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MCD Year 1 > Cellular Organisation of Tissues > Flashcards

Cellular Organisation of Tissues Flashcards

1
Q

What are the three main types of cytoskeleton filaments?

A

Microtubules, Intermediate filaments and Microfilaments.

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2
Q

What are the structural properties of microtubules?

A

Polymers of alpha and beta tubulin heterodimers; 20 nm thick; often radiate from central structure in the cell called Microtubule Organising Centre.

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3
Q

What are the functions of the microtubules?

A

They acts as tracks for movement of organelles in the cell; involved in cell shape; major component of cilia and flagella; form the mitotic spindle.

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4
Q

What are the structural properties of Intermediate filaments?

A

Made up of a group of filamentous proteins that form rope-like filaments. Diameter of 10-15 nm.

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5
Q

What are the different types of Intermediate filaments?

A

Epithelia have cytokeratins; mesenchymal cells have vimentin; neurons have neurofilament protein; muscle cells have desmin.

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6
Q

What is the function of intermediate filaments?

A

They give mechanical strength to the cells.

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7
Q

What are the structural properties of microfilaments?

A

They are polymers of actin that associate with other plasma membrane proteins. 5-9 nm in diameter.

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8
Q

What are the functions of microfilaments?

A

They are important in cell movement and cell shape. For e.g. myosin and actin together facilitate muscle contraction.

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9
Q

What are the four main cell types?

A

Epithelial: cells forming continuous layers and lining surfaces.
Mesenchymal: cells of connective tissues such as chondrocytes, osteocytes and muscle cells.
Haematopoietic: cells derived from the bone marrow.
Neural: cells of the nervous system, both neurons and glial cells.

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10
Q

What are the names of tumours which originate from each cell type?

A

Epithelial are carcinomas; mesenchymal are sarcomas; hematopoietic are leukaemias (from bone marrow) or lymphomas (from lymphocytes); neural cells are neuroblastomas from (neuron precursors) and gliomas (from glial cells).

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11
Q

What is the difference between the apical and the basolateral surface?

A

The apical surface of epithelial cells face the lumen. The basolateral surface is the rest of the cell.

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12
Q

What are the different types of junctions between epithelial cells?

A

Tight (occluding) junctions; belt junction; desmosome (spot junction); gap (communicating) junction.

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13
Q

What are tight junctions?

A

They are points on the apical lateral membranes that form a network of close contacts. the more elaborate the network, the tighter the seal.

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14
Q

What is the function of the tight junctions?

A

They seal paracellular pathways and also segregates apical and basolateral membrane polarity.

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15
Q

What is the adhesion belt?

A

A junction that forms basal to the tight junction using a transmembrane adhesion molecule called cadherins which associates with the microfilament cytoskeleton.

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16
Q

What is the function of the adhesion belt?

A

This is the master junction that controls the assembly of the other junctions.

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17
Q

What are desmosomes?

A

They are junctions found at multiple spots between adjacent cells and use a cadherin-like transmembrane adhesion molecule.

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18
Q

What is the function of desmosomes?

A

They are linked to the intermediate filament cytoskeleton and provide good mechanical continuity between cells.

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19
Q

What are gap junctions?

A

They are junctions made of cluster of pores formed from 6 identical subunits that care continuous with the two cell membranes.

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20
Q

What is function of gap junctions?

A

They are used for communication between cells because they allow passage of ions and small molecules and can be opened and closed depending pH, Ca2+ concentration, voltage and signalling molecules. They also transmit electrical signals.

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21
Q

What is the extracellular matrix?

A

It is insoluble material deposited by cells that forms the extracellular environment. It’s made of fibrillar or reticular proteins embedded in a hydrated gel.

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22
Q

What are the two ways of classifying epithelial cells?

A

Epithelia are classified based on their shape (squamous, cuboidal or columnar) and layering (simple or stratified).

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23
Q

Describe and give function of simple squamous epithelia.

A

It’s a single layered flattened shape which means it line exchange surfaces such as vascular endothelium.

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24
Q

Describe and give examples of simple cuboidal epithelia.

A

It’s a single layer and approximately cube shaped. E.g kidney lining collecting ducts.

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25
Q

Describe and give function of simple columnar epithelia.

A

It’s single layered with a pillar shape and is often absorptive or secretory such as in enterocytes.

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26
Q

Describe stratified squamous epithelia.

A

It’s multilayered and the top layer has a flattened shape. The shape of cells in other layers vary.

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27
Q

What are the two types of stratified squamous epithelia and what is the difference?

A

Keratinising ones don’t have nuclei visible in the top layer and are found on the epidermis. Non-keratinising has visible nuclei and are found in linings of opening in the body.

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28
Q

Describe and give examples of pseudostratified epithelia.

A

It looks multilayered but the apical cells are also in contact with the basal lamina. E.g. trachea and bronchi epithelium.

29
Q

What is epithelial polarity?

A

It means that one surface of the epithelium is different from the other which allows for directionality to epithelial function.

30
Q

What are the domains created by the belt junction on epithelial cells?

A

The apical domain which is on the lumen side and the basal domain in contact with extracellular matrix. The lateral side between the two is usually classed with the basal side to form the basolateral membrane.

31
Q

What are the three functional groups of epithelia?

A

Absorptive, secretory and protective. The first two can be classed together into transportive.

32
Q

What are the structural properties of transporting epithelium?

A

The plasma membranes have high concentrations of ion transporters; increased surface area using villi; mitochondria on the basal side to provide energy for active transport.

33
Q

What is constitutive secretion?

A

The secretory vesicles move to the plasma membranes as they are made and release their contents.

34
Q

What is stimulated secretion?

A

Te secretory vesicles are stored in the cytoplasm and only fuse with the plasma membrane after a stimulus.

35
Q

Describe protective epithelium.

A

Protective epithelium is made of stratified squamous epithelium. Their function is to protect the underlying tissue from the surroundings.

36
Q

What is cell proliferation?

A

The process of increasing the number of cells to balance the cells being made and cells being lost.

37
Q

What is the pattern of cell proliferation and turnover in the intestinal villi?

A

The cells in the villi are made by the crypt stem cells at the base in the Crypt of Lieberkuhn. they move up as more cells are made and are lost at the villus tip.

38
Q

What is the effect of decreasing cell proliferation in the intestinal villi?

A

The rate of cell loss from the tip remains the same but cell production is reduced which means the villi shorten. This is why chemotherapy has strong gut side effects.

39
Q

What is the effects of increasing cell proliferation?

A

Because cell turnover is not maintained, possibly due to a mutation, the tissue volume increases to form a benign tumour. This has a high risk of acquiring more mutations and becoming cancerous.

40
Q

What is the pattern of cell proliferation and turnover in the epidermis?

A

The surface cells are constantly lost. New cells are made at the basal layer and migrate up the layers of the skin. They undergo a programmed differentiation that eventually makes them keratinised squamous epithelia at the top.

41
Q

What is the function of the Extracellular Matrix (ECM)?

A

Provide physical support; determine mechanical and physicochemical properties of the tissue; influence growth and differentiation of surrounding tissues; essential for development and organogenesis.

42
Q

What are the main components of the ECM in connective tissues?

A

The ECM, along with a cellular component, contains collagens, multi-adhesive glycoproteins and proteoglycans.

43
Q

What are collagens?

A

The most abundant protein found in mammals (25% of total protein mass). A fibrous protein found in bone, tendon and skin.

44
Q

What is the layout of collagen in the skin and other areas?

A

It has layers that are at right angles to each other which means the skin can resist tensile force in any direction.

45
Q

What is the general structure of a collagen molecule?

A

Each collagen has three alpha chains forming a triple helix. These can be different because there are 42 genes encoding collagens in humans.

46
Q

What is the composition of Type I, II and III collagens?

A

Type I has chains from two different genes while types II and III has only one chain types each.

47
Q

What is the molecular structure of a collagen alpha chain?

A

It is a repeated pattern of glycine-x-y. X is often proline and y is often hydroxyproline. Every third is glycine because it is the only one small enough to occupy the interior when it forms the triple helix.

48
Q

Describe the assembly of collagen alpha chain into fibers.

A

The alpha chains form a triple stranded collagen molecule (1.5 nm) which turns into collagen fibrils (10-300 nm) and then into collagen fibers (500-3000 nm).

49
Q

What are the steps of fibrillar collagen biosynthesis that happens in a cell?

A

The originally synthesised collagen alpha chain is called a pro-alpha chain. It has N and C-propeptides at either end. Hydroxylation happens to selected prolines and lysines in this chain followed by glycosylation to to selected hydroxyprolines. the pro-alpha chains then self-assemble into a pro-collagen triple helix before being secreted.

50
Q

What happens to fibrillar pro-collagen once outside the cell?

A

The N and C-propeptides are cleaved to form collagen which self-assembles into fibrils and then fibers.

51
Q

What is the purpose of lysine and proline modifications inside and outside the cell?

A

Hydroxylation inside the cell contributes to hydrogen bonds between the chains. Modifications outside are important for covalent cross-linkages.

52
Q

Why does vitamin C deficiency affect collagen?

A

Prolyl and Lysyl hydroxylase enzymes need Fe2+ and vitamin C to function. Lack of it forms under hydroxylated collagen which affects tissue stability.

53
Q

What are fibril associated collagens?

A

These are type IX and XII collagens which associate with fibrillar collagens to regulate their organisations into fibrils.

54
Q

What is the purpose of type IV collagen?

A

It is a network forming collagen and is an essential component of basement membranes.

55
Q

What is the function of elastic fibres?

A

It is important for elasticity of tissues such as skin, blood vessels and lungs. It usually works with collagen to limit the stretching.

56
Q

What is the overall structure of elastic fibres?

A

They have a core of elastin and microfibrils rich in fibrillin on the outside.

57
Q

What is the structure of elastin?

A

It has alternating hydrophobic regions and alpha-helical regions which is rich in alanine and lysine. The lysine side chains are covalently cross-linked.

58
Q

What are basement membranes (BMs)?

A

They are flexible, thin mats of ECM underlying muscle, peripheral nerves, fat cells and most epithelia.

59
Q

What is the basement membrane mainly composed of?

A

It is mainly made of Type IV collagen and laminin. But they are also highly specialised with a distinct spectra of collagens, glycoproteins and proteoglycans.

60
Q

Name diseases caused by gene mutations affecting matrix proteins and identify the mutated protein.

A

Osteogenesis Imperfecta - Type I collagen
Marfan’s syndrome - Fibrillin 1
Alport’s syndrome - Type IV collagen (alpha 5)
Epidermolysis Bullosa - Laminin 5 (all three chains)
Congenital Muscular Dystrophy - Laminin 2 (alpha 2 chain)

61
Q

Name a disease caused by gene mutations affecting ECM catabolism and identify affected enzyme.

A

Hurler’s Syndrome - L-alpha-iduronidase

Causes inability to degrade GAGs.

62
Q

Name diseases caused by excessive deposition and loss of ECM.

A

Deposition - Liver fibrosis (cirrhosis), kidney fibrosis (diabetic nephropathy) and lung fibrosis (silicosis).
Loss - Osteoarthritis.

63
Q

What is meant by modular architecture of the ECM?

A

They have characteristic protein domains of 50-200 amino acid residues which means they are multi-adhesive, binding to various matrix components and cell-surface receptors.

64
Q

Describe the structure of laminins.

A

They are made of three chains (alpha, beta and gamma), each between 160 and 400 kDa, forming a cross-shaped molecule.

65
Q

What is the function of laminins?

A

They interact with cell surface receptors such as integrins and dystroglycan. They also interact with components of the BM such as Type IV collagen and also self-associates.

66
Q

What is Congenital Muscular Dystrophy?

A

Hypotonia (decreased muscle tension), muscle weakness and deformation of joints caused by absence of alpha-2 in laminin 2.

67
Q

What are fibronectins?

A

Family of glycoproteins that exist as an insoluble fibrillar matrix or soluble plasma protein. It’s derived from one gene with alternate splicing at the mRNA level.

68
Q

What are the function of Fibronectins?

A

It’s multi-adhesive. So it interacts with cell surface receptors and other matrix components. They have an important role in regulating cell adhesion, migration in embryogenesis, tissue repair and wound healing. There are no known mutations in humans which suggests its essential for life.

MCD Year 1 (8 decks)

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