Learning Outline

Blood

A&P 2

Overview of blood tissue

Introduction

Blood connects all the various tissues of the body

• Blood is part of every organ and every system
  
  
• Is a "connective" tissue in a functional sense
  
  
• Will relate directly to remaining topics of this course: cardiovascular, respiration, etc.

Structure

Connective tissue with liquid matrix (plasma)

Cells and cell fragments are also called formed elements

Flows within cardiovascular system (heart and blood vessels)

Blood volume

• 71 ml/kg (70 kg adult male would have about 5,000 ml total blood volume)
  
  
• About 55% is fluid and about 45% formed elements
  

Function

Primary functions

• Transportation of molecules within the internal fluid environment
  
  
• Exchange between tissues and between internal/external environment
  

Secondary functions

• Immunity — defense
  
  
• Thermoregulation — acts as "radiator fluid"
  
  
• Fluid volume homeostasis
  
  
• pH homeostasis
  

Blood and cardiovascular problems are a major health concern

FYI Interested in learning more? I recommend this book for further reading—Five Quarts: A Personal and Natural History of Blood

 

Formed elements - overview

Hematopoiesis

Hematopoiesis — formation of new blood cells

• All are descended from stem cells in red marrow (myeloid tissue)
  
  
• Divide into "lines" of daughter cells, each line producing different groups of blood cells (differentiation)
  

Main types

• Platelets — clotting cells
  
  
• Red blood cells — carry blood gases
  
  
• White blood cells — immune cells
  

FYI Cells of the blood is a visualization of each type of blood cell.

Blood cell types
Red cell (left), platelet (center), white cell (T lymphocyte; right). SEM

Red blood cells

Name

Also called RBCs or erythrocytes [lit. "red cells"]

Number

4-6 million per cubic mm of blood (RBC count)

45% of total blood volume (packed cell volume [PCV] or hematocrit)

Hematocrit (PCV "packed cell volume")

Shape

Biconcave disk

• 7 micron (µm) diameter
  

Deformable

• PGE increases deformability
  
  
• PGE₂ decreases deformability
  

Crenation — shrinkage from water loss (as in a hypertonic solution)

Schizocyte — broken cell (schizo = "split")

RBC inside blood capillary. The RBC must deform to flow through this tiny blood vessel.

Cytoplasm

Organelles few in number (no nucleus)

• Lost during development
  

Contain about 300 million molecules of hemoglobin (Hb)

• Quaternary protein made of four polypeptides, each with an iron (Fe) containing heme group in the center (of each folded polypeptide)
  
  
• Oxyhemoglobin (HbO₂) forms when O₂ combines with heme groups
  
  
• Carbaminohemoglobin (HbCO₂) forms when CO₂ combines with amino acids in polypeptide chains
  
  
• Anemia — less normal hemoglobin than usual (< 10g/100ml)
  
  
  • Normal male: 14-16 g/dl (g/dl = g/100ml)
    
    
  • Normal female: 12-14 g/dl
    
    
  • Examples
    
    
    • Sickle cell anemia
      
      
    • Pernicious anemia
      
      
    • Fe-deficiency anemia (target cells/codocytes)
      

Life cycle

RBC hematopoiesis

• Erythropoiesis
  
  
  • Stem cells (hemocytoblasts) in red bone marrow (myeloid tissue)
    
    
• Stimulated by hormone erythropoietin (EPO), which is formed in kidney in response to low O₂ delivery to tissue cells (tissue hypoxia)
  
  
• Example: hematocrit (RBC%) goes UP when you stay at higher elevations, where O₂ concentration in air is lower
  
  
• Requires: vitamin B₁₂ (and intrinsic factor), folic acid (folate or vitamin B₉), iron (Fe)
  
  
• Blood doping
  
  
  • Add blood to increase hematocrit, and thus O₂ capacity
    
    
  • Add EPO to increase RBC production, increasing O₂ capacity
    

RBC destruction

• Last about 4 months (can't repair themselves because they lack nuclei)
  
  
• Run through "obstacle courses" in spleen and liver and aged cells break apart
  
  
• Macrophages eat them
  
  
• Globin (polypeptide) part is reduced to amino acids and recycled
  
  
• Heme is stripped of its iron, which is recycled
  
  
  • Remain part of heme is converted to bilirubin (yellowish pigment that gives plasma its characteristic "straw" color)

Formation of blood cells
The RBCs in this diagram look strange. What is odd about them?

Blood types

Blood typing is the earliest form of "tissue typing"

• Karl Landsteiner discovered ABO system (1902), Rh system (1904) and later other blood types, for which he won a Nobel Prize
  

Based on glycoprotein markers (antigens) on surface of RBCs

ABO system looks for A or B markers (antigen)

• Type A — antigen A only
  
  
• Type B — antigen B only
  
  
• Type AB — both A and B antigens
  
  
• Type 0 — neither A nor B antigen present
  

Rh (D antigen) system (named for Rhesus monkeys)

• Rh positive — Rh (D) antigen present
  
  
• Rh negative — Rh antigen absent
  

Other systems of blood typing exist —looking for different antigens (markers)

Read over textbook material on practical applications of this theory

White blood cells

Name

White blood cells are also called WBCs or leukocytes [lit. "white cells"]

Number

Less than 1% of whole blood

• 5,000 - 10,000 per cubic mm of blood (WBC count)
  
  
• Leukopenia — abnormally low WBC count
  
  
• Leukocytosis — abnormally high WBC count
  
  
  • Often observed in leukemia (tumor of WBCs)
    

Life cycle

Leukopoiesis is development of new WBCs

• Produced in bone marrow, but some migrate to lymphoid tissue for most of development (lymphoid tissue is found in lymph nodes, thymus gland, spleen, liver, elsewhere)
  

Lifespan is uncertain, perhaps 3 days to a year, depending on type

Location

Not confined to blood stream

Chemotaxis — move toward chemical attractants (chemotactic factors)released at site of injury/infection

Diapedesis — move between, or even through, other cells to get to their target

Diapedesis of WBC across wall of blood vessel.

Functions

Immune functions of various sorts, for example

• Phagocytosis
  
  
• Release of cell toxins
  
  
• Release of immune function regulators
  
  
• More on immunity later (see Chapter 21)
  

Types

Types distinguished by how they stain with Wright's stain —a mix of different cell stains

Differential WBC count — distinguished how many of each type of WBC in sample

Granulocytes (look granular when stained)

• Basophils (stain with the basic stain in Wright's mixture)
  
  
• Eosinophils (stain with the acid stain called eosin)
  
  
• Neutrophils (stain with a neutral stain)
  

Agranulocytes (do not look granular when stained)

• Lymphocytes (small—8 microns (µm); develop in lymphoid tissue)
  
  
• Monocytes (large—15-20 microns (µm); develop into macrophages)

click image to enlarge

Platelets

Name

Also called thrombocytes

Structure

Tiny, irregular fragments

• 2-3 microns (µm)

Do not have nuclei

Life Cycle

Thrombopoiesis is development of new platelets

• Formed in red marrow
  
  
• Fragments of larger ancestor cells
  
  
  • Megakaryoblasts develop into megakaryocytes, which each release 2-3 thousand tiny platelets
    

Life span — about a week

Regulated by hormone thrombopoietin

Function

Play important role in stopping leaks in vessels

More on this role follows

Stopping leaks

Overview

Hemostasis — process of stopping leakage of blood

Coagulation — part of hemostasis, it involves a complex process that eventually forms a blood clot to stop leaking blood

• Also called the clotting mechanism
• Involves a cascade of processes in which one step triggers another, then another
  • Opportunities at various steps to enhance or inhibit process

Process

Injury to blood vessel occurs, exposing collagen fibers in wall of blood vessel

Platelet plug forms (short-term fix)

• Platelets have net positive charge on outside surface (recall membrane potentials)
  
  
• Collagen has slightly negative charge, so platelets are attracted to site of injury
  
  
• Platelets release thromboxane, making them sticky and also calling in more platelets (chemotaxis in action)
  

Blood clot (thrombus) forms (medium-term fix)

• Thromboplastin is released from platelets (intrinsic mechanism) and damaged tissue cells (extrinsic mechanism)
  
  
  • This is an example of redundancy . . . often seen in safety mechanisms
    
    
• Triggers conversion of prothrombin (plasma protein) into thrombin
  
  
• Thrombin converts fibrinogen (plasma protein) into fibrin
  
  
• Fibrin is stringy protein that traps cells and tightens to form a rather solid mass (clot)
  

Blood clot dissolves as new tissue replaces injured tissue (long-term fix)

• Dissolution of clot starts when clot is formed (pre-programmed dissolution)
  
  
  • Otherwise, thrombus may break off and float away (an embolus) and block blood flow in brain, heart, lungs —-killing you
    
    
• Plasmin is chemical largely responsible for dissolving fibrin
  

Clotting mechanism requires many different chemicals (clotting factors)

• Clotting factors are often identified by Roman numerals (Factor I, Factor II, etc.)
  
  
• If any one factor is missing (or abnormal), hemophilia (clotting disorder) is likely to result
  

Queen Victoria (1819-1901) of Great Britain had a defective gene for Clotting Factor VIII, which caused "royal hemophilia" in her son Leopold as well as many other of Victoria's numerous royal descendants. Many of Victoria's descendants married into other royal families, spreading the defective gene widely and greatly affecting world history. For example, Victoria's great-grandson Alexis was the heir to the Russian throne and circumstances surrounding his successful treatment for pain by the controversial monk Rasputin may have triggered the timing of the downfall of the Czarist regime in Russia and thus events subsequent to the Russian revolution. Today, people with abnormal Factor VIII can use powdered, freeze-dried CF VIII to help them cope with this disorder. Unfortunately, it was originally derived from human donor blood and risks blood-borne disease transmission including hepatitis and HIV. In fact, the HIV epidemic took a huge toll on hemophilia sufferers during the 1980s and 1990s. However, today synthetic (recombinant) sources of CF VIII and other therapies have made hemophilia treatments safer and more effective.

Plasma

Location

Extracellular liquid part of blood tissue

Composition

See diagram in text for specific proportions

Mostly water

Plasma protein

• Albumins "thicken" blood and because they are relatively impermeant, hold water in the blood by way of osmosis
  
  
• Globulins include immunoglobulins (Ig) —antibodies— for immunity
  
  
• Fibrinogen is a protein needed for blood clotting
  

Other solutes

• Ions such as Na⁺, Cl^-, K⁺, Ca⁺⁺, H⁺, HCO₃^-, and others
  
  
• Nutrients such as glucose, fatty acids, amino acids
  
  
• Waste products such as
  
  
  • Lactic acid from anaerobic processes
    
    
  • Urea from breakdown of amino acids used in cellular respiration
    
    
  • Yellowish pigments from breakdown of hemoglobin (from old red blood cells)
    
    
  • Gases such as CO₂ and O₂
    
    
• Regulatory substances such as hormones, prostaglandins, clotting factors
  

Blood serum (pl. sera) — plasma without the clotting factors