Digestion, Secretion, Absorption And Motility

Front 1

What process occurs in the gall bladder when have a meal?

Why?

Back 1

During a meal the smooth muscle of the gall bladder contract.

This causes concentrated bile solution to be injected into the duodenum via the common bile duct.

Front 2

What functions does that pancreas have?

Back 2

1. Exocrine functions

-- Secretes digestive enzymes and HCO3- rich fluid into the stomach.

2. Endocrine functions

Front 3

What is the role of the gall bladder?

Back 3

Stores bile

Front 4

What is a critical component of bile?

Back 4

Bile salts, a group of substances which solubilise dietary fats.

Front 5

What are the crucial components of the small intestine wall?

Back 5

1. Villi

2. Submucosa

3. Muscularis Externa

4. Serosa

5. Myenteric plexus

Front 6

What is the role of the villi in the small intestine?

Back 6

Covered with microvilli which increase surface area (300 metres squared)

Front 7

What is the submucosa?

Back 7

Layer below the mucosal layer - a connective tissue layer.

Front 8

Describe the submucosal plexus.

Back 8

Neural network within the submucosa which penetrate into the smooth muscle of the intestine.

Front 9

What is the muscularis externa?

Back 9

The GI smooth muscle

Front 10

What are the layers of the muscularis externa?

How does contraction of each type of muscle affect the GI tract?

Back 10

1. Thick inner layer of circular muscle - contraction narrows the GI tract

2. Longitudinal muscle - Contraction shortens the GI tract.

Front 11

What lies between the two layers of the muscularis externa?

Back 11

A further neuronal network - the myenteric plexus

Front 12

What is the role of the myenteric plexus?

Back 12

Innervates the muscularis externa throug communication with the autonomic nervous system.

Front 13

Describe the structure of starch.

Back 13

A glucose polymer which is made up of amylose and amploypectin monomers.

Front 14

What is glycogen?

Back 14

A basic glucose polymer

Front 15

What are the main disaccharides?

Back 15

1. Sucrose (glucose + fructose)

2. Lactose (glucose + galactose)

Front 16

How are carbohydrates digested?

Back 16

Carbohydrates are digested into simple monosaccharides by 'Brush border enzymes' and pancreatic enzymes.

Front 17

How is fructose absorbed into the gut epithelium?

Back 17

Absorbed into cell via cotransport with Na+. Facilitated diffusion via a GLUT transporter.

Front 18

How are glucose and galactose absorbed into the gut epithelium?

Back 18

Cotransported via a symporter - Sodium glucose transporter (SGLT)

Front 19

How are carbohydrate monomers absorbed into the blood?

Back 19

Facilitated diffusion via a GLUT transporter. Energy for transportation is provided by Na+/K+ ATPase pumps.

Front 20

How are proteins digested?

Back 20

In the stomach (acidic environment) pepsinogen becomes pepsin - a protease. Pepsin cleaves proteins into small peptides & amino acids.

Front 21

What produces pepsinogen in the stomach?

Back 21

Produced by 'Chief cells' in gastric mucosa

Front 22

When pepsin cleaves proteins in the stomach what compounding effect does this cause?

Back 22

1. The duodenum senses this can releases cholecystokinin (CCK)

Front 23

What effect does choleycystokinin (CCK) have on digestion?

Back 23

CCK is a hormone which causes the release of pancreatic peptidases such as:

1. Trypsinogen

2. Chyotrypsin

3. Pro-Elastase

4. Carboxypeptide A

5. Carboxypeptide B

Front 24

How are protease zymogens activated?

Back 24

Activated by enteropeptidase which activates via removal of 6 x Amino acids from the N terminal.

Front 25

What are the brush border peptidases?

Back 25

1. Endopeptidases

2. Aminopeptidases

3. Carboxypeptidases

4. Dipeptidases

Front 26

When and how can proteins begin to be absorbed?

Back 26

Once metabolised into small peptidases and amino acids by brush border enzymes they can enter the cell.

Amino acids enter via Na+/AA symporters

Small peptides enterv via Small peptide / Na+ symporters.

Front 27

Once amino acids / small peptides are within the gut epithelium how do they enter the blood?

Back 27

1. Small peptides - Fully digested in the cytosol via cytosolic peptidases

2. Amino acids are absrobed into the interstitial fluid via AA transporters (driven by Na+/K+ ATPase).

3. The AAs then diffuse into the blood capillaries via pores.

Front 28

What are the two types of dietary iron?

Back 28

1. Haem iron - attached to proteins

2. Non - Haem - free iron.

Front 29

What are the basics of Iron absorption?

Back 29

Iron is actively absorbed into the intestinal epithelial cells.

Front 30

Describe the processes of iron transportation into the gut epithelium.

Back 30

1. First Non heme iron (Fe+++) is reduced into Fe++ by D Cyt B1 Ferrireductase (a brush border enzyme)

2. Fe++ is then symported with H+ intro the intestinal epithelial cells

Front 31

What is the name of the Fe++ channel in the gut epithelium?

Back 31

the DMT1 symporter

Front 32

How does Iron enter cells?

Back 32

The Heme carrier protein 1 (HCP1) channel

Front 33

How is Iron effectively used in cells?

Back 33

1. Binds to Ferritin - Intracellular Fe store

Front 34

Describe the process from when Iron enters a cell to its binding with Ferritin.

Back 34

Fe++ can bind directly to ferritin

Heme Fe++ must first be split away from its peptide via haem oxygenase

Front 35

How does Iron leave the cell?

Back 35

Dissociates from ferritin and must be oxidised before leaving.

Front 36

What enzyme oxidises iron in the cell allowing its departure from the cell?

Back 36

Ferroxidase

Front 37

What is the name of the channel through which Fe+++ leaves the cell/

Back 37

Ferroportin

Front 38

What happens to Fe+++ when it enters the plasma?

Back 38

Hoovered up by a carrier protein transferin

Front 39

Where does fat digestion predominantly occur?

Back 39

In the small intestine

Front 40

What enzymes break down lipids?

Back 40

Lipases

Front 41

What problem does the solubility of lipases and Triglycerides pose?

Back 41

Lipases are water soluble and TGs are not - TGs therefore aggregate into fat droplets. This presents a problem as the lipase would only be able to act on the surface of the fat droplets.

This would mean a very low surface area of action and thus a very slow rate of action.

Front 42

How are TGs prepared for digestion by lipases?

Back 42

TGs are emulsified into very small droplets. This is done by amphiphatic TGs binding to also amphiphatic bile salts.

Front 43

What does TG binding to bile salts prevent?

Back 43

TGs bound to bile salts will not reaggregate into a larger lipid droplet as they will repel each other - as their polar heads areas are exposed.

Front 44

What is the role of 'colipase'?

Back 44

Colipase lodges between the emulsifying bile salts and assists with lipase binding to the emulsification droplets. This solves the issue of a partially occupied reaction surface being occupied by emulsification molecules.

Front 45

What does phospholipase A2 cleave?

Back 45

Phospholipase A2 cleaves Lecithin into 1 x Fatty acid + Lysolecithin

Front 46

What do emulsified droplets further split down into?

Back 46

V small emulsification droplets called micelles which are made up of the products of fat digestion.

Front 47

Describe the process by which insoluble fat products manage to be uptaken by the gut.

Back 47

Some, a very small number, of fat digestion products exist in solution. These products become absorbed by the gut epithelium. Some fat digestion products then dissociate from their micelles. The cycle continues.

Front 48

What is the function of micelles?

Back 48

Micelles provide a means of keeping most of the insoluble fat digestion products in small soluble aggregates.

While at the same time replenishing the small amount of products in solution which are free to diffuse into the intestinal epithelium.

Front 49

What are chylomicrons made up of?

Back 49

TGAs, phopholipids, cholesterol and fat soluble vitamins covered wit han amphiphatic proein coat.

Front 50

What is the fate of a chylomicron?

Back 50

Exocytosed from the gut epithelium and then pass into Lacteals via large pores - lymphatic vessels on the intestinal villi and thus enter the lymphatic system.