circulatory system Flashcards
What is physiology?
The dynamic study of life that describes the vital functions of living organisms and their organs, cells & molecules.
What does physiology deal with?
How the human body functions, depending on individual organ systems, cell functions, and interactions between subcellular organelles and molecules.
What is the circulatory system composed of?
The heart and a series of vessels through which the blood circulates.
What type of system is the circulatory system?
A closed system where blood does not come in direct contact with tissues.
How many chambers does the heart have?
Four chambers: right atrium, right ventricle, left atrium, and left ventricle.
What guards the apertures between each atrium and its respective ventricle?
Atrioventricular valves: tricuspid valve on the right side and mitral valve on the left side.
What valves guard the exits from the right ventricle and left ventricle?
Pulmonary semilunar valve and aortic semilunar valve, respectively.
What is the structural composition of the heart?
Composed of cardiac muscle fibers characterized by branching and interconnecting fibers, each surrounded by a cell membrane.
What proteins are contained in cardiac muscle fibers?
Actin, myosin, troponin, tropomyosin, and dystrophin.
What is the role of intercalated discs in cardiac muscle?
They allow for free diffusion of ions and provide resistance bridges for rapid spread of excitation waves.
What is the significance of cardiac muscle functioning as a syncytium?
It leads to the heart contracting as one unit, resulting in more efficient pumping.
What types of cardiac muscle are present in the heart?
Atrial muscle, ventricular muscle, and specialized excitatory and conductive muscle fibers.
What is the primary function of the heart?
To act as a pressure pump that delivers oxygenated blood to the systemic circulation.
What is the function of arteries?
To stretch during systole and maintain blood flow during diastole through elastic recoil.
What is the main site for nutrient and waste exchange?
Capillaries, due to their very thin walls and large cross-sectional area.
What is the role of veins in the circulatory system?
To collect and return blood from capillaries to the heart.
What is the resting membrane potential of cardiac myocytes?
-90 mV.
What initiates the depolarization of cardiac myocytes?
An adequate stimulus that causes rapid depolarization to about -65 mV.
What characterizes phase 0 of the action potential in cardiac myocytes?
Rapid upstroke from resting value to a positive value of about +20 mV, initiated by fast Na+ channels.
What occurs during phase 1 of the cardiac action potential?
A rapid small initial repolarization caused by inactivation of fast Na+ channels and efflux of K+.
What is the plateau phase in the cardiac action potential?
A phase where membrane repolarization slows down, maintaining membrane potential around zero mV.
What is the duration of the plateau phase in ventricular myocytes?
About 200 msec.
What currents balance during the plateau phase of the cardiac action potential?
A balance between inward Ca2+ currents and outward K+ currents.
What increases during the action potential phase related to K+ conductance?
The conductance of the membrane to K+ increases gradually during this phase but is still less than its value under resting conditions.
At what membrane potential do long-lasting Ca²⁺ channels start to open?
Long-lasting Ca²⁺ channels start to open during phase 0 when the membrane potential reaches -40 mV.
What is the role of Ca²⁺ during the plateau phase of the cardiac action potential?
One Ca²⁺ is carried out and 3 Na⁺ are carried in, resulting in a net influx of one positive ion, which prolongs the duration of the plateau.
What happens during the rapid repolarization phase?
Long-lasting Ca²⁺ channels close while delayed rectifier K+ channels become maximally activated, causing outward K+ current that leads to repolarization.
What is the resting membrane potential typically in cardiac cells?
-90 mV.
Define the absolute refractory period in cardiac muscle.
The period during which the fiber does not respond to any stimulus, coinciding with phases 0, 2, and about half of phase 3.
What is the relative refractory period?
The period during which a stronger stimulus than normal is needed to produce an action potential, remaining until phase 4.
What specialized fibers generate impulses for the heart?
Fibers of the conducting system of the heart, including the sinoatrial node, atrioventricular node, and Purkinje fibers.
What is the property of rhythmicity in the heart?
The property of auto-generation of impulses acquired by the fibers of the conducting system.
Where is the sinoatrial (SA) node located?
In the wall of the right atrium near the opening of the superior vena cava.
What is the normal discharge rate of the SA node?
90 — 105 beats per minute.
What is the function of the atrioventricular (AV) node?
It is the only conducting pathway between the atria and ventricles.
What occurs during the initiation of the cardiac excitation wave?
The wave is initiated by the cardiac pacemaker (the SA node) as it has the most rapid rate of diastolic depolarization.
What is the significance of conduction delay in the AV node?
It allows sufficient time for the atria to empty their blood into the ventricles before ventricular systole begins.
What is the effect of sympathetic stimulation on the A-V delay?
It shortens the A-V delay.
What initiates the contractile response of cardiac muscle?
The contractile response begins just after the start of depolarization.
What is Starling’s Law of the heart?
Within physiological limits, the more the initial length of the muscle fibers, the more is its force of contraction.
What factors improve the inotropic state of cardiac muscle?
Positive inotropics, which shift the Starling curve up and to the left.
What are negative inotropics?
Factors that decrease the inotropic state of cardiac muscle, shifting the Starling curve down and to the right.
What role do catecholamines play in cardiac muscle contraction?
They act on β-receptors, causing voltage-gated Ca²⁺ channels to spend more time open.
What effect do negative inotropics have on the Starling curve?
They shift the Starling curve down and to the right.
Which catecholamines act on B receptors to affect cardiac contraction?
Norepinephrine.
What is the role of calcium ions in cardiac muscle contraction?
They improve the inotropic state of the cardiac muscle.
What happens at very high calcium concentrations in the heart?
The heart stops in systole (calcium rigor).
Which drug has a negative inotropic effect on atrial muscle?
Acetylcholine.
What is the stroke volume (SV) in ml?
70 ml.
What is the end diastolic volume (EDV) in ml?
135 ml.
What is the end systolic volume (ESV) in ml?
65 ml.
How is stroke volume (SV) calculated?
SV = EDV - ESV.
What is cardiac output (CO)?
CO = Stroke Volume (SV) x Heart Rate (HR).
What is the average cardiac output at rest?
About 5 L/min.
What factors influence cardiac output (CO)?
- Excitement
- Inspiration
- Exercise
- Exposure to high temperature
- Eating
- Epinephrine secretion
- End of pregnancy
- Body position
True or False: Cardiac output must equal venous return.
True.
What is the role of the parasympathetic nervous system in heart function?
It inhibits atrial properties and decreases heart rate.
What is the effect of the sympathetic nervous system on the heart?
It stimulates atrial and ventricular properties, increasing heart rate and cardiac work.
What is arterial blood pressure (ABP)?
It is the pressure of blood on arterial walls.
What is systolic pressure (SP)?
It is the maximal pressure reached during systole, typically 120 mmHg.
What is diastolic pressure (DP)?
It is the minimal pressure reached during diastole, typically 70 mmHg.
How is pulse pressure calculated?
Pulse pressure = SP - DP.
What is the average systemic arterial pressure throughout the cardiac cycle?
It is calculated as DP + 1/3 Pulse pressure.
What happens to arterial blood pressure with age?
ABP increases due to loss of elasticity.
True or False: Females generally have higher ABP than males after age 45.
False.
What is the impact of sympathetic stimulation on ABP?
It increases SP due to increased stroke volume and DP due to peripheral vasodilatation.
What does the capillary fluid shift mechanism regulate?
It regulates blood volume and arterial blood pressure.
How does the kidney regulate arterial blood pressure?
By regulating extracellular fluid volume and releasing renin.
What is the effect of renin release on blood pressure?
It leads to the release of angiotensin II, causing vasoconstriction and increased blood pressure.
What is the role of the kidney in regulation of drop in ABP?
The kidney regulates drop in ABP through renal ischemia, renin release, and release of angiotensin II, which causes vasoconstriction and aldosterone secretion.
What does aldosterone secretion lead to?
Aldosterone secretion leads to salt and water absorption.
What are atrial mechanoreceptors responsible for?
Atrial mechanoreceptors are responsible for sensing blood volume and ABP, leading to secretion of aldosterone and antidiuretic hormone (ADH).
How does an increase in ABP affect salt and water excretion?
An increase in ABP causes excretion of salt and H2O.
What is the primary process through which equilibrium with interstitial fluid occurs?
Equilibrium occurs through the exchange of materials across capillary walls.
What factors influence the diffusion of substances across capillary walls?
Factors include molecular weight, concentration gradient, and solubility of substances.
Fill in the blank: Substances with a molecular weight less than _______ will diffuse easily.
5000
What type of substances diffuse through the pores of capillaries?
Water-soluble but lipid-insoluble substances diffuse through the pores.
What is the process of bulk transport of electrolytes and crystalloids dependent on?
It depends on the balance of hydrostatic pressure gradient and osmotic pressure gradient.
What are the types of edema?
Types of edema include generalized and localized edema.
What causes generalized edema?
Generalized edema can be caused by increased capillary blood pressure, decreased plasma protein synthesis, and lymphatic obstruction.
What is the significance of venous pressure in right-side heart failure?
In right-side heart failure, venous pressure increases, leading to generalized edema.
What is the typical pressure drop across veins?
There is a slight drop of pressure across veins of about 10 mmHg.
True or False: Veins act as blood reservoirs.
True
What mechanisms aid venous return?
Venous return is aided by muscle contraction, respiratory movement, and cardiac suction.
What is inadequate tissue perfusion due to inadequate cardiac output called?
Shock
What are some causes of shock?
Causes of shock include hemorrhage, burns, trauma, vasogenic shock, and heart disease.
What are the mechanisms that maintain ABP for adequate perfusion?
Mechanisms include nervous factors and humoral regulators.
What are some humoral regulators of ABP?
Humoral regulators include catecholamines, angiotensin II, and vasopressin.
What is the role of arterial baroreceptors?
Baroreceptors monitor blood pressure and send inhibitory impulses to depressor areas.
What happens to blood flow during early ventricular systole?
During early ventricular systole, blood is sucked into the atria due to the downward movement of the AV ring.
What is autoregulation in coronary blood flow influenced by?
Autoregulation is influenced by hypoxia, CO2 levels, and adenosine.
What type of receptors are found in coronary arteries?
Coronary arteries contain alpha-adrenergic and beta-adrenergic receptors.
What is the phase of maximal relaxation in coronary circulation?
6 in Coronary 1Iow
Refers to the relaxation phase of coronary blood flow
What happens to coronary blood flow during the rest of diastole?
Gradually due to aortic pressure
Indicates the influence of aortic pressure on coronary blood flow
What types of receptors are found in coronary arteries?
2 types: *α adrenergic, *β adrenergic
These receptors mediate vascular responses
What is the effect of α adrenergic receptors in coronary arteries?
Mediate vasoconstriction (VC)
α adrenergic receptors are involved in narrowing blood vessels
What is the effect of β adrenergic receptors in coronary arteries?
Mediate vasodilation (VD)
β adrenergic receptors promote widening of blood vessels
What is the effect of sympathetic stimulation on vasodilation?
Causes vasodilation due to work
Sympathetic stimulation can lead to increased blood flow despite vasoconstriction effects
What is the role of the vagus (parasympathetic) system in coronary blood flow?
Causes vasodilation by direct effect
The vagus nerve influences heart rate and blood vessel dilation
What is the resultant effect of vagus stimulation on coronary circulation?
Vasoconstriction due to work
The vagus nerve’s activity can also lead to constriction under certain conditions
