Physiology of Circulation - PPT PDF

The Physiology of Circulation Asst Prof Sule Gunter https://www.youtube.com/watch?v=odERkoPTwoY MEDI11-102 Week 4 Title Physiology of circulation Presenter Asst Prof Sulé Gunter...

The Physiology of Circulation Asst Prof Sule Gunter https://www.youtube.com/watch?v=odERkoPTwoY MEDI11-102 Week 4 Title Physiology of circulation Presenter Asst Prof Sulé Gunter The session will continue the introduction to the cardiovascular Why you should attend this session system focusing on the vasculature and the regulation of blood pressure. What you will need to do in Review the introduction to the CVS and the functions of the preparation heart from Week 3. What you will need to bring A pen and paper or laptop.  e a r Describe the major structures and functions of the Y es c o m cardiovascular system. u t o Session outcomes 1. Explain the relationships between pressure, resistance and blood flow. 2. Describe how pressure changes across the circulation. 3. Explain the mechanisms to increase venous return to maintain unidirectional blood flow. 4. Explain the major mechanisms that regulate mean arterial pressure. 5. Describe the forces influencing fluid movements in capillaries (capillary exchange and bulk flow).  LEARNING OUTCOME 1 UNDERSTAND THE RELATIONSHIP BETWEEN PRESSURE, RESISTANCE AND FLOW  Stroke volume = the volume of blood ejected per beat (mL). Heart rate and stroke volume determine the cardiac output Heart rate = number of beats Cardiac output = the volume of blood per minute flowing through the circulation in one minute Regulation of heart rate Medulla Vagus nerve SA node AV node Spinal cord Cardiac Through ganglion in sympathetic trunk accelerator nerve  Factors affecting stroke volume Preload (Frank-Starling law) Preload is the amount of sarcomere stretch experienced by cardiomyocytes, at the end of ventricular filling during diastole Contractility Contractility describes the relative ability of the heart to eject a stroke volume (SV) at a given prevailing afterload and preload (end-diastolic volume) Afterload Afterload is the amount of work the heart has to do to pump blood to the rest of the body Image from: The Frank-Starling’s Law - Why a lot isn’t necessarily good — Firstclass (firstclassmed.com) Let’s recap the determinants of the cardiac output CO = SV X HR *think of the cardiac output as the volume of blood flowing from the heart through the circulation. As blood flows through the blood vessels, it encounters resistance. The sum of the resistance encountered throughout the circulation is known as the total peripheral resistance (TPR) For the blood to overcome the resistance and keep flowing forwards, a pressure gradient is required. The relationship between blood flow, resistance and the pressure gradient across the circulation is described by the Hagen–Poiseuille equation.  re ssure gradient Blood flow= p resistance  Determinants of blood flow Pi Pf Pressure gradient - difference in the pressure between the beginning and ending of a vessel. Blood flow is directly proportional to the pressure difference. Resistance - is the opposition to blood flow through a vessel. Blood flow is inversely proportional to the resistance. Blood flow (F) = Pressure gradient (Pi-Pf)/ Resistance (R) Resistance to blood flow As blood flows it comes into contact with factors that resist flow. The main factors that alter resistance are: Blood viscosity Directly proportional to resistance Total blood vessel length Directly proportional to resistance Blood vessel radius Inversely proportional Resistance (R) = 8ηL πr4 4 Resistance ≈ 1/r  Think of it another way: If blood flow = pressure gradient / resistance CO MAP TPR then MAP = CO x TPR The mean arterial pressure is the average pressure exerted by the blood against the vessels. It is determined by the cardiac output and the total peripheral resistance.  Determinants of mean arterial pressure Cardiac Total peripheral output resistance Heart rate Stroke volume Vessel radius Blood viscosity Vessel length *Antihypertensive agents will target one of these determinants of blood pressure  Blood pressure 120 SBP (mm Hg) Systole Diastole 80 DBP (mm Hg) Systolic blood pressure = Diastolic blood pressure = Mean arterial pressure = average pressure exerted against the pressure exerted against the pressure exerted against the walls of the arteries during walls of the arteries during vessels systole diastole MAP = diastolic pressure + 1/3 pulse pressure  LEARNING OUTCOME 2 DESCRIBE HOW PRESSURE CHANGES ACROSS THE CIRCULATION Pressures within the systemic circulation Marieb & Hoehn. Human anatomy and Physiology Copyright © 2019 Pearson Education, Inc Elastic arteries experience high pressure - Windkessel effect Muscular arteries distribute blood flow and dampen pulsatility Arterioles regulate blood flow to capillaries. Windkessel effect distension accommodates increased volume with only moderate increase in pressure. recoil maintains relatively high pressure as blood flows away and volume is reduced. ike rm sd nk h a #t  The amazing arterioles Why are arterioles special? Primary site of vascular resistance: Arterioles regulate blood flow and total peripheral resistance (TPR) through vasoconstriction and vasodilation. Control of blood pressure: By adjusting their diameter, arterioles play a key role in short-term blood pressure regulation. Regulate blood flow to tissues: They adjust blood flow based on local metabolic needs, ensuring tissues get the appropriate oxygen and nutrients. Responsive to various stimuli: React to neural, hormonal, and local chemical signals, adapting blood flow dynamically. Arterioles are crucial for regulating blood pressure, controlling blood flow, and ensuring effective capillary exchange Super Mario 3D World Tour - Guide - Nintendo World Report  Arterioles adjust for pressure drops by altering their diameter through vasoconstriction and vasodilation, which allows them to regulate blood flow and maintain proper pressure within the systemic circulation. Decreased O2/ Increased CO2 Decreased Increased sympathetic tone Adenosine sympathetic tone Angiotensin II Stretch Increased H+ Atrial natruiretic Antidiuretic hormone Endothelins Increased K+ peptide Nor/adrenaline Prostaglandins Nitric oxide Vasodilation Vasoconstriction Intrinsic controls (autoregulation) Distribute blood flow to individual organs and tissues as needed. Extrinsic control Maintain mean arterial pressure Redistribute blood flow during exercise/thermoregulation  LEARNING OUTCOME 3 DESCRIBE THE MECHANISMS TO INCREASE VENOUS RETURN Veins Are both conduits and capacitance vessels The distribution of blood throughout the vasculature at rest : Pulmonary vessels 9% Heart 7% Systemic arteries and arterioles 13% Systemic veins & venules Systemic capillaries Venous return 64% 7% The rate of blood flow back to the heart. How do we get blood to flow back to the heart?  Where is the blood going? Why Factors affecting venous return: is this important? Postural changes Muscular “pump” contraction of skeletal muscles ‘milk’ blood towards heart Respiratory “pump” thoracic pressure changes during inspiration Venoconstriction Marieb & Hoehn. Human anatomy and Physiology Copyright © 2019 Pearson Education, Inc  LEARNING OUTCOME 4 DESCRIBE THE MAIN MECHANISMS TO REGULATE BLOOD PRESSURE Autonomic innervation of the heart and vasculature Baroreceptors located in the aortic arch and carotid sinus detect changes in pressure. This information is relayed to the cardiovascular centre in the medulla. The medulla adjusts sympathetic and parasympathetic activity appropriately. SA and AV nodes - innervated by SNS and PNS Ventricles - innervated by SNS only Blood vessels - innervated by SNS only Totosen. Principles of Anatomy and Physiology 2018 Short term control of blood pressure: The baroreceptor reflex Marieb & Hoehn. Human anatomy and Physiology Copyright © 2019 Pearson Education, Inc  The power up! The sympathetic nervous system The SNS is responsible for immediate changes in flow (e.g. during exercise). SNS fibers release the neurotransmitter noradrenaline (NA). In the heart NA acts on β1-receptors to increase HR and SV. In blood vessels NA acts on: ⍺1-receptors to cause vasoconstriction β2-receptors to cause vasodilation Long term control of blood pressure Marieb & Hoehn. Human anatomy and Physiology Copyright © 2019 Pearson Education, Inc  LEARNING OUTCOME 5 DESCRIBE THE FORCES INFLUENCING FLUID MOVEMENT IN CAPILLARIES Draw along Elastic arteries Large vein Muscular arteries Small vein Arterioles Postcapillary venule Terminal arteriole Capillary exchange Oxygen, carbon dioxide, most nutrients and metabolic wastes pass between blood and the interstitial fluid by diffusion. Diffusion occurs when a substance moves from an area of higher concentration to an area of lower concentration. Lipid soluble substances (incl gases) diffuse through the lipid bilayer of the plasma membrane. Small, water-soluble solutes pass through intercellular clefts/fenestrations. however, substances can also cross due to a pressure gradient  Fluid filtration across capillaries (Starling forces) Hydrostatic pressure = the pressure exerted Net Filtration Pressure = against the vessel wall. net pressure out – net Osmotic pressure = the osmotic pressure pressure in created by the concentration of colloidal proteins in the blood  Net Filtration Pressure Net Filtration Pressure (NFP) at the (NFP) at the venous end arterial end of capillaries of capillaries NFP = (BHP+ IFOP) – (BCOP + IFHP) NFP = (BHP + IFOP) – (BCOP+IFHP) = = = = BHP: Blood hydrostatic pressure; IFOP: Interstitial fluid osmotic pressure; BCOP: Blood colloidal osmotic pressure; IFHP: Interstitial fluid hydrostatic pressure