Gastrointestinal Lecture 3 Part 2 Physiology of GI secretions Flashcards
In order to maximize absorption the digestive system has to _______?
secrete
Approximately how much do we consume?
- Daily fluid intake = ~1.2 L
- daily solids intake = ~500-800 g
Daily volume of secretions
~7 L
What happens to the majority of fluids, solids and secretions?
Majority absorbed back into the body, only small volume lost in the feces
- ~ 100 mL fluid and 50-100 g solids leave through feces
Origins of gastrointestinal secretions>
most come from the accessory glands
- Salivary glands
- Liver
- Gallbladder
- Pancreas (exocrine)
and small intestine
Daily saliva production approx.
approx. 1500 mL
saliva components
- water (98%)
- electrolytes
- mucus
- enzymes
- immune modulators
What saliva components provide lubrication?
- water (98%)
- electrolytes
- mucus
Purpose of saliva lubrication
protects oral cavity and makes food easier to swallow
immune modulators of saliva
antibacterial antibodies, WBCs, etc.
Which phase of GI regulation does saliva secretion play a role in?
Primarily cephalic phase responses
Which nervous system does saliva secretion usually occur?
autonomic nervous system
saliva secretion of PNS and SNS
saliva secretion when anxious
Anxiety → increased sympathetic drive → decreased salivation/thickening
Saliva secretion with appetizing food
Appetizing food
Daily production of gastric secretions?
approx. 2000 mL
Gastric secretions components
- mucus
- HCl
- enzymes
- hormones
mucus from gastric secretions
Lubricates and protects stomach lining
HCl from gastric secretions
- Solubilizes some food
- kills ingested microbes
- cleaves pepsinogen*
enzymes from gastric secretions
Pepsinogen → pepsin, cleaves proteins OTHERS
hormones from gastric secretions
Not secreted into stomach, but are secreted from stomach into bloodstream in response to stomach contents
Origins of gastric secretions
cells of the gastric glands → Exocrine glands within the wall of the stomach lining
- mucus → surface mucous cells
- HCl → parietal cells
- enzymes → chief cells (pepsinogen)
- hormones → ECL cell (Enterochromaffin-like cell) (histamine)
What GI regulation phase egulates HCl production from gastric secretion?
Mediated by cephalic and gastric phase responses
what part of gastric secretes HCl?
Parietal cells (also known as oxyntic cells) are epithelial cells in the stomach that secrete hydrochloric acid (HCl) and intrinsic factor. These cells are located in the gastric glands found in the lining of the fundus and body regions of the stomach.
How do parietal cells release HCl?
Signal received and second message may increase secretion by having vesicles with the H+/K+ ATPase pump dock with the membrane and so pumps gets expressed on the cell surface and pumps acid into lumen of the stomach.
What detects aa to be present for release of HCl?
G-cells (antrum)
Detect the aa in lumen suggesting presence of a protein rick meal, and produce gastric which will enter circulation and signal to ECL cells which in turn will secrete histamine which will signal parietal cells to increase HCl production. Gastric can also work directly on parietal cells
What stimulates and inhibits HCl production?
- Stimulated by Gastrin, histamine, and ACh
- Inhibited by somatostatin
WHat happened that was opposite of fletcherism?
Daily production of pancreatic secretions
approx. 1500 mL
Pancreatic secretions sometimes referred to as _____?
“pancreatic juice”
Pancreatic secretion components
- Bicarbonate (HC03-)
- enzymes
Bicarbonate (HC03-) from pancreatic secretions
buffer
acts to neutralize the acidity of chyme
anatomic considerations for pancreatic secretions
- exocrine cells & duct cells → produce juice and then travel down to duodenum
- sphincter to help control secretions
- pancreas and gallbladder secretion are mixed and secreted at the same time
GI regulation phase for pancreatic secretions
Primarily intestinal phase control, but also cephalic and gastric phase inputs
Regulation of HCO3- pancreatic secretion
Regulation of enzyme pancreatic secretion
Daily production of bile
approx. 500 mL
Where is biliary secretion produced?
Continuously produced by the liver (dilute bile)
Where is biliary secretions stored and concentrated?
stored and concentrated in the gallbladder
Bile components
- water (~97%)
- Bile salts (<1%)
- Bilirubin (<1%)
- Fats (<1%)
Bile salts in biliary secretions
solubilize water-insoluble fats
Bilirubin in biliary secretions
Hemoglobin breakdown product; excreted
fats in biliary secretions
Includes cholesterol and lecithin (phospholipids); aid digestion
What happens when the sphincter of Oddi is closed?
The gallbladder also fills up when the sphincter of Oddi is closed, preventing its secretion into the duodenum
How is bile concentrated?
While in the gallbladder, water and NaCl are absorbed from it – making it more concentrated
How does the gallbladder respond to CCK?
In response to CCK, the gallbladder contracts and the sphincter of Oddi relaxes, allowing bile to be secreted into the duodenum
GI regulation phase of bile secretion
Primarily an intestinal phase response
Regulation of bile secretion
Daily intestinal secretions
approx. 1500 mL
intestinal secretion components
- water/electrolytes
- mucus
- enzymes
water/ electrolytes in intestinal secretions
Maintains fluidity of intestinal contents
mucus in intestinal secretions
Lubrication and protection of lining of epthelium
enzymes in intestinal secretions
aid digestion
what primarly drives secretion of water into the small intestine?
osmosis
Where does water secretion into SI occur?
Base of intestinal villi surrounded by invaginations of the intestinal wall called the crypts of Lieberkuhn
- water follows the ions
In general, villi are primarily ________, whereas crypts are _________
absorptive, secretory
What can change water osmolarity?
Chyme leaving the stomach and entering the duodenum can change its osmolarity
- A high concentration of solutes in chyme creates a hypertonic environment
- Osmotic forces drive water from the plasma into the intestinal lumen
Approximately how much of total secretions are absorbed?
~6700 mL
