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Exam 4 Review: Digestive System Physiology

by: Samantha Bubb

Exam 4 Review: Digestive System Physiology BSC 2086

Marketplace > Florida Atlantic University > Biological Sciences > BSC 2086 > Exam 4 Review Digestive System Physiology
Samantha Bubb

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About this Document

- Goes over the components of Digestive System physiology, as explained by Professor Lovelace - Contains physiological info from all of chapter 23
Anatomy Phy II
Matthew Lovelace
Study Guide
anatomy and physiology, Biological Science
50 ?




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This 10 page Study Guide was uploaded by Samantha Bubb on Monday April 11, 2016. The Study Guide belongs to BSC 2086 at Florida Atlantic University taught by Matthew Lovelace in Spring 2016. Since its upload, it has received 29 views. For similar materials see Anatomy Phy II in Biological Sciences at Florida Atlantic University.


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Date Created: 04/11/16
Samantha Bubb ANATOMY AND PHYSIOLOGY 2 FAU SPRING 2016 PHYSIOLOGY OF THE DIGESTIVE SYSTEM •   Regulated by the enteric nervous system and a set of extrinsic nerves that are apart of the autonomic nervous system •   Enteric nervous system (ENS): “The brain of the guts” o   Contains interneurons, motor neurons and sensory neurons o   Arranged into 2 separate plexuses §   Myenteric Plexus: Between the longitudinal and circular layers of the muscularis •   Controls GI tract movement §   Submucosal Plexus: Within the submuscosa •   Monitors secretion cells in the mucosal epithelium, controlling secretion of the GI tract o   Interneurons in the ENS connect the neurons of these plexuses together o   Sensory neurons give mucosal epithelium: §   Function as chemoreceptors •   Activated by certain chemicals in food §   Some are stretch receptors or mechanoreceptors •   Activated when food stretches the GI tract walls •   Autonomic Nervous System (ANS): o   May/may not regulate the ENS o   Consists of parasympathetic and sympathetic divisions §   Parasympathetic: Increases GI secretion and movement •   Some directly innervate smooth muscle/glands in the GI tract while others do not •   Stimulates GI movement and secretions §   Sympathetic: Decreases GI secretion and movement •   Emotions like fear, anger and anxiety slow down digestion by stimulating the sympathetic NS •   GI reflex pathways o   Most of the neurons in the ENS are part of this §   Regulate secretion and mobility in response to changes in GI tract lumen or stimuli from the CNS o   Initial components: Sensory receptors §   Synapse other neurons from ANS, CNS and ENS telling them about stretch of GI tract and its contents o   Short reflexes: Enteric nerve plexuses respond to stimuli in GI tract Samantha Bubb ANATOMY AND PHYSIOLOGY 2 FAU SPRING 2016 o   Long reflexes: Respond to changes inside or outside the GI tract, incorporate CNS and autonomic nerves •   Metabolic processes of the GI tract : o   Catabolism (digestion): Larger molecules being broken down into smaller ones o   Anabolism: Small molecules used as building blocks of larger ones •   The peritoneum is the body’s largest serous membrane o   2 layers: §   Visceral peritoneum: Forms the serosa §   Parietal peritoneum: Outermost part, continues around the abdominal wall o   Has 5 folds: §   Greater omentum: Layer of fat that lays over the transverse colon and anterior coils of the small intestine •   Many lymph nodes are present here to fight infection §   Falciform ligament: Attaches the liver to the anterior abdominal wall and diaphragm §   Lesser omentum: Suspends the stomach and duodenum from the inferior edge of the liver •   Forms a pathway for blood vessels •   Contains common bile duct and lymph nodes §   Mesentery and Mesocolon •   Mesentery: Small intestine •   Mesocolon: Large intestine •   Bind the bowel to the posterior abdominal wall •   Holds the intestines in place loosely Special Features of the Stomach •   Rugae, large folds in the mucosa of an empty stomach, enable stretching depending on the contents in it •   Expands to accommodate large quantities of food o   Acts as a holding chamber and mixing reservoir •   The muscularis externa has a 3 layer to do the churning during mechanical digestion o   The oblique layer •   Mixes contents with the gastric juice to begin chemical digestion (will be discussed further) •   Simple columnar cells line the mucosal surface and secrete mucous o   These form gastric glands Samantha Bubb ANATOMY AND PHYSIOLOGY 2 FAU SPRING 2016 o   Gastric glands open up into gastric pits •   Exocrine gland cells: o   Mucuos neck cells: Make alkaline mucus o   Parietal cells: Make hydrochloric acid and intrinsic factor o   Chief cells: Secrete pepsinogen and gastric lipase o   All of these secretions make gastric juice •   Gastric juice is multifunctional o   Kills microbes, denatures the 3D shape of proteins in the food you eat and converts pepsinogen into pepsin o   Components: §   Pepsin: Only active proteolytic enzyme in stomach •   Starts as pepsinogen, and is converted to pepsin after coming in contact with HCl or other pepsin enzymes §   Gastric lipase: Breaks down lipids into fatty acids, monoglycerides and glycerol §   Intrinsic factor: Needed for absorption of12 in the terminal ileum Mechanical and Chemical Digestion •   The body digests food mechanically and chemically •   Mechanical digestion: Chewing, churning, mixing, peristalsis etc. o   This all begins in the oral cavity o   When you begin chewing, there is a crushing of food with your teeth o   As food travels down the esophagus, the skeletal and smooth muscle in the esophagus move the food down into the stomach through peristalsis §   Understand that the swallowing is voluntary at first, but then becomes involuntary •   Upper esophageal sphincter: Skeletal muscle = voluntary •   Lower esophageal sphincter: Smooth muscle = involuntary o   Continues in the end of stomach and throughout the small intestine through segmentation: §   Peristalsis that sends food back and forth to break up the contents §   Controlled through the myenteric plexus of the muscularis externa Samantha Bubb ANATOMY AND PHYSIOLOGY 2 FAU SPRING 2016 •   Chemical digestion: Use of acids, salivary amino acids, etc. o   There are 3 salivary components that are secreted by the salivary glands to begin chemical breakdown of food: §   Salivary amylase: Breaks down carbohydrates §   Salivary lipase: Breaks down fats §   Salivary protease: Breaks down proteins o   When food moves into the stomach, food mixes with gastric juice, which is highly acidic o   Salivary lipase is activated in the stomach when the food is in contact with the gastric juice §   This allows both gastric and salivary lipase to break down the triglycerides into monoglycerides and fatty acids o   Hydrochloric acid causes the pH of gastric juice to be so low §   This acid plays a vital role in break down of food and bacteria o   Parietal cells secrete hydrogen and chlorine into the stomach separately, which allows hydrogen to be transported into the lumen on its own §   Proton pumps pump H+ into the lumen and send K+ out of the lumen into the cell (H+/K+ ATPase) §   Proton pump inhibitors block the action of this pump to decrease acid production o   These parietal cells contain carbonic anhydrase which also provides H+ supply for the H+/K+ ATPase §   Carbonic anhydrase catalyzes carbon dioxide and H O 2nto H 2O i3 the parietal cell §  H2CO d3ssociates into H+ and HCO - th3s gives the H+ supply for the H+/K+ ATPase §   The bicarbonate ion HCO 3 is swapped for chloride in the parietal cell using the Cl-/ HCO 3 antiporter §   This process is called the ALKALINE TIDE   HCl Secretion can be stimulated and inhibited by different factors. •   HCl stimulated is stimulated by: o   Acetylcholine: Parasympathetic neurotransmitter o   Gastrin: Secreted by G cells and intestinal mucosal cells o   Increased acidity = Decreased gastrin secretion Samantha Bubb ANATOMY AND PHYSIOLOGY 2 FAU SPRING 2016 o   Histamine: Paracrine substance, released by mast cells in the lamina propria in the stomach; binds to H 2eceptors in parietal cells •   HCl is secretion is inhibited by: o   Somatostatin o   Sympathetic stimulation PHASES OF HCL SECRETION: •   Cephalic Phase: Thought, smell or sight of food o   Increases HCl secretion o   A conditioned reflex •   Gastric Phase: Stretching of stomach, decrease in stomach pH o   Long and short neural reflexes are activated o   Increase in gastrin secretion §   Increased gastrin = Increased HCl secretion •   Intestinal Phase: Stretching of small intestine, increase in duodenal pH, increased nutrient concentration o   Long and short reflexes activated o   Secretin and CCK is secreted (more about these on next page) §   Decreases HCl secretion Accessory Organs and their Digestive Functions •   Liver: Makes bile and participates in storage and breakdown of nutrients o   Bile is released into chyme and helps in the digestion of lipids through the help of bile salts (more info on page 8) §   Has a dark color due to bilirubin o   Contains stellate reticuloendothelial cells (Kupffer cells) §   Phagocytes that destroy worn out blood cells and bacteria from the GI blood stream •   Gallbladder: Stores and preserves bile which is made by the liver o   With the stimulation of the CCK cells (talked about on following page), this organ contracts and releases bile into the chyme o   This organ is not essential for life §   BUT, this could cause problems for those who are attempting to digest high fat meals Samantha Bubb ANATOMY AND PHYSIOLOGY 2 FAU SPRING 2016 Important Features of the Small Intestine Villi: Projection in the small intestine used to increase surface area and enhance absorption in the small intestine •   Contain enteroendocrine, absorptive, goblet and paneth cells Enteroendocrine cells: Secrete hormones into the small intestine, which affect the secretion of gastric juice S cells: Secrete secretin that CCK cells: Secrete cholecystokinin stimulates secretion of pancreatic that stimulates pancreatic juice secretion, bile ejection and opening juice and bile, slightly reduces gastric of sphincter of Oddi juice and enhances the effect of CCK • Reacts to fatty chyme in the • Reacts to acidity in small small intestine intestine K cells: Secrete glucose dependent insulinotropic peptide (GIP) • Induces insulin secretion Absorptive cells: Digest/absorb nutrients from chyme in the SI •   Contain microvilli that create a brush border o   Microvilli increases surface area, increasing the rate of absorption Goblet cells: Secrete mucous Paneth cells: Secrete lysozyme, and have phagocytizing abilities •   Submucosa has Brunner’s glands that secrete mucus to neutralize the acidity in chyme •   Lamina propria in the mucosa has Preyer’s patches found only in the ileum •   The jejunum has neither Brunner’s glands or Preyer’s patches Samantha Bubb ANATOMY AND PHYSIOLOGY 2 FAU SPRING 2016 NUTRIENT BREAKDOWN AND ABSROPTION IN THE SMALL INTESTINE Digestion: Breakdown of foodstuffs for absorption •   Done with the the help of: o   Intestinal juice o   Pancreatic and gallbladder secretions o   Brush border enzymes Intestinal juice: Contains water, mucous, enzymes, electrolytes and hormones •   With the help of this and the other components allows for breakdown of important substances Brush border enzymes: Line the villi and assist in carbohydrate, peptide and nucleic acid digestion Digesting Carbohydrates •   Pancreatic amylase continues the break down of large carb molecules o   Acts on starch and glycogen but does not break down cellulose §   Cellulose = Fiber §   Cannot be digested due to different chemical bonds •   Alpha-dextrinase (brush border enzyme) breaks off glucose molecules one by one •   ALL CARBS MUST BE BROKEN DOWN INTO MONOSACHARIDES BECAUSE ONLY THEY CAN BE ABSORBED •   Other brush border enzymes that break down carbs: o   Sucrase: Breaks down sucrose à glucose and fructose o   Lactase: Breaks down lactose à glucose and galactose §   Lack of this enzyme = Lactose intolerance o   Maltase: Breaks down maltose à glucose Digesting Proteins •   Begins primarily in the stomach with the help of pepsin •   But with protease, only certain bonds between certain amino acids can be broken •   In the small intestine pancreatic proteases continue digestion of proteins o  2 enzymes found in the brush border of absorptive cells: §  Aminopeptidases and dipeptidases •   Break down proteins into amino acids, dipeptides and tripeptides Digesting Lipids •   Most abundant form: triglycerides (Glycerol bound to 3 fatty acids) Samantha Bubb ANATOMY AND PHYSIOLOGY 2 FAU SPRING 2016 •   Begins primarily in the stomach with lingual and pancreatic lipase o  Lingual lipase does a small part in the mouth •   Most of it happens in the small intestine because of pancreatic lipase o  Rate of break down is dependent on bile salt concentration o  Because fats are hydrophobic, they form globules o  Bile salts are needed to break these globules apart for digestion Digesting Nucleic Acids •   Pancreatic juice has deoxyribonuclease and ribonuclease o  Break down DNA and RNA •   The remains of the nucleic acid digestion are broken down further by brush border enzymes called nucleosidases and phosphates Absorption: Passage of digested nutrients from GI to blood and lymph •   90% is done in the small intestine •   10% is done in the stomach and large intestine •   Done with the help of: o   Diffusion o   Facilitated Diffusion o   Osmosis o   Active transport •   If it’s not absorbed, it is defecated Absorbing Monosaccharides •   Almost all monosaccharides are absorbed o  Cellulose is one of the main ones § Becomes a main component of feces •   Monosaccharides pass through the apical membrane of absorptive cells through: o  Fructose: Facilitated diffusion o  Glucose and Galactose: Secondary active transport § Paired with the transport of sodium § 2 sites for sodium, 1 site for glucose •   Monosaccharides move out the basilar layer through facilitated diffusion •   3 products of carb digestion: o  Glucose o  Galactose o  Fructose Absorbing Amino Acids, Dipeptides and Tripeptides •   Most protein absorption is done through active transport •   Happens mainly in the duodenum and jejunum Samantha Bubb ANATOMY AND PHYSIOLOGY 2 FAU SPRING 2016 •   Different carriers carry specific amino acids o   Some use active transport o   Some use sodium dependent secondary active transport o   Some use H+ dependent secondary active transport §   Di/Triglycerides §   Broken down into indiv. amino acids •   Amino acids exit the basilar layer of the cell through facilitated diffusion through protein channels •   Transported through the hepatic portal vein States of Proteins in Different Parts of Digestive System Stomach: Proteins à Large polypeptides •   Broken down by pepsin Small intestine: Large polypeptides à Small polypeptides à Amino Acids •   Broken down by pancreatic enzymes and then brush border enzymes Absorbing Lipids •   Absorbed via simple diffusion through the phospholipid bilayer of absorptive cells •   Lipid digestion products: o   Monoglycerides o   Short chained fatty acids §   Have an easy time passing through high water environments o   Long chained fatty acids §   Have a hard time passing through high water environments •   Bile salts contain micelles o   These carry the fatty acids to the apical layer of epithelial cells o   Phospholipids, monosachharides and fatty acids diffuse across the membrane freely o   However, these micelles go back into the time to continue carrying fatty acids •   After the monoglycerides are broken down, they recombine to form triglycerides o   The triglyceride combines with phosphate to form a chylomicron and leaves the cell via exocytosis o   Due to their size, they enter lacteals and travel through the bloodstream to get to their destination of the subclavian vein •   The chylomicrons are later removed from the bloodstream, and broken down by lipase in the liver and fat tissue Absorbing Electrolytes Samantha Bubb ANATOMY AND PHYSIOLOGY 2 FAU SPRING 2016 •   Secreted into the lumen to be reabsorbed •   Small intestine: o   Absorbs net amounts of: Na+, Cl- and K+ o   Secretes net amounts of: Bicarbonate Absorbing Vitamins and Minerals •   Water soluble vitamins like B and C are absorbed through diffusion or passive/active transport •   Calcium absorption occurs through active transport and passive cellular transport Absorbing Water •   Most is reabsorbed, and done through osmosis •   Absorption is dependent on transport of nutrients to provide concentration gradients that pull the water from the lumen into cells, ISF and blood Cholera: Bacterial disease that causes watery diarrhea and vomiting •   Derived from Vibrio cholerae •   Increases secretion of Cl- into the small intestine o   Increases the tonicity of the lumen when compared to enteric tissue •   Pulls water from intestinal walls into the lumen, causing watery diarrhea •   Can cause fatal dehydration Oral Rehydration Solution: Drinks that create osmotic gradients, taking advantage of the sodium/glucose and sodium/amino acid symporters •   Electrolyte, glucose and amino acid transport is maximized •   This creates a hypertonic environment, increasing the osmotic gradient between the intestinal cells and lumen o   This means more water is absorbed increasing the rate of rehydration


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