Connective Tissue: Active & Non-active Cells

• Connective tissue (CT) originates from the mesoderm layer.
• CT consists of cells found on a matrix.
• Ground substance and fibers are components of the matrix

Active cells

• Active cells function to synthesize proteins.
• With LM, the cytoplasm of Active cells are basophilic, and the nuclei are pale.
• Using EM, it can be seen that Active cells have many ribosomes, RER, Golgi apparatus and mitochondria
• Euchromatin is present within Active cells

Non-active cells

• Non-active cells have sedentary life.
• With LM, cytoplasm of Non-active cells are acidophilic, and their nuclei are deep basophilic.
• Non-active cells have few organelles.
• Heterochromatin is present in large qualities within Non-active cells

Connective Tissue, Matrix and Interstitial Fluid

• Connective tissue provides a matrix that supports and physically connects other tissues and cells.
• This connection forms the organs of the body.
• Interstitial fluid provides metabolic support through nutrient and waste diffusion.
• Connective tissues originate from embryonic mesenchyme.
• It is a tissue primarily developing from the middle embryonic layer, the mesoderm

Fibroblasts

• Fibroblasts are active cells that specialize in the function and synthesis of tissue
• Fibroblasts form and synthesize fibers

The Connective Tissue is formed of:

• Connective tissue cells
• Connective tissue fibers
• Connective tissue matrix
• The connective tissue is based on the the matrix that builds it

Types of Connective Tissue

• Types are based on the nature of the intercellular matrix:
• Connective tissue proper which has a soft matrix
• Cartilage, which has a rubbery matrix
• Bone, which has a solid matrix

Connective Tissue Proper

• Connective Tissue Proper supports, binds, and connect various tissues and organs
• Forms from: C.T.Cells, C.T. Fibers and Soft matrix or ground substance

Types of Connective Tissue Proper

• Areolar C.T
• Adipose C.T
• Yellow elastic C.T
• White collagenous C.T
• Mucoid C.T
• Reticular C.T

Types Of Connective Tissue Cells

• Resident (Fixed) C.T. Cells: Fibroblast, Fixed macrophages,
• Transient (Wandering) C.T. Cells: Mast Cells, Plasma Cells Leukocytes, Melanocyte are another kind of transient cell, but have a short life
• White Blood Cells are WBCs, functioning in the immune system

Cell Types and their Activity

• Fibroblasts/fibrocytes create extracellular fibers and ground subtance Lymphocytes, in several types, perform various functions for immune defense
• Macrophages phagocytose the ECM components and debris, perform antigen processing and presentation to immune cells, and secrete growth factors, cytokines, and other agents.
• Adipocytes have the major action of Storing neutral fats

Fibroblast

• Fibroblasts are the most common cells in connective tissue proper
• They produce and maintain most of the tissue's extracellular components
• Fibroblasts originate from mesenchymal cells and pericytes.
• They have a large, ovoid, euchromatic nucleus, as well as a prominent nucleolus
• Fibroblasts are very numerous in areolar C.T. They are branched cells with multiple processes.
• They have basophilic cytoplasm.
• DO NOT have secretory granules because the protein is in vessels Their number increases during wound healing and in cases of C.T. damage.
• Fibroblasts can change into Myofibroblasts, which can close wounds during injuries
• Cytoplasm is high in RNA, endoplasmic reticulum, golgi apparatus and mitochondria
• Fibroblast are able to divide
• Fibroblast's function to form collagen, elastin and reticulin substances in order to form C.T fibers
• Fibroblasts can also form the mucoprotein of the C.T. matrix.

Fibrocyte

• Fibrocytes are mature fibroblasts
• Fibrocytes are small spindle-shaped cells with dense nuclei.
• They have acidophilic cytoplasm with few cell organelles.
• They are unable to divide
• Fibroblast originate from undifferentiated mesenchymal cells and secrete ground substance & fibers
• Fibrocytes originate from Fibroblast after being inactive and function of Maintain the matrix
• Fibroblast have Spindle shape has processes. It also have Large & pale,Deep basophilic., Protein synthesizing cells: Many rER, well developed Golgi but no secretory granules and Fibrocyte shape is Smaller with fewer processes.
• It as Small & dark, Acidophilic and also a Less active cell: Few rER, small Golgi

Macrophages

• Macrophages develop a phagocytic ability and specialize in:
• Turnover of protein fibers
• Removing apoptotic cells and tissue debris
• Removing particulate material
• Macrophages are derived from circulating blood monocytes
• The originate in small blood vessels and go into connective tissue
• They become morphologically macrophages
• Monocytes formed in the yolk sac during early embryonic development circulate
• They become resident in developing organs except within the brain, and called the mononuclear phagocyte system
• They are branched cells with multiple processes.
• They have irregular cell membranes due to the presence of pseudopodia Their cytoplasm is not clear and is rich in lysosomes
• They are basophilic in staining
• They are rich in cell inclusions and contain phagocytosed particles
• Their nucleus is small, may be indented or kidney-shaped, and is rich in chromatin and darkly stained
• The character differentiate it from fibroblast which has a pale faintly stained basophilic nucleus.
• Macrophages in tissue are histiocytes.
• Histiocytes can be stained with Trypan blue
• Macrophages have a characteristic irregular surface with pleats, protrusions, and indentations
• These features are related to their active pinocytotic and phagocytic activities and generally have well-developed Golgi complexes and many lysosomes

Adipocytes

• Adipocytes are fat cells, and present in many organs' connective tissue.
• These large, mesenchymal derived cells are specialized for cytoplasmic storage of lipid as neutral fats and sometimes for the production of heat .
• Connective tissue with many adipocytes is adipose
• Adipose cushions and insulates the skin and other organs,
• They specialize in concentrating triglycerides as lipid droplets
• Normally, other cells accumulate little lipid
• Adipocytes are metabolically active cells responding to nervous, and hormonal stimuli. They release hormones and other important substances
• Adipose tissue is now recognized as an endocrine organ at the center of nutritional homeostasis

Types of Adipocytes

• There are 2 different types of adipocytes: Uni-locular and Multi-locular

Uni-locular adipocytes

• They are more common type and specialized for fat storage
• Consists of cells containing one large cytoplasmic droplet of whitish yellow fat
• Nucleus is peripheral, crescent and sometimes said to have a signet-ring appearance, with the lipid droplet flattening the nucleus against the cell membrane

Multi-locular adipocytes

• Made up of cells that These cells have multiple lipid droplets interspersed among abundant mitochondria, gives the tissue a darker apperance
• Brown adipocytes release heat and warm the blood.
• Each kind of adipose tissue have a rich blood supply
• Adipocytes, besides other CTT cells, are surrounded by a external lamina containing Collagen IV.
• Its Nucleus central and round

Plasma Cells

• Plasma cells, derived from B-lymphocytes, produce antibody. They’re large, oval cells containing basophilic cytoplasm rich in RER
• They also contain a large Golgi apparatus near the nucleus, potentially appearing pale (negative Golgi image). Their nucleus is spherical and eccentric Nuclei have a prominent nucleolus and peripheral heterochromatin
• This gives and appearance is known as cartwheel or a “clock-face”
• These cells originate from lymphocytes Their average life span is only 10-20 days and come from B lymphocytes they are responsible for immunoglobulin antibodies
• Each antibody is specific for the one antigen Antibody-antigen reaction lead to the reactions which usually neutralize harmful effects caused by antigens and quickly removed from tissues by phagocytosis

Mast Cells

• Mast cells are small cells that develop in bone marrow and differentiate in connective tissue
• These are large, ovoid, connective tissue cells (20 to 30 mu in diameter) with a spherical nucleus and intensely basophilic granules in the cytoplasm.
• Mast cells are not easily identified in human tissue sections unless special fixatives are used to preserve the granules, which they are stained with toluidine blue solution
• They are responsible for nose, digestive and skin sensitivity/allergies
• Basophilic cytoplasm and Nucleus appears pale under microscope due to the granules
• Granules stain intensely and metachromatically due to heparin, a highly sulfated proteoglycan and histamine
• The cytoplasm displays rER, mitochondria, plus a Golgi apparatus

Different Types of Mast Cells

• Heparin secretory: Present in the C.T. of skin, they secrete Heparin which is an anticoagulant
• Histamine secretory: Present under the mucosa of respiratory and digestive tracts, secrete histamine, which can contract smooth muscles, dilate blood capillaries and increase the capillary permeability

Functions of Mast Cells

• Considered as Paracrine cells, they secrete heparin or histamine and release chemical mediators as immediate hypersensitivity factors which may cause anaphylactic shock

Undifferentiated Mesenchymal Cells

• These stem cells of connective tissues originate from embryonic mesenchyme, which is a tissue developing from the embryo, and the mesoderm
• Mesenchymal cells are undifferentiated and have large nuclei, prominent nucleoli and fine chromatin.
• "Spindle-shaped," with cytoplasm extended as two or more thin cytoplasmic processes
• The embryonic mesenchyme are the stem cells of other tissues like blood, vascular endothelium and the muscle

Leukocytes

• Leukocytes, leave blood by migrating between the endothelial cells of venules to enter connective tissue.
• This process increases greatly during inflammation and inflammation begins with the local release of chemical mediators.
• These are cells in the ECM, blood and plasma proteins and act on local blood vessels, induce mast cells and macrophages.
• Leukocytes function in connective tissue for a few hours/days and undergo apoptosis.
• lymphocytes+ phagocytic antigen-presenting cells leave interstitial fluid of connective tissue and enter blood/lymph to move to selected lymphoid organs.

Pigment Cells and Melanocytes

• The Pigment cell precursor is the melanoblast and the mature pigment cell is the melanocyte.
• Pigments made by melanocytes are: eumelanin (brown or black) and pheomelanin (yellow/red).
• Neural crest-derived Melanocytes reside in the bottom layer/skin’s stratum basale.
• Can also be located in the eye, the inner ear, vaginal epithelium, meninges, bones, and heart.
• Dark pigment-melanin is mostly responsible for skin color
• Synthesized melanin- then is contained in certain organelles/ melanosomes, transporting to nearby keratinocytes inducing pigmentation.
• Functionally, melanin protects VS. UV radiation
• The DOPA test identifies differences between melanocytes + pigmented cells.

This lesson covers connective tissue, its origin from the mesoderm layer, and its cellular components within a matrix. It differentiates between active and non-active cells based on their protein synthesis function, cytoplasmic properties, and organelle composition.