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TRANSPORT
HEART
STRUCTURE
· THE HUMAN HEART, IS A HOLLOW,MUSCULAR ORGAN ABOUT A SIZE OF A CLENCHED FIST.
· IT IS SHAPED LIKE AN INVERTED CONE.
· THE HEART LIES IN THE THORACIC CAVITY BETWEEN THE LUNGS, IN A POSITION PROTECTED BY THE STERNUM.
· THE HEART WALL CONSIST OF CARDIAC MUSCLE, A SPECIAL TYPE OF MUSCLE THAT IS UNIQUE TO THE HEART.
· CORONARY ARTERIES ARISE FROM THE BASE OF THE AORTA AND PASS OVER THE SURFACE OF THE HEART , SUPPLYING THE CAPILLARIES OF THE CARDIAC MUSCLE WITH OXYGENATED BLOOD.
· THE CAVITY OF THE HEART IS DIVIDED INTO FOUR CHAMBERS, THE CHAMBERS OF THE RIGHT SIDE OF THE HEART ARE COMPLETELY SEPARATE FROM THE CHAMBERS OF THE LEFT SIDE.
· THE TWO UPPER CHAMBERS ARE THIN-WALLED, AND ARE CALLED ATRIC (SINGULAR ATRIUM).
· CORONARY ARTERIES SUPPLY CARDIAC MUSCLE WITH OXYGENATED BLOOD.
· THE TWO LOWER CHAMBERS ARE THICK-WALLED AND ARE CALLED VENTRICLES
· THE RIGHT ATRIUM RECEIVES BLOOD FROM THE VENA CAVA
· THE LEFT ATRIUM RECEUVES BLOOD FROM THE PULMONARY VEINS.
· WHEN THE ATRIA CONTRACT, BLOOD PASSES INTO THE LOWER CHAMBERS, CALLED VENTRICLES.
· WHEN THE RIGHT VENTRICLE CONTRACTS, IT PUMPS BLOOD OUT INTO THE PULMONARY ARTERIES.
· WHEN THE LEFT VENTRICLE CONTRACTS, IT PUMPS BLOOD OUT INTO THE AORTA.
· THE THICKNESS OF THE WALS OF EACH CHAMBER OF THE HEART IS RELATED TO THE DISTANCE THAT IT HAS TO PUMP THE BLOOD.
· WHY DO YOU THINK THAT THE ATRIA HAVE LESS MUSCULAR WALLS THAN THE VENTICLES?
· THE TWO ATRIA ONLY HAVE TO PUMP BLOOD A SHORT DISTANCE DOWN TO THE VENTRICLES.
· THE VENTRICLES HAVE MUCH THICKER WALLS BECAUSE THEY HAVE TO DEVELOP ENOUGH PRESSURE TO FORCE THE BLOOD FURTHER.
· THE RIGHT VENTRICLE HAS ONLY TO FORCE BLOOD TO THE LUNGS, WHICH ARE VERY NEAR THE HEART.
· WHEREAS THE LEFT VENTRICLE PUMPS BLOOD ALL ROUND THE BODY.
· THEREFORE THE BLOOD ENTERING THE AORTA FROM THE LEFT VENTRICLES IS AT A MUCH HIGHER BLOOD PRESSURE THAN THE BLOOD ENTERING THE PULMONARY ARTERY.
· TWO SETS OF VALVES ARE PRESENT IN THE HEART TO KEEP THE BLOOD FLOWING IN ONE DIRECTION.
· THE ATRIO-VENTRICULAR VALVES ARE FOUND ON EACH SIDE, BETWEEN THE ATRIA AND THE VENTRICLES.
· THEY PREVENT THE BACKFLOW OF BLOOD INTO THE ATRIA WHEN THE VENTRICLES CONTRACT.ON THE RIGHT SIDE, THE TRICUSPID VALVE HAS THREE FLAPS.ON THE LEFT SIDE, THE BICUSPID VALVE HAS TWO FLAPS.
· THE EDGES OF ATRIO-VENTRICULAR VALVES ARE SUPPORTED BY NON –ELASTIC STRANDS, THE CHORDAE TENDINAE, WHICH ARE ENCHORED TO THE MUSCULAR WALL OF THE VENTRICLES.
· THE SEMI-LUNAR VALVES ARE FOUND AT THE BASE OF THE PULMONARY ARTERY ANDD THE AORTA.
· THESE VALVES CLOSE TO PREVENT THE BACKFLOW OF BLOOD INTO THE VENTRICLES WHEN THEY RELAX.
THE CARDIAC
CYCLE
v THE CARDIAC CYCLE IS THE SEQUENCE OF EVEENTS OF THE HEARTBEAT BY WHICH BLOOD IS PUMPED ROUND THE BODY.
v IT IS DESCRIBED IN TERMS OF ALTERNATE CONTRACTIONS (SYSTOLE) AND RELAXATION (DIASTOLE).
v THE TIME TAKEN FO SECONDS WHEN THE HEART AND RELAXATION IS BEATING AT A RATE OF 75 BEATS PER MINUTE.
v THE VALVES IN THE HEART RESPOND TO PRESSURE CHANGES DURING A CARDIAC CYCLE.
v THE NOISE OF THE BLOOD WHEN THE VALVES OPEN AND CLOSE MAKES THE SOUND OF YOUR HEARTBEAT (LUB-DUB)
v CONTRACTION AND RELAXATION OCCURS AS FOLLOWS
ü ATRIAL DIASTOLE
ü ATRIAL SYSTOLE
ü VENTICULAR SYSTOLE
ü VENTRICULAR DIASTOLE
v DIASTOLE ATRIUM
ü BOTH ATRIUM RELAXED
ü OXYGENATED BLOOD FLOWS FROM PULMONARY VEIN INTO THE LEFT ATRIUM.
ü DEOXYGENATED BLOOD FLOWS FROM VENA CAVA INTO THE RIGHT ATRIUM.
v ATRIAL SYSTOLE
ü BOTH THE ATRIA CONTRACT SIMULTANEOUSLY.
ü THE BLOOD PASSES DOWN TO THE VENTRICLES
ü THE ATRIO-VENTRICULAR VALVES OPEN DUE TO THE PRESSURE OF BLOOD AGAINST THEM.
v VENTRICULAR SYSTOLE
ü THE THICK MUSCULAR WALLS OF THE VENTRICLES COTRACT
ü THE PRESSURE IN THE VENTRICLES RISES AND CLOSES THE ATRO-VENTRICULAR VALVES, PREVENTING BLOOD FROM RETURNING TO THE ATRIA.
ü THE PRESSURE FORCES OPEN THE SEMI LUNAR VALVES OF THE AORTA AND PULMONARY ARTERY AND BLOOD ENTERS THESE VESSELS.
ü THE CLOSING OF THE ATRIO VENTRICULAR VALVES DURING VENTRICULAR SYSTOLE PRODUCES THE FIRST HEART SOUND, DESCRIBED AS LUB.
v VENTRICULAR DIASTOLE
ü THE VENTRICLES RELAXED
ü THE PRESSURE INSIDE THE VENTRICLES DROPS BELOW THAT IN THE AORTA AND PULMONARY ARTERY.
ü BLOOD UNDER HIGH PRESSURE IN THE AORTA AND PULMONARY ARTERY CAUSE THA SEMI- LUNAR VALVES TO SHUT, PREVENTING BLOOD FROM GOING BACK INTO THE VENTRICLES.
ü THIS PRODUCES THE SECOND HEART SOUND DUB.
PULSE
Ø VENTRICULAR SYSTOLE (CONTRACTION) FORCES A BLOOD AT HIGH PRESSURE THROUGH THE ARTERIES.
Ø THE EXPANSION OF THE ARTERIES CAN BE FELT AS A ‘PULSE’.
Ø THE PARTICULAR WHERE THE ARTERY IS NEAR THE SKIN SURFACE.
Ø THE PULSE IS TRADITIONALLY TAKEN ABOVE THE WRIST (RADIAL PULSE)
CONTROL OF THE
HEARTBEAT (CARDIAC CONDUCTION SYSTEM)
o CARDIAC MUSCLES CONTINUOUS TO CONTRACT RHYTMICALLY EVEN AFTER THE HAS BEEN REMOVED FROM THE BODY.
o THE CARDIAC MUSCLE IN THE HEART IS MYOGENIC.IT CONTRACTS AND RELAXES AUTOMATICALLY AND DOES NOT DEPEND ON STIMULATION BY NERVES.
o THE STIMULUS OF CONTRACTION OF THE HEART ORIGINATES IN A SPECIFIC REGION OF THE RIGHT ATRIUM CALLED THE SINO-ATRIAL NODE (SAN)
o THIS IS LOCATED NEAR THE ENTRANCE OF THE SUPERIOR VENA CAVA.
o THE SAN DETERMINE THE BASIC RATE OF HEART BEAT AND IS THEREFORE KNOWN AS THE PACEMAKER
o THE SAN SEND OUT ELECTRICAL IMPULSES TO THE REST OF THE ATRIA.
o THESE IMPULSES SPREADS OUT OVER THE ATRIAL WALL.
o SO BOTH RIGHT AND LEFT ATRIA CONTRACT AT THE SAME TIME.
o THE IMPULSES DO NOT PASS DOWN TO THE VENTRICLES
o IT IS IMPORTANT THAT THE VENTRICLES DO NOT START TO CONTRACT UNTIL THE ATRIA HAVE FINISHED CONTRACTING.
o THE DELAYS ENSURES THAT THE VENTRICLES DO NOT START TO CONTRACT BEFORE THEY FILL WITH BLOOD.
o THE IMPULS THEN REACHES A SECOND NODE,THE ATRIO-VENTRICULAR NODE (AVN) WHICH LIES BETWEEN THE TWO ATRIA.
o TO ALLOW BLOOD TO BE FORCE UPWARD INTO THE ARTERIES, THE VENTRICLES NEED TO CONTRACT FROM THE APEX UPWARDS.
o TO ACHIEVE THIS, THE NEW WAVE OF EXCITATION FROM THA AVN IS CONDUCTED ALONG THE PURKYNE FIBRES (PURKINJE FIBRES) WHICH COLLECTIVELY MAKE UP THE BUNDLE OF HIS.
o BOTH VENTRICLES ARE STIMULATED SIMULTANEOUSLY.
o THE VENTRICULAR CONTRACTION BEGINS AT THE BOTTOM OF THE HEART AND SPREAD UPWARDS.
o SO BLOOD IS SQUEEZED UP AND OUT TROUGH THE ARTERIES.
ELECTROCARDIOGRAM (ECG)
v THE ELECTRICAL ACTIVITY THAT SPREADS THROUGH THE HEART DURING THE CARDIAC CYCLE CAN BE DETECTED USING ELECTRODES PLACED ON THE SKIN.
v THE PATTERN PRODUCED CAN BE EITHER SHOWN ON AN OSCILLOSCOPE SCREEN OR TRACED ON PAPER.
v THE TRACING IS CALLED AN ELECTROCARDIOGRAM AND THE APPARATUS USED IS AN ELECTROCARDIOGRAPH.
v ELECTROCARDIOGRAM IS TAKEN TO DETECT ABNORMALITIES THAT MAY CONFIRM A SUSPECTED HEART ATTACK FOR EXAMPLE
v A NORMAL TRACING, AS SHOWN IN FIGURE , SHOWS FIVE WAVESWHICH ARE CALLED P,Q,R,S, AND T
v A TYPICAL ECG CONSISTS OF CHARACTERISTIC WAVES WHICH CORRESPOND TO PARTICULAR EVENTS IN THE CARDIAC CYCLE.
v THE WAVES IS CAUSED BY ATRIAL SYSTOLE (THE SPREAD OF ACTION POTENTIAL FROM SAN THROUGH THE TWO ATRIA)
v THE QRS WAVES IS CAUSED BY VENTRICULAR (THE SPREAD OF ACTION POTENTIAL THROUGH THE TWO VENTRICLES)
v THE T WAVES COINCIDES WITH VENTRICULAR DIASTOLE.
CARDIOVASCULAR
REGULATION THAT INVOLVES NERVES AND HORMONES.
§ ALTHOUGH THE PACEMAKER (SAN) TRIGGERS THE HEARTBEAT, IT DOES NOT MEAN THAT THE HEART IS NOT SUPPLIED WITH ANY SPECIFIC NERVES
§ IN FACT, THE CONTROL OF THE CARDIAC CYCLE IN HUMANS AND OTHER MAMMALS IS THROUGH THE AUTONOMIC NERVOUS SYSTEM.
§ THE AUTONOMIC NERVOUS SYSTEM IS LOCATED IN THE HINDBRAIN KNOWN AS MEDULLA OBLONGATA.
§ THE SAN IS SUPPLIED WITH TWO SETS OF NERVES.
§ PARASYMPATHETIC NERVES
§ SYMPATHETIC NERVE
§ BOTH THESE SETS OF NERVES DO NOT TRIGGER THE HEARTBEAT, BUT CAN AFFECT THE ACTIVITY OF THE PACEMAKER SO AS TO INFLUENCE THE RATE OF THE HEARTBEAT.
§ PARASYMPATHETIC---STIMULATION OF THE PARA SYMPATHETIC NERVES CAUSE A RELEASE OF ACETYLCHOLINE IN THE SAN, THE AVN AND THE HEART MUSCLE.THIS SLOW DOWN THE RATE OF THE HEARTBEAT.
§ SYMPATHETIC-----STIMULATION OF THE SYMPATHETIC NERVE CAUSESA RELEASE OF NORADRENALINE.NORADRENALINE INCREASES THE RATE OF HEARTBEAT
§ THE MEDULLA HAS TWO REGION AFFECTING HEART RATE*** (1) THE CARDIAC INHIBITORY CENTRE WHICH REDUCES THE HEART RATE.*** (2) THE CARDIAC ACCELERETOR CENTRE WHICH STIMULATES THE HEART RATE.
