Anatomy & Physiology
Tissues/Histolgy
Tissues
• Groups of cells similar in structure and function
• The four types of tissues
• Epithelial
• Connective
• Muscle
• Nerve
Epithelial Tissue
• Cellularity – composed almost entirely of cells
• Special contacts – form continuous sheets held together by tight junctions and desmosomes
• Polarity – apical and basal surfaces
• Supported by connective tissue – reticular and basal laminae
• Avascular but innervated – contains no blood vessels but supplied by nerve fibers
• Regenerative – rapidly replaces lost cells by cell division
Classification of Epithelia
• Simple or stratified
• Squamous, cuboidal, or columnar
Epithelia: Simple Squamous
• Single layer of flattened cells with disc-shaped nuclei and sparse cytoplasm
• Functions
• Diffusion and filtration
• Provide a slick, friction-reducing lining in lymphatic and cardiovascular systems
• Present in the kidney glomeruli, lining of heart, blood vessels, lymphatic vessels, and serosae
Epithelia: Simple Cuboidal
• Single layer of cubelike cells with large, spherical central nuclei
• Function in secretion and absorption
• Present in kidney tubules, ducts and secretory portions of small glands, and ovary surface
Epithelia: Simple Columnar
• Single layer of tall cells with oval nuclei; many contain cilia
• Goblet cells are often found in this layer
• Function in absorption and secretion
• Nonciliated type line digestive tract and gallbladder
• Ciliated type line small bronchi, uterine tubes, and some regions of the uterus
Epithelia: Pseudostratified Columnar
• Single layer of cells with different heights; some do not reach the free surface
• Nuclei are seen at different layers
• Function in secretion and propulsion of mucus
• Present in the male sperm-carrying ducts (nonciliated) and trachea (ciliated)
Epithelia: Stratified Squamous
• Thick membrane composed of several layers of cells
• Function in protection of underlying areas subjected to abrasion
• Forms the external part of the skin’s epidermis (keratinized cells), and linings of the esophagus, mouth, and vagina (nonkeratinized cells).
Epithelia: Stratified Columnar
• Several cell layers with cuboidal basal cells and columnar superficial cells
• Functions in protection and secretion
• Present in large ducts of some glands, and in portions of the male urethra
Epithelia: Transitional
• Several cell layers, basal cells are cuboidal, surface cells are
dome shaped
• Stretches to permit
the distension of the urinary bladder
• Lines the urinary bladder, ureters, and part of the urethra
Glandular Epithelia
• A gland is one or more cells that makes and secretes an aqueous fluid
• Classified by:
• Site of product release – endocrine or exocrine
• Relative number of cells forming the gland – unicellular or multicellular
Endocrine Glands
• Ductless glands that produce hormones
• Secretions include amino acids, proteins, glycoproteins, and steroids
Exocrine Glands
• More numerous than endocrine glands
• Secrete their products onto body surfaces (skin) or into body cavities
• Examples include mucous, sweat, oil, and salivary glands
• The only important unicellular gland is the goblet cell
• Multicellular exocrine glands are composed of a duct and secretory unit
Multicellular Exocrine Glands
• Classified according to:
• Simple or compound duct type
• Structure of their secretory units
Modes of Secretion
• Merocrine – products are secreted by exocytosis (e.g., pancreas, sweat, and salivary glands)
• Holocrine – products are secreted by the rupture of gland cells (e.g., sebaceous glands)
Connective Tissue
• Found throughout the body; most abundant and widely distributed in primary tissues
• Connective tissue proper
• Cartilage
• Bone
• Blood
Functions of Connective Tissue
• Binding and support
• Protection
• Insulation
• Transportation
Characteristics of Connective Tissue
• Connective tissues have:
• Mesenchyme as their common tissue of origin
• Varying degrees of vascularity
• Nonliving extracellular matrix, consisting of ground substance and fibers
Structural Elements of Connective Tissue
• Ground substance – unstructured material that fills the space between cells
• Fibers – collagen, elastic, or reticular
• Cells – fibroblasts, chondroblasts, osteoblasts, and hematopoietic stem cells
Ground Substance
• Interstitial (tissue) fluid
• Adhesion proteins – fibronectin and laminin
• Proteoglycans – glycosaminoglycans (GAGs)
• Functions as a molecular sieve through which nutrients diffuse between blood capillaries and cells
Fibers
• Collagen – tough; provides high tensile strength
• Elastic – long, thin fibers that allow for stretch
• Reticular – branched collagenous fibers that form delicate networks
Connective Tissue: Fundamental Cell Type
• Fibroblasts – connective tissue proper
• Chondroblasts – cartilage
• Osteoblasts – bone
• Hematopoietic stem cells – blood
• White blood cells (WBCs), plasma cells, macrophages, and mast cells
Connective Tissue (CT): Embryonic
• Mesenchyme – embryonic CT
• Gel-like ground substance with fibers and star-shaped mesenchymal cells
• Gives rise to all other connective tissues
• Found in the embryo
Connective Tissue Proper: Loose
• Areolar CT
• Gel-like matrix with all three CT fibers
• Fibroblasts, macrophages, mast cells, and some WBCs
• Wraps and cushions organs
• Widely distributed throughout the body
Connective Tissue Proper: Loose
• Adipose CT
• Matrix similar to areolar CT with closely packed adipocytes
• Reserve food stores, insulates against heat loss, and supports and protects
• Found under skin, around kidneys, within abdomen,
and in breasts
Connective Tissue Proper: Loose
• Reticular CT
• Loose ground substance with reticular fibers
• Reticular cells lie in a fiber network
• Forms a soft internal skeleton, or stroma, that supports other cell types
• Found in lymph nodes, bone marrow, and the spleen
Connective Tissue Proper: Dense Regular
• Parallel collagen fibers with a few elastic fibers
• Major cell type is fibroblasts
• Attaches muscles to bone or to other muscles, and bone to bone
• Found in tendons, ligaments, and aponeuroses
Connective Tissue Proper: Dense Irregular
• Irregularly arranged collagen fibers with some elastic fibers
• Major cell type is fibroblasts
• Withstands tension in many directions providing structural strength
• Found in the dermis, submucosa of the digestive tract, and fibrous organ capsules
Connective Tissue: Cartilage
• Hyaline cartilage
• Amorphous, firm matrix with imperceptible network of collagen fibers
• Chondrocytes lie in lacunae
• Supports, reinforces, cushions, and resists compression
• Forms the costal cartilage
• Found in: embryonic skeleton, the end of long bones, nose, trachea, and larynx
• Elastic cartilage
• Similar to hyaline cartilage but with more elastic fibers
• Maintains shape and structure while allowing flexibility
• Supports external ear (pinna) and the epiglottis
• Fibrocartilage
• Matrix similar to hyaline cartilage but less firm with thick collagen fibers
• Provides tensile strength and absorbs compression shock
• Found in intervertebral discs, the pubic symphysis, and in discs of the knee joint
Connective Tissue: Bone (Osseous Tissue)
• Osseous tissue
• Hard, calcified matrix with collagen fibers found in bone
• Osteocytes are found in lacunae and are well vascularized
• Supports, protects, and provides levers for muscular action
• Stores calcium, minerals, and fat
• Marrow inside bones is the site of hematopoiesis
Connective Tissue: Blood
• Blood
• Red and white cells in a fluid matrix (plasma)
• Contained within blood vessels
• Functions in the transport of respiratory gases, nutrients, and wastes
Epithelial Membranes
• Cutaneous – skin
• Mucous – lines body cavities open to the exterior
(e.g., digestive and respiratory tracts)
• Serous – moist membranes found in closed ventral body cavity
Nervous Tissue
• Branched neurons with long cellular processes and support cells
• Transmits electrical signals from sensory receptors to effectors
• Found in the brain, spinal cord, and peripheral nerves
Muscle Tissue: Skeletal
• Long, cylindrical, multinucleate cells with obvious striations
• Initiates and controls voluntary movement
• Found in skeletal muscles that attach to bones or skin
Muscle Tissue: Cardiac
• Branching, striated, uninucleate cells interdigitating at intercalated discs
• Propels blood into the circulation
• Found in the walls of the heart
Muscle Tissue: Smooth
• Sheets of spindle-shaped cells with central nuclei that have no striations
• Propels substances along internal passageways (i.e., peristalsis)
• Found in the walls of hollow organs
Tissue Trauma
• Causes inflammation, characterized by:
• Dilation of blood vessels
• Increase in vessel permeability
• Redness, heat, swelling, and pain
Tissue Repair
• Organization and restored blood supply
• The blood clot is replaced with granulation tissue
• Regeneration and fibrosis
• Surface epithelium regenerates and the scab detaches
• Fibrous tissue matures and begins to resemble the adjacent tissue
• Results in a fully regenerated epithelium with underlying scar tissue
Developmental Aspects
• Primary germ layers: ectoderm, mesoderm, and endoderm
• Three layers of cells formed early in embryonic development
• Specialize to form the four primary tissues
• Nerve tissue arises from ectoderm
• Muscle, connective tissue, endothelium, and mesothelium arise from mesoderm
• Most mucosae arise from endoderm
• Epithelial tissues arise from all three germ layers
M.khadar Ali MD
Tissues
• Groups of cells similar in structure and function
• The four types of tissues
• Epithelial
• Connective
• Muscle
• Nerve
Epithelial Tissue
• Cellularity – composed almost entirely of cells
• Special contacts – form continuous sheets held together by tight junctions and desmosomes
• Polarity – apical and basal surfaces
• Supported by connective tissue – reticular and basal laminae
• Avascular but innervated – contains no blood vessels but supplied by nerve fibers
• Regenerative – rapidly replaces lost cells by cell division
Classification of Epithelia
• Simple or stratified
• Squamous, cuboidal, or columnar
Epithelia: Simple Squamous
• Single layer of flattened cells with disc-shaped nuclei and sparse cytoplasm
• Functions
• Diffusion and filtration
• Provide a slick, friction-reducing lining in lymphatic and cardiovascular systems
• Present in the kidney glomeruli, lining of heart, blood vessels, lymphatic vessels, and serosae
Epithelia: Simple Cuboidal
• Single layer of cubelike cells with large, spherical central nuclei
• Function in secretion and absorption
• Present in kidney tubules, ducts and secretory portions of small glands, and ovary surface
Epithelia: Simple Columnar
• Single layer of tall cells with oval nuclei; many contain cilia
• Goblet cells are often found in this layer
• Function in absorption and secretion
• Nonciliated type line digestive tract and gallbladder
• Ciliated type line small bronchi, uterine tubes, and some regions of the uterus
Epithelia: Pseudostratified Columnar
• Single layer of cells with different heights; some do not reach the free surface
• Nuclei are seen at different layers
• Function in secretion and propulsion of mucus
• Present in the male sperm-carrying ducts (nonciliated) and trachea (ciliated)
Epithelia: Stratified Squamous
• Thick membrane composed of several layers of cells
• Function in protection of underlying areas subjected to abrasion
• Forms the external part of the skin’s epidermis (keratinized cells), and linings of the esophagus, mouth, and vagina (nonkeratinized cells).
Epithelia: Stratified Columnar
• Several cell layers with cuboidal basal cells and columnar superficial cells
• Functions in protection and secretion
• Present in large ducts of some glands, and in portions of the male urethra
Epithelia: Transitional
• Several cell layers, basal cells are cuboidal, surface cells are
dome shaped
• Stretches to permit
the distension of the urinary bladder
• Lines the urinary bladder, ureters, and part of the urethra
Glandular Epithelia
• A gland is one or more cells that makes and secretes an aqueous fluid
• Classified by:
• Site of product release – endocrine or exocrine
• Relative number of cells forming the gland – unicellular or multicellular
Endocrine Glands
• Ductless glands that produce hormones
• Secretions include amino acids, proteins, glycoproteins, and steroids
Exocrine Glands
• More numerous than endocrine glands
• Secrete their products onto body surfaces (skin) or into body cavities
• Examples include mucous, sweat, oil, and salivary glands
• The only important unicellular gland is the goblet cell
• Multicellular exocrine glands are composed of a duct and secretory unit
Multicellular Exocrine Glands
• Classified according to:
• Simple or compound duct type
• Structure of their secretory units
Modes of Secretion
• Merocrine – products are secreted by exocytosis (e.g., pancreas, sweat, and salivary glands)
• Holocrine – products are secreted by the rupture of gland cells (e.g., sebaceous glands)
Connective Tissue
• Found throughout the body; most abundant and widely distributed in primary tissues
• Connective tissue proper
• Cartilage
• Bone
• Blood
Functions of Connective Tissue
• Binding and support
• Protection
• Insulation
• Transportation
Characteristics of Connective Tissue
• Connective tissues have:
• Mesenchyme as their common tissue of origin
• Varying degrees of vascularity
• Nonliving extracellular matrix, consisting of ground substance and fibers
Structural Elements of Connective Tissue
• Ground substance – unstructured material that fills the space between cells
• Fibers – collagen, elastic, or reticular
• Cells – fibroblasts, chondroblasts, osteoblasts, and hematopoietic stem cells
Ground Substance
• Interstitial (tissue) fluid
• Adhesion proteins – fibronectin and laminin
• Proteoglycans – glycosaminoglycans (GAGs)
• Functions as a molecular sieve through which nutrients diffuse between blood capillaries and cells
Fibers
• Collagen – tough; provides high tensile strength
• Elastic – long, thin fibers that allow for stretch
• Reticular – branched collagenous fibers that form delicate networks
Connective Tissue: Fundamental Cell Type
• Fibroblasts – connective tissue proper
• Chondroblasts – cartilage
• Osteoblasts – bone
• Hematopoietic stem cells – blood
• White blood cells (WBCs), plasma cells, macrophages, and mast cells
Connective Tissue (CT): Embryonic
• Mesenchyme – embryonic CT
• Gel-like ground substance with fibers and star-shaped mesenchymal cells
• Gives rise to all other connective tissues
• Found in the embryo
Connective Tissue Proper: Loose
• Areolar CT
• Gel-like matrix with all three CT fibers
• Fibroblasts, macrophages, mast cells, and some WBCs
• Wraps and cushions organs
• Widely distributed throughout the body
Connective Tissue Proper: Loose
• Adipose CT
• Matrix similar to areolar CT with closely packed adipocytes
• Reserve food stores, insulates against heat loss, and supports and protects
• Found under skin, around kidneys, within abdomen,
and in breasts
Connective Tissue Proper: Loose
• Reticular CT
• Loose ground substance with reticular fibers
• Reticular cells lie in a fiber network
• Forms a soft internal skeleton, or stroma, that supports other cell types
• Found in lymph nodes, bone marrow, and the spleen
Connective Tissue Proper: Dense Regular
• Parallel collagen fibers with a few elastic fibers
• Major cell type is fibroblasts
• Attaches muscles to bone or to other muscles, and bone to bone
• Found in tendons, ligaments, and aponeuroses
Connective Tissue Proper: Dense Irregular
• Irregularly arranged collagen fibers with some elastic fibers
• Major cell type is fibroblasts
• Withstands tension in many directions providing structural strength
• Found in the dermis, submucosa of the digestive tract, and fibrous organ capsules
Connective Tissue: Cartilage
• Hyaline cartilage
• Amorphous, firm matrix with imperceptible network of collagen fibers
• Chondrocytes lie in lacunae
• Supports, reinforces, cushions, and resists compression
• Forms the costal cartilage
• Found in: embryonic skeleton, the end of long bones, nose, trachea, and larynx
• Elastic cartilage
• Similar to hyaline cartilage but with more elastic fibers
• Maintains shape and structure while allowing flexibility
• Supports external ear (pinna) and the epiglottis
• Fibrocartilage
• Matrix similar to hyaline cartilage but less firm with thick collagen fibers
• Provides tensile strength and absorbs compression shock
• Found in intervertebral discs, the pubic symphysis, and in discs of the knee joint
Connective Tissue: Bone (Osseous Tissue)
• Osseous tissue
• Hard, calcified matrix with collagen fibers found in bone
• Osteocytes are found in lacunae and are well vascularized
• Supports, protects, and provides levers for muscular action
• Stores calcium, minerals, and fat
• Marrow inside bones is the site of hematopoiesis
Connective Tissue: Blood
• Blood
• Red and white cells in a fluid matrix (plasma)
• Contained within blood vessels
• Functions in the transport of respiratory gases, nutrients, and wastes
Epithelial Membranes
• Cutaneous – skin
• Mucous – lines body cavities open to the exterior
(e.g., digestive and respiratory tracts)
• Serous – moist membranes found in closed ventral body cavity
Nervous Tissue
• Branched neurons with long cellular processes and support cells
• Transmits electrical signals from sensory receptors to effectors
• Found in the brain, spinal cord, and peripheral nerves
Muscle Tissue: Skeletal
• Long, cylindrical, multinucleate cells with obvious striations
• Initiates and controls voluntary movement
• Found in skeletal muscles that attach to bones or skin
Muscle Tissue: Cardiac
• Branching, striated, uninucleate cells interdigitating at intercalated discs
• Propels blood into the circulation
• Found in the walls of the heart
Muscle Tissue: Smooth
• Sheets of spindle-shaped cells with central nuclei that have no striations
• Propels substances along internal passageways (i.e., peristalsis)
• Found in the walls of hollow organs
Tissue Trauma
• Causes inflammation, characterized by:
• Dilation of blood vessels
• Increase in vessel permeability
• Redness, heat, swelling, and pain
Tissue Repair
• Organization and restored blood supply
• The blood clot is replaced with granulation tissue
• Regeneration and fibrosis
• Surface epithelium regenerates and the scab detaches
• Fibrous tissue matures and begins to resemble the adjacent tissue
• Results in a fully regenerated epithelium with underlying scar tissue
Developmental Aspects
• Primary germ layers: ectoderm, mesoderm, and endoderm
• Three layers of cells formed early in embryonic development
• Specialize to form the four primary tissues
• Nerve tissue arises from ectoderm
• Muscle, connective tissue, endothelium, and mesothelium arise from mesoderm
• Most mucosae arise from endoderm
• Epithelial tissues arise from all three germ layers
M.khadar Ali MD
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