Human Biology: Blood and Extracellular Fluids

Extracellular Fluids

• Blood, interstitial fluid, and lymph are the three extracellular fluids of the body.
• Nutrients move from blood to interstitial fluid to cells of tissues.

Blood Function

• Blood is composed of formed elements and a liquid ECM called blood plasma.
• Responsible for transportation, regulation, and protection.
• Makes up 8% of total body mass.

Blood Composition

• Blood plasma: contains dissolved substances, mostly proteins.
  • Albumin: maintains osmotic pressure.
  • Globulins: includes antibodies and transport proteins.
  • Fibrinogen: functions in blood clotting.
• Formed elements: erythrocytes, leukocytes, and platelets.

Formed Elements

• Erythrocytes (RBCs): transport oxygen and carbon dioxide.
• Leukocytes (WBCs): fight infection and invasion.
• Platelets: anucleate cell fragments, responsible for blood clotting.

Hematocrit

• Percentage of blood volume occupied by erythrocytes.
• Normal range: 40-65%
• Low hematocrit (anemia) indicates a low count of red blood cells, leading to reduced oxygen carrying capacity.
• High hematocrit (polycythemia) can lead to thickened blood, increasing risk of blood clots.

Blood Cell Formation

• Hemopoiesis: process of blood cell formation, occurs in red bone marrow.
• Begins with pluripotent stem cells, which differentiate into myeloid or lymphoid stem cells.
• Myeloid stem cells produce erythrocytes, platelets, and some types of leukocytes.
• Lymphoid stem cells produce lymphocytes.

Erythropoiesis

• Erythropoiesis is the production of red blood cells.
• Regulated by a negative feedback loop involving erythropoietin (EPO) hormone.
• EPO is secreted by the kidneys in response to low oxygen levels in the blood.
• EPO stimulates the production of erythrocyte precursors in the red bone marrow.

Leukocyte Function

• WBCs defend the body from infection and invasion.
• Major histocompatibility complex (MHC) proteins present in all leukocytes.
• Mucous membranes trap invaders and cilia sweep them away from tissues.

Granular Leukocytes

• Neutrophils: phagocytic cells, defend against bacterial infections.
• Eosinophils: defend against parasites.
• Basophils: release histamine, involved in inflammatory responses.

Agranular Leukocytes

• Lymphocytes: B lymphocytes differentiate into plasma cells and secrete antibodies.
• T lymphocytes and natural killer cells fight viral-infected and cancerous cells.
• Monocytes: differentiate into macrophages or fuse to form osteoclasts, responsible for engulfing debris and pathogens.

Platelet Formation

• Myeloid stem cells exposed to thrombopoietin (TPO) develop into megakaryoblasts.
• Megakaryoblasts mature into megakaryocytes, which splinter into platelet fragments.

Hemostasis

• Prevents hemorrhage.
• Consists of three steps: Vascular spasm, platelet plug formation, and blood clotting (coagulation).

Vascular Spasm

• Contraction of smooth muscle in blood vessels, reducing blood flow.
• Triggered by damaged smooth muscle or activated platelets.

Platelet Plug Formation

• Platelets adhere to the damaged vessel wall.
• Activated platelets release chemicals, causing vasoconstriction and platelet aggregation.

Blood Clot Formation

• Platelet plug reinforces by fibrin protein fibers.
• Requires clotting factors, including calcium ions.
• Intrinsic pathway: activated by contact with collagen.
• Extrinsic pathway: initiated by tissue factor release from damaged blood vessel cells.

Blood Clotting Regulation

• Tightly controlled to prevent thrombosis (clots forming too easily) and hemorrhage (clots not forming properly).
• Thrombosis can lead to embolism, potentially causing stroke or pulmonary embolism.

ABO Blood Groups

• Blood typing based on glycolipid antigens in erythrocyte plasma membranes.
• Agglutinins: antibodies that bind to A and B antigens.
• Individuals make antibodies against foreign antigens.
• Blood transfusion compatibility depends on the presence or absence of these antigens and antibodies.

Hemolytic Disease of the Newborn (HDN)

• Rhesus (Rh) factor: protein antigen expressed by some erythrocytes.
• Rh- individuals do not express the antigen, but can develop anti-Rh antibodies after exposure.
• If an Rh- mother has an Rh+ fetus, Rh+ antigens can trigger the production of anti-Rh antibodies in the mother.
• These antibodies can cross the placenta and agglutinate fetal erythrocytes, causing HDN.

Other Blood Disorders

• Anemia: insufficient red blood cells or inadequate hemoglobin, reducing oxygen carrying capacity.
• Sickle Cell Disease: genetic disorder causing abnormal hemoglobin, leading to misshapen red blood cells.
• Hemophilia: inherited disorder causing a deficiency in clotting factors, leading to excessive bleeding.
• Polycythemia: excessive red blood cells, leading to thickened blood and increased risk of blood clots.

This quiz covers the components and functions of blood, including its role in transportation, regulation, and protection. It also explores extracellular fluids such as interstitial fluid and lymph, along with the composition and types of formed elements in blood. Test your knowledge on these essential aspects of human physiology.