❤️ Topic 4: The Platelets

What are platelets sometimes referred to as?

thrombocytes

Where do platelets originate from?

derived from precursor cells in the bone marrow called megakaryocytes.

How long do platelets circulate in peripheral blood?

circulate in peripheral blood for 7–10 days

Where are aged or nonviable platelets removed from circulation?

removed by the spleen or liver.

What are the primary functions of platelets?

Hemostasis

Wound healing

Vascular endothelial cell integrity

What is the role of megakaryocytes in platelet production?

Platelet production depends on the proliferation and maturation of megakaryocytes in the bone marrow.

What processes are involved in platelet production?

Megakaryopoiesis (megakaryocyte proliferation)

Thrombopoiesis (platelet maturation and release)

How many platelets does the bone marrow produce per day under normal conditions?

produces approximately 1x10^11 platelets per day.

How does platelet production change during times of increased demand?

platelet production can increase 10- to 20-fold.

What is the first stage in megakaryopoiesis (platelet production)?

Megakaryopoiesis begins with the common myeloid progenitor (CMP) and the megakaryocyte progenitor (MkP).

What is the earliest morphologically identifiable platelet precursor in megakaryopoiesis?

megakaryoblast

What are the two main types of cells in the megakaryocytic lineage?

Actively proliferating progenitor cells

Postmitotic (nonproliferating) megakaryocytes

What are platelets?

cytoplasmic fragments of mature megakaryocytes.

What are the four stages of megakaryocyte development?

Stage I: Megakaryoblast

Stage 2: Promegakaryocyte

Stage 3: Granular megakaryocyte

Stage 4: Mature megakaryocyte

What occurs during Stage I (Megakaryoblast) of megakaryocyte development?

During Stage I, nuclear maturation occurs first and is completed before cytoplasmic maturation. Endomitosis takes place, where the DNA content doubles without nuclear division, and the cells become polyploid. The DNA content ranges from 4N to 64N.

What is the second stage of megakaryocyte development?

Promegakaryocyte

What is the third stage of megakaryocyte development?

Granular Megakaryocyte

What is the final stage of megakaryocyte development?

Mature Megakaryocyte

Endomitosis

division of chromosomes not followed by nuclear division that results in an increased number of chromosomes in the cell

Polyploid

having or being a chromosome number that is a multiple greater than two of the monoploid number

What happens to the cytoplasm during megakaryocyte development?

The cytoplasm increases in volume and changes from being basophilic, nongranular, and scant to granular and acidophilic.

How does the nucleus change during megakaryocyte development?

The nucleus transforms from a single round lobe with fine chromatin and visible nucleoli to lobulated, with coarse chromatin and no visible nucleoli.

How much larger is a megakaryocyte compared to a mature RBC?

A megakaryocyte is 10–30x larger than a mature RBC.

What is the nuclear to cytoplasmic ratio in a megakaryocyte?

A megakaryocyte has a low nuclear to cytoplasmic ratio.

How many lobes are present in the nucleus of a megakaryocyte?

The nucleus of a megakaryocyte is multilobated, with 2–8 lobes stacked on top of each other, and has clumped chromatin.

Are nucleoli present in a megakaryocyte?

No, nucleoli are absent in a megakaryocyte.

What is the appearance of the cytoplasm in a megakaryocyte?

The cytoplasm in a megakaryocyte is abundant, light blue, and usually lacks granules.

What is thrombopoiesis?

the process of platelet production in the bone marrow.

Where are mature megakaryocytes located in the bone marrow?

Mature megakaryocytes are located near the marrow sinus.

What are proplatelets?

protrusions of megakaryocyte cytoplasm that eventually break up into individual platelets.

How many platelets can each megakaryocyte produce?

Each megakaryocyte produces 1000–3000 platelets, depending on the parent ploidy.

What color are platelets, and what color are their granules?

small, lavender-blue or colorless, with reddish-purple granules.

What shape are platelets?

typically round or oval in shape.

Do platelets have nuclear material?

Platelets lack nuclear material.

What cellular remnants are present in platelets?

contain remnants of the Golgi complex, a small number of ribosomes, and a small amount of RNA.

What is hemostasis, and what is its purpose?

Hemostasis is the controlled process that arrests vascular bleeding after an injury.

What is the first step in hemostasis after an injury?

The first step in hemostasis is the formation of the primary hemostatic plug.

How do platelets contribute to secondary hemostasis?

Platelets provide a surface for fibrin generation, which is essential for secondary hemostasis.

How do platelets contribute to tissue repair after an injury?

Platelets promote the repair of injured tissues and contribute to vascular integrity and vessel wall repair following injury.

What are the primary functions of B cells?

B cells primarily defend against bacteria, fungi, and other microbes.

How do B cells help neutralize microbes and toxins?

B cells produce antibodies (Abs) that neutralize and eliminate microbes and toxins.

Where are antibodies produced, and where do they circulate?

Antibodies are produced by plasma cells and circulate throughout the body.

How do platelets contribute to immune function?

Platelets contribute to both innate and adaptive immunity.

What do platelets do when interacting with leukocytes?

Platelets adhere to and interact with various leukocytes.

What types of molecules do platelets synthesize?

Platelets synthesize cytokines, chemokines, and inflammatory mediators.

How do platelets modulate immune responses?

modulate both inflammatory and immune responses.

What antimicrobial activity do platelets have?

Platelets secrete antimicrobial peptides.

How do platelets contribute to neutrophil extracellular trap (NET) formation?

Platelets trigger the formation of neutrophil extracellular traps (NETs).

How do platelets assist with lymphocyte function?

Platelets assist with the trafficking, activation, and differentiation of lymphocytes.