Gastrointestinal System Flashcards
describe the 2 general units of the digestive system
1) receiving and processing, which is the mouth through the stomach 2) extraction and disposal, or the small intestine to the anus
what are the 4 layers of the gut tube?
-mucosa -submucosa -muscularis -serosa/adventitia
what components make up the mucosa of the gut tube?
-epithelium -lamina propria -muscularis mucosa
what components make up the submucosa of the gut tube?
-dense irregular CT
what components make up the muscularis of the gut tube?
-smooth muscle -this is where peristalsis occurs
what components make up the serosa/adventitia of the gut tube?
-CT holding everything together -adventitia is the CT -serosa is when the CT is covered in mesothelium -retroperitoneal organs can have both
what 2 components are in the dense irregular CT of the gut tube submucosa?
-large blood vessels -meissner’s submucosal enteric nerve plexus - this regulates mucosal epithelium and muscularis mucosa
what are the functions of the circular and longitudinal muscles of the muscularis externa?
- inner circular muscles propel things forward
- outer longitudinal muscles provides directionality
what nerve plexus is found in the muscularis externa, and what does it regulate?
-auerbach’s enteric plexus found between inner circular and outer longitudinal layers -regulates motility
what does adventitia do?
CT that attaches one organ to another
describe how retroperitoneal organs have both serosa and adventitia
-adventitia where attached to another organ -serosa everywhere else
describe the difference between peristalsis and segmentation
peristalsis
- adjacent segments alternatively contract and relax, moving food along tract distally
segmentation
- nonadjacent segments alternately contract/relax to move food forward and backward; food mixing
what are the 3 histological layers of the pharynx?
1) mucosa - non-keratinized stratified squamous; lamina propria (loose CT) contains longitudinal elastic fibers
2) muscularis externa - circular & longitudinal layers of skeletal muscle
3) adventitia - outer CT
describe the steps in swallowing
at what location do the 4 standard histological layers of the digestive tract become apparent?
esophagus
describe the differentiation of the 3 sections of the esophagus with respect to the muscle
- top 1/3 is skeletal muscle
- middle 1/3 is mixxed smooth and skeletal
- lower 1/3 is all smooth
T or F:
esophageal glands in the submucosa and lamina propria of the esophagus add secretions to aid the passage of bolus down the tube
true
T or F:
esophagus looks histologically like the vagina, with the exception of esophageal glands
true
what can lead to GERD? (gastro-esophageal reflux disease)
improper contraction of the lower esophageal sphincter, allowing acid to enter the esophagus, causing irritation/inflammation
what happens to the epithelium at the junction of the esophagus and the stomach?
it transitions from stratified squamous to simple columnar
describe primary digestion in the stomach
- acidic fluid is added, mixed around, generating chyme
- break down of CHO continues
- lipase secreted to break down lipids
- pepsin secreted to break down proteins
- no absorption yet
what are the 4 regions of the stomach?
- fundus
- cardia - epithelium changes here
- body
- pylorus
gastric pits are indentations found in the mucosa of the stomach. what do they lead to?
gastric glands
under the control of parasympathetic nervous system, what layer of the stomach will contract to mix the food?
muscularis externa
in the cardia, are pits shorter or longer than glands?
shorter
in the body/fundus, describe the height of glands and pits
- long glands
- pits more defined in cardia than fundus/body
are pits shorter or longer than glands in the pylorus?
longer
T or F:
the epithelial structure of the cardia is heterogenous
false:
it is homogenous
in the body/fundus, pits are substantial and glands are longer. what do the glands contain?
- chief cells - pepsin and lipase
- parietal cells - gastric acid and intrinsic factor
the glands of the cardia and pylorus are primarly mucous glands, which serve to do what?
slide everything through
what does the pylorus do functionally?
-fractionally pass along the chyme mixed in the body/fundux of the stomach via the pyloric sphincter
know the cell types in the stomach epithelium
T or F:
stem cells of the stomach epithelium are found in the bottom of the gland
false:
found in the top of the gland in the isthmus - between pits and glands
what are surface mucous cells?
- create the mucous lining of the stomach
- serves to protect tissues from acid and enzymes
- release bicarbonate to neutralize acid, prostaglandins, mucosal blood flow, and growth factors
- want to keep pepsin away from this area so that it doesn’t eat the protective proteins
- histologically, they are more columnar than mucous neck cells
what are mucous neck cells?
- round cells with apical granules in the lining of the stomach
- fewer neck cells than surface mucous cells
what are chief cells?
- found in the bottom of glands of the stomach and secrete into apical side
- secrete pepsinogen (pepsin) and gastric lipase
- aka peptic cells
what are parietal cells?
- found in the stomach
- secrete 0.1 N HCl when stimulated by gastrin and histamine
- secrete gastric intrinsic factor (GIF) for vit B12 absorption
- highly eosinophilic and have “fried egg” appearance
what would a loss of parietal cells in the stomach result in and why?
- pernicious anemia
- wouldn’t be able to absorb vit B12
what are G cells?
- part of the Diffuse NeuroEndocrine System
- secrete many things, primarily gastrin, to effectively tell the rest of the body what is in the stomach and how much of it there is
what are some of the things that DNES cells secrete in the stomach?
- gastrin and histamine - HCl secretion by parietal cells
- ghrelin - satiation
- serotonin - psychotropic effects of eating etc.
- many more
describe the control of parietal cell acid secretion
what does GRP do?
GRP = gastrin releasing peptide
-stimulates the release of gastrin, which stimulates parietal cells to release HCl
describe unified secretory control of gastric acid secretion
what is a main characteristic of the small intestine?
- site of absorption
- location where 90% of nutrients and water are absorbed by cells of the epithelial lining
what are functions of the duodenum?
- site of most chemical digestion
- bile from gall bladder
- bicarbonate and digestive enzymes from pancreas
- brunner’s glands secrete mucus
what are functions of the jejunum?
- absorbs nutrients and water that were broken down in the duodenum
what are functions of the ileum?
- absorption of bile-lipid micelles
- anything not absorbed by the jejunum
- peyer’s patches involved in immunity
describe structures in the small intestine that aid in absorption
in descending scale:
- plicae circulares that increase the absorptive area 3x
- villi, finger like projections, increase the absorptive area 10x
- microvilli, individual cell membrane folds, increase absorptive area 20x
what are plica circulares?
- permanent circular or semilunar folds found in the small intestine
- consist of mucosa and submucosa
- more prominent in jejunum
- increase absorption 3x
what are villi?
- found in the small intestine
- dense covering of fingerlike projections
- internally: contain lamina propria with microvasculature and lacteals, lymphatics which absorb fats
- externally: covered in simple columnar epithelium
- microvilli at apical ends
what do brunners glands do and where are they found?
- secrete mucus in the duodenum to protect the surface
- limited bicarbonate
where are plicae circularis most prominent in the small intestine?
jejunum
where are peyer’s patches primarily found, and what do they do?
- found in the ileum
- lymphoid tissue that stores immune cells
what are microfold (M) cells and mucosal associated lymphatic tissue (MALT)?
- specialized epithelial cells that sit over peyer’s patches
- endocytose antigens, bring to lymphocytes and dendritic cells
- activate immune response (antibody production)
what 5 main components are found in the mucosa of the small intestine?
- epithelium - simple columnar, microvilli projections (brush border)
- enterocytes - absorptive columnar cells
- goblet cells - mucus production
- paneth cells - secrete antimicrobial molecules, regulate immune response
- enteroendocrine cells - local/systemic signals relating to digestion and transit
how are lipids absorbed?
- bile acids emulsify lipids to micelles
- gastric lipase digest lipids to produce glycerol, FA, monoglycerides
- these diffuse across membrane into cell
- resynthesized in SER to triglycerides
- pass through RER, golgi, eventually packaged into chylomicrons
- transported to lymph
*fats bypass the liver due to their entry into lymph circulation
describe the absorption of protein and CHO
- Enterocytes secrete disaccharidases and amino Peptidases
- Digest disaccharides and dipeptides into monosaccharides and amino acids
- Amino Acids absorbed via active co-transport with sodium
- Carbohydrates also absorbed via active co-transport with sodium (glucose & galactose) , or direct diffusion (fructose)
- Released for uptake into capillaries
describe the absorption of water in the small intestine
- Na comes in with co-transporters and is pumped out of the lumen of the intestines
- This creates a high sodium concentration in the intercellular space
- Water diffuses from the lumen into intercellular space and eventually into the capillary blood
where are the requisite vessels for protein, CHO, and lipid absorption located in the small intestine?
- lamina propria at the core of each villus
- blood vessels for protein and CHO
- lacteal (lymph) for lipids
- sympathetic nervous system will close off these vessels
how many children die yearly from diarrhea?
1.6 million
what type of diarrhea is the result of malabsorption?
osmotic diarrhea
what cells are found at the bottom of intestinal crypts?
paneth cells
what are paneth cells?
- innate immune cells that regulate the microenvironment
- release lysozyme, phospholipase A, defensins
- may also regulate progenitor cell activity for renewal of tissues
what do intestinal enteroendocrine cells do?
- respond to the presence of certain chemical signals or environmental cue to regulate the process of digestion
- negative feedback - help GI tract keep track of how much of what is where and respond appropriately
- secrete secretin, CCK, GIP, and peptide YY
how does the submucosa function in intestinal motility?
- muscularis mucosa produce local movements of villi and plica circulae to mix contents in the intestinal crypts
- submucosal plexus is a collection of parasympathetic nerve fibers which regulate contraction
how does the muscularis externa function in intestinal motility?
- same circular/longitudinal bands as upper tract
- myenteric plexus (aaurbach’s plexus) is a collection of both sympathetic and parasympathetic nerve fibers and sensory nerves that regulate the GI function
what are 3 functions of the large intestine
- absorbs water and electrolytes, but not much nutrients
- secrete bicarbonate and mucous
- storage of indigestible material as feces
it is around 1.5 meters long
describe characteristics of the mucosa of the colon
- mucosa lacks villi
- penetrated by tubular intestinal glands
- goblet and absorptive cells (colonocytes), active fluid absorption (dehydration of feces)
describe the tubular intestinal glands of the colon
- simple columnar
- embedded in lamina propria with lymphocytes
describe the absorptive cells of the colon
- colonocytes
- have short microvilli
- passive water transport after active Na+ transport into the cell basally
what are characteristics of the taeniae coli of the colon?
- muscularis externa has typical circular/longitudinal layers
- outer layer has 3 extra longitudinal bands called taeniae coli
- contract lengthwise to aid in segmental/peristaltic movement; parasympathetic control
- can produce a mass movement to empty whole sections of the colon at a time
describe the rectum
- some skeletal muscles, ie. external anal sphincter
- transitional zone between mucosa of the GI tract and external skin
what is the function of secretin in the small intestine?
- secreted by enteroendocrine cells
- stimulates HCO3 and H2O secretion by the pancrease and bile ducts
- inhibits H+ secretion by parietal cells in stomach
what is the function of CCK in the small intestine?
- secreted by enteroendocrine cells
- CCK (cholecystokinin) stimulates pancreatic acinar cell secretion and smooth muscle contraction by gall bladder
- signals immediate satiety to the brain
what is the function of GIP in the small intestine?
- secreted by enteroendocrine cells
- GIP (gastric inhibitory peptide, glucose-dependent insulinotropic hormone) stimulates insulin secretion by beta cells in pancreas
what is the function of peptide YY in the small intestine?
- secreted by enteroendocrine cells
- signals long term satiety to the brain
