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chapter 41

Terms in this set (16)

Why is homeostasis of water and electrolyte balance important?
Homeostasis of water and electrolyte concentration is critical for normal physiological function in all organisms and is crucial for survival. The internal environment of a cell is maintained within a narrow window of conditions.
Severe electrolyte imbalances can lead to muscle spasms, cognitive deficits, confusion, irregular heart rhythms, etc.
What is diffusion and when is an equilibrium established?
Electrolytes move by diffusion and water moves by osmosis
Diffusion is the movement of substances from regions of higher concentration to regions of lower concentration along their concentration gradient
What is osmosis? What is osmolarity? How does osmolarity differ from molarity?
Osmosis is the diffusion of water (through a selectively permeable membrane) from areas of "higher water concentration" to areas of "lower water concentration"
Alternatively, osmosis is movement of water from lower solute concentration (high water concentration) to higher solute concentration (low water concentration)
The concentration of dissolved dissociated substances in a solution, measured in moles per liter, is referred to as its osmolarity
Osmolarity = molarity x number of particles that dissociate per molecule (1 for glucose, 2 for NaCl)
What does hypotonic mean? What does hypertonic mean?
Hypotonic = low osmolarity (low solute, high water concentration). Also hypoosmotic
Hypertonic = high osmolarity. (high solute, low water concentration) Also hyperosmotic
Isotonic?
isotonic: having the same osmotic pressure as some other solution
What is an osmoconformer? What animals are osmoconformers?
Osmoconformers keep internal fluids at the same osmotic pressure as that of their surrounding environment
Marine invertebrates such as sponges and jellyfish do not need to osmoregulate to achieve homeostasis. They are called osmoconformers
Seawater is a fairly constant ionic and osmotic environment and nearly matches the electrolyte concentrations found within these animals.
Relative to seawater, their tissues are isotonic, although they may expend energy to regulate concentrations of a particular ion.
Sharks and rays maintain a high internal concentration of urea to achieve osmotic equilibrium with the surrounding water
What is an osmoregulator? What animals are osmoregulators?
Marine fish are osmoregulators—they actively regulate osmolarity inside their bodies to achieve homeostasis
Osmoregulation is required because their tissues are hypotonic to salt water—the solution inside the body contains fewer solutes than the solution outside. They lose water by osmosis and gain electrolytes through gills by diffusion.
Marine fish must replace lost water and rid cells of excess electrolytes. They drink a lot and pump salts out with chloride cells in the gills

Freshwater fish lose salt and gain water
Gill epithelium of freshwater fish is hypertonic to the surrounding water. They gain water through osmosis and lose electrolytes by diffusion
Freshwater fish must get rid of incoming water and replace electrolytes. They don't drink, produce copious urine and pump electrolytes in via chloride cells with reversed polarity
What is osmotic stress?
Osmotic stress occurs when the concentration of dissolved substances in a cell or tissue is abnormal
Marine fish must replace water lost and get rid of electrolytes or cells will shrivel and die
Freshwater fish must get rid of excess water and keep electrolytes or the cells will swell and burst
Terrestrial animals need water to prevent dehydration
What problems with osmotic stress do terrestrial animals face? How do they deal with them?
What are some examples of glands organisms have developed to get rid of excess salt?
Land animals constantly lose water to the environment typically via gas exchange by evaporation (rather than osmosis as with ocean animals)
They also lose water through urine, sweat or panting
Gain water by drinking and cellular respiration
Depending on conditions terrestrial animals may need to conserve or excrete electrolytes to maintain homeostasis
Sharks and rays excrete excess salt via a rectal gland which eliminates salt with digestive wastes using a combination of pumps and co-transporters
Marine birds have evolved specialized nasal salt glands that pump ions from the blood to gland cells and excrete salt through the gland and nasal cavity. This allows them to gain water by drinking sea water.
Where does nitrogen waste come from? What are the 3 main forms in which nitrogen is excreted?
When proteins and nucleic acids are broken down by metabolism, one of the by-products is ammonia. Ammonia contains nitrogen and is toxic to organisms, so it is a form of nitrogenous waste
Animals excrete three forms of nitrogenous waste that vary in their toxicity and cost to produce. Ammonia is the most toxic but is easily released in water. Uric acid is the least toxic, but is energetically costly to produce.
Urea is in the middle.
What makes ammonia so toxic?
Ammonia (NH3) is a strong base; it readily gains a proton to form an ammonium ion (NH4+) which in excess is toxic to cells. It can disturb the pH balance of cells and cause neuronal cell injury
Compare and contrast ammonia, urea and uric acid in regard to solubility in water, amount of water required for excretion, energy cost and toxicity.
Animals that excrete ammonia directly usually lose a lot of water.
Freshwater fish detoxify ammonia by diluting it to a low concentration in watery urine. Freshwater and salt water fish excrete ammonia from gills.
Mammals convert ammonia to less toxic urea which can be stored before being excreted in urine. Urea excretion requires less water than direct ammonia excretion
Birds, reptiles and terrestrial arthropods convert ammonia to uric acid. Because uric acid is very insoluble in water it can be excreted as a dry paste

The type of nitrogenous waste produced by an animal correlates with its evolutionary history and with its habitat, and thus the amount of osmotic stress it endures.
There is a trade-off between the energetic cost of excreting urea or uric acid and the benefit of conserving water.
What general strategies are used to get rid of wastes? (filtration, reabsorption, secretion) What happens during filtration, reabsorption and secretion? What is the advantage of this strategy? (do electrolyte and water balance at same time as getting rid of wastes). How is this done in the flatworm, earthworm and insect?
Filtration. Circulatory pressure pushes waste to an extracellular space. Non-selective, but energetically inexpensive. The filtrate contains waste products, water, electrolytes and other solutes
Reabsorption. From the filtrate, electrolytes, amino acids, vitamins, sugars and water are reabsorbed via active or passive processes or with water by osmosis
Secretion. Toxic compounds and excess ions not filtered earlier are secreted via active processes. Expensive.

flatworm: Needs to excrete water
Water and solutes pass through slits into the tip forming a non-specific pre-urine
Cilia move the fluid down to the tubules drawing more fluid in through the slits
Reabsorption of desired solutes takes place in the tubule system leaving a hypotonic (dilute) urine which is excreted

earthworm: Fluid filtered out of blood goes to a ciliated funnel, where fluid (a non-specific pre-urine) is pushed into the tubules in the next segment
Capillaries surrounding tubules selectively reabsorb solutes
This leaves a dilute urine with wastes for excretion

insect: Hemolymph bathes tissues
Malpighian tubules use pumps, transporters and diffusion to get materials from the hemolymph, forming a non-selective pre-urine
Filtrate is passed to hindgut where uric acid precipitates out and ions are reabsorbed with water following
Uric acid is excreted
What structures make up the human urinary system?
Functional unit of kidney is the nephron composed of the glomerulus, capsule, renal tubules and collecting duct
How do blood vessels serve the nephron? Do all nephrons extend deep into the medulla?
A large blood vessel (renal artery) brings blood filled with nitrogenous and other wastes into the organ; another large blood vessel (renal vein) carries "cleaned" blood away
The urine formed in the kidney is transported via a long tube, the ureter, to the bladder and from there to the body surface via a tube called the urethra, and then excreted
Most of the approximately one million nephrons in a human kidney are located entirely in the cortex, while some extend into the medulla (20%)
What happens in the renal corpuscle? What are the parts of the renal corpuscle? How would a change in blood pressure affect what goes on here? Why?
The glomerulus is a tuft of capillaries with blood entering by an afferent arteriole and leaving by an efferent arteriole.
The tuft of capillaries is encased in a membranous sac called Bowman's capsule and the space enclosed is called Bowman's space
The cells that line the capillaries in the glomerulus have large pores and are also surrounded by podocytes whose membranes fold into a series of slits and ridges
Blood pressure in the glomerular capillaries is higher than the pressure in the surrounding capsule, forcing water, waste and small solutes out of the blood and into the Bowman's space, forming a filtrate—a pre-urine
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