Normal structure & Function Flashcards
Main function of Heart?
Pump blood to all organs and tissues in body
Bloods role?
Oxygen and nutrients to tissues and removes waste products
Prime function of right heart?
Via the pulmonary trunk drives the low pressure pulmonary circulation
Prime function of left heart?
Via the aorta drives high pressure systemic circulation
How many pumps does heart have?
Two
High pressure pump?
On the left side. Forces blood to flow to other tissues around body and then back to the heart
Low pressure pump?
On the right side. Forces blood to flow to the lungs and back to the heart.
Blood circulates body via?
Arteries
Blood returns to the heart via?
Veins
Features of Arteries?
The walls of larger central arteries are elastic and recoil to help propel blood
The walls of smaller arteries and arterioles are much more muscular and are mainly responsible for peripheral resistance to blood flow.
Features of veins?
Thin walls and easily distensible- act as a major reservoir of blood
Larger veins have valves that support unidirectional blood flow- important during standing and exercise
Capillaries structure and function?
Tiny vessels forming a network linking arterial and venous blood flow. In this gases and nutrients or waste are exchanged at a cellular level
Capillary walls?
Thin single layer of endothelial cells
Permeable to small molecules facilitating exchange of hormones, fluid and nutrients, electrolytes etc between interstitial fluid and blood.
What does the lymphatic system do?
It comprises of a network of thin walled vessels which enable excess interstitial fluid to return to the circulation
Where does the heart lie?
Lies in the chest cavity, deep to the sternum within the rib cage, between the lungs, superior to the diaphragm in the mediastinum.
Where is the base of your heart?
Closer to the head than the apex
Describe the position of the apex of the heart?
Lowest most lateral point of heart
5th left intercostal space just medial to the mid-clavicular line
4 reasons it is clinically important to know the location of the heart?
- It directs you to where you could normally find the apex beat
- Indicates listening areas on chest wall for where you could best hear heart sounds and murmurs
- Helps you know were best to place electrodes when recording a trace of hearts electrical activity
- Helps you know where to put pressure in CPR
CAME- CPR Apex Murmurs & heart sounds ECG- electrodes
Coronary Sulcus
Groove on the external surface of the heart that separates atria from ventricles
What do superior and inferior vena cavae do?
Drain blood from upper and lower parts of the body into the right atrium
What does aorta do?
Carries oxygenated blood from left ventricle to body
What do pulmonary arteries do?
Carry systemic venous blood from the right ventricle to the lungs
Where do the left and right coronary arteries rise from?
Root of the aorta just above the aortic valve, and lie within the coronary sulcus
Why is the left ventricular wall thicker than the right?
Pumps blood against high pressure in the systemic circulation, whereas RV pumps blood into low pressure pulmonary circulation
What are valves in heart for?
To maintain unidirectional blood flow between chambers and between chambers and vessels
How many pair of valves does heart have?
2- atrioventricular and semilunar
AV valves?
Atrioventricular valves
Located between atria and ventricles
Right side AV valve has 3 cusps and is called tricuspid
Left side valve has 2 cusps and is called mitral valve
SL valves?
Semilunar valves
Located within aortic and pulmonary trunk
Valve cusps are half moon shaped
They are called the aortic and pulmonary valves
Cardiac skeleton?
Consists of strong fibrous framework that prevents main components of heart pulling themselves apart during contraction. Heart valves are also anchored by this.
Were does drainage of the lymphatic system occur?
Right and left subclavian veins
What empties into the coronary sinus?
Large veins that drain myocardium which converge towards the coronary sulcus
How many veins drain blood from the lungs into the left atrium?
4
What does cardiac skeleton consist of?
Strong central framework of fibrous rings(annuli) that surround heart valves giving attachment to valve cusps and muscle fibers of heart chambers
How many layers of tissue is the heart composed of?
3-
epicardium
myocardium
endocardium
Epicardium description?
serous membrane of simple squamous epithelium overlaying loose connective tissue and fat
Forms smooth outer surface of the heart
Myocardium description?
Thick middle layer of cardiac muscle cells responsible for contracting ability of heart
Endocardium description?
Simple squamous epithelium overlaying a layer of connective tissue which allows blood to flow easily through the heart chambers
Factors which affect blood flow through the body?
Pressure difference
Resistance within vessels
Viscosity of blood
Why is blood flow required?
To supply nutrients to and remove metabolic waste products from the cells of the body.
When will blood flow through a vessel?
When a pressure difference exists between the 2 ends of the vessel- larger pressure is driving force so blood moves away from it
What is resistance?
Measure of how difficult it is for fluid to flow along a vessel
Frictional forces also exist within the fluid itself depending on it’s level of viscosity
What is blood viscosity affected by?
Haematocrit (volume of blood with red blood cells)- RBCs exert frictional drag on eachother and against vessel wall
What conditions could a patient with low blood velocity and high blood viscosity have?
Increased risk of thrombotic tendencies
which would equal vascular complications such as
-Coronary thrombosis
-Myocardial infarction
Describe laminar flow?
Blood flowing in an organized streamlined pattern
What does laminar flow refer to?
Fluid moving along a vessel behaves as if it has many concentric layers
Little mixing between layers
Fluid next to vessel wall experience lowest velocity of flow
Central blood has greatest velocity
This creates a pressure gradient
What is blood flow (Q)within the cardiovascular system determined by?
Head of pressure developed by the heart (P1-P2)
Resistance to flow encountered within the vessels (R)
Resistance to blood flow equation?
Q=[(P1-P2) / R]
In systemic circulation which of the following represents the driving pressure and which the exit pressure. Mean pressure in right atrium and mean pressure in ascending aorta.
Mean pressure in ascending aorta is P1 (driving pressure)
Mean pressure in right atrium is P2 (exit pressure)
What equation describes all factors that influence flow through a vessel?
Poiseuille equation
What is resistance to flow through a vessel affected by?
Length (L)
Inner radius (R)
Viscosity (n) of a fluid flowing through a vessel
What is blood flow primarily affected by?
Changes in the radius of blood vessels
What is vascular tone a result of?
Balance between constrictor and dilator influences
What is vasomotor tone?
During resting conditions a continuous low frequency sympathetic discharge from the vasomotor center in the medulla oblongata to the peripheral vessels (arterioles) maintains these vessels in a partially constricted state.
When does vasodilation commonly occur?
Following increased skeletal muscle metabolism (exercise) to increase blood flow and oxygen delivery to the muscles
What are initial electrical impulses in the heart generated by?
SA node
Initial electrical heart impulse?
SA node generates APs which spread through the atrial wall to the AV node
The AV nodes role?
Propagation of an AP through the AV nodal region is very slow and imposes a delay of excitation between atria and ventricles. This delay allows time for atria to empty contents into ventricles before ventricular contraction begins.
Where does impulse travel to from AV node?
Bundle of His (AV bundle)
What happens after the AV node receives AP?
AP passes through bundles of His and branches into ventricular muscle
Bundle branches terminate in purkinje fibers transferring potential to ordinary cardiac muscles = rapid simultaneous excitation of all ventricular muscle cells
When does a cardiac muscle fibre contract?
When an action potential is transmitted along its plasma membrane
How many types of cardiac myocytes and their names?
2 types ventricular myocyte (non-pacemaker) Pacemaker myocyte
Resting phase of myocyte AP?
Transient depolarization of a cell followed by repolarisation as a result of movement of ions across its cell membrane via ion channels
At rest membrane has a low permeability to Na+ and Ca++ and a high permeability to K+.
Depolarization of myocyte AP?
Increased Membrane permeability to Na+
-This is caused by rapid transient entry of Na+ through voltage- gated Na+ channels into the myocyte
Simultaneously membrane potential to K+ falls causing membrane potential to move away from the K+ equilibrium potential and towards the Na+ equilibrium potential (+60mV) = rapid upstroke on graph
Plateau phase of myocyte AP?
Increased membrane potential to Ca++
-membrane permeability to Na+ returns to its resting value due to inactivation of Na+ channels and membrane potential decays slowly (over 0.25secs)= plateau phase
What is plateau phase primarily due to ?
Slow influx of Ca++ via long lasting voltage gated Ca++ channels (L type) which activate relatively slowly until membrane potential reaches 40mV= increased permeability to Ca++- vital for muscle contraction
What is Ca++ entry into the cell vital for during the plateau phase of an AP?
Muscle contraction
Repolarization phase of myocyte AP?
Increased membrane permeability to K+
-At the end of plateau the voltage gated K+ channels open causing an increased permeability to K+ while Ca++ permeability decreases
Membrane potential returns to its resting level.
Membrane permeabilities in each stage of an AP?
Resting phase- Membrane permeable to K+
Depolarization phase- Increased Na+ permeability
Plateau phase- Increased membrane permeability to Ca++
Repolarization phase- Increased membrane permeability to K+
When is an action potential initiated?
When the membrane is depolarized to threshold potential
What will understanding the characteristics of pacemaker APs help you understand?
Origins of cardiac arrhythmias and treatment used to control them
What do pacemaker cells make up?
SA node
Resting phase of a pacemaker potential membrane potential?
Less negative than that of ventricular muscle fibers (it is around -55->-60mv)
What happens in the resting phase of a pacemaker AP?
- A progressive decrease in K+ membrane permeability results in fewer K+ moving out of the cells
- Slight increase in Na+ permeability results in a slow influx of Na+ (funny current) contributing towards depolarization
- Around this time a small rise in Ca++ conductance into cell via T type Ca++ channels which open very briefly causing membrane potential to rise very gradually towards threshold potential (-40mV)—-This unstable resting potential is called pacemaker potential
Threshold potential for pacemaker AP?
-40mV
What is pacemaker potential?
Membrane potential gradually rising towards threshold potential due to a small rise in Ca++ conductance into cells via T type Ca++ channels opening very briefly.
Depolarization of pacemaker AP?
As potential reaches threshold potential many (L type) slow long lasting Ca++ channels begin to open and the slow influx of Ca++ into the cell is primarily responsible for this phase.
Repolarization phase of pacemaker AP?
Voltage gated Ca++ (L type) channels become inactivated together with the opening of a large number of voltage gated K+ channels - causing diffusion of K+ out of fibers
Hyperpolarization of pacemaker AP?
K+ channels remain open for a few ?/10 of a second carrying a great XS of K+ ions out of fibre and resulting in an XS negativity inside the fibre. This = hyperpolarization (-55mv–>-60mv)
Hyperpolarization membrane potential?
-55mv–>-60mv
What does an excessive HR mean for cardiac filling?
Insufficient time to do it properly
Consequences of excessive HR?
Decreased CO
Possible death
What protects against insufficient cardiac filling?
Refractory period of cardiac myocyte
Explain what the refractory period is?
The refractory period of the heart is the interval of time during which a normal cardiac impulse cannot re-excite an already excited area of cardiac muscle. The normal refractory period of the ventricle lasts from 250 to 300 milliseconds. This corresponds to the duration of the action potential.
There is an additional relative refractory period of about 50 milliseconds during which the muscle is more difficult than normal to excite, but nevertheless can be excited.
The long refractory period ensures that cardiac muscle contraction and relaxation are almost complete before the next action potential is initiated. Thus tetanic contraction is prevented in cardiac muscle.
What is recorded in an ECG?
The coordinated rhythmical stimulation of the heart by the cardiac conduction system.
What equipment is used in an ECG?
Electrodes
What conditions are ECGs used to diagnose?
Myocardial Infarctions
Arrhthymias
Ventricular Hypertrophy
What is an arrhthymia?
Variation from the normal rhythm of the heart beat
What is ventricular hypertrophy?
Abnormal enlargement of the ventricular muscle cells of the heart
How many leads in an ECG?
12
What is an ECG?
Summation of all of the hearts electrical activity
What is the P wave of an ECG?
Caused by atrial depolarization
What does a P wave usually look like?
Contour is usually Positive Smooth Uniform size Less than 0.12secs
What does the QRS complex represent?
Time taken for depolarization of ventricles
What does the QRS complex look like?
R wave= dominant, looks like spike
Duration= 0.04-0.12secs)
What is the T wave of an ECG represent?
Ventricular repolarization
What does a T wave look like in an ECG?
Normally positive
What is the PR interval?
Portion of the ECG wave from the beginning of the P wave to the beginning of the QRS complex (onset of ventricular depolarization)
Duration of PR interval?
0.12->0.2secs
Where is the QT interval?
Extends from the start of the QRS complex to the end of the T wave
What is the QT interval?
Represents time between start of ventricular depolarization and the end of ventricular repolarization
What is the QT interval dependent on?
Heart rate
Varies inversely with heart rate
What does the ST segment represent?
Period from the end of ventricular depolarization to the beginning of ventricular repolarization
What does intrinsic regulation of the heart depend on?
Depends on normal functional characteristics of heart and not hormonal or neural regulation
What law is the main intrinsic mechanism set out in?
Starlings law
What is venous return?
The amount of blood flowing into the right atrium from veins during diastole.
Relationship between Venous return and end diastolic volume?
As venous return increases so too does end diastolic volume
Relationship between EDV and stretch of ventricular walls?
Greater the EDV
Greater the stretch of ventricular walls
What is the pre-load?
The extent to which the ventricular walls are stretched
What does it mean that cardiac muscle exhibits a “length versus tension” relationship?
Increased preload causes cardiac muscle fibres to increase with larger force and produce greater STROKE VOLUME
Cardiac output equation?
CO= HR x SV
What does
a) increased preload
b) decreased preload cause?
a) Increased CO
b) Decreased CO
What is Starlings law of the heart referring to?
Relationship between preload and stroke volume
Describes relationship between changes in pumping effectiveness of heart and changes in preload
Relatively small changes in preload do not effect pumping effectiveness of heart. True or false?
False ]Relatively small changes can have a great affect on pumping effectiveness
What is after load?
The resistance that contracting ventricles must overcome in order to propel blood downstream from the heart
(into pulmonary arteries from right ventricle and into aorta from left ventricle)
Ventricular function is relatively insensitive to small changes in after load. True or False
True
What does extrinsic control of the heart involve?
Hormonal control mechanisms
Neural control mechanism
What is neural regulation through?
Parasympathetic and sympathetic mechanisms
What is hormonal regulation through?
Adrenaline and noradrenaline secreted by adrenal medulla
Define parasympathetic?
Part of the autonomic nervous system -which is the portion of the nervous system concerned with regulation of activity of cardiac muscle, smooth muscle and glands
