A&P2:Chpt20-Heart
Circulatory System
* = blood vessels.
Cardiovascular System
*blood, heart & blood vessels. *the heart is the pump.
Blood Circulation: Body
*2 circuits, the systemic and pulmonary
Atrioventricular Valves Close
*A-V valves close preventing backflow of blood into atria: -ventricles contract -chordae tendinae pulled taut -papillary muscles contract -cannot open due to increased pressure in ventricles
Atrioventricular Valves: Valves between Atria and Ventricles
*A-V valves open and allow blood to flow from atria into ventricles when ventricular pressure is LOWER than atrial pressure: -ventricles relaxed -chordae tendineae slack -papillary muscles relaxed
One Cardiac Cycle- Vocabulary
*At 75 beats/min, one cycle requires 0.8 sec *End diastolic volume (EDV)-volume in ventricle at end of diastole, about 130ml *End systolic volume (ESV)-volume in ventricle atr end of systole, about 60ml *Stroke volume (SV)-the volume ejected per beat from each ventricle, about 70ml. (SV=EDV-ESV)
The Cardiac Cycle: Systole and Diastole
*Atrial systole/ventricular diastole -the atria contract, increasing pressure forces the AV valves to open -the amount of blood in the ventricle at the end of diastole is the End Diastolic Volume (EDV) *Ventricular systole/ atrial diastole -ventricles contract and increasing pressure forces the AV valves to close -pressure continues to rise opening the SL valves leading to ventricular ejection
Conduction System of Heart
*Autorhythmic Cells *SA node: cluster of cells in wall of right atria. Begins heart activity that spreads to both atria. Excitation spreads to AV node. *AV node: in atrial septum, transmits signal to bundle of HIS *AV bundle of HIS: the connection between atria and ventricles. Divides into bundles branches & purkinje fibers.
Relaxation Period fo the Cardiac Cycle
*Both atria & ventricles are relaxed. Pressure in the ventricles fall & the SL vavles close. *Brief time all four valves are closed = isovolumetric relaxation
Cardiac Output
*Cardiac output (CO)- is the volume of blood ejected from the left ventricle each minute. (CO=SV x HR) *Cardiac reserve- is the ratio between the maximum cardiac output a person can achieve and the cardiac output at rest. Important for determining relative fitness level. (sometimes a large cardiac output does not mean good health. ie-very high heart rate)
Electrocardiogram---ECG or EKG
*EKG-action potentials of all active cells can be detected and recorded *Depolarization=signal begins *Excitation=transmission of signal w/i region *Repolarization=preparation to recieve new signal *P wave-atrial depolarization (atrium contracts) *P to Q interval-conduction time from atrial to ventricular excitation. *QRS complex-ventricular depolarization -atrium repolarization T wave- ventricular repolarization
3 Layers of the Heart Walls
*Epicardium -visceral layer of serous pericardium *Myocardium -cardiac muscle layer is the bulk of the heart *Endocardium -chamber lining & valves
Heart rate is also affected by...
*Epinephrine, norepinephrine, thyroid hormones *Ions (Na+, K+, Ca2+) *Age, gender, physical fitness, external temperature
Chambers and Sulci of the heart
*Four chambers -2 upper = atria -2 lower = ventricles *Sulcus -groove on surface of heart containing coronary blood vessels and fat.
Coronary Arteries
*Left coronary artery -circumflex branch: supplies left atrium & left ventricle -anterior interventricular artery: supplies both ventricles *Right coronary artery -marginal branch: supplies right ventricle -posterior interventricular artery: supplies both ventricles
Regulation of Heart Rate
*Nervous control from the cardiovascular center in the medulla -Sympathetic impulses +increase heart rate & force of contraction -Parasympathetic impulses +decrease heart rate -Baroreceptors (pressure receptors) +detect change in BP and send info. to the cardiovascular center +located in the arch of the aorta and carotid arteries.
Other Influences on Heartbeat
*Note: signals from the autonomic nervous system & hormones, such as epinephrine, do modify the heartbeat (in terms of rate & strength of contraction), but they do not establish the fundamental of rhythm.
Influences on Stroke Volume
*Preload (affect of stretching) - Frank-Starling Law of Heart -More muscle is stretched greater force of contraction -more blood, more force of contraction results *Contractility -Autonomic nerves, hormones Ca+2 or K+ levels. *Afterload -Amount of pressure created by the blood in the way.
Fibrous Skeleton of Heart
*Purpose of fibrous skeleton: -support structure for heart valves -insertion point for cardiac muscle bundles -electrical insulator between atria & ventricles
Rhythm of Conduction System
*SA node fires spontaneously 90-100 times per minute *AV node fires at 40-50 times per minute *If both nodes are suppressed fibers in ventricles by themselves fire only 20-40 times per minute (note: normal is 60-70 times per minute)
Timing of Atrial & Ventricular Excitation How quick is the response?
*SA node setting pace since it is the fastest. *Excitation spreads through both atria and to AV node (50msec) *Delay at AV node due to atria to fully contract filling ventricles before ventricles contract (100msec) *Excitation spreads through both ventricles simultaneously (50msec)
Semilunar Valves: Valves between ventricles and aorta or pulmonary trunk
*SL valves open w/ ventricular contraction. -allow blood to flow into pulmonary trunk & aorta *SL valves close w/ ventricular relaxation -prevents blood from returning to ventricles, blood fills valve cusps, tightly closing the SL valves.
the Cardiac Cycle
*a cardiac cycle consists of the systole (contraction) and the diastole (relaxation) of both atria, rapidly followed by the systole and diastole of both ventricles. *Pressure & volume both change during the cardiac cycle. *Remember, valves open and close in response to PRESSURE changes.
Electrocardiogram
*a recording of the electrical changes that accompany each cardiac cycle is called an electrocardiogram (ECG or EKG) *the CARDIAC CYCLE is the complete set of contractions and relaxations of all heart chambers in a sequence.
Autorhythmic Cells: The Conduction System
*cardiac muscle cells are autorhythmic cells because they are self-excitable. They repeatedly generate spontaneous action potentials that then trigger heart contractions *these cells act as a pacemaker to set rhythm for the entire heart *they form the conduction system, the route for propagating action potential through the heart muscle
coronary veins
*collects wastes from cardiac muscle *coronary sinus (enlarged posterior) then to right atrium
Pericardium Layers
*fibrous pericardium -dense irregular CT -protects & anchors the heart *serous pericardium -thin delicate membrane -pericardial cavity w/ fluid is between parietal & visceral layers
Cardiac muscle and the cardiac conduction system
*how does a heart know how and when to beat? *the cardiac conduction system is involved
Left Ventricle
*left ventricle recieves blood from left atrium *chordae tendineae / papillary muscles / trabeculae carneae *aortic semilunar valve (aortic valve on diagram)
Right Ventricle
*papillary muscles / trabeculae carneae *chordae tendineae *interventricular septum *pulmonary semilunar valve (note: labeled as pulmonary valve on diagram in textbook)
Right Atrium
*receives blood from 3 sources -superior vena cava -inferior vena cava -coronary sinus *interatrial septum *fossa (shallow depression) ovalis / foramen (hole) ovale -present in the fetus- *tricuspid valve (right artrioventricular valve)
Left Atrium
*recieves blood from lungs *bicuspid valve (mitral valve, left atrioventricular valve)
Auscultation
*the act of listening to sounds w/i the body is called auscultation. *the sound of a heartbeat comes primarily from the turbulence in blood flow caused by the closure of the valves. *The first heart sound (lubb) is created by blood turbulence associated w/ the closing of the atrioventricular valves. *The second heart sound (dupp or dubb) represents the closing blood turbulence of the semilunar valves.
Coronary Circulation
*the flow of blood through the many vessels that flow through the myocardium of the heart is called the coronary (cardiac) circulation. *the heart as a very active muscle needs lots of O2 *many anastomoses -connections between arteries supplying blood to the same region, provide alternate routes if one artery becomes occluded (blocked) -stoma = opening
Pericardium
*the heart is enclosed and held in place by the pericardium. -fibrous pericardium -serous pericardium +parietal layer +visceral layer +pericardial cavity (between parietal and visceral layer) +pericardial fluid (contained in cavity)
Location of the Heart
*the heart is situated between the lungs in the mediastinum. *mediastinum = region between lungs, vertebral column & sternum.
Myocardial thickness and function
*the thickness of the myocardium of the four chambers varies -atrial walls are thin -ventricular walls are thicker -right ventricles walls are thinner than the left ventricle
heart valves and circulation of blood
*valves open & close in response to PRESSURE changes as the heart contracts & relaxes *in order for valves to work properly, they need support in addition to muscle attachments
Systemic Circulation (Pathway)
-left ventricle to aorta -aorta branches to arteries to organs -arteries to arterioles in tissure -arterioles to thin walled capillaries -deoxygenated blood returns in venules -venules to veins (superior & inferior vena cava) to right atrium.
Pulmonary Circulation (Pathway)
-right ventricle to pulmonary trunk -pulmonary trunk to pulmonary arteries (blood is deoxygenated at this point- came from body) -pulmonary arteries to lungs for exchange of gases -arterides. capillaries, venuals -oxygenated blood to heart in pulmonary veins -to the left atrium
Conduction System of Heart
1. sinoatrial (SA) node 2. atrioventricular (AV) node 3. atrioventricular (AV) bundle (bundle of HIS) 4. right and left bundle branches 5. purkinje fibers
systemic and pulmonary circulations
Right Atrium (deoxygenated blood)->Tricuspid Valve->Right Ventricle->Pulmonary Valve->Pulmonary Trunk & Right & Left Pulmonary Arteries (still deoxygenated blood)-> Pulmonary Arterioles-> Pulmonary Capillaries, blood loses CO2 & gains O2->Pulmonary Venules->Left & Right Pulmonary Veins(oxygenated blood)->Left Atrium->Bicuspid Valve->Left Ventricle->Aortic Valve->Aorta & Systemic Arteries->Systemic Arteriols->Systemic Capillaries, blood loses O2 & gains CO2->Systemic Venules->Systemic Veins->Superior Vena Cava, Inferior Vena Cava, Coronary/Cardiac Sinus->back to Right Atrium (deoxygenated blood)