digestive part C Flashcards

1
Q

what is the small intestine structure?

A
  • The Small intestine is the major organ of digestion and absorption
  • 2–4 m long (7–13 f t) from pyloric sphincter to ileocecal valve, point at which it joins the large intestine
  • Small diameter of 2.5–4 c m (1.0–1.6 inches)
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2
Q

what is a duodenum?

A

– Duodenum: mostly retroperitoneal; ~25.0 c m (10.0 in) long; curves around head of pancreas
 Has most features
– Jejunum: ~2.5 m (8 f t) long; attached posteriorly by mesentery
– Ileum: ~3.6 m (12 f t) long; attached posteriorly by mesentery; joins the large intestine at ileocecal valve

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3
Q

what is the blood supply in the small intestine?

A

– Superior mesenteric artery brings blood supply
– Veins (carrying nutrient-rich blood) drain into superior mesenteric veins, then into hepatic portal vein, and finally into liver

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4
Q

what is the nerve supply in the small intestine?

A

– Parasympathetic innervation via vagus nerve, and sympathetic innervation from thoracic splanchnic nerves

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5
Q

what are the modifications of the small intestine for absorption?

A

– Small intestine’s length and other structural modifications provide huge surface area for nutrient absorption
 Surface area is increased 600 × to ~200m2 (size of a tennis court)
– Modifications include:
 Circular folds
 Villi
 Microvilli
– Circular folds
 Permanent folds (~1 c m deep) that force chyme to slowly spiral through lumen, allowing more time for nutrient absorption
– Villi
 Fingerlike projections of mucosa (~1 m m high) with a core that contains dense capillary bed and lymphatic capillary called a lacteal for absorption
– Microvilli
 Cytoplasmic extensions of mucosal cell that give fuzzy appearance called the brush border that contains membrane-bound enzymes brush border enzymes, used for final carbohydrate and protein digestion

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6
Q

what is the histology of the small intestine?

A

– Modifications of mucosa and submucosa of the small intestine reflect its function in digestion
– Intestinal crypts: tubular glands scattered between villi
– Five main types of cells found in villi and crypts

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7
Q

what are enterocytes?

A

make up bulk of epithelium
– Simple columnar absorptive cells bound by tight junctions and contain many microvilli
– Function
* Villi: absorb nutrients and electrolytes
* Crypts: produce intestinal juice, watery mixture of mucus that acts as carrier fluid for chyme

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8
Q

what is goblet cells?

A

mucus-secreting cells found in epithelia of villi and crypts

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9
Q

what is enteroendocrine cells?

A

source of enterogastrones (e.g.: C C K and secretin)
– Found scattered in villi but some in crypts

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10
Q

what are pentad cells?

A

found deep in crypts, specialized secretory cells that fortify the small intestine’s defenses
– Secrete antimicrobial agents (defensins and lysozyme) that can destroy bacteria
 Stem cells that continuously divide to produce other cell types
– Villus epithelium renewed every 2–4 days
– Mucosa-associated lymphoid tissue protects intestine against microorganisms and includes:
 Individual lymphoid follicles

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11
Q

what are Peyer’s patches?

A

 Peyer’s patches (aggregated lymphoid nodules), located in lamina propria
– Found in great numbers in distal part of the small intestine, where bacterial numbers increase
 Lamina propria also contains large numbers of plasma cells that secrete I g A
– Submucosa consists of areolar tissue
 Duodenal glands of duodenum secrete alkaline mucus to neutralize acidic chime

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12
Q

Homeostasis imbalance for small intestine

A
  • Chemotherapy targets rapidly dividing cells, such as cancer cells
  • Negative side effect is that it also targets rapidly dividing G I tract epithelium
  • Reason why many patients undergoing chemotherapy have symptoms of nausea, vomiting, and diarrhea
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13
Q

what is intestinal juice?

A
  • 1–2 L secreted daily in response to distension or irritation of mucosa
  • Major stimulus for production is hypertonic or acidic chyme
  • Slightly alkaline and isotonic with blood plasma
  • Consists largely of water but also contains mucus
    – Mucus is secreted by duodenal glands and goblet cells of mucosa
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14
Q

what is the digestive process in the small intestine?

A
  • Chyme from stomach contains partially digested carbohydrates and proteins and undigested fats
  • Takes 3–6 hours in the small intestine to absorb all nutrients and most water
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15
Q

what is t source of enzymes for digestion?

A

– Substances such as bile, bicarbonate, and digestive enzymes (not brush border enzymes) are imported from liver and pancreas
– Brush border enzymes bound to plasma membrane perform final digestion of chyme

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16
Q

how t regulate chyme entry?

A

– Chyme entering duodenum is usually hypertonic; therefore, chyme delivery has to be slow to prevent osmotic loss of water from blood
– Low p H of chyme has to be adjusted upward
– Chyme has to be mixed with bile and pancreatic juice to continue digestion
– Enterogastric reflex and enterogastrones control movement of food into duodenum to prevent it from being overwhelmed

17
Q

what is the motility of the small intestine?

A

– After a meal
 Segmentation is most common motion of the small intestine
– Initiated by intrinsic pacemaker cells
– Mixes/moves contents toward ileocecal valve
– Intensity is altered by long and short reflexes and hormones
* Parasympathetic increases motility; sympathetic decreases it
– Between meals
 Peristalsis increases, initiated by rise in hormone motilin in late intestinal phase (every 90–120 minutes)
 Each wave starts distal to previous wave; referred to as migrating motor complex (M M C)
 Meal remnants, bacteria, and debris are moved toward the large intestine
 Complete trip from duodenum to ileum takes ~2 hours
* Ileocecal valve control
– Ileocecal sphincter relaxes and admits chyme into the large intestine when:
 Gastroileal reflex enhances force of segmentation in ileum
 Gastrin increases motility of ileum
– Ileocecal valve flaps close when chyme exerts backward pressure
 Prevents regurgitation into ileum

18
Q

what is the structure of large intestine?

A

has three unique features not seen elsewhere:
– Teniae coli: three bands of longitudinal smooth muscle in muscularis
– Haustra: pocketlike sacs caused by tone of teniae coli
– Epiploic appendages: fat-filled pouches of visceral peritoneum

19
Q

what are the subdivisions of the large intestine?

A

– Cecum: first part of large intestine
– Appendix: masses of lymphoid tissue
 Part of M A L T of immune system
 Bacterial storehouse capable of recolonizing gut when necessary
 Twisted shape of appendix makes it susceptible to blockages
– Colon: has several regions, most of which are retroperitoneal (except for transverse and sigmoid regions)
 Ascending colon: travels up right side of abdominal cavity to level of right kidney
– Ends in right-angle turn called right colic (hepatic) flexure
 Transverse colon: travels across abdominal cavity
– Ends in another right-angle turn, left colic (splenic) flexure
– Colon:
 Descending colon: travels down left side of abdominal cavity
 Sigmoid colon: S-shaped portion that travels through pelvis
– Rectum: three rectal valves stop feces from being passed with gas (flatus)
– Anal canal: last segment of large intestine that opens to body exterior at anus
 Has two sphincters
– Internal anal sphincter: smooth muscle
– External anal sphincter: skeletal muscle

20
Q

what is the relationship of the large intestine to the peritoneum?

A

– Cecum, appendix, and rectum are all retroperitoneal
– Colon is also retroperitoneal, except for its transverse and sigmoid parts
– Intraperitoneal regions are anchored to posterior abdominal wall by mesentery sheets called mesocolons

21
Q

what is the homeostatic imbalance of large intestine?

A
  • Appendicitis: acute inflammation of appendix; usually results from a blockage by feces that traps infectious bacteria
    – Most common in adolescence when entrance to appendix is at widest
  • Venous drainage can be impaired, leading to ischemia and necrosis (tissue death)
  • Ruptured appendix can cause peritonitis
  • Symptoms: pain in umbilical region, moving to lower right abdominal quadrant
    – loss of appetite, nausea, and vomiting are also seen
  • Treatment: surgical removal (appendectomy), or in some cases, with antibiotics.
22
Q

what are anal recesses?

A

located between anal columns; secrete mucus to aid in emptying

23
Q

what is a pectinate line?

A

the horizontal line that parallels anal sinuses

24
Q

what is bacterial flora?

A

consist of 1000+ different types of bacteria
– Outnumber our own cells 10 to 1
* Enter from small intestine or anus to colonize colon

25
Q

what is metabolic functions?

A

– Fermentation
 Ferment indigestible carbohydrates and mucin
 Release irritating acids and gases (~500 ml/day)
– Vitamin synthesis
 Synthesize B complex and some vitamin K needed by liver to produce clotting factors
* Keeping pathogenic bacteria in check
– Beneficial bacteria outnumber and suppress pathogenic bacteria
– Immune system destroys any bacteria that try to breach mucosal barrier
 Epithelial cells recruit dendritic cells to mucosa to sample microbial antigens and present to T cells of M A L T, triggering production of I g A that restricts microbes

26
Q

what is gut bacteria and health?

A

Gut bacteria and health
– Mounting evidence supports findings that the kinds and proportions of gut bacteria can influence:
 Body weight
 Susceptibility to various diseases (including diabetes, atherosclerosis, fatty liver disease)
 Our moods
– Manipulating gut bacteria may become a routine health-care strategy in future

27
Q

what is Clostridium difficile?

A

an anaerobic bacterium that many carry in intestine, is most common cause

28
Q

what is Haustral contractions?

A

most contractions of colon, where haustra sequentially contract in response to distension
 Slow segmenting movements, mostly in ascending and transverse colon

29
Q

what is Gastrocolic reflex?

A

initiated by the presence of food in stomach
 Results in mass movements: slow, powerful peristaltic waves that are activated three to four times per day
– Descending colon and sigmoid colon act as storage reservoir

30
Q

what is defecation?

A

– Mass movements force feces toward rectum
– Distension initiates spinal defecation reflex
– Parasympathetic signals
 Stimulate contraction of sigmoid colon and rectum
 Relax internal anal sphincter
– Conscious control allows relaxation of external anal sphincter

31
Q

defecation pt2

A

– Muscles of rectum contract to expel feces
– Assisted by Valsalva’s maneuver
 Closing of glottis, contraction of diaphragm and abdominal wall muscles cause increased intra-abdominal pressure
 Levator ani muscle contracts, causing anal canal to be lifted superiorly and allowing feces to leave body

32
Q

what is ileostomy?

A

a procedure that brings back the ileum through the abdominal wall if a colon is removed