Chapter 4: Histology Flashcards
Histology
Study of normal structures of tissues
All tissues share what two basic components?
- Discrete population of cells, related in structure and function
- Extracellular matrix (ECM)
Types of tissue
- Epithelial tissue (epithelium)
- Connective tissue
- Muscle tissue
- Nervous tissue
Epithelial tissue (epithelium)
- Covers a surface of lines cavities of the body
- Also forms glands
Connective tissue
Connects, supports, protects, insulates, and transports
Muscle tissue
Contracts to produce movement
Nervous tissue
Produces and conducts nervous impulses
Extracellular matrix
Substances in liquid, thick gel, or solid form that surrounds cells of tissue
Components of extracellular matrix
- Ground substance
- Protein fibers
Functions of extracellular matrix
- Provides tissue with strength to resist tensile and compressive forces
- Directs cells to proper positions within tissue and holds those cells in place
- Regulates development, mitotic activity, and survival of cells in a tissue
Ground Substance
- Most of the ECM
- Extracellular fluid (ECF or interstitial fluid) with water, nutrients, ions, and three families of macromolecules
Families of macromolecules in ground substance
- Glycosaminoglycans (GAGs)
- Proteoglycans
- Cell-adhesion molecules (CAMs)
Glycosaminoglycans (GAGs)
Chondroitin sulfate (small) and hyaluronic acid
Proteoglycans
GAGs bound to protein core (resembles bottle brush)
- Thousands of proteoglycans bind to very long GAG to form huge proteoglycan “aggregates”
Cell-adhesion molecules (CAMs)
- Difference types of glycoproteins
- Adhere cell to cell and cells to surroundings
- Hold everything in place within ECM
- CAMs bind to cell surface proteins as well as protein fibers and proteoglycans
- Maintains normal tissue architecture
Types of protein fibers in ECM
- Collagen
- Reticular
- Elastic
Collagen Fibers
- Most common protein in body
- Strong, flexible, inelastic
- Unbranched and arranged in bundles
Reticular Fibers
- Fills spaces between tissues and organs
- Fine callagenous
- Forms branching networks
Elastic Fibers
- Returns to its original shape after distension or compression
- Contains molecules of protain elastic that resemble coiled springs
- Molecules are cross-linked
Cell Junctions
A way cells bind to one another
Integral Proteins
Proteins which link neighboring cell’s plasma membranes
Types of cell junctions
- Tight junctions
- Desmosomes
- Gap junctions
Tight Junctions
Holds cells together, forms permeability barrier
Zonula Adherens
- Between adjacent cells, weak glue holds cells together
- Simple epithelium
Zonula Occludens
- Permeability barrier (e.g. stomach and urinary bladder)
- Chemicals cannot pass between cells
Gap Junctions
- Protein channels aid intercellular communication
- Allows ions and small molecules to pass through
- Coordinate function of cardiac and smooth muscle
- May help coordinate movement of cilia in ciliated types of epithelium
Desmosomes
- Disk-shaped regions of cell membrane
- Often found in areas that are subjected to stress, can resist stretching and twisting
- Contains especially adhesives glycoproteins
- Intermediate protein filaments extend into cytoplasm of cells for reinforncement
- Striated squamous epithelium of the skin
Hemidesmosomes
- Half of a desmosome
- Attaches epithelial cells to basement membrane
Where are epithelial tissues located?
- On EVERY internal and external body surface
- Barrier between body and external environment
- Lines organs and fluid-filled cavities
Functions of Epithelial Tissue
- Protection: shields underlying tissues from mechanical and thermal injury
- Immune defenses: forms physical barriers to prevent invasion by microorganisms
- Secretion: forms glands that produce substances like hormones and oils; secreted into blood or through ducts respectively
- Transport into other tissues: selectively permeable membranes; substances are able to cross these barriers via passive or active transport and enter other tissues
- Sensation: most associated with rich nerve supply; detects changes in internal and external environments
What are the implications of the avascular nature of epithelial tissue?
- They must obtain oxygen and nutrients by diffusion from deeper tissues
- This requirement limits thickness
Components of basement membrane
- Basal lamina
- Reticular lamina
- Together these layers glue epithelial tissue and provide a barrier to underlying connective tissue
Basal Lamina
- ECM synthesized by epithelial cells
- Consists of collagen fibers and ground substance
Reticular Lamina
- Synthesized by underlying connective tissue
- Consists of reticular fibers and ground substance
Criteria for classifying epithelial tissue
- Number of cell layers
- Shape of cells
Simple epithelia
Single cell layer
Stratified epithelia
More than one cell layer
Squamous cells
Flattened
Cuboidal cells
Short
Columnar cells
Tall and elongated
Classifications of epithelial tissue
- Simple squamous
- Simple cuboidal
- Simple columnar
- Stratified squamous
- Stratified cuboidal
- Stratified columnar
Simple Squamous Structure
Single layer of flat cells
Simple Squamous Location
Lining of : - Blood vessels Lymphatic vessels and small ducts - Alveoli of lungs - Loop of Henle in kidney tubules - Serous membrane - Inner surface of the eardrum
Simple Squamous Functions
- Diffusion
- Filtration
- Some protection against friction
- Secretion
- Absorption
Simple Cuboidal Location
- Kidney tubules
- Sweat glands and their ducts
- Choroid plexus of the brain
- Lining of terminal bronchioles
- Surface of the ovaries
Simple Cuboidal Structure
- Single layer of short cells
- Some types have microvilli (kidney tubules)
Simple Cuboidal Functions
- Secretion and absorption in the kidney
- Secretion in glands and choroid plexus
- Movement of mucus out of the terminal
Simple Columnar Location
- Stomach
- Intestines
- Glands and some ducts
- Bronchioles of lungs
- Auditory tubes
- Uterus
- Uterine tubes
- Gallbladder
- Bile ducts
- Ventricles of the brain
Simple Columnar Structure
- Single layer of tall, narrow cells
- Some have cilia or microvilli
Simple Columnar Functions
- Secretion and absorption in stomach and the intestine
- Movement of particles out of the bronchioles by ciliated cells
- Aids in movement of oocytes in the uterine tubes by ciliated cells
Pseudostratified Columnar Epithelium
- Appears layered because nuclei are at various heights
- Only one layer thick with basal plasma membranes
- Found in trachea and nasal cavity
- Ciliated
Stratified Squamous Locations
- Mouth
- Tongue
- Throat
- Larynx
- Esophagus
- Anus
- Vagina
- Inferior urethra
- Cornea
Stratified Squamous Structure
Multiple layers of flat cells
Stratified Squamous Functions
Protection against abrasion, caustic chemicals, water loss, and infection
Keratinized
Skin
Stratified Cuboidal Location
- Sweat gland ducts
- Ovarian follicular cells
- Salivary gland ducts
Stratified Cuboidal Structure
Multiple layers of somewhat cube-shaped cells
Stratified Cuboidal Functions
Secretion, absorption, and protection
Stratified Columnar Location
- Salivary glands
- Mammary gland duct
- Larynx
- Portion of male urethra
Stratified Columnar Structure
- Multiple layers of cells with tall thin cells resting on layers of more cuboidal cells
- Cells ciliated in the larynx
Stratified Columnar Function
Protection and secretion
Transitional Epithelium Location
Lining of urinary bladder, ureters, and superior urethra
Transitional Epithelium Structure
- Stratified
- Cells change shape depending upon amount of stretching or distention of the organ
Gland
- Structure of epithelial origin
- Synthesizes and secretes product from designated secretory cells
- Arises from epithelial tissue that migrated into deeper connective tissue instead of remaining at the surface
- Classified by shape or by how products are released
Endocrine Glands
Without ducts
Exocrine Glands
With ducts
Secretion Types
- Merocrine
- Apocrine
- Holocrine
Merocrine Glands
- No loss of cytoplasm
- Secretion leaves by either active transport or exocytosis
- EX: sweat glands
Apocrine Glands
- Fragments of the gland go into the secretion
- Apex of cell pinches off
- EX: mammary glands
Holocrine Glands
- Cell ruptures and dies
- Whole cell becomes part of secretion
- Secretion accumulates in cell
- EX: Sebaceous glands
Types of Connective Tissue
- Connective tissue proper
- Fluid connective tissue
- Supporting connective tissue
Types of connective tissue proper
- Loose (areolar)
- Dense
- Reticular
- Adipose
Types of fluid connective tissue
- Blood
- Lymph
Types of supporting connective tissue
- Cartilage
- Bone
Connective Tissue Functions
- Connecting and binding: anchor tissue layers in organs and link organs together
- Support: bone and cartilage support body weight
- Protection: bones protect internal organs, cartilage and fat absorb shock
- Transport: blood
Connective tissue proper
- Syrupy ground substance
- Contains varied cell populations
- Various fiber types
Fluid connective tissue
- Dense ground substance
- Less diverse cell population
Supporting connective tissue
- Watery ground substance with dissolved proteins
Blasts
Create the matrix
Cytes
Maintain the matrix
Clasts
Break the matrix down for remodeling
Hyaluronic acid
- Polysaccharide
- Good lubricant
- Vitreous humor of the eye
Proteoglycans
- Protein and polysaccharide
- Protein part attaches to hyaluronic acid
- Traps large amounts of water
Adhesive molecules
- Hold proteoglycan aggregates together
Loose Connective Tissue
- Loose packing material of most organs and tissues
- AKA stroma
- Attaches skin to underlying tissues
- Contains collagen, reticular, elastic fibers, and all five types of cells
- Cells include fibroblasts, mast cells, lymphocytes, adipose cells, and macrophages
What is included in the superficial fascia?
- Epidermis, dermis, and hypodermis or subcutaneous layer
Dense Regular Connective Tissue
- Parallel, tightly packed collagen fibers
- Has abundant collagen fibers that resist stretching
- Tendons and ligaments
Tendons
- Connects muscles to bones
- Fibers are not necessarily parallel
Ligaments
- Connects bones to bones
- Collagen often less compact, usually flattened
- Forms sheets or bands
Dense Irregular Collagenous Connective Tissue
- Collagen fibers arranged in a randomly oriented network
- Forms innermost layer of the dermis of the skin, scars, capsules of kidney and spleen
- Allows tissue to tolerate extension and recoil
- Elastic ligaments help stabilize the positions of the vertebrae in the spinal column
- In walls of elastic arteries
Reticular Connective Tissue
- Forms find 3D networks that support small structures (blood and lymphatic vessels) called stroma
- Mostly reticular fibers produced by fibroblasts
Adipose Connective Tissue
- Fat-storing adipocytes and surrounding fibroblasts and ECM
- Can increase in size to a point where fibroblasts and ECM are scarcely visible
Functions of adipose tissue
- Fat storage (major energy reserve of the body)
- Insulation (retains warmth)
- Shock absorption and protection
Types of adipose tissue
- Yellow
- Brown
Yellow Adipose Tissue
- Most abundant type, has wide distribution
- What at birth and yellows with age
Brown Adipose Tissue
Found only in specific areas of the body:
- Axillae, neck, and near kidneys
Cartilage Tissue
- Cells are called chondrocytes located in matrix-surrounded spaces called lacunae
- Avascular and no nerve supply
Ground substance of cartilage
Proteoglycans and hyaluronic acid with large amounts of water
Perichondrium
- Separates cartilage from surrounding tissues
- Dense irregular connective tissue that surrounds cartilage
- Fibroblasts of perichondrium can differentiate into chondroblasts
Types of cartilage
- Hyaline
- Fibrocartilage
- Elastic
Hyaline Cartilage
- Most common type
- Avascular
- Glassy appearance and contains collagen (not easily seen)
- Reduce friction and provide shape
Hyaline cartilage location
- B/t tips of ribs and bones of sternum
- Covering bone surfaces at synovial joints
- Supports larynx, trachea, and bronchi
- Forms part of nasal septum
Hyaline cartilage function
- Provides stiff but somewhat flexible support
- Reduces friction between bony surfaces
Fibrocartilage Structure
- Thick collagen fibers distributed in proteoglycan matrix
- Slightly compressible and very tough
Fibrocartilage Locations
- Found in areas of body where a great deal of pressure is applied to joints
- Knee, jaw, intervertebral disk
Fibrocartilage Functions
- Resists compression
- Prevents bone-to-bone contact
- Limits relative movement
Elastic Cartilage Structure
- Elastic and collagen fibers embedded in proteoglycans
- Rigid by elastic properties
Elastic Cartilage Locations
External ears and epiglottis
Elastic Cartilage Functions
- Involved in flexible support
- Avascular
Bone Connective Tissue
- Hard connective tissue composed of living cells (osteocytes) and mineralized matrix
Bone Matrix
- Gives strength and rigidity
- Allows bone to support and protect other tissues and organs
Types of bone
- Cancellous or spongy bone
- Compact bone
Osteocytes
- Osteoblasts that have surrounded themselves with ECM in lacunae
- Mature cells, mostly inactive
- Continue to make and secrete substances important for bone maintenance
Osteoblasts
- “Bone-builders” on outer surface of bones
- Closely associated with dense irregular collagenous connective tissue covering (periosteum)
- Carry out process of bone deposition
Osteoclasts
- Large, multinucleated bone destroyers
- Carry out process of bone resorption
- Secrete hydrogen ions enzymes that break down both inorganic and organic ECM
Hemopoietic Tissue
Forms blood cells, found in bone marrow
Types of bone marrow
- Red
- Yellow
Red bone marrow
- Hemopoietic tissue surrounded by a framework of reticular fibers
- Produces red and white cells
Yellow bone marrow
- Yellow adipose tissue
- As children grow, yellow marrow replaced much of red marrow
Blood
- ECM is fluid
- Plasma proteins
- Erythrocytes
- Leukocytes
- Platelets
Plasma proteins
- Not like fibers found in other connective tissues
- Smaller with a variety of functions, including transport of substances and blood clotting
Erythrocytes
Bind to and transport oxygen throughout body
Leukocytes
Function in immunity
Platelets
- Cell fragments
- Major role in blood clotting
Characteristics of muscle tissue
- Contracts or shortens with force
- Moves entire body and pumps blood
Types of muscle tissue
- Skeletal
- Cardiac
- Smooth
Skeletal Muscle
- Most attached to skeleton
- Some attached to other types of connective tissue
- Striated and voluntary
Cardiac Muscle
- Muscle of the heart
- No conscious control
- Cells are short, branched
- Striated and involuntary
Smooth Muscle
- Muscle associated with tubular structures and with the skin
- Flattened cells with one centrally located ovoid nucleus
- Neighboring cells are linked together by gap junctions
- Nonstriated and involuntary
Intercalated disc
- Dark line separating individual cardiac muscle cells
- Contains gap junctions and modified tight junctions
- Heart muscle contracts as unit
Nervous Tissue
- Makes up majority of brain, spinal cord, and nerves
- ECM is unique, ground substance has unique proteoglycans and contains few protein fibers
Main cell types in nervous tissue
- Neurons
- Neuroglial cells
Neurons
Capable of sending and receiving messages
Neuroglial Cells
- Performs various functions
- Supports neuron activities
- Able to dividid by mitosis
Functions of Neuroglial cells
- Anchoring neurons and blood vessels in place
- Monitoring composition of extracellular fluid
- Speeding up rate of nerve impulse transmission
- Circulating fluid surrounding brain and spinal cord
Types of membranes
- Mucous
- Serous
- Synovial
Mucous Membrane
- Secrete mucus
- Contains epithelium with goblet cells, basement membrane, lamina propria (sometimes with smooth muscle)
- Found in respiratory, digestive, urinary, and reproductive systems
Serous Membrane
- Simple squamous epithelium called mesothelium, basement membrane, thine layer of loose connective tissue
- Lines cavities not open to the exterior
Synovial Membrane
- Lines freely moveable joints
- Produces fluid rich in hyaluronic acid