Flashcards in Epithelial Tissues Deck (46):
What does a mucous membrane do?
- Lines certain internal tubes which open to the exterior.
- Bear mucus-secreting cells to varying degrees
Where are mucous membranes found?
What does a mucous membrane consist of?
• An epithelium (type depends on site) lining the lumen of a tube.
• An adjacent layer of connective tissue often referred to as the lamina propria (literally ‘one’s own layer’).
• In the alimentary tract, a third layer consisting of smooth muscle cells, referred to as the muscularis mucosae.
What is a serous membrane?
Thin, two-part membranes which line certain closed body cavities (spaces which do not open to the exterior). They envelop the viscera.
These serous membranes (or serosae) secrete a lubricating fluid which promotes relatively friction-free movement of the structures they surround.
What do serosae line?
Peritoneum = envelops many abdominal organs
Pleural sacs = envelop the lungs.
Pericardial sac = which envelops the heart.
What does a serous membrane consist of?
• A simple squamous epithelium (mesothelium) which secretes a watery lubricating fluid.
• A thin layer of connective tissue which attaches the epithelium to adjacent tissues (also carries blood vessels and nerves).
How do organs become surrounded by the serous membrane?
During embryonic development the heart, lungs, and gut develop next to a bag-like cavity into which they invaginate. So they each become surrounded by serous membrane.
(NB - they do not lie within the serous cavity itself, but are surrounded by it - like placing your fist into a balloon)
What is the difference between the visceral and parietal serosa?
Visceral serosa - inner wall (closest to organ)
Parietal serosa - outer wall
Lubricating fluid of serous cavity in between
What are epithelia?
Sheets of contiguous cells, of varied embryonic origin, that cover the external surface of the body and line internal surfaces.
Where do you find epithelial linings?
•Interior spaces opening to exterior
•Interior spaces which do not open to the exterior
How do you classify epithelia?
- Number of cell layers
- Shape of cells
What is the difference between simple and stratified epithelia?
• Simple = one layer, found where rapid diffusion occurs
• Stratified = more than one layer, found in regions where protection against abrasion, friction or bacteria is required e.g. The skin
How would you describe the shape of epithelial cells?
• Squamous = flat
• Cuboidal = cube like
• Columnar = column like
What is pseudostratified columnar epithelium?
Pseudostratified columnar = looks stratified but is actually just one layer thick, all cells touch basement membrane. Secrete mucus, has cilia. Mucus traps dust in the air preventing it getting to your lungs. Cilia move the dust to your throat where it is swallowed and destroyed. E.g. In the nasal cavity and trachea
What is transitional epithelium and where might this be found?
Transitional = special type of stratified epithelium. Can stretch without breaking, e.g. In the bladder. Cells change shape.
Where can you find simple squamous epithelium?
- Lining of lymph vessels and blood vessels (endothelium)
- Lining of body cavities, pericardium, pleura, peritoneum (mesothelium)
- Gas exchange epithelium (pulmonary alveoli)
- Bowman’s capsule
- Loop of Henle
What are the functions of simple squamous epithelium?
- Lubrication (pericardium, pleura, peritoneum/viscera)
- Gas exchange
- Barrier (Bowman’s capsule)
- Active transport by pinocytosis (mesothelium and endothelium)
Where can you find simple cuboidal epithelium?
- Thyroid follicles
- Small ducts of many exocrine glands
- Kidney tubules
- Surface of ovary (germinal epithelium)
What is the function of simple cuboidal epithelium?
- Absorption and conduit (exocrine glands)
- Absorption and secretion (kidney tubules)
- Barrier/covering (ovary)
- Hormone synthesis, storage and mobilisation (thyroid)
Where can you find simple columnar epithelium?
- Stomach lining and gastric glands
- Small intestine and colon
What are the functions of simple columnar epithelium?
- Absorption (small intestine, colon, gallbladder)
- Secretion (stomach lining and gastric glands, small intestine and colon)
- Lubrication (small intestine and colon)
- Transport (oviduct)
Where can you find pseudostratified epithelium?
- Lining of nasal cavity, trachea and bronchi
- Epididymis and ductus deferents
- Auditory tube and tympanic cavity
- Lacrimal sac
- Large excretory ducts
What is the function of pseudo-stratified epithelium?
- Secretion and conduit (respiratory tract, ductus deferens)
- Absorption (epididymis)
- Mucus secretion (resp tract)
- Practical trapping and removal (resp tract)
Where can you find stratified squamous non- keratinised epithelium?
- Oral cavity
- Part of anal canal
- Surface of cornea
- Inner surface of eyelid
Whats the function of stratified squamous non- keratinised epithelium?
- Protection against abrasion
- Reduces water loss but remains moist
Where can you find keratinised stratified squamous epithelium?
- Surface of skin
- Limited distribution of oral cavity
What are the functions of keratinised stratified squamous epithelium?
- protection agains abrasion and physical trauma
- Prevents water loss
- Prevents Ingres of microbes
- Shields against UV light damage
How does keratinised stratified squamous epithelium form?
• Outer most layers loose nucleus
• Become highly keratinised
• Surface of skin
• Made up of mainly keratinocytes and their products
Where can you find transitional epithelium?
- Renal calyces (singular = calyx)
What are the functions of transitional epithelia?
- Distensibility (stretching for urine)
- Protection of underlying tissue from toxic chemicals
What is the basement membrane and what is responsible for its structure?
• Name for thin, flexible, acellular layer between epithelial cells and the subtending CT
• CT contributes to structure produces type 3 collagen reticular fibres = thickness
• Epithelium contributes to structure by producing basal lamina
• It consists of basal lamina which is laid down by the epithelial cells and therefore lies closest to them
• Cellular and molecular filter
• It is relevant because a lot of cancer starts in epithelia
• NB: basement membrane and basal lamina are used inconsistently in literature, they are different but see them as the same
What are the functions of the skin?
- Insulation/ thermo-regulation
- Excretion and Secretion
How does the skin act as a protective mechanism?
- Physical barrier
- Keratinocytes – produce keratin, gives skin strength and protects skin from water/ impermeability
- Collagen and elastin fibres in epidermis and hypodermis – give skin strength and elasticity, protecting body from physical and mechanical forces.
- Protects from skin damage – Excessive UV radiation (melanocytes release melanin which absorbs UV), bacterial and micro-organisms, dehydration and dangerous chemicals
How is the skin involved in sensation?
- Many somatic sensory receptors (pressure, light, thermal, pain etc.)
- Merkel cells involved in sensation
How is the skin involved in thermal regulation?
- Adipose cells create layer of insulation
- Homeostatic changes: sweating/perspiration (evaporation) and radiation
- Cellular respiration produces energy and heat
- Blood radiates heat through skin
- Sweat glands – produce sweat, water is caused to evaporate by heat from blood
What is transepidermal water loss?
Water can diffuse across upper portion of skin (different to sweating)
How is the skin involved in the immune response?
- Langerhon cells are responsible for interacting with T cells
- Hypodermis contains macrophages to engulf pathogens
Describe the skins endocrine functions
- Skin needs some UV radiation to produce cholecalciferol (inactive vitamin D3)
- This can be activated to the hormone calcitrol in the kidneys
- Regulates calcium and phosphate ions
Describe the structure of the skin
• Epidermis = outer most portion of the skin, contains four specialised cells (keratinocytes, melanocytes, langeron cells and merkel cells)
• Dermis = middle section containing blood vessels and excretory glands (sebaceous oil gland and sweat gland)
• Hypodermics/ subcutaneous layer = lowest layer containing adipose cells and macrophages.
Describe the structure of the epidermis
1. Horny layer (stratum corneum)
- made of layers of flattened corneocytes
- Major role in skin barrier function
2. Granular layer (stratum granulosum)
- Contains keratohyalin granules = Keratins, other fibrous proteins and enzymes
3. Prickle cell layer (stratum spinosum)
- prickles between cells = plasmodesmata
4. Basal layer (stratum basale)
(Heterosexual girls pick boys)
How is the epidermis formed?
• Keratinocyte mitosis occurs mainly in basal layer
• Daughter keratinocytes then move upwards to form prickle cell layer
• Lose nuclei and ability to divide
• Synthesise keratin – contribute to skin strength
What is a melanocyte?
• Dendritic cells of neural crest origin
• Occur at intervals along the basal layer of the epidermis
• Difficult to see histologically without special stains
• Produce melanin
• All people have same number of melanocytes
• Pale skinned people these don’t last so long
What is a Langerhan cell?
• Dendritic cells (APC) of bone marrow origin
• Scattered throughout the prickle cell layer
• Difficult to see histologically without special stains
• Highly specialised capacity to present antigens to T lymphocytes
• Mediated immune reactions e.g. Allergic contact dermatitis
How does a melanoma form?
• Melanocytes are positioned at epidermal/dermal junction around cell bodies with dendrite extensions
• Formation of melanin occurs in melanosome cell body
• Transported in microtubules in dendrites to neighbouring keratinocyte
• Melanosomes then released into cytoplasm of keratinocyte
• When UV radiation is absorbed by double bond in thymine base, the bond opens allowing base to react with nearby molecules
• Two thymine molecules--> thymine dimmer go to four membrane rink
• Kinks DNA = blocks DNA replication
What are the two types of melanin?
Feomelanin = pink/yellow pigment
U melanin = dark black pigment