Blood
• The only fluid tissue in the human body
• Classified as a connective tissue
– Living cells = formed elements
– Non-living matrix = plasma
Physical Characteristics of
Blood
• Color range
– Oxygen-rich blood is scarlet red
– Oxygen-poor blood is dull red
• pH must remain between 7.35–7.45
• Blood temperature is slightly higher than
body temperature
Blood Plasma
• Composed of approximately 90% water
• Includes many dissolved substances (the other 10%)
– Nutrients (amino acids, glucose, fatty acids)
– Electrolytes (K+, Na+, Ca++, Cl-)
– Respiratory gases (CO2, O2, N2)
– Hormones
– Waste products( urea, lactic acid)
– Proteins*
Plasma Proteins
• Albumin – 60% - regulates osmotic
pressure
• Fibrinogen – 4% - help to stem blood
loss when a blood vessel is injured
• Gamma Globulins (antibodies) - help
protect the body from antigens
Formed Elements
• Erythrocytes = red blood cells
• Leukocytes = white blood cells
• Platelets = cell fragments
They are shaped
like biconcave
discs about 7.5µm
in diameter and
2.0µm thick at the
edges. The shape
increases surface
area making gas
diffusion in and out
more efficient.
Erythrocytes (Red Blood Cells)
• The main function is to carry oxygen
• Anatomy of circulating erythrocytes
– Biconcave disks about 7.5µm in diameter and
2.0µm thick at the edges.
– Essentially bags of hemoglobin
– Anucleate (no nucleus) – can’t reproduce
– Contain very few organelles – no mitochondria.
Produce ATP by anaerobic means
• Outnumber white blood cells 1000:1
Fate of Erythrocytes
• Unable to divide, grow, or synthesize proteins
• RBC counts: Males – 6,000,000 per mm3
Females – 5,000,000 per mm3
• Average of 30 trillion RBCs in circulation at all
times
• Wear out in 100 to 120 days
• When worn out, are eliminated by phagocytes
in the spleen or liver. Iron is recycled
• Your body must make RBCs at the rate of 3
million per second to keep up.
Hemoglobin
• Iron-containing protein
• Binds strongly, but reversibly, to
oxygen
• Each hemoglobin molecule has four
oxygen binding sites
• Each erythrocyte has 250 million
hemoglobin molecules
Control of Erythrocyte Production
• Rate is controlled by a hormone
(erythropoietin)
• Kidneys produce most erythropoietin as a
response to reduced oxygen levels in the blood
• Homeostasis is maintained by negative
feedback from blood oxygen levels
Polycythemia – Too many Red Blood cells.
Caused by living in high altitudes or bone
marrow cancer. Increases blood viscosity
Anemia. Reduced oxygen carrying ability of blood.
Can be caused by too few RBCs or not
enough Hemoglobin.
1. Nutritional
A) Not enough iron in plasma headed for bone
marrow (16g/mL for men, 14 g/mL women)
B) Not enough folic acid and vitamin B12 –
necessary for DNA replication needed to make
any cells, and thus more Red Blood Cells cells
(RBCs).
2. Pernicious
Body can not absorb vitamin B12 necessary to make
new cells.
3. Aplastic
Bone marrow can not function properly
4. Renal
Kidneys can not make enough erythropoietin
Leukocytes (White Blood Cells)
• Crucial in the body’s defense against disease
• These are complete cells, with a nucleus (they
have DNA) and organelles
• Able to move into and out of blood vessels
(diapedesis)
• Can move by ameboid motion
• Can respond to chemicals released by damaged
tissues
Leukocyte Levels in the Blood
• Normal levels are between 4,000 and 11,000 cells
per cubic millimeter
• Abnormal leukocyte levels
– Leukocytosis
• Above 11,000 leukocytes/mm3
• Generally indicates an infection
– Leukopenia
• Abnormally low leukocyte level
• Commonly caused by certain drugs
5 types of WBCs subdivided into 2
groups
• 3 types are called Granulocytes – Have
cytoplasmic granules. All have short life
spans averaging 12 hours.
1. Neutrophil – Most abundant WBC.
– 54%-62% of WBCs.
– Mobile phagocytic cell that engulfs bacteria.
2. Eosinophil
• 1% - 3% of WBCs. Bilobed nucleus.
Cytoplasmic granules stain red.
• Weakly phagocytic.
• Engulfs parasitic worms. (tapeworms,
flatworms)
3. Basophils
• <1% of WBCs. Stains dark blue.
• Release Histamine, a vasodilator.
Agranulocytes
Lack cytoplasmic granules
• 4. Monocytes
• Largest WBC. Have much longer life
spans. (weeks not hours)
• 3% to 9% of the WBCs.
• Phagocytic – engulf large invaders.
Monocyte engulphing a cell
5. Lymphocytes
• 25% to 33% of the WBCs
• Produce antibodies that act against
specific foreign substances.
• Very long life spans.
Platelets - Thrombocytes
Anucleate cell fragments.
Function to seal up small breaks in damaged blood
vessels and help initiate coagulation.
Normal count of 300,000 per mm3
Hemostasis – stoppage of bleeding
• Platelet plug formation – Platelets stick
to connective tissue exposed when the
vessel is injured and to each other forming
a platelet plug.
• Blood vessel spasm – Platelets release
serotonin, causing smooth muscle in the
wall of the blood vessel to contract and
narrow.
activated
platelet –
shape
changed and
sticky
Non-activated
platelet
Coagulation – Blood clot formation
• 1. Damaged tissues release TF (tissue
factor) when in the presence of Ca++ and
PF3 (an enzyme found on platelets) form
Prothrombin Activator.
• 2. Prothrombin (present in the plasma) is
converted to Thrombin by Prothrombin
Activator and Ca++.
• 3. Thrombin acts as an enzyme and
converts molecules of fibrinogen into long
strands of Fibrin. Ca++ must be present.
• 4. Fibrin threads cling to the edge of the
damaged tissue forming a mesh that
catches blood cells and platelets forming a
clot.
• Normally blood clots in 3 – 6 minutes.
• A blood clot in a vessel is a Thrombus. If
it breaks loose and is carried away by
blood flow it is an Embolus.
RBC caught
in a
meshwork
of fibrin
Blood Types
• Blood types are determined by the
presence of certain proteins
(agglutinogens) found on the cell
membrane of RBCs and proteins
(agglutinins) dissolved in the plasma
• ABO blood group – based on the presence
or absence of 2 major agglutinogens on
the RBC membrane.
• Agglutinogen A & Agglutinogen B
4 Possible combinations
•
•
•
•
Agglutinogen A only – Type A blood
Agglutinogen B only – Type B blood
Agglutinogen A & B – Type AB blood
Neither – Type O blood
• A person with type A blood has anti-B
agglutinin in the plasma.
• Type A blood has Anti-B agglutinin in the
plasma
• Type B blood has Anti-A agglutinin in the
plasma
• Type AB blood has neither
• Type O blood has both
• The agglutinogen of one type will react
with the agglutinin of the same type.
• Example – Agglutinogen A and Agglutinin
Anti-A cause Red Blood Cell clumping
(Agglutination)
Transfusions
• Cells in the transfused blood must not be
agglutinated by the agglutinins in the
recipients plasma.
• Type O – Universal Donor
• Type AB – Universal Recipient
Rh Factor
• Rh+ blood has Agglutinogen D on the cell
membranes. Rh- blood lacks the protein.
• Rh+ blood lacks anti-Rh agglutinins. Rhblood forms anti-Rh agglutinins only in
response to the presence of Rh+ blood.
Erythroblastosis Fetalis
• Occurs when an Rh- mother gives birth to
a second Rh+ baby.
• When an Rh- mother gives birth to the first
Rh+ baby some blood mixing can occur
causing the mother to produce anti-Rh
agglutinin. This agglutinin will cross the
placenta of the 2nd Rh+ fetus causing the
fetal blood to agglutinate.