Thrombocytes (Platelets) & Plasma

Structure 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.

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

Platelet Plug Formation 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

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

Hemostasis 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.

Animation hemostasis animation

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

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

Contents of Plasma 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

Plasma Proteins 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

Other Substances 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

Blood Types 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

Human Blood Types

Intrinsic Clotting (Agglutination) 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

Rh Blood Group 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

Erythroblastosis Fetalis