GI 2 - Part Deux - The Basic Plan, the Peritoneum, and the Stomach.doc

11 Pages
Unlock Document

Health Sciences
Cale Zavitz

G.I. 2: Part Deux: The Basic Plan, the Peritoneum, and the Stomach Esophagus: histology • Basic plan of GI tract consists of four primary layers: ⁃ Mucosa (most superficial, towards lumen) ⁃ Nonkeratinized stratified squamous epithelium (not as tough as integument)- need stratified squamous here b/c of friction forces from food- need multiple layers so they can be sloughed off- rest of GI consists of simple cuboidal epithelium ⁃ Lamina propria ⁃ Muscularis mucosae ⁃ Submucosa ⁃ Muscularis ⁃ Two muscle layers: Inner circular and outer longitudinal (shortens path) ⁃ Two work together to help push food from mouth to stomach ⁃ Peristalsis- Causes lumen to get smaller, contraction will ride down entire length of esophagus, pushing food ⁃ Adventitia- loose connective tissue that ties the esophagus to all of the loose connective tissues in neck and plasters it to posterior thoracic wall so that esophagus does not move around much ⁃ Rest of GI tract, if sitting in abdominal-pelvic cavity, outer layer is serosa- thin layer of epithelial tissue which secretes serial fluid, allowing visceral organs to move around within cavity Late Deglutition- Final stages of swallowing • Food being passed from lower portion of esophagus into stomach. To do so, must pass through lower esophageal sphincter. • Lower esophageal sphincter (LES): between esophagus and stomach, at level of diaphragm- muscles of diaphragm aid sphincter • This part is all involuntary- first third of esophagus is skeletal muscle (striated)- next one third is a mixture of smooth and striated muscle- last one third is smooth muscle Review of Deglutition • Tongue pushes masticated food towards the oropharynx- voluntary • Uvula and soft palate closes off nasopharynx so food will not go into nasal cavity • Larynx elevates to aid epiglottis in closing off trachea • Pharyngeal muscles push bolus past Upper Esophageal Sphincter (skeletal muscle, has to relax to allow food to go by) • Skeletal muscle in first one third of esophagus pushes bolus toward involuntary section (smooth muscle controlled by ANS and ENS) • Enteric Nervous System- set of neurons that exists within wall of GI tract which help to coordinate peristaltic movement to aid in movement of bolus to stomach • Lower esophageal sphincter opens and bolus enters the stomach (AKA the "grinder") GERD- Gastroesophageal reflux disease • Acidic contents of stomach is getting up into esophagus • Lower esophageal sphincter is not very good- requires help of diaphragm muscles to help pinch off lower opening of esophagus • Hiatal Hernia- if stomach herniates through this hole in the muscle, no longer have support of diaphragm helping lower esophageal sphincter- can have acidic contents of stomach pushed up into esophagus • Esophagus was not designed to handle extremely acidic environment, will erode mucosal lining of esophagus- that's where the heartburn comes from • Often mistaken for cardiac disease- associated pain from this area feels like a heart attack • Hernia creates an intra-thoracic reservoir- part of stomach now exists up in thoracic cage • Causes are numerous but is worsened by: ⁃ Smoking, alcohol- relaxes LES, allowing acid into esophagus ⁃ Coffee, chocolate, peppermint, stress- increase hydrochloric acid produced by stomach ⁃ Obesity (store a lot of fats in peritoneal folds of abdominal cavity, creating pressure on stomach) and pregnancy- alterations in anatomy that put pressure on stomach • Treatment options include: ⁃ Smaller meals- will not produce so much hydrochloric acid or distend stomach which creates pressure ⁃ Maintaining an upright position after a meal ⁃ Avoiding problematic foods ⁃ Antacids- consuming bicarb anion (calcium or sodium) neutralizing acid The "Basic" Plan (also above) • Mucosa ⁃ Epithelium- simple cuboidal ⁃ Lamina propria- connettive tissue tying epithelium to underlying structures ⁃ Muscularis mucosa- layer of muscle associated w/ mucosa that helps epithelium above fold • Submucosa- find glands associated w/ GI tract- tend to be mucous glands, but in stomach will secrete hydrochloric acid- well vascularized to create secretions • Muscularis- helps peristalsis throughout entire GI tract ⁃ Inner circular ⁃ Outer longitudinal • Serosa- visceral organs in abdominal cavity, esophagus has adventitia ⁃ Mesothelium- secrete serosal fluid, lubricating organs ⁃ CT (thin) The Enteric Nervous System • Control of peristalsis • Network of neurons in wall of GI tract, can function independently of any CNS input- doesn't involve spine • Helps to control peristalsis • 100+ million neurons from esophagus to anus • 2 components ⁃ Myenteric plexus (between circ. and long. layers)- branch associated with muscles ⁃ Submucosal plexus (in submucosa)- helps to control gastric secretions throughout GI tract ⁃ Interstitial cells of Cajal- pacemakers of the gut, set up rhythm and intensity of peristaltic movements- turned up or down by other neural inputs from parasympathetic and sympathetic nervous system- just like our heart, gut will function on its own- has own reflexes and pacing inherent in design The ANS and ENS Meet • Sensory neurons provide signals to myenteric and submucosal plexi • When food enters small intestine, it is sensed by mechanoreceptors (stretch receptors) in wall of intestine- will signal to submucosal plexus to increase mucous secretion to aid food along- will also signal muscle to set up for peristaltic wave • Collateral branches send some signals out to the spinal cord- this is how visceral pain is perceived- e.g. excess distension caused by gas will be sent through afferent fibres to spinal cord, and you will perceive that pain • Parasympathetic and sympathetic NS interact at the level of both the myenteric plexus and submucosal plexus ⁃ Parasympathetic: Gastric secretions go up, mucosal secretions go up, peristalsis will be more intense- In addition, can "whisper" directly to organs- can actually do it directly to the muscles in muscularis as well as with epithelial cells associated with the glands of the muscles- can fine tune activities by talking directly to the organs ⁃ Sympathetic: Inhibits digestion- turns all of these things down Sympathetic Innervation • Thoraco-lumbar in origin- helps turn down digestion, slow peristalsis, decrease secretions • Sympathetic NS tends to constrict blood vessels in gut- can't make secretions (mucous, gastric juices) if you do not have blood flow- liquid is being pulled from blood stream Parasympathetic Innervation • Cranio-sacral in origin- turns up all activities • Major one is CN X- Vagus nerve- does most of visceral organs inferior to diaphragm, almost to tip of large intestine • Last bit of large intestine and defecation are controlled by the pelvic splanchnic nerves, which come out through sacral plexus The Abdominal Cavity • Lesser omentum- Flap of tissue connecting stomach to inferior surface of liver- a peritoneal fold • Large intestine- ascending on right, transverse, then descending on left- will turn into S-shaped segment- Sigmoid colon- becomes straight at rectum The Peritoneum • Abdominal viscera are suspended from posterior abdominal wall by peritoneal folds • Mesentery- largest fold- suspends entire section of small intestine from posterior abdominal wall- this is b/c as organs were developing to go into abdominal cavity, were developing from posterior wall- pushed into abdominal cavity- in doing so, pulled along parietal layer associated with that wall- parietal peritoneum became visceral peritoneum as it was associated with organs itself- saw this with heart and lungs • Retroperitoneal- Any structures associated with posterior abdominal wall that sit behind the parietal peritoneum • Any cross-sectional view is from the patient's feet (Aorta on left, Inf. Vena Cava on right) • Falciform Ligament- midline of liver- splits liver in two- suspends liver from inferior surface of diaphragm and has small portion that attaches liver to anterior abdominal wall- only visceral organ in this cavity attached to the anterior abdominal wall- rest are suspended from posterior • Greater omentum- flap of peritoneum extends from greater curvature of the stomach, will then reflect down, come back up, and attach to transverse colon- full of fat and blood vessels- later on in life, this is where fat usually ends up accumulating • Lesser omentum- helps to suspend stomach from inferior surface of liver • All peritoneal folds are continuous with each other • Small intestines- suspended from posterior abdominal wall by mesentery • Mesocolon- fold that helps to suspend transverse colon from posterior abdominal wall Five Peritoneal Folds • Important retroperitoneal structures that you will find adhered to posterior abdominal wall in behind parietal peritoneum ⁃ Pancreas ⁃ Duodenum (wraps around pancreas) ⁃ Ascending and descending colon- pushed against posterior abdominal wall- don't move around much ⁃ Kidneys- plastered on posterior abdominal wall Concepts of Digestion • Depends on mechanical (e.g. stretch) and chemical (e.g. pH) stimuli- a lot of local reflexes are generated in GI tract (stomach, small intestines, large intestines) • Digestion is controlled by: ⁃ Extrinsic and intrinsic nervous input ⁃ Intrinsic: local reflexes engendered by ENS ⁃ Extrinsic: includes input from cortex- e.g. thoughts of food will get stomach moving- also includes ANS (parasympathetic and sympathetic) ⁃ Hormonal input- more importantly, locally at the level of the GI tract, there are many cells that produce hormones affecting other cells within other sections of the GI tract- endocrine hormones that trav
More Less

Related notes for HTHSCI 1H06

Log In


Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.