Lecture Digestive Part II
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What portion of the small intestine is retroperitoneal?
Where does the bile come from that enters the duodenum?
The bile duct and the main pancreatic duct joi at the hepatopanceratic ampulla
are controlled by the hepatopancreatic sphincter
What structural modification of the small intestine mucosa increases space for absorption?
Circular folds (plica)
- -simple columnar epithelium with goblet cells
- -fingerlike extensions that absorb
- -preojections of absorpative vells
- -bear brush border enxymes that help complete the digestion of carbs and protiens
- Intestinal crypts
- -secretory cells that produce intestinal juice
- -enteroendocine cells
- -Intraepithlial lymphocytes (IEL) release cytokins that kill infected cells
- -Paneth cells secrete antimicrobial agents (Defensins and lysozyme)
What is special about the submucosa od the duodenum and the ileum?
Duodenum has brunners glands that secrete alkaline mucus
Ileum has peyers patches that protect distal part against bacteria
What is intestinal juice made of?
secreted in response to distension or irritation of mucosa
slightly alkaline and isotonic with blood plasma
largley water, enzyme poor because the enzymes are on the brush border, but it contains mucus
facillitates transport and absorption of nutrients
What is the liver composed of and explain a portal triad
- the liver is composed of hepatocytes that make up liver lobules
- these are all connected to a central vein
- There is a portal triad at the corner of each lobule
- -Hepatic venule
- -Portal arteriole
- -bile duct
- liver sinusoids are leaky capillaried between hepatic plates
- jupffer cells are phagocytes in liver sinusouds that remove bacteria and worn out blood cells
- Hepatocyte functions:
- -process bloodborne nutrients
- -store fat-soluable viatmins
- -perform detoxification (huge filter)
- -produce !90 ml bile per day
What are the characteristics of bile?
Yello green alkaline solution
Bile salts: cholesteral derivatices that function in fat emulsification and absorption
Bilirubin: pigment formed from heme
cholesteral, neutral fats, phospholipids, and elecrtolytes
- Enteroheaptic circulation:
- -recyles bile salts
- -bile salts --> duodenum--> reabsorbed from ileum-->hepatic portal blood-->liver-->secreted back into bile
What is the gallbladder and what does it do?
thin walled muscular sac on the ventral surface of the liver
stores and concentrates bile by absorping its water and ions
releases bile via the cystic duct, which dlows into the bile duct
How does the pancreas have both endocrine and exocrine functions?
pancreatic islets of langerhorns secretre insulin and glicafon as its endocrine function
its exocrine function is that the acini secretre pancreatic juice - zymogen granules of secretory cells contain digestive enzymes
What is pancreatic juce made of?
watery alkaline solution neutralizes chymee
electroclyes (primarily HCO3-)
- amylase, lipases, nucleases are secreted in acive form but require ions or bile for optimal activity
- proteases are secreted inactive form but activated in the duodenum
- -trypsinogen is activated to trypsin by brush border enzymes
- -procarboxypeptidase and chymotrysingogen are activated by trypsin
How is bile secretion regulated?
bile secretion stimualted by bile salts in enterohepatic circulation or secretin from intestinal cells expose to HCl and fatty chyme
- gallbladder is stimulated by:
- -CCK from intestinal cells exposed to protiens and fat in chyme
- -Vagal stimulation (minor stimulus)
*CCK also caused the hepatopancreatic sphincter to relax
What are the mechanisms promoting secretion and release of bile and pancreatic juices?
1. Chyme entering duodenum causes release of CCk and secretin from duodenal enteroendocrine cells
2. CCK and secretin enter the blood stream
3. CCK induces secretion of enzyme rich pancreatic juice. Secretin causes secretion of HCO3- rich pancreatic juice
4.Bile salts, and to alesser exten secretin transported via bloodstream timulate liver to produce bile more rapidly
5. CCK (via bloodstream) causes gallbladder to contract and hepatopancreatic sphincter to relax; bile enters duodenum
6. during cephalix and gastric phases, vagal nerve stimulation causes weak contractions of gallbladder
What is the motility of the small intestine?
Describe segmentation and peristalsis
- -initiated by intrinsic pacemaker cells
- -mixes and moves contents slowly and steadily toward the ileocecal valve
- -intensity altered by long and short reflexes
- -wanes in the late intestinal phase when most nutrients have been absorbed
- -initiated by motilin in the late intestinal phase
- -each wave starts distal to the previous
- -meal remnants, bacteria, and debris are moved to the large intestine
local enteric neurons coordinate intestinal motility
- cholinergic sensory neurons may activate the myenteric plexus
- -causes contraction of the cirucular muscle proximally and of longitudinal muscle distally
- -forces chyme along the tract
- ileocecal sphincter relaxes and admits chyme into the large intestine when...
- -gastroileal reflex enhances the force of segmentation in the ileum
- -gastrin increases hte motility of the ileam
ileocecal flap closes when chyme exerts backwards pressure
Describe the anatomy of the large colon
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