42 Questions
What type of cells are responsible for the synthesis of ECM components?
Fibroblasts
What is the main function of connective tissue proper?
All of the above
Which type of cells are observed during wound healing?
Myofibroblasts
What are the two elements that connective tissue is composed of?
Cells and extracellular matrix
What is the function of adipose tissue?
Forming a site for storage of fat
Which type of cells are long-living and can survive for months in tissues?
Macrophages
What is the function of macrophages?
Phagocytosing foreign substances
What is the function of connective tissue proper in organs?
Forming the capsules of organs and membranes
What is the main difference between fibroblasts and fibrocytes?
Fibroblasts are active, fibrocytes are quiescent
What is the origin of macrophages?
Monocytes of blood
Where are mucosal mast cells typically found?
Connective tissue of the intestinal mucosa and lungs
What type of immunoglobulin is produced by plasma cells and binds to mast cell receptors?
IgE
What triggers the degranulation process in mast cells?
Cross-linking of IgE molecules by an antigen
What is the result of the degranulation process in mast cells?
Release of chemical mediators promoting allergic reactions
Where are connective tissue mast cells typically found?
Skin and peritoneal cavity
What is the outcome of the intracellular fusion of specific granules and exocytosis?
Release of chemical mediators
What happens to the mast cell after degranulation?
The cell synthesizes new granules
What is the role of IgE molecules in the degranulation process?
To bind to surface receptors on mast cells
What is the result of the release of histamine and leukotriens from mast cells?
Increased capillary permeability
What is the term for the movement of leukocytes through the walls of capillaries and postcapillary venules?
Diapedesis
What is the result of the activation of B lymphocytes by antigens?
Formation of plasma cells
What is the main function of adipose cells?
Storage of neutral fats
What is the term for the proteins that polymerize into elongated structures in connective tissue?
Fibers
What is the main component of ground substance in connective tissue?
Glycosaminoglycans (GAGs)
What is the function of fibroblasts in connective tissue?
Formation of the extracellular matrix
What is the average lifespan of plasma cells?
10-20 days
What is the primary function of macrophages in regards to foreign substances and bacteria?
To phagocytose them
What is the term for macrophages that process and present antigens to other cells?
Antigen Presenting Cells (APC)
What is the name of the cells that macrophages can fuse to form in certain conditions?
Multinuclear giant cells
What is the main function of histamine secreted by mast cells?
To increase vascular permeability
What is the term for the cells that are distributed throughout the body and have special names in certain regions?
Macrophages
What is the function of heparin secreted by mast cells?
To act as an anticoagulant in the blood
What is the shape of the nucleus in mast cells?
Small and spherical, situated centrally
What is the function of collagenase secreted by macrophages?
To break down collagen in the extracellular matrix
What is the main function of multilocular adipose tissue in human newborns?
To produce heat
What percentage of the body weight does multilocular adipose tissue constitute in human newborns?
2-5%
What is the role of leptin in weight regulation?
Appetite-suppressing hormone
What is the characteristic shape of nuclei in multilocular adipose cells?
Spherical and central
What is the source of estrogens in postmenopausal women?
Adipose tissue
What is the term for the uncoupling protein found in the mitochondria of multilocular adipocytes?
Thermogenin
What is the percentage of body weight represented by adipose tissue in men of normal weight?
15-20%
What is the term for the type of obesity characterized by an increase in the number of adipose cells?
Hyperplastic obesity
Study Notes
Categories of Connective Tissues
- Embryonic connective tissues:
- Mesenchymal
- Mucous
- Adult connective tissues:
- Specialized connective tissues
- Connective tissue proper
- Supporting tissues
- Adipose tissue
Characteristics of Connective Tissues
- Origin: Mesenchyme
- Structure: Cells and extracellular matrix (ECM)
- Cells are widely separated by ECM components
Components of Connective Tissues
- Cells:
- Fibroblasts
- Fibrocytes
- Adipoblasts
- Adipocytes
- Chondroblasts
- Chondrocytes
- Osteoblasts
- Osteocytes
- Formed elements (erythrocytes, leukocytes)
- Extracellular matrix (ECM):
- Fibers: Collagen, elastic, reticular
- Ground substance: Glycosaminoglycans (GAGs), proteoglycans, multiadhesive glycoproteins
Functions of Connective Tissues
- Providing structural support
- Serving as a medium for exchange
- Aiding in defense and protection of the body
- Forming a site for storage of fat
Connective Tissue Proper
- Forms capsules of organs and membranes
- Forms trabeculae and walls inside organs
- Medium for exchange of metabolic waste, nutrients, and oxygen between blood and cells
Cells of Connective Tissue Proper
- Fibroblasts:
- Originate from undifferentiated mesenchymal cells
- Produce ECM components
- Can proliferate
- Fibrocytes:
- Quiescent fibroblasts
- Smaller than fibroblasts
- Fewer processes
- Smaller, darker, elongated nucleus
- Small amount of RER
Pericytes and Myofibroblasts
- Pericytes: Major source of myofibroblasts during fibrosis in multiple organs
- Myofibroblasts:
- Combine features of fibroblasts and smooth muscle cells
- Produce ECM and contain actin and myosin filaments
- Observed during wound healing
- Responsible for wound contraction after tissue injury
Resident Cells of Connective Tissue
- Macrophages:
- Derived from monocytes of blood
- Mature and acquire morphological features of macrophages
- Long-living cells, can proliferate locally
- Distributed throughout the body
- Have different names : kupffer cells , microglia and osteoclast
- Mast cells:
- Derive from stem cells of bone marrow
- Oval to round connective tissue cells
- Contain basophilic secretory granules
- Small, spherical nucleus
- Leukocytes:
- Wandering cells of connective tissue
- Migrate through walls of capillaries and postcapillary venules from blood into connective tissue
- Plasma cells:
- B lymphocyte + antigen → B lymphoblast (mitotic division) → B lymphocyte + plasma cell
- Large, ovoid cells with basophilic cytoplasm
- Well-developed RER
- Spherical nucleus
- Adipose cells:
- Fat cells
- Store neutral fats or produce heat
Adipose Tissue
- Multilocular adipose tissue (brown fat):
- Polygonal cells with multiple lipid droplets
- Rich in capillaries
- Receives direct sympathetic innervation
- Important in newborns for heat production
- Found mainly around shoulder blades and kidneys
Function of Multilocular Adipose Tissue
- Produces heat
- Stimulated by nerve impulses releasing epinephrine
- Lipase releases fatty acids, metabolized to produce heat
- Thermogenin (UCP1) in mitochondria dissipates energy as heat
- Warmed blood circulates throughout the body
Learn about the classification of connective tissues, including embryonic, adult, loose, dense, and specialized types.
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