2. Epithelia Flashcards
General Features of Epithelia Functional Classification of Epithelia ECM and Connective Tissue Skin
Name the four types of animal tissue.
Epithelial, Connective, Muscle and Nervous Tissue
Give an example of why epithelia moves.
Important in making new tissues, cancer invasion and wound formation.
List the four functions of epithelial tissue
Protection, Permeability, Sensation, Secretion
Epithelia is described as polarised. What does that mean.
Has different ends (apical and basal ends) containing different proteins seperated by cell junctions
What does Avascular mean?
No blood vessels
How does epithelia get molecules found in blood without a blood supply.
Join to connective tissue with blood supply. Molecules diffuse from connective tissue to epithelial cells
Give a property of epithelial tissue
Cellular, polarised, cell-cell or cell-substrate attachment avascular an regeneration and repair.
What is covering epithelia?
Covers or lines body surface, cavities and tubes
What is glandular epithelia?
Form functional units of secretory glands
What do cell junctions do?
Maintain distinctions between the different membranes (apical, lateral and basal) and prevents molecules entering from other cells.
What is the function of basement membrane?
Holds the cells in place and seperates it from other tissues
Which membrane faces the lumen?
Apical
How do nutrient get through epithelial layer.
Transported into epithelial cells and then releases into intercellular space.
Which membrane would contain enzymes for digestion?
Apical
What does squamous mean?
Width greater than height. Central nucleus
If epithelial cells have equal height and width, what are they called?
Cuboidal - Central nucleus
What does columnar mean?
Height greater than width. Basal nucleus
What is a simple cell layer
One cell thick, all connected to basement membrane (absorption, secretion)
What is a stratified cell layer?
Multiple cell layers, only base in contact with basement membrane. May contain more than one shape (protective)
What is a pseudo-stratified layer?
Appears multi-layered but only one cell thick (simple), all contact basement membrane but not lumen. Nucleus all at different levels.
What does keratinised mean?
Has protein that makes surface water proof (skin)
What type of epithelia would you expect to find simple, squamous cells?
Exchange Epithelia (for short diffusion of gases) (lungs and blood vessels)
What type of epithelia would you expect to find cuboidal cells with microvilli and lots of mitochondria?
Transport Epithelia (for selective exchange of non-gaseous materials (ions))(Digestive system and kidney)
What is the function of cilia?
Moves fluid and molecules along tissue surface.
What type of epithelia would you expect to find in your skin
Protective Epithelia - stratified and of different shapes.
What are exocrine glands)
Glands that are made up of secretory epithelia that secretes tears, sweat and mucus. They contain duct.
Do endocrine gland contain a duct?
No they are ductless and secrete hormones
What shape of cell would you expect to see in the alveoli of lungs?
Simple Squamous (for passive transport of gases and fluid)
What shape of cell would you expect to see in the pancreas?
Simple cuboidal (secretory, excretory and absorptive)
Where would i find simple columnar ciliated epithelia?
Fallopian Tube and small intestine (moves food along lumen)
What is the function of non-keratinised stratified squamous cells?
Protective
What is the function of keratinised stratified squamous cells?
Waterproof
What are Cilia?
Hair-like extensions of the cytoskeleton composed of a core of microtubules (2 central microtubules and 9 surrounding ones)
What are microtubules made up of?
Tubulin Heterodimers
How many protofilaments do isolated microtubules contain?
13
What is the function of cilia?
Moves molecules along the surface, sensory antennae, generate and send signals.
How is the shape of microvilli maintained?
Actin microfilaments run entire length of microvillus with + end at the tip and - end anchored to bottom attached to intermediate filaments
How small are microvilli
about 700nm
Number and shape of microvilli correlates with what?
Cell’s absorptive capacity
What do microvilli do?
Increase SA for highly absroptive cells in small intestine and kidney.
Where are Stereocilia found?
Ear cochlea
What supports the structure of stereocilia?
Actin filaments and cross-linked by fimbrin
What is longer, microvilli or stereocilia?
Stereocilia
What are basolateral folds?
Deep invaginations of the lateral surface of the cell that faces adjacent cells and underlying connective tissue which increase SA (mainly found in cells involved in ion transport)
What are Podocytes?
Found in the visceral layer of bowman’s capsule wrap around capillaries of glomerulus, leaves slits around bowman’s capsule to allow small molecules to be forces out of capillaries but prevent large molecules entering.
Name the 4 types of cell junctions
Tight, Adherens and Gap Junctions and Desmosomes.
What is the function of tight junctions?
Block the passage of contents in between the cells and restricts movement of proteins and lipids between the apical and basolateral membranes
What is the function of adherens junction and desmosomes?
Attach cells to each other via cytoskeleton
What is the difference between adherens and desmosomes?
Desmosomes linked to intermediate filaments whereas adherens linked to actin filaments
What is the function of gap junctions?
Coordination and communication between adjacent cells for contraction or electrolyte transport.
Name the two cell-matrix junctions.
Hemidesmosomes and focal adhesions
What is the difference between the two cell-matrix junctions?
Hemidesmosomes are linked to intermediate filaments and focal adhesions are linked to actin filaments
Where would you find the basement membrane?
Between epithelial cells and connective tissue
What is the composition of the basement membrane?
Collagen, Proteoglycans, Laminin, Enactin and Fibronectin
Name the 5 functions of the basement membrane.
Structural attachment, compartmentalisation, filtration, tissue scaffold and signalling
Secretory cells which are organised into functional groups are called what?
Glands
What is the difference between endocrine and exocrine glands?
Endocrine are ductless and secreted directly into bloodstream (hormones) whereas exocrine have a duct.
Describe the merocrine secretory mechanism.
Exocrine - Membrane bound vesicles containing product fuse with membrane - exocytosis - releasing molecules into lumen
Describe the apocrine secretory mechanism
Exocrine - Release product in vesicles surrounded by cytoplasm and plasma membrane
Describe the holocrine secretory mechanism
Exocrine - whole cell containing product undergoes programmeed cell death and products released
Describe the endocrine secretory mechanism
Exocytosis of product from cell which diffuses into bloodstream
Name the 3 secretory products
Protein, Mucin (mucus) and Steroid (lipid)
What organelles would you expect to see in protein secreting cells?
Large nucleus, abundant RER and electron dense vesicles
Describe the structure of endocrine glands
Consists of clumps of secretory cells surrounded by network of blood vessels
List 5 connective tissue components
Fat cells, lymphocyte. Macrophage, Capillary, Melanocyte, Reticular Fibres, Mast Cells, Elastic fibres, Collagen fibres and ECM
Describe the structure of bone in terms of it being a connective tissue.
Has less ECM and dense fibres for strength
Name a disease that can be causes by lack of connective tissue.
Arachnodactyly, Scurvy, Marfan Syndrome and Hypermobility
The nucleus of epithelial cells is influenced by what?
The position of actin.
What is fibronectin?
Mutlifunctional glycoprotein - mediates adhesion between a wide range of cells and ECM components
List 4 functions of connective tissue.
Provides form and support, physical barrier, connects and anchors, medium for exchange of molecules, defence and protection, cushioning and thermoregulation, signalling, ageing and stem cell biology.
Describe the structure of loose (areolar) connective tissue
Flexible, multiple cell types, collagen fibres thin and sparse (less packed together), ECM occuies greater volume than fibres, viscous but permits diffusion
Describe the structure of irregular dense connective tissue
Mostly collagen fibres, little ECM, provides strength, collagen irregularly in bundles
Where would you find loose connective tissue?
Dermis
Where would you find irregular dense connective tissue?
Muscle, Nerve Sheaths
Describe the structure of regular dense connective tissue
Mostly collagen fibres, little ECM, parrallel array, main constituents of ligaments, tendons and aponeuroses
Where would you find regular dense connective tissue?
Tendons, ligaments
What do tendons link together?
Muscle to bone
List the 6 specialised connective tissue
Bone, Cartilage, Adipose Tissue, Blood, Haemopoietic Tissue, Lymphatic Tissue
What can connective tissue do for defence against pathogens?
Undergo swelling (inflammatory), contains immune cells
Describe the structure of tendons
Parallel bundles of collagen fibres with rows of fibroblasts in between, less elastic fibres.
What does Epidtendinium mean?
Outer capsule collagen fibres less regularly orientated
What does Endotendinium mean?
Connective Tissue partitioning in the tendon also contains nerves and blood vessels.
Describe the structure of ligaments
Contain fibres and fibroblasts in parallel, less regularly orientated than in tendons and mostly collagen, some with nervous system consist of elastic fibres.
Describe the structure of aponeuroses
Broad, flattened tendons, have collagen fibres in layers with adjacent fibres at right angles to each other (orthogonal array),
What produces connective tissue fibres?
Fibroblasts
Name the 5 connective tissue fibres
Collagen fibres, Reticular fibres, Elastin Fibres, Fibrillin and Fibronectin
What is the most abundant connective tissue fibre?
Collagen fibres
Describe structure of collagen fibres.
Flexible, high tensile strength, made up of collagen fibrils, straight fibres but overlapping, triple helix (3 polypeptides)
Describe the structure of Reticular fibres
Composed of type III collagen. branched and arranged in a network, found in the boundary between connective tissue and epithelium and around fat cells, small blood vessels, nerves and muscles.
Describe the structure of elastin fibres
Thinner than collagen, coiled, linked by covalent links producing 3D meshwork, interwoven with collagen fibres to prevent tearing, produced by fibroblasts smooth muscle, central core of elastin, surrounded by fibrillin microfibrils
List 2 functions of the extracellular matrix
Provides mechanical strength and structural support, biochemical barrier, anchors cells, cellular migration pathways in development and repair and binds and retains growth factors
What is the ground substance composed of?
Protoglycans, Glycosaminoglycans and glycoproteins
Where is ground substance found?
Found between cells and fibres of connective tissue. Gel like consistency with lots of water.
What ability do multiadhesive glycoproteins have?
Ability to bind multiple cell surface proteins and ECM components
Name the 6 fixed components of connective tissue
Fibroblasts, myofibroblasts, macrophages, adipose cells, mast cells and undifferentiated mesenchymal cells
Name the 6 wandering components of connective tissue
Lymphocytes, Plasma Cells, Neutrophils, Eosinophils, Monocytes and Basophils
What do myofibroblasts do?
Synthesize fibres and ECM (wound closing and healing) – contain contractile machinery plus RER, have gap junctions
What do macrophages do?
Immune response (find and present foreign antigens)
I am a lipid storing cell and synthesise hormones and growth factors. What cell am i?
Adipose Cells
Name a cell that conducts an immune response
Macrophages, Mast Cells. Lymphocytes, Plasma Cells, Neutrophils, Basophils
Which cell promotes inflammation?
Mast Cells
What do undifferentiated mesenchymal cells do?
Potential to rise to differentiated cells that repair and grow tissues, for neo-vascularization
Which cells secrete antibodies?
Plasma Cells
Which cells are responsible for phagocytosis?
Neutrophiles
What do eosinophils do?
Cause allergic reactions
What is the link between macrophages and monocytes?
Monocytes develop into macrophages
What is the link between basophils and mast cells?
They both have similar functions
What is the largest organ?
Skin
Name the 5 functions of the skin
Protection, Sensation, Thermoregulation, Metabolism and Sexual Attraction
How does the skin protect the body?
mechanical, chemical and microbial barrier, waterproof, UV protection, camouflage,
Skin type is dependant on what?
Genotype
Where would you expect skin to be very thick?
Soles of Feet
Name the 3 layers of skin ranking them in order of outside body inwards
Epidermis, Dermis and Hyperdermis
Name the 4 cell types that make up the epidermis
Keratinocytes, Melanocytes, Langerhans cells and Merkel cells
What separates the epidermis from the dermis
Basement membrane
Name the 4 layers of the epidermis.
Cornified layer (stratum corneum), granular layer (stratum granulosum), spinous (prickle) layer (stratum spinosum) and basal layer (stratum basale/ stratum germinativum
Describe the cornified envelope
Crosslinked protein layer under membrane of cornified cells.
What features do melanocytes provide to skin?
Produce Melanin for skin Colour and protection against UV
Where are melanocytes found in the epidermis?
Basal layer bound to basement membrane
What is a melanoma?
Malignant melanocytes due to repeated exposure to UV light
What is the function of Langerhan cells?
Component of immune system - recognise antigens and present it to T cells. Has cytoplasmic processes extending between cells.
Where are Langerhan cells found in the epidermis?
Spinous layer.
What is the function of merkel cells?
Sensory receptors in the epidermis (light, touch), form synaptic junctions with peripheral nerve endings (mainly in fingertips)
What stain shows all the cells in the epidermis?
H+E
Where in the epidermis would you find a merkel cell?
Basal layer
What am i describing: Thin epidermis, thick dermis, poorly developed rete ridge system, hair present, few sweat glands present
Thin skin
What am i describing: Thick epidermis, thin dermis, well developed rete ridge system, no hair present, many sweat glands present, many sensory organs present.
Thick skin
Which of the 3 layers of the skin is connective tissue
Dermis
What does the dermis contain?
Connnective Tissue, Nerves, Blood vessels, Fibroblasts, fibrocytes, macrophages, lymphocytes mast cells, ECM, epidermal appendages, sensroy cells.
What is papillary dermis?
Less collagen and elastic fibres and more glycosaminoglycans and small capillaries. (thin and vertically orientated
What is Reticular dermis?
Dense collagen and thick elastic fibres, major blood vessels and lymphatics (thick and horizontal)
What does the hypodermis contain?
Composed mostly of adipose tissue and collagen fibres, contains epidermal appendages, major blood supply and nerves
What is the function of the hypodermis?
Acts as an insulator, shock absorber and food source
List the 4 epidermal appendages.
Hair follicles, sebaceous glands, eccrine or merocrine sweat glands and apocrine sweat glans in man.
What determines the colour of hair follicles?
Melanocytes
What does sebaceous glands secrete?
Sebum (lipids, waxes - coats hair and skin)
How do sebaceous glands secrete its product?
Holocrine secretion (cell die and release contents into duct)
Why do we need eccrine and merocrine sweat glands?
Regulates body temperature - sweat
What controls eccrine and merocrine sweat gland?
Autonomic NS
What cells secrete watery component of sweat
Clear Cell
What do dark cells do?
Secrete proteinaceous component of sweat
What do myoepithelial cells?
Contractile - expel secretions
Apocrine sweat glands are found where?
Genitalia, anus and armpits (hair follicle rich)
What does apocrine sweat glands produce?
Produce milky viscous oily liquid (rich in proteins and lipids)
What causes the strong odour produced from apocrine sweat gland?
Microbial Activity
What is the main function of apocrine sweat glands?
Product mark territory and cause sexual attraction (e.g. pheromones)
Name 3 sensors found in skin.
Merkels disc, pacinian corpuscles, meissners corpuscles, organ of Ruffini, Root hair plexus, Free nerve endings
State the stimulus and location of free nerve endings
Pain, itch temperature - Epidermis
State the stimulus and location of pacinian corpuscle
Pressure, Vibration - Lower Dermis
State the stimulus and location of Organ of Ruffini
Mechanoreceptors - Dermis
List 4 skin properties
Protection, Absorption, Response to injury, sensory organ, thermoregulation, immunity, endocrine functions, appearance
What causes waterproof?
Keratin and Sebum
What causes thermal insulation?
Fat tissue in hypodermis
What induces inflammation?
Cytokines secreted by keratinocytes
What is the pacinian corpuscle?
Encapsulated nerve ending, nerve fibres surrounded by lamella structure formed from modified Schwann cells. Mainly in palms and soles.
What is meissners corpuscle?
Encapsulated nerve ending, spirally arranged, mainly in hands and feet
Describe basal keratinocytes.
Cuboidal or low columnar epithelium, mitosis (stem cells and daughters) bound to basement membrane by hemidesmosomes and bound to each other by desmosomes
Describe spinous keratinocytes.
No mitosis, cell move upwards from basal layer. Cell tightly bound together by desmosomes. Cells rich in keratohyalin granules and keratin filaments
Describe granular keratinocytes.
cell flatten, lose nucleus and other organelles. Cells contain many keratohyalin granules and keratin bundles. Cells secrete lipids and change the composition of cell membrane – produce surface keratin and waterproof substances.
Describe stratum keratinocytes.
tightly packed flattened, dead remains of the cells, cornified envelope: cross linked protein layer under the membrane of cornified cells. Cornified Envelopes + lipids = Epidermal Barrier
