White Blood Cells, Hemostasis, and Heart Sounds Explained
White Blood Cells (WBCs)
WBCs are an important part of the immune system, defending the body against infections and foreign invaders. They are classified based on function and production process in bone marrow.
Types of White Blood Cells
Granulocytes
Neutrophils
- Function: Primary defense against bacterial infections. Phagocytic cells ingest and destroy pathogens.
- Production: In bone marrow.
Eosinophils
- Function: Defend against parasitic infections and are involved in allergic reactions. Help modulate inflammatory responses.
- Production: In bone marrow.
Basophils
- Function: Release histamine and other chemicals during inflammatory and allergic responses. Play a role in immune response.
- Production: In bone marrow.
Agranulocytes
Lymphocytes
- T cells: Cell-mediated immunity, killing infected cells or helping other immune cells.
- B cells: Produce antibodies for humoral immunity, recognize specific antigens.
- Natural Killer cells: Target and kill virus-infected cells and tumor cells.
- Production: Formed in bone marrow, but T cells mature in the thymus while B cells mature in bone marrow.
Monocytes
- Function: Become macrophages or dendritic cells in tissues and are involved in phagocytosis, antigen presentation, and immune activation.
- Production: In bone marrow.
Importance of WBCs
WBCs play an important role in the immune response, ranging from direct pathogen elimination (neutrophils, macrophages) to the regulation and coordination of immune responses (T and B cells). Their ability to recognize, attack, and remember specific pathogens helps in adaptive immunity, ensuring protection against reinfections.
Hemostasis
Hemostasis prevents and stops bleeding/hemorrhage. It occurs in three stages:
Stages of Hemostasis
Vasoconstriction
Blood vessels constrict at the injury site to reduce blood flow and minimize blood loss.
Platelet Plug Formation
Platelets are activated on exposure to collagen in the damaged blood vessel. They adhere to the site, become sticky, and release chemicals that attract more platelets, forming a temporary “plug.”
Coagulation (Clotting)
A series of enzymatic reactions that lead to the conversion of fibrinogen into fibrin, which forms a stable clot over the platelet plug. The clotting cascade involves clotting factors (proteins), each activated in sequence:
Intrinsic Pathway
Involves Factor XII, XI, IX, and VIII, leading to activation of Factor X.
Extrinsic Pathway
Involves Factor VII, activated by tissue factor, activates Factor X.
Common Pathway
Factor X activates thrombin (Factor II), which converts fibrinogen into fibrin.
Role of Clotting Factors
Clotting factors are proteins, mostly synthesized by the liver, that play critical roles in the coagulation cascade. Without these factors, blood wouldn’t clot properly, leading to excessive bleeding or clotting disorders. Each factor must be activated in a specific sequence for proper hemostasis.
Heart Sounds
The heart produces characteristic sounds during the cardiac cycle, which can be heard through auscultation. These sounds are described as “lub-dub.”
Heart Sounds Explained
First Heart Sound (S1 Lub)
- Cause: Closure of AV valves (mitral and tricuspid) at the start of ventricular systole.
- Best Heard: At the apex of the heart (around the 5th intercostal space, midclavicular line).
Second Heart Sound (S2 Dub)
- Cause: Closure of semilunar valves (aortic and pulmonary) at the end of ventricular systole and the beginning of diastole.
- Best Heard: At the base of the heart (2nd intercostal space, right and left of the sternum).
Additional Heart Sounds
S3
Heard early in diastole due to rapid ventricular filling. Often associated with heart failure.
S4
Heard late in diastole due to atrial contraction; seen in hypertensive heart disease or left ventricular hypertrophy.