Blood Composition and Function

Blood Composition and Function

• Blood is a liquid connective tissue
• Plasma is the non-living matrix of blood
• Formed elements are the living cells suspended in the plasma
• Plasma is about 55% of whole blood
• Water makes up about 91% of plasma.
• Plasma proteins are the most abundant solutes in plasma, with albumin contributing about 60% of the plasma proteins.
• Plasma has over 100 dissolved solutes, including nutrients, gases, hormones, waste products, proteins (like fibrinogen), and inorganic ions (like Na+, K+, and Cl-).
• Plasma functions as a transport medium for other molecules, a blood buffer, contributing to osmotic pressure.

Erythrocytes (Red Blood Cells)

• Erythrocytes (RBCs) are dedicated to respiratory gas transport (CO2 and O2).
• Hemoglobin (Hb) reversibly binds to oxygen, and each Hb molecule carries four oxygen molecules.
• Each RBC contains approximately 250 million Hb molecules.
• Normal RBC count is approximately 5 million/ml.
• Hemoglobin is composed of heme pigment bound to the protein globin.
• RBCs lack a nucleus and other organelles, which allows space for hemoglobin, and they have concave shape to allow better oxygen uptake and transport.

Blood Cell Formation (Erythropoiesis)

• Hematopoietic stem cell is the precursor cell for all blood cells.
• Myeloid stem cells give rise to RBCs, WBC, and platelets.
• Proerythroblast is an early stage in RBC development. 
• Basophilic erythroblasts are immature RBCs.
• Polychromatic erythroblasts have both pink and blue-colored areas due to hemoglobin synthesis.
• Orthochromatic erythroblasts are mature RBCs.
• Reticulocytes are immature RBCs still containing some ribosomes.
• Mature erythrocytes (RBCs) are the final stage of RBC development.
• Reticulocyte count indicates the rate of RBC formation.

Blood Plasma Composition

• Plasma consists of water, proteins, and other substances.
• Water accounts for the largest part of plasma (about 91%).
• Plasma proteins are the most abundant solutes (approximately 8%).
• Albumin makes up about 60% of plasma proteins, and plays crucial roles in transporting molecules, acting as a blood buffer, and contributing to the osmotic pressure of plasma.

Blood pH

• Blood pH is maintained between 7.35 and 7.45
• Buffers help in maintaining this pH range.

Blood Protection (Immune System)

• Blood carries cells and antibodies for the immune system.
• Blood plays a role in protecting the body from blood loss via coagulation mechanisms.
• Blood carries clotting and immune factors.

Red Blood Cell Lifespan and Destruction

• RBCs have a lifespan of 100-120 days.
• Old RBCs become fragile and Hb begins to break down.
• Macrophages in the spleen engulf and break down the old RBCs.
• Bile is produced as a result of components of hemoglobin being broken down.

Reproductive Endocrine Glands

• Estrogen, progesterone, and gonadotropins influence reproductive development and functions.
• The ovaries produce estrogen and progesterone.
• The placenta produces hormones like estrogen, progesterone, and gonadotropins.
• The testes produce testosterone.
• Spermatogonia are the precursor cells for sperm production.