GI Secretions Flashcards
What is Ghrelin?
Endocrine hormone/Gut Peptide released into the blood from Oxyntic Cells (epithelial secretory cells of the stomach) that travels to the Arcuate Nucleus of the Hypothalamus to stimulate NPY (Neuropeptide Y) a orexigenic peptide that stimulates hunger
What Gut to Brain Peptide stimulates hunger?
Ghrelin
Chyme moving down the Duodenum further into the Jejunum stimulates what?
“Feeling of Satiety”
Secretion of Gut peptides into the blood that travel to the Hypothalamus and suppress NPY thus decreasing appetite such as:
- Peptide YY
- GLP-1 (Glucagon-Like Peptide)
What does eating slowly do to Gut Peptide secretion?
Allows time for Chyme to make its way down the small intestine and stimulate the secretion of Peptide YY and GLP-1 into the blood so they can travel to the Hypothalamus and suppress NPY release and decrease appetite
What is Leptin?
- A hormone that is produced and released by Adipose tissues when glucose and insulin are present in the blood (from eating) causing a decrease in appetite by suppressing NPY production in the Arcuate Nucleus (Hypothalamus)
- Works in conjunction with Peptide YY and GLP-1
What are the Gut Peptides that regulate Hunger and Satiety? Do any other hormones work in conjunction with these Gut Peptides?
3 Gut Peptides:
- Ghrelin (stimulates Hunger)
- Peptide YY (decreases appetite)
- GLP-1 AKA Glucagon Like Peptide (decreases appetite)
Leptin (produced by Adipose tissues) also works in conjunction with Peptide YY and GLP-1 to DECREASE APPETITE
What Hypothalamic Peptide is regulated by the Gut Peptides? What does it stimulate?
NPY (Neuropeptide Y) which is produced in the Arcuate Nucleus and stimulates hunger
What is important about the Salivary Glands?
They are highly vascularized Exocrine Glands that secrete Saliva into ducts
What does increased blood flow to the Salivary Glands cause?
- Increased blood flow to the Salivary Glands increases filtrate that enters Acinar Cells
- Increased Primary Secretion (Serous and/or Mucous Fluid) into the Duct including ions and Alpha-Amylase (first enzyme)
- Saliva is secreted containing electrolytes, mucus, and Alpha Amylase (starts first digestion of Starches which are Carbs)
What is Salivary Alpha-Amylase?
The first enzyme produced by the Salivary glands that cleaves the linkages of Starches producing Maltose (mostly) and Isomaltose which are 3-9 Glucose molecules in length
What percentage of nutrients are digested pre-Duodenally by enzymes from the mouth and stomach?
25-30%
NOTE: 70-75% are digested in the intestines by Pancreatic Enzymes
What are some important factors found in Saliva?
- Electrolytes
- Alpha-Amylase
- Mucus
- Transcobalamin-1 (TC-1)
- Lingual Lipase (produced by tongue)
What is the purpose of Transcobalamin-1 (TC-1)?
Binds to Vitamin B-12 in whatever is ingested to protect them from Gastric Pepsins
What is Lingual Lipase?
Enzyme produced by the tongue to start the first hydrolization of LIPIDS
Enzymes found in the saliva can start the digestion of what materials?
- Carbohydrates (via Alpha-Amylase from the Salivary Glands)
- Lipids (via Lingual Lipase from the tongue)
Production of Saliva is dependent on what? How does it control Salivary Flow?
PNS via:
- Facial Nerve (CN 5) stimulates Submaxillary and Sublingual Glands
- Glossopharyngeal Nerve (CN 7) stimulates Parotid Glands
How is SNS stimulated Saliva different from PNS stimulated Saliva?
SNS barely stimulates salivary flow and what is produced is very “mucousy” and thick
What does Saliva do?
“COLD TAP”
- Coagulation Factors
- Oral Hygiene (spit removes bacteria from mouth)
- Lubrication (Mucus)
- Digestion (starts lipids and starches)
- Taste (breaks down lipids and starches for taste buds)
- Antimicrobial Action
- Protection
What increases Salivary flow?
- PNS
- CNS (anticipatory)
- Nausea
- Esophageal Distention (Secondary Peristalsis when something is stuck)
- Food
What decreases Salivary flow?
- SNS
- Dehydration and its Hormones (ADH, Aldosterone)
- Sleep
- Drugs
- Aging
Less Saliva leads to more or less Cavities?
Less Saliva leads to more Cavities because Saliva promotes oral hygiene
What are the Gastric Secretions?
“HIP GLOM”
- HCl
- Intrinsic Factor
- Pepsinogens
- Gastrin
- Lipase
- Other (Histamine and Somatostatin)
- Mucus
HCl Overview:
- Secreted by Parietal Cells (like IF)
- Signaled by Vagus Nerve and Gastrin
- General Chemical Digestion of food to increase surface area
- Very Caustic (Acidic)
Intrinsic Factor Overview:
- Secreted by Parietal Cells (like HCl)
2. Binds to and Protects Vitamin B-12 from the Pancreatic Proteases
Pepsinogen Overview:
- Secreted by Chief Cells
- Inactive Zymogen that is converted to the active Pepsin by the acidic environment
- Active form Pepsins do 25-30% of protein digestion
Gastrin Overview:
- Hormone secreted by G-Cells located in the Antrum of the stomach (just before pyloris) INTO THE BLOOD
- Released when mechanoreceptors sensing stretch and chemoreceptors sensing chyme feedback to Endocrine cells
- STIMULATES HCl SECRETION
Gastric Lipase Overview:
- Secreted by Chief Cells
2. Continues Lipid Hydrolysis
Why is Mucus a necessary Gastric Secretion?
It will protect the Gastric Epithelial Cells from the Acidic Environment by sequestering HCO3 to neutralize acid
Histamine Overview:
- Secreted by ECL cells (Enterochromaffin-Like Cells)
- PRIMARY STIMULUS FOR HCl SECRETION
- Vagus Nerve and presence of food in stomach stimulates Histamine secretion
Somatostatin Overview:
- Work directly on Parietal Cell to decrease HCl a little bit
Easy way to remember where things are secreted in the stomach:
- Chief Cells produce Enzymes (Pepsinogen and Lipase)
- Parietal Cells produce Acid and Intrinsic Factors
- “PARents said AS IF”
Parietal Cells Overview:
- ONLY LOCATED IN THE STOMACH
- Undergo morphological change where Canaliculi (Tubular Vesicles) intercalate (fold in) and decrease Surface Area when they do not need to secrete acid
What 3 factors stimulate the Parietal Cells directly to increase the secretion of acid? What do they do?
STIMULATION INSERTS PROTON PUMPS (H+/K+ ATPase) ONTO PARIETAL CELLS TO PUMP H+ IONS INTO LUMEN AGAINST A H+ GRADIENT OF 1 MILLION TO MAKE HCl
- Histamine (PRIMARY)- local effect on Parietal Cells
- Acetycholine (PNS)
- Gastrin (Hormone from G-Cells)
What makes Histamine stimulation of Acid Secretion unique?
ECL Cells can be stimulated by Vagus Nerve (Neural) and Gastrin (Hormonal) to produce Histamine that will cause an increase in secretion of Acid from Parietal Cells
What proton pump is the Rate Limiting Step for Acid Secretion?
H+/K+ ATPase
NOTE: Insertion of the Proton Pump H+/K+ ATPase is stimulated by Histamine, Gastrin, and ACh
Where does the H+ ion used in the H+/K+ ATPase pump come from?
Carbonic Anhydrase in the cell converts CO2 and H2O in to HCO3 (reabsorbed in blood) and H+ (goes to make HCl)
What is the significance of K+ in Parietal Cells and Acid Production?
K+ concentration is high in Parietal Cells because it is pumped in by Na+/K+ ATPase and H+/K+ ATPase so it can flow out into the Lumen and create KCl as well
What is the significance of Cl- in Parietal Cells and Acid Production?
Cl- flows from the blood down into the positive Parietal Cell and into the even more positive Lumen of the stomach where it can bind to H to form HCl
Helicobacter Pylori (H. Pylori) Overview:
- Gram-Negative Bacteria that can live in the Mucus Layer protecting epithelial cells of stomach
- Secretes Urease that makes Ammonia (NH3) to combine with and neutralize the Acid in its area (NH3+H+=NH4)
- Disrupts Mucus and allows Acid to attack Epithelial Cells causing Ulcers
How is H. Pylori treated?
- Proton Pump Inhibitor (binds irreversibly to H+/K+ ATPase)
- Histamine Antagonist
- Antibiotics
What factors inhibit Acid Secretion?
- Secretin (suppress Gastrin)
- Somatostatin (Enteroendocrine Cells adjacent to Parietal Cells)
- GIP (decrease Gastrin release)
- Peptide YY (suppress Gastrin)
- Prostaglandins (decrease Histamine Secretion)
How can chronic NSAIDS use cause Stomach Ulcers?
NSAIDS block Prostaglandin secretion so without Prostaglandins Histamine will stay high and stimulate Acid Secretion which can lead to ulcers.
Why are Brush Border Villus Cells important in the Jejunum?
- Surface Area for absorption
2. Source of Brush Border Hydrolases such as Saccharidases (carbs) and Peptidases (proteins)
What is the significance of Celiac Disease in the Small Intestine?
Celiac Disease causes the atrophy of the Brush Border resulting in a loss of surface area and Brush Border Enzymes resulting in a decrease in digestion and absorption
What is the importance of the Crypts of Lieberkuhn in the Small Intestine?
Source of secretions of buffer and Mucus for the Lumen:
***CFTR (Cystic Fibrosis Transmembrane Conductance Regulator) is a Chloride channel stimulated by Secretin to secrete Cl- into the gut which is followed by Na+ and H2O
What hormones are released in the Duodenum?
“GaGi SC”
1. Gastrin (via Duodenal G-Cells) to increase HCl secretion and motility of lower GI Tract
- Secretin (senses highly acidic chyme) increases Pancreatic and Intestinal Buffers to neutralize Acid
- CCK (in conjunction with the Vagus Nerve) increases Bile Production in the liver, contracts Gallbladder, relaxes Sphincter of Oddi, and stimulates production of Pancreatic Enzymes
- GIP has 2 functions:
A. Gastric Inhibitory Peptide that decreases Gastrin release to decrease HCl secretion
B. Glucose Insulinotropic Peptide goes to the Pancreas to increase Insulin Secretion into the blood in preparation of Glucose
Where is CCK produced and what functions does it serve?
- Hormone produced in the Duodenum
- Increases Bile Production in the Liver
- Contracts Gallbladder
- Relaxes Sphincter of Oddi
- Stimulates production of Pancreatic Enzymes
Where is GIP produced and what functions does it serve?
- GIP is produced in the Duodenum
- 2 main functions:
A. Gastric Inhibitory Peptide that decreases Gastrin release to decrease HCl secretion
B. Glucose Insulinotropic Peptide goes to the Pancreas to increase Insulin Secretion into the blood in preparation of Glucose
What hormones act on the Pancreatic Acini? What do they stimulate the production of?
- CCK stimulates the production of Enzymes
2. Secretin stimulates the production of Buffers
What are the types of Pancreatic Enzymes secreted? What stimulates their secretion?
CCK stimulates the secretion of Pancreatic Enzymes to do 70-75% of digestion such as:
- Proteases- secreted as inactive Zymogens until Trypsinogen is activated to Trypsin by Enterokinase (EK) located in the Duodenum. Trypsin goes on to activate Chymotrypsionogen into Chymotrypsin, Pro-Carboxypeptidase into Carboxypeptidase, and Procolipase into Colipase (Helps form Micelles)
- Pancreatic Lipase (hydrolyzes lipids once inside of Bile “Taxi”)
- Pancreatic Amylase (finishes Starch Digestion)
Talk about the complexities of the Pancreatic Enzymes known as Proteases and what stimulates their secretion:
- CCK is released and travels to the Pancreas to stimulate the release of Proteases
- Proteases are secreted as inactive Zymogens
- Trypsinogen is converted into its active form Trypsin by Enterokinase (EK) in the Duodenum
- The active Trypsin goes on to activate the other inactive Proteases secreted by the Pancreas
- Trypsin converts:
A. Chymotrypsionogen into Chymotrypsin
B. Pro-Carboxypeptidase into Carboxypeptidase
C. Procolipase into Colipase (Get Pancreatic Lipase past Bile membrane)
What happens at the end of a meal?
Chyme moves out of the upper GI Tract into the lower GI Tract resulting in:
- Reduced Vagal Stimualtion
- Cessation of Pancreatic Secretions
- Somatostatin, Glucagon, and Peptide YY effects
Movement of what substances facilitate Na+ and Cl- reabsorption in the Ileum and Jejunum?
Secretion of H+ and HCO3- into the Lumen of the Ileum helps to reclaim Na+, Cl-, and H2O into the ECF
Methods to do so:
1. Na+/H+ Antiporter
2. Cl-/HCO3 Antiporter
Gets Na and Cl into the cell while sending HCO3 and H to become H2O and CO2
What reabsorption takes place in the Colon? What is this stimulated by?
Aldosterone stimulates:
- The addition of Epithelial Na channels to bring Na in from the Lumen
- Na+/K+ Pump to reclaim Na which is followed by water and Cl-
- K+ leak into the Lumen
What electrolytes are found in normal feces?
In small amounts:
- HCO3
- K+
