Gastrointestinal Lab Flashcards
What four types of vessel like structures would you expect to see running through the mesentery?
Arteries, veins, lymphatics and nerves
Peristalsis and segmentation
Peristalsis is responsible for the movement of food through the gastrointestinal tract, whereas segmentation is responsible for the mixing of the food with secretions and exposure of the digestive products to the absorptive surfaces. Segmentation is NOT a form of mechanical digestion.
Components of the small intestine and the function of the small intestine
The small intestine is comprised of three segments: the duodenum, the jejunum and the ileum. The primary function of the small intestine is to complete the digestion of the food material and absorb the products of digestion as well as water and salts.
Which basic tissue type must be present in the gut tube to modulate digestive motility
Nervous tissue
How does peristalsis help to move food through the small intestine?
Contraction of the smooth muscle behind the food bolus helps to propel/push food material along the GI tract at an appropriate rate.
How does segmentation assist with digestion and absorption of material in the small intestine?
By constantly turning over the chyme, it exposes the chyme to the enzymes allowing for digestion and then brings those products of digestion to the absorptive surface so that can be absorbed into the body.
Why is segmentation described as a “mixing” motility pattern, rather than a component of mechanical digestion?
Because mechanical digestion of the food has already occurred in the mouth and the stomach.
Segmentation allows for mixing of chyme with enzymes responsible for the final stages of digestion.
Stomach regions and function
The stomach is divided into four regions, the cardia, fundus, body and pylorus (sometimes referred to as the antrum). The fundus is at the proximal end (adjacent to and above the opening of the esophagus), the body is the central region of the stomach and the pylorus is the distal region of the stomach (which connects to the small intestine).
The body and pylorus (antrum) have a significantly thicker layer of smooth muscle than the fundus, which aids in increasing contractility and therefore aiding in the mechanical digestion of food material.
Two possible functions of rugae
Allows for the expansion of the stomach without increasing the pressure.
Increases the surface area of the mucosa and therefore increases the number of chief and parietal cells.
Which region of the stomach displays a greater degree of movement- the fundus or pylorus (antrum)?
Pylorus (antrum)
Motility pattern in the pylorus (antrum)
Mechanical and chemical digestion
Pyloric sphincter
Modulates the passage of chyme from the stomach into the initial part of the small intestine (the duodenum)
The esophagus pierces the diaphragm, and runs for about 3-4 cm in the abdominal cavity before it enters the stomach. At the proximal end of the stomach, the lower esophageal sphincter or cardiac sphincter is present as a thickening of smooth muscle. What is the function of this sphincter?
Constricts the esophagus to prevent reflux/backflow of stomach contents.
Regions involved with mechanical digestion
Mouth and stomach
Regions involved with storage
Stomach, colon and rectum
Regions involved with movement
Throughout the whole tract
Regions involved with mixing
Mouth, stomach, small and large intestine
Regions involved with exposure to absorptive surfaces
Small intestine (and to a lesser extent large intestine)
Expulsion
Anal canal
Exocrine components of the pancreas
In the exocrine component, the pancreas is arranged into an acinar structure (which means grape-like) and the secretions produced by each acinus are emptied into a small duct. These ducts then all join to form the main pancreatic duct, which empties into the duodenum.
Describe how there structure of the chief cell is specialised for its function
Chief cells secrete enzymes (pepsinogen). Because of this they have abundant rough endoplasmic reticulum to produce proteins. They also have numerous apical zymogen granules to transport the enzymes to the apical membrane where they will be secreted into the lumen. The nucleus has a basal location.
Describe how the structure of the parietal cell is specialised for its function
Parietal cells secrete acid. To do this the cell must pump H+ against its concentration gradient. This requires energy and so the parietal cells have abundant mitochondria. They are also highly folded when active to increase the surface area for secretion.
Name the basic tissue that has been modified to form this secretory tissue of the pancreas
Epithelial tissue
Peritoneum
When the peritoneum lines the walls of the abdominal cavity it is called parietal peritoneum; when it is deflected from the wall and lies on the surface of the organs it is called the visceral peritoneum. The visceral peritoneum is continuous with the parietal peritoneum and therefore holds the abdominal organs in place. Some organs lie against the abdominal wall and are termed retroperitoneal.
The lesser and greater omentum
The lesser omentum, which attatches the lesser curvature of the stomach to the liver, and the greater omentum, which attaches the greater curvature of the stomach to the transverse colon. The greater omentum drapes down over the intestines like an apron and is important in preventing the spread of infections.
How does the greater omentum prevent the spread of infection?
The greater omentum contains clusters of immune cells
What normally anchors the small intestine to the abdominal wall?
The mesenteries
If the appendix ruptured, which space would pus be released into?
Peritoneal cavity. This would cause inflammation of the peritoneum covering the cecum and adjacent small intestine.
Mucus
Lubricates the gastrointestinal tract, limiting the amount of abrasion that will occur as the food passes through the tract and protects the stomach lining from corrosive acid. Secreted throughout the tract
Enzymes
The enzymes carry out digestion of the food material. Secreted in the mouth, stomach and small intestine.
Serous fluid
Dissolves the food material and also creates the optimum condutions for the function of the various digestive enzymes. Secreted in mouth and small intestine.
Gastrin
Gastrin is formed by cells in the gastric mucosa and stimulates the secretion of gastric juice.
Gastric inhibitory peptide
The presence of fats in the small intestine stimulates the production of Gastric Inhibitory peptide which inhibits gastric secretion and motility.
Secretin and cholecystokinin
Secretin stimulates the secretion of pancreatic juice rich in bicarbonate whereas Cholecystokinin (CCK) stimulates the secretion of pancreatic juice rich in digestive enzymes.
Main cation and anion of salivary glands
pH and volume per day
1.5L/day
pH=7.5
Cation = Na+
Anion = HCO3-
Main cation and anion of stomach
pH and volume per day
3.0L/day
pH = 1
Cation = H+
Anion = Cl-
Main cation and anion of pancreas
pH and volume per day
1.5L/day
pH=7.8
Cation = Na+
Anion = HCO3-
Main cation and anion of liver
pH and volume per day
0.5L/day
pH=7.5
Cation = Na+
Anion = Cl-
Main cation and anion of plasma
pH and volume per day
Not volume per day
pH = 7.4
Cation = Na+
Anion = Cl-
Why doesn’t the hydrolysis of starch by amylase continue in the stomach?
No, the amylase is denatured by the acidic contents of the stomach
What enzyme is secreted in the stomach?
Pepsinogen is secreted. It is then converted to the active enzyme pepsin by the acidic environment in the stomach.
What effect would an acidic pH have on the rate of digestion of proteins in the stomach?
It would increase the rate as pepsin has an acidic optimum.
Why does the pancreas secrete a large amount of bicarbonate?
To neutralise the acid delivered from the stomach into the duodenum, thus raising the luminal pH. This is necessary as the optimum pH for operation of the pancreatic and intestinal enzymes is alkaline.
What are the three layers of the musculature in the muscularis externa, going from the innermost region (closest to the lumen) to the outermost region?
Oblique (innermost)
Circular (middle)
Longitudinal (outermost)
What did the detergent do in the mechanical digestion of food in the GI tract experiment?
The detergent stabilises the emulsion droplets by coating them and preventing them from coercing again
The ‘detergent’ secreted into the GI tract to assist with the emulsification and digestion of fats is bile salts/ lecithin
When the villi move there is localised mixing of gut contents. Which structures causes this movement?
Muscularis mucosae
Why are there so many blood vessels in the lamina proprietary of the villus
To take away absorbed nutrients
Functions of mucus in the small intestine
To protect the epithelium
Which products of digestion are linked to the active absorption of sodium by transport proteins?
Amino acids and monosaccharides
Which products of digestion are absorbed by simple diffusion through the epithelial cell membranes?
Monoglycerides and fats
There are not many villi in the mucosa of the large intestine…what does this indicate about its function ?
Little nutrient absorption occurs so the villi aren’t necessary
