Cardiac Physiology 2022 PDF

Cardiac physiology Ch 25 Hill et al. (2022)  Learning Objectives By the end of this lecture, you will be able to describe: 3 types of animal “pumps” Differences in heart structure across taxa Systems to supply blood to heart Regulation of cardiac output Components of ci...

Cardiac physiology Ch 25 Hill et al. (2022)  Learning Objectives By the end of this lecture, you will be able to describe: 3 types of animal “pumps” Differences in heart structure across taxa Systems to supply blood to heart Regulation of cardiac output Components of circulatory systems Circulatory systems move fluids by increasing the pressure of the fluid in one part of the body Fluid flows through body, “down” pressure gradient Three main components are needed 1. Pump or propulsive structures 2. System of tubes, channels, or spaces 3. Fluid that circulates through the system  Pumps a) Contractile chamber: The heart is composed of chambers which act as individual pumps b) Skeletal muscle may contract to propel flow c) Pulsating blood vessels: Tube-like hearts in invertebrates and early vertebrate embryos Heart structure varies across taxa  Fish heart chambers are in series Serial contractile chambers Valves are passive – Open and close according to pressure differences – Ensure unidirectional blood flow – Blood flows into spongy myocardium In teleosts, bulbus arteriosus is volume and pressure reservoir – Called conus arteriosis in cartilaginous fishes (sharks/rays) Figure 9.22a Amphibian hearts have 3-chambers Two atria, one ventricle. Atria: – Left: Oxygenated from lungs – Right: Deoxygenated from systemic circulation; oxygenated from skin. Ventricle – Oxy- and deoxy- kept separate. Trabeculae – Spiral fold keeps blood separate in conus arteriosus Figure 9.22 Moyes and Schulte 2016 Heart structure varies across taxa Turtles, lizards and snakes have “5-chambered” hearts Two atria + ventricle Conus has disappeared Ventricle: Cavum venosum Leads to systemic aortas Cavum pulmonale Leads to pulmonary artery Cavum arteriosum Figure 9.23 Moyes and Schulte 2016  Shunting in reptile hearts Deoxy- Oxy- RL associated with diving; LR associated with oxygenating the heart; functions of both are debated Figure 9.23 Moyes and Schulte 2016 4 systems have evolved to supply O2 to hearts of animals Mammalian and avian heart Coronary vessels Spongy myocardium of most teleosts No coronary vessels Ancestral heart Blood not well oxygenated 4 systems have evolved to supply O2 to hearts of animals Some fishes: Outer layer compact; inner layer spongy Image: World Tuna Trade Some octopuses From lumen to coronary veins Image: AlphaSouth SARL Percentage of compact myocardium increase with migration effort  Blood supply to the heart Heart is active muscle demanding large amount of O2 and nutrients Mammalian heart is “compact” –Myocardial cells backed close together –Blood from ventricles cannot perfuse cardiac muscle Coronary arteries supply blood to heart  Mammalian cardiac cycle Movement from the atria to ventricles relies on pressure gradients Contraction of the ventricles actively moves blood to the aorta or pulmonary artery Two phases – Diastole » Relaxation » Blood enters the heart – Systole » Contraction » Blood is forced out into the circulation Mammalian heart (review on your own) Figure 49.2 Sadava et al. 2008  Cardiac output (CO) CO (mL/min) = HR (beats/min)× SV (mL/min) Volume of blood pumped per unit time Cardiac output (CO) can be modified by either term: Heart rate (HR) – Modulated by nervous and endocrine system – Bradycardia - Greek bradús "slow;" – Tachycardia - Greek takhús, “swift” Stroke volume (SV) – Modulated by various nervous, hormonal, and physical factors  Frank-Starling mechanism Stretching of cardiac muscle tends to increase the force of contraction [by an effect exerted at the level of the individual muscle cells] The more the heart fills, the stronger the force of contraction Physiologic stretch: increased HR – ventricle fills faster – contraction is stronger (CO is increased!)  CO (mL/min) = HR (beats/min) × SV (mL/beat) Based on Frank-Starling mechanism we could speculate a large heart fills with more blood than a small heart – heart size matters (SV) Can hearts beat as quickly as possible with no maximum? Or is there a finite heart rate? Two examples: The pygmy shrew Secretariat Whales and human hearts are 0.6% of body mass Pigmy shrew (3g) –has heart is 1.3% of body mass Why do shrews have relatively large hearts? Shrews Body mass (kg) HR (bpm) …but slow HR also have a Whale 130000 kg 6 relative to BM very fast Human Pygmy 65 kg 0.01 kg 70 600 absolute Shrew (max is 1200!) HR… Secretariat – Belmont Stakes 1973 https://www.youtube.com/watch?v=AG_27cCW5bw “We were all shocked…the heart of the average horse weighs about 9 pounds. This was almost twice the average size, and a third larger than any equine heart I'd ever seen… I think it told us why he was able to do what he did.” – Dr. Thomas Swerczek  Learning Objectives By the end of this lecture, you will be able to describe: 3 types of animal “pumps” Differences in heart structure across taxa Systems to supply blood to heart Regulation of cardiac output