Chapter 4: Circulation and Gas Exchange AP Biology 13 1 Gas Exchange Unicellular organisms - gas exchange occurs directly with the environment Multicellular organisms - direct gas exchange is not possible Fig. 4.1 Gills are and example of a gas exchange mechanism O diffuses from water to blood vessels diffuses from blood to water Circulatory System and Phylogeny Transport systems connect the organs of exchange with body cells Internal transport systems circulate fluid that provides a link between the aqueous cell environment and the exchange organs (lungs) Invertebrate circulation Circular canal Radial canals Mouth 5 cm Gastrovascular cavity Mouth Pharynx mm (a) The moon jelly Aurelia, a cnidarian (b) The planarian Dugesia, a flatworm Simple animals (like cnidarians) have a body wall only two cells thick with a gastrovascular cavity (functions in both digestion and distribution of substances throughout the body) More complex animals have either an open or closed circulatory system (a) An open circulatory system Heart Hemolymph in sinuses surrounding organs Pores (b) A closed circulatory system Heart Interstitial fluid Blood Small branch vessels in each organ Dorsal Auxiliary vessel hearts (main heart) Tubular heart Both have a circulatory fluid (blood), set of tubes (vessels), and a muscular pump (heart) Figs. 4. & 4.3 Ventral vessels 3
Cardiovascular System Vertebrates - closed circulatory system called a cardiovascular system Blood flows in a closed system consisting of blood vessels and a two to four chambered heart Arteries carry blood to (site of chemical exchange between blood and intestinal fluid) Veins return blood from to heart (a) Single circulation Artery Heart: Atrium (A) Ventricle (V) Vein Key Oxygen-rich blood Oxygen-poor blood Gill Body Figs. 4.4 & 4.5 Fish - heart has two chambers (one ventricle and one atrium) Amphibians Pulmocutaneous circuit Blood pumped from ventricle travels to gills where it picks up O and disposes of Amphibians - have a three chambered heart with two atria and one ventricle Atrium (A) Lung and skin Atrium (A) Ventricle pumps blood into a forked artery and splits the output into pulmocutaneous circuit and systemic circuit Right Ventricle (V) Systemic circuit Systemic Key Oxygen-rich blood Oxygen-poor blood 4 Reptiles (Except Birds) Cardiovascular System circuit Lung Reptiles - have double circulation with a pulmonary circuit and a systemic circuit Turtles, snakes, and lizards have a three-chambered heart Mammals and birds - ventricle is completely divided into separate right and left chambers side of the heart pumps and receives only oxygen-rich blood Atrium (A) Ventricle (V) Right systemic aorta Right A V Systemic circuit Figs. 4.4 & 4.5 systemic aorta Incomplete septum Systemic (b) Double circulation Key Oxygen-rich blood Oxygen-poor blood circuit Lung Right side receives and pumps only oxygen-poor blood A V Right A V Four-chambered heart was an essential adaptation of the endothermic way of life Key Systemic circuit Oxygen-rich blood Oxygen-poor blood Systemic 5 Double Circulation Depends on anatomy and pumping cycle of the heart Structure and function of the human circulatory system can serve as a model for exploring mammalian circulation in general Heart valves - dictate one-way flow of blood through the heart Pattern of flow: Blood flow begins with the right ventricle pumping blood into the lungs (loads O and unloads ) Oxygen-rich blood then enters the left atrium and is pumped to the body tissues by the left ventricle Superior vena cava artery of right lung vein Right atrium Right ventricle Inferior vena cava Aorta of head and forelimbs artery of left lung atrium ventricle Aorta vein of abdominal organs and hind limbs Blood returns to the heart through the right atrium Fig. 4.6 6
Mammalian Heart Contract and relaxes in a rhythmic cycle called the cardiac cycle artery Right atrium Semilunar valve Aorta artery atrium Semilunar valve Systole - contraction/ pumping phase Diastole - relaxation/ filling phase Heart rate is called the pulse (beats per minute) 1 Atrial and ventricular diastole Atrioventricular valve Right ventricle Atrial systole and ventricular diastole ventricle Atrioventricular valve Cardiac output - volume of blood pumped into the systemic circulation per minute.1 sec.3 sec.4 sec Figs. 4.7 & 4.8 3 Ventricular systole and atrial diastole 7 Heart Rhythm Some muscle cells are self-excitable (contract without any signal from the nervous system) Sinoatrial (SA) node (pacemaker) - sets the rate and timing at which all cardiac muscle cells contract (influenced by nerves, hormones, body temperature, and exercise) Impulses from the SA node travel to the atrioventricular (AV) node Impulse is delayed at the AV node and then travels to the Purkinje fibers that make the ventricles contract Impulses can be recorded by an electrocardiogram (ECG or EKG) 1 3 4 SA node (pacemaker) ECG AV node Bundle branches Heart apex Purkinje fibers Fig. 4.9 8 Artery Vein Blood Circulation Same physical properties that govern water flowing through a pipe govern blood circulation. LM Red blood cells 1 µm Basal lamina Endothelium Endothelium Smooth Smooth muscle muscle Connective Capillary Connective tissue tissue Valve All blood vessels are built of similar tissues and have three similar layers Artery Vein Structural differences in arteries, veins, and correlate with different functions Arteriole Red blood cell Capillary Venule 15 µm Arteries have thicker walls to accommodate high pressure blood pumped from the heart Veins have thinner walls because blood flows back to the heart as a result of muscle contraction Direction of blood flow in vein (toward heart) Valve (open) Skeletal muscle Valve (closed) LM Fig. 4.1 & 4.13 9
Blood Circulation Velocity of blood flow varies in the circulatory system Slowest in the capillary beds because of high resistance and large total crosssectional area Blood pressure is the hydrostatic pressure that blood exerts against the wall of a vessel Systolic pressure is the pressure in the arteries during ventricular systole (highest pressure in the arteries) Area (cm ) Velocity (cm/sec) Pressure (mm Hg) 5, 4, 3,, 1, 5 4 3 1 1 1 8 6 4 Diastolic pressure Aorta Systolic pressure Arteries Arterioles Venules Veins Venae cavae Blood pressure reading: 1/7 1 3 Diastolic pressure is the pressure in the arteries during diastole (lower than systolic pressure) 1 1 7 Determined by cardiac output and resistance Artery closed Sounds Sounds audible in stop stethoscope Figs. 4.11 & 4.1 1 Precapillary sphincters Thoroughfare channel Usually filled to capacity Two mechanisms that regulate distribution of blood in capillary beds: One mechanism involves contraction of smooth muscles in the wall of an arteriole to constrict the vessel Arteriole (a) Sphincters relaxed Venule Second involves precapillary sphincters to control the flow of blood between arterioles and venules Critical exchange of substances between the blood and interstitial fluid takes place in the thin endothelial wall of the Arteriole Venule (b) Sphincters contracted Fig. 4.14 11 Difference between blood pressure and osmotic pressure drives fluid out of the at the arteriole end and into the at the venule end The lymphatic system returns fluid from the body from the capillary beds and also aids in defense Fluid directly reenters circulation at the venous end of the capillary bed and indirectly through the lymphatic system INTERSTITIAL FLUID Net fluid movement out Body cell Blood pressure Osmotic pressure Arterial end of capillary Direction of blood flow Venous end of capillary Fig. 4.15 1
Lymphatic System Returns fluid that leaks out from the capillary beds Fluid (called lymph) reenters the circulation directly at the venous end of the capillary bed and indirectly through the lymphatic system which drains into veins in the neck Valves in the lymph vessels prevent the backflow of fluid Lymph nodes filter lymph and help in body defenses Fig. 4.16 13 Connective tissue with cells suspended in plasma Blood Plasma 55% Constituent Major functions Fig. 4.17 Consists of several kinds of cells (45% of blood) Red blood cells (transport oxygen) Water Ions (blood electrolytes) Sodium Potassium Calcium Magnesium Chloride Bicarbonate Solvent for carrying other substances Osmotic balance, ph buffering, and regulation of membrane permeablity Separated blood elements White blood cells (defense) Plasma proteins Albumin Osmotic balance, ph buffering Fibrinogen Clotting Immunoglobulins (antibodies) Defense Platelets (involved in clotting) Substances transported by blood Nutrients Respiratory gases Waste products Hormones Blood plasma is about 9% water with solutes like inorganic salts in the form of dissolved ions (electrolytes) Plasma also contains proteins which influence ph, osmotic pressure, and viscosity. These proteins also function in lipid transport, immunity, and blood clotting. Separated blood elements Cellular elements 45% Cell type Number per µl Functions (mm 3 ) of blood Leukocytes (white blood cells) 5, 1, Defense and immunity Lymphocytes Basophils Eosinophils Monocytes Neutrophils Platelets 5, 4, Blood clotting Erythrocytes (red blood cells) 5 6 million Transport of O and some 14 Blood Cells Stem cells (in bone marrow) Erythrocytes - red blood cells (transport oxygen) Leukocytes - white blood cells (defense) Monocytes, neutrophils, basophils, eosinophils, and lymphocytes Function by phagocytizing bacteria and debris by producing antibodies B cells T cells Lymphocytes Lymphoid stem cells Myeloid stem cells Erythrocytes Neutrophils Basophils Monocytes Platelets Eosinophils Stem cells help to replace worn out cells throughout an animal s life Fig. 4.16 All blood cells develop from a common source 15
Clotting When the endothelium of a blood vessel is damaged the mechanism of clotting begins A cascade of reactions converts fibrinogen to fibrin forming a clot 1 3 Collagen fibers Platelet Platelet plug Fibrin clot Red blood cell 5 µm Clotting factors from: Platelets Damaged cells Plasma (factors include calcium, vitamin K) Fibrin clot formation Enzymatic cascade + Prothrombin Thrombin Fibrinogen Fibrin Fig. 4.18 16 Cardiovascular Disease Disorders of the heart and blood vessels (account for more than half of the deaths in the U.S.) Lumen of artery Endothelium 1 Smooth muscle Plaque Atherosclerosis - caused by buildup of cholesterol within arteries Hypertension - high blood pressure (promotes atherosclerosis and increased risk of heart attack or stroke) Heart attack (myocardial infarction) - death of cardiac muscle tissue resulting from a blockage of one or more coronary arteries LDL 3 Foam cell Macrophage Plaque rupture Extracellular matrix 4 Smooth muscle cell T lymphocyte Fibrous cap Cholesterol Stroke - death of nervous tissue in the brain usually from a rupture or blockage of arteries in the brain Fig. 4. 17 Gas Exchange Supplies oxygen for cellular respiration and disposes of carbon dioxide Animals require large, moist, respiratory surfaces for the adequate diffusion of respiratory gasses between the cells at the respiratory medium (either air or water) 18
Gills Outfoldings of the body surface specialized for gas exchange In some invertebrates the gills have a simple shape and are distributed all over the body Parapodium (functions as gill) (a) Marine worm Segmented worms have flaplike gills that extend over body segments Gills (b) Crayfish Clams and crayfish are restricted to a local body region Coelom Fig. 4. Gills Tube foot 19 (c) Sea star Gills Effectiveness of gas exchange in some gills (including fish) Increased by ventilation and countercurrent flow of blood and water O-poor blood Gill arch O-rich blood Lamella Blood vessels Gill arch Water flow Operculum Water flow Blood flow Countercurrent exchange PO (mm Hg) in water 15 1 9 6 3 Gill filaments Fig. 4.3 Net diffusion of O 14 11 8 5 PO (mm Hg) in blood Tracheal Systems Insects have a tracheal system that consists of tiny branching tubes that penetrate the body The tubes supply oxygen directly to the body cells Muscle fiber.5 µm Tracheoles Mitochondria Tracheae Air sacs Body cell Air sac Tracheole Fig. 4.4 Trachea External opening Air 1
Lungs Spiders, land snails, and most terrestrial vertebrates have internal lungs System of branching ducts that conveys air to the lungs Air passes through the nostrils passes through the pharynx, trachea, bronchi, bronchioles, and alveoli (where gas exchange occurs) Pharynx Larynx (Esophagus) Trachea Right lung Bronchus Branch of pulmonary vein (oxygen-rich blood) Nasal cavity lung Terminal bronchiole Branch of pulmonary artery (oxygen-poor blood) Alveoli 5 µm Bronchiole Diaphragm (Heart) Dense capillary bed enveloping alveoli (SEM) Fig. 4.5 Ventilation of the lungs Breathing Amphibians ventilate by positive pressure breathing which forces air down the lungs Mammals ventilate lungs by negative pressure breathing (pulls air into the lungs) Lung volume increases as the rib muscles and diaphragm contract 1 Rib cage expands. Air inhaled. Rib cage gets smaller. Air exhaled. Lung Diaphragm Fig. 4.8 3 Birds Breathing Anterior air sacs Also have air sacs that function as bellows which keep air flowing through the lungs Air passes through the lungs in one direction only (every exhalation completely renews the lungs) Posterior air sacs Lungs Posterior Lungs air sacs 3 1 First inhalation 1 mm 3 Second inhalation First exhalation 4 Second exhalation Airflow Air tubes (parabronchi) in lung Anterior air sacs 4 1 Fig. 4.7 4
Control of Breathing Main breathing control centers are in two regions of the brain (medulla oblongata and the pons) Medulla regulates the rate and depth of breathing in response to ph changes in the cerebrospinal fluid Adjusts breathing rate and depth to match metabolic demands level decreases. Homeostasis: Blood ph of about 7.4 Response: Rib muscles and diaphragm increase rate and depth of ventilation. Sensor/control center: Cerebrospinal fluid Stimulus: Rising level of in tissues lowers blood ph. Carotid arteries Aorta Sensors in the aorta and carotid arteries monitor O and concentrations in the blood and exert a secondary control Medulla oblongata Fig. 4.9 5 Gas Transport Gasses diffuse down pressure gradients in the lungs and other organs Diffusion of a gas depends on differences in quantity called partial pressure Gases always diffuse from a region of high partial pressure to a region of low partial pressure In the lungs and tissues, O and diffuse from where their partial pressures are higher to where they are lower Partial pressure (mm Hg) 16 1 8 4 Inhaled air 1 Fig. 4.3 7 8 Exhaled air 1 Alveolar epithelial cells arteries O 6 Systemic 4 veins Heart Inhaled air Alveolar spaces Alveolar veins Systemic arteries Systemic O 5 Body tissue (a) The path of respiratory gases in the circulatory system (b) Partial pressure of O and at different points in the circulatory system numbered in (a) 3 P O P Exhaled air 3 4 5 6 7 8 6 Gas Transport Respiratory pigments are the proteins that transfer oxygen Hemoglobin is the respiratory pigment in almost all vertebrates Contained in erythrocytes Must reversibly bind O when loading in the lungs and unloading at the other body tissues Binding of O to one subunit of hemoglobin increases the O affinity in the other subunits Drop in ph lowers affinity for O Heme group Iron atom Polypeptide chain O loaded in lungs O unloaded In tissues O O O saturation of hemoglobin (%) 1 8 6 4 4 6 8 1 Tissues during exercise (a) P O and hemoglobin dissociation at ph 7.4 O unloaded to tissues at rest O unloaded to tissues during exercise Tissues at rest P O (mm Hg) O saturation of hemoglobin (%) 1 8 6 4 Lungs Fig. 4.31 ph 7.4 ph 7. Hemoglobin retains less O at lower ph (higher concentration) 4 6 8 1 P O (mm Hg) (b) ph and hemoglobin dissociation 7
Gas Transport Hemoglobin also helps in the transport of Also assists in buffering Carbon from respiring cells diffuses into the blood plasma and then into erythrocytes and is ultimately released in the lungs Body tissue Interstitial fluid Plasma within capillary Red blood cell H O produced H CO 3 Carbonic acid HCO 3 - Bicarbonate + HCO 3 - H + Hb To lungs transport from tissues Capillary wall Hemoglobin (Hb) picks up and H +. Fig. 4.3 HCO 3 - H O HCO 3 - + H CO 3 To lungs H + Hb transport to lungs Hemoglobin releases and H +. Alveolar space in lung 8 Helpful Adaptations Migratory and diving mammals have adaptations that allow them to perform extraordinary feats Extreme O consumption of the antelope-like pronghorn allows it to run at high speeds over long distances Deep-diving air breathers have to stockpile O and deplete it slowly 9