Circulation and Gas Exchange (42)

Circular canal Radial canal Mouth (a) The moon jelly Aurelia, a cnidarian 5 cm Simple animals-- body wall that is only two cells thick and that encloses a gastrovascular cavity --- digestion and distribution of substances throughout the body. Gastrovascular Cavities

Heart Hemolymph in sinuses surrounding organs Heart Interstitial fluid Small branch vessels In each organ Blood Dorsal vessel (main heart) Auxiliary heartsVentral vessels (b) A closed circulatory system (a) An open circulatory system Tubular heart Pores In insects, blood bathes the organs directly in an open circulatory system Closed systems are more efficient at transporting circulatory fluids to tissues and cells Open systems compared to closed systems

Amphibians Lung and skin capillaries Pulmocutaneous circuit Atrium (A) Ventricle (V) Atrium (A) Systemic circuit Right Left Systemic capillaries Reptiles (Except Birds) Lung capillaries Pulmonary circuit Right systemic aorta Right Left systemic aorta Systemic capillaries AA V V Pulmonary circuit Systemic circuit RightLeft AA V V Lung capillaries Mammals and Birds Double Circulation

Superior vena cava Pulmonary artery Capillaries of right lung Aorta Pulmonary vein Right atrium Right ventricle Inferior vena cava Capillaries of abdominal organs and hind limbs Pulmonary vein Left atrium Left ventricle Aorta Capillaries of left lung Pulmonary artery Capillaries of head and forelimbs Coordinated cycles of heart contraction drive double circulation in mammals The mammalian cardiovascular system meets the body’s continuous demand for O 2

Pulmonary artery Right atrium Semilunar valve Atrioventricular valve Right ventricle Left ventricle Atrioventricular valve Left atrium Semilunar valve Pulmonary artery Aorta The Mammalian Heart

ArteryVein SEM 100 µm Endothelium Artery Smooth muscle Connective tissue Capillary Basal lamina Endothelium Smooth muscle Connective tissue Valve Vein Arteriole Venule Red blood cell Capillary 15 µm LM Patterns of blood pressure and flow reflect the structure and arrangement of blood vessels

Blood Pressure Blood pressure is the pressure that blood exerts against the wall of a vessel Vasoconstriction and vasodilation help maintain adequate blood flow as the body’s demands change

Direction of blood flow in vein (toward heart) Valve (open) Skeletal muscle Valve (closed) Blood is moved through veins by smooth and skeletal muscle contraction Blood flow in veins

Precapillary sphincters Thoroughfare channel Arteriole Capillaries Venule (a) Sphincters relaxed (b) Sphincters contracted ArterioleVenule Two mechanisms regulate distribution of blood in capillary beds: Precapillary sphincters control flow of blood between arterioles and venules Contraction of the smooth muscle layer in the wall of an arteriole constricts the vessel

Body tissue Capillary INTERSTITIAL FLUID Net fluid movement out Direction of blood flow Net fluid movement in Blood pressure Inward flow Outward flow Osmotic pressure Arterial end of capillaryVenous end Pressure The exchange of substances between the blood and interstitial fluid takes place across the thin endothelial walls of the capillaries The difference between blood and osmotic pressure drives fluid exchange.

Fluid Return by the Lymphatic System The lymphatic system returns fluid that leaks out in the capillary beds

Plasma 55% ConstituentMajor functions Water Solvent for carrying other substances Ions (blood electrolytes) Osmotic balance, pH buffering, and regulation of membrane permeability Sodium Potassium Calcium Magnesium Chloride Bicarbonate Osmotic balance pH buffering Clotting Defense Plasma proteins Albumin Fibrinogen Immunoglobulins (antibodies) Substances transported by blood Nutrients (such as glucose, fatty acids, vitamins) Waste products of metabolism Respiratory gases (O 2 and CO 2 ) Hormones Separated blood elements Cellular elements 45% Cell typeFunctionsNumber per µL (mm 3 ) of blood Erythrocytes (red blood cells) 5–6 million Transport oxygen and help transport carbon dioxide Leukocytes (white blood cells) 5,000–10,000 Defense and immunity Basophil Neutrophil Eosinophil Lymphocyte Monocyte PlateletsBlood clotting 250,000– 400,000 Blood Composition and Function

Collagen fibers Platelet plug Platelet releases chemicals that make nearby platelets sticky Clotting factors from: Platelets Damaged cells Plasma (factors include calcium, vitamin K) ProthrombinThrombin FibrinogenFibrin 5 µm Fibrin clot Red blood cell When the endothelium of a blood vessel is damaged, the clotting mechanism begins Blood Clotting

Gas Exchange

Parapodium (functions as gill) (a) Marine worm Gills (b) Crayfish (c) Sea star Tube foot Gills Diversity of Gills in Aquatic Animals Gills are outfoldings of the body that create a large surface area for gas exchange

Anatomy of gills Gill arch Water flow Operculum Gill arch Gill filament organization Blood vessels Oxygen-poor blood Oxygen-rich blood Fluid flow through gill filament Lamella Blood flow through capillaries in lamella Water flow between lamellae Countercurrent exchange P O 2 (mm Hg) in water P O 2 (mm Hg) in blood Net diffu- sion of O 2 from water to blood Gill filaments Fish gills use a countercurrent exchange system, where blood flows in the opposite direction to water passing over the gills; blood is always less saturated with O 2 than the water it meets

Pharynx Larynx (Esophagus) Trachea Right lung Bronchus Bronchiole Diaphragm Heart SEM Left lung Nasal cavity Terminal bronchiole Branch of pulmonary vein (oxygen-rich blood) Branch of pulmonary artery (oxygen-poor blood) Alveoli Colorized SEM 50 µm Lungs are an infolding of the body surface

Lung Diaphragm Air inhaled Rib cage expands as rib muscles contract Rib cage gets smaller as rib muscles relax Air exhaled EXHALATION Diaphragm relaxes (moves up) INHALATION Diaphragm contracts (moves down) Mammals ventilate their lungs by negative pressure breathing, which pulls air into the lungs

Breathing control centers Cerebrospinal fluid Pons Medulla oblongata Carotid arteries Aorta Diaphragm Rib muscles Sensors in the aorta and carotid arteries monitor O 2 and CO 2 concentrations in the blood

Alveolus P O 2 = 100 mm Hg P O 2 = 40 P O 2 = 100 P O 2 = 40 Circulatory system Body tissue P O 2 ≤ 40 mm HgP CO 2 ≥ 46 mm Hg Body tissue P CO 2 = 46 P CO 2 = 40 P CO 2 = 46 Circulatory system P CO 2 = 40 mm Hg Alveolus (b) Carbon dioxide(a) Oxygen Loading and Unloading of Respiratory Gases

Respiratory Pigments Most vertebrates and some invertebrates use hemoglobin contained within erythrocytes  Chains Iron Heme  Chains Hemoglobin A single hemoglobin molecule can carry 4 molecules of O2. Binding of O2 to one unit induces the others to slightly change shape, increasing their affinity for oxygen.

O 2 saturation of hemoglobin (%) P O 2 (mm Hg) pH 7.4 pH 7.2 Hemoglobin retains less O 2 at lower pH (higher CO 2 concentration) Dissociation curve for hemoglobin demonstrates the Bohr shift

Carbon Dioxide Transport CO 2 from respiring cells diffuses into the blood and is transported either in blood plasma, bound to hemoglobin, or as bicarbonate ions (HCO 3 – ) Body tissue CO 2 produced CO 2 transport from tissues Interstitial fluid CO 2 Plasma within capillary Capillary wall H2OH2O H 2 CO 3 Carbonic acid Red blood cell Hemoglobin picks up CO 2 and H + Hb H+H+ HCO 3 – Bicarbonate + HCO 3 – To lungs

HCO 3 – H+H+ + CO 2 transport to lungs Hemoglobin releases CO 2 and H + Hb H 2 CO 3 H2OH2O CO 2 Plasma within lung capillary CO 2 Alveolar space in lung

GHOSTS

Stem cells (in bone marrow) Myeloid stem cells Lymphoid stem cells Lymphocytes B cellsT cells Erythrocytes Platelets Neutrophils Basophils Eosinophils Monocytes Where do blood cells come from?

Signals spread throughout ventricles. 4 Purkinje fibers Pacemaker generates wave of signals to contract. 1 SA node (pacemaker) ECG Signals are delayed at AV node. 2 AV node Signals pass to heart apex. 3 Bundle branches Heart apex Impulses that travel during the cardiac cycle can be recorded as an electrocardiogram (ECG or EKG)

Semilunar valves closed 0.4 sec AV valves open Atrial and ventricular diastole 1 Cardiac Cycle

Fig Semilunar valves closed 0.4 sec AV valves open Atrial and ventricular diastole sec Atrial systole; ventricular diastole

Fig Semilunar valves closed 0.4 sec AV valves open Atrial and ventricular diastole sec Atrial systole; ventricular diastole sec Semilunar valves open AV valves closed Ventricular systole; atrial diastole