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Many red blood cells with a single larger cell. The larger cell is pink with a purple region that fills nearly the entire cell. The purple region is labeled perforin-containing granules.
Natural killer cell with perforin-containing granules. (credit: modification of work by Rolstad B)

Monocytes

The largest of the white blood cells, monocytes have a nucleus that lacks lobes, and they also lack granules in the cytoplasm ( [link] ). Nevertheless, they are effective phagocytes, engulfing pathogens and apoptotic cells to help fight infection.

When monocytes leave the bloodstream and enter a specific body tissue, they differentiate into tissue-specific phagocytes called macrophages and dendritic cells . They are particularly important residents of lymphoid tissue, as well as nonlymphoid sites and organs. Macrophages and dendritic cells can reside in body tissues for significant lengths of time. Macrophages in specific body tissues develop characteristics suited to the particular tissue. Not only do they provide immune protection for the tissue in which they reside but they also support normal function of their neighboring tissue cells through the production of cytokines. Macrophages are given tissue-specific names, and a few examples of tissue-specific macrophages are listed in [link] . Dendritic cells are important sentinels residing in the skin and mucous membranes, which are portals of entry for many pathogens. Monocytes, macrophages, and dendritic cells are all highly phagocytic and important promoters of the immune response through their production and release of cytokines. These cells provide an essential bridge between innate and adaptive immune responses, as discussed in the next section as well as the next chapter.

Monocytes are large cells with a large purple nucleus. There is a cluster of them in a field of smaller red blood cells. A PMN is also visible with a dark, multi-lobed nucleus. Macrophages are large cells with a defined nucleus.
Monocytes are large, agranular white blood cells with a nucleus that lacks lobes. When monocytes leave the bloodstream, they differentiate and become macrophages with tissue-specific properties. (credit left: modification of work by Armed Forces Institute of Pathology; credit right: modification of work by Centers for Disease Control and Prevention)
Macrophages Found in Various Body Tissues
Tissue Macrophage
Brain and central nervous system Microglial cells
Liver Kupffer cells
Lungs Alveolar macrophages (dust cells)
Peritoneal cavity Peritoneal macrophages
  • Describe the signals that activate natural killer cells.
  • What is the difference between monocytes and macrophages?

Key concepts and summary

  • The formed elements of the blood include red blood cells ( erythrocytes ), white blood cells ( leukocytes ), and platelets (thrombocytes ). Of these, leukocytes are primarily involved in the immune response.
  • All formed elements originate in the bone marrow as stem cells (HSCs) that differentiate through hematopoiesis .
  • Granulocytes are leukocytes characterized by a lobed nucleus and granules in the cytoplasm. These include neutrophils (PMNs) , eosinophils , and basophils .
  • Neutrophils are the leukocytes found in the largest numbers in the bloodstream and they primarily fight bacterial infections.
  • Eosinophils target parasitic infections. Eosinophils and basophils are involved in allergic reactions. Both release histamine and other proinflammatory compounds from their granules upon stimulation.
  • Mast cells function similarly to basophils but can be found in tissues outside the bloodstream.
  • Natural killer ( NK ) cells are lymphocytes that recognize and kill abnormal or infected cells by releasing proteins that trigger apoptosis.
  • Monocytes are large, mononuclear leukocytes that circulate in the bloodstream. They may leave the bloodstream and take up residence in body tissues, where they differentiate and become tissue-specific macrophages and dendritic cells .

Matching

Match each cell type with its description.

___natural killer cell A. stains with basic dye methylene blue, has large amounts of histamine in granules, and facilitates allergic responses and inflammation
___basophil B. stains with acidic dye eosin, has histamine and major basic protein in granules, and facilitates responses to protozoa and helminths
___macrophage C. recognizes abnormal cells, binds to them, and releases perforin and granzyme molecules, which induce apoptosis
___eosinophil D. large agranular phagocyte that resides in tissues such as the brain and lungs

C, A, D, B

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Match each cellular defense with the infection it would most likely target.

___natural killer cell A. virus-infected cell
___neutrophil B. tapeworm in the intestines
___eosinophil C. bacteria in a skin lesion

A, C, B

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Fill in the blank

Platelets are also called ________.

thrombocytes

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The cell in the bone marrow that gives rise to all other blood cell types is the ________.

pluripotent hematopoietic stem cell (HSC)

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PMNs are another name for ________.

neutrophils

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Kupffer cells residing in the liver are a type of ________.

macrophage

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_____________ are similar to basophils, but reside in tissues rather than circulating in the blood.

mast cells

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Short answer

Explain the difference between plasma and the formed elements of the blood.

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List three ways that a neutrophil can destroy an infectious bacterium.

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Questions & Answers

reactions if viruses to physical and chemical agents?
VICTOR Reply
All viruses contain the following two components: 1) a nucleic acid genome and 2) a protein capsid that covers the genome. Together this is called the nucleocapsid. In addition, many animal viruses contain a 3) lipid envelope. The entire intact virus is called the virion.
Asali
assume you have performed a gram stain on a sample of pus from a patients urethra. you see red, nucleated cells and purple rods. what can you conclude
Petty Reply
bacteria
ABUBAKAR
Study of micro organisation which we cannot see with naked eye...
shyam Reply
Despite their bad reputation, microbes are mostly beneficial or have a neutral effect on our lives. Microbiology is the scientific study of these microorganisms. Microorganisms are those organisms that are too small to see with the naked eye and include things like bacteria, fungi, and viruses.
Asali
yes
Dhirender
not 'things'...'organisms' like bacterias, viruses and fungi
Sinmi
simi, it's not bacterias but bacteria which is the plural form of the word while bacterium is the singular of it
Richard
bacterium is obvio in a singular form but plural of bacterium is bacterias
Sinmi
Richard is right it's bacterium which is the singular form and plural is bacteria. *Bacterias* doesn't exist.
Aakriti
what is microbiology?
Sandeep Reply
what is microbiology
Glory
is the study of small microorganisms that can't be viewed by our naked eyes under a microscope
Nabukwasi
it's the study of microbes their classification, diversity, their cellular structure and processes, their applications and interaction with other organisms.
Chaitanya
what is EMP pathway
rajesh
which organism is implicated in meningoencephalitis
Peter Reply
Herpes virus
Carlos
Yeah
Laxmi
which mold is called dairy mold?
Gopinath
mushroomm
Top
Geotrichum candidum
Gopinath
hi
bio
Hlw
Laxmi
which infectious agent is the smallest
Sinmi
spore or virus
Anushree
prion ....it is a single protein in a misfolded form..there is also a theory based on it
Sinmi
yup...m sry
Anushree
yes it can be turned as a virus
Sinmi
which gram positive bacteria is responsible for food poisoning?
Sinmi
prion is not a living organism yet it is infectoois why
Jeevan
prions are virus like organism. and it is a misfolded protein that may cause disease to us.
Tharra
Clostridium perfringens, B.cereus
Sneha
Who is the father of the biology
Dhirender
I have one more question. . that who is the father of botany and medicine? ? can any one tell
Dhirender
define polar bond in simple way
Rashmi Reply
when there is formation of positive and negative poles i.e. one atom is +ve and other is -ve which further results in the dipole moment. Such bond is know as polar bond. It is a convalent bond only.
Aakriti
Hi everyone, is these site only about microbiology? I want a site which I can download articles on hematological and biochemical profile
Peter Reply
I think it is only about micro biology.
Kimberly
so whats happening
Michael
I am about to enter school and am going for MCB
Olugbenga Reply
What is DNA damage and repair
Sree Reply
removal of nucleotide bases from DNA is damage n addition or insertion of bases in DNA is repair.
Rashmi
replication is a term related to generation of new DNA from a parental DNA.
Rashmi
role of microorganism as pathogens
Parteek Reply
to live inside the host body, reproduction n destroy the immune system of host body.
Rashmi
what is replication
rajesh
please give me ans
rajesh
replication is a term related to generation of new DNA from parental DNA.
Rashmi
difference between endotoxin and exotoxin
Binkheir Reply
toxins released inside the cell or a body is endotoxin n toxins released outside the cell or a body is exotoxin.
Rashmi
Generally, exotoxins are produced by gram positive bacteria and endotoxins are the integral part of the cell wall of gram negative bacteria. But some gram negative bacteria can also produced exotoxins such as E.coli.
Aakriti
Yeah u r ryt aakarti exotoxins screted by gram postive bacteria nd secreted by cell surface and they are secondary metabolites ....On the other hand endotoxin released by gram negtive bacteria nd released inside the cell (lipopolysaccharide) ..
Bharat
Heat stable lipopolysaccharides to be exact.
Aakriti
yup..
Bharat
please I want the names of bacteria and the diseases they cause.
Ibrahim Reply
there are many we classify it according to their shapes gram negative or gram positive
Tharra
so u may refer the book u guess or by when u want I can do a list for you and send u here
Tharra
😊
Tharra
please do a list for me
Ibrahim
I have the lost but it's too much to type ..
Tharra
MSc entrance prepare books and questions LA etha base pani irukum..
Guhan Reply
kushal always prescott is the imp book to follow.search some objective mcqs books based on your syllabus
deepthi Reply
I want to clear entrance of ms university so I have no more idea so my preparation is based on my bachlor studies.
Kushal
what are the opportunistic infection in aids stage
Kalkak
certain cancer or pneumonia 🤔
Kushal
penicillium crysogenum
Kushal Reply

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Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
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