Survey
* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project
Download Digestion
Transcript
Biology 20 Digestive System OR From Food to Feces in a couple hundred steps! DIGESTIVE SYSTEM HETEROTROPHIC NUTRITION Unable to manufacture food from inorganic molecules. Depend on autotrophs. AUTOTROPHIC NUTRITION Organisms capable of synthesizing organic molecules from simple inorganic material. Types: photosynthesizers and chemosynthesizers. Steps of Heterotrophic Nutrition 1) Ingestion • eating or drinking • Putting organic molecules into the system. • Heterotrophs need: – Sugars – Amino Acids – Fatty Acids – Glycerol – Minerals – Vitamins Steps of Heterotrophic Nutrition 2) Digestion • Breakdown of macromolecules into smaller ones that can be absorbed by the cells – Mechanical -- chewing – Chemical -- digestive enzymes Steps of Heterotrophic Nutrition 3) Absorption • Nutrients are absorbed into the blood – Digested monomers – Water – Minerals – Vitamins 4) Egestion • Elimination of undigested material • Poop but because this is a Biology class we will call it FECES Steps of Heterotrophic Nutrition 5) Assimilation • The conversion of nutrients into fluid or solid parts of the organism. Assimilation can only occur after absorption has taken place. • “You will be assimilated. Resistance is futile. ” Locutus of Borg Digestion Terms • Mastication • To chew food • Increases surface area for digestion • Peristalsis • The wavelike muscular contractions of the alimentary canal by which contents are forced onward 8 Digestion Terms • Sphincter • A ring-like muscle that normally maintains constriction of a body passage or orifice and that relaxes as required by normal physiological functioning. Digestion Enzyme Amylase (Salivary amylase) Protease (pepsin) Lipase (Pancreatic lipase) Source Substrate Product Optimum pH Digestion 6.1.1 - Macromolecules must be digested into their respective monomers so that our bodies can absorb them. – Enzymes are needed by our body to increase the rate of digestion at our body temperature 6.1.2 Digestion H.2.1 Digestive juices are secreted into the alimentary canal by glands • • • • salivary glands gastric glands in the stomach wall pancreas wall of the small intestine. Digestion H.2.2 Exocrine glands – have secretory cells around hollow spaces (acini) (lt. berries) which are grouped around ducts into which they secrete their products Digestion H.2.2 Sweat Gland Exocrine Gland Parts Organs •Mouth •Pharynx •Esophagus •Stomach •Small Intestine •Large Intestine •Anus Glands • • • • Salivary Glands Pancreas Liver Gall Bladder Order of Events Mouth Hard Palate • hard part of roof of mouth Soft Palate • back of roof of mouth Pharynx • chamber in throat where – nasal cavity and mouth meet – esophagus and trachea meet Mucus Membranes • lubricates walls of mouth for easy passage of food Mouth Purpose • Mechanical digestion by teeth and tongue –increases surface area for action by enzymes –Mixes food thoroughly with teeth and tongue • Chemical digestion by enzymes in saliva Value • food easily swallowed • increases SURFACE AREA exposed for action by digestive enzymes • thoroughly mixes the food with the TEETH AND TONGUE •Secretions Salivary •Saliva •1 to 2 liters per day •from 3 pairs of glands in the mouth •Sub-lingual •Sub-mandibular Glands •parotid Mouth Composition of Saliva • Water – moistens food • Amylase (ptyalin) – begins STARCH digestion • Mucin – lubricant – binds food together for easier swallow 3 salivary glands • Parotid salivary gland – secrete amylase • Sublingual salivary gland – mucous secretion that acts as a buffer and lubricant • Submandibular salivary gland – secrete mixture of buffer, mucins and salivary amylase • Buffers in saliva keep pH of mouth near 7.0 • Prevent build up of acids produced by bacterial action • Increase saliva when feel sick • These are exocrine glands - secretion goes outside of body and not into the circulatory system. Mouth Control of Salivary Secretions • Mechanical pressure – food in the mouth • Nervous system - glands – Brain thinking of food in the mouth – Signal sent to salivary glands from the brain – Pavlov’s Dog anyone? “ring a bell and I’ll salivate” Pharynx Pharynx Throat • Common tube through which both air and food pass Four openings • Nasal Cavity • Trachea Mouth Cavity Esophagus Contains a flap of tissue called the EPIGLOTTIS to prevent food from entering the trachea Esophagus Hollow muscular tube Connects pharynx to the stomach What makes the food go to the stomach? Movement of food by peristalsis • rhythmic waves of contraction and relaxation of muscular walls • food is squeezed through esophagus into stomach Epiglottis and uvula shunt food into esophagus during swallowing Peristalsis Peristalsis Esophagus Structure • thick walled and muscular • from pharynx to stomach • walls contain mucus glands which secrete mucin to lubricates food for easy passage Stomach Structure a hollow muscular pouch J shaped – shape and volume changes from meal to meal. located high in the abdominal cavity, just under the diaphragm where your ribs come up together – not at your waist/belt. Structure of Stomach (con’t) Connection between esophagus and the stomach is regulated by cardiac sphincter. • muscular ring surround esophagus at this point • acts like a valve to open and close the tube • keeps the food from falling out of your stomach when standing on your head. Water demo!!!! Connection between the small intestine and the bottom end of the stomach is regulated by the pyloric sphincter. • Regulate the release of chyme into small intestine when food is liquefied it is called chyme. Stomach FUNCTIONS • temporary storage of ingested food • mechanical breakdown of ingested food –churning of the stomach mixes juice with food • liquefaction of food • beginning of protein digestion (disruption of chemical bonds in food through action of acids and enzymes) Secretions -- Gastric Juice pH plays an essential role in gastric activity • Regulated by amount of gastric juice secretion Gastric juice is secreted into the stomach cavity by stomach cells Secretions -- Gastric Juice Contains 1. Hydrochloric Acid – HCl(aq) –pH of 1-2 –H+ and Cl- are secreted separately, becomes HCl in stomach –Acidity: • destroys bacteria present in food • Denatures proteins and inactivates enzymes in food • Break down plant cell walls and connective tissues in meat • Activates Pepsin!!!! Secretions -- Gastric Juice Contains 2. Pepsin –an enzyme which begins protein digestion –Pepsin is produced and secreted in an inactive form called pepsinogen • Pepsinogen convert to pepsin when pH gets to 2 Secretions -- Gastric Juice Why is pepsin secreted as pepsinogen, an inactive form? Pepsin is secreted as pepsinogen first is to protect the stomach lining. stomach lined with a mucus coating • prevents acid and protein digesting enzymes from damaging wall • Hence, stomach only digests food, and does not have any food absorption Digestion in Stomach pH of stomach is decreased by gastric juice When food just arrives in the stomach, pH of stomach is still high • When pH is still above 4.5 – salivary amylase is still active – break down carbohydrates • When HCl in gastric juice lowers pH to 1-2, pepsin is activated – breaks down protein – Complex proteins are broken into smaller peptide and polypeptide chain Regulation of Gastric Activity 1. Central Nervous System • See, smell, taste, or think of food will stimulate increase production of gastric juice in stomach • Nervous system prepares stomach to receive food • Production of gastric juice accelerates 500mL per hour • Emotional states can also affect – e.g. Anxiety – decrease stimulation & slows digestion Regulation of Gastric Activity 2. Hormones • Gastrin – Produced by stomach cells – Enters blood stream – Increase secretion of HCl and Pepsinogen by stomach cells • pH decrease – Increase gastric motility • When chyme enters small intestine, stomach cells secrete other hormones to temporarily inhibit gastric juice secretion Small Intestine FUNCTION • complete the digestion of food – important secretions from the pancreas and the liver. • absorb the nutrients into the circulatory system (blood) Small Intestine STRUCTURE + FUNCTION About 6 meters long • Three sections 1) Duodenum • • • • first 25 cm Digestion Neutralize acids in chyme Receives and mixes pancreatic and liver secretions 2) Jejunum • next 2 meters • Bulk of chemical digestions and nutrient absorption 3) Ileum • next 4 or 5 meters • absorption Small Intestine STRUCTURE (con’t) the inside of the S.I. is covered with millions of tiny finger-like projections called villi • each villus is actually covered with millions of microvilli • the villi and microvilli increase surface area for absorbing food molecules into blood. • 600 times more surface area Surface of small intestine contains membrane-bound digestive enzymes Secretions -- Pancreatic Fluid Contains 1. NaHCO3 – sodium bicarbonate – raises pH to 8 (important for enzymes to function) 2. Pancreatic Amylase – an enzyme which continues the digestion of starch into maltose units 3. Lipase – enzyme digesting lipids into fatty acids & glycerol Secretions -- Pancreatic Fluid 4. Proteolytic Enzymes -enzymes which continue protein digestion -2 types: 1. protease – break down large protein complexes 2. peptidases – break down small peptide chains into individual amino acids Example: Trypsin (protease) – Secreted as trypsinogen in pancreas (similar to pepsinogen) – Activated into trypsin by an enzyme in membrane surface of small intestine Liver and Gallbladder Secretion The liver produces bile – brown fluid Bile is stored in the gallbladder when fats enter the small intestine, the gallbladder contracts and squirts bile into the duodenum Small Intestine • Lipase is water-soluble, only contact fat droplets on the outside surface – Cannot break down the fat on the inside of the droplet • bile emulsifies fats – physically prevents fats to coalesce with each other – Fats are in smaller droplets –greater surface area for action by lipase • bile is NOT an enzyme because it does not cause a chemical change in fat. Small Intestine H.2.9 • Explain the problem of lipid digestion in a hydrophilic medium and the role of bile in overcoming this. –Lipid molecules tend to coalesce and are only accessible to lipase at the lipid–water interface. Bile molecules have a hydrophilic end and a hydrophobic end, and thus prevent lipid droplets coalescing. The maximum surface is exposed to lipases. Lipase needs to be water-soluble and to have an active site to which a hydrophobic substrate binds. Small Intestine All types of foods are acted upon. Small Intestine H.2.5 digestion of disaccharides and dipeptides is completed by enzymes on surface membrane of intestinal villi in small intestine • sucrase – digests sucrose • maltase – digests maltose • lactase – digests lactose • aminopeptidase – breaks down dipeptides into amino acids Small Intestine once all food molecules are at monomer stage, they are ready to be absorbed into the circulatory system through the villus on small intestine surfaces Assignment H.3.1 Draw and label a diagram showing a transverse section of the ileum as seen under a light microscope. Include mucosa and layers of longitudinal and circular muscle. Absorption in the Small Intestine H.3.3 Digested Nutrient Product Method of Absorption Site of Absorption Small Intestine notice that glycerol recombines with 3 fatty acids to form a fat molecule which enters the lacteal instead of the capillary Why is fat completely digested and then recombined to form a fat molecule again? H.3.2 Explain the structural features of an epithelial cell of a villus as seen in electron micrographs. • Microvilli – folds of the cell membrane that increase the surface area of the epithelial cell. • Mitochondria – provide energy for the cell to transport nutrients. • Pinocytotic vesicles – assist with endocytosis of nutrients. • Tight junctions – connections between epithelial cells that maintain structure integrity of the tissue. Large Intestine Large Intestine Material NOT absorbed by this point will enter the large intestine through another sphincter – the ilial-caecal sphincter The caecum is a small pouch at the beginning of the large intestine. • contains a small projection called the appendix – this is a vestigial organ which functions in cellulose digestion in some herbivorous mammals Functions of the Large Intestine absorb water into blood absorb vitamins and minerals into blood eliminate undigested material from digestive tract (cellulose, lignin, bile pigments, bacteria and intestinal cells.) Large Intestine Some bacteria live in the large intestine of mammals • they digest material that we are not able to digest a byproduct of this activity results in the synthesis of vitamins • Vitamin K Rectum & Anus last section of digestive tract rectum is a holding pouch for feces feces exits the digestive tract through a sphincter muscle called the anus. rectal veins are found near opening • if they get inflamed… – the inside diameter of anus decreases – passage of feces is difficult and painful – called hemorrhoids or piles. What About Fiber??? fiber in the diet serves to retain water throughout the digestive tract resulting in soft feces. H.2.6 Outline the reasons for cellulose not being digested in the alimentary canal. See above. H.3.4 The materials that are not absorbed but are egested are cellulose, lignin, bile pigments, bacteria and intestinal cells. Biology 20 Control of Digestive Secretions Saliva Nervous • Pavlov • Sight, smell, presence, or even thought of food stimulates vagus nerve • results in the production of saliva Gastric Juice Nervous • Stimulation of vagus nerve also stimulates cells of stomach to begin producing gastrin Gastric Juice Hormonal • Gastrin (a hormone) is released from certain upper stomach cells into the bloodstream. • gastrin circulates until it reaches the lower stomach cells resulting in the release of gastric juices. • Once pH falls below 2, gastrin stops being secreted. • If pH rises above 2.5 gastrin secretion begins again. Pancreatic Juice Nervous • presence of food in mouth and stomach stimulates pancreatic secretions Hormonal • presence of chyme in the S.I. causes the cells of the duodenum to secrete the hormone secretin into the blood • Secretin (a hormone) causes the pancreas to begin producing pancreatic juice • Pancreatic Juice will enter the duodenum through the pancreatic duct. • when acidic chyme becomes alkaline, production of secretin stops Liver & Gall Bladder Bile Hormonal • presence of chyme in the S.I. causes the cells of the duodenum to secrete the hormone cholesystekinin into the blood. • This causes the gall bladder to contract, propelling bile into the duodenum through the bile duct DISORDERS H.2.8 Discuss the roles of gastric acid and Helicobacter pylori in the development of stomach ulcers and stomach cancers. •Burrows into mucus layer in stomach and produces toxins and enzymes that destroy gastric lining •One enzyme breaks down the mucus, exposing the stomach cells to gastric juices •Can get it from contaminated food or water. Can pass from human-to-human contact. •Treated with combination of antibiotic and antacid. How did they figure this out?? Barry Marshall – scientist in Australia No one would believe him that ulcers could be due to a bacteria – the stomach is too acidic! To prove his suspicion he drank a mixture of H. pylori himself and gave himself ulcers! Won the Nobel prize in Medicine or Physiology, 2005 for this research Disorders Tapeworms are a group of parasitic worms that live in the intestinal tracts of some animals. Several different species of tapeworms can infect humans. Tapeworm disease or cestodiasis occurs most commonly after eating raw or undercooked meat or fish that contains the immature form of the tapeworm. Tapeworm Tapeworm IntestinalDisorders Appendicitis Cancer Celiac Disease Constipation Diarrhea Diverticulitis Hernias Inflammatory Bowel Disease Irritable Bowel Syndrome Lactose Intolerance Short Bowel Syndrome Anorectal Disorders Anal Fissures Cancer Constipation Hemorrhoids Imperforate Anus Stomach Disorders Cancer Cyclic Vomiting Syndrome Indigestion Peptic Ulcer Reflux Disease Gallbladder Disorders •Gallstones Liver Disorders Alagille Syndrome Alpha1-Antitrypsin Deficiency Associations Cancer Children Crigler-Najjar Syndrome Hepatic Encephalopathy Hepatitis Support Groups Transplant Wilson's Disease Zellweger Syndrome Pancreatic Disorders Cancer Cystic Fibrosis Pancreatitis Oral Disorders Drooling Dysphagia Mouth Ulcers
