Exam 4 Study Aid
Exam 4 Study Aid ZOOL 4380
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This 20 page Study Guide was uploaded by Tiffany Schweda on Friday April 22, 2016. The Study Guide belongs to ZOOL 4380 at University of Texas at El Paso taught by DR. ZAINEB AL-DAHWI in Spring 2016. Since its upload, it has received 81 views. For similar materials see Vertebrate Physiology in Animal Science and Zoology at University of Texas at El Paso.
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Exam4Study Aid Chapter 8: Respiratory Systems The Alveoli are the Site of Gas Exchange in Mammals Mammalian respiratory system located within chest cavity – thorax – and is divided into an upper respiratory tract and a lower respiratory tract Upper respiratory contains Mouth Nasal cavity Pharynx Larynx Trachea Lower respiratory contains Bronchi Gas exchange surfaces Trachea branches into two primary bronchi which branch into smaller tubes called secondary ad tertiary bronchi and then into bronchioles Bronchioles terminate in thin-walled, blind-ended sacs called alveoli Alveoli are the site of gas exchange Alveolar epithelium is composed of two types of cells Type I Type II Thin Type I alveolar cells are responsible for gas exchange Thicker Type II alveolar cells are responsible for a variety of functions Maintaining the fluid balance across the lungs Secreting lipoproteins called surfactants Alveoli are wrapped with an extensive capillary network that covers 80-90% of the alveolar surface Both lungs are surrounded by the pleural sac Pleural sac consists of two layers of cells with a small amount of fluid between them forming a space called the pleural cavity Pleural fluid lubricates the pleura and allows the two layers to slide past each other during ventilation The pressure within the fluid of the pleural cavity is normally subatmospheric because the chest wall pulls on the outer layer of the pleura whereas the elasticity of the lungs tends to pull on the inner layer of the pleura Figure 9.24: Structure of mammalian lungs. Mammalian lungs consist of conducting airways, not involved in gas exchange, that terminate in a series of interconnected blind-ended sacs called alveoli that form the respiratory surface. The alveoli are polygonal in shape, with flattened walls and are wrapped in blood vessels and suspended in collagenous matrix. Figure 9.25: The relationship between the lungs, pleura and chest wall. At rest, the intrapleural pressure is lower than atmospheric pressure. This low pressure pulls on the lungs and keeps them expanded. Mammals Ventilate Their Lungs Tidily Mammals exhibit a tidal pattern of ventilation Inspiration begins when somatic motor neurons trigger the contraction of the diaphragm and the external intercostal muscles of the rib cage Contractions cause ribs to move outward and upward and the diaphragm to move down, expanding the volume of the thorax Increase in volume decreases intrathoracic pressure which pulls on outer layer of pleural sac, decreasing pressure within pleural cavity Decrease in intrapleural pressure results in an increase in the pressure difference across the alveolar walls Increase in the transpulmonary pressure gradient causes the lungs to expand, decreasing the pressure in the alveoli Expiration begins when the nerve impulses from the somatic motor neurons that innervate the external intercostal muscles and diaphragm stop Elastic recoil of the lungs decreases lung volume, causing alveolar pressure to increase and air to flow out of the lungs. Figure 9.26: Pressure changes in a mammalian lung during quiet breathing The Work Required for Ventilation Depends on Lung Compliance and Resistance Amount of energy needed to ventilate the lungs depends on the elastic properties of the lungs and chest wall and on the resistance to airflow in the pulmonary airways Compliance which expresses how easy it is to stretch a structure and elastance which expresses how readily the structure returns to its original shape Lung compliance can change as a result of disease Lung elastance is a measure of the degree of return to resting volume after the lung is stretched Surfactants Increase Lung Compliance One important force that resists lung inflation is surface tension in the thin layer of fluid that lines the small airways and alveoli of the lungs Surface tension can be altered by the addition of surfactant that disrupt these cohesive forces In humans, surfactant synthesis doesn’t begin until relatively late in embryonic development Airway Resistance Affects the Work Required to Breathe Airway resistance is the final determinant of the energy required for breathing Law of bulk flow and Poiseuille’s equation tell that airway diameter has an extremely large effect on airway resistance When airway diameter is small, airway resistance is high and the pressure gradient driving bulk flow must be larger During bronchodilation airway diameter increases, whereas during bronchoconstriction airway diameter decreases Oxygen Transport Oxygen can be transported from the respiratory surface to the tissues dissolved in the circulatory fluid Because the solubility of oxygen in aqueous fluids such as plasma is low, the amount of oxygen that can dissolve in the plasma is relatively small Metalloproteins greatly increase the amount of oxygen that can be carried in the blood At the respiratory surface much of the oxygen that diffuses into the blood binds to the metalloprotein oxygen carriers, thereby reducing blood PO2 There Are Three Main Types of Respiratory Pigment Metalloprotein oxygen carriers are often referred to as respiratory pigments Hemoglobins the most common type of respiratory pigment in animals, are found in a wide variety of taxa including vertebrates, nematodes, some annelids, some crustasceans and some insects Globins are structurally diverse but all share a characteristic tertiary structure called the globin fold Myoglobin is found in the muscles where it helps to provide the oxygen needed for metabolism Active hemoblobin molecules can be made up of between one and several hundred globin molecules and their associated heme groups A few families of marine annelids have unusual respiratory pigments called chlorocruorins Hemocyanins are found in both the arthropods and molluscs hoever the hemocyanin in these two groups appear to have independent evolutionary origins Hemerythrins are found in species from four invertebrate phyla The significance of the great variety of animal respirator pigments is not well understood Respiratory pigments likely represent an example of multiple independent solutions to the common problem of oxygen transport and storage Figure 9.29: Structure of mammalian hemoglobin. All hemoglobins consist of one or more globin proteins complexed to an iron-containing porphyrin ring. Most vertebrate hemoglobins are tetramers, composed of four globins and their heme groups. Mammalian hemoglobins are compsed of two alpha and two beta globin chains. Respiratory Pigments Have Characteristic Oxygen Equilibrium Curve An oxygen equilibrium curve shows the relationship between the partial pressure of oxygen in the plasma and the percentage of oxygenated respiratory pigment in a volume of blood As partial pressure increases, more and more pigment molecules will bind oxygen until the available molecules are fully bound to oxygen At this point the blood is saturated with oxygen Figure 9.30: Oxygen equilibrium curves. A: The percentage of saturation of a respiratory pigment as a function of oxygen partial pressure. B: The oxygen content of blood as a function of partial pressure for blood with high and low content of respiratory pigment. Figure 9.31: Cooperativity in oxygen binding. A: Monomeric respiratory pigments, such as mammalian myoglobin, do not bind oxygen cooperatively and have a hyperbolic oxygen equilibrium curve. Multimeric respiratory pigments, such as mammalian hemoglobin, often display cooperative binding. The result of this cooperative binding is a sigmoidal oxygen equilibrium curve. B: A model for mammalian hemoglobin cooperativity. Oxygenation causes tetrameric hemoglobin to transition between the tense state that is stabilized by salt bridges and has low oxygen affinity, and the relaxed state that is stabilized only by hydrogen bonds and has high oxygen affinity. Blood pH and Pco2 Can Affect Oxygen Affinity Changes in pH and Pco2 alter the shape of the oxygen equilibrium curve for the respiratory pigments in many species, a phenomenon called The Bohr effect The size of the Bohr effect differs among respiratory pigments Figure 9.32: The Bohr effect. Decreases in pH or increases in CO2 cause a right shift of the oxygen equilibrium curve Temperature Affect Oxygen Affinity Increases in temperature can decrease the oxygen affinity of respiratory pigments such as hemoglobin in many species Exercising muscles generate heat, which can increase the local temperature in the blood that perfuses the tissues Decrease in temperature increases hemoglobin oxygen affinity which could promote oxygen uptake Figure 9.34: Effects of temperature on oxygen equilibrium curves Oxygenic Modulators Can Affect Oxygen Affinity A variety of organic compounds can act as modulators of the oxygen affinity of respiratory pigments With increases in these compounds there is an increase in oxygen affinity Carbon Dioxide Transport Mitochondrial respiration produces carbon dioxide that must be transported out of the body Carbon dioxide is much more soluble in body fluids than is oxygen The circulatory system transports carbon dioxide from the tissues to the respiratory surface where it diffuses into the external environment Vertebrate Red Blood Cells Play a Role in CO2 Transport Carbonic anhydrase is present primarily within the red blood cells Most of the bicarbonate is carried in the plasma CO2 is produced by aerobic metabolism and rapidly diffuses out of tissues and into the red blood cells Process of Cl-/HCO3- exchange is known as the chloride shift Figure 9.37: Carbon dioxide transport in vertebrate blood. A: Carbon dioxide diffuses from the tissues into the red blood cell. Some binds to hemoglobin, forming carbaminohemoglobin (Hb*CO2). Carbonic anhydrase (CA) within the red blood cell catalyzes formation of HCO3-. The HCO3- is transported out of the red blood cell in exchange for Cl- (the chloride shift). The H+ ions produced by the CA reaction are buffered by hemoglobin. B: In the lungs, CO2, diffuses into the alveoli, and the CA equilibrium shifts to favor the formation of CO2, reducing the amount of HCO3- within the red blood cell. HCO3- enters the red blood cell in exchange for Cl-, and is converted to CO2, which then diffuses into the alveoli. Regulation of Vertebrate Respiratory Systems Ventilation is an automatic rhythmic process that continues even during the loss of consciousness Central pattern generators initiate ventilator movements in animals Respiratory rhythm generation has been most extensively studied in mammals Precise mechanisms of respiratory rhythm generation are still not fully understood Rhythm generators can work in a variety of ways Some combination of cells with intrinsic pacemaker properties and networks of groups of neurons cause the rhythmic firing of neurons in the respiratory rhythm generators Respiratory pattern generators send signals that are integrated by a variety of interneurons that ultimately send signals to the somatic motor neurons that control the skeletal muscles involved in breathing Figure 9.39: Location of the respiratory central patter generators in mammals Chemosensory Input Influences Ventilation Chemosensory input helps to modulate the output of the central pattern generators Oxygen sensing is of primary importance in water-breathing vertebrates The central chemoreceptors respond to pH changes in the cerebrospinal fluid Figure 9.40: Reflex regulation of ventilation in mammals Chapter 11: Digestion The Digestive of Complex Animals Maximize Surface Area The surface of the gut has a complex topography that serves to maximize surface area Where the surface of the gut tissue is arranged into fingerlike projections called villi Enterocytes possess microscopic protrusions, supported by the actin cytoskeleton, called microvilli Intestinal epithelium is often called the brush border Figure 11.18: Intestinal topography. A: The inner surface of the intestine is a series of folds or ridges that run circularly around the intestine. B: The surface of the tissue is arranged into fields of fingerlike projections called villi. C: Each of the absorptive cells within the villi possesses projections called microvilli. This structural topography – circular folds, villi, and microvilli – increases the surface area that is available for absorption. Salivary Glands Secrete Water and Digestive Enzymes Digestion depends on secretions from multicellular exocrine glands working in conjunction with single secretory cells scattered throughout the GI tract Figure 11.20: Ruminants. Many mammals possess chambers derived from the GI tract that house bacteria that can ferment cellulose. Ruminants, including the cow shown here, possess four chambers Figure 11.21: Salivary glands. Like most mammals, the dog has multiple sets of salivary glands that secrete liquid and enzymes into the oral cavity. The Stomach Secretes Acid and Mucus The surface of the stomach is an epithelium composed of columnar epithelial cells The cells are linked together via tight junctions that prevent the leakage of lumen fluids into the tissue Mucous neck cells, found near the pit opening, secrete an acid type of mucus Parietal cells in the middle of the pit secrete acid, mainly HCl Chief cells near the base of the pit secrete digestive enzymes, primarily the protease pepsin Enteroendocrine cells secrete several hormones into the blood in response to stomach contents Figure 11.22: Stomach cell structure. The smooth surface of the stomach has numerous cavities called gastric pits. These pits are composed of four main cell types that control the secretions of mucus, acid, enzymes, and hormones. They are also the location where the Helicobacter pylori accumulate. Most Nutrients Are Absorbed in the Intestines The intestines are also rich in histological diversity A cross-section through the intestine reveals the four major layers Mucosa Submucosa Circular smooth muscle Longitudinal smooth muscle Much of the mucosa is composed of enterocytes, the absorptive cells with abundant microvilli Mucus-secreting goblet cells are scattered among the enterocytes Enteroendocrine cells secrete the hormones that help regulate digestion and nutrient assimilation At the base of each villus is a region call the crypt of Lieberkuhn In addition to enterocytes there are also Paneth cells which secrete antimicrobial molecules into the lumen The small intestine also receives secretions of bile from the gallbladder Bile is a complex solution of digestive chemicals and liver waste products Only two types of molecules in bile have a role in digestion Phospholipids Bile salts Phospholipids aid in the uptake of lipids Bile salts help emulsify fats in the duodenum Part of the pancreas is an exocrine gland that secretes digestive enzymes into the duodenum Proteases are produced in the form of inactive proenzymes which prevent the enzyme from digesting the secretory cell itself Figure 11.24: Bile production, storage and secretion. Bile is produced by hepatocytes and released into small adjacent ducts. These ducts collect bile and empty into the common hepatic duct. When the bile duct sphincter is closed, bile is routed through the cystic duct to the gallbladder for storage. When the sphincter opens, bile is released from the gallbladder into the duodenum. Figure 11.25: Trypsinogen cascade. The pancreas secretes three important proteases, all in inactive forms. Trypsinogen is activated by proteolytic cleavage by enterokinase. The activated typsin then activates chymotrypsinogen and procarboxypeptidase by proteolytic cleavage. Hormones Control the Desire to Feed Control of appetite has been best studied in mammals because of the implications for human obesity These studies have identified more than 20 different regulatory factors that link nutrition, metabolism, and feeding Some regulatory factors are produced in the vicinity of the GI tract Figure 11.26: Control of appetite. Appetite is controlled by the neurons of the arcuate nucleus of the hypothalamus, which interacts with hormones secreted from the GI tract and adipose tissue. Release of the neurotransmitter neuropeptide Y (NPY) stimulates appetite, whereas release of the neurotransmitter proopiomelanocortin (POMC) depress appetite. These neurons, through their neurotransmitters, affect the appetite centers of the brain directly, or antagonize the release of neurotransmitters from other neurons. Leptin exerts its appetite-suppressing effects by inhibiting NPY-releasing neurons and stimulating POMC-releasing neurons. Appetite is increased by the actions of other hormones on NPY-releasing neurons: ghrelin stimulates and peptide YY inhibits these neurons. Hormones and Neurotransmitters Control Secretions Once food enters the gut the GI tract secretes a spectrum of chemicals and enzymes that digest the food in forms that can be taken up The stomach is acidified when parietal cells in the gastric lining secrete HCl Once food passes from the stomach to the upper intestine, secretions alter the pH of the bolus and bombard it with a different suite of digestive chemicals Figure: 11.27: Control of gastric secretion of acid and pepsinogen. Gastric cells secrete acid (parietal cells) and pepsinogen (chief cells) in response to signals relayed from the central nervous system and from the food itself, acting through chemoreceptors and mechanoreceptors. Figure 11.28: Control of intestinal secretion. The acidic fluids that exit the stomach trigger intestinal secretion. The secretions neutralize the acidic fluids (via bicarbonate and bile), and aid in digestion through digestive enzymes (proteases, lipase, nucleases, amylases) and bile, which emulsifies lipids.
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