HISTOLOGY Lecture TWO DR. ASHRAF SAID

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TISSUES

TISSUE: A DEFINITION A group of connected and interdependent cells that cooperate to perform a specific function

CONNECTIVE TISSUE The Major Structural Constituents of The Body

Categories of Tissue 1. Epithelial Tissue 2. Connective Tissue 3. Muscle Tissue 4. Nervous Tissue

Function of CT Responsible for: providing & maintaining form in the body. Provide a matrix that connects and binds: cells & organs and ultimately supports body.

Components of CT Cells Extracellular matrix Fibers Collagenous, reticular, elastic Ground substance Hydrophilic macromolecules (glycoproteins, glycosaminoglycans, proteogycans) bind to receptors on cells & add strength and rigidity to matrix

Origins of CT Mesenchyme Embryonic undifferentiated tissue Develops from mesoderm Cells migrate from origins penetrate & surround organs Develop into other types of structures: blood cells Muscles bones

Embryonic Mesenchyme

CT Cells Fibroblasts Differentiate from mesenchyme Remain local Synthesis of all fibers Synthesis of all ground substance. Mast cells* Contain granules with: Histamine Heparin Leukotrienes. Macrophages* (histiocytes) Phagocytosis Plasma cells* Derived from lymphocytes Produce antibodies. * Originate from hematopoietic stem cells in bone marrow, circulate in blood, move to CT where they remain and perform their functions

Fibroblasts (inactive) Synthesize collagen, elastin and macromolecules of ground substance. Rarely undergo division.

Macrophages Characterized by phagocytic ability Morphological features correspond to activity they inhabit. to tissue they inhabit. Derived from bone marrow cells (monocytes): that circulate in blood Mature leave vessels & enter organs. Long-living cells (months) Become Kupffer cells in liver Microglial cells in CNS Osteoclasts in bone.

Mast Cells Function storage of chemical mediators of the inflammatory response. Contain many secretory granules. Release histamine Release heparin Release leukotrienes Receptors on cell surface allow binding of IgE

Mast cells

Extracellular matrix Fibers Ground substance

Fibers Collagenous Reticular Elastic

Collagenous Fibers Collagenous Most common protein in the body (30% of dry weight) Stain pink with eosin Stain blue with Mallory s trichrome Stain green with Masson s trichrome Make up: mesenteries Tendons Cartilage Ligaments lamina propria Every organ.

Collagenous Fibers (Dense Irregular CT)

Reticular Fibers Reticular Are not stained by H&E Stain black with silver Very delicate Hold cells together in organs. Provide framework for: Spleen Lymph nodes Red bone marrow Liver, Endocrine glands. Makes flexible network in: Arteries Intestinal muscle layer Uterus

Reticular CT (Adrenal Cortex)

Reticular Fibers

Reticular CT

Elastic Fibers Stretchable, highly resistant to pulling forces. Found in arteries, cartilage, mesenteries

Collagen, Elastic Fibers (Areolar CT)

Extracellular Matrix Fibers Collagenous (collagen) Reticular (collagen) Elastic (elastin) Amorphous ground substance Gel-like matrix in which fibers, cells are embedded and through which fluid diffuses. Tissue fluid

ADULT CT CT proper Loose Reticular Adipose Dense irregular Dense regular Collagenous Elastic Specialized CT Cartilage Bone Blood

Loose (Areolar) Conn Tissue Structure Many cells Jello-like matrix Collagen + elastic fibers

Binding Tissue Function: Binds organ parts together Sample Locations: Skin, kidney, lungs

Loose CT

Elastic, Reticular Fibers

Dense Irregular CT

Section of rat skin. The subepithelial connective tissue (dermis) is loose connective tissue. In this area, the cells, most of which are fibroblasts, are abundant. The deepest part of the dermis consists of dense irregular connective tissue, which contains many randomly oriented thick collagen fibers, scarce ground substance, and few cells. H&E stain. Medium magnification. (Courtesy of TMT Zorn.)

Elastic Connective Tissue

Dense Regular C T Structure Few cells Dense matrix Aligned collagen fibers

DENSE CT

Tendons

E-P-M

Elastic, Reticular Fibers

Dense Irregular CT

Epididymis Pseudostratified microvilli

ELASTIC CARTILAGE

Loose CT