L23 Digestive System Flashcards
What is the alimentary tract of the digestive system?
The main path from mouth to anus - a muscular tube, lined internally by an epithelium. While the epithelial type varies along the length of the tract, the structure of the musculature remains similar throughout.
The functions of the alimentary tract are supported by accessory organs.
What accessory organs support the function of the digestive system?
Salivary glands: secretes enzymes and lubricants
Liver: secretes bile, stores nutrients
Gallbladder: stores and concentrates bile
Pancreas: secretes buffers, digestive enzymes and hormones
What is the major histology of the oral cavity?
Lined by stratified squamous epithelium
Filiform, fungiform, circumvallate and foliate are all types of what?
Lingual papillae - they cover the surface of the tongue and are involved with taste
What type of tissue lines the oesophagus? Does it change?
Above the diaphragm it is lined by stratified squamous epithelium; this changes to columnar epithelium below the diaphragm.
The duodenum, jejunum and ileum are all parts of which organ?
The small intestine
The caecum, appendix, colon and rectum are all parts of which organ?
The large intestine
Define ‘fundus’.
the part of a hollow organ (such as the uterus or the gall bladder) that is furthest from the opening.
e. g.
- the upper part of the stomach, which forms a bulge above the level of the opening of the oesophagus (furthest from the pylorus).
- the part of the eyeball opposite the pupil.
In the digestive system, which common layer is closest to the digestive lumen?
Mucosa
Mainly composed of columnar epithelial cells.
Lamina propria is loose connective tissue that provides vasculature and immunocompetency.
Describe the submucosa of the digestive tract.
2nd layer - made of connective tissue
Separates mucosa from muscle
Contains neural tissue - submucosal (Meissner’s) plexus
Describe the muscularis externa of the digestive tract.
3rd layer, made of 2 layers of smooth muscle (inner circular layer and outer longitudinal layer) that allows peristalsis.
Contains myenteric (Auerbach’s) nerve plexus.
Describe the serosa and adventitia of the digestive tract
Outermost layer(s), covers muscularis and delimits alimentary canal.
Serosa (visceral peritoneum) is outermost layer when it lies adjacent to peritoneal cavity - which is most of it.
Adventitia is outermost layer when connected to surrounding tissue.
Which parts of intestines have an outer serosa?
Majority of small and large intestine except part of duodenum and an area of the colon.
Where in the alimentary tract will you not find any serosa?
Oral cavity, pharynx, oesophagus, and rectum.
What is a mesentery?
A double layer of visceral peritoneum that attaches organs to the abdominal wall.
The adventitia is made of what type of tissue?
Fibrous connective tissue
What are the four anatomical regions of the stomach?
Cardia, fundus, corpus (body), pylorus
What muscular layer forms part of the stomach mucosa?
Muscularis mucosae
Muscularis externa of the stomach is made of which three layers?
Oblique, circular, longitudinal
What are ‘rugae’?
Gastric folds (in the stomach) that are apparent when the stomach is empty but disappear when stomach is distended.
What epithelium is found in the stomach?
Columnar
Why does the gastric mucosa contain lots of glands?
Mucus is secreted to cover the stomach in order to protect it from stomach acid.
Define zymogenic
Produces enzymes
Where do you find gastric glands?
In cardia region of stomach.
These are heavily branched, mucus-producing glands.
Where do you find principal glands?
In the corpus-fundic region of the stomach.
Various types:
- Mucus neck cells
- Chief cells (produce enzymes)
- Parietal cells (produce acid)
- Enteroendocrine cells (stimulate secretion in other cells)
Pyloric glands
- More coiled than principal glands
- More endocrine cells
- No chief cells
What is the function of plicae in the muscosa of the small intestine?
Increase surface area x3
Plicae increase the intestinal surface area by 3 times. How much do villi increase the surface area? What about microvilli?
Villi: x10
Microvilli: x20
What are Crypts of Lieberkuhn?
Tubular glands in the mucosa of the small intestine.
Extend from base of villi, through lamina propria to muscularis mucosae.
Paneth cells at base secrete intestinal juice and control infection.
Where are the cells found that regenerate the intestinal epithelia?
Undifferentiated stem cells at the base of Crypts of Lieberkuhn.
Where do you find Brunner’s glands?
In the submucosa of the duodenum only.
They secrete mucus to protect the duodenal lumen
What is the main function of the large intestine?
Reabsorb water and inorganic salts
What are the three main sections of the large intestine?
- Caecum (inc. appendix)
- Colon (ascending, transverse, descending, sigmoid)
- Rectum (inc. anal canal)
True or false: The mucosa of the large intestine is covered in plicae and villi.
False.
The mucosa has a smooth surface.
True or false: The mucosa of the large intestine contains Crypts of Lieberkuhn.
True.
They are longer here than in the small intestine.
True or false: Goblet cells are more numerous in the large intestine than in the small intestine.
True.
How many layers are found in the muscularis mucosae of the small and large intestines?
Two
Does the large intestine have many or few endocrine cells?
Few.
How does the histology of the anal canal change through its length?
Proximally (colorectal zone) it is simple columnar epithelium.
This changes to stratified columnar/cuboidal in the anal transitional zone.
At the distal end (squamous zone) it is stratified squamous.
What are ‘haustra coli’?
Sacculations of the colon
What are ‘taenia coli’
Three flattened strips of muscle that run along the large intestine.
Where in the digestive tract would you find the ‘oblique layer’?
In the submucosa of the stomach
Where in the digestive tract would you find bile and pancreatic ducts?
Duodenum
Where in the digestive tract would you find Brunner’s glands?
Submucosa of the duodenum.
