Circulation

1. Circulation Chapter 32 Pages 617-639

2. Major Features and Functions of Circulatory Systems • Circulatory systems evolved to bring the outside world to each cell in a multicellular organism • The earliest cells were nurtured by the primordial sea in which they evolved • In complex organisms, individual cells are farther away from the outside world, but require diffusion for adequate nutrients and to ensure they aren’t poisoned by their own waste • With the evolution of the circulatory system, a sort of “internal sea” was created, which transports food and oxygen close to each cell and carries away wastes

3. All circulatory systems have three major parts • A pump, the heart, that circulating • Blood – liquid that serves as a medium of transport • A system of tubes, blood vessels, to conduct the blood throughout the body

4. Two types of circulatory systems • Open circulatory systems - invertebrates, including arthropods and mollusks • One or more simple hearts, network of vessels, and series of interconnected spaces within the body called a hemocoel • Tissues and organs in the hemocoel are directly bathed by hemolymph - acts as both blood and the extracellular fluid that bathes all cells

5. Insect Example • Heart is a modified blood vessel with a series of contracting chambers • When chambers contract, valves in the heart are pressed shut, forcing the hemolymph out through vessels and into hemocoel spaces throughout the body • When the chambers relax, blood is drawn back into them from the hemocoel

6. Animation: Open Circulatory Systems

7. Closed Circulatory Systems • Invertebrates - earthworm and active mollusks (squid and octopuses) and all vertebrates • Blood is confined to heart and blood vessels, which branch throughout the organs and tissues of the body • more rapid blood flow • more efficient transport of dissolved substances • higher blood pressure than in open systems

8. Animation: Closed Circulatory Systems

9. Functions of Vertebrate Circulatory System • Transport O2 from lungs or gills to tissues • Transport CO2 from tissues to lungs or gills • Distribution of nutrients from the digestive system to body cells • Transport of wastes and toxic substances to the liver, where they are detoxified, and to the kidneys for excretion

10. Distribution of hormones from the glands and organs to the tissues • Regulation of body temperature by adjustments in blood flow • Wound healing and blood clotting to prevent blood loss • Protection against disease by circulating white blood cells and antibodies

11. Vertebrate Heart • The vertebrate heart consists of muscular chambers capable of strong contractions • Chambers called atria collect blood • Atrial contractions send blood into ventricles, chambers whose contractions circulate blood through the lungs and to the rest of the body

12. Evolution of the Vertebrate Heart • Increasingly complex and efficient hearts • The heart has become increasingly complex • Separation of oxygenated and deoxygenated blood • Fish (first vertebrates to evolve) has two chambers: a single atrium that empties into a single ventricle • Blood from the ventricle passes first through the gills, where it picks up O2 and gives off CO2 • Blood then travels from the gills through the rest of the body, picking up CO2 and returning it to the single atrium

13. Fish Heart gill capillaries ventricle atrium body capillaries (a) Fish

14. Animation: Two-Chambered Hearts

15. Three Chambered Hearts • Fish gave rise to amphibians and amphibians to reptiles • Three-chambered hearts consist of two atria and one ventricle • Amphibians, snakes, lizards, and turtles • Deoxygenated blood from the body is delivered to the right atrium, blood from the lungs enters the left atrium • Both atria empty into the single ventricle • Although some mixing occurs, deoxygenated blood remains in the right portion of the ventricle and is pumped into vessels that lead to the lungs, while most of the oxygenated blood remains in the left portion of the ventricle and is pumped to the rest of the body

16. Three Chambered Heart lung capillaries atria ventricle body capillaries (b) Amphibians and some reptiles

17. Animation: Three-Chambered Hearts

18. Four Chambered Hearts • Some reptiles - crocodiles, birds, and mammals have separate right and left ventricles • Completely isolate oxygenated and deoxygenated blood

19. Four Chambered Heart lung capillaries atria ventricles body capillaries (c) Mammals, crocodiles, and birds

20. Four Chambers – Two Pumps • An atrium collects the blood before passing it to a ventricle which propels it into the body • One pump, the right atrium and ventricle, deals with deoxygenated blood • Oxygen-depleted blood enters the right atrium through two large veins - the superior and inferior vena cava • After filling with blood, the right atrium contracts, forcing blood into the right ventricle • Contraction of the right ventricle sends the oxygen-depleted blood to the lungs through the pulmonary arteries

21. Two Pumps, part II • The second pump, the left atrium and ventricle, deals with oxygenated blood • Oxygen-rich blood from the lungs enters the left atrium through the pulmonary veins and is squeezed into the left ventricle • Contraction of the left ventricle sends the oxygenated blood through the aorta to the rest of the body

22. Heart Valves • Maintain the direction of blood flow • When the ventricles contract, blood must be prevented from flowing back into the atria • Blood entering the arteries must also be prevented from flowing back into the ventricles as the heart relaxes • Pressure in one direction opens valves easily, but reverse pressure forces valves closed • Atrioventricular valves blood flows from atria into the ventricles • Semilunar valves blood enters the pulmonary artery and aorta when ventricles contract, but prevent blood from returning as the ventricles relax

23. The Human Heart pulmonary artery (to left lung) aorta superior vena cava left atrium pulmonary artery (to right lung) pulmonary veins (from left lung) pulmonary veins (from right lung) atrioventricular valve semilunar valves right atrium left ventricle atrioventricular valve thicker muscle of left ventricle inferior vena cava descending aorta (to lower body) right ventricle

24. Animation: The Human Cardiovascular System

25. Cardiac Muscle Cells • Cardiac muscle cells are small, branched, and striated • Linked to one another via intercalated discs, appear as bands between the cells • Adjacent cell membranes are attached to one another by desmosomes, prevent heart contractions from pulling muscle cells apart • Intercalated discs also contain gap junctions to allow the electrical signals that trigger contractions to spread from one muscle cell to another, producing synchronous heart muscle contractions

26. The Structure of Cardiac Muscle nucleus cell Intercalated discs containing desmosomes and gap junctions link adjacent cardiac muscle cells

27. Cardiac Cycle • The coordinated contractions of atria and ventricles produce the cardiac cycle • The heart beats in a coordinated fashion • Both atria contract and pump blood into the ventricles • Both ventricles contract and pump blood into the arteries that exit the heart • All chambers relax briefly before the cycle repeats • This cardiac cycle lasts less than 1 second Cardiac Cycle

28. The Cardiac Cycle Oxygenated blood is pumped to the body Deoxygenated blood is pumped to the lungs Blood fills the atria and begins to flow passively into the ventricles Deoxygenated blood from the body enters the right ventricle Oxygenated blood from the lungs enters the left ventricle 3 Atria contract, forcing blood into the ventricles The cycle ends as the heart relaxes 1 Then the ventricles contract, forcing blood through the arteries to the lungs and the rest of the body 2

29. Blood Pressure • The cardiac cycle generates the forces that are measured when blood pressure is taken • Systolic pressure, the higher of the two readings, is measured during ventricular contraction • Diastolic pressure is the minimum pressure in the arteries as the heart rests between contractions • A BP reading of less than 120/80 is healthy; higher than 140/90 is defined as high • High blood pressure, or hypertension, is caused by the constriction of small arteries, which causes resistance to blood flow and strain on the heart

30. Animation: Blood Pressure

31. Electrical Impulses Coordinate the Contractions • The contraction of the heart is initiated and coordinated by a pacemaker, a cluster of specialized muscle cells that produce spontaneous electrical signals at a regular rate • The heart’s pacemaker is the sinoatrial (SA) node, located in the upper wall of the right atrium • Electrical signals from the SA node pass freely into the connecting cardiac muscle cells and then throughout the atria • The electrical signal then passes from the right atrium to a specialized group of muscle cells between the right atrium and right ventricle called the atrioventricular (AV) node

32. The signal to contract spreads along specialized tracts of rapidly conducting muscle fibers called the atrioventricular bundle, which sends branches to the lower portion of both ventricles • Here, the bundles branch further, forming Purkinje fibers that transmit the electrical signal throughout the ventricle

33. The Pacemaker and Its Connections 1 An electrical signal from the sinoatrial (SA) node starts atrial contraction SA node 2 Inexcitable tissue separates the atria and ventricles The electrical signal spreads through the atria, causing them to contract AV node AV bundle 3 The signal enters the atrioventricular (AV) node, which transmits it to the AV bundle with a slight delay AV bundle branches Purkinje fibers 4 The signal travels through the AV bundle branches to the base of the ventricles 5 Purkinje fibers transmit the signal to ventricular cardiac muscle cells, causing contraction from the base upwards

34. Disorders • When the pacemaker fails, rapid, uncoordinated, weak contractions called fibrillation may occur • Treated with a defibrillating machine, which applies a jolt of electricity, synchronizing the contractions of the ventricular muscle cells, and the pacemaker resumes its normal coordinating function

35. Heart Rate • Influenced by nervous system and hormones • On its own, the SA node pacemaker maintains a heart rate of 100 beats per minute • Nerve impulses and hormones alter the heart rate • At rest, the parasympathetic nervous system slows the heart rate to about 70 beats per minute • During exercise and stress, the sympathetic nervous system increases the heart rate to meet the demand for greater blood flow to the muscles

36. What Is Blood? • Blood has two major components • A liquid or plasma, 55% of total volume • The cellular portion, 40–45% of total volume • Red blood cells • White blood cells • Platelets

37. Types of Blood Cells red blood cells (a) Erythrocytes (red blood cells) platelets neutrophil neutrophil monocyte megakaryocyte basophil eosinophil lymphocyte (b) Leukocytes (white blood cells) (c) Megakaryocyte forming platelets

38. Plasma • Water with proteins, salts, nutrients, and wastes • 90% water, > 100 different molecules - hormones, nutrients, cellular wastes, ions • Proteins are the most abundant dissolved molecules by weight and include: • Albumin, maintains the blood’s osmotic strength • Globulins, antibodies - important in immune response • Fibrinogen, important in blood clotting

40. Cellular Components of Blood • Formed in bone marrow • Of the 3 cell-based components - only the white blood cells are complete, functional cells • Mature RBCs are not cells because they lack a nucleus, which is lost during development • Platelets are small fragments of cells • All 3 components originate from blood stem cells or megakaryocytes • Stem cells are unspecialized cells that can divide to produce one or more types of specialized cells

41. Red Blood Cells • Carry oxygen from the lungs to the tissues • 99% of all blood cells, and 45% total volume • Oxygen-carrying red blood cells or erythrocytes • Red color of erythrocytes is caused by the protein hemoglobin, each binds to 4 oxygen molecules, one on each iron-containing heme group • Oxygenated hemoglobin is bright cherry-red color • Hemoglobin becomes bluish as it releases O2 and picks up CO2 at tissues

42. Hemoglobin

43. Red Blood Cells • Life span of 4 months, replaced by new cells from bone marrow • Macrophages (white blood cells) in spleen and liver engulf and break down dead red blood cells • Iron from erythrocytes is returned to the bone marrow and recycled into new red blood cells

44. Regulated by Negative Feedback • Red blood cell count is maintained by a negative feedback system involving hormone erythropoietin • Erythropoietin is produced by the kidneys and released into the blood in response to O2 deficiency • Stimulates rapid production of new RBC by bone marrow • When the 02 level is restored, erythropoietin production declines and rate of RBC production returns to normal

45. Red Blood Cell Regulation Oxygen deficiency stimulates Erythropoietin production by the kidneys stimulates inhibits Red blood cell production in the bone marrow Restored oxygen level causes

46. White Blood Cells • Defend the body against disease • Five types of white blood cells or leukocytes • Neutrophils • Eosinophils • Basophils • Lymphocytes • Monocytes

47. WBC Details • Cell life spans range from hours to years • <1% of the cellular portion of blood • All WBC help to protect the body against disease • Monocytes, enter tissues and transform into macrophages that engulf bacteria and cellular debris

48. Platelets • Cell fragments that aid in blood clotting • Megakaryocyte pieces, reside in bone marrow • Megakaryocytes pinch off membrane-enclosed pieces of cytoplasm to form platelets, which enter the blood • Platelets survive 10 days

49. How it works… • Blood clotting plugs damaged blood vessels • Complex process that plugs damaged blood vessels and protects excessive blood loss • Clotting begins following a break in a blood vessel wall, exposing collagen fibers that attract platelets, which form a platelet plug • The platelets and ruptured cells release chemicals that initiate a series of reactions, producing the enzyme thrombin from its inactive form, prothrombin

50. Blood Clotting 1 2 3 Damaged cells expose collagen, which activates platelets, causing them to stick and form a plug Both damaged cells and activated platelets release chemicals that convert prothrombin into the enzyme thrombin Thrombin catalyzes the conversion of fibrinogen into protein fibers called fibrin, which forms a meshwork around the platelets and traps red blood cells collagen fibers fibrin platelet plug platelets red blood cells thrombin thrombin prothrombin fibrinogen blood vessel