Connective Tissue: Classification and Cells

Today's tutorial covers the basics of connective tissue with specific focus on connective tissue proper, cell types, and tissue types.
Table of Contents: Time Stamps
- Functions 1:04
- Types of CT 1:24
- CT Origins 1:36
- Loose Connective Tissue 2:32
- Dense Irregular CT 3:20
- Dense Regular CT 5:03
- Fibroblasts 7:02
- Macrophages 7:36
- Adipocytes 8:37
- Mast Cells 9:06
- Lymphocytes 9:51
- Plasma Cells 10:23
- Neutrophils + Eosinophils 10:59
- Summary 11:22

[@SamiUllah-yr6di]

Smooth cells

[@tylerheckman4922]

Are melanocytes considered to be a cell within connective tissue proper? I feel like my professor might have made a mistake by telling us that melanocytes are part of connective tissue proper because I can't find anything that says it is true.

[@thehistologywizard5783]

Hi Tyler- Melanocytes are found in the layer of basal cells at the deepest part of the epidermis. They are also found in the dermis of skin at hair follicles. I suppose that your professor might be referring to their presence in hair follicles-but that's not the same as being resident cells in connective tissue. Hope that helps. -KM

[@tylerheckman4922]

@@thehistologywizard5783 that helps a lot, thank you so much!

[@Alenilsson]

What type of tissue do we se in 10:22?

[@spacesax1]

Looks like loose connective tissue since it's right under the basement membrane. Are you a doctor now?

[@Alenilsson]

Thanks for the fast reply! 😉 Yes I am!@@spacesax1

[@iramhadi9773]

Sorry to say; you have made a mistake. Mast cells and macrophages originated from bone marrow are the transient cells of connective tissue and not resident cells.

[@kathrynmoore4370]

Hi Iram, I see why this can be confusing. But when I refer to permanent cells, I am talking about those specific long-lived cell populations that reside in the connective tissue. Macrophages, Langerhans cells, and mast cells all belong to tissue-resident immune "sentinels". Sometimes you will see these called "fixed" populations. These cell populations all complete their development before birth and are derived from yolk sac erythro-myeloid precursors (EMPs). In terms of macrophages, these cells actually bypass the monocyte stage and develop directly into macrophages. There is also a contribution of monocytes from fetal liver that migrate out and give rise to these tissue resident macrophages and there is likely a contribution of mast cells from fetal liver as well. In contrast, most of the macrophages that accumulate at diseased sites typically derive from circulating monocytes that are born in and released from the bone marrow. Similarly, if more mast cells are needed in a tissue, mast cell progenitors can arise in the bone marrow, circulate as immature precursors, and develop into functional mast cells after entering peripheral tissues. Hope that this helps clarify.

[@kathrynmoore4370]

In connective tissue, the resident macrophages are called "histiocytes".

[@iramhadi9773]

@@kathrynmoore4370 thankyou for the explanation.. its well cleared now

[@kathrynmoore4370]

@@iramhadi9773 You are most welcome. Immunology is very complicated and our understanding is moving so quickly.

[@malaymukhi578]

​@@kathrynmoore4370hello Dr Kathryn, hope you are well. I am a second year resident in pathology and i have never seen such amazing and organised content in histology. Just writing to you to appreciate the efforts ma'am. It's truly amazing and a perfect example of why technology is a blessing. I am absolutely blessed to listen to you, sitting in India. Thank you so much for your efforts. They have been extremely helpful. May God bless you.