Cardiac Cycle & Blood Physiology

• The circulatory system is composed of the heart, blood vessels, and blood.
• The circulatory system's functions include transport, protection, and regulation.
• Blood is made up of plasma and formed elements.

Formed Elements of Blood

• Erythrocytes are red blood cells.
• Platelets are fragments of certain bone marrow cells.
• Leukocytes are white blood cells.
• Erythrocytes are heaviest and settle first, making up 37-52% of total volume, otherwise known as the hematocrit.
• White blood cells and platelets make up 1% volume in the Buffy coat.
• Plasma makes up 47-63 percent, containing a mixture of water, protein, nutrients, electrolytes, nitrogenous waste, hormones, and gases.
• Plasma is the liquid portion of blood
• Serum is identical to plasma except for the absence of fibrinogen, which is the clotting portion.

Plasma Proteins

• Albumins are the smallest and most abundant plasma proteins, contributing to viscosity and osmolarity, and influencing blood flow and fluid balance.
• Globulins include alpha, beta, and gamma, performing immune system functions as antibodies.
• Fibrinogen is a precursor of fibrin threads that help form blood clots.
• Hypoproteinemia is a deficiency of plasma proteins, which can be caused by extreme starvation and liver or kidney issues and severe burns.
• Kwashiorkor is a condition in children with severe protein deficiency characterized by thin arms and a swollen abdomen.

Hemopoiesis

• Hemopoiesis is the production of blood.
• Yolk sacs produce stem cells for initial blood cell formation, colonizing fetal bone marrows, liver, spleen, and thymus.
• The liver ceases blood cell production after birth.
• The spleen remains involved with lymphocyte production.
• Red bone marrow produces all formed elements.
• The RBC lifecycle lasts for 120 days.

Hemoglobin Structure

• Hemoglobin consists of four polypeptide subunits called globins.
• The globin section of adult hemoglobin consists of two alpha and two beta chains.
• Globins can bind small amounts of carbon dioxide.
• Each chain possesses an iron molecule in the center that binds oxygen.
• Hemoglobin has four oxygen binding sites per molecule.
• Hematocrit is the percentage of whole blood volume composed of RBCs.
• Hypoxemia increases erythropoiesis through negative feedback control.
• The kidney produces erythropoietin, which stimulates bone marrow.
• Polycythemia is an excess of RBCs.
• Primary polycythemia is cancer of the erythropoietin cell line within red bone marrow.
• Secondary polycythemia can be caused by dehydration and emphysema and high altitude conditioning.
• Dangers of polycythemia include increased blood pressure, volume, and viscosity.
• Sickle cell anemia results when a recessive allele modifies hemoglobin structure.

Leukocytes

• Leukocytes are the least abundant formed element.
• Leukocytes protect against disease by spending a few hours in the bloodstream before traveling to connective tissue.
• Leukocytes have a visible nucleus.
• Leukocytes keep organelles for protein synthesis and contain granules in the cytoplasm, and all have lysosomes.

Types of Granulocytes

• Neutrophils, making up 60-70%, are aggressively antibacterial and the most abundant.
• Eosinophils, at 2-4%, increase in numbers in parasitic infections, collagen diseases, and allergies, and diseases of the spleen and CNS.
• Basophils, less than 1%, increase in numbers in chickenpox, sinusitis, and diabetes, secreting histamine to speed up blood flow to injury, and heparin to promote mobility of other WBCs in the area.
• Lymphocytes, 25-33%, increase in number in diverse infection and immune responses, destroying cells, coordinating actions of other immune cells, and secreting antibodies and providing immune memory.
• Monocytes, 3-8%, are the largest WBC, with a horseshoe shaped nucleus, and increased numbers in vital infections and inflammation, leaving bloodstreams and transforming into macrophages, phagocytizing pathogens, and presenting antigens to activate other immune cells.

Blood Vessel Anatomy

• Tunica intera (tunica intima): lines blood vessels, exposed to blood and simple squamous epithelium.

Cardiovascular System

• Heart is enclosed in pericardium inside thoracic cavity.
• Heart sits posterior to the sternum, left of the body midline, in between the lungs in the mediastinum.
• Apex points toward the left hip.

Pericardium

• Fibrous pericardium: dense irregular connective tissue, attaches to diaphragm and base of aorta, anchors heart and prevents overfilling.
• Serous pericardium parietal layer: attached to fibrous pericardium.
• Serous pericardium visceral layer: is attached directly to the heart.
• Two serous layers are continuous but separated by the pericardial cavity, and holds small amount of fluid that acts as a lubricant.

Layers of the Heart Wall

• Epicardium is the (visceral pericardium) outermost heart layer.
• Myocardium: thickest layer, cardiac muscle tissue that contracts.
• Endocardium covers the internal surface of heart and external valve surface, simple squamous epithelium.

Heart Sounds

• S1, lub sound, is the closing of AV valves (tricuspid/bicuspid).
• S2, dub sound, closing of semilunar valves (pulmonary/aortic).
• Heart murmur is a result of turbulence of blood passing through the heart.

Types of Heart Murmurs

• Valvular insufficiency and valvular stenosis.
• Valvular stenosis occurs with valves that do not open fully, valve cusps scarred and cannot open properly, resistance to flow, reduces chamber output.
• Valvular insufficiency occurs with valves that are not closing fully, valves leak because cusps do not close tightly and blood regurgitates back through valve, and may cause enlargement.
• Cardiac muscle is striated, short, thick, branched, and has one or two nuclei surrounded by light staining mass of glycogen.
• Cells are connected by intercalated discs.
• Sarcolemma is folded and interior spaces between cells.
• Mechanical junctions tightly join cardiomyocytes.
• Desmosomes are mechanical linkages that prevent contracting myocytes from being pulled apart.
• Gap junctions electrically join cells to allow for ions to flow between cells.

Cardiac Conduction System

• SA node, the pacemaker, initiates heartbeat, and is located high in the right atrium.
• AV node is located in floor of right atrium.
• AV bundle (bundle of his) – extends from AV node through interventricular septum and divides into left and right bundles.
• Purkinje fibers extend from left and right bundles at hearts apex, house through walls of ventricles.
• Heart contraction involves two events
  • The conduction system initiates and propagates an AP.
  • Cardiac muscle cells initiate action potentials and contract.
• Cardiac output is the amount of blood pumped by a single ventricle in one minute, determined by heart rate and stroke volume (amount of blood ejected per beat.)

The Cardiac Cycle Includes

• Ventricular filling as ventricles expand, pressure drops below atria, AV valves open and blood flows in.
  • Rapid filling with doors open, first third.
  • Diastasis second third, slower filling, P wave.
  • Atrial systole at final third, atria contract.
• Isovolumetric contraction when the volume of blood in chambers does not change.
  • Atria repolarize, relax, and stay relaxed the rest of the cycle.
  • Ventricle depolarize and contract (QRS Complex).
  • AV valves close, producing heart sound

Ventricular Ejection

• Pressure becomes too high, blowing open semilunar valves.
  • First rapid ejection with blood spurting out quickly.
  • Next with reduced ejection slower flow with lower pressure, corresponding with plateau of cardiac action potential.

Stroke Volume

• Amount of blood pumped out during ventricular contraction but pushing out all blood from the contraction.
  • Isovolumetric relaxation with all valves closed.
  • Blood from aorta and pulmonary trunk flows back filling cusps and closing semilunar valves.
  • Semilunar valves close creating heart sound.
• Phase 1: atrial depolarization (P Wave).
• SA node fires-Na flows in, threshold is met, depolarization occurs (Ca enters cell).
• Depolarization k exits cell causing cell to go back negative.
• Action potential distribution through atria with gap junctions, atria contracting together.
• Ventricles are filling passively, action potential is delayed at av node to allow
• Atrial contraction completes switching pressure gradient
• AV valves close creating heart sound
• Phase 2 - Isovolumetric Contraction (QRS)
• AV node moves to AV bundle, branches and purkinje fibers
• Ventricles begin to contract, pressure builds
• For a moment all valves are closed while contraction occurs
• No blood moves -Phase 3 - Rapid ejection
• Ventricular pressure exceeds that of pulmonary and aortic
• Semilunar valves open
• Blood goes out to ventricles
• Phase 4 - Reduced Ejection
• Ventricular repolarization occurs (T Wave)
• As ventricular drops semilunar valves close creating heart sound
• Marks end of systole
• Phase 5 - Isovolumetric Relaxation
• Ventricles move
• All valves are closed
• Atria are filling with blood
• Phase 6 - Ventricular filling
• Pressure in atria builds,
• AV valves open
• Ventricular filling begins

Explore the phases of the cardiac cycle, including atrial depolarization and ventricular filling. Understand the events triggering valve openings, the start of diastole, and isovolumetric contraction. Learn about the role of plasma proteins, erythropoiesis, and conditions like edema and high red blood cell count.