Connective Tissue Flashcards
Connective Tissue
Provides structural and metabolic support to organs and other tissue types
Functions of connective tissue
Support, Packing, Storage, Transport, Repair, and Defense
Connective tissue is composed of Resident cells, and Wandering cells (transient)
Resident Cells- fibroblasts, adipocyte, macrophage, mesenchymal cell, mast cell
Wandering Cells- lymphocytes, plasma cells, eoisinophils, basophils, neutrophils, manocytes
Extracellular Matrix
Major constituent
Composed of Protein fibers (Morphous) such as collagen, elastic, reticular.
Also composed of Ground substances (Amorphous)
Embryonic Connective Tissue
Mesenchyme, Mucous connective tissue
Connective Tissue Proper
Loose connective tissue, Dense connective tissue-regular and irregular
Specialized Connective Tissue
Cartilage, Bone, Adipose Tissue, Blood, Hemopoietic Tissue, Lymphatic Tissue
Embryonic tissue Mesenchyme
Contains Elongate spindle shaped cells, loosely organized
Viscous ground substance
Few collagen fibers
Reticular Fibers
Mucous Connective Tissue
Principal component of umbilical cord
Consists of Wharton’s Jelly, which is rich in hyaluronan
Thin collagen fibers
Therapeutic potential in regenerative medicine
Loose Connective or Areolar Tissue
Thin, sparse collagen fibers, elastic fibers, cells
Used for diffusion of oxygen and nutrients from small blood vessels
Most of the cells are migratory
Loose Connective or Areolar Tissue
the site of inflammatory reactions-primarily between epithelia called lamina propira, also associated with epithelium of glands
surrounds small blood vessels
Dense connective tissue: two types
Dense regular and irregular connective tissue
dense regular connective tissue
Mostly bundles of Type 1 Collagen fibers and fibroblasts, they arranged parallel, which provides resistance to prolonged stress
Poorly vascularized-does not repair easily
Found in tensons, ligaments, aponeuroses
Where is dense regular connective tissue found in?
Tendons, ligaments, aponeuroses
Dense irregular Connective Tissue
Contains mostly collagen fibers, not as much ground resistance
Bundles of fibers are oriented in various direction, gives resistance to tearing when stretched
Found in reticular layer of dermis, submucosa of GI tract
Dense Irregular Connective Tissue can be found where?
Reticular layer of dermis of skin, submucosa of HI tract
Resident Cells Connective tissue exhibit what
Exhibit little movement, known as permanent residents of the tissue- fibroblasts and myofibroblasts, fixed histocytes, adipocytes, mast cells, undifferentiated mesenchyme cells
Wandering cells
Lymphocytes, plasma cells, eosinophils, basophils, neutrophils, monocytes
Fibrolblasts
Principal cell of connective tissue
fibroblasts synthesize:
Collagen, elastin, reticular fibers, complex carbohydrates of ground substance (GAG, multi-adhesive glycoproteins)
Fibroblast structure shows
morphological variation based on activity level:
Fibroblasts- intense synthetic activity
Fibrocyetes- are quiescent fibroblasts that are scattered in the matrix
Typical fibroblast structure holds
Spindle shaped, tapered off in both directions along axis of nucleus
Active Firboblasts
Basophilic cytoplasm
Inactive fibroblasts or fibrocytes
small cells, heterochromatic nucleus
Collagen Biosynthesis
Transcription of mRNA in the nucleus: genes for pro-a1 and pro-a2 chains are transcribed
translation of collagen biosynthesis is referred to as :
Pre-pro-polypeptide chain
Chain travels through rER for post translational modification
Post translational modification in rER- three major modifications are made to the pre-pro-polypeptide for it to become pro-collagen
-Signal peptide on the N-terminal is removed
-Lysine and proline residues get additional hydroxyl groups added via hydroxylase enzymes, which require Vitamin C as a cofactor
-Glycosylation of the hydroxyl groups on lysine with glactose and glucose b
Three of the hydroxylated and glycosylated pro-a-chains assemble by:
Twisting into a triple helix by zipper-like folding:
Pro-collagen
The pro-collagen molecule then moves into the Golgi apparatus:
Gets packaged into secretory vesicles:
Ready to enter the extracellular space
Collagen Biosynthesis- Protein cleavage
enzymes known as collagen peptidases cleave procollagens, molecules becomes Tropocollagen
Collagen fibril assembly
Lysine and hydroxylysines, and tropocollagens molecules form covalent bonding between them: collagen fibril
Myofibroblasts
implicated in wound contraction: results in wound closure
Myofibroblasts do not have external lamina
Myofibroblasts are located in
seminiferous tubules of the testis, beneath basal lamina
Myofibroblasts show characteristics of both fibroblasts and the smooth muscle cell:
Moderate amount of eER, comparable to fibroblasts
Filaments and dense bodies, comparable to smooth muscle cell
Macrohphages are also known as
Tissue Histiocytes
Macrophages are phagocytic cells derived from
monocytes
Macrophages display a large
kidney shaped nucleus
Types of macrophages
Classically Activated Macrophages (M1)-which destroy microorganism at site of inflammation
Alternatively Activated Macrophages (M2)- anti-inflammatory, promote wound repair, secrete multi-adhesive proteins
end digestion of macrophages is :
Product is exocytosed, or resist digestion and will remain in the cytoplasm as residual bodies
When macrophages encounter large foreign bodies
They may fuse to form a large cell, up to 100 nuclei, these cells are called LANGHAN’S CELLS or foreign body giant cells
Ex. of horseshoe nuclear array in tuberculosis
Adipose or fat cells originate from
mesenchymal cells
adipocytes
specialized to store fat
two types of adipose tissue
white adipose tissue (unicellular)
brown adipose tissue (multicellular)
white adipose tissue
predominant in adults
brown adipose tissue
predominant in fetal life
postnatally reduces
present around internal organs
Adipocyte stem cells form preadipocytes
develop within the lateral mesoderm: form white adipocytes and beige adipocytes
beige adipocytes
have cytological features and gene expression patterns of both white and brown adipocytes
Preadipocytes located in paraxial mesoderm form
brown adipocytes: remain multicellular, mitochondrial metabolism of lipid brown adipocytes releases
heat rather than ATP
cells functioning as brown adipocytes can also develop from beige adipocytes during:
adaption to cold temperatures
White adipose tissue is
unicellular, supplied with blood vessels and nerves
lipid drops are not membrane bound
White adipose tissue
stores energy insulation and cushioning to vital organs
white adipose tissue functions as major endocrine organ and produces:
(AGE) Angiotensionogen-controls blood pressure, frequent complication of obesity
Steroids-testosterone, estrogen, glucocorticoids
Leptin- polypeptide hormone, targest the hypothalamus, regulates eating behavoir
Brown adipose tissue is
uncommon in adult humans, sole purpose is heat generation especially in hibernation, after birth, and during cold stress
brown adipocytes in the adult human body, found only around deep structures (kidney)
associated with capillaries, direct sympathetic innervation
have many small lipid inclusions (multicellular)
mast cells are
large ovoid connective tissue cells,
granulated cytoplasm, contain similar cytoplasmic granules (similar to basophils in blood)
mast cells arise from
basophil/mast cell progenitors in bone marrow
mast cells are a part of
innate immune system
mast cells are found in
skin, gut, tissues near blood vessels and nerves
mast cells respond to various stimuli and release inflammatory mediators
Histamine and Tryptase
mast cells produce 2 categories of inflammatory mediators
Performed mediators and newly synthesized mediators
mast cells performed mediators
histamines-make blood vessels leaky, cause edema, increase mucus production
serine proteases: Typtase and Chymase- generates angiotesin II in vascular injury, activates MMPs and induces apoptosis
Eosinophil adn neutrophil chemotactic factors
Heparin
mast cells newly synthesized mediators
leukotriene C-product of which cause bronchospasm and recruit eosinophils
Tumor Necrosis Factor alpha- major cytokine, produce by mast cells
Several interleukins
undifferentiated mesenchymal cells
found in adult loose connective tissue
undifferentiated mesenchymal cells function in
wound healing, development of new blood vessels
undifferentiated mesenchymal cells have Pericytes, also called
adventitial cells or perivascular cells, found around capillaries and venules
wrapped around capillaries
lymphocytes
principally involved in immune responses
normally small number are found in all connective tissue
increases dramastically at sites of inflammation
most numerous in lamina propria of respiratory and GI tracts
lymphocytes are small cells
deeply staining nucleus
three types of lymphocytes
B cells-originate in bone marrow, can differentiate into plasma cells, secrete antibodies
T cells-originate in bone marrow, mature in thymus, function in cell mediated immunity, naice, effector, memory
Natural killer cells or NK cells-destroy virus infected and some tumor cells
lymphocytes function in
adaptive immunity
Plasma Cells
derived from B lymphocytes, produce antibodies
plasma cells distribution
in lamina propria of GI tract, and respiratory tract
plasma cells are in lamina propria of
urogenital tract, salivary glands, lymph nodes, hemopoietic tissue
plasma cells structure
cytoplasm-strongly basophilic due to high developed rER
extensive golgi complex
plasma cell structure
nucleus is large, spherical, large clumps of heterochromatin alternated with euchromatin-cartwheel or clock face arrangement
prominent nucleolus
each PLASMA cell makes large amount of mostly one type of protein
a specific antibody
eosinophils, basophils, neutrophils, and monocytes
cells rapidly mirgate from blood to connective tissue in response to- injury and inflammation, especially neutrophils followed by monocytes
monocytes differentiate into macrophages
Structural details of these cells will be done in the secretion on blood
extracellular matrix of connective tissue are major constituent of
connective tissue
extracellular matrix consists of
protein fibers- collagen fibers, elastic fibers, reticular fibers
Ground substance- proteoglycans, GAGs, multiadhesive glycoproteins such as laminin, and fibronectin
collagen fibers
Most important!
most abundant fibers of connective tissues
appear wavy in LM
stain easily with Eosin, and other acidic dyes
collagen fibers in TEM
fibers are made up of fine fibrils
fibrils exhibit a 68nm banding pattern, due to precipitation to TEM stain
collagen breakdown has two types
proteolytic degradation- occurs outside the cell via matrix metalloproteinases MMPs, invasive cancer cells secrete MMPs to break down ECM
Phagocytic degradation-macrophages or fibroblasts phagocytize and degrade collagen
collagen fiber types
29 types, type I to type XXIX
type 1 collagen
most common,
occurs in loose and dense connective tissue and bone
scurry-vitamin c levels are low
collagen will not be formed properly, not enough collagen, bleeding from gums symptoms
osteogenesis imperfecta of collagen type I
mutation of type I collagen gene: repeated fractures after minor trauma, brittle bones, thin skin, abnormal teeth
type II collagen present in
cartilage (hyaline, elastic, and firbo
Vitreous body of the eye
Kniest dysplasia type II collagen
mutation of type II collagen gene- short stature, restricted joint mobility, occular changes leading to blindness, wide metaphyses
holes in the cartilage on xray
type III collagen
also known as reticular fibers
synthesized by fibroblasts in connective tissue, reticular cells in bone marrow, smooth muscle cells
ehlers-danlos syndrome
13 different types
mutation of collagen genes, type I, typeIII, type IV, and type V mostly
hypermobility of joints of digits (Type III)
rupture of vessels and internal organs (type IV)
ehlers-danlos syndrome
13 different types
mutation of collagen genes, type I, typeIII, type IV, and type V mostly
hypermobility of joints of digits (Type III)
rupture of vessels and internal organs (type IV)
Type IV collagen
present as meshwork sheets in basal lamina/external lamina
synthesized by- epithelial cells, muscle cells, schwann cells
Alport Syndrome
hematuria resulting from structural changes in glomerular basement membrane of kidney, progressive hearing loss
Type V collagen
present in fibers in dense irregular connective tissue, placenta, blood vessel walls, bone
Classic Ehlers Danlos Syndrome
hypermobility of joints of digits, fragile skin, delayed wound healing
Type VII collagen
known as anchoring fibrils
present in epidermal dermal interface
synthesized by fibroblasts
Dystrophic epidermolysis bullosa including kindler syndrome
severe blistering and scarring of the skin after minor trauma, resulting from absence of anchoring fibers
elastic fibers
thinner than type I collagen fibers
