Digestive System Notes.docx

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Biological Sciences Program
BSCI 201
Justicia Opoku

Digestive System The Digestive System Functions Ingestion is moving foods form one region of the digestive system to another Propulsion is moving foods form one region of the digestive system to another Peristalsis Segmentation Absorption is the movement of nutrients into the bloodstream, end products of digestive are absorbed in the bloodor lymph of food that was chemically and physically broken down Defecation rids the body of indigestible waste. Movement of Digestive Materials Visceral smooth muscle shows rhythmic cycles of activity caused by pacemaker cells Circular and Longitudonal 2 types of movements Peristalsis causes waves that move a bolus Segmentations churns and fragments a bolus Control of DigestiveActivity Mostly controlled by reflexes via the parasympathetic NS Neural and hormonal mechanisms coordinate glands GI activity stimulated by parasympathetic and inhibited by sympathetic innervations Chemical and mechanical receptors are located in organ walls that trigger reflexes People should eat slowly so that the stimuli (below) can get to your brain. This way people can balance their diet. Stimuli Include Stretch of organ pH of the contents Stomach Acid Acidic Beverages causes you to eat more (fruit juices and soda) Presence of breakdown Activity of the digestive tract in the old age Problems of the digestive system Gastroenteritis is inflammation of the GI tract Appendicitis is inflammation of the appendix Metabolism decreases with old age. Activity of the digestive tract in old age Fewer digestive juices Peristalsis slows Diverticulosis and cancer are more common. The longer food sits in the GI tract, the more water it absorbs. Colon Cancer: Food is absorbed into the blood stream. There is a lot of blood flow to GI Tract. Easy for it to metastasize. Organs of the Digestive System Alimentary Canal (Gastrointestinal or GI tract) is a continuous coiled hollow tube. Mouth Pharynx Esophagus Stomach Mainly just sterilizes it Small Intestine Main Organ for Digestion Large Intestine Anys Accessory digestive organs Accessory Digestive Organs Teeth Salivary Gland Lubricate it Pancreas: Endocrine gland; secretes hormones Exocrine gland: Secretes chemicals Liver: Creates Bile Gallbladder: Stores bile. Mouth (Oral Cavity) Anatomy Vestibule is the space between lips externally and teeth and gums internally Oral cavity proper is the area contained by the teeth Tongue is attached at hyoid bone and styloid processes of the skull, and by the lingual frenulum to the floor of the mouth Tongue’s primary functions include: Mechanical processing Assistance in chewing and swallowing Sensory analysis by touch, temperature, and taste receptors Lubrication Tonsils – Immune System. Palatine Lingual GidestiveActivities of the Mouth The mouth opens into the oral (buuccal) cavity Mechanical breakdown Mastication (chewing) of food, food is physically broken down by chewing Mixing masticated food with saliva Initiation of the swallowing by the tongue Allows for the sene of taste (works with smell) Chemical Digestion Food is mixed with saliva Starch is broken down into maltose by salivary amylase Teeth Function is to masticate (chew) food Humans have two sets of teeth Deciduous (baby or “milk”) teeth 20 teeth are fully formed by age two Permanent Teeth Replace deciduous teeth between ages of 6 and 12 rd Afull set if 32 teeth, but some people do not have wisdom teeth (3 molars) If they do emerge, the wisdom teeth appear between ages of 17 and 25. Classification of Teeth Incisors used for cutting Canines used for tearing or piercing Premolars used for grinding Molars used for grinding Salivary Glands Three pairs of salivary glands empty secretions into the mouth Parotid glands Submandibular glands Sublingual glands Saliva Mixture of mucus and serious fluids Helps to form a food bolus Contains salivary amylase to begin starch digestion Dissolves chemicals so they can be tasted Pharynx Physiology Serves as a passageway for air and food; common passageway for food, liquids, and air Pharyngeal muscles assist in swallowing Pharyngeal constrictor muscles Palatal muscles Food is propelled to the esophagus by two muscle layers Longitudinal outer layer Circular Inner layer Food movement is by alternating contractions of the muscle layers (peristalsis) Deglutition (Swallowing) Buccal Phase Voluntary and occurs in the mouth Food is formed into a bolus and forced into the pharynx by the tongue Pharyngeal-esophageal phase Involuntary transport of the bolus All the passageways except to the stomach are blocked Tongue blocks off mouth Soft palate (and uvula) blocks the nasopharynx Epiglottis blocks the larynx Cardioesophageal sphincter is opened when food presses against it Closes it because stomach has acid Esophagus Anatomy and Physiology Anatomy About 10 inches long Run from pharynx to stomach through the diaphragm Physiology Conducts food by peristalsis (slow rhythmic squeezing) Passageway for food only (respiratory system branches off after the pharynx) Activities of the Pharynx and esophagus They have no digestive function Serve as passageways to the stomach. Functions of the Stomach Bulk storage of undigested food Don’t have to eat (or forge for elders) Mechanical breakdown of food Disruption of chemical bonds via acids and enzymes Production of intrinsic factor Temporary storage tank for food Chemical breakdown for protein begins Delivers Chyme (processed food) to the small intestine Site of some food breakdown. Stomach Anatomy Located on the left side of theAbdominal Cavity Food enters at the cardioesophageal sphincter Food empties into the small intestine at the pyloric Sphincter (valve) Sphincters keep the chyme in place Regions of the Stomach Cardiac Region is near the heart Fundus is the expanded portion lateral to the cardiac region Body is the midportion Pylorus is the funnel-shaped terminal end Rugae Mechanical resistance (turbulence to help breakdown food) Secrete Digestive juices External Regions Lesser Curvature: Concave medial surface Greater Curvature: Convex lateral surface Acid reflux/Heart Burn Turcture of Stomach Mucoas Mucosa is simple columnar epithelium Mucous neck cells produce a sticky alkaline mucus Gastric glands are situatied in gastric pits and secrete gastic juice Chief cells produce protein digesting enzymes Pepsinogens Parietal cells produce hydrochloric acid. Enterendocrine cells produce gastrin and somatostatin (hormones) Gastrin (makes more gastric juice) Peptic Ulcers Peptic ulcers are most common in the lower half of the stomach (gastric ulcer) on in the supper part of the duodenum (duodenal ulcer) Ulcers can affect all ages, and about 1 in 10Americans develops a peptic ulcer at some point Ulcers are the result of damage to the cells that produce a layer of mucus and other factors that neutralize any acid Cells lining the stomach and intestine are constantly renewed, with normal turnover occurring every 72 hours Problems arise cell function is disrupted by helicobacter pylori infection, aspiring or other non- steroidal anti-inflammatory drugs (NSAIDS), alcohol, nutrient deficiencies, long term hunger and stress. Digestion and Absorption in the Stomach Preliminary digestion of proteins Permits Digestion of Carbohydrates Very little absorption of nutrients Some drugs may be absorbed: aspirin, alcohol Mucous secretion containing several hormones Enteroendocrine cells G cells secrete gastrin D cells secrete somatostatin Food Breakdown in Stomach Gastric juice is regulated by neural, local, and hormonal factors Presence of food or rising pH causes the release of the hormone Gastrin causes stomach glands to produce protein-digesting enzymes Mucus HydrochloricAcid Hydrochloric acid makes the stomach contents very acidic to sanitize Also activates pepsinogen to pepsin for protein digestion Provides a hostile environment for microorganisms Denatures most proteins Protein digestion enzymes Pepsin is an active protein-digestive enzyme Rennin works on digesting milk protein in infants, not adults Phases of Gastric Secretion Cephalic Phase Thinking about Food Stimulus: Sight, smell, taste, or thoughts of food (CNS) Function: prepare stomach for arrival of food Duration: (Short, Minutes) Mechanism Neural, via preganglionic fibers in vagus nerve and synapses in submucosal plexus) Actions Primary: stimulation of mucus, enzyme and acid production, leading to increased volume of gastric juice Secondary: Stimulation of gastrin release by G cells Gastric Phase Food Is in stomach Functions: Enhance secretion started in cephalic stage; homogenize and acidify chyme; initate digestion or proteins by pepsin Duration: Long (3-4 hours) Mechanisms: Neural Stimulation of stretch recetpros as stomach fills Stimulation of chemoreceptors and pH increases Hormonal Stimulation of gastrin Released by G cells through parasympethtic activityes and presence of peptiedes and amino acids Actions: Increase acid and pepsinogen production and increased motility and initiation of mixing waves. Intestinal Phase Function: Control rate of chyme entry into duodenum Enzymes (CCK, GIP, Secretin) tell stomach to stop producing gastric juice and Propulstion in the Stomach Segmental movement mix chyme with digestive juices and aid in propelling food Gastroenteric reflexes initaed by stretch receptors in stomach Gastroileal reflex triggers relaxation of ileocecal Valve Food must first be well mixed The Pylorus meters out chyme into the small intestine (30 mL at a time) The stomach empties in 4-6 hours Gastric Bypass: Hormone Ghrelin is produced by the stomach and stimulates hunger With a large stomach, usually means there is a large amount of ghrelin People would eat smaller and smaller meals for this. What happens with a gastric Bypass? Bypassing the stomach. Circumventing the stomach so that people don’t eat as much because stomach is now smaller. Problems This can be ruptured is people eat too much. Too much food in a small pouch. May not be able to keep up with nutrition values. Won’t be able to drink because it fills them up too quickly. Small Intestine The body’s major digestive organ, site of nutrient absorption into the blood Muscular tube extending from the pyloric sphincter to the ileocecal valve Suspended from the posterior abdominal wall by the mesentery The majority of chemical digestion begins in the small intestine Enzymes are produced by intestinal cells and pancreas Pancreatic Ducts carry enzymes to the small intestine Bile formed by the liver, enters via the bile duct Helps in emulsifying fat. Small Intestine Three subdivision Duodenum: the first and shortest, and widest part of the small intestine that in humans is about 25 cm long. Jejunum: the section beyond the duodenum is larger, thicker-walled, and more vascular and has more circular folds and fewer peyer’s patches than the ileum. Ileum: the last division, smaller and thinner-walled than the jejunum, fewer circular folds but more numerous Peyer’s patches Ileocecal Sphincter: transition between small and large intestine Crohn’s Diseases The inflammation of Crohn’s Disease usually found in the ileocecal valve Crohn’s Diseases is an inflammatory bowel disease May be caused by body’s immune system attacking gut bacteria and foods Use Cortisol or steroids because it inhibits your immune system. The most common complication is blockage of the intestine Treatment includes drug therapy to control inflammation and possibly surgery to remove damaged tissue. Bacteria is your gut: Based on genetics. Children with C sections, don’t have right bacteria in stomach, rather than natural birth. Small IntestineAnatomy Lacteals are terminal lymphatics in villi (help absorb fat) Intertinal glands are lined by enteroendocrine, goblet and stem cells Three structural modification that increase surface area: Microvilli are tiny projections of the plasma membrane (create a brush border appearance Villi are fingerlike structure formed by the mucosa Circular folds (plicae circulares) are deep folds of mucosa and submucosa. Digestion in the Small Intestine Enzymes from the bursh border functions to Break down disaccharides into simple sugars Complete some protein digestion Pancreate enzymes play the major digestive function Help complete digestion of starch (pancreatic amylase) Carry out about half of all protein digestion Carbohydrate digestion Digest fats using lipases from the pancreas Digest nucleic acids using nucleases. Akaline content neutralized acidic chyme: rich in bicarbonate Can Cause MetabolicAcidosis because of a loss of the base. Lactose Intolerance Evolutionary speaking, as we age, we produce less lactase to break down lactose: We only have milk when we are younger, not when we are older. Some people have mutations in their DNAthat allow them to digest lactose their entire lives People who can break down lactose: Mutation. The gene never gets turned off. Allows them to drink milk or consume fairy products (digest lactose) all the time. If you do not break down lactose, it ends up in the large intestine, where bacteria will digest the lactose and produce gas, excess lactose will also pull water out of neighboring tissue, leading to water-down stool (diarrhea)…TREATMENT? Absorption int eh Small Intestine Water is absorbed along the length of the small intestine End products of digestion Most substances are absorbed by active transport through cell membranes Lipids are absorbed by diffusion Substances are transported to the liver by the hepatic portal vein or lymph Large Intestine Larger in diameter, but shorter in length than the small intestine That’s why it’s called large intestine (diameter) Colon Ascending: Travels up right side of abdomen Transverse: Travels across abdominal cavity Descending: travels down the left side Sigmoid: Enters the Pelvis Rectum and anal canal, also in the pelvis Appendix Accumulation of lymphatic tissue that sometimes becomes inflamed Hangs from the cecum. Functions of the Large Intestine Absorb water and compact material in feces Reabsorption includes Water Vitamins such as K, biotin and B5 Organic wastes such a urobilinogens and stercobilinogen Bile Salts Toxins These are absorbed because we have no Mass movements of material through colon and rectum, the defecation reflex triggered by distention of rectal walls Absorb vitamins produced by bacteria Store fecal matter prior to defecation Meat Consumption seems to correlate with colon cancer The more fat in one has in a diet, the most toxins that can be prevalent in the fats that they each, which can result in colon cancer. Large IntestineAnatomy No villi present Because not much absorption Goblet cells produce alkaline mucus which lubricates the passage of feces Muscularis Externa is reduced to three bands of muscle called teniae coli These bands cause the wall to pucker into haustra (pocket-like sacs) No digestive enzymes are produced Resident bacteria digest remaining nutrients Produce vitamin K and B Release gases Remaining materials are eliminated via feces Feces contains: Undigested food residues, mucus, bacteria, and water. Large Intestinal Movements Peristalsis is the major means of moving food Sluggish peristalsis Mass movements: slow, powerful movements and occur one to four times per day Presences of feces in the rectum causes a defecation reflex InternalAnal Sphinct
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