Cardiovascular System: Blood Composition & Functions

• Chapter 19 is about blood

Cardiovascular System

• The cardiovascular system includes a pump: the heart
• It also has conducting hoses (blood vessels)
• It is made of fluid connective tissue (blood)

Blood Composition and Functions

• Blood is a specialized connective tissue containing cells suspended in a fluid matrix
• Blood transports dissolved gases, nutrients, hormones, and metabolic wastes
• Blood regulates the pH and ion composition of interstitial fluids
• It restricts fluid losses at injury sites
• Blood defends against toxins and pathogens
• Blood helps to stabilize the body temperature

Blood Characteristics and Volume

• Blood temperature is 38°C or 100.4°F
• Blood has high viscosity and is slightly alkaline with a pH of 7.35-7.45
• Blood volume is 7% of body weight in kilograms,
• A 75-kg (165 lb) person has approximately 5.25 liters (5.4 quarts) of circulating blood

Fractionation of blood

• Whole blood consists of plasma, fluid, formed elements, cells and cell fragments
• Fractionation is the process of separating whole blood into plasma and formed elements

Plasma Composition

• Plasma makes up 55% of blood volume
• Plasma is made up of >90% of water
• Plasma also contains dissolved plasma proteins and other solutes
• Plasma composition is simlar to interstitial fluid as water, ions and small solutes are exchanged across capillary walls

Plasma Proteins

• Albumins make up 60% and are major contributors to plasma osmolarity
• Albumins transport fatty acids, thyroid hormones, and some steroid hormones
• Globulins make up 35% and include antibodies (immunoglobulins)

Other Plasma Proteins and Origins

• Includes transport globulins, hormone-binding proteins, metalloproteins, apolipoproteins, and steroid-binding proteins
• Fibrinogen constitutes 4% and is a soluble protein that functions in clotting and is converted to insoluble fibrin, leaving serum
• Other plasma proteins make up 1% and include varying concentrations of enzymes and hormones
• Over 90% of plasma proteins are produced in the liver, including all albumins, fibrinogen, most globulins, and various proenzymes
• Antibodies are made by plasma cells
• Peptide hormones are made by endocrine organs

Formed Elements and Hemopoiesis

• Formed elements include red blood cells, white blood cells, and cell fragments (platelets)
• Hemopoiesis is the process of producing formed elements

Red Blood Cells

• Red blood cells, or erythrocytes, are the most abundant blood cells.
• RBCs make up 99.9 percent of formed elements and contain hemoglobin which gives whole blood its colour
• Hemoglobin is also the red pigment that binds and transports oxygen and carbon dioxide

Red Blood Cell Count and Hematocrit

• Red blood cell count is the number of RBCs per microliter of whole blood
• Adult male normal range: 4.5-6.3 million
• Adult female normal range: 4.2-5.5 million
• Hematocrit is the packed cell volume (PCV) or percentage of formed elements in blood
• Adult male normal range: 46
• Adult female normal range: 42

Structure of Red Blood Cells

• RBCs are small and highly specialized cells and are biconcave discs
• The biconcave discs have a thin central region and thicker outer margin
• The large surface-area-to-volume ratio allows RBCs to quickly absorb and release oxygen
• They form stacks called rouleaux to smooth blood flow through narrow blood vessels
• RBCs bend and flex when entering small capillaries and a 7.8 µm RBC can pass through a 4 µm capillary

Mature Red Blood Cells

• Mature red blood cells are anucleate: they lack nuclei
• RBCs lack mitochondria and ribosomes; they are unable to divide, synthesize proteins, or repair damage
• RBCs live for about 120 days

Hemoglobin

• Hemoglobin (Hb or Hgb) are proteins in RBCs that transport respiratory gases
• Normal Hemoglobin for adult males: 14–18 g/dL whole blood
• Normal Hemoglobin for adult females: 12–16 g/dL whole blood
• Hemoglobin has a complex quaternary structure with four globular protein subunits
• The four subunits are two alpha (α) chains and two beta (β) chains and each chain has one molecule of heme

Hemoglobin Interactions

• Each heme unit contains one iron ion
• Iron interacts with oxygen to form oxyhemoglobin, HbO2 ; this dissociates easily to form deoxyhemoglobin
• Fetal hemoglobin is a form of Hb in an embryo or fetus that binds oxygen more readily than does adult hemoglobin and takes up oxygen from maternal blood at placenta

Hemoglobin Processes

• Each RBC contains about 280 million Hb molecules allowing red blood cells to carry over a billion molecules of O2
• In peripheral capillaries where O2 is low, hemoglobin releases O2 and binds CO2, forming carbaminohemoglobin
• Where O2 is high in the lungs, hemloglobin binds O2 and releases CO2
• Anemia relates to a low level of red blood cells where the hematocrit or Hb content of RBCs is reduced, interfering with oxygen delivery to peripheral tissus

Red Blood Cell Turnover

• About 1 percent of circulating RBCs are replaced per day,
• That means approximately 3 million new RBCs enter bloodstream each second
• Erythropoiesis refers to red blood cell formation
• In embryos, embryonic blood cells move from bloodstream to liver, spleen, thymus, bone marrow then they differentiate into stem cells that divide to produce blood cells
• In adults, this occurs only in myeloid tissue: red bone marrow

Hemocytoblasts and Maturation

• Hemocytoblasts, also called hematopoietic stem cells (HSCs), are stem cells in myeloid tissue that can divide
• Myeloid stem cells can become RBCs and some WBCs
• Lymphoid stem cells become lymphocytes
• Hematologists distinguish between:
  • Myeloid stem cell
  • Proerythroblast
  • Erythroblast stages
  • Reticulocyte
  • Mature RBC

Erythropoietin

• Erythropoietin (EPO) is the hormone that stimulates erythropoiesis and is secreted by the kidneys and liver when oxygen in peripheral tissues is low, known as hypoxia
• Blood doping is a dangerous practice used by some athletes that re-infuses packed RBCs to elevate hematocrit
• Erythropoiesis requires amino acids, iron, folic acid, and vitamins B12 and B6
• A lack of vitamin B12 leads to pernicious anemia

Hemoglobin Recycling

• Hemoglobin recycling sees macrophages from the spleen, liver, and red bone marrow engulfing aged RBCs
• The Hb is removed from hemolyzed (ruptured) RBCs and broken down into heme components
• Only the iron of each heme unit is recycled

Hemoglobinuria and Hematuria

• Hemoglobinuria is red or brown urine due to abnormally high hemolysis in the bloodstream
• Hematuria is whole RBCs in urine and is usually due to kidney or blood vessel damage
• Iron is removed from each heme unit, forming green biliverdin that is converted to orange-yellow bilirubin
• Bilirubin is either excreted by liver in bile or jaundice is caused by buildup of bilirubin and it gets converted by intestinal bacteria and oxygen to urobilins and stercobilins

Iron Processing

• Iron that is removed from heme is stored in phagocytic cells or released into the bloodstream
• In the bloodstream, iron is bound to transferrin
• Developing RBCs in red bone marrow absorb transferrins and use them to synthesize Hb
• Excess transferrins are removed in liver and spleen, storing iron in ferritin and hemosiderin

Blood Types, Surface Antigens and Blood Groups

• Surface antigens are substances on plasma membranes that identify cells to the immune system
• Normal cells displaying surface antigens are ignored and foreign cells are attacked
• Blood type is determined by presence or absence of surface antigens on RBCs with types A, B, and Rh (or D)
• Four blood are based on surface antigens:
  • Type A (surface antigen A)
  • Type B (surface antigen B)
  • Type AB (antigens A and B)
  • Type O (neither A nor B)
• Rh positive blood contains the Rh surface, eg Type O+
• Rh negative blood lacks Rh surface, eg Type O-

Agglutinogens and Agglutinins

• Agglutinogens are surface antigens on RBCs that are screened by immune system
• Agglutinins are antibodies in plasma that attack antigens on foreign RBCs and cause agglutination (clumping) of foreign cells
• Type A blood has anti-B antibodies
• Type B blood has anti-A antibodies
• Type O blood has both anti-A and anti-B antibodies
• Only sensitized Rh- blood has anti-Rh antibodies

Testing For Blood Compatibility

• A cross-reaction, or transfusion reaction can occur if incompatible blood is transfused between two people
• This occurs when the plasma antibody meets its speific antigen
• As a result, RBCs agglutinate and may hemolyze
• Cross-match testing helps to prevents this and reveals cross reactions during transfusions
• Type O-blood is the universal donor, but cross-reactions can still occur
• At least 48 surface antigens can exist besides A and B

Hemolytic Disease of the Newborn

• This disease can develop when a Rh- woman carries and Rh+ fetus
• First pregnancies are typically unaffected because the mother's immune system is not yet stimulated
• However, hemorrhaging during delivery, can expose the mother's blood to fetal red blood cell antigens and produce anti-Rh antibodies

White Blood Cells, Characteristics and Function

• White blood cells (WBCs), also called leukocytes, have nuclei and other organelles
• They lack hemoglobin and circulate in the bloodstream 5000 to 10,000 per microliter
• Most WBCs exist in the connective tissue proper in the organs of the lymphatic system
• WBCs functions are:
  • defending body against pathogens
  • removing toxins and wastes
  • attacking abnormal or damaged cells
• Circulation WBCs can migrate out of bloodstream
• WBCs can move with amoeboid movement
• WBCs go to chemical stimuli: positive chemotaxis
• Some WBCs are phagocytic

Types of White Blood Cells

• Neutrophils
• Eosinophils
• Basophils
• Monocytes
• Lymphocytes

Neutrophils and Eosinophils

• Neutrophils, also called polymorphonuclear leukocytes, make up 50-70 percent of circulating WBCs
• Neutrophils contain pale cytoplasmic granules, are very active phagocytic cells and attack and digest bacteria
• Degranulation is a reduction in number of its cytoplasmic granules and occurs when vesicle containing pathogen fuses with lysosomes containing enzymes and defensins
• Neutrophils release prostaglandins and leukotrienes, live in bloodstream for 10 hours or less and contribute to pus
• Eosinophils make up 2-4 percent of circulating WBCS and engulf bacteria, protozoa, and cellular debris
• They attack large parasites by releasing nitric oxide and cytotoxic enzymes
• They are sensitive to allergens and release enzymes that reduce inflammation caused by mast cells and neutrophils

Basophils, Monocytes, and Lymphocytes

• Basophils make up less than 1 percent of circulating WBCs and cross capillary endothelium and accumulate in damaged tissues
• They release histamine to dilate blood vessels and Heparin that prevents blood clotting
• Monocytes are large, spherical cells that constitute 2-8 percent of circulating WBCS
• After 24 hours in bloodstream they enter peripheral tissues to become macrophages that engulf pathogens and release chemicals to attract phagocytic cells
• There are three classes of lymphocytes
  • T cells - cell mediated immunity
  • B cells - humoral immunity
  • Natural killer cells: detect and destroy abnormal cells

WBC Differential Count and Disorders

• Differential count is the population of WBC that can detect infection, inflammation, and allergic reactions
  • Leukopenia: Low WBC count
  • Leukocytosis: High WBC count
  • Leukemia: Cancer of WBCs indicated by extreme leukocytosis

Leukopoiesis and WBC Development

• Leukopoiesis is WBC production
• Hemocytoblasts produce myeloid stem cells and lymphoid stem cells
• The myeloid stem cells divide to produce progenitor cells while giving rise to all formed elements except lymphocytes
• Lymphocytes stem from lymphoid stem cells
• WBC development
• Some lymphoid stem cells that remain in red bone marrow will differentiate into B cells B or natural killer cells other migrate from red bone marrow to peripheral lymphatic tissues
• Thymus, spleen, produce lymphocytes and T cells are produced in thymus
• Colony-stimulating factors (CSFs) are hormones that regulate leukocyte populations

WBC Development Factors

• Multi-CSF: accelerates production of granulocytes, monocytes, platelets, and RBCs
• GM-CSF: stimulates granulocyte and monocyte production. G-CSF stimulates granulocyte production
• M-CSF: stimulates monocyte production

Platelets

• Platelets (thrombocytes) are cell fragments involved in clotting system and circulate for 9–12 days
• Thrombocytopoiesis is also known as platelet production
• Platelets production occurs in bone marrow
• Megakaryocytes function in the red bone marrow Giant cells in red bone marrow
• Some platelets store in body vascular organs like the spleen as an emergency supply, in which case the spleen may mobolize these during a bodily crisis
• 150,000 to 500,000 are removed by phagocytes and are present per blood
• Hormonal control of platelet production involves thrombopoietin (TPO), Interleukin-6 (IL-6) and Multi-CSF from the blood

Hemostasis

• Hemostasis relates to the cessation of bleeding and has three phases

1. Vascular phase
2. Platelet phase
3. Coagulation phase

Vascular Phase

• Vascular phase is triggered off with a cut leads in blood from vessels
• Contraction of smooth muscle fibers of vessel wall within 30 minutes
• Endothelial cells contract, thereby exposes basement membrane to blood thereby cause smooth muscle contraction and cell division
• These membranes become sticky and prevent blood flow from tears of such magnitude

The Platelet Phase

• Platelet adhesion occurs as platelets attach to exposed surfaces and stick to each other
• During platelet aggregation, the cells begins within 15 seconds after injury which platelet plugs may close small tears
• These aggregation factors include:
  • Adenosine diphosphate (ADP)
  • Thromboxane A₂ and serotonin
  • Clotting factors
    • Platelet-derived growth factor (PDGF) and calcium ions from the blood
• Growth of platelet is controlled by -Prostacyclin inhibiting platelet aggregation and from the blood

The Coagulation Phase

• Platelets form chains in react with multiple pathways
• Begis 30 seconds with clotting
• The multiple pathways include:
• extrinsic *intrinsic *common pathways of the blood
• A bleeding time of 30 mins

The Coagulation Pathways

• Extrinsic pathways in the form of damaged tissues result in III tissue formation for release
• Intrinsic involves platelets reacting to PF3 by enzymatic complex factor in response to such injury
• A common pathway is the activation of X factor prothrombin(proenzymes)that convert to to a thombin
• Thombin converts fibrogen to Fibren
• Thombing acts to form these chains in this process

Feedback Control, Vitamins, and Bleeding Issues

• Feedback is controlled with protien
• Calciums ions and vitmain K are needed to stimulate this reaction
• Vitmain K is also needed to synthesize a factor in that pathway of vitamin synthesis
• Bleeding in this situation can result from various conditions of hemaphilia
• Vitmain is essentail for this reaction
• All three phases can effect such effects
• A clot can be formed on such a wound

Blood clot retraction process

• pulls torn edges of vessel closer together and is reduced
• this in turn reduces residual bleeding and stabilizes injury site . This is a gradual process. The process will lead to thrombonin (tPA) Activates Plasnogin producting plasmin and plasmin digests fibirant
• The process requires activation of PLASMINOGEN, producing plasmin. -Plasmin digests fibrin strands

Understand blood's role in the cardiovascular system. Learn about its composition as a connective tissue with cells in a fluid matrix. Explore its functions in transporting gases, regulating pH, and defending against pathogens, plus key characteristics like temperature and volume.