Platelets and Hemostasis

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Questions and Answers

What is a distinguishing feature of lymphocytes?

They are large and contain abundant granules.

Their cytoplasm appears bluegray and foamy.

They have a kidney-shaped nucleus.

They possess a round and dark-staining nucleus. (correct)

What type of macrophage remains in a specific tissue, such as the lungs?

Wandering macrophages

Migratory macrophages

Fixed macrophages (correct)

Activated macrophages

What is the appearance of the cytoplasm of monocytes?

Clear with prominent vacuoles

Bluegray with a foamy appearance (correct)

Pink with coarse granules

Bright yellow with large granules

Which statement about the characteristics of lymphocytes is NOT true?

They possess visible granules under a light microscope. Signup and view all the answers

Monocytes differentiate into which type of cells once they leave the bloodstream?

Macrophages Signup and view all the answers

What is the primary function of platelets in the blood?

Promoting blood clotting Signup and view all the answers

Which component of hemostasis involves the immediate constriction of blood vessels?

Vascular spasm Signup and view all the answers

What is the typical lifespan of platelets in circulation?

5 to 9 days Signup and view all the answers

Which of the following is NOT a mechanism involved in reducing blood loss during hemostasis?

Blood vessel dilation Signup and view all the answers

How are aged and dead platelets removed from circulation?

By fixed macrophages in the spleen and liver Signup and view all the answers

What is the primary function of B cells in the immune system?

Destroying bacteria and inactivating their toxins Signup and view all the answers

Which type of cell primarily attacks viruses and fungi?

T cells Signup and view all the answers

How do platelets develop from megakaryocytes?

By splintering into 2000 to 3000 fragments Signup and view all the answers

What role does thrombopoietin play in platelet formation?

Acts on myeloid stem cells to develop into megakaryocytes Signup and view all the answers

What types of cells do Natural Killer (NK) cells attack?

A wide variety of infectious microbes and certain tumor cells Signup and view all the answers

What is the initial cell type involved in erythropoiesis?

Proerythroblast Signup and view all the answers

What happens to the proerythroblast during erythropoiesis?

It ejects its nucleus. Signup and view all the answers

What do reticulocytes retain during their development?

Mitochondria, ribosomes, and endoplasmic reticulum Signup and view all the answers

How long does it take for reticulocytes to develop into mature red blood cells?

1 to 2 days Signup and view all the answers

From where do reticulocytes enter the bloodstream?

Red bone marrow Signup and view all the answers

What role do neutrophils play in response to tissue damage?

They respond most quickly and use strong oxidants to combat bacteria. Signup and view all the answers

Which type of white blood cell is primarily responsible for intensifying inflammatory reactions?

Basophils Signup and view all the answers

What process characterizes the action of monocytes during an immune response?

They enlarge and differentiate into macrophages. Signup and view all the answers

How do eosinophils contribute to the immune defense?

They phagocytize antigen-antibody complexes and target parasitic worms. Signup and view all the answers

What is a common characteristic of both neutrophils and macrophages?

Both are active phagocytes responding to pathogens. Signup and view all the answers

What process describes the movement of white blood cells (WBCs) from the bloodstream into the tissue?

Emigration Signup and view all the answers

Which molecules on endothelial cells assist in the rolling of white blood cells along the vessel lining?

Selectins Signup and view all the answers

Which statement accurately describes the role of integrins in the emigration of WBCs?

They help WBCs to adhere to the endothelium. Signup and view all the answers

What is the primary reason different types of WBCs have varying signals for emigration?

WBCs respond to specific pathogens. Signup and view all the answers

Which of the following accurately describes the composition of MHC antigens?

They are unique to each individual, except identical twins. Signup and view all the answers

What occurs after a white blood cell sticks to the endothelium during emigration?

It squeezes between the endothelial cells to enter the tissue. Signup and view all the answers

What is the primary function of vascular spasm following damage to an artery?

To decrease blood loss temporarily Signup and view all the answers

Which of the following substances is NOT involved in platelet activation?

Fibrinogen Signup and view all the answers

What initiates the reflex that may contribute to vascular spasm?

Pain receptor activation Signup and view all the answers

During platelets’ release reaction, which of the following is a function of thromboxane A2?

Acting as a vasoconstrictor Signup and view all the answers

What role do activated platelets play during platelet plug formation?

They become activated and help recruit more platelets Signup and view all the answers

What is the primary stimulus for erythropoiesis?

Cellular oxygen deficiency Signup and view all the answers

Which of the following conditions can lead to hypoxia?

High altitude Signup and view all the answers

Which type of white blood cell is classified as a granular leukocyte?

Basophil Signup and view all the answers

Which vitamin deficiency can contribute to anemia?

Vitamin B12 Signup and view all the answers

What defines the controlled condition in the regulation of erythropoiesis?

Amount of oxygen delivered to body tissues Signup and view all the answers

What color do the granules of eosinophils stain with acidic dyes?

Red-orange Signup and view all the answers

Which characteristic is unique to basophils compared to eosinophils?

Granules stain blue-purple Signup and view all the answers

Which statement about the nucleus of the eosinophil is true?

It has two lobes Signup and view all the answers

What type of granules do basophils possess?

Round, variable-sized granules Signup and view all the answers

What makes eosinophils eosinophilic?

Their granules stain with acidic dyes Signup and view all the answers

What is the characteristic lifespan of lymphocytes compared to other white blood cells?

They can live for months or years. Signup and view all the answers

Which of the following statements about leukocytosis is true?

It is a protective response that can occur during strenuous exercise. Signup and view all the answers

How are neutrophils commonly identified under a light microscope?

They possess a pale lilac color with small granules. Signup and view all the answers

What happens to the number of nuclear lobes in neutrophils as they age?

It increases to two to five lobes. Signup and view all the answers

Which condition is described as never being beneficial in terms of white blood cell levels?

Leukopenia Signup and view all the answers

Study Notes

Platelets (Thrombocytes)

Normal range: 150,000 to 400,000 platelets per µl of blood
Shape: Irregular disc, 2-4 µm diameter, lacks a nucleus but contains vesicles
Vesicles store chemicals essential for coagulation (blood clotting)
Lifespan: 5 to 9 days; aged platelets are cleared by macrophages in the spleen and liver
Development involves thrombopoietin influencing myeloid stem cells to become megakaryocytes, which fragment to release platelets

Hemostasis

Hemostasis is a series of processes to stop bleeding from damaged blood vessels
Characteristics of hemostatic response: quick, localized, and tightly regulated
Mechanisms for reducing blood loss:
- Vascular spasm
- Platelet plug formation
- Blood clotting (coagulation)

Agranular Leukocytes

Lack visible cytoplasmic granules under a light microscope
Lymphocyte Characteristics:
- Nucleus: Round and dark-staining
- Cytoplasm: Stains sky blue
- Size classification: Large and small lymphocytes
Monocyte Characteristics:
- Nucleus: Kidney-shaped or horseshoe-shaped
- Cytoplasm: Blue-gray with a foamy appearance due to azurophilic granules
- Monocytes differentiate into macrophages in tissues
Macrophages Types:
- Fixed (tissue) macrophages: Reside in specific tissues
- Wandering macrophages: Roam tissues to sites of infection

Lymphocyte Function

Major players in the immune response:
- B cells: Target and destroy bacteria and toxins
- T cells: Attack viruses, fungi, cancer cells, and some bacteria
- Natural Killer (NK) cells: Attack various infectious microbes and certain tumors

White Blood Cells (WBCs)

Active phagocytes include:
- Neutrophils: Respond quickly to bacterial infection using lysozymes and defensins
- Monocytes: Arrive later but in greater numbers, differentiating into macrophages
Basophils:
- Release granules (heparin, histamine, serotonin) at inflammation sites
- Play a role in allergies and intensify inflammatory reactions
Eosinophils:
- Release histaminase, phagocytize complexes, and combat parasitic infections

WBC Emigration

WBCs leave the bloodstream via emigration (previously known as diapedesis)
Process involves rolling along the endothelium, adhering, and squeezing between endothelial cells
Signals for emigration vary by WBC type, involving selectins and integrins

Erythropoiesis: Production of RBCs

Begins with proerythroblasts in red bone marrow, which synthesize hemoglobin
Proerythroblast divides, eventually ejecting the nucleus to become reticulocytes
Reticulocytes mature into RBCs within 1-2 days after entering circulation

Vascular Spasm

Immediate contraction of smooth muscle in damaged blood vessels to limit blood loss for minutes to hours
Initiated by smooth muscle damage, platelet release substances, and pain reflexes

Platelet Plug Formation

Adhesion: Platelets stick to damaged vessel areas (collagen fibers)
Activation: Platelet activation leads to projection extension and vesicle content release; ADP and thromboxane A2 recruit more platelets
Function of serotonin and thromboxane A2: Vasoconstriction to reduce blood flow

Hypoxia and Feedback Mechanism

Hypoxia: Cellular oxygen deficiency, stimulating erythropoiesis
Conditions leading to hypoxia: High altitudes, pneumonia, anemia (iron, amino acids, vitamin B12), and circulatory problems
The primary controlled factor is oxygen delivery to tissues

White Blood Cell Overview

WBCs (leukocytes) possess nuclei and organelles; do not contain hemoglobin
Classified as granular (neutrophils, eosinophils, basophils) and agranular (lymphocytes, monocytes)
Live for varying durations: a few days for most, but lymphocytes can last months to years
Leukocytosis: Increase in WBCs as a normal response to infection or stress
Leukopenia: Abnormally low WBC count, indicating potential health issues

Granular Leukocytes Identification

Neutrophils: Multilobed nucleus, light-staining granules
Eosinophils: Dual-lobed nucleus, red-orange granules
Basophils: Dual-lobed nucleus, blue-purple granules

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Description

Learn about the structure and function of platelets, also known as thrombocytes, and the process of hemostasis, which stops bleeding when blood vessels are damaged.