The Digestive System Flashcards
Name the structures of the alimentary canal (GI tract) from mouth to anus.
Mouth Tongue Pharynx Oesophagus Stomach Small intestine Colon of large intestine Appendix Rectum Anus
What are some accessory organs of the digestive system?
Salivary glands
Pancreas
Liver
Gall bladder
What are the 4 layers of the gut wall?
Mucosa
Submucosa
Muscularis externae
Serosa
What is the structure of the mucosa of the gut?
Epithelium
Lamina propria
Muscularis mucosae
What is the lamina propria?
Middle layer of the mucosa
Layer of connective tissue with peyer’s patches/mucosal glands
What is the structure of the submucosa layer of the gut wall?
Connective tissue with vessels, veins and glands
What is the structure of the muscularis externae of the gut wall?
2 layers of smooth muscle
Inner circular layer
Outer longitudinal layer
What is the structure of the serosa layer of the gut wall?
Serous membrane
Mesothelium + thin layer of CT
What is mesothelium?
The simple squamous epithelium found in serous membranes
What is the function of the muscularis externae?
Contracts to create successive peristaltic waves - moving contents of lumen along the gut
What is digestion?
The conversion of what we eat into a solution from which we absorb our nutrients
What are some functions of the GI tract?
Provides a port of entry for food into the body Mechanical disruption of the food Chemical digestion of the food Kills pathogens in the food Nutrients absorbed Waste eliminated
What enzymes does saliva contain, what are the functions of these?
Amylase, lipase - to begin chemical digestion of the food
What are the bacteriostatic features of saliva?
Contains IgA
Where is IgA secreted?
Throughout the GI tract
What are some features of saliva?
High in calcium (protecting the teeth) Bacteriostatic (IgA) Contains digestive enzymes Alkaline Assists in swallowing Protects the mouth
What is a bolus?
Circular mass of food
Where does the bolus move once it has been formed in the mouth?
Oesophagus
What muscle is present in the oesophagus?
Upper end (voluntary) - contains skeletal muscle Lower end (involuntary) - contains smooth muscle
What is the structure of the wall of the oesophagus?
Same as normal gut wall layer but NO serosa –> adventitia (connective tissue) instead
Why does the oesophagus not contain serosa in its wall?
It is not surrounded by a serous membrane and is outside the peritoneum
What innervation is found in the walls of the gut?
Submucosal plexus (found between submucosa and muscle) Myentric plexus (found between external layers of muscle)
How is food physically disrupted in the stomach?
By churning
How is food chemically disrupted in the stomach?
Digestion by HCl and pepsin (enzyme)
In what way does the stomach contract?
Rhythmically
What epithelium is found in the oesophagus?
Stratified squamous epithelium
What does the stomach produce that passes to the duodenum of the small intestine?
Hypertonic chyme
What is chyme?
Produced in the stomach, partially digested food and gastric juices that pass to the duodenum
What epithelium is found in the GI tract (excluding the oesophagus)?
Simple columnar
What does the mucosa secrete in the stomach?
Acid, enzymes and the hormone GASTRIN
What is the structure of the wall of the stomach?
Same as usual with its 4 layers EXCEPT
Muscularis externae contains 3 layers of smooth muscle
Oblique, circular and longitudinal
What are rugae? Where do they exist?
Folds of mucosa forming ridges
In the stomach
Where are surface mucous cells found? What is their function?
In the gastric pits in the stomach
Secretes mucus in response to distension
What are some features of mucus?
Is resistant to pepsin
Contains HCO3- which neutralises the H+ protecting the stomach lining
What sort of cell renewal do surface mucous cells show?
Quickly divide by mitosis if damaged by aspirin/alcohol
What is the position and shape of the duodenum in the body?
Start of the small intestine
C shaped
Curved around the head of the pancreas
Which organs does the duodenum connect with?
Pancreas
Liver
What structure secretes mucus in the duodenum?
Brunner’s glands
What mixture does the duodenum receive from the stomach?
Acid chyme
What is the function of the duodenum?
To neutralise and dilute the chyme
What does the duodenum receive from the pancreas?
Pancreatic juices
What does the duodenum receive from the liver?
Bile (via the gallbladder)
How is chyme neutralised in the duodenum?
Bile is alkali
Alkali secretions from the pancreas/liver
How is chyme diluted in the duodenum?
Water drawn in from extracellular fluid
The pancreas, liver and intestine secrete specific _____ to complete digestion of chyme
Enzymes
What does absorption of nutrients from solution require?
Large surface area
Adequate contact time
Energy - is an active process
Good blood supply/drainage
What is the surface area found in the small intestine?
Very large due to folding
What is the structure of the jejunal wall?
Same + mucosa contains microvilli
What are pilcae circulares?
Long extensions of the mucosa/villi found in the jejunum
What parts does the small intestine consist of?
Duodenum
Jejunum
Ileum
What nutrients does the duodenum absorb?
Iron
What nutrients does the jejunum absorb?
Sugars, amino acids and fatty acids
What nutrients does the ileum absorb?
Vitamin B12, bile acids and remaining nutrients
By the time the contents of the small intestine pass to the colon of the large intestine, what has been absorbed and what still needs to be absorbed?
Nutrients have been absorbed
Water needs to be absorbed
What are the different parts of the large intestine?
Caecum Ascending colon Transverse colon Descending colon Sigmoid colon Rectum Anus
What is the structure of the wall of the large intestine?
Same 4 layers as normal
Mucosa form numerous Krypts of Lieberkuhn
What is absorbed in the large intestine? And by which cells?
Water and electrolytes
Surface epithelial cells
What mixture exits in the lumen of the large intestine once it has passed through?
A semi-solid content that awaits expulsion
Where is most of the bacteria in the GI tract found? How is most of it lost?
In the colon
In faeces
What is bacteria in the colon useful for?
Synthesis of vitamin K, B12, thiamine, riboflavin
Breakdown of bilirubin and bile acids
By which 3 methods is the gut controlled?
Endocrine control
Paracrine control
Neural
What is an example of paracrine control in the gut?
Release of histamine - controls production of acid in the stomach
Vasoactive substances affecting blood flow in the gut
What are some examples of neural control in the gut?
Control of ingestion and excretion due to skeletal muscle
Autonomic nervous system controls the rest
Generally the gut is controlled by hormones made in the _____
Gut
What is the function of secretin in the gut?
Hormone
Promotes HCO3- secretion from duct cells of pancreas
Promotes production of bile in liver
Inhibits acid secretion by parietal cells of the stomach
Where is cholecystokinin (CCK) produced/secreted?
Enteroendocrine cells of the duodenum
What is the function of CCK in the gut?
Promotes bile release from gallbladder
Promotes digestive enzyme release from pancreas
Acts as a hunger suppressant
Where is gastrin released and by which cells?
G cells of the stomach, pancreas and duodenum
What is the function of gastrin?
Promotes production of HCl by parietal cells of the stomach
