Lecture Digestive Part II

Duodenum

The bile duct and the main pancreatic duct joi at the hepatopanceratic ampulla

are controlled by the hepatopancreatic  sphincter

Circular folds (plica)

• Villi
• -simple columnar epithelium with goblet cells
• -fingerlike extensions that absorb

• Microvilli
• -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)

Duodenum has brunners glands that secrete alkaline mucus

Ileum has peyers patches that protect distal part against bacteria

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

• 
• 
• largest gland in the body
• lesser omentum anchors liver to stomach
• hepatic artery and vein at the porta hepatis
• bile ducts:
• -common hepatic duct leaves the liver
• -cystic duct joins the gallbladder
• -bile duct formed by the joining of both
• 

• 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

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

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

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

watery alkaline solution neutralizes chymee

electroclyes (primarily HCO3-)

• Enzymes:
• 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

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

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

• Segmentation:
• -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

• peristalsis
• -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