Circulatory System - Blood Cells

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Structure Function
Plasma

more than 90% water, it carries the blood cells and particles through the circulatory system

Red blood cells

contain hemoglobin for oxygen transport
White blood cells

produce proteins called antibodies to fight infection
Platelets

not actually cells, platelets help blood clot

Blood Types

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  • Blood type is determined by two alleles. 
  • The O allele is recessive.  Type O is only expressed when both alleles are O.
  • The A and B alleles are both dominant.  AA and BB are homozygous dominant.  AO and BO are heterozygous.
  • When A and B occur together both are expressed.  This is codominance.
  • People who have type A blood produce anti-B antibody.  If they receive type B blood, their immune systems will attack the type B cells.
  • People who have type B blood produce anti-A antibodies.  If they receive type A blood, their immune systems will attack the type A cells.
  • People who have type AB blood produce no antibodies to A or B and can receive blood from any type donor.
  • People who have type O blood produce both anti-A and anti-B antibodies.  They can receive only type O blood.  They produce not antigens, therefor they can donate to any blood type.
Another important antigen is the Rhesus factor or Rh factor.  The dominant allele for this trait results in a positive Rh factor.  The recessive allele is Rh negative.  The Rh factor status is stated after the blood group type, for example, a person with A positive blood has antigens for group A and the Rh factor.  A person with Rh positive blood can receive either positive or negative blood.  A person with Rh negative blood can only receive blood that is Rh negative.  A person with Rh negative blood produces antibodies to the Rh factor.

Blood Flow Through the Circulatory System

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To watch the flow of blood through the heart, refresh the image.  This will activate the arrows.

 

Heartbeat

The heart rate is controlled by a group of nerve cells called the pacemaker.

Arteries carry blood away from the heart.  Blood pressure is highest in the arteries.  When the heart pumps, it exerts a force on the arterial walls.  When the heart rests, the pressure drops.  Arteries have strong walls to withstand the fluctuations in pressure.  In general, arteries carry oxygenated blood.  The exceptions are the pulmonary arteries that are carrying oxygen-poor blood from the heart to the lungs.

Veins carry blood to the heart. Pressure is lower in the veins than in the arteries.  The blood vessel walls are not as thick.  Valves in the veins open when the heart pumps to allow blood to flow.  The valves close when the heart rests to keep the blood from backwashing.  Valves are very important for veins that move blood against gravity, for example the veins of the legs.

Capillaries connect arteries to veins and are the thin walled vessels across which gases, nutrients, and water are exchanged between body cells and blood.  Capillaires have only on layer of epithelial cells and no connective or muscle tissue.  Gas and waste exchange occurs across these tiny vessels.

Test yourself.

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