Histology

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Histology

• Epithelial
• Connective
• Muscle
• Nervous

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Epithelial Tissue (General)

• Functions
• Protection
• Control permeability
• Specialized secretions via exocrine glands
• Structure
• Covers internal and external surfaces
• Cells bound closely together
• Exposed surface, surface attached to connective
  tissue by basement membrane
• Basement Membrane Network of protein fibers that
  forms barrier between epithelium and connective
  tissue
• Avascular obtain nutrients across attached
  surface
• Continual division of stem cells
• Damaged cells are continually replaced
• Epithelial cells only survive 1-2 days

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Intercellular Connections

• Protective barrier formed by Cell Adhesion
  molecules (CAMs) hold cells close together
• Tight Junctions
• Prevents passage of water and solutes
• Interlocking membrane proteins
• Basal adhesion belt binds cells together
• Gap Junctions
• Adjacent channel proteins form passageway for
  small molecules and ions to pass through
• Allows rapid cellular communication
• Desmosomes
• Durable interconnections
• 2 types
• Button desmosomes- small disk
• Hemidesmosomes half button shape

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Figure 4.2
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Apical Surface

• Microvilli
• Increase surface area
• Allow absorption and secretion
• Cilia
• Beat to move materials across surface

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Squamous Epithelium

• Simple Squamous
• Thin and flat cells, 1 Layer
• Function diffusion filtration
• Found forms capillary walls, lining air sacs of
  lungs, lining body cavities
• Stratified Squamous
• Thin and flat cells, More than 1 layer
• Function protection
• Found in places of mechanical stress, skin
  surface, lining tongue, mouth, esophagus, and
  anus

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Cuboidal Epithelium

• Simple Cuboidal
• Box shaped cells, 1 layer
• Function Secretion or absorption
• Found covering surface of ovaries, lining kidney
  tubules, salivary ducts, and pancreatic ducts
• Stratified Cuboidal
• Box shaped cells, more than 1 layer
• Function strengthen lumen walls
• Found ducts of large sweat glands, salivary
  glands, and pancreas

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Columnar Epithelial

• Simple Columnar
• Tall, rectangular cells, 1 layer
• Function absorption, secretion, protection
• Found Lines stomach, intestinal tract, excretion
  ducts, gall bladder
• Pseudostratified Columnar
• Single layer irregularly shaped cells (looks like
  multiple layers)
• Function protection, secretion
• Found Lining respiratory passageways, and
  auditory tubes

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Transitional Epithelial Tissue

• Transitional
• Numerous layers of rounded cells
• Function Withstands stretching
• Found Lines urinary bladder and portions of
  ureters and urethra

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Exocrine Glandular Epithelia

• Exocrine glands excrete secretions thru ducts
  onto surface
• Unicellular Goblet cells scattered among
  epithelial cells
• Multicellular Secretory sheet, classified by
  pattern of ducts
• ex mucin lining stomach
• Mode of Secretion
• Merocrine via exocytosis
• Ex. Skin Perspiration, Mucus Glands, Saliva,
• Apocrine lose cytoplasm and secretory product
• Ex. Mammary glands, Axillary Perspiration
• Holocrine cell fills with secretion then bursts
  and dies
• Ex. Sebaceous glands oils from base of hair

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Connective Tissues

• 3 Components
• Specialized cells
• Matrix that surrounds cells
• Protein Fibers
• Ground Substance (fluid)
• Functions (vary widely)
• Support Protect - framework
• Transport materials fluid with dissolved
  material
• Energy reserve fat in adipose tissue
• Defense responds to pathogens by releasing
  antibodies
• Highly Vascular
• Protect Organs

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Classification of Connective tissues 3 Types

• Connective Tissue Proper
• Syrupy ground matrix
• Ex. Loose (areolar, adipose) Dense (tendons
  ligaments)
• Fluid Connective tissue
• Cells suspended in watery ground substance
  w/dissolved proteins
• Ex. Blood Lymph
• Supporting Connective Tissue
• Dense ground substance
• Ex. Cartilage (Hyaline, Elastic, Fibrocartilage)
  and Bone

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Connective Tissue Proper Cell Types

• Fibroblasts
• Produce and maintain connective tissue fibers and
  ground substance
• Local maintenance repair
• permanent
• Macrophages
• Defense Engulf damaged cells and pathogens
• Release chemicals to stimulate immune response
• Fixed or migrating (reinforcement)
• Adipocytes
• Permanent fat cells
• Droplet of lipid pushes nucleus to side
• Mast Cells
• Mobile, found near blood vessels
• Have vesicles filled with chemicals to be
  released after an injury or infection

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Connective Tissue Fibers

• Collagen
• Long, straight, unbranched, flexible
• Elastic
• Protein elastin
• Wavy, branched, stretchy
• Reticular Fibers
• Thin, branching interwoven network

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Ground Substance

• Fills spaces between cells, surrounds fibers
• Connective tissue proper clear, colorless,
  syrupy to slow movement of pathogens

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Loose Connective Tissue

• Areolar Tissue
• Contains all cells and fibers of connective
  tissue proper
• Separates skin from muscles
• Provides padding
• Allows movement
• Extensive blood supply
• Adipose tissue dominated by adipose cells
• Behind eyes, kidneys, heart, abdomen, buttocks,
  and breasts

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Dense Connective Tissue

• Consists of mostly collagen fibers
• Regular collagen fibers are parallel
• Tendons connect skeletal muscle to bone
• Ligaments contain elastin, connect bone to bone
• Irregular meshwork of collagen fibers
• Provides support in many directions n (i.e.
  skin)

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Fluid Connective Tissues

• Blood
• Plasma- watery matrix w/dissolved proteins
• Red blood cell (rbc)
• White blood cells (wbc)
• Platelets
• Lymph
• Interstitial fluid (water and solutes) enters
  lymphatic vessels

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Supporting Connective Tissue Cartilage

• Cartilage gel w/embedded fibers
• Chondrocytes cells found in lacunae
• No blood vessels, therefore difficult to repair
• Types
• Hyaline tightly packed collagen fibers, tough
  but flexible
• Connects ribs to sternum, supports passageways of
  respiratory tract, covers bone surfaces in joints
• Elastic elastic fibers, resilient and flexible
• Flap of outer ear, epiglottis, auditory tube
• Fibrocartilage mostly collagen fibers, durable
  and tough
• Between vertebrae, between pubic bones, around or
  within joints

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Hyaline Cartilage
Elastic Cartilage
Fibrocartilage
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Supporting Connective Tissue Bone

• Osseous tissue Bone
• Matrix hard calcium and flexible collagen, very
  little ground substance
• Osteocytes found w/in lacunae
• Lacunae surround blood vessels
• Canaliculi extend from central (Haversian) canal

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Osseous Tissue
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Membranes

• Membranes - epithelia and connective tissues
  combine to form 4 types of membranes
• Mucous Membranes
• Serous membranes
• Cutaneous membranes
• Synovial membranes

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Mucous Membranes

• Mucosae line cavities with exterior contact
• Digestive, respiratory, reproductive, and urinary
  tracts
• Epithelial surfaces kept moist
• Ex.
• Simple columnar epithelia of dig. tract
• Stratified squamous epithelia of mouth
• Transitional epithelia of urinary tract

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Serous Membranes

• Minimizes friction when organ moves
• Line internal subdivisions of ventral body cavity
• Parietal lines inner surface of cavity
• Visceral lines outer surface or organs
• Simple epithelia supported by loose connective
  tissue
• Pleura covers pleural cavity and lungs
• Peritoneum lined abdominal cavity and
  associated organs
• Pericardium lines pericardial cavity and heart

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Cutaneous Membrane

• Aka Skin covers surface of body, thick, dry
• Stratified squamous epithelium and underlying
  dense connective tissue

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Synovial Membranes

• Lines articulation (joint) capsule
• Loose connective tissue and incomplete layer of
  epithelial tissue
• Produce synovial fluid for smooth movements

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Mucous Membrane
Serous Membrane
Cutaneous Membrane
Synovial Membrane
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Muscle Tissue

• Muscle tissue interaction between myosin and
  actin create a contraction
• Skeletal striated voluntary muscle
• Large, multinucleated cells (long and slender)
• Incapable of dividing, but produced through stem
  cells
• Striations (series of bands)
• Only contract when stimulated by nerves
• Cardiac striated involuntary muscle
• Smaller striated cells, single nucleus
• Interconnected by intercalated discs
• Limited ability to repair
• Pacemaker cells establish a regular rate of
  contraction
• Smooth nonstriated involuntary muscle
• Walls of blood vessels, hollow tubelike organs
• Small, slender cells w/ one nucleus
• Actin and myosin are scattered so no striations
• Can be repaired
• Can contract on own or by nervous system

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Skeletal Muscle
Cardiac Muscle
Smooth Muscle
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Neural Tissue

• Specialized for conducting electrical impulses
• 2 Types Cells
• Neurons communicate thru electrical events
• Neuralgia physical support for neural tissue,
  supply nutrients to neurons
• Long cells w/ 3main parts
• Cell body w/ nucleus
• Dendrites branching projections that receive
  info
• Axon long projection (w/synaptic terminals)
  relays info to other cells
• Limited ability to repair

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Tissue Injury and Repair

• Inflammation
• In response to pathogens, impact, abrasion,
  extreme temperatures, or chemical irritation
• Mast cells release histamine and heparin that
  dilate blood vessels to induce swelling, warmth,
  redness and pain
• Regeneration
• Fibroblasts produce dense collagen fibers called
  fibrous tissue (scar tissue)
• Fibrosis is the permanent replacement of normal
  tissues with fibrous tissue (i.e. heart and
  muscle tissues)

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Tissues and Aging

• Speed and effectiveness of tissue repair
  decreases with age (change of hormones and
  lifestyle)
• Epithelia gets thinner, bones become brittle,
  cardiac muscle fibers and neurons cannot be
  replaced
• Osteoporosis inactivity, low calcium, and
  decrease in estrogen result in poor bone strength