Week 2 Flashcards
When chyme moves into jejunum (BLANK) levels go down and this induces the pyloric tone to diminish and allow more chyme to go into duodenum
CCK
- When does the function of migrating motor complex occur?
- What stimulates them? (hormone)
- during fasting- purpose is to clear indigestible residues from lumen of stomach and small intestine and prevent bacterial overgrowth
- motilin
Does peristalsis occur at the same time as segmentation does?
No, peristalsis increases as segmentation decreases. Peristalsis is when proximal portions contract and distal portions of GI tract relax to propel bolus through GI tract
What causes the formation of haustra in colon?
myenteric plexus
what contraction/relaxation has to happen to open or close ileocecal sphincter?
- Distention of ileum relaxes ileocecal sphincter (open)
- Distention of cecum contracts the ileocecal sphincter (closes)
What is the function of colonic phase of digestion?
- reabsorption of remaining fluid, electrolytes, and storage of waste before defecation
- What ions are absorbed in the colonic phase of digestion?
- How are they absorbed (hint: two ways)
- Na is absorbed so water can follow and water reabsorption occurs
- proximal part of colon (image)→ coupled function of Na/H exchanger and Cl/HCO3- exchanger (electroneutral) - this happens between meals
- distal part of colon → through ENaCs (electrogenic))
What ions are secreted in the colonic phase of digestion?
- Chloride secretion - occurs via CFTR channel - this determines water content of feces → increased Cl secretion means increased H2O secretion (diarrhea)
- K+ secretion → can occur paracellular/passive or active/transcellular (image)
note: for K+ secretion this can be increased via aldosterone because aldosterone increases presence of ENaC
In colon - short duration contractions
- Their purpose
- Their length
- What conducts these contractions
- used for mixing
- 8 seconds
- produced by circular muscle
In colon - long duration contractions
- Their purpose
- Their length
- What conducts these contractions
- For mixing
- 20-60 seconds
- taeniae coli
In colon - high amplitude propagating contractions
- Their purpose
- used to clear colonic contents - pushes aborally (away from mouth) - occurs about 10 times a day - 20+ cm segment of colon loses haustrations and contracts as a unit to propel fecal matter forwards
- What needs to contract or relax (for internal and external anal sphincter) in order to defecate?
- What nerve system innervates the internal anal sphincter (IAS)
- What nerve system innervates the external anal sphincter (EAS)
- simultaneous relaxation of IAS (involuntary) and relaxation of EAS (voluntary) → (along with relaxation of puborectalis muscle + contraction of abdominal muscle )
- pelvic nerves (parasympathetic) - involuntary
- pudendal nerves (somatic) - voluntary
- (Blank A) stimulation stops colonic movement
- (Blank B) stimulation causes segmental contractions in colon
- sympathetic
- vagal
- What is gastrocolic reflex?
- What is orthocolic reflex?
- increased colonic motility shortly after ingestion
- When you wake after sleep, stretching and sitting and then standing, the orthocolic reflex excites nerves that stimulate muscular contractions in the large intestine (to help produce a bowel movement).
What do dilated intestines due to small bowel obstruction look like in x-ray?
step ladder appearance - can be caused by adhesions, hernias, malignancy, crohn’s etc
What is this an imaging of ?
- Diverticulosis - small pouches that arise along colon
What radiology findings can be associated to ulcerative colitis and crohn’s disease? (3)
- Transmural inflammation
- Luminal narrowing
- Skip lesions (A skip lesion is a wound or inflammation that is clearly patchy, “skipping” areas that thereby are unharmed)
Late cancer shows apple core or saddle lesions in radiology but what does early colorectal cancer show?
sessile (flat) or pedunculated (image) polyps
What is a toxic megacolon?
Toxic megacolon occurs when swelling and inflammation spread into the deeper layers of your colon. As a result, the colon stops working and widens. In severe cases, the colon may rupture.
- What is microscopic colitis?
- What are the two types of microscopic colitis
- Microscopic colitis is an inflammation of the large intestine (colon) that causes persistent watery diarrhea. - chronic, watery diarrhea (w/out weight loss) w/ normal appearing mucosa
- lymphocytic colitis and collagenous colitis
Differentiate between lymphocytic colitis and collagenous colitis (both are microscopic colitis)
- Lymphocytic colitis - increased epithelial lymphocytes (associated with celiac and autoimmune disease)
- Collagenous colitis - thickened sub-epithelial collagen in older women (normal appearing mucosa)
Irritable bowel syndrome
- what part of intestine does it affect?
- Symptoms?
- large intestine
- relapsing abdominal pain, bloating, changes in bowel habits
What pattern is necessary to dx someone with irritable bowel movement?
(Hint: it is a pattern of symptoms + 2 of 3 criteria)
- 3 days/moth of recurrent abdominal pain over 3 MONTHS w/at least 2 criteria
- improvement with defecation
- onset associated with change in frequency in stool
- onset associated with a change in form of stool
- What are some extraintestinal manifestations of irritable bowel syndrome?
- How is IBS treated
- painful menstruations, painful intercourse, urinary symptoms
- diet modification (avoiding short-chain carbs), stool softeners, anti-diarrheals
Differentiate between visceral, somatic, and referred pain
- Visceral pain - vague, dull, and nauseated - poorly localized pain bc there is low nerve density (autonomic nerve fibers) in abdominal viscera
- Somatic pain - sharp and localized pain - comes from parietal peritoneum that is innervated by somatic nerves
- Referred pain - comes from distant source due to convergence of nerve fibers at spinal cord
Digestive tract pain is usually localized where?
Midline due to bilaterally symmetric innervation
lateralized pain - usually unilateral, somatic innervation
- Epigastric may indicate issues with what structures? (3)
- heart, stomach, pancreas
Describe the current tools and methods used in determining gut microbiota composition?
- DNA-based approaches
- RNA-based approaches
- Protein-based approaches
- Metabolite-based approaches
- Determining what microbiota are present and what can they do
- Determining how microbiota respond and what pathways are activated (metatranscriptomics)
- How are they interacting with host and/or what proteins are being produced (metaproteomics) - considered best way!
- what are the chemical outcomes of their activity (metabolomics) -not the best because if substrate of bacteria is not present then metabolite will not be present
What is the structural function of microbiota of gut?
- they form a barrier fortification to more harmful pathogens
- induces formation of IgA that neutralize pathogens
- Regulate immune system development
What is the metabolic function of microbiota of gut?
(hint: what molecule(s) can we not make but gut microbiota can)
- gut microbiota provides enzymes that we can’t make ourselves.
- Provide SCFAs (butyrate) - products of bacterial fermentation of fiber → preferential energy source of colonocytes
In obese humans the (Blank:Blank) ratio is increased
firmicute:bacterioidetes
difference between probiotics and prebiotics?
- Probiotics- live active microorganisms that have beneficial effects to the host - displace the harmful bacterial species in gut (good for IBD, IBS, acute infectious diarrhea)
- Prebiotics - nonliving, non-digestible special form of fiber or carbohydrate - nourishes the bacteria that live in intestine (good for obesity, IBD, constipation, traveler’s diarrhea, diabetes)
- What are the types of carbohydrates? (4)
- Where are these carbs absorbed? (part of GI tract)
- starch (includes polysaccharides), disaccharides, monosaccharides, indigestible fibers (cellulose and pectin)
- Small intestine
Explain how starch (polysaccharides) are digested before being absorbed in small intestine? (2)
- Starch is digested/broken down in the lumen of the small intestine by amylase enzyme
- After initial digestion some products are still not able to be absorbed because they are terminal linkages or branching linkages. Special amylase enzymes break these down AT THE BRUSH BORDER MEMBRANE and then they can be absorbed
Function of
- Amylose
- Amylopectin
- Glucoamylase
- Isomaltase
these are all enzymes meant to digest/break down starch
- amylose works on polysaccharides of straight chain polymers
- amylopectin works on branched chain polymers
- Glucoamylase breaks down maltotriose and maltose (products that were part of starches but not able to be absorbed until further break down at brush border membrane)
- Isomaltase breaks down alpha-limit-dextran (product that was part of starches but not able to be absorbed until further break down at brush border membrane)
Explain how disaccharides are digested before being absorbed in small intestine?
- Digested AT THE BRUSH BORDER MEMBRANE and then absorbed.
* disaccharide examples are lactose, sucrose, etc
Explain how monosaccharides are digested before being absorbed in small intestine? (2)
- Monosaccharides are freely absorbable. Glucose can go directly through intestinal epithelial cells via SGLT1 - no need for digestion. (SGLT1 relies on Na concn to move along with monosaccharide through SGLT1)
- Then capillaries and then liver
monosaccharides include glucose, fructose, galactose
- Where are proteins absorbed?
- Function of endopeptidases?
- function of aminopeptidases and carboxypeptidases?
- where does these peptidases come from?
- small intestine
- cleave peptide bonds except terminal peptide bonds
- cleave peptide bonds at terminal ends (either amino or carboxyl end)
- pancreas
Explain how proteins are digested before being absorbed in small intestine? (6)
- Protein digestion starts in the stomach with pepsin
- At small intestine proteins get broken down in the lumen → broken into amino acids
- the amino terminal ends get further digested AT THE BRUSH BORDER MEMBRANE because this is where aminopeptidase is found
- These amino acids get absorbed (image) in di or tripeptides via active transport (using Na+ gradient)
- Di and tripeptides are further digested within the epithelial cells of small intestine
- Then go to capillaries and eventually liver
Function of
- GLUT5
- GLUT2
- Absorbs fructose from intestinal lumen
- Secretes glucose, galactose, fructose from basolateral membrane of epithelial cells of small intestine into blood
- Explain process of endocytosis of proteins in small intestine
- When does endocytosis of proteins occur?
- this is when entire proteins are absorbed directly into epithelial cells without digestion
- this allows transfer of passive immunity from mother to child postnatal.
- Once full protein is in inside epithelial cells then it can be transferred to M-cells on basolateral side with is endocytosis by M cells
What are the types of lipids we ingest? (3)
- triglycerides, phospholipids, cholesterol
- Why are lipids trickier to digest in the GI tract?
- Explain how lipids are digested before being absorbed in small intestine?
- Need to emulsify lipids bc they do not easily mix with aqueous environment
- starts in stomach - lingual and gastric lipases digest lipids
- Lipases from pancreas do majority of lipid digestion in small intestine
Triglyceride (lipid)
- Where in the small intestine are they digest (lumen or brush border)
- What are triglycerides broken up into and absorbed?
- lumen
- broken down into glycerol and fatty acids. Then in the epithelial cells they are reformed inside the cell before leaving the cell on the basolateral side
Phospholipids (lipid)
- What enzyme digests these?
Phospholipase A2
Cholesterol (lipid)
- What enzyme digests these?
- Through what channel is cholesterol absorbed into epithelial cells?
- What drug can inhibit this channel?
- cholesterol ester hydrolase digests cholesterol
- NPC1L1
- ezetimibe
What two techniques are used for emulsification of lipids in GI tract?
- mechanical disruption by mechanical movements in stomach
- Use of detergent like bile acids. colipase anchors pancreatic lipase to the bile salts to allow for lipid digestion
How are lipids absorbed in the small intestine? (3)
- Lipid digestion products are transported to the enterocytes in mixed micells and then absorbed into the epithelial cell
- Inside the epithelial cell they are reformed inside the cell before leaving cell via chylomicrons
- chylomicrons go to lacteals before going into blood (too big for blood capillary) → by going to lacteals (lymphatic system) they can bypass the liver and enter circulation from thoracic duct
where in small intestine are bile acids reabsorbed?
- Distal ileum
- What minerals are absorbed in the small intestine (2)
- In what part of the small intestine?
- calcium and iron
- proximal part of the small intestine (calcium can also be absorbed in the rest of the small intestine)
- How is calcium absorbed in the small intestine?
- Diffusion through paracellular gaps (only occurs if there is low calcium in blood such as in pregnancy)
- Actively absorbed via transporters on epithelial cells (transporters are regulated by vitamin D)
- What are the two forms iron is absorbed through?
- How is each absorbed/what changes need to happen to each form?
- heme (more efficient_ and non-heme
- Heme - taken up and degraded inside cell ;;; Non-Heme : iron is in ferric (Fe3+) form and needs to be converted to ferrous (Fe2+) form and then it can be absorbed
Vitamin B12 is absorbed in the small intestine but what part of the small intestine?
- distal ileum
Duodenum of small intestine
- villi are [long/short] and [thin/fat]
- [A lot or few] goblet cells
- [Adventitia or serous] covering
- Marker of duodenum (structure)?
- long and thin
- a few goblet cells
- adventitia
- Brunner’s glands are found in submucosa- secrete bicarbonate to neutralize stomach acids
Jejunum of small intestine
- villi are [long/short] and [thin/fat]
- [A lot or few] goblet cells
- [Adventitia or serous] covering
- Marker of jejunum? (structure)
- Villi are long and thin
- more goblet cells than duodenum but less than ileum
- Serosa covering
- Paneth cells - produce antimicrobial compounds (defensins and lysozyme)
Ileum of small intestine
- villi are [long/short] and [thin/fat]
- [A lot or few] goblet cells
- [Adventitia or serous] covering
- Marker of ileum (structure)
- villi are short and fat
- a lot of goblet cells
- serosa covering
- Peyer’s patches are marker of ileum
Large intestine
- Main roles
- goblet cells are [present/absent]
- how do villi look?
- What types of cells are found here? (hint: one of them is enterocytes obviously)
- How does the large intestine make vitamin K and B12?
- absorption of water, electrolytes and gases and feces compaction
- HIGH number of goblet cells
- no villi in large intestine
- enterocytes, DNES cells, and stem cells
- there is a lot of microorganisms that make and release vitamin K and B12
What is glycocalyx?
- specialized mesh of glycoproteins, carbs, and enzymes. this is found on the apical parts of microvilli of the small intestine. Essential for nutrient absorption.
How are enterocytes bonded close together?
- bound via tight junctions and adherens junctions - prevents fluid leakage but in duodenum this is leaky
- What parts of the colon are surrounded by serosa and adventitia?
- serosa covers cecum, transverse, and sigmoid colon - adventitia covers ascending and descending colon
- The appendix contains high amount of what type of tissue?
- lymphoid tissue - may act as storage for normal gut microbes during severe GI infections
- Differentiate what epithelial types are found in the colorectal zone and the anal transition zone?
- colorectal zone: simple columnar epithelium with goblet cells, lymphoid follicles, blood vessels
- anal transition zone: stratified squamous epithelium (w/keratinization more distally)
- What does the endoderm create in the abdomen?
- What does the mesoderm create in the abdomen?
- GI tract epithelium and glands + abdominal organs
- Surrounding GI structures like stroma, muscles, peritoneum, spleen, mesentery
- Pharynx
- Thoracic esophagus
- Abdominal esophagus
- Stomach
- Superior half of duodenum (1st and 2nd parts)
- Liver parenchyme and hepatic duct epithelium
- Gallbladder, cystic duct, and common bile duct
- Dorsal and ventral pancreatic rudiments (exocrine cells, pancreatic duct epithelium, endocrine cells)
WHAT DERIVES THIS? (foregut, midgut, hindgut)
Foregut
- Inferior half of the duodenum (3rd and 4th parts)
- Jejunum
- Ileum
- Cecum and its appendix
- Ascending colon
- Right ⅔ of transverse colon
WHAT DERIVES THIS? (foregut, midgut, hindgut?)
Midgut
- Left ⅓ of the transverse colon
- Descending colon
- Sigmoid colon
- Rectum
- Anorectal canal to the pectinate line
WHAT DERIVES THIS? (foregut, midgut, hindgut)
Hindgut