Capillary Action and
Blood Components
Biology 20
Unit D: Body Systems – Circulation
1
Remember….
 Capillaries are so small that blood cells
can only pass through single file
 Important because they are the only vessels
THIN enough for diffusion of nutrients, wastes,
and gases
2
Network
 Capillaries work in
NETWORKS or
BEDS throughout
body
 Bed is formed
between a branch of
an artery and a
branch of a vein
3
Precapillary Sphincters
 Blood flow not always constant in capillaries
 If cells beside certain capillaries don’t
need to be serviced by the blood, blood
flow can be stopped from going to that
capillary
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Precapillary Sphincters Con’t
 Done by PRECAPILLARY
SPHINCTERS that
contract and close the
opening to that specific
capillary
 Blood then passes right
from artery to vein
through main capillary
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When do the these sphincters constrict
blood flow?
 After eating
 Capillaries feeding certain muscles are closed
 All the capillaries of the digestive system are
open
 Ie) capillaries in villi of small intestine
 While exercising
 Capillaries feeding muscles are open, and the
some capillaries feeding the digestive system
would be closed
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Interstitial Fluid
 Liquid that surrounds body
cells and capillaries
 Material exchanged
between body cells and
capillaries must travel
through this fluid
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Sections of Capillaries
 Arterial end
 Blood is bright red because hemoglobin in red
blood cells contain lots of oxygen
 Mid-section
 Where diffusion of materials takes place
 Direction of diffusion decided by a material’s
concentration gradient
 Venous end
 Blood is blue looking because there is minimal
oxygen present and lots of carbon dioxide
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Blood Flow Speed in Capillaries
 Slower than any other part of system
 Allows time for diffusion of materials
 Pressure is lower than arteries, but still
more than veins
 Ensures blood keeps moving
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Blood Components
 2 main elements: fluid and solid portions
 PLASMA = fluid portion
 FORMED PORTION = solid portion
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Plasma
 Consists of water, dissolved gas, proteins, sugars,
vitamins, minerals, hormones, and waste products
 55% of blood volume
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Formed Portion
 Consists of:
 red blood cells
 white blood cells
 platelets
 All produced in bone
marrow
 45% of blood volume
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Red Blood Cells (RBC)
 Aka Erythrocytes
 ~44% of the total volume of
blood
 Specialized for O2 transport
 The O2 carrying capacity of blood is
based on # of RBC present and the
amount of HEMOGLOBIN on each
 Mature RBC has no nucleus
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Hemoglobin
 Each RBC contains ~280 million
 Iron-containing
 Allows large sums of O2 to be transported in
blood
 Special properties that let it chemically bind with O2
 Then releases O2 by diffusion to cells that need it
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Hemoglobin Con’t
 After CO2 (waste) is diffused into the blood, it enters
the RBC where a small amount is chemically binded
to hemoglobin
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Anemia
 Disorder that occurs when there are:
  too few RBC
OR
  too little hemoglobin inside the RBC in blood
 These deficiencies reduce the amount of O2 that is
flowing through body
 May be caused by not eating enough iron (mineral)
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White Blood Cells (WBC)
 AKA Leucocytes
 Apart of body’s response to infection
 ~1% of total blood volume (X2) when fighting
infection
 Colorless and have a nuclei
 Divided into 3 groups:
 Granulocytes
 Monocytes
 Lymphocytes
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1. Granulocytes
 Consist of:
 Neutrophils
 Basophils
 Eosinophils
 Typically found circulating in blood with
granulocytes engulfing foreign bodies
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2. Monocytes
 Can leave bloodstream and
become further specialized into
MACROPHAGES (destroy
bacteria – engulf it)
 Typically found circulating in blood
with granulocytes engulfing
foreign bodies
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3. Lymphocytes
 Some produce
ANTIBODIES
 Proteins that
incapacitate pathogens
and allow them to be
easily detected and
destroyed
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Platelets
 Pieces of cells that form when
larger cells in the bone
marrow break apart
 No nucleus
 Breaks down quickly in blood
 Play key role in blood clotting
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Stages of Clotting
1.  Blood vessel broken due to injury
2.  Substances released at site to attract
platelets
3.  Platelets at site rupture, releasing chemicals
that combine with blood components to
produce enzyme called
THROMBOPLASTIN
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Clotting Con’t
4.  As long as there is Ca+ present,
THROMBOPLASTIN will react with
PROTHROMBIN to produce THROMBIN
  Prothrombin is a plasma protein produced in liver
5.  THROMBIN (enzyme) reacts with
FIBRINOGEN (protein) to produce FIBRIN
6.  FIBRIN forms mesh strands around injured
area, thus preventing more blood loss
  Forms clot
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What if your blood doesn’t clot?
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Plasma
 Fluid portion of blood
 Carries all blood cells
 Is a mixture:
 92% water
 7% Blood Proteins
 0.1% Organic Substances (ie.urea)
 0.9% Inorganic Ions (sodium, chlorine, magnesium,
potassium, calcium, biocarbonates, phosphates, etc)
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Plasma Con’t
 CO2 is dissolved in the water portion of
plasma when transported in the blood
 Forms carbonic acid in cytoplasm of RBC
 Then diffuses out of RBC into the plasma as
bicarbonate ions and is carried from tissues to
the lungs for gas exchange
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