Osmoregulation 2 Flashcards
epithelial tissues
- form boundry btw animal and environment
- external=skin
- internal=lumen of digestive system and excretory systems
specialized epithelial tissues for water and ion regulation found in the…
kidney!
animals change flux of water across epithelial tissues by mediating…
permeability of integument
-ie. number of aquaporin proteins open
animals reduce water flux on external surface via
- layer of hydrophobic molecues
- in the form of mucus, cuticle with chitin, keratonocytes, or stratum corneum with keratin
mucus
- lipoprotein mixture
- primarily found in lungs and GI
- also on skin of semiaquatic animals (frogs, etc)
cuticle
- main component is CHITIN (polysaccharide)
- ie arthropod exoskeleton, sometimes used for locomotion attachment
- covers all surfaces, including gut and trachea
- can be many different layers
keratinocytes
-terrestrial amphibians and amniotes epidermal layer
stratum corneum
- amniotes and tetrapods have this extra layer over keratinocytes
- keratinocytes that have differentiated into corneocytes
- eventually produces the envelope stratum corneum “cornified”
epithelial properties for ion movement
- asymmetrical distribution of membrane transporters
- cells interconnected to form impermeable sheet of tissue
- high cell diversity within tissue (specialized for transport or structural support)
- abundant mitochondria
asymmetrical distribution of membrane transporters
- solutes selectively transported across membrane depending on needs
- transport proteins stay in place in membrane (do not migrate)
cells interconnected forming impermeable sheet of tissue
- little leakage btw cells
- restricts movement of membrane proteins
- 2 paths of transport, transcellular and paracellular
transcellular transport vs. paracellular
- aka leaky vs tight
- trans=movement through the cell across membranes (usually via channels or aquaporins)
- para=movement between cells gap junctions
digestive epithelia
- water and salts from drinking and food transported across digestive epithelium’s high surface area
- transcellular and paracelluluar transport involved (both directions)
- absorbed water and salts enter blood
types of transporters
-ATPases (ie Na+/K+ atpase)
-ion channels (Cl-, K+, Na+)
-electroneutral cotransporters
-electroneutral exchangers
(pg 66-72)
abundant mitochondria
-largue supply of ATP for ATPases
specialized fish gills
- gills possess ion-pumping cells that cause net uptake of Na and Cl in freshwater and net export in seawater
- gill lamellae composed of mitochondria-rich chloride cells (PNA+)
- pavement cells (PNA-)
problems of fish cells
direction of ion transport depends on water salinity, so…
- salinity gradient changes with life history phase
- transporters are “fixed” in membrane
- transporters are expensive to maintain
saltwater-freshwater transitions
because salinity forces direction of ion transport, salinity gradients may change during life phase transitions
catadromous=fresh to salt when spawning
anadromous=salt to fresh when spawning
-accomplished by hormone-controlled genetic expression of different ion transport fuctions of epithelia
salt glands
- reptiles and seabirds must deal with high salt burden from seawater (direct or food) they ingest, but can’t afford to dilute with water/urine (also problem for desert animals)
- solution: salt glands=near eyes, drain into ducts that empty near nostrils, excreting hyperosmotic solutions of Na and Cl, removing large amounts of salt in small volume of water
- produced by ion pumps and countercurrent multiplier
rectal glands
- accessory organ in elasmobranhs
- empties into digestive tract
- active transport of Na and Cl from blood into lumen of gland, similar ion transport to gills and salt glands
- controlled by atrial natriuretic hormone
rectal gland pathway
change in osmotic pressure and blood vol=>release of ANH from heart=> vasocative inestinal peptide=>adenylate cyclase=>activates protein kinase a=>activates Cl-channel in membrane for Cl into gland lumen