Circulatory System Overview

Introduction

• The circulatory system is a transport system for the body.
• It plays a role in body defenses and the coagulation process.
• It also helps regulate body temperature.
• The circulatory system is made up of the cardiovascular system:
  • Blood: the transport medium
  • Blood vessels: arteries, veins, and capillaries
  • Heart: circulates blood through the vessels
  • The heart is a hollow, muscular organ.
  • The heart is made of cardiac muscle.
  • The heart's chambers contract simultaneously due to depolarization.
  • The heart is capable of automaticity.

Blood

• Blood is a type of connective tissue.
• Blood is a complex mixture of cells, chemicals, and fluid.
• Blood transports substances throughout the body and helps to maintain a stable internal environment.
• Blood contains:
  • Red blood cells
  • White blood cells
  • Platelets (formed elements)
  • Plasma

Blood Plasma

• Blood plasma is the straw-colored, sticky fluid portion of blood.
• Plasma is approximately 90% water and contains:
  • Ions, including Na and Cl ions
  • Nutrients, including sugars, amino acids, lipids, cholesterol, vitamins and trace elements.
  • Three main proteins:
    • Albumin (60%)
    • Globulin (35%)
    • Fibrinogen (4%)
  • Dissolved Gases, including O2 and CO2
  • Waste Products, including other protein wastes such as urea and bilirubin

Formed Elements

• Blood cells are formed elements and include:
  • Erythrocytes
  • Leukocytes
  • Platelets

Hematopoiesis

• Hematopoiesis is the process of blood cell formation.

Red Blood Cells (RBCs)

• Erythrocytes are the most abundant type of blood cell (99%).
• RBCS structure:
  • Biconcave, anucleate, and 8 m in diameter.
  • Components:
    • Hemoglobin
    • Lipids
    • ATP
    • Carbonic anhydrase

Red Blood Cell Function

• RBCs transport O2 and CO2.
• RBCs transport the majority of CO2 as HCO3-.
• RBCs play a role in pH homeostasis.
  • Carbonic anhydrase converts CO2 and H2O to HCO3- and H+.
• RBCs bend to pass through small capillaries.
• RBCs are destroyed in the spleen.
• Phagocytic WBC’s clear the debris from RBC destruction.

Hematocrit

• Hematocrit is the percentage of red blood cells in blood.
• Men have 5 million cells/mm3 of blood.
• Women have 4.5 million cells/mm3 of blood.

Regulation of Red Blood Cells

• The total number of RBCs remains relatively constant due to a negative feedback mechanism involving erythropoietin.
• Erythropoietin is released from the kidneys and liver in response to the detection of low oxygen levels.

Dietary Factors Affecting Red Blood Cell Production

• Vitamins B12 and folic acid are needed for DNA synthesis.
• Iron is necessary for hemoglobin synthesis.

Red Blood Cell Disease

• Anemia is a reduction in hemoglobin or red blood cell concentration in blood.
• Polycythemia is an excess of erythrocytes.
  • Often caused by cancer, tissue hypoxia, and dehydration.
  • However, polycythemia can occur naturally at high elevations.

White Blood Cells

• White blood cells are also known as leukocytes.
• WBCs function to protect the human body from infection and disease.
  • Neutrophils: 60–70% of WBCs: have multilobed nuclei; blue granules; phagocytize and destroy bacteria
  • Eosinophils: 2–4% of WBCs: have bilobed nuclei; red or yellow granules containing digestive enzymes; play a role in ending allergic reactions.
  • Basophils: have bilobed nuclei; contain histamine and heparin.