A look at the digestive system Animal Nutrition A look at the digestive system

What do animals need to live? Animals make energy using: Food Oxygen Animals build bodies using: Food for raw materials Amino acids, sugars, fats, nucleotides ATP energy for synthesis food ATP O2

Nutritional requirements Animals are heterotrophs Need to take in food Why? Fulfills 3 needs … Fuel = chemical energy for production of ATP Raw materials = carbon source for synthesis Essential nutrients = things animals cannot make Elements (N, P, K, Fe, Na, Ca …), NAD, FAD, etc

Different ways to obtain food filter (suspension) feeding substrate feeding fluid feeding bulk feeding

Different diets; different lives All animals eat other organisms Herbivores Eat mainly plants Giraffes, cows, rabbits, snails Carnivores Eat other animals Sharks, hawks, spiders, snakes Omnivores Eat plants & animals Cockroaches, bears, raccoons, humans Humans evolved as hunters, scavengers, & gatherers

intracellular digestion extracellular digestion Getting & using food Ingest Taking in food Digest Mechanical digestion Breaking up food into smaller pieces Chemical digestion Breaking down food into molecules small enough to be absorbed into cells Enzymes (hydrolysis) Absorb Absorb across cell membrane Diffusion Active transport Eliminate Undigested extracellular material passes out of digestive system intracellular digestion extracellular digestion

Getting & using food Don’t forget about enzymes Specialized proteins that catalyze reactions Lower activation energy, and, therefore, increase the rate of digestion Most enzymes prefer an environment of 37OC Generally fall into 3 main categories: Amylase Produced in salivary glands & pancreas Digests starch into maltose & glucose, prefers pH 7 Example: salivary amylase Proteases Produced by stomach glands Digests proteins into amino acids; prefers pH 3 Example: pepsin Lipase Produced by pancreas Digests lipids into glycerol & fatty acids; prefers pH 7 (or slightly above) Example: pancreatic lipase

Human digestive system Alimentary Canal

Common processes & structures Movement & control Peristalsis Push food along by rhythmic waves of smooth muscle contraction Sphincters Muscular, ring-like valves that regulate the passage of material between sections of digestive system Accessory glands Salivary glands, pancreas, liver & gall bladder Secrete digestive juices (enzymes + fluid)

Swallowing (& not choking) Epiglottis Problem: breathing & swallowing through the same orifice Flap of cartilage Closes trachea (windpipe) when swallowing Food travels down esophagus Esophagus Moves food to stomach by peristalsis

Ingestion Mouth Mechanical digestion Chemical digestion Teeth Saliva Breaking up food Chemical digestion Saliva Amylase Enzyme digests starch Mucin Mucus protein (slippery) Protects soft lining of digestive system Lubricates food for easier swallowing Buffers Neutralizes acid to prevent tooth decay Anti-bacterial chemicals Kill bacteria that enter mouth with food

mouth break up food moisten food digest starch kill germs

The stomach epithelium Functions Food storage Can stretch to fit ~2L of food Disinfect food HCl = pH 2 Kills bacteria Breaks apart cells Mechanical digestion Chemical digestion Gastric juice Mucus, HCl, & pepsinogen Gastric gland The stomach epithelium cells must regenerate every 3 days

Pepsin Enzyme that breaks down protein Secreted as pepsinogen Activated by HCl But the stomach is made out of protein! What stops the stomach from digesting itself? mucus secreted by stomach cells protects stomach lining

mouth break up food moisten food digest starch kill germs stomach kills germs store food break up food digest proteins cardiac sphincter pyloric sphincter

Ulcers Used to think ulcers were caused by stress Tried to control with antacids Now know bacterial infection is cause in majority of cases Helicobacter pylori 15% of infected individual develop ulcers Bacteria live in neutral zone between epithelial cells and mucus Now cure with antibiotics Additional causes: Excess HCl secretion Loss of mucus barrier Excess use of aspirin/ibuprofen Coevolution of parasite & host Free of H. pylori Colonized by H. pylori inflammation of stomach inflammation of esophagus H. pylori cell damaging proteins (VacA) inflammatory proteins (CagA) helper T cells cytokines neutrophil cells white blood cells

Small intestine Functions Chemical digestion Absorption through lining Major organ of digestion & absorption Chemical digestion Enzymes Absorption through lining Over 6 meters long Huge surface area = 300m2 (~size of tennis court) Structure 3 sections Duodenum = most digestion Jejunum = absorption of nutrients & water Ileum = absorption of nutrients & water

Duodenum 1st section of small intestines Acidic food from stomach mixes with digestive juices from accessory glands Pancreas Liver Gall bladder

Pepsinogen & trypsinogen What stops pancreas from digesting itself? Digestive enzymes Trypsinogen Activated by peptidase Becomes trypsin Digests proteins Pancreatic amylase Buffers Reduces acidity from stomach Alkaline solution rich in bicarbonate (HCO3-) small intestines Pepsinogen & trypsinogen Call called zymogens What stops pancreas from digesting itself?

Pancreas Exocrine & endocrine gland without ducts Exocrine = with ducts Pancreas Exocrine & endocrine gland Acinar (or secretory) cells secrete digestive enzymes into the ductile The ductile takes the enzymes to larger and larger ducts until the pancreatic duct is reached

Structure of an exocrine gland

mouth break up food moisten food digest starch kill germs stomach kills germs break up food digest proteins store food pancreas produces enzymes to digest proteins & starch

Circulatory System Connection Liver Digestive system functions Produces bile Stored in the gall bladder until needed Breaks up fats Acts like detergents to breakup fats Circulatory System Connection bile contains colors from old red blood cells collected in liver = iron in RBC rusts & makes feces brown

Digesting lipids Bile is produced in the liver & stored in the gall bladder Bile salts have a hydrophobic side & a hydrophilic side Hydrophobic attaches to lipid Hydrophilic interacts with water Breaks fat globules into smaller, digestible lipids

mouth break up food moisten food digest starch kill germs stomach kills germs break up food digest proteins store food liver produces bile - stored in gall bladder break up fats pancreas produces enzymes to digest proteins & starch

Digestive enzymes

Transverse section of the ileum Perpendicular to longitudinal muscle layer Used for peristalsis Control diameter of ileum Used for peristalsis

Absorption by small intestine Absorption through villi & microvilli Finger-like projections Increases surface area for absorption Ooooh… Structure & Function

Absorption by small intestine

Absorption by small intestine A villus Capillary network: allows transport of absorbed nutrients Single epithelial layer: ensures minimum distance for diffusion Lacteals: absorb lipids into lymphatic system Membrane proteins: enzymes that do not pass through the digestive system Can be reused Can help with membrane transport

Mitochondria: provide energy for active transport Pinocytotic vesicles: transport material in bulk Tight junction: impermeable membrane between cells, maintains concentration gradient

Absorption of nutrients Lipids are absorbed via diffusion Water-soluble molecules are absorbed via facilitated diffusion Glucose, amino acids, & minerals are absorbed by active transport Glucose uses a sodium-glucose transporter and secondary active transport (see previous slide) Endocytosis/pinocytosis is used for bulk transport

What is NOT absorbed? B: bile pigments E: epithelial cells of the intestinal lining L: lignin (carb found in plants) C: cellulose (roughage or fiber) H: human microflora (bacteria)

mouth break up food moisten food digest starch kill germs stomach kills germs break up food digest proteins store food liver produces bile - stored in gall bladder break up fats small intestines breakdown all foods - proteins - starch - fats - nucleic acids absorb nutrients pancreas produces enzymes to digest proteins & starch

Absorption vs Assimilation The process of taking in substances Assimilation The process of using subunits (amino acids, fatty acids, glycerol) to build macromolecules, which then become part of the body

Large intestine (colon) Function Reabsorption of water Use ~9 L of water every day in digestive juices >90% of water is reabsorbed No enough water reabsorbed back into body diarrhea Too much water reabsorbed back into body constipation

Microflora of large intestine Living in the large intestine is a rich flora of harmless, helpful bacteria Over 700 species of bacteria, plus fungi & protozoa Escherichia coli (E. coli) Bacteria produce vitamins Vitamin K, biotin, folic acid, & other B vitamins Generate gases By-product of bacterial metabolism Methane, hydrogen sulfide You’ve got company!

Rectum Last section of colon (large intestine) Eliminates feces Undigested materials B-E-L-C-H Does not use peristalsis Uses general contractions Inner muscle layer only Generally occurs 1-3 times a day Involves (voluntary) relaxation of anal sphincter & increase in intra-abdominal pressure

mouth break up food moisten food digest starch kill germs stomach kills germs break up food digest proteins store food liver produces bile - stored in gall bladder break up fats small intestines breakdown food - proteins - starch - fats absorb nutrients pancreas produces enzymes to digest proteins & carbs large intestines absorb water

Appendix Found at the junction of the small intestine & large intestine About 4 inches long Function still unknown Storehouse for good bacteria “reboot” digestive system after illness Vestigial structure Useless remnant from our evolutionary past Additional surface area for a cellulose-rich diet

Cecum stores food material and bacteria capable to digesting cellulose Compare these digestive tracts- how do they demonstrate structure fits function? Cecum stores food material and bacteria capable to digesting cellulose

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