Digestive Tract Flashcards
The digestive system includes which structures?
- Salivary glands
- Mouth/tongue
- Esophagus
- Stomach
- Liver
- Gallbladder
- Pancreas
- Small intestine
- Colon
- Rectum
What is the alimentary tract?
Tubular passage of mouth to anus
What is the small intestine/basic function?
upper part of the intestine where digestion is completed and nutrients absorbed
What are the large intestine components?
Cecum, appendix, colon, and rectum
What are the 4 fundamental layers of the digestive system? (inner to outer)
- Mucosa
- Submucosa
- Muscularis propria
- Outer layer
What 3 layers comprise the muscosa? (inner to outer)
- Epithelium
- Lamina propria
- Muscularis mucosae
What comprises the submucosa? what is another name for it?
aka the plexus
comprised of glands, blood vessels, and nerves
What two layers comprise the muscularis propria? what differentiates them
- Inner muscle layer (circular)
- involuntary control/smooth muscle - Outer muscle layer (longitudinal)
What makes up the outer layer?
the adventitia or serosa
What are the 4 types of papillae found on the tongue?
- Circumvallate papillae
- Filiform papillae
- Fungiform papillae
- Foliate papillae
Which of the 4 types of papillae lack taste buds?
Filiform papillae
What is another name for circumvallate papillae? Where are they found? what shape do they have?
Aka the vallate papillae
Dome shaped, sunken structures
- contain TB
Found near the dorsal end of the tongue
What shape are the filiform papillae? where are they found?
small conical prominences on the lingual surface
** no taste buds **
What is the shape of the fungiform papillae ? where are they found? Where are their taste buds?
Mushroom shaped projections on the surface among the filiform
- mainly at the tip and lateral margins
- taste bugs on the upper surface
What is the shape of the foliate papillae? where are they found? where are their taste buds?
short vertical folds
on the lateral margins
Taste buds scattered over the surface
What drain into the folds of the foliate papillae to clean the taste buds?
serous glands
What are the 5 tastes that the taste buds can perceive?
salty, sour, sweet, bitter, umami
Papillae are among which type of epithelium?
stratified squamous non-keratinized epithelium
How many deciduous (primary) teeth do children have?
20
How many adult teeth should we have?
32 - 8 in each quadrant
What are the two main parts of the tooth?
Crown and root
What are the layers of the tooth from inner to outer?
Pulp –> dentin –> enamel
What are the layers of the gum around the tooth from inner to outer?
Periodontal ligament –> alveolar bone –> gingiva
What are the 3 types of salivary glands?
- Parotid
- Sublingual
- Submandibular
What cells secrete amylase which digests starch into maltose?
serous cells
What are the 3 types of cells in salivary glands?
- Serous cells
- Intercalated duct cells
- Striated duct cell
What do intercalated duct cells secrete? what do they absorb?
secrete bicarbonate, absorb Cl-
What do striated duct cells do?
modify saliva to be hypotonic with plasma
What kind of stimulation innervates salivary glands?
Parasympathetic stimuli
How many bacterial species have been isolated in culture from the oral cavity? How many do they think there are total (including ones that can’t be cultured?)
500 to 700
What are 7 positive effects of host-microbiome symbiosis?
- Confers resistance to colonization
- Regulation of cardiovascular system
- Supports host defense functions
- Has anti-inflammatory properties
- Provides additional metabolic potential
- Has antioxidant activity
- Maintains a healthy digestive tract
What are some common diseases of the oral cavity?
- Ulcers
- thrush
- Canker sores
- tooth decay
- grinding teeth in sleep
- gingivitis
- cancer
- congenital defects like cleft lip/palate
- trauma
What muscle controls the opening of the esophagus?
the inferior pharyngeal constrictor muscle
What covers the trachea to prevent food and fluids from entering the lung?
the trachea
What controls the movement of food from the esophagus into the stomach ?
Lower esophageal sphincter
**refresh: what are the 4 layers of tissue?
- mucosa
- submucosa
- muscularis propria
- adventitia
What kind of epithelium make up the mucosa of the esophagus?
stratified squamous
What glads are present in the esophagus near the stomach ? What layer are they in and what do they secrete
Cardial glands
Found in the mucous layer and secrete mucous
What is special about the upper third of the muscularis propria in the esophagus?
is it striated muscle
What is Gastroesophageal reflux disease? (GERD)
Failure of the lower esophageal sphincter to close properly causing stomach contents to leak back
get frequent heartburn and potential ulcer formation
What disease is characterized by inflammation/swelling of the esophagus due to large numbers of eosinophils?
Eosinophilic esophagitis
How do you diagnose eosinophilic esophagitis?
with an endoscopy and biopsy
What is dysphagia? What can cause it?
difficulty swallowing due to stiffening or narrowing of the esophagus
- due to infiltration of large numbers of eosinophils
What main event happens in the stomach?
Denaturation of proteins and initiation of enzymatic breakdown by the action of pepsin
What 3 kinds of glands are there in the stomach?
- Cardiac glands
- Pyloric glands
- Gastric/fundic glands
What allows for expansion of the stomach?
gastric rugae
What are the 4 sections of the stomach?
- Cardia
- Fundus
- Body
- Antrum or pylorus
What re the 4 types of cells in the stomach glands?
- Mucous cells
- Parietal/oxyntic cells
- Chief cells
- Enteroendocrine cells
What cells secrete HCL and intrinsic factor into the stomach?
Parietal cells
What is the purpose of intrinsic factor?
Used in vitamin B12 absorption
What happens if you don’t produce intrinsic factor?
you will develop pernicious anemia
What cells produce pepsinogen?
Chief cells
What do enteroendocrine cells release? where? what is an example?
secrete hormones
G cells specifically secrete gastrin into the lamina propria
What does gastrin do?
promotes the secretion of HCL
What cells secrete bicarbonate? where?
Parietal cells do into the lamina propria
What happens to the bicarbonate?
diffuses into capillaries and then back into the upper epithelium
What two factors help the stomach not be harmed by the acid?
Mucous and bicarbonate
The epithelium in the stomach is what type?
Simple columnar epithelium
What is unique about the muscularis propria of the stomach?
it has 3 layers of muscle
and oblique muscle layer before the circular layer
What is Barrett’s esophagus?
stratified squamous epithelium of the esophagus is replaced with simple columnar epithelium by goblet cells
at the gastroesophageal junction
There is a strong connection between Barrett’s esophagus and….
esophageal adenocarcinoma
What is an ulcer?
an open sore on an external or internal surface of the body caused by a break in the skin or mucous membrane that fails to heal
What is the leading cause of gastritis?
Helibobacter pylori
What % of the worlds population harbour H. pylori in their GI tract?
more than 50%
What are two risks associated with having H. pylori in the stomach?
~10–20% of infected will ultimately develop gastric and duodenal ulcers.
associated with a 1–2% lifetime risk of stomach cancer
What is the product called from stomach digestion that enters into the small intestine?
chyme
What causes the release of cholecystokinin and secretin? What does this accomplish?
the presence of fats in the duodenum
inhibits further gastric activity
What is the order of segments in the small intestine?
Duodenum, jejunum, ileum
How many litres of fluid pass through the small intestine every day? From that, how much goes on to the large intestine?
9 L to the small intestine
Only 1.5 L actually makes it to the large intestine
While the architecture of the layers is the same in the small intestine, which layer is expanded? why?
the submucosa because of increased glands
What glands are located in the submucosa of the small intestine?
Brunner’s glands
What do Brunner’s glands secrete?
Alkaline mucous (pH 8.1-9.3) - contains neutral and alkaline glycoproteins and bicarbonate ions
What secretes carbohydrases, proteases, and lipases?
Crypts of Lieberkühn
Where are the crypts of Lieberkühn located?
in the mucosa also
What % of starches are digested by amylase in the stomach? what is the product?
about half are turned into maltose in the stomach
What happens to the remainder of starches that reach the small intestine?
broken down into di and monosaccharides
What is the breakdown of proteins like in the small intestine?
- proteins are digested by pepsin and pancreatic enzymes
2. free amino acids are then broken down by carbxypeptidases on the villi
What % of ingested protein is absorbed by the end of the jejunum?
70-80%
What are the 4 principal epithelial cell types scattered along the crypts and villi?
- Enterocytes
- Paneth cells
- Goblet cells
- Enteroendocrine cells
What is the function of enterocytes?
absorption
What do Paneth cells secrete?
- Lysozyme
2. Defensins
What do goblet cells secrete?
mucous
What do enteroendocrine cells of the small intestine secrete?
Hormones like secretin, Cholecystokinin, glycogen inhibitory peptide and others into the lamina propria
What is the distribution of cells in the villi vs the crypts of the small intestine?
Paneth cells are most numerous at the bottom of the crypt = highest concentration of antimicrobial peptides in the bottom of the crypt
What is Periodic-acid-Schiff?
a stain used to detect polysaccharides such as glycogen, glycoproteins, glycolipids, and mucins
The epithelium of the small intestine is…
Simple columnar epithelium
The small intestine replaces its epithelium completely every…
week
What is the difference between endo and exo peptidases?
Endopeptidases cleave the polypeptide at interior peptide bonds
Exopeptidases cleave the terminal amino acid
What are the two further subclassifications of exopeptidases?
- Aminopeptidases: cleave the terminal amino acid at the amine end of the chain
- Carboxypeptidases: cleave off the terminal amino acid at the carboxyl end of the chain
What kind of peptidases can be intracellular?
di and tripeptidases
What are the two key enzymes involved in carbohydrate digestion? which are found in the microvilli?
oligosaccharidases
disaccharidases
Both found in the microvilli!
What are the 5 phases of fat digestion?
- emulsification
- Hydrolysis
- Micelle formation
- Absorption
- Chylomicron formation
What is the function of colipase?
Binding to the lipidase during the emulsification step and enhances its activity
How do amino acids and monosaccharides reach the capillaries?
- diffuse through the apical membrane
- diffuse across the cell
- Through the basolateral membrane either by diffusion or actively transported by carrier proteins
- Reach capillaries in the lamina propria
How do lipids reach blood circulation?
- Processed into chylomicrons
- Enter lacteals (lymphatic capillaries) in lamina propria
- Travel to blood circulation via lymphatic vessels
What is paracellular uptake?
uptake of materials by passing between cells
Tights junctions are called __ and held together by ___
Zonula occludens
held together by occludins and claudins
What are the proteins involved in adherens, intermediate, and belle desmosome junctions?
cadherins and catenins linked to cellular actin
What is another name for macula adherens? what proteins are involved?
Desmosomes
Cadherins and demoplakin linked to intermediate filaments
What is the glycocalyx?
acidic mucopolysaccharides and glycoprotein matrix on the apical surface, on the microvilli.
Does the large intestine have villi?
no, has crypts only
What are 5 important features that increase the surface area of the intestine?
- Long length
- Plicae circulares
- Villi
- Crypts
- Brushborder/microvilli
What cells secrete Cholecystokinin? where? where does it act on?
L cells in the epithelium of the small intestine
acts on the pancreas and gallbladder
What does cholecystokinin do? (6 things)
mediates digestion by:
- inhibiting gastric emptying
- inhibiting gastric acid secretion
- Stimulating acinar cells of the pancreas to release digestive proenzymes
- Increased production of bile
- Contraction of the gall bladder
- relaxation of the sphincter permitting delivery of bile into the duodenum
What cells release gastric inhibitory peptide (GIP)?
K cells of the small intestine
What is another name for GIP?
glucose-dependent insulinotropic peptide
What 2 things does GIP do? where does it act on
- Induces insulin secretion
- Inhibits gastric secretion and motility
acts on the stomach and the pancreas
What main event occurs in the large intestine?
complete absorption of food and formation of feces
What are haustra?
pouches formed by the taenia coli
What are the taniae coli?
3 independent long ribbons of smooth muscle just below the serosa, along the colon length (condensations of the longitudinal muscle layer)
What is the histology of the large intestine compared to the small intestine?
layers are identical but only have the crypts of Lieberkühn
What are the levels of goblet cells like in the large intestine?
abundant
What glands are noticeably absent from the large intestine?
Brunner’s glands
in fact there are no submucosal glands in the large intestine
What is the smooth muscle layer like in the large intestine?
thin and longitudinal
What does the adventitia of the large intestine form?
Small pouches (appendices epiploicae) filled with fatty tissue along length, though mainly on ascending and transverse colon
What is the shape of the cecum? what controls the contents?
• sac-like, controlled contents
through the ileocecal valve
What are 5 functions of the cecum?
- Reservoir
- Churning activity
- Salt recovery
- Lubrication of solid waste
- Bacterial digestion of cellulose
What is the appendix?
Small blind ended pouch (diverticulum) of the cecum
What is the histology of the appendix like?
- Thickened walls due to lymphoid tissue
2. Longitudinal smooth muscle layer that does not aggregate into the taenia coli
What is the rectum a continuation of?
the sigmoid colon
What is noticeably lacking from the rectum?
taenia coli
What occurs when there is expansion of the rectum?
nerves send signals to the brain that you need to have a bowel movement*. Muscles around the anal canal control the action
What happens at the recto anal junction ?
transition between epithelium types
What are the 4 epithelium types that exist and where between the lower rectum and the anal canal?
- simple columnar epithelium in the upper zone
- Stratified squamous epithelium in the middle and lower zones
- Simple columnar epithelium of the anal glands
- Stratified columnar epithelium of the anal sinuses, crypts, and ducts of anal glands
Besides water resorption, what are some roles of the large intestine? what is produced
- Fermentation of carbohydrates by bacteria and further protein decomposition
- products: organic acids, carbon dioxide, methane, hydrogen sulfide
- toxic products: phenol, skatole, indole, cresol - Cellulose split by microbial fermentation
- vitamins, amino acids, electrolytes, and glucose produced by microbes and absorbed
What are the 2 plexi of the enteric nervous system?
- Myenteric plexus (aka Auerbach’s plexus)
2. Submucosal plexus (aka Meissner’s plexus)
What is the role of the Myenteric plexus?
Major role in motility and passing food through the digestive tract
What is the role of the submucosal plexus? what is it formed from?
Secondary plexus derived from and formed by branches having perforated the circular muscle
Innervates the epithelial layer and the muscularis mucosae
What is celiac disease? symptom?
genetic predisposition of an autoimmune crossreactive reaction to gluten
pale, loose, and greasy stool affecting absorption
What is the cause of lactose intolerance? what is the result?
lack of lactase enzyme to cleave lactose into glucose and galactose
results in high concentrations of lactose reaching the colon and affecting the osmotic state
- water gets drawn passively into the lumen
- not a hypersensitivity or inflammatory disease
What is colitis? symptoms?
inflammation of the colon due to multiple causes
results in abdominal pain and diarrhea
What are two inflammatory bowel diseases?
Crohn’s disease: inflammation affects the alimentary tract.
Ulcerative colitis: inflammation affects colon and rectum.
What is irritable bowel syndrome?
A non-inflammatory, symptom based diagnosis with chronic abdominal pain, discomfort, bloating and diarrhea/constipation
What is diverticulosis?
small weak areas in the colon wall allow the mucosa to protrude forming diverticuli (pouches)
Usually not a problem but can bleed, become inflamed or infected
What are 3 common causes of diarrhea?
- Salmonellosis: food contamination, diarrhea and stomach cramps, which resolve without treatment.
- Shigellosis: food contamination, invaded the colon. Fever, stomach cramps and diarrhea, which may be bloody.
- Travelers’ diarrhea: Many different bacteria or protozoa (Giardia) may contaminate water or food.
What are colon polyps?
small growths where some may develop into cancer over a long period of time
Blood in the spleen, stomach, pancreas, gallbladder and intestines passes through and collects in the…
hepatic portal vein
Where does blood leaving the liver collect? where does it travel?
collects into the hepatic veins then goes to into the vena cava to the heart
cells of the liver are organized into lobules around…?
the central vein, and the hepatic artery/bile duct/portal vein triad
lymph vessels are also present
What are the low pressure channels that receive blood from terminal branches of the hepatic artery and portal vein? Where do they deliver it to?
Sinusoids
Deliver it into the central veins
What are the sinusoids lined with? Flanked with? populated with?
Fenestrated endothelial cells
Flanked by hepatocytes
Populated with numerous Kupffer cells
What is the space of Disse?
the space between the endothelium and hepatocytes
What are Kupffer cells?
liver macrophages
Hepatocytes make bile which is dumped into __ between the cells?
Bile canaliculi
Hepatocytes are bathed in plasma derived party from…
venous blood from the small intestine
Plasma which collected in the space of Disse flows back towards the …
portal tracts and collects in lymphatic vessels
what % of bile is reabsorbed by hepatocytes vs. what % is newly produced bile?
10% new bile that is produced and 90% reabsorbed
What are 5 functions of hepatocytes?
- Bile production/uptake/transport
- Lipid uptake & metabolism
- Glycogen synthesis
- Detoxification by p450 enzymes
- Protein synthesis
What kinds of proteins are synthesized by hepatocytes?
Albumin, complement, fibrinogen, lipoproteins
Are all hepatocytes carrying out the same functions at the same time?
no there is a division of labour between the hepatocytes at different locations in the lobule
What do Kupffer cells do?
Eliminate foreign particles and gut endotoxins
Where are stellate cells located? What do they produce?
Found in the space of Disse
Produce collagen fibrils and extracellular matrix materials
What is bile a mixture of?
Water, bile salts, cholesterol, bilirubin
What happens to bilirubin in the intestine?
Intestinal bacteria further convert it into the brown pigment stercobilin
The bile/hepatic ducts join with the ___ which brings bile to and from the gall bladder?
cystic duct
The gallbladder is ___ and the mucosa has ___
stretchable and has folds
What is the epithelial lining of the gallbladder like? what does this do?
lined with high columnar epithelium
modifies bile, largely by absorbing water
also acts as a way to remove toxins
What is bilirubin a product of?
the digestion by Kupffer cells of expired rbc, makes bile green
What is the name of the vessels collecting bile from the canaliculli?
Hering’s canals
What collect bile from the Hering’s canals? where do they lie?
the bile ducts
lie parallel to the hepatic arteries and portal veins
What collects bile from the bile ducts?
hepatic ducts
What does the common hepatic duct do? what does it branch into?
collects bile from the hepatic ducts
branches into the cystic duct and then the common bile duct
Where does the common bile duct empty into?
the duodenum
What causes Jaundice?
increased bilirubin in the blood
What is cirrhosis?
When normal liver cells are replaced by scar tissue due to chronic liver disease
What is the most common cause of liver disease in North America
alcohol abuse
What is Steatosis ?
fatty liver disease
- where cholesterol/triglycerides accumulate in the liver
What causes gall stones?
accretion of bile, blockage and then inflammation
the pancreas has both __ and ___ functions
endocrine and exocrine functions
what are the two types f exocrine cells in the pancreas?
- Acinar cells
2. Ductal cells
What do acinar cells do?
secrete digestive enzymes
How many types of ductal cells are there? What do they secrete?
4 types
- intercalated duct cells secrete bicarbonate
What are the 3 main types of endocrine cells in the pancreas? what do they secrete?
- Alpha cells - glucagon
- beta cells - insulin
- Delta cells - somatostatin
What is the purpose of the bicarbonate secreted by ductal cells of the pancreas?
to neutralize the acid pH of the chyme in the duodenum
What 5 precursor enzymes are released from the acinar cells?
- Trypsinogen
- Chymotrypsinogen
- Proelastase
- Procarboxydase A
- Procarboxydase B
What acts as an activator for all the pancreatic zymogens? which one is different?
tyrpsin for all of them
Enteropeptidase and trypsin will activate trypsinogen
What activates enteropeptidase?
duodenase
what is the effect of glucagon on blood glucose levels? what cell types does it act on?
raises blood glucose levels by stimulating the liver to metabolize glycogen into glucose and release it into the blood
stimulates adipose tissue to metabolize triglycerides into glucose and release them into the blood
What is the effect of insulin on blood glucose levels? what cell types does it act on?
lowers blood glucose by stimulating absorption of glucose by the liver, muscle, and adipose tissues
triggers formation of glycogen in the muscles and liver and triglycerides in adipose to store the absorbed glucose
What does somatostatin do?
reduces smooth muscle contractions in the tract and gall bladder
What is a common cause of acute pancreatitis (inflammation)
alcohol abuse
What are 3 common diseases of the pancreas (besides inflammation)
- Cancer
- Pancreatic insufficiency
- Cystic Fibrosis
What happens to patients with pancreatic insufficiency?
Lose of about 90% of their ability to secrete digestive enzymes
Patients are unable to digest food –> results in malabsorption of nutrients/malnutrition
What happens in terms of pancreatic function in patients with CF?
Decreased production of sodium bicarbonate makes secretions dehydrated, thickened, which blocks the ducts
Pancreas continues to make enzymes which accumulate and damage the pancreas and lead to fibrosis
At what age does breast feeding history cease to impact gut microbiome profile?
18-36 months
What are some innate barrier properties of the immune system that contribute to protection of the digestive system?
- Low pH in the stomach
- Alkaline mucous of Brunner’s glands
- Lubricating & protective mucous of goblet cells
- Tight junctions between enterocytes
- Steady epithelial replacement and capacity for regeneration
- Diarrhea, peristalsis
- Commensal microbiota
What are 2 secretions of paneth cells that contribute to innate immunity in the digestive system?
lysozyme and secretory phospholipase A2
What are α and β defensins?
ancient, evolutionarily conserved class of antimicrobial peptides made by many eukaryotes, including mammals, insects, and plants
What are histadins? what secretes them? where are they made?
epithelial cells of the digestive system
made in the salivary glands
Have antifungal properties
What are some receptors the innate immune system uses to detect pathogens?
MAMPS which include TLRs, and formyl-peptide receptors (FPR)
What are some humoral components of innate immunity ?
Immunoglobulin and complement
What are some cellular components of innate immunity in the digestive system?
epithelial cells, granulocytes (macrophages, eosinophils, meutrophils, basophils, mast cells and DCs)
What is GALT and what can it be subdivided into?
Gut associated lymphoid tissue for T and B cells
- IEL populations
- Highly organized lymphoid aggregates
What are 5 “highly organized lymphoid aggregates” of GALT
- Pharyngeal tonsils
- Peyer’s patches
- Mesenteric Lymph nodes
- Cryptopatches
- Isolated lymphoid follicles
What are peyer’s patches? Where are they?
The mucosal inductive site where cells become stimulated
located throughout the jejunum, ileum, with few in the colon
What is FAE in the Peyer’s patches? What kind of cells does it contain?
FAE = follicle-associated epithelium
contains M (mother or membranous) cells
What are M cells? What do they do?
Cytoplasmic extensions that surround T and B cells in an apparent “pocket”
Transport and present luminal antigens
What are M cells the route of entry for?
Lymphocyte entry into the lumen and also for some infectious agents to gain entry
What do T and B cells exposed to antigen in the intestines do?
they will leave, circulate, and then home back to the intestine due to expression of certain adhesion molecules and chemotactic molecules
What is the distribution of T and B cells within the epithelium/lamina propria?
Lamina propria: mostly CD4 T cells and scattered B cells secreting IgA
Epithelia: Mainly CD8 cells (many gamma δ)
What are intraepithelial lymphocytes thought to do? What properties do they have?
Function is not entirely clear..
Thought to play a role in detecting pathogens or reacting to infected/damaged epithelial cells
Have cytotoxic properties that allow them to kill abnormal cells
What is the most abundant immunoglobulin in the mucosa?
IgA
What receptors do epithelial cells have for IgA?
polymeric IgA receptors
What are Innate Lymphoid cells and how many groups are there?
Cells seemingly highly excited by commensal microbes and involved in modulating the tone of gut inflammation
There are 3 groups
What plays a large role in the tolerance of the digestive system to the wide variety of foreign molecules it is exposed to?
the stimulation of regulatory T cells
What is the state of tolerance of the gut called?
oral tolerance
What can induce oral tolerance?
can be purposely induced to a foreign molecule with a suitable exposure to the molecule, typically ingesting very high or very low amounts.
What is one example of loss of regulation of tolerance resulting in disease?
Loss of IL-10 resulting in colitis
