circulatory system

• The circulatory system functions to transport nutrients and gases around the body
• Major organs of the circulatory system include the heart, blood vessels, and blood
• An average adult contains about 5 liters of blood, which is about 3 times more viscous (thicker) than water
• The pH of blood has a narrow range from 7.35 to 7.45
• Composition of Blood:

  • 55% plasma
  • 1% white blood cells and platelets
  • 44% red blood cells
• Blood plasma, which makes up 55% of blood, prevents infection and regulates blood loss and body temperature
• Blood plasma is composed of:

  • 90% water volume
  • 10% dissolved gases, salts, minerals, nutrients, enzymes, hormones, waste, and proteins
• Three basic types of proteins found in plasma are:

  • Albumin: regulates osmosis between blood and tissues
  • Globulins: transport substances or fight infection
  • Fibrinogen: used in blood clotting
• Formed elements in blood include:

  • White blood cells
  • Erythrocytes
  • Leukocytes
  • Platelets
• Erythrocytes, or red blood cells:

  • Approximately 5 million in a mL of blood
  • Produced in red bone marrow
  • Due to their lack of nuclei and mitosis, they are not actually classified as "cells"
  • Must carry oxygen through the bloodstream and get their red color from hemoglobin
• Hemoglobin, the oxygen-carrying molecule in red blood cells:

  • Composed of 4 chains, each containing a flat molecule called a "heme" that holds iron
  • Each iron atom can bind to one O2 molecule, allowing one hemoglobin to hold 4 O2 molecules
• White blood cells:

  • Types include lymphocytes, leukocytes, basophils, neutrophils, eosinophils, and monocytes
  • Neutrophils contain nuclei and live longer than red blood cells
  • White blood cells flow through plasma, can move on their own, and pass out of blood vessels
  • Have different types with unique functions to protect the body from foreign cells or substances
• Granulocytes consist of neutrophils, basophils, and eosinophils with lobe-shaped nuclei and visible granules
• Agranulocytes, like lymphocytes and monocytes, have no visible granules, with spherical or kidney-shaped nuclei
• Neutrophils are the most common leukocyte, engulf and destroy foreign bacteria, and are produced more during an infection
• Eosinophils have two-lobed nuclei, kill parasitic worms ingested in food, and lessen allergic reactions
• Basophils release histamines which dilate blood vessels to allow other leukocytes to rush to an infection or allergen
• Lymphocytes have a large, spherical nucleus and are mostly found in lymph cells, with two types: T-cells and B-cells
• Monocytes have a kidney-shaped nucleus and become macrophages when they leave the blood and enter surrounding tissue, attacking and engulfing viruses, parasites, and bacterial infections
• Thrombocytes, or platelets, lack a nucleus, are much smaller than red blood cells, and are responsible for clotting
• Platelets stick to the opening of an injured blood vessel, plugging the hole, and begin the process of forming a blood clot (coagulation) to restrict blood loss after a cut or bruise
• Hemostasis, the process of clot formation, involves the contraction of the blood vessel, platelets being attracted to the wounded epithelium and sticking together, and fibrin filaments from the blood forming a net-like structure at the wound
• An abnormal clot in a blood vessel is called a thrombus; if it dislodges and floats through the blood, it is called an embolus, which can be very serious due to the restriction of blood flow and can lead to conditions like stroke, heart attack, or death
• Blood types are determined by the presence of antigens on red blood cells, which stimulate the blood to agglutinate when they encounter a different blood cell
• There are 4 blood types:

  • Type A: A antigens
  • Type B: B antigens
  • Type AB: both antigens
  • Type O: neither antigens, but has antibodies
  • Presence of antibodies in blood makes blood typing essential before a blood transfusion
  • Type O is the universal donor, while Type AB is the universal recipient
• The RH factor is determined by the presence or absence of an Rh antigen on red blood cells; most Americans (85%) are Rh positive, and Rh-negative individuals form anti-Rh antibodies when they come in contact with Rh-positive blood
• RH factors are closely monitored during blood transfusions to ensure donated blood matches the recipient's blood type to prevent adverse reactions