GI Tract Part 1 Flashcards by sophie rosen

Alimentary canal extends from

oral cavity to anus

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Breakdown of food occurs in 5 phases—

ingestion, fragmentation, digestion, absorption, & elimination

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— occurs in oral cavity, accompanied by —; results in — formation

Ingestion
fragmentation
bolus

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Stomach completes fragmentation & initiates —

digestion

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Contractions of smooth Mm

peristalsis

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peristalsis is under — control

autonomic

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In duodenum, pancreatic & biliary secretions results in

emulsificationof fat

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In jejunum & ileum, 1’ absorption of

nutrients

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In colon, resorption of — & elimination of —

water

waste

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GI tract is a muscular tube lined by

mucus membrane

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Large #’s of — associated with GI tract

glands

e.g., liver, pancreas & intestinal glands; embryological outgrowths of GI tract

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— scattered throughout GI tract

Diffuse lymphoid tissue (MALT, GALT)

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4 distinct layers of GI tract:

mucosa, submucosa, muscularis externa& adventitia(=serosa)

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Mucosa has 3 overall functions:

protection, secretion & absorption

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GI tract is subdivided into 3 layers:

epithelium, lamina propria, & muscularis mucosae

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epithelium—

secretory & absorptive functions; different modifications at different levels of GI tract

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lamina propria—

underlying connective tissue; contains lymphoid nodules, glands, blood vessels & lymphatics

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muscularis mucosae—

thin layer of smooth Mm; boundary between mucosa & submucosa

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Submucosa—

loose to dense irregular connective tissue layer beneath muscularis mucosae

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submucosa supports —, and contains (3)

mucosa

larger blood vessels, nerves, lymphatics

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Muscularis externa(= propria)—

usually inner circular & outer longitudinal smooth Mm layers

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Muscularis externa mm fibers oriented at —

right angles

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Segmentation—

local contractions

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local contractions results in

mixing of food

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how does segmentation occur? both...

proximally and distally, in either direction

Peristalsis—propels food --- only

distally | aborally

Adventitia—

outer loose connective tissue layer, contains major Nn, vessels, & adipose tissue

Within abdominal cavity, referred to as

serosa(= visceral peritoneum)

Continuous with supporting ---

mesentery

Lined by simple squamous epithelium (= ---)

mesothelium

In other areas, adventitia merges with --- tissue

retroperitoneal

Smooth Mm of gut controlled by

autonomic nervous sys

parasympathetic stimulation ---

excitatory

sympathetic stimulation is ---

inhibitory

Parasympathetic motor Nn synapse with ganglia located

near effector organ

in GI tract, ganglia located

within wall of gut, within submucosa & muscularis externa

Clusters of parasympathetic ganglia within submucosa; called

Meissner’s plexus(= submucosal plexus)

Larger clusters located between inner circular & outer longitudinal Mm layers called

myenteric or Auerbach’s plexus

Short, muscular tube, lined by stratified squamous nonkeratinized epithelium

esophagus

In upper third, muscularis | externa composed of

voluntary skeletalMm

Middle third is made of

skeletalMm & | smoothMm

Lower third is made of

smooth Mm only

Gastro-esophageal junction between esophagus & stomach contains

gastroesophageal | sphincter

Pyrosis

“heartburn”

heartburn is due to

regurgitation of stomach acid into distal esophagus from cardia of stomach

Regions of stomach: (3)

cardia, fundus, & pylorus

cardia—surrounded by

smooth Mm cardiac sphincter

cardiac sphincter

gastroesophageal sphincter

cardiac spinchter is located adjacent to

esophagus

cardia contains predominately

mucous secreting glands

glandular portion of stomach

fundus

what does fundus secrete (3)

acid, pepsin, & some mucus

Some texts differentiate fundus from corpus (body); both

glandular (fundus closer to cardia, corpus closer to pylorus)

pylorus contains 1’

mucus (& gastrin) secreting glands

--- controls outflow from stomach into duodenum

Smooth Mm pyloric sphincter

Peptic/gastric ulcer

loss of stomach/duodenal epithelium/ mucosa

Ulcer

damage extends below level of basement membrane (=> bleeding)

Erosion

partial loss of | epithelium (no bleeding)

Tx of peptic/gastric ulcer with

antacids (e.g., | tagamet, cimetidine)

Ulcers frequently associated | with chronic infection with

Helicobacter pylori

stomach produces

urease

increases gastric pH | secondarily increases acid production

Tx of ulcers with

“triple therapy”—2 long-term abx & proton pump inhibitor (prevents H+ secretion)

stomach

distensible organ used for food storage

how many chambers in the stomach

single in most animals

Food undergoes mechanical breakdown via --- & chemical breakdown via

muscular activity | gastric secretions to form chyme

In addition to inner circular & outer longitudinal Mm layers of stomach, also third inner --- layer in muscularis externa

oblique

Little absorption occurs in stomach, except for (3)

water, alcohol, & some drugs (e.g., aspirin)

Stomach lining contains prominent longitudinal folds, ---

rugae

In glandular body of stomach, mucosa contains prominent

gastric pits (= foveolae)

what do gastric pits form?

entrance to gastric glands (straight, tubular glands)

gastic glands secrete ~-- liters watery gastric juice/ day

what does gastric juice contain (5)

``` HCl (pH ~1) pepsinogen (inactive precursor of pepsin, hydrolyzes protein) gastrin rennin lipase ```

Pepsinogen converted to pepsin by action of ---

HCl

Mucosa itself protected by thick layer of ---

mucus

Gastric glands contain several types of cells—5 different classes:

``` mucous secreting cells acid secreting cells pepsin secreting cells enteroendocrine cells undifferentiated stem cells ```

acid secreting cells =

= parietal cells= oxyntic cells

what do acid secreting cells secrete (2)

HCl & intrinsic factor

HCl & intrinsic factor are necessary for

absorption of Vit B12 from ileum

Most numerous in middle third of gland, stain pinkto purple

acid secreting cells

pepsin secreting cells = (3)

chief cells, pepticcells, or zymogeniccells

what do pepsin secreting cells secrete?

inactive pepsinogen

where are pepsin secreting cells located

base of gland (bottom third)

how do pepsin secreting cells stain? why?

stain purple due to large #’s of ribosomes

Parietal & chief cells have long life spans; replaced every..

1 yr

Parietal & chief cells controlled by --- & hormones from ---

autonomic nervous system | endocrine cells in region of pylorus

enteroendocrine cells =

APUDcells (amine precursor uptake & decarboxylation)

paracrine cells target cells within --- vicinity

local

what do paracrine cells secrete

variety of peptide hormones in response to local factors; control GI motility, gastric secretion

gastrin

secreted by “G” cells | stimulates secretion of HCl & pepsin

somatostatin

sec by “D” cells | inhibits secretion of gastrin

secretin(secreted by “S” cells), inhibits --- & stimulates ---

gastric secretion | smooth Mm contraction

Undifferentiated stem cells—mainly in --- of gland

neck

undifferentiated stem cells continuously divide to

replace lost or damaged epithelial cells

As undifferentiated stem cells mature, migrate

up or down gland