Lecture 6: Epithelial cells & specialised surfaces Flashcards
What is a mucous membrane?
3 layers of epithelium, connective and smooth muscle tissue that line internal tubes that open to exterior.
Where can you find mucous membranes?
GI tract
Respiratory tract
Urinary tract
What is a serous membrane?
2 thin layers of mesothelium and connective tissue that lines closed body cavities; exude lubricants and envelop viscera (internal organs)
Where can you find serous membranes?
Peritoneum of abdominal organs
Pleural sacs of lungs
Pericardial sac of heart
Compare and contrast serous and mucous membranes.
S= lines closed body cavities M= lines open-to-exterior cavities
S= 2 thin layers of tissue M= 3 layers of tissue
Both carry blood, lymph vessels and nerves
Describe and explain the analogy of serous membranes.
Balloon analogy: outer balloon wall is parietal serosa & inner balloon wall is visceral serosa. Air inside balloon is cavity and (balloon surrounded) hand is an organ.
Where is the parietal serosal membrane in relation to the cavity?
It lines the outer edges of the cavity.
Where is the visceral serosal membrane in relation to the cavity?
It is closest to the organs surrounded by the membrane.
What is the definition of epithelium?
Adjacent cell sheets that cover external surfaces of the body and line internal surfaces; derived from embryological germ layers.
What are the names of the embryological germ layers and what do they become?
Ectoderm: epidermis
Mesoderm: inner & outer GI tract lining
Endoderm: inner linings of body cavities
Give some surfaces (exterior, interior to exterior and closed interior) with epithelial linings.
Exterior: skin
Interior to exterior: GI tract; respire. tract; genitourinary
tract.
Closed interior: pericardial sac; pleural sacs; blood vessels, lymphatic vessels
How can you classify epithelial tissue? (8 points)
- simple squamous
- simple cuboidal
- simple columnar
- stratified squamous (non and keratinised)
- stratified cuboidal
- stratified columnar
- pseudostratified columnar
- transitional
How can you tell the difference between stratified columnar and pseudostratified columnar?
Stratified columnar has more than 1 cell thick whereas pseudo. columnar is 1 cell thick but the nuclei are at different levels: hence looks stratified.
What is the basement membrane?
Basal lamina and reticular layer found at the basal (bottom) part of cells and this anchors epithelium and underlying connective tissue.
Give the functions of simple squamous epithelia.
Fast material exchange
Barrier to fluids (lymphatics and vasculature)
Barrier in the brain and CNS (prevent fluid leaking out)
What are some examples of simple squamous epithelium?
Bowman’s capsule barrier
Lungs, heart, viscera serosa
Mesenchymal cells of cavities
What are 3 functions of epithelia?
Secretion Protection Reproduction Reabsorption Lubrication
Name the 2 opposing surfaces of an epithelial cell and describe what you find at these surfaces.
Apical: microvilli, cilia, keratin(skin)
Basal membrane: basal & reticular lamina
Give the functions of simple cuboidal.
Absorption
Absorption & secretion
Barrier/ covering
Hormone syn. storage and mobilisation
What are some examples of simple cuboidal?
Lining of exocrine glands
Follicle cells of thyroid
Lining of ovaries
epithelial lining kidney tubules
Give the functions of simple columnar.
Absorption
Secretion
Lubrication
What are some examples of simple columnar?
Small intestine
Colon
gallbladder
gastric glands
Give the functions of pseudostratified columnar.
Secretion
Mucus secretion
Particle trapping and removal
What are some examples of pseudostratified columnar?
Nasal cavity
Trachea
Bronchi
Upper respiratory tract
Give functions of stratified non-keratinised squamous epithelia.
Protection against abrasion
Reduce water loss but maintain moisture
What are some examples of stratified non-keratinised squamous?
Vagina Anal canal Surface of cornea Inner surface of eyelid Oral cavity Oesophagus
How does stratified keratinised squamous & stratified non-keratinised squamous differ?
Top layers of keratinised cells have lost their nuclei and become cornified. The outermost cells of epithelium are called the stratum corneum.
Give the functions of stratified keratinised squamous epithelial.
Reduce water loss
Protection against abrasion
Prevents pathogen entry
Reduce microbial colonisation (top surface cells = dead)
What are some examples of stratified keratinised epithelium?
Mainly epidermis of skin
Limited in oral cavity
Describe the epidermis structure.
Mainly keratinocytes but also has…
Melanocytes
Langerhans cells
How do keratinocytes get to the apical surface and why are they important?
- Keratinocyte mitosis occurs in basal layer.
- Daughter keratinocytes force upper layers (mature
keratinocytes) to apical surface - Daughter keratinocytes differentiate and lose their
mitotic ability.
Important as they syn. keratins which enforces strength of epidermis.
How are keratinocytes and psoriasis related?
Psoriasis is where the transit time (basal –> stratum corneum) is reduced from a normal 28-40 to 2-4 days. Causing too many mature keratinocytes to be at apical surface. Thus, there isn’t enough time for keratin to be produced and enforce the skin. Resulting in patches of silvery, scaly, itchy skin.
Skin colour is based off the number of melanocytes in the skin.
True or False?
False
Skin colour depends on the amount of melanin (pigment) the melanocytes produce. More melanin = darker/tanned skin
What do Langerhans cells do?
Langerhans cells are skin immune cells that present antigens to T lymph. which mediates an immune reaction: allergic contact dermatitis.
Why do melanosomes sit above the nucleus?
Their pigment protects the nuclei from UV damage.
Give the functions of transitional epithelium.
Distensibility
Protecting underlying tissue from toxic chemicals
Where would you find transitional epithelium?
Urinary tract: bladder, ureters, proximal urethra
Give some functions of stratified columnar.
Secretion
Absorption
Protection
Where would you find stratified columnar?
Male urethra
Conjunctiva of eye
Give some examples of cell specialisations and their roles.
Keratin: prevents water loss, protects against abrasions
Cilia: controls micro-movement of lumen contents
Goblet cells: mucus secretions that lubricate, moisten and trap particles
Club cells: protects bronchioles and acts as stem cells for respiratory epithelium
Microfold cells: allows rapid sampling of gut microflora
Stereocilia: converts pressure waves–> electrical signals
What prevents goblet cells from secreting very thick mucus?
Have microvilli on surface to reabsorb more H2O for release of more watery mucins. Cl- needed to be released out of goblet cell: H2O moves via osmosis (with Cl-). Hence thinner mucus.
What is cystic fibrosis (CF)?
Hereditary disease in which a mutation in CFTR gene prevents sufficient Cl- being released out of goblet cells. Results=thick, sticky mucus.
How can cystic fibrosis (CF) affect the body?
Breathlessness: thick mucus blocks & infects bronchial passages=damages lungs
Salty sweat: malfunctioning sweat glands as less H2O absorbed so Cl- and Na+ crystallises on skin.
Thick, non-motile stools: need surgery to fix in neonates
Infertility: MEN=sperm can’t move in fine ducts so decrease sperm vol.
FEM.=sperm can’t move up cervix during intercourse as blocked by mucus plug.
Can’t digest food: less H2O means enzymes can’t move as dehydrated secretions=stagnations
Describe the role of club cells.
Protect bronchiolar epithelium by secreting uteroglobin and a surfactant.
Detoxify harmful substances inhaled by cytochrome P450 enzymes in SER.
Act as stem cells: become ciliated cells to regenerate epithelium.
Where is the only place you’ll find microfold cells?
Small intestine near lymph nodes.
What is an advantage and disadvantage of having microfold cells?
Ad=trap pathogens and foreign particles for immune response
Con=pathogens can exploit open area as entry to deeper tissues
How do microfold cells contribute to the immune response?
- Trap particles + pathogens
- Presents to dendritic cells and processes them
- Presents to lymphocytes + macrophages to raise an
immune ‘alert’
What are the hair cell organelles responsible for hearing and balance?
Stereocilia
Aside from balance and hearing, what is the other role that stereocilia have?
Facilitate residual sperm absorption after spermiation.
Could be involved in sperm movement along ejaculatory ducts.
What are vas deferens/ ductus deferens?
Thick-walled tube that transports sperm from epididymis (where sperm is stored).
Smoking affects the lungs, what happens in earlier stages?
- Normal mucus layer thickens
- Cilia die
- Ciliogenesis occurs in 2-4 days
Smoking can cause chronic health issues, what happens at the chronic stages?
- Goblet + basal cells divide.
- Club cells die (no bronchiolar protection)
- Carcinogens cause mutations + cancerous growth
- Alveoli pneumocytes die
- Fibroblast lay scar tissue
Order the cell renewal rates from shortest to longest…
Trachea, Club cells, Alveoli, Goblet cells
- Alveoli (8 days)
- Goblet cells (10 days)
- Trachea ( 1-2 months)
- Club cells (never)
What are some respiratory conditions associated with smoking?
Acute bronchitis Chronic bronchitis Emphysema COPD Asthma
Describe the difference between acute and chronic bronchitis physiologically.
Acute: not as serious with less lung function, breathlessness, cough & mucus production due to inflammation, swollen, narrowed and mucus blocked airways.
Chronic: more serious + is the same as acute physiologically but will start to have irreparable damage to bronchiolar passages.
What is emphysema?
Shortness of breath because air sacs lost elastic recoil due to permanent widened air spaces. Thus, normal alveoli size is larger.
Which 2 diseases combined would give chronic obstructive pulmonary disease (COPD)?
Emphysema and chronic bronchitis.
What is a bronchospasm?
Tightened smooth muscle layer in bronchiolar passages.
Which condition is a combination of bronchospasms, mucus obstruction and narrowed airways?
Asthma
