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NURS 8022 Advanced Pathophysiology Exam 4 & Study Guide NURS 8022 $7.49   Add to cart

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NURS 8022 Advanced Pathophysiology Exam 4 & Study Guide NURS 8022

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NURS 8022 Advanced Pathophysiology Exam 4 & Study Guide NURS 8022

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  • March 15, 2022
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Exam 4 Study Guide

GASTROINTESTINAL PHYSIOLOGY

Anatomy of the GI system – NOT ON STUDY GUIDE




•Digestive system – enteric nervous system (extrinsic and intrinsic)
o
Autonomic (involuntary) and hormonal control [except chewing, swallowing, defecation]
▪Vagus nerve
o Ingested substances trigger hormones that stimulate or inhibit
▪Muscular contractions – GI motility; timely secretion of substances that aid in digestion
o Located near the areas that they innervate and control


• Mouth
o Reservoir for chewing and mixing of food with saliva
o Taste buds (chemoreceptors) and olfactory nerves are stimulated – initiates salivation and
secretion of gastric juices in the stomach

• Salivary glands
o Submandibular, sublingual, parotid (largest; secretes saliva)
o Saliva is composed of water with mucus, sodium, chloride, bicarbonate, potassium and salivary
a-amylase (carb digestion) and is controlled by ANS
▪Cholinergic parasympathetic fibers stimulate salivary glands
• Ex: anticholinergic meds inhibit salivation
▪Sympathetic beta-adrenergic stimulation decreases salivary secretion – none, little, or little
with rich protein content
▪A pH of 7.4 which neutralizes bacterial acids aiding to prevent injection
▪Contains IgA – prevents orally ingested microorganisms


• Esophagus
o Conducts substances from oropharynx to stomach
o Upper esophageal sphincter prevents entry of air into the esophagus during respiration
o Lower esophageal sphincter (cardiac sphincter) prevents regurgitation from the stomach
Increase tone by cholinergic vagal stimulation and the digestive hormone gastrin

, Decrease tone/relax by non-adrenergic, non-cholinergic vagal impulse and the hormones
progesterone, secretin, and glucagon

o Vagus nerve allows relaxation of esophagus during swallowing
o Swallowing: complex event mediated by the swallowing center in reticular formation of brainstem
Phases: oropharyngeal (voluntary) and esophageal (involuntary)
Must coordinate with respiratory center
• Respiration is inhibited – epiglottis slides downward to prevent food from entering
larynx and trachea

o Peristalsis:
Primary: immediately follows oropharyngeal phase of swallowing
Secondary: bolus of food becomes stuck – wave of contraction and relaxation occurs that is
independent of voluntary swallowing




• Stomach

o Hollow muscular organ – stores food, secretes digestive juices, mixes food with juices – propels
chyme into duodenum
o Muscle layers – outer (longitudinal), middle (circular), inner (oblique)
o Sphincters – lower esophageal (chyme enters from esophagus into stomach), pyloric (chyme exits
stomach into duodenum of small intestine
o Functional portions – upper (fundus), middle (body), lower (antrum)
o Blood supply via branch of celiac artery; drainage via splenic vein and tributaries
o Few substances absorbed in stomach – can absorb alcohol, aspirin, NSAIDS
o Innervated by sympathetic and parasympathetic
o Gastric motility


Swallowing causes fundus to relax
Gastrin and cholecystokinin enhance relaxation of stomach
Gastrin and motilin and low blood glucose enhance peristalsis
Sympathetic activity, secretin, cholecystokinin inhibit peristalsis
Vagus nerve (parasympathetic) stimulates gastric secretion and motility
Gastric mixing enhanced by retropulsion
Gastric emptying


 Increased by larger volumes of food
 Delayed by solids, fats, and non-isotonic solutions
- Fat – cholecystokinin – inhibits intake, gastric motility, decreases gastric emptying
so that fats do not exceed rate of bile and enzyme secretion

,Basics of gastric secretion; what cells secrete what
-Composition of gastric juice depends on volume and flow rate
-Potassium levels higher in gastric secretions than in plasma – important in vomiting, suctioning, etc.
-Rate of secretion varies with time of day – lower in AM, higher in PM
-Products: mucus (protective), HCl acid, enzymes (pepsinogen), hormones (gastrin), intrinsic factor
(vit B12), gastroferrin (iron absorption) - empty into gastric pits

o Gastric hydrochloric acid

▪Secreted by parietal cells of the stomach
▪Dissolves food fibers
▪Acts as bactericidal agent
▪Converts pepsinogen to pepsin
▪Stimulated by: acetylcholine via vagus nerve, caffeine, calcium, gastrin, histamine ▪Inhibited
by: prostaglandins (mucus), gastric inhibitory peptide, somatostatin, secretin

o Pepsin

▪Breaks down protein-forming polypeptides in the stomach
▪Strongest stimulation: acetylcholine via vagal stimulation
▪Inactivation: alkaline environment of duodenum – needs HCl to be converted from pepsinogen

o Mucus
Prostaglandins and nitric oxide: protect the mucosal barrier by stimulation of mucous and
bicarbonate to inhibit acids
Protect against aspirin, NSAIDS, H. Pylori, ethanol, regurgitated bile, and ischemia to prevent
inflammation and ulceration

o Intrinsic factor (IF)
Required for absorption of vitamin B12 in the ileum – combines with vit B12 in the stomach
Gastritis and failure of absorption mechanisms of vit B12 can lead to pernicious anemia

o Gastric glands: primary secretory units
▪Parietal cells: HCl acid and intrinsic factor, gastroferrin
▪Chief cells: pepsinogen – pepsin
▪G cells: gastrin (hormone)
▪Enterochromaffin-like cells: histamine
▪D cells: somatostatin

• Phases of gastric secretion:

o Celiac phase (mouth)
▪Begins with smelling, seeing, tasting, chewing, swallowing
▪Mediated by vagus nerve
▪Acid, pepsinogen, gastrin secreted
▪Insulin secreted by pancreas to hyperglycemia and is strong stimulus to gastric secretion

, o Gastric phase (stomach)
▪Begins with arrival of food to stomach
▪2 major stimuli to secretory effect – distension of stomach and presence of digested protein

 Vagus nerve stimulated by distention – contributes to secretion stimulus
 Mediated by acetylcholine and can be blocked by atropine

o Intestinal phase

▪Begins with movement of chyme from stomach to duodenum
▪Decelerated gastric secretion – when chyme enters alkaline environment of duodenum –
inhibitory vagal reflexes decrease gastric motility
▪Secretin and cholecystokinin stimulate pancreatic secretions and inhibit gastric secretions

Basic function of small intestine, and large intestine

• Small intestine
o Three segments:
-Duodenum: begins at pylorus and ends where it joins the jejunum called the Treitz
ligament
-Jejunum
-Ileum: ilecocecal valve controls the flow of digested material from the ileum into the large
intestine and prevents reflux into the small intestine

o Peritoneum: serous membrane surrounding the organs of the abdomen and pelvic cavity
▪Visceral: lies over the organs
▪Parietal: lines the wall of the abdominal cavity
▪Peritonitis: inflammation of the peritoneum – occurs with perforation of the intestine or after
surgery
▪Peritoneal Cavity: space between the two layers of the peritoneum

o Muscle layers: outer longitudinal and inner circular
▪Mucosal folds (plica): within the small intestine slow the passage of food providing more time for
digestion and absorption
• More numerous in the jejunum and upper ileum

o Blood flow provided by superior mesenteric artery
o Myenteric plexus and mucosal plexus: site of intrinsic motor innervation mediation
-Parasympathetic: secretion, motility, pain sensation, intestinal reflexes
-Sympathetic: inhibits motility and produces vasoconstriction

o Villi: cover the mucosal folds and are the functional units of the intestine

▪Where absorption occurs – villi and microvilli increase surface area for absorption
▪Secretes enzymes necessary for digestion and absorbs nutrients
▪Composed of absorptive columnar cells (enterocytes) and mucus secreting goblet cells
of mucosal epithelium – contain microvilli
▪Water and electrolytes absorbed through intracellular spaces called tight junctions
▪Entire epithelial population of cells is replaced every 4-7 days

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