Anatomy and Physiology PDF

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afratafreeh.com ecxclusive NOTES NOTES ANATOMY & PHYSIOLOGY ANATOMY osms.it/gastrointestinal-anatomy-physiology ▪ Alimentary/GI tract: continuous muscular ▪ Lesser omentum: double layer arises from tube from mouth to anus lesser curvature of stomach, extends to ▪ Many digestive organs reside in abdominal, liver pelvic cavity; covered by mesentery ▪ Greater omentum: four layers (double sheet folds back upon itself); arises from greater curvature of stomach, covers intestines PERITONEUM ▪ Thin connective tissue composed of GI tract layers mesothelium, connective tissue supporting ▪ Four basic tissue layers from esophagus to layer, simple squamous epithelium anus ▪ Lines abdominal, pelvic cavities; binds ▪ Serosa/adventitia organs together, holds them in place ▫ Outermost layer of intraperitoneal ▪ Contains blood vessels, lymphatics, nerves organs; also visceral peritoneum innervating abdominal organs ▫ Primarily composed of simple squamous ▫ Parietal peritoneum: lines abdominal, epithelial cells, connective tissue pelvic cavities ▫ Secretes slippery fluid, prevents friction ▫ Visceral peritoneum: covers organ between viscera, digestive organs surfaces ▫ Esophagus has adventitia instead of ▫ Peritoneal cavity: potential space serosa between parietal, visceral layers ▫ Retroperitoneal organs have serosa, ▪ Intraperitoneal organs: digestive organs; adventitia keep mesentery during embryological ▪ Muscularis propria development, remain in peritoneal cavity ▫ Outer longitudinal, inner circular smooth (e.g. stomach) muscle for involuntary contractions; ▪ Retroperitoneal organs: lose mesentery regions of thickened circular layer forms during embryological development, lay sphincters posterior to peritoneum (e.g. kidneys, ▫ Skeletal muscle in esophagus for pancreas, duodenum) voluntary swallowing ▪ Mesentery: double layer of parietal ▫ Contains myenteric plexus (between peritoneum on dorsal peritoneal cavity, longitudinal, circular layers of smooth provides routes for vessels, lymphatics, muscle) nerves to digestive organs ▫ Myenteric plexus responsible for Omentum peristalsis, mixing ▪ Visceral peritoneum layer covering ▪ Submucosa stomach, intestines; contains adipose ▫ Connective tissue that binds muscularis, tissue, many lymph nodes provides elasticity, distensibility ▫ Expands during weight gain; “fat skin” ▫ Contains Meissner’s plexus ▫ Richly vascularized, innervated OSMOSIS.ORG 293  ▪ Mucosa BLOOD CIRCULATION ▫ Innermost layer composed of epithelial ▪ Splanchnic circulation membrane lining entire GI tract ▪ Celiac trunk: supplies stomach, liver, spleen ▫ Functions: exocrine glands secrete ▪ Superior mesenteric artery: supplies small water, mucus, digestive enzymes, intestine hormones; absorb digested nutrients; ▪ Inferior mesenteric artery: supplies large provides protective surface intestine ▫ Muscularis mucosae: smooth muscle layer responsible for mucosa movement; contains folds to increase surface area INNERVATION ▫ Lamina propria: loose areolar connective ▪ Supplied by autonomic nervous system tissue; contains blood, lymphatic (ANS) vessels; contains MALT (lymphoid tissue ▪ Sympathetic component: thoracic that protects against pathogens) splanchnic nerves → celiac plexus ▫ Epithelium: mouth, esophagus, anus ▪ Parasympathetic component: vagus nerve composed of stratified squamous cells; ▪ Enteric division provides local control of GI rest of GI tract simple columnar with activity; “the brain in the gut”; can function mucus secreting cells independently of ANS Figure 36.1 Cross section from small intestine showing the four basic tissue layers that line gastrointestinal tract: (from the outermost) serosa/adventitia, muscularis propria, submucosa, and mucosa. 294 OSMOSIS.ORG  Chapter 36 Gastrointestinal System: Anatomy & Physiology STRUCTURES osms.it/gastrointestinal-anatomy-physiology ORAL (BUCCAL) CAVITY ▪ Cardiac sphincter: AKA lower esophageal sphincter; smooth muscle at cardiac orifice Function that prevents acidic contents of stomach ▪ Ingestion, mechanical, chemical digestion, from moving upward into esophagus propulsion ▪ Saliva contains antibacterial properties that Histology cleanses, protects oral cavity, teeth from ▪ Mucosa infection ▫ Nonkeratinized stratified squamous ▪ Propulsion: swallowing (performed by epithelium (simple columnar epithelium tongue) propels food into pharynx, starts near cardiac orifice) propulsion through GI tract ▪ Mucosa, submucosa form longitudinal folds ▪ Mechanical digestion: via mastication by when empty teeth, tongue ▪ Submucosa ▪ Chemical digestion: salivary amylase starts ▫ Mucus secreting glands carbohydrate chemical breakdown ▪ Muscularis externa Secretions ▫ Superior ⅓: skeletal muscle ▪ Chemical digestion: salivary amylase starts ▫ Middle ⅓: skeletal, smooth muscle carbohydrate chemical breakdown; mucin, ▫ Inferior ⅓: smooth muscle water provide lubrication ▪ Adventitia instead of serosa ▪ Lysozyme: kills some microbes Secretions ▪ Lingual lipase: digests some lipids ▪ Mucus: lubrication, protection from gastric acid ESOPHAGUS ▪ Muscular tube extending from STOMACH laryngopharynx to stomach ▪ Located in upper left abdominal cavity ▪ Esophageal hiatus: diaphragm opening quadrant where esophagus, vagus nerve pass ▪ Contains rugae (mucosa, submucosa) through to abdominal cavity when stomach empty → expands to ▪ Cardiac orifice: junction of esophagus, accommodate food stomach Function Function ▪ Churning, digestion, storage ▪ Propulsion/peristalsis ▪ Beginning of chemical digestion turning ▪ Epiglottis closes larynx, routes food into food into chyme to be delivered into small esophagus intestine ▪ Lower end of esophagus contains mucous cells to protect esophagus from stomach Regions acid reflux ▪ Cardia: most superior area surrounding cardiac orifice where food from esophagus Sphincters enters stomach ▪ Upper esophageal sphincter: skeletal ▫ Defined by Z-line of gastroesophageal muscle; regulates movement from pharynx junction to esophagus ▫ Z-line: epithelium changes from stratified squamous → simple columnar OSMOSIS.ORG 295  ▪ Fundus: area lying inferior to diaphragm, Secretions upper curvature ▪ Mucous cells: neck, basal regions of glands; ▫ Food storage produce mucus that protects stomach ▪ Body: central, largest area of the stomach lining, lubricates food ▪ Pylorus: connects to duodenum via pyloric ▪ Parietal cells: gland apical region amongst sphincter chief cells; produce HCl, intrinsic factor ▫ Controls gastric emptying, prevents ▪ Chief cells: gastric gland base; produce backflow from duodenum into stomach pepsinogen (protein digestion) ▪ Enteroendocrine cells (ECL cells): located Histology deep in glands; secretes histamine, ▪ Muscularis contains regular GI tract layers somatostatin, serotonin, ghrelin with three-layered muscularis propria ▪ G-cells: gastrin unique to stomach allowing for vigorous ▪ D-cells: somatostatin contractions, churning ▫ Inner oblique layer ▫ Middle circular layer (contains myenteric SMALL INTESTINE plexus) Function ▫ Outer longitudinal layer ▪ Primary organ of digestion, nutrient Glands absorption; segmentation (localized mixing area), peristalsis ▪ Lined with simple columnar epithelium; forms gastric pits (tube-like opening for ▪ Absorption: food breakdown products gastric glands) absorbed ▪ Cardia, pylorus glands mainly secrete ▪ Contains circular folds, villi, microvilli to mucus maximize absorption surface area ▪ Fundus, body glands secrete majority of ▫ Circular folds are permanent, composed digestive stomach secretions of mucosa, submucosa ▪ Pyloric antrum glands mainly secrete mucus, hormones (mainly gastrin) Figure 36.2 Stomach anatomy. 296 OSMOSIS.ORG  Chapter 36 Gastrointestinal System: Anatomy & Physiology Innervation ▫ Suspended from posterior abdominal ▪ Relayed through celiac, superior mesenteric wall by mesentery plexus ▫ Peyer’s patches: lymphatic tissue ▪ Sympathetic: thoracic splanchnic sections composed predominantly of ▪ Parasympathetic: vagus proliferating B lymphocytes, mostly located in ileal lamina propria as Blood supply protection against pathogenic bacteria; ▪ Arterial: superior mesenteric artery B lymphocytes release IgA ▪ Veins from small intestine → hepatic portal Secretions vein → liver ▪ Brush border enzymes on microvilli Histology complete food digestion (e.g. mucus, water, peptidases, disaccharidases) ▪ Epithelium of villus: simple columnar absorptive cells ▪ Pancreas, liver contribute to most small intestine digestion ▫ Main function is absorbing nutrients ▪ Mucus secreting goblet cells in epithelium ▪ Mucosa contains pits called intestinal LARGE INTESTINE crypts ▪ Retroperitoneal except for transverse, ▫ Crypt cells: secrete intestinal juice sigmoid parts containing mucus ▫ Intraperitoneal transverse, sigmoid ▫ Enteroendocrine cells: within crypts, sections anchored to posterior intraepithelial lymphocytes (T cells) abdominal wall by mesocolon ▫ Paneth cells: located deep in crypts, (mesentery) release defensins, lysozyme to protect ▫ Connects ileum via ileocecal valve, against pathogens sphincter Sections Function ▪ Duodenum ▪ Digestion, absorption, propulsion, ▫ Mostly retroperitoneal defecation ▫ Curves around head of pancreas, ▪ Digestion: enteric bacteria digests receives bile from liver via bile duct, remaining food pancreatic secretions from pancreas via ▫ Bacteria also produce vitamin K, other B main pancreatic duct vitamins ▫ Ampulla of vater: bulb-like point where ▪ Absorption: absorbs mainly water, bile duct, main pancreatic duct unite, electrolytes, vitamins to concentrate, form deliver secretions into duodenum feces ▫ Major duodenal papilla: ampulla ▪ Propulsion: propels feces towards rectum opening into duodenum releasing bile/ ▪ Defecation: stores, eliminates feces from pancreatic secretions body ▫ Hepatopancreatic sphincter: controls Unique features bile entry, pancreatic secretions ▪ Tenia coli: three longitudinal ribbons of ▫ Duodenal glands (Brunner’s) in smooth muscle on ascending, transverse, duodenal submucosa secrete alkaline descending, sigmoid colons that contract to mucus to neutralize acidic chyme produce haustra ▪ Jejunum ▪ Haustra: small pouches/segments of large ▫ Intraperitoneal intestine created by tenia coli ▫ Suspended from posterior abdominal ▪ Epiploic appendages: small pouches of wall by mesentery peritoneum filled with fat ▪ Ileum ▫ Intraperitoneal ▫ Joins large intestine at ileocecal valve OSMOSIS.ORG 297  Regions Flora ▪ Cecum → ascending colon → right colic/ ▪ Large intestine contains largest bacterial hepatic flexure → transverse colon → left ecosystem in body colic/splenic flexure → descending colon → ▪ Function of bacteria sigmoid colon → rectum → anal canal → ▫ Synthesize vitamins (vitamin K, some B anus vitamins) ▫ Cecum: pouch that lies below ileocecal ▫ Ferment indigestible carbohydrates (e.g. valve at large,small intestine junction; cellulose) beginning of large intestine ▫ Metabolism/digestion of certain ▫ Appendix: pouch of lymphoid tissue molecules (e.g. hyaluronic acid, mucin) (part of MALT) located in cecum, harbors ▫ Live symbiotically with host bacteria to recolonize gut when needed ▫ Present pathogens to nearby lymphoid ▪ Anal canal has two sphincters tissue (MALT) ▫ Internal anal sphincter: involuntary, composed of smooth muscle Secretions ▫ External anal sphincter: voluntary, ▪ Mucus composed of skeletal muscle Histology ▪ Muscularis mucosae consists of inner circular, outer longitudinal layers ▪ Large intestine mucosa: simple columnar epithelium ▪ Anal canal: stratified squamous epithelium ▪ Does not contain folds, villi, microvilli as in small intestine ▪ Many crypts with goblet cells Pectinate line ▪ Divides upper ⅔ from lower ⅓ of anal canal where many distinctions made ▪ Embryological origin ▫ Above: endoderm Figure 36.3 Large intestine anatomy. ▫ Below: ectoderm ▪ Epithelium ▫ Above: columnar epithelium ▫ Below: stratified squamous epithelium ▪ Innervation ▫ Above: inferior hypogastric plexus ▫ Below: inferior rectal nerves ▪ Lymph drainage ▫ Above: internal iliac ▫ Below: superficial inguinal lymph nodes ▪ Vascularization ▫ Above: superior rectal artery, superior rectal vein (drains into inferior mesenteric vein → hepatic portal system) ▫ Below: middle, inferior rectal arteries; middle, inferior rectal veins 298 OSMOSIS.ORG  Chapter 36 Gastrointestinal System: Anatomy & Physiology ACCESSORY ORGANS ▪ Gallbladder, liver, pancreas ▪ Liver ▫ Hepatocytes produce bile which emulsifies lipid globules, aids in absorption ▫ Stores glucose in form of glycogen ▪ Gallbladder ▫ Bile storage; releases bile into small intestine in response to hormonal stimulus ▪ Pancreas ▫ Exocrine function: acini secrete various digestive enzymes; “pancreatic juice;” e.g. secretin, cholecystokinin (CCK) ▫ Endocrine function: islets produce glucagon, insulin to maintain normal glucose levels; somatostatin, pancreatic Figure 36.4 Overview of gastrointestinal polypeptide production tract, accessory organs structures. PHYSIOLOGY osms.it/gastrointestinal-anatomy-physiology PROCESSING OF FOOD GI MUSCLE PROPERTIES 1. Ingestion ▪ Smooth muscle of GI tract acts as 2. Mechanical digestion syncytium ▫ Carried out by teeth; increases surface ▫ Muscle fibers connected by gap area to facilitate enzymatic digestion junctions allowing electrical signals to 3. Propulsion initiate muscle contractions from one muscle fiber to next rapidly along length ▫ Movement, mixing of food through GI of bundle tract, starts with swallowing ▪ Normal resting membrane potential of GI 4. Secretion smooth muscles: -50mV to -60mV ▫ Exocrine glands secrete various ▪ Two types of electrical waves contributing digestive juices into digestive tract to membrane potential lumen 5. Digestion Slow waves ▫ Complex food broken down via ▪ Generated, propagated by interstitial cells enzymes of Cajal (pacemaker cells) 6. Absorption ▪ Slow-wave threshold: potential that must ▫ Digested nutrients absorbed by GI be reached by slow wave to propagate mucosal cells into blood/lymph smooth muscle 7. Elimination ▪ Does not cause smooth muscle contraction ▫ Indigestible substances eliminated via ▪ Slow-wave threshold reached → L-type anus in form of feces calcium channels activated → calcium influx → motility initiation OSMOSIS.ORG 299  ▪ Occur at 12 cycles/minute in duodenum, GASTROINTESTINAL MOTILITY decreases towards colon Gastric motility ▪ Regulated by innervation, hormones ▪ Peristaltic contractions originate in upper ▫ Excitatory stimulants (e.g. acetylcholine, fundus, move to pyloric sphincter substance P), inhibitory stimulants (e.g. VIP, nitric oxide) ▪ Moves gastric chyme forward → gastric emptying into duodenum Spikes Small intestinal motility ▪ True action potentials occurring automatically when GI smooth muscle ▪ Mix chyme, digestive enzymes, pancreatic potential becomes more positive than secretions, bile → digestion -40mV ▪ Expose nutrients to mucosa → maximize ▪ Digestive activity controls absorption ▫ Involves regulation by autonomous ▪ Advance chyme along small intestine via smooth muscle, intrinsic nerve plexuses, segmentation actions → ileocecal valve → external nerves (ANS), GI hormones ileocecal sphincter → large intestine Large intestinal motility ENTERIC NERVOUS SYSTEM ▪ Unabsorbed small intestine material → ▪ Intrinsic nervous system of the GI system large intestine ▪ Division of ANS ▫ Contents now feces (destined for ▪ Provides major nerve supply to GI tract excretion) controlling GI function, motility ▪ Segmental contractions (cecum, proximal ▫ Parasympathetic system activates colon) associated with haustra (sac-like digestion segments characteristic of large intestine) ▫ Sympathetic system inhibits digestion mixes contents ▫ Also capable of self-regulation, ▪ Mass movements autonomous function ▫ Function: move contents long distances (e.g. transverse → sigmoid) Receptors and plexus ▫ Occur 1–3 times daily ▪ Chemoreceptors respond to chemicals from ▫ Water absorption: fecal contents → food in gut lumen increasingly solid (hard to mobilize) ▪ Stretch receptors respond to food ▫ Final mass movements propel contents distending GI tract wall to rectum → stored until defecation ▪ Two plexus consist of motor neurons, ▪ Gastrocolic reflex interneurons, sensory neurons ▫ Stomach distension → ↑ colonic motility ▫ Submucosal (Meissner’s) nerve plexus: → ↑ mass movements innervates secretory cells → controls ▫ Afferent limb (from stomach) → digestive secretions parasympathetic nervous system ▫ Myenteric nerve plexus: innervates mediates → efferent limb → CCK, smooth muscle layers of muscularis → gastrin production → ↑ colonic motility controls GI motility ▪ Segmentation, peristalsis mostly automatic mediated by pacemaker cells, reflex arcs Reflex mediation ▪ Short reflexes: intrinsic control (enteric nervous system) ▪ Long reflexes: extrinsic control outside of GI tract (e.g. CNS, autonomic nerves) 300 OSMOSIS.ORG  Chapter 36 Gastrointestinal System: Anatomy & Physiology ▪ Defecation remains tonically contracted (striated ▫ Rectum 25% full → defecation urge skeletal muscle under voluntary control) ▫ Rectum fills with feces → rectal wall → when appropriate, external anal distends → stretch receptors send sphincter relaxed voluntarily → rectal afferent signals to spinal cord → to smooth muscle contracts → ↑ pressure brain (awareness of need to defecate) → Valsalva maneuver (expire against + afferent signals to myenteric plexus closed glottis) → ↑ intra-abdominal → peristaltic waves → move feces pressure → ↑ defecation pressure → forward → internal anal sphincter feces forced out through anal canal relaxes → external anal sphincter OSMOSIS.ORG 301