Ch18

Functions of blood

Transport, regulate, protect

Formed elements

RBCs, WBCs, platelets

Hematocrit

Percent of RBCs in blood; reflects oxygen-carrying capacity.

RBC structure

Biconcave, no nucleus, hemoglobin-filled cells for gas transport

Hemoglobin structure

4 globins + 4 hemes + iron center

Erythropoiesis stimulus

Low oxygen triggers kidney release of EPO.↑ RBC production.

WBC types

Neutrophils, lymphocytes, monocytes, eosinophils, basophils

Hemostasis steps

Vascular spasm → platelet plug → coagulation

Hemostasis: 3 steps stop bleeding

1. Vascular spasm – vessel constricts

2. Platelet plug – platelets stick to collagen

3. Coagulation – fibrin forms the clot

Universal donor

O negative

Universal recipient

AB positive

Erythrocytes (RBCs)

Biconcave, no nucleus, filled with hemoglobin

– Main function: carry oxygen and CO₂

– Live ~120 days

Erythropoiesis

Production of RBCs in red bone marrow

– Stimulated by EPO from kidneys when blood oxygen is low

– Requires iron, B12, folate

Platelets

– Cell fragments (from megakaryocytes) that stick together to form the early plug.

Clotting factors:

– Proteins (mostly from liver) that create the fibrin mesh.

– Vitamin K needed for many factors.

Fibrinolysis

Breakdown of the clot after healing

– Uses plasmin to dissolve fibrin

Thrombus

– A stationary blood clot in a vessel

– Can block blood flow

– Example: coronary thrombosis → heart attack

Embolus

– A moving clot that travels through bloodstream

– Dangerous because it can lodge in lungs or brain

– Example: pulmonary embolism (PE)

Rh− can donate to

Rh+ or Rh−