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CIRCULATION AND GAS EXCHANGE CHAPTER 42 CIRCULATION Figure 42.1 Internal transport in the cnidarian Aurelia SOME TERMS • Open circulatory system – blood bathes internal organs directly • Closed circulatory system – blood is confined to vessels and is distinct from interstitial fluid • Atrium (atria) – chambers of heart that receive blood • Ventricle - chambers of heart that pump blood out of heart Figure 42.2 Open and closed circulatory systems • Arteries – carry blood away from heart • Arterioles (small arteries) • Capillaries – microscopic vessels where gas and chemical exchanges takes place • Venules (small veins) • Veins – carry blood to heart • Pulmocutaneous circuit – leads to gas exchange in tissues • Systemic circuit – carries oxygen rich blood to body and oxygen poor blood to right atrium • Double circulation – when blood is pumped a second time after it loses pressure in capillaries Figure 42.3 Generalized circulatory schemes of vertebrates MAMMALIAN HEART • Atrioventricular valve – valves between each atrium and ventricle; prevent back-flow • Semilunar valves – valves at two exits of heart (at pulmonary artery and aorta) • Heart rate – number of heartbeats per minute (measured by taking pulse) Figure 42.4 The mammalian cardiovascular system Animations • • • • Just heart pumping Basic circulation Breathing http://www.smm.org/heart/lessons/lesso n5.htm Figure 42.5 The mammalian heart: a closer look CARDIAC CYCLE • One complete cycle of pumping and filling –Systole – contraction phase –Diastole – relaxation phase • Blood pressure is systole over diastole (For example: 110/80) Figure 42.6 The cardiac cycle HEART BEAT • Sinoatrial (SA) node or pacemaker – maintains heart beat by setting rhythm at which all cardiac cells contract – Located in wall of right atria – Generates nerve pulses – First pulse contracts atria together – SA node controlled by two nerves, hormones (ex. Epinephrine), body temp, exercise • Hits atrioventricular (AV) node –In wall between right atrium and right ventricle –Pulse contracts both ventricles about 0.1 seconds behind atria’s contractions • Electrocardiogram (ECG OR EKG) – currents recorded Figure 42.7 The control of heart rhythm STRUCTURE OF VESSELS • Veins have flaps to prevent back flow • Arteries have thicker layers than veins in order to handle the higher pressure • Capillaries thinnest and lack outer two walls Figure 42.8 The structure of blood vessels BLOOD FLOW • Blood moves fastest in arteries and slowest in capillaries –Total diameter of capillaries is greater than arteries so blood moves slowest in capillaries –Speeds up a little in veins because of a decrease in area Figure 42.9 Blood flow in veins Figure 42.12 Blood flow in capillary beds Figure 42.13 The movement of fluid between capillaries and the interstitial fluid BLOOD PRESSURE • The hydrostatic force that blood exerts on the wall of a vessel • Greatest in arteries –Blood enters arteries faster than it can leave so arteries stretch –Heart contracts and send more blood into arteries before artery is completely relaxed –This means there is always at least some pressure in arteries caused by the impedance of the arterioles = peripheral resistance –Smooth muscles relax, blood flow increases and pressure decreases –Almost no pressure in capillaries –Veins use flaps, smooth muscle contractions and skeletal muscles Figure 42.11 Measurement of blood pressure Figure 42.10 The interrelationship of blood flow velocity, crosssectional area of blood vessels, and blood pressure LYMPHATIC SYSTEM • Lost fluid and proteins from capillaries returns to heart via lymphatic system • fluid is then called lymph • vessels like veins (flaps) • empties back into blood near venae cavae and right atrium junction • lymph nodes filter lymph –filled with white blood cells BLOOD • Plasma - liquid matrix; 90% water; also includes ions, proteins, gases, and nutrients • Erythrocytes (red) –lack nuclei in mammals –lack mitochondria –hemoglobin carries oxygen Figure 42.14 The composition of mammalian blood Figure 42.14x Blood smear • Leukocytes (white) –fight disease –monocytes, neutrophils, basophils, esinophils, lymphocytes • Platelets –fragments –aid in blood clotting CELL DIFFERENTIATION • Pluripotent cells in red bone marrow develop into white and red cells • Erythropoietin - stimulates production of red blood cells if low oxygen in tissues Figure 42.15 Differentiation of blood cells BLOOD CLOTTING • Inactive fibrinogen is activated by clotting factors from platelets to make fibrin • Fibrin forms thread-like clot • Hemophiliac cannot make one of the clotting factors Figure 42.16a Blood clotting Figure 42.16x Blood clot • • • • CARDIOVASCULAR DISEASE Heart attack- death of cardiac muscle tissue resulting from blockage of coronary arteries (supply oxygen to heart) Stroke - death of nervous tissue in brain, usually resulting from blockage of arteries in head Thrombus - blood clot Embolus - transported clot (to brain or heart) • Atherosclerosis - chronic cardiovascular disease where plaques develop on inner walls of arteries –Arteriosclerosis – when plaque becomes even more hardened by calcium deposits –Common sites of thrombus formation –Embolus more likely to get trapped Figure 42.17 Atherosclerosis: normal artery and artery with plaque • Hypertension – high blood pressure increases risk of heart attack and stroke –Possibly because high blood pressure damages lining and promotes plaque formation • Low density lipoproteins – deposits cholesterol • High density lipoproteins – may reduce cholesterol deposition GAS EXCHANGE Figure 42.18 The role of gas exchange in bioenergetics Figure 42.19 Diversity in the structure of gills, external body surfaces functioning in gas exchange OVERVIEW • Gas exchange can occur across cell membranes (in unicellular organisms), moist skin, gills, tracheae, and lungs • All respiratory surfaces must be moist. • Gills – outfoldings of body surface specialized for gas exchange –Advantage – cells always moist –Disadvantage – lower oxygen in water than air and saltier/warmer water has less oxygen –Ventilation – increases flow of water over cells Figure 42.0 External gills of a salmon –Countercurrent exchange – as blood flows through capillaries it becomes loaded with more oxygen, but also encounters water that has higher oxygen levels • This allows diffusion of oxygen into blood for entire length of capillary Figure 42.20 The structure and function of fish gills Figure 42.21 Countercurrent exchange TRACHEAL SYSTEMS • In insects, made up of air tubes throughout body • Largest tubes (tracheae) open to outside –Diffusion –Larger insects’ body movements contract tubes (move air through) Figure 42.22 Tracheal systems LUNGS • Restricted to one location • Must be connected to circulatory system –Frogs supplement lungs with moist skin –Turtles supplement lungs with moist mouth and anus • • • • MAMMALIAN RESPIRATORY SYSTEM Larynx – upper part of trachea –Vocal cords Trachea, bronchi, bronchioles, alveoli (air sacs) Beating cilia and mucas trap contaminants Alveoli (air sacs) – millions of single cells where gas exchange occurs between the sacs and the blood Figure 42.23ab The mammalian respiratory system Figure 42.23c Alveoli Figure 42.23cx1 Alveolar structure of mouse lung Figure 42.23cx2 Alveolar structure of mouse lung BREATHING • Positive pressure breathing – air pushed down trachea • Negative pressure breathing – air pulled down trachea –Diaphragm – skeletal muscle at bottom of rib cage Figure 42.24 Negative pressure breathing • Tidal volume – normal breath volume • Vital capacity – maximum volume of air that can be exhaled and inhaled • Residual volume – air remains in alveoli even after we exhale • Birds –Air sacs that help keep air flowing through lungs and trim density of bird Figure 42.25 The avian respiratory system CONTROL OF BREATHING • Medulla oblongata and pons are two control centers • Medulla monitors CO2 levels by monitoring pH level and increases breathing if CO2 levels are too high • Carotid arteries monitor O2 and CO2 levels and report to brain Figure 42.26 Automatic control of breathing DIFFUSION OF GASES • Gas always move from region of higher partial pressure to lower pressure • Partial pressure of oxygen in atmosphere at sea level is 160 mm Hg Figure 42.27 Loading and unloading of respiratory gases Figure 42.28 Oxygen dissociation curves for hemoglobin OXYGEN TRANSPORT • Protein pigments with metal ions that carry oxygen • Hemocyanin – in many mollusks and arthropods; has copper • Hemoglobin – in most vertebrates; has Fe; can carry 4 oxygen molecules • Hemoglobin unloads its oxygen when the partial pressure of oxygen surrounding the red blood cell decreases. • disassociation curve • Bohr shift – slight drop in pH causes hemoglobin to give up more oxygen CARBON DIOXIDE • 7% dissolved in blood • 23% binds to hemoglobin • 70% transported in blood as bicarbonate ions –Buffers blood – can release and add H+ as needed thereby changing pH of blood Figure 42.29 Carbon dioxide transport in the blood Figure 42.30 The Weddell seal, Leptonychotes weddelli, a deep-diving mammal Dissociation curves for two hemoglobins