18.4: Leukocytes Form and Function

Leukocytes / White Blood Cells WBC

• least abundant of the formed elements

• usually 5,000 - 10,000 WBC/uL

• Cannot live without

• Protection

• Can be recognized by light violet/dark purple stain of the nuclei

• Spend a few hours in bloodstream, migrate the connective tissues and stay there

• Retain organelles throughout their life

Types of Leukocytes

• Granulocytes - neutraphils, eosinophils, and basophils have both nonspecific granuales in cytoplasm (azurophilic granules) and specific granuales that stain different colors and distinguish one from the other

  • Basophils stain methylene blue - basic dye

  • Eosinophiles stain with eosin - an acid dye

  • Neutrophils don’t stain with basic or acidic stains

• Agranulocytes - lack specific granuales

  • Monocytes

  • lymphocytes

Inconspicuous on light microscopes, relatively clear cytoplasm

Neurtophils

• most abundant WBC

• 4,150 cells/uL 60 - 70% of what is circulating

• nucleus is visible

• mature cells have 3 - 5 lobes connected to slender nuclear strands

• delicate, hard to see nuclear strains

• young neurophils have undivided band shaped nucleus called band cells

• also called polymorphonuclear leukocytes (PMN) because of varied nuclear shapes

• Cytoplasm contains reddit to violet grannuales, contains lysozyme and anibacterial agrens

• granuales are barely visible with light microscope, combined together they look pale lilac

• Aggressively anti-bacterial, their numbers rise called neutrophilia in response to bacterial infection

Eosinophils

• hard to find only 2 - 4 % of circulating population, about 170 cells/uL

• hard to find in blood, but are abundant in lower mucous membranes of respiratory, digestive, and lower urinary tracts

• the nucleus is two large lobes connected with thin strand, cytoplasm has abundance of coarse rosy to orange granuales

• secrete chemicals that weaken/destroy large parasites such as hookworms, tapeworms, that are too big for any one WBC to phagocytize

• Phagocytize and dispose of inflammatory chemicals, antigen-antibodies complexes and allergens

• Allergies, parasitic infections, collagen disease, and disease in spleen or CNS can cause elevated eosinophil count called eosinophillia

• count fluctuates greatly from from day to night and seasonally, and with the phase of the menstrual cycle

Basophils

• rarest of all formed elements

• average 40 cell/uL and constitute .5% of WBC

• recognized by abundance of very coarse dark violet granuales

• nucleus is hidden by granuales

• large, pale, S or U shaped

• secrete two chemicals aiding in bodys defense

  • 1: histamine: vasodilator, widens the blood vessels, speeds flow of blood to injured tissue, makes blood vessels more permeable so blood components such as neutrophils and clotting proteins can get to connective tissue quickly

  • 2: heprin: anticoagulant that inhibits blood clotting and thus promotes mobility of other WBC in area

• release chemical signals that attract eosinophiles and neutrophiles to sites of infection

Lymphocytes

• 2nd most abundant WBC, spotted quickly with 2,200 cells/uL 25 - 44% of WBC

• Range in size and can be the smallest WBC, can be smaller than RBC or 2.5X as large

• There are three size differences in them

• Medium and large usually seen in fibrous connective tissue and sometimes circulating blood

• Small are usually seen in blood tests

• Can be hard to distinguish between basophils and lymphocytes but lymphocytes nucleus if uniform, and basophils are grainy, lymphocytes also have rim of cytoplasm

• large lymphocytes are hard to distinguish from momcytes but lymphocytes have a round, oval, or dimpled nucleus, and stain dark violets

• in small lymphocytes the nucleus takes up nearly the whole cell

• cytoplasm is more abundant in medium and large lymphocytes

• they destroy cells that have been infected with viruses or turned malignant, as well as foreign cells (and parasites)

• secrete chemicals and communicate with each other, other WBC, and coordinate their actions

• present antigens to activate immune response, give rise to the cells that secrete antibodies, and provide long term immunity to pathogens

Monocytes

• largest WBC, 2 - 3 x the diameter of RBC

• average 460 cells/uL and are about 3 - 8 % of WBC count

• nucleus is large, clearly visible , light violet, oval, horseshoe, or kidney shaped

• cytoplasm is abundant and contains sparse, fine granuales

• monocytes often look sharp or spikey shaped in blood films

• their count rises in inflammation and viral infections

• go to work after leaving the bloodstream and transform into large tissue cells called macrophages

• marocphages are highly phagocytic cells that consume dead or dying host and foreign cells, pathogenic chemicals and microorganisms as well as other foreign matter as much as 25% of their own volume per hour

• chop up or process foreign antigens, and then display fragments of them on the cell surface to alert the immune system to their presence

• also called antigen-presenting cells

What is leukopoiesis?

Production of white blood cells beginning with the same hematopoietic stem cells (HSC) as erythropoiesis

What are the colony forming unit (CFUs) cells?

• Myeoblasts - differentiate into three types of granulocytes (neutrophils, eosinophils and basophils)

• Monoblasts - identical to myeoblasts but lead ultimately to monocytes

• Lymphoblasts - produce all lymphocyte types

How does a white blood cell stimulate creation of different WBCs?

Colony forming units have receptors for colony stimulating factors (CSF). Mature lymphoctes and macrophages secrete several types of CSF in response to infection or other immune challenges

Each situation would require a different WBC type

What does red bone marrow store?

Stores granuloytes and monocytes until they are needed, containing 10 to 20 times more than circulating

Lymphocytes begin to develop in the bone marrow but doesn’t stay there, some do mature there while others migrate to the thymus to complete development

Where do lymphocytes live?

Colonize in the spleen, lymph nodes, and other lymphatic organs and tissues

Where do circulating leukocytes go?

They circulate in the blood stream

Granulocytes circulate for 4 - 8 hours and then migrate to tissues and stay for 4 or 5 days and then die

Monocytes travel in the blood for 10 - 20 hours then go into tissues and transform into machrophages, which can live for a few years

Lymphoctes are responsible for long term immunity, and survive from a few weeks to a decade - leave blood stream for tissues and eventually enter the lymphatic system which empties back to the bloodstream so they are continually recycled from blood to tissue fluid back to lymph and back to blood

When leukocytes die, they phagocytize and are digested by macrophages, the exception is dead neutrophils where are responsible for the creamy color of pus, and sometimes disposed by the rupture of a blister

What is a normal WBC and what is it called if it is under or below?

• normal WBC is 5,000 to 10,000 WBC/uL

• Below is called leukopenia (seen in lead, arsenic, and mercury poising, radiation sickness, and infectious diseases such as measles, mumps, chickenpox, polio, influenza, typhoid fever, and AID. Can be produced by glucocorticoids, anticancer drugs, and immunosupperesssant drugs given to organ transplant patients) - presenting higher risk for infection and cancer

• ABover this is leukocytosis (seen in infection, allergy, other diseases, can be seen in dehydration or emotional distrubances)

• A differential WBC shoes how many of each type of leukocyte is present

What is leukemia?

Cancer of the hematopoietic tissue, producing an extraordinarily high number of circulating leukocytes and their precursors

Classified by myeloid or lymphoid, acute or chronic

Myeloid leukemia vs lymphoid leukmia

Myeloid - Uncontrolled granulocyte production

Lymphoid - Uncontrolled lymphocyte or monocyte production

Acute leukemia or chronic leukemia

Acute - suddenly appears, progresses rapidly, causes death within a few months if not treated

Chronic - develops more slowly, can go undetected for several months, if untreated typical survival is 3 years

What treatment is most successful?

Typically seen with acute lymphoblastic leukemia which is the most common type of childhood cancer

treatment is a mix of chemotherapy, marrow transplants, along with control of side effects such as anemia, hemorrhaging, and infection

How does leukemia work?

Leukemic cells proliferate and replace normal bone marrow - then there is a deficiency of normal granulocytes, erythrocytes and platelets

Although there is a huge amount of leukocytes that are made and in the blood stream they do not act as normal protective WBC, they are too immature to perform the usual defense

An opportunistic infecection usually can then establish pathogenic organisms that cannot usually get a foothold in people with healthy immune systems this renders the patient anemic and fatigued.

The platelet deficiency results in hemorrhaging and impaired blood clotting

The immediate cause of death is usually hemmorrhage or infection

Cancerous hematopoietic tissues often metastasizes from bone marrow or lymph nodes to other organs in the body where cells displace or compete with normal cells

Metasisis to the bone tissue is common and leads to bone and joint paint