Chapter 4 Histology
Biol 2401
Intercellular
Junctions
• All cells (except blood) anchored to each other or their
matrix by intercellular junctions
Tight Junctions
• Encircle the cell joining it to surrounding cells
– zipperlike complementary grooves and ridges
• Prevents passage between cells
– GI and urinary tracts
Desmosomes
• Patch between cells holding them together
– cells spanned by filaments terminating on protein plaque
• cytoplasmic intermediate filaments also attach to plaque
• Uterus, heart and epidermis
Gap Junctions
• Ring of transmembrane
proteins form a waterfilled channel
– small solutes pass
directly from cell to
cell
– in embryos, cardiac
and smooth muscle
Glands
• A gland is a cell or organ that secretes substances in the
body or releases them for elimination.
• Secrete substances
– composed of epithelial tissue
• Exocrine glands connect to surface with a duct (epithelial
tube)
• Endocrine glands secrete (hormones) directly into
bloodstream
• Mixed organs do both
– liver, gonads, pancreas
• Unicellular glands – endo or exocrine
– goblet or intrinsic cells of stomach wall
Exocrine Gland
Structure
• Stroma = capsule
and septa divide
gland into lobes
and lobules
• Parenchyma =
cells that secrete
• Acinus = cluster of
cells surrounding
the duct draining
those cells
Types of Exocrine Glands
• Simple glands - unbranched duct
• Compound glands - branched duct
• Shape of gland
– acinar - secretory cells form dilated sac
– tubuloacinar - both tube and sacs
Types of Secretions
• Serous glands
– produce thin, watery secretions
• sweat, milk, tears and digestive juices
• Mucous glands
– produce mucin that absorbs water to form a sticky
secretion called mucus
• Mixed glands contain both cell types
• Cytogenic glands release whole cells
– sperm and egg cells
Holocrine
Gland
• Secretory cells disintegrate to deliver their
accumulated product
– oil-producing glands of the scalp
Merocrine and Apocrine Secretion
• Merocrine glands release their
product by exocytosis
– tears, gastric glands, pancreas,
etc.
• Apocrine glands are merocrine
glands with confusing appearance
(apical cytoplasm not lost)
– mammary and armpit sweat
glands
Mucous
Membranes
• Epithelium, lamina propria and muscularis mucosae
• Lines passageways that open to the exterior: reproductive, respiratory,
urinary and digestive
– Mucous (movement of cilia) trap and remove foreign particles and
bacteria from internal body surfaces
Membrane Types
• Cutaneous membrane = skin
– stratified squamous epithelium over connective tissue
– relatively dry layer serves protective function
• Synovial membrane lines joint cavities
– connective tissue layer only, secretes synovial fluid
• Serous membrane (serosa) –internal membrane
– simple squamous epithelium over areolar tissue, produces
serous fluid
– covers organs and lines walls of body cavities
Membranes
Cutaneous Membrane
Serous Membrane
Synovial Membrane
Tissue Growth
• Hyperplasia = tissue growth through cell
multiplication
• Hypertrophy = enlargement of preexisting
cells
– muscle grow through exercise
• Neoplasia = growth of a tumor (benign or
malignant) through growth of abnormal tissue
Changes in Tissue Types
• Tissues can change types
• Differentiation
– unspecialized tissues of embryo become
specialized mature types
• mesenchyme to muscle
• Metaplasia
– changing from one type of mature tissue to
another
• simple cuboidal tissue before puberty changes to
stratified squamous after puberty
Stem Cells
• Undifferentiated cells with developmental plasticity
• Embryonic stem cells
– totipotent (any cell type possible)
• source = cells of very early embryo
– Pluripotent (tissue types only possible)
• source = cells of inner cell mass of embryo
• Adult stem cells (undifferentiated cells in tissues of
adults)
– multipotent (bone marrow producing several blood cell
types)
– unipotent (only epidermal cells produced)
Tissue Shrinkage and Death
• Atrophy = loss of cell size or number
– disuse atrophy from lack of use (leg in a cast)
• Necrosis = pathological death of tissue
– gangrene - insufficient blood supply
– gas gangrene - anaerobic bacterial infection
– infarction - death of tissue from lack of blood
– decubitus ulcer - bed sore or pressure sore
• Apoptosis = programmed cell death
– cells shrink and are phagocytized (no inflammation)
Tissue Repair
• Regeneration
– replacement of damaged cells with original cells
– skin injuries and liver regenerate
• Fibrosis
– replacement of damaged cells with scar tissue
• function is not restored
– healing muscle injuries, scarring of lung tissue in TB or healing of
severe cuts and burns of the skin
– keloid is healing with excessive fibrosis (raised shiny
scars)
Tissue Engineering
• Production of tissues and organs in the lab
– framework of collagen or biodegradable polyester fibers
– seeded with human cells
– grown in “bioreactor” (inside of mouse)
• supplies nutrients and oxygen to growing tissue
• Skin grafts already available
– research in progress on heart valves, coronary arteries,
bone, liver, tendons
Wound Healing of a Laceration
• Damaged vessels leak blood
• Damaged cells and mast cells
leak histamine
– dilates blood vessels
– increases blood flow
– increases capillary
permeability
• Plasma carries antibodies,
clotting factors and WBCs into
wound
Wound Healing of a Laceration
• Clot forms
• Scab forms on
surface
• Macrophages start
to clean up debris
Wound Healing of a Laceration
• New capillaries grow
into wound
• Fibroblasts deposit new
collagen to replace old
material
• Fibroblastic phase
begins in 3-4 days and
lasts up to 2 weeks
Wound Healing of a Laceration
• Epithelial cells multiply
and spread beneath
scab
• Scab falls off
• Epithelium thickens
• Connective tissue
forms only scar tissue
(fibrosis)
• Remodeling phase may
last 2 years