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The Living World Fourth Edition GEORGE B. JOHNSON 26 The Path of Food Through the Animal Body PowerPoint® Lectures prepared by Johnny El-Rady Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 26.1 Food for Energy and Growth Food provides animals with energy and essential nutrients for growth A healthy diet contains more carbohydrates than fats It also contains a lot of proteins Fig. 26.1 The pyramid of nutrition Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Sources Energy content Use Cereals, grains, 4.1 calories Carbohydrates breads, fruits per gram and vegetables For energy and raw materials Dairy products, 4.1 calories poultry, fish, per gram meat and grains For energy and raw materials Proteins Fats Oils, butter, 9.3 calories For energy Margarine, fried per gram storage and foods and chips raw materials Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display The body mass index is used to determine who’s overweight body weight in kg BMI = (height in m)2 (body weight in lbs) X 703 = (height in in)2 Fig. 26.3 Obesity Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Essential Substances for Growth Many vertebrates are unable to manufacture one or more of the 20 amino acids needed to make proteins Humans are unable to synthesize 8 amino acids These essential amino acids must be obtained through food In addition, all vertebrates cannot synthesize certain polyunsaturated fats Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Essential Substances for Growth Trace elements Minerals required in small amounts Iodine, cobalt, zinc, molybdenum, manganese Vitamins Essential organic substances required in small amounts Humans require at least 13 different vitamins Vitamin C (ascorbic acid) If not in diet, the disease scurvy will develop Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 26.2 Types of Digestive Systems Heterotrophs are divided into three main groups based on food sources Herbivores – Eat plants exclusively Carnivores – Eat meat exclusively Omnivores – Eat both plants and meat Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Single-celled organisms and sponges digest their food intracellularly Other animals digest their food extracellularly, within a digestive cavity In cnidarians and flatworms, this gastrovascular cavity has only one opening Therefore, no specialization Fig. 26.4 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Specialization occurs when the digestive tract has a separate mouth and anus This allows transport of food in one direction Ingested food may be stored in a specialized region of the digestive tract Or it may be subjected to physical fragmentation, followed by chemical digestion Products are then absorbed into the blood Molecules that are not absorbed are excreted as wastes from the anus Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display The most primitive Fig. 26.5 One-way digestive tracts Specialization in different regions Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 26.3 Vertebrate Digestive Systems The vertebrate digestive system consists of tubular gastrointestinal tract and accessory digestive organs Mouth and pharynx Esophagus – Delivers food to the stomach Stomach – Some preliminary digestion Small intestine – Digestion and absorption Large intestine – Water and mineral absorption Rectum (mammals) – Waste excretion Cloaca (other vertebrates) – Waste excretion Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Fig. 26.6 The human digestive system Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 26.3 Vertebrate Digestive Systems In general, herbivores have relatively longer intestines than carnivores Plant cellulose resists digestion Herbivores solicit the help of bacteria 1. Ruminants (such as cows) have stomach with multiple chambers 2. Other herbivores (horses and rabbits) have a cecum at the beginning of the large intestine Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display The gastrointestinal tract has a characteristic layered structure Fig. 26.7 Mucosa Epithlelium Submucosa Connective tissue Muscularis Smooth muscles Serosa Connective tissue Regulate gastrointestinal activities Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 26.4 The Mouth and Teeth Specializations of the digestive system reflects differences in the way vertebrates live Birds, for example, lack teeth They break up food with the help of stones in their twochambered stomachs For food storage Fig. 26.9 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Many vertebrates have teeth that are used for chewing (mastication) Carnivores have pointed teeth adapted for cutting and shearing Herbivores have large flat teeth well suited for grinding plant cellulose Omnivores have carnivorous teeth in front and herbivorous teeth in the back Fig. 26.8 Diagram of generalized vertebrate dentition Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Fig. 26.10 Human teeth Incisors Premolars and molars Cuspids Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display The tongue mixes food with a solution called saliva Saliva moistens and lubricates food It contains amylase which initiates breakdown of starch into maltose The secretions of the salivary glands are controlled by the nervous system A continuous secretion of about 0.5 milliliters per minute keeps the mouth moist The presence of food in the mouth triggers an increased rate of secretion Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Prior to swallowing, the tongue moves food to the back of the mouth The soft palate elevates, pushing against back wall of pharynx This stimulates neurons to send impulses to the swallowing center in the brain Muscles contract and raise the larynx The glottis is pushed against the epiglottis This keeps food out of the respiratory tract, and into the esophagus Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Fig. 26.11 The human pharynx, palate and larynx Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 26.5 The Esophagus and Stomach The esophagus is a muscular tube that connects the pharynx to the stomach The swallowing center stimulates successive waves of contraction Peristalsis moves food along the esophagus to the stomach Fig. 26.12 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Movement of food from esophagus into stomach is controlled by a ring of smooth muscle, the sphincter Humans lack a true sphincter and thus, can regurgitate The stomach is a saclike portion of the tract with a convoluted surface enabling expansion It contains an extra layer of smooth muscles for mixing food with gastric juices Two kinds of secretory cells Parietal cells – Secrete hydrochloric acid Chief cells – Secrete pepsinogen Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Fig. 26.13 The stomach and gastric glands Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display The human stomach produces about 2 liters of HCl and other gastric secretions every day This gastric juice has a pH of ~ 2 It kills most bacteria ingested with food It also denatures food proteins The mixture of partially digested food and gastric juice is termed chyme Chyme leaves the stomach to the small intestine through the pyloric sphincter Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Ulcers The hormone gastrin regulates the synthesis of HCl Overproduction of gastric acid can occasionally eat a hole through the stomach wall These gastric ulcers are rare Susceptibility increases when mucosal barriers are weakened by Helicobacter pylori infection Over 90% of gastrointestinal ulcers are duodenal ulcers Caused by too much chyme in the small intestine Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 26.6 The Small and Large Intestines The small intestine is the body’s true digestive vat It breaks down large molecules into smaller ones These are then absorbed into the bloodstream The small intestine is ~ 6 m long The first 25 cm (~ 4%) constitute the duodenum The duodenum is the actual site of digestion The pancreas secretes digestive enzymes into it The liver secretes bile salts into it, to make fats easier to digest Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 26.6 The Small and Large Intestines The ileum is the rest of the small intestine (~ 96%) It is devoted to absorption The lining is covered with finger-like projections called villi Each cell covering a villus has cytoplasmic projections called microvilli These increase the absorptive surface Indeed, the absorptive efficiency approaches 99% Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Fig. 26.14 The small intestine Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 26.6 The Small and Large Intestines The large intestine, or colon is only 1 meter long But has a larger diameter than the small intestine No digestion and little absorption take place in the large intestine Its primary function is to act as a refuse dump It collects and compacts solid wastes Feces pass through the rectum as a result of peristalsis Leave the body through the anus Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 26.7 Variations in Vertebrate Digestive Systems Most animals lack the enzymes that digest cellulose Their digestive tracts contain prokaryotes and protozoa that have such enzymes Herbivores tend to have long digestive tracts with specialized pouches for breakdown of plant matter Insectivorous and carnivorous mammals have short digestive tracts with few specialized pouches Protein diets are more easily digested Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Ruminants have stomachs with four chambers Rumen Reticulum Omasum Abomasum The contents of the rumen can be regurgitated and rechewed (rumination) Fig. 26.15 Contains prokaryotes and protozoa Only chamber equivalent to the human stomach Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display In some animals digestion of cellulose by microbes occurs in the cecum Regurgitation of contents is not possible However, these animals engage in coprophagy They eat their feces to absorb the nutrients on the second passage of food All mammals rely on intestinal bacteria to synthesize vitamin K Necessary for blood clotting Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Fig. 26.16 The digestive system of different mammals Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Fig. 26.16 The digestive system of different mammals Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 26.8 Accessory Digestive Organs Pancreas Functions as an exocrine gland in digestion Cell clusters called acini secrete Trypsin and chymotrypsin which digest proteins Amylase which digests starch Lipase which digests fats Bicarbonate which neutralizes HCl in chyme Functions as an endocrine gland Cell clusters called Islets of Langerhans secrete Insulin and glucagon Regulate sugar levels in blood Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Liver Largest internal organ of the body Its main exocrine secretion is bile Aids in the digestion of fats in the duodenum Chemically modifies substances absorbed in the gastrointestinal tract Converts poisons into less toxic forms Produces most of the proteins found in plasma Gall bladder Stores and concentrates bile Delivers it to the duodenum via the bile duct Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Fig. 26.17 The pancreatic and bile ducts empty into the duodenum Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 26.9 Homeostasis Homeostasis is the dynamic constancy of the internal environment Conditions fluctuate continuously within narrow limits Homeostasis is essential for life Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Regulating Body Temperature Humans, like other mammals, are endothermic They maintain a body temperature of 37oC (98oF) The hypothalamus coordinates the regulation of the body temperature When body temperature rises Heat is dissipated via sweating and dilation of skin blood vessels When body temperature drops Heat is conserved via shivering and constriction of skin blood vessels Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Regulating Blood Glucose Blood glucose levels are monitored by the Islets of Langerhans in the pancreas When levels are high, insulin is released When levels are low, glucagon is released Fig. 26.19 Stimulate glycogen breakdown Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Eliminating Nitrogenous Wastes Catabolism produces nitrogenous wastes that must be eliminated from the body The first by-product is ammonia, which is toxic It is released through the gills of bony fish Mammals convert ammonia into urea (less toxic) It is water-soluble and thus, excreted in urine Reptiles and birds convert ammonia to uric acid It is largely insoluble in water, and is excreted as a semisolid White paste in bird droppings Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Fig. 26.20 Nitrogenous wastes Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 26.10 Osmoregulatory Organs Osmoregulation is the regulation of the body’s osmotic (water and salt) composition Sponges use contractile vacuoles Invertebrates use a system of tubules from which water and metabolites are reabsorbed Wastes are excreted through excretory pores In flatworms, the tubules are called protonephridia In earthworms, the tubules are called nephridia Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Insects use Malpighian tubules for excretion K+ is secreted into these tubules, and water is drawn osmotically Much of this is reabsorbed in the hindgut Waste products are secreted from the rectum Vertebrates use kidneys for excretion Unlike in insects, tubular fluid is created by filtration of the blood under pressure Selective reabsorption of water and molecules The final waste product, urine, is expelled Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 26.11 Evolution of the Vertebrate Kidney The kidney is a complex organ made of thousands of repeating disposal units called nephrons Blood pressure forces the fluid in blood through a capillary bed called the glomerulus It retains large molecules and allows water and small molecules to pass through Useful sugars and ions are then recovered What remains forms urine Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Fig. 26.25 Basic organization of the vertebrate nephron Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Freshwater Fish Face two serious problems 1. Water tends to enter body from environment The fish don’t drink water They also excrete a large volume of dilute urine 2. Solutes tend to leave body to the environment The fish reabsorb ions across the nephron tubules Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Marine Bony Fish Their body fluids are hypotonic to seawater Thus, water leaves by osmosis across gills They compensate by drinking large amounts of seawater Most monovalent ions are actively transported out of blood across gills Divalent ions that enter blood are secreted into nephron tubules and excreted in urine Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Fig. 26.26 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Cartilaginous Fish Most common are elasmobranchs – sharks and rays Reabsorb urea from the nephron tubules Maintain a blood urea concentration that is 100 times higher than that of mammals The higher urea makes their blood about isotonic with seawater Water loss is prevented Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Fig. 26.27 Osmoregulation in elasmobranchs Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Amphibians Amphibians produce very dilute urine Compensate for loss of Na+ by active transport of Na+ across their skin from the surrounding water Fig. 26.28a Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Reptiles Marine reptiles drink seawater and excrete an isotonic urine Excess salt is secreted by salt glands Fig. 26.28b Terrestrial reptiles reabsorb salt and water in nephron tubules Reabsorb additional water in the cloaca Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Mammals and Birds The only vertebrates able to produce urine with higher osmotic concentrations than body fluids They can thus excrete waste products in a small amount of water, and thus retain more water The kidneys of the kangaroo rat are so efficient, it does not have to drink water! Fig. 26.29 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Hypertonic urine is produced by the loop of Henle Most mammals have nephrons with long tubes Birds have relatively few nephrons with long tubes Produce less concentrated urine than mammals Marine birds minimize water loss by drinking seawater and excreting salt through glands Additional water is absorbed in the cloaca Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Fig. 26.30 26.12 The Mammalian Kidney Each kidney receives blood from a renal artery and from this it produces urine Urine drains from each kidney through a ureter to a urinary bladder Renal tissue is divided into Renal cortex – on the outside Renal medulla – on the inside The kidney is composed of ~ 1 million nephrons Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Fig. 26.31 The mammalian urinary system Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Each nephron is composed of three regions 1. Filter Bowman’s capsule located on top Contains a fine network of capillaries called a glomerulus 2. Tube Loop of Henle is bent back on itself in the center Reabsorption device 3. Duct Tube empties into a collecting duct Water conservation device Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Fig. 26.31 The mammalian urinary system Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display The formation of urine occurs in five steps 1. Pressure filtration Blood pressure pushes water and small molecules across the glomerulus walls and into the Bowman’s capsule This glomerulus filtrate contains water, urea, nutrients and ions 2. Reabsorption of water The walls of the descending arm of the loop of Henle are impermeable to salts and urea but not to water Water exits the loop leaving behind a concentrated fitrate Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 3. Selective reabsorption The walls of the ascending arm of the loop of Henle become permeable to salts & nutrients but not to water Nutrients pass out to the surrounding tissue NaCl is actively exported out of the loop 4. Tubular excretion Active transport excretes into the urine other nitrogenous wastes such as uric acid and ammonia Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 5. Further reabsorption of water Lower portions of collecting duct are permeable to urea Urea leaves and water follows Fig. 26.33 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display