Chapter 41 - Animal Nutrition

Transcription

1 Chapter 41 - Animal Nutrition

2 Introduction to Anatomy and Physiology -Form matches function -Natural selection acts upon variations in form that allows for populations of organisms to be successful -Material exchange with the internal and external environments is dependent on the size and shape of the animal! -Exchange is dependent upon diffusion across a plasma! cell membrane Diffusion (a) Single cell Simple multicellular organisms possess few membranous layers over which materials must be exchanged

3 Complex Multicellular Organisms Cannot Freely Exchange Materials with their Environment External environment Mouth Food CO 2 O 2 Animal body Blood Respiratory system 50 µm 0.5 cm Nutrients Heart Circulatory system Cells A microscopic view of the lung reveals that it is much more sponge-like than balloon-like. This construction provides an expansive wet surface for gas exchange with the environment (SEM). 10 µm Digestive system Interstitial fluid The lining of the small intestine, a digestive organ, is elaborated with fingerlike projections that expand the surface area for nutrient absorption (cross-section, SEM). Anus Unabsorbed matter (feces) Metabolic waste products (urine) Excretory system Inside a kidney is a mass of microscopic tubules that exchange chemicals with blood flowing through a web of tiny vessels called capillaries (SEM). Solution = Highly, folded internal membranes w/ maximal surface area

4 Organizational Hierarchy in Organisms 1. Cells 2. Tissues 3. Organs 4. Organ Systems 5. Organisms All organisms are composed of cells (Duh!) Tissues are groups of cells with a similar structure and function Different (2 or more) tissues are used to construct organs Various organs work together as part of organ systems Organ systems are required for the maintenance of homeostasis within an organism

5 Organ Systems Found in Most Animals Through the combined actions of all of the organ systems, an organism is capable of maintaining homeostasis (balance between the internal and external environments)

6 Model for a Homeostatic Regulatory Mechanism The control center must have a receptor, a control center, and an effector Room temperature decreases Response No heat produced Set point Control center: thermostat Too hot Too cold Heater turned off Set point Set point Negative feedback: If temperature increases (detected by receptor and processed by control center), heater is turned off (effector), and temperature decreases Negative feedback - A response that counteracts or works in opposition to the stimulus Room temperature increases Response Heater turned on Positive feedback - A response that reinforces the stimulus Heat produced

7 Thermostat in hypothalamus activates cooling mechanisms. Sweat glands secrete sweat that evaporates, cooling the body. Blood vessels in skin dilate: capillaries fill with warm blood; heat radiates from skin surface. Increased body temperature (such as when exercising or in hot surroundings) +ΔT -ΔT Body temperature decreases; thermostat shuts off cooling mechanisms. Homeostasis: Internal body temp. of approx C Body temperature increases; thermostat shuts off warming mechanisms. Skeletal muscles rapidly contract, causing shivering, which generates heat. +ΔT Blood vessels in skin constrict, diverting blood from skin to deeper tissues and reducing heat loss from skin surface. -ΔT Decreased body temperature (such as when in cold surroundings) Thermostat in hypothalamus activates warming mechanisms.

8 Digestive System Discussion Questions A peanut butter and jelly sandwich contains a variety of carbohydrates, fats, and proteins. Complete the graph below to indicate the relative percentages of carbohydrate, fat, and protein that remain in this ingested food as it progresses from your mouth through your digestive tract. Be prepared to explain your reasoning. Percent remaining Mouth-esophagus-stomach-small intestine-large intestine-rectum

9 Digestive Physiology Discussion Questions 1. Saliva contains water (to moisten food), mucus (to lubricate food), salivary amylase (to break down starch), bicarbonate (to buffer acids in food), and antibacterial agents. Why might these last three components be necessary when the stomach is the next destination anyway? 2. Everyone knows different parts of the tongue are especially sensitive to different tastes. But why should we devote tongue space to bitterness? 3. In humans, the uvula hangs as a pendant from the posterior end of the soft palate. During swallowing, it lifts upward and closes off the nasopharynx. Why is this important? 4. Is diarrhea a defensive strategy to rid your body of pathogens or a way for intestinal pathogens to spread to others (still occurs in less developed countries with no sewage treatment)? 5. Would you expect carnivores to have longer or shorter intestine than herbivores? 6. What happens if the contents of the colon pass too rapidly through the colon? Too slowly?

10 Complete the concept map for the functions of the digestive system. Do your best to fill in all of the ovals. The main function of the digestive system is to Break down food into smaller molecules so that it can be used as energy This is accomplished by Ingestion Digestion Absorption Elimination

11 The Four Stages of Food Processing Small molecules Pieces of food Mechanical digestion Chemical digestion (enzymatic hydrolysis) Nutrient molecules enter body cells Food Undigested material 1 INGESTION 2 DIGESTION 3 ABSORPTION 4 ELIMINATION

12 Animals with simple body plans have a gastrovascular cavity that functions in both digestion and distribution of nutrients Tentacles Epidermis Mesenchyme Gastrodermis Mouth Food Gastrovascular cavity Simple invertebrates such as cnidarians and platyhelmenthes utilize extracellular digestion followed by endocytosis to absorb nutrients Nutritive muscular cells Flagella Gland cells Food vacuoles Mesenchyme More complex animals possess a complete digestive tract (i.e. alimentary canal) with an opening (mouth) and an exit (anus).

13 Anatomy of the Digestive System (Alimentary Canal and Accessory Organs) Pharynx Mouth Salivary glands Esophagus Liver Gallbladder (behind liver) Stomach Pancreas (behind stomach) Large intestine Small intestine Rectum

14 Mammalian Digestive System A long digestive tube with accessory glands that secrete digestive juices that aid digestion Salivary glands Tongue Parotid gland Sublingual gland Submandibular gland Oral cavity Pharynx Esophagus Cardiac orifice Mouth Esophagus Salivary glands Liver Pyloric sphincter Stomach Gallbladder Stomach Ascending portion of large intestine Gallbladder Pancreas IIeum of small intestine Small intestine Large intestine Duodenum of small intestine Liver Pancreas Small intestines Large intestines Rectum Anus Rectum A schematic diagram of the human digestive system Figure Appendix Anus Cecum Human Digestive System Overview

15 In the oral cavity, food is lubricated and digestion begins Teeth chew food into smaller particles that are exposed to salivary amylase, initiating the breakdown of glucose polymers The stomach stores food and secretes gastric juice, which converts a meal to acid chyme -- Gastric juice is made up of hydrochloric acid and the enzyme pepsin The small intestine is the longest section of the alimentary canal - Primary organ involved in digestion and absorption The large intestine completes the absorption of water and compaction of feces prior to defecation -Bacteria in the lower bowel produce vitamins

16 From Mouth to Stomach Tongue Pharynx Glottis Larynx Trachea To lungs Bolus of food Epiglottis up Esophageal sphincter contracted To stomach 1 When a person is not swallowing, the esophageal sphincter muscle is contracted, the epiglottis is up, and the glottis is open, allowing air to flow through the trachea to the lungs. Esophagus Epiglottis down Glottis up and closed 2 The swallowing reflex is triggered when a bolus of food reaches the pharynx. 4 The esophageal sphincter relaxes, allowing the bolus to enter the esophagus. Esophageal sphincter relaxed 3 The larynx, the upper part of the respiratory tract, moves upward and tips the epiglottis over the glottis, preventing food from entering the trachea. 5 After the food has entered the esophagus, the larynx moves downward and opens the breathing passage. 6 Waves of muscular contraction (peristalsis) move the bolus down the esophagus to the stomach. Stomach Epiglottis up Glottis down and open Esophageal sphincter contracted Relaxed muscles Contracted muscles Relaxed muscles

17 Movement of Digested Materials Movement through the digestive system (i.e. the alimentary canal) is created by muscle contractions called peristalsis Peristalsis progressive contraction of muscle around an organ; moves contents in one direction Peristalsis Animation What is reverse peristalsis?

18 Journey Through the Digestive System Food that has been chewed and swallowed travels down the esophagus to the stomach Esophageal sphincters or gates regulate the passage of food at the beginning and end of the esophagus Sphincters located at the beginning of the small intestine (i.e. pyloric sphincter --> duodenum) regulate the passage of digested food from the stomach into the rest of the digestive system

19 Stomach Primary function To continue digestion of food particles that have passed through the mouth, pharynx, and esophagus The combination of partially digested food and gastric juices produces chyme, a thick mixture of partially digested food The digestion of protein begins in the stomach due to the action of pepsin, a hydrolytic protease! -Pepsin is synthesized from an inactive precursor called! pepsinogen (a zymogen); HCl responsible for conversion

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21 Anatomy of the Stomach Esophagus Cardiac orifice Interior surface of stomach. The interior surface of the stomach wall is highly folded and dotted with pits leading into tubular gastric glands. Gastric gland. The gastric glands have three types of cells that secrete different components of the gastric juice: mucus cells, chief cells, and parietal cells. Mucus cells secrete mucus, which lubricates and protects the cells lining the stomach. Chief cells secrete pepsinogen, an inactive form of the digestive enzyme pepsin. Parietal cells secrete hydrochloric acid (HCl). 5 µm Pyloric sphincter Small intestine Epithelium Pepsinogen 2 HCl Chief cell 1 3 Pepsin (active enzyme) Parietal cell Folds of epithelial tissue Stomach 1 Pepsinogen and HCI are secreted into the lumen of the stomach. 2 HCl converts pepsinogen to pepsin. 3 Pepsin then activates more pepsinogen, starting a chain reaction. Pepsin begins the chemical digestion of proteins.

22 Stomach Wall The inside of the stomach is lined with thick mucus Mucus serves as an internal coating that protects the stomach from highly acidic stomach acid Very little, if any, absorption takes place inside of the stomach because of the mucus Bacteria Gastric ulcers, lesions in the lining are caused mainly by the bacterium Helicobacter pylori Mucus layer of stomach 1 µm

23 Functions of the Small Intestine Primary Functions 1) To continue digestion with the assistance of various enzymes from the pancreas and bile from the liver! 2) To begin the absorption of nutrients from chyme! -90% of nutrient absorption takes place in the! small intestine A cross-section through the small intestine reveals an intriguing structure

24 Structure of the Small Intestine Vein carrying blood to hepatic portal vessel Microvilli (brush border) Blood capillaries Epithelial cells Muscle layers Villi Large circular folds Lacteal Epithelial cells Key Nutrient absorption Intestinal wall Villi Lymph vessel Villi (s. villus) increase the surface area inside of the small intestine helping the organ absorb nutrients from digested food

25 Cross-section through the Small Intestine Increased surface area is essential for absorption in the intestine The small intestine is organized into folds. Each fold is called a villus. Villi increase the surface area inside of the small intestine Microvilli at the tip of each villus further increase the area available for absorption

26 Digestive Enzymes and Their Location in the Human Body Site Mouth Stomach Small intestine (from pancreas) Liver Enzyme Salivary amylase Pepsin Pancreatic Amylase and other carbohydrases Trypsin, Chymotrypsin Pancreatic Lipase Bile Role in Digestion Breaks down starches into smaller polysaccharides Breaks down proteins into small peptides Continues the breakdown of polysaccharides Continues the breakdown of proteins Breaks down fat into components Emulsification of fat

27 Digestive System Discussion Questions 1. Although enormous quantities of various enzymes are added to the contents of the duodenum of the small intestine, no traces of enzymatic activity are left in the intestinal contents when they pass into the large intestine (colon). Why? What happens to the enzymes?

28 Anatomy of the Liver, Gall Bladder, Pancreas, and Small Intestine Liver Bile duct Gallbladder Pancreas Duodenum Pancreatic duct To rest of small intestine

29 Structure of the Liver Liver cells synthesize and secrete bile! -1 liter of bile is synthesized daily! Bile enters the small intestine through the bile duct Bile can also be stored in the gall bladder Bile is responsible for the digestion of fats How does bile help the small intestine to digest fats???

30 Pancreas Primary Functions of the Pancreas 1) To produce a mixture of digestive enzymes that help to neutralize the acidic chyme arriving from the stomach!! Important enzymes coming from the pancreas include:!! Lipases = Fat-digesting enzymes!! Carbohydrases = Carbohydrate-digesting enzymes!! Proteases = Protein-digesting enzymes 2) The production of insulin and glucagon! -Insulin and glucagon regulate the amount of glucose! in the blood at any time

31 Structure of the Pancreas

32 Pancreatic Enzymes As mentioned before the pancreas secretes a mixture of digestive enzymes as food enters the small intestine Lipases: Responsible for digesting lipids or fats! Ex. Pancreatic lipase Proteases: Responsible for digesting proteins! Ex. Trypsin, Chymotrypsin Carbohydrases: Responsible for digesting carbohydrates (i.e. sugars and starches)! Ex. Pancreatic amylase

33 Functions of the Large Intestine Primary Functions 1) Absorption of water from digested food/chyme 2) Compaction and storage of feces 3) Production of essential vitamins! -Bacteria (E.coli) in! the large intestine! convert chemical! precursors into! vitamins (B 5, K,! biotin)

34 Digestive System Discussion Questions 2. Most of the blood that leaves the digestive tract of a human is collected into a series of veins that merge to form the hepatic portal vein. The hepatic portal vein carries blood to the liver. Liver capillaries drain into the hepatic vein which carries blood to the vena cava. The vena cava transports blood from the body to the right atrium. Some of the products of digestion enter a different system of transport, the lacteal system. The lacteal system bypasses the liver and carries its contents directly to the right atrium. Which products of digestion are carried in the blood to the liver? Which products of blood are carried via the lacteal system? How does the concentration of fat leaving the small intestine compare to the concentration in the right atrium?

35 Do Now - Digestive System Discussion Questions A friend of yours has come up with a new idea for people who don t have time to eat. She has developed a high-powered Blenderizer that breaks food up into very small particles. She has tested her product on amoeba and Paramecia. Both of these single-celled organisms can pick up these small particles and incorporate them into food vacuoles. Your friend is hoping to market the Blenderizer to busy people who could blenderize their food and use an IV bag and tube to run the food directly into their blood system. Your friend comes to you for advice and possible financial support to get her idea off the ground. What would you say to her?

36 Hormones Help Coordinate the Secretion of Digestive Juices into the Alimentary Canal Amino acids or fatty acids in the duodenum trigger the release of cholecystokinin (CCK), which stimulates the release of digestive enzymes from the pancreas and bile from the gallbladder. Gallbladder CCK Liver Duodenum CCK Enterogastrone Stomach Pancreas Secretin Key Stimulation Inhibition Gastrin Enterogastrone secreted by the duodenum inhibits peristalsis and acid secretion by the stomach, thereby slowing digestion when acid chyme rich in fats enters the duodenum. Gastrin from the stomach recirculates via the bloodstream back to the stomach, where it stimulates the production of gastric juices. Secreted by the duodenum, secretin stimulates the pancreas to release sodium bicarbonate, which neutralizes acid chyme from the stomach.

37 1. Barry is participating in a nutrition study in which he must follow a prescribed diet and have his blood tested regularly. On one of his visits, his test results indicate low levels of insulin, elevated levels of glucagon, and normal levels of cortisol and growth hormone. What would you expect his levels of blood glucose to be? Hormone Function Physiological condition Insulin Glucagon Lowers blood glucose levels Raises blood glucose levels; signals conversion of stored glycogen to glucose Insulin levels increase after large meal; decrease during fasting or between meals Glucagon levels increase during fasting or between meals, decrease upon consumption of food Epinephrine Increase blood glucose levels by signaling glycogen breakdown Increased metabolic activity; loss of blood volume or reduction in blood pressure

38 Homeostasis - Regulation of Glucose Levels 1 When blood glucose level rises, a gland called the pancreas secretes insulin, a hormone, into the blood. STIMULUS: Blood glucose level rises after eating. 2 Insulin enhances the transport of glucose into body cells and stimulates the liver and muscle cells to store glucose as glycogen. As a result, blood glucose level drops. 4Glucagon promotes the breakdown of glycogen in the liver and the release of glucose into the blood, increasing blood glucose level. Homeostasis: 90 mg glucose/ 100 ml blood STIMULUS: Blood glucose level drops below set point. 3 When blood glucose level drops, the pancreas secretes the hormone glucagon, which opposes the effect of insulin.

39 Negative Feedback - Regulation of Blood Sugar Insulin and Glucagon Signaling Stimulus: Rising blood glucose level (After a meal)

40 Negative Feedback - Regulation of Blood Sugar Insulin and Glucagon Signaling Stimulus: Removal of excess glucose from blood (Skipping a meal)

41 Hormones Regulate Both Long-term and Short-term Appetite by Affecting a Satiety Center in the Brain Produced by adipose (fat) tissue, leptin suppresses appetite as its level increases. When body fat decreases, leptin levels fall, and appetite increases. Secreted by the stomach wall, ghrelin is one of the signals that triggers feelings of hunger as mealtimes approach. In dieters who lose weight, ghrelin levels increase, which may be one reason it s so hard to stay on a diet. Ghrelin The hormone PYY, secreted by the small intestine after meals, acts as an appetite suppressant that counters the appetite stimulant ghrelin. Leptin PYY Insulin A rise in blood sugar level after a meal stimulates the pancreas to secrete insulin (see Figure 41.3). In addition to its other functions, insulin suppresses appetite by acting on the brain.

42 Leptin is a Critical Satiety Hormone Ob -/- (leptin-deficient) mouse Wild-type littermate