Overview of the CV System Flashcards
Define homeostasis
The process of maintaining the “constancy” of our internal environment (temperature, oxygen concentration, pH, osmolarity, etc.)
Briefly define the cardiovascular system
The CV system is an elaborate transport network for blood, nutrients, gases, hormones and waste products.
Transport in the CV system may occur by… (2)
diffusion
convection
Describe transport by diffusion (4)
Transport due to gradients in concentration.
- Diffusion is used for short distance transport (e.g. across capillaries).
- Substances move along their concentration gradients.
- Very rapid process
- Can move large quantities of material over short distances
Describe transport by convection
Transport of a constituent by bulk motion of fluid.
- Convection is used for long distances (e.g. from one organ to another)
- Substances dissolved or contained in the blood move along with the blood flow
No cell in the body is located farther than … from a capillary.
10um
Both transport by diffusion and transport by convection require…
fluid (water)
Describe the body water compartments.
Total Body Water = 45L (for a standard white male)
2/3 of TBW is INTRAcellular fluid (ICF)
1/3 of TBW is EXTRAcellular fluid (ECF)
* Interstitial fluid (ISF) is 3/4 of ECF
* Plasma is 1/4 of ECF
As blood passes through capillaries, solutes exchange between … and … by ….
As blood passes through capillaries, solutes exchange between PLASMA and INTERSTITIAL FLUID by DIFFUSION.
The right heart supplies…
the lungs (pulmonary circulation)
The left heart supplies…
the organs (systemic circulation)
The pulmonary and systemic circulation are …
a) in parallel
b) in series
b) in series
Most systemic organs are functionally arranged…
a) in parallel
b) in series
a) in parallel
Explain the two advantages of parallel arrangement of systemic organs
- Systemic organs receive arterial blood of identical composition (each organ receives freshly oxygenated blood, rather than “used” blood that has already passed through another organ).
- Flow through any of the systemic organs can be controlled independently (blood supply to specific organs can be increased or decreased without affecting blood flow to other organs).
What are blood conditioning organs?
They are organs that filter, replenish or modify the contents of blood to maintain overall homeostasis. Blood flow to these organs is in excess of that necessary to maintain basal metabolic needs.
Name 3 examples of blood conditioning organs
- Lungs: Replenish oxygen and remove carbon dioxide from the blood
- Kidneys: Adjust electrolyte composition
- Skin: Regulate temperature
Describe the blood supply to organs that do not have a reconditioning function and name some examples.
These organs receive only enough blood flow to meet the metabolic needs of the tissue. Examples include the heart, brain and skeletal muscles.
How is flow through the vessels controlled (formula for flow)?
Flow (Q) = Pressure difference (ΔP) / Resistance (R)
- ΔP= Inlet pressure-Outlet pressure *
Define blood flow
Movement of blood through a vessel, tissue or organ (measured in volume/time).
Define resistance
Opposition to blood flow within blood vessels
How can we increase blood flow (2)?
Decrease resistance
Increase the pressure (increase inlet pressure or decrease outlet pressure)
How is blood flow regulated in the body most of the time?
By altering the resistance of the vasculature (more resistance means less blood flow and vice versa).
What is the equation for resistance? What factors does vascular resistance depend on?
Resistance = (8ηL)/(πR^4)
Resistance is directly proportional to the viscosity (η) of the blood and tube length (L).
Resistance is inversely proportional to the 4th power of the radius (R) of the tube.
What is Poiseuille’s law?
- Hint: combine the equation for flow with the equation for resistance *
Q = (ΔPπR^4)/8ηL
Flow is directly proportional to:
* pressure difference
* 4th power of the radius
Flow is inversely proportional to:
* viscosity of the blood
* length of the tube
Explain the implication of the flow being proportional to the fourth power of the radius of the tube.
Even minute changes in the internal radius will have a big influence on the resistance to flow and therefore the flow.
What generates the pressure difference in the CV system?
The heart generates the pressure difference, i.e. the driving force for flow
What is the normal mean arterial pressure, average central venous pressure and pressure difference in a standard individual?
- Mean arterial pressure: 100mmHg
- Average central venous pressure: 0mmHg
- Pressure difference = 100mmHg
Since the pressure difference is nearly identical across all systemic organs, cardiac output is distributed among the various organs primarily based on…
individual resistances to flow
The lower the resistance, the…
a) higher the flow
b) lower the flow
a) higher the flow (and vice versa)
Starting from the right atrium, describe the pathway of blood flow through the heart.
Deoxygenated blood from the right atrium passes through the tricuspid valve into the right ventricle, from where it is pumped through the pulmonary valve and into the pulmonary trunk which diverges into the left and right pulmonary arteries. The blood becomes oxygenated in the lungs and return to the heart via the 4 pulmonary veins, which connect to the left atrium.From there, the blood passes through the mitral valve into the left ventricle, and is pumped out across the aortic valve into the aorta. After traveling through the systemic organs, deoxygenated blood returns to the right atrium via the superior and inferior vena cava.
What is an AV valve?
It is an atrioventricular valve, i.e. a heart valve located between an atrium and ventricle.
*There are 2 AV valves in the heart. *
Define systole.
Systole is the phase of the heartbeat when the ventricles contract, pumping blood out into the pulmonary trunk and aorta.
During systole, the ventricular pressure is greater than the pressure in the pulmonary trunk (right pump) and aorta (left pump). Therefore, blood is forced out of the chamber through the outlet valves (pulmonic and aortic valve).
How does systole affect the AV valves?
Because the ventricular pressure during systole exceeds the pressure in the atrium, the AV valves (inlet valves) are closed to prevent back-flow of the blood.
Define diastole.
Diastole is the phase of the heartbeat when the heart relaxes, allowing the chambers to fill with blood. The pressure in the ventricle is lower than that in the atrium, so the AV valves (inlet valves) open and the ventricle fills with blood.
Why are the outlet valves (pulmonic and aortic) closed during diastole?
Because the arterial pressure (right and left pump i.e. pulmonary trunk and aorta) is greater than the intraventricular pressure (prevents back-flow).
Name the two AV valves.
Mitral valve (left)
Tricuspid valve (right)
Define the cardiac output and describe the formula.
The amount of blood pumped out by the heart per minute.
Cardiac output = Heart rate x Stroke volume
Define heart rate and stroke volume.
Heart rate = number of beats per minute
Stroke volume = volume of blood ejected per heartbeat
What is the formula for stroke volume?
Stroke volume = EDV - ESV
EDV: End diastolic volume
ESV: End systolic volume
Define the end diastolic volume (EDV) and end systolic volume (ESV)
EDV: blood volume in the ventricle at the end of diastole
ESV: blood volume in the ventricle at the end of systole
How are action potentials conducted from one cardiac muscle cell to the next, ensuring coordinated contraction of the heart?
Via gap junctions that connect all cells of the heart
What is the sinoatrial (SA) node? What is its function?
A cluster of specialized cells referred to as the heart’s pacemaker. It initiates the action potential that is conducted through the heart and controls the heart rate.
What is the atrioventricular (AV) node?
A cluster of specialized cells containing SLOWLY conducting cells that function to create a slight delay between atrial and ventricular contraction.
What are the Purkinje fibres?
Specialized cardiac muscle fibres in the ventricular walls with the ability of rapid conduction; they ensure that all ventricular cells contract close to simultaneously.
“Superhighways”
What system is responsible for modulating cardiac function and output?
The autonomic nervous system will send neural inputs from its sympathetic and parasympathetic divisions to meet the needs of the body.
What is the overall effect of sympathetic inputs to the heart?
Increase in pumping
What is the overall effect of parasympathetic inputs to the heart?
Decrease in pumping
Describe the innervation of the heart by the SNS and the effects of sympathetic stimulation of cardiac muscle cells (4).
- All portions of the heart are innervated by adrenergic sympathetic fibres
- Adrenergic sympathetic fibres release norepinephrine (NE)
- NE interacts with beta-1 adrenergic receptors on cardiac muscle cells
Outcomes:
* SA node increases the heart rate
* Action potentials are propagated faster
* Increase in the rate of contraction and relaxation
* Increase in the force of contraction of atrial and ventricular muscle cells
Describe the innervation of the heart by the PSNS and the effects of sympathetic stimulation of cardiac muscle cells (4).
- Cholinergic parasympathetic nerve fibres travel through the heart via the vagus nerve
- These nerves innervate the SA node, the AV node and the atrial muscle
- These nerves release acetylcholine (ACh)
- ACh interacts with muscarinic receptors on cardiac muscle cells
Outcomes:
* SA node decreases the heart rate
* Action potentials are propagated slower (AV node)
* Decrease in the rate of contraction and relaxation
* Decrease in the force of contraction of ATRIAL muscle cells
What is Starling’s law of the heart?
A principle describing how the heart automatically adjusts its pumping force to match the volume of blood filling the ventricles.
Thus, if cardiac filling increases (during diastole), the volume of blood ejected during systole also increases.
In other words, stroke volume increases in proportion to end-diastolic volume.
Name the 5 requirements for effective ventricular pumping action of the heart.
- Contraction of individual cardiac muscle cells must occur at regular intervals and be synchronized (not arrhythmic).
- The valves must open fully (not stenotic).
- The valves must not leak (not insufficient or regurgitant).
- The heart’s contractions must be forceful (not failing).
- The ventricles must fill adequately during diastole.
What do arteries do during systole? What do they do during diastole?
In systole: arteries expand to accept and temporarily store blood ejected by the heart
In diastole: by passive recoil, arteries supply blood to the organs downstream
How is the structure of arterioles different from arteries?
- Arterioles have thicker walls relative to lumen size
- Arterioles have more smooth muscle cells and less elastic material
What type of blood vessel is important for blood flow regulation?
Arterioles (their diameters can be actively changed to regulate blood flow through peripheral organs, hence why their walls are rich in smooth muscle).
Which type of blood vessel has the largest total cross-sectional area?
Capillaries
Describe the walls of veins and venules.
They have very thin walls with smooth muscle cells; they are very distensible and diameters change actively.
What is the purpose of one-way valves in larger veins?
They prevent back-flow of the blood when standing or during exercise.
How much of the total blood volume is stored in veins?
Over 50% of total blood volume!
Changes in venous blood volume can greatly affect… (2)
- cardiac filling
- cardiac pumping
Remember Starling’s law!
Name the major function of each of the following vessels:
1. Arteries
2. Arterioles
3. Capillaries
4. Veins and venules
- Arteries: Conduit vessels
- Arterioles: Resistance vessels
- Capillaries: Exchange vessels
- Veins and venules: Capacitance vessels
How is the blood flow through individual vascular beds controlled?
Blood flow through individual vascular beds is heavily influenced by sympathetic innervation of arterioles.
Describe the innervation of arterioles and its effects.
Sympathetic nerves innervate the arterioles. They release norepinephrine (NE) on alpha-adrenergic receptors of smooth muscle cells to cause constriction.
Constriction = reduced arteriolar diameter = increased resistance = reduced blood flow
How does increased metabolism impact arterioles?
Arteriolar smooth muscle is very responsive to changes in local chemical conditions that result from the changes in the metabolic rate of an organ. Certain metabolic by-products can act as vasodilators.
Therefore, an increased metabolism results in arteriolar dilatation and increased blood flow.
Describe the innervation of capillaries.
Capillaries are NOT innervated by the sympathetic nervous system!
Describe the innervation of veins and venules, and its effects.
Veins and venules, like arterioles, are richly innervated by sympathetic nerves. When activated, these nerves result in the constriction of veins and venules (venoconstriction).
Venoconstriction moves the blood out of the venous reservoir into the heart, resulting in increased cardiac filling and thereby increased cardiac output (Starling’s law).
Define blood and describe its composition.
Specialized fluid that serves as a medium for transporting substances between the tissues of the body.
40% cells (RBC, WBC, platelets)
60% plasma
Hematocrit
Red blood cell volume/Total blood volume multiplied by 100
RBCs, WBCs and platelets are also called…
erythrocytes, leukocytes and thrombocytes
Define and describe plasma
Plasma is the liquid component of blood. It is a complex solution of electrolytes and proteins.
What kinds of electrolytes are found in plasma? What types of proteins?
Electrolytes: sodium, potassium, chloride, bicarbonate
Proteins: albumin, globulins, fibrinogen
Define serum
Serum is the fluid obtained from a blood sample after the blood has been allowed to clot. In other words, it is identical to plasma minus the clotting proteins (fibrinogen).
What is the most abundant protein in the blood (plasma)?
Albumin
True or false: Plasma protein can cross the capillary walls.
False! Plasma proteins do NOT cross the capillary walls
Plasma proteins are more concentrated in the …. compared to ….
Plasma proteins are more concentrated in the plasma compared to the interstitial fluid.
