The Cardiovascular System
Blood
Composition & Functions:
Transports oxygen, waste, and hormones.
Regulates body temperature, pH (e.g. running releases carbonic acid), and fluid volume.
Prevents infection and blood loss (via platelets).
Blood Composition:
Blood is a liquid tissue that connects body systems by transporting cells within a fluid known as Plasma (fluid matrix).
When blood is sampled in a centrifuge:
Plasma rises to the top.
Formed Elements fall to the bottom.
Components:
Plasma: makes up 55%
White Blood Cells & Platelets: make up 1%
Red Blood Cells: make up 44%.
Hematocrit:
The percentage of red blood cells in a blood sample.
Blood is 5x more viscous than water, indicating thickness and stickiness compared to water.
Color and pH of Blood:
Ranges from bright red (oxygen-rich) to purplish shade (oxygen-poor).
Normal blood pH is maintained between 7.35 to 7.45.
Importance: Maintaining proper pH is crucial for enzyme function, oxygen delivery, and cellular metabolism.
Consequences of Abnormal pH:
Less than 7.35 (Acidosis): Can cause fatigue, confusion, deep/fast breathing, coma, and potential death.
More than 7.45 (Alkalosis): Can cause muscle spasms, nausea, and dizziness; both can lead to heart failure, shock, or severe organ damage.
Blood Composition Details
Total Blood Volume: Approximately 5-6 liters in the human body.
90% is made up of water.
10% consists of dissolved gases, salts, minerals, nutrients, enzymes, hormones, waste, and proteins.
Plasma Proteins:
Albumin: Regulates osmosis between blood and tissue.
Globulins: Fights infections.
Fibrinogen: Active in blood clotting.
Regulatory Factors of Plasma Composition:
Kidneys: Filter waste and balance water and electrolytes.
Liver: Synthesizes most plasma proteins, including albumin.
Formed Elements
Erythrocytes (Red Blood Cells)
Function: Transport oxygen throughout the body via hemoglobin molecules.
Structure:
Biconcave shape allows for a greater surface area.
Round sides facilitate more efficient flow through blood vessels.
Contains no nucleus and minimal organelles to avoid consuming oxygen while transporting it.
Erythrocytes are optimal for oxygen transport due to the nonpolar nature of oxygen (does not dissolve in blood).
Hemoglobin
An iron-rich protein in red blood cells, responsible for oxygen transport from the lungs to body tissues and organs, and returning carbon dioxide back to the lungs.
Each hemoglobin molecule contains a flat component called “Heme” that holds an iron atom.
One iron atom can bind to one O2 molecule; thus, one hemoglobin can hold four O2 molecules.
Leukocytes (White Blood Cells)
Function: Protect the body from foreign cells or substances.
Comparison to Erythrocytes:
Outnumbered by approximately 1000 to 1.
Mature leukocytes possess nuclei; erythrocytes do not.
Lifespan: Erythrocytes live for about 100-120 days; leukocytes usually live only a few days, though some can live for years.
Concentration in blood remains consistent for erythrocytes, whereas leukocytes fluctuate based on need.
Types of Leukocytes
Granulocytes:
Lobed-shaped nuclei and visible granules.
Types:
Neutrophils: Most common leukocyte; engulf and destroy foreign bacteria; production increases during infections.
Eosinophils: Two-lobed nuclei; kill parasitic worms ingested in food and respond to allergies.
Basophils: Release histamines, dilating blood vessels to allow other leukocytes to rush to an infection or allergen.
Agranulocytes:
Spherical or kidney-shaped nuclei; no visible granules.
Types:
Monocytes: Kidney-shaped nucleus; when they leave the blood and enter surrounding tissues, they become macrophages.
Lymphocytes: Large, spherical nucleus; mainly found in lymph nodes rather than in the bloodstream, includes:
T cells.
B cells.
Thrombocytes (Platelets)
Composed of tiny fragments of other cells; primarily function in blood clotting when a vessel is broken.
Blood Processes
Hematopoiesis
Definition: The process of blood cell production occurring in the red bone marrow.
Stimulated by hormones.
Stem Cells:
Common stem cell type: Hemocytoblasts.
Differentiate into:
Lymphoid stem cells (produce lymphocytes).
Myeloid stem cells (produce all other blood cells).
Hormones Stimulating Blood Cell Production
Red Blood Cells: Stimulated by Erythropoietin.
White Blood Cells: Stimulated by colony-stimulating factors and interleukins.
Platelets: Stimulated by Thrombopoietin.
Hemostasis
Definition: The process that prevents blood loss when a blood vessel is injured.
Steps of Hemostasis:
Vasoconstriction: The injured blood vessel tightens to reduce blood flow.
Platelet Plug (Primary Hemostasis): Platelets stick to the damaged vessel and to each other, forming a temporary plug.
Clot Formation (Secondary Hemostasis): Clotting proteins activate in a cascade;
Thrombin converts fibrinogen into fibrin.
Fibrin forms sticky threads that weave through the platelet plug, creating a stable clot.
Blood Clots:
An abnormal clot within a blood vessel is termed a thrombus. If dislodged, it becomes an embolus, which can restrict blood flow and lead to strokes or heart attacks.
Blood Groups
Antigens and Antibodies
Antigen: Substances (typically proteins, sugars, or lipids) on the surface of cells that trigger the immune response.
In presence of an antigen, the immune system produces antibodies that bind to and neutralize the antigen, resulting in agglutination (clumping of cells).
Consequences of Agglutination:
Can obstruct blood flow, stopping oxygen-rich blood from reaching organs, potentially causing embolism and widespread organ damage or failure.
ABO Blood Groups
Types:
Type A: Has A antigens.
Type B: Has B antigens.
Type AB: Has both A and B antigens.
Type O: Has neither A nor B antigens.
Rh Factor
The Rh factor is an inherited protein on the surface of red blood cells, determining blood type:
Positive (Rh+): Protein present.
Negative (Rh-): Protein absent.
Unlike ABO groups, anti-Rh antibodies are not produced immediately; the immune system requires time to recognize the Rh antigen.
Implications of Rh Factors in Pregnancy
Risks arise if an Rh-negative mother carries an Rh-positive baby; possible blood leakage may cause the mother to form anti-Rh antibodies.
Subsequent pregnancies with Rh-positive babies can lead to the mother’s immune system attacking the fetal red blood cells.
Monitoring and administration of RhoGam can prevent this immune response.
Intro to the Heart
Size and Location: The heart is a hollow, muscular organ about the size of a fist, located between the lungs.
Apex: Points toward the left hip.
Pericardium: Protective layer around the heart made of two layers:
Fibrous Pericardium: Provides protection and anchors the heart.
Serous Pericardium: Produces lubricating fluid to reduce friction between the heart and other tissues.
Circulatory Pathways
Pulmonary Circuit: Carries blood from the heart to the lungs for oxygenation and back; releases CO2 and picks up O2.
Major blood vessels: Pulmonary Trunk (branches into right and left pulmonary arteries) and Pulmonary Veins.
Systemic Circuit: Carries blood from the heart to body tissues and back; delivers O2 and removes CO2.
Major blood vessels: Venae Cavae (superior and inferior) and Aorta.
Chambers of the Heart
The human heart consists of 4 chambers:
Atria: 2 upper chambers that receive blood.
Ventricles: 2 lower chambers that pump blood out of the heart.
Function: The left side receives oxygenated blood from the pulmonary veins, while the right side receives deoxygenated blood from body tissues. The septum prevents mixing of oxygenated and deoxygenated blood.
Internal Structures
Valves: Flaps of tissue that prevent backflow of blood; they include:
Atrioventricular Valves (between atria and ventricles):
Right side: Tricuspid valve (3 flaps).
Left side: Bicuspid valve (Mitral valve, 2 flaps).
Semilunar Valves (between ventricles and blood vessels):
Right side: Pulmonary valve.
Left side: Aortic valve.
Blood Flow Through the Heart
Process:
Deoxygenated blood returns from the body into the right atrium.
Moves through the tricuspid valve into the right ventricle.
Pumped through the pulmonary valve to the lungs for oxygenation.
Oxygen-rich blood returns to the left atrium, passes through the mitral valve into the left ventricle.
Finally, pumped out through the aortic valve into the aorta to supply the body.
Valves: Ensure unidirectional blood flow.
Intrinsic Conduction System
Function: Sets the pace for heart contractions via special tissue that generates impulses.
Key Components:
Sinoatrial Node (SA Node): The heart's natural pacemaker; initiates electrical impulse causing atrial contraction.
Atrioventricular Node (AV Node): Delays impulse, allowing atria to empty into ventricles before passing the impulse onward.
AV Bundle and Purkinje Fibers: Conduct impulses to ventricles to initiate ventricular contraction.
Cardiac Cycle
Definition: One complete contraction and relaxation of the heart muscle.
Diastole: Relaxation phase of the heart and filling with blood.
Systole: Contraction phase of the heart.
Cardiac Output
Definition: Amount of blood pumped by each ventricle in one minute.
Formula: ext{Cardiac Output} = ext{Heart Rate} imes ext{Stroke Volume}
Stroke Volume: Volume of blood pumped out by a ventricle in a single heartbeat.
Heart Rate: Number of heartbeats per minute.
Factors Influencing Cardiac Output
Changes in Stroke Volume:
Exercise: Increases blood return from muscles.
Rapid Blood Loss: Decreases blood volume returning to the heart.
Changes in Heart Rate:
Stress: Sympathetic and parasympathetic nervous systems affect rate.
Hormones: Epinephrine and thyroxine increase heart rate.
Ions: Electrolyte imbalances affect heart contractility.
Physical Factors: Age, body temperature, and overall health influence heart rate.
Blood Vessels
Types of Blood Vessels
Arteries: Carry blood away from the heart.
Veins: Carry blood back to the heart.
Capillaries: Smallest vessels where gas exchange occurs.
Blood travels: Artery → Arterioles → Capillaries → Venules → Veins.
Function of Blood Vessels
Arteries: Blood is pumped from the heart under high pressure. The walls are thick, especially in the tunica media layer, allowing flexibility.
Veins: Receive blood from tissues under lower pressure, with thinner walls.
Three Methods of Blood Flow Maintenance Under Low Pressure:
Muscular Pumping: Muscle contractions help propel blood through veins.
Respiratory Pumping: Chest expansion during inhalation aids blood movement.
Valves: Present in larger veins to prevent backflow.
Structures of Blood Vessels
Capillaries: Consist of only one cell layer allowing the easy exchange of gases with surrounding tissues.
Arteries and Veins: Comprise three layers:
Tunica Intima: Slippery, thin layer facilitating smooth blood flow.
Tunica Media: Thicker layer of muscle that can alter vessel diameter.
Tunica Externa (Adventitia): Fibrous connective tissue providing support and protection.
Blood Vessel Differences
Arteries:
Thick walls, especially the tunica media layer.
High-pressure blood flow requires flexibility.
Veins:
Thinner walls due to lower pressure.
Capillaries Role
Comprised of shunts (shortcuts between arteries and veins) and true capillaries (actual sites of gas exchange).
Sphincters located between arterioles and shunts help regulate blood flow to tissues as needed.