Renal

Question 1

Regarding osmoregulation, describe the “osmoconformer” strategy.

Answer 1

An osmoconformer is an animal that matches the environment while maintaining cellular function.

Question 2

Regarding osmoregulation describe the “osmoregulator” strategy

Answer 2

An osmoregulator is an animal that maintains tight control of its internal environment regardless of outside conditions.

Question 3

Are osmoregulation and osmoconformation mutually exclusive?

Answer 3

No. An organism can have some mechanisms under regulatory control and some not.

Question 4

What are some mechanisms under regulatory control?

Answer 4

Osmotic regulation (maintaining total dissolved solutes for osmo pressure), ionic regulation, volume regulation

Question 5

What is one way to identify an osmoconformer versus an osmoregulator on a graph?

Answer 5

Plot blood osmotic pressure and ambient osmotic pressure. An osmoconformer will have a visible increasing slope, an osmoregulator will remain relatively constant. This also shows those with mixed systems.

Question 6

What are the challenges of freshwater regulators?

Answer 6

Freshwater regulators live in a hypo osmotic environment and thus they struggle to maintain needed ions and rid excess water.

Question 7

What are the challenges of marine regulators?

Answer 7

Marine regulators live in a hyperosmotic environment and thus they struggle to rid excess ions and keep water.

Question 8

What is the main surface of aquatic ion exchange?

Answer 8

The gills. They have a high surface area to meet oxygen demands and thus are also key to the intake/loss of water and ions.

Question 9

What are the important cells of the gill?

Answer 9

Pavement cells which make up most of the gill’s surface, Mitochondria rich cells (mRc) which maintain internal [solute], and chloride cells/ionophores. Accessory cells are also important but exclusively found in marine fish.

Question 10

What is the role of a pavement cell in a gill?

Answer 10

It is the main site of oxygen exchange and makes up 90% of the gill.

Question 11

What is the role of an MRC in a gill?

Answer 11

MRCs deal with ion loading challenges and will uptake Chloride, Sodium, and Calcium ions in freshwater and remove Chloride and Sodium ions in saltwater. It is under hormonal control partially and the density and type of MRCs can change depending on the external environment.

Question 12

What is one way MRCs change in response to different conditions?

Answer 12

In soft water there is low calcium, thus calcium from within the organism will want to diffuse out because of concentration gradients. Thus, the organism will have more and larger MRCs to take up more calcium because of the calcium that is lost.

Question 13

What role does active transport play in MRCs?

Answer 13

In freshwater MRCs actively transport ions into the organism, and in saltwater MRCs actively transport ions out of the organism. This is active transport because it is against a concentration gradient.

Question 14

Describe the role of V-type ATPase in the gills.

Answer 14

In freshwater gills, it constantly pumps out protons using ATP on the apical membrane of MRCs. This attracts sodium ions due to a net negative charge.

Question 15

Describe the role of Na/K ATPase in the gills.

Answer 15

In freshwater gills, it exchanges 3 sodium to the blood for 2 potassium into the cell which leaks back out into the blood by leak channels, this further adds to the negativity. It is in the basolateral membrane of MRCs. It is the same in marine gills.

Question 16

Describe the role of the electroneutral anion exchanger in the gills.

Answer 16

In freshwater gills, it exchanges bicarbonate waste for chloride. It’s in the apical membrane of pavement cells and MRCs. The binding of bicarbonate causes a conformation change that has a strong chloride binding site. It is either not present in marine gills or not worth mentioning.

Question 17

Describe the role of the Cystic Fibrosis Transmembrane Regulator in the gills.

Answer 17

In freshwater gills, it’s a chloride channel that is not active transport. It is in pavement cells and MRCs, and its driven by the eventual build up of chloride becoming so high it is pushed through the CFTRs into the blood. Mutations cause cystic fibrosis, which reduces chloride clearance, maintains high electroneg potential, reduces extracellular cation removal, and increases mucosal build up (tissue water retention) leading to resp and digest difficulties. It is either not present in marine gills or not worth mentioning.

Question 18

Describe the role of the calcium co-transporter and calcium ATPase in the gills.

Answer 18

In freshwater gills, the calcium co-transporter relies on the gradient established by the NA/K ATPase to exchange a sodium into the cell for a calcium into the blood. It is on the basolateral membrane of MRCs. Calcium ATPase is also on the basolateral membrane and actively transports calcium into the blood. It has the same role in marine gills.

Question 19

Why does drinking seawater dehydrate you?

Answer 19

Because the salt water is hyperosmotic to your blood plasma, and thus the water in your blood plasma is drawn into the salt water in your gut and sodium and chlorine will diffuse into the blood plasma.

Question 20

How do saltwater fish differ from mammals in their ability to drink sea water?

Answer 20

They have active transport mechanisms for sodium and chloride into the blood plasma later in their intestine, this allows water retention but keeps a lot of excess ions which have to get removed via ion exchange mechanisms in the gills.

Question 21

What is the role of the accessory cell in the gills?

Answer 21

In saltwater fish exclusively it has a tight junction to the MRC and it created a paracellular path for sodium, which is moved through the path by electromotive forces.

Question 22

What is the role of the NKCC cotransporter in the gills?

Answer 22

In saltwater fish, it transports one sodium, one potassium, and two chloride into the cell using the very high attractive force for sodium (maintained by sodium ATPase). Eventually enough chloride builds up it diffuses out of channels on the apical membrane. It is on the basolateral membrane of MRCs. It is not present in freshwater fish.

Question 23

Identify these gill ion transporters by whether they are present in marine, freshwater, or both types of fish. Also describe their function and location in a couple of words.
1. V-type ATPase
2. Na/K ATPase
3. Electroneutral anion exchangers
4. Cystic Fibrosis Transmembrane Regulators
5. Calcium co-transporters
6. Calcium ATPase
7. Paracellular sodium pathway
8. NKCC cotransporter

Answer 23

1. Freshwater. Apical membrane of MRCs. Proton pump (out of organism). Maintains negative charge in cell
2. Both. Basolateral membranes of MRCs. Exchange 3 sodium to blood for 2 potassium into cell. Further maintain membrane potential.
3. Freshwater. Apical membrane of pavement cells and MRCs. Exchange equal negative charges. Usually bicarb out, chloride in. Builds up chloride.
4. Freshwater. Pavement cells and MRCs. Huge buildup of chloride drives diffusion through these channels into the blood.
5. Both. Basolateral membrane of MRCs. Transports a sodium into the cell and a calcium into the blood. Relies on gradient established by Na/K ATPase.
6. Both. Basolateral membrane of MRCs. Actively transports calcium into the blood.
7. Marine. Between the accessory cell and the MRC. Provides a pathway for sodium to exit the cell driven by electromotive forces.
8. Marine. Basolateral membrane of MRCs. Transports 1 sodium, 1 potassium, 2 chloride into the cell. Driven by Na/K ATPase gradient to use sodium’s attraction force to also move the other ions. Eventually chloride builds up enough to leak out of diffusion channels on the apical membrane.

Question 24

How do marine birds and reptiles deal with osmoregulation challenges?

Answer 24

Salt glands in the nose/head secrete salt. Blood vessels close to the secretory cells secrete salt into collecting tubules which drain into a duct and are excreted through the nostrils. They work similarly to marine gills and have a paracellular pathway, Na/K ATPase, and NKCC cotransporters. If they drink salt water they will also have exchangers in the gut to retain water similar to saltwater fish.

Question 25

How do the elasmobranchii osmoregulate?

Answer 25

They are osmoconformers that maintain the same total concentration of solutes to the environment, but not the SAME solutes, mostly organic ones like urea and TMAO. They don't have to struggle with losing or gaining water as much.

Question 26

How do salmon osmoregulate?

Answer 26

Born in fresh, migrate to salt, move back to fresh. They spend time in brackish waters with salinity gradients and thus slowly acclimate. They also reduce or increase their water consumption as needed. Their kidney function also changes to produce concentrated or dilute urine and their MRCs will either take up or remove ions dependent on their environment, this proves that MRCs are recycled and can change.

Question 27

What are some sources of water loss for terrestrial organisms?

Answer 27

Respiratory water loss, evaporative water loss (depending on environment), excretory water loss (removing metabolic products (i.e. urine))

Question 28

How does respiratory water loss work? What are some ways terrestrial organisms combat it?

Answer 28

Our respiratory organs have large surface area for gas exchange and the surface is moist and prone to water loss, this is counteracted by having mostly internal respiratory systems. Additionally, our body temperature is warmer than the surrounding air and warmer air holds more water, so external air coming in is humidified and air leaving cools and wets the nose.

Question 29

What factor causes evaporative water loss to vary?

Answer 29

SA/V ratio. Smaller animals have larger evaporative water loss by mass due to more volume per SA unit, whereas larger animals have lower evaporative water loss by mass due to less volume per SA unit.

Question 30

How do we combat excretory water loss?

Answer 30

By changing the composition of urine.

Question 31

What is the U/P ratio?

Answer 31

The ratio of urine osmotic pressure to plasma osmotic pressure. It can be used to show how concentrated or dilute urine is compared to the blood.

Question 32

What is the role of the mammalian kidney in osmoregulation?

Answer 32

It produces urine in different concentrations and volumes, it regulates water loss and it regulates solute concentrations.

Question 33

What is the functional unit of urine concentration?

Answer 33

The nephron.

Question 34

What is primary urine?

Answer 34

Fluid that has just moved from the renal corpuscle into bowman's capsule (collectively known as the glomerulus). It will change in composition before being excreted as definitive urine and has similar concentration to the blood plasma.

Question 35

What drives the flow of fluid into Bowman's capsule?

Answer 35

Hydrostatic pressure! Blood pressure is the highest contributor and is positive and opposed by colloid osmotic pressure (more solutes in plasma b/c large proteins cannot pass into capsule) and capsular fluid hydrostatic pressure (capsule like balloon. Doesn't want more fluid). Overall positive, fluid moves into capsule.

Question 36

Describe the ultrafilter of the renal corpuscle.

Answer 36

Capillaries: Fenestrations allow small things to diffuse, excluding large proteins. Basement membrane: collagen protein, further preventing large proteins from escaping. Podocytes: a specialized epithelial cell extending from the central cell body that forms a mesh preventing large cells from passing.

Question 37

What is glomerular filtration rate?

Answer 37

The rate of production of primary urine and the overall amount of fluid moving from blood across all nephrons. It is relatively constant.

Question 38

Define the two types of nephrons and highlight their differences.

Answer 38

Cortical nephrons: closer to the renal cortex, with a short loop of henle that doesn't descend far. Long loop nephrons: less common and descend far into the medulla. These concentrate urine more than cortical nephrons.

Question 39

How does the thickness of the renal medulla connect with an animal's ability to concentrate urine?

Answer 39

A thicker renal medulla = more + longer long loops of Henle, allowing more concentrated urine to be produced.

Question 40

How does permeability vary across the loop of Henle?

Answer 40

Thin descending: highly permeable to water, moderately permeable to solutes Thin ascending: impermeable to water, moderately permeable to solutes Thick ascending: impermeable to water, active transport of NaCl into interstitium.

Question 41

How does active transport in the thick ascending loop of Henle work?

Answer 41

There's an NKCC cotransporter from the lumen to the cell and a paracellular pathway for sodium from the lumen to the interstitium. Na/K ATPase transports sodium into the interstitium from the cell and chloride when built up from NKCC diffuses into the interstitium.

Question 42

How does the single effect work?

Answer 42

It's an initial osmotic pressure gradient established in the loop of Henle's ascending and descending limb based on their permeabilities. Since the descending loop is permeable to solutes and water and the ascending loop is impermeable to water and actively transports out sodium and chloride, we end up with a highly concentrated insterstitium and descending loop and a low concentrated ascending loop which creates a transverse osmotic pressure gradient called the single effect!

Question 43

Describe how countercurrent multiplication works.

Answer 43

Essentially given the properties of the single effect, these osmotic pressure differences are multiplied since the fluids are moving in different directions through the nephron. It creates an axial concentration gradient with super high concentration in the inner medulla and lower concentration closer to the cortex of the interstitial fluid.

Question 44

Describe how (and why) the permeability of the collecting duct changes.

Answer 44

Antidiuresis: concentrated urine. The collecting duct is permeable to water, so due to the axial concentration gradient water exits the duct into the interstitium. Diuresis: Dilute urine. The collecting duct is impermeable to water, so water cannot exit the duct into the intersitium. This is controlled by ADH which causes insertion or removal of Aquaporin-2 (via its absence or presence, its presence inserts, its absence removes).

Question 45

What stimulates the release of ADH?

Answer 45

ADH release is stimulated by low levels of blood plasma (water retention and concentrated urine needed). It's detected by baroreceptors in large blood vessels and osmoreceptors in the hypothalamus. Osmoreceptors detect blood osmolality, if plasma is dilute then they swell because of greater osmoreceptor concentration which triggers a decrease in ADH release and vice versa in the reverse scenario.

Question 46

How does Aquaporin-2 insertion and removal in the collecting duct work?

Answer 46

Vasopressin receptors (V2R) are activated by the binding of vasopressin (ADH) to it. It is a g-coupled receptor which triggers the activation of adenylyl cyclase and stimulates PKA to cause the exocytosis of aquaporin-2 from aquaporin water containing vesicles (AQWCV) and the insertion of them into the collecting duct membrane. In the absence of ADH, PKA is inhibited and it triggers the endocytosis of AQ into AQWCVs.

Question 47

What is urea?

Answer 47

Nitrogenous waste converted from ammonia to keep blood pH from changing due to ammonia.

Question 48

How does urea permeability change across the nephron?

Answer 48

Low permeability: distal convoluted tubule, thick ascending segment of loop of Henle, cortical and outer renal medulla High permeability: collecting duct and inner renal medulla.

Question 49

How does urea transporter protein function?

Answer 49

Urea transporter proteins transport urea from the collecting duct into the interstitium, because of this high concentration it flows into the lowest parts of the loop of Henle. It's powered by positive feedback. It's up and downregulated by ADH. It's called UT.A1

Question 50

How does the blood supply to the renal medulla avoid losing water, gaining ions, and ruining the single effect?

Answer 50

The Vasa Recta is a collection of very thin and small arterioles that travel to the deepest parts of the medulla to supply their needs. There is very little bloodflow and countercurrent exchangers to minimize solute washout and preserve osmotic pressure gradients. It functions similarly to the loop of Henle in how solutes move in and out. Additionally, since it's net osmolarity is higher due to plasma proteins there's a net loss of water from the interstitium to the blood!