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

LIVER

GALL BLADDER

PANCREAS

STOMACH

BILE DUCT

THE DUODENUM – PANCREAS & LIVER

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)

THE SMALL INTESTINE – 5m long

Villi

Crypts of Lieberkuhn

Goblet cellsPaneth cells

LUMEN

One villus has lots of MICROVILLI

MICROVILLI: 1 µ m long and 0.1 µ m wide

GOBLET CELL secretes mucus

Artery, vein & lymphaticCapillary are all importantIn removing digested food.

Crypt of Lieberkuhn

Goblet cells are found hereSo are ………..PANETH cells.

Phagocytosis?

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