Unit 2 Honors Physiology Tissues

Tissue

Tissue

An organized group or layer of cells working together to carry out a similar function

Matrix

a nonliving portion of all tissues, an intercellular substance

4 major types of tissues

Epithelial, connective, muscle, and nervous tissue

Epithelial tissue

Covers organs, lines body cavities, forms glands

2 forms of epithelium

• Covering and lining epithelium 

  • skin, lining of stomach

• Glandular epithelium – glands; cells specialized to produce and secrete substances

  • Sweat glands & pituitary gland

Special characteristics of covering and lining epithelia

• Closely packed cells 🡪 Make good barriers

• May have cilia or microvilli

• Have polarity

• Supported by connective tissue

• Contain nerves (innervated) but not blood vessels (avascular)

• Regenerate frequently

Polarity of epithelial tissue

• Free on one side – the apical surface

• Anchored to connective tissue on the other (basal) side by a basement membrane 

Functions of epithelial tissue

• Protection 

• Secretion 

• Absorption 

• Excretion 

• Sensory reception

Simple

• 1 layer

  • Most concerned with absorption, secretion, filtration

Stratified

2 or more layers

• Common in high-abrasion areas where protection is important

Squamos

flattened and scale-like

cuboidal

box-like

Columnar

tall and column shaped

Simple squamous

• Single layer of thin, flattened cells

• Disc-shaped, central nucleus

• Resembles floor tiles, but easily damaged

• filtration and diffusion

• Location:  

  • Lining air sacs of lungs

  • Walls of capillaries 

  • Inside blood & lymph vessels

  • Covering membranes that line body cavities

Simple Cuboidal

• Functions: secretion & absorption in kidneys; secretion in glands

• Single layer of cube-shaped cells

• Round, centrally located nuclei

• Location:  

  • Covers ovaries 

  • Lines kidney tubules

  • Lines the ducts of salivary glands, thyroid gland, pancreas, & liver

simple columnar

• Single layer of elongated cells

• Nuclei are oval & evenly distributed close to the basement membrane 

• May have microvilli to increase the surface area for absorption

• accompanied by goblet cells which secrete mucus

• Location:  

  • Lining of uterus, stomach, small & large intestine

• Functions:  

  • Protection

  • Secretion of digestive fluids

  • Absorption of nutrients from digested food

Pseudostratified Columnar

• Appearance of being layered due to uneven nuclei but not stratified

• Commonly have cilia & goblet cells

• Location:  

  • Line passages of the respiratory system

• Function:  

• Trap dust & microorganisms with mucus, then move them out with cilia

Stratified Squamous

• Many layers of cells making up the outer layer of skin

• Skin cells divide in deeper layers, then get pushed up as they age

• Aging skin cells accumulate keratin, harden, & die

  • Produces a dry, tough, protective materia

• Locations:  

  • Epidermis (external part of skin) & body openings: 

    • Lining the mouth, throat, vagina, anal canal

      • SSE that lines openings may or may not be keratinized 

Stratified cuboidal

• 2-3 layers of cube-shaped cells

• Form the lining of a lumen

• ocation:  

  • Lining larger ducts of mammary glands, sweat glands, salivary glands, pancreas, developing ovarian follicles, & seminiferous tubules

Stratified Columnar

• Location:  

  • Urethra

  • Vas deferens

  • Pharynx

• Several layers of cells elongated on the surface, and cube-shaped underneath

  • Rare in the body

Transitional epithelial

• Function:  

  • Provides an expandable lining & a barrier to contain the contents of the urinary tract

• Specialized to change in response to tension

• Location:  

  • Inner lining of bladder, ureters, urethra

Gland

• One or more cells that secrete a product

Secretion

• The process by which a substance is released from a cell

  • e.g.,  the skin secretes sweat from sweat glands

Endocrine glands

• Ductless (tubeless)

• Produce hormones that are
  released directly into
  extracellular space
  (blood or other fluid)

• More to come later in year

Exocrine Glands

• More numerous than endocrine glands

• Secrete product through duct and/or onto an epithelial surface

Unicellular Exocrine Glands

• Scattered among cells with other functions

• Produce mucin – a complex glycoprotein that dissolves in water when secreted mucus

  • e.g., goblet cells in respiratory, digestive and urinary tracts

Multicellular Exocrine Glands

Composed of duct (tube) and secretory unit

goblet cells

a column-shaped cell found in the respiratory and intestinal tracts, which secretes the main component of mucus.