Functional Histology of the Gut Flashcards
What structures does the oral cavity consist of?
salivary glands and teeth
What is the function of the oral cavity and what type of epithelia is present?
ingestion, fragmentation and has stratified squamous epithelium
What do the simple passages of the alimentary tract consist of, what’s their function and what type of epithelium is present?
Oesophagus and anus, involved in transport of food and waste and has stratified squamous epithelium
What does the main body of the digestive tract consist of, and what is it’s function?
stomach, intestines and glands which are involved in digestion and absorption
What type of epithelium is present in the stomach?
simple columnar epithelia
What type of epithelium is present in the small intestine?
simple columnar of villi
Name the 4 components of nutrient absorption and elimination
fragmentation, digestion, absorption and elimination
Describe ‘fragmentation’
where food is chewed and broken down by enzymes in the oral cavity using saliva containing amylase
Describe ‘digestion’
where food is broken down by enzymes in the stomach and duodenum
Describe ‘absorption’
where enterocytes absorb nutrients and capillaries and lacteals transport these nutrients from the mucosa
Describe ‘elimination’
liquid residue is passed to the colon where water is absorbed from it and solid faeces is expelled through the anal canal
Outline the structures that food passes through after it is ingested
mouth, oropharynx, oesophagus, stomach, duodenum, jejunum, ileum, large intenstine, anus
What are the four basic layers of the wall of the alimentary tract?
1) mucosa
2) submucosa
3) muscularis propria
4) serosa/adventitia
Describe the mucosa of the gut wall
consists of a lumen, epithelium, lamina propria and muscularis mucosae and varies with region and function
Describe the submucosa of the gut wall
this is a thicker layer of fibrocollaginous tissue which carries vessels and nerves as well as the submucosal neural plexus
Describe the muscularis propria of the gut wall
this consists of two layers; an inner circular layer and an outer longitudinal layer
Describe the adventitia/serosa of the gut wall
the most external part of the gut wall
When is the outside called the adventitia?
where the gut is retroperitoneal it is called adventitia, is referred to as serosa when intraperitoneal
Describe what is meant by the enteric nervous system
consists of autonomic functioning ganglia with inputs from the parasympathetic and sympathetic nervous systems
What does the submucosal plexus innervate?
muscularis mucosae and mucosal glands
What does the myenteric plexus innervate?
muscularis propria (inner circular and outer longitudinal layers)
Define ‘MALT’
mucosa associated lymphoid tissue
Define ‘GALT’
gut associated lymphoid tissue
Name four characteristics that prevent gastroesophageal reflux
the oesophagus joins the stomach at an acute angle (at the cardia), the contracn of the diaphragm on the oesophagus prevents reflux, intra-abdominal pressure on the oesophagus at rest prevents reflux, there is unidirectional peristalsis
Describe the mucosa in the oesophagus
non-kertainised stratified squamous epithelium
Describe the submucosa in the oesophagus
contains mucous glands, blood vessels, nerves, ganglion cells and lymphoid tissue
Describe the muscularis propria in the oesophagus
the top 1/3 is skeletal muscle to facilitate swallowing and bottom 2/3 is smooth muscle for peristalsis
Does the oesophagus have adventitia or serosa?
adventitia
Outline the gross anatomy of the stomach
cardia, body, fundus (above body), antrum, pylorus then duodenum
Which secretions are facilitated in the cardia of the stomach?
mucus from mucous neck cells
Which secretions are facilitated in the fundus/body of the stomach?
mucus from mucous neck cells, HCl and intrinsic factor from parietal cells, pepsin from chief cells and gut hormones from endocrine cells
Which secretion are facilitated in the pylorus of the stomach?
mainly mucus from MNC and gut hormones from endocrine cells
How many layers are there in the muscularis propria of the stomach?
Three instead of two: inner oblique, middle circular and outer longitudinal
How do parietal cells appear in a stain?
have a lot of cytoplasm and central nucleus
How do chief cells appear in a stain?
dark staining and are smaller
How do mucous neck cells appear in a stain?
small cells with light staining within the epithelium
What is the pyloric sphincter?
a marked thickening of the circular layer of the muscularis propria
Describe the structure of the duodenum
has Brunner’s glands in the submucosa (secrete alkaline mucus), receives bile and pancreatic juice through the ampulla of vater controlled by the sphincter of oddi
Describe the structure of the jejunum
has the most specialised surface area for absorption
Describe the structure of the ileum
greatest amount of GALT in the form of Peyer’s patches
What are the plicae circulares?
circular folds including the submucosa in the jejunum and ileum
What are villi?
extensions of the mucosa that possess the central core of the lamina propria and at their bases are the crypts of Leiberkuhn
What are microvilli?
apical processes known as the brush border
What are the crypts of Leiberkuhn
the crypts of the small intestine, which have a secretory and stem cell role
Describe the lamina propria of the cells of the small intestine
there is areolar connective tissue containing strands of smooth muscle from the muscularis mucosae as well as GALT
Which cells of the small intestine are involved in absorption?
villus enterocytes
Which cells of the small intestine are involved in secretion?
crypt enterocytes
What types of cells are found in the crypts of Leiberkuhn in the small intestine?
endocrine cells, stem cells (involved in epithelium regeneration) and paneth cells (secrete antimicrobial agents)
Describe the histology of the large intestine
abundant goblet cells, no villi, and the outer longitudinal muscularis propria is organised into 3 bundles known as taeniae coli which act to sacculate the colon and form haustra
What is taeniae coli?
three separate longitudinal ribbons of smooth muscle on the outside of the ascending, transverse, descending and sigmoid colon
What is haustra?
small pouches which give the colon its segmented appearance
