Digestive System: GI Tract Structure and Function

Flashcards covering the structure and function of the digestive system, focusing on the esophagus, stomach, small intestine, and large intestine.

What is the esophagus?

A muscular tube that connects the pharynx to the stomach, approximately 25 centimeters long.

What sphincters are located within the esophagus?

Upper and lower esophageal sphincters, preventing air entry and gastric reflux.

What are the muscle types and their locations within the muscularis externa of the esophagus?

Skeletal muscle in the upper third, a mix of skeletal and smooth muscle in the middle third, and only smooth muscle in the distal third.

What is a key feature of the submucosa in the esophagus?

Esophageal glands that secrete mucus to facilitate bolus transport and protect the mucosal layer.

What type of epithelium forms the mucosal layer of the esophagus?

Non-keratinized stratified squamous epithelium serving as a tough protective layer.

What are the four main anatomical regions of the stomach?

Cardia, fundus, body, and pylorus.

What is the main function of the stomach?

To store and mechanically break down ingested food into chyme.

What are rugae?

Folds in the mucosa and submucosa of the stomach wall that allow for expansion.

What is the function of the pyloric sphincter?

Controls the exit of chyme into the small intestine.

What is unique about the muscularis externa layer of the stomach?

An extra oblique layer of smooth muscle, along with circular and longitudinal layers, to aid in churning.

What are the key secretory cells found in the gastric glands?

Mucus cells, parietal cells, chief cells, and enteroendocrine cells.

What is the function of mucus cells in the stomach?

Secrete mucus and bicarbonate ions to protect the stomach epithelium.

What is the function of parietal cells in the stomach?

Secrete hydrogen and chloride ions to form hydrochloric acid, and produce intrinsic factor.

What is the function of chief cells in the stomach?

Produce pepsinogen, which is converted to pepsin to break down proteins.

What is the function of enteroendocrine cells in the stomach?

Produce and release hormones like histamine and gastrin to regulate stomach acid and function.

What mechanisms prevent the stomach from digesting itself?

Alkaline mucus, rapid epithelial cell turnover, and tight junctions between epithelial cells.

What are the three regions of the small intestine?

Duodenum, jejunum, and ileum.

What unique features increase the absorptive surface area of the small intestine?

Circular folds, villi, and microvilli.

What are circular folds in the small intestine?

Deep ridges in the mucosa and submucosa that slow the movement of chyme and increase absorption.

What are villi in the small intestine?

Small, hair-like projections on the circular folds that contain a capillary bed and a lacteal for absorption.

What are microvilli in the small intestine?

Cylindrical extensions of the epithelial cells that form a brush border and greatly enhance absorption.

What enzymes are found in the brush border of the small intestine?

Enterokinase, disaccharidases (maltase, sucrase, lactase), and aminopeptidases.

What is a key feature of the lamina propria in the small intestine?

Mucosal-associated lymphoid tissue (MALT), including Peyer's patches in the ileum.

What are the specialized cells that make up the epithelial lining of the small intestine?

Enterocytes (absorptive cells), goblet cells, Paneth cells, and enteroendocrine cells.

What is the function of enterocytes in the small intestine?

Absorb nutrients and secrete enzymes for macronutrient breakdown.

What is the function of goblet cells in the small intestine?

Secrete mucus to protect the small intestine from acidic contents and lubricate.

What is the function of Paneth cells in the small intestine?

Provide host defense against microbes by secreting antimicrobial molecules.

What are the six parts of the large intestine?

Cecum, ascending colon, transverse colon, descending colon, sigmoid colon, and rectum.

What are the unique anatomical features of the large intestine?

Teniae coli, haustra, and epiploic appendages.

What are the taeniae coli?

Bands of smooth muscle that bunch up the colon into pouches called haustra.

What are haustra?

Pouches in the colon created by the contraction of the taeniae coli.

What are epiploic appendages?

Small, fat-filled sacs attached to the taeniae coli.

What is the mucosa of the large intestine made of?

Primarily made of enterocytes and goblet cells, with intestinal glands/crypts largely lined with goblet cells.

Where and how do haustral contractions occur?

Transverse and descending colon, aiding in water absorption.

How does chemical digestion occur in the large intestine?

Bacteria in the lumen, breaking down remaining carbohydrates.

What are feces composed of?

Undigested food residues, bacteria, epithelial cells, inorganic salts, and water.

What are the major nutrients absorbed in the small intestine?

Monosaccharides, amino acids, fatty acids, vitamins, minerals, and water.

How are glucose and galactose absorbed in the small intestine?

Through secondary active transport coupled with sodium ions.

How is fructose absorbed in the small intestine?

Via facilitated diffusion.

How are amino acids absorbed in the small intestine?

Through active transport mechanisms.

What is the role of bile salts in fat absorption?

Form micelles that transport them to the enterocytes.

What happens to fatty acids and monoglycerides inside enterocytes?

They are re-esterified to form triglycerides, combined with lipoproteins to form chylomicrons, and secreted into lacteals.

How is water absorbed in the small intestine?

By simple diffusion, facilitated by aquaporins.

How are vitamins absorbed in the small intestine?

By active transport and diffusion, depending on the specific vitamin.

Where are minerals absorbed, and what regulates iron absorption?

In the duodenum and jejunum. Iron absorption is regulated by hepcidin.

Where are bile salts absorbed?

In the ileum. Bile salts are then transported back to the liver via enterohepatic circulation.

What is the primary function of the large intestine in absorption?

Water and electrolytes are absorbed, and undigested material is compacted into feces.

How is water absorbed in the large intestine?

Via osmosis, following the absorption of solutes.

How are electrolytes absorbed in the large intestine?

By active transport, such as the sodium-potassium pump.

What short-chain fatty acids are absorbed in the large intestine?

Produced by gut bacteria through fermentation of undigested carbohydrates.

Why are short-chain fatty acids important?

To provide energy for colonocytes and influence gut health.

What vitamins are absorbed in the large intestine?

Vitamin K and some B vitamins are synthesized by gut bacteria and absorbed in the large intestine.

What are mass movements in the large intestine?

Mass movements are long, slow, powerful contractions that move colonic contents toward the rectum.

What is the gastrocolic reflex?

The gastrocolic reflex is initiated by gastric distension and increases colonic motility and mass movements.

What is the defecation reflex?

The defecation reflex is triggered by rectal distension and leads to elimination of feces.

What sphincters control defecation?

Internal anal sphincter (involuntary) and external anal sphincter (voluntary).

What are feces composed of?

Undigested food residues, bacteria, epithelial cells, inorganic salts, and water.

What is the role of the Enteric Nervous System (ENS) in digestion?

The enteric nervous system (ENS), a division of the autonomic nervous system, regulates GI motility, secretion, and local blood flow independently of the brain and spinal cord.

What are the two major nerve plexuses of the Enteric Nervous System (ENS)?

The submucosal plexus (Meissner's plexus) controls glandular secretions and mucosal blood flow, while the myenteric plexus (Auerbach's plexus) controls gastrointestinal motility.

What are short and long reflexes in the context of gastrointestinal regulation?

Short reflexes are mediated entirely within the ENS, whereas long reflexes involve the central nervous system and can be triggered by stimuli inside or outside the digestive tract.

What is the function of Gastrin?

Gastrin is secreted by G cells in the stomach and stimulates gastric acid secretion and gastric motility.

What is the function of Secretin?

Secretin is secreted by S cells in the small intestine and stimulates the secretion of bicarbonate-rich pancreatic juice, neutralizing acidic chyme entering the duodenum.

What is the function of Cholecystokinin (CCK)?

CCK is secreted by I cells in the small intestine and stimulates the release of bile from the gallbladder and digestive enzymes from the pancreas.

What is the function of Gastric Inhibitory Polypeptide (GIP)?

GIP is secreted by K cells in the small intestine and inhibits gastric acid secretion while stimulating insulin release from the pancreas.

What is the function of Motilin?

Motilin is secreted by M cells in the small intestine and stimulates gastrointestinal motility, especially during fasting periods.

What are the phases of gastric secretion: Cephalic Phase

The cephalic phase is initiated by sensory stimuli (smell, sight, taste) and prepares the stomach for food arrival through vagal stimulation.

What are the phases of gastric secretion: Gastric Phase

The gastric phase is triggered by the presence of food in the stomach, leading to acid and pepsin secretion, as well as increased gastric motility.

What are the phases of gastric secretion: Intestinal Phase

The intestinal phase begins when chyme enters the small intestine and involves both stimulatory and inhibitory components to regulate gastric emptying and intestinal function.

What is the function of salivary amylase and lingual lipase in the digestion process?

Salivary amylase initiates the breakdown of carbohydrates in the mouth, while lingual lipase begins the digestion of fats.

What is the function of pepsin and gastric lipase in the stomach?

In the stomach, pepsin breaks down proteins int smaller peptides, while gastric lipase contributes to fat digestion.

What are the functions of bile, pancreatic amylase, pancreatic lipase, and proteases in the small intestine

Bile emulsifies fats, pancreatic amylase digests carbohydrates, pancreatic lipase digests fats, and proteases (trypsin, chymotrypsin, carboxypeptidase) digest proteins in the small intestine.

What are the Migrating Motor Complex (MMC)?

The migrating motor complex (MMC) consists of peristaltic waves that sweep undigested material toward the colon during fasting periods, preventing bacterial overgrowth in the small intestine.

What is Segmentation?

Segmentation involves localized contractions that mix chyme with digestive juices and bring nutrients into contact with the absorptive epithelium.

What is Peristalsis?

Peristalsis consists of progressive waves of contraction that propel chyme through the intestines.

What are the major nutrients absorbed in the small intestine?

Monosaccharides, amino acids, fatty acids, vitamins, minerals, and water.

How are glucose and galactose absorbed in the small intestine?

Through secondary active transport coupled with sodium ions.

How is fructose absorbed in the small intestine?

Via facilitated diffusion.

How are amino acids absorbed in the small intestine?

Through active transport mechanisms.

What is the role of bile salts in fat absorption?

Form micelles that transport them to the enterocytes.

What happens to fatty acids and monoglycerides inside enterocytes?

They are re-esterified to form triglycerides, combined with lipoproteins to form chylomicrons, and secreted into lacteals.

How is water absorbed in the small intestine?

By simple diffusion, facilitated by aquaporins.

How are vitamins absorbed in the small intestine?

By active transport and diffusion, depending on the specific vitamin.

Where are minerals absorbed, and what regulates iron absorption?

In the duodenum and jejunum. Iron absorption is regulated by hepcidin.

Where are bile salts absorbed?

In the ileum. Bile salts are then transported back to the liver via enterohepatic circulation.

What is the primary function of the large intestine in absorption?

Water and electrolytes are absorbed, and undigested material is compacted into feces.

How is water absorbed in the large intestine?

Via osmosis, following the absorption of solutes.

How are electrolytes absorbed in the large intestine?

By active transport, such as the sodium-potassium pump.

What short-chain fatty acids are absorbed in the large intestine?

Produced by gut bacteria through fermentation of undigested carbohydrates.

Why are short-chain fatty acids important?

To provide energy for colonocytes and influence gut health.

What vitamins are absorbed in the large intestine?

Vitamin K and some B vitamins are synthesized by gut bacteria and absorbed in the large intestine.

What are mass movements in the large intestine?

Mass movements are long, slow, powerful contractions that move colonic contents toward the rectum.

What is the gastrocolic reflex?

The gastrocolic reflex is initiated by gastric distension and increases colonic motility and mass movements.

What is the defecation reflex?

The defecation reflex is triggered by rectal distension and leads to elimination of feces.

What sphincters control defecation?

Internal anal sphincter (involuntary) and external anal sphincter (voluntary).

What enzymes are involved in the final stages of carbohydrate and protein digestion at the small intestinal surface?

Brush border enzymes such as disaccharidases(maltase, sucrase, lactase) and peptidases.

What is the role of chylomicrons in nutrient absorption?

Transports dietary lipids and fat-soluble vitamins (A, D, E, K) from the small intestine to the rest of the body.

Which organ is responsible for producing bile?

Liver.

Where is the bile stored?

Gallbladder

What are the components of the Bile?

A green-yellow fluid containing bile salts, cholesterol, bilirubin, and electrolytes.

Which blood vessel transports absorbed nutrients from the small intestine to the liver?

Hepatic portal vein