BIOL 373 Unit 6a

9.0 L/day

Total volume of fluid entering the GI lumen daily (2L diet + 7L secretions)

0.1 L/day

The average volume of water lost in feces under normal conditions

Meissner’s Plexus

Submucosal nerve network that primarily regulates GI secretion

Auerbach’s Plexus

Myenteric nerve network located between muscle layers that regulates motility

Mucosa

The innermost GI layer containing the epithelium, lamina propria, and muscularis mucosae

Serosa

The outermost layer of the GI tract, a continuation of the peritoneal membrane

Pylorus

The sphincter and distal region of the stomach that regulates gastric emptying

Isotonic Saline

The solution secreted by crypt cells to lubricate gut contents

NKCC Transporter

Basolateral transporter bringing Na, K, and 2Cl into cells for secretion

CFTR Channel

Apical chloride channel; its defect causes thick mucus in Cystic Fibrosis

Alkaline Tide

Post-meal increase in blood pH due to HCO3- absorption into the blood

Parietal Cells

Stomach cells that secrete Gastric Acid (HCl) and Intrinsic Factor

H+/K+-ATPase

The apical "proton pump" used by parietal cells to secrete H+

Carbonic Anhydrase

Enzyme required by pancreatic duct cells to produce bicarbonate

Zymogens

Inactive enzyme precursors (e.g., Trypsinogen) that prevent auto-digestion

Enteropeptidase

The enzyme that converts inactive trypsinogen into active trypsin

Goblet Cells

Intestinal cells dedicated to the secretion of mucus (mucins)

Hepatocytes

Liver cells arranged in lobules that secrete bile

Sphincter of Oddi

The muscle valve controlling the flow of bile into the duodenum

Bilirubin

A bile pigment from hemoglobin breakdown; high levels cause jaundice

Hepatic Portal Vein

Vessel that carries absorbed nutrients (except fats) directly to the liver

Xenobiotics

Foreign substances (like drugs) that the liver must process before they reach systemic circulation

Amylase

Enzyme that breaks down starch and glycogen into disaccharides

SGLT

Apical transporter for Glucose and Galactose using Na+ co-transport

GLUT5

The specific apical transporter for Fructose facilitated diffusion

GLUT2

The basolateral transporter for all monosaccharides (Glucose, Galactose, Fructose)

Endopeptidases

Proteases like Pepsin and Trypsin that attack internal peptide bonds

Exopeptidases

Enzymes like Carboxypeptidase that release single amino acids from the ends of chains

Transcytosis

The process by which infants absorb intact proteins/antibodies

Bile Salts

Amphipathic cholesterol derivatives that emulsify large fat droplets

Colipase

Pancreatic protein that allows lipase to bypass the bile salt coating on fats

Micelles

Small disks of bile salts and lipids that ferry fats to the enterocyte surface

Chylomicrons

Large droplets of triglycerides, cholesterol, and proteins used for fat transport

Lacteal

The lymphatic capillary in a villus where chylomicrons are absorbed

Smooth ER

The organelle where monoglycerides and fatty acids are re-synthesized into triglycerides

Intrinsic Factor

Parietal cell secretion essential for Vitamin B12 absorption in the ileum

DMT1

The apical transporter used for regulated Iron (Fe2+) absorption

Ferritin

The protein used by the liver to store excess iron

Plicae

Large circular folds in the small intestine wall that increase surface area

Brush Border

The name for the microvilli-covered surface of the intestinal epithelium

Pernicious Anemia

The clinical result of Vitamin B12 deficiency (often due to lack of Intrinsic Factor)

Acinar Cells

Pancreatic cells responsible for secreting digestive enzymes

Duct Cells

Pancreatic cells responsible for secreting bicarbonate solution

Secondary Bile Acids

Bile acids that have been modified by gut bacteria

Transferrin

The plasma protein responsible for transporting iron through the blood

Ferritin

The primary storage protein for iron, located mainly in the liver

Spleen

The organ responsible for destroying old RBCs and initiating hemoglobin breakdown

Heme

The portion of hemoglobin converted into bilirubin and iron during RBC recycling

Globin

The protein portion of hemoglobin broken down into amino acids for reuse

120 Days

The average lifespan of a Red Blood Cell in systemic circulation

Transferrin Receptor

The receptor used by bone marrow cells to take up iron for RBC synthesis

Urobilinogen

A bilirubin metabolite that contributes to the color of excrement

Jaundice

A yellow pigmentation of the skin/eyes caused by high plasma bilirubin levels

Hyperbilirubinemia

The clinical term for elevated bilirubin levels in the blood

Stercobilin

The specific metabolite of bilirubin that gives feces its brown color