NSCI5720 CVS 2 Circulation 2023 (2).pptx

Cardiovascular System 2 Circulation NSCI5720 Vertebrate Anatomy & Physiology Objectives Name the layers of the blood vessels and briefly describe the function of each layer Explain the functions of arteries vs veins and how their wall composition contribute to these functions Explain the structure a...

Cardiovascular System 2 Circulation NSCI5720 Vertebrate Anatomy & Physiology Objectives Name the layers of the blood vessels and briefly describe the function of each layer Explain the functions of arteries vs veins and how their wall composition contribute to these functions Explain the structure and role of capillaries Name the major arteries and veins (see pictures) Name and explain the role of the pacemaker of the heart and the cardiac cycle Describe what systolic and diastolic blood pressures are and explain what part of the cardiac cycle they represent Explain what process produces heart sounds and where to listen for them Lecture Plan Intro to blood vessels Structure of the blood vessel wall Cardiac cycle - electrical conduction through the heart New Terms Tunica – “tunic” enveloping membrane/layer of tissue Tachycardia – fast heart rate Bradycardia – slow heart rate Asystole – no ventricular contraction “cardiac arrest” Lumen - the cavity or channel within a tube/tubular organ such as a blood vessel or intestine - the space within the blood vessel where the blood flows Vaso- - pertaining to/relating to a vessel Intro to the Blood Vessels Arteries Carry blood away from the heart Carry oxygenated blood apart from…… Pulmonary arteries Veins Carry blood toward the heart Carry deoxygenated blood apart from….. Pulmonary veins Oxygenated blood leaves the heart through aorta – divides into smaller and smaller arteries until it gets to the capillaries (smallest vessels) Then after the capillaries the vessels converge and get larger and larger until the deoxygenated blood enters the cranial and caudal vena cavae and returns to the heart Gas and nutrient exchange occurs in the capillaries (smallest blood vessels) by passive diffusion Blood Vessel Structure Three layers: Tunica externa (adventitia) Outer connective tissue layer Tunica media Middle layer – muscle and elastic tissue Tunica intima Innermost layer – endothelial cells Tunica externa Outer layer Fibrous connective tissue and collagen – strong and flexible Prevents the vessel from overexpanding aka Tunica adventitia = “additional layer” outer most fibrous covering surrounding an organ Tunica media Media = middle layer Made up of smooth muscle, elastic fibres or a combination of both The amount of each varies depending on the type of vessel eg. artery vs vein Smooth muscle allows these vessels to contract  active change (helps regulate blood pressure) Elastic fibres provide stretch to the wall of the vessel  passive change, prevents blood vessel rupture during pulsing when the heart contracts Thickest and most variable layer Vasoconstriction and Vasodilation Vasoconstriction – narrowing (constriction) of blood vessels through contraction of the muscle in their walls Increases blood pressure Vasodilation – opening (dilation) of the blood vessels through relaxation of the muscle in their walls Decreases blood pressure Primarily occurs in arterial vessels – have the greatest amount of smooth muscle in their tunica media Very important for regulating blood pressure Tunica intima Intima – the innermost layer Made up of endothelial cells (type of epithelial cells lining blood vessels) continuous with endothelium of endocardium Provides a smooth surface so that blood can flow through without friction Ngā pātai? Any questions? Peripheral Circulation Systemic circulation – blood supply around the body Diagrammatic representation Site of gas exchange Artery Arteriole Capillary The Heart Direction of blood flow Venule Vein Arteries Arteries of the systemic circulation carry oxygenated blood away from the heart to the body Arteries of the pulmonary circulation carry deoxygenated blood from the heart to the lungs Arteries have thick tunica media (smooth muscle and elastic layers) Muscle – allows contraction, maintain steady blood pressure Elastic fibres – allows stretching and recoiling without rupturing Allows arteries to expand and contract as blood pulses Blood within arteries is at high pressure Can feel a pulse with gentle compression of the artery Arterioles Thinner walls (still have same 3 layers) Small branches of arteries Capillaries Site of gas and nutrient exchange – very important Microscopic blood vessels – only one endothelial cell thick  allows for transfer of nutrients and gas exchange with the tissues Found in networks called capillary beds – LOTS of vessels Mucous Membranes & Capillary Refill Time (not examined) Part of the patient’s clinical examination Evaluate gum colour – can give us an indication of oxygenation of blood in the peripheral tissues Capillary refill time (CRT): Pressing on gums pushes blood out of the capillaries Then we count how long it takes for the capillaries to go back to the normal colour Should be less than 2 seconds Video Venules & Veins Thinner walled than arteries – still have the same three layers But has a smaller Tunica media – minimal muscle Carry deoxygenated blood back to the heart Veins have valves  ensure uni-directional flow Lower pressure than arteries – cannot feel pulse Slow return of blood to the heart Major blood vessels Arteries Aorta – the main artery of the body. Originates from the left ventricle. Supplies the entire body Pulmonary arteries – take deoxygenated blood to the lungs to be re-oxygenated Veins Cranial Vena Cava and Caudal Vena Cava - Largest veins in the body. (In humans they are called superior and inferior). Caudal – collects blood from the thorax, abdomen and hindlegs Cranial – collects blood from the forelegs and head Pulmonary veins – collect oxygenated blood from the lungs and to left atrium Each organ has its own arterial supply and venous drainage Arteries Learn these arteries Veins Learn these veins Major arteries and veins Feeling for the femoral pulse (feeling for the pulse is not examined, but still need to know where it is and what it is called) Ngā pātai? Any questions? Electrical Conduction & Cardiac Cycle Heart Contraction Your heart beats regularly on it’s own without you having to think about it happening There are two types of cardiac muscle cells (myocytes): Automatic cells Non-automatic cells Automatic cells = spontaneously contract Non-automatic cells = do not spontaneously contract, they require their contractions to be initiated by the automatic cells  most cardiac myocytes When the automatic cells contract, they signal to the non-automatic cells contract Sinoatrial Node – Pacemaker Sinoatrial (SA) node A bundle of automatic cells that controls the heart rhythm and rate SA node is located at the junction of the cranial vena cava and the right atrium Has a baseline rate of contraction that can be altered (increased or decreased) by input from the body SA node sends out a signals: Causes both atria to contract Signal then spreads to the atrioventricular node (AV node)  in the atrioventricular septum AV node - initiates ventricular contraction. Then they relax and it starts again – the cardiac cycle Heart Sounds When auscultating the heart, the lub-dub sounds we hear are due to the valves snapping shut “Lub” S1 – sound 1 Closing of the AV valves  in what part of the cardiac cycle do they close? Ventricular contraction, beginning of systole Prevents blood flowing from the ventricles back into the atria “Dub” S2 – sound 2 Closing of the semilunar valves  in what part of the cardiac cycle do they close? Relaxation of ventricles, end of systole/beginning of diastole Prevents blood flowing from the pulmonary artery/aorta back into the ventricles Sounds (20s) Blood Pressure The heart contracts and relaxes in a cyclical pattern in response to electrical changes within the cells. This is called the “cardiac cycle” Systole Ventricular contraction Ventricular empties into the aorta/pulmonary arteries High pressure – Big number Diastole Ventricular relaxation Filling of ventricles from the atria Low pressure – small number ACT SYSTematically or you will DIA PASSIVEly Systole = active contraction of ventricles Diastole = passive Blood Pressure It is important that blood pressure is maintained within a range to prevent having a pressure that is too high or too low. If the pressure is too high  can cause organ damage Can cause damaged to the tissues Hypertension If the pressure is too low  won’t supply the organs with enough blood/oxygen Not enough oxygen or nutrients supplied to the tissue/waste products build up resulting in cell death Hypotension There are a number of systems to maintain blood pressure within the ideal range: stretch receptors in blood vessels, nervous detection and response, hormonal Things that assess the cardiovascular system in clinical examination (not examined) Heart rate Heart rhythm Pulses Mucous membrane colour Capillary refill time Ngā pātai? Any questions?