Gastrointestinal System Quiz

Physiology (0603302)

• Course name: Physiology
• Chapter: Gastrointestinal system
• Semester: Summer 2023/2024
• Instructor: Dr. Mohammad A. Abedal-Majed
• Institution: The University of Jordan, School of Agriculture

The Digestive System

• The gastrointestinal (GI) system is responsible for providing the body with nutrients and electrolytes from outside the body to maintain homeostasis.

Structure of the Gastrointestinal System

• The digestive system consists of two main parts:
  • GI tract (mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, and anus)
  • Accessory glandular organs (salivary glands, liver, gallbladder, exocrine and endocrine glands)

Mouth

• Contains muscles for mechanical digestion
• Salivary glands secrete saliva for lubrication, food degradation, and carbohydrate digestion
  • Carbohydrate digestion begins in the mouth with salivary amylase.
• Food passes through the pharynx, a passageway for food and connecting the GI and respiratory system.
• The esophagus carries food rapidly.
• Minimal absorption occurs except for some drugs.

Stomach

• Contains a special lining that secretes digestive juices (pepsinogen and HCl acid) for protein digestion.
• Digestive enzymes originate within gastric pits.
• Gastric pits contain cells that secrete HCL and pepsinogen.
• Strong muscular walls mix food and digestive juices.
• Food moves from the stomach to the small intestine through the pylorus sphincter.

Small Intestine

• Contains enzymes from the pancreas and small intestine for further food digestion.
• Villi and microvilli increase surface area for absorption and digestion.
• Cells lining villi and microvilli (enterocytes) help with carbohydrate and protein digestion.
• Villi cells renew every 2-3 days from stem cells in the crypts.
• Microvilli (brush border) contain enzymes that aid in carbohydrate and protein digestion.

Large Intestine

• Absorbs a small amount of water and electrolytes.
• Contains beneficial bacteria for vitamin K production and lipid molecule processing.
• Patients with issues in beneficial bacteria may develop health problems like diabetes and obesity.
• Compacts and forms feces for elimination.
• Fiber in the diet aids in movement for constipation prevention.

Structure of the Gastrointestinal System (Layers)

• Mucosa: The innermost layer of the GI tract, composed of epithelial cells lining the tract, which plays a protective role, and is responsible for secretion and absorption.
• Submucosa: The layer below the mucosa, containing connective tissue and a network of neurons called the submucosal plexus, enabling the tract to expand and contract.

Muscle Layer

• Two perpendicular smooth muscle layers:
  • Inner, thick circumferential layer for constricting and narrowing the lumen.
  • Outer longitudinal layer for shortening the lumen.
• The GI tract is largely under involuntary control, but the mouth and end of the rectum are under voluntary control.
• The enteric nervous system (network of neurons) regulates the GI tract functions.
• Serosa: The outermost layer, a thin layer of connective tissue that lubricates and prevents friction with neighboring structures.

Processing of Food (General)

• Ingestion: The process of eating.
• Digestion: Chemical and mechanical breakdown of food.
• Motility: Muscular contractions in the digestive tract for mixing food and propelling it through the digestive tract (peristalsis.)
• Phasic contractions: Short, alternating contractions that propel food (e.g., peristalsis.)
• Segmental contractions: Move food back and forth for mixing with digestive juices.
• Tonic contractions: Long, sustained contractions found at sphincters.

Processing of Food and Secretion

• Secretion: Glands release substances like water, electrolytes, enzymes, bile salts, and mucus into the digestive tract.
  • It's an energy-dependent process mediated by neural or hormonal stimulation.
  • Specific examples of fluid and volume secretion include saliva, gastric, bile, and pancreatic secretions.

Gastric Gland Cells

• Exocrine cells
  • Parietal cells secrete HCl acid and intrinsic factor.
  • Chief cells secrete pepsinogen (converted to pepsin by HCl) for protein digestion.
  • Mucous neck cells secrete mucus for protection.
• Pyloric gland contains G cells that secrete gastrin (stimulates parietal cell activity), and mucus.
• Cardiac glands secrete alkaline mucus.
• Endocrine cells include G and D cells.

Stomach Acid (HCl) Secretion

• Parietal cells actively transport H+ (hydrogen ions) into the gastric lumen.
• Cl- (chloride ions) are transported and actively join H+ in the lumen.
• Carbonic anhydrase regulates this process.

HCl Functions

• Activates digestive enzymes.
• Breaks down connective tissue.
• Denatures proteins.
• Kills ingested microorganisms.

Pepsinogen Secretion

• Present in chief cells, is released by regulated exocytosis.
• Pepsinogen is inactive; HCl converts it to the active pepsin enzyme used in protein digestion.
• Autocatalysis: Pepsin also cleaves pepsinogen, forming more active pepsin.

Intrinsic Factor

• Secreted by parietal cells.
• Forms a complex with vitamin B12, enabling its absorption in the intestines.

Gastric Mucosal Barrier

• Luminal membranes of gastric cells are impermeable to H+.
• Tight junctions prevent HCL from passing between cells.
• Mucus coating provides a physical barrier.
• HCO3- rich mucus serves as a chemical barrier by neutralizing acid near epithelial cells.

Pancreatic Secretion

• Endocrine part secretes insulin and glucagon (blood sugar control.)
• Exocrine part secretes digestive enzymes and bicarbonate.
  • Secretion is stimulated and regulated by hormones like secretin and cholecystokinin.

Bile Secretion (Liver)

• Bile salts and phospholipids emulsify fats into smaller pieces, aiding in lipase access and digestion.
• Bile is produced by the liver and stored in the gallbladder.
• The Sphincter of Oddi controls bile entry into the duodenum.
• 95% of bile salts are recycled via enterohepatic circulation.

Small Intestine Secretion

• Aids in lubrication and facilitates enzymatic digestion.
• Doesn't secrete digestive enzymes, but the enterocytes (cells lining the villi and microvilli) contain digestive enzymes assisting with the absorption of digested nutrients from the lumen into the blood or lymphatic system.

Digestion (Overview

• Mechanical digestion: Chewing, mixing, churning in the stomach
• Chemical Digestion: Actions by enzymes in digestive juices.

Digestion: Overview (Table)

• Table summarizes the digestion processes for carbohydrates, proteins, and fats.

Carbohydrate Digestion

• Breaks down complex carbohydrates into monosaccharides (glucose, galactose, and fructose) for absorption.
• Salivary amylase and pancreatic amylase are involved in the initial breakdown.
• Intestinal enzymes (sucrase, maltase, and lactase) further break down disaccharides to monosaccharides.

Protein Digestion

• Breaks down proteins into amino acids for absorption.
• Pepsin acts in the stomach, breaking down protein.
• Pancreatic enzymes (trypsin, chymotrypsin, carboxypeptidase) and intestinal aminopeptidases and carboxypeptidases continue the breakdown in the small intestines.

Fat Digestion

• Bile salts emulsify fat globules, increasing surface area for lipase action.
• Lipase breaks down triglycerides into fatty acids and monoglycerides for absorption.

Absorption

• The passage of digested nutrients into the bloodstream (or lymph) for the body to use.
• Most occurs in the small intestine (specialized villi and crypts.)

Defecation

• Elimination of indigestible food substances.

Regulation of Gastrointestinal Tract Functions

• Intrinsic (intrinsic nervous system and endocrine cells in digestive tract walls) and extrinsic (nervous system and endocrine systems outside digestive tract) controls.
• Hormones like secretin and gastrin regulate various digestive functions.

Test your knowledge on the anatomy and physiology of the gastrointestinal tract. This quiz covers smooth muscle functions, neural controls like the myenteric plexus, and processes involved in digestion and absorption. Perfect for students studying human biology or medical professionals wanting a refresher.