Blood — Core Principles

Core Principles

Blood is a vital fluid connective tissue, comprising about 7-8% of body weight. It consists of a liquid matrix, plasma (55%), and formed elements (45%). Plasma, mostly water, carries proteins (albumin, globulins, fibrinogen), nutrients, hormones, and waste.

Formed elements include Red Blood Cells (RBCs/erythrocytes) for oxygen transport via hemoglobin, White Blood Cells (WBCs/leukocytes) for immunity, and Platelets (thrombocytes) for blood clotting. RBCs are biconcave, anucleated, and live for ~120 days.

WBCs are diverse, categorized into granulocytes (neutrophils, eosinophils, basophils) and agranulocytes (lymphocytes, monocytes), each with specific defensive roles. Platelets are cell fragments crucial for hemostasis.

Blood groups (ABO, Rh) are determined by antigens on RBCs and are critical for safe transfusions. Blood coagulation is a complex cascade involving clotting factors, culminating in fibrin clot formation to prevent blood loss.

All blood cells originate from hematopoietic stem cells in bone marrow.

Important Differences

vs Lymph

Aspect	This Topic	Lymph
Composition	Contains plasma, RBCs, WBCs (all types), and platelets. Rich in proteins.	Contains plasma-like fluid, WBCs (mainly lymphocytes), no RBCs, and very few platelets. Lower protein content than blood plasma.
Color	Red, due to hemoglobin in RBCs.	Colorless or pale yellow.
Circulation	Circulates throughout the body in a closed circulatory system (blood vessels). Pumped by the heart.	Circulates in an open lymphatic system. Moves slowly due to muscle contractions and valves, not a central pump.
Functions	Transport of gases, nutrients, hormones, waste; regulation of temperature, pH; defense and clotting.	Immune surveillance (transporting lymphocytes), fat absorption from intestine, returning interstitial fluid to blood.
Clotting Ability	Clots readily due to high concentration of fibrinogen and platelets.	Clots slowly or not at all due to very low fibrinogen and platelet count.

Blood and lymph are both vital body fluids, but they differ significantly in composition, color, circulation, and primary functions. Blood, the 'river of life,' is a red, protein-rich fluid containing all formed elements, pumped by the heart in a closed system, primarily for transport and defense. Lymph, a colorless fluid, is essentially filtered blood plasma that has entered the lymphatic vessels. It lacks RBCs and most plasma proteins, circulates slowly in an open system, and is crucial for immune responses and returning interstitial fluid to the bloodstream. Understanding these distinctions is key for comprehending their respective roles in maintaining homeostasis.