• Fragments of giant cells
(megakaryocytes) (each produces b/t 5-10,000 platelets)
• Pieces break off these cells in bone marrow
• Enter circulation – live for approx.
1 wk.; destroyed by spleen & liver
• Disk-shaped, w/o nucleus
• ½ the size of an RBC
• Release serotonin to contract blood vessel walls.

• Normal platelet count –
130,000-360,000/mm³
• Stem blood flow (hemostasis) 2 ways:
1. Form a platelet plug
2. Initiate the clotting process

1. B.V.damaged
2. Some blood escapes
3. Platelets adhere to each other & rough surfaces
4. When platelets come in contact w/collagen from connective tissue, they develop spiny projections; helps them adhere
5. Eventually platelet plug is formed & bleeding stops

• Cascade effect series of steps, each one activating the next step
• Extrinsic clotting – occurs when b.v.
are damaged; platelets
1 st release serotonin

• Blood coagulation uses biochemicals called clotting factors.
– Coagulants vs. anticoagulants
• During an injury coagulants prevail.
• Final portion of hemostasis is conversion of protein fibrinogen into insoluble protein threads called fibrin.
– Fibrin forms network of threads that attaches to exposed surfaces. Prevents blood loss.

• hemostasis animation

• Thrombus – blood clot that forms in a b.v. abnormally
• Embolus – blood clot or fragment of one that dislodges & travels to major organ

• Clear, straw-colored fluid; matrix of blood
• 92% water
• Functions:
1. transport
2. maintain fluid balance
3. maintain pH

• Contains 3 plasma proteins (all produced in the liver):
1.
Albumin – accounts for 60% of all plasma proteins maintains osmotic pressure (keeps concentration of
H
2
O & solutes in plasma stable
- example – a decrease in albumin causes cells to lose
H
2
O; it collects in interstitial spaces (b/t cells) & causes edema

2. Globulins – Accounts for 36% of all plasma proteins
- transports lipids & vitamins
3. Fibrinogen – Accounts for 4% of all plasma proteins
- responsible for blood clotting

Plasma also contains:
• nonprotein nitrogenous substances – amino acids, urea, uric acid
• electrolytes – release ions when dissolved in H
2
O; maintain osmotic pressure & pH; include Na, K, Cl, Ca Mg, bicarbonate,
PO
4
& SO
4 ions

• Antigen – protein on surface of RBC’s
• Determined by genes
• Determines blood type
• Possible antigens – A or
B
• Antibody – protein in plasma
• Possible antibodies – A or B

• Occurs when antigen comes in contact with foreign antibody
(example – b.t. A receiving a transfusion of b.t. B)
• Effects – RBC’s burst, hemoglobin released
• Symptoms – anxiety, difficulty breathing, chest pain, pain in neck & lumbar area

• 85% of humans have an additional protein on their RBCs; called the Rh factor
• Named after the species of monkey it was discovered in (Rhesus)
• Termed Rh+
• Remaining 15% of humans don’t have this protein
• Termed Rh-
• Rh- individuals cannot receive Rh+ blood