histology

• histology: the study of the normal structure of tissues
• • tissues are made up of cells and extracellular matrix
  • extracellular matrix is made up of ground substance and fibrous proteins
• ground substance: gelatinous to rubbery substance due to:

  • glycosaminoglycans (GAGs)
  • e.g. chondroitin sulfate, heparin, hyaluronic acid
  • GAGs are charged, attract water molecules
  • proteoglycan
  • "bottle brush" like structures
  • slow pathogens, connect extracellular matrix to cell membranes
  • glycoproteins
  • bind plasma membranes to extracellular collagen & proteogylcans
• fibrous proteins

  • collagenous fibers
  • tough, resist stretching
  • reticular fibers
  • thin collagen fibers with glycoprotein coat
  • form spongelike frameworks for spleen and lymph nodes and liver
  • elastic fibers
  • made of elastin and have elasticity
• elasticity: coiled protein with ability to recoil
• major human cellular morphologies

  1. squamous
  2. polygonal
  3. discoid
  4. cuboidal
  5. stellate
  6. fusiform
  7. columnar
  8. spheroidal
  9. fibrous
• cell junctions: physical connections between tissue cells found in the epithelial cells in epithelium
• types of cell junctions:

  1. tight junctions
  2. desmosomes
  3. gap junctions
• tight junctions: integral membrane proteins of adjacent cells lock together to form impermeable seal
• desmosomes: integral membrane proteins of adjacent interweave between cells and connect to intermediate filaments within cells. resist mechanical stress
• gap junctions: interlinked protein pores that allow substances to pass between cells
• types of epithelial tissue:

  1. coverings and linings: boundaries between external and internal environments
  2. glands: secrete mucous, sweat, enzymes, hormones, etc
• general characteristics of epithelial tissue:

  1. polarity
  2. apical = external environment or organ cavity
  3. basal = basal lamina
  4. specialized contacts
  5. cell junctions
  6. avascular
  7. no blood capillaries
  8. supported by connective tissue
  9. basal membrane and blood vessels
  10. innervated
  11. nerve endings present
  12. regenerative
  13. capable of cell division
• simple epithelia types

  1. simple squamous
  2. simple cuboidal
  3. simple columnar
  4. pseudostratified columnar
• goblet cells: wineglass shaped cells amongst columnar cell tissues, secrete mucus

  e.g. GI and respiratory tracts
• stratified epithelia

  • 2-20 layers of cells
  • only deepest layer contacts basal membrane
• stratified epithelia types:

  1. stratified squamous
  2. stratified cuboidal
  3. stratified columnar (rare)
  4. transitional epithelium
• functions of epithelial tissues:

  1. protection
  2. secretion
  3. excretion
  4. absorption
  5. filtration
  6. sensation
• simple squamous

  • single layer of thin, flat cells bound together by tight junctions
  • functions: filtration, diffusion, excretion
  • e.g. air sacs of the lung, kidney glomeruli, endothelium, serosa
• simple cuboidal

  • single layer of square of round cells
  • function: absorption and secretory
  • ciliated in lungs
  • e.g. liver, thyroid, mammary, salivary, kidney and bronchioles
• simple columnar

  • single row of tall, narrow cells
  • brush border of micovilli
  • often possess goblet cells
  • function: absorption & secretion
  • GI tract lining, intestine, uterus, kidneys, uterine tubes
• pseudo-stratified columnar

  • all cells touch basement membrane
  • includes cilia and goblet cells
  • secretes and propels mucous
  • e.g. upper respiratory tract and portions of male urethra
• types of transport across epithelia

  1. transcellular
  2. paracellular
  3. less common due to tight junctions
• transcellular transport:

  1. osmosis
  2. simple diffusion
  3. facilitated diffusion
  4. active transport
  5. vesicular transport
• stratified squamous

  • most abundant epithelia in body
  • deepest layers undergo continuous mitosis
  • die and flake off
  • e.g. esophagus
• types of stratified squamous epithelia

  1. keratinized
  2. multiple cell layers, flat & scaly towards surface with some dead cells and keratin
  3. resists abrasion, retards water loss
  4. e.g. epidermis, palms and soles
  5. non-keratinized
  6. no keratin, no dead cell layers
  7. e.g. tongue, oral mucosa, esophagus, vagina
  8. resists abrasion
• stratified cuboidal

  • two or more cell layers, cuboidal or round
  • function: secretion of sweat, sperm production & ovarian hormone production
  • e.g. sweat gland ducts, ovarian follicles, and seminiferous tubules
• transitional stratified epithelial

  • multilayered epithelium cells that change shapes from round to flattened when stretched
  • apical surface provides protective, flexible lipid layer
  • e.g. ureter and bladder
• endocrine glands: no ducts, secrete products into blood stream (hormones)
• exocrine glands: maintain contact with body surfaces via ducts

  • e.g. sweat, mammary, salivary glands
• glands: cell or organ that secretes or excretes substances
• organs: two or more tissues with the same structure working together to perform same function
• label

  A) mucin

  B) golgi apparatus

  C) nucleus

  D) mucous cell

  
• label

  A) septa or trabeculae

  B) capsule

  C) duct

  D) parenchyma

  
• septa (trabeculae): connective tissue that compartmentalize interior

  capsule: connective tissue covering

  stroma: capsule and septa

  parenchyma: cells that synthesize and secrete (cuboidal)
• name these.

  A) ductal

  B) simple

  C) compound

  D) secretory

  E) tubular

  F) acinar

  G) tubuloacinar

  H) simple tubular

  I) simple acinar

  J) compound acinar

  K) compound tubuloacinar

  
• acinar = alveolar
• simple tubular = glands in large intestine

  simple acinar = glands in urethra

  compound tubuloacinar = mammary glands

  compound tubular = kidneys and testes

  compound acinar = exocrine pancreas portion
• exocrine secretion modes

  1. merocrine (eccrine): products released during exocytosis
  2. e.g. tear glands, pancreas, gastric glands, sweat
  3. apocrine: similar to merocrine, but part of cytoplasm broken off along with vesicles from apical portion
  4. e.g. mammary glands
  5. holocrine: cells accumulate product, then rupture to release it
  6. sebaceous glands on scalp
• stroma = septa and capsule