3/24/08 Digestive System Chapter 22 – Day 1

3/24/08 Digestive system  Respiratory System ♦Brings O 2 to the body  Cardiovascular System ♦Brings O 2 to the cells  In tissues O 2 is used for cellular respiration, BUT…  O 2 is only one of the ingredients – you also need ♦Glucose  Digestive System ♦Brings glucose to the body ♦Other sources of nutrients ♦And other building blocks to make cells

3/24/08 Digestive system  Food is broken down & processed  Nutrients are absorbed  Waste products are eliminated  All of this happens in the digestive tract  A.K.A. alimentary canal or GI tract  The digestive tracts is a long, continuous muscular tube starting at the esophagus

3/24/08 Digestive system Fig

3/24/08 Digestive system - Processes  In order for nutrients to reach cells the digestive system carries out several processes ♦Ingestion = food in the mouth ♦Mechanical processing = physically breaking food into bits ♦Digestion = enzymes and hormones ♦Absorption = organic molecules enter interstitial fluid ♦Excretion = elimination of unwanted materials

3/24/08 Fig Digestive system – Cell/Tissue layers  The digestive system has a distinct system of tissue layers  There is an “open” surface inside the GI tract – epithelial tissue covering on outside  4 layers – from inside to outside ♦These are there ALL ALONG the GI tract ♦Mucosa innermost layer ♦Submucosa ♦Muscularis externa ♦Serosa outermost layer

3/24/08 Cell/Tissue layers - MUCOSA  Digestive epithelium  Connective tissue – lamina propria  (smooth) muscle tissue – muscularis mucosa  Type of epithelium varies along the GI tract ♦Pharynx & esophagus handle large masses of food = stratified epithelium ♦In the stomach – food becomes liquid & passes to intestines ♦A great deal of absorption happens in the intestines Simple columnar epithelium Secrete mucous Highly folded epithelial surface (small intestine)  Lamina propria – areolar connective tissue right below basement membrane of epithelium  Contains blood vessels, nerves, mucous glands (in the intestines this is where you find the Peyer’s patches)  Muscularis mucosa = smooth muscle – helps movement in the GI tract

3/24/08 Cell/Tissue layers - SUBMUCOSA  Dense connective tissue  Nerve network ♦Submucosal plexus  Communication with the nervous system – helps muscle movement

3/24/08 Cell/Tissue layers – MUSCULARIS EXTERNA  Smooth Muscle Tissue  Nerve network ♦Mysenteric plexus  More forceful contractions for movement  2 layers of muscle ♦Longitudinal ♦Circular  Allows 2 types of movement ♦Rocking motion ♦Forward movement

3/24/08 Cell/Tissue layers – SEROSA  Fibrous tissue on outside  Protective covering which helps in attachment to abdominal wall Fig. 22.3

3/24/08 Other important general features  Membranes ♦Perotineal cavity 2 membrane layers ♦Encloses abdominal portion of digestive tract ♦Serosa = visceral peritoneum (inner layer) ♦Parietal peritoneum = lines abdominal wall (outer layer) ♦Additional serous membrane connects serosa/visceral to parietal peritoneum ♦The space between the 2 layers if filled with fluid Peritoneal fluid Secreted by cells of the peritoneum

3/24/08 Other important general features  Mesenteries ♦Sheets of serous membrane allow blood vessels, nerves, and lymph vessels to pass through & network ♦Stabilize the position of the GI tract Prevents “flopping around” ♦OMENTUS – associated with the stomach (Fig ) Lesser omentum & greater omentum Contains adipose tissue (fat around the belly) ♦Mesentery proper Within small intestine, between loops ♦Mesocolon Stabilizes large intestine ♦Areas without mesentaries = pancreas & duodenum – which are attached to the abdominal wall for stability

3/24/08 Secretions  Within the digestive tract – secretions are evident throughout ♦Mucus To lubricate food & “walls” ♦Digestive enzymes Break chemical bonds ♦Electrolytes Buffers - change pH Cofactor for enzymes  Parts of digestive system & direction of food… Oral cavity → Pharynx → Esophagus → Stomach → → Small Intestines → Large Intestines → Rectum → Anus  Explore important structures, secretions, absorption, digestion process, movement of food

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Oral Cavity = Mouth  Consists of ♦Cheek/walls Buccal walls (lined with membrane) ♦Teeth ♦Tongue ♦Palate (roof of mouth)  Function of Oral Cavity ♦Mastication = chewing ♦Food is broken into smaller pieces ♦Tough fibers are separated for access to enzymes ♦Your teeth can apply up to 2 tons of pressure

3/24/08 Oral Cavity = Mouth  During chewing secretions are produced ♦Saliva (& mucus) ♦Saliva = water + mucus + digestive enzymes + solutes ♦Water – dissolves food as it is broken up Chemicals are then able to bind to taste buds = taste sensation ♦Mucus – lubricates food makes it smaller & smoother for swallowing ♦Digestive enzymes – break chemical bonds α – amylase: breaks starch (polysaccharide) into maltose (disaccharide) Also have lysozymes – destroy bacteria (control population) ♦Other solutes – help maintain pH ( )

3/24/08 Oral Cavity = Mouth  Saliva is secreted by SALIVARY GLANDS  Mucus is secreted by BUCCAL GLANDS ♦Located in the epithelium of the mouth  Salivary glands: there are 3 types/locations ♦Parotid: Pair Inferior & anterior to ears Empty into roof of mouth Secretes digestive enzymes ♦Sublingual Under tongue Empties near base of tongue Secretes mucus ♦Submandibular Back of tongue

3/24/08 Oral Cavity = Mouth  Chewing and lubrication converts food particles into a slimy ball = BOLUS (mass of food)  Bolus is then swallowed  The process of swallowing – begins DEGLUTITION ♦Bolus leaves mouth to enter esophagus and then travels to stomach ♦Forces epiglottis to close larynx ♦Triggers deglutition center in medulla To start involuntary muscle movement ♦Bolus tracks from Oral cavity → pharynx = buccal phase Pharynx → esophagus = pharyngeal movement/phase Esophagus → stomach = esophageal movement/phase

3/24/08 Oral Cavity: Food Movement  Movement through the pharynx is fast → slides through oropharynx → laryngopharynx  Esophagus ♦10 inch long tube Contains 2 special muscular areas = sphincters (openings) UPPER ESOPHAGEAL SPHINCTER: ◦guards entrance to esophagus ◦Contracted – constricts & closes opening ◦For food to pass muscle must be relaxed ◦Relaxes at the time of swallowing ◦Food slides into the esophagus from pharynx CARDIAC SPHINCTER ◦At junction of esophagus and stomach

3/24/08 Oral Cavity: Food Movement  In the esophagus – the bolus makes its way to the stomach, more mucus is secreted to keep up lubrication  The bolus moves with the help of SMOOTH muscle activity  There are 2 types of movement in digestive system  Forward Direction & Side – to – Side Movement (next)  For muscle contraction to take place: ♦Submucosal plexus & submyenteric plexus must be activated by the autonomic nervous system

3/24/08 Movement of Bolus  Forward movement ♦Waves of contraction in muscularis externa ♦Along length of tube ♦Process of peristalsis ♦Circular muscles contract behind bolus ♦Longitudinal muscles contract at cardiac sphincter ♦Wave of relaxation opens entrance to stomach

3/24/08 Movement of Food (bolus) Fig. 22.4

3/24/08 Movement of Bolus  Forward movement ♦Waves of contraction in muscularis externa ♦Along length of tube ♦Process of peristalsis ♦Circular muscles contract behind bolus ♦Longitudinal muscles contract at cardiac sphincter ♦Wave of relaxation opens entrance to stomach  Side to side movement ♦No set direction ♦Helps to mix bolus with mucus for more lubrication ♦Contraction in muscles → segmentation ♦Mostly in large & small intestine – helps to fragment bolus

3/24/08 Stomach Anatomy  Shape  Sphincters ♦Cardiac ♦Pyloric  Folds = rugae ♦Deep muscular folds  Mucosa Fig

3/24/08 Stomach Anatomy  Mucosa ♦Gastric pits with gastric glands ♦Secretory cells  4 types of secretory cells: CellSecretion  Chief cells→ Pepsinogen  Parietal cells →HCl (acid)  Mucus cells →Mucus  Enteroendocrine cells →Gastrin (hormone)

3/24/08 Stomach Processes  What happens to food when it enters the stomach?  Digestion & Secretion – almost no absorption  3 phases of secretion in the stomach 1.Cephalic ♦Begins at the sight of food ♦Gastrin is secreted ♦Stimulates HCl & pepsinogen  Food enters the stomach

3/24/08 Phases of Gastric Secretion in Stomach 2.Gastric Phase Secretion  Mucus is secreted to protect stomach lining  More gastrin, more pepsinogen  Acidic environment – pH drops (pepsinogen → pepsin at low pH)  Secretions stop when pH reaches 2.0 Digestion  Proteins in food →pepsin →amino acids  Milk proteins →gastric lipase → amino acids & renin

3/24/08 Phases of Gastric Secretion in Stomach 2.Gastric Phase Mixing  Rugae become stretched – stomach is distended  Muscular contractions mix food for several hours  Food becomes watery mixture ♦Chyme (acidic)  After several hours of mixing waves of contractions (peristalsis) reach the lower end/base of the stomach – near the pyloric sphincter  Sphincter opens & closes with each wave  Squirts chyme into the duodenum  The Duodenum secretes enteric gastrin ♦starts next phase

3/24/08 Phases of Gastric Secretion in Stomach 2.Gastric Phase General info/reminders  After 2-6 hours, the stomach is emptied  Some macromolecules move faster through the stomach: ♦Carbohydrates ♦Proteins ♦Then fats  Remember NO absorption in the stomach except for EtOH, H2O, aspirin (alcohol is absorbed fast – gets to brain fast)  On to next phase = intestinal phase

3/24/08 Phases of Gastric Secretion in Stomach 3.Intestinal Phase Food moves to intestine = gastric emptying  Small intestine secretes 2 hormones:  Cholecystokinin (CCK) ♦Is released when proteins & fat are in the chyme ♦Inhibits gastric secretions ♦Triggers pancreas secretion  Secretin ♦Released when pH in duodenum drops below 4.5 ♦Stimulates bicarbonate release from pancreas Deactivates pepsin Inhibits stomach secretions Stimulates bile secretion from liver

3/24/08 Swallowing Fig

3/24/08 Alvioli – Capillary Interface Fig. 22.4

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3/24/08 Mechanics of Respiration  Ventilation ♦= mechanical process ♦involves the diaphragm and skeletal muscles (intercostal muscles)  Breathing consists of 2 phases: ♦Inspiration air is taken into the lungs ♦Expiration Air passes out of the lungs

3/24/08 Alvioli – Capillary Interface Fig