Digestive System Anatomy and Physiology II Fall 2024 PDF

Anatomy and Physiology II IPAP 501 Dr. Teresa Walters, PA-C 1 DIGESTIVE SYSTEM 2 Nutrition and Metabolism  Nutrition  Slight differences in individual genetic codes and individual lifestyles and environmen...

Anatomy and Physiology II IPAP 501 Dr. Teresa Walters, PA-C 1 DIGESTIVE SYSTEM 2 Nutrition and Metabolism  Nutrition  Slight differences in individual genetic codes and individual lifestyles and environments affect how nutrition is perceived  Lends to multiple types of diets  Mediterranean diet  DASH diet (dietary approaches to stop hypertension)  Vegetarian/Vegan  Ketogenic  Southbeach Diet  Raw Food  Paleo  Gluten free  So…many….more….  The Drinking Man’s Diet  The Cigarette Diet  The WWII Ration Diet Micronutrients & Macronutrients  Types of Nutrients  Micronutrients are readily absorbed in their original form  Macronutrients need to be small enough to be absorbed  Carbohydrates need to be  Monosaccharides such as  Glucose  Fructose  Galactose  Proteins need to be  Amino acids or small chains of amino acids (di/tripeptides)  Lipids need to be  Fatty acids (FAs) and monoglycerols (MGs)  Nutrition Overview Micronutrients Macronutrients  Vitamins  Carbohydrates (per gram)  Provides 4 calories of energy  Minerals  Proteins (per gram)  Provides 4 calories of energy  Lipids (per gram)  Provides 9 calories of energy ** Needed in much smaller ** These are the source for quantities in the body energy in the body **Do not provide calories of **We require these in much energy larger quantities than micronutrients  Macronutrient CARBOHYDRATES  Carbohydrates  Major source of water-soluble biologic energy used by organisms  Brain requires glucose as its chief energy source  All other cells can use alternative forms  Can be used by every cell in the body, but not a requirement  Other cells can use energy from the breakdown of proteins and fats  Comes in multiple forms  Monosaccharides (absorbable form)  Disaccharides  Polysaccharides  Digestion requires enzymes called amylases  Carbohydrates  Absorbable forms  Glucose - fruits  Fructose - fruits  Galactose - dairy (mostly)  Carbohydrates that require digestion (breaking down)  Disaccharides  Sucrose, lactose, maltose  Polysaccharides  Starches, glycogen  Cellulose (fiber) – cannot be broken down or absorbed  Fruit skins, whole-grain rice (the husk is the fiber), legumes (the shell is the fiber), corn (skin on kernel is the fiber) Macronutrient PROTEINS  Proteins  Required for growth in general  Whether at the micro (cellular) level, or macro (tissue) level  Required to maintain a proper nitrogen balance in the body  Required for repair and maintenance of tissues  Considered to be the “building blocks” of all cells  Water-soluble like carbohydrates  Involved in the synthesis of certain neurotransmitters and hormones  Serotonin, epinephrine, melatonin, histamine, etc…  Protein Digestion  Basic structure of proteins are amino acids  Absorption of proteins requires them to be broken down into any of the following:  Amino acid (single)  Dipeptide (two amino acids linked together)  Tripeptide (three amino acids linked together)  Anything larger than 3 amino acids together is too large for absorption therefore requiring something to break it down smaller  Broken down by proteases (pepsin, trypsin etc)  Amino Acids (Proteins)  There are 20 amino acids  9 are essential  These have to be consumed as they cannot be made in the body  Complete proteins are those that contain all 9 essential amino acids  Includes animal meat, milk, eggs, quinoa, soy, hemp seed, etc  7 are conditionally essential  Only required in times of illness or increased stress on the body  4 are non-essential Macronutrient LIPIDS  Lipids  Consists of triglycerides, phospholipids and glycolipids  Triglycerides (triacylglycerides; TAGs) are most common form of lipid found in the diet and in the body  Consists of one glycerol subunit that is attached to three fatty acids  A high-energy nutrient synthesized and stored in adipocytes (adipose cells) as well as hepatocytes (liver cells)  Can be used by most cells in the body to power metabolism  Not efficient in neural cells for sole source of energy (only glucose)  Triglycerides are required for absorption of fat-soluble vitamins including  A, D, E, K  Triglycerides provides constituent molecules for cellular membranes  Lipid Digestion  In order to be absorbed at the cellular level, triglycerides have to be hydrolyzed (broken down) into smaller components  Fatty acids (FAs)  Monoglycerides/monoglycerols (MGs)  They are hydrolyzed by certain lipase enzymes  Emulsification & Absorption  Most lipids are too large to be absorbed  Lipids encounter lingual and gastric lipases in stomach which starts the emulsification process (10-30%)  These work best at acidic pH below 6.9  Once in the small intestine, bile is encountered, emulsification continues, pulls lipid globules further apart into droplets (70-90%)  This works best in alkaline pH 7.2-8.0  Pancreatic lipase then has more surface area to help with continued digestion  Lipases break droplets down into monoglycerol + 3 fatty acids  Emulsification & Absorption  Micelles  Monoglycerols and fatty acids then mix with bile which forms a lipid-transport vessel  Micelles dump their contents into enterocytes  Once the fatty acids and monoglycerols enter the cell  Fatty acids and monoglycerols are packaged together again as triacylglycerols (TAGs)  TAGs are then packaged with cholesterol and other lipoproteins  This package is now known as a chylomicron  Size of chylomicrons are so large it cannot cross capillary membrane  Is instead dumped into a lacteal (lymphatic duct) which then converges with thoracic duct (at subclavian vein)  Lipid Transport  Lipids are transported as multiple things  Chylomicrons (a lipoprotein)  During absorptive state blood may contain so many chylomicrons that it can appear turbid, or yellowish (usually for 20-30 minutes after lipid-rich meal)  In post-absorptive state (usually ~4 hours after meal) few chylomicrons exist in blood  Contents have moved mostly into adipose tissue  Other lipoproteins (most active in post-absorptive state)  Produced mostly in the liver from lipids and proteins  Very low-density lipoproteins  Low-density lipoproteins  High-density lipoproteins  Lipoproteins  Chylomicrons  Delivers mostly triglycerides to cells throughout the body  Synthesized in enterocytes (intestinal cells) from fat and cholesterol absorbed in the small intestine  Because of large size, have to enter lacteals (lymphatic capillaries) which carries them to thoracic duct to be dumped into blood  Very triglyceride-rich  Very large particle  Very low-density lipoproteins (VLDL’s)  Delivers mostly triglycerides to cells throughout the body  Synthesized in the liver from excess fats and cholesterol that have made it there from portal circulation  Very triglyceride rich  Large particle, smaller than chylomicron  Lipoproteins  Low-density lipoproteins (LDL’s)  Delivers cholesterol to cells throughout the body  As VLDL’s are stripped of their triglycerides, the “leftovers” get remodeled in the liver to form LDL’s  Smaller particles than VLDL’s  High-density lipoproteins (HDL’s)  Reverse cholesterol transport for excess cholesterol  Returns excess cholesterol to the liver for recycling or to tissues that synthesize steroid hormones  Adrenals, ovaries, testes  Are synthesized in both the liver and the small intestines  Lipoproteins Largest - - - - - - - - - - - - - - - - - - - - - - - - - Smallest Low protein - - - - - - - - - - - - - - - - - - - - - High protein The Digestive System  General Information  Helps to maintain homeostasis by breaking down food  This puts food (energy) into forms that the body can use  Also absorbs water, vitamins, minerals  Eliminates wastes from the body  Food is our only source of chemical energy  Most food particles are too large to be used by cells in their original form  Digestion  Food must be broken down into molecules small enough to enter cells  General Information  Digestive system  Consists of all of the organs involved in the breakdown of food  This system is a tubular system  Extends from the mouth to the anus  Forms extensive surface area in contact with the external environment  Closely associated with cardiovascular system because of the blood vessels involved in the digestive process  Gastroenterology (stomach-intestines-study of)  Proctology (rectum-study of) Overview of Digestive System Abdominal Organ Placement Gastrointestinal tract (GI tract)  Also known as the alimentary (nourishment) canal  Continuous tube extending from mouth to anus  Travels through thoracic cavity, through abdominopelvic cavity  Consists of  Mouth, most of pharynx, esophagus, stomach, small intestine, large intestine (and anus)  Approximately 16-23 feet long in living human  In a state of tonus (sustained contraction)  Approximately 23-29 feet long in cadaver  Variation is due to loss of muscular tone after death  Digestive System  Accessory digestive anatomy  Teeth  Aid in physical breakdown of food  Tongue  Aids in chewing and swallowing food  Salivary glands, liver, gallbladder, pancreas  Never come in contact with food but produce and store secretions that flow into the GI tract through ducts  These secretions aid in chemical breakdown of food Abdominal Accessory Organs 1. Liver 2. Gallbladder 3. Spleen 4. Pancreas 5. Aorta bifurcation to common iliac arteries 6. Superior mesenteric vein  Digestive System  Six Basic Processes 1. Ingestion- taking in foods and liquids into the mouth 2. Secretion- everyday, cells within the GI tract and accessory organs secrete ~7L of water, acid, buffers, enzymes into lumen of tract 3. Mixing and propulsion- alternating contraction/relaxation of smooth muscle in walls of tract mix food and secretions and propel towards anus  Motility- mix and movement of material along tract  Digestive System  Six Basic Processes (continued) 4. Digestion- mechanical and chemical process to breakdown food into small molecules  Mechanical digestion- teeth cut and grind food before swallowed, smooth muscles of stomach and small intestine churn food- this helps to mix with enzymes to dissolve food  Chemical digestion- large carbohydrate, lipid, protein, molecules are split into smaller molecules by hydrolysis- enzymes produced by salivary glands, tongue, stomach, pancreas, small intestine catalyze these catabolic reactions  A few substances can be absorbed without chemical digestion, these include vitamins, ions, essential fatty acids and water  Digestive System  Six Basic Processes (continued) 5. Absorption- entrance of ingested and secreted fluids, ions, and products of digestion into the epithelial cells lining the GI tract  Absorbed substances pass into blood or lymph and circulate to various locations in the body 6. Defecation- wastes, indigestible substances, bacteria, cells sloughed from lining of tract, digested materials not absorbed leave the body through the anus  Eliminated material is called feces or stool  Also….ass kabobs, butt clusters, doodie, jobby, keester cakes, rectum warriors, toilet twinkies…. Layers of GI Tract Digestive System  Layers of GI Tract  Wall of GI tract from lower esophagus to anal canal has same basic four-layered arrangement of tissue  From outer layer to inner-most layer (contact with tract contents) 1. Serosa or adventitia (depends on the location) 2. Muscularis 3. Submucosa 4. Mucosa  Layers of GI Tract  Serosa  Found on almost all parts of the GI tract (see adventitia)  Serous membrane composed of areolar connective tissue and simple squamous epithelium (mesothelium)  Also called the visceral peritoneum  Forms from a portion of the visceral peritoneum  Adventitia  Single layer of connective tissue for  Esophagus  Proximal duodenum  Head/body of pancreas (tail is intraperitoneal)  Ascending colon and descending colon  Layers of GI Tract  Muscularis  Skeletal muscle- voluntary  Mouth, pharynx, superior aspect of esophagus  Also present in external anal sphincter, permits voluntary control of defecation  Smooth muscle- involuntary  Found in the rest of the tract  Involuntary contractions help break down food, mix it with secretions, and propel it forward  Inner sheet of circular fibers, outer sheet of longitudinal fibers  Contains myenteric plexus (plexus of Auerbach)-  Network of enteric neurons between the circular and longitudinal muscle layers  Layers of GI Tract  Submucosa  Consists of areolar connective tissue that binds the mucosa to muscularis  Contains many blood and lymph vessels that receive absorbed food molecules  Contains submucosal plexus (plexus of Meissner)  Found between the submucosal layer and the muscularis mucosae of the mucosal layer  Layers of GI Tract  Mucosa- inner lining of GI tract  Composed of three layers 3. Muscularis mucosae (outer-most layer of mucosa)  Thin layer of smooth muscle fibers  This layer is what causes the mucous membrane of the small intestine and stomach to have the folded appearance  These folds increase surface area for digestion and absorption  Movement of this layer ensures all absorptive cells are fully exposed to contents of GI tract  Layers of GI Tract  Mucosa- inner lining of GI tract  Composed of three layers 2.Lamina propria (Middle layer of mucosa)  Areolar connective tissue containing many blood and lymphatic vessels which allow nutrients to reach other tissues of the body  Supports the epithelium and binds to the muscularis mucosae  Contains majority of mucosa-associated lymphatic tissue (MALT)  This lymphatic nodular tissue contains immune cells that protect against disease  MALT tissue present along GI tract especially tonsils, small intestine, appendix, and large intestine  Layers of GI Tract  Mucosa- inner lining of GI tract  Composed of three layers 1. Epithelium- every 5-7 days these cells are replaced by new cells, old slough off and are excreted a. Non-keratinized stratified squamous found in mouth, pharynx, esophagus and anal canal  Protective function b. Simple columnar found in stomach and intestines  Secretion and absorption function  Tight junctions between cells here prevent leakage c. Exocrine cells- secrete mucous/fluid/enzymes into lumen d. Enteroendocrine cells- secrete hormones into bloodstream  Development of Gastrointestinal Tract  Embryonic Development of “Gut”  Begins to differentiate as early as week 3 into  Foregut  Midgut  Hindgut  Embryonic Development of “Gut”  Digestive system arises from three regions  Foregut  Salivary glands, esophagus, stomach, liver, gall bladder, pancreas, proximal duodenum  Midgut  Middle and distal duodenum, jejunum, ileum, cecum, appendix, ascending colon, proximal 2/3 of transverse colon  Hindgut  Distal 1/3 of transverse colon, descending colon, sigmoid colon, rectum, proximal anal canal  Embryonic Development of “Gut”  Viscera-Somatic Convergence  Abdominal organs lack dedicated SENSORY pathways, pain is often “referred” to skin or muscle  Foregut pain referred to epigastrium via greater splanchnic nerves (T5-T9)  Midgut pain referred to peri-umbilical region via lesser splanchnic nerves (T10-T11)  Hindgut pain referred to suprapubic region via the least splanchnic nerve (T12) Neural Innervation of the GI Tract Regulated by intrinsic nerves (enteric nervous system; ENS) and extrinsic nerves (autonomic nervous system; ANS)  Enteric Nervous System  Considered to be the “brain” of the gut  Consists of ~100,000,000 neurons that extend from the esophagus to the anus  Arranged in two plexuses  Myenteric (or Auerbach) plexus located between longitudinal and circular smooth muscle layers of the muscularis  Submucosal plexus (plexus of Meissner) between the submucosal layer and the muscularis mucosae of the mucosal layer  Both plexuses consist of neurons, interneurons, and sensory neurons  Enteric Nervous System  Myenteric (Auerbach) plexus- supply motor impulses to longitudinal and circular smooth muscle layers of muscularis  This leads to this plexus controlling the majority of GI tract motility  Particularly the frequency and strength of contraction of muscularis  Submucosal (Meissner) plexus- motor neurons supply the secretory cells of the mucosal epithelium  This leads to this plexus controlling secretions of the organs of the GI tract  Enteric Nervous System  Interneurons- connect the myenteric and submucosal plexuses  Sensory neurons- supply the mucosal epithelium  Some function as chemoreceptors  Activated by certain chemicals in food located in the lumen of GI organs  Others function as baroreceptors (stretch receptors)  Activated when food stretches distends the wall of a GI organ  Autonomic Nervous System  Helps to regulate the enteric nervous system (ENS)  Vagus (X) nerves supply parasympathetic fibers to most parts of GI tract  These parasympathetic nerves form neural connections with the enteric nervous system  Stimulation of the parasympathetic nerves that innervate the GI tract  Causes an increase in GI secretion and motility by increasing activity of the ENS  Autonomic Nervous System  Sympathetic nerves that supply GI tract arise from thoracic and upper lumbar regions of spinal cord  These nerves also form connections with the ENS  Stimulation of the sympathetic nerves connected to the GI tract  Cause a decrease in GI secretion and motility by inhibiting the ENS neurons  Emotions such as fear (fight or flight), anger, anxiety may slow digestion because they stimulate the sympathetic nerves that supply the GI tract Peritoneum Digestive System  Peritoneum  The largest serous membrane in the body  Consists of a layer of simple squamous epithelium (mesothelium) with underlying layer of areolar connective tissue  Peritoneum is divided into  Parietal peritoneum- lines the wall of the abdominopelvic cavity  Visceral peritoneum- covers some of the organs in the cavity and is also considered their serosa  Peritoneal Cavity-  space between the two layers that contains lubricating serous fluid (small amount)  Peritoneum  Retroperitoneal  Space that is behind the peritoneum  Organs in this space are anteriorly covered by the peritoneum  Kidneys  Ascending colon (large intestine)  Descending colon (large intestine)  Proximal duodenum (small intestine)  Pancreas (Head and body; tail is intraperitoneal)  Peritoneum  Contains large folds that weave between the viscera  These bind organs together and then also to abdominal walls  Contain blood vessels, lymph vessels, and nerves that supply the abdominal organs  Five major folds  The greater omentum  Falciform ligament  Lesser omentum  Mesentery  Mesocolon  The Greater Omentum  Largest peritoneal fold  Drapes over transverse colon and small intestine  Attaches to portions of stomach and duodenum, extending downward, anterior to small intestines, folds and extends upwards to attach to transverse colon  Contains considerable amount of adipose tissue which can expand with weight gain  Characteristic “beer belly”  Many lymph nodes here contribute macrophages and antibody-producing cells that combat GI tract infections  Falciform Ligament  Peritoneal “fold” that attaches the liver to the ventral surface (anterior) of the abdominal wall  Free border of this ligament contains the ligamentum teres (aka round ligament; remnant of the umbilical vein)  Liver is the only digestive organ attached to anterior abdominal wall  The Lesser Omentum  Arises as anterior fold in the serosa of the stomach and duodenum connecting it to the liver  This is the pathway for blood vessels entering liver  Contains portal vein, common hepatic artery, common bile duct and some lymph nodes  Mesentery  Fan shaped fold  Binds jejunum and ileum of small intestine to posterior peritoneal wall  Also a large fold, adding to abdominal girth when weight is gained  Extends from posterior peritoneal wall (same place the mesocolon arises from), wraps around small intestine, returns to its origin  Between layers are blood and lymphatic vessels, as well as lymph nodes  Mesocolon  Two separate folds that bind portions of large intestine to posterior abdominal wall  First binds the transverse colon  Second binds the sigmoid colon  Carries blood and lymphatic vessels to intestines  Along with the mesentery, the mesocolon holds small intestines loosely in place  This allows slight movement as muscular contractions mix and move the contents of the GI tract Clinical Correlation- Ascites  Ascites  When excess fluid (as in disease) accumulates in this potential cavity (several liters) Most common cause is from liver failure  Clinical Correlation-Peritonitis  Acute inflammation of the peritoneum  Usually caused by contamination from infectious microbes  Often from accidental or surgical wounds  Can occur from perforation or rupture of abdominal organs/structures (appendix)  Can occur from rubbing together of inflamed peritoneal surfaces  Can occur in those undergoing peritoneal dialysis  Peritoneum is used to filter wastes/provide nutrients when kidney’s aren’t functioning properly Mouth  Mouth  Oral or buccal cavity  Formed by  Cheeks  Hard and soft palates  Tongue  Cheeks form lateral walls of oral cavity  Lips are fleshy folds surrounding opening of the mouth  Frenula – fold of tissue that restricts the movement to which it is attached  Labial frenula (mandibular, maxillary)  Lingual frenula  Maxillary frenulum Mandibular frenulum  Mouth  Oral vestibule- oral space completely bound by cheeks, lips, gums and buccal side of teeth  Oral cavity proper- space that extends from lingual side of teeth back to the fauces  Mouth  Palate-  Forms the roof of the mouth  A wall or septum that separates the oral cavity from nasal cavity  Allows us to chew and breath at the same time  Hard palate  Anterior portion of roof of mouth  Formed by palatine and maxillae bones  Covered by mucous membrane  Soft palate  Posterior portion of roof of mouth  Arch shaped muscular partition between oropharynx and nasopharynx line with mucous membrane  Mouth  Uvula  Hangs from free border of soft palate  Conical muscular process  During swallowing, soft palate and uvula are drawn superiorly  This closes off nasopharynx preventing food and saliva from entering the nasal cavity  At base of uvula, two muscular folds run down lateral sides of soft palate  Palatoglossal arch is anterior fold that extends to the side of the base of the tongue  Palatopharyngeal arch is posterior fold that extends to side of pharynx  Mouth  Tonsils- small masses of lymphatic tissue that produce antibodies to fight infection  Palatine tonsils- situated between the arches  Most commonly infected tonsils, often removed in childhood after multiple infections  Lingual tonsil- located at base of tongue (only one)  Pharyngeal tonsils- (also known as adenoids) located on superior portion of nasopharynx  Often removed with palatine tonsils in children as they can inflame and close off sinus drainage and cause difficulty breathing through the nose  Salivary Glands  Usually just enough saliva is secreted to keep mucous membranes of mouth and pharynx moist and to cleanse the mouth and teeth  When food is consumed, saliva production increases  This helps to lubricate, dissolve and chemically break down food  Mucous membrane of mouth and tongue contain many small salivary glands that open directly into oral cavity or indirectly via ducts  Salivary Glands  Salivary gland types  Minor glands in lips, cheeks, palate, and tongue  Labial  Buccal  Palatal  Lingual  Major glands- secrete most of the saliva  Parotids  Submandibular  Sublingual  Salivary Glands  Parotid Glands  Located inferior and anterior to the ears between skin and masseter muscle  Secrete saliva into oral cavity via the parotid duct (Stenson’s duct)  This pierces the buccinator muscle to open into oral vestibule opposite the second maxillary molar (upper)  Salivary Glands  Submandibular Glands  Found in the floor of the mouth, medial and partly inferior to the body of the mandible bone  Submandibular ducts open on either side of the lingual frenulum in the oral cavity proper (Wharton’s ducts)  Sublingual Glands  Found beneath the tongue and just superior to the submandibular glands  Their ducts, lesser sublingual ducts, open into the floor of the mouth in the oral cavity proper  Numerous small openings just lateral to the openings of the submandibular ducts Saliva  Saliva  Chemically, saliva is 99.5% water and 0.5% solutes  Solutes consist of:  sodium (Na+)  potassium (K+)  chloride (Cl_)  bicarbonate (HCO3--)  phosphate (HPO43-)  Also present are some dissolved gases, various organic substances (including urea and uric acid), mucous, immunoglobulin A, lysozymes (bacteriolytic enzyme) ,  AND salivary amylase (a digestive enzyme)  Saliva  Parotid Glands (serous fluid)  Secrete serous (watery) liquid containing salivary alpha-amylase  Submandibular Glands (seromucous fluid)  Similar to parotids with the serous fluid and salivary alpha-amylase  Also contain mucous cells, the secretion from them is a thicker version of what the parotid glands secrete  Sublingual Glands (mucous)  Contains mucous cells  Saliva  Water in saliva provides a medium for dissolving foods  Allows for tasting by the gustatory receptors  Allows for digestive reactions to begin  Salivary amylase starts the breakdown of carbohydrates  Chloride (Cl-) found in saliva activates this  Bicarb and phosphate helps to buffer acidic environment in the mouth  Saliva ends up being slightly acidic (pH 6.35-6.85)  Clinical Correlation – Sjogren Syndrome  Auto-immune disease  Mainly attacks salivary and lacrimal (tear) glands  Leaves person with  Xerostomia – chronic dry mouth  Keratoconjunctivitis sicca – chronic dry eyes  Very dry joints = arthritis, sometimes severe  Not fatal but  Alters taste drastically  Effects ability to eat because of decreased salivation  Constant eye pain  Clinical Correlation – Sjogren Syndrome  Treatment  No treatment to cure this condition  Frequent eye lubrication drops  Hydration  Sialogogues – stimulants of salivation  Lemon drops  Sour candies The Process of Salivation  Salivation  Controlled by the autonomic nervous system  Amounts of saliva secreted daily vary considerably but average is 1000-1500mL (1- 1.6qts)  Normally parasympathetic stimulation promotes continuous secretion of moderate amount  This lubricates the mucous membranes, and helps keep the movements of the tongue and lips moist during speech  Saliva is then swallowed which helps to keep the esophagus moist  Salivation  Sympathetic stimulation dominates during times of stress  This is why during these times, the mouth and throat become dry  Called xerostomia  If the body becomes dehydrated, the salivary glands stop producing saliva to conserve water (remember ADH?)  Salivation  Feel and taste of food are potent stimulators of salivation  Chemicals in food stimulate receptors in taste buds on tongue  These impulses are conveyed to the brain  Returning parasympathetic impulses stimulate salivation, returned along the fibers of both the  Facial (VII) nerve - all three glands  Glossopharyngeal (IX) nerve - parotid glands  Trigeminal (V) nerve (mandibular branch) - parotid glands, sublingual and submandibular glands  Salivation  Saliva continues to be secreted heavily after food is swallowed  Washes out the mouth  Dilutes and buffers remnants of irritating chemicals (ghost peppers!! Not enough saliva in the world….)  Often just the sight, smell, or thought of food can stimulate secretion of saliva  Pavlov‘s dog? Tongue  Tongue  Considered an accessory digestive organ  Composed of skeletal muscle covered with a mucous membrane  With associated muscles forms the floor of the oral cavity  Divided into symmetric lateral halves by a median septum that extends entire length  Attached inferiorly to the hyoid bone, styloid process of the temporal bone, and mandible  Tongue  Lingual frenulum is a fold of mucous membrane in the midline of the ventral aspect (undersurface) of the tongue  Attaches to the floor of the mouth  Aids in limiting the movement of the tongue posteriorly  Clinical Correlation: Tongue  Ankyloglossia  A persons lingual frenulum is abnormally short, rigid, or anteriorly placed  Person is said to be “tongue-tied” because of the lack of movement of the tongue  Usually congenital, can be acquired by trauma with scarring in the region Ankyloglossia  Lingual glands (Von Tongue Ebners glands) in the lamina propria of the tongue secrete  Watery serous fluid  Contains lingual lipase  Lingual lipase  Gets secreted in the mouth, but is not activated until in the stomach  Tongue  Dorsal (upper surface) and lateral surfaces of tongue are covered with papillae  Nipple shaped projections of the lamina propria covered with stratified squamous epithelium  Many contain taste buds (receptors for gustation or taste)  Some lack taste buds but have receptors for touch instead  Helps to increase the friction between food and tongue making it easier for tongue to move food  Tongue  Types of papillae (ch17, Tortora) 1. Vallate (circumvallate)  Approximately 12 form an inverted “V” shaped row at the back of the tongue  Each of the 12 contain 100-300 taste buds 2. Fungiform  Mushroom shaped elevations scatter over entire tongue surface  Each contains about 5 taste buds  Tongue  Types of papillae (ch17, Tortora) continued 3. Foliate  Located in small trenches on lateral margins of tongue  Most of their taste buds degenerate in childhood 4. Filiform  Pointed, threadlike; found on entire surface of tongue  Contain no taste buds but do have tactile receptors  These help to increase friction between tongue and food Mechanical and Chemical Digestion In the Mouth  Mechanical Digestion  Mechanical digestion results from mastication (chewing)  Food is reduced to a soft, flexible, easily swallowed mass called a bolus  Food molecules begin to mechanically break apart in saliva  This is important as enzymes can only react with food in a liquid environment  Chemical Digestion  Two enzymes that contribute to chemical digestion are secreted in the mouth  Salivary amylase  Initiates breakdown of carbohydrates  Chloride ions in saliva activate this in the mouth  Stomach acid deactivates this  Due to excess amount to pancreatic amylase, salivary amylase plays small role in carbohydrate digestion unless in infancy (pancreas not fully functioning yet) and in pancreatic insufficiency (cancer, etc)  Lingual lipase  Initiates breakdown of triglycerides (lipids)  Activated in the stomach by stomach acid (HCl acid) Pharynx  Pharynx  When food is first swallowed, passes from mouth into pharynx  Funnel-shaped tube that extends from the internal nares to the esophagus posteriorly and to the larynx anteriorly  Composed of skeletal muscle and lined with mucous membrane  Pharynx  Divided into three parts  Nasopharynx- functions only in respiration  Oropharynx- function in digestion and respiration  Hypo/Laryngopharynx- function in digestion and respiration  Swallowed food passes from mouth into oropharynx then laryngopharynx  Muscular contractions of these areas help propel food into the esophagus and then into stomach Esophagus  Esophagus  Collapsible muscular tube  Usually 10in long  Lies posterior to the trachea  Begins at inferior end of hypo/laryngopharynx, passes through the inferior portion of neck, enters mediastinum, pierces the diaphragm, ends at superior portion of stomach  Pierces diaphragm through esophageal hiatus  Sometimes part of the stomach herniates through this opening (called hiatal hernia)  Esophagus  Physiology  Secretes mucous (protective function)  Transports food to the stomach  Does NOT produce digestive enzymes  Does NOT participate in absorption  Esophagus- Histology  Superficial surface to lumen 1. Adventitia  Attaches esophagus to surrounding structures 2. Muscularis  Superior 1/3 esophagus is skeletal muscle (voluntary)  Middle 1/3 esophagus is skeletal transitioning to smooth muscle  Inferior 1/3 esophagus is smooth muscle (involuntary) 3. Submucosa  Contains areolar connective tissue, blood vessels, mucous glands  Esophagus- Histology 4. Mucosa (3 layers)  Muscularis mucosae (smooth muscle)  Lamina propria (areolar connective tissue)  Nonkeratinized stratified squamous epithelium  Affords considerable protection against abrasion from food particles  Esophagus- Histology  At either end of the esophagus, muscularis layer thickens forming sphincters  Upper esophageal sphincter (UES) which is skeletal muscle  Regulates movement of food from hypopharynx into esophagus  Lower esophageal sphincter (LES) which is smooth muscle  Regulates movement of food from esophagus into stomach  Opens via a vago-vagal reflex (afferent/efferent fibers of vagus nerve)  Relaxation of LES: alcohol, dopamine, NO, certain prostaglandins, chocolate, acid gastric juice, fat, smoking, etc Deglutition Act of swallowing  Deglutition  Movement of food from the mouth into the stomach  Facilitated by the secretion of saliva and mucous and involves the mouth, pharynx, esophagus  Assisted by swallowing which is completed in three phases 1. The voluntary stage 2. The pharyngeal stage 3. The esophageal stage  Deglutition 1. The Voluntary Stage  Swallowing starts when bolus is forced to back of the oral cavity  Bolus begins to travel backward toward the oropharynx by the movement of the tongue upward and backward against the palate  Deglutition 2. The Pharyngeal Stage  Passage of bolus into oropharynx then subsequently through the hypo/laryngopharynx  Bolus stimulates receptors in the oropharynx as it passes through which sends impulses to deglutition center  The returning impulses cause the soft palate and uvula to move upwards to close off the nasopharynx  Prevents food and liquids from entering the nasal cavity  Impulses also cause the epiglottis to move to cover the opening to the larynx  Prevents the bolus from entering the respiratory tract   Deglutition 3. The Esophageal Stage  Begins once the bolus has entered the esophagus  During this phase, peristalsis pushes the bolus onward  Peristalsis is a progression of coordinated contractions and relaxations of the circular and longitudinal layers of the muscularis  As the bolus is moved down the esophagus, the lower sphincter relaxes allowing food into the stomach  Passage of solid or semisolid food from mouth to stomach takes 4-8 seconds  Passage of very soft foods or liquids takes about 1 second Clinical Correlation- GERD  If the lower esophageal sphincter fails to close adequately after food has entered the stomach, contents can reflux into esophagus  This is known as gastroesophageal reflux disease (GERD)  Hydrochloric acid from the stomach contents can irritate the esophageal wall resulting in burning sensation known as “heart burn”  Causes epithelial metaplasia (may lead to cancer) in distal esophagus (Barrett’s esophagus) Clinical Correlation- GERD Stomach  Stomach  J-shaped enlargement of the GI tract directly inferior to diaphragm  Connects the esophagus to the duodenum (first part of the small intestine)  Stomach serves as a mixing chamber and holding reservoir  When food mixes with gastric juices, this becomes chyme  Most distensible part of the GI tract, can expand and accommodate a large quantity of food  Because the mucosa lies in rugae (temporary folds)  Stomach  Has four main regions 1. The cardia  Surrounds the superior opening of the stomach 2. The fundus  Rounded portion superior to and left of the cardia 3. The body  Inferior to the fundus, large central portion 4. The pyloric part (divided into three parts)  Pyloric antrum connects to the body of the stomach  Pyloric canal leads to the third region  Pylorus- connects to the duodenum via pyloric sphincter  Stomach-Histology  Superficial to lumen 1. Serosa 2. Muscularis (three layers of smooth muscle) 3. Submucosa (connective areolar tissue) 4. Mucosa (lamina propria and muscularis mucosae)  Contains gastric glands/pits  Contains specialized exocrine gland cells  Contains an enteroendocrine cell type  Stomach-Histology  Superficial to lumen 1. Serosa  Greater curvature of stomach serosa continues as the greater omentum  Lesser curvature of stomach projects upward towards liver as the lesser omentum 2. Muscularis (three layers of smooth muscle)  Contains Auerbach’s plexus (myenteric plexus) 3. Submucosa (connective areolar tissue)  Contains Meissner’s plexus (submucosal plexus)  Stomach- Histology 4. Mucosal layer (3 layers external to internal) a. Muscularis mucosae (smooth muscle) b. Lamina propria (connective areolar tissue) c. Mucosa 1. The surface mucous/goblet cells (EXCLUDING gastric pits/glands) produce/secrete a mucous rich in bicarb (HCO3-) 2. Gastric pits/glands form deep crevices within the mucosa a. These pits are where digestive products are made 3. Gastric pits/glands contain three types of cells that secrete their products into stomach lumen OR into the interstitium a. Chief cells (exocrine - lumen) b. Parietal cells (exocrine - lumen) c. Enteroendocrine cells (endocrine – interstitium/blood vessels)  Stomach- Histology  Exocrine Cells  Chief cells  Stimulated by  Luminal peptides (proteins)  HCl acid  Secretes pepsinogen (inactive precursor enzyme)  Pepsin (active enzyme) is the chief protein digesting enzyme in stomach  Stomach- Histology  Exocrine Cells (continued)  Parietal cells  Stimulated by  Luminal peptides (proteins)  Gastrin-releasing peptide (neurotransmitter released by vagus nerve endings)  Secretes hydrochloric acid (HCl)  Deactivates salivary amylase  Activates lingual lipase  Activates pepsinogen  Secretes intrinsic factor (IF)  Intrinsic factor is needed to aid in absorption of vitamin B12/cyanocobalamin in the small intestines  Secretes bicarbonate  This gets formed inside the cell and is secreted into the interstitium  Stomach- Histology  Enteroendocrine cells  G-Cells (GASTRIN)  Found only in the pyloric antrum  Secretes gastrin into interstitium (is endocrine and paracrine) which then  Stimulates HCl acid production from parietal cells  Stimulates epithelial cell repair/proliferation  Stimulates histamine to be released from enterochromaffin cells  Stomach- Histology  Enteroendocrine Cells (continued)  D-Cells (SOMATOSTATIN; aka GHIH)  Found in stomach, pancreas, and hypothalamus  Secretes hormone into interstitium (is endocrine and paracrine) which then  Inhibits/decreases gastrin release  Enterochromaffin Cells  Secretes histamine  Activates parietal cells to produce more HCl acid  Anyone heard of Zantac (ranitidine) or Tagamet (cimetidine)?  Histamine (H2) blockers  No histamine…less HCL  Stomach- pH  Basal luminal pH of stomach – 4 to 6  This is when there is no food to digest and no stimulation of gastric motility  When food is present, or gastric motility stimulated  HCl acid is released in significant amounts  Brings pH down to ~2  Helps to deter bacterial growth throughout the digestive process  At pH < 3, pepsinogen is rapidly activated, so this helps with digestion Stomach- Gastric Diffusion Barrier  Arguably the most important type of cell in the stomach  Mucosal (Goblet) cells – line the mucosal layer of the stomach  All other types of cells are intermixed amongst these  Provides a constant thick (1-3mm) layer of mucous protection from the very acidic luminal contents  The cells on the other side of this barrier operate in an almost neutral pH zone  If they came into contact with highly acidic chyme, those cells would not operate properly  If HCl acid reached a chief cell, it would activate the protein- digesting enzyme pepsinogen INSIDE the cell  This would then digest every protein containing portion of that cell (peptic ulcers) Mechanical and Chemical Digestion In the stomach  Mechanical - Stomach  Propulsion - peristaltic waves in the stomach  Gastric “pacemaker” cells located along the greater curvature begin a propulsion wave every 15-20 seconds  This propels chyme forward into the pylorus (smaller space) where it undergoes “grinding” of larger particles  Particles are usually ground until they are