Epithelial Cells

Why do epithelia cells undergo regeneration?

To replace damaged cells (cells undergo mitosis)

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What is the purpose of mucosecretory elevator?

Cilia beat in unison to trap dirt and move mucous away from the lungs

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What is a hemidesmosome?

Modified mechanical links (desmosomes) which bind cells together

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Give general examples, functions and special features of epithelial cells

Lining gut, blood vessels, covering skin. Barrier, absorption, secretion. Tightly bound together by cell junctions

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Give general features of epithelial cells

All share common characteristics (exception to glandular epithelia). Highly exfoliative (exception is lung and gland epithelia). Role is to cover surfaces/line ducts (morphology may confer specialist function) - absorption, secretion, protection

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Describe single layer epithelia

One endothelium cell thick (e.g. part of capillary)

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Describe features of multi-layer epithelium

Different layers of skin. Change in morphology - changes in function. Bottom (alive/regeneration), top (dead cells/keratin/outer surface protection). Basale, spinosum, granulosum, lucidum, corneum

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Describe features of duct epithelia

Found in the kidney. Wrap to form a tube. Produce urine. Absorption/excretion

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Describe features of glandular epithelium

Secretes from epithelial surface. E.g. section of lung. Secretions e.g. mucus. Very specialised

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In what tissues would you expect to find glandular epithelia?

Glands. Thyroid gland. Adrenal glands do not have glandular epithelia

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Describe features of simple squamous epithelia

Squashed. Single cell thick. Thin - nucleus bulges out. Allow transportation. Wrap forming ducts. Secretes fluid in serous membranes. Lines organs, cardio system, forms glomerular capsules in kidney

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Describe features of simple cuboidal epithelia

Ressembles a cube. Nucleus in the centre. Form tubules. Form secretory cells. Interspersed with goblet cells. In exocrine glands

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Describe features of simple columnar epithelia

Nucleus towards bottom of cell. Nuclei lie toward basal surface. Apical surface (top) - may have cilia or nuclei - beat in unison. Allows space at top of cell. Non-ciliated in GI tract/stomach intestines. Ciliated in respiratory/genitourinary tract

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Describe features simple columnar with microvilli

Contains goblet cells which secrete mucous. Ciliated epithelium used to move mucous. Column built from basal membrane

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Describe features of stratified squamous non-keratinizing (1)

Stratified - different levels. Squamous - squashed. Non-Keratinising - not part of the skin. Each layer has different morphology Top surface is alive. Junctions line up - breaks easily, force goes down and across (regular arrangement)

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Describe features of stratified squamous non-keratinizing (2)

Torsional force. Top layer comes off (doesn’t affect other layers) - top layer still have nuclei. Not rough/flaky. Alive. Provide environment for function. Needed in reproductive system. Columnar, cuboidal, squamous

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Describe features of stratified squamous keratinizing

Waterproof. Strong. Skin. Top surface cells are dead (keratinised) with no nuclei. Not needed in reproductive system. Change from cuboidal to squamous

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Describe features of transitional

Lots of stretching. Bladder, uterus. Don’t want tearing. Maintain shape and is waterproof. Cells in resting state are not lined up/in columns. Cells are overlapped. Force is spread across all directions. Allowed to stretch/maintain cell integrity

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What holds a cell's morphology?

Cell junctions

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What are cell junctions?

Join cells together. 3 different types - hold at the side. Hemidesmosomes - connects between cells and basal membrane

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What are the three types of cell junctions?

Gap junction, desmosome and tight junction

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Describe features of a tight junction

Localised towards apical surface. Doesn't allow passage between cells or from cell to cell. Protein between cells. Torsional force at top of cell (main stitching). Intracellular space to store Ca2+. Microenvironment

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Describe features of a gap junction

Allows cell to cell transfer. Regulated by closing/opening of junctions (one direction)

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What are connexins?

Connexins - protein part of membrane, 6 connexins form a connexon - bind to connexons on other side to form gap junction. Shift conformation to open channel. Able to open and close. Maintain gap junction

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Describe features of a spot desmosome

Acts as an anchor for cytoskeleton. Cadherin - move/bind within intercellular space. Project into cell, bind to plaque. Desmoplakin produce plaque. Cytoskeleton attaches to plaque. Filaments bind to anchor point (desmoplakin)

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Describe features in basement membrane

Hemidesmosomes (half desomosome). Anchoring cell onto foundation (basal membrane). Cadherin bind to basal membane

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Why do cells need a basement membrane?

To act as a filter

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What are the functions of epithelial cells?

Absorption (intestines), secretion (mucous secretory escelator), transport (loop of Henle), excretion (sweat glands), protection (skin), regeneration (mitosis)

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Describe features of absorption

Epithelial lining provides large SA: Vol ratio (e.g. GI tract, lungs, renal tubules). Villi in GI tract. Villi has extensive blood supply (short diffusion distance). Microvilli (finger-like projections from apical surface) - maximise absorption

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Describe features of secretion

Mucus to trap particulates within mucosecretory escalator. Goblet cells (Clara cells) release secretions onto cuboidal epithelia, have microvilli/cilia. Extensive protein machinery (absence of this leads to build up of fluid in lungs). Nucleus below

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Describe what happens when you have a chest infection

Goblet cells increase release of mucus as part of the immune response

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Describe the effect of smoking on cilia

Smoking paralyses the movement of cilia (damages cilia) - becomes less efficient in moving particles and mucus

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Describe features of transport

Convoluted tubule in the kidney. Reabsorption of water/solutes via transportation (passive diffusion/active transport). Associated with cuboidal epithelia

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Describe features of excretion

Sweat gland, maintaining hair, antibacterial and production of body odour/pheromone release

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Describe features of protection

Skin, largest organ of the body, main function is part of the immune system, when you get burns you get shock from fluid loss or infection. Outer layers of skin designed to flake off (replaced). Skin exfoliative

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Describe features of regeneration

Epithelia (barrier between inside and out). In areas of high torsional force, epithelial cells regenerate (allows body to maintain integrity of its barriers) e.g. air flow - trachea, water flow - urethra, external forces - skin

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Epithelial Cells

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