Skin Flashcards
What is the plasma membrane?
The plasma membrane is a phospholipid bilayer that gives the cell a barrier between its intracellular and extracellular environment
What do the cholesterol molecules and carbohydrates on the plasma membrane add?
Cholesterol inhibits packing of the lipids allowing the membrane to be fluid, and carbohydrates allow for recognition of the cell
What does amphipathic mean?
Having both hydrophobic and hydrophilic qualities
What do membrane receptors do?
interact with signalling molecules on the outside and initiate a reaction inside the cell
Describe the double membrane of the nucleus
the inner membrane is the nuclear lamina supported by intermediate filaments, the outer membrane is continuous with the ER
What are the four compartments of the mitochondria?
Outer Membrane-selectively permeable
Inner Membrane- folded into cristae (ETC)
Matrix
Intermembrane space
What is the ER and its function?
The endoplasmic reticulum is a series of flattened membranes with a Rough ER where ribosomes can synthesise proteins and a smooth ER where lipid synthesis occurs.
Golgi Apparatus description
The Golgi Apparatus receives proteins from the ER and is the sorting office for these proteins final destinations via post-translational modification,
What do lysosomes do?
lysosomes contain hydrolytic enzymes and degrade unwanted molecules
Cytoskeleton
supports the plasma membrane and gives the cell some shape and structure
What are the three classes of filaments?
microtubules made of tubulin monomers
microfilaments made of actin
intermediate filaments made from proteins like keratin
Describe microtubules?
They are cylindrical tubes that grow outwards from the MTOC, and facilitate the movement of vesicles and organelles around the cell
What are axonemes?
they’re made from microtubules and dynein and make up the cytoskeleton of cilia and flagella.
Kartagener’s Syndrome is a mutation in the dynein, meaning sperm are immotile due to the flagella being useless and recurrent respiratory infections with cilia not being able to clear mucus
What are junctions?
Junctions are transmembrane protein complexes that connect cells to each other or to the ECM.
What are the three types of junction?
Anchoring, Tight, Gap
What is an anchoring junction?
Anchoring junctions provide stability for epithelial cells to work together. Focal Adhesions join cells to the ECM, Adherens join cells together (for microfilament Actin cytoskeleton)
In an intermediate filament network, desmosomes connect cell to cell, hemidesmosomes cell to ECM
Describe Tight junctions
Tight junctions are cell to cell contact and have two functions:
prevent diffusion of molecules to neighbouring cells and create a barrier within epithelial cell membranes preventing mixing of membrane proteins, creating an apical and basolateral membrane.
What are Gap junctions?
Gap junctions allow communication between cells and are intercellular channels connecting the cytoplasms of two cells. this allows passage of small ions and molecules. gap junctions are made of connexins.
How are proteins dispatched to their required location?
They contain an amino acid sequence that shows where they need to go
Describe the three ways in which proteins are transported around the cell
Nuclear pores- gates on the nuclear membrane
Transport vesicles- for movement from the ER onwards
Translocators- move proteins from the cytosol onwards to ER etc
How do ribosomes know to travel to the ER?
The proteins they are assembling contain a specific sequence that is recognised by a signal recognition particle (SRP) in the cytosol and this guides the ribosome and protein to the ER. Signal peptidase will cleave off the redundant signal peptide.
Describe the Cis Maturation model
The first membrane of the Golgi is the Cis Cisternae, which is made of fused vesicles from the ER containing proteins. The proteins move through the Golgi in waves, and the first thing that happens is the Cis moves into the Medial cisternae. one of the medial will then move into the transmembrane where the proteins are sorted for their final destination.
List examples of post translational modifications that happen in the Golgi
Glycosylation- addition of a sugar to a core oligosaccharide. Proteoglycans (much glycosylation), glycoproteins (little glycosylation).
Phosphorylation- addition of a phosphate
Acetylation- addition of a an acetyl group
What are the two pathways of protein degradation?
Proteasomal- occurs within proteasomes (usually for proteins with a short half life that can be dangerous if around for long)
Lysosomal- occurs by lysosomes (proteins with long half life)
Describe the proteasomal pathway
The proteasomal pathway is where proteins either tagged with ubiquitin or PEST (proline, glutamic acid, serine or Threonine) are taken to a proteasome which is a long cylindrical complex. the active site is within the cylinder.
What are the three functions of the skin?
Protection, physiological regulation and sensation
What are the three layers of the skin?
The epidermis, dermis and hypodermis (subcutis)
What are the four layers of the epidermis?
The stratum basale, stratum spinosum, stratum granulosum and the stratum corneum. all the cells are a type of epithelial cell, keratinocytes
Describe the stratum basale
The stratum basale is the deepest layer and connects to the basement membrane via hemidesmosomes which separates the epidermis and dermis. it is mitotically active and populates all the layers of the epidermis
Describe the stratum spinosum
The spinosum layer is more superficial and here the keratinocytes are held together by desmosomes.
Describe the stratum granulosum
The granulosum layer contains keratinocytes filled with keratohyalin granules
What is the stratum corneum?
The stratum corneum is the most superficial layer, where the cells are flattened and without a nuclei. they’re filled with keratin and lipids to form a water barrier.
What are the two layers of the dermis?
The dermis is below the basement membrane and is a layer of connective tissue. the superficial papillary layer contains fine collagen and most of the blood vessels whilst the lower reticular layer contains the elastin and stronger collagen.
What is the dermis composed of?
Collagen- gives the skin tensile strength
Fibroblasts- synthesise all the cells within the dermis
Elastin- gives the skin its stretch
ground substance
Describe the subcutis
It is composed of adipose tissue and provides insulation and shock absorption.
eccrine glands secrete sweat
apocrine glands secrete the scent in the genitals and such
sebaceous glands secrete sebum that lubricates the skin
How do skin and hair get their pigmentation?
Melanosomes contained within melanocytes produce melanin which migrates to the keratinocytes
What do langerhans and Merkel cells do?
Merkel cells are responsible for sensation and found in the basale.
Langerhans are important in the immune response and are antigen presenting cells.
What are the three stages of skin repair?
Inflammatory phase, proliferative phase and the remodelling phase
What is the initial inflammatory phase?
partial or full thickness wound, then a blood clot is formed initiated by platelets. any infections will be fought by macrophages and neutrophils.
What is the proliferative phase?
the proliferative phase is where fibroblasts replace lost molecules, e.g. type 3 collagen. endothelial cells repair and form new blood vessels. re-epithelialisation is the formation of new epithelium.
What is the remodelling phase?
This phase can last several months and type 3 collagen is converted to the stronger type 1. fibroblasts can become myo-fibroblasts that close the wound by contractile force. the skin will be 80% strength of what it used to be.
What is EGF (epidermal growth factor?)
It tells keratinocytes to divide and migrate to close a wound.
What is parenchyma tissue?
The tissue that carries out the specific function.
What is stroma tissue?
The tissue that provides nutrients and the scaffolding.
What are the four types of tissue?
Connective- space filling tissue that provides protection and support
Muscle- contract to generate force
Epithelial- lines the body surfaces
Nervous tissue- neurons etc
What is sectioning?
Sectioning is a step in preparing a slide of a tissue sample, where the tissue is cut into very thin slices.
What is the purpose of staining with haematoxylin and eosin?
Haematoxylin stains acidic structures a purplish blue like the nucleus, while eosin stains the basic structures a pink/red e.g. the cytoplasm
What does the number of layers of epithelial cells mean?
One- simple
Two or more- stratified
one but with varied cell shapes- pseudostratified
How do the shapes of cells correspond with the name they’re given?
Squamous-flat
Cuboidal- cube shaped
Columnar- tall and cylindrical
Transitional- change shape
Describe some common types of epithelium
Simple squamous- lines blood vessels and alveoli, good for diffusion and filtration.
Simple cuboidal- good for absorption and secretion, found in kidney tubules.
Simple Columnar- movement of substance, stomach lining. can have cilia or microvilli depending on where they’re found.
Stratified squamous- skin. protection against abrasion and infection as a barrier.
Pseudostratified- almost always ciliated and associated with goblet cells that secrete mucus. lining of nasal cavity and bronchi etc.
Transitional epithelium- located in structures where considerable expansion occurs e.g. bladder
