Blood composition and hemodynamics are crucial aspects of the cardiovascular system. Understanding the components of blood and how they interact is key to grasping the system's function in oxygen transport, immune defense, and maintaining homeostasis.
Blood flow dynamics, including pressure, viscosity, and , play a vital role in circulation. These factors influence how efficiently blood moves through vessels, delivering nutrients and removing waste products throughout the body.
Blood Cells and Plasma
Erythrocytes and Leukocytes
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, also known as red blood cells, are the most abundant cells in the blood
Responsible for transporting oxygen to tissues throughout the body
Contain , a protein that binds to oxygen (lungs) and releases it in areas of low oxygen concentration (tissues)
, or white blood cells, play a crucial role in the body's immune response
Can be categorized into granulocytes (, eosinophils, and basophils) and agranulocytes (lymphocytes and monocytes)
Each type of leukocyte has specific functions in defending the body against pathogens and foreign substances (bacteria, viruses, and fungi)
Platelets and Plasma
, also called thrombocytes, are small, disc-shaped cell fragments that contribute to blood clotting
When a blood vessel is damaged, platelets adhere to the injury site and release chemicals that attract more platelets
Platelets aggregate and form a plug, which helps stop bleeding (hemostasis)
Plasma is the liquid component of blood, consisting primarily of water, proteins, and dissolved substances
Transports nutrients, hormones, and waste products throughout the body
Contains clotting factors essential for blood (fibrinogen)
Hematocrit
is the volume percentage of red blood cells in the blood
Normal hematocrit ranges are approximately 40-50% for men and 35-45% for women
Low hematocrit may indicate , while high hematocrit can be a sign of dehydration or polycythemia vera
Hematocrit can be measured using a centrifuge to separate blood components (packed cell volume)
Hemoglobin and Blood Flow
Hemoglobin
Hemoglobin is an iron-containing protein found in red blood cells that binds to oxygen
Each hemoglobin molecule can carry up to four oxygen molecules
Oxygen binding to hemoglobin is influenced by factors such as pH, temperature, and the partial pressure of oxygen (oxygen-hemoglobin dissociation curve)
Abnormalities in hemoglobin structure can lead to disorders like sickle cell anemia and thalassemia
Blood Viscosity and Flow
Blood viscosity refers to the thickness and stickiness of blood, which affects its ability to flow through blood vessels
Viscosity is influenced by factors such as hematocrit, plasma proteins, and temperature
High blood viscosity can increase resistance to blood flow and contribute to cardiovascular problems (atherosclerosis)
Laminar flow describes the smooth, orderly movement of blood through vessels, with layers of fluid sliding past each other
Laminar flow is characterized by a parabolic velocity profile, with the highest velocity in the center of the vessel
Turbulent flow occurs when blood flow becomes chaotic and disorganized, often due to obstructions, sharp turns, or high velocities
Turbulent flow can cause damage to blood vessel walls and contribute to the development of atherosclerotic plaques
Cardiovascular Dynamics
Blood Pressure
Blood pressure is the force exerted by blood against the walls of blood vessels
Systolic blood pressure is the pressure during heart contraction, while diastolic pressure is the pressure during relaxation
Normal blood pressure is considered to be 120/80 mmHg (systolic/diastolic)
High blood pressure, or hypertension, can lead to increased risk of cardiovascular events (heart attack, stroke)
Cardiac Output and Stroke Volume
Cardiac output is the volume of blood pumped by the heart per minute, calculated as the product of heart rate and stroke volume
Cardiac output = Heart rate × Stroke volume
Typical resting cardiac output is around 5 liters per minute
Stroke volume is the volume of blood ejected from the left ventricle with each heartbeat
Stroke volume is influenced by factors such as ventricular contractility, preload (end-diastolic volume), and afterload (resistance to ejection)
Increased stroke volume can occur due to enhanced contractility (exercise) or increased preload (increased venous return)