Tissues Flashcards
What are mesenchymal cells?
Cells of connective tissues
What are the names of the tumours arising from the following ells? Epithelial cells Mesenchymal cells Haematopoietic cells Neural cells
Carcinomas
Sarcomas
Leukaemias (from bone marrow cells); lymphomas
Neuroblastomas; gliomas
What are the 3 components of a tissue?
Cells, extracellular matrix and fluid
What are the flattened sacs of the ER known as?
Cisternae
Give the structure and function of microtubules. Indicate relative size.
Polymers of a and b tubulin heterodimers. Involved in cells shape and acts as tracks for organelles and other cytoplasmic components of the cell to follow. They also form the mitotic spindle. -20nm thickness - thickest polymers in the cytoskeleton
Give the structure of cilia and flagella
9 microtubule doublets and 2central microtubules (9+2 arrangement). ATP dependent motor proteins distort organelles to produce movement.
Give the structure and function of intermediate filaments
Polymers of filamentous proteins. IFs give mechanical strength to cells. About 15nm thick.
What are nuclear lamins?
Intermediate filaments which form a network on the internal surface of the nuclear envelope called the nuclear lamina.
Give the structure and function of microfilaments.
Polymers of actin. Associate with adhesion belts in epithelia; involved in cell shape and movement. 5-9nm thick.
What are the types of shape and layering present in epithelia.
Squamous, cuboidal and columnar. Simple and stratified layering.
What is a keratinising stratified epithelium?
Cells of the upper layer of the epithelium are “dry” because they have died and hardened. Their nuclei are not visible.
Junctions separate epithelial membranes into 2 biochemically and functionally distinct domains, which are…
The apical domain and basolateral domain.
What are maculae and zonulae?
Maculae are junctions arranged as discrete spots. Zonulae are junctions arranged as continuous belts.
Describe briefly the apical junctional complex of simple epithelia.
Typically, there is a tight junction nearest the apex with an adherens junction just below it. Desmosomes (spot adhering junctions) are scattered throughout the lateral membrane.
How do tight junctions seal the paracellular pathway? What are the implications of this?
Proteins on adjacent membranes closely interact to form sealing strands.
This means concentration differences across cell layers can be maintained and the cells control the passage of solutes crossing the cell layer.
Define exocrine and endocrine secretory functions?
Exocrine = into a duct or lumen Endocrine = into blood stream
What are the 3 main layers of the skin, what type of epithelium is this and which is the keratinising layer?
The epidermis, dermis and hypodermis. Stratified squamous epithelium. The epithelium is keratinising.
Describe the function of desmosomes and hemidesmosomes.
Desmosomes link cells to each other to give mechanical stability to tissues including epithelia and cardiac tissue. Hemidesmosomes link the cells to the ECM.
How are epithelial cells on the surface of villi in the lumen of the small intestine replaced?
Stem cells in the crypts of Lieberkühn produce new epithelial cells to replace the cells lost at the villus tip, which then migrate upwards.
Describe the cell turnover of the epidermis.
Surface cells are constantly being lost, but are replaced by new cells being formed in the basal layer which migrates up which undergoing differentiation leading them to flatten and keratinise. Each layer replaces the one above as the layers are lost from the surface.
What is the ECM?
Complex network of macromolecules deposited by cells filling the space between them.
What are the main components of the ECM?
Collagens, glycoproteins and proteoglycans.
Describe the structure of a collagen molecule.
Triple helical structure formed of 3 a-chains. Every third position must be occupied by glycine, as there is no room near the helical axis for the side chain of any other residue.
Describe the biosynthesis and assembly of collagen.
Procollagen has non-collagenous domains (propeptides) at the N and C terminals which are removed after secretion by extracellular peptidases. The collagen helices associate laterally to from collagen fibrils, which associate laterally in turn to form collagen fibers.
Describe simply the structure of elastic fibers
Core made of the protein elastin and microfibrils rich in the protein fibrillin.
What are basement membranes / basal lamina?
Flexible, thin sheets of highly specialised ECM underlying epithelial sheets and tissues.
What type of collagen assembles into sheet-like networks and is an integral part of basal lamina? What is the other major component?
Collagen type IV. Laminins (these are glycoproteins).
Describe the structure of laminins.
Three chains: an alpha, a beta and a gamma chain. Form a cross-shaped molecule. They are very large: each chain can be up to 400kDa.
Mutations in which component of the basal lamina are associated with muscular dystrophy? What are the symptoms of DMD?
Laminins.
Hypotonia (abnormally decreased muscle tension), generalised weakness, deformities of the joints. All evident from birth.
What are fibronectins?
A family of closely related glycoproteins found in the ECM.
How is a mechanical continuum between the ECM and actin cytoskeleton produced?
Collagen fibers of the ECM associate with fibronectin. Fibronectin interacts with integrin receptors at the cell surface. These span the plasma membrane and connect the ECM to actin filaments via an adaptor protein.
What is a proteoglycan?
A protein to which one or more glycosaminoglycan (GAG) chains are covalently attached.
Describe the structure of glycosaminoglycans (GAGs)
Long, unbranched sugars consisting of repeating disaccharides. They occupy a huge volume relative to their mass.
What is the function of proteoglycans?
Their GAG chains form hydrated gels, making tissues resistant to compression.