Epithelium + Skin

Question 1

what is epithelium and give some examples

Answer 1

• tissue that forms the internal and external surfaces of the body > found by palpation and biopsy
• e.g. skin, GI tract etc.

Question 2

endothelium

Answer 2

epithelium of the CV system (simple squamous)

Question 3

functions of epithelium

Answer 3

• protection: skin
• absorption: small intestine, kidney, capillaries
• secretion: small intestine, trachea
• transport: kidney
• sensory reception: epidermis

Question 4

5 characteristics of epithelium

Answer 4

• tightly packed: little space between cells and strong attachments b/n cells (tight junctions)
• oriented/polarised: apical and basal surfaces are different
• sit on a basal lamina (basement membrane) and exposed area is the apical surface
• avascular > otherwise susceptible to abrasions, instead gets nutrients from underlying connective tissue
• fast rate of regeneration

Question 5

2 ways to categorise epithelia

Answer 5

• cell layers: simple (1 cell thick), stratified (multilayered)
• shape of most superficial cell: squamous (squashed/flat), cuboidal (cube), columnar

Question 6

where to find all types of simple epithelium

Answer 6

• simple squamous: diffusion and filtration b/c thin e.g. endothelium, alveoli
• simple cuboidal: secretion and absorption e.g. salivary glands and renal tubules
• simple columnar: absorption and mucus secretion e.g. lining stomach + intestines, bronchi, uterus, fallopian tubes

Question 7

where to find all types of stratified epithelium

Answer 7

• stratified squamous: protects against abrasion e.g. mouth, tongue, oesophagus, vagina, skin (keratinised)
• stratified cuboidal: protective tissue e.g. sweat glands, mammary glands, salivary glands
• stratified columnar: protects and secretes e.g. male urethra

Question 8

where to find pseudostratified epithelium

Answer 8

• trachea, bronchi, epididymis, vas deferens
• pseudo because technically every cell is connected to the basement membrane but looks multilayered b/c nuclei are seen at diff levels

Question 9

where to find transitional epithelium (stratified)

Answer 9

• ureter, bladder, urethra
• can change shape (thinner or thicker)

Question 10

apical specialisations

Answer 10

• microvilli: extensions of apical cell membrane w/ large SA for absorption, containing actin filaments
• cilia: elongated motile structures that beat in a synchronised manner: made of microtubules in a 9+2 structure e.g. ovaries, respiratory tract

Question 11

lateral specialisations from most apical to basal

Answer 11

• tight junction (zonula occludens)
• belt desmosome (zonula adherens)
• spot desmosome (macula adherens)
• gap junctions (nexus)
• hemidesmosome (basal)

Question 12

function of tight junction (zonula occludens)

Answer 12

• prevents flow of material between cells, occluding (blocking) intercellular space

Question 13

belt desmosome (zonula adherens)

Answer 13

• actin filaments which provide adhesion between adjacent cells

Question 14

(spot) desmosomes (macula adherens)

Answer 14

small, plaque-like thickenings on membranes of adjacent cells made of INTERMEDIATE FILAMENTS for adhesion

Question 15

function of gap junctions (nexus)

Answer 15

• ion flow (electrical coupling) between cells via connexons
• important in cardiac & smooth muscle so it can contract at the same time with one signal

Question 16

hemidesmosome

Answer 16

attaches epithelial cells to basal membrane

Question 17

structure and function of basal lamina

Answer 17

• S = collagen IV, proteoglycans, glycoproteins
• F = epithelial cell orientation and adhesion
• normal epithelial cells do not cross basal lamina but cancer cells can

Question 18

compare endocrine vs exocrine glands with relation to epithelium

Answer 18

• exocrine: retain connection w/ surface epithelium ie secrete substances onto epithelium e.g. sebaceous, sudoriferous, mucus
• endocrine: lose attachment w/ surface epithelium ie secrete substances into the blood

Question 19

meissner’s corpuscle

Answer 19

• ENCAPSULATE nerves in dermal papillae
• barrel-shaped w/ capsule on top
• abundant in fingertips
• fine touch + sensation

Question 20

pacinian corpuscle

Answer 20

• looks like an onion
• ENCAPSULATED sensory nerve endings in deep dermis
• deep pressure + vibration (type of mechanoreceptor)

Question 21

myoepithelial cells

Answer 21

• modified smooth muscle cells
• help to facilitate secretion surrounding sweat + sebaceous glands
• mammary versions are ‘natural’ tumour suppressors b/c they prevent epithelial cells penetrating through the basement membrane

Question 22

structure of the dermis

Answer 22

• papillae (invaginations - loose CT)
• reticular layer underneath (dense irregular CT - pink stuff is collagen and white stuff is ground substance)

Question 23

structure of epidermis

Answer 23

• Langerhans cells (dendritic cells)
• thin skin epidermis replaced every few weeks (quicker than thick skin)
• Come Let’s Get Sun Burnt
• stratum corneum (hundreds of layers of keratin)
• stratum lucidum (only thick skin - lose nucleus and organelles)
• stratum granulosum: releases keratohyalin which forms keratin
• stratum spinosum: many desmosomes
• stratum basale/ germinativum (melanocytes, single epithelium layer on basement membrane)

Question 24

function of melanocytes

Answer 24

• secrete melanin to protect deeper cells of the epidermis and DNA from UV radiation
• dead keratinocytes don’t need it
• can give rise to melanoma

Question 25

structure and function of sweat glands

Answer 25

• S = simple coiled tubular glands
• F = secretes water, NaCl, urea etc
• eccrine: open to skin, smaller, more numerous, thermoregulation
• apocrine: open to hair, larger, less numerous, acted upon by bacteria > produce odour

Question 26

structure and function of sebaceous glands

Answer 26

• S = fat, juicy glands associated with a hair follicle and surrounded by myoepithelial cells (only in hairy/thin skin)
• F = cells fill with lipids and burst to secrete sebum (holocrine excretion)

Question 27

thin/thick/hairy/non-hairy skin

Answer 27

• thin = hairy
• thick = non-hairy (e.g. palms and soles) - stratum lucidum only on thick skin