BL1004 Animal Digestion Oct 2024 PDF

BL1004-Animal Digestion Prof. Sarah Culloty, School of BEES Digestion Three dietary categories: Herbivores Carnivores Omnivores Nutritional needs: Fuel for all animals requirements Biosynthesis – making new molecules Essential nutrients – cannot be synthesised (10 amino acids, so...

BL1004-Animal Digestion Prof. Sarah Culloty, School of BEES Digestion Three dietary categories: Herbivores Carnivores Omnivores Nutritional needs: Fuel for all animals requirements Biosynthesis – making new molecules Essential nutrients – cannot be synthesised (10 amino acids, some fatty acids, vitamins, minerals)  The four stages of food processing Small molecules Pieces of food Chemical digestion Nutrient Mechanical (enzymatic hydrolysis) molecules digestion enter body cells Undigested Food material 1 INGESTION 2 DIGESTION 3 ABSORPTION 4 ELIMINATION Digestion Digestion  can be Intracellular – within a cell e.g. food vacuole + lysosomes  can be Extracellular – in a specific compartment e.g. cnidarians (hydra) have gastrovascular cavity  Animals must avoid self- digestion by processing food in compartments Intracellular Digestion (Endocytosis) Amoeba  Animals with simple body plans hydr Phylum a  Gastrovascular Cnidaria – jellyfish and cavity: corals 1. Digests food and Tentacles Mouth 2. distributes Food Digestion begins in nutrients Gastrovascular cavity (gastrodermis Epidermis cavity secretes enzymes) Mesenchyme Gastrodermis and Nutritive muscular cells is completed Flagella intracellularly Gland cells (engulfed by Food vacuoles Mesenchyme Simple versus complex systems  Porifera (sponges) and Cnidaria (jellyfish) (mainly intracellular digestion) have one opening that functions as both mouth and anus  Most animals have a digestive tube with 2 openings (mouth and anus) = a complete digestive tract or alimentary canal (extracellular digestion)  Food moves in one direction and this allows specialised compartments Revision  What is intracellular digestion?  What is extracellular Digestion?  What are 2 functions of a gastrovascular cavity?  What is the difference between a complete and incomplete digestive systems? Alimentary Canal - complete digestive tract  Human digestive system Tongue Cardiac Salivary orifice glands Oral cavity Parotid gland Mouth Salivary Sublingual gland glands Pharynx Submandibular gland Esophagus Esophagus 5 – 6 sec Pyloric sphincter Liver Stomach Gall- bladder Stomach 2 – 6h Ascending Gall- Small portion of bladder intestines large intestine Liver Pancreas Pancreas 5 – 6h IIeum Large of small Small intestine intestines intestine Duodenum of small intestine 12 – 24h Rectum Large intestine Anus Rectum A schematic diagram of the human digestive system Appendix Anus Peristalsis moves the food Cecum and sphincters control its passage Summary of enzymatic digestion Carbohydrate digestion Protein digestion Nucleic acid digestion Fat digestion Oral cavity, Polysaccharides Disaccharides (starch, glycogen) (sucrose, lactose) pharynx, Salivary amylase esophagus Smaller polysaccharides, maltose Proteins Stomach Pepsin Small polypeptides Polysaccharides Polypeptides DNA, RNA Fat globules (Insoluble in water, fats aggregate as Pancreatic amylases globules.) Pancreatic trypsin and Pancreatic chymotrypsin (These proteases nucleases Bile salts cleave bonds adjacent to certain Maltose and other amino acids.) Lumen of disaccharides Fat droplets (A coating of bile salts prevents small drop- small Smaller Nucleotides lets from coalescing into polypeptides larger globules, increasing intestine exposure to lipase.) Pancreatic carboxypeptidase Pancreatic lipase Amino acids Glycerol, fatty acids, glycerides Small peptides Epithelium Nucleotidases of small Disaccharidases Dipeptidases, carboxypeptidase, Nucleosides intestine and aminopeptidase (These proteases split off one amino acid at a time, Nucleosidases working from opposite ends of a and (brush polypeptide.) phosphatases border) Monosaccharides Nitrogenous bases, Amino acids sugars, phosphates Initial movement of food  Oral cavity - salivary amylase + mucin + food = Bolus (1 L saliva/day)  Salivary amylase hydrolyses starch and glycogen  Esophagus– food moves to stomach by involuntary contractions (peristalsis)  When you swallow, epiglottis-covers glottis-the vocal chords and opening  From mouth to stomach 4 The esophageal sphincter relaxes, allowing the bolus to enter the Epiglottis esophagus. Bolus of food up Tongue Glottis Epiglottis up down Pharynx and open Esophageal Esophageal Glottis Epiglottis sphincter Esophageal sphincter Larynx down relaxed 5 After the food sphincter contracted has entered the contracted Trachea Esophagus esophagus, the larynx moves Relaxed To lungs To stomach Glottis up downward and muscles opens the and closed breathing Contracted passage. muscles 3 The larynx, the 1 When a person is not upper part of the swallowing, the esophageal 6 Waves of muscular Relaxed respiratory tract, sphincter muscle is contracted, moves upward and contraction muscles 2 The swallowing the epiglottis is up, and the tips the epiglottis (peristalsis) reflex is triggered glottis is open, allowing air over the glottis, move the bolus when a bolus of to flow through the trachea preventing food down the esophagus food reaches the to the lungs. from entering the to the stomach. pharynx. trachea. Stomach Summary of enzymatic digestion Carbohydrate digestion Protein digestion Nucleic acid digestion Fat digestion Polysaccharides Disaccharides (starch, glycogen) (sucrose, lactose) Oral cavity, pharynx, Salivary amylase esophagus Smaller polysaccharides, maltose Proteins Stomach Pepsin Small polypeptides Polysaccharides Polypeptides DNA, RNA Fat globules (Insoluble in water, fats aggregate as Pancreatic amylases globules.) Pancreatic trypsin and Pancreatic chymotrypsin (These proteases nucleases Bile salts cleave bonds adjacent to certain Maltose and other amino acids.) disaccharides Fat droplets (A coating of Lumen of bile salts prevents small drop- small Smaller Nucleotides lets from coalescing into intestine polypeptides larger globules, increasing exposure to lipase.) Pancreatic carboxypeptidase Pancreatic lipase Amino acids Glycerol, fatty acids, glycerides Small peptides Nucleotidases Epithelium Dipeptidases, carboxypeptidase, Nucleosides Disaccharidases and aminopeptidase (These proteases of small Nucleosidases split off one amino acid at a time, intestine working from opposite ends of a and (brush polypeptide.) phosphatases border) Monosaccharides Nitrogenous bases, Amino acids sugars, phosphates Stomach Esophagus Cardiac orifice Stomach Pyloric sphincter 5 µm Small intestine Folds of epithelial tissue Interior surface of stomach. The interior surface of the stomach wall is highly folded and dotted with pits leading Epithelium 3 into tubular gastric glands. 1 Pepsinogen and HCI are secreted into the Pepsinogen Pepsin (active enzyme) lumen of the stomach. 2 Gastric gland. The gastric glands have three types of cells HCl that secrete different components of the gastric juice: mucus cells, 1 chief cells, and parietal cells. 2 HCl converts pepsinogen to pepsin. Mucus cells secrete mucus, which lubricates and protects the cells lining the stomach. 3 Pepsin then activates more pepsinogen, starting a chain Chief cells secrete pepsino- reaction. Pepsin gen, an inactive form of the begins the chemical digestive enzyme pepsin. digestion of proteins. Parietal cell Chief cell Parietal cells secrete hydrochloric acid (HCl). in the stomach…  Gastric juices contain HCl  pepsinogen + acid (pH 2) = pepsin  pepsin + acid => ulcer, BUT prevented by mucus  chyme = gastric juices + partly digested food  Backflow of acid chyme through cardiac orifice => heartburn (in oesophagus)  pyloric sphincter regulates passage of chyme to small intestine Summary of enzymatic digestion Carbohydrate digestion Protein digestion Nucleic acid digestion Fat digestion Polysaccharides Disaccharides (starch, glycogen) (sucrose, lactose) Oral cavity, pharynx, Salivary amylase esophagus Smaller polysaccharides, maltose Proteins Stomach Pepsin Small polypeptides Polysaccharides Polypeptides DNA, RNA Fat globules (Insoluble in water, fats aggregate as Pancreatic amylases globules.) Pancreatic trypsin and Pancreatic chymotrypsin (These proteases nucleases Bile salts cleave bonds adjacent to certain Maltose and other amino acids.) disaccharides Fat droplets (A coating of Lumen of bile salts prevents small drop- small Smaller Nucleotides lets from coalescing into intestine polypeptides larger globules, increasing exposure to lipase.) Pancreatic carboxypeptidase Pancreatic lipase Amino acids Glycerol, fatty acids, glycerides Small peptides Nucleotidases Epithelium Dipeptidases, carboxypeptidase, Nucleosides Disaccharidases and aminopeptidase (These proteases of small Nucleosidases split off one amino acid at a time, intestine working from opposite ends of a and (brush polypeptide.) phosphatases border) Monosaccharides Nitrogenous bases, Amino acids sugars, phosphates  Humans – accessory glands salivary glands Tongue Cardiac Salivary orifice glands Oral cavity Parotid gland Mouth Salivary Sublingual gland glands Pharynx Submandibular gland Esophagus Esophagus 5 – 6 sec gallbladder liver Pyloric sphincter Liver pancreas Stomach Gall- bladder Stomach 2 – 6h Ascending Gall- Small portion of bladder intestines large intestine Liver Pancreas Pancreas 5 – 6h IIeum Large of small Small intestine intestines intestine Duodenum of small intestine 12 – 24h Rectum Large intestine Anus Rectum A schematic diagram of the human digestive system Appendix Anus Cecum  Enzymatic action in the small intestine Duodenum – first part of intestine – enzymes are secreted from pancreas Liver Bile Gall- bladder Stomach Acid chyme Intestinal juice Pancreatic juice Pancreas Duodenum of small intestine  Pancreas produces: proteases amylases lipases nucleases bicarbonate Pancreas Membrane-bound enteropeptidase Inactive trypsinogen Trypsin Other inactive proteases Active Trypsin activates proteases proteases Lumen of duodenum  Pancreas The pancreas has both endocrine and exocrine functions Endocrine: Acts on distant cells via the circulation, 0 e.g. secretion of insulin and glucagon into the blood Exocrine: Acts via ducts or channels rather than blood, e.g. secretion of digestive enzymes Liver The liver produces bile which is stored in the gallbladder. Bile consists of:  bile salts, which act as emulsifiers (fat digestion)  pigments from destruction of red blood cells (eliminated in faeces)  Hormonal control of digestion Enterogastrone secreted by Liver the duodenum inhibits peristalsis and acid secretion by the stomach, thereby slowing digestion when acid chyme rich in fats enters the Entero- duodenum. gastrone Gall- bladder Gastrin CCK Gastrin from the stomach Stomach recirculates via the bloodstream back to the stomach, where it stimulates the production Amino acids or fatty acids in the duodenum of gastric juices. Pancreas trigger the release 0f cholecystokinin), which timulates the release of digestive enzymes Secretin from the pancreas and bile from the Duodenum gallbladder. Secreted by the duodenum, CCK secretin stimulates the pancre Key to release sodium bicarbonate, which neutralizes acid chyme Stimulation from the stomach. Inhibition Absorption of nutrients in small intestine Vein carrying blood to Microvilli (brush border) hepatic portal vessel Blood capillaries Epithelial cells Muscle layers Epithelial cells Large circular (in between villi) Villi folds Lacteal Key Lymph vessel Villi Nutrient Intestinal wall absorption The Large Intestine (Colon)  Colon is 1.5 m long  Appendix has some defense role  Reabsorption of water  Rich microflora, mostly harmless, including E.coli. They produce vitamins, which are absorbed by the large intestine  Production of faeces Revision  Where does absorption of nutrients occur?  Where does protein digestion commence in humans?  What food group does amylase break down into its constituent blocks  What is the inactive form of pepsin?  3 functions of the colon?  The Cecum  Most mammalian herbivores have a relatively large caecum, hosting a large number of bacteria, which aid in the enzymatic breakdown of plant materials such as cellulose; in many species, it is considerably wider than the colon.  In contrast, obligatory carnivores, whose diets contain little or no plant material, have a reduced cecum, which is often partially or wholly replaced by the appendix. Microbiome: Current and future research  500 – 1,000 microbial species in human gut  commensal bacteria convert dietary fibre to short chain fatty acids + Vitamin K absorption  Microbiome-gut-brain axis research. Microbial composition affects anxiety levels, obesity and memory in mice – many human trials ongoing Gut microflora affected by:  antibiotics  fermented foods (e.g. sauerkraut, yoghurt)  faecal transplants  https://www.ucc.ie/en/apc/  Acknowledgements  Majority of text and Powerpoint slides from Campbell’s Biology.