Physiology and Anatomy: Small Intestine Flashcards
3 regions of the small intestine?
- Duodenum (shortest)
- Jejunum
- Ileum (longest)
T/F: The majority of the duodenum is retroperitoneal?
True
The jejunum has large _______
Plicae circulares
The ileum has many large ________
Lymphoid nodules (Peyer’s Patches)
Arterial supply of the first 2/3 of duodenum?
Hepatic artery of celiac trunk => superior pancreaticoduodenal art.
What branch of the superior mesenteric artery also supplies the duodenum?
Inferior pancreaticoduodenal art.
Arterial supply of the rest of the small intestine?
Superior mesenteric artery => jejunal and ileal arteries
Venous drainage of the intestines?
Superior mesenteric (SI, LI, stomach and pancreas) + Splenic vein => portal hepatic vein
Mucosa epithelium?
Simple columnar, villi
Where are crypts of Lieberkuhn found?
In the mucosa of the duodenum, jejunum, and ileum
What type of glands does the duodenum contain?
Brunner’s glands
Are there any glands in the jejunum and ileum?
No
What are plica circulares? What do they do? (3)
Folds in mucosa and submucosa
- Enhance absorption
- Increase SA
- Encourage mixing
Each villus is covered by _______ with core of ______
Epithelium; Lamina Propria
What is in the connective tissue of villi? (4)
Arteriole, venule, capillary network, lacteal
What are microvilli and what do they do?
- Projections of apical membrane too small to be seen individually = brush border
- Greatly increase SA
Where are goblet cells in the SI and what are they for?
Scattered among absorptive cells - secrete mucous to facilitate passage of materials
What do Paneth cells do? (2)
- Regulate the microenvironment of intestinal crypts
- Initiate immune response
Where are I cells? What do they secrete? What is their main function?
- Location: SI/duodenum
- Hormone: CCK
- Fun: Pancreatic enz secretion, GB contraction
Where are S cells? What do they secrete? What is their main function?
- Location: SI
- Hormone: Secretin
- Fun: Bicarb and H2O secretion from pancreas, inhibit gastric emptying
What do D cells secrete?
Somatostatin
What do K cells secrete?
GIP
Where are L cells? What do they secrete? What is their main function?
- Location: SI
- Hormone: Peptide YY
- Fun: Inhibit gastric secretion and motility
Where are Mo cells? What do they secrete? What is their main function?
- Location: SI
- Hormone: Motilin
- Fun: Migrating motor complex
What does stretch from chyme against the intestinal wall elicit?
Concentric contractions
What does the spacing between contractions cause? What is it?
Segmentation - chyme from one segment forced into relaxed next = mixes and circulates
A powerful wave of contractile activity that travels long distances down the small intestine?
Peristaltic rush
Control of peristalsis can be _____ or ______
Nervous or Hormonal
Nervous control of the gut? (3)
- Law of the gut
- Chyme entering duodenum
- Gastroenteric reflex initiated by distension
What is the “law of the gut”? What mediates it?
- Distention in the alimentary canal causes distal parts of the canal to relax and proximal parts to contract (circular muscle)
- Mediated by ENS
Hormonal control of peristalsis: Enhanced by…? (3)
- Gastrin
- CCK
- Serotonin
Hormonal control of peristalsis: Inhibited by…? (3)
- Secretin
- Peptide YY
- Epinephrine
Requirements for chyme entering the duodenum? (3)
- Food particles must be very small
- Small volumes of low pH fluid
- Gradual release
What is the major organ that regulates the rate of gastric emptying?
Duodenum
Nervous control that can inhibit gastric emptying? (2)
- SNS: level of spinal cord
- ENS: submucosal and myenteric plexuses
What will nervous control inhibit gastric emptying in response too? (4)
- Change osmolarity in duod.
- Decrease pH in duod.
- Distention/irritation of duod.
- Breakdown products of proteins/FAs
Substances that elicit CCK release?
Fats > peptides > carbs
What is likely the major paracrine regulator of gastric emptying?
CCK
Substances that elicit secretin release?
low pH > fats, capsaicin, bile acids
What kind of impact does secretin have on gastric emptying?
Mild impact
What major hormone performs the role of “ileal brake”?
Peptide YY
Substances that elicit peptide YY release?
Fats > carbs, amino acids
What does Peptide YY do if undigested foods are reaching the distal small intestine?
Slows everything down
The ileocecal valve protrudes into the _____ of the cecum
lumen
The ileocecal valve is forcefully ____ when excess ______ builds up in the cecum
Closed; pressure
What supplies a watery vehicle for absorption of substances from chyme as it comes in contact with villi?
Intestinal digestive juices by enterocytes
Glands found proximal to Sphincter of Oddi?
Brunner’s glands
What do Brunner’s glands secrete? What is it in response to?
Mucous in response to:
- Tactile/irritating stimuli
- Vagal stimulation
- GI hormones (secretin)
Function of Brunner’s glands?
Protect duodenal wall from digestion of gastric juices
What inhibits Brunner’s glands?
Sympathetic stimulation
_____ and ______ chemically digest macromolecules in the chyme?
Bile and Pancreatic enzymes
What does bile digest/do?
Emulsification of lipids
What do pancreatic enzymes do?
Hydrolysis of fats, proteins, carbs into smaller molecules
Bile is secreted by the liver by what ducts? What do they join to form?
Right and left hepatic ducts => common bile duct
What regulates the secretion of bile into the duodenum?
Sphincter of Oddi
If the Sphincter of Oddi is closed, where is bile stored?
Gall Bladder
The main pancreatic duct meets the common bile duct where?
Ampulla of Vater
Digestive enzymes of the pancreas: protein digestion? (4)
- Trypsin
- Chymotrypsin
- Elastase
- Carboxypeptidase
Digestive enzymes of the pancreas: carb digestion?
- Pancreatic amylase
Digestive enzymes of the pancreas: lipid digestion? (2)
- Pancreatic lipase/co-lipase
- Phospholipase A2
What enzyme is contained in saliva? What is it secreted from?
Ptyalin (salivary amylase) - secreted by parotid gland
What does ptyalin hydrolyze? What blocks its activity?
- Hydrolyzes starch
- Inhibited by acid of gastric secretions
Most important for digestion of starches?
Pancreatic amylase
3 major enzymes of the brush border? What do they digest?
- Lactase, Maltase, Sucrase
- Digest major disaccharides
Monosaccharides can be absorbed via what? (2)
- Facilitated diffusion
- Co-transport via Na+ gradient
Digestion of proteins in the mouth?
Only mechanical, no enzymatic digestion
Digestion of proteins in the stomach? (2)
- HCL: denatures proteins
- Pepsin: begins process of digestion (can digest collagen)
Where does most of protein digestion occur?
Duodenum and upper jejunum
When proteins/peptides enter the small intestine, what enzymes attack them? (4)
- Trypsin
- Chymotrypsin
- Carboxypeptidase
- Proelastase
What activates trypsinogen? => trypsin ?
Enterokinase (brush border enzyme) in the lumen
What zymogens can trypsin activate? (4)
- Chymotrypsin
- Pro-elastase
- Pro-carboxypeptidase
- Pro-phospholipase A2
What does trypsin do after food “runs out”?
Digests pancreatic hormones
Membrane-bound peptidases that aid in digestion of large peptides to di- and tri-peptides?
Brush border peptidases
33% of absorption is ____ and 67% is ______
Free amino acids; peptides
Amino acid absorption? (2)
Active transport or secondary transport with Na+
Dipeptide or tripeptide absorption? (3)
- Some Na+ dependent
- Some secondary transport with H+
- Within cytoplasm of enterocyte, most are hydrolyzed to FAAs
Why does digestion of fat present a problem?
Not water soluble so tends to accumulate in large droplets = reduced SA
Solution to challenge of fat digestion?
Emulsify fat droplet into small droplets with amphipathic outer molecule = micelle
Amphipathic molecules in bile that help form micelles? (3)
- Lecithins
- Bile salts
- Cholesterol
Once micelles have been formed, ________ can act on the triglycerides in “interior” of the micelle
Pancreatic lipase
What does pancreatic lipase need to help it insert into the micelle and activate it?
Co-lipase
What does pancreatic lipase break triglycerides into?
2 FFAs and 2 monoacyl glycerols
What happens to lipids after they have been chemically digested and absorbed into the enterocyte?
They’re reassembled into triglycerides and other lipids and inserted into chylomicrons
Where are chylomicrons built and secreted into?
- Built: enterocyte
- Secreted: Lymphatic vessels
What do the proteins on the outside of the chylomicron help it with?
Helps it be delivered to and used by cells throughout body
Carbohydrates and amino acids are transported across the __________ of the enterocyte, and diffuse into the capillary loops within the _______
Basement membrane; villus
Small free fatty acids can diffuse into the blood and be carried by ________
Serum proteins
Chylomicrons are secreted via ______ into the lamina propria
Exocytosis
What can malabsorption result in? (3)
- Diarrhea
- Micronutrient deficiency
- Macronutrient deficiency
Types of malabsorption can be pathophysiologically organized into four major problems…?
- Disturbances in intra- luminal digestion
- Disturbances in terminal digestion
- Disturbances in trans-epithelial transport
- Disturbances in lymphatic transport
Celiac disease:
- Intra-luminal digestion?
- Terminal digestion?
- Trans-epithelial transport?
- No
- Yes
- Yes
Chronic pancreatitis:
- Intra-luminal digestion?
- Terminal digestion?
- Trans-epithelial transport?
- Yes
- No
- No
Lactose Intolerance:
- Intra-luminal digestion?
- Terminal digestion?
- Trans-epithelial transport?
- No
- Yes
- No
Gastroenteritis:
- Intra-luminal digestion?
- Terminal digestion?
- Trans-epithelial transport?
- No
- Yes
- Yes
