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Anatomy and Physiology > digestive iii > Flashcards

digestive iii Flashcards

1
Q

Small intestine gross anatomy

A

Major organ of digestion and absorption
-2-4 m long; from pyloric sphincter to ileocecal valve

Subdivisions:

  • duodenum (retroperitoneal)
  • jejunum (attached posteriorly by mesentery)
  • ileum (attached posteriorly by mesentery)
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2
Q

Duodenum

A

Curves around head of pancreas; shortest part (25 cm)

Bile duct from liver and main pancreatic duct from pancreas

  • join at hepatopancreatic ampulla
  • enter duodenum at major duodenal papilla
  • entry controlled by hepatopancreativ sphincter
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3
Q

Gross anatomy of small intestine

A

Vagus nerve and sympathetics from thoracic splanchnic nerves serve small intestine

Superior mesenteric artery brings blood supply

Veins drain into superior mesenteric veins –> hepatic portal vein –> liver

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4
Q

Structural modifications

A
  1. Circular folds (plicae circularis)
    - permanent folds (1 cm deep) that force chyme to slowly spiral through lumen –> more nutrient absorption
  2. Villi
    - extensions (1 mm) of mucosa with capillary bed and lacteal for absoption –> increase surface area
  3. Microvilli (brush border)
    - contain enzymes for carbohydrate and protein digestion –> increase surface area
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5
Q

Intestinal crypts

A

Intestinal crypt epithelium renewed every 2-4 days

  • most = secretory cells that make intestinal juice
  • enteroendocrine cells –> enterogastrones
  • intraepithelial lymphocytes (IELs) release cytokines that kill infected cells
  • Paneth cells secrete antimicrobial agents (Defensins and lysozymes)
  • stem cells divide to make crypt cells
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6
Q

Mucosa

A

Peyer’s patches protect especially distal part against bacteria (may protrude into submucosa)

B lymphocytes leave intestine, enter blood, protect intestine lamina propria with their IgA

Duodenal (Brunner’s) glands of duodenum secrete alkaline mucus to neutralize acidic chyme

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7
Q

Intestinal juice

A

1-2 L per day in response to distension or irritation of mucosa

slightly alkaline; isotonic with blood plasma

Largely water; enzyme poor (enzymes of small intestine only in brush border); contains mucus

Facilitates transport and absoption of nutrients

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8
Q

Digestion in small intestine

A

Chyme from stomach containes

  • partially digested carbs and prots
  • undigested fats

3-6 hrs in small intestine

  • most water absorbed
  • pretty much all nutrients absorbed

small intestine, like stomach, has no role in ingestion or defecation

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9
Q

Requirements for digestion and absorption in small intestine

A

slow delivery of acidic, hypertonic chyme

Delivery of bile, enzymes, an bicarbonate ions from liver and pancreas

mixing

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10
Q

Motility of small intestine: segmentation

A

Segmentation

  • most common motion of small intestine
  • initiated by intrinsic pacemaker cells
  • mixes and moves contents toward ileocecal valve
  • intensity altered by long and short reflexes and hormones (remember parasymp increases)
  • wanes in late intestinal (fasting) phase
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11
Q

Motility of small intestine: peristalsis

A

Initiated by rise in hormone, motilin, in late intestinal phase (every 90-120 mins)

Each wave starts distal to previous
-migrating motor complex

Meal remnants, bacteria, and debris moved to large intestine

From duodenum to ileum takes about 2 hrs

Carb meals move faster, fatty ones move slower

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12
Q

Motility of small intestines: neurons

A

Local enteric neurons coordinate intestinal motility

Cholinergic sensory neurons may activate myenteric plexus

  • causes contraction of circular muscle proximally and of longitudinal muscle distally
  • forces chyme along tract
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13
Q

Motilty of small intestine: Ileocecal junction

A

Ileocecal sphincter relaxes, admits chyme into 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

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14
Q

Large intestine unique feature

A

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

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15
Q

Large intestine regions

A 
cecum
appendix
colon
rectum
anal canal
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16
Q

Cecum and Appendix

A

Cecum = first part of large intestine

Appendix = masses of lymphoid tissue

  • part of MALT of immune system
  • bacterial storehouse –> recolonizes gut when necessary
  • Twisted –> enteric bacteria accumulate and multiply –> can lead to appendicitis
17
Q

Colon

A

Retroperitoneal except for transverse and sigmoid regions

Ascending colon (right side- to level of right kidney) –> right colic/hepatic flexure

Transverse colon –> left colic/splenic flexure

Descending colon (left side)

Sigmoid colon in pelvis –> leads to rectum

18
Q

Rectum, anus, and anal sphincters

A

Rectum

  • three rectal valves stop feces from being passed with gas
  • hemorrhoidal veins

Anal canal

  • last segment of large intestines
  • opens to body exterior at anus

Sphincters

  • internal anal sphincter = smooth muscle
  • external anal sphincter = skeletal muscle
19
Q

Large intestine microscopic anatomy

A

Thicker mucosa of simple columnar epithelium except in anal canal (stratified squamous)

No circular folds, villi, or digestive secretions

Abundant deep crypts with goblet cells

superficial venous plexuses of anal canal form hemorrhoids if inflamed

20
Q

Bacterial flora

A

Enter from small intestine or anus

  • colonize colon
  • synthesize B complex vitamins and vitamin K
  • metabolize some host-derived molecules (mucin, heparin, hyaluronic acid)
  • ferment indigestible carbs
  • release irritating acids and gagsses (500 ml per day)
21
Q

Intestinal flora

A

viruses and protozoans

Bacteria prevented from breaching mucosal barrier
-epithelial cells recruit dendritic cells to mucosa –> sample microbial antigens –> present to T cells of MALT –> B cell produce IgA antibody-mediated response –> restricts microbes

22
Q

Digestive processes in large intestine

A

Residue remains in large intestines for 12-24 hrs

No food breakdown except by enteric bacteria

Vitamins (made by bacterial flora), water, and electrolytes (esp Na and Cl) reclaimed

Major funcs = propulsion of feces to anus and defecation

colon isn’t essential for life

23
Q

Motility of Large intestine

A

Most contraction of colon are haustral contractions

  • slow segmenting movements
  • haustra sequentially contract in response to distension

Also have gastrocolic reflex

  • initiated by presence of food in stomach
  • activates three to four slow powerful peristaltic waves per day in colon (mass movements)
24
Q

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

Muscles of rectum conract to expel feces

25
Q

Valsalva’s maneuver in defecation

A

closing of glottis, contraction of diaphragm and abdominal wall muscles –> increased intra-abdominal pressure

Levator ani muscle contracts –> anal canal lifted superiorly –> feces leave body

26
Q

Steps of defecation

A
  1. feces move into and distend the rectum, stimulating stretch receptors which transmit signals along afferent fibers to spinal cord neurons
  2. a spinal reflex is initiated in which parasym motor fibers stimulate contraction of rectum and sigmoid colon as well as relaxation of internal anal sphincter
  3. if it’s convenient to defecate, voluntary motor neurons are inhibited, allowing external anal sphincter to relax so feces may pass

Anatomy and Physiology (50 decks)

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