produces bile
• Breaks down excess amino acids to form urea
• Converts excess carbohydrates to fats
• Converts glucose to glycogen for storage
• Stores vitamins like vitamin D
• Produces heat to warm the blood
• Makes chlorestol to form hormones
Liver
01 Liver Video - YouTube
Bile
• Formed from the remains of dead red blood
cells.
• Yellow/ green liquid.
• Made in liver and stored in gall bladder.
What are gallstones:
They form in the bile duct and prevent the
release of bile.
Bile and Gall stones
Gallstones - YouTube
Functions of bile:
1) It emulsifies Fats ( breaks down fats and oils
into tiny droplets). This increases the surface
area for the enzyme digestion.
2) Contains sodium bicarbonate which helps
neutralise the chyme from the stomach.
Small Intestine
Consists of two parts:
• Duodenum --- 25 cm long --- carries out digestion
• Ileum --- 5.5 metres long --- absorption of food
Duodenum
• Carries out digestion
• Products of liver and pancreas
enter the duodenum
Structure of small intestine
• Inner lining of small intestine contain many
infoldings called villi.
• Each villi have 600 microvilli.
• Villi increase surface area for digestion
(duodenum) and absorption (ileum) .
Villi and Micro villi
End products of digestion
Food
Digested to
Carbohydrates
Monsaccharides (glucose)
Proteins
Amino acids
Lipids
Fatty acids and glycerol
Videos on villi
• Digestive System: Small Intestine – YouTube
• Villi Model - YouTube
Substance
Made in
Active in
Preferred
pH
Substrate
Product
Amylase
(enzyme)
Salivary
glands
Mouth
7–8
Starch
Maltose
Pepsin
(enzyme)
Stomach
lining
Stomach
2
Protein
Peptides
Amylase
(enzyme)
Pancreas
Duodenum
7–8
Starch
Maltose
Lipase
(enzyme)
Pancreas
Duodenum
7 -8
Lipids
Fatty acids
and glycerol
Bile Salts
Liver
Duodenum
Lipids
Lipid droplets
Sodium
hydrogen
carbonate
Liver/
pancreas
Duodenum
Acid
Neutralises
acid
Hydrochloric
acid
Stomach
lining
Stomach
Bacteria
Kills bacteria
and softens
food
Ileum
• Food entering ileum is fully digested.
• Ileum absorbs the nutrients into the blood.
Villi
• Small intestine consist of many villi
• Villi increase surface area for absorption
• Villi absorb glucose, amino acids, vitamins and
minerals.
Adaptions of the villi
• It is very long
• Numerous villi and
microvilli
• Rich supply of blood
to carry away products
• Villi are only one cell
thick (very thin)
• Each villi has a lacteal
to carry away fats.
Lacteal
• Each villi contains a lacteal
• Each lacteal contains lymph liquid.
• Fatty acids and glycerol enter the lacteals and
are transported away in the lymph fluid to the
bloodstream.
Liver, small intestine and hepatic
portal vein
• Nutrients are carried from the small intestine
to the Liver by the hepatic portal vein.
Liver, small intestine and hepatic
portal vein
• Amino acids cannot be stored in the body.
• Amino acids are broken down in the liver to
form urea (deamination)
• Urea and other waste leaves the liver in the
hepatic vein which travels to the heart and
then the kidneys.
Large Intestine
• Only 1.5 metres long.
• Food stays in large intestine for 10 hours to a
few days.
Caecum and appendix:
• These organs have lost their functions
(vesitigal organs)
• Herbivores use them to digest cellulose.
Colon
• Colon is used to reabsorb water.
• Contains faeces (its colour is due to the bile).
• Faeces is stored in the rectum.
NOTE: Diarrhoea is formed when not enough
water has been reabsorbed. Constipation occurs
when to much water is reabsorbed.
Large Intestine
Symbiotic bacteria in the digestive system
Symbiosis: where two organisms live in a close association with
each other and at least one benefits.
• Symbiotic bacteria feed on waste products to produce
vitamins B and K.
• Symbiotic bacteria break down food (cellulose) which is
absorbed into the body.
• Symbiotic bacteria help prevent the growth of disease causing
bacteria.
What is a balanced diet:
• A balanced diet consists of the right amount
of each of the following foods:
1)
2)
3)
4)
5)
6)
7)
Proteins
Carbohydrates
Lipids
Vitamins
Minerals
Fibre
Water