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What is the primary origin of connective tissue?
What is the primary origin of connective tissue?
Which of the following best describes fixed cells in connective tissue?
Which of the following best describes fixed cells in connective tissue?
What type of connective tissue is characterized by having a rubbery and firm matrix?
What type of connective tissue is characterized by having a rubbery and firm matrix?
Which type of cells are considered free cells in connective tissue?
Which type of cells are considered free cells in connective tissue?
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Pericytes in connective tissue are primarily responsible for which function?
Pericytes in connective tissue are primarily responsible for which function?
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What characteristic is true of undifferentiated mesenchymal cells in adults?
What characteristic is true of undifferentiated mesenchymal cells in adults?
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Which of the following fibers is commonly found in connective tissue proper?
Which of the following fibers is commonly found in connective tissue proper?
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What feature distinguishes free cells from fixed cells in connective tissue?
What feature distinguishes free cells from fixed cells in connective tissue?
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What is the primary function of plasma cells?
What is the primary function of plasma cells?
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Which staining technique is used to visualize mast cells?
Which staining technique is used to visualize mast cells?
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What is a characteristic of reticular fibers?
What is a characteristic of reticular fibers?
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What type of connective tissue fiber is described as strong, flexible, and not elastic?
What type of connective tissue fiber is described as strong, flexible, and not elastic?
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Where are mast cells primarily located in the body?
Where are mast cells primarily located in the body?
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Which type of cells are free macrophages derived from?
Which type of cells are free macrophages derived from?
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Which is NOT a characteristic of collagen fibers?
Which is NOT a characteristic of collagen fibers?
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What type of connective tissue is primarily responsible for providing elasticity?
What type of connective tissue is primarily responsible for providing elasticity?
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Which type of fat cell is primarily responsible for heat generation?
Which type of fat cell is primarily responsible for heat generation?
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What is one of the primary functions of fibrocytes?
What is one of the primary functions of fibrocytes?
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What is the appearance of unilocuolar (white) fat cells when stained with H&E?
What is the appearance of unilocuolar (white) fat cells when stained with H&E?
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Which cell type is vital for the process of phagocytosis in connective tissue?
Which cell type is vital for the process of phagocytosis in connective tissue?
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Pericytes are known for their ability to do what regarding blood vessels?
Pericytes are known for their ability to do what regarding blood vessels?
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Which of the following statements about fibroblasts is true?
Which of the following statements about fibroblasts is true?
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What key function do reticular cells perform in the organs?
What key function do reticular cells perform in the organs?
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What distinguishes multilocuolar (brown) fat cells from unilocuolar (white) fat cells?
What distinguishes multilocuolar (brown) fat cells from unilocuolar (white) fat cells?
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What is a primary function of loose (areolar) connective tissue?
What is a primary function of loose (areolar) connective tissue?
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Where is mucoid connective tissue typically found?
Where is mucoid connective tissue typically found?
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What distinguishes brown adipose connective tissue from white adipose connective tissue?
What distinguishes brown adipose connective tissue from white adipose connective tissue?
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Which of the following sites is associated with regular white fibrous connective tissue?
Which of the following sites is associated with regular white fibrous connective tissue?
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Which type of connective tissue forms a network of branched cells and fibers?
Which type of connective tissue forms a network of branched cells and fibers?
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What is the primary function of white adipose connective tissue?
What is the primary function of white adipose connective tissue?
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What type of connective tissue is characterized by fine collagen fibers and large amounts of jelly-like ground substance?
What type of connective tissue is characterized by fine collagen fibers and large amounts of jelly-like ground substance?
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What property of irregular white fibrous connective tissue allows it to withstand stress in multiple directions?
What property of irregular white fibrous connective tissue allows it to withstand stress in multiple directions?
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Study Notes
Connective Tissue Overview
- Originates from mesoderm
- Composed of widely separated cells with a large amount of ground substance (matrix)
- Contains blood vessels, nerves, and lymphatic vessels
- Connects, supports, and protects other tissues (e.g., epithelium and organs)
Connective Tissue Cells
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Fixed Cells: Stable population, long-lived cells produced in the connective tissue and remain there.
- Undifferentiated mesenchymal cells: Stem cells in embryos that can differentiate into other connective tissue cells. In adults, they remain undifferentiated in bone marrow and act as stem cells; pericytes, and bone marrow cells. Small, irregular, branched cells with a pale basophilic cytoplasm, central, large oval pale nucleus and nucleoli. Few organelles (many ribosomes).
- Function (in embryo): act as stem (mother) cells, differentiating into all types of CT cells, smooth muscle cells, and endothelial cells. Function (in adult): remain undifferentiated in certain areas to act as life-long source for some cells (e.g., in bone marrow -- blood cells, around blood vessels -- pericytes).
- Pericytes: Present around blood capillaries, branched with an oval nucleus and pale cytoplasm. Give rise to fibroblasts and smooth muscles throughout life. Involved in vasoconstriction.
- Function (injury): can differentiate into fibroblasts, smooth muscle cells, and endothelial cells.
- Fibroblasts: Most common type in connective tissue proper. Originate from mesenchymal cells, pericytes. Flat, elongated cells with processes. Produce protein-forming cells. Functions: formation of connective tissue fibers; build connective tissue matrix; repair connective tissue after injury.
- Fibrocytes: Old, inactive fibroblasts; smaller, fewer processes; less basophilic cytoplasm; less rER; dark nucleus. Continuous slow turnover of connective tissue fibers and matrix (maintenance of connective tissue).
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Adipocytes (fat cells):
- Unilocular (white): Large oval cells with a flattened nucleus to the periphery; cytoplasm is thin film around a large fat globule. H&E stain - signet ring appearance; Special stain - Sudan III (orange). Function: storage of fat, heat insulator.
- Multilocular (brown): Small, rounded cells with a central rounded nucleus; many small fat droplets; many mitochondria which contain cytochrome pigment causing brown color. Less common; function: heat generation.
- Fixed Macrophage (hisitoctye): Derived from monocytes; attached to connective tissue fibers, mainly collagen fibers; large, branched cells with pseudopodia (variable shape); small, dark, oval or kidney-shaped nucleus with vacuolated cytoplasm. Vital stain: trypan blue. Functions: phagocytosis, clean wounds, fuse with other forms to form giant cells to engulf large foreign bodies; antigen presenting to lymphocyte; destruction of old RBCs (liver, spleen).
- Reticular cells: Present in the stroma of organs; small, branched cells with long processes. Silver stain can demonstrate them. Functions: form reticular fibers; act as supporting cells; form a reticular network with reticular fibers; act as phagocytic cells as needed.
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Free Cells: Changeable population, motile cells belonging to the immune system that enter the connective tissue from the blood; short-lived and wander through connective tissue.
- Plasma cells: Originate from B-lymphocytes; differentiate to plasmablasts then plasma cells. Oval with eccentric nucleus (cart-wheel or clock-face); cytoplasm is deep basophilic with a visible Golgi image. Sites: abundant in lymphoid tissue, rarely found in blood. EM: well-developed Golgi apparatus; closely spaced cisternae of rER & mitochondria. Functions: formation and secretion of antibodies.
- Mast cells: Originate from mesenchymal cells in bone marrow. Sites: around blood vessels and sub-epithelial connective tissue (respiratory and digestive systems). Oval cell, with eccentric nucleus; basophilic cytoplasm. Stain: metachromatic stain with toluidine blue. Function: secretion of histamine, heparin, and eosinophil chemotactic factor.
- Free Macrophages: The same as fixed macrophages but they wander in connective tissues.
- Blood Leukocytes: All types migrate from the bloodstream to the connective tissue to perform their defensive functions (e.g., lymphocytes, monocytes, basophils, neutrophils, eosinophils)
Connective Tissue Fibers
- White Collagen Fibers: Synthesized by fibroblasts, chondroblasts, and osteoblasts; wavy branching bundles of non-branching parallel fibers; stain pink in H&E; strong, flexible, not elastic; give tissues strength and resist stretching.
- Yellow Elastic Fibers: Synthesized by fibroblasts and chondroblasts; thin, long branching fibers running singly; stain pink in H&E, brown with Orcein; stretchable; give elasticity to tissues.
- Reticular Fibers: Synthesized by fibroblasts and reticular cells; very thin fibers branching and anastomosing to form a network; not seen by H&E; brown with silver stain (argyrophilic); delicate, flexible; form the stroma (background) that supports organs.
Types of Connective Tissue Proper
- Loose (Areolar) Connective Tissue: Contains all types of connective tissue cells and fibers, embedded in an abundant matrix; contains potential cavities (areolae); present throughout the body; functions: binds tissues together, surrounds organs, and supports organs and tissues.
- Reticular Connective Tissue: Reticular fibers form network; presence of reticular cells.
- Mucoid Connective Tissue: Large amount of jelly-like ground substance rich in mucus and hyaluronic acid; UMCs and fibroblasts that communicate via processes; fine collagen fibers; found in umbilical cord (Wharton's jelly), pulp of growing teeth, vitreous humor of the eye. Protects near-by structures from pressure.
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Adipose Connective Tissue:
- White Adipose: Unilocular fat cells; each cell contains a large single fat droplet; fat is not pigmented; located under skin, mammary gland, around kidneys; functions: storage of fat, heat insulator, support of organs, forms body contours.
- Brown Adipose: Multilocular fat cells; each cell contains many fat droplets; fat is pigmented due to high vascularity and cytochrome pigments; abundant in newborns; limited to supraclavicular, interscapular, axillary, thoracic, and paravertebral regions in adults; function: heat generation.
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Dense Connective Tissue:
- Regular White Fibrous: Parallel collagen bundles with fibroblasts between; located in tendons and cornea; functions: withstand stretch in one direction.
- Irregular White Fibrous: Irregularly arranged collagen bundles with fibroblasts between; located in periosteum, perichondrium, dermis of skin, capsule of organs; functions: withstand stretch in different directions.
- Yellow Elastic: mainly elastic fibers; appears yellow in fresh state; located in the aorta, bronchi/bronchioles, and ligaments; function: recoil after stretch.
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Description
Test your knowledge on connective tissue, its origins, and the various types of cells involved. This quiz covers the fundamental concepts of how connective tissue supports and protects other tissues in the body. Explore the characteristics of fixed cells and their functions in both embryos and adults.
