The Heart • Structure of the heart – 4 chambers • 2 upper atria • 2 lower ventricles • Each pair of chambers is separated by a septum – Heart wall • Major portion is the myocardium- cardiac muscle • Inner surfaces lined with endocardium • Outer surfaces lined with pericardium
The heart cont’d. • Heart valves – Atrioventricular valves • Lie between the atrium and ventricle on each side • Mitral (bicuspid) valve- between the left atrium and left ventricle • Tricuspid valve- between the right atrium and right ventricle
The heart cont’d. • Heart valves – Semilunar valves • Between the ventricle and great vessel on each side • Aortic valve-between the left ventricle and aorta • Pulmonary valve-between the right ventricle and the pulmonary artery – Valves control the flow of blood through the heart
The heart cont’d.• Passage of blood through the heart – Superior and inferior vena cavae bring O2-poor blood to the right atrium – Blood flows through tricuspid valve to right ventricle – From right ventricle blood passes through the pulmonary valve to the pulmonary artery – Blood picks up oxygen in the lungs and returns to the heart through the pulmonary veins – Pulmonary veins empty oxygenated blood into the left atrium – Blood flows through the mitral valve to the left ventricle – From the left ventricle blood flows through the aortic valve to the aorta – Aorta carries blood out to the body
The heart cont’d. • Blood flow through the heart cont’d. – The heart is actually 2 pumps • Right side is the pulmonary pump – Pumps deoxygenated blood to pulmonary circuit and lungs • Left side is the systemic pump – Pumps oxygenated blood out to systemic circulation – Note that deoxygenated and oxygenated blood never mix – Left ventricle pumps blood under higher pressure • Left ventricular wall is more muscular
Cardiac Cycle• The heartbeat – The events of each heartbeat are called the cardiac cycle • Highly coordinated so that both atria contract together and then both ventricles contract together • Systole- ventricular contraction of heart muscle • Diastole-ventricular relaxation of heart muscle – Normal heart rate at rest is about 60-80 beats/minute – “Lub dup” heart sounds are produced by turbulence and tissue vibration as valves close • “lub” sound occurs as atrioventricular valves (AV) close • “dup” sound occurs as semilunar valves close – Other abnormal sounds are referred to as heart murmurs
semilunarvalves aorta pulmonary vein left atrium left ventricle a. right ventricle
semilunarvalves aorta pulmonary vein left atrium left ventricle a. right ventricle pulmonary arteries aorta atrioventricular valves b.
semilunar superiorvalves vena cava aorta pulmonary vein right left atrium atrium left ventricle c. inferior a. vena cava right ventricle pulmonary arteries aorta atrioventricular valves b.
Conduction system of the heart • Intrinsic control of heartbeat – Heart has its own intrinsic conduction system – Nodal tissue-2 areas in the heart • Has both muscular and nervous characteristics • Can generate action potentials to cause contraction • SA node and AV node
Control of Heartbeat• When the SA node "fires", the nerve impulse spreads quickly over both atria, causing the atrial muscles to contract. The impulse then reaches a second node of tissue, the atrioventricular node (AV node), located in the septum between the ventricles but in contact with the lower portion of the right atrium. The stimulation of the AV node causes nerve impulses to be sent down the bundle of nerve fibers, known as the Bundle of His. The Bundle of His branches into a pair of nerve fibers through the septum and circling around the base of each ventricle. The impulse started in the SA node and picked up by the AV node reaches the muscles of the ventricles and causes them to contract.• The heart has special muscle fibers called Purkinje fibers that conduct impulses five times more rapidly than surrounding cells. The Purkinje fibers form a pathway for conduction of the impulse that ensures that the heart muscle cells contract in the most efficient pattern.
Control of Heartbeat• Extrinsic control of the heartbeat – Cardiac control center in the medulla has inputs to heart through the ANS – Parasympathetic stimulation causes a decrease in heart rate – Sympathetic stimulation causes an increase in heart rate and contractility – Hormones also can control heartbeat • Epinephrine and norepinephrine cause increased heart rate • Occurs during exercise, “fight or flight” response
The Electrocardiogram – An electrocardiograph is an instrument that is used to measure electrical activity in the heart. It measures changes in electrical potential across the heart and can detect the contraction pulses that pass over the surface of the heart. The resulting record is called an electrocardiogram (ECG or EKG). – The EKG shows three slow, negative changes, known as P, R, and T. Positive deflections are the Q and S waves.
Conduction system of the heart •P wave- atrial depolarization (prior to atrial contraction) •QRS complex- ventricular depolarization (just prior to ventricular contraction •T wave- ventricular repolarization (ventricles are recovering from contraction)
The Vascular Pathways • The pulmonary circuit – Right ventricle pumps deoxygenated blood to pulmonary artery – Branches into left and right pulmonary arteries that go to the lungs – Within the lungs blood is distributed to alveolar capillaries – Oxygen diffuses into the blood and carbon dioxide diffuses out – Oxygenated blood now travels through pulmonary veins to the left atrium
The Vascular Pathways cont’d. • The systemic circuit – Oxygenated blood is pumped from the left ventricle to the aorta – Aorta distributes blood through the systemic arteries – As blood travels through the systemic capillaries it drops off oxygen and picks up carbon dioxide – The deoxygenated blood is returned by venules and then veins to the vena cavae – The inferior vena cava drains the body below the chest – The superior vena cava collects blood from the head, chest, and arms – Blood is returned to the right atrium
Blood Pressure • Blood pressure is defined as the force of blood against the walls of arteries. • The pressure in any artery varies as a result of two major factors. – 1. Cardiac Output o Volume of blood. o Heart rate – 2. Arteriolar Resistance o Size o Elasticity
Blood Pressure• Measuring Blood Pressure Two different pressures are measured and compared in a blood pressure reading. o Systolic pressure o Diastolic pressure• Blood pressure is measured using a device called a sphygmomanometer. o Normal blood pressure is less than 130 mm Hg systolic and less than 85 mm Hg diastolic. o Optimal blood pressure is less than 120 mm Hg systolic and less than 80 mm Hg diastolic. o A typical reading for a healthy adult is 120/70
Blood Pressure in the Vessels• Blood pressure in the Capillaries – The pressure of arterial blood is significantly reduced when the blood enters the capillaries.• Blood pressure in the veins – When blood leaves the capillaries and enters the venules and veins, little pressure remains to force it along.• Blood pressure in the Arteries – Blood pressure is the greatest in these vessels because the heart has just pumped the blood.
Exchanges between Blood and Cells • Our blood does not come into direct contact with the cells it nourishes. • When blood enters the arteriole end of a capillary, some components filter through the walls of the capillaries into the tissue space. This fluid, called interstitial fluid, is blood plasma minus most of the proteins. • Substances in the fluid can enter the cells by diffusion or active transport. Substances, like carbon dioxide, can diffuse out of cells and into the interstitial fluid. • Near the venous end of a capillary, the blood pressure is greatly reduced. Here the osmotic pressure causes fluid to re-enters the capillary at the venous end.
Hypertension • High blood pressure or hypertension is defined in an adult as a blood pressure greater than or equal to 140 mm Hg systolic pressure or greater than or equal to 90 mm Hg diastolic pressure. • Risk Factors You Can Control – Smoking - Physical Inactivity – Obesity - Diet (Salt Intake) – Diabetes - Stress • Risk Factors You Can’t Control – Age – Ethnicity (South Asians, First Nations/Aboriginal Peoples or Inuit and Blacks are at increased risk) – Family history