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50 Cards in this Set

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


Why?

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.

What functions does that pancreas have?

1. Exocrine functions


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


2. Endocrine functions



What is the role of the gall bladder?

Stores bile



What is a critical component of bile?

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

What are the crucial components of the small intestine wall?

1. Villi
2. Submucosa
3. Muscularis Externa
4. Serosa
5. Myenteric plexus


1. Villi


2. Submucosa


3. Muscularis Externa


4. Serosa


5. Myenteric plexus

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

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

What is the submucosa?

Layer below the mucosal layer - a connective tissue layer.

Describe the submucosal plexus.

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

What is the muscularis externa?

The GI smooth muscle

What are the layers of the muscularis externa?


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



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


2. Longitudinal muscle - Contraction shortens the GI tract.

What lies between the two layers of the muscularis externa?

A further neuronal network - the myenteric plexus

What is the role of the myenteric plexus?

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

Describe the structure of starch.

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

What is glycogen?

A basic glucose polymer

What are the main disaccharides?

1. Sucrose (glucose + fructose)


2. Lactose (glucose + galactose)

How are carbohydrates digested?

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

How is fructose absorbed into the gut epithelium?

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

How are glucose and galactose absorbed into the gut epithelium?

Cotransported via a symporter - Sodium glucose transporter (SGLT)

How are carbohydrate monomers absorbed into the blood?

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

How are proteins digested?

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

What produces pepsinogen in the stomach?

Produced by 'Chief cells' in gastric mucosa

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

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

What effect does choleycystokinin (CCK) have on digestion?

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

How are protease zymogens activated?

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

What are the brush border peptidases?

1. Endopeptidases


2. Aminopeptidases


3. Carboxypeptidases


4. Dipeptidases

When and how can proteins begin to be absorbed?

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.

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

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.

What are the two types of dietary iron?

1. Haem iron - attached to proteins


2. Non - Haem - free iron.

What are the basics of Iron absorption?

Iron is actively absorbed into the intestinal epithelial cells.

Describe the processes of iron transportation into the gut epithelium.

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

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

the DMT1 symporter

How does Iron enter cells?

The Heme carrier protein 1 (HCP1) channel

How is Iron effectively used in cells?

1. Binds to Ferritin - Intracellular Fe store



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

Fe++ can bind directly to ferritin


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

How does Iron leave the cell?

Dissociates from ferritin and must be oxidised before leaving.

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

Ferroxidase

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

Ferroportin

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

Hoovered up by a carrier protein transferin

Where does fat digestion predominantly occur?

In the small intestine

What enzymes break down lipids?

Lipases

What problem does the solubility of lipases and Triglycerides pose?

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.

How are TGs prepared for digestion by lipases?

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

What does TG binding to bile salts prevent?

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.

What is the role of 'colipase'?

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.

What does phospholipase A2 cleave?

Phospholipase A2 cleaves Lecithin into 1 x Fatty acid + Lysolecithin

What do emulsified droplets further split down into?

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

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

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.

What is the function of micelles?

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.

What are chylomicrons made up of?

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

What is the fate of a chylomicron?

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.