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Lecture 15

BIO 102 Lecture 15: Lecture 15-16: Chapter 33 - Circulation

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Quinnipiac University
BIO 102
Jack Kronengold

● Arteries bring blood away from heart, veins bring blood to heart ● All circulatory systems have three major parts: ○ Blood (transport gases, nutrients, and cellular waster) ○ Blood Vessels ○ Heart ● Two types of circulatory systems: ○ Open ○ Closed ● Open Circulatory Systems: ○ Found in most Invertebrates ○ One or more simple hearts, some blood vessels, series of interconnected spaces within the body (hemocoel) ○ Within hemocoel - tissues and organs are in a fluid (hemolymph) that acts as blood and the extracellular (interstitial) fluid that surrounds each cell within a multicellular organism ○ Heart chambers contract → valves in heart are pressed shut → hemolymph forced out through vessels and into hemocoel spaces throughout the body ○ Chambers relax → hemolymph drawn back into them from the hemocoel ● Closed Circulatory Systems: ○ Confine the blood to the heart and to vessels that carry blood throughout the body ○ Blood pressure and flow rates are higher (than what is possible in open system) ○ Better able to direct blood to specific tissues as needed delivering O2 and nutrients ○ Present in: all vertebrates, a few invertebrates, earthworms ● Vertebrates - circulatory system functions: ○ Transport O2 and CO2 (gills or lungs) ○ Distribution of nutrients ○ Transport of waste to kidneys ○ Distribution of hormones ○ Regulation of body temperature (adjust blood flow) ○ Prevent blood loss and heals wounds (blood clots) ○ Protect against disease (circulating white blood cells and antibodies ● First vertebrate heart to evolve = two chambered heart of fishes ○ Fish hearts consist of two main contractile chambers: a single atrium that empties into a single ventricle ○ Blood from ventricle passes through gills where it picks up O2 and gives off CO2 → then travels through the rest of the body, delivering O2 to the tissues and picking up CO2 → then returns to the single atrium ● Terrestrial Vertebrates - hearts evolved ○ Three-chambered heart - two atria and one ventricle ■ Found in amphibians (salamanders, frogs) that came from fish and reptiles that evolved from amphibians (snakes, turtles, lizards) ○ Double Circulation - two separate circuits of blood ■ Pulmonary circuit - directs blood from the heart through the lungs - CO2 is exchanged for O2, and back to the heart ■ Systemic Circuit - carries blood between the heart and the rest of the body - O2 is exchanged for CO2 ○ Blood from the systemic circulation enters the right atrium ○ Blood from the pulmonary circuit enters the left atrium ○ Both atria empty into the single ventricle ● Four - chambered hearts ○ Consist of two separate pumps ○ Right atrium and right ventricle completely isolated from its left atrium and left ventricle - acts like two hearts beating as one ○ Found in a few groups of reptiles (birds and crocodiles) and mammals ○ Advantage: Separation of O2-rich and O2-poor blood maximizes O2 levels in blood ○ “Right Heart” - deals with oxygen-poor blood ■ Receives oxygen-depleted blood from the body through the two largest veins (superior vena cava and inferior vena cava) ■ After filling with blood, right atrium contracts, forcing blood into the right ventricle ■ Contraction of the right ventricle sends the oxygen-poor blood to the lungs through the pulmonary arteries ○ “Left Heart” - deals with oxygenated blood ■ Oxygen-rich blood from the lungs enters the left atrium through the pulmonary veins - then squeezed into the left ventricle ■ A strong contraction of the left ventricle (hearts most muscular chamber) sends the oxygenated blood out through the largest artery (aorta) and then to the rest of the body ○ Directionality of blood flow is maintained by one-way valves ■ Pressure in one direction opens them, but reverse pressure closes them ■ Atrioventricular valves - allow blood to flow from the atria into the ventricles, but not the reverse ■ Semilunar valves - allow blood to enter the pulmonary artery and the aorta when the ventricles contract, but prevent blood from returning as the ventricles relax ○ Cardiac muscle - present only in the heart ■ Cells are connected by intercalated discs (bands between the cells) ■ Discs: cell membranes attached by junctions called desmosomes, which prevent the strong heart contractions from pulling the muscle cells apart ■ Intercalated discs also contain gap junctions that allow for synchronous heart muscle contractions ○ Coordinated contractions of atria and ventricles produce the cardiac cycle ■ During each cycle: ● Atrial systole - Both atria contract in synchrony, emptying their contents into the ventricles ● Ventricular Systole - the two ventricles contract simultaneously ● Diastole - both atria and both ventricles relax briefly before the cardiac cycle repeats ■ Heart rate = the number of cardiac cycles per minute ○ Blood pressure has two measurements: ■ Systolic pressure - measured during ventricular contraction ■ Diastolic pressure - the minimum pressure in the arteries as the heart rests between contractions ■ Blood pressure less than 120/80 (systolic/diastolic) and about 90/60 is healthy ■ Hypertension (high blood pressure) is caused by the constriction of small arteries, which causes resistance to blood flow and strain on the heart ● 140/90 + is high blood pressure ○ Electrical impulses - coordinate the sequence of heart chamber contractions ■ Pacemaker (cluster of specialized heart muscle cells that produce spontaneous electrical signals at a regular rate) - initiate and coordinate the contraction of the heart ■ Pacemaker cells are in the sinoatrial (SA) node - located in the upper wall of the right atrium ○ The nervous system and hormones influence heart rate ■ On its own SA node pacemaker would maintain a heart rate of about 100 beats per minute ■ 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 ○ Blood has two major components: ■ Plasma (liquid) - comprises about 55-60% of the blood volume ■ Cell-based portion consisting of red blood cells, white blood cells, and platelets suspended in the plasma ○ Average person has roughly 5.3 quarts (5 liters) of blood ○ Plasma: ■ 90% water in which proteins, salts, nutrients, and wastes are dissolved ■ Contains more than 100 different types of molecules dissolved in it ■ Transports hormones, nutrients, cellular wastes (CO2) and a variety of ions ■ Some of these maintain blood pH, while others are crucial for the functioning of nerve and muscle cells ■ Three most abundant plasma proteins: ● Albumin - helps maintain the blood’s osmotic pressure ● Globulins - antibodies that play an important part in immune response ● Fibrinogen - important in blood clotting ○ Cell-based components of blood are formed in bone marrow ■ Only the white blood cells are complete, functional cells ■ Mature red blood cells of mammals are technically not cells because they lose their nuclei during development ■ Platelets are actually small fragments of cells ○ Red Blood Cells (RBCs) ■ Also called erythrocytes ■ Make up 99% of all blood cells ■ Carry oxygen from lungs to tissues ■ Human erythrocy
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