HUBS192_Lect10_2024.pdf

HUBS192 Lecture Material This pre-lecture material is to help you prepare for the lecture and to assist your note-taking within the lecture, it is NOT a substitute for the lecture ! Please note that although every effort is made to ensure this pre-lecture material...

HUBS192 Lecture Material This pre-lecture material is to help you prepare for the lecture and to assist your note-taking within the lecture, it is NOT a substitute for the lecture ! Please note that although every effort is made to ensure this pre-lecture material corresponds to the live-lecture there may be differences / additions.  HUBS 192 Jeff Erickson – Department of Physiology Lecture 10 Controlling the Heart and Blood Pressure © The content and delivery of all resources in this course are copyrighted. This includes video and audio recordings, PowerPoints, lecture notes and handouts. You may access the materials provided for your private study or research but may not further distribute the materials for any purpose, or in any other form, whether with or without charge.  Example exam question Which ONE of the following events occurs during the P wave in an ECG? A. Atrial relaxation B. Repolarization of the ventricles C. Atrial depolarization D. Ejection of blood from the ventricles 2  Objectives and Study Guide After this lecture you should be able to: Define cardiac output and identify its two major determinants. Understand how cardiac output can affect arterial blood pressure. Understand how the arterial and nervous systems communicate to maintain blood pressure. Related reading: Martini et al. Modules 18.12 (p. 722), 18.14 (p. 726-727), and 19.7 (p. 750-751) 3 The left ventricle generates pressure for the systemic circulation High pressure in the large systemic arteries Linked to ventricular contraction and ejection of blood. Pulsatile in major arteries (systolic / diastolic). Mean arterial blood pressure (MAP) is a critically important determinant of blood flow 160 Arterial Pressure (mmHg) 120 Systolic 80 Pulse Diastolic pressure 40 0 0.4 1.0 1.4 2.0 0 Time (s) 4  Blood pressures throughout the systemic circulation Blood pressure high in major arteries – Oscillatory Blood pressure falls steeply across the arterioles, capillaries, and venules – Oscillatory nature is reduced. Blood pressure is very low in veins. Large difference in pressure (ΔP) between the arterial and venous sides. – creates a driving force for blood flow Martini et al., Visual Anatomy and Physiology (3rd ed), Module 19.7, pg 751. 5  Haemodynamics: how blood flows in a single vessel Flow = Pressure Difference / Resistance Q = P/R Pupstream Pdownstream Q R MAP = Q * R 6  Ejection of blood into the arterial system maintains arterial blood volume and blood pressure R L blood flow in “blood flow in” – fills arteries – increases arterial blood volume heart – raises arterial pressure. a r t e “blood flow out” r – drains arteries i – decreases arterial blood volume e – lowers arterial pressure. veins s Arterial blood volume and pressure blood flow out are determined by: – balance between blood flows “in” and “out”. Note that the microcirculation has been omitted 7  Cardiac output and arterial resistance affect blood pressure Cardiac Output “blood flow in” R L blood flow in – Ventricular contraction – Ejection of blood heart – CARDIAC OUTPUT a r t “blood flow out” e r – Capillary flow i – Controlled by resistance of the arteries e veins s Balance flow in / out determines pressure blood flow out – Increase cardiac output (increase inflow) – Increase resistance (decrease outflow) – Increase arterial volume and Pressure Arterial Resistance 8  Cardiac output and arterial resistance affect blood pressure Cardiac Output “blood flow in” – Ventricular contraction R L blood flow in – Ejection of blood – CARDIAC OUTPUT heart a “blood flow out” r – Capillary flow t e – Controlled by resistance of the arteries r i e Balance flow in / out determines pressure veins s – Increase cardiac output (increase inflow) – Increase resistance (decrease outflow) – Increase arterial volume and Pressure blood flow out Arterial Pressure = Cardiac output x Total Peripheral Resistance Arterial Resistance MAP = CO x TPR 9  Cardiac output is determined by stroke volume and heart rate CO = SV x HR Cardiac Output = Stroke Volume x Heart Rate (L/min) (L/beat) (beats/min) contraction contraction strength speed 10  Let’s put it all together! Stroke Volume Marieb & Hoehn, Human Anatomy and Physiology (10th ed), Figure 18.19, pg 706. 11  Cardiac output is determined by stroke volume and heart rate CO = SV x HR Cardiac Output = Stroke Volume x Heart Rate (L/min) (L/beat) (beats/min) contraction contraction strength speed 12  Stroke Volume vs. Heart Rate Two approaches for meeting cardiac output needs Mouse Blue Whale a-z-animals.com npr.org and Denis Scott/Corbis Total mass 20 g 140,000 kg Stroke volume 0.07 mL/beat 80 L/beat Heart rate 700 beats/min 8-10 beats/min 13  Stroke Volume vs. Heart Rate Two approaches for meeting cardiac output needs Healthy Heart Failing Heart Clipart library NicePNG Stroke volume ~70 mL/beat ~40 mL/beat Heart rate ~60-80 beats/min ~120-130 beats/min 14  Cardiac output is variable due to changes in heart rate and/or stroke volume Exercise at VO2max: CO ~ 25 L/min HR = 180 bpm SV = 140 mL/beat CO Rest: CO ~ 5 L/min CO HR = 70 bpm SV = 70 mL/beat 15  Example exam question Which of the following statements about electrical and contractile cells is CORRECT? A. Electrical cells have nuclei, while contractile cells do not B. Electrical cells have less actin/myosin filaments than contractile cells C. Electrical cells have intercalated discs, while contractile cells do not D. Electrical cells are heavily striated, while contractile cells are pale with fewer striations. 16  Homeostasis of arterial blood pressure Mean arterial pressure is tightly regulated – Narrow range. CNS input MAP = CO x TPR – heart (cardiac output) – blood vessels (vascular resistance). efferent Coordinated within the output brainstem (to heart and blood vessels) – Afferent input from both the CNS and ‘periphery’. afferent input – Efferent output to heart and vessels (from periphery, including baroreceptors) 17  Baroreceptors are blood pressure sensors carotid artery Afferent input (feedback) aorta http://www.blobs.org/science/articl http://www.lookfordiagnosis.com/mesh_info.php e.php?article=60 ?term=Carotid+Sinus&lang=1 18  Neural control of cardiac output “brake” “accelerator” Brake vs. Accelerator Marieb & Hoehn, Human Anatomy and Physiology (10th ed), Figure 18.14, pg 702. 19  Did you catch it? Courtesy of the San Diego Zoo What are baroreceptors? Where are they primarily located? What afferent signal do they send to the brain? What is the difference between sympathetic and parasympathetic signaling? How does signaling through the vagus nerve affect the heart? Conversely, how does signaling through the sympathetic trunk ganglion affect the heart? 20 Baroreflex in action: Posture (Whole body tilt) 100 SV (ml) 0 6 min-1) CO (l 0 0 5 Duration in tilted position (min) 21  Cardiac output is determined by stroke volume and heart rate CO = SV x HR Cardiac Output = Stroke Volume x Heart Rate (L/min) (L/beat) (beats/min) contraction contraction strength speed 22 Baroreflex in action: Posture (Whole body tilt) 100 SV (ml) 0 6 min-1) CO (l 0 100 (bpm) HR 60 0 5 Duration in tilted position (min) 23 Baroreflex in action: Posture (Whole body tilt) 100 SV (ml) 0 6 min-1) CO (l 0 100 (bpm) HR 60 120 (mmHg) MAP 80 0 5 Duration in tilted position (min) 24  MAP = CO x TPR Mean Arterial Pressure = Cardiac Output X Total Peripheral Resistance 25 Baroreflex in action: Posture (Whole body tilt) 100 SV (ml) 0 6 min-1) CO (l 0 100 (bpm) HR 60 120 (mmHg) MAP 80 ml-1) 30 (mmHg min VR 15 0 5 Duration in tilted position (min) 26  Main Points Cardiac output is: – blood flow leaving the heart (L / min) – determined by stroke volume and heart rate (CO = SV  HR) – greatly increased during exercise Blood pressure is sensed by baroreceptors and controlled by changes to cardiac output via efferent signaling from the brain – Parasympathetic signaling through the vagus nerve slows heart rate – Sympathetic signaling through the sympathetic trunk ganglion speeds heart rate and increases stroke volume Blood pressure is also controlled by controlling the drainage of blood from the arteries (the resistance)…we’ll discuss this next time! 27  Example exam question Which of the following statements about the human cardiovascular system is INCORRECT? A. Blood flow throughout the cardiovascular system is unidirectional. B. Arteries in the systemic circuit carry oxygen rich blood, while arteries in the pulmonary circuit carry oxygen poor blood. C. Blood flow is lower in the shorter pulmonary circuit than in the longer systemic circuit. D. Blood flows away from the heart in arteries and towards the heart in veins. 28  HUBS192 Copyright Warning Notice This coursepack may be used only for the University’s educational purposes. It includes extracts of copyright works copied under copyright licences. You may not copy or distribute any part of this coursepack to any other person. Where this coursepack is provided to you in electronic format you may only print from it for your own use. You may not make a further copy for any other purpose. Failure to comply with the terms of this warning may expose you to legal action for copyright infringement and/or disciplinary action by the University