Tissue

Introduction to Tissues

• Similar cells form tissues, which perform specific functions in the body
• Different tissue structures lead to differences in function
• The four major types of tissues in the human body are epithelial, connective, muscular, and nervous

Tissue Types

• Epithelial tissues create protective coverings and function in secretion and absorption
• Connective tissues support soft body parts to bind structures together
• Muscular tissues produce body movement
• Nervous tissue conducts impulses to control and coordinate body activities

General Tissue Characteristics

• Epithelial Tissue: Protection, secretion, absorption, excretion; covers body surface, internal organs
• Connective Tissue: Binds, supports, protects, fills spaces, stores fat, produces blood cells; widley distributed throughout body
• Muscle Tissue: Movement; attached to bones, walls of hollow internal organs, heart
• Nervous Tissue: Conducts impulses for coordination, regulation, integration, sensory reception; brain, spinal cord, nerves

Examining Tissues

• Micrographs are used to view the structure of tissue specimens under a microscope

Tissue Observation

• Tubular body structures appear as circles or ovals in cross or oblique sections under a microscope
• Longitudinal sections of tissues show rows of cells with an elongated space between them

Epithelial Tissue

• Epithelial tissues are widespread throughout the body
• They cover organs and the body surface lining cavities
• They also form glands
• Epithelial have an apical surface exposed to the outside or an open space
• They are anchored to underlying connective tissues by a basement membrane
• Tightly packed cells with minimal intercellular material compose this tissue
• They readily divide and replaced
• Epithelial tissues lack blood vessels but are nourished by cells in underlying connective tissues

Epithelial Functions

• Functions include protection, secretion, absorption, and excretion
• Cell shapes are squamous (thin, flattened), cuboidal (cube-shaped), or columnar (tall, elongated)
• May find simple (one layer) or stratified (two or more layers) arrangements
• Free surfaces can be modified with cilia or microvilli to reflect specific functions

Simple Squamous Epithelium

• Consists of a single layer of thin, flattened cells
• These cells are tightly packed together and have broad, thin nuclei
• Locations are in diffusion and filtration sites, the alveoli of the lungs, blood and lymph vessels, and body cavities
• Simple squamous epithelium is very delicate and easily damaged

Simple Cuboidal Epithelium

• Consists of a single layer of cube-shaped cells with centrally located nuclei
• Lines kidney tubules, covers ovaries, and lines ducts of some glands
• It participates in urine formation in the kidneys and glandular secretion
• Faces the lumen, a hollow channel when it lines tubules or ducts

Simple Columnar Epithelium

• Composed of one row of tall, elongated cells
• Nuclei are located near the basement membrane
• May be ciliated or nonciliated
• Lines the uterus, stomach, and intestines
• Protection of tissues, secretion of digestive fluids, and absorption of nutrients are key functions

Simple Columnar Structures

• Cilia are long extensions from the free surfaces of certain cells that beat in one direction to move cells or mucus
• Ciliated cells found in the uterine tubes, help move egg cells toward the uterus
• Microvilli, smaller than cilia, increase surface area for absorption
• Goblet cells secrete mucus onto the tissue surface for lubrication and protection
• Goblet cells are scattered among the simple columnar cells

Pseudostratified Columnar Epithelium

• Appears layered because the nuclei sit at varying postitions, they are not truly layered
• Cells vary in shape
• All cells reach basement membrane, but not all reach the free surface
• Most contain cilia along their free surface
• Goblet cells scattered among the epithelial cells secrete mucus
• These tissues are located in the passageways of the respiratory system
• Mucus in the respiratory tract traps microorganisms and dust, which cilia sweep away

Stratified Squamous Epithelium

• Made up of many layers of cells
• Protects deeper tissues
• Named for the shape of the outermost layers of cells, which always consist of squamous cells
• Cell in the deeper layers of tissue can be cuboidal

Stratified Squamous Characteristics

• Makes up the outer layer of skin (epidermis), mouth lining, esophagus, vagina, and anal canal
• The outer layers of skin cells undergo keratinization, producing a dry, waterproof protective layer made of dead cells
• Keratinization does not occur in tissues that need to stay moist and alive, such as the oral cavity, esophagus, vagina, and anal canal

Stratified Cuboidal Epithelium

• Composed of two to three layers of cuboidal cells
• Forms the lining of a lumen
• Offers greater protection than a single cell layer
• Lines the ducts of mammary glands, sweat glands, salivary glands, pancreas, ovarian follicles, and seminiferous tubules

Stratified Columnar Epithelium

• Consists of several layers of cells
• Surface cells are columnar and basal layers mainly consist of cuboidal cells
• Rare tissue type
• Found in the male urethra and linings of large gland ducts

Transitional Epithelium

• It expands (stretch) and return to its normal size in response to changing tension
• Transitional lines the urinary bladder, urethra, and ureters
• Upon contraction, several layers of irregularly-shaped cells make up tissues of the urinary organs
• Cells elongate upon distension
• Its function includes expansion and prevention of urine from diffusing back into the internal environment

Types of Epithelial Function and Location

• Simple Squamous Epithelium: Filtration, diffusion, osmosis; covers surface; air & lung sacs
• Simple Cuboidal Epithelium: Protection, secretion; surface of ovaries, kidney tubule
• Simple Columnar Epithelium: Protection, secretion, absorption; uterous lining, stomach
• Pseudostratified Columnar Epithelium: Protection, secretion, movement of mucus; Lining of respiratory passages
• Stratified Squamous Epithelium: Prtection; vagina lining, superficial layer of skin
• Stratified Cuboidal Epithelium: Protection; lining of salivary glands, sweat glands
• Stratified Columnar Epithelium: Protection secrection; male eurethra part
• Transistional Epithelium: Stretchability, protection; inner lining of bladder and urethra/uerters

Glands

• Organs composed of epithelial tissues
• Made up of cuboidal or columnar cells
• Produce and secrete substances into ducts or into body fluids

Exocrine Glands

• Secrete products into ducts that open onto a body surface

Endocrine Glands

• Release products into body fluids or blood

Classification of Exocrine Glands by Secretion

• Merocrine glands are the most common type that release fluid products by exocytosis
• Apocrine glands pinch off a portion of their cell bodies during secretion
• Holocrine glands release entire cells that disintegrate to release their secretions

Secretion Types

• Merocrine: a watery serous fluid, sometimes with high enzyme concentration
• Mucous: a thicker, protective substance
• Some merocrine glands are serous; secrete serous fluid
• Pancreas, salivary glands, sweat glands produce mucous

Apocrine and Holocrine

• Apocrine example: Mammary glands produce cellular product portions with secretion
• Holocrine example: Sebaceous (oil) glands produces disintergrated entire cells with secretory products

Connective Tissues

• Bind, support, protect, serve as frameworks, fill spaces, store fat, produce blood cells, protect against infection, and repair tissue damage
• Connective tissue cells lie far apart from each other unlike epithelial tissue
• Rich in extracellular matrix, or intercellular material, composed of protein fibers and ground substance

Connective Tissue Characteristics

• Consistency varies from liquid to rigid, based on ground substance
• Most connective tissues can divide
• Most have a rich blood supply with the exception of cartilage

Cell Categories

• Categories of connective tissue cells can be fixed or wandering
• Fixed cells stay in the tissue for a long time
• Wandering cells move through tissues in response to infection or injury or stay in a tissue temporarily

Connective Tissue Cells

• Fibroblasts produce fibers and are the most common fixed cell type
• Macrophages (histiocytes) are phagocytes that defend against infection and foreign particles
• Mast cells are large, fixed cells
• Mast cells release heparin (anticoagulant) and histamine (promotes inflammation)
• Mast cells are located near blood vessels

Connective Tissue components

• Collagen fibers are thick threads of collagen protein
• Collagen has high tensile strength to hold structures together
• Collagen commonly found in long, parallel bundles, with some elasticity
• Examples tissues of collagen includes tendons and ligaments
• Elastic fibers are made of the protein elastin and are stretchy
• Elastic fibers are found in thin branching fibers arranged in a network that adds flexibility
• Example tissue of elastic fiber: vocal cords
• Reticular fibers are thin collagen fibers that form branching, supportive networks
• Example of reticular fibers: Spleen

General Components of Connective Tissue

• Cellular components includes fibroblasts that produce fibers
• Macrophages carry out phagocytosis
• Mast cells secrete heparin and histamine
• Extracellular matrix components includes collagen fibers to hold great tensile strength
• Elastic fibers stretches easily
• Reticular fibers give delicated support
• Ground substance composes the fiber space around cells

Types of Connective Tissue

• Connective tissue proper: loose
• Loose connective tissue
• Dense connective tissue
• Specialized connective tissue: rigid
• Cartilage
• Bone
• Blood

Loose Connective Tissue

• Areolar tissue: thin delicate membranes, fibroblasts, gel ground of collagen and fibers
• Adipose tissue: contains adipocytes which store fat in cytoplasm, cushions
• Reticular connective tissue: contains thin reticular fibers, forms a dimensional network

Areolar Tissue

• Forms thin, delicate membranes
• Main cell type is fibroblasts
• Matrix consists of a gel-like ground substance containing collagen and reticular fibers
• Locations are between muscles, under skin, underlies epithelial layers

Adipose Tissue

• Contains adipocytes store fat in cytoplasm
• Underlies skin, between muscles, around organs kidney/eyeball
• Cushions joints and organs and provides body insulation
• Key functions are to stores energy

Reticular Connective Tissue

• Contains thin, reticular fibers
• Forms a 3-dimensional network
• Forms a framework for certain internal organs like the liver and spleen

Dense Connective Tissue

• Consists of densely packed collagen fibers and a network of elastic fibers
• Has few cells with most being fibroblasts
• Collagen fibers of dense connective tissue can withstand strong pulling forces
• Has a poor blood supply, which affects healing
• Tendonds and ligaments also constrict, includes deep skin and white sclera of eyes

Cartilage

• A rigid connective tissue
• Gives supportive framework for body
• Lacks a vascular system, so it heals slowly and cells do not divide frequently
• Has collagen fibers in a gel-like ground substance

Components of Cartilage

• Chondrocytes (cartilage cells) lie within lacunae (chambers) in the matrix
• Cartilaginous structures are enclosed within a connective tissue covering called the perichondrium

Types of Cartilage

• Hyaline cartilage: common cartilage with fine collagen fibers
• Elastic cartilage: network, flexibile
• Fibrocartilage: many collagen fiber strands

Hyaline Tissue

• Appearance is glassy
• Fine collagen strands of fiber is apparent throughout matrix
• Ends of bones and supports respiratory passages

Elastic Tissue

• Location: Framework of the external ears and parts of the larynx
• Has network of elastic fibers in a flexible network

Fibrocartilage Tissue

• Shock absorber
• Common between intervertebral discs, knees and knee joints

Bone (Osseous Tissue)

• Rigid connective tissue due to mineral salts
• Mineral includes calcium strands
• Collagen fibers in matrix, has some flexibilty
• Functions include muscle attachment, blood cell formation, stores and releases chemicals

Compact and Spongy Bone

• Compact and spongy are two bones
• Composed of osteocytes bone cells within lacunae chambers
• Units of bone is arranged in concentric circles are lamellae central/haversian canals
• Cylinder form are Haversian systems
• Good blood vessel system, with tiny tubes called canaliculi

Blood

• Transports substances throughout the body
• Transports substances between interior cells and cells that exchange nutrients, gases, and wastes with the environment
• Plasma forms elements suspended in a liquid matrix
• Red blood cells give oxygen, white blood cells protect infections and platelets helps form blood clots
• Most blood cells are produced by the red bone marrow within certain long bones

Types of Connective Tissue Function and Location Information

• Areolar: Binds organs; between muscles, under tissues and skin
• Adipose: Stored fat, protects, insulates; around kidney, eyeball, heart surface
• Reticular: Structures support; inside organs
• Dense: Structures bind; Ligaments under skin
• Hyaline: Supports, protects, provides framework; End of bones around nose/air passages
• Elastic: Supports, protects, provides flexible framework; Structure around ears, larynx
• Fibrocartilage: Supports, protects, absorbs shock; Under bones around knees, discs around pelvic girdle
• Bone: supports, absorbs shock; skeleton
• Blood: Transports substance, helps internal health; Body circulation/vessels

Membranes

• There exist 4 types of membranes in the body which are epithelial and connective

Epithelial Membranes

• Includes epithelial with connective tissues
• Has surfaces that covers surfaces, cavities and linings
• Serous membranes
• Mucous membranes
• Cutaneous membrane

Serous membranes

• Do not open to the outside (thoracic and abdominal cavities)
• Examples: pleura, pericardium, the peritoneum, the lining of our abdominal cavity and organs
• Double-layered, includes Parietal outer portion
• Visceral covers organs Small amount of lubricating serous fluid helps lubricate the walls

Mucous Membrane

• Has tubes that open to the outside of the body
• Includes the digestive, respiratory, urinary, and reproductive systems
• There exist a goblet cell mucous produce

Cutaneous Membrane and its qualities

• The skin outer lining/membrane
• Waterproofing and protections

Muscle Tissues

• Muscle cells, or muscle fibers, have ability to generate force
• Contract and shorten to provide movement of body
• Three types includes skeletal, smooth and cardiac
• Body is 40% skeletal muscle, 10% smooth and cardiac

Skeletal Muscle Information

• Attach to bones, so is controllable by conscious effort
• Is long + cylindrical in shape in addition has many nuclei
• Only contracts because of nerve cells (neurons)
• Structures that this muscle support is head, limbs and trunk

Smooth Muscle Info

• Lacks striations, found in blood system and hollow organs
• Spindle shape, with one singular nucleus
• Involuntary

Cardiac Muscle

• Only in heart/muscle type
• Only one sole nucleus in cells (fibers)
• Linked by intercalated discs from cell to cell
• Involuntary, as well is striated

Muscle Types Quick Overview

• Skeletal (striated): Voluntary movement of skeleton parts
• Smooth: (Lacks striations) Involuntary movement of organs; walls of hallow vessels and organs
• Cardiac(Striated): Contraction for heart beats; heart muscle

Types of Muscle Tissues Function and Location Information

• Skeletal: voluntary movements of skeletal parts usually attached to bones.
• Smooth: Involuntary movements of internal organs walls of hollow internal organs.
• Cardiac: Contraction for heart beats heart muscle.

Nervous Tissue

• Brain, spinal cord and nerves consist of such
• Neurons or nerve cells conducts responses to specific stimuli to form electrical impulses
• These impulses reach, glands/neruons or muscles
• Each soma consists of a cell body, and processes called dendrites (stimuli) and axons (signal)
• Neuroglia are cells that support and nourish neurons