Blood

Overview of blood tissue

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 pp

Primary functions

Transportation of molecules within the internal fluid environment

Exchange between tissues and between internal/external environment

Secondary functions

Immunity = defense

Thermoregulation ("radiator fluid")

Fluid volume homeostasis

pH homeostasis

Blood and cardiovascular problems are a major health concern pp

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Formed elements - overview

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

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.

Red blood cells (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)

Shape GA

Biconcave disk (7 micron diameter) FIG

Deformable

PGE increases deformability

PGE₂ decreases deformability

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

Schizocyte = broken cell (schizo = "split")

Few organelles (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 FIG ANIM ANIM

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 (EP), 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 (B₉), iron (Fe)

Blood doping

Add blood to increase hematocrit, and thus O₂ capacity

Add EP 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)

Blood types (the earliest form of "tissue typing")

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 text material on practical applications of this theory

White blood cells (WBCs or leukocytes [lit. "white cells"])

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)

Leukopoiesis

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

Not confined to blood stream

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

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

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 of WBCs GA

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; develop in lymphoid tissue)

Monocytes (large--15-20 microns; develop into macrophages)

Platelets (thrombocytes) GA

Thrombopoiesis

Fragments of larger ancestor cells (megakaryoblasts, which each release 2-3 thousand tiny platelets)

Life span: about a week

Regulated by hormone thrombopoietin

Play important role in stopping leaks in vessels

More on this role follows

Stopping leaks (hemostasis)

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) ANIM

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

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 respiration

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