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 40-45% 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 Wednesday!

• Prepare to learn the secrets of your heart!