What is not absorbed and digested in the duodenum
- No fat digestion
- Fibre not absorbed
What is the most common motion in the SI?
What is it initiated by?
What valve does it move the contents towards?
- Most common is segmentation
- initiated by intrinsic pacemaker cells (cajal cells)
- moves contents toward the ileocecal valve
How does control of motility work?
Where is the most frequency?
Segmentation
- Frequency does NOT change
- we only control INTENSITY
- most frequency in the duodenum
What enhances long reflex of segmentation?
PNS activity
When does peristalsis occur?
What hormone is release?
What happens to each successive wave?
- after most nutrients absorbed
- hormone motilin is released
- each successive wave is initiated a bit more distally called the migrating motility complex (MMC)
What occurs when ACh impulses (cholinergic) are sent PROXIMALLY?
contraction and shortening of the circular muscle
What occurs when ACh impulses are sent DISTALLY?
cause shortening of the longitudinal muscle layer and distension of the intestine
Explain the regulation of pancreatic secretion (HCO3)
- Acidic chyme enters duodenum to release SECRETIN
- fatty protein rich chyme induces release of Cholecystokinin (CCK) - CCK and secretin enter bloodstream
- CCK induces the secretion of enzyme-rich pancreatic juices
- secretin causes copious secretion of bicarbonate-rich pancreatic juice
- CCK induces the secretion of enzyme-rich pancreatic juices
Both act as buffer for acid
- also stimulates secretion of bile from liver
What valve controls the flow of digestive juices and is relaxed by the hormone CCK.
- also allows the release of bile in the duodenum
Sphincter of Oddi
(hepatopancreatic sphincter)
What enzymes are released in inactive form (zymogen) and activated?
Trypsin
Chymotrypsin
Elastase
Carboxypeptidase
Phospholipase
What activates trypsinogen?
Enterokinase
What does vasoactive intestinal peptide (VIP) release cause?
lead to dilation of capillaries to help with absorption
What does GIP release help with?
releases insulin to help with nutrient absorption
What does the following enzymes do for absorption of carbs:
Salivary amylase
Pancreatic amylase
brush border enzymes
Salivary amylase
- begins starch digestion
Pancreatic amylase
- digest starch to oligosaccharides
brush border enzymes
- hydrolyze oligosaccharides
What enzymes help break disaccharides down to monosaccharides?
What is the exception?
Brush border enzymes
Exception: is B-1,4 bonds in cellulose
What is the breakdown of each?
Sucrose
Maltose
Lactose
Sucrose
- Glucose + Fructose
Maltose
- Glucose + glucose
Lactose
- Glucose + galactose
What enzymes are used to breakdown proteins?
what enzymes act in the SI
Pepsin
-pancreatic enzymes that need to be activated (trypsin, chymotrypsin, carboxypeptidases)
- brush border enzymes
How are single AA transported?
How are dipeptides and tripeptides transported?
- Active transport or secondary active transport with NA+
- secondary active transport using H+ gradient
How are glucose and galactose transported?
How is fructose transported?
- Secondary active transport with Na+
- Facilitated diffusion
How are nucleic acids transported?
active transport
How are water-soluble & fat-soluble vitamins transported?
How is vitB12 transported?
- diffusion
- Active transport
- must be bound to intrinsic factor prior to absorption
How are short-chain fatty acids transported?
How are micelles transported (LONG chain fatty acids)
Simple diffusion
Processed in the epithelial cells of villus first to make triglyceride then it is transported
When does Net osmosis occur for water absorption?
when a concentration gradient is established by active transport of solutes into the mucosal cells
How are haustra made in the large intestine?
caused by slight contractions of teniae coli
