Sangre

Cardiovascular System Overview

Components of the Cardiovascular System

• The cardiovascular system consists of blood, the heart, and blood vessels. Blood is a liquid connective tissue made up of plasma and circulating formed elements. The heart acts as a pump to circulate blood throughout the body.

• Blood vessels vary in diameter and distribute blood to organs and cells after proper preparation for venipuncture, including tourniquet placement and area cleaning. Blood is drawn from peripheral veins into tubes with or without anticoagulants based on testing needs.

Blood Composition

• Blood components are separated through centrifugation, revealing three layers: plasma (55%), a white layer containing white blood cells and platelets, and red blood cells (45%). Plasma contains water, dissolved substances like proteins, electrolytes, nutrients, gases, hormones, and waste products such as creatinine and bilirubin.

• Formed elements include cellular fragments or cells: white blood cells (in thousands per microliter) and red blood cells (in millions per microliter). Almost half of the blood volume consists of red blood cells formed in the bone marrow from pluripotent stem cells. After maturation, they lose their nucleus and take on a biconcave shape with hemoglobin as their main component for oxygen transport.

Red Blood Cell Lifecycle

• Red blood cells contain approximately 1.2 billion hemoglobin molecules each; they transport oxygen to body tissues for energy production. Lacking nuclei allows them to live only 120 days before being degraded by phagocytic cells in the liver or spleen; amino acids are reused while iron is recycled into new hemoglobin molecules. Bilirubin results from heme breakdown affecting urine color; high levels can cause jaundice in skin or sclerae.

• Erythropoiesis (red cell production) is regulated by oxygen availability; lower oxygen pressure detected by kidneys increases erythropoietin hormone production that stimulates more red cell formation in bone marrow to enhance tissue oxygen supply. The formed elements include red/white blood cells and platelets.

White Blood Cells: Types & Functions

Normal White Blood Cell Count

• Normal white blood cell count ranges from 5,000 to 10,000 per microliter; they vary in size/shape/nuclear structure with granules visible under Wright's stain—granulocytes include eosinophils (stain well), basophils (blue), neutrophils (acid/base affinity). Neutrophils make up about 60% of total white cell count with multi-lobed nuclei aiding in injury response via phagocytosis using enzymes like lysozyme for digestion.

Eosinophils & Basophils

• Eosinophils constitute about 2–4% of leukocytes with lobulated nuclei aiding in phagocytosis against antibody-coated objects while releasing cytotoxic enzymes against parasites/allergic reactions via histamine release which promotes inflammation/allergy responses; basophils represent less than 1% but produce heparin (anticoagulant) and histamine mediating inflammatory responses attracting other immune cells like neutrophils/eosinophils during allergic reactions/infections.

Monocytes & Lymphocytes

• Monocytes account for 3–8% of leukocyte population; largest type measuring between 12–20 micrometers that migrate into tissues becoming macrophages involved in phagocytosis while secreting substances attracting other immune responders like neutrophils/fibroblasts to sites needing repair/infection control.

• Lymphocytes comprise about 20–30% of circulating white blood cells migrating between bloodstream/tissues continuously; B lymphocytes produce specific antibodies against pathogens while T lymphocytes mediate cellular immunity targeting infected/cancerous tissues alongside natural killer (NK) lymphocytes destroying abnormal tissue without specificity towards antigens present during infections/cancers.

Platelets: Formation & Function

Platelet Characteristics

• Platelets are cellular fragments produced during megakaryocyte destruction within bone marrow; approximately 2,000–3,000 platelets circulate per destroyed megakaryocyte with normal counts ranging from 150,000 to 400,000 per microliter.

• These anucleate fragments measure between 2–4 micrometers across surviving around seven to twelve days within circulation before participating actively in hemostasis processes following vascular injury.

Activation of Platelets and Formation of the Platelet Plug

Mechanism of Platelet Activation

• When platelets are activated, they release substances stored in their granules, including serotonin, ADP, calcium, fibrin stabilizing factor, and platelet-derived growth factor.

• The activation process occurs when blood exits through a wound; this triggers a series of responses from the platelets.

• Key processes involved in platelet response include adhesion to the site of injury, release of chemical signals (degranulation), and aggregation with other platelets.