Lecture 21 - The Stomach and Pancreas

Question 1

The esophagus

Answer 1

Tube that connects the pharynx to the stomach
Posterior to the trachea

Muscosa - epithelium
Stratified squamous epithelium
Protection from abrasion

Muscularis - modified to propel food down to the stomach

Mucosa and submucosa are highly folded which gives the oesophagus the capacity to stretch/expand to accommodate the food bolus as it travels down to the stomach

Question 2

Location of the stomach

Answer 2

J shaped organ
Located at the base of the oesophagus
Esophagus passes through the diaphragm (esophageal hiatus = hole/break in the diagphragm that allows the oesophagus to open up into the stomach)
Lower esophageal sphincter (LES) prevents reflex - to allow the bolus into the stomach the lower oesophageal sphincter has to relax but once the bolus has entered the stomach the LES can contract to prevent reflex of acidic material back up into the oesophagus - reflect of acidic material can cause damage to the epithelial lining of the oesophagus which can lead to the sensation of heart burn

Question 3

Gross structure of the stomach

Answer 3

4 main parts = 
Cardia 
Fundus 
Body 
Pylorus (pyloric antrum) 

Important sphincter in this region of the stomach is called the pyloric sphincter which regulates the passage of the lumenal contents from the stomach into the first part of the small intestine called the duodenum - regulating the process of gastric emptying

Question 4

4 main parts of the stomach

Answer 4

4 main parts =
Cardia - The small region which the oesophagus opens up into
Fundus - Proximal region located up towards the diaphragm and it is an area where you find lots of gastric glands and gases produced as a byproduct of digestion will be able to rise up to here
Body - central portion of the stomach that makes up the bulk of it
Pylorus (pyloric antrum) - gatekeeper

Question 5

Lesser curvature

Answer 5

Concave notch that is more medial in the stomach

Question 6

Greater curvature

Answer 6

Convex area that is a little more lateral in the stomach

Question 7

Omentum

Answer 7

Way to remember = O equals organ to organ

A double layer of peritoneum that connects one organ to another

Question 8

Greater omentum

Answer 8

Stomach to transverse colon

Contains a significant cluster of immune cells
A few blood vessels running through here but also lots of adipose so the greater momentum is going to provide some cushioning anteriorly

Question 9

Lesser omentum

Answer 9

Stomach to the liver

You find important verse structures like blood vessels that are faint to and from the liver

Question 10

Modifications of the gut tube for the stomach

Answer 10

The 4 layers of the gut tube is modified to carry out specific functions

Muscularis = motility
Thicker in the distal region of the stomach than in the proximal region such as the fundas because we actually need a lot more contractility to happen distally to aid in mechanical and chemical digestion therefore thickest distally

3 layers
Oblique (inner)
Circular (middle)
Longitudinal (outer)

Question 11

3 layers of the stomach

Answer 11

3 layers
Oblique (inner)
Circular (middle)
Longitudinal (outer)

The layers allows the stomach to contract and churn in many different directions

Question 12

Internal surface of the stomach

Answer 12

Rugae are temporary folds that allow for the expansion of the stomach
These have an important storage function
Spincters are also important in the storage function - sometimes have to keep food material in the stomach for 2-3 hours to allow for mechanical and chemical digestion to take place and in order t=for this we need the pyloric sphincter and the lower oesophageal sphincter to be closed

Question 13

Rugae

Answer 13

Rugae are temporary folds that allow for the expansion of the stomach

Rugae are important for the storage function of the stomach, because when the stomach is empty it can collapse and shrink to a small size and after a big meal the rug can flatten out in order to allow the stomach to expand and increase its volume to accommodate the arrival of the food material

Have a folded core of submucosa with overlying mucosa
Submucosa is the core of the rugae - it is because of the connective tissue elements of the submucosa that the rugae are able to flatten out and accomodate the food material
Mucosa is also folded into simple gastric glands but unlike the rugae, these glands of mucosa are permanent structures so even when the rugae are flattened out these glands remain in tact

Question 14

Gastric glands - modification of the gut tube

Answer 14

Mucosa
Simple columnar epithelium
In-folding increases surface area for secretion (1.5L/day). When you infold into the lamina propriety underneath you form simple gastric glands.
Glands are permanent
Glands are not in the submucosa or muscular

We need
Acid and enzymes for digestion
Mucous for protection
Hormones for regulation

Question 15

Cells of the gastric glands

Answer 15

Mucous epithelial cells
Parietal cells
G cells
Chief cells

Question 16

Mucus epithelial cells

Answer 16

Secrete mucus for protection

These are close to the surface, in the neck of the gastric glands are the mucus secreting cells and they provide an alkaline mucus layer that protects the epithelial lining of the stomach from the acid and enzymes that will be secreted

Question 17

Parietal cells

Answer 17

Secrete acid and intrinsic factor
Particularly hydrochloric acid and intrinsic factor which is important for vitamin B12 absorption

Parietal cells produce acid
Pump ions (H+) - to secrete HCl, we need to be able to pump ions against their concentration gradient and to pump ions against their concentration gradient we are going to need a lot of energy in the form of ATP so they have an abundance of mitochondria to provide this energy to power the proton pumps
Abundant mitochondria
Central nucleus
Folded structure to increase surface area - if we increase the membrane surface area we will be able to fit a lot more ion pumps in so that we can carry out a lot more acid secretion

Question 18

G cells

Answer 18

Secrete hormones (gastrin) 
Secretes hormones into the blood and gastrin is important for regulating the motility and secretatory events in the stomach

Question 19

Chief cells

Answer 19

Secrete pepsinogen (an inactive precursor of pepsin, pepsin is important for protein digestion)

Chief cells produce enzymes
They have an abundant rough endoplasmic reticulum because this is the protein producing organelle and this therefore makes enzymes
Apical zymogen granules (contains enzymes) - zymogen is another word for enzyme, and these little granules are important for transporting the enzymes towards the apical membrane where they can be exocytosed and secreted into the lumen
Basal nucleus - since apical aspect is so packed full of zymogen granules other organelles like the nucleus get forced to the basal aspect of the cell

Question 20

Zymogen

Answer 20

Another word for an enzyme

Question 21

Regulation of stomach function

Answer 21

Endocrine control
Endocrine cells in mucosa
Gastrin and Ghrelin secreted into the bloodstream (Ghrelin is sometimes referred to as the hunger hormone)
Hormones are secreted into the blood stream and there are blood vessels located in the lamina propria close by to the gastric glands

Neural control
Enteric nervous system (ENS) - local reflexes (primary control)
CNS modulates ENS function - long neural reflexes

Question 22

What do we need to control the passage from the stomach to the small intestine?

Answer 22

Need controlled release of the digested material (chyme) into the small intestine therefore there is the pyloric sphincter

Big difference in diameter between the stomach and the first region of the small intestine, the duodenum, and this means that you cannot just unload all of the contents from the stomach into the duodenum at once and we actually need to control the rate of gastric emptying and release the material into the small intestine at a rate that it can handle which brings us back to the gatekeeper function of the pyloric sphincter

Question 23

Chyme

Answer 23

Digested material that is released into the small intestine, it is quite acidic

Question 24

Pyloric sphincter

Answer 24

Thickened region, contracts to prevent movement from the stomach to the duodenum and can relax to allow the passage of lumenal contents

Question 25

Stomach to small intestine

Answer 25

Acidic chyme enters the small intestine

Requires: (by now all the mechanical digestion has probably been done so it is now just going to require some further chemical digestion using enzymes) 
Further digestion (enzymes) 
Protection from acidic chyme - mucous and a way to neutralise the acid (bicarbonate) 

Mucus is provided by the glands in the submucosa of the duodenum. Enzymes and bicarbonate provided by the pancreas (the bicarbonate neutralises the acid)

Question 26

Pancreas location

Answer 26

Head in C shaped duodenum (wider part of the pancrease)
Tail to spleen
Posterior to the stomach
Duct into duodenal lumen
Reteroperitoneal - sits behind the peritoneum i.e. peritoneum is on the anterior side
Has important endocrine secretions such as insulin and the exocrine secretions are carried through the duct into the lumen of the duodenum

Question 27

Duodenum location

Answer 27

Most of the duodenum is actually reteroperitneal because it doesn’t need to carry out any movement to fulfil its function as all it needs to do is receive chyme from the stomach and to receive secretions coming from the pancreas (enzymes and the bicarbonate)

Question 28

Pancreas

Answer 28

Bile duct meets the pancreatic duct at the entrance to the hepatopancreatic ampulla
Duodenal papilla - projects into the duodenal lumen
Release controlled by hepatopancreatic sphincter

Question 29

Endocrine and exocrine functions

Answer 29

Endocrine
Pancreatic islet alpha cells secrete glucagon
Pancreatic islet beta cells secrete insulin

Exocrine
Acinar cells secrete digestive enzymes - enzymes get secreted into the ducts and travel along and the duct is also lined with cells which produce the bicarbonate which helps neutralise the acidity of the chyme coming into the small intestine
Ducts cells secrete bicarbonate

Secretions into the lumen in the GI tract are technically secretions to the outside of the body because the lumen is just an extension of the outside world hence it is exocrine

Question 30

Pancreatic acinar cells

Answer 30

Structure
Apical zymogen granules
Basal nucleus
Abundant rER

Function
Secrete enzymes

Similar to the chief cells of the stomach and salivary acinar cells (same function as trying to produce enzymes)

Question 31

What structures allow storage in the stomach?

Answer 31

Sphincters

Rugae

Question 32

What do you need for mechanical digestion in the stomach?

Answer 32

Smooth muscle - additional oblique layer in the stomach

Spincter (material being pushed up against a closed sphincter helps to churn it)

Question 33

What is needed for chemical digestion in the stomach?

Answer 33

Secretion of strong chemicals (acids, enzymes)

Protective epithelium