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Advanced Biology
Chapter 46
WAGGY
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 Describe the structure & function of the heart
 Trace the flow of blood through the heart & the body
 Distinguish between veins, arteries
& capillaries

 The blood, heart & blood vessels make up the cardiovascular system
 Along with the lymphatic system , nutrients, hormones & gases are delivered to each cell & wastes are removed
 the Cardiovascular & lymphatic system together help to control body temperature

 The central organ of the cardiovascular system is the heart
 The heart beats more than 2.5 billion times in an average life span
 The heart is slightly larger than a fist & is located between the lungs, behind the sternum in the thoracic cavity

 The heart is surrounded by a tough membrane called the pericardium which secretes a fluid that reduces friction as the heart beats
 The outside of the heart is covered with numerous cardiac arteries & veins that nourish the heart muscle
 A septum (wall) vertically separates the heart into two sides
 The right side pumps blood to the lungs
 The left side pumps blood to the rest of the body

 Each side is divided into two portions
 The upper portions are called atria
(atrium)
 The lower portions are ventricles
 Each portion of the heart is separated by valves

 Valves are flaps of tissue that open in only ONE direction
 The atrioventricular valves (AV valve) allow blood to flow from the atria to the ventricles
 The right AV valve is the tricuspid valve & the left valve is the bicuspid valve

 The semilunar valves (SL valves) are between the ventricles & the blood vessels connected to the heart
 The SL valve on the right side is called the pulmonary valve & the one on the left is called the aortic valve

 Blood returning to the heart from the body contains a high concentration of
CO
2
& travels through the inferior vena cava
 This O atrium
2 poor blood enters the right
 The right atrium contracts sending the blood through the tricuspid valve & into the right ventricle

 The right ventricle contracts & the blood is pushed through the pulmonary valve into the pulmonary artery
 The pulmonary artery leads to the lungs where gas exchange occurs
& now the blood is O
2 rich
 O
2 rich blood returns to the heart through the pulmonary veins

 The oxygenated blood enters the left atrium & is then pushed through the bicuspid valve into the left ventricle
 The left ventricle contracts sending the blood through the aortic valve into the aortic artery (aorta)
 The left ventricle has the thickest muscle wall because it is responsible for pumping blood to the entire body

 Often oxygenated blood is color coded bright red in textbooks & deoxygenated blood is color coded blue
 In real life, oxygenated blood is bright red, but deoxygenated blood is dark red in color
 The deoxygenated blood appears blue when we look at our veins but it really is not!

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 Cardiac muscles are specialized muscle tissue
 When it contracts, it does so in waves
 The heart also coordinates all of its contractions into a steady rhythm of both atria contracting & then both ventricles contracting

 The contractions begin at specific places in the heart
 The sinoatrial node (SA node) is a group of specialized cardiac muscle cells in the right atrium
 The SA node generates an electrical pulse that moves outward throughout the rest of the atrial cells
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 When the electrical pulse reaches the atrioventricular
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node (AV node) located between the atria & ventricles, the pulse is relayed to the ventricular cells causing them to contract
 The ventricular contraction is a fraction of a second after the atrial contraction

 A heartbeat has two phases:
 1. Systole: occurs when the ventricles contract closing the AV
valves & opening the SL valves (lub)
 2. Diastole: occurs when the ventricles relax closing the SL valves
& opening the AV valves (dub)

 This creates the characteristic ‘lubdub’ sound of a human heartbeat
 If one of the valves does not close completely, then some blood is allowed to move backwards in the heart - this is called a murmur

 A persons pulse is a series of pressure waves within an artery caused by the contraction of the left ventricle
 When the blood surges through the arteries, the elastic walls of the vessels expand and stretch
 The average pulse rate is 70-90 beats per minute (bpm)

 The large muscular vessels that carry blood away from the heart are called arteries
 The walls of the arteries have three layers:
 1. A smooth endothelial layer
 2. A middle layer of smooth muscle
 3. Outer layer of connective tissue for strength

 As the arteries move away from the heart, they split into smaller & smaller vessels
 First arteries become arterioles , then capillaries
 A capillary is so tiny that blood cells must move through it in single file!
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 After gas exchange occurs between the cells & the capillaries it is time to begin the journey back to the heart
 The capillaries, now carrying O
2 poor blood turn into veinules
 Several veinules will merge to become larger veins
 Veins continue to merge to form the very large vein, the Vena
Cava

 Veins & the Vena Cava have small valves inside to prevent the blood from moving backwards
 The blood pressure from the left ventricle is much lower in the veins
& so valves are needed to ensure that the blood makes it all the way back to the heart

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