Cellular Organisation of Tissues Flashcards
What occurs in the nucleolus?
The production of the subunits of the ribosomes. It contains ∼300 clusters of rRNA gene on the tips of 5 pairs of chromosomes
What is the size of a eukaryotic ribosome?
80S (60S + 40S)
What is the relationship between the nuclear envelope and the endoplasmic reticulum?
The nuclear envelope is continuous with the endoplasmic reticulum
What ER is associated with protein synthesis?
Rough endoplasmic reticulum
What ER is associated with lipid metabolism?
Smooth endoplasmic reticulum
Where are the cis and trans-Golgi located in relation to the ER and the periphery of the cell
Cis-phase Golgi- towards the endoplasmic reticulum
Trans-phase Golgi- towards the periphery of the cell
What are peroxisomes? Give one example.
A membrane-bound organelle containing enzymes involved in lipid and oxygen metabolism
eg catalases, peroxidases
What are microtubules, what is their function?
Polymers of α and β-tubulin, ∼20nm in diameter. Involved in cell shape and act as tracks for movement of other organelles and cytoplasmic components within the cell.
What protein monomer is the major component of cilia and flagella?
Microtubules
What protein monomer forms the mitotic spindle?
Microtubules
What are intermediate filaments and what is their function?
A group of polymers of filamentous proteins which form rope-like filaments. 10-15nm in diameter
What protein monomer gives mechanical strength to a cell?
Intermediate filaments
What type of intermediate filament do epithelial have, which also connects desmosomes?
Cytokeratins
What type of intermediate filament do mesenchymal cells have?
Vimentin
What are mesenchymal cells? (4)
Cells of the connective tissue Fibroblasts (many tissues) Chondrocytes (cartilage) Osteocytes (bone) Muscle cells (skeletal, cardiac, smooth)
What kind of intermediate filament do neurones have?
Neurofilament protein
Where are nuclear laminins found? What is their function?
They form a network on the internal surface of the nuclear envelope and are involved in stabilising the envelope
What are actin microfilaments? Where are they found?
Polymers of the filamentous actin (f-actin). Associated with adhesion belts in epithelia and endothelia, and with other plasma membrane proteins. Involved in cell shape and cell movement (crawling of cells; cell contractility especially in muscle). Has accessory proteins (e.g. myosin- acts with actin to control actin organisation and cell movement)
What are haematopoietic cells?
Cells of the blood and of the bone marrow from which they are derived
What are neural cells? (2)
Cells of the nervous system having two main types Neurones (carry electrical signals) Glial cells (support cells)
What cell type do carcinomas originate?
Epithelial cells
What cell type do sarcomas originate?
Mesenchymal cells
What cell type do leukaemias originate?
Haematopoietic cancer from bone marrow cells
What cell type do lymphomas originate?
Haematopoietic cancer from lymphocytes
What cell type do neuroblastomas originate?
Neural cell cancer from neurones
What cell type do gliomas originate?
Neural cell cancer from glial cells
What is the apical surface of a cell?
Faces in towards the lumen
What is a cell junction?
A multiprotein complex that provides contact between neighbouring cells
What is the extracellular matrix?
Material deposited by cells which form the “insoluble” part of the external environment. It is a complex network of proteins and carbohydrates filling the space between cells. It comprises of both fibrillar and non-fibrillar components
It may be poorly organised (e.g. loose connective tissue) or highly organised (e.g. tendon, bone, basal lamina)
Generally in what two forms to you find cell-cell junctions?
Zonulae (belts) and maculae (spots)
What is an apical junctional complex found in epithelia?
Cell-cell junctions
Tight junctions nearest the apex, then an adhesion belt , then desmosomes scattered throughout the lateral membrane
What is a zonular occludens?
Belt/occluding junctions- points on adjacent membranes that form close contacts at apical lateral membranes
What is a zonula adherens?
Adhesion belt- Usually formed just basal to the apical tight junction. The transmembrane adhesion molecule is cadherin. Cadherin is associated with the actin cytoskeleton
What is a Macula adherens?
A desmosome. Found at multiple spots between adjacent cell membranes, provides good mechanical continuity between cells.
What is a macula communicans?
A gap junction. Made up of clusters of pores formed from 6 identical subunits in the membrane. These pores are continuous with pores in adjacent membranes. They allow passage of ions and small molecules between cells.
What can effect the opening and closing of a gap junction? (4)
pH, Ca2+ concentration, voltage and some signalling molecules
What is a chemical synapse, where are they found?
Mainly in neural tissue. They are button-like junctions formed between neurones or between neurones and target cells (e.g. muscle). Information is passed one-way via a chemical signalling system.
What are the different types of epithelial cell classification? (5)
Simple squamous Simple cuboidal Simple columnar Stratified squamous Pseudostratified
Why is cell polarity important in epithelial cells?
For secretion, transport and absorption it must be unidirectional. Cell polarity gives directionality to epithelial function. Membrane polarity is key to epithelial polarity
Give an example of a cell feature that would organise it for absorption, secretion, protection or transport?
Absorption- Microvilli brush border or enterocytes
Secretion- goblet cells
Protection- thick skin, made up of the epidermis, dermis and hypodermis
Transport- mitochondria (for active transport)
What is an exocrine secretory function?
Secretes into a duct or lumen
What is an endocrine secretory function?
Secretes into the bloodstream
What are the different types of exocrine gland epithelium organisation? (6)
Simple tubular Simple branched tubular Simple coiled tubular Simple branched alveolar Compound tubular Compound alveolar
What is constitutive secretion?
Secretory vesicles, as they are formed, move directly into the plasma membrane and release their contents
What is stimulated secretion?
Secretory vesicles are stored in the cytoplasm and only fuse with the plasma membrane to release their contents when stimulated
What cell type is the epidermis?
Keratinized stratified squamous epithelium
What is the function of ECM?
It provides physical support, it determines the mechanical and physicochemical properties of the tissue. It influences growth, adhesion and differentiation status of the cells and tissues with which it interacts and it is essential for development, tissue function and organogenesis
What is connective tissue?
Tissue that is rich in ECM. They contain a spectrum of collagens, multi-adhesive glycoproteins and proteoglycans (ECM) together with component cells
ECM+cells
What is the structure of collagen, what amino acids?
Three α-chains forming a triple helix
Characteristically it is [gly-x-y]repeat: x is often proline and y is often hydroproline
What is the process of fibrillar collagen biosynthesis?
1) Synthesis of pro-α chain
2) Hydroxylation of selected prolines and lysines
3) Glycosylation of selected hydroxylysines
4) Self-assembly of three pro-α chains
5) Procollagen triple helix formation
6) Secretion
7) Cleavage of propeptides
8) Self-assembly into fibril
9) Aggregation of collagen fibrils to form a collagen fibre
What effect does vitamin C have on collagen?
Vitamin C deficiency results in under hydroxylated collagens with dramatic consequences for tissue stability
What residues are responsible for covalent cross-link formation in collagen?
Lysine and hydroxylysine
What are elastic fibres made up of?
Elastin core, and microfibrils which are rich in the protein fibrillin
What causes Marfan’s syndrome?
Mutation in fibrillin 1
What is the structure of elastin?
Consists of two types of segments that alternate along the polypeptide chain: hydrophobic regions and α-helical regions rich in alanine and lysine. Many lysine chains are covalently cross-linked
What is the structure of laminins?
It consists of three chains, one of each α, β, and γ forming a cross-shaped molecule. It is a very large multi-adhesive molecule that interacts with cell surface receptors (integrins and dystroglycan)
What are fibronectins?
A major connective tissue glycoprotein. They can exist as insoluble fibrillar matrix or soluble plasma protein (both derived from one gene- alternate splicing at mRNA level). They are multi adhesive and have no known mutations in humans- they are essential for life
What connective tissue is important in migration in embryogenesis, regulating cell adhesion, tissue repair, and wound healing?
Fibronectins
What proteins are responsible for connecting the ECM to the actin cytoskeleton of cells?
Integrins
What is the structure of proteoglycans?
A core protein to which one or more glycosaminoglycan (GAG) chains are covalently attached. Some have one single GAG chain attached, whereas some large proteoglycans carry ∼100 GAG chains
What is the structure of glycosaminoglycans (GAGs)
They are long unbranched sugars consisting of repeating disaccharides. One of the two sugars in repeating disaccharides is always amino sugar. Many GAGS are sulfated or carboxylated and highly negatively charged.
They occupy a huge volume compared to their mass and they can be very resistant to compression.
What are the 4 types of GAG chains that attach to a proteoglycan?
Hyaluronan
Chondroitin sulphate or dermatan sulphate
Heparan sulphate
Keratan sulphate
What are the distinct features of hyaluronan (hyauronic acid)?
Unique- simply a carbohydrate chain, no core protein. It is synthesised at the cell surface, not in the ER/Golgi. It is unsulphated and is a single long chain, up to 25,000 repeated disaccharides. It has a huge size- save volume as a bacterium
What is decorin, what is it’s function?
It is a small proteoglycan. It binds to collagen fibres and is essential for fibre formation.
What is the most abundant type of cartilage?
Hyaline Cartilage
What is hyaline cartilage, where is it found, what is it’s function?
Most abundant type of cartilage found in the nose, larynx, trachea, bronchi, the ventral ends of ribs and the articular ends of bones. It is rich in aggrecan (core protein) and functions to cushion the ends of long bones
Why is aggrecan suited to a role in cartilage?
It is perfectly suited to resist compressive forces The GAGs (e.g. chondroitin sulfate) of aggrecan are highly sulfated, and there are also a large number of carboxyl groups. These multiple negative charges attract cations such as Na+ that are osmotically active. Large quantities of water are therefore retained by this highly negatively charged environment. Under compressive load, water is given up but regained once the load if reduced.
What causes congenital muscular dystrophy?
Absence of α2 in laminin 2
What symptoms are characteristic of congenital muscular dystrophy?
Hypotonia (abnormally decreased muscle tension), generalised weakness and deformities in the joint
What causes osteoarthritis? What is it?
Excessive loss of extracellular matrix (ECM degradation). Characteristic thinning and destruction of cartilage.
With age: cleavage of aggrecan by aggrecanase and metalloproteinase. Loss of aggrecan fragments to synovial fluid
What are the main fluid compartments of the body and roughly what size are each?
Intracellular=55% of body water Extracellular= 45% of body water made up of: Interstitial fluid= 36% of body water Blood plasma= 7% of body water Transcellular fluid= 2% of body water
What percentage fluid are men and women?
Women 55%
Men 60%
What is the main extracellular and intracellular cation?
Extracellular: Na+
Intracellular: K+
What is the main extracellular and intracellular anion?
Extracellular: Cl-
Intracellular: Organic phosphates
Is pH higher intracellularly or extracellularly?
Intracellularly
Is osmolarity higher intracellularly or extracellularly?
Osmolarity is equal
What is diffusion?
The spontaneous movement of solutes
What is osmosis?
The diffusion of water down its own concentration gradient
What is osmolarity?
A measure of the concentration of all solute particles in a solution
What is tonicity?
The measure of the effective osmotic pressure gradient of two solutions separated by a semi-permeable membrane. It is only influenced by cells which cannot cross the membrane (e.g. is a solution is hypertonic it has a greater concentration than the other side of the membrane)
Is transport of ions or urea across a membrane through a ligand or voltage-gated channel active or passive?
Passive
What are three types of passive transport across a membrane?
Diffusion
Through channels (ligand or voltage-gated)
On carriers
What are two examples of transport against the concentration gradient?
Active transport On carriers (uses down-hill movement of one solute coupled to another)
What is the colloid osmotic pressure?
The osmotic pressure due to plasma proteins
What substances are exchanged through capillary endothelial cells?
Plasma
Exchangeable proteins are moved across by vesicular transport
Lipid-soluble substances pass through endothelial cells
Small water-soluble substances pass through the pores between cells
In oedema what happens to the relationship between hydrostatic pressure and colloid osmotic pressure?
Hydrostatic pressure > Colloid osmotic pressure
What is oedema?
The swelling of a tissue because of excess interstitial fluid