Chapter 22 Notes
Chapter 22 Notes 80887 - BIOL 3150 - 001
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This 7 page Class Notes was uploaded by Abigail Towe on Monday November 9, 2015. The Class Notes belongs to 80887 - BIOL 3150 - 001 at Clemson University taught by Tamara L. McNutt-Scott in Fall 2015. Since its upload, it has received 36 views. For similar materials see Functional Human Anatomy in Biological Sciences at Clemson University.
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Date Created: 11/09/15
Chapter 22- Heart • To maintain body homeostasis, blood circulates continuously throughout the body ● accomplished via the pumping action of the heart ● very important to have constant circulation ● our circulatory system is a closed system to allow adjustment of pressures to control flow of blood throughout the body ● flow: body to inferior vena cava to RA to RV to pulmonary trunk to lungs to pulmonary veins to LA to LV to aortic to body Functions of the heart: • Serving as a pump ● propels blood through hollow vessels • main vessels of heart are “great vessels” • delivery & removal of varied substances to/from tissues/organs • “Center” of cardiovascular system because blood is brought to the heart and sent away from the heart ● connected to entire body by conduit system of blood vessels • types: • arteries- always carry blood AWAY from heart • it’s not always oxygenated, exception is pulmonary artery • veins- always carry blood TO the heart • capillaries - functional unit that is the site of exchange • Anatomical characteristics that assist with function: ● heart designed to have unidirectional flow of blood ● side-by-side pump ● develops blood pressure • mechanism for blood flow through vessels: using pressure gradient to move blood through blood vessels Side-by-side pump: Pulmonary and Systemic Circuit ● Heart is a “side-by-side” pump, serving 2 separate blood circuits ○ pulmonary and systemic circuit ● Blood flows through network of vessels that extend between heart and peripheral tissues (out to body) ○ blood flows through circuits in sequence from one place to another ● Although equal volumes in each circuit, right side requires less work because pulmonary circuit is short, and low pressure system ● Systemic Circuit (left side) is longer and more resistant to blood flow, thus requires more work ● physiologically there are equal volumes of blood in each circuits to provide equal balance for the system. problems arise when blood volume is not balanced. Anatomy of Heart ● modest weight (~300 grams or 1 pound) ● and size is about the size of your fist ● masks incredible strength and endurance to pump all blood needed each day ● located in thoracic cavity between lungs within mediastinum ● between 2 and 5th rib ● superior placed upon diaphragm ● extends obliquely to mediastinum ● posterior to sternum ● anterior to vertebral column ● obliquely placed ● apex- tip of heart at bottom ● base- top ● the heart is tipped: ○ apex is tipped anteriorly (forward) ○ base is tipped posteriorly (backward) ○ thus, obliquely oriented ○ and heart is more to the left of body Pericardium ● Heart enclosed by a double-walled sac called the pericardium ● constructed of: ○ fibrous pericardium ■ loose fitting, tough dense connective tissue layer ■ protects heart as it wraps around it,and also anchors heart to surrounding structures & prevents overfilling so you don’t blow out the wall of your heart ○ serous pericardium ■ parietal layer (inner layer) ● lies next to fibrous pericardium ■ visceral layer (outermost layer of serous pericardium) ● “epicardium” ○ integral part of heart wall ● myocardium ○ packaged in spiral/circular bundles- uses connective together. crisscross fibers to link areas of heart ○ when atria contract, their primary function is just to fill the ventricles. ○ The contractions start in the apex and work upward. when it contracts, it twists and pushes up based on the organization of the spiral muscle bunders. ○ This allows compression so that the heart can pump large amounts of blood out of ventricles. ● endocardium ○ lines the chambers of the heart ○ layers of endothelium supported by connective tissue ■ endothelium = simple squamous epithelium ○ also covers the valves ○ endocardium layer is continuous with the endothelium with the vessels that are leaving the heart ● pericardial cavity ○ slit like structure between layers of serous pericardium ○ contains film of serous fluid ■ permits free movement within sac ■ every time the heart contracts and beats- it moves. so the serous fluid is important to provide friction free environment. ● Cardiac muscle tissue: ○ has intercalated disks provide “interlocking” of the cardiac muscles together. ■ consists of two elements: desmosomes & gap junctions ● desmosomes- keep the cells attached to keep them from pulling apart during contraction with all the pressure ● gap junctions- set up a situation where they are electrically coupled. so once we have a depolarizing wave on one cell, it spread to all cells. ■ this forms a functional syncytium - allows a bunch of individual cells to work as a single unit. result in highly coordinated contractions. ○ nuclei found in center ■ in skeletal muscle it’s peripherally located ○ there is loose connective tissue in between the intercalated discs. ■ the matrix fills intercellular spaces along vascular connects to fibrous skeleton of heart ■ it acts as a tendon to provide an insertion for cardiac muscle tissue ■ Microscopically: cardiac muscle cells have sarcomeres, z lines, A bands, I bands, ● but has numerous mitochondria to give cardiac muscles high resistance to fatigue ○ important because we don’t want heart to stop beating ● calcium delivery system is less developed (less robust than skeletal muscle) and the T tubules are wider and fewer. enter once per sarcomeres. no triads. ○ physiologically- similar to skeletal but it’s different. if you look at cellular level, it’s designed the same but slightly different. ○ there is fibrous skeleton of the heart is located between the valves (in a cross-section) ■ it’s a dense connective tissue network found between atria and ventricles ■ functions: ● physically and electrically separate atria and ventricles ● anchor heart valves with supportive rings (important because valves are just flaps of connective tissues) ● provides a rigid framework for attachment of cardiac muscles - reinforces myocardium internally and anchors cardiac muscles Anatomy of heart: ○ atria - superior located ■ smaller, and thin-walled ○ ventricles- inferior located ■ larger, thick-walled ■ all vessels leave from the base (basal surface) ○ anterior side: trunk or aora. or interventricular sulcus. ○ posterior side: inferior or superior vena cava & coronary sulcus ■ coronary sinus sits on coronary sulcus ○ suli of heart- ■ anterior and posterior ventricular sulcus ■ and coronary sulcus : holds coronary circulation that provides heart with private circulation internal anatomy: ○ opening of coronary sinus : where blood returns to heart in right atria ○ all valves are atrioventricular valves ○ tendinae hooked to papillary muscles ○ papillary muscles do not contract- the heart wall contracts and creates tension on the papillary tendinae to cause movement. ○ in right ventricular: septomarginal trabecular - makes sure the right ventricle doesn’t blow out ○ trabeculae carnae - the ridges and valleys (remnant left over from when we had 2 chambers) it makes sure blood doesn’t stay sedentary in the heart to prevent a clot - keeps blood flowing. heart doesn’t eject ALL blood, some are residual. ○ semilunar valves- folds of connective tissue on the wall that open and close depending on blood flow ○ ligamentum arteriosum - arises after birth - remnant of ductus arteriosus (fetal structure that shunts blood) so this detours from pulmonary trunk to the atria. this is bypassing pulmonary circuit- important because fetus isn’t breathing. but once you are born, you can breathe so this is closed off and becomes a fibrous structure. ○ crista terminalis- separates the pectinate muscle from heart ○ fossa ovalis- shunt between left and right because we don’t always use full circuit. it’s a hollow depression where foramen ovale existed in fetal heart. ● left vs right ventricle ○ in left, the heart wall is thicker because it pumps to the entire body ○ right ventricle sends blood to pulmonary circuit so it’s weaker because it’s a shorter distance with less pressure and less resistance. ● atria vs ventricles ○ ventricles are larger. ○ the difference in function between atria and ventricles is reflected in size ○ atria contract enough to fill up ○ atria are primer pumps ○ ventricles are power pumps that generate pressure to move blood ● why is the heart constructed this way? why is left larger than right ventricle? why atria and ventricle size difference? ○ because of the functional demands placed on it ■ left side- systemic ■ right side- pulmonary circulatory Heart Valve ● blood flows in a specific direction in the heart ● one-way flow is accomplished by heart valves ● valves open and close in response to different in blood pressure ● systole- ventricles contracting ● diastole- ventricles relaxing ● ventricles contract - then the semilunar are open because V pressure is greater than the systemic circuit ○ heart can only pump blood out when pressure inside ventricle is greater than pressure in circuit ● as pressure falls in ventricles (relaxing), the atria pressure is greater so the atrioventricular valves open and fill ventricles. ● when systemic circuit pressure is greater, blood flows back and fills ?? ● so why no valves on vena cavas or pulmonary veins? couldn’t blood backflow into those? ○ pressure is really low, thin walls, so when the heart contracts - the heart compresses them shut so there is no backflow ● when ventricles contract, the atrioventricular valves are closed -little blood in atria so no pressure so it creates compression to prevent no backflow Cardiac Cycle ● it represents the period from the time of one contraction (one heartbeat) to the next contraction/heartbeat ● video: http://www.youtube.com/watch?v=rguztY8aqpk&feature=related conduction system of heart: ● shows us what is happening during cardiac cycle ● to be efficient pump, we need to have contraction element of heart coordinated ● it’s coordinated by conduction system ● the conduction system- made up of specialized cardiac (myocardial) cells that are noncontractile. serve as mechanism to distribute impulses that are generated at sinoatrial node. so the heart contracts in orderly, sequential manner. ● conduction system ensures signal moves fast enough through heart ● autorhythmicity- heart initiates its own contraction ● self depolarize ● heart initiates self contraction ● does not need NS ● from the SA node -- internodal pathway brings the signal to the right side and the atria contracts. ● atrioventricular node - a delay so the atria contracts and then ventricular contraction. stay in order. ● the AV bundle (bundle of His) conducts the muscle impulse into the interventricular septum ● within the interventricular septum, the L and R bundles split from the AV bundle ● the muscle impulse is delivered to purkinje fibers in each ventricle and disturbed throughout the ventricle myocardium ● why do we have this? ?? ● have an idea of how blood flows: INnervation of the Heart ● The heart is innervated by the autonomic nervous system via the coronary plexus. ● main layers of coronary plexus- sympathetic through cardiac nerve and parasympathetic through the vagus nerve. ● It’s cardiac muscle so it has a conduction system/ pacemaker to set the pace. ● so why need innervation? the brain stem can modify heart rate and force of contraction. BUT they do NOT initiate contraction- that is by the pacemaker (sinoatrial node) ● the SA node sets a rhythm ● parasympathetic is the dominant and can decrease heart rate because SA would have too increased heart rate ● sympathetic increases heart rate and can increase force of contraction Coronary Circulation of Heart ● “3rd circuit” - (aside from pulmonary and systemic) - that only feeds the heart itself ● the coronary arteries arise at the base itself and goes out to supply oxygenated blood to the heart ● Coronary arteries are referred to functional end arteries. ● What is the function of the functional end arteries? They have anastomoses - which allows us to have alternative blood vessels. ● Coronary veins for coronary sinus ● coronary sinus is a large vessel that enters to the right atrium Interesting fact: ● heart represents 1/200th of the body weight but it requires of 1/20th of the body’s blood supply