Flashcards in Metabolism Histology (Alimentary System) Deck (51):
Name the 4 phases of nutrient absorption
Fragmentation, digestion, absorption, elimination
What is MALT?
Mucosa associated lymphoid tissue - in lamina propria of GI tract with organised lymphoid aggregates
Where is MALT found?
Lamina propria of cells in the GI tract
What are Peyer's patches?
Lymphoid follicles in the ileum of the small intestine
Where are Peyer's patches found?
Describe IgA secretion in the gut?
Synthesised by plasma cells as monomer --> forms dimer (joined by J-linkage) --> binds to poly-Ig receptor on basolateral surface (secretory component attached)--> internalisation --> transported across mucosa --> secreted into gut lumen (secretory component protects from proteolysis)
What is the role of the secretory component in IgA secretion?
Protect IgA from proteolysis
Outline the basic structure of the GI tract
Mucosa, submucosa, muscularis propria (externa), adventitia/serosa
Outline the composition of alimentary mucosa generally
Epithelium, lamina propria and muscularis mucosae
Outline the composition of alimentary submucosa generally
Loose connective tissue containing blood/lymph vessels and submucosa/Meissner's plexus of parasympathetic nerves (to muscularis mucosae, glandular secretions and local blood flow)
Outline the composition of alimentary muscularis propria (externa) generally
Inner circular layer and outer longitudinal smooth muscle responsible for peristalsis AND myenteric/Auerbach's plexus are found between muscle layers (control activity)
Outline the composition of alimentary adventitia/serosa generally
Major vessels and nerves travel in this outermost layer
What is Meissner's plexus?
Paraympathetic nerve ganglia in the submucosa of alimentary trac involved in local blood flow, glandular secretions and control of muscularis mucosa
What is Auerbach's plexus?
Myenteric plexus supplying the muscularis externa/propria and controls peristalsis (in alimentary system)
What is the structural difference between adventitia and serosa?
Serosa has a thin loose CT covered by mesothelium whereas adventitia just has an outer CT layer
When is the outermost part of the alimentary tract referred to as a serosa?
When it is located within the peritoneal cavity
Describe the histological characteristics of the small intestine
Mucosa has finger-like villi, has crypts in the mucosa (below epithelia), then light staining submucosa, then smooth muscle, then muscularis externa
Where are villi found?
Small intestine only (duodenum, jejunum, ileum)
What is chyme?
Watery digesting food
What are lacteals?
Lymphatic vessels in the lamina propria which carry absorbed materials away from the small intestine
What type of epithelia is present in the oesophagus?
Stratified squamous epithelia (resists abrasion)
Where are the glands in the oesophagus located?
Describe the histological structure of the muscularis externa in the oesophagus
Upper 1/3 of oesophagus has muscularis externa with skeletal muscle within it, middle 1/3 contains a mix of skeletal and smooth muscle and the lower 1/3 is comprised of only smooth muscle
Describe the histological characteristics of the stomach
Has glandular mucosa with tubular glands
What are the 4 divisions of the stomach?
Cardia, fundus, body and pylorus
Which cells secrete mucus in the stomach, and where?
Mucous neck cells, in all areas of the stomach
Which cells secrete HCl in the stomach and where?
Parietal cells in the fundus and body
Which cells secrete pepsin in the stomach and where?
Chief cells (pepsin hydrolyses proteins) in the fundus and body
Which cells secrete gut hormones (including gastrin) in the stomach and where?
Endocrine cells in the fundus and body and G cells in the pylorus (Gastrin here)
How can you identify chief cells histologically?
Largest of the glandular cells in the stomach and have a dark staining
How can you identify mucous neck cells histologically?
Smaller cells pf the stomach (than chief cells) and have a dark staining
How can you identify parietal cells histologically?
Have a high cytoplasm:nucleus ratio
What is the 'gastric pit'?
The opening of a gland lined by surface mucous cells
What are plicae circularis?
Larger folds of the small intestine (than microvilli) to further increase surface area for absorption
What type of epithelia is present in the stomach?
Simple columnar epithelia
What type of epithelia is present in the small intestine?
What type of epithelia is present in the large intestine?
What are brush border enzymes?
Enzymes present on the luminal surface of enterocytes which facilitate digestion
What type of stain allows visualisation of goblet cells?
PAS stain, stains the carbohydrate in mucin --> red/pink
What is a glycocalyx?
A coating of glycoproteins and polysaccharides that protects the small intestine against autodigestion and binds digestive enzymes to facilitate final stages of digestion (stained pink by PAS)
What are the intestinal glands of the small intestine known as?
Crypt of Lieberkühn
What is the location of enterocytes in the small intestine and what is their function?
Lining villi - digestion (brush border enzymes) and absorption
Crypt - secretion of watery intestinal juice
What is the location of goblet cells in the small intestine and what is their function?
Along villus between enterocytes (mucus secretion)
What is the location of endocrine cells in the small intestine and what is their function?
Crypts - regulation of gut function
What is the location of stem cells in the small intestine and what is their function?
Crypts - regeneration of epithelium
What is the location of Paneth cells in the small intestine and what is their function?
Crypts - antimicrobial agents, defensins and lysozyme
What is the role of enteropeptidase?
Crypt enterocytes secrete this to activate pancreatic trypsin
Describe Paneth cells histologically
Found only in small intestine and have bright pink granules and are at the base of crypts
What is taenia coli?
The collection of three band of longitudinal smooth muscle in the muscularis externa of the large intestine