BIOL 1800 - The Digestive System 1 Intro to Digestion and the Oesophagus PDF

Lecture 9: Introduction to the Gastrointestinal Tract The Oral Cavity and Oesophagus BIOL 1800 Dr Marie Conway Learning Objectives At the end of this lecture you should be able to do the following: Provide an overview of the gastrointestinal tract (GIT) Describe the functions of the...

Lecture 9: Introduction to the Gastrointestinal Tract The Oral Cavity and Oesophagus BIOL 1800 Dr Marie Conway Learning Objectives At the end of this lecture you should be able to do the following: Provide an overview of the gastrointestinal tract (GIT) Describe the functions of the GIT Describe the layers of the GIT Provide an overview of the functions of the oral cavity Describe to anatomy of the oesophagus Discuss the stages of swallowing  got⑨Getting I.Edge Yeates!*5.Is :P:*#◦Egest The Digestive System particular elements (liver = lipid) tubes  making decisions and choices Functions of the Digestive System - to digest and absorb food/nutrients, excrete the waste products Ingestion – active process - taking food in month (voluntary-making decisions and choices) Mechanical processing - structural - crushing the food, propeling it further to the tract (swallowing), prepares food for the chemical digestion Digestion – chemical breakdown - breaking down food → large molecules → smaller fractures → absorbtion to blood Secretion – H2O, enzymes, buffers, acid - glandular organs/cells → secret → tract Absorption - CHO, lipid, protein, ions, vitamins, water, minerals → from interstitial fluid to cells Excretion - Removal of waste Cavities 7 L of fluid is moved in/out of peritoneum each day, only small volume (20 ml) there at any one time Peritoneum A serous membrane encapsulating with peritioneal fluid membranes (enables movement without friction) - lubricates, separates the parietal and visceral Outer parietal membrane lines the inner surface of the body wall Inner visceral membrane covering the organs of the peritioneal cavity (aka serosa) 7 L of fluid is moved in/out of peritoneum each day, only small volume (20 ml) there at any one time Peritoneum & Disease Peritonitis - result of surgery or appendicitis (→ inflammation) Abnormal accumulation of peritoneal fluid associated with liver disease/cirrhosis, renal disease, heart failure & infection (laparoscopy) Clinical signs Abdominal swelling/redness Clinical symptoms Severe abdominal pain Heartburn/indigestion Mesentery =" holds everything together" Doubled sheets of “sandwiched” - fold of membrane that attaches the peritoneum intestine to the wall around the stomach area and holds it in place Forms access route for blood/lymph vessels & nerves Organs of GIT suspended/fixed by mesentery’s within peritoneal cavity Martini Fig 24.2 Histological organisation of the digestive tract Layers of the GIT (alimentary canal) 1. Mucosa 2. Submucosa 3. Muscularis Externa 4. Adventitia / Serosa Layers of the GIT (alimentary canal) 1. Mucosa Inner lining; epithelium (enterocytes) & underlying lamina propria Epithelium; simple or stratified Lamina propria; loose irregular CT, blood/lymph vessels, nerves & muscularis mucosa Martini Fig 24.3 Layers of the GIT (alimentary canal) 1. Mucosa - enterocytes = intestinal absorptive cells Inner lining; epithelium - simple columnar, line intestines (enterocytes) & underlying lamina propria - supplier, mucosal glands - differs along the tract → secretory goblet cells, microvilli Epithelium; simple or stratified Lamina propria; loose irregular CT, blood/lymph vessels, nerves & muscularis mucosa ⇒ mucosa is folded Martini Fig 24.3 Layers of the GIT (alimentary canal) 2. Submucosa Dense irregular connective tissue Larger blood/lymph vessels Exocrine glands (buffers & mucus) Submucosal nerve plexus Martini Fig 24.3 Layers of the GIT (alimentary canal) 2. Submucosa Dense irregular connective tissue Larger blood/lymph vessels Exocrine glands (buffers & mucus) Submucosal nerve plexus - controls musoca - nerve fibres network Martini Fig 24.3 Layers of the GIT (alimentary canal) 3. Muscularis Externa Transverse (circular) & longitudinal smooth muscle layers of SM Peristalsis (motility) & segmentation Myenteric intrinsic nerve plexus - controls the motility Regional differences - it' motility Martini Fig 24.3 Layers of the GIT (alimentary canal) 3. Muscularis Externa Muscle layers in the Muscularis The combination of circular and longitudinal smooth muscle gives the tube an ability to perform complex movements that squeeze and propel ingesta in the lumen Layers of the GIT (alimentary canal) 4. Serosa - covers the muscular layers Outermost layer Visceral peritoneum Loose irregular CT covered by simple squamous epithelia Double layered mesentery, houses vascular and nervous supplies to the GIT + colon, rectum Adventitia at oesophagus - outer layer of connective tissue that surrounds the tubular organs - from collage nous and elastic fibres Martini Fig 24.3 - not covered with peritoneum Layers of the GIT (alimentary canal) 4. Serosa Outermost layer Visceral peritoneum Loose irregular CT covered by simple squamous epithelia Double layered mesentery, houses vascular and nervous supplies to the GIT Adventitia at oesophagus Martini Fig 24.3 Histological organisation of the digestive tract Summary Mucosa lines digestive tract (mucous epithelium) – Moistened by glandular secretions – Lamina propria and epithelium form mucosa Submucosa – Layer of dense irregular connective tissue Muscularis externa – Smooth muscle arranged in circular and longitudinal layers – Adventitia 2 - Serosa – Serous membrane covering most of the muscularis externa Control of digestive function Control of digestive function… Motility Rate of digestion / absorption Coordinated via Enteric nervous system - division of the autonomic nervous system - neurons around - peristalsis Submucosal & Myenteric plexes ↗ Long & Short reflexes - control the digestion Enterogasterones by the mucosa Hormone “like” chemicals secreted locally that impact digestion/absorption Motility Rhythmic cycles of contraction induced by pace-setter cells within the muscularis externa (basal electrical rhythm; BER) - colon expands and elongate → segmentation - does not push food in any direction Peristalsis Segmentation Haustral Esophagus, stomach & SI SI - mixing bolus with intestinal secretions LI - compaction ⅔:& :ith :ÉÉÉ" %:{""' ÷: Martini Fig 24.4 Germann & Stanfield Fig 30 Moore Fig 12.45 Control of the digestive system Movement of materials along the digestive tract is controlled by: 1. Local mechanisms – Coordinate response to changes in pH or chemical stimuli 2. Neural mechanisms – Parasympathetic and local nervous reflexes 3. Hormonal mechanisms – Enhance or inhibit smooth muscle contraction  NEURAL CONTROL SHE'S" trig:&abettors LOCAL CONTROL HORMONAL CONTROL peptides from endocrine cells Control of digestive function Short & Long reflexes (enteric) Short reflexes - intrinsic nerve-motality, growth Local stimulus & local effectors (smooth muscle & glands) Enterogasterones (gastrin, secretin, CCK, motilin, ghrelin) Long reflexes Cephalic reflexes (smell etc) - response to stimuli from outside the GIT (sensory neurons) Afferents from GIT to CNS (chemo/mechano/osmo etc) sensitive to sensitive to sensitive to the osmolarity chemicals stretch/tention of the lumenal content central and autonomic his. Long & short reflexes Submucosa Germann & Stanfield Fig 22 Enterogasterones  ENTEROGASTERONES Gastroenterones / Gastric Hormones The Oral Cavity and Oesophagus Oral/ buccal cavity → PHARYNX Functions Analysis of food sensory analysis of food before swallowing Mechanical digestion through the actions of the teeth, tongue, and palatal surfaces; = chewing includes mechanical processing and mastication Lubrication by mixing with mucus and saliva epithelium: stratified squamous keratinized - hard palate,tongue Limited digestion non-Keratin lips, cheeks limited chemical digestion of carbohydrates and lipids Martini Fig 24.6 The Oesophagus - 25cm, narrow point-C6 → empties to the stomach-T7 Anatomically and functionally, the Oesophagus is the least complex section of the digestive tube. Its role in digestion is simple: – to convey boluses of food from the pharynx to the stomach. The oesophagus begins as an extension of the pharynx in the back of the oral cavity – It then courses down the neck behind the trachea, – through the thoracic cavity, – and penetrates the diaphragm – to connect with the stomach in the abdominal cavity Oesophagus & Stomach Normal Location of Oesophagus aorta oesophagus trachea diaphragm THORACIC CAVITY ABDOMINAL CAVITY stomach The Oesophagus Carries solids and liquids from the pharynx (mouth) to the stomach The wall of the oesophagus contains mucosal, submucosal, and muscularis layers. Histology of the Oesophagus Distinctive features of the oesophageal wall include: – Non-keratinized, stratified squamous epithelium – Folded mucosa and submucosa – Mucous secretions by oesophageal glands – A muscularis with both smooth and skeletal muscle portions soft palate-keeps the pharynx closed – Lacks serosa – Anchored by an adventitia Muscle Layers in the Oesophagus = cardiac sphincter Histology of lower 2/3 of oesophagus circular muscle long..- muscle Deglutition 2400 times per day - unconscious every 40s ! Voluntary & involuntary 1. Buccal phase 2. Pharyngeal phase 3. Oesophageal phase Martini Fig 24.11 Deglutition 1. Buccal phase chewing and mixing food with saliva → bolus Voluntary Compression of bolus (hard palate) Tongue pushes bolus posteriorly Soft palate lifts (nasopharanx) Bolus enters oropharynx Martini Fig 24.11 Deglutition 2. Pharyngeal phase Involuntary/reflex Pre-programmed all or none sequence Bolus contacts palatal arches and uvula Receptors relay afferents via trigeminal & glossopharyngeal nerves to swallowing centre in medulla. Martini Fig 24.11 Deglutition 2. Pharyngeal phase Efferents to pharyngeal constrictor muscles move the bolus into the oesophagus by constricting the pharyngeal wall Elevation of larynx, folding of epiglottis direct bolus past trachea Respiration inhibited Martini Fig 24.11 Deglutition 3. Esophageal phase Involuntary/reflex Primary peristaltic waves drives bolus down esophagus (10 s). Secondary stronger peristaltic waves may be required. Martini Fig 24.11 Deglutition 3. Oesophageal phase Local stretch receptors detect distension and peristaltic contractions are modified (submucosal & myenteric plexus) Martini Fig 24.11 Swallowing (deglutition) Buccal phase -→completion of bolus against the lift of the soft palate hard palate Pharyngeal phase -- bolus contacts the pharyngeal arches enter oesophagus through upper oesophageal sphincter Oesophageal phase - bolus enters the stomach through the lower oesophageal sphincter Dysphagia Difficulty swallowing Oropharyngeal / esophageal – Genetic (cleft palate) – Obstructive (tumor) – Neurological (stroke) – Muscular (scleroderma) Nasogastric tube Hammil 2017 Dysphagia Difficulty swallowing Oropharyngeal / esophageal – Neurological (stroke) – Genetic (cleft palate) – Obstructive (tumor) – Muscular (scleroderma) Nasogastric tube PEG (percutaneous endoscopic gastrostomy) tube Schwarts 2015 Oesophagus Barrett's Oesopagus Gastroesophageal reflux disease (GERD) Caused by adaptation to chronic acid exposure from reflux esophagitis Mucosa replaced by metaplastic columnar epithelium Strong association with esophageal cancer Spechler et al., 2013 JAMA