Ch. 43 Water & Electrolyte Balance in Animals Flashcards
electrolyte
any compound that dissociates into ions when dissolved in water
- (in nutrition) any of the major ions necessary for normal cell function
- active ions
- dissipate quickly
(ie) Na, Cl, K & Ca
diffusion
the movement of substances from regions of higher concentration to regions of lower concentration, along their concentration gradients
SUBSTANCES
osmosis
the diffusion of water through a selectively permeable membrane from areas of higher water concentration to areas of lower water concentration
WATER
solutes
dissolved substances
- move down their concentration gradients across a selectively permeable membrane via diffusion
concentration gradient
difference across space (ie. membrane) in the concentration of a dissolved substance
osmolarity
the concentration of dissolved substances in a solution, measured in moles per liter
osmotic stress
occurs when the concentration of dissolved substances in a cell or tissue is abnormal
osmoregulation
process by which a living organism controls the concentration of water and salts in its body
(ie) living organisms control the concentration of water and salt in their bodies through osmoregulation
osmoconformer
an animal that does not actually regulate the osmolarity of its tissues but conforms to the osmolarity of the surrounding environment
- make inside same as outside (in between)
(ie) jellyfish make tissue concentration equal to water (isotonic)
osmoregulator
an animal that actively regulates osmolarity inside their bodies to achieve homeostasis
- required in marine vertebrates because their tissues are hypotonic to salt water
- lose water by osmosis
- gain electrolytes by diffusion
(ie) most marine fish by removing/gaining water or salt
hypotonic
solution inside the cells contains fewer solutes than the solution outside
- cells gain water through osmosis
- lose electrolytes by diffusion
ways land animals lose water
when they produce urine/sweat or pant
passive transport
diffusion of a substance across a membrane
- driven by diffusion along an electrochemical gradient
- does not requireATP
- type: facilitated difussion
- transport smaller substances
facilitated diffusion
passive movement of substance across a membrane with the assistance of transmembrane carrier proteins or channel proteins
active transport
the movement of of ions or molecules across a membrane against an electrochemical gradient
- requires energy (ATP)
most important type of pump in animals
sodium-potassium pump (Na+/K+-ATPase)
secondary active transport
transport of an ion or miolecule in a defined direction that is often against its electrochemical gradient, in company with an ion or molecule being transported along its electrochemical gradient
- once a pump establishes a concentration gradient, secondary active transport can occur
cotransporter
a transmembrane protein that facilitates diffusion of an ion down its previously established electrochemical gradient and uses the energy of that process to transport some other substances, in the same or opposite direction, AGAINST its concentration gradient
- energy released when a solute is transported along its concentration gradient can be used by a cotransporter to transport another molecule against its concentration gradient
types of cotransporters
1) symporter
2) antiporter
sympoter
move solutes in the same direction
anitporter
move solutes in the same direction
rectal gland
a salt-secreting gland in the digestive system of sharks, skates, and rays
- ions can be concentrated only if they are actively transported against a concentration gradient
location of sodium-potassium pumps in shark
epithelial cells along the inner surface, or lumen, of the shark rectal gland
ouabain
a plant defense compound that is toxic to animals
- prevents Na+/K+-ATPase from functioning
Na+/K+-ATPase
essential for salt secretion
common molecular mechanism of salt extension
1) drink salt water, excrete NaCl via glands in their nostrils
2) marine fish excrete salt from their gills
3) mammals transport salt in their kidneys
cystic fibrosis transmembrane regulator (CFTR)
80% identical to the shark chloride channel
hypothesis for cause of cystic fibrosis
defect in a chloride channel
how do insects minimize water loss from the body surface?
1) tracheae connects to spiracles, which can open or close as needed to minimize water loss
2) exoskeleton/chitin + wax
tracheae
any of the small air-filled tubes that extend throughout the body and function in gas exchange
- an extensive system of tubes that functions as the insect’s respiratory organ
spiracle
a small openings that connects air-filled tracheae to the external environment, allowing for gas exchange
chitin
a tough polysaccharide, and layers of protein
- part of insect exoskeleton
- prevents water loss
cuticle
a protective coat secreted by the outermost layer of cells of an animal or a plant
- FCN: reduce evaporative water loss
ammonia (NH3)
- by-product of catabolic reactions
- a strong base
- readily gains a proton to form ammonium ion (NH4)
- high water solubility
- high water loss required for excretion of waste
- low energy cost (amount of ATP required)
- high toxicity
- groups where it is the primary waste: bony fishes, aquatic invertebrates
- method of synthesis: product of breakdown of amino acids & nucleic acids
- method of excretion: in urine, diffuse across gills
ammonium ion (NH4)
toxic to cells
ways to get rid of ammonia (NH3)
from least expensive (most water) to most expensive (least water):
1) fish dilute to a low concentration & excrete as watery urine
2) fresh-/saltwater fish diffuse across gills into water along a concentration gradient
3) humans convert to less toxic urea & excrete it in urine
4) birds, reptiles, and terrestrial arthopods convert to uric acid & excrete as dry paste
urea
- medium water solubility
- medium water loss required for excretion of waste
- high energy cost (amount of ATP required)
- medium toxicity
- groups where it is the primary waste: mammals, amphibians, cartilaginous fishes
- method of synthesis: synthesized in liver, starting w/ amino groups from amino acids
- method of excretion: in urine (mammals); diffuses across gills (sharks)
uric acid
- very low water solubility
- very low water loss required for excretion of waste
- high energy cost (amount of ATP required)
- low toxicity
- groups where it is the primary waste: birds & otro reptiles, most terrestrial insects & spiders (arthopods)
- method of synthesis: synthesis starts with amino acids & nucleic acids
- method of excretion: with feces
how do insects maintain homeostasis?
they carefully regulate the composition of hemolymph (blood-like fluid)
hemolymph
the circulatory fluid of animals w/ open circulatory system (ie. insects) in which the fluid is not confined to blood vessels
reasons why regulating hemolymph composition is important
1) nitrogenous wastes have to be removed before they build up to toxic concentrations
2) excess electrolytes must be excreted before they lead to osmotic stress
3) water balance must be regulated constantly
how do insects maintain water & electrolyte balance?
through Malpighian tubules (excretory organ) and the hindgut (posterior portion of digestive tract)
Malpighian tubules
a major excretory organ of insects, consisting of blind-ended tubes that extend from the gut into the hemocoel
- filter hemolymph to form “pre-urine”
- send “pre-urine” to hindgut for further processing
- important feature of maintaining water & electrolyte balance in insects
- large surface area
- in direct contact w/ hemolymph
- similar to rectal gland in shark
*impermeable to sodium ions but contain a pump that actively transports potassium ions into the tubules
hindgut
posterior portion of digestive tract
how is hypertonic urine produced in insects?
when an insect is stressed due to shortage of electrolytes & water
- electrolytes & water from filtrate are reabsorbed in hindgut and returned to the hemolymph
- hypertonic urine formation results in water conservation & nitrogenous waste elimination
types of active pumps found in insect hindguts
1) Na+/K+-ATPase
2) chloride pump
how do terrestrial vertebrate replace the water they lose?
they drink water and ingest electrolytes in food
in land-dwelling vertebrates, where does osmoregulation primarily take place?
the kidney
kidney
(in terrestrial vertebrates) one of a paired organ situated at the back of the abdominal cavity that filters the blood, produces urine, and secretes several hormones
- responsible for water balance
- responsible for osmoregulation
- responsible for electrolyte balance
- responsible for excretion of nitrogenous wastes
function of the kidney
1) filters blood
2) produces urine
3) secretes several hormones
4) osmoregulation
5) water balance
6) electrolyte balance
7) excretion of nitrogenous wastes
renal artery
brings blood containing nitrogenous wastes INTO the kidney
artery = into
renal vein
carries the cleaned blood AWAY from kidney
vein = away
ureter
(in vertebrates) a tube that transports urine from one kidney to the bladder
bladder
a mammalian organ that holds urine until it can be excreted
- connected to kidney via ureter
nephron
one of many tubules inside the kidney
- FCN: formation of urine
- makes up most of kidney’s mass
- basic functional unit of the kidney
- involved in maintaining water & electrolyte balance
- located in the cortex (outer region of the kidney)
cortex
(in animals) the outermost region of an organ (ie. kidney or adrenal gland)
medulla
the innermost part of an organ (ie. kidney or adrenal gland)
vein
any blood vessel that carries blood (oxygenated or not) under relatively low pressure from the tissues toward the heart
- big to small
- no muscles to move fluids (rely on gravity)
- blue
OUT
artery
any thick-walled blood vessel that carries blood (oxygenated or not) under relatively high pressure AWAY from the heart to organs throughout the body
- small to big
- need muscles to move fluids
- red
IN
the function of the kidney: an overview
1) the renal corpuscle filters blood, forming a “pre-urine” consisting of ions, nutrients, wastes, and water
2) in the proximal tubule, epithelial cells reabsorb nutrients, vitamins, valuable ions, and water
3) the loop of henle establishes a strong osmotic gradient in the tissues outside the loop, with osmolarity increasing as the loop descends
4) in the distal tubule, ions and water are reabsorbed in a regulated manner–one that helps maintain water and electrolyte balance
renal corpuscle
(kidney) the ball-like structure at the beginning of the nephron
- consists of a glomerulus & the Bowman’s capsule
- acts as filtration device
- urine forms here
- capable of producint 180 liters (60 gallons) of filtrate per day
- filtration based on size
dead end wall
proximal tubule
(kidney) the convoluted section of a nephron into which filtrate moves from Bowman’s capsule
- involved in unregulated reabsorption of electrolytes, nutrients, and water
- involved in active transport of selected molecules out of the filtrate
- reabsorption selectively retrieves small substances that are valuable
- active transport
loop of Henle
(kidney) a long U-shaped loop in a nephron that extends into the medulla
- FCN: countercurrent exchanger to set up an osmotic gradient that allows reabsorption of water from the collecting duct
- less water available, longer loop of Henle
- maintains osmotic gradient from outer to inner medulla
Bowman’s capsule
the hollow, double-walled, cup-shaped portion of a nephon (in kidney)
- surrounds a glomerulus in the kidney
function of the kidney: simple overview
1) filter pre-urine
2) reabsorb
3) osmotic gradient
4) water & electrolyte balance
collecting duct
(in kidney) a large straight tube that receives filtrate from the distal tubules of several nephrons
- involved in regulated reabsorption of water
- high pressure in the inner medulla & low in the outer medulla
glomerulus
(in kidney) a ball-like cluster of capillaries that brings blood to the nephron from the renal artery
- surrounded by Bowman’s capsule
- located at the beginning of a nephron
- have large pores
- surrounded by unusual cells whose membranes fold into a series of slits & ridges
- higher pressure inside than in surrounding capsule
how does water and solutes enter the glomerulus?
Pressure is much higher inside the glomerulus than its surrounding capsule
- pressure forces water & solutes out of blood through the pores in the glomerulus
- result: formation of a filtrate (pre-urine)
up 25% of water/solutes present in blood is removed when filtrate forms
how much filtrate (pre-urine) is actually secreted?
about 1%
- 99% of the filtrate is recycled
filtration + reabsorption =
minimizes water & nutrient loss
microvilli
tiny protrusions from the surface of an epithelial cell that increase the surface area for absorption of substances (nutrients/water)
how are valuable solutes and water reabsorbed and returned to the body?
when solutes leave the proximal tubule and enter epithelial cells, water follows along the osmotic gradient
molecule mechanism required for selective reabsorption
1) Na+/K+-ATPase in basolateral membranes removes intracellular Na+, creating gradient for Na+ entry from the lumen
2) in the apical membrane, Na+-dependent cotransporters use the gradient to remove valuable ions and nutrients selectively from the filtrate
3) the solutes that move into the cell diffuse across the basolateral membrane into nearby blood vessels
4) water follows ions from the proximal tubule into the cell and then into the blood vessels
aqauporin
water channel
- moves by osmosis across a plasma membrane
- FCN: helps water leave the proximal tubule (kidney)
loop of Henle regions
1) descending limb
2) thin ascending limb
3) thick ascending limb
descending limb
loop of Henle region that is:
- highly permeable to water
- almost completely impermeable to solutes
- free water movement via aquaporins
passive transport out of filtrate
thin ascending limb
loop of Henle region that is:
- highly permeable to Na+ and Cl-
- moderately permeable to urea
- almost completely impermeable to water
passive transport out of filtrate
vasa recta
(in kidney) a network of blood vessels that runs alongside the loop of Henle of a nephron
- functions in reabsorption of water and solutes from the filtrate (pre-urine)
- water & salt that move out of the loop of Henle diffuse into the vasa recta
- result: water & electrolytes are returned to the body
blood vessel around loop of Henle
distal tubule
(in kidney) the convoluted portion of a nephron into which filtrate moves from the loop of Henle
- involved in the regulated reabsorption of sodium & water
- this fluid = slightly hypotonic (less solutes) to blood (more solutes)
solutes in distal tubule fluid
slightly hypotonic to blood
- solutes contains mainly urea & other waste products
aldosterone
a hormone that stimulates the kidney to conserve salt and water
- promotes retention of sodium
- produced in adrenal cortex/glands
- released when sodium levels in blood are low
- fast process
low electrolytes, ↑ aldosterone, ↑ channel size
antiduretic hormone (ADH)
(vasopressin or arginine vasopressin)
a peptide hormone, secreted from the posterior pituitary gland
- stimulates water retention by the kidney
- released when dehydrated
- slower process than aldosterone since its a hormone
antiduretic hormone (ADH) process
1) aquaporin - ADH triggers the insertion of aquaporins into the apical membrane
- cells more permeable to water & large amounts of water are reabsorbed
2) ↑ urea - ADH ↑ permeability to urea, which increases the osmolarity of the surrounding fluid and thus water loss from the filtrate
When ADH is present:
- water is conserved
- urine is strongly hypertonic (less solutes) relative to blood
When ADH is absent
- few aquaporins are found in the collecting duct epithelium
- epithelium is relatively impermeable to water
- epithelim is hypotonic to urine
diabetes insipidus
defective form of ADH or aquaporins
- produces large amounts of urine
- aquaporins always open
diabetes mellitus
a disease caused by defects in insulin production (type 1) or in the response of cells to insulin (type 2)
- characterized by abnormally high blood glucose levels and large amounts of glucose-containing urine
type 1 diabetes
defects in insulin production
- body does not produce insulin
- least common
type 2 diabetes
defects in the response of cells to insulin
- body does not use insulin properly (insulin resistance)
- blood glucose levels rise higher than normal
- most common
- common predictor: obesity or overweight
thick ascending limb
loop of Henle region that is:
- highly permeable to Na+ and Cl-
- moderately permeable to urea
- almost completely impermeable to water
active transport of Na+, Cl- out of filtrate
