Download ANPS 020 Black 01-15

The Cardiovascular System
Ellen Black, Ph. D.
Department of Neurological Sciences
Office phone : 656-9397
E-mail : [email protected]
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Overview of the Cardiovascular System
The Cardiovascular system comprises the blood, the vessels which transport
the blood, and the heart that pushes the blood through the system
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Overview of the Cardiovascular System
The heart is two pumps in one organ
The RIGHT side
pump collects
oxygen-depleted,
carbon-dioxide rich
blood from the
body through 2
venae cavae, and
pumps it to the
lungs through the
pulmonary arteries.
The LEFT side
pump collects
newly oxygenated
blood from the
lungs through
pulmonary veins,
and pumps it out to
the body through
the aorta.
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Overview of the Cardiovascular System
Blood passes to and from
most organs of the body
through the
Systemic Circuit
Arteries carry blood away from the heart
Veins carry blood toward the heart
In the systemic circuit, arteries carry
blood that has high levels of oxygen and
low levels of carbon dioxide; systemic
veins returning from organs carry blood
depleted in oxygen, with high CO2
content.
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Overview of the Cardiovascular System
Blood passes to
and from the lungs
through the
Pulmonary Circuit
Arteries carry blood away from the heart
Veins carry blood toward the heart
In the pulmonary circuit, pulmonary
arteries carry blood to the lungs that still
needs to be oxygenated, and is
therefore oxygen-poor, CO2 rich.
Pulmonary veins return freshly
oxygenated blood to the left side of the
heart.
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Overview of the Cardiovascular System
Topics :
Blood
Anatomy of Blood Vessels
Anatomy of the heart
The Conduction System
The Cardiac Cycle
Cardiodynamics
Blood Flow and its Regulation
Adaptation and Disorders of the Cardiovascular System
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Blood
Text reading: chapter 18
Classified as a connective tissue, but a fluid rather than solid
Functions:
– Transporting dissolved gases, nutrients, hormones, and
metabolic wastes
– Regulating pH and ion composition of interstitial fluids
– Restricting fluid loss at injury sites (clotting reaction)
– Defending the body against toxins and pathogens
– Regulating body temperature by absorbing and
redistributing heat
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The Composition of blood
Blood can be fractionated
into 2 main components:
Plasma
Cell Fraction
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Plasma
• Approximately 46-63% of blood volume
• 92% of plasma is water
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The formed elements fraction contains
red and white blood cells
plus cell fragments called platelets
99.9% of cell fraction are RBC
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Hemopoiesis
= hematopoiesis
The process of blood cell formation
Occurs in the hollow center of
bones (as “red marrow”)
In fetal life, occurs mainly in
liver and spleen
With aging, fat takes over
marrow cavity
“yellow marrow”
Hemocytoblasts are the stem
cells that divide to form all
types of blood cells; also
called Pluripotent stem
cells
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Red Blood Cells = Erythrocytes
• Carry oxygen to cells in the body
• Erythrocytes account for slightly less than half the blood
volume, and 99.9% of the formed elements
• Hematocrit measures the percentage of whole blood
occupied by formed elements
– Commonly referred to as the volume of packed red cells
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Erythrocyte Production
Erythropoeisis = the formation of new red blood cells
Process speeds up with in the presence of Erythropoietin
(EPO = Erythropoiesis stimulating hormone)
Blood doping strategies often involve this hormone
RBCs pass through erythroblast and reticulocyte stages,
during which time the cell actively produces hemoglobin
A normal sample of peripheral blood usually does not contain
nucleated RBCs : the nucleus and organelles are ejected
after producing hemoglobin
~5 days to reticulocyte
~7 days to mature RBC
Life span ~ 120 days
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Red Blood Cells (Erythrocytes): Structure
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Erythrocyte Structure
Biconcave disc
provides a large surface to volume ratio
shape allows RBCs to stack, bend and flex
RBCs lack organelles : NO NUCLEUS
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Red Blood Cells travel single file through capillaries
(the smallest diameter blood vessels)
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Hemoglobin
Hemoglobin molecules account for 95%
of the proteins in RBCs
Hemoglobin is a globular protein, formed
from two pairs of polypeptide subunits
– Two alpha subunits, 2 beta subunits
– Each subunit contains one molecule
of heme
– Each heme has an iron (Fe) ion at its
center
– The iron reversibly binds an oxygen
molecule
– One hemoglobin molecule can bind
up to 4 oxygen molecules
• Damaged or dead RBCs are recycled
by phagocytes
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Life Span of Erythrocytes
Approximately 1% of RBC are replaced per day
Replaced at a rate of approximately 3 million new blood cells entering the
circulation per second.
Old or damaged RBC are removed from circulation by spleen before they
hemolyze (rupture)
Components of hemoglobin are individually recycled
– Heme is stripped of iron and converted to biliverdin (greenish), then
bilirubin (yellowish), which is processed by the liver
– Globin protein fraction is broken down to amino acids, which are
used to build other proteins
– Iron is recycled by being stored in phagocytes, or transported
through the blood stream bound to transferrin (free iron is toxic) 18
The Ultimate in Recycling
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Disorders of Blood: Jaundice
• Of the bilirubin formed in RBC breakdown, approximately
85% is removed from the blood and processed by the
liver.
• Failure of the liver to “keep up” with RBC breakdown or
blockage of the bile ducts leads to a buildup of bilirubin
in the blood. The bilirubin then diffuses out of the blood
into tissues all over the body, giving the tissues a yellow
color, readily apparent in the sclera of the eyes and the
skin.
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Disorders of Blood: Anemia
A decrease in the oxygen-carrying capacity of blood
Symptoms: lethargy, weakness, muscle fatigue, low energy
Some types of anemia:
• iron deficiency: hemoglobin is not functional without the iron
• hemorrhagic: from hemorrhage, or severe blood loss; fewer RBC
• anaplastic: bone marrow fails to produce enough RBC (radiation,
immunologic diseases)
Disorders of Blood: Sickle cell anemia
Caused by a mutation of the amino sequence of
the beta chain of hemoglobin.
Without sufficient oxygen bound to it,
hemoglobin molecules cluster into rods and
force the cell into a stiffened, curved shape.
These cells get stuck in capillaries, obstructing
blood flow to the tissues, which causes pain and
potentially damage to the organs.
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Leukocytes : White Blood Cells
• Lifespan varies by cell types; may be hours to years
• Defend the body against pathogens
• Remove toxins, wastes, and abnormal or damaged cells
• Are capable of amoeboid movement and positive chemotaxis
• Some are capable of phagocytosis
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White blood cells can leave the bloodstream
in response to chemical signals
by squeezing through the vessel wall
“diapedesis”
Details to come in
later lecture block
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Types of White Blood Cells
Granulocytes
Named according to
staining properties of
cytoplasmic granules
50 to 70 % total WBC
population (very
mobile, 1st response to
injury)
phagocytes attracted to
foreign compounds that
have reacted with
antibodies
migrate to damaged
tissue and release
histamine and heparin
Agranulocytes
Lack cytoplasmic
granules
Leave circulation to
become macrophages
Immune system cells
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The Complete Blood Count (CBC)
One of the most common clinical tests performed
Simple blood test measuring most parameters of blood
• Hematocrit and hemoglobin concentrations
• Platelet count
• White blood cell count
Includes counts of relative numbers of each of the types of white blood cell,
providing valuable information relative to the type of infection
e.g. High neutrophil counts indicative of bacterial infections
e.g. High eosinophil counts indicative of allergy or parasitic infections
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The Origin and
Differentiation of
Blood Cells
note the pattern, not the
details
1. Know common stem cell
2. Note the role of Colony
Stimulating Factors (CSFs)
3. Know end products, not
intermediate cells
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Disorders of Blood: Leukemia
• Leukemia is cancer of the white blood cell lines
– Myeloid leukemia: abnormal granulocytes or other cells of marrow
– Lymphoid leukemia: abnormal lymphocytes
• Immature and abnormal cells enter circulation, invade tissues
– Highly active cells, high energy requirements
– May take over bone marrow, replacing normal cells
• Loss of normal RBC, WBC and platelet formation results in anemia,
infection and clotting problems
normal
leukemia
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Platelets
Pieces of a
megakaryocyte
membrane bound sacs
of chemicals
NOT CELLS
Flattened discs
Circulate for 9-12 days
before being removed by
phagocytes
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Steps in Blood Clotting: Early role for Platelets
1. Vascular spasm
Smooth muscle in the vessel wall contracts on injury,
reducing the diameter of the vessel
2. Formation of a platelet plug
a positive-feedback loop causing platelet aggregation to
block the hole in the vessel wall.
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Steps in
Blood
Clotting :
Coagulation
Phase
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Steps in Blood Clotting : Coagulation
Cascade
3.
4.
Formation of a blood clot: the clotting cascade
•
Clotting can be initiated from damage within the vessel (intrinsic
pathway) or around the vessel (extrinsic pathway)
•
Eventually, an enzyme called thrombin is activated, which converts
soluble fibrinogen molecules in the blood to insoluble, loose fibrin
threads.
•
The clot is a gel formed from a network of fibrin threads which trap
blood cells and platelets.
Clot Retraction
Fibrin threads pull in on vessel wall, helping to plug the area and
stopping blood loss.
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Steps in Blood Clotting
Eventual dissolution of clot :
Fibrinolysis
An inactive plasma enzyme called
plasminogen is incorporated into
the clot
Chemicals in the clot (thrombin, tissue
plasminogen activator (tPA) )
convert plasminogen to plasmin
Plasmin digests fibrin threads and
inactivates clotting mechanism
Note: a genetically
engineered version of
tPA is now used to
treat heart attacks and
strokes caused by
blood clots
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There are MANY factors involved in the clotting process
Do not memorize, but note that the liver is the source of many of these clotting factors
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Excessive Clotting
• Blood clots may form in the bloodstream in the absence
of any injury.
• A thrombus is an attached blood clot formed by
platelets adhering to the blood vessel wall, often at sites
of arterial disease.
• If a piece of a thombus may detach and travel in the
bloodstream as an embolus which may block blood
vessels
• There are many anti-clotting drugs available
Heparin, Coumadin, tPA, Aspirin
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Blood Types
The surfaces of RBC are coated with glycoproteins and glycolipids which
are capable of stimulating an immune response. These molecules
(antigens) form the basis for the different blood groups.
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