Tissues Flashcards
What is meant by the “fluid mosaic” model?
The fluid mosaic model describes a dynamic cell membrane. The phospholipids move, and are peppered with proteins which appear randomly distributed, but in reality and are in specific locations, and grouped together for optimal physiological functioning. These proteins may be free flowing in the membrane, or may be tethered to specific sites.
Which types of molecules are lipid membranes permeable and impermeable to?
Lipid membranes are high permeable to small and fat-soluble molecules, such as oxygen, carbon dioxide, water, urea, and glycerol. They are impermeable to large and highly charged molecules, such as ions and sugars.
What is the purpose of signal sequences (tags) on precursor proteins?
Tags are used to discriminate between different proteins are how/where they are to be translocated. These are recognised by signal recognition peptides (SRPs).
How does BOTOX reduce wrinkling?
BOTOX involves the injection of a neurotoxin which prevents the fusion of certain secretory vesicles within synaptic clefts. These vesicles contain neurotransmitters which ultimately cause the contraction of facial muscles which cause wrinkling.
What are the main components of the cytoskeleton? Describe their structures and functions.
The cytoskeleton is composed of microfilaments, microtubules, and intermediate filaments.
Microfilaments are helical polymers of actin protein. These give rigid structural support around the external cells surfaces.
Microtubules are hollow cylinders made of tubulin protein. They have centrosomes from which they protrude (have directionality), are rigid, and may rupture if stretched.
Intermediate filaments are made of fibrous proteins which form rope-like structures. These are more fluid, but still quite rigid, and allow the cell to cope with mechanical stress.
What are kinesins and dyneins?
Kinesins and dyneins are proteins which carry cargo around the cell via microtubules. Most kinesins carry cargo towards the +end, whilst most dyneins carry cargo towards the -end.
Explain the histology and functions of epithelial tissue
Epithelial tissues are layers of cells which sit on basement membranes. They have tight and cohesive junctions to protect and cover surfaces - epithelium lines internal cavities and vessels, as well as external surfaces. It also forms glands, barriers, and can combine with nervous tissues to make special senses (e.g. olfaction, gustation). It is highly cellular, avascular, and very good at regenerating (uses an abundance of epithelial stem cells). Epithelial cells are bipolar (have distinct apical and basal side, as well as lateral surfaces), and each surface has its own specialisations.
Describe some potential specialisations exhibited on apical and basolateral aspects of epithelial cells.
Microvilli are cytoplasmic protrusions (form a brush border). They are often found lining passages, and their function is to increase the surface area of the epithelium (beneficial for secretion, exchange, diffusion, etc).
Sterocilia are long, rigid protrusions which are non-motile. They are found in inner ear hair cells, and in the epididymis.
Cilia are motile, hair-like protrusions - each cell can have hundreds of these, and they beat in coordination to move substances over them.
Basolateral surface specialisations are generally for joining cells together - they also exchange information and metabolites with neighbouring cells and the basal membrane.
What are the main differences between the three epithelial cell junctions (tight, anchoring, and gap)?
Occluding/tight junctions seal cells together to prevent leaking - the most common tight junction is zona occludens (apical-lateral domain fuses 2 cells to stop anything apart from desired molecules travelling through, for example in the BBB).
Anchoring junctions allow for some exchange. They mechanically attach cells to neighbours, and are subject to severe stress.
Gap junctions allow passage of chemical/electrical signals between cells (larger).
What are the three characteristics which epithelial tissues are based on?
Number of layers - simple/stratified/pseudostratified
Shapes of cells - squamous/columnar/cuboidal/transitional
Surface specialisations
Describe the histology and functions of connective tissue.
Connective tissue is the most abundant and widely spread tissue type. It arises exclusively from the mesoderm. It is comprised of cells separated by an ECM. It can have a huge variety of functions - ligaments and tendons provide physical connection between muscle and bone, or bone and bone, respectively. Bones are cartilage provide structural support. Capsules enclose and protect surfaces such as joints and organs. Connective tissue also separates structures from each other, cushions/insulates, stores substrates, and transports them.
Name and describe the three cell types of connective tissue.
Blasts create the extracellular matrix (ECM), cytes maintain the ECM, and clasts break down the ECM. These are the resident cells of connective tissues, but there are usually many other cell types with specific functions as well as these.
Describe the functions and main components of the extracellular matrix.
ECM allows connective tissue to bear weight and withstand tension and trauma - it provides a “scaffold” for organs.
ECM is composed of ground substance and extracellular protein fibres. ground substance is a gel-like substance which fills spaces between connective tissue cells. It contains water and two main groups of soluble proteins - cell adhesion proteins (which have a glue-like function), and proteoglycans (which are macromolecules with a protein core). glycosaminoglycans (GAGs) are attached to this core, and they increase the viscosity of the ECM to make it more tolerant to mechanical stress.
Extracellular fibres provide support in connective tissue, and are composed of 3 fundamental fibre types - collagen, elastin, and reticular.
Describe the structure and function of the three connective tissue fibre types.
Collagen fibres are the thickest and most abundant in the body. They are produced by fibroblasts. 3 chains of amino acids wind around each other to form a rope-like collagen molecule called tropocollagen, which form fibrils which bundle together into collagen fibres (10um in diameter). Type I collagen is the most abundant type, and it is found in tendons and ligaments (as well as scar tissue). Type II collagen is found in cartilage.
Elastic fibres are longer, thinner, and more stretchy than collagen fibres. They are also produced by fibroblasts, and are found in areas where lots of flex and recoil take place (lungs, blood vessel walls, etc).
Reticular fibres are shorter and thinner than the other types - they branch to form networks to fill spaces between tissues and organs (found in abundance in the liver, spleen, and lymph nodes).
Describe the three categories of connective tissue, as well as their subcategories.
Connective tissue can be divided into connective tissue proper, supporting connective tissue, and fluid connective tissue.
Fluid connective tissue includes tissues where the ECM is a liquid (e.g. blood).
Supporting connective tissue includes bone and cartilage.
Connective tissue proper can be subdivided into loose and dense.
Loose connective tissue proper has an ECM which is mostly comprised of ground substance, and is not densely packed with fibres (e.g. adipose tissue).
Dense connecive tissue proper is very densely packed with fibres (can be packed regularly or irregularly).
