-a pump which is the heart
-transporting vessel , arteries , veins , capillaries , lymphatic vessel
-transporting fluid which is the blood and lymph
-heart is actually a muscular pump
-heart wall consists of cardiac muscle
-very specialized muscle which is myogenic
-cardiac muscle consists of striated muscle fibre, joined one another by intercalated discs
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| CARDIAC MUSCLE |
CORONARY VEINS-transport deoxygenated blood
PERICARDIUM SAC
-the heart is tightly contained in a fluid filled, double membranous pericardium sac
-this fluid reduce friction between the heart and the surrounding tissues
-elastic nature of pericardium prevents the heart from being overstretched
-due to overfill of blood
-attached to diaphragm , firmly anchoring the heart in position
HUMAN HEART
1.Right atrium collects deoxygenated blood from superior and inferior vena cava
2.Left atrium collects oxygenated blood from the pulmonary vein
3.Right ventricles pumps deoxygenated blood into the pumonary arteries
4.Left ventricles pumps oxygenated blood into the aorta at high pressure
CONFUSED? CHECK THIS OUT..
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| VALVES |
-There are 4 chambers in heart
-right and left atrium & right and left ventricles
-Atriums are seperated by interatrial septum
-ventricles are seperated by interventricular septum
-outer part of ventricles are thicker , transport blood to lungs and body
SA NODE AND AVN
-SA NODE (sinoatrial node) located close to entry of vena cava
-responsible for initiation and excitation of the heartbeat
-known as heartbeat pacemaker
-AVN (atrioventricular node) located in the centre of the heart
-is responsible in spreading electrical impulses from the atria to ventricles
AVN (ATRIOVENTRICULAR NODE)
-Connected with two bundle of His
-and their network of conducting fibres called purkinje tissue
-conducting fibres help to spread the electrical impulses from the AVN to the apex of the heart to initiate ventricles to contract
SA NODE (SINOATRIAL NODE)
-supplied with two nerve sets of the autonomic nervous system
-vagus nerve (parasympathetic) and the sympathetic
-they do not trigger the heartbeat
-but affect the pacemaker so as to influence the rate of heartbeat
-sympathetic nerve speed up the heartbeat
-parasympathetic slows it down
CARDIAC CYCLE
-SYSTOLE@CONTRACTION OF THE CARDIAC MUSCLE
-DIASTOLE@RELAXATION OF THE CARDIAC MUSCLE
-When the atria are at their systolic stage, the ventricles are in diastole stage and vice versa
-Each cycle of contraction and relaxation of the heart is called one beat of the heart
-Average of heartbeats in one minutes is 70
WATCH THESE 2 VIDEOS FOR BETTER UNDERSTANDING
1.ATRIAL SYSTOLE
-begins with the contraction of left and fight atrium
-causes the atrial pressure to increase
-force the tricuspid and bicuspid valves to open
-allowing blood to flow from atria to ventricle
-contraction of atrial walls also seals off the vena cava and pulmonary veins
-due from previous cycle, the ventricles are at lower pressure
-thus allowing blood to flow in from the atria to the ventricle
2.VENTRICULAR SYSTOLE
-right and left ventricles contract
-pressure begin to build up
-blood is forced to be pumped into the pulmonary artery and aorta
-forcing the semilunar valves to open
-increase in ventricular pressure and decrease in atrial pressure pressure forces the tricuspid and bicuspid valve to close
-the recoil of blood against the bicuspid and tricuspid valve makes the first lub sound
-at the same time, relaxing of the atrial wall and the contraction of ventricles wall
-allow the refilling of the atria under relatively low pressure
-deoxygenated blood flows into the right atrium
-oxygenated blood flows from pulmonary vein to left atrium
3.VENTRICULAR AND ATRIAL DIASTOLE
-when the ventricular systole ends, followed by short period where both are relaxed
-in ventricular diastole, the pressure of aorta and the pulmonary artery become higher
-forces the semilunar valves to shut
-recoil of the blood against the valve makes the second DUP sound
-closing of the semilunar valves also prevent backflow blood from aorta and pulmonary arteries
-fall in the ventricular pressure allows the increasing blood of atrium
-from here the sequence returns to atrial sytole
THE INITIATION OF HEARTBEAT
-heartbeat starts from SA NODE found in the cardiac muscle
-contraction of cardiac muscle is stimulated by electrical impulse
-cardiac muscle can contract by itself and is characterized as myogenic
-this rhythm of contraction can be made to go slower or faster by nervous impulses or hormone
-SA NODE is sometimes known as pace maker
SEQUENCE OF HEARTBEAT INITIATION
1.Electrical impulse initiated by the pacemaker SA node spread out of the wall of atrium
2.But are prevented to spread in the walls of ventricles
3.By artrioventricular septum
4.Instead, the impulse will travel to ventricles via the AV node
5.The impulse reach the AV node after 0.3 seconds after being emitted by SA NODE
6.When the AV node receive the impulse, it pauses for 0.9 seconds
7.This delay of impulses give time for the impulses to spread all over the atrium
8.From the AV node, the impulses are reemitted along the bundle of His and the purkinje fibres
9.Spread all the impulses to the ventricular wall
10.Causes simultaneous contraction through the ventricles
ELECTROCARDIOGRAM (ECG)
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| ECG |
1. P-wave@ depolarisation of the cardiac muscle at the atria arises from the electrical impulse emitted from the SA node, depolarisation spread as a wave of impulse in both atria
2. P-Q interval@ time required for the impulse to spread to the ventricles
3. QRS complex@ depolarisation of ventricles that leads to ventricular contraction. This wave is large because the ventricles are thicker
4. ST ridge@occurs as the ventricles slowly repolarise leading to ventricular diastole
5.The heart rate can be calculated from the time taken between one P wave to next
CONTROL OF HEART RATE
-The heart rate means number of heartbeats per minute
-heart muscle has its own inherent rhythm
-however , can still be controlled by hormones and autonomic nervous system
-although the pacemaker trigger the heartbeat,its also supplied with specific nerve
-SA node is supplied with two nerve sets of autonomic nervous system
-vagus nerve(parasympathetic) and sympathetic
-both these originate from medulla oblongata of the brain
SYMPATHETIC NERVE
1. Stimulating impulse are transported to the SA node
2. Causing in increase of depolarisation(voltage increased)
3. Result in an increase in the rate of contraction of the cardiac muscle
4. Thus increase the heart rate increase
PARASYMPATHETIC NERVE
1. Inhibitory impulses are transmitted to the SA node
2. Causing a decreased depolarisation
3. Activity of the heart is retarded, resulting in a decrease of rate of heartbeat
HORMONAL CONTROL OF HEART RATE
-Stimulation of the adrenal gland by the sympathetic nerve triggers the release of two hormones
-Noradrenline and Adrenaline
-Noradrenaline hormone increase both heart rate and ventricular contraction
-Adrenaline triggers a (flight and fight) response by speeding up the heart rate
-thus preparing the body for extreme exertion
-blood pressure increase and deliver the blood to where it needs such as muscle cells
-increase of thyroxine, a hormone secreted by thyroid gland also increase the heart rate
-heart rate also influenced by body size , gender , age , stress , state of health ,body temperature , drugs , smoking habits and alcoholic drinks
CARDIOVASCULAR DISEASE
-most of the disease are caused by atheroma
-atheroma@deposit of cholestrol, fibrous tissue, dead muscle cells , blood platelets inside lining of arteries
-atheroma is also known as arteriosclerosis or hardening of the arteries
-patches of atheroma are called plaque
1. HYPERTENSION ( HIGH BLOOD PRESSURE)
-when arteies become narro due to atheroma
-heart has to pump blood more forcefully to maintain blood flow
-consequently , blood pressure exerted on the artery walls build up
-if this continue , result in hypertension
-hardening of the artery wall due to atheroma will cause the wall to loose its elasticity
-this loss in elasticity will result in higher blood pressure
-hypertension can also cause tiny arteries to rupture
-blood capillaries in the brain rupture , the person suffers a stroke
-resulting in brain damage and paralysis of the body
2. CORONARY HEART DISEASE, ANGINA PECTORIS, MYOCARDIAL INFARCTION
-If an embolus , atheroma , thrombus(blood clot) occurs in the coronary arteries
-a region of the heart muscle will be deprived of oxygenated blood
-will lead to a gripping , acute chest pain known as angina pectoris
-which sometimes extends down the left arm
-in a severe coronary thrombosis, the heart muscle supplied by the blocked coronary arteries may be suffocated
-due to inadequate supply of oxygen
-commonly called heart attack or myocardial infarction
-the heart beat muscle becomes increasingly fast and irregular
-this condition called ventricular fibrillation
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