Digestive System - Lower Flashcards
description of small intestine
- > 6 meters long
- 3 regions: duodenum, jejunum, ileum
functions of small intestine
- hormone secretion
- digestion
- nutrient absorption
description of duodenum
- Brunner’s glands in submucosa
- short and broad villi
- incomplete serosa
- mostly adventitia
description of jejunum
- long, finger-like villi
- well developed lacteals
- numerous Paneth cells in crypts
desription of ileum
- short, finger-like villi
- Peyer’s patches
- Paneth cells
tissue modifications to increase SA in small intestine
- plicae circulares
- villi
- microvilli
how much do tissue modifications increase SA in small intestine?
400-600x
plicae circulares
vales of Kerckring
- permanent spiral folds of the mucosa and submucosa
- found in duodenum distal half, jejunum, and proximal half of ileum
intestinal villi
finger/leaf-like projections of mucosa
composition of villus core
lamina propria with:
- plasma cells
- lymphocytes
- fibroblasts
- mast cells
- smooth muscle cells
- capillaries
- a single lacteal
lacteal
blind-end lymphatic channel
crypts of Lieberkuhn
-simple tubular glands that extend from the middle of the villus to base of epithelium near muscularis mucosae
composition of crypts of Lieberkuhn
- goblet cells
- columnar cells
- enteroendocrine cells
- regenerative cells
- Paneth cells
where are microvilli located?
apical surface of enterocytes (striated border)
composition of microvillus core
-actin filaments linked w/ fimbrin and villin
how does actin of the microvillus core attach to the plasma membrane?
anchored to membrane by myosin I and calmodulin
what is at the base of the actin bundle and how do these link?
rootlet - crosslinked by an intestinal form of spectrin to adjacent rootlets
what does the end of the rootlet attach to?
cytokeratin-containing intermediate filaments
composition of terminal web of microvillus
spectrin + cytokeratin-containing intermediate filaments
how is small intestine motility controlled?
ANS - submucosal Meissner’s plexus and Auerbach’s myenteric plexus (b/w inner and outer smooth muscle layers of muscularis externa)
intestinal epithelium
simple columnar
cells of intestinal epithelium
- goblet cells
- absorptive cells (enterocytes)
- paneth cells
- antigen processing cells (M cells and dendritic cells)
- enteroendocrine cells
goblet cells
unicellular glands that produce mucinogen (not same as stomach) which accumulates in membrane-bounded granules in apical region
what does mucinogen become?
after being released, it becomes mucous
distribution of goblet cells in small intestine
increase in number from duodenum to ileum
surface absorptive cells (enterocytes)
- tall columnar cells
- microvilli on apical surface covered by glycocalyx
- well-developed zonulae occludens, zonulae adherens, and lateral plications
how often are enterocytes renewed and how does this happen?
every 5-6 days - cells divide down in crypt and migrate up villus; slough off at villus tip
what enzymes digest carbohydrates?
lactase, maltase, sucrase in brush border cell membrane
what does deficiency in lactase result in?
lactose intolerance -> diarrhea
initial digestion of proteins
by enzymes in lumen - pepsin, trypsin, chymotrypsin
digestion of proteins in microvilli
enterokinase and aminopeptidase - degrade oligopeptides into di- and tripeptides and aa’s
digestion of proteins in cytoplasm
cytoplasmic peptidase - degrade di-, tripeptides to aa’s
what happens to aa’s in enterocytes?
aa’s diffuse or are transported across the basal plasma membrane into blood
digestion of lipids in lumen
pancreatic lipase - breakdown to FA’s and monoglycerides and micelles formed
what are micelles bound to?
diffuse into microvilli and attach to FABP - fatty acid binding protein
what happens to micelles once bound to FABP?
transported to sER and esterified to form triglycerides
where are triglycerides transported to from sER?
golgi to form apolipoprotein complex - chylomicron (35 nm diameter)
where happens to chylomicrons after formation in golgi?
fuse with basolateral plasma membrane -> intercellular space -> lacteals
DNES/APUD cells - what do they produce and secrete?
- gastrin
- cholecystokinin
- gastric inhibitory peptide
- other hormones
M cells
microfold cells - has surface microfolds instead of microvilli
where are M cells found?
in epithelium over lymphoid nodules in ileum
what may form in the basolateral portion of M cells?
an intraepithelial pocket that contains lymphocytes (B cells)
function of M cells
antigen uptake, processing, and transport to lymphocytes and macrophages in the lamina propria
how are antigens processed in M cells?
in protease (cathepsin E) containing vesiles and trnascytosed to B cells
where are dendritic cells?
associated with lymphoid follicular epithelium in Peyer’s patches
dendritic cell description
may extend cell processes across basal lamina and b/w tight junctions so that a small portion is exposed to the intestinal lumen
paneth cells
- contain large eosinophilic apical secretory granules
- occur at bottom of crypts of Lieberkuhn
what do paneth cells produce?
- lysozyme continuously - cleaves peptidoglycan in bacteria cell wall
- TNF-a - proinflammatory cytokine
life span of paneth cells
20 days
what do paneth cells secrete?
microbicidal defensins in response to bacteria, bacterial antigens, or food-related stimulation by ACh to protect regenerative cells in crypt
defensins
antimicrobial peptides also called cryptidins
where are regenerative/intermediate cells found?
lower half of crypt
what can regenerative/intermediate cells become?
absorptive or goblet cells
where is the lamina propria located?
villi cores and interstices b/w the crypts of Lieberkuhn
small intestine lamina propria composition
loose CT with:
- lymphoid cells
- fibroblasts
- mast cells
- smooth muscle cells
- nerve endings
- lymphoid nodules
- lacteals
where are Brunner’s glands found?
submucosa of duodenum
description of Brunner’s glands
-branched tubuloalveolar glands
Brunner’s gland secretion?
alkaline secretion of neutral and alkaline glycoproteins, HCO3-, and GIP
GIP
gastric inhibitory peptide = urogastrone
-polypeptide hormone that enhances epithelial cell division and inhibits gastric HCl production
describe lymphatics in ileum
contain aggregate lymphoid nodules - part of the gut-associated lymphoid tissue (GALT)
primary function of cecum and colon
absorption of water and electrolytes
villi of cecum and colon
no villi or specialized mucosal folds
epithelium of cecum and colon
simple columnar epithelium with:
- goblet cells
- absorptive cells
- some enteroendocrine cells
lamina propria of cecum and colon
similar to small intestine - lymphoid nodules and closely packed crypts
submucosa of cecum and colon
- fibroelastic CT
- Meissner’s plexus
- NO glands
muscularis externa of cecum and colon
inner circular and modified outer longitudinal layer of smooth muscle - outer layer gathered in 3 longitudinal smooth muscle bands = teniae coli
what do teniae coli form in the walls of the colon and cecum?
sacculations = haustra coli
what is found b/w muscle layers in the cecum and colon?
Auerbach’s (myenteric) plexus
appendix
short diverticulum arising from cecum
lumen of appendix
narrow, irregularly shaped - often contains debris
what do walls of appendix contain?
large aggregates of lymphoid nodules in the mucosa and submucosa - in middle-aged people
function of appendix
- function in immune system in young people
- reservoir of bacteria to repopulate gut after diarrheal disease
what are people with appendectomies at higher risk of later in life?
intestinal carcinomas
appendix mucosa
- simple columnar epithelium w/ goblet cells
- lamina propria has lymphoid nodules capped by M cells
- no villi
- shallow crypts
- goblet cells
- surface columnar cells
- regenerative cells
- some paneth cells
- many enteroendocrine cells deep in crypts
rectum
similar to colon - contains fewer and deeper crypts of Lieberkuhn
anal mucosa
- longitudinal folds called anal columns
- regions b/w adjacent columns = anal sinuses
anal epithelium
-simple columnar that changes to simple/stratified cuboidal/columnar occasionally then to stratified squamous nonkeratinized distal to anal valves, then to stratified squamous keratinized (epidermis) at the anus
gastritis
gastric mucosal inflammation common in middle-aged and older individuals w/ unknown etiology - may be superficial or affect the entire thickness -> mucosal atrophy
malabsorption disorders
can lead to malnutrition and result in wasting diseases
gluten enteropathy - nontropical sprue
due to destructive effects of certain glutens (rye and wheat) on the intestinal villi - reduce SA available for absorption
how is gluten enteropathy treated?
eliminating wheat and rye products
idiopathic steatorrhea
malabsorption of digested fats of unknown etiology - results in stools w/ high fat content
malabsorption of vitamin K
clotting insufficiency
malabsorption of vitamin B12
can cause pernicious anemia - results from inadequate production of gastric intrinsic factor by the parietal cells
2nd highest cause of cancer death in US
colorectal carcinoma
what does colorectal carcinoma usually arise from?
adenomatous polyps - may be asymptomatic for years
colorectal carcinoma may be diet related how?
high fat and refined carb diet that is low in fiber
age group that most often presents with colorectal carcinoma
individuals > 50 y/o w/ highest incidence in 60-70 y/o
how do you treat colorectal carcinoma?
colon resection - highest survival rates in patients whose tumors do not extend beyond muscularis mucosae
appendicitis
associated with pain and/or discomfort in the lower right abdominal region - fever, nausea, vomiting + elevated WBC count
what can happen if appendix ruptures?
death from peritonitis and endotoxic shock
hemorrhoids
rectal bleeding during defecation
what causes hemorrhoids?
breakage of dilated, thin-walled vessels of venous plexuses above (internal hemorrhoids) or below (external hemorrhoids) the anorectal line
age group that hemorrhoids are common in
> 50 y/o
hirschsprung’s disease
prevents migrattion and differentiation of neural crest cells into neurons of enteric nervous system
cause of hirschsprung’s disease
mutations in 1 of 4 genes:
- endothelin B receptor or ligand
- endothelin 3
- rearranged during transfection RET
megacolon
enlarged colon due to lack of ganglia - causes back up b/c part that is not innervated cannot continue peristalsis
