Term
| what are the main functions of the bowel? |
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Definition
| absorption (minerals, water, fats, drugs), secretion (enzymes secreted by the small intestine and mucus secreted by the colon to help lubricate the feces), synthesis (synthesizes some vitamins), storage (unabsorbed food residue), and elimination (propulsion of fecal matter and absorption of fluid) |
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Term
| what is reabsorbed in the large intestine? |
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Definition
| water, vitamins (K, biotin, B5), organic wastes (urobilinogens and sterobilinogens), bile salts and toxins |
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Term
| what are the travel times for food in different parts of the GI? |
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Definition
| food travels from mouth to stomach: 4-8 sec. stomach: 6+ hrs. SI: 3-6 hrs (depending on composition of meal). LI: 12-72 hrs (sometimes more, depending upon individual differences and pathology) |
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Term
| what happens to chyme in the large intestine? |
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Definition
| chyme is transitioned into feces, from which water/Na+/Cl- is absorbed. at this point, it is really the colon's job to propel the material and form the feces. |
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Term
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Definition
| removal of the feces through the anus by digestion |
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Term
| what is the bacteria in the large intestine's job? |
|
Definition
| vitamin recovery and breaking down sugars indigestible to us into short chain fatty acids which can then contribute to calories/nutrition of overall diet |
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Term
| what are the teniae coli? |
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Definition
| three bands of longitudinal smooth muscle in the muscularis that form haustra, which are pocketlike sacs caused by the tone of the teniae coli which are important for sloshing the material back+forth to extract all the nutrients. |
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Term
| what are the epiploic appendages found in the large intestine? |
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Definition
| these are fat-filled pouches of visceral peritoneum which act as cushioning, fat stores, reservoirs for blood that can absorb toxins, barriers for infection, and some surgeons use them to close perforations/protect the suture line |
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Term
| are there villi or permanent circular folds in the mucosa of the large intestine? |
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Definition
|
|
Term
| what kind of epithelium is found in the large intestine? |
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Definition
| a simple columnar epithelium (except around the anus) which has a large number of goblet cells perforating the wall and producing a lot of mucus to help move the feces along. |
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Term
| what do the wall of the intestine do towards the anus? |
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Definition
| compress the feces and give them form |
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Term
| where do the bacterial flora of the large intestine come from? |
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Definition
| bacteria surviving the small intestine that enter the cecum and those entering via the anus (strains present in environment when you were born) |
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Term
| what do the bacteria in the large intestine do? |
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Definition
| colonize the colon, ferment indigestible carbohydrates, release irritating acids and gases (flatus), synthesize B complex vitamins and vitamin K, and make up a large component of the feces |
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Term
| what can happen when using a mannitol (indigestible sugar) bowel preparation in the geriatric population? |
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Definition
| an explosion of the bacterial flora in the intestine |
|
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Term
| what can happen when using a sodium phosphate bowel preparation in the geriatric population/others renally compromised? |
|
Definition
| hyperphosphatemia due to increased absorption of phosphate in the large intestine |
|
|
Term
| how do the small and large intestine compare in terms of flora? |
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Definition
| the small intestine is usually sterile and the large intestine contains an enormous population |
|
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Term
| what is the term used to describe the symbiotic relationship between the human body and the bacterial flora found in its large intestine? |
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Definition
| commensalism: "at the table together" meaning one organism consumes the unused food of another |
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Term
| what do colonic bacteria produce from digestion of undigested complex sugars? |
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Definition
| short chain fatty acids such as butyrate, propionate, and acetate which are then utilized by colonic epithelium via the beta oxidative pathway (can contribute up to 500 cal/day) |
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Term
| what might be a risk with a strict vegetarian taking an antibiotic? |
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Definition
| antibx wipe out bacteria, lose up to 500 cal from their digestion of undigestible (by humans) sugars |
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Term
| how is Na+ reabsorbed in the large intestine? |
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Definition
| it flows down an electronegative gradient (negative inside cell) and is extruded via active transport on the apical side, stimulating movement of more Na+ into the cell. aldosterone increases Na+ uptake - probably reflects common embryological development of distal colon along w/ renal tubules |
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Term
| how is Cl- reabsorbed in the large intestine? |
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Definition
| Cl- is electrogenically transported following Na+ into the cell and is paired w/co-transport of HCO3- |
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Term
| how is water reabsorbed in the large intestine? |
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Definition
| it is passively drawn in (water “obligated” to transport of nutrients), due to the concentration gradient established by Cl- and Na+. it also travels in paracellularly |
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|
Term
| what are mass movements? how are they generated? |
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Definition
| strong peristaltic waves from the middle of the transverse colon that push contents into the rectum. they are generated by the gastrocolic reflex during or immediately following a meal 3-4x/day |
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Term
| how do the haustrations of the large intestine compare to segmentation in the small intestine? what governs them? |
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Definition
| they are more anatomically pre-defined locations of the circular muscle layer. the haustrations are governed by the BER from interstitial cells (~6x/min) usually w/no AP. stronger contractions (via ACh) are produced by prolonging the BER. |
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Term
| the rectum is normally ___________. |
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Definition
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|
Term
| what happens when the rectum is distended? |
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Definition
| that is the first time the body feels an urge to defecate. (mass movements must be strong enough to get feces to the rectum) |
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|
Term
| how long is the human rectum? |
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Definition
| 12 cm long. at the beginning its caliber is similar to that of the sigmoid colon, but near its termination - it is dialated - forming the rectal ampulla. |
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|
Term
| how is urinal continence achieved during defecation? |
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Definition
| the levator ani, a hammock-shaped group of pelvic floor muscles contact and maintain abdominal muscle and support the pelvic organs. |
|
|
Term
| what kind of muscle are the levator ani? |
|
Definition
|
|
Term
| of all the levator ani, which is the most important? why? |
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Definition
| the puborectalis muscle - which contracts and forms a sling around the rectum, maintaining the "carrying position" of the rectum, keeping it from being a straight-line chute until the body is ready to defecate, which it will then relax to allow. |
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Term
| is the external anal sphincter under voluntary control? how does it compare to the internal anal sphincter? |
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Definition
| yes - it is composed of true skeletal muscle, and therefore stronger. the internal anal sphincter is composed of smooth muscle however, and is thus weaker and more likely to be damaged by events such as childbirth/aging. |
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Term
| why is squatting a better position to poop from? |
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Definition
| squatting better relaxes the puborectalis muscle and straightens the rectum |
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Term
| how can we distinguish between solid and gas in the rectum? |
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Definition
| gas exerts less of a pressure and when this is sensed, opening the external sphincter allows gas to escape |
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|
Term
| what things need to be in order to defecate? what about to maintain continence? |
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Definition
| the puborectalis and external anal sphincter need to be able to relax for the rectal canal to straighten in order to defecate. in order to maintain continence, the *puborectalis needs to contract, normal rectal sensations need to be perceived correctly, and the external anal sphincter needs to be strongly contracted. |
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Term
| what initiates the defecation reflex? |
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Definition
| a change in pressure in the terminal colon against the wall (we can distinguish around 5-6 atm of pressure). |
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Term
| what things affect the defecation reflex/stool quality? |
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Definition
| there is very variable physiology of reflex and quality of stool – age, physiology, diet, social/cultural influences, access |
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Term
| why might bedridden pts have more trouble defecating on schedule? |
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Definition
| there is a certain amount of force applied to the stool due to gravity, which is lost in the supine/recumbent/prone position |
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Term
| how might a vegetarian's stool consistency be different than an omnivores? |
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Definition
| more fiber -> looser stool |
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|
Term
| what is the sequence prior to defecation? |
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Definition
| peristaltic waves carry feces along, gradually filling the ascending colon. the haustrations remove everything necessary and mass movements move undigestibles toward the rectum. |
|
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Term
| upon reaching the transverse colon, how much water out of total water that will be absorbed, has been absorbed? |
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Definition
| ~80% (this is the same for electrolytes) |
|
|
Term
| what is the first stop of normal defecation? |
|
Definition
| distention in the full rectum stimulates stretch receptors in the rectal wall, pelvic floor and upper anal canal |
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Term
| after the rectal stretch receptors have been stimulated, what happens next in the process of defecation? |
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Definition
| correct posture is adopted and intra-abdominal pressure is raised to a point exceeding that in the anal canal (straining) |
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Term
| after the intra-abdominal pressure has been increased, what happens next in the process of defecation? |
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Definition
| the internal/external anal sphincters relax and the rectum contracts to expel the stool. the sphincter "snaps shut" after completion |
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|
Term
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Definition
| soft-formed stools should pass w/minimal effort. once initiated, defecation is either continuous or there is passage in bits preceded by periodic straining. |
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|
Term
| what is "normal" in terms of rate of defecation? |
|
Definition
|
|
Term
| what kind of innervation is the defecation reflex? skeletal muscle? |
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Definition
| defecation reflex: parasympathetic. skeletal muscle control: pelvic nerves (S2 and S3 of pudendal nerve). |
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Term
| what is the path of autonomic/somatic innervation controlling defecation? |
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Definition
| afferent signals go up to the cerebral cortex (where the urge to defecate is recognized) and also to the autonomic ganglia which then synapse, go to the ganglia and control the rectum/internal anal sphincter. *efferent signals come down via pelvic nerves and voluntary skeletal muscle signals to the external anal sphincter |
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Term
| if the body perceives the environment to be appropriate for defecation, what happens? |
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Definition
| the external anal sphincter relaxes and the abdominal walls contract |
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Term
| if the body perceives the environment to be inappropriate for defecation, what happens? |
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Definition
| there will be inhibition of reflex and the stool remains in the rectum. after a while, the pelvic floor returns to its resting state and the stool is withdrawn back out of the rectum and the process starts over again. |
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Term
| what is receptor adaptation in the rectum? |
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Definition
| if the urge to defecate is ignored enough times, stretch receptors become accustomed to the new change in pressure and the urge slowly diminishes. fecal matter builds up, becomes more dehydrated and eventually other, more fluid stool may find there way around that obstruction and cause "soiling" |
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Term
| what does fecal continence require? |
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Definition
| 1) anal sphincter must have structural integrity (IAS - relaxes as soon as stool is in rectum, EAS - important in retention). 2) pelvic floor contraction. 3) sensory (must perceive stool to deal w/consciously). 4) stool consistency. 5) motility of gut. 6) emotional factors. 7) lifestyle/toilet accessibility. |
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Term
| what is withholding behavior? |
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Definition
| retentive posturing, a contraction of the gluteal muscles to preserve continence (voluntary to a certain point). this can be often mistaken for a defecatory attempt. *continence is learned behavior. |
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Term
| what is the sampling reflex? |
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Definition
| local, transient relaxation of the internal anal sphincter which allows recognition of the rectal content by the proximal anal mucosa. this is a learned behavior to distinguish between gas and fecal matter. |
|
|
Term
| what gasses make up flatus? |
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Definition
| N2 usually predominates (due to diffusion from blood to bowel), but can also have CO2, H2, CH4 and low levels of O2 |
|
|
Term
| where does most flatus come from? |
|
Definition
| fermentation of substances we are unable to digest in the bowels |
|
|
Term
| what gives flatulence its "bang"? its "bite"? |
|
Definition
| bang = N2, bite = H2S and CH4 |
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|
Term
| why do vegetarians produce more flatulence? |
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Definition
| b/c they have more indigestible carbs such as cellulose for bacteria to digest |
|
|
Term
| what does the flora of the large intestine largely depend on? why is this important? |
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Definition
| the environment within a few hours of wherever that person was born. though generally everyone has the same intestinal flora, only 1/3 of humans have specifically CH4 producing bacteria |
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|
Term
| how do you know if someone has CH4-producing intestinal flora? |
|
Definition
|
|
Term
| what determines the sound associated with flatulence? |
|
Definition
| volume of gas and the presence of hemorrhoids |
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|
Term
| what do most complaints about flatulence have to do with? |
|
Definition
| disordered motility causing more gas to reflux back into the stomach OR abnormal pain response to bowel distention |
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Term
| what is the valsalva maneuver? what happens when you do it? (*definitely know this*) |
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Definition
| attempted forced expiration against a closed glottis - accomplished by contracting the intra-abdominal muscles. doing this increases thoracic cavity pressure (which is usually low) and in heart pts, the thin walled vena cava can be affected and lead to transient ischemia of the heart or an MI with straining on a stool |
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|
Term
| is constipation a symptom or disease? |
|
Definition
|
|
Term
| why are feces brown? what makes them paler? |
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Definition
| bilirubin makes feces brown and the paler they are, the higher the fat content |
|
|
Term
| what is the odor of feces due to? |
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Definition
| indole/skatole (from tryptophan digestion), and H2S + other gasses which result from decomposition of undigested food residue, unabsorbed amino acids, dead bacteria and cell debris |
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Term
| what is the anal wink? what is the innervation involved? |
|
Definition
| reflexive contraction of the external anal sphincter due to palpation or noxious stimuli. this response is via the pudendal nerve (from S1-3) |
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|
Term
| what is the gastrocolic reflex? |
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Definition
| an increase in colonic activity after a meal. distention of the stomach stimulates evacuation of the colon. chewing gum can also initiate this reflex. |
|
|
Term
| what is the enterogastric reflex? |
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Definition
| distention and irritation of the small intestine which results in suppression of secretion and motor activity of the stomach |
|
|
Term
| what is the intestinointestinal reflex? |
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Definition
| when a part of the intestine becomes overdistended, or its mucosa becomes excessively irritated, activity in other parts of the intestine is inhibited as long as the distention persists |
|
|
Term
| what is the gastroileal reflex? |
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Definition
| an increase in ileal motility and opening of the ileocecal valve when food enters the empty stomach |
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|
Term
|
Definition
| watery stool resulting from any condition that makes material go through the large intestine too fast, not allowing enough time for water absorption (which is a passive process). |
|
|
Term
|
Definition
| loss of control of the bowel's retentive function which can result in passive leakage |
|
|
Term
|
Definition
| flaccid relaxation of gut in response to touching or a traumatic event that prolongs transit time until it starts to contract a gain |
|
|
Term
|
Definition
| prolonged transit time in the colon marked by the passage of small, hard stools, painful passage (straining), and prolonged interval between bowel movements. |
|
|
Term
| what does the form a stool takes depend on? |
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Definition
| its transit time (motility of gut, emotional factors, lifestyle, accessibility) and consistency (diet, functioning of absorptive processes in gut) |
|
|
Term
| what are the causes of diarrhea? |
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Definition
| malabsorption diarrhea (unabsorbable osmolytes in lumen), genetics (sugar enzyme disorders), disease (pancreatitis/stones), and secretory diarrhea (most common - bacterial toxins) |
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|
Term
| what are the physiologically related causes of constipation? |
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Definition
| too dry feces due to absorption of water, prolonged distention of the large intestine, ignoring the urge, reduced intestinal motility, obstruction (tumor or spasm), impairment of the defecation reflex, history of painful defecation and fear (esp children), impaction with "overflow diarrhea" (most common in frail dependent individuals. |
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|
Term
| why does constipation frequently occur in pregnancy? |
|
Definition
| progesterone decreases the motility of the gut, the stomach and intestines are displaced, and more water/nutrients are absorbed (gastric overloading and transit times increased) |
|
|
Term
| what are diseases which involve autonomic neuropathology (can cause bowel disturbanced)? |
|
Definition
| DM, spinal cord disease, and chemotherapy |
|
|
Term
| what is nausea? what is it associated with? |
|
Definition
| a psychic experience, an awareness of the urge to vomit - it is associated with decreased gastric tone OR w/increased gastric tone (not a stimulus, it is an *accompaniment). |
|
|
Term
| what is nausea usually accompanied by? |
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Definition
| decreased motility, increased SI tone, reverse peristalsis in the proximal SI bringing contents back into stomach if the pyloric sphincter is incompetent, and autonomic effects (perspiration, salivation, tachycardia, anorexia, and headache - emotionally involved and very variable) |
|
|
Term
| what is nausea usually accompanied by? |
|
Definition
| decreased motility, increased SI tone, reverse peristalsis in the proximal SI bringing contents back into stomach if the pyloric sphincter is incompetent, and autonomic effects (perspiration, salivation, tachycardia, anorexia, and headache - emotionally involved and very variable) |
|
|
Term
| what is nausea? what is it associated with? |
|
Definition
| a psychic experience, an awareness of the urge to vomit - it is associated with decreased gastric tone OR w/increased gastric tone (not a stimulus, it is an *accompaniment). |
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|
Term
| what is retching (dry heaves)? |
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Definition
| an actual physiological process (as compared to nausea), retching is a spasmodic respiratory movement against a closed glottis where the antrum of the stomach contracts and the fundus/cardia relax. the abdominal muscles also raise intra-thoracic pressure, which is normally very low, so whatever contents are in the stomach are sent into the esophagus. *UES doesn’t open - nothing comes out.* a secondary wave (primary has to start from the top w/the UES) of peristalsis brings the contents back down the esophagus. this can occur in cycles. |
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|
Term
| what innervation is involved with vomiting? |
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Definition
| vagal and phrenic nerves to the diaphragm as well as sympathetic innervation |
|
|
Term
| what does the stomach do during vomiting which facilitates the process? |
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Definition
| the antrum spasms and the pressure in the body and fundus are very low/flaccid - facilitating movement of substances up into the esophagus |
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|
Term
| where are the vomition centers in the brain? |
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Definition
| in the *dorsal portion of the lateral reticular system in the medulla, this is an important area in regulating interaction of the pulmonary and GI systems (its dysfunction can result in aspiration). this center receives input from distention of the gut, vestibular apparatus, eyes, and other sensory organs. |
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|
Term
| how can sensors in the heart stimulate vomiting? |
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Definition
| there is chemoreceptor trigger zone on the floor of the 4th ventricle which is not protected by the BBB, so it is exposed to all stimuli/toxins circulating in the blood |
|
|
Term
| what are the mechanics of vomiting? |
|
Definition
| the hypopharyngeal sphincter (UES) is open, (which the jaw thrust out to facilitate), the antrum of the stomach spasms, the LES is relaxed, the fundus and body are relaxed and strong contractions of the abdominal muscles force contents up into the esophagus then through the relaxed UES and out. |
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|
Term
| how is vomiting different in an infant? |
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Definition
| there is usually no intra-abdominal segment of the esophagus, so the function of the LES is compromised/absent. therefore, when the infant eats a large meal, they will regurgitate - which is different than vomiting. |
|
|
Term
| what is the final common pathway in vomiting? |
|
Definition
| duodenal contents go into stomach, pylorus of the stomach is not competent, and the person takes a deep breath, the stomach is squeezed between the diaphragm and abdominal muscles and empties very rapidly |
|
|
Term
| what are other inputs to the vomiting center? |
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Definition
| the higher cortical centers (terror, visual signals) and disturbed vestibular functions (stimulation of cranial nerve VII and vomiting center) |
|
|
Term
| what is most incidence of vomiting supposed to be for? |
|
Definition
| protection of the GI tract against noxious toxins |
|
|
Term
| what is the theory as to why vestibular imbalances cause nausea/vomiting? |
|
Definition
| b/c there is a disconnect between what the eye see (faster) and what the vestibular apparatus experiences (slower) |
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|
Term
| what are the serious consequences of vomiting? |
|
Definition
| acid/base balance achieved by the kidneys is thrown off (vomiting HCl causes alkalosis/diarrhea of HCO3 causes acidosis), volume/electrolyte depletion, malnutrition, and aspiration pneumonia |
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