Epithelium Flashcards
What are mucous membranes?
- Line internal tubes which open to exterior:
- GI tract
- Respiratory tract
- Urinary tract
What do mucous membranes consist of?
- Epithelium lining the lumen of a tube
- Adjacent layer of connective tissue, referred to as lamina propria
- Layer consisting of smooth muscle cells called muscularis mucosae
- Also carries blood and lymphatic vessels and nerves
- All mucosae bear mucus-secreting cells to varying degrees
What are serous membranes?
- Thin two-part membranes which line closed body cavities and envelop the viscera:
- Peritoneum (envelops abdominal organs)
- Pleural sacs (envelops the lungs)
- Pericardial sacs (envelops the heart)
What are the features of serous membranes?
- These serosae secrete a watery lubricating fluid that promotes friction-free movement from a simple squamous epithelium
- A thin layer of connective tissue that attaches the epithelium to adjacent tissues
- Also carries blood and lymphatic vessels and nerves
What is are pseudostratified epithelia?
Tissues where all cells make contact with the basement membrane, but not all of the cells reach the epithelial cell surface.
This results in nuclei lying at different levels giving the impression of multiple layers
What epithelium lines the trachea, bronchi, mucociliary escalator?
Pseudostratified ciliated epithelium
How is the epithelium adapted for the mucociliary escalator?
- Motile cilia and mucus secreting goblet cells.
- Goblet cells secretes a viscoelastic mucous blanket
Where else is pseudostratified epithelium present?
Lining the nasal cavity.
Trachea
Bronchi
What cell surface specialisations are present in epithelium?
- Keratin (prevents water loss and protects against abrasion)
- Cilia (controls micro-movement of luminal contents)
- Goblet cells (mucous secretions, moistens and lubricates)
- Club cells (previously known as Clara cells- protect bronchioles and act as stem cells for respiratory epithelium)
- Microfold cells (allow rapid sampling of gut microflora)
- Stereocilia (in the auditory system and converts pressure waves into electrical signals)
What are the features of goblet cells?
- Lack cilia so have microvili on apical surface
- Release mucins through exocytosis
- Water release increased by release of ions
Where are goblet cells found?
- Epithelium of the upper respiratory tract
- Epithelium of an intestinal villus
What effect do chloride ions have on goblet cells?
- Deficiency of chloride ions release results in a very sticky and immovable mucous
- This is a characteristic of cystic fibrosis due to mutation in CFTR gene (cystic fibrosis transmembrane conductance regulator)
What are the structural features of club cells and where are they found?
- Found on the airway side of terminal bronchioles
- ‘Club-like’ apical surfaces
- No cilia
- No basal bodies
What are the functions of club cells?
- Protects the bronchiolar epithelium
- –> Secretion of a small variety of products including club cell secretory protein uteroglobin, and a solution similar to pulmonary surfactant
- Detoxification of harmful substances inhaled
- –> Using cytochrome P450 enzymes found in the smooth endoplasmic reticulum
- Act as a stem cell, multiplying and differentiating into ciliated cells to regenerate the bronchiolar epithelium
Where does cystic fibrosis affect the body?
Tissues that have mucins and cilia are all affected
- Airways (clogging and and infection of bronchial passages with thick sticky mucus obstructs breathing and progressively damages the lungs)
- Liver (the small bile duct becomes blocked, disrupts digestion)
- Pancreas (zymogen secretions not released in 85% of patient)
- Small Intestine (Thick, non-motile stools in neonates require surgery)
- Reproductive tracts (Absence of fine ducts such as vas deferens causes 95% CF males infertile and mucous plug in cervix causes female infertility)
- Skin (Malfunctioning of sweat glands causing salt crystals on skin surface)
