Last unit Flashcards
_____ _______ occurs whenever cells touch appropriate substrata
cell adhesion
In epithelia, cells form specialized, morphologically distinct devices called _______ ________
intercellular junctions
Four major classes of molecules in the ECF
- glycosaminoglycans (GAGs), usually linked covalently to proteins to form proteoglycans;
- fibrous proteins, such as collagen and elastin;
- multidomain adapter proteins, such as fibronectin and laminin;
- water and many solutes.
glycosaminoglycans (GAGs) are usually linked covalently to proteins to form _________
proteoglycans
elastin and collagen are examples of
fibrous proteins
Fibronectin and laminin are examples of
multidomain adapter protiens
The proteoglycan molecules form a highly ________ ___ in which the fibrous and multidomain proteins are embedded
hydrated gel
Two of the basal lamina’s characteristic components are:
collagen IV and laminin
GAGs consist of unbranched ________ chains composed of ________ repeats.
polysaccharide, disaccharide
Sulfation and carboxyl groups convey to the GAGs a high negative charge and, thus, the capacity to become _____ ______
highly hydrated
Glucosamines typically bind to specific proteins, with the exception of ______ ______
hylaluronic acid
purposes of GAGs
- create hydrogel in ECM
- Maintain gradients of different signaling morphogens
- Cell adhesion
- Preventing liquid leakage between high and low pressure environments
proteoglycans are covalently linked complexes of _____ and _______, typically of very high molecular weight.
GAGs and protein
_____ ______ are the most abundant proteins in mammals (about 25% of protein mass)
fibrous proteins
Which type of collagen is the most common form, abundant in connective tissues?
Collagen I
Which type of collagen is characteristic of the basal lamina
Collagen IV
Fibronectin
Component of ECM:large, dimeric glycoprotein whose two large subunits are linked together by disulfide bonds. Each subunit is folded into a series of functionally distinct binding domains.
Laminin
very large protein, composed of three subunits (α,β,γ) that form an asymmetric, disulfide-linked cross with the longer arm formed by a helical structure containing long stretches of all three subunits. Laminin is found in the basal lamina only (hence its name).
Cadherins
single-pass transmembrane glycoproteins that operate as homodimers. They are very common in intercellular junctional complexes. Must be anchored to actin cytoskeleton
Integrins
These are the “classic” adhesion molecules interacting with the ECM. Thus, their binding is heterophilic. Integrins are composed of α/β heterodimers. Many different α and β sub-units exist (both are transmembrane glycoproteins). They are mixed and matched to some degree.
What accounts for the large variety of integrins?
Since both subunits participate in ligand binding, this results in a large variety of integrins with distinct binding selectivities
CAMs
proteins located on the cell surface involved in binding with other cells or with (ECM) in cell adhesion.
Structure of CAMs
an intracellular domain that interacts with the cytoskeleton, a transmembrane domain, and an extracellular IgG like domain that interacts with other CAMs
Signaling molecules can be ________ by cell-cell adhesion
activated
endosymbiont hypothesis
the inner mitochondria membrane is derived from bacteria, while the outer membrane would be derived from eukaryotic cell.
Comment on the permeability of the mitochondrial membranes
The outer membrane is semi-permeable. The inner membrane is much less-permeable and contains most of the machinery required for oxidative phsophorylation
cristae
area of inner membrane with large number of infoldings
Mitochondrial matrix
The central space of mitochondria
TOM (translocase of outer membrane) and TIM (translocase of inner membrane) complexes
Import mitochondrial proteins into the mitochondria after they are synthesized in cytosol
Mitochondria are very dynamic organelles that undergo constant ____ and ____.
fusion and fission
Fusion plays a key role in:
repairing damaged mitochondria
Fission is required for
mitophagy
cellular GTPases for fusion
Mfn and OPA1
Cellular GTPases for fission
Fis1 and Drp
Most of the free energy released during oxidation of glucose is retained in the:
reducing coenzymes such as NADH
Electron transport across the inner membrane generates
a proton concentration gradient, electric potential
ATP synthase consists from two main parts:
F1 and F0.
F0 protein complex of ATP synthase
spans the inner mitochondria membrane and forms a proton channel.F0 uses the energy of proton movement through the channel to generate ATP.
How many protons are needed to generate 1 ATP molecule in ATP synthase?
3
Once made, ATP is transported out of mitochondria via the—–
ATP-ADP antiporter
Release of cytochrome c from the mitochondria depends on
Bak/Bax-dependent permeabilization of outer mitochondria membrane
apoptosome
Cytochrome c bound to several cytpolasmic proteins forming protein complex
Apoptosome activates ______, thus intiating apoptosis
caspases
When/why might ATP synthase become an ATPase
in the absence of proton gradient, ATP synthase is converted into ATPase, thus using up available ATP. That leads to ATP depletion and necrosis.
Damaged mitochondria are incapable of producing ATP, and also generate excessive amounts of:
reactive oxygen (ROS)
mitochondrial proteases responsible for recognizing and degrading misfolded proteins
mAAA, iAAA and Lon
Regulation of mitochondrial quality
- mitochondrial proteases mAAA, iAAA and Lon recognize and degrade misfolded proteins.
- damaged mitochondria can be “fixed” by fusing with healthy mitochondria, or eliminated by mitophagy.
- If mitochondria damage is extensive, mitochondria induces apoptotic cell death
hereditary spastic paraplegia
caused by a Mutation in mAAA protease, no quality control of misfolded proteins so they aggregate and cause ROS which kill neurons
Byproducts of glycolysis
2ATP, 2NADH, Pyruvate
Products of the TCA cycle
4 NADH, 1 FADH, Acetyl CoA
of H+ pumped across membrane per NADH
3 H+
What degrades misfolded proteins in the outer membrane of the mitochondria?
Proteosome, as usual
What degrades misfolded proteins in the inner membrane of the mitochondria?
mAAA
What recognizes and degrades misfolded proteins in the matrix?
Lon
Parts of ATP synthase
H+ channel, globular head (alternates alpha and beta subunits) and a shaft that secures the head
Steps of ATPase action (conformational changes)
1) binds ADP and Pi
2) Brings them together to make ATP
3) Affinity for ATP decreases, releases it
2 times when a cell can “decide to die” or not
1) Bax/Bac-if they get apoptotic signal they oligimerize and form channel so that cyt c leaks out
2) If cyt c is reduced at the last minute, cell will survive
ketoconazole
anti fungal drug but used in prostate cancer because it suppresses the adrenal glands, and therefore a circulating source of testosterone
Structural parts of the androgen receptor
- N terminus transactivation domain (NTD)
- DNA binding domain (DBD)
- Hinge region
- C-terminus ligand binding domain (LBD
Androgen receptor mechanism
The AR resides in the cytoplasm when not associated with an androgen
Testosterone is the most common androgen
Upon ligand binding inhibitory chaperones are dissociated and AR moves to the nucleus
AR undergoes homo-dimerization and binds to the androgen-responsive elements of the DNA
After binding, AR recruits co-activators and gene expression occurs.
Sources of testosterone
Testis – 90-95% of systemic testosterone
Adrenal glands 5-10% of systemic testosterone
Intracrine androgen production in the prostate cancer cells themselves
Ways to reduce testosterone
1) Surgical orchiectomy or medical castration
2) Block receptor activity with an anti-androgen (e.g. bicalutamide)
Mechanisms of resistance to hormone therapy in PCA
- AR activation via non-gonadal testosterone (most common)
- Overexpression of AR
- AR mutation leading to promiscuous AR activation
- Truncated form of AR, with constitutive activation of the ligand binding domain
Abiraterone
potent inhibitor of CYP 17 that blocks testosterone production from all 3 sources
Main side effects of Abiraterone
Excess of mineral corticoid, causing:
Hypokalemia
Edema
Hypertension
Enzalutamide (MDV3100)
antiandrogen drug
Mechanism of action of Enzalutamide
Blocks testosterone binding
Inhibits nuclear translocation
Inhibits Co-activator recruitment
Inhibits DNA binding of AR
Benefits of Enzalutamide over old therapy (bicalutamide)
5-8X stronger binding
No known partial agonist properties like biclutamide
Does Enzalutamide reduce the levels of testosterone?
No, it inhibits receptor activity
Epithelia function
- Protection
- Selective transport
- Biochemical modification of molecules (e.g. liver detoxifies)
- Communication (i.e. olfaction, taste, etc)
endothelium
A tissue that faces blood and lymph
mesothelium
the sheets of cells that line the enclosed internal spaces of the body cavities
The surface layer of all mucosae is an _______
epithelium
Which germ layer is epithelium derived from?
all 3!
mucosae
moist internal linings (mouth, nose, throat, GI tract, reproductive systems, etc.) that separate “outside” from “inside”
submucosa
deeper CT tissue
Most common CF mutation
F508del, although 1500 disease causing mutations are known
Typical features of CF
- Greasy, bulky, malodorous stools;
- failure to thrive due to exocrine pancreatic insufficiency
- Recurrent respiratory infections with opportunistic bacteria (e.g. Staphylococcus aureus, Pseudomonas aeruginosa and Burkholderia cepacia)
- Chronic sinus infections
- Digital clubbing on examination.
- Bronchiectasis
- Sweat chloride > 60 mmol/L.
most common presentation of CF
failure to thrive
What causes “failure to thrive” in CF patients
Children don’t gain weight despite good appetite and have frequent, bulky, foul-smelling, oily stools. A result of exocrine pancreatic insufficiency, the failure of the pancreas to produce sufficient digestive enzymes to break down and absorb fats and protein. Pancreatic insufficiency occurs in > 85% of persons with CF.
Infants with undiagnosed CF may also present with :
- hypoproteinemia with or without edema,
- anemia
- deficiency of the fat-soluble vitamins A, D, E, and K, because of ongoing steatorrhea
Other findings that should prompt a diagnostic evaluation for CF include:
bronchiectasis, rectal prolapse, nasal polyps, chronic sinusitis, and unexplained pancreatitis or cirrhosis
What GI issue present at birth might indicate CF?
Meconium ileus, a severe intestinal obstruction resulting from inspissation of tenacious meconium in the terminal ileum. Approximately 15% of newborns with CF present at birth with meconium ileus
Respiratory clinical manifestations of CF
productive cough, wheezing, chronic bronchitis and recurrent pneumonias, progressive obstructive airways disease, exercise intolerance, dyspnea, and hemoptysis. Chronic airway infection with bacteria
The predominant pathogen present in CF patients with infection
Pseudomonas aeruginosa
Infection associated with rapid decline in pulmonary function in CF patients
characteristic mucoid Pseudomonas
An acute change in respiratory signs and symptoms from the subject’s baseline is generically termed a ________ _________.
pulmonary exacerbation
Clinically, a CF exacerbation is typically manifested by:
increased cough and sputum production, decreased exercise tolerance, malaise, and anorexia
Symptoms of a CF exacerbation are typically associated with what?
decreased measures of lung function, new chest radiographic findings, or both.
Treatment for pulmonary exacerbations generally consists of:
antibiotics and augmented airway clearance and often requires hospitalization for 1-2 weeks.
CF is a syndrome of chronic _____ _______, malabsorption and _______ ________
sinopulmonary infections, nutritional abnormalities
Median predicted survival age for CF
37
Sinus symptoms in CF patients
sinusitis, nasal polyps
Lung dysfunction in CF
Endobronchitis, bronchiectasis
Pancreas dysfunction in CF
exocrine insufficiency, CF related diabetes
Intestinal dysfunction in CF
meconium ileus, constipation
Liver dysfunction in CF
Focal sclerosis
Reproductive implications of CF
Vas deferens doesn’t develop in males, functionally infertile but can still father children
Where is the CF gene located and how large is it?
Large gene of 250,000 base pairs with 27 exons
located on chromosome 7
At what stage of molecular processing does the DF508 mutation cause problems?
AA deletion, blocks protein processing
End stage CF is characterized by:
Bronchiectasis
Infection
Inflammation
Mucus Plugging
The CTFR protein is a member of the ____________ superfamily
ATP-binding cassette (ABC)
CTFR protein structure
2 six membrane spanning domains (MSD)
2 nucleotide-binding domains (NBD)
Unique, highly charged regulatory (R) domain
Because CL- can not exit the cell but Na+ (and with it water) continue to enter the cell, what happens?
The mucous layer is excessively sticky and it depletes the pericilliary layer
Criteria for diagnosis of CF
Positive NBS OR
>1 clinical feature of CF OR
Family h/o CF
+
Sweat chloride 60 mmol/L &/OR
2 CF mutations
Typical treatment for CF
- Pancreatic enzymes,
- vitamins (problems digesting fat soluble vitamins), -salt
- Vit. E (deficiency=cognitive problem)
- Vest to break up mucus, Huff coughs to cough up mucus
- Inhaled medicine to break up mucus
- Antibiotics because bacteria get trapped
Ivacaftor
CFTR potentiator, Only approved for patients with at least one G551D mutation (4% of CF patients)
Epithelial tumor is called a ______
carcinoma
What value indicates a sweat test positive for CF?
Cl- > 60 mmol/L is diagnostic for cystic fibrosis
Characteristics of epithelial stem cells
1) Capacity for self-renewal
2) Capacity for cell division
3) Generates cells that differentiate and become specified
4) Tightly regulated
Stem cell lineage
Stem cell, its intermediate progeny, and all of the differentiated progeny it makes
Transit amplifying cells
transitional intermediates: daughters that also proliferate themselves (undergo cell division cycles), often at faster rates
Main developmental signaling pathways
Wnt, sonic hedgehog, notch, FGF(RTKs), TGFB
Gland
an elaboration of epithelial sheets that exists for specific secretion
Exocrine glands
secrete on the surface of epithelial sheets and secrete from the APICAL membrane
Endocrine glands
Secrete hormones into blood and work at long distances, Secrete final product from the BASOLATERAL membrane
2 general classes of secretions
Mucous and serous (watery:sweat)
Goblet cells
single cell that creates mucous of the gut (a single-cell exocrine gland)
Acini
A cluster of cells that resembles a “berry,” the berry-shaped termination of an exocrine gland, where the secretion is produced
Simple epithelia
one sheet of cells, one side faces the space and the other the connective tissue
Stratified epithelia
multiple layers of cells, layers of cells do not attach to the basal lamina (not every cell touches the basal lamina)
Transitional epithelium
found in the bladder. Stratified but when it is stretched they form a single sheet
Polarization of epithelial cells
Apical vs basolateral
also internally polarized (secretory vessels and cytoskeleton, for example)
Transcytosis
endocytosis–> crossing of cell–> exocytosis without stopping at the ER or golgi
Claudins
The most important components of the tight junctions, proteins that establish the paracellular barrier that controls the flow of molecules in the intercellular space between the cells of an epithelium
Desmosomes
A cell-to-cell adhesion structure localized on the LATERAL sides of plasma membranes.
Desmosomes help to resist shearing forces. Contain cadherins that attach to intermediate filaments
Adherence junctions
adhesion structure in the lateral membrane. Promotes polarity. Contains cadherins that are bound to actin. Serve as junctions and also function in cell signaling of gene expression, stem cell behavior in epithelial sheet
2 functions of adherens junctions
1) Connect cells, provide structural integrity
2) signaling info to specify type of epithelial cells made, division rate of stem cells, and polarity
Gap junctions
Rapid communication device between cells: intercellular connection that directly connects the cytoplasm of two cells, allowing various molecules and ions to pass freely between cells
Functions of the basal lamina
1) Attachement of epithelia to underlying CT
2) Filtration/barrier
3) polarity
4) Highways for migration of cells through CT compartment
5) controls gene expression of cells: their proliferation or development.
7) control the development, morphogenesis, and organization of epithelial cells, providing a sort of “tissue scaffolding” function.
Basal lamina
meshwork of fibrous proteins, glycoproteins, lamininins, enactin. VERY diverse between cell types
How does the epithelial cell attach to the basal lamina? What is the key class of proteins that form these connections?
- “Focal adhesion” associated with actin
- “hemi-desmosomes” associated with intermediate filaments
- formed by integrins
“Filtration” mechanism of basal lamina
ions and water flow through freely but cells do not. Any cell that wants to travel to the bloodstream needs to breach the basal lamina. Pathological bacteria and tumors do this.
Tight junctions
selective barrier that limits/prevents diffusion of substances between epithelial cells. These also limit/control diffusion of membrane proteins through the plasma membrane bilayer. Key core proteins of tight junctions are OCCLUDINS and CLAUDINS: In some epithelia the “tightness” of this barrier is regulated. Tight barriers ensure that substances absorbed or secreted must pass through the epithelial cell by specific transport pathways.
Functions of Polarity
unidirectional secretion and/or absorption of molecules to or from one side of the epithelium. Polarity is also necessary for “trans-epithelial” transport of ions and macromolecules from the apical to basal surfaces (or visa versa). Transcytosis possible
Epithelial to mesenchymal transition
embryonic epithelia oftn disassemble and move into the mesenchymal (connective) tissues; there they may migrate to other locations to form new epithelia, or they may transform into distinct non-epithelial cell lineages that give rise to other tissues
A typical cell signaling pathway consists of
(i) extracellular ligand secreted by signaling cells
(ii) a receptor in receiving cells that binds the ligand
(iii) downstream effector proteins in the cytoplasm and nucleus
(iv) modulator proteins that promote or suppress pathway components.
stereocilia
found in the epididymis and in sensory cells in the ear. These are extremely long, actin-filled microvilli, and are not related to cilia. In the ear, stereocilia function in the reception of sound.
key principles of signaling pathways:
(i) Each pathway is used by multiple, distinct stem cell systems in different organs/tissues.
(ii) A single signaling pathway often triggers different developmental outcomes in different stem cell lineages.
Glands secrete their substances in one of two general ways:
(1) Exocytosis: (common)
(2) Total cell disintegration, which leads to the entire cellular contents becoming part of the secretion
Ducts
tubular structures that emanate from the secretory units. Ducts function as passageways to conduct secretions to their destinations
Most endocrine cells secrete hormone molecules from the __________ _______.
basolateral membrane
adenocarcinomas
cancers derived from glandular epithelium
The functions of connective tissues (CT):
- mechanical strength and support for the specialized tissues of organs.
- conduct and control exchange of nutrients, metabolites, and signaling ligands between different cell types of organs, and between organ cell types and blood vessels.
- To control the behavior and functions of cells that contact the connective tissue matrix (the ECM).
Known or suspected regulatory functions of this matrix:
a. control of epithelial polarization and shape
b. guidance and regulation of cell migration through the matrix
c. control of cell proliferation, differentiation, and metabolism
d. Defense against infectious agents (viruses and bacteria).
e. Control of tissue formation, organization, and modification of tissue structure upon physiological stimulation and disease.
f. control of inflammation and repair due to injury.
The cells found in connective tissues are of two general categories:
- Core “resident” cells of the CT family
2. Immigrant blood-derived cells:
Purpose of core “resident” cells of the CT family:
These cells produce and secrete the components of the extracellular matrix (ECM)
Core “resident” cells of the CT family:
(i) . Mesenchymal cells
(ii) . Fibroblasts
(iii) . Myofibroblasts
(iv) . Adipocytes
(v) . Osteoblasts and osteocytes
(vi) . Chondrocytes
(vii) . Some smooth muscle cells.
Mesenchymal cells
precursors to all of the connective tissue family members; they primarily function in embryogenesis, but small numbers of them may persist through adulthood to function as stem cells for generation of new connective tissues
Fibroblasts
the pre-eminent cells of most connective tissues in the body
Myofibroblasts
derivatives of fibroblasts are capable of smooth muscle-like function, and are found in connective tissues that require a contractile function. These cells are often generated at the site of wounds where their contractile function contributes to retraction and shrinkage of scar tissue.
Adipocytes
derivatives of fibroblasts and/or primitive mesenchymal cells. The main type of adipocyte found in adults functions to store fat as energy for other cell types; tissue containing these cells is called “white fat”. A distinct type of adipocyte is prominent in newborns and children; it contains many mitochondria that convert fatty acid into heat. Tissue with these cells is called “brown fat”.
Immigrant blood-derived cells
white blood cells that are produced from blood cell precursors (hematopoietic cells) in the bone marrow, and migrate from blood into connective tissue. Many are part of immune system. They are also important for responses to tissue damage, allergic hypersensitivities
Types of Immigrant blood-derived cells
a. Lymphocytes
b. Macrophages
c. Neutrophils and eosinophils
d. Mast cells .
e. Osteoclasts
Lymphocytes
central to acquired immunity to foreign organisms/viruses/materials
Macrophage functions
(i) engulf (phagocytose) invading microorganisms, (ii) promote blood vessel formation (angiogenesis), (iii) remodel damaged tissue,
(iv) remodel normal developing tissue and organs as part of their morphogenesis.
Mast cells
secretory cells that, when stimulated by immune responses, release various substances, including vasodilators to promote swelling in connective tissue; important in edema and allergic hypersensitivities.
Osteoclast origin
phagocytic cells that appear to be derived from blood monocytes and are very similar to macrophages.
Mast cells differentiate from:
blood basophils
Features of fibroblasts
- secretory:produce the fibrous proteins, proteoglycans, and other components of the extracellular matrix (the ECM).
- Capable of cell division to produce new fibroblasts, and possibly other connective tissue types.
- activity and proliferation highly regulated.
- not a single cell type-comprise a diverse collection of closely related cell types.
- developmentally flexible: They can differentiate into other connective tissue cell types
Fibrillar collagen
collagen molecules assembled in large bundles (fibrils). Alignend and stacked to generate length and thickness- great tensile strength. Collagen Type I is an abundant component of fibrillar collagen.
Macrophages and osteoclasts derive and differentiate from _____ _______
blood monocytes
Fibril-associated collagen
These collagens decorate the surfaces of collagen fibrils, and are thought to link collagen fibrils to each other, or to link collage fibrils to other tissue components.
Network-forming collagen
very thin fibers (perhaps a few molecules thick) and assemble into networks that form porous sheets. Found in the basal laminae, and also as anchoring fibers that attach basal lamina and cells to the ECM. Filtration barriers (as in the kidney). Collagen Type IV is a common component of the network-forming sheets in basal lamina
Intracellular collagen modification
- Collagen polypeptides are synthesized on the ER and translocated during synthesis to the ER lumen
- Collagens are PTM (glycosylated and hydroxylated)
- The individual polypeptides are assembled into a triple helix
Extracellular collagen modification
- The N- & C-termini of collagen cleaved. N-terminal fragments = N-telo peptides. Proteolytic release of these fragments initiates:
- Formation of bundles and end-to-end polymers of the collagen fibrils
- Enzymes catalyze chemical cross-links between collagen molecules. These covalent cross-links increase tensile strength of bundles
Elastic fibers are found in connective tissues that require ___ and____. Elastic fibers contain the proteins ____ and ___ that assemble into stretchable and resilient fibers and sheets
distensibility, resiliency
elastin, fibrillin
Three basic steps of wound healing
1) inflammation and blood clotting
2) New tissue formation
3) tissue remodeling
Skeletal system functions
- Protect organs
- Mechanical support for locomotion
- Calcium and phosphate homeostasis
- To house, protect, and regulate the hematopoietic blood system/stem cells
Cartilage has two main functions
(1) resilient but pliable support structure.
(2) to direct the formation and growth of bone.
perichondrium
external layer of connective tissue that surrounds the cartilage
lacuna
As chondrocytes secrete and surround themselves with matrix they become isolated from other cells, eventually residing in an isolated compartment called a lacuna
Hyaline cartilage
contains collagen that forms thin fibrils arranged in an irregular 3D pattern. The ground substance of hyaline cartilage is rich in proteoglycans and the free GAG hyaluronic acid- promotes hydration and flexibility.
Elastic cartilage
contains thin collagen fibrils and proteoglycans, abundant elastic fibers. Found in the external ear, in the epiglottis, and the larynx. Designed for elasticity and flexibility, does not calcify
Fibrocartilage
large bundles of regularly arranged collagen similar to dense regular connective tissue. A continuation of dense regular connective tissue where tendons attach to bones, and also in the intervertebral discs. This ECM is designed to resist compression and sheer forces.
Since cartilage is avascular, how do chondrocytes get nutrients
nutrients must diffuse within the matrix to and from the perichondrium. This is facilitated by the large amounts of hydrated glycosaminoglycans.
compact bone provides most of the strength of the bone for support, while the trabeculae provide extensive surface area for ________.
metabolism
red bone marrow vs white bone marrow:
Red bone marrow: hematopoietic tissue
White bone marrow: adipose cells
periosteum
The outer surface covering the bone which contains dense connective tissue containing fibroblasts, bone precursors and bone cells
endosteum
The inner surface where trabeculae contact internal soft tissue which is where most calcium mobilization and storage occurs
Osteoprogenitor cells, location
stem cells capable of generating osteoblasts and osteocytes. Present in both the periosteal and endosteal surfaces, and in the soft connective tissue of the channels.
Osteoblasts, location
line the inner layers of periosteal and endosteal surfaces where bone growth or remodeling is occurring. Secrete initial un-mineralized ECM of bone (osteoid). Osteoblasts also pinch off matrix vesicles, containing enzymes that initiate bone mineralization. Osteoblasts are connected to each other and to nearby osteocytes by gap junctions. Capable of cell division.
Osteocytes
derived from osteoblasts, they do not divide. They extend long processes through canaliculi, in the calcified matrix; these processes form gap junctions with processes from other osteocytes. Thus, the cells of bone form a living interconnected lattice.
Osteoclasts role in bone dynamics
(1) degrade cartilage or bone matrix to allow inward growth of blood vessels during bone formation
(2) resorb bone to promote remodeling of the bone matrix.
(3) resorb bone to mobilize Ca2+ into the bloodstream
Are osteoclasts related to osteoblasts? Who are they most closely related to?
No, they are derived from monocytes in the blood, which originate from hematopoietic stem cells.They resemble and are related to macrophages. Osteoclasts are phagocytic cells.
Mineral substance in bone
hydroxyapatite
Haversian canals
In long bones, channels that traverse the long axis through compact bone. Bone lamellae tend to surround a Haversian canal in concentric rings (like the rings of a tree)
osteon
functional unit of bone: lamellae surrounding a Haversian canal in concentric rings
Volkmann’s canals
canals link Haversian canals to each other and to the periosteum at the bone surface
When does net bone growth stop?
puberty, but remodeling continues
two general ways that bone is formed:
Intramembranous ossification and Endochondral ossification
Process of Intramembranous ossification
mesenchymal cells–>osteoprogenitors–>osteoblasts. Osteoblasts secrete osteoid. More cells convert into osteoblasts adding to the mass of developing bone. “Bone islands” join. Calcification of the matrix–>trabecular network of bone. Blood vessels grow in within this network.
Endochondral ossification
- Periosteum invades perichondrion
- Matrix calcification of bone collar
- Osteoclasts degrade bone.
- Blood vessels, nerves, osteoblasts, and osteoprogenitors come with the osteoclasets to degraded region
- Some of osteoclast-led blood vessels penetrate deep into the diaphysis to form the primary ossification center.
- zone of ossification expands towards ends of the model.
- new ossification centers in epiphyseal end.
Which bones from by intramembranous ossification?
flat bones
epiphyseal plate.
At birth, the only region of proliferative cartilage that remains is beneath epiphyseal ossification regions
appositional growth
Growth in the diameter of the bone occurs on the outer surface of the bone in the periosteum. Net growth in bone diameter occurs as long as bone resorption is significantly less than deposition in this region.
In mature adult bone, where does most of the resorptive activity occur?
at the endosteal surface
Osteoblasts initiate mineralization of the osteoid by secreting :
matrix vesicles
How do osteoblast matrix vesicles lead to mineralization?
Matrix vesicles contain Ca2+, PO4, and AlkPhos. Alkphos inside vesicles somehow become activated, generates free phosphate, forms hydroxyapatite precipitates. Precipitates grow, rupture vesicles, then act as nucleation sites to trigger mineralization
Control of bone formation, remodeling and calcium homeostasis:
Short-range signals (BMPs)
Long-range signals from endocrine glands.
Mechanical stress
Neuronal stimulation
Parathyroid hormone
stimulates calcium liberation (bone resorption)
Basal bodies
core anchors from which cilia are formed. MT rich cylinder formed from 9 triplet microtubules. 150-200 nm in diameter and 500 nm in length.
axoneme
skeleton of the cilium. formed from doublet MTs that assemble from the A- and B-tubules of the basal body. The plus-ends of MTs are at the ciliary tip. Lengths range from < than a micron to tens of microns in the case of sperm flagella. Axonemes also provide the tracks for movement w/i cilia.
Calcitonin
stimulates calcium uptake into bone
Major domains that build the cilium
centriole/basal body, axoneme, transition zone, ciliary membrane, and intraflagellar transport (IFT) machinery
intraflagellar transport (IFT)
Transport along axoneme with kinesin motors IFT-B protein complex directing movement to the ciliary tip (anterograde transport). Retrograde transport: dynein 2 motor with the IFT-A protein complex. Both mechanisms required for cilium formation and function.
transition zone
links basal body to axoneme and to the ciliary membrane. “gatekeeper” b/c it limits diffusion of membrane and soluble proteins in/out of the cilium.
ciliary membrane
continuous with the cellular plasma membrane but is compartmentalized (by the transition zone) so that it is a distinct membrane with unique phospholipids and receptor molecules.
Centriole duplication occurs during the ___________cell cycle boundary coincident with DNA synthesis.
G1 to S-phase
Ciliogenesis
the distal end of the basal body is capped by a “ciliary vesicle”. MT doublets assemble into the ciliary vesicle before the entire structure fuses with the plasma membrane of the cell.
Motile cilia
required for the movement of fluid in the respiratory, neural, and reproductive tracts. Motility is produced by axonemal dynein dependent sliding motion between the doublet microtubules of the ciliary axoneme.
Non-motile, sensory or primary cilia
possess a 9+0 microtubule arrangement and lack axonemal dynein arms. These cilia normally perform signaling functions
Hh signaling, downstream targets facilitate:
Limb formation
Bone formation and homeostasis
Neurogenesis
Clinical abnormalities associated with ciliopathies
Cystic kidneys • Nephronophthisis • Obesity. • Polydactyly • Retinal degeneration • Amnosia • Cancer / Tumorigensis • Urinary tract malformation • Cognitive impairment • T2D • Infertility
Characteristics of ciliopathies
Rare. Pleiotropic Overlapping Structural Diverse. ~50 genes are known to be mutated in ciliopathies to date. Genetically complex.
Bardet-Biedl Syndome (BBS):
Autosomal recessive, proteins deal with vesicle transport within the cilium. Symptoms: • Photoreceptor degeneration • Anosmia • Mental retardation / Developmental delay • Neural tube defects • Obesity • Hypogonadism • Kidney defects • Polydactyly • Diabetes • situs inversus
Polycystic kidney disease (PKD)
Autosomal dominant and recessive forms (ADPKD and ARPKD, respectively).
Genes encode channels for calcium signaling. These channels sense mechanical flow of urine in the kidney lumen to transduce calcium signaling.
Symptoms:
• Renal cysts
• Liver and pancreas cysts
• Intracranial aneurysms
How do bones grow in length after birth?
the only region of proliferative cartilage that remains is beneath these epiphyseal ossification regions, and is called the epiphyseal plate.
What differentiates a motile cilia from a sensory cilia?
dyein arms
How do cilia est. laterality?
cilia on cells of ciliary node beat morphogen from Left to Right. Primary cilia sense the morphogens
2 ways of targeting cancer from EGFR mutation
TKIs and monoclonal antibodies
How did Gefitinib affect lung cancer patients with
EGFR mutations?
they have better progression free survival with EGFRTKIs vs. chemotherapy alone
How did results of Cetuximab vary based on protein expression. What ethnic group benefitted?
No difference in unselected group, helped in high EGFR expression group, helped Caucasians specifically.
How did gene copy # affect results of Cetuximab on progression free survival and DCR?
FISH + group had good outcome with Cetuximab (DCR, progression free survival, and overall survival)
Anaplastic Lymphoma Kinase (ALK) gene
Translocation resulting in EML4-ALK fusion gene drives oncogenesis and chimeric proteins with kinase activity
ALK therapy
targets fusion gene. After failed chemo, dramatic change in baseline tumor size, prolongs survival (10 mo. vs 3-4 mo.)
Prognostic biomarker
tells us the outcome (survival) based on natural course of the disease without any therapeutic intervention.
Predictive biomarker
Predictive marker relates to outcome based on a specific therapy.
National Lung Cancer Screening Trial showed
low dose spiral CT led to a 20% reduction in mortality among current/former smokers and a 6.7% all cause mortality reduction.
Problem with low dose spiral CT screening of lung cancer
95% false positive
components of tunica intima
- endothelial cells
- elastic/collagen layer in larger arteries
components of tunica media
- multiple layers of elastic lamina
- smooth muscle
- collagen
components of tunica adventitia
- collagen
- vasa vasorum in large vessels
Which layer is very robust in large arteries?
tunic media
Elastic arteries
The aorta and larger arteries branching from it
Elastic artery layer characteristics
- intima: endothelial cells and an underlying layer of collagen/elastin-rich fibers and contains fibroblasts and myointimal cells which have similar structural features to smooth muscle cells.
- media contains multiple elastic layers with some collagenous fibers and smooth muscle cells sandwiched in between.
- adventitia contains vasa vasorum
Muscular arteries
- intima: thin, contains endothelial cells and a thin connective tissue.
- Inner elastic lamina between the intima and the media
- media is primarily comprised of smooth muscle cells.
- The outer elastic lamina between the media and adventitia.
- adventitia is comparatively thick and contains collagen and elastin
Small muscular arteries
NO outer elastic lamina, but retain the inner. The intima is comprised of the endothelial cell layer and a thin layer of collagenous material. They have a relatively large layer of smooth muscle in the media which can control vessel diameter. The adventia is about the same width as the media, and usually merges with surrounding con- nective tissue.
Arteriole structure
inner lining of endothelial cells on thin basement membrane. This is immediately surrounded by 1-2 layers of smooth muscle cells, and outer colla- genous tissue which typically blends in with surrounding connective tissue
Arterioles are the gatekeepers to local capillary beds and can greatly restrict the ___ __ ___through them
flow of blood
Capillaries
endothelial cells surrounding the lumen. There is no muscular layer, but the endothelial cells are often surrounded by pericytes. These are surrounded by collagenous fibrils which connect the capillary to adjacent connective tissue.
Pericytes
unspecialized cells that surround endothelium of capillaries. Can give rise to smooth muscle cells during vessel growth and wound healing, and may be contractile in nature
continuous capillaries
endothelial cells form an uninterrupted lining, transfer across the lining occurs via pinocytotic vesicles
fenestrated capillaries
there are pores or fenestrations in the endothelial cells. In some fenestrated endothelia the pores are covered by a thin diaphragm. A good example of fenestrated endothelium is found in the glomerulus of the kidney.
intercalated disc of cardiac muscles functions
- physically ties together adjacent cells so that they don’t pull apart when contracting.
- Contains gap junctions for the transmission of electrical current from one cell to the next (for propagation of AP, so heart contracts synchronously
Smooth muscle cells are ______ in diameter
2-5 μm
Sarcomeres are defined as extending from
one Z line to the next Z line
How does the sarcomere generate force
as thick and thin filaments slide past each other
myofibrils
contractile filaments covered with its own network of sarcoplasmic reticulum
There are two primary filaments: thin (_____) and thick (_____).
actin, myosin
structure of filamentous actin
double stranded and helical
The thick filaments are ___ μm long and contain _______ myosins
1.6 μm, 300-400
In the relaxed state, the binding of myosin to actin is prevented because:
the binding site on actin is covered by tropomyosin
What uncovers the myosin binding site?
As intracellular Ca2+ rises, troponin binds the Ca++ and changes confo. Each troponin is bound to the end of one of tropomyosin, and induces a conformational change in the tropomyosin that exposes the binding sites.The myosin head can now bind to actin
When does myosin exert a force on the actin?
as soon as myosin binds, it exerts a force and causes a shortening of the sarcomere of about 8 nm
How does the myosin dissociate from the actin?
myosin is stuck to the actin until ATP binds to myosin. Binding of ATP allows myosin to dissociate from actin and hydrolysis of ATP also occurs, putting myosin into a high-energy state (compressing the spring
The rate of myosin turnover is faster in ____ _____ muscle than in ___ ____ muscle (different myosin genes)
fast twitch (20x/sec), slow twitch (5x/sec)
Contraction of smooth muscle
Increased Ca2+ in the smooth muscle cell binds to calmodulin and the Ca-calmodulin binds to CaM kinase, activates it, one of the light chains on the myosin head is phosphorylated. The phosphorylated myosin binds to actin and force is generated.
How is Ca2+ removed from smooth muscle cells?
by Ca pumps and Na-Ca exchangers in the sarcolemma
What causes smooth muscle to relax
The removal of Ca inactivates the kinase, and the myosin is dephosphorylated by a phosphatase.
dystrophin
the mutation of this gene responsible for Duchenne muscular dystrophy. It is a large, filamentous protein that is associated with cortical actin beneath the plasma membrane and the surface membrane. like laminin. It links the cytoskeleton with the extracellular matrix.
titin, nebulin, and α-actinin
structural proteins that maintain the highly ordered sarcomeres
Titin
enormous protein that links the myosin thick filaments to the Z-line. titin keeps the myosin thick filaments centered in a sarcomere
About half of all cases of sudden death due to cardiac arrest in young athletes are due to
familial hypertrophic cardiomyopathy
Examples of how single amino acid mutations in the regulatory regions of a myofilament protein or a regulatory protein produce muscle disease
The majority of people with FHC have mutations in the cardiac myosin heavy chain. In some cases FHC is due to mutations in troponin.
How many places does a nerve innervate a single muscle cell at? Where does the synaptic contact take place?
Each skeletal muscle cell of a mammal is innervated at one spot. This synaptic contact is usually near the center of the cell
How does an action potential on the motor neuron transfer to the sarcolemma?
AP in motor axon causes release of ACh. ACh diffuses across the synaptic clef, binds to a receptor (AChR) in the muscle post-synaptic membrane. The AChR is an ion channel that opens and causes depolarization. The depolarization in turn will open Na channels and an action potential is initiated
Two protein complexes that that connect the t-tubule and SR:
DHPR (dihydropyridine receptor) in the t-tubule membrane.
RyR (ryanodine receptor) in the SR membrane and
DHPR (dihydropyridine receptor) is a complex of several membrane proteins and is in the t-tubule membrane. What is its function in muscle contraction?
One of the subunits of the DHP receptor is a voltage-gated Ca channel.
RyR
ryanodine receptor in the SR membrane and is a Ca release channel.
How does sarcolemma depolarization lead to calcium release in the triad?
depolarization causes a conformational change in the DHP receptor that in turn causes the calcium release channel to open and Ca flows out of the SR.
malignant hyperthermia (MH)
AD disorder, 70% have RYR1 mutations reaction to anesthesia. abnormal skeletal muscle RYR1 or associated structure that allows abnormal calcium release when exposed to an anesthetic triggering agent
Difference between contraction of skeletal and cardiac muscle
cardiac Ca-release channel binds Ca so Ca entry is required to trigger Ca release by the Ca-release channel of the SR.
How does Ca2+ cause smooth muscle contraction
Smooth muscle cells are so thin that Ca entering via Ca channels in the surface membrane can easily diffuse to the center of the cell (however, some smooth muscle cells do have a rudimentary SR).
What else affects the tension produced?
The length of the muscle fiber
motor unit
The muscle fibers innervated by a motor neuron
Size of motor unit in muscles that perform fine movements (e.g. finger muscles or extraocular eye muscles)
Muscles that perform fine movements tend to have small motor units
Size of motor unit in large muscles that perform gross movements
large muscles that make gross movements have large motor units (hundreds of muscle fibers)
explain how size recruitment of motor units works during voluntary movement:
small motor units are recruited first and progressively larger motor units are recruited as the strength of contraction is increased. This allows a fine control of movement.
In contrast to skeletal muscle cells which are not electrically coupled, both cardiac and smooth muscle cells are linked by __ ________
gap junctions
Mammalian skeletal muscle fibers can be grouped into three classes:
slow, fast, and an intermediate
Differences between different muscle fiber classes:
These cells have different myosin isoenzymes, different proportions of mitochondria and oxidative enzymes, different resistance to fatigue, and different speeds of contraction
The slow oxidative fibers are used for:
Color:
postural or relatively maintained contractions
reddish in color due to their high myoglobin content
The fast twitch fibers have high glycolytic content and are used for:
rapid bursts of activity (sprinting or jumping, for example)
How can tension be graded in skeletal muscle?
(1) Increase frequency of APs.
(2) Recruit additional motor units.
(3) Change length of the muscle is a minor factor for skeletal muscle because it normally operates near the optimal length.
_____ ___ ___ _______ plays a minor role in skeletal muscle contraction but is important for smooth and cardiac muscle?
length of the cell since this length is not fixed by attachments to bone
satellite cells. Where are they present?
stem cells associated with each skeletal muscle cell, source of new myoblasts to repair injured muscle. ONLY PRESENT in skeletal muscle
Satellite stem cell action
if a muscle fiber is so seriously damaged that the cell degenerates, the satellite cells on the surface of that fiber will divide and fuse, forming a new muscle cell.
How does smooth muscle repair itself?
the cells can dedifferentiate, enter mitosis and regenerate new muscle cells. This extraordinary ability to proliferate may contribute to the occurrence of smooth muscle tumors, such as leiomyosarcoma.
Where can smooth muscle tumors occur?
anywhere in the body since blood vessels contain smooth muscle
What happens to muscle fibers during exercise and atrophy?
Lifting weights to increase strength does not add new skeletal muscle fibers. The cross sectional area of each cell is increased; i.e. new myofibrils are formed. During atrophy (e.g. when a limb is put in a cast) the cross sectional area of individual muscle fibers decreases.
Who has more fast fibers, marathon runners or sprinters?
sprinters
fatigue
reduced performance during prolonged or intense activity. It is both a decrease in force production and speed of contraction.
Muscle contraction steps affected by fatigue:
(1) propagation of AP into the t tubule,
(2) release of Ca from the SR,
(3) effect of Ca on the myofilament interaction
(4) force generation by the myofilaments.
ATP levels change very little during strenuous contraction because _________ regenerates the ATP
phosphocreatine
What is the effect of Ca on troponin during fatigue?
The effect of Ca on troponin is reduced during fatigue (possibly because hydrogen ions compete with Ca for binding to troponin) causing fewer myosin-binding sites to be exposed.
How do Viagra and Cialis work?
preventing the breakdown of cGMP and thus maintaining NO’s action (relaxation of helicine arteries in the penis)
Do arterial smooth muscle, trachea, and the gastric fundus have action potentials?
NOPE
The majority of mutations in HCM are what type?
missense mutations in structural genes
Muscle cell phenotype in HCM
organ hypertrophy, myocyte disarray, interstitial and replacement fibrosis, dysplastic intramyocardial arterioles
Clinical presentations of HCM
cardiac murmur, cardiac pump failure, arrhythmia
How to diagnose HCM
Echo, EKG, MRI, family history, genetic testing, chest x-ray
Myostatin and a _____ _____ _____
muscle growth regulator (inhibitor)
Which anesthetic agents can induce Malignant Hyperthermia in affected patients?
Typically inhalation agents (halothane) and/or succinylcholine
Occurrence of malignant hyperthermia in the US
1:5,000 – 1:100,000 anesthesia exposures
Dantrolene sodium
the treatment for malignant hyperthermia, is known to inhibit calcium release via RYR1 antagonism. It binds to RYR1, causing it to favor the closed state- reversing the uninhibited flow of calcium into the sarcoplasm
Clinical signs of hyperthermic malignancy
Muscle rigidity Masseter spasm Increased CO2 production Rhabodomyolysis Hyperthermia
How to predict hyperthermic malignancy
Clinical History
Family History +/- Genetic testing
Halothane/Caffeine test on muscle biopsy
Immediate management
Stop inhalation agents
Hyperventilate with 100% O2
Bicarbonate
Dantrolene 2.5 mg/kg
Cool patient: gastric lavage, surface cooling, wound cooling
Treat arrhythmias: (don’t use Ca channel blockers)
Duchenne Muscular Dystrophy: mutation, indication while walking
X-linked disease Dystrophin (DMD) mutations Boys: Onset of skeletal muscle disease ages 3-5 years toe walking
What enzyme is high in Duchenne muscular dystrophy patients?
High creatinine kinase (1000s)
What causes death in DMD patients, and how prevalent is this?
Death in 20s (cardiopulmonary)
Cardiomyopathy 100% by 18 yrs
General treatment for DMD
*******Corticosteroids: Prolong independent ambulation (lots of side effects) Leg braces Surgical tendon releases Pulmonary therapy (CPAP)
difference between abiraterone and enzalutimide
Abiraterone is a cyp-17 inhibitor that blocks testosterone. Enzalutimide is an anti androgen drug that inhibits the ability of the AR to act as a transcription factor (binding, nuclear transport, co activator recruitment, DNA binding)
Common characteristics shared by ciliopathies
1l rare
- pleiotrophic
- overlapping phenotypes
- structural
- diverse
- genetically complex
What are the two proteins responsible for release of Ca2+ from the SR?
DHPR and RYR
Mechanism for cadriac muscle contraction
calcium induced calcium release. Relies on extracellular calcium to bind a calcium channel. The Ca that flows through causes RYR to open and release massive amounts of Ca2+
