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What happens where?
STARCH to MALTOSE SALIVARY AMYLASE
REACTANT/PRODUCT ENZYME
PROTEINS to PEPTIDES
LIPASE
Chymo/trypsin
LIPIDS to FAs & GLYCEROL
PROTEINS to PEPTIDESPROTEINS to A.ACIDS
PEPSIN
Carboxypeptidase
LIPIDS to FAs & GLYCEROL LIPASE
MALTOSE to GLUCOSE
SUCROSE to GLUCOSE + FRUCTOSE
LACTOSE to GLUCOSE + GALACTOSE
PEPTIDES to AMINO ACIDS
MALTASE
SUCRASE
LACTASE
PEPTIDASE
LUMEN
MUCOSA – layer closest to the lumen. First layer is epithelial cellswith goblet cells that secrete a mucus to protect epithelium from enzymes. Beneath this is connectivetissue
SUBMUCOSA – made up of Connective tissue. Here Blood vessels and nerves lie & fibrous proteins (elastin)
MUSCULARIS EXTERNA – Two bands of muscle lie here (longitudinal & circular).- this aids peristalsis & mixes food.
SEROSA – thin layer ofConnective tissue
4 LAYERS !
We are going to look at the following areas ofthe digestive system in more detail:
The mouth and the oesophagus
The stomach
The liver and pancreas
The small intestine
The colon
MASTICATION – chewing food using molars &premolars.
3 pairs of Salivary glands release saliva. Soluble materials dissolve. Starch to Maltose (S.Amylase)
C & L musclesHelp to swallowFood.
Bolus enters theStomach.
Cardiac sphincter – opensTo let bolus into stomach
Pyloric sphincter –opens to letbolus into the duodenum
CHYME
A Gastric Pit
Creates a very foldedsurface which secretesgastric juices.
Creates a very foldedsurface which secretesgastric juices.
Gastric juices are approx. pH 1.
A Gastric PitParietal (oxyntic) cellsrelease HCL.
pH 1 kills lots of Bacteria.
Chief cells release Pepsinogen.
Pepsinogen is an inactive enxyme
HCL + pepsin work together to convertinactive PEPSINOGENto PEPSIN
A Gastric Pit
Gastric juice also contains gastric LIPASEGastric mucus is produced to protect epithelium from low pH
Little absorption occurs in the stomach
THE DUODENUM – PANCREAS & LIVER
Pyloric sphincter relaxes – chyme leavesthe stomach.
The liver prdc. bileThis is stored in thegall bladder.
Bile moves down thebile duct and into theDuodenum.
THE DUODENUM – PANCREAS & LIVER
What is bile?
Salts:Sodium glycocholateSodium taurocholate
Salts are derived fromcholesterol
Ions:Hydrogencarbonate ions
Hydrogencarbonate ionsThese neutralise the acidic Chyme from the stomach
SaltsThese emulsify fats
Droplets to single fats
pH 1
pH 7
THE DUODENUM – PANCREAS & LIVER
PANCREAS
Pancreas has a dual
function……
……as an ENDOCRINE &
EXOCRINE gland
Pancreas as an ENDOCRINE
gland.Pancreatic juice
isMade in the
pancreas and secreted into
theduodenumEnzymes:
TRYPSINCHYMOTRYPSINENTEROKINASE
LIPASEAMYLASE
CARBOXYPEPTIDASE
They are initially release in their inactive formsTRYPSINOGEN
CHYMOTRYPSINOGEN
TRYPSIN & CHYMOTRYPSIN - are both proteases
ENTEROKINASE catalyses the following reactionsTRYPSINOGEN to TRYPSIN
CHYMOTRYPSINOGEN to CHYMOTRYPSINOGEN
Pancreatic juice also contains HYDROGENCARBONATE ions, this keeps the pH at
NEUTRAL.
THE SMALL INTESTINE –
5m long
THE SMALL INTESTINE –
Composed of 3 parts:
(1) DUODENUM (25cm
(2) JEJUNUM(2m)
(3) ILEUM(2.75m)
GOBLET CELL secretes mucus
Artery, vein & lymphaticCapillary are all importantIn removing digested food.
Two types of digestion in the Small Intestine
Occurs in the LUMEN
Pancreatic juices continue to work.
Occurs on the surface of VILLI.
Many epithelial cellshave enzymes
embedded into theirplasma membranes.
Some enzymes become adsorbed
into the GLYCOCALYX
The final products of digestion are:AMINO ACIDSFATTY ACIDS
GLYCEROLMONOSACCHARIDES
We have moved from large insoluble polymers to small soluble monomers
All of these products then cross the plasma membrane of the villi and then enter blood
lymphatic capillaries
Diffusion, active transport and facilitated diffusion all have a role