Cardiovascular System (Part 2) Flashcards
What are the 7 phases of the cardiac cycle?
1) atrial systole
2) isovolumetric ventricular contraction
3) rapid ventricular ejection
4) reduced ventricular ejection
5) isovolumetric ventricular relaxation
6) rapid ventricular filling
7) reduced ventricular filling or diastasis
What 2 major events occur during atrial systole?
- atria contraction
- final phase of ventricular filling
What portions of an EKG are represented by atrial systole?
P wave and PR interval
What sound does the heart make during atrial systole?
the fourth heart sound
What 3 major events occur during isovolumetric ventricular contraction?
- ventricle contraction
- ventricular pressure increases and reaches maximum
- ventricular volume is constant
What portion of an EKG is represented by isovolumetric ventricular contraction?
QRS complex
What valves are closed during isovolumetric ventricular contraction?
all valves
What sound does the heart make during isovolumetric ventricular contraction?
the first heart sound
What 5 major events occur during rapid ventricular ejection?
- ventricle contraction
- ventricular pressure increases and reaches maximum
- ventricles eject blood into arteries
- ventricular volume decreases
- aortic pressure increases and reaches maximum
What portion of an EKG is represented by rapid ventricular ejection?
ST segment
What valve opens during rapid ventricular ejection?
aortic valve
What 3 major events occur during reduced ventricular ejection?
- ventricles eject blood into arteries at a slower rate
- ventricular volume reaches minimum
- aortic pressure starts to fall as blood runs into arteries
What portion of an EKG is represented by reduced ventricular ejection?
T wave
What 3 major events occur during isovolumetric ventricular relaxation?
- ventricular relaxation
- ventricular pressure decreases
- ventricular pressure is constant
What valve closes during isovolumetric ventricular relaxation?
the aortic valve
What sound does the heart make during isovolumetric ventricular relaxation?
the second heart sound
What 4 major events occur during rapid ventricular filling?
- ventricular relaxation
- ventricles fill passively with blood from atria
- ventricular volume increases
- ventricular pressure is low and constant
What valve opens during rapid ventricular filling?
mitral valve
What sound does the heart make during rapid ventricular filling?
the third heart sound
What 2 major events occur during reduced ventricular filling or diastasis?
- ventricles relax
- final phase of ventricular filling
What is blood flow driven by?
the difference in pressure between the arterial and venous sides of the circulation
What is the driving force for blood flow?
mean arterial pressure
At what level should mean arterial pressure be maintained at?
A high, constant level of approximately 100 mm Hg (set point)
Mean arterial pressure = pressure in what artery?
the aorta
How do you calculate mean arterial pressure?
Cardiac output times total peripheral resistance
What happens to mean arterial pressure if cardiac output is halved? Explain why…
Mean arterial pressure decreases, but it will not be halved because there is a compensatory increase in total peripheral resistance
What are the 2 major systems in which mean arterial pressure is regulated?
- baroreceptor reflex (fast)
- renin-angiotensis-aldosterone system (slow)
The baroreceptor mechanisms are fast, _____ mediated reflexes
neurally
How do the baroreceptor mechanisms attempt to keep arterial pressure constant?
via changes in the output of the sympathetic and parasympathetic nervous systems to the heart and blood vessels
Pressure sensors located within the walls of the carotid sinus and aortic arch are called what?
baroreceptors
What do these baroreceptors do?
They relay information about blood pressure to cardiovascular vasomotor centers in the brain stem
Once information from the baroreceptors is relayed to cardiovascular vasomotor centers in the brain stem what do they do?
The vasomotor centers coordinate a change in output of the ANS to effect the desired change in mean arterial pressure
Where are the 2 places in which baroreceptors are found?
- carotid sinus
- aortic arch
Baroreceptors in the carotid sinus are responsive to what?
changes in arterial pressure and the rate of pressure change
Baroreceptors in the aortic arch are responsive to what?
increases in arterial pressure
Baroreceptors are mechanoreceptors, therefore they are sensitive to what?
pressure or stretch
Increases in arterial pressure cause an increase in baroreceptor stretch which causes an ____ firing rate of the afferent nerves
increase
Decreases in arterial pressure cause a decrease in baroreceptor stretch which causes a ____ firing rate of the afferent nerves
decrease
What is the strongest stimulus for the baroreceptors?
a rapid change in arterial pressure
How does chronic hypertension (elevated BP) effect the baroreceptors?
They do not “see” the elevated BP as abnormal, therefore the hypertension will be maintained, rather than corrected, by the baroreceptor reflex
Information from the carotid sinus baroreceptors is carried to the brain stem on the carotid sinus nerve which joins which cranial nerve?
The glossopharyngeal nerve (CN IX)
Information from the aortic arch baroreceptors is carried to the brain stem on which cranial nerve?
vagus nerve (CN X)
Where are brain stem cardiovascular centers located?
in the reticular formations of the medulla and in the lower one third of the pons
Information from the vagus and hypoglossal nerves is integrated where?
in the nucleus tractus solitarius
What is the function of the nucleus tractus solitarius?
directs increases or decrease in outflow from the sympathetic and parasympathetic nervous systems via the cardiovascular systems
The ___pathetic outflow is the effect of the vagus nerve on the SA node to decrease HR.
parasympathetic
What are the 4 components of the sympathetic outflow?
- an effect on the SA node to increase HR
- an effect on cardiac muscle to increase contractility and stroke volume
- an effect on the arterioles to produce vasoconstriction and increase TRP
- an effect on veins to produce venoconstriction and decrease unstressed volume
What are the 3 cardiovascular brain stem centers?
- vasoconstrictor center
- cardiac accelerator center
- cardiac decelerator center
Where is the vasoconstrictor center located?
in the upper medulla and lower pons
Efferent neurons from the vasoconstrictor center are part of the ___pathetic nervous system
sympathetic
Efferent neurons from the cardiac accelerator center are part of the ___pathetic nervous system
sympathetic
Efferent neurons from the cardiac decelerator center are part of the ___pathetic nervous system
parasympathetic
Describe the steps of the baroreceptor reflex following an increase in arterial pressure
1) an increase in mean arterial pressure is detected by the baroreceptors in the carotid sinus and aortic arch
2) this increase in pressure results in increased firing rate of the carotid sinus nerve (CN IX) and in afferent fibers in the vagus nerve
3) glossopharyngeal and vagus nerve fibers synapse in the nucleus tractus solitarius of the medulla, where they transmit information about BP
4) the nucleus tractus solitarius directs a series of coordinated responses to reduce mean arterial pressure back to normal via increase in parasympathetic activity and decreases in sympathetic activity
5) once mean arterial pressure is reduced back to the set-point pressure the activity of the barareceptors return to the tonic (baseline) level
Hemorrhage produces a ____ in mean arterial pressure
decrease
How can the integrity of the baroreceptor reflex be tested?
Valsalva maneuver, which results in an increase in HR
How does the renin-angiotensin II-aldosterone system regulate mean arterial pressure?
by regulating blood volume
Describe why the renin-angiotensin II-aldosterone system is slower than the baroreceptor reflex
It is hormonally, rather than neutrally, mediated
What activates the renin-angiotensin II-aldosterone system?
decreases in mean arterial pressure
Describe the steps of the renin-angiotensin II-aldosterone system following a decrease in arterial pressure
1) a decrease in P(a) causes a decrease in renal perfusion pressure, which is sensed by mechanoreceptors in afferent arterioles of the kidney
2) this decrease in P(a) causes prorenin to be converted to renin
3) renin catalyzes the conversion of angiotensinogen to angiotensin I
4) angiotensin I is converted to angiotensin II in the lungs and kidneys via ACE
5) angiotensin II has many biologic actions in the adrenal cortex, vascular smooth muscle, kidneys, and brain
Describe angiotensin II’s role in the adrenal cortex
It acts on the glomerulosa cells of the adrenal cortex to stimulate the synthesis and secretion of aldosterone which acts on the principal cells of the renal distal tubule and collecting duct to increase sodium reabsorption and, thereby, to increase ECF volume and blood volume
Describe angiotensin II’s role in vascular smooth muscle
It acts directly on the arterioles to cause vasoconstriction, thereby producing an increase in total peripheral resistance and an increase in mean arterial pressure
Describe angiotensin II’s role in the kidneys
It stimulates Na+ - H+ exchange in the renal proximal tubule and increases the reabsorption of sodium and bicarbonate
Describe angiotensin II’s role in the brain
It acts on the hypothalamus to increase thirst and water intake and also stimulates the secretion of antidiuretic hormone, which increases water reabsorption, both of which increase ECF volume, blood volume, and BP
What are 4 other mechanisms that aid in regulating mean arterial pressure?
- chemoreceptors for oxygen in the carotid and aortic bodies
- chemoreceptors for CO2 in the brain
- antidiuretic hormone
- atrial natriuretic peptide
What are peripheral chemoreceptors in the carotid and aortic bodies sensitive to?
- Decreases in the partial pressure of O2 (PO2)
- Increases in the partial pressure of CO2 (PCO2) and decreases in pH
The response of the peripheral chemoreceptors to decreased PO2 is greater when the PCO2 is _____ or the pH is _____.
increased
decreased
What happens when arterial PO2 decreases?
There is an increased firing rate of afferent nerves from the carotid and aortic bodies that activates sympathetic vasoconstrictor centers and there is also an increase in parasympathetic outflow to the heart which decreases HR
Where are central chemoreceptors found?
in the medulla
What do central chemoreceptors respond to?
decreases in brain blood flow
What are central chemoreceptors sensitive to?
- Increases in partial pressure of CO2 (PCO2)
- Decreases in pH
- Decreases in partial pressure of O2 (PO2)
Describe the reflex that involves cerebral chemoreceptors when there is decreased cerebral blood flow
1) PCO2 increases and pH decreases
2) medullary chemoreceptors sense these changes and direct an increase in sympathetic outflow which causes intense arteriolar vasoconstriction in many vascular beds and there is an increase in TPR and mean arterial pressure
3) blood is thereby redirected to the brain
The ____ reaction illustrates the role of the cerebral chemoreceptors in maintaining cerebral blood flow
Cushing
What gland secretes ADH?
the posterior lobe of the pituitary gland
What are the functions of ADH?
- regulate fluid osmolarity
- participate in the regulation of arterial blood pressure
What are the 2 types of ADH receptors?
V1 and V2 receptors
Where can V1 receptors be found?
In vascular smooth muscle
Where can V2 receptors be found?
In the principle cells of the renal collecting ducts
The V1 receptors cause vaso___ of arterioles and _____ TPR
vasoconstriction
increased
What are the V2 receptors involved in?
water reabsorption in the collecting ducts and the maintenance of body fluid osmolarity
What 2 types of stimuli increase ADH release?
- increases in serum osmolarity
- decreases in BP
Where are low-pressure baroreceptors found?
In the veins, atria, and pulmonary arteries
What are these low-pressure baroreceptors called?
Cardiopulmonary baroreceptors
What do the cardiopulmonary baroreceptors sense changes in?
Blood volume on the venous side of the circulation
How do the cardiopulmonary baroreceptors return blood volume to normal?
by increasing the excretion of sodium and water
Increases in blood volume produces ____ secretion of ADH
decreased
Increases in blood volume produces renal vaso____
vasodilation
Increases in blood volume produces _____ secretion of atrial natriuretic peptide (ANP)
increased
Increases in blood volume produces _____ HR
increased
What does the term microcirculation refer to?
The functions of the smallest blood vessels, the capillaries and lymphatic vessels
Describe the structure of the capillaries
They are thin walled structures composed of a single layer of endothelial cells with water-filled clefts between the cells
What blood vessels control the blood flow to capillaries?
arterioles
Exchange of solutes and gases across the capillary wall occurs by way of what?
simple diffusion
What are the 2 routes in which solutes can diffuse into and out of capillaries?
Some solutes can diffuse through the endothelial cells, and others must diffuse between the cells
What does the route of diffusion depend on?
Whether the solute is lipid soluble
What types of substances can readily cross the capillary wall by diffusing through the endothelial cells?
Gas such as O2 and CO2 which are highly lipid soluble
What types of substances can readily cross the capillary wall by diffusing between the endothelial cells?
Water-soluble substances such as ions, glucose, and amino acids
What is the most important mechanism for fluid transfer across the capillary wall?
osmosis
What 2 pressures drive osmosis?
hydrostatic and osmotic which are called the Starling forces
Can proteins cross the capillary walls?
No, they are too large and are retained in the vascular compartment
What is the only thing that contributes to effective osmotic pressure in capillaries?
protein
What does the Starling equation state?
That fluid movement across a capillary wall is determined by the net pressure across the wall, which is the sum of hydrostatic pressure an oncotic pressures
When net fluid movement is out of the capillary into the interstitial fluid what is it called?
filtration
When net fluid movement is from the interstitium into the capillary what is it called?
absorption
How do you calculate net pressure?
Sum up the 4 Starling pressures
If net pressure equals +6 mmHg there will be net _____.
filtration out of the capillary
If net pressure equals -5 mmHg there will be net _____.
absorption into the capillary
What is K(f)?
K(f) is hydraulic conductance and it is the water permeability of the capillary wall
The magnitude of fluid movement for a given pressure difference is largest in the capillaries with the ____ K(f)
highest
What increases hydraulic conductance?
capillary injury
What is P(c)?
P(c) is capillary hydrostatic pressure and it is a force favoring filtration out of the capillary
What determines P(c)?
Both arterial and venous pressures determine capillary hydrostatic pressure, however the value of P(c) is closest to arterial pressure
Is P(c) more affected by changes in arterial or venous pressure?
venous
Where is capillary hydrostatic pressure P(c) highest and lowest?
Highest at the arteriolar end of the capillary and lowest at the venous end
What is P(i)?
P(i) is interstitial hydrostatic pressure and it is a force that opposes filtration
What does P(i) normally equal?
zero
What is pi(c)?
capillary oncotic pressure
What determines pi(c)?
the protein concentration of capillary blood
Increases in protein concentration result in _____ in pi(c)
increases
What is pi(i)?
interstitial oncotic pressure
What determines pi(i)?
The interstitial fluid protein concentration
Describe why pi(i) is determined by the interstitial fluid protein concentration
Because normally there is little loss of protein from capillaries, therefore there is little protein in the interstitial fluid
What can changes in Starling forces influence?
The direction and magnitude of fluid movement across capillaries
Increases in filtration produce increases in what?
P(c), which is capillary hydrostatic pressure
What is the function of the lymphatic system?
To return interstitial fluid and proteins to the vascular compartment
Where can lymphatic vessels be found?
In the interstitial fluid, close to the vascular capillaries
Describe the structure of lymphatic capillaries
They have one-way flap valves that permit interstitial fluid and protein to enter, but not leave.
They have a smooth muscle wall, which has intrinsic contractile ability
An increase in interstitial fluid volume is called what?
edema
When does edema form?
When there is increased filtration or when lymphatic drainage is impaired
A(n) _____ in capillary hydrostatic pressure produces edema
increase
A(n) ____ in capillary oncotic pressure produces edema
decrease
A(n) _____ in hydraulic conductance produces edema
increase
How are changes in blood flow to an individual organ achieved?
By altering arteriolar resistance
What are the 2 broad mechanisms that regulate blood flow?
- local (intrinsic) control
- neural or hormonal (extrinsic) control
What are 3 examples of local control of blood flow?
- autoregulation
- active hyperemia
- reactive hyperemia
What is autoregulation?
The maintenance of a constant blood flow to an organ in the face of changing arterial pressure
What organs exhibit autoregulation?
the kidneys, brain, heart, and skeletal muscle
What does active hyperemia illustrate?
The concept that blood flow to an organ is proportional to its metabolic activity
What is reactive hyperemia?
An increase in blood flow in response to or reacting to a prior period of decreased blood flow
The ____ hypothesis can be invoked to explain autoregulation
myogenic
What does the myogenic hypothesis state?
That when vascular smooth muscle is stretched, it contracts
The _____ hypothesis can be invoked to explain all 3 mechanisms of local control of blood flow
metabolic
What is the basic premise behind the metabolic hypothesis?
O2 delivery to a tissue can be matched to O2 consumption of the tissue by altering the resistance of the arterioles, which in turn alters blood flow
Greater level of metabolic activity lead to _____ in resistance, and therefore flow is ______ to meet the increased demand for oxygen
decreases
increased
The most important example of neural control of regional blood flow involves the _____ innervation of vascular smooth muscle in some tissues.
sympathetic
What are a few examples of vasoactive substances?
histamine, bradykinin, serotonin, and prostaglandins
What do histamine and bradykinin do?
They cause dilation of arterioles and constriction of venules which results in increased filtration out of the capillaries and local edema
What does serotonin do?
It causes vasoconstriction in an attempt to reduce blood flow and blood loss following blood vessel damage
What do prostaglandins do?
Cause both vasodilation and vasoconstriction
What is normal body temperature set at?
37°C (98.6°F)
What are the 3 mechanisms for generating heat?
- Thyroid hormone produciton
- Activation of the sympathetic nervous system
- Shivering
How do thyroid hormones generate heat?
Their actions on target tissues results in heat production
Describe heat production in hyperthyroidism and hypothyroidism
In hyperthyroidism heat production increases
In hypothyroidism heat production decreases
How does activation of the sympathetic nervous system generate heat?
Beta receptors in brown fat are activated, which increases metabolic rate and heat production
- Alpha1 receptors in vascular smooth muscle of the skin cause vasoconstriction which reduces blood flow to the skin and consequently reduces heat loss
What are the 2 mechanisms for dissipating heat?
- Decreased sympathetic nervous system activity
- Increased sweating
Where is the temperature-regulating center located?
In the anterior hypothalamus
What can be defined as an abnormal elevation of body temperature?
fever
_____ produce fever by increasing the hypothalamic set-point temperature.
Pyrogens
What role do prostaglandins play in fever?
Prostaglandins that are released by the anterior hypothalamus increase the set-point temperature
When does heat exhaustion occur?
As a consequence of the body’s responses to elevated environmental temperature
When does heat stroke occur?
When body temperature increases to the point of tissue damage
What is malignant hyperthermia?
A massive increase in metabolic rate, increased O2 consumption, and increased heat production in skeletal muscle which can lead to excessively high body temperature
The cardiovascular responses to exercise involve a combination of what 2 mechanisms?
- CNS
- local
What do the CNS responses to exercise include?
A central command from the cerebral motor cortex, which directs changes in the ANS
What initiates the central command?
the anticipation of exercise
The central command response to exercise ____ sympathetic and _____ parasympathetic outflow to the heart
increases
decreases
The central command response to exercise increases 3 what things?
- heart rate
- contractility
- cardiac output
The central command response to exercise causes arterioles and veins to do what?
constrict
The constriction of veins that results from the central command response to exercise causes unstressed volume to _____.
decrease
Local control of blood flow in the exercising skeletal muscle is orchestrated by what?
active hyperemia
As the metabolic rate of skeletal muscle increases the production of what increases?
vasodilator metabolites that increase blood flow and oxygen delivery to the exercising skeletal muscle
What is the overall response to exercise?
An increase in blood flow to skeletal muscle
What is the initiating event in hemorrhage?
Loss of blood and decreased blood volume which results in a decrease in mean arterial pressure
Following hemorrhage there are a series of ______ responses that gradually increase men arterial pressure back to normal
compensatory
What are the 3 mechanisms by which these compensatory responses occur?
- baroreceptor reflex
- renin-angiotensin II-aldosterone system
- capillaries
The baroreceptor reflex serves to increase sympathetic outflow to the heart which has for consequences, what are they?
- increased HR
- increased contractility
- increased TPR
- constriction of the veins
What are the 2 major actions of angiotensin II?
- causes arteriolar vasoconstriction which increases TPR
- stimulates secretion of aldosterone which increases sodium reabsorption resulting in increased blood volume
What is the compensatory response to hemorrhage in the capillaries?
Vasoconstriction causes a decrease in capillary hydrostatic pressure which opposes filtration out of the capillary and favors absorption
What happens in response to a person who stands up too quickly?
There is an initial decrease in mean arterial pressure which activates the baroreceptor reflex which increases sympathetic outflow to the heart, causing increases in HR, contractility, CO, TPR, and a decrease in the unstressed volume
