Lecture 4 Epithelia 2

Question 1

Cilia

Answer 1

Extension of the cytoskeleton composed of a core of microtubules.
Motile cilia - have a 9 microtubule ring and two central microtubules. Move with a beating motion creating directional fluid flow. Found in resp tract and middle ear.

Primary cilia - do not move, one per cell act as antenna sensing movement and temp lack the two central microtubules ( have just the 9 microtubule ring)

Question 2

Microvilli

Answer 2

Approx 700nm cannot be detected by light microscope but possible by ICC and EM.
Capping protein attached to F actin filaments at end of microvillus
F actin filaments run full length of each microvillus, F actin binding proteins (villin, plastins) bundle the microfilaments and link them to the plasma membrane
Myosin lateral arms

Question 3

Stereocilia (inner/ outer hair cells)

Answer 3

Allow us to hear - sound hits, vibrates fluid, causes cilia to react as outer changes shape

Found in cells within inner ear specifically cochlea

3 rows of cells

Primary structure necessary for hearing, fluid in cochlea vibrates w/sound causing cilia to change shape amplifying sound signal to brain

Question 4

Basolateral folds

Answer 4

Deep invaginations of lateral cell surfaces found in renal tubule cells and some secretory glands

Question 5

Podocyte function in kidneys

Answer 5

Part of the kidney nephron moving blood to the glomerulus out by afferent arteriole cleaning the blood.

It prevents plasma protein entering urinary ultrafiltrate by acting as a barrier w/filtration slits.

Question 6

Function of epithelial junctions

Answer 6

Selectively maintains a seal between epithelial cells - tight junction e.g. zonula occludens

Attach cells to each other via cytoskeleton - structural strength
Adherens junction e.g. zonula adherens and desmosomes e.g. macula adherens

Allow cell to cell communication via small substances - gap junctions

Question 7

Tight junctions (zona occludens)
E.g. claudins

Answer 7

Collar around each cell
Block passage of content in between cells
Restricts movement of proteins and lipids between apical and basolateral membrane

Question 8

Gap junction

Answer 8

Used in contraction e.g. smooth muscle in gut and cardiac muscle
Epithelia engaged in fluid or electrolyte transport
Gap junction proteins called connexins
Pore opening can be regulated

Question 9

Adhering junctions

Answer 9

Adherens: initiation and stabilization of cell to cell adhesion regulates actin cytoskeleton intracellular signalling and transcription

Desmosomes: e.g. Macula adherens. Provide cell to cell adhesion increasing mechanical strength. Bind to keratin filaments ( intermediate filaments) have transmembrane proteins desmocolins and desmogleins

Adhesion belt - transmembrane protein, anchoring protein and actin filaments.

Hemidesmosomes: connect cells to basement membrane as do focal adhesions. They have transmembrane proteins known as integrins.

Cell matrix adhesion complexes

Question 10

Basement membrane aka basal lamina

Answer 10

Actually complex connective tissue resembling a membrane under a microscope.

Located below basal surface of epithelial cells aka basal lamina
Composed of collagen/proteoglycans/laminin/ enactin/ fibronectin

Function:

Structural attachment - epithelial cells attach to basal lamina that is attached to connective tissue

Compartmentalization - isolates epithelia muscles and nerves from connective tissue. Can maintain compartments w/diff composition

Filtration- allows selective movement to and from connective tissue

Tissue scaffold - when tissue repairs after damage it guides cells to new locations

Signalling - regulated epithelial cell behaviour

Question 11

Reticular fibres

Answer 11

Found below basal lamina they form the reticular lamina madu up of type 3 or 4 collagen

Question 12

Endocrine glands

Answer 12

Most endocrine glands consist of clumps of cords or secretory cells surrounded by a network of blood vessels these are pituitary glands.

The other type of endocrine gland is follicular- follicle surrounded by secretory cells and capillaries

Question 13

Glandular epithelia

Answer 13

Secretory cells are organised into functional groups called glands some form large organs e.g. Liver and pancreas

Exocrine - product is secreted via duct

Simple gland- single duct
Compound - branched duct

Endocrine- glands are ductless, product sent straight to blood stream, products called hormones

Question 14

Secretory mechanisms

Answer 14

Exocrine

Merocrine- vesicles of product fuse w/plasma membrane - exocytosis

Apocrine - release of a vesicle containing products in cytoplasm surrounded by a plasma membrane.

Holocrine - whole cell containing products undergoes programmed cell death and is shed

Endocrine
Exocytosis of products from cell which diffuses into blood stream

Question 15

Exocrine glands

Answer 15

Simple tubular
Simple coiled tubular
Simple branched tubular (two branches)
Simple acinar (rounded)
Simple branched acinar
Compound branched tubular
Compound acinar
Compound tubuloacinar

Question 16

Secretory cell structure/ products

Answer 16

Protein secretor- large nucleus, abundant rough ER, electron dense vesicles

E.g. acinar cells of the pancreas

Mucin secretor - flattened nucleus, well developed Golgi, secretory vesicles at cell apex (appear as vacuoles)

E.g. goblet cells in small intestine

Steroid secretor - well developed smooth ER, abundant mitochondria, vacuoles containing lipid

E.g. Steroid secreting cells of the adrenal gland