Digestive System Anatomy Final Study Guide PDF

Functions of the Digestive Tract - Digestion is the chemical and enzymatic breakdown of ingested materials into simple molecules that can be absorbed by the cells of the digestive tract (small intestine) Essential processes: 1. Ingestion ​ Function: The intake of food into the mouth. ​ Orga...

Functions of the Digestive Tract - Digestion is the chemical and enzymatic breakdown of ingested materials into simple molecules that can be absorbed by the cells of the digestive tract (small intestine) Essential processes: 1. Ingestion ​ Function: The intake of food into the mouth. ​ Organ: Mouth ○​ Significant Features: ​ Teeth (mechanical breakdown) ​ Salivary glands (secrete saliva for lubrication and enzymes) 2. Mechanical/Chemical Processing ​ Function: Breakdown of food through both mechanical and chemical means. ​ Organ: Mouth ○​ Mechanical Processing: ​ Teeth grind food into smaller pieces. ​ Tongue aids in moving food for chewing and mixing with saliva. ○​ Chemical Processing: ​ Saliva contains enzymes (e.g., amylase) that begin carbohydrate digestion. 3. Digestion ​ Function: Breakdown of food into smaller, absorbable molecules. ​ Organ: Stomach ○​ Significant Features: ​ Gastric glands secrete digestive enzymes (pepsin) and hydrochloric acid (HCl).  ​ Churning action: Mechanical digestion through muscular contractions, converting food into chyme. ​ Pepsin: Begins protein digestion. 4. Motility (Peristalsis and Segmentation) ​ Function: Movement of food along the digestive tract. ​ Organ: Esophagus, Stomach, Small Intestine, Large Intestine ○​ Peristalsis: Wave-like contractions that push food along the digestive tract. ○​ Segmentation: Rhythmic contractions that mix food with digestive enzymes to increase digestion and absorption efficiency. 5. Secretion ​ Function: Release of digestive enzymes and other fluids to aid in digestion. ​ Organ: Small Intestine ○​ Significant Features: ​ Pancreatic enzymes: Digest carbohydrates, proteins, and fats. ​ Bile (from the liver via the gallbladder): Emulsifies fats for easier digestion. ​ Intestinal juices: Help neutralize stomach acids and continue enzymatic breakdown. 6. Absorption ​ Function: Absorption of nutrients into the bloodstream. ​ Organ: Small Intestine ○​ Significant Features: ​ Villi and microvilli: Increase surface area for nutrient absorption. ​ Transport mechanisms: Active and passive transport of nutrients (carbohydrates, proteins, fats, vitamins, and minerals) into the blood and lymphatic systems. 7. Compaction ​ Function: Formation and concentration of waste into feces. ​ Organ: Large Intestine ○​ Significant Features: ​ Water absorption: Absorbs water and electrolytes from the chyme to form solid feces. ​ Bacterial action: Fermentation of undigested carbohydrates, production of gases, and absorption of certain vitamins (e.g., vitamin K). 8. Excretion ​ Function: Elimination of undigested and waste material from the body. ​ Organ: Rectum and Anus ○​ Significant Features: ​ Feces formation: Indigestible substances are compacted into feces. ​ Defecation: Expulsion of feces from the body Peritoneum and Peritoneal Cavity Layers of the Peritoneum:  1.​ Parietal Peritoneum ○​ Location: Covers the inner surface of the abdominal cavity walls. ○​ Function: Provides a protective layer for the abdominal wall and helps anchor the peritoneal cavity. 2.​ Visceral Peritoneum ○​ Location: Covers the outer surfaces of the organs (viscera) within the peritoneal cavity. ○​ Function: Protects and supports the organs, while allowing movement within the cavity. ​ Peritoneal Cavity ​ Location: The internal chamber contained within the abdominopelvic cavity. ​ Serous Fluid ​ Watery fluid secreted into the peritoneal cavity. ○​ Role: Lubricates the peritoneal surfaces to reduce friction and facilitate smooth movement of the organs during digestion ​ Mesenteries: ▪ Double layer of peritoneum that suspends some organs ▪ Contains blood & lymphatic vessels and nerves Intraperitoneal vs Retroperitoneal Organs Intraperitoneal Organs: ​ Definition: Organs that are completely surrounded by the peritoneum and are located within the peritoneal cavity. ​ Function: These organs are freely movable within the abdominal cavity, supported by mesenteries that allow them to remain connected to the body wall. ​ Examples: ○​ Stomach ○​ Liver ○​ Spleen ○​ Jejunum and ileum ○​ Cecum ○​ Appendix ○​ Transverse colon Retroperitoneal Organs: ​ Definition: Organs that lie posterior to the peritoneal cavity and are only partially covered by the peritoneum on their anterior surface. ​ Function: These organs are generally less mobile and are positioned between the peritoneum and the posterior abdominal wall, often for stability and protection. ​ Examples: ○​ Kidneys ○​ Adrenal glands ○​ Pancreas (except the tail) ○​ Duodenum  ○​ Ascending colon ○​ Descending colon Histology of the Digestive Tract - 1. Serosa (or Adventitia) ​ Function: Outer layer of the digestive tract, providing protection and anchorage. ​ Serosa: ○​ Also known as visceral peritoneum. ○​ Covers the external surface of intraperitoneal organs. ​ Adventitia: ○​ A fibrous connective tissue layer that covers the external surface of retroperitoneal organs (e.g., kidneys, pancreas). 2. Muscular Layer ​ Function: Mechanically processes and propels materials through the digestive tract. ​ Composition: ○​ Made up of smooth muscle arranged in two layers: 1.​ Inner circular layer: Constricts the lumen to push contents forward. 2.​ Outer longitudinal layer: Shortens the tract to move the material forward. ○​ Enteric Nervous System (ENS): Embedded within this layer, controlling digestive processes. ○​ Myenteric Plexus: A network of nerves located between the smooth muscle layers, coordinating contractions for peristalsis (wave-like muscle contractions). 3. Submucosa ​ Function: A layer of connective tissue that supports the mucosa and regulates digestive secretions. ​ Composition: ○​ Connective tissue: Typically dense irregular connective tissue that provides elasticity and structural support. ○​ Contains: ​ Blood vessels and lymphatic vessels for nutrient absorption and immune response. ​ Submucosal plexus (Meissner’s plexus): A network of nerves that regulates secretion and blood flow in the digestive tract. ​ Glands: Secrete digestive enzymes and mucus, contributing to digestion. 4. Mucosa ​ Function: The innermost layer responsible for secretion, absorption, and protection of underlying structures. ​ Composition: ○​ Epithelium: Varies along the digestive tract, but is generally simple columnar epithelial tissue in most areas (e.g., stomach, small intestine).  ○​ Lamina Propria: Loose (areolar) connective tissue that supports the epithelium and houses blood vessels and lymphatic vessels. ○​ Muscularis Mucosae: A thin layer of smooth muscle that helps to move and fold the mucosa, assisting in secretion and absorption. Histology of the Digestive Tract - Oral Cavity ​ Functions: Ingestion, digestion (mechanical and chemical), secretion, and communication. ​ Type of Epithelium: ○​ Stratified squamous epithelium to protect against abrasion from food particles. ​ Key Features: ○​ Salivary glands (parotid, submandibular, sublingual) secrete saliva, which contains enzymes like salivary amylase for chemical digestion, mucus for lubrication, and water for hydration. ○​ Glands: Salivary glands are exocrine glands that secrete substances via ducts. Salivary Glands ​ Function: Produce saliva for digestion and mouth lubrication. ​ Types of Salivary Glands: ○​ Parotid gland: Produces watery, serous saliva. ○​ Submandibular gland: Produces mixed saliva (serous and mucus). ○​ Sublingual gland: Primarily mucus secretion. ​ Innervation: Controlled by the autonomic nervous system (sympathetic and parasympathetic). ○​ Parasympathetic stimulation increases watery saliva secretion. ○​ Sympathetic stimulation results in thicker saliva. Pharynx ​ Regions: 1.​ Nasopharynx: Respiratory epithelium (pseudostratified ciliated columnar epithelium). 2.​ Oropharynx and Laryngopharynx: Stratified squamous epithelium for protection from abrasion during food passage. ​ Function: Passageway for food and air; shared with the respiratory system. Esophagus ​ Function: Transports food from the pharynx to the stomach. ​ Histology: ○​ Epithelium: Stratified squamous epithelium to resist abrasion. ○​ Muscle layers: Transition from skeletal muscle (upper esophagus) to smooth muscle (lower esophagus). ○​ Adventitia (outer connective tissue) or serosa depending on its location in the body. Stomach  ​ Functions: Stores food, mechanical and chemical digestion, produces chyme. ​ Histology: ○​ Epithelium: Simple columnar epithelium in the mucosa, specialized for secretion and absorption. ○​ Mucus surface cells: Secrete mucus to protect the stomach lining from acidic secretions. ○​ Secretory Cells: ​ Parietal cells: Secrete hydrochloric acid (HCl) and intrinsic factor (for Vitamin B12 absorption). ​ Chief cells: Secrete pepsinogen, which is activated to pepsin for protein digestion. ​ Enteroendocrine cells: Release hormones like gastrin to regulate secretion and motility. ​ Muscle Layers: ○​ Three muscular layers: Longitudinal, circular, and oblique muscles for mixing and churning food into chyme. ○​ Rugae: Folds in the stomach lining that allow for expansion. Small Intestine ​ Functions: Digestion, absorption, motility, and production of GI hormones and immune cells. ​ Segments: ○​ Duodenum: Shortest segment; retroperitoneal. ○​ Jejunum: Primary site of nutrient absorption. ○​ Ileum: Longest segment. ​ Histology: ○​ Epithelium: Simple columnar epithelium (enterocytes) with microvilli for absorption. ○​ Goblet cells: Secrete mucus to lubricate and protect the intestinal lining. ○​ Granular cells: Provide immune protection. ○​ Endocrine cells: Secrete hormones like cholecystokinin (CCK) and secretin. ○​ Villi: Finger-like projections that increase surface area for absorption. ○​ Lamina propria: Contains blood capillaries and lacteals for nutrient absorption. Large Intestine ​ Functions: Absorption (mainly water and electrolytes), compaction of waste, protection from pathogens. ​ Histology: ○​ Epithelium: Simple columnar epithelium with abundant goblet cells for mucus secretion. ○​ No villi: Unlike the small intestine, the large intestine has no villi, which helps in absorption but with less surface area. ○​ Peyer’s patches: Lymphoid nodules in the submucosa for immune function.  ○​ Taenia coli: Three longitudinal muscle bands that create haustra (sac-like structures for mixing contents). ○​ Larger diameter, thinner walls compared to the small intestine. Rectum and Anus ​ Histology: ○​ Rectum: Both smooth and skeletal muscle are present, enabling voluntary and involuntary control. ○​ Epithelium: Changes from simple columnar epithelium in the rectum to stratified squamous epitheliumat the anus. ​ Voluntary Control: The external anal sphincter (skeletal muscle) is under voluntary control, while the internal anal sphincter (smooth muscle) is under involuntary control 4 Digestive Sphincters - ​ Lower Esophageal Sphincter (LES): ○​ Between the esophagus and the stomach. ○​ Prevents stomach contents from refluxing into the esophagus. ​ Pyloric Sphincter: ○​ Between the stomach and the duodenum. ○​ Controls the passage of partially digested food (chyme) from the stomach to the small intestine. ​ Ileocecal Sphincter: ○​ Between the ileum (small intestine) and the cecum (large intestine). ○​ Regulates the flow of chyme from the small intestine into the large intestine and prevents backflow. ​ Anal Sphincters: ○​ Located at the anus. ○​ Internal anal sphincter (involuntary control) and external anal sphincter (voluntary control). ○​ Regulate the passage of feces from the rectum to the anus, allowing for controlled defecation. Liver, Gallbladder, and Pancreas - Liver: Key Functions: ​ Detoxification: Breaks down harmful substances (e.g., alcohol, drugs). ​ Regulates metabolism: Manages nutrient storage (e.g., converts glucose to glycogen). ​ Bile production & secretion: Aids in fat digestion. Histology: ​ Liver Lobes: Right, left, caudate, quadrate. ​ Hepatocytes: Responsible for: ○​ Bile production ○​ Nutrient metabolism ○​ Detoxification  ​ Reticular CT: Forms liver structure and supports lobules. ​ Portal Triad: Includes: ○​ Hepatic Portal Vein: Nutrient-rich blood. ○​ Hepatic Artery: Oxygen-rich blood. ○​ Bile Duct: Carries bile to the gallbladder or duodenum. Gallbladder: Key Functions: ​ Stores & concentrates bile: Bile stored when fasting, released when eating. ​ Fat emulsification: Bile helps break down fats in the small intestine. Bile Pathway: ​ Storage: Bile is stored in the gallbladder via hepatic duct → cystic duct. ​ Release: Bile released into duodenum via common bile duct. Pancreas: Key Functions: ​ Endocrine: ○​ Insulin: Lowers blood glucose. ○​ Glucagon: Raises blood glucose. ​ Exocrine: Produces digestive enzymes and bicarbonate (HCO3-) for digestion. Histology: ​ Pancreatic Acinus: ○​ Simple cuboidal epithelium: Secretes pancreatic juice (enzymes + bicarbonate). ○​ Enzymes include amylase (carbs), lipase (fats), and proteases (proteins). ​ Main Pancreatic Duct: Carries digestive enzymes to the duodenum. Endocrine Cells (Islets of Langerhans): ​ Alpha Cells: Secrete glucagon (raises blood sugar). ​ Beta Cells: Secrete insulin (lowers blood sugar). Key Blood Vessels of the Liver - 1. Hepatic Artery ​ Purpose: ○​ Provides oxygen-rich blood to the liver. ○​ Carries blood from the abdominal aorta to the liver. ​ Pathway: ○​ Blood from the hepatic artery flows into the central vein within the liver lobules. 2. Hepatic Portal Vein ​ Purpose: ○​ Carries nutrient-rich blood from the gastrointestinal tract (intestines, stomach) to the liver. ○​ Blood is rich in digested nutrients, toxins, and other substances absorbed from food. ​ Functional Significance:  ○​ Detoxification: The liver processes the blood from the hepatic portal vein to remove toxins and harmful substances. ○​ Nutrient Processing: The liver processes nutrients (e.g., glucose, amino acids, fatty acids) for metabolism and storage. ○​ Blood Flow Pathway: ​ Blood flows from the hepatic portal vein → liver sinusoids → central vein → hepatic vein → inferior vena cava (ultimately returning blood to the heart). 3. Central Vein ​ Function: Collects processed blood from the liver lobules and drains into the hepatic vein. 4. Hepatic Vein ​ Function: Drains processed blood from the liver and returns it to the inferior vena cava, which brings blood back to the heart Key Blood Flow Pathway in the Liver - 1.​ Hepatic Artery (oxygenated blood) → Central Vein. 2.​ Hepatic Portal Vein (nutrient-rich blood) → Liver Processing. 3.​ Central Vein → Hepatic Vein → Inferior Vena Cava → Heart.