PSIO120 CVS Revision Slides T2 2024 PDF

PSIO120 Module 2 Revision The Cardiovascular System James Dries [email protected]  IMPORTANT These revision slides are designed to assist you with your final exam revision by focusing on important broad concepts, however, they should not be...

PSIO120 Module 2 Revision The Cardiovascular System James Dries [email protected]  IMPORTANT These revision slides are designed to assist you with your final exam revision by focusing on important broad concepts, however, they should not be solely relied upon. All material covered in PSIO120 is examinable, including textbook readings, information presented in lecture slides, information spoken during lectures, and presented/spoken in tutorials. Refer to the textbook and lectures for a more thorough explanation of concepts if required. Overview The CVS is composed of heart, blood vessels, and blood. Main functions: Transport nutrients to the tissues Transport respiratory gases (O2 and CO2) Remove waste products Transport hormones Blood Vessels Blood vessels act as transportation routes Connect heart, lungs, and tissues Carry oxygenated and deoxygenated blood Complete a closed circulatory loop – Arteries – Arterioles – Capillaries – Venules – Veins Varying diameter Varying pressure inside Varying microstructure Blood Vessels Blood Vessels  Structure of Blood Vessels 1. Tunica interna (innermost layer) – Endothelium – Subendothelium – Internal elastic lamina (arteries only) 2. Tunica media (middle layer) – Smooth muscle fibres (no conscious control) – External elastic lamina (arteries only) 3. Tunica externa (or adventitia) – Connective tissue – Vasa vasorum (internal blood supply to large blood vessels)  Types of Capillaries Continuous Fenestrated Sinusoid Abundant in skin, lungs, muscle and Found only in areas of active filtration Found in liver, bone marrow, spleen, CNS (kidneys) or absorption (intestine) or adrenal medulla hormone secretion Least permeable Moderately permeable Most permeable Tight endothelial lining; pinocytotic Fenestrated pores found throughout cells Incomplete basement membrane; large vesicles ferry fluid across cells; often intercellular cleft allows large molecules associated with pericytes or cells to pass through  Capillary Exchange Movement of materials in & out of a capillary: Diffusion (most important method) › substances move down concentration gradient › plasma solutes (e.g., O2, CO2, glucose, amino acids, etc.) except large proteins pass freely across › through lipid bilayer, fenestrations or intercellular clefts Transcytosis › passage of material across endothelium in tiny vesicles by endocytosis and exocytosis › large, lipid-insoluble molecules such as insulin or maternal antibodies passing through placental circulation to foetus Bulk flow › movement of fluid and its dissolved substances in one direction due to a pressure gradient  Pressures that Operate in Body Fluids Hydrostatic pressures: Blood hydrostatic pressure – BHP ̶ pressure in circulation generated by pumping of the heart Interstitial fluid hydrostatic pressure – IFHP ̶ pressure generated by water molecules in tissue fluid Osmotic pressures: Blood colloid osmotic pressure – BCOP ̶ pressure caused by plasma proteins in the blood Interstitial fluid osmotic pressure – IFOP ̶ pressure caused by solutes in the tissue fluid Dynamics of Capillary Exchange Circulatory System Two circuits: Pulmonary → lungs Systemic → body  Pulmonary Circulation Arteries carry deoxygenated blood Pulmonary arteries Arteries are large, low resistance vessels Circuit is relatively short Less pressure needed to pump blood Lower blood pressure in comparison with systemic circulation Capillaries in lungs for gas exchange CO2 out, O2 into circulation Veins return oxygenated blood to heart Pulmonary veins  Systemic Circulation Arteries carry oxygenated blood Circuit is much longer than pulmonary More pressure needed to pump blood Highest blood pressure in the body in aorta Capillary beds throughout body allow gas exchange O2 out, CO2 into circulation Veins return deoxygenated blood to heart Inferior and superior venae cavae  Pericardium The heart is enclosed and held in place by the pericardium ̶ Inner serous pericardium (visceral and parietal layers) ̶ Outer fibrous pericardium  Pericardium Heart enclosed by a sac called the pericardium – made up of three layers Superficial, single-layered fibrous pericardium - Protects, anchors to surrounding structures, and prevents overfilling - Composed of tough, inelastic, dense irregular connective tissue Deep two-layered serous pericardium: 1. Parietal layer lines the internal surface of the pericardium 2. Visceral layer (epicardium) on the external surface of the heart Two layers separated by fluid-filled pericardial cavity (decreases friction)  Heart Structure Approximately the size of a fist Four chambers: two atria; two ventricles - (right and left) Superior and inferior vena cava Bicuspid and tricuspid valves Aortic and pulmonary valves Pulmonary arteries and veins Aorta (ascending and descending) Heart Structure Heart The heart is enclosed in the pericardium Base (posterior surface) leans toward right shoulder Apex points toward left hip Apical impulse palpated between fifth and sixth ribs, just below left nipple  Heart Chambers Four chambers − Two Atria (superior) − Two Ventricles (inferior) Atria separated by interatrial septum Interventricular septum separates ventricles Atria and ventricles separated by AV valves Right side is thinner than the left side − reflects the pressure which each side pumps against  Atria Receive blood from the body and lungs “Priming pumps” Needed to pump blood into ventricles – ventricular filling is passive initially Thin walled, little pressure generated RA receives blood (deoxygenated) from the superior and inferior vena cava and the coronary sinus Sends blood to RV via tricuspid valve LA receives blood (oxygenated) from the pulmonary veins Pumps blood to the LV via the mitral valve  Ventricles Receives blood from atria Right ventricle – pumps blood through pulmonary circuit (pulmonary trunk) Left ventricle – pumps blood through systemic circuit (aorta) Pulmonary circuit is shorter, less resistant to flow Right ventricle wall moderately thick Systemic circuit is longer, more resistant to flow − More pressure needed to circulate blood Very thick muscular wall in left ventricle  Heart Valves Semilunar (SL) valves: Pulmonary semilunar valve (right ventricle) Aortic semilunar valve (left ventricle) Each SL valve has three leaflets Prevents blood backflow from pulmonary trunk and aorta into the ventricles Heart Valves Heart Valves Heart Valves Blood Flow Through the Heart  Systemic and Pulmonary Circulations Pulmonary circulation: deoxygenated blood is pumped from right ventricle to the lungs for reoxygenation, then returned to the left atrium Systemic circulation: oxygenated blood is pumped from the left ventricle to the body (including the heart) and deoxygenated blood is returned to the right atrium Pulmonary Circuit Body Body https://www.myphteam.com/resources/how-the-pulmonary-artery-functions Systemic and Pulmonary Circulations  Coronary Circulation Coronary arteries: Originate at the base of the aorta Left coronary artery – Anterior interventricular artery – Circumflex artery Right coronary artery – Right marginal artery – Posterior interventricular artery  Coronary Circulation Coronary veins: Drains into coronary sinus Empties blood into right atrium – Great cardiac vein – Middle cardiac vein – Small cardiac vein – Anterior cardiac vein  Cardiac Muscle Tissue Intercalated discs: Irregular transverse thickenings of the sarcolemma at the ends of cardiac muscle fibres that connect neighbouring fibres Desmosomes: found within the intercalated discs – hold cardiac fibres together Gap junctions: allow muscle action potentials to conduct from one muscle fibre to the next – allows the entire myocardium of the atria or the ventricles to contract as a single, coordinated unit Electrical Pathway of the Heart A specialised network of electrical pathway in myocardium. Allow rapid transmission of electrical impulses across the heart. Contracts myocardial cells in order (first atria, then ventricles). Cardiac muscles have the ability of create their own action potential without external excitation (neuronal or hormonal). Called autorhythmicity. Self-excitability and propagation of action potential. Electrical Pathway of the Heart Electrical excitation begins in SA node located in the right atrial wall. Rapidly transmits across atria by fast pathway Allows atrial contraction Impulse transmits to AV node Atria and ventricles are electrically connected by AV bundle (Bundle of His) Impulse transmits down right and left bundle branches and up the Purkinje fibre system Ventricle contraction begins after atrial contraction Ventricles contract from bottom to top (apex upwards) Electrocardiography (ECG) Electrocardiography (ECG) Electrocardiography (ECG) Action potentials can be detected at the surface of the body ECG records these electrical signals for each heartbeat Electrodes placed in arms and legs (limb leads) and 6 positions across the chest (chest leads) 12 Different combinations of limb and chest electrodes (12 leads) Record electrical activity in different views of the heart. Limb lead II used as the rhythm strip. Single-lead ECG typically looks at limb lead I ECG ECG Lead I Combined Cardiac Cycle Events a) Electrical events b) Pressure changes c) Heart sounds d) Volume changes e) Mechanical events Heart Sounds Due to valves closing and blood turbulences First heart sound - S1 (lubb) closure of AV valves (beginning of ventricular systole) Second heart sound – S2 (dupp) closure of SL valves (beginning of ventricular diastole) Third and fourth heart sounds (not usually heard) S3 – caused by rapid ventricular filling S4 – caused by atrial systole  Volume Changes in Ventricles EDV reaches due to atrial systole Ventricular systole causes blood ejection from ventricles (SV) ESV – blood remaining in ventricles following systole Relaxation period – EDV increases due to passive ventricular filling  Cardiac Pressure Changes Red – aortic pressure Blue – left ventricular pressure Green – left atrial pressure Phases of Cardiac Cycle 1. Ventricular filling 2. Atrial contraction 3. Isovolumetric contraction 4. Ventricular ejection 5. Isovolumetric relation Cardiac Output Volume of blood pumped by each ventricle in one minute CO = Heart rate (HR) × Stroke volume (SV) HR = number of beats per minute (e.g. 75 bpm) SV = volume of blood pumped out by one ventricle with each beat (e.g. 70 mL) Normal at rest CO = 75 X 70 = 5.25 L/min CO increases if either/both SV or HR increased SV = EDV – ESV EDV - (end diastolic volume) volume blood in ventricles at end of relaxation ESV - (end systolic volume) volume blood in ventricles at end of systole  Stroke Volume Diastole: relaxation of the atria and ventricles Systole: contraction of the atria and ventricles End diastolic volume (EDV): volume of blood in each ventricle at the end of diastole (130 mL) End systolic volume (ESV): volume of blood remaining in each ventricle at the end of systole (60 mL) Stroke volume: blood ejected from the ventricles during systole; difference between EDV and ESV (e.g., 130 – 60 = 70 mL)  Regulation of Stroke Volume and Heart Rate Factors that regulate stroke volume: Preload – force that stretches the cardiac muscle prior to contraction (influences venous return) Contractility – strength of heart contraction Afterload – force resisting the ejection of blood by the heart (aortic and pulmonary arterial pressures) Factors that regulate heart rate: Autonomic nervous system (PNS and SNS) Hormones (e.g., adrenaline) Ions (Na+, K+, Ca2+) Age (newborn baby HR is 120 bpm] Gender (adult females have slightly higher resting HR) Physical fitness (regular exercise decreases resting HR) Temperature (hyperthermia increases HR) Factors that Increase Cardiac Output Blood Pressure Systolic BP: highest pressure attained in arteries during systole (~120 mm Hg) Diastolic BP: lowest arterial pressure during diastole (~80 mm Hg) Depends on Cardiac Output (CO) and Total Peripheral Resistance (TPR) BP = CO x TPR Cardiac output depends on stroke volume and heart rate CO = SV x HR TPR depends mainly on diameter of blood vessels (level of vasoconstriction) MAP = diastolic BP + 1/3 (systolic BP – diastolic BP) MAP = [80 + 1/3 (120 – 80)] = 93 mm Hg Factors Affecting Blood Pressure Measurement of Blood Pressure Hormonal Regulation of BP  Shock Is a failure of CVS to deliver enough oxygen (hypoxia due to ischemia) and nutrients to meet cellular metabolic needs › Cell membranes dysfunction, cell metabolism is abnormal, and cell death may occur Types of shock: 1. Hypovolemic – internal or external sudden blood loss 2. Cardiogenic – heart fail to pump; myocardial infraction 3. Vascular – inappropriate vasodilation [anaphylactic / neurogenic / septic] 4. Obstructive – portion of circulation in blocked; pulmonary embolism Responses to Hypovolemic Shock RAAS activation Vasopressin release SNS activation ̶ Leads to reduced water and Na+ loss at the kidneys, and vasoconstriction ̶ Increases blood volume, TPR and CO ̶ BP restored despite some loss of RBCs (lowered haematocrit)  Congenital Heart Defects Coarctation of the aorta – characterised by a narrowing of the aorta, which can lead to hypertension and reduced blood flow to the lower parts of the body Patent ductus arteriosus (PDA) – the ductus arteriosus, a temporary blood vessel fails to close after birth, causing abnormal blood flow between the aorta and the pulmonary artery Atrial septal defect (ASD) – characterised by an abnormal opening in the atrial septum, allowing blood to flow between atria and potentially causing oxygen-rich blood to mix with oxygen-poor blood Ventricular septal defect (VSD) – characterised by an abnormal opening in the ventricular septum, allowing blood to pass from the left to the right ventricle, which can lead to increased blood flow to the lungs and less to the systemic circulation Tetralogy of Fallot – condition consisting of four abnormalities: an interventricular septal defect, pulmonary stenosis, right ventricular hypertrophy, and an aorta that emerges from both ventricles (overriding aorta)