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The Circulatory System Chapter 50

Blood Type of connective tissue composed –Fluid matrix called plasma –Formed elements Functions of circulating blood 1.Transportation 2.Regulation 3.Protection 3

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Blood plasma 92% water Contains the following solutes –Nutrients, wastes, and hormones –Ions –Proteins Albumin, alpha (  ) and beta (  ) globulins Fibrinogen –If removed, plasma is called serum 5

Formed elements Red blood cells (erythrocytes) –About 5 million per microliter of blood –Mature mammalian erythrocytes lack nuclei –RBCs of vertebrates contain hemoglobin Pigment that binds and transports oxygen 6

Formed elements White blood cells (leukocytes) –Less than 1% of blood cells –Larger than erythrocytes and have nuclei –Can migrate out of capillaries into tissue fluid –Types Granular leukocytes –Neutrophils, eosinophils, and basophils Agranular leukocytes –Monocytes and lymphocytes 7

Formed elements Platelets Cell fragments that pinch off from larger cells in the bone marrow Function in the formation of blood clots 8

Formed elements All develop from pluripotent stem cells Hematopoiesis is blood cell production Occurs in the bone marrow Produces 2 types of stem cells –Lymphoid stem cell  Lymphocytes –Myeloid stem cell  All other blood cells Erythropoietin stimulates the production of erythrocytes (erythropoiesis) 9

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Invertebrate Circulatory Systems Sponges, Cnidarians, and nematodes lack a separate circulatory system Sponges circulate water using many incurrent pores and one excurrent pore Hydra circulate water through a gastrovascular cavity (also for digestion) Nematodes are thin enough that the digestive tract can also be used as a circulatory system 11

Invertebrate Circulatory Systems Larger animals require a separate circulatory system for nutrient and waste transport Open circulatory system –No distinction between circulating and extracellular fluid –Fluid called hemolymph Closed circulatory system –Distinct circulatory fluid enclosed in blood vessels and transported away from and back to the heart 12

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Vertebrate Circulatory Systems Fishes –Evolved a true chamber-pump heart –Four structures are arrayed one after the other to form two pumping chambers First chamber – sinus venosus and atrium Second chamber – ventricle and conus arteriosus –These contract in the order listed Blood is pumped through the gills, and then to the rest of the body 14

15 Vertebrate Circulatory Systems

Amphibians –Advent of lungs required a second pumping circuit, or double circulation –Pulmonary circulation moves blood between the heart and lungs –Systemic circulation moves blood between the heart and the rest of the body 16

Vertebrate Circulatory Systems Amphibian heart –3-chambered heart 2 atria and 1 ventricle –Separation of the pulmonary and systemic circulations is incomplete –Amphibians living in water obtain additional oxygen by diffusion through their skin –Reptiles have a septum that partially subdivides the ventricle, thereby further reducing the mixing of blood in the heart 17

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Vertebrate Circulatory Systems Mammals, birds, and crocodilians –4-chambered heart –2 separate atria and 2 separate ventricles –Right atrium receives deoxygenated blood from the body and delivers it to the right ventricle, which pumps it to the lungs –Left atrium receives oxygenated blood from the lungs and delivers it to the left ventricle, which pumps it to rest of the body 19

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21 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. LanceletsFishMammalsTurtlesAmphibiansCrocodilians Squamates Birds 4-chamber heart 4-chamber heart 3-chamber heart 2-chamber heart

The Cardiac Cycle Heart has two pairs of valves –Atrioventricular (AV) valves Maintain unidirectional blood flow between atria and ventricles Tricuspid valve = On the right Bicuspid, or mitral, valve = On the left –Semilunar valves Ensure one-way flow out of the ventricles to the arterial systems Pulmonary valve located at the exit of the right ventricle Aortic valve located at the exit of the left ventricle 22

The Cardiac Cycle Valves open and close as the heart goes through the cardiac cycle Ventricles relaxed and filling (diastole) Ventricles contracted and pumping (systole) “Lub-dub” sounds heard with stethoscope –Lub – AV valves closing –Dub – closing of semilunar valves 23

The Cardiac Cycle Heart contains “self-excitable” autorhythmic fibers Most important is the sinoatrial (SA) node –Located in wall of right atrium –Acts as pacemaker –Autonomic nervous system can modulate rate 24

The Cardiac Cycle Each SA depolarization transmitted –To left atrium –To right atrium and atrioventricular (AV) node AV node is only pathway for conduction to ventricles –Spreads through atrioventricular bundle –Purkinje fibers –Directly stimulate the myocardial cells of both ventricles to contract 25

Seconds R T wave 1 sec +1 0 Purkinje fibers Left atrium Right atrium Purkinje fibers AV bundle SA node (pacemaker) AV node AV bundle Interventricular septum Left and right bundle branches 1. The impulse begins at the SA node and travels to the AV node. Internodal pathway AV 2. The impulse is delayed at the AV node. It then travels to the AV bundle. P wave Millivotts Q S Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26

Seconds R T wave 1 sec +1 0 Purkinje fibers AV bundle Interventricular septum 3. From the AV bundle, the impulse travels down the interventricular septum. Left and right bundle branches 5. Finally reaching the Purkinje fibers, the impulse is distributed throughout the ventricles. 4. The impulse spreads to branches from the interventricular septum. P wave Millivotts 27 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Q S

The Cardiac Cycle Right and left pulmonary arteries deliver oxygen-depleted blood from the right ventricle to the right and left lungs Pulmonary veins return oxygenated blood from the lungs to the left atrium of the heart 28

The Cardiac Cycle Aorta and all its branches are systemic arteries, carrying oxygen-rich blood from the left ventricle to all parts of the body –Coronary arteries supply oxygenated blood to the heart muscle Blood from the body drains into the right atrium –Superior vena cava drains upper body –Inferior vena cava drains lower body 29

The Cardiac Cycle Arterial blood pressure can be measured with a sphygmomanometer Systolic pressure is the peak pressure at which ventricles are contracting Diastolic pressure is the minimum pressure between heartbeats at which the ventricles are relaxed Blood pressure is written as a ratio of systolic over diastolic pressure 30

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Characteristics of Blood Vessels Blood leaves heart through the arteries Arterioles are the finest, microscopic branches of the arterial tree Blood from arterioles enters capillaries Blood is collected into venules, which lead to larger vessels, veins Veins carry blood back to heart 32

Characteristics of Blood Vessels Arteries and veins are composed of four tissue layers –Endothelium, elastic fibers, smooth muscle, and connective tissue –Walls too thick for exchange of materials across the wall Capillaries are composed of only a single layer of endothelial cells –Allow rapid exchange of gases and metabolites between blood and body cells 33

34 Characteristics of Blood Vessels

Vasoconstriction and vasodilation are important means of regulating body heat in both ectotherms and endotherms 35

Characteristics of Blood Vessels Capillaries –Every cell in the body is within 100 micrometers (μm) of a capillary 36

Characteristics of Blood Vessels Veins and venules –Thinner layer of smooth muscles than arteries –Venous pump helps return blood to heart Skeletal muscle contractions and one- way venous valves 37

The Lymphatic System Significant amount of water and solutes in the blood plasma filter through the walls of the capillaries to form the interstitial (tissue) fluid Most fluid leaves at the arteriole end of the capillary and returns at the venule end Fluid that does not return to capillaries is returned to circulation by the lymphatic system 38

39 Blood pressure Osmotic pressure Capillary bedArterioleVenule a. b. Capillary Direction of blood flow Filtration Absorption Arteriole Lymphatic capillary Interstitial fluid Lymphatic capillary Excess interstitial fluid becomes lymph Interstitial fluid Venule Blood flow Pressure Net filtration due to blood pressure Net absorption due to osmotic pressure Venule Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

The Lymphatic System Consists of lymphatic capillaries, lymphatic vessels, lymph nodes, and lymphatic organs (spleen and thymus) Excess fluid in the tissues drains into blind-ended lymph capillaries Lymph passes into progressively larger vessels with one-way valves Eventually drains into subclavian veins 40

Cardiovascular Diseases Leading cause of death in the United States Atherosclerosis –Accumulation of fatty material within arteries –Impedes blood flow Arteriosclerosis –Arterial hardening due to calcium deposition 41

Cardiovascular Diseases Heart attacks (myocardial infarctions) –Main cause of cardiovascular deaths in U.S. –Insufficient supply of blood to heart Angina pectoris (“chest pain”) –Warning sign that the blood supply to the heart is inadequate but is still sufficient to avoid myocardial cell death Stroke –Interference with blood supply to the brain 42

Blood Flow and Blood Pressure Autonomic nervous system modulates heart rhythm and force of contraction Cardiac center of the medulla oblongata modulates heart rate –Norepinephrine, from sympathetic neurons, increases heart rate –Acetylcholine, from parasympathetic neurons, decreases heart rate 43

Blood Flow and Blood Pressure Cardiac output is the volume of blood pumped by each ventricle per minute –Increases during exertion because of an increase in both heart rate and stroke volume Arterial blood pressure (BP) depends on the cardiac output (CO) and the resistance (R) to blood flow in the vascular system BP = CO x R 44

Blood Flow and Blood Pressure Baroreceptor reflex –Negative feedback loop that responds to blood pressure changes –Baroreceptors detect changes in arterial blood pressure –If blood pressure decreases, the number of impulses to cardiac center is decreased Ultimately resulting in blood pressure increase –If blood pressure increases, the number of impulses to cardiac center is increased Ultimately resulting in blood pressure decrease 45

46 Blood Flow and Blood Pressure

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Blood Flow and Blood Pressure Blood pressure increases with blood volume Blood volume is regulated by four hormones –Antidiuretic hormone (ADH) –Aldosterone –Atrial natriuretic hormone –Nitric oxide (NO) 48