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BIOM Unit 4 Notes.docx

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Biomedical Sciences
BIOM 2000
Nicole Campbell

Aristotle (4th century BC) • Identified the heart as the most important organ of the body (intelligence, motion and sensation) • He described it as 3-chambered organ, center of vitality of the body (other organs surrounded it-brain, lungs-just to cool the heart) Leonardo da Vinci (c 1490) • Heart itself is not beginning of life but vessel made of dense muscle vivified and nourished by an artery and a vein as are the other muscles Part A: Components of circulatory system 1 1. • (Vascular System) Circulatory system: series of tubes (blood vessels) connected to a pump (heart) • Job: 1. To circulate blood to all regions of the body, 2. Supply body cells with nutrients and gases, 3. Remove toxic materials for excretion 2. Circulatory system made of 3 structural components: • Pump that powers everything (heart-4-chambered pump, left and right sided) • Carrying Vessels that conducting blood to and from body tissues: arteries (A), arterioles, venules and veins (V) • Networks of small vessels, capillary beds, within which transfer of materials between blood and body cells occurs 3. Vessels • Artery: carries blood away from the heart • Arteriole: smaller artery • Capillary: micro-circulation, only 1 cell thick (high resistance so blood moves slow, and are metabolically active for gas exchange) • Vein: carries blood towards the heart • Venuole: small vein 4. (Pulmonary and Systemic Vessels) 2 different circulatory systems linked and function in sync: • Pulmonary Circuit: pumps blood from right side of the heart to the lungs, returns blood to the left side of the heart • Systemic Circuit: pumps blood from left side of the heart to all parts of the body then returns blood back to right side Pulmonary Circuit (from right side of heart to lungs): blood releases CO2, picks up oxygen Systemic Circuit (from left side of heart): blood releases oxygen , picks up CO2 5. (Heart) • Mammalian heart is an embryonic fusion of 2 separate 2-chambered pumps to make single 4-chambered pump • Atriums: couch potatoes (least strongest), garage for blood when heart is relaxed, then it's pumped into ventricles • Left ventricle: strongest • Right ventricle: 2nd strongest • Atria have relatively thin walled compared with ventricle walls • Wall of left ventricle is much thicker than of left ventricle 6. (Heart) • Diastole: period when cardiac muscles are relaxing to allow blood to fill atria and ventricles • Systole: period of atrial and then ventricular muscles contraction (moving blood to the system) The Heart Valves 2 types of valves in heart prevent back flow of flow during contraction (systole) of ventricular muscle: • Atrio-ventricular valves: Left AV (Mitral), Right AV (Tricuspid) (goes from atrium to ventricules), preventing backflow into the atria • Semilunar valves: Left SL (Aortic), Right SL (Pulmonary) lie at the base of the two large arteries leading from the heart, the pulmonary artery (PA) and the aorta (AT) 8. (Heart Rate) • Contraction of cardiac muscle is regulated by action potentials that originate in the heart pacemaker - sinoatrial (SA) Node • Cells of the sinoatrial node (SAN) spontaneously initiate action potentials that spread over the atrial muscle causing it to depolarize and then contract • After depolarization of the atria, action potential moves to atrioventricular node (AVN) which slows down electrical transmission before allowing it into ventricles allowing coordinated contraction • As pacemaker impulses pass through heart, they cause cardiac muscle to contract, this generates minuscule waves of electric current that can be detected at skin's surface as an electrocardiogram (ECG) • Ventricular depolarization biggest spike- ventricules give more force (pumping blood further away) so there are big changes/energy differences 11. (Heart Cardiac Output) CO=HR*SV • Cardiac Output, CO = volume of blood pumped per minute • Heart Rate, HR = cardiac beats per minute • Stroke Volume, SV = amount of blood pumped with each cardiac contraction • SAN depolarization rate (HR) - influenced by Ach from PSNS (HR slower) and E/NE (epi/norepi) from SNS (HR faster) 12. (Heart Cardiac Output) • Stroke volume mainly determined by force of ventricular contraction (force of contraction of ventricular muscle depends on amount of stretch of muscle when it begins to contract (Starling's Law) • Stroke volume - largely regulated by amount of blood returning to heart via major veins • When heart stretched out, actin & myosin in better alignment (stronger contraction) Heart Murmur Back flow of fluid (into atria after left ventricle contracts) creates sound of heart murmur • Arteries have thick smooth muscle wall, encased in thick connective tissue (CT) sheath • Carry blood away from heart • Artery like broccoli elastic, vein like loose hair tie • Capillary beds = networks of extremely thin-walled vessels in body tissues • transfer of nutrients occur in capillary beds • Lactic acid gets picked up in capillary beds • Precapillary sphincters relax (open), blood goes in (regulation of flow of blood by these smooth muscle bands) • When precapillary sphincter (PCS) muscles relax, blood passes through capillary bed • Vascular shunt = when PCS muscles contract, blood bypasses the capillary vessels • Veins = expansive vessels that carry blood towards the heart • Blood pressure in veins is low therefore these vessels have a series of valves that prevent back-flow of blood • Skeletal muscles compress veins helping move blood along Blood Pressure • blood pressure = force that moves blood through closed circulatory system • systemic arteriole pressure (left side) is a good way of knowing how you are doing because of left ventricle Blood Pressure and Blood Flow • BP refers to arterial pressure which is determined by volume of blood and arteriole resistance • MAP = CO*SVR • Mean arterial pressure, MAP = blood pressure • Cardiac output, CO = HR*SV • Systemic vascular resistance, SVR = arterial constriction MAP = CO*SVR • Since CO = HR*SV, increasing HR and/or SV (Force of Contraction) will increase cardiac output and therefore increase bp • Systemic Vascular Resistance refers to degree of peripheral arteriolar constriction and/or relaxation (changes in response to SNS/PSNS activation, heat, stress, etc. Fluid Flow • Fluid flows from high pressure to low pressure (through vascular system along pressure gradient) • Once blood reaches capillaries, most pressure dissipates • Venous blood gets back to heart mainly by pumping of skeletal muscles Blood Pressure • Healthy bp is 120/80 mmHg (systole/diastole) • Systole = cardiac contraction (goes to system), diastole = period of cardiac rest • Heart is a pulse pump: blood flows speed up and slow down but don't stop, bp rises and falls but does not go through major cycles because of elastic recoil (why it's not 120/0) Elastic Recoil • Flexible nature of major arteries, have elastic recoil after each systole as a means to maintain pressure How does exercise increase bp? MAP = CO*SVR, CO = HR*SV • Heart pumps faster when you exercise contracting skeletal muscles, pushing more blood back to veins and back to heart (otherwise clogging of blood occurs) • MAP increases: skeletal muscles contract (SV increases), increase in sympathetic stimulation (HR,SVR increases) • Frank Starling Law: increase force of contraction if more blood moving back to heart Hypertension (HTN) • HTN = bp that is chronically greater than 120/80 mmHg; when we exercise we have hypertension but it's transient (goes back) • approx 25% people in the world have HTN, approx. 90-95% cases are primary • Risk factors: smoking, sedentary lifestyle, obesity, stress, etc.
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