Systems Physiology and Anatomy Epithelium PDF

Systems Physiology and Anatomy - ciliated epithelia Epithelium e. g in airways Dr Pip Garner [email protected] Learning Outcomes 1. Know what epithelia are...

Systems Physiology and Anatomy - ciliated epithelia Epithelium e. g in airways Dr Pip Garner [email protected] Learning Outcomes 1. Know what epithelia are 2. Know their common characteristics 3. Know the function and characteristics of the different surfaces 4. Show an understanding of structure and function 5. To know, and be able to recognise, the different types of epithelia based on classification and cell shape 6. To know the structure and functions of different body membranes Definition Epithelia are tissues that serve as protective layers and/or secretory components of body organs and systems. Most epithelia possess common characteristics that contribute to their functional capabilities. Function C GI tract is adapted to be protected from Stomach acid) > - Endogenous chemicals Protect underlying cells. others : Bleach on Skin drying, injury, infections and from harmful effects of chemicals. Selectively permeable tissue. regulating the exchange of materials between the body an external environment and between different body parts. Absorption of water and nutrients in diffusion of gases. Elimination of waste products from the body Epithelia Formed into tightly cohesive cellular sheets. Function is to cover/line body surfaces e.g. alimentary canal, exocrine ducts. Form functional units of secretory glands e.g. salivary, mammary, sweat.  Common attributes Limited intercellular space: Specialised intercellular junctions hold cell membranes close together – effective barrier – blocks infiltration of fluids between cells. Single or multiple layers of cells: Form linings or coverings. Where diffusion/filtration is important, epithelia is a single layer – where protection e.g. abrasion is needed – multiple layers eating I drinking · constant abrasion so multiple layers needed Free apical surfaces: All epithelia possess a free apical surface during development or at maturity. The apical surface is where cells of an epithelium face internal lumens. Common attributes Basement membrane: Basal surface attaches to underlying tissues via basement membrane derived from underlying connective tissue (which kind?). Areolar (loose tissue CT) Epithelia covering or lining tissues are constantly subjected to wear and tear. Mitotic capability – why is this important? need be quickly replaced to  Describing epithelial tissues Epithelia described by 2 structural simple= one cell thick characteristics: stratified = multiple cell thick (column like) Cells layers: Thin flat square Simple epithelium mixture Pseudostratified epithelium Stratified epithelium Cell shape: Squamous cells messy nuclei > seems like Cuboidal cells - layers but aren't Columnar cells Transitional cells Cell Layers Simple epithelia – one cell thick Stratified epithelia – many cells thick, but only bottom layer in contact with basement membrane. Pseudostratified epithelia – appear more than one cell thick, but all cells rest on basement membrane Cell shape Squamous – flattened cells like paving stones Columnar – cells are taller than they are wide Cuboidal – cells are of similar height, depth and width Transitional – cells in layers which change their shape when they are stretched they are stretched (only found in urological tract) Simple squamous e.g. alveoli & capillaries of lungs Permits exchange of nutrients, waste and gases Simple cuboidal e.g. kidney tubule Secretes and reabsorbes water and small molecules Simple Columnar e.g. small intestine replaced every 6 weeks Absorbs nutrients and produces mucous Transitional -only in urinary tract -stretches to accommodate fluid changes Stratified Squamous - Oesophagus - Protects against abrasion, drying out and infection food isn't always ? sterile Keratinised stratified 6 High in Squamous Keratin Lots of fibres (dead skin cells) - only found in skin Pseudostratified - e.g trachea, nasal mucosa - Helps in protection, secretes mucous to trap foreign particles and to excrete them e. g cilia (which wafts mucous ↳ directional purpose Stratified cuboidal e.g. sweat gland duct Secretes water and ions (not that common Stratified columnar e.g. Salivary gland duct Secretes mucous Basal surface of epithelia Basement membrane: Separation from the underlying connective tissue – acts to support epithelia a selectively permeable filter between epithelium and connective tissue. Anchors epithelium to connective tissue via cell-matrix adhesions. Basal lamina: (part of basement membrane) Supportive sheet between epithelium and underlying connective tissue Apical surface of epithelia Microvilli: Finger like extensions of the plasma membrane of apical epithelial cell Increase surface area for absorption (small intestine). Cilia: Whip like, motile extensions Moves mucus, etc, over epithelial surface, in once direction. (trachea and respiratory bronchus).  Pseudostratified Microvilli One cell thick. All cells rest on basement membrane -’brush border’ of small intestine Cilia in trachea Lateral surface of Epithelia Cells are connected to neighbouring cells via cell junctions: Desmosomes/Adhesion Junctions: Adhesive spots on lateral sides Involves proteins called cadherins Tight junctions: Plasma membrane of adjacent cells fuse Nothing passes (GI tract doesn’t let enzymes from gut into blood stream) Gap junction: Present in many locations Lets small molecules pass (cardiac muscle tissue)  Epithelial membranes Thin sheets of flexible tissue that line or cover parts of the body – membranes Epithelial membranes contain epithelium and an underlying connective tissue: Mucous membranes – digestive system Serous membranes – body cavities Cutaneous membrane - skin Synovial membrane - joints Synovial membranes contain only connective tissues and line the cavities of synovial joints. Epithelial membranes Serous (serosa) Simple squamous (usually) Resting on thin layer of loose connective tissue Found in body cavities Serous fluid – lubrication Mucous (mucosa) Lines cavities open to outside Mucus cells/glands lumen of digestive (microvilli), reproductive, respiratory systems (ciliated) Epithelial cells vary in morphology and function. Mucous membranes Cutaneous membrane and synovial membrane The cutaneous membrane is the skin, covering the outer surface of the body Serous membranes Serous membranes cover the surface of organs that are not exposed to the outside and secrete a watery fluid Serous membranes have two layers: 1. The parietal layer attaches to the body around the organ 2. The visceral layer attaches to the organs themselves.  Lung pleura Pleura: Parietal: lines the chest cavity and contains the lungs. Visceral: lines the lung surface. Cavity between the pleura is called the pleural space. Pleural fluid lubricates the pleural space and prevents friction during respiration. Serous membranes Summary Epithelia – specialised component of many organs Characterised by common structural features Diverse functions Specialised adaptations: absorption (gut), secretion (glands), barrier (epidermis/skin).