Chapter 42: Circulation / Gas Exchange. d = t 2

Transcription

1 Chapter 42: Circulation / Gas Exchange Transport systems connect organs of exchange with body cells Diffusion Lung Blood 100 m 1 s 1 mm 100 s 1 cm s d = t 2 Bulk Flow (Pressure) Blood Cells Methods of Fluid Circulation: 1) Gastrovascular Cavities (e.g. cnidarians / flatworms) Digestive cavity also serves to distribute nutrients (diffusion to body cells) Campbell et al. Figure

2 Methods of Fluid Circulation: 2) Open Circulatory Systems (e.g., insects / arthropods / mollusks) Three basic components: 1) Circulatory fluid (= blood) 2) Set of tubes (= blood vessels) 3) Muscular pump (= heart) No distinction between blood and interstitial fluid ( blood = hemolymph) Campbell et al. Figure ) Closed Circulatory System (e.g., vertebrates) Blood is confined to vessels (distinct from interstitial fluid) Cardiovascular System: Elastic Arteries Muscular Arteries Arterioles Heart Vessel Types: 1) Arteries (away from heart) 2) Capillaries 3) Veins (toward heart) Capillaries Veins Venules 2

3 Campbell et al. Figure 42.4 / 42.5 Metabolic rate critical factor in evolution of cardiovascular systems: ( metabolic rate = complexity of system) 2 Chambered Heart (e.g., fish) 3 Chambered Heart (e.g., amphibian) 4 Chambered Heart (e.g., mammals / birds) Slow flow of blood to systemic circuit (= constrains O 2 movement to tissue) Mixing of oxygen-rich blood and oxygen-poor blood (= constrains O 2 delivery) Complete separation of O 2 -rich and O 2 -poor blood (= enhanced O 2 delivery) Overview of Mammalian Cardiovascular System: Atria: Receiving chambers Small, thin-walled Ventricles: Discharging chambers Large, thick-walled (Left >> Right) Campbell et al. Figure

4 Campbell et al. Figure 42.8 Cardiac Cycle (one complete pumping and filling of the heart): Systole: Contraction phase of heart Diastole: Relaxation phase of heart Valves supply one-way flow of blood: Atrioventricular valves Semilunar valves Heart murmur Cardiac Output: Volume of blood / minute pumped out by a ventricle CO average = 70 beats / min x 75 ml / beat = 5.25 L / min CO = HR x SV Heart Rate Stroke Volume Campbell et al. Figure 42.9 Intrinsic Conduction System (coordinates heart beat): Step 1: Depolarization wave initiated by sinoatrial node (SA Node = pacemaker) Located in right atrial wall; auto-rhythmic cells (100 beats / min) Step 2: Impulse briefly delayed at atrioventricular node (AV Node) Allows for atria to complete contractions Parasympathetic control Step 3: Impulses pass down bundle branches to apex of heart before racing up Purkinje fibers, triggering contraction of ventricles 4

5 Similar to Campbell et al. Figure Anatomy of Blood Vessels: Elastic Fibers Thick muscular layer elasticity Thin-walled Large lumen Vascular Sink (~ 65% of blood) Only endothelium (nutrient exchange) 5

6 Physical Laws Govern Movement of Blood Through Vessels: Blood Flow Velocity: Law of Continuity: When the diameter of a pipe narrows along its length, fluids will flow through the narrow section faster than the wider sections (volume constant) Thus, blood should move most rapidly through capillaries - Right? WRONG Capillaries are arranged in beds Total cross sectional area much larger than found in arteries and veins Benefits: 1) Nutrient exchange 2) Damage control Campbell et al. Figure Campbell et al. Figure Physical Laws Govern Movement of Blood Through Vessels: Blood Pressure: Pressure gradients drive blood flow through body Blood Pressure = Force per unit area on wall of vessel (mm Hg) Systolic Pressure: Pressure from ventricular contraction (~ 120 mm Hg) Valves Muscular pumps Diastolic Pressure: Pressure from ventricular relaxation (~ 80 mm Hg) Blood Pressure = Cardiac Output x Peripheral Resistance Regulatory mechanisms adjust CO / PR to keep relatively constant BP Amount of friction blood encounters passing through vessels Blood viscosity Vessel length Vessel diameter 6

7 Campbell et al. Figure Transfer of Nutrients Occurs at the Capillaries: Capillary bed activity varies over time time depending on needs of tissues Regulatory Mechanisms: 1) Arterioles constrict Flow to bed decreased 2) Capillary sphincters constrict Flow through bed decreased Lymphatic System Returns Fluid to Blood: ~ 4 L of fluid lost to tissues per day Fluid enters lymph capillaries (fluid = lymph) Empties into blood near right atrium Utilize valves & muscular pumps Lymph Nodes = Organs that filters lymph (part of body defense) Elephantiasis Blood Components: 1) Formed Elements (living cells) Erythrocytes (RBC s) Small, bi-concave, anucleate Hematocrit % of whole blood containing formed elements (~ 45 50%) Contain hemoglobin (iron-containing protein) Transports oxygen Erythropoietin (kidney) stimulates production Leukocytes (WBC s) Function in defense against disease Five types (neutrophils / eosinophils / basophils lymphocytes / monocytes) Use blood for transport Platelets Cell fragments; function in blood clotting 2) Plasma Plasma Formed Elements Non-cellular fluid matrix (~90 % water) Dissolved proteins (clotting / transport / defense) 7

8 Campbell et al. Figure Blood Clotting: Gas Exchange in Animals: Gas Exchange: The uptake of molecular oxygen (O 2 ) from the environment And the discharge of carbon dioxide (CO 2 ) to the environment Respiratory medium = air (~ 21% O 2 ) or water ( than air) Respiratory surface = Location where gas exchange occurs Thin; large surface area (gases move via diffusion) Moist (maintain cellular integrity) Types of Respiratory Systems: 1) No Specialized System A) All cells have access to external environment (e.g. sponges, flatworms) B) Skin functions as respiratory surface (e.g. earthworms, amphibians) surface area / volume ratio (small, thin, and long / flat) 8

9 Gas Exchange in Animals: Types of Respiratory Systems: 2) Gills: Out-folds of body surface that are suspended in water (aquatic animals) Advantage: Respiratory surface always moist Disadvantage: [O 2 ] in water (system must be efficient) 1) Ventilation: Increased flow of respiratory medium over respiratory surface Move appendages (e.g. crayfish) Swim / pump operculum (e.g. fish) 2) Counter-current Exchange: Campbell et al. Figure Campbell et al. Figure Gas Exchange in Animals: Types of Respiratory Systems: 3) Tracheal System: Air tubes that branch throughout body to individual cells (smaller terrestrial animals - insects) Circulatory system not involved in gas transport / exchange Larger insects ventilate system via muscle contractions (e.g., flight) 9

10 Gas Exchange in Animals: Types of Respiratory Systems: 4) Lungs: Internal respiratory organs restricted to single location (larger terrestrial animals e.g. spiders, land snails, vertebrates) Circulatory system required to transport gases to / from body cells Size / complexity of lung correlated with animal s metabolic rate Warms, humidifies, & cleans air Reinforced with cartilage; vocal cords Rings / plates of cartilage, ciliated Dead-end air sacs; where gas exchange actually occurs ~ 100 m 2 (surface area) Similar to Campbell et al. Figure Campbell et al. Figure Ventilation of Lung (= breathing): Examples of Ventilation Adaptations: 1) Mammals ventilate by negative pressure breathing: Air is pulled into lungs via changes in thoracic cavity volume Boyle s Law: P = Pressure P 1 V 1 = P 2 V V = Volume 2 Example: 4 mm Hg (2 mm 3 ) = P 2 (4 mm 3 ) P 2 = 2 mm Hg CHANGING THE VOLUME RESULTS IN INVERSE CHANGE OF PRESSURE! Tidal Volume: Volume of air exchanged with each breath Vital Capacity: The maximum tidal volume during forced breathing (~ 4.5 L) Residual Volume: Air remaining in lungs after forced exhalation 10

11 Campbell et al. Figure Ventilation of Lung (= breathing): Examples of Ventilation Adaptations: 2) Frogs ventilate by positive pressure breathing: Air is pushed into lungs shrinkage of oral cavity size (i.e. swallow air) 3) Birds have air sacs that add complexity to system: Air completely exchanged from lung with every breath (no residual volume) Regulation of Breathing: Breathing control centers located in the pons and medulla oblongata: Medulla sets basic breathing rhythm Measures CO 2 level in blood (via ph change in CSF) O 2 only triggers respiratory response when severely depressed Gas Exchange at Lungs / Tissues: Gas exchange at lungs driven by partial pressures of gases: PO 2 in alveoli = ~ 100 mm Hg Net movement of O 2 into blood PO 2 in blood = ~ 40 mm Hg PCO 2 in alveoli = ~ 40 mm Hg Net movement of CO 2 into alveoli PCO 2 in blood = ~ 45 mm Hg Reverse is true at tissues 11

12 Campbell et al. Figure Transport of Gases in Blood: Oxygen has low solubility in liquid needs respiratory pigments for transport: Hemocyanin: Hemolymph of arthropods; copper-containing protein Hemoglobin: Blood of vertebrates; iron-containing protein (4 O 2 / unit) Myoglobin: Muscles of vertebrates; iron-containing protein Cooperative O 2 Binding: Binding of one O 2 molecule causes conformational change of hemoglobin resulting in rapid binding of 3 other O 2 molecules Dissociation Curve Campbell et al. Figure Transport of Gases in Blood: Carbon dioxide is primarily carried in blood as bicarbonate ion: Requires carbonic anhydrase (enzyme) 12