2Animals are Heterotrophs A nutritionally balanced diet must satisfy 3 main needs:Fuel or chemical energyOrganic raw materials for biosynthesis (food containing carbon to make carbon skeletons)Essential nutrients that the body cannot make and must be obtained from food
3Homeostatic Regulation of Cellular Fuel Glucose is the main cellular fuel. Its storage and use is closely monitored by the animal body. After a meal, glucose and other monomers are absorbed into the blood from the digestive tract.If blood glucose levels rise above a set point,The pancreas release insulin, a protein hormone into the bloodInsulin causes the uptake of glucose by cells and stimulates liver and muscle cells to store glucose as glycogenWhen blood glucose levels drop below a set point, the pancreas release glucagon that stimulate the liver and muscle cells to breakdown glycogen and release glucose into the blood.
4Nutritional Requirements Essential Fatty Acids(certain unsaturated fatty acids like linoleic acid which is an omega-6 fatty acid – found in sunflower oil and others)Essential Amino Acids(Trp,Met,Val,Thr,Phe,Leu,Iso,Lys)Minerals(Ca, P, S, Cl, Na, K, F, Mn, Mg, Fe, Cu, I, Co, Se, Cr, Mo)Vitamins (13 needed)- Water-soluble(B1, B2, B6, B12, Niacin, Folic acid, Biotin, Vitamin C, Pantothenic acid)- Fat-soluble(A, D, E, K)
6Feeding Mechanisms Deposit-feeders Fluid-feedersSuck nutrient-rich fluids from hostDeposit-feedersSift through dirt and other deposits for foodBulk-feedersEat large amounts and pieces – most animals are bulk feeders.Suspension-Feeders (Filter feeders)Filter food from their water, so have to be aquatic animalsSubstrate-feedersLive on their food source and eat through it
8Where does digestion occur? IntracellularFood vacuoles are helped by lysosomes to break down food in the cytoplasm – simplest digestive compartmentsExtracellularDigestive organs and gastrovascular cavities involved in digestion outside of cells. Complex animals have the alimentary canal or digestive tracts
10All animals conduct both – Intracellular and Extracellular digestion Large foods are ingestedThe digestive tract will release enzymes into its lumen to breakdown the food into monomersThese are absorbed by the individual cells that line the tractIntracellularAutophagy of dead organelles by lysosomesPhagocytosis by some cells such as macrophages
11The Mammalian Digestive System The oral cavity, pharynx and esophagusThe stomachThe small intestineThe large intestine
12The Oral CavitySaliva contains an enzyme called Salivary Amylase, that breaks down starch and glycogen into maltoseSaliva contains a slippery glycoprotein called mucin that protects lining of mouth from abrasionsSaliva also contains anti-bacterial agents, buffers that prevent tooth decayTeeth mechanically break food downTongue tastes food and manipulates it during chewingTongue shapes the chewed food into a “bolus” for swallowing
13The PharynxIntersection between the esophagus and tracheaDuring swallowing, the tracheal opening is blocked by a cartilaginous flap called epiglottisThe EsophagusGuides the bolus into the stomach, with the help of involuntary smooth muscle spasms called peristalsisThe muscles at the top of the esophagus are striated and so swallowing begins voluntarilyAmylase continues to work on bolus on the way down
15The StomachLocated under the diaphragm, to the left of the abdominal cavityLarge enough to hold 2 liters of food and water – so constant eating is not neededThe inner epithelium secretes gastric juices – which contains HCl, has pH of 2Juice also contains pepsin (secreted as pepsinogen by chief cells in folds of stomach lining), an enzyme that hydrolyzes proteins – works best in acidic environmentsEpithelial cells release mucous, that prevents the erosion of the stomach lining – however, it does eventually erode and mitosis replaces the cellsBolus mixed with gastric juices is now a nutrient broth called Acid Chyme
16Cardiac sphincter is the same as the gastro esophageal sphincter
17Hiatal HerniaA hernia occurs when one part of the body protrudes through a gap or opening into another part.A hiatal hernia forms at the gastroesophageal sphincter, where the esophagus joins the stomach. Part of the stomach pushes through this opening causing a hiatal hernia.A large hiatal hernia can allow food and acid to back up into the esophagus, leading to heartburn and chest pain.
21Helicobacter pyloriBacteria that cause gastric ulcers – lesions in the stomach liningH. pylori is a spiral-shaped gram-negative bacterium.it requires oxygen but at lower levels than those contained in the atmosphere.With its flagella and its spiral shape, the bacterium drills into the mucus layer of the stomach, and then can either be found suspended in the gastric mucosa or attached to epithelial cells.It excretes the enzyme urease, which converts urea into ammonia and bicarbonate. The release of ammonia is beneficial to the bacterium since it partially neutralizes the very acidic environment of the stomach (whose very purpose is to kill bacteria). Ammonia is, however, toxic to the epithelial cells, and with other products of H. pylori, including protease, catalase, and phospholipases, causes damage to those cells
23The Small Intestine Workhorse of digestion and absorption Longest section of alimentary canalFirst 25 cm called the duodenum where Acid Chyme from stomach mixes with digestive juices from pancreas, liver, gall bladder and gland cells of the intestinal liningThe middle section of the SI is called the jejunumThe last section of the SI is called the ileum
24Small IntestineThe lumen of the small intestine receives secretions fromthe pancreas andLiverThe small intestine itselfThe SIcompletes digestion of the nutrients in chyme,absorbs the products of digestion, andtransports the remaining residues to the large intestine.
27Enzymatic Actions in the Duodenum Pancreas- Proteases called trypsinogen, chymotrypsinogen and procarboxypepsidase are secreted into the SI lumen and then become their active forms – trypsin, chymotrypsin and carboxypepsidase. The activation of these enzymes is triggered by an SI enzyme called enteropeptidase.These 3 activated enzymes help break down protein in the acid chyme.- Pancreatic Lipase breaks down dietary fat into 1 monoglyceride and 3 fatty acids- Pancreatic Amylase hydrolyzes dietary starch into maltose- Bicarbonate (HCO3- ) and Water neutralize the acidity in the acid chyme- Two nucleases breakdown DNA and RNA.Small Intestine- Secondary protein hydrolyzing enzymes called aminopepsidase and dipeptidases found in the lining of the small intestine also help speed the process of protein digestion.
28Summary of Protein Digestion in SI AminopeptidaseDipeptidase
30Regulation of Pancreatic Secretion The nervous and endocrine systems regulate release of pancreatic juice.Secretin from the duodenum stimulates the release of pancreatic juice with a high bicarbonate ion concentration but few digestive enzymes.Cholecystokinin from the wall of the small intestine stimulates the release of pancreatic juice with abundant digestive enzymes.
31Enzymatic Actions in the SI Liver- Produces bile, which is a combination of bile salts, lecithin, *bilirubin, water and cholesterol- Bile is stored in the gall bladder and released into the SI lumen through the common bile duct- Bile emulsifies dietary lipids, so that pancreatic lipase can breakdown each triglyceride into fatty acids and glycerol.*Bilirubin is the main bile pigment that is formed from the breakdown of heme in red blood cells. The broken down heme travels to the liver, where it is secreted into the bile by the liver. Bilirubin is passed in the feces and gives it the yellow-brown color. Excess bilirubin causes jaundice and stains skin, eyes and nails yellow.
33Composition of BileBile is a yellowish-green liquid that hepatic cells secrete; it includes water, bile salts, bile pigments (bilirubin, biliverdin), cholesterol, and electrolytes.Bile pigments are breakdown products from red blood cells.Only the bile salts have a digestive function.
34The gallbladderThe gallbladder is a pear-shaped sac lying on the interior surface of the liver.It is connected to the cystic duct, which joins the hepatic duct; these two ducts merge to form the common bile duct leading to the duodenum.A sphincter muscle controls the release of bile from the common bile duct.
35Regulation of Bile Release Bile does not normally enter the duodenum until cholecystokinin stimulates the gallbladder to contract.The hepatopancreatic sphincter remains contracted unless a peristaltic wave approaches it, at which time it relaxes and a squirt of bile enters the duodenum.
36Functions of Bile Salts Bile salts emulsify fats into smaller droplets, so that pancreatic lipase can hydrolyze the triglyceridesAids in the absorption of fatty acids, cholesterol, and certain vitamins
37The Jejunum and IleumMost of the digestion in the SI occurs in the first section – the DuodenumThe next sections of the SI – the Jejunum and the Ileum, are mainly involved in the absorption of nutrients and water
38Absorption of Nutrients in the SI Circular folds in the epithelial tissue lining of the intestines have finger-like projections called villi.Each epithelial cell of the villi has many microscopic microvilli.This increases the surface area for absorptionCapillaries and a lymphatic vessel called a lacteal penetrate the villi – this is so that nutrients can be absorbed across the intestinal lining, across the capillaries, into the blood stream or lymphatic system.Nutrients have to traverse only two layers of cells – one layer of intestinal epithelial cells and one layer of capillary cellsThe movement of nutrients can be either active or passive transport.
39Absorption in the Small Intestine The small intestine is the major site of absorption within the alimentary canal.There are digestive enzymes on microvilli, including peptidases, sucrase, maltase, and lactase, and intestinal lipase.Monosaccharides and amino acids resulting from carbohydrate and protein digestion are absorbed by the villi through active transport and enter blood capillaries.The intestinal villi also absorb water (by aquaporins) and electrolytes (by active transport).
40Fat AbsorptionFatty acids are absorbed and transported differently than the other nutrients.Fats are digested into individual fatty acids in the SI lumen by bile and lipase.These fatty acids enter the cells of the SI lining via microvilliThe endoplasmic reticula of the cells reconstruct the fats (triglycerides).These fats collect in clusters that become encased in proteinThese protein+ fat clusters are called chylomicrons.Chylomicrons are carried away in lymphatic lacteals until they eventually join the bloodstream.
44The Lymphatic System Consists of organs, ducts, and nodes. Transports a watery clear fluid called lymph. This fluid distributes immune cells and other factors throughout the body. It also interacts with the blood circulatory system to drain fluid from cells and tissues. The lymphatic system contains immune cells called lymphocytes, which protect the body against antigens (viruses, bacteria, etc.) that invade the body. Main functions of lymphatic system: to collect and return interstitial fluid, including plasma protein to the blood, and thus help maintain fluid balance, to defend the body against disease by producing lymphocytes, to absorb lipids from the intestine and transport them to the blood.
46After AbsorptionThe capillaries carrying the nutrient-rich blood join to form the hepatic portal vessel which carries the nutrients to the liverThe blood then goes to the heart, which pumps the nutrient and oxygen to the rest of the body cells
47Hormones That Regulate Digestion The hormones that control digestion are gastrin, secretin, and cholecystokinin (CCK):Gastrin (Secreted by cells in stomach lining)causes the stomach to produce acidnecessary for the normal growth of the lining of the stomach, small intestine, and colon.Secretin (An enterogastrone secreted by cells in wall of duodenum)causes the pancreas to release juices with bicarbonate.stimulates the stomach to produce pepsin,stimulates the liver to produce bile.CCK (cholecystokinin) (An enterogastrone secreted by cells in wall of duodenum)causes the pancreas to grow and to produce its digestive enzymescauses the gallbladder to empty stored bile into the SI.
48hormones in the GI that regulate appetite: Ghrelin is produced in the stomach and upper intestine in the absence of food in the digestive system and stimulates appetite.Peptide YY is produced in the GI tract in response to a meal in the system and inhibits appetite.Both of these hormones work on the brain to help regulate the intake of food for energy.
50Parts of the Large Intestine The large intestine absorbs water and electrolytes and forms and stores feces.Parts of the Large IntestineThe large intestine consists of the cecum (pouch at the beginning of the large intestine), colon (ascending, transverse, descending, and sigmoid regions), the rectum, and the anal canal.The anal canal opens to the outside as the anus; it is guarded by an involuntary internal anal sphincter and a voluntary external anal sphincter muscle.
51The Large Intestine AKA colon Carnivores have a small cecum ; the appendix is a part of itWater absorption is the main task of LI (90% reabsorbed)Waste (feces) is eliminated, after being stored in the rectumLarge population of bacteria – most harmless, some mutualistic – E.coli produce vitamin , others produce vitamin B, folic acid, biotin, etc.Some of these bacteria breakdown the undigested cellulose for food for themselves.Bacteria produce gases like methane and hydrogen sulfideFeces contain undigested food like cellulose, bacteria, salts, bilirubin makes it yellow!
52Evolutionary Adaptations of Digestive Systems Teeth – sharp incisors, canines vs. molarsCecum – long vs. shortFour-chambered stomach – ruminants like cows and sheep can regurgitate and re-chew food – their stomachs contain cellulose-digesting bacteria.Symbiotic bacteria – vitamin production, cellulose digestion
53Carnivores – have sharp teeth to tear flesh Herbivores have sharp front teeth to cut vegetation and flat rear teeth then to grind it down.
54Teeth that fit the diet Carnivores – have sharp teeth to tear flesh Herbivores have sharp front teeth to cut vegetation and flat rear teeth then to grind it down.Omnivore teeth