Transcript Blood and Circulation

Blood and Circulation
By the end of this class you should
understand:
• The components of blood by volume and their
functions
• The most vital materials circulated by blood
• The purpose and process of hemostasis
• The process of producing and removing red
blood cells
• The nature of blood types and the risks of
improper transfusions
Blood!
• Blood is the liquid inside
us all that keeps us alive
• Essentially functions as a
common liquid that all
cells have equal access
to
– Think of roads in a city
– How cells send molecules
to other cells
Blood Flow
• Blood flows through the
entire body thanks to the
heart
• Heart failure results in blood
stagnation
• All cells in the body depend
on a steady flow of blood to
live and will die once blood
flow stops
Nutrient Delivery
• Blood is responsible for
delivering all nutrients and
removing all waste
products
– Glucose
– Oxygen
– Vitamins, amino acids, &
fats
– CO2
– Waste such as urea,
creatinine, and lactic acid
Blood Plasma
• Almost all materials in blood
dissolve directly into the
liquid, called plasma
• Plasma is also filled with
plasma proteins such as
antibodies (for the immune
system) and clotting proteins
• Only one nutrient does not
dissolve in the blood plasma
– Which one?
Oxygen
• Oxygen must be delivered to all
cells of the body that use
aerobic respiration
(mitochondria)
– Essentially all living cells of the
body
• Oxygen does not mix with water
and so must be transported in
molecules called hemoglobin
Hemoglobin
• Hemoglobin is a protein that
contains a pigment called heme
(contains iron)
– Same way rhodopsin containing
retinal
• Each heme can bind to one O2
molecule, so a hemoglobin can
carry 4 O2 molecules
• These hemoglobin molecules are
not allowed to float freely in blood
– This can cause severe kidney damage
Red Blood Cells
• Red blood cells, or
erythrocytes, are essentially
cell membranes packed with
hemoglobin
– Virtually no organelles remain
in a mature erythrocyte, not
even a nucleus
– This is to improve the amount
of oxygen a RBC can carry
– This also means the cell cannot
regenerate and is no longer
technically alive
Red Blood Cell Lifespan
• Red blood cells are produced
in the red marrow of bone
• They circulate through the
blood for around 3-4 months
• Because they have no
organelles, they cannot repair
wear and tear and so are
broken down in the liver and
spleen
Red Bone Marrow
• Red bone marrow is filled with
stem cells called hemocytoblasts
– Literally means “blood cell
creators”
• These stem cells constantly
reproduce to replace the ones
that differentiate into blood cells
– Hemocytoblasts produce all the
blood cells of the body
Erythrocyte Formation
• A hemocytoblast that has been signaled to
become a RBC produces hemoglobin in large
quantities using its organelles (nucleus and
mitochondria)
• The cell then degrades its organelles once it has
about 300 million hemoglobin molecules
– It is now a mature erythrocyte!
Erythrocyte Signal?
• There is a hormone in the
blood called
erythropoietin (EPO)
• The kidneys monitor
oxygen delivery in the
body and the lower
oxygen delivery is, the
more EPO they release
• This is also why people at
high altitudes have more
red blood cells
Hematocrit
• The percent by volume of
red blood cells in the blood
is called the hematocrit
– Most visible when the blood
is spun in a centrifuge
• Hematocrit is influenced by
EPO levels and also reflects
health and athleticism
• Low hematocrit: anemia
• High hematocrit:
polycythemia
Blood Cells
• The hematocrit is usually 4045% of blood volume
– Most of the rest is plasma
• The buffy coat between the
two is all of the other cells of
the blood
– Platelets (hemostasis)
– White blood cells (immune
system)
• Will be covered in chapter 9
Platelets and Hemostasis
• Platelets, like RBCs, are
incomplete cells
– Lack any organelles except for
granules (vesicles) filled with
clotting agents
• Platelets assist with blood
clotting (hemostasis)
– Physically stick to the
damaged blood vessels
– Release chemicals that
stimulate coagulation
Coagulation
• As blood is exposed to
damaged blood vessels,
an enzyme called
thrombin is formed from
factors in the blood and
in platelets
• Thrombin catalyzes other
proteins in the blood to
form a fiber called fibrin
– Fibrin is sticky and makes
the blood viscous
Hemophilia
• The blood proteins for
coagulation are produced by the
liver
• A problem with the gene for
these proteins can cause a
condition called hemophilia,
where the blood cannot clot
when injured
– Absence of platelets can also
cause bleeding disorders but is
much rarer
– Now treatable with injections of
the missing proteins
Blood Loss
• When a person has lost a lot
of blood, the remaining RBCs
have difficulty delivering
oxygen
• One treatment is to inject
blood from a donor into the
patient
• A serious problem with this
approach is that the body has
an immune system (the white
blood cells) that may attack
foreign markers
ABO Blood Type
• The most common and well-known difficulty
with blood transfusion is the gene for a
particular marker on red blood cells
• This gene has three major versions: A, B and O
– Since everyone has two of each chromosome (one
from each parent) everyone has two of these
genes
• The O marker is small and the immune system
will not recognize it as an antigen (trigger)
Blood Antigens
• A and B are antigens only if the body
does not already have these markers
– The immune system is trained when the
person is a fetus, so blood injections
into a fetus will train its immune system
not to attack those markers
• A blood type A person will accept type
A blood but reject type B and type AB
blood
• A type AB person will accept all four
blood types
• A type O person will reject all other
blood types
ABO Blood Types
Blood Rejection
• Antibodies produced by the
immune system cause antigens
to stick together
• In the case of transfused blood,
this means blood will
agglutinate (clot) inside blood
vessels
– This can potentially be very
harmful to any organs they get
stuck in
What About the + or -?
• A+ and A- are the same ABO blood type
– The second symbol refers to another blood type
antigen, the Rh factor
• The immune system, for reasons unknown, is
already sensitized to ABO antigens in most
adults, but rarely to the Rh marker
• Sensitization can occur from a blood
transfusion (A+ into A- person) or by giving
birth to a baby with Rh+ blood
Rh Factor Sensitization
See you Thursday!
• Prepare to learn the secrets of your heart!