Cardiovascular System: Anatomy and Circulation

Cardiovascular System

• Blood circulates within the circulatory system, driven by the heart's pumping action.
• The circulatory system consists of two circuits originating from the heart.
  • Pulmonary circuit (heart and lungs).
  • Systemic circuit (heart and the rest of the body).
• Blood remains within blood vessels at all times, functioning as a closed circulatory system.
• Arteries carry blood away from the heart.
• Veins carry blood back to the heart.
• Branching, fine capillary beds connect arteries and veins, facilitating the exchange between blood and tissues.

Heart Anatomy

• The mediastinum in the thoracic cavity houses the heart, slightly off-center to the left.
• Anterior to the vertebral Column and superior to the diaphragm, separating the thoracic and abdominal cavity.
• The heart is flanked and partly obscured by the lungs.
• The heart is enclosed by the pericardium which is a double-walled sac to protect and prevent overfilling.
  • Serous membranes.
  • Fibrous membrane.
• The pericardium consists of several tissue layers.
  • Fibrous pericardium: Dense connective tissue that protects and anchors the heart.
  • Serous Pericardium: A serous membrane that forms a sac around the heart; includes parietal and visceral layers separated by the pericardial cavity filled with fluid.
• Myocardium: "Heart Muscle".
  • Cardiac muscle: Striated cardiac muscle cells called cardiomyocytes form a hollow muscle.
  • Cardiomyocytes: Mechanically interconnected by connective tissue fibers, known as the cardiac skeleton, for structural support and electrical insulation.
• Cardiomyocytes have no origin and no insertion.
• Intercalated Discs and Desmosomes connect cardiomyocytes.
• The heart has two functional/contractile subunits which are Electrically insulated and Contract Independently.
  • Atria (2).
  • Ventricles (2).
• Systole refers to contraction, usually of the ventricles.
• Diastole refers to relaxation usually of the ventricles.
• Ventricular systole corresponds to atrial diastole and vice versa.
• Endocardium: The inner heart wall.
  • Squamous epithelial tissue is on the connective tissue that lines the heart chambers and heart valves.
  • Continuous epithelial lining of the heart with the endothelial lining of blood vessels acts as a "blood proof" barrier.
• The human heart has four chambers.
  • Two superior atria (atrium).
  • Two inferior ventricles (ventricle).
• Atria are longitudinally separated by the interatrial septum.
• Ventricles are longitudinally separated by the interventricular septum.
• The right ventricle receives blood from the right atrium.
• The left ventricle receives blood from the left atrium.
• The right atrium receives blood from the left ventricle via the systemic circuit (body circuit).
• The left atrium receives blood from the right ventricle via the pulmonary circuit (lung circuit).
• Afferent blood vessels carry blood back to the heart (veins).
• Efferent blood vessels carry blood away from the heart (arteries).
• Atria fill ventricles, ventricles fill arteries, veins fill atria.
• The right side of the heart (right atrium/ventricle) drives the pulmonary circuit.
• The left side of the heart (left atrium/ventricle) drives the systemic circuit.
• Veins connect and bring blood to atria.
• Atria connect and bring blood to ventricles.
• Ventricles connect to arteries for blood to be carried away.
• Capillary beds facilitate transitions from the arterial to the venous system.
• The logic or reason the right and left sides of the hearts drive the pulmonary and systemic circuits is unknown, just that evolution has made it this way.
• Pressure-operated valves in afferent (veins) and efferent (arteries) blood vessels, and between the atria and ventricles, ensure unidirectional blood flow.
• Heart valves are connective tissue flaps that open and close in response to blood pressure changes in the different heart sections.
• The returning blood fills the atria, which forces the atrioventricular (AV) valves open when the atria are contracting.
• As the returned blood fills the ventricles, the AV valve flaps hang limply.
• AV valves open when the atrial pressure exceeds the ventricular pressure.
• As the ventricles contract, the AV valves close to prevent backflow of blood into the atria.
  • Papillary muscles and chordae tendineae prevent valve flaps from everting into the atria.
• When AV valves are closed, atrial pressure is less than ventricular pressure.
• Valves in Afferent Veins work the same way and Valves in Arteries work the same way!
• High blood pressure upstream forces them open.
  • "Upstream" means further away from the heart.
• Higher blood pressure downstream forces them closed.
  • "Downstream" means closer to the heart.
• The left ventricle is stronger to generate more force and pressure.

Heart Physiological Requirements

• Muscle contraction consumes substantial amounts of energy.
• Only energy metabolism by aerobic respiration is sustainable over an extended time, fueled by organic substrates and O₂.
• Circulatory system transports O₂ and nutrients to muscles and other energy consumers.
• Heart requires constant activity 24/7 or the deficiency stops the flow of blood and nutrients to the tissues causing necrosis.
• The heart has top priority for O₂ and nutrient supply next to the brain.
• Blockage of coronary blood vessels damages cardiac tissue irreversibly and compromises heart function.
  • Also known as "coronary" infarct, otherwise called a heart attack.
• Myocardium is striated with cardiomyocytes.
• Heart cells branch and connect with intercalated discs.
• Firm mechanical joints form between cell membranes via desmosomes.
• The myocardium acts as an electrical syncytium by forming gap junctions.
• The heart beats and contracts and is controlled by intrinsic "pacemakers" that are specialized cardiomyocytes and frequently auto-depolarize called a myogenic heart.
• Pacemakers' cell excitation spreads over the entire myocardium.
• Human hearts are not innervated by motor neurons.
• It has a longer action potential duration, which ensures complete contraction.
• The longer refractory period prevents tetanus and ensures full muscle relaxation between contractions.
• There are multiple pacemaker centers in the human heart.
• The SA Node is the fastest Spontaneous Electrical Depolarization.
• The SA-node is the primary pacemaker, fastest spontaneous electrical depolarization frequency, imposed on secondary and tertiary pacemakers, entire heart.
• When the SA Node fails then the AV Node takes over, and when the AV Node fails then the Purkinje Fibers take over.
• There is a connective tissue barrier electrically isolates atria and ventricles which causes depolarization to not spread directly from the atira to ventricles.
• Depolarizing pacemaker potential is intrinsically generated by the specialized cardiac muscle cells/pacemakers.
• Pacemaker action potential spreads via gap junctions over the entire myocardium (syncytium).
• Cardiac muscle contracts simultaneously.
• The refractory period in cardiac cells prevents tetanus as it repolarizes.
• Atrial muscle is active before ventricles.
• Ventricles only become active after the atria have ceased activity where Atria have ended activity!

Heart Regulation

• Atrial pressure fills ventricles as ventricular blood pressure fills atria.
• Blood pressure opposes to the cardiac muscle system without muscular antagonists.
• Contraction of the myocardium generates blood pressure.
• When muscle cells of the atria are excited and contract, ventricle cells relax and the reverse.
• There is extrinsic innervation of the heart by the Autonomic Nervous System (ANS).
  • The sympathetic branch accelerates to increase the heart rate / contraction force.
  • The Vagus nerve(parasympathetic) branch to decelerate slows heart rate and vigor.
• The cardiac control center is located in the medulla oblongata.
• Efferent ANS neurons connect to the cardiac plexus, innervating the SA and AV nodes, myocardium, and smooth muscles of the coronary arteries.
• ANS innervation occurs indirectly via chemical synapses with varicosities in the vicinity of target cells where the neurotransmitters of ANS are released in the extracellular space near target cells/tissues.
• Diffuse hormone-like influence at some distance of the target cells.
• The sympathetic system releases norepinephrine (NE), which increases heart rate and vigor and lowers the pacemaker threshold, thus generating more frequent APs.
• The parasitic system releases acetylcholine (ACh), which reduces heart rate by hyperpolarizing pacemakers and slows down AP frequency.
• Epinephrine, also known as adrenaline, is released by the adrenal medulla and has the same effect as norepinephrine but works in a long-term chronic stress response.
• Thyroxin is released by the thyroid glands and controls metabolic rate and body heat, causes a sustained heart rate increase, and enhances epinephrine/norepinephrine effects (synergistic action).
• An electrolyte imbalance can cause abnormal ion gradients between cells and extracellular space with altered dynamics and kinetics of ion flow across the membrane.
  • The shift in the membrane potential affects the generation of APs and repolarization.

Electrolyte Regulation

• Low Ca²⁺: Depresses heart rate.
• High Ca²⁺: Increases heart rate.
• Very High Ca²⁺: Disrupts heart function (arrhythmias).
• High or Low K⁺: Both Dangerous and lead to cardiac arrest because cardiac cells are polarized..
  • High K⁺: Hyperpolarizes.
  • Low K⁺: Leads to arrhythmias.

Other Regulatory Factors:

• Average heart rate is fastest in the fetus (140-160 bpm) and declines with age.
• Average BPM in females is 72-80 bpm in females.
• Average BPM in males is 64-72 bpm.
• Lower heart rates are found in physically trained individuals.
• Heat(fever) increases heart rate by generally increasing metabolic activity.
• Cold slows metabolism and heart rate.
• Tachycardia is an abnormally fast heart with over 100bpm, caused by high body temperature, drugs, or heart disease, chronic tachycardia increases risk of fibrillation.
• Bradycardia is unusually slow with under 60bpm, caused by low body temperature, drugs, or endurance training, and inadequate by trauma or edema.
• Congestive Heart Failure(CHF): Inadequate heart function due to the Coronary Arteriosclerosis.
  • Coronary Arteriosclerosis can lead to hypoxia with clots of fat deposits.
• The left ventricle with a higher than 90mm HG can lead to the heart having to work harder to generate hypertension.
• Myocardial Infarctions(coronary, heart attack) can lead to heart weakening and scar tissue development.
• Dilated Cardiomyopathy degeneration of myocardium affecting mainly ventricles, probably caused by infections and or drugs.
• Imbalances of Maintainance in Blood Circulation due to weakened ventricles lead to Pulmonary Congestion.
  • Lack of blood moved caused by one side of the heart, typically the left ventricle, leading to overload of blood and leaking into the lungs(Pulmonary Congestion).
• Peripheral Congestion may occur if there is insufficient volume moved by the side of the heart causing hypoxia and shortage of blood flow.

Congenital "brith" Defects of human hearts:

• Ventricular Septal Defect: An Incomplete formation of Interventricular Septum and incomplete separation of both ventricles which mixing of blood and shunting of blood with weakened Right Ventricle that causes low oxygen levels.
• Narrowed Aorta(Corartation aorta): Increased heart workloads that impact pressure and proper blood volumes pumped into the systemic circuit that can be surgically widened.
• Tetralogy of Fallout(Multiple defects) with a narrowed Pulmonary trunk and pulmonary Valve stenosed (constricted), thus impacting the volume released from the pulmonary circuit.
• Hypertrophy (enlargement) of the right ventricle due to workload with a Ventricular septal defect and Aorta connects to both ventricles for maximized blood volumes.

Blood Vessels

• Lymphatic system vessels form with and are the circulatory system.
• Closed System: Lumen with hearts in the middle. Lymph stays in their vessels at all times.
• Arteries carry blood away
• Veins carry blood toward
• Capillary beds perfuse through tissue.
• Exchange between blood and tissue is all in lymph vessels.
• Flow is driven by fluids.
• Generated by hear drives ventricle to sustain contractions to a larger blood pressure in lymphatic Arterials. -Systolic is pressure at 99 to 120 at Contraction or >140 mm Hg for hyper -Diastolic blood pressures 60+ that are hypertension above this level the person needs immediate attention.
• Tonic beds require much more Differences must be maintained to meet.
• Vascular all made by layers, also called tunnelis or three layers with lumen Inner tunnels are in contact with the blood.
• Middles are middle layers.
• Externus is outside the middle. -Connective tissue which loose collogen support and support. -infiltraded vessel to protect tissue

Arteries and Veins

• Smooth muscle controls cross Section VASOCONSTRICTION restricts cell movement.
• VASOSODULATION for greater.
• Tunics are external as ANS.
• Tynica is to reduce pressure.
• Vasular as most
• Veins are lower pressure
• Veinus walls are different as aterial is stronger
• Lacking vessels
• Pressure needed for the heart.
• Valves provide pressure
• Samples and infusions should be performed before.
• Collaterals must be continuous.
• Collatorations
• The volumes moved have a limit to 5 feet,
• Blood moves throughout or in winds at an increase to cardiac output and resistance.
• Arterial system pressure is highest.
• Action generates is higher from the system to overcome heart failure.
• Strotic pressure maintains ventricle contractions at 90 and the diastolic maintains between 60
• The pulse from the beats maintains systemic functions.
• Higher velocity of blood requires more.
• Maintains flow is maintained required .
• Pressure systems must be controlled with Low pressure with High pressure.
• The highest pressures are in the lymphatic regions.
• Valves maintain resistance.
• High intensity exercises are high levels of C02.
• Blood volume is maintained by control in water pressure as hyrdo smotic concentrations.
• Neuronal controls for short term for c02 control.
• Controls over all functions. Control bloods distrobution , the body.
• Baroreceptors Chemoreceptors Chemo control over a large system of the medulla. Hyerthsamus to command center over the kidneys regulation and filteration. Angiotension promotes kidney filtration
• Aldestrone promotes sodium increases
• Potent pressure for regulation increases. Total flow depends on how high or low. Flow is also based on level. Cardio, cardio shock causes tissues to require more nutrients.
• Aorta supplies major blood vessels.
• Lung veins for O2 blood and supply. Systems are divided to two circuits that control bodily functions and the circulatory system.
• Short to light and back for respiratory gas exchange.
• "Long" long from lungs for vessels.

Systemic Circuits

• Pulmonary Trunk/Circulation Main Arteries
• O2 lungs and supplies a lung wing. Lobar Arteries and Alveoli.
• Arterial supplies in aortic arches to parts of body and smaller arterioles.
• Veins drain system from the body and are Atypical while lymph vessels are opposite.

Overview of the cardiovascular system, including the heart's role in circulating blood through pulmonary and systemic circuits. Discussion of heart anatomy, its location in the mediastinum, and the protective pericardium.