MCB11 - Assembly of Cells Into Tissues II Flashcards
What are the main cell types. Give brief definition for each.
Neural cells. - neurones and glial cells
Connective tissue cells. - fibroblasts, chondrocytes, osteocytes.
Contractile tissues. - muscle
Haematopoietic cells. - all blood cells.
Epithelial cells - continuous layers of cells
What are the shapes of epithelial Cells. Describe each shape.
Squamous - flattened, plate shapes
Columnar - column shaped
Cuboid - cube shaped
What are the methods of layer in epithelial cells.
Single layer - simple epithelium.
Multi layer - stratified epithelium
What is the role of epithelia
Lining the internal and external surfaces of body and organs for transport, absorption, secretion and protection
How do epithelial cells form continuous layers
By forming stable organised cell cell junctions which are vital for formation and maintenance
How many different cell types are there in the body
Over 200
Give types of neural cells and their functions.
Neurones - carry nerve impulses
Glial cell - support nervous system
Give types of connective tissue and their functions.
Fibroblasts - synthesis of ECM and collagen.
Chondrocytes - cartilage cells
Osteocytes - bone cells either formation or break down
Adipose - storage of lipids
Give types of contractile tissue and their functions
Skeletal muscle - movement
Cardiac muscle - heart beat
Smooth muscle - lining of organs and secretion of material
Give types of haematopoietic cells and their functions
Blood cells, RBCs, all white blood cells, bone marrow cells, lymphoid and myeloid lineage, mast cells, natural killer cells, platelets etc.
Discuss simple squamous structure of epithelial layer and give example.
Single cell layer that is flattened. Present in lung alveolar sacs and blood vessel lining, aiding exchange of material .
Discuss simple cuboidal structure of epithelial layer and give example.
Single cell layer with cuboid shape. Present in lining of kidney collecting ducts.
Discuss simple columnar structure of epithelial layer and give example.
Single cell layer that is column in shape.present in intestinal lining of intestines.
Discuss stratified squamous structure of epithelial layer and give example.
Multiple cell layers that are flattened. Present in epidermis both keratinising and non keratinising tissue.
Where is keratinising tissue present.
Epidermis - skin epithelium.
Where is non-keratinising tissue present.
Lining of mouth, anus, vagina, cervix
Discuss pseudo-stratified structure of epithelial layer and give example.
Appears multi layered however all cells have contact with the basal lamina. Present in airway epithelium.
Why do epithelial cells require polarity.
In order to give directionality to the cell so that secretion and transport etc. Happens in one direction only.
What are the two domains of an epithelial cell and how do their differ.
Apical and basolateral domains . Differ in lipid and protein composition, therefore have different polarities.
What occurs for transportation In epithelial cells if the cell is not polarised.
Plasma membrane would be able to pump material apically and basolaterally meaning there is no directional flow.
What occurs for transportation In epithelial cells if the cell is polarised.
Polarised means there is directionality to the cell. Transport would happen only on one aspect of the plasma membrane - either apically or basolaterally.
What occurs for secretion In epithelial cells if the cell is not polarised.
Secretion would occur both apically and basolaterally.
What occurs for secretion In epithelial cells if the cell is polarised.
Secretion would occur on one side only either apically into the lumen or basolaterally, into the interstitial space.
Define apical-basolateral epithelial membrane polarity.
Difference in lipid and protein composition of apical and basolateral plasma membrane, resulting in polarity and directionality.
Discuss purpose and structure of cell cell junctions.
Highly dynamic structure which provide mechanical stability and integrity whilst sealing intracellular pathways. Can be assembled and disassembled rapidly in response to extracellular and intracellular stimuli,
What are the four types of junctions present in cells.
Tight junctions. Adherens junctions. Desmosomes. Gap junction.
What are the two major formats of junctions.
Zonulae (belts) and maculae (spots)
Discuss tight junctions between cells - structure and role.
Tight junctions are belts formed in the apical region of lateral membranes. Involved in sealing gaps between cells.
What are the two major integral membrane proteins of tight junctions.
Occludin and Claudins
Discuss presence of claudins and occludins in the formation of tight junctions.
Transmembrane proteins which associate with same type on next cell. These proteins associate with linker proteins on intracellular side, connecting them to the actin cytoskeleton. The more elaborate the network of occludins and Claudins, the tighter the seal between the two cells, as a result of the tight junction.
Why are tight junctions vital.
Maintain the apical basolateral plasma membrane polarity aiding transportation and secretion.
Discuss the gap function of tight junctions. Give effects of this.
Tight junctions seal paracellular pathway which limits the passage of fluids and solutes between cells. Ensures that concentration differences across cell layers can be maintained and that any solutes crossing the cell layer must pass through the cells themselves, therefore controlled.
Difference between paracellular and transcellular pathways.
Paracellular - between cells.
Transcellular- through cells.
Discuss fence function of tight junctions.
Establishment of polarity of apical basolateral membrane, acting as a fence for transportation and secretion.
What is the main purpose of adherens junctions.
Controlling functions of other junctions - tight junctions, desmosomes and gap junctions
Discuss homophilic binding in adherens junctions.
Cadherins which are cell cell adhesion molecules bind directly to same type cadherins on another cell by homophilic binding
Are adherens junctions forming zonulae or maculae
Zonulae- belts
Which terminal of proteins Interact with each other
N terminus.
Role of calcium in cadherin binding.
Calcium ions ensure adhesive functions. Without calcium, rigidity of junctions is lost meaning that adhesion cannot be mediated. Calcium acts as the hinge regions
What are the role of catenins.
Catenins are proteins that link cadherins to the actin cytoskeleton, controlling the dynamics of the adherens junction.
Discuss process by which adherens junctions expand and form tighter junctions.
Protrusions within the membrane initially intimidate cell cell contact, resulting in the formation of a small cadherin and catenin cluster. Following this, actin and cadherin recruitment expands the junction. Furthermore, actin remodelling and myosin recruitment further expands the adherens junction.
How do epithelial tubes form in regards to
Adherens junctions form an adherens belt through the interactions of cadherins. An organised tightening of the adhesions belt in selected regions results in invagination of the epithelial sheet, resulting in the formation of the epithelial tube.
Difference between desmosomes and hemidesmosomes.
Desmosomes are junctions between two cells. Hemidesmosomes are junctions between cells and the basal lamina.
What happens if desmosomes are damaged.
Epithelial layer is damaged which can lead to varying skin conditions. Epidermis is fragile leading to severe blistering.
Discuss an autoimmmune disease involved desmosomes.
Body can produce auto antibodies to desmosomal cell-cell adhesions which reduces their adhesive characteristic, resulting in a fragile epidermis.
Discuss structure of a desmosome.
Non classical cadherin proteins interact with each other from different cells, forming the desmosome. Closer interaction of these, results in a tighter desmosome.
How are desmosomes linked to the cytoskeleton.
Receptor proteins on membrane surface are linked to internal cytoskeleton e.g. intermediate filaments, by linker proteins.
Where are non classical cadherin proteins found
Desmosomes.
What is the role of gap junctions.
Allows cells to communicate as it links the cytoplasm of adjacent cells together.
Give generalised overview of what gap junctions are.
Clusters of membrane junctions, allowing cells to form ‘communities’ and synchronise their activities.
Discuss structure of gap junction channel and their role.
6 subunits of connexin join to form a connexon. Two connexons (one from either cell)line up together to form an open channel between adjacent cells. Allows the passage of ions and small molecules between cells.
How are gap junctions opened and closed.
Open and close is controlled by pH, concentration of calcium, voltage differences and some signalling molecules.
How do gap junctions control which substances can pass through.
Only allows passage of small molecules, molecular weight must be 1000 or less. E.g. allows inorganic ions and small water soluble molecules.
What are the four major functions of epithelial cells.
Absorption. Secretion. Fluid and ion transport. Protection.
How are epithelial cells adapted to aid their function as transporters.
Contain high concentrations of ion transporters. Also contain mitochondria in high numbers on basolateral region of epithelial cell which provides energy for ion pumps. Also commonly contain in folding which increase the area of basal membrane available for transportation.
How are epithelial cells adapted to aid their absorptive function.
Contains in folding which increase surface area available to absorb molecules from tissue. The more surface area of epithelium lining available for absorption, the more efficient it will be.
Discuss structure of intestines in relation to its function.
Small intestine has infoldings known as villi (singular villus) which increases surface area. These contain further infoldings known as microvilli. Thin layer of enterocytes is present aiding absorption.
Discuss maintenance of concentration gradients in enterocytes in intestinal lining.
As concentration of nutrients increases in the cytoplasm of the enterocytes, the nutrients diffuse down their concentration gradient into the basal interstitial space to be collected in capillaries and distributed in circulation.
Difference between constitutive and stimulated secretion.
Constitutive secretion - secretory vesicles move to plasma membrane as they form, and they release their contents.
Simulated secretion - secretory vesicles are stored in cytoplasms until appropriate signal is obtained, which then causes them to release their contents.
Where are secretory cells commonly found,
Dispersed in epithelium or clustered into specialised secretory glands
Discuss endocrine and exocrine in relation to secretory epithelia.
Endocrine - into blood stream
Exocrine - into lumen.
Discuss structure and role of exocrine secretory cells in secretory epithelia. Give examples.
Contain abundant RER in basal region to produce proteins. Contain secretory vesicles in apical region for secretion. Examples include goblet cells which secrete mucus and pancreatic acinar cells which secrete digestive enzymes.
Discuss structure and role of endocrine secretory cells in secretory epithelia.
Secretory vesicles located in basal cytoplasmic region aiding secretion directly into bloodstream.
What is the usual shape and layering of protective epithelia.
Stratified squamous.
What are the three regions of skin
Epidermis, dermis and hypodermis
Discuss cell structure in keratinising vs non keratinising cells.
Keratinising cells - nuclei not visible, hardened dry surfaces.
Non-keratinising - nuclei visible, wet surfaces.
Give examples of different rates of cell turnover.
Epithelial lining - 3-10 day turnover
Fat tissue,heart,muscle - 8-10 years
Give examples of infectious agents that alters turnover of cells.
HPV increases cell proliferation, resulting in the formation of warts as cellular protrusions.
Chemotherapy decreases cell division, resulting in reduced hair.
Discuss how cells are replaced in the microvilli.
Stem cells in the Crypt of Leiberkhun, located between non differentiating Paneth cells, differentiate to form new enterocytes. These migrate up the villus, replacing cells that are lost from the villus tip by apoptosis.
What are paneth cells.
Non differentiating cells in the Crypt of Leiberkhun.
Discuss cell turnover in epidermis.
Surface cells are constantly being lost and replaced by new cells formed in the basal layer of the epidermis. As cells migrate away from the basal lamina, they flatten and keratinise.
