Cardiovascular System (Week 6) Study Guide PDF

Study Guide Cardiovascular System (Week 6) NOTE – It is beneficial to relate the material on here to those from Weeks 4 and Weeks 5, as they do connect. For instance, venous return is presented in detail on here, and is related to various concepts descr...

Study Guide Cardiovascular System (Week 6) NOTE – It is beneficial to relate the material on here to those from Weeks 4 and Weeks 5, as they do connect. For instance, venous return is presented in detail on here, and is related to various concepts described earlier (such as distensibility, vasoconstriction, end diastolic volume, etc.) Neural Control of Blood Pressure A. Reflexes 1. Describe the basic anatomy of a reflex arc (this is not just for the cardiovascular system, but true for ANY reflex) i. Afferent component: An input signal, usually from a specialized receptor (a) Specialized receptor sends signal along afferent nerve, back to CNS ii. CNS component: The central nervous system (brain and/or spinal cord) interprets the afferent information iii. Efferent component: An output signal, which travels from the CNS to a target site, and produces a physiologic response 2. Remember – a reflex happens automatically. HOWEVER, higher brain centers can over-ride the reflex i. Examples (a) Knee jerk reflex: (a) Afferent component – patellar tendon being stretched out by a clinician tapping on it with a specialized hammer (b) CNS – interpretation is that the tendon is being rapidly stretched, so we must shorten it to prevent injury. So, we send and efferent signal for the quadriceps to contract (c) Efferent component – the signal telling the quadriceps to contract (d) OVERRIDE – if you consciously try to stop your quadriceps from contracting, you can do so (pre-motor cortex and motor cortex will send a signal which overrides the efferent component). (b) Cough / sneeze reflex (to be covered in detail separately): (a) Think about a time where you have been in a situation where you suddenly need to sneeze or cough, but for whatever reason (usually a social purpose) you fight the urge to do so. That is an example of overriding a reflex with higher brain centers B. Baroreceptor Basics 1. Briefly describe what a baroreceptor is i. Specialized receptors which detect changes in blood pressure (a) Important to recognize they are best at identifying CHANGES in pressure, not what the absolute pressure is ii. Baroreceptors are CRITICAL for maintaining SHORT-TERM homeostasis of blood pressure (a) Respond rapidly – not instantaneous, but less than 1 second  2. Name the two anatomical sites where baroreceptors are most abundant i. Internal carotid arteries ii. Aortic arch 3. Name the two sites where low-pressure receptors for sensing blood pressure are found. i. Low pressure receptors are simply baroreceptors which are “fine tuned” for areas where pressure is low ii. Found in the atria and pulmonary arteries (a) These are the sites where pressure is the lowest! iii. Low-pressure receptors change small changes in pressure, such as those due to changes in blood volume (a) Think of the aorta – it is regularly experiencing a blood pressure range of 80mmHg (diastolic) to 120mmHg (systolic) during rest – that’s a range of 40mmHg (b) Compare that to the right atrium – which is generally going to experience pressure around 0 to 5mmHg… Baroreceptors there needs to be “fine tuned” to respond to smaller fluctuations in pressure C. Central Nervous System 1. Describe the location of the vasomotor center within the brain, and name the three key areas within it i. Reticular substance of medullar and lower third of pons ii. Three areas (a) Vasoconstrictor area (b) Vasodilator area (c) Sensory area 2. Briefly explain the concept of vasomotor tone i. Continual firing of sympathetic nervous system which causes slight vasoconstriction 3. Appreciate that other parts of the brain can excite or inhibit the vasomotor center i. [This just means that you should recognize that the brain’s activity can influence vasodilation / vasoconstriction. Vasovagal syncope is an example of this.] D. Adrenergic Receptors 1. Summarize the role of epinephrine and norepinephrine on blood vessel tone, including their sources and the receptors they bind to i. Binds to alpha adrenergic receptors to cause vasoconstriction (a) This is a broad generalization (b) Different blood vessels in the body have different types of adrenergic receptors, including various different types of alpha adrenergic receptors 2. Differentiate between the responses of epinephrine and norepinephrine to alpha and beta adrenergic receptors in the vasculature i. Alpha adrenergic receptors cause vasoconstriction (a) GENERALLY, found throughout the blood vessels in the body ii. Beta adrenergic receptors cause vasodilation (a) Found in coronary arteries iii. So, in situations where there are major releases of epinephrine and norepinephrine (e.g., exercise, anxiety, etc.) we have the following: (a) Binding to alpha adrenergic receptors causes:  (a) Vasoconstriction of arteries / arterioles, especially in kidneys and GI tract (i) Increased total peripheral resistance (b) Vasoconstriction of veins (i) Increases venous return 1. That thus increases EDV, and ultimately SV, and CO (b) Binding to beta adrenergic receptors causes (a) Increase in cardiac contractility (i) That increases SV, and ultimately CO (b) Vasodilation of coronary arteries (since beta adrenergic receptors are found there) (i) This allows more blood flow to the myocardium, to support the increased contractility 3. Describe the three major changes brought about by sympathetic activation and parasympathetic inhibition which simultaneously occur to rapidly increase blood pressure (THIS IS REPEATED A FEW TIMES, THIS SHOULDN’T FEEL “NEW”!) i. Sympathetic Activation (turning “on” the sympathetic nervous system) (a) Arteriolar vasoconstriction (b) Venous vasoconstriction (c) Increased HR and SV ii. Parasympathetic Inhibition (turning “off” the parasympathetic nervous system) (a) Increased HR 4. Important point that people often confuse: i. Vasoconstriction refers to blood vessels. It is NOT related to cardiac contractility. [The ventricles are not a blood vessel, so they do not “vasoconstrict” – they “contract”!] E. Fully explain the baroreceptor reflex 1. Afferent signal: Upon increased signals of rapidly increasing blood pressure, baroreceptors increase their rate of action potentials 2. CNS response: i. Inhibition of the vasoconstrictor center ii. Excitation of vagal parasympathetic center 3. Efferent response: i. Blood pressure decreases because of (a) Vasodilation (or inhibition of vasoconstriction) (a) Decreases TPR (b) Heart rate decreases (c) Stroke volume decreases F. Apply principles of the baroreceptor reflex to describe how blood pressure is maintained during postural transitions 1. Upon standing, pressure in head and upper body decrease 2. Baroreceptors sense this decreasing pressure 3. Reflex stimulated, causing a strong sympathetic discharge throughout the body i. This reverses the decreasing blood pressure Venous Return G. Recognize that blood pressure gradients influence blood flow 1. Blood (and all fluids) move from high pressure to low pressure 2. The bigger the difference, the easier it is for blood to move H. State the normal value for right atrial pressure 1. Approximately