GI Secretions Flashcards
What are the sources of gut secretions?
Epithelial cells
Salivary glands
Stomach
Pancreas and liver (gall bladder)
What are the epithelial secretions?
Water and electrolytes
Mucus
Special molecules
Water and electrolytes secretion
Reaction medium
Used to liquify, lubricate and dissolve
Moves ingesta from the mouth to the anus
H+ and Bicarbonate
Mucus secretion for epithelial cells
For lubrication and protection
What are the special molecules for epithelial secretion?
Digestive enzymes like lipase and amylase
Used for digestion and absorption
How much does ruminants secrete a day?
80 L
What are the 2 types of salivary secretions?
- Organic
- Inorganic (ions)
Digestive enzymes of organic salivary secretions
- Amylase (carbs)- neutral pH, pa1,4 glycoside bond
- Lipases (fats)- Triglycerides, acidic pH
What is the difference between lipase and amylase in pancreas vs. saliva?
Pancreatic lipases/ amylases are 10x more effective/ potent in digesting lipids and carbs compared to saliva
Why is mucus important for salivary glands?
Because it has lactoferase used to kill bacteria (bactericidal)
How is saliva regulated?
Salivary nuclei is either stimulated (neuronal) or inhibited (hormonal) by certain factors, it will activate the hindbrain that regulates salivation
What are the organic salivary secretions?
Digestive enzymes
Mucus/ glycoproteins
Lysozymes/ Lactoferrin
Kallikrein
Kallikren
Converts plasma protein to bradykinin (vasodilator)
Bradykinin
Opens up blood vessels (easy blood flow)
Decrease in bradykinin leads to the constriction of blood vessels and high blood pressure
Inorganic Salivary Secretions
Ions (Cl-, Na+, K+ and HCO3-)
Increase during meals
Gastric secretions
HCl
Pepsinogen
Mucus
Intrinsic Factor
What of the function of HCI
Converts pepsinogen into active pepsin
Bacteriostatic (bacteria won’t grow)
When you have a max need for digestion
Pepsin
Protein digestion
Secreted as inactive pepsinogen
Stimulated by vagus and secretin
What is the function of gastric mucus?
Protection, lubrication and barrier
Intrinsic factor
Binds B12 to facilitate absorption
Secreted by parietal cells
Absent in pernicious anemia
2 Component Theory
When the same cell secretes both secretions depending on the state of the gut
Where is the 2 component theory used?
The parietal cell secretes HCl in the digestive state is replaced with salt in the interdigestive state
What is interdigestive state of the gastric acid secretion inhibited by?
Vagotomy
Antrectomy
H2 Antagonists
How is gastric acid secretion controlled?
Digestive phase
1. Cephalic phase
2. Gastric phase
3. Intestinal phase
Cephalic Phase of the stomach
Vagally mediated
Treatment for hyperactivity
30% of secretion
Increased by hypoglycemia, insulin and glucose analogues
Gastric Phase of the stomach
Major player (70%)
Inhibit with H2 blocker
Increased by alcohol, Ca and caffeine
Intestinal Phase of the stomach
Vagally mediated
10% (not gastrin related)
Stimulated by duodenal amino acids
What are the 2 types of gastric mucus?
Soluble mucus
Insoluble mucus
Soluble mucus of gastric secretions
Source: mucous neck cells
Lubrication
Stimulated vagally
Insoluble mucus of gastric secretions
Source surface mucous cells
Barrier between gastric mucosa and food (broken= ulcers)
Stimulated mechanically or chemically (food)
Pancreatic Secretions
Islands of Landerhans - insulin/ glucagon
Ductal cells- ions
Acinar cells- digestive enzymes
Endocrine secretions
Islands of Landerhans
Hormones
4% total secretion
Exocrine secretions
Ions (6%)- ductal cells
Enzymatic (90%)- acinar cells
What happens when there’s low blood pressure (needs to increase)?
- Secretes glycogen
- Order liver to convert glycogen into glucose
- Release into the blood
What happens when there’s high blood pressure (needs to decrease)?
- Insulin secreted
- Liver concerts it to glycogen
- Glycogen held in liver until body needs it
Ionic secretions in the pancreas
Ductal cells will secrete salt from pancreas @ low rate
Then will secrete bicarbonate @ high rate
2 component theory
Enzymatic secretions of the pancreas
Active enzymes: lipase and amylase
Inactive enzymes: trypsinogen activated by enterokinase
Control of pancreatic secretions
Secretes and stops pancreas from eating itself
1. Synthesized inactive
2. Trypsin inhibitors
3. membrane bound
4. Autodigestion by trypsin
What are the phases of pancreatic secretions?
Cephalic
Gastric
Intestinal
Cephalic (pancreas) phase
20%
Vagally mediated
Low vol/ high concentration
Gastric (pancreas) phase
5-10%
Vagally mediated
Intestinal (pancreas) phase
70%
Hormonal control (CCK)
Secretion clinical considerations
Chronic Pancreatitis
Tumors
Cystic Fibrosis (low chloride)
80% damage to produce steatorrhea
Secretion tumors
Decrease trypsin, chymotrypsin and lipase but NOT Amylase
Chronic pancreatitis
Active proteases
Low bicarbonate
Obstructions
Trypsin
Gall Bladder
Sac/ container of bile
Function: digest and absorb fat
Hormonal (CCK) and vagal control
What are the functions of the bile?
Fat digestion (emulsification)
Fat absorption (micelle formation)
Elimination of cholesterol, heavy metals, bile pigments, drugs
Components of bile
Organic (bile acids, phospholipids, cholesterol, bile pigment)
Inorganic (water, bicarbonate and ions)
Bile Acids function
Binds to fat droplets –> allow lipase to work on fatty droplets by adding an electrical charge–> digest
Synthesized and recycled daily
Phospholipds function
Prevents aggregation of fat droplets
Increase surface area for fat
Characteristics of bile acids
From hepatocytes
Continuous production
30 min after a meal
Hormonal/ Vagal control
Absorption of bile acids
50% passive re-absorption (upper intestine, unconjugated)
50% active re-absorption (low intestine, conjugated)
Characteristics of Phospholipids
Lecitin is amphipathic (has electrical charge and affinity to water)
30-40%
Micelle formation to solubilize cholesterol
Characteristics of cholesterol
4%
Excess served as Gallstone Nidus (center)
Characteristics of bile pigment
2%
Bilirubin- RBC- liver damage
Damage causes jaundice
Secreted as glucuronic salt
Not found in micelle
When is bile pigment soluble?
When conjugated with glucuronic acid in the liver
Cholecyectomy
Removing gall bladder
Secretions will be coming directly from liver and not gall bladder
What are the 2 types of gallstones?
Cholesterol (50-75% cholesterol)
Pigment (unconjugated bilirubin with Ca++)
