Human Blood Anatomy and Functions Quiz

Cardiovascular System

• Consists of a pump (the heart), a series of conducting hoses (blood vessels), and fluid connective tissue (blood).

Blood

• Specialized connective tissue, with cells suspended in a fluid matrix.

Functions of Blood

• Transports dissolved gases, nutrients, hormones, and metabolic wastes.
• Regulates pH, ion composition of interstitial fluids.
• Restricts fluid losses at injury sites.
• Defends against toxins and pathogens.
• Stabilizes body temperature.

Characteristics of Blood

• 38°C (100.4°F).
• High viscosity.
• Slightly alkaline (pH of 7.35-7.45).
• Blood volume is 7 percent of body weight (in liters).

Blood Fractionation

• Process of separating whole blood into plasma and formed elements.
• Whole blood: Plasma (55% total volume), Buffy coat (<1% total volume), Erythrocytes (45% total volume).

Plasma

• Makes up about 55 percent of blood volume.
• More than 90 percent of plasma is water.
• Dissolved plasma proteins and other solutes.
• Similar in composition to interstitial fluid.

Plasma Proteins

• Albumins (60 percent): Major contributors to plasma osmolarity, Transport fatty acids, thyroid hormones, some steroid hormones.
• Globulins (35 percent): Antibodies, Transport globulins (hormone-binding proteins, lipoproteins, and steroid-binding proteins)
• Fibrinogen (4 percent): Soluble protein that functions in clotting. Converted to insoluble fibrin.
• Other plasma proteins (1 percent): Varying concentrations of enzymes and hormones.

Plasma Proteins: Origins

• More than 90 percent made in the liver (including all albumins, fibrinogen, most globulins, and various proenzymes).
• Antibodies made by plasma cells.
• Peptide hormones made by endocrine organs.

Hemopoiesis

• Process of producing formed elements (red blood cells, white blood cells, cell fragments (platelets)).

Red Blood Cells (RBCs)

• Also called erythrocytes.

• Make up 99.9 percent of formed elements.

• Contains hemoglobin (red pigment that gives whole blood its color).

• Binds and transports oxygen and carbon dioxide.

• Normal red blood cell counts: Adult male (4.5-6.3 million per microliter), Adult female (4.2-5.5 million per microliter).

• Packed cell volume (PCV) (Hematocrit): Adult male (46), Adult female (42).

RBC Structure

• Small, highly specialized cells.
• Biconcave discs.
• Thin central region and thicker outer margin.

Important Effects of RBC Structure on Function

• Large surface area-to-volume ratio: Quickly absorb and release oxygen.
• Form stacks (rouleaux): Smooth blood flow through narrow blood vessels.
• Bend and flex easily: Pass through small capillaries (7.8-µm RBC can pass through a 4-µm capillary).

Mature RBCs

• Anucleate (Lack nuclei).
• Lack mitochondria and ribosomes.
• Unable to divide, synthesize proteins, or repair damage.
• Live about 120 days.

Hemoglobin

• Protein in RBCs that transports respiratory gases.
• Normal Hemoglobin: Adult male (14-18 g/dL), Adult female (12-16 g/dL).
• Hb molecules contain iron.
• Iron + oxygen= oxyhemoglobin
• Hb without oxygen = deoxyhemoglobin

Hemoglobin Function

• Each RBC contains approximately 280 million Hb molecules.
• In peripheral capillaries, where oxygen is low, hemoglobin releases oxygen.
• Binds CO2, forming carbaminohemoglobin.
• In the lungs, where oxygen is high, hemoglobin binds oxygen, and releases CO2.
• Fetal hemoglobin (form of hemoglobin in the embryo or fetus): Binds oxygen more readily than adult hemoglobin.

Anemia

• Results when hematocrit or Hb content of RBCs is reduced.
• Interferes with oxygen delivery to peripheral tissues.
• Approximately 1 percent of circulating RBCs are replaced per day (about 3 million enter the blood stream each second)

Erythropoiesis

• Red blood cell formation.
• In embryos, embryonic blood cells move from the bloodstream to the liver, spleen, thymus, and bone marrow.
• Differentiate into stem cells.
• In adults, occurs only in myeloid tissue (red bone marrow). Hemopoietics stem cells (HSCs) are also involved, giving rise to myeloid tissue producing progenitor cells that then give rise to RBCs.
• Specific stages are identified by hematologists: Myeolid stem cell, Proerythroblast, Erythroblast stages, Reticulocyte, and Mature RBC.
• Stimulated by erythropoietin (EPO), secreted by the kidneys and liver when oxygen in peripheral tissues is low (hypoxia).

Blood Doping

• Dangerous practice used by athletes.
• Re-infuse packed RBCs to elevate hematocrit.

Hemoglobin Recycling

• Macrophages of the spleen, liver, and red bone marrow engulf aged RBCs, remove Hb molecules from hemolyzed (ruptured) RBCs, and break Hb into components.
• Iron from the heme unit is recycled.
• Residual bilirubin bound to albumin is excreted in bile; metabolized by intestinal bacteria to stercobilin/urobilins and excreted in feces or urine.

WBCs

• Also called leukocytes.

• Have nuclei and other organelles.

• Lack hemoglobin.

• Defend the body against pathogens.

• Remove toxins and wastes, and attack abnormal or damaged cells.

• Some WBCs circulate in the blood.

• Most WBCs are in connective tissues proper and organs of the lymphatic system.

• WBC count: 5000-10,000 per microliter of blood.

WBC types

• Neutrophils: 50-70% (most abundant); defend body against pathogens, phagocytic, attack and digest bacteria, degranulation (release enzymes to destroy pathogens), live in blood stream for 10 hours, and contribute to pus.
• Eosinophils: 2-4% (engulf bacteria, protozoa, and cellular debris, attack parasites).
• Basophils: less than 1% (cross capillary endothelium, concentrate in damaged tissues- histamine and heparin (blood clotting).
• Monocytes: 2-8%; Aggressive phagocytes that engulf large pathogens, release chemicals to attract other phagocytic cells to injured areas.
• Lymphocytes: 20-40% (Continuously migrate in and out of bloodstream, reside in lymphatic system). (T cells, B cells, and Natural killer cells (NK cells))

WBC disorders

• Leukopenia: low WBC count.
• Leukocytosis: high WBC count.
• Leukemia: cancer of WBCs, indicated by extreme leukocytosis.

Platelets

• Cell fragments involved in the clotting system.

• Circulate for 9-12 days; removed by phagocytes mainly in the spleen

• 150,000-500,000 per microliter.

• One-third of platelets are stored in vascular organs like the spleen.

• Mobilized during a circulatory crisis.

Platelet functions

• Release important clotting chemicals and temporarily patch damaged vessel walls, reducing the size of breaks.
• Thrombocytopoiesis: platelet production occurs in the red bone marrow via megakaryocytes.

Hemostasis

• The cessation of bleeding (has 3 phases)
• Vascular phase, platelet phase and coagulation phase, and clot retraction.
• 1. Vascular phase (about 30 minutes): A cut triggers vascular spasm (contraction of smooth muscle fibers of vessel wall- lasts about 30-minutes). Endothelial cells contract and expose basement membrane to bloodstream.
• 2. Platelet phase (within 15 seconds of injury): Platelet adhesion (platelets attach to exposed surfaces) and platelets aggregation (platelets stick to each other) forming a platelet plug. Chemicals released that promote aggregation, vascular spasm, clotting, and vessel repair (ADP, PDGF, Ca2+, and clotting factors).
• 3. Coagulation phase (blood clotting): Begins 30 seconds or more after injury; highly regulated. Dependent on clotting factors (Ca2+ and 11 proteins) and highly regulated mechanisms (proenzymes, which converts to active enzymes that direct reactions in the clotting response). The extrinsic and intrinsic pathways, leading to the common pathway, all converging to produce a stable fibrin clot.
• 4. Clot retraction: Pulling torn edges of vessel closer together, reducing residual bleeding, stabilizing the injury site, making it easier for fibroblasts, smooth muscle cells, and endothelial cells to complete repairs. (Fibrin meshwork forms, platelets and red blood cells stick to the fibrin strands and contract).
• Fibrinolysis: Gradual process of dissolving clot. Plasmin digests fibrin strands; thrombin and tissue plasminogen activator activate plasminogen, producing plasmin.

Compatibility testing

• Performed in advance to avoid transfusion reactions when donor's RBCs and recipient's plasma are not compatible
• Type O- is the universal donor.
• AB+ is the universal recipient

Rh factors

• Surface antigen on RBCs, used to determine blood types and compatibility. Involved in Hemolytic disease of the newborn.

Hemolytic Disease of the Newborn

• Problems seldom develop during a first pregnancy with an Rh+ fetus.
• Exposure to fetal red blood cell antigens during delivery causes the mother's immune system to develop anti-Rh antibodies leading sensitization.
• Subsequent pregnancies with an Rh+ fetus can result in destruction/lysis of fetal RBCs as the maternal anti-Rh antibodies enter the fetal bloodstream.
• Prevents maternal sensitization to Rh factor: Administering RhoGAM to Rh- mothers during and after pregnancy (crucial for avoiding hemolytic disease).