A&P 2: Digestive

Intestinal Phase

"Stomach Emptying" Has both an excitatory & inhibitory component As partially digested food fills the duodenum of the SI, receptors in duodenum cause: an increase intestinal activity a reflexive decrease in gastric secretory activity (enterogastric reflex) Hormonal influences 2 hormones released by the SI in response to the presence of food in the duodenum Tells the stomach to stop 2 and 3 go bk and for about 4 hours till food is all gone

Cephalic Phase

"Stomach getting ready" Occurs before food even enters stomach Sight, smell, thought, taste of food activates neural centres (cerebral cortex) Parasympathetics are stimulated Salivary glands are stimulated Gastric glands to secrete gastric juice Prepares the stomach for food that is about to be eaten Increase secretion and motility of contractions

Gastric Phase

"Stomach working" Stretch receptors and chemoreceptors provide information Main stimuli are: distension, peptides, and low acidity Causes secretion of gastrin into bloodstream Gastrin: increases stomach glandular secretion increases stomach churning pyloric sphincter relaxation Stimulate stomach to start working, because of the enzyme** (goes into bloodstream) gastrin (= get it out of here), Change in ph or food enters Make less acidic\ Food stretches stomach walls Send nerve impulse to sub mucosal plexus (part of the cns) Output to the effectors Contractions Respond and mix up Removed Start again Increase secretion, muscle contraction and opens pyloric sphincter and put in some chyme (then Intestinal Phase)

Describe the mechanism of deglutition (swallowing)

1. The Buccal Phase • Is this stage voluntary or involuntary? Voluntary • Occurs in the mouth • Bolus is pushed from the oral cavity to the oropharynx (by the tongue) 2. Pharyngoesophageal Phase • Is this stage voluntary or involuntary? Involuntary • There is a swallowing center located in the brain • All other routes are blocked off: o tongue blocks off mouth o soft palate & uvula move up & block off nasopharynx o Epiglottis seals off larynx • upper esophageal sphincter relaxes and bolus moves into the esophagus • bolus passes through by rhythmic waves of muscle contraction called peristalsis

Describe the gross anatomy of the large intestine

5 feet long by 2½ inches in diameter Ascending & descending colon are retroperitoneal 4 principle regions Cecum Colon (ascending, descending, transverse) Rectum last 8 inches of GI tract anterior to the sacrum & coccyx Anal Canal last 1 inch of GI tract Left colic flecture = splenic flecture

• Esophagus (upper and lower esophageal sphincters

A collapsible muscular tube 25 to 30 cm long Skeletal muscle in upper one-third, mixture in middle one-third, and only smooth muscle in the bottom one-third Connects pharynx to the stomach (passes through esophageal hiatus in diaphragm Lower esophageal sphincter (LES) food pauses at this point because of this constriction Prevents stomach contents from regurgitating into the esophagus and eroding the mucosal lining Heartburn—burning sensation produced by acid reflux into the esophagus Nonkeratinized stratified squamous epithelium Tennis ball through pantyhose, if it were to allowed to reguragate up it would errode

Explain the term retroperitoneal

Behind/outside the parietal peritoneum. cavity. Ascending & descending colon are retroperitoneal.

Explain the general functions of the digestive system.

Break food down into chyme for the body's use, to secrete and absorb nutrients and bodily fluids into the gastrointestinal tract or the blood, and to store and eliminate waste.

Describe the 3 phases of digestion (cephalic, gastric, intestinal)

Cephalic phase Stimulates gastric secretion and motility (get stomach ready) Gastric phase Neural and hormonal mechanisms (food goes in and hormones get ready, particular gastrin, contract and eject chyme) Intestinal phase Neural and hormonal mechanisms (CCK)

Understand the effects of aging on the digestive system

Decreased secretory mechanisms and motility Loss of strength and tone of digestive muscular tissue Changes in neurosecretory feedback Diminished response to pain and internal sensations (can cause ulcerations and herniations) Smooth muscle decreases and so does smooth muscle, not as strong contractions to move something

•Enzymes

Enzymes begin the chemical breakdown of starches

•Mastication

First step in mechanical digestion, AKA chewing Breaks food into smaller pieces to be swallowed and exposes more surface to the action of digestive enzymes Food stimulates oral receptors that trigger an involuntary chewing reflex Work of many muscles Tongue Temporalis Masseter Buccinator others

Describe the anatomy and digestive secretions of the gall bladder and the bile duct system

Gall bladder Location: • on the inferior, ventral surface of the liver Structure: • thin walled, green, muscular sac • 4 cm long • the hepatic duct from the liver joins with the cystic duct from the gall bladder to form the common bile duct that enters into the duodenum of the small intestine Function: • to concentrate bile (reabsorbs the water) • Stores bile Bile: • yellow-green alkaline solution • contains bile salts, pigments, cholesterol, fats, phospholipids & electrolytes • Emulsify fats • conserved by recycling mechanism Regulation of bile secretion & ejection: • produced continually by liver backs up cystic duct and stored in gallbladder • released into when gallbladder contracts • contraction of gall bladder stimulated by small intestine intestinal hormone called cholecystokinin (CCK) • CCK release is stimulated by the presence of acidic and fatty acid in the duodenum • CCK: a) stimulates contraction of gallbladder b) stimulates release of pancreatic juice c) relaxes the hepatopancreatic sphincter so these secretions can enter the duodenum - Explain bilirubin metabolism: Worn out RBC are broken down and the iron, globin, and bilirubin are released. The iron and globin are recycled and the bilirubin is used to make bile. Once in the intestine the bilirubin is eventually broken down by bacteria. The bile salts are reabsorbed. One of the breakdown products is what gives feces its brown colour.

•Churning

Haustral churning Distension reaches a certain point and the walls of the haustra contract to squeeze contents onward Occurs every 30 min or so

Describe the types of contractions that occur in the colon

Haustral churning Distension reaches a certain point and the walls of the haustra contract to squeeze contents onward Occurs every 30 min or so slow, soak up more water as it moves through Peristalsis Propulsive contractions Mass peristalsis A strong peristaltic wave that begins in the transverse colon and quickly drives the contents of the colon into the rectum Occurs 1-3 times per day Technically you're supposed to go after every time you eat

Discuss the steps in processing food: Ingestion, Digestion, Absorption, Elimination

Ingestion: taking food into the mouth Absorption: passage of digestive products from GI tract into blood and lymph Elimination: getting rid of waste

Briefly explain the control of salivary secretion

Intrinsic Salivary Gland Small glands spread out in oral cavity Continually secrete saliva to keep mouth moist Extrinsic Salivary Glands Secrete saliva when you eat 3 pairs: Parotid Submandibular Sublingual

Describe the anatomy and digestive secretions of the liver, gall bladder, bile duct system and the pancreas

Liver Location: • occupies most of the upper right quadrant • under the diaphragm • covered almost entirely by the rib cage (protection) Structure: • largest gland in the body • roughly 3 lbs in the adult • reddish-brown (healthy) • 4 lobes Digestive role: - produces bile for export by the gallbladder - The principle pigment in bile is: bilirubin - Define emulsification: Break down of fat globules in the duodenum into tiny drops so that it can be digested, by the bile salts. More surface area = easier to digest • Activates vitamin D (the skin can also do this with 1 hr of sunlight a week) • Detoxifies the blood by removing or altering drugs & hormones • Stores iron, copper and the fat soluble vitamins-----A, B12, D, E, K • Metabolizes carbohydrates, fats and protein • Excretion of bilirubin • Synthesizes of bile salts help digestion by emulsification • Phagocytizes worn out blood cells & bacteria

Differentiate between mechanical and chemical digestion.

Mechanical digestion Chewing mixes food with saliva and forms a bolus which can be easily swallowed Chemical digestion Salivary amylase converts polysaccharides to disaccharides

Identify the location and function of the mesentery, greater omentum

Mesentary (small intestine and duodenum) • a double layer of visceral peritoneum (folds back on itself) • attaches the jejunum & ileum to the posterior abdominal wall (2nd and 3rd parts of sm. Intestine) • provides routes for the blood vessels, lymph vessels, and nerves to reach these organs Greater Omentum • connecting the stomach to the transverse colon • drapes like an apron over the small intestine • contains adipose (fat deposits) and lymph nodes

Describe the digestion that occurs on the brush border of the intestine

Microvilli Cell surface feature known as brush border Where the main action of digestion occurs Enzymes are produced here Brush border enzymes, found on the surfaces of the microvilli of absorptive cells, break down food products Enzymes are not secreted into the lumen Chyme must come in contact with the microvili

What is the significance of the intestinal bacteria

More bacteria cells in your body than your own cells, it's okay because we have a mucus membrane that they can't/don't cross. We are symbiotic with them, give to each other. Only problems when the bacteria crosses Bacteria ferment (in colon) Undigested carbohydrates into carbon dioxide and methane gas Undigested proteins into simpler substances (odour) Turn bilirubin into simpler substance (colour)

Describe and locate the digestive system.

Most nutrients we eat cannot be used in existing form Must be broken down into smaller components before the body can make use of them Essentially a disassembly line Ie. Polysacchrides into monosaccharides Proteins into amino acids Digestive system: the organ system that processes food, extracts nutrients from it, and eliminates the residue Most nutrients we take in is the larger form and we have to break it down Waste can have toxins Longer feces sit inside colon is bad, can cause cancer

Describe and locate the components of the digestive system and the accessory organs.

ORGANS ACCESSORY Mouth Liver Pharynx Gallbladder Esophagus Pancreas Stomach Salivary Glands Small intestine Tongue and Teeth Large intestine (in backwards order^)

Describe the anatomy and digestive secretions of the pancreas

Pancreas - located deep to the curvature of the stomach - 4 parts: head, neck, body and tail - What is the composition of pancreatic juice? Explain the role of each. Water and electrolytes (salts): dilute chyme making it less acidic Sodium bicarbonate: neutralize chyme Enzymes: - Why are the pancreatic enzymes released in an inactive form? They are released actively it would digest the pancreas itself Regulation of Secretion of Pancreatic Juice - Regulated by local hormones & the nervous system - When chyme enters the small intestine, it stimulates the endocrine glands of the duodenum to release 2 hormones. - Describe the effect these 2 hormones have on the pancreas: Cholecystokinin (CCK) Stimulate the secretion of pancreatic juice Ejects bile from the gallbladder Secretin Released due to HCL in intestine which causes the release of bicarbonate in the pancreas

•Peristalsis

Peristalsis Propulsive contractions Mass peristalsis A strong peristaltic wave that begins in the transverse colon and quickly drives the contents of the colon into the rectum Occurs 1-3 times per day (technically you're supposed to get this after everytime you eat)

Describe the location and structure of the peritoneum, distinguish between visceral and parietal components.

Peritoneum • Largest serous membrane of the body • Lines a body cavity and does not open to exterior • 2 types: i) Visceral peritoneum • Covers the surface of most digestive organs ii) Parietal peritoneum • lines the wall of the entire abdominal cavity • What is the function of the peritoneum? The folds that make up the peritoneum bind the organs to one another and the abdominal cavity. Contains blood vessels, lymphatic vessels and the nerves that supply the abdominal organs

Explain the process of defecation

Rectum is usually empty, mass peristalisis pushes feces into rectum distending wall Usually occurs after a meal--- gastroileal (gastrocolic)reflex Stretch receptors send sensory nerve impulses to the sacral spinal cord Motor impulses travel back to the descending colon, sigmoid colon, rectum, and anus Longitudinal rectal muscles contract and the internal anal sphincter opens If the external anal sphincter is voluntarily relaxes, defecation occurs and the feces are expelled

Describe the function and components of saliva

Saliva Moisten mouth Begin starch and fat digestion Cleanse teeth Inhibit bacterial growth Dissolve molecules so they can stimulate the taste buds Moisten food and bind it together into bolus to aid in swallowing Bolus—a soft, slippery easily swallowed mass formed as a result of saliva binding food particles (what you swallow) 4 functions of saliva a) Enzymes begin the chemical breakdown of starches b) Cleanse mouth and teeth done by lysozymes c) Breakdown of food chemicals done by water for taste d) Lubricate done mucous • Saliva contains enzymes that begin to digest starch

Describe the types of movements that occur in the small intestine

Segmentation: Localized contraction that mix the chyme with the digestive juices and bring the food particle sin contact with mucosa for absorption. (mixing up and stirring together) Peristalsis: Muscular contractions that occur at the wall of the small intestine and move food along that tract (not always happening, not ongoing)

Describe the anatomy of the small intestine identifying the 3 structures that increase the absorptive area of this organ

Small Intestine - Site of the majority of digestion - Identify the 3 regions of the small intestine from proximal to distal a) Dudoenum b) Jejunum c) ileum - It starts after the pyloric sphincter and continues to the ileocecal (valve) where the large intestine starts - The small intestine functions to: a) receive chyme from the stomach b) receive secretions from the gallbladder and pancreas c) Chemical (enzymes) and mechanical (muscle contractions) breakdown - Differentiate between the 2 types of motility seen in the small intestine Segmentation: Localized contraction that mix the chyme with the digestive juices and bring the food particle sin contact with mucosa for absorption. (mixing up and stirring together) Peristalsis: Muscular contractions that occur at the wall of the small intestine and move food along that tract (not always happening, not ongoing) - Chyme is acidic and needs to be neutralized in the duodenum. Explain how the chyme is neutralized. Secretion of alkaline bile from the gall bladder and bicarbonate from the pancreatic juice neutralize the Ph OF THE CHYME. Chyme is also hyertonic and would result in osmotic water loss into the small intestine, dehydration. Bicarbonate secretion, secretion into small intestine, neutralizes chyme - Explain 2 reasons why this is important: a) Will eat away at small intestine and all the way down, cause ulcers b) If it's too acidic it will kill all the (good) enzymes, optimal environment for enzymes to digest food particles - Describe how the anatomical structure of the small intestine is designed for maximal absorption: a) circular folds (of mucosa and submucosa) Increase surface area causing the chyme to spiral, mixing together. b) villi Increase surface area and a velvety appearance. Hair like projection on folds. It has a rich blood supply with a modified lymphatic capillary called a lacteal is designed to absorb fats. c) microvilli (membrane of each villi) Increase surface area allows for larger amounts of digested nutrients. Sometimes called a brush border because it appears fuzzy.

Describe the chemical digestion proteins, lipids and carbohydrates.

The chyme entering the small intestine contains partially digested carbohydrates, fats, protein, and nucleaic acids The remainder of chemical breakdown in the SI is a result of the pancreatic juice, bile and intestinal juice Chemical Digestion in the Colon Once this final breakdown occurs the products are ready for absorption The last stages of digestion occur through bacterial action Bacteria ferment Undigested carbohydrates into carbon dioxide and methane gas Undigested proteins in to simpler substances (odour) Turn bilirubin into simpler substance (colour) Some vitamins (vitamin K and some B)are synthesized by bacterial action

• Mouth (teeth, tongue, palate, salivary glands)

The mouth is formed by the cheeks, hard and soft palates, and tongue Functions: ingestion, digestion, swallowing, speech & respiration Is lined by stratified squamous epithelium (Squamous, flat Stratified, stacks of them which makes them good for protection) Tongue The tongue, together with associated muscle, forms the floor of the oral cavity Composed of skeletal muscle covered with mucous membrane Participates in chewing, swallowing, and speech The upper and lateral surfaces of the tongue are covered with papillae some of which contain taste buds Salivary Glands Exocrine glands that empty their contents into ducts Deliver saliva into the oral cavity 2 types: Intrinsic Salivary Gland Small glands spread out in oral cavity Continually secrete saliva to keep mouth moist Extrinsic Salivary Glands Secrete saliva when you eat 3 pairs: Parotid Submandibular Sublingual Palate Separates the oral cavity from the nasal cavity Makes it possible to breathe while chewing food Hard (bony) palate—anterior 2/3 Soft palate—posterior 1/3 Composed of skeletal muscle and glandular tissue (No bone) Uvula conical medial projection visible at the rear of the mouth Helps retain food in the mouth until one is ready to swallow Palatine tonsils found on the lateral muscular walls. If the Uvula is drifted to one side can indicate a problem with one of the cranial nerves

• Pharynx (tonsils, 3 regions of the pharynx)

The pharynx is a muscular funnel that extends from the internal nares to the esophagus posteriorly and the larynx anteriorly Digestive and respiratory tract intersect 3 parts: nasopharynx (does not have a digestive role) oropharynx Laryngopharynx (decide go to esophagus or trachea?) Skeletal muscle lined by mucous membrane

Explain how the stomach is designed to prevent autodigestion.

The presence of a protective layer of the mucos. Pepsin is release in its inactive form (pepsinogen)

• Stomach (4 main regions, gastric glands/secretions)

The stomach is a J-shaped enlargement of the GI tract inferior to the diaphragm in the upper left quadrant Both chemical and mechanical digestion Divided into four main regions Cardia Lower espohageal sphincter opens to allow the bolus to enter the stomach Fundus Body Pylorus Pyloric (gastroduodenal) sphincter—regulates the passage of chyme into the duodenum (can't eject all at once or it would burn a hole in the duodenum). Gastric glands are to secrete gastric juice, 2-3 L of is produced daily by the gastric glands

Explain the terms visceral and parietal.

Visceral: Directly on the organ and Parietal: "Parent" layer, the protective outer covering

Identify the end products of digestion and their sites of absorption.

fats digested to fatty acids/glycerol carbohydrates digested to monosaccharides (starches and disaccharides) proteins digested to amino acids other end products vitamins, minerals, water. The end product of protein digestion are amino acids unlike that of carbohydrate which maybe glucose, galactose or fructose. The end product of fat digestion are triglycerides, free fatty acids and glycerol. The end products of protein digestion are very different from those of carbohydrates

Describe the generic structure of the walls of the digestive organs.

i) Visceral peritoneum • Covers the surface of most digestive organs ii) Parietal peritoneum • lines the wall of the entire abdominal cavity • What is the function of the peritoneum? The folds that make up the peritoneum bind the organs to one another and the abdominal cavity. Contains blood vessels, lymphatic vessels and the nerves that supply the abdominal organs b) Peritoneal cavity • a potential space located between the visceral & parietal membranes • contains serous fluid to prevent friction between moving organs in the abdominal cavity • Not all organs are found within this cavity. Some of the organs are located behind the parietal peritoneum. • These organs are referred to as: Retroperitoneal

Explain the role of the hormones CCK, secretin, and gastrin in digestion

• CCK release is stimulated by the presence of acidic and fatty acid in the duodenum. Stimulate the secretion of pancreatic juice and Ejects bile from the gallbladder a) stimulates contraction of gallbladder b) stimulates release of pancreatic juice c) relaxes the hepatopancreatic sphincter so these secretions can enter the duodenum Secretin Released due to HCL in intestine which causes the release of bicarbonate in the pancreas Gastrin: Promotes stomach emptying

Locate the peritoneal cavity and identify its contents.

• a potential space located between the visceral & parietal membranes • contains serous fluid to prevent friction between moving organs in the abdominal cavity • Not all organs are found within this cavity. Some of the organs are located behind the parietal peritoneum. • These organs are referred to as: Retroperitoneal • Identify some of these organs: Kidneys Ascending and descending colons of the large intestine Duodenum of the small intestine Pancreas Ureters