GI Physiology Document notes Flashcards by Shubham Agwan

What are the 4 layers of the digestive tract

Mucosa
Submucosa
Muscularis Externa
Serosa (bock)

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What 5 things are in the mucosal layer

epithelial cells, 
exocrine cells, 
endocrine cells, 
lamina propria, 
muscularis mucosa

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What 3 things are in the submucosal layer

connective tissue,
lymph tissue,
submucous (meissner’s) plexus

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What 3 things are in the muscularis externa layer

circular muscle,
myenteric (Auerbach’s) plexus,
longitudinal muscle

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What is in the serosa bock

connective tissue

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The mucosa is the outermost layer

True or False

False

that would be the serosa bock

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Where does the primary salivary secretion come from

Acinar cells

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Which cells are responsible for the secondary modification of the primary saliva secretion

Ducts cells

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What do the duct cells do to the primary secretion

Remove Na & Cl

Add K & HCO3

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Parasympathetic saliva is…

Large volume
Watery
Enzyme rich

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Sympathetic saliva is…

Low volume
Thick
Mucus rich

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Parasympathetic control of saliva is mediated by which receptors and which NT

M1/M3 Ach receptors

VIP

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Sympathetic control of saliva is mediated by which receptors and which NT

α and B1-adrenoceptors

Doesn’t say but probes noradrenaline?

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What is the unconditioned (simple) salivary reflex

Activation of chemo/pressure receptors when food is in mouth leads to saliva production

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What is the conditioned (acquired) reflex

Saliva production due to thinking of, seeing or smelling food

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Which organ stores food before passing it to the small intestine

The stomach obviously

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What is chyme

The mixture of gastric secretions and partially digested food - formed in the stomach

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What gastric factors favour gastric emptying

Increased volume of chyme.

Finely divided chyme.

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What duodenal factors go against gastric emptying

High volume of fat in duodenum.
High volume of acid in duodenum.
Distension of duodenum.
Lots of products of carbohydrate/protein breakdown in duodenum.

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Which cells secrete HCL and where are they located

Parietal cells located in oxyntic mucosa

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What, apart from, HCl do parietal cells secrete and what is it’s function

Intrinsic factor

Binds to B12 to allow absorption in terminal ileum

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What are the 3 functions of HCL

Denatures proteins
Activates pepsinogen to pepsin
Kills micro-organisms

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Which cells secrete pepsinogen and where are they found

Chief cells

oxyntic mucosa

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What is pepsinogen

Inactive precursor of pepsin, activated by HCL

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Which cells secrete histamine and where are they located

Enterochromaffin like cell | Oxyntic mucosa

What is the function of histamine

Stimulates HCL production

Which cells secrete gastrin and where are they located

Secreted by G cells (duh) | Pyloric Gland Area

What is the function of gastrin

Stimulates HCL production

Which cells secrete somatostatin and where are they located

Secreted by D cells | Pyloric Gland Area

What is the function of somatostatin

Inhibits HCL production

What does vagal stimulation do in terms of acid secretion

Increases secretion of substances which stimulate acid production

Name 4 mechanisms protecting mucosa from HCL and pepsin

Hydrophobic monolayer Bicarbonate secretion Elimination of H+ in exchange for Na+ Locally produced prostaglandins which reduce acid secretion

How do NSAIDs cause gastric ulceration and bleeding

NSAID’s reduce prostaglandin formation by COX 1 INHIBITION; can lead to gastric ulceration and bleeding

Name 2 drugs which affect acid secretion

Protein Pump Inhibitors (PPI's) | H2 receptor antagonists

How do PPI's work and give an example

``` Inhibit active (membrane inserted) proton pumps omeprazole ```

How do H2 receptor antagonists work and give an example

Competitively antagonise H2 receptors Completely block histamine mediated acid secretion Ranitidine

Name the two types of pancreatic secretions

Endocrine Exocrine well done

Name the 2 endocrine secretions and where they are secreted

Insulin Glucagon secreted into bloodstream

Name the 2 exocrine secretions and where they are secreted to

Digestive enzymes Sodium bicarbonate Secreted into duodenum as pancreatic juice

Where are pancreatic digestive enzymes secreted from

Acinar cells

Where is sodium bicarbonate secreted from

Duct cells

What is the function of the sodium bicarbonate that is secreted from pancreatic duct cells

Neutralises acid chyme thus protecting mucosa and providing optimum pH for pancreatic enzymes

Which cells secrete secretin and what does it do

S cells funnily enough | Increases secretion of aqueous NaHCO3 solution into duodenum

What cells secrete CCK and what does it do

``` i cells (not C cells) Increases secretion of digestive enzymes into duodenum ```

Where is bile secreted from

Bile duct cells | Hepatocytes

The presence of what stimulates gallbladder SM to contract

Presence of chyme in the duodenum

What is the function of bile

Aids in the digestion of fat

Name 3 features of the small intestine which make it well adapted for absorption

Circular folds Villi Microvilli

What are the two types of starch

Amylose | Amylopectin

What is the difference between the two types of starch

Amylose only has α 1-4 bonds | Amylopectin has α 1-6 and α 1-4 bonds

Does glycogen have α 1-6 bonds

Yes | but more commonly than amylopectin (1 in 10 rather than 1 in 30 like amylopectin)

What does salivary α amylase do

attacks 1-4 glycosidic links

What breaks down sucrose

Sucrase | wow

What breaks down lactose

Lactase | na wa

What is sucrose made up of

GLUCOSE + FRUCTOSE

What is lactose made up of

GLUCOSE + GALACTOSE

How are proteins broken down in the stomach

HCl denatures proteins, pepsin cleaves proteins into peptides.

How are proteins broken down in duodenum

pancreatic enzymes split peptide bonds between amino acids, brush border enzymes cleave amino acids from amino end of molecule.

Hydrophilic amino acids are absorbed by passive diffusion | True or False

False | HydroPHOBIC amino acids are absorbed by passive diffusion

How does bile affect lipids

Emulsifies them to allow a larger surface area for pancreatic lipase to act

What is the co-factor that allows pancreatic lipase to do it's job

Co-lipase | incredible

What are free fatty acids and how are they absorbed

Short-medium length chains | Absorbed by passive diffusion

How are long chain fatty acids and mono-glycerides absorbed

Resynthesised into triglycerides in the ER and incorporated into chylomicrons

What are lacteals

lymphatic vessels of the small intestine

Which protein surrounds a chylomicron before it is incorporated into a lacteal

Apolipoprotein | ApoB-48

What is a chylomicron that isnt bound to ApoB-48 called

Nascent chylomicron

Where do chylomicrons drain to and via which vessel

Left venous angle | via thoracic duct