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287 Cards in this Set

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ectoderm
gives rise to the oral and nasal mucosae, cornea, epidermis of the skin, and glands of the skin and the mammary glands
endoderm
give rise to the liver, pancreas, lining of the respiratory and gastrointestinal tract
mesoderm
uriniferous tubules of the kidney, the lining of the male and female reproductive systems, the endothelial lining of the circulatory system, and the mesothelium of the body cavities
functions of epithelial tissue
protection
transcellular transport
secretion
absorption
selective permeability
detection of sensations
striated border vs. brush border
striated border found in intestinal absorptive cells, brush border found in the kidney tubules
terminal web
composed of actin, spectrin, and intermediate filaments
myosin I and calmodulin
connect actin filaments in the terminal web to the microvillus to give support
apical domain of epithelium
rich in ion channels, carrier proteins, H+-ATPase, glycoproteins, hydrolytic enzymes, and aquaporins
microvilli
small finger like cytoplasmic projections emanating from the free surface of the cell into the lumen, represent the striated border of the intestinal absorptive cells and the brush border of the kidney proximal tubule cells, greatly INC SA, contains a core of 25 to 30 actin filaments, cross-linked by villin and attached to the terminal web
glycocalyx
represents carbohydrate residues attached to the transmembrane proteins of the plasmalemma, function in protection and cell recognition
sterocilia
long microvilli found only in the epididymis and on the sensory hair cells of the cochlea, function to INC SA (epididymis) and signal generation (hair cells)
cilia
long, motile, hair-like structures emanating from the apical cell surface, their core is composed of a complex arrangement of microtubules known as the axoneme, function to propel mucus and other substances, contains an axoneme (composed of microtubules in a 9+2 arrangement), attached basally to the basal body (which has 9 triplets and no singlets), doublets have a subunit A (13 protofilaments) and B (10)
radial spokes
project from subunit A inward toward the central sheath surrounding the two singlets
nexin
connect neighboring doublets, A -> B, elastic protein that restrains the movements of dynein somewhat
dynein
has ATPase activity, radiates from subunit A of one doublet toward subunit B of the neighboring doublet, provides energy for ciliary bending
terminal bars
where epithelial cells attach to each other, continuous around the entire circumference of the cell, are composed of junctional complexes
junctional complexes
three types:
1. occluding junctions-function in joining cells to form an impermeable barrier preventing material from taking an intercellular route
2. anchoring junctions-function in maintaining cell to cell or basal to cell lamina adherence
3. communicating junctions-function in permitting movement of ions or signaling molecules between cells
zonulae occludentes
aka tight junctions, most apically located, belt-like, composed of claudins (reinforced by cadherins and Z01, Z02, and Z03 proteins) and occludins binding to each other, prevent the movement of membrane proteins from the apical domain to the basolateral domain, and they fuse plasma membranes of adjacent cells to prohibit water-soluble molecules from passing between cells (P-face has tight junction strands and E-face has corresponding grooves)
zonulae adherentes
assist joining cells to adhere to one another, located basal to the zonulae occludentes, cadherins (are Ca2+ dependent) bind to each other intercellularly and actin binds intracellularly (to anchor proteins catenin, vinculin and actinin), this junction joins the cell membrane to each other and links the cytoskeleton of the two cells, goes around entire circumference of cell
desmosomes (maculae adherents)
weld-like junctions along the lateral cell membranes that help to resist shearing forces, randomly distributed in the wall, have disk shaped attachment plaques that attach to each other on adjacent cell membranes, intermediate filaments insert into the plaques where they make a hairpin turn
desmoplakins and pakoglobins
attachment proteins of attachment plaques
desmoglein and desmocollin
members of the cadherin linker protein, found extracellulary in association w/ desmosomes, in the presence of Ca2+ they bind to linker proteins of the adjoining cell, in the presence of Ca2+ chelating agents the desmosomes halve
gap junctions
aka nexus or communicating junctions, regions of intercellular communication, couple adjacent cells metabolically and electrically, also widespread, found everywhere except the skeletal muscle cells, built by six closely packed transmembrane channel-forming proteins (connexins) that assemble to form channel structures called connexons, hydrophilic communication channel, regulated and may be opened and closed rapidly (close w/ low cytoscolic pH or INC in cytosolic Ca2+)
basal surface specializations
include the basal lamina, plasma membrane enfoldings and hemidesmosomes
plasma membrane enfoldings
INC SA available for transport at the basal end, mitochondria found within the enfoldings, use energy for transport
hemidesmosomes
attach the basal cell membrane to the underlying basal lamina, attachment plaques are present on the cytoplasmic side of the plasma membrane, keratin tonofilaments insert into these plaques, linker proteins (integrin not cadherin) bind to laminin and type IV collagen of the basal lamina
parenchyma of a gland
secretory units of a gland including the duct
stroma of a gland
represents the elements of the connective tissue that invade and support the parenchyma
exocrine glands
secrete their products via ducts onto the external or internal epithelial surface
endocrine glands
ductless, having lost their connections to the originating epithelium, secrete their products into the blood or lymphatic vessels for distribution
cytokines
responsible for cell-to-cell communications
autocrine
signaling cell is its own target, cell stimulates itself
paracrine
target cell is located in the vicinity of the signaling cell, cytokine does not have to enter the vascular system for distribution to its target
endocrine
target cell and signaling cell are far, cytokine has to be transported either by the blood or lymph system
mucous glands
secrete mucinogens that swell to become thick lubricant called mucin (component of mucus), lighter colored
-ex: goblet cells and the minor salivary glands of the tongue and palate
serous glands
secrete an enzyme rich watery fluid, darker colored
-ex: pancreas
mixed glands
contain acini (secretory units) that produce mucous and serous secretions, some mucous acini possess serous demilunes (cells that secrete a serous fluid)
-ex: sublingual and submandibular glands
holocrine secretion
entire secretory cell dies and becomes the secretory product
-ex: sebaceous glands
aporcrine secretion
questioned existence, a small portion of the apical cytoplasm is released
-ex: mammary glands
merocrine glands
occurs via exocytosis, cell membrane and cytoplasm are not part of the secretion
ex: parotid gland
diffuse neuroendocrine system (aka amine precursor uptake and decarboxylation cells APUD)
make up endocrine cells widespread throughout the digestive tract and in the respiratory system, manufacture various paracrine and endocrine hormones
Glycosaminoglycans (GAGs)
negatively charged, long rod-like chains of repeating disaccharides that have the capability of binding large quantities of water, all but one GAG (hyaluronic acid) is sulfated
the disaccharide of the GAG
two subunits, one is always an amino sugar (N-acetylglucosamine or N-acetylgalactosamine) and the other is uronic acid
amino sugar of GAG
normally sulfated and (-) charged, attract Na+ which attracts extracellular fluid which assists in the resistance of compression
sulfated GAGs
keratin sulfate, heparin sulfate, heparin, chondroitin 4-sulfate, chondroitin 6-sulfate, and dermatan sulfate, these are usually linked to form proteoglycans, synthesized by the golgi
hyaluronic acid
nonsulfated GAG, doesn’t form covalent links to protein molecules, synthesized as a free linear polymer at the cytoplasmic face of the plasma membrane, proteoglycans (through protein cord) do attach here via link proteins
proteoglycans
composed of a protein core to which GAGs are covalently bonded, looks like a brush
aggrecan
type of proteoglycan, found in cartilage and CT proper
hyaluronic acid with proteoglycans
forms large macromolecule responsible for the gel state of the ECM, also accounts for slow diffusion
function of proteoglycans
resist compression, slow movement of microorganisms, molecular filters, binding sites for signaling molecules
syndecan
type of proteoglycan, act as transmembrane proteins, permit the cell to become attached to components of the matrix
glycoproteins
have binding sites for several components of the ECM that facilitate the attachment of cells to the ECM, usually bind to integrins, collagen fibers or proteoglycans
types of glycoproteins
fibronectin, laminin, entactin, tenascin, chodronectin and osteonectin
fibronectin
dimmer composed of two polypeptide subunits, has binding sites for extracellular components and integrins, has an RGD sequence for adhering, produced by fibroblasts, when they stretch expose binding sites for other fibronectins to bind forming the fibronectin matrix
plasma fibronectin
facilitates healing, phagocytosis and coagulation
cell-surface fibronectin
attached to the plasma membrane, regulates pathways for embryonic cells to reach their destination
laminin
three large polypeptide chains (A, B1, and B2), B’s wrap around A, found in the basal lamina and has binding sites for heparin sulfate, type IV collagen, entactin and the cell membrane
entactin
sulfated, binds to laminins three short arms to facilitate the collagen meshwork
tenascin
composed of six polypeptide chains, bug with six legs, has binding sites for the transmembrane proteoglycan syndecans and for firbronectin, usually found in embryonic tissue
chondronectin
similar to fibronectin, binds type II collagen, chondroitin sulfates, hyaluronic acid and integrins
osteonectin
binds type I collagen, proteoglycans, and integrins, may facilitate the binding of calcium hydroxapatite to type I collagen of bone
collagen
composed of tropocollagen subunits, resists tensile forces, constitutes about 20-25% of the body, three categories (fibril forming, fibril associated, and network forming), 67 nm cross bridge, made from collections of tropocollagens (each of which is composed of three alpha chains
elastic fibers
give the elastic property to CT, 50% of aorta, manufactured by fibroblasts, composed of elastin (rich in G, K, A, V, P), core of elastin surrounded by a sheath of microfibrils (composed of fibrillin)
desmosine cross links
hold elastin fibers together, 4 K molecules for covalent bonds with each other
basal lamina
composed of the lamina lucida and the lamina densa, functions in filtering and support
lamina lucida
consists mainly of laminn, entactin, and integrin
lamina densa
meshwork of type IV collagen, coated by perlacan,
how is basal lamina bound to the reticular lamina
dibronetin, anchoring fibrils, and microfibrils
lamina reticularis
derived from CT, responsible for affixing the lamina densa to the underlying CT, composed of type I and III collagen, made from fibroblast, thickness depends on the level of friction on the superficial epithelium
integrins
transmembrane proteins, linked to the cytoskeleton and binds to collagen, laminin and fibronectin, weak bonds, but numerous in the ECM, a heterodimer composed of alpha and beta glycoproteins, binding site on amino end, can also activate second messenger system cascades
mesoderm
origination of connective tissue, develops mesenchyme
functions of connective tissue
provide structural support, serve as an exchange medium, aid in defense and protection of the body, and form a site for storage of fat
extracellular matrix
composed of ground substance and fibers, resist compression and stretching
aggrecan aggregates
the name for the complex of hyaluronic acid and proteoglycans
ground substance
hydrated, amorphous material composed of glycosaminoglycans, proteoglycans (which link glycosaminoglycans) and adhesive glycoproteins
collagen fibers
inelastic, have great tensile strength, composed of three alpha-chains wrapped around one another in a helical configuration, most common forms are glycine, proline, hydroxyproline, and hydroxylysine
Type 1 collagen fibers
found in tissue proper, bone, dentin, and cementum
Type 2 collagen fibers
found in hyaline and elastic cartilages
Type 3 collagen fibers
found in reticular fibers
Type 4 collagen fibers
found in lamina dansa of the basal lamina, not assembled into fibers
Type 5 collagen fibers
found in the placenta, associated with type 1 collagen
Type 7 collagen fibers
found attached to the basal lamina to the lamina reticularis
elastic fibers
composed of elastin (made mainly of glycine and proline) and microfibrils (fibrillin), highly elastic
fixed cells of connective tissue
resident cells that remain in the CT, fibroblasts, adipose cells, pericytes, mast cells, macrophages
transient cells of CT
originate mainly in bone marrow and circulate in the blood stream to the CT, include plasma cells, lymphocytes, neutrophils, eosinophils, basophils, monocytes, and macrophages
fibroblasts
most abundant cell type in the CT, responsible for the synthesis of almost all of the extracellular matrix, has dark staining nucleus w/ nucleolus, immature fibroblasts may differentiate into different cells of the CT, has prominent golgi and numerous RER
myofibroblasts
modified fibroblasts, abundant in areas of wound healing where they function in wound contractrion, similar to smooth muscle cells, also found in the periodontal ligament where they assist in tooth eruption
pericytes
surround endothelial cells of capillaries and small venules, have their own basal lamina, also similar to smooth muscle cells (contain actin, myosin) may function in contraction
adipose cells
fully differentiated (no cell division), function in the synthesis, storage and release of fat (triglycerides), may be given rise by fibroblasts, 2 types (white, unilocular and brown multilocular), have cytoplasm and nucleus displaced peripherally, presence of small Golgi, a few mito, sparse RER, but lots of free ribosomes
white fat vs. brown fat
white fat more abundant, brown are smaller and more polygonal, brown also carry more mito but fewer ribosomes, do have SER
chylomicrons
complex of triglycerides and protein, carried to bloodstream by lymph and may enter a adipocyte
transport and storage of fat
lipids transported to bloodstream as chylomicrons and VLDLs, lipoprotein lipase hydrolyzes the lipids to fatty acids and glycerol, fatty acids enter the adipocyte and are resterified into triglycerides for storage, when needed, they are hydrolyzed by hormone sensitive lipase, these fatty acids enter the capillary and attach to albumin and are transported in the blood
insulin and fat formation
can stimulate adipose cells to convert glucose and amino acids into fatty acids
norepinephrine and epinephrine in fat
binds to receptors which activates cAMP cascade which activates hormone-sensitive lipase, this cleaves triglycerides in adipocytes into fatty acids and glycerol and release them into bloodstream
mast cells
arise from bone marrow stem cell and function in mediating the inflammatory process and immediate hypersensitivity reactions, have numerous granules in the cytoplasm containing heparin, contain histamine (primary mediator, present in granules, also has ECF and NCF) and other secondary mediators (formed at the time of release), contains several mito, sparse RER, and small golgi
mucosal mast cells
found in the alimentary tract (respiratory and digestive tracts) and contain chondoritin sulfate as opposed to heparin
immediate hypersensitivity reaction
induced by antigens and subsequent formation of IgE antibodies (which bind to the FceRI receptors, steps include
1. binding of the antigen causing cross-linking of IgE and clustering of receptors
2. activation of adenylate cyclase
3. activation of protein kinase
4. phosphorylation of protein
5. INC in intracellular [Ca2+] leading to degranulation of primary mediators (heparin, histamine, ECF, NCF)
6. for secondary release, activation of phospholipases which acts on membrane phospholipids to form arachidonic acid
7. arachidonic acid is converted into secondary mediators and secretion of leukotrienes, thromboxanes and prostaglandins occurs
this causes an initiation of the inflammatory response, attracting leukocytes to sites of inflammation and modulates the degree of inflammation
histamine
causes vasodilation and INC vascular permability, causes bronchiospasm and INC mucus production
neutral proteases
cleavage of proteins to activate other agents of inflammation
eosinophil chemotactic factor (ECF)
attracts eosinophils to site of inflammation, phagocytose antigen-antibody complexes, destroys parasites
neutrophil chemotactic factor (NCF)
attracts neutrophils to site of inflammation, phagocytose and kill microorganisms
leukotrienes C4, D4, and E4
INC vascular permeability and cause bronchiospasm, more potent than histamine
prostaglandin D2
causes bronchiospasm and INC secretion of mucus
Platelet activating factor (PAF)
causes greater vascular permeability
Thromboxane A2
vasoconstrictor, platelet aggregate mediator
bradykinin
vascular dilator, responsible for pain
macrophages
belong to the mononuclear phagocytic system (which arise from bone marrow stem cells) and are subdivided into two groups of cells (phagocytes and antigen presenting cells), can be fixed or transient, fxn in removing cellular debris and in protecting the body against foreign invaders, as well as initiating the immune response, use their lysosomes to degrade ingested material, has well developed golgi, prominent ER, lott of lysosomes
macrophage colony stimulating factor (M-CSF)
activate the transformation of monocytes into macrophages
plasma cells
derived from B lymphocytes and manufacture antibodies, responsible for humorally mediated immunity, have clock face nucleus, present in greatest amounts in areas of chronic inflammation, lots of RER, few mito, large golgi, pair of centrioles
leukocytes
exit the bloodstream during inflammation, invasion by foreign elements, immune responses in order to perform various functions, white blood cells, types include monocytes, neutrophils, eosinophils, basophils, and lymphocytes
neutrophils
phagocytose and digest bacteria, result in formation of pus
eosinophils
combat parasites by releasing cytotoxins, moderate the allergic reaction and phaocytose antibody-antigen complexes
basophils
release preformed and newly synthesized pharmacological agents, control inflammatory response, like mast cells
messenchymal CT
contain mesenchyma cells and ground substance containing reticular fibers, only found in embryos and maybe the pulp of teeth
Wharton’s jelly
found only in the umbilical cord and subdermal CT of the embryo, composed of hyaluronic acid and Type 1 and 3 collagen fibers and fibroblasts
loose (areolar) CT
fills in the spaecs of the body just deep to the skin, lies below the mesothelial lining of the internal body cavity, adventitia of blood vessels and surrounds the parenchyma of glands, has nerve fibers and blood vessels coursing throughout, first site where the body fights antigens, bacteria, and foreign invaders
dense irregular CT
coarse collagen fibers that resists stress from all directions, also has some elastic fibers, constitutes the dermis of the skin, the sheaths of nerves and the capsules of the spleen, testes, ovary, kidney and lymph nodes
dense regular collagenous CT
composed of coarse collagen bundles oriented in parallel sheets that resist tensile forces, make up tendonds, ligaments, and aponeuroses
dense regular elastic CT
coarse elastic fibers with only a few collagenous ones, arranged parallel direction, found in large blood vessels, ligamenta flava, and suspensory ligament of peni
reticular tissue
composed of type 3 collagen, forms framework of liver sinusoids, adipose tissue, spleen and islets of Langerhans
white (unilocular) adipose tissue
single lipid droplet, heavily vascular, septa partition fat into lobules, in men found in the neck, shoulders, hips, and in women found in breasts, buttocks, hips and thighs
brown (multilocular) adipose tissue
store fat in multiple droplets, heavily vascular, abundant mito, innervated directly, found in newborns, can oxidize fatty acids 20 times the rate of white, INC body heat
cartilage vasculature
is avascular, lacks nerves and lymphatic vessels as well
functions of Cartilage
resists mechanical stresses
shock absorber
friction free movement of joints
hyaline cartilage
contains type II collagen (40% of dry weight, basophillic), most abundant cartilage in the body, forms template for endochondral bone formation, can resist both tension (interaction of proteoglycans w/ collagen) and compression (aggrecans)
found in nose and larynx, ends of ribs, trachea and bronchi
elastic cartilage
contains type II collagen and elastic fibers, more chondrocytes than in hyaline, elastic fibers in perichondrium as well
found in pinna of ear, epiglottis
fibrocartilage
contains type I collagen (acidophilic), no perichondrium
found in IV disks, pubic symphysis, and articular disks
perichondrium
vascular CT, an outer fibrous layer (type I collagen and fibroblasts) and an inner cellular layer (chondrogenic cells), responsible for growth and maintanence of the cartilage
chondrification centers
dense masses of mesenchymal cells that differentiate into chondroblasts
interstitial growth of hyaline cartilage
when isogenous groups manufacture matrix and push away from each other forming two separate chondrocytes, occurs only in the early stages, serves to lengthen bone
appositional growth of hyaline cartilage
when chondrogenic cells of the cellular layer of the perichondrium differentiate into fibroblasts and secrete matrix on the periphery of the cartilage
territorial matrix
surrounds lacunae, poor in collagen but rich in chondroitin sulfate, stain darker
interterritorial matrix
righer in type II collagen and poorer in proteoglycans
pericellular capsule
surrounds the lacunae, may protect chondrocytes from mechanical stress
thyroxine, testosterone, and somatotropin effect on hyaline cartilage
stimulate cartilage growth and matrix formation
cortisone, hydrocortisone, and estradiol effect on hyaline cartilage
inhibit cartilage growth and matrix formation
hypovitaminosis A effect on hyaline cartilage
reduces width of epiphyseal plates
hypervitaminosis A effect on hyaline cartilage
accelerates ossification of epiphyseal plates
hypovitaminosis C effect on hyaline cartilage
inhibits matrix synthesis and deforms architecture of epiphyseal plate, scurvy
absence of vita D
results in deficiency in absorption of calcium, matrix is not calcified resulting in rickets
pressure vs. tension on bone
pressure leads to resorption of bone while tension on bone results on development of new bone
endosteum
lines the central cavity of bone, a thin CT layer composed of osteoprogenitor cells and osteoblasts
osteoclasts
multinucleated giant cells derived from fused bone marrow precursors responsible for bone resorption and remodeling
advantage and disadvantage for decalcified vs. ground sections of bone
decalcified-distorted osteocytes
ground-cells are destroyed and the lacunae and canaliculi are filled in with bone debris
inorganic component of bone
calcium hydroxyappatite, mostly calcium and phosphorous, 65% of dry weight, gives bone its hardness and strength, has a hydration shell that permits ion exchange with the EC fluid (crystals attract H2O)
organic component of bone
type I collagen, 35% of dry weight, stained with PAS bec. of sulfated GAGs
osteocalcin
a glycoprotein, binds to hydroxyapatite
osteopontin
a glycoprotein, binds to hydroxyapatite but has additional binding sites for integrins
bone siaolprotein
binding sites for matrix components and integrins
osteoprogenitor cells location
can be found in the cellular layer of periosteum, on the inner lining of the haversian canal, and in the endosteum
bone morphogenic protein (BMP) and transforming growth factor-beta
turn osteoprogenitor cells into osteoblasts
osteoid
substance secreted by osteoblasts, it is an uncalcified bone matrix
bone-lining cells
inactive osteoblasts, more flattened, can be reactivated by the proper stimulus
osteoblast cell membrane
has integrins and parathyroid hormone receptors, when PTH binds it stimulates osteoblasts to secrete osteoprotegerin ligand (OPGL) (induces differentiation of preosteoclasts into osteoclasts, INC RANKL (receptor for NF-kappa B) expression
osteocytes
bone maintanence, also implicated in mechanotrsnduction (respond to stimuli that place tension on bone by releasing cAMP and osteocalcin that recruit osteoblasts to assist in bone remodeling)
periosteocytic space
interval between the osteocyte plasmalemma and the walls of the lacunae, filled with EC fluid (~1.3 L of space) and exposed to as much as 20 g of calcium for exchange
osteoclasts
acidophilic cytoplasm, has receptors for osteoclast stimulating factor, colongy-stimulating factor, osteoprotegerin (OPG) and calcitonin, precursors arise from bone marrow, part of the mononuclear phagocyte system
regulation of osteoclast differentiation
three signals released by osteoblasts (but osteoclast may be activated by different cells of other tissues, such as cardiovascular or lung):
1. macrophage colony stimulating factor (M-CSF)-binds to a receptor on a macrophage and stimulates it to become a osteoclast precursor, also induces expression of RANK (receptor for NF-kappa B)
2. RANKL-binds to RANKL receptor on the osteoclastic precursor and activating it
3. osteoprotegerin (OPG)-member of TNF receptor family, serves as a decoy by interacting with RANKL, inhibiting osteoclast formation
inhibition of osteoclast resorption
can be inhibited by cytokines, peptides, hormones or even tensional forces
regions of ostecolast resorption
1. basal zone-farthest from the Howship lacunae, houses most of the organelles
2. ruffled border-portion of the cell responsible for bone resorption, have finger-like processes that project into the subosteoclastic compartment (resorption compartment)
3. clear zone-immediately surrounds the periphery of the ruffled border, organelle free, contains actin that forms an actin ring (which is regulated by the presence of OPGL), helps integrins stay in contact with the Howship lacunae (forms sealing zone)
4. vesicular zone-consists of numerous endocytotic and exocytotic vesicles that ferry lysosomal enzymes into the subosteoclastic compartment and the products of bone degradation into the cell, between the basal zone and the ruffled border
mechanism of bone resorption
presence of carbonic anhydrase, have Na+ bind to bicarbonate ion and leave through capillary, H+ pumps in the ruffled border pump H+ into the subosteoclastic compartment to DEC pH dissolving the inorganic compartment
lysosomal hydrolases and metalloproteinases (function in bone resoprtion)
ex: collagenase and gelatinase
responsible for degrading the organic component, byproducts broken down by osteoclasts into aa’s and monosaccharides which are then released into capillaries
hormonal control of bone resorption
PTH and calcitonin
periosteum
covers diaphysis of bone (except where muscle or tendons attach), not epiphysis, also absent from sesamoid bones, a dense irregular CT, outer fibrous layer responsible for the blood and nerve supply to the bone, inner cellular layer house osteoprogenitor cells and osteoblasts
calvaria
skull cap
primary (immature) bone
first bone to form during fetal development and repair, abundant osteocytes and irregular collagen bundles, DEC mineral content
secondary (mature) bone
composed of parallel or concentric bony lamellae, osteocytes dispersed at regular intervals, canaliculi present, more calcified matrix, stronger bone, parallel collagen bundles
lamellar system of compact bone
4 layers
1. outer circumferential-just deep to the periosteum, containing Sharpey’s fibers
2. inner circumferential-completely encircles the marrow cavity, trabeculae extend from here into the marrow cavity
3. osteons-haversian canal system, bounded by cementing line (calcified ground substance w/ some collagen fibers)
4. interstitial lamellae-remnants of osteons, irregular arcs of lamellar fragments
intramembranous bone formation
makes most flat bone, formation occurs within mesenchymal tissue, mesenchyme differentiates into osteoblasts, osteoblasts secrete bone matrix that becomes spicules and trabeculae (which are randomly oriented initially), calcification occurs and osteocytes form, vascular CT is transformed into bone marrow while uncalcified mesenchymal tissue becomes the periosteum and endosteum, spongy bone just deep to the pericranium and dura matter becomes compact bone
endochondral bone formation
occurs from a hyaline cartilage template, most of the long and short bones
at the primary center of ossification:
1. perichondrium at the midriff of diaphysis becomes vascularized
2. osteoblasts secrete matrix, forming subperiosteal bone collar
3. chondrocytes within the diaphysis core hypertrophy, die and degenerate
4. osteoclasts etch holes in subperiosteal bone collar, permitting entrance of osteogenic bud
5. calcified cartilage/calcified bone complex is formed
6. osteoclasts begin resorbing the calcified cartilage/bone complex
7. subperiosteal bone collar thickens, beings growing toward the epiphyses
at the secondary center of ossification
1. ossification begins at the epiphysis (no bone collar, osteoblasts lay down bone matrix on calcified cartilage scaffold)
2. growth of bone occurs at epiphyseal plate (growth added to epiphyseal end of plate, bone is added at the diaphyseal end)
3. epiphysis and diaphysis become continuous
bone growth in length
depends on the epiphyseal plate, 5 zones:
1. zone of reserve cartilage-mitotically active chondrocytes
2. zone of proliferation-rapidly proliferating chondrocytes in rows of isogenous groups
3. zone of maturation and hypertrophy-accumulate glycogen here
4. zone of calcification-lacunae become confluent, hypertrophied chondrocytes die, and cartilage matrix becomes calcified
5. zone of ossification-osteoprogenitor cells invade the area and differentiate into osteoblasts, place matrix on the calcified cartilage
bone growth in width
appositional, osteoprogenitor cells proliferate and differentiate into osteoblasts that place bone matrix on the subperiosteal bone surface
stimulation of calcification
by osteonectin and bone sialoprotein
heterogeneous nucleation
collagen fibers are nucleation sites for calcium and phosphate solution which begins to crystallize in the gap region, once nucleated, calcification proceeds
nidi of crystallization
calcium hydroxyapatite released from matrix vesicles fosters the calcification of matrix
bone remodeling
cortical and cancellous bone remodeling is under the influence of bone marrow paracrine hormones (IL-1, TNF-alpha), compact bone remodeling is under the influence of systemic factors (PTH and calcitonin)
absorption cavities
site of bone remodeling and resorption for osteoclasts, once resorbed to the right amount, it become vascularized and osteoblasts lay down new bone matrix
coupling in terms of bone remodeling
bone resorption followed by bone replacement
bone repair
involves both intramembanous and endochondral bone formation as well as cartilage formation, involves three zones
1. a layer of new bone cemented to the bone of the fragment
2. an intermediate layer of cartilage
3. a proliferating osteogenic surface layer
granulation tissue in bone repair
invasion of a blood clot by small capillaries and fibroblasts
internal callus
bony trabeculae from the clot being invaded by osteoprogenitor cells of the endosteum
somatotropin
growth hormone, influence bone development, stimulating growth of the epiphyseal plates
IL-1 in bone-related function
released by osteoblasts, activates osteoclasts proliferation and stimulation
TNF in bone-related function
released by activated macrophages, acts similar to IL-1
Colony-stimulating factor-1 in bone-related function
released by bone marrow stromal cells, induces osteoclast formation
OPG in bone-related function
inhibits osteoclast differentiation
IL-6 in bone-related function
released by various bone cells, stimulates the formation of other osteoclasts
interferon-gamma in bone-related function
released by T lymphocytes, inhibits differentiation of osteoclast precursors into osteoclasts
transforming growth factor beta
induces osteoblasts to manufacture bone matrix
synarthroses joints
bones closely bound together with only a minimum of movements, 3 types
1. synostosis-skull bones in adult, joint-uniting tissue is bone
2. synchondrosis-joint of first rib and sternum, joint uniting tissue is hyaline cartilage
3. syndesmosis-pubic symphisis, joint uniting tissue is dense connective tissue
diarthrosis (synovial joint)
joints in which the bones are free to articulate with a wide range of motion, covered by hyaline cartilage, 2 kinds of cells:
1. type A cells-macrophages, remove debris from the joint space
2. type B cells-resemble fibroblasts, secrete synovial fluid (high conc. of hyaluronic acid and lubricin
mesoderm
gives rise to muscle tissue
myoblasts
precursors of muscle fibers
myotubes
long multinucleated cells formed by the fusion of myoblasts
strength of a muscle fiber as opposed to the strength of the entire muscle
muscle fiber strength dependent on the length of the muscle fiber while the entire muscle’s strength is dependent on number and thickness of its component fibers
red slow muscle fibers
rich vascular supply
smaller nerve fibers
small fiber diameter
slow, repetitive, weaker contraction, not easily fatigued
not extensive sarcoplasmic reticulum
numerous mitochondria
rich myoglobin
rich in oxidative enzymes, poor in ATP
white fast muscle fibers
poor vascular supply
larger nerve fibers
large fiber diameter
fast, stronger contraction, easily fatigued
extensive sarcoplasmic reticulum
few mitochondria
poor myoglobin
poor in oxidative enzymes, rich in ATP
type of muscle fiber depends on:
innervation, if switched then can switch fiber type
epimysium
outer layer surrounding entire muscle, dense irregular CT
endomysium
has reticular fibers and an external lamina
satellite cells
act as regenerative cells
T-tubules
lie specifically at the junction of the A and I band
terminal cisternae
a meshwork of sarcoplasmic reticulum around each myofibril at each A-I junction
triad
a t-tubule flanked by two terminal cisternae
what holds myofibrils together
intermediate filaments desmin and vimentin, secure the periphery of Z disk to each other
dystrophin
protein that binds to actin
myomesin (C protein)
compose the M line that bisects the H band, responsible for cross-linking thick filaments
Huxley’s sliding filament theory
theory of contraction, actin slides over myosin towards the center
muscle fiber arrangement
each thick filament is surrounded by 6 thin filaments
titin
help in the positioning of thick filaments within the sarcomere, an elastic protein, 2 for each half that projects to the Z disk, so 4 total that anchor a thick filament to the z disk
alpha actinin
rod shaped protein that holds thin filaments in their position
Cap Z
holds plus end (z-disk side) of the thin filament in place, also prevents the addition or subtraction of G-actin molecules to or from the thin filament
nebulin
two wrap around the entire length of each thin filament, further anchoring it to the Z disk, acts as a ruler ensuring the precise length of the actin
tropomodulin
cap on the minus end (near the center) of the actin that helps nebulin ensure proper size of thin filament
thick filament composition
composed of 200 to 300 myosin II molecules, each myosin II has two identical heavy chains and two pairs of light chains (so 2 heavy chains and 4 light chains), each myosin II also has two flexible regions (at the junction of the heavy and light meromyosin and the junction of the S1 and S2 subfragments)
heavy chain of myosin
can be cleaved by trypsin into a light meromyosin and heavy meromyosin
light meromyosin
rod-like tail composed of most of the two rod-like polypeptide chains wrapped around each other, functions in proper assembly
heavy meromyosin
two globular heads with the attendant short proximal proation of the two rod-like chains, cleaved further into 2 S1 globular moieties and a short, helical S2 rod
S1 subfragment of heavy meromyosin
binds ATP and functionsin the formation of cross-bridges between the thick and thin myofilaments
light chain of myosin
two types, one of each type is associated with each S1 subfragment
thin filament composition
2 F-actin components (+ end bound to Z-disk and minus end extending toward the center of the sarcomere) wound around each other
tropomyosin
occupy the shallow grooves of the double stranded actin helix masking the active site of the F-actin
troponin
binds to tropomyosin, composed of three globular polypeptides (TnT (tropomyosin), TnC (Ca2+), and TnI (actin))
calsequestrin
binds Ca2+ ions that are driven back into the sarcoplasmic reticulum when the stimulus for muscle contraction ceases
phosphogen energy system
composed of both ATP and creatine phosphate in the skeletal muscle cells, enough energy for about 9 seconds of maximal muscle activity (3 for ATP and 6 for creatine phosphate)
glycolysis
anaerobic system of energy that brings about a build up of lactic acid, about 90 to 100 sec. worth of energy
aerobic energy system
manufactures ATP through the normal diet and aerobically, can sustain indefinite contraction as long as nutrition levels are kept where they need to be
phosphocreatine kinase
switches phosphate group from creatine phosphate to ADP to make ATP
myotendinous junction
allows for the transfer of the muscle contraction to reach the tendon that the muscle is attached to
motor unit
group of muscle fibers that are innervated by one motor neuron, muscles contract in unison
junctional folds (secondary synaptic clefts)
modifications of the sarcolemma that allow for INC SA for synaptic transmission
sarcoplasm in the vicinity of the synaptic cleft
rich in glycogen, nuclei, ribosomes, and mito
dense bars
linearly arranged structures that house the voltage gated Ca2+ channels
sodium-choline symport
transports choline back into the axon terminal after degradation by acetylcholinseterase
choline acetyl transferase
within the axon terminal, catalyzes the production of acetylcholine from the transported choline and activated acetate (produced in mito) and puts it back into synaptic vesicles
clathrin coated endocytotic vesicles
allow for the recycling of synaptic vesicle membranes, becomes the newly formed synaptic vesicles
muscle spindles
provide feedback about the changes in muscle length as well as the rate of alteration in muscle length, an encapsulated sensory receptor located among the muscle cells, composed of 8-10 intrafusal fibers surrounded by the fluid-containing periaxial space, which in turn is covered by the capsule
intrafusal fibers
two types (nuclear bag fibers (static and dynamic) and nuclear chain fibers)
golgi tendon organs
monitor the tension as well as the rate at which the tension is being produced during movement (the intensity of contraction), composed of wavy collagen fibers, when the muscle contracts it places tensile forces on the collagen fibers, straightening them, the rate of firing of the entwined nerve ending is related to the amount of tension placed on the tendon, provide an inhibitory feedback resulting in relaxation of the contracting muscle
mito in cardiac muscle
mito occupy about half the volume of cardiac muscle cells attesting to the great energy consumption, energy supply of the heart provided by glycogen (some) and triglycerides (most)
atrial natriuretic peptide
substance that functions to lower blood pressure, acts by DEC the capabilites of renal tubules to resorb (conserve) sodium and water
intercalated disks
has a transverse portion (where fasciae adherents (analogous to Z disks) and desmosomes abound) and lateral portions (rich in gap junctions)
thin myofilaments
attach to fasciae adherents
dyad in cardiac muscle
T-tubule is only approximated by one small terminal of sarcoplasmic reticulum, located at the vicinity of the Z-line, Ca2+ still comes through the T-tubule, but the supply comes from the extracellular fluid (and also from the (-) charge T-tubule which also has some stores)
fast sodium channels
open and close rapidly leading to the generation of a very rapid action potential
slow sodium channels (Ca2+-Na+ channels)
slow to open initially, remain open for a considerable time, Na+ and Ca2+ enter the cardiac muscle cell cytoplasm and INC [Ca2+], also K+ leaves quickly, restoring the membrane potential quickly
multiunit smooth muscle
contract independently of one antoher, each muscle has its own nerve supply
unitary smooth muscle
form gap juntions with those of contiguous smooth muscle cells, nerve fibers form synapses with only a few of the muscle fibers, these cannot contract independently of each other
dense bodies
adhere to the cytoplasmic aspect of the cell membrane of smooth muscle cells, insertion point for intermediate filaments and thin filaments (like Z disk),
thin filaments of smooth muscle
composed of actin (with its associated caldesmon (which blocks the active site) and tropomyosin)
thick filaments of smooth muscle
also composed of myosin II, the S1 heads project throughout the length of the fiber, with the ends lacking the heavy meromyosin, also light meromyosin covers the actin binding site on myosin II, this arrangement allows for contractions of long duration
all or none and smooth muscle
doesn’t exist, only a portion of the cell may contract, or all
caveolae
act as T-tubules in regulating the cytosolic free Ca2+ ion concentration
calmodulin and smooth muscle contraction
Ca2+ binds here (through the help of caveolae), then binds to caldesmon, causing its release from the active site on actin and activates myosin light chain kinase
myosin light chain kinase and smooth muscle contraction
phosphorylates the regulatory chain on the myosin light chain permitting the unfolding of the light meromyosin moiety to form the typical gold club shape myosin II permitting the interaction between actin and the S1 subfragment of myosin II resulting in contraction
smooth muscle contraction
takes longer, prolonged and requires less energy
hypolemmal cisternae
formed from SER that enters the dendrites and axon, function in sequestering Ca2+ and containing protein
mitochondria of cell body
numerous, but most abundant in the axon terminals
melanin granules in nervous tissue
thought to be a by-product of the synthesis of dopamine and noreadrenaline
lipofuscin
remnant of lysosomal enzymatic activity, not found in Purkinje cells of the cerebellum
types of neurofibrils in neuron
microtubules
neurofilaments
microfilaments
lack of ER and mito in the nervous tissue
at the axon hillock and at the nodes of Ranvier
horseradish peroxidase
when injected into the axon terminal, can follow to the cell body, helped in the study of axonal retrograde transport
kinesin
a microtubule associated protein used in anterograde transport, one end attaches to a vesicle and the other end interacts in a cyclical fashion with a microtubule
dynein
responsible for moving vesicles along the microtubules in retrograde transport
unipolar neurons
impulse transmission does not involve the cell body, found in the DRG and some cranial nerve ganglia
types of neuroglia
astrocytes
oligodendrocytes
microglial cells
ependymal cells
Schwann cells
astrocytes
provide structural and metabolic support to neurons and act as scavengers of ions and neurotransmitters released into the extracellular space, largest of the neuroglial cells, consist of two types (protoplasmic and fibrous), may assist in maintaining the blood-brain barrier, may also form cellular scar tissue
protoplasmic astrocytes
found in the gray matter of the CNS, tips of some processes (which are short) end as pedicels that come into contact with blood vessels, can form pia-glial membrane, may also act as satellite cellsfibrous astrocytes
fibrous astrocytes
present mainly in the white matter of the CNS, store glycogen, may be released to the cerebral cortex by insulin stimulation, may assist in maintaining the blood-brain barrier, may also form cellular scar tissue
oligodendrocytes
myelination in the CNS, darkest staining neuroglial cells
microglial cells
members of the mononuclear phagocyte system, function as phagocytes
ependymal cells
form limiting membranes and function in the transport of CSF, line ventricles of the brain and central canal of the spinal cord, may be ciliated, participate in the formation of the choroid plexus
choroid plexus
responsible for secreting and maintaining the chemical composition of the CSF, simple cuboidal epithelium, composed of folds of pia matter
Meissner’s plexus and Auerbach’s plexus
axons of the parasympathetic system project to these terminal ganglia, are in the walls of the lower GI tract, synaps on cell bodies of postganglionic parasympathetic neurons
cerebral cortex
responsible for learning, memory, sensory integration and motor responses
1. molecular layer-composed mostly of nerve terminals originating in other areas of the brain, horizontal cells, and neuroglia, deep to the pia matter
2. external granular layer-contains mostly granule (stellate) cells and neuroglial cells
3. external pyramidal layer-neuroglial cells and pyramidal cells
4. internal granular layer-closely arragned granule cells, pyramidal cells and neuroglia, greatest cell density
5. internal pyramidal layer-contains the largest pyramidal cells and neuroglia, lowest cell density
6. multiform layer-consists of Martinotti cells and neuroglia
cerebrellar cortex
responsible for balance, equilibrium, muscle tone, and muscle coordination, the layer of gray matter
1. molecular layer-below the pia matter, superficial stellate cells, dendrites of Purkinje cells and unmyelinated axons from the granular layer
2. purkinje cell layer-purkinje cells (dendrites in molecular layer, axons in white matter), purkinje cells always have an inhibitory output using GABA
3. granular layer-consists of small granule cells and glomeruli (place of synapse)
neuron regeneration
damage to CNS is permanent
peripheral nerve fiber regeneration
attempts are made to repair the damage, regenerate the process and restore function by activating the axon reaction, cuts must be near each other or regeneration is unsuccessful
axon reaction
reaction to the trauma is localized to three regions
1. at the site of damage (local changes)
2. distal to the site of damage (anterograde changes)
3. proximal to the site of damage (retrograde changes)
local reaction in axon reaction
involves repair and removal of debris by neuroglial cells, ends fuse to prevent loss of axoplasm, macrophages and fibroblasts secrete cytokines and growth factors and upregulate the expression of their receptors
anterograde reaction in axon reaction
1. the axon terminal becomes hypertrophied and degenerates within a week, Schwann cells proliferate and phagocytose remnants of the axon terminal and a new Schwann cell occupies the synaptic space
2. undergo wallerian degeneration (orthograde degeneration), the axon and myelin disintegrate, Schwann cells dedifferentiate and myelin synthesis is discontinued, phagocytosis of disintegrated remnants
3. schwann cells proliferate, forming a column of Schwann cells
retrograde reaction and regeneration in axon reaction
1. perikaryon of damaged neuron becomes hypertrophied, nissl bodies disperse and nucleus is displaced (all three called chromatolysis), soma produces free ribosomes and proteins, proximal axon stump and myelin degenerate to the nearest collateral axon
2. from the proximal axon stump, several sprouts of axons emerge and are guided by the Schwann cells to their target cell
3. Schwann cells redifferentiate and begin to manufacture myelin
transneuronal degeneration
where target cells of the dead neuron atrophy and degenerate
glial scar
mass of glial cells that occupy a space made by microglia that phagocytose injured cells in the CNS, these hinder repair