Osmoregulation Part Two Flashcards Preview

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Flashcards in Osmoregulation Part Two Deck (43):

Osmoregulators are able to maintain what regardless of osmotic changes in the external environment?

Osmoregulators maintain a steady extracellular fluid (ECF) osmotic pressure.


Marine osmoregulators are usually: hypo-osmotic or hyper-osmotic?

Hypo-osmotic, with an inside of 400 mOsm and an environment of 1000 mOsm.


Freshwater osmoregulators are usually: hyper-osmotic or hypo-osmotic?

Hyper-osmotic, with an inside of 300 mOsm and an environment of <5 mOsm.


What is important about hypo-osmotic osmoregulators?

They maintain extracellular fluid and cellular osmotic concentrations of 250-400 mOsm. They have low concentrations of organic osmolytes, and marine animals must drink seawater and absorb NaCl in order to absorb water, creating an excess of salt in the blood.
Gills use epithelial chloride cells to actively transport Na+ and Cl- outward.


What is important about hyper-osmotic osmoregulators?

They must cope with the low osmolarity of freshwater. Valuable solutes are lost through the gills, but they have several mechanisms for regulating extracellular fluid osmolarity. These mechanisms include: the active uptake of ions across the gills and skin, hypotonic fluid excretion by kidneys or other structures, lower internal osmolarities, and low permeability of integument.


True or False: Some fish can alternate between modes of osmotic adaptation.

True. For example, they can be hypo-osmotic in oceans but hyper-osmotic in rivers. This is done through acclimatization regulation coupled with an anticipation mechanism.


In water animals are Salt Glands found?

Marine birds and reptiles; helps with salt water because they may never have access to fresh water and due to the ion concentration, the kidneys are unable to obtain water from the sea.


What does the Salt Gland consist of?

Ducts, nostrils with salt secretions, and nasal salt glands that are two structures located above the eye and are osmoregulator organs. They secrete a hyper-osmotic NaCl solution through active NaCl transport, allowing the animal to drink sea water. This is a countercurrent exchange with the blood, offering the maximum transport rate.


How much water does a Salt Gland-lidded animal get per litre of salt water?

They get .5 litres of water per 1 litre of saltwater.


In the regulation of salt glands in birds, what happens to the kidneys with a high intake of saltwater?

The kidneys shut down to help with water conservation with a high blood osmolarity/high intake of seawater.


What stimulates nasal salt glands?



What is the Kidney?

A group of organs that share one property - they produce a primary fluid, primary urine, that goes through a series of tubes to produce urine. It is an internal organ mostly concerned with osmoregulation, that has common architectural and physiological principles.


Where in the Kidney does major changes in the osmotic concentration of urine take place?

In the Distal tubule; minor change in osmotic concentration take place in the proximal tubule.


Where in the Kidney does major changes in ionic concentration take place?

In the Proximal tubule.


What occurs with the blood in the collecting area?

This first step leads to primary urine (the urine before further modification). There are two different mechanisms that lead to primary urine; ultrafiltration (gradients are used to push fluid into and through the kidney) and active secretion (uses ATP to move ions that push water).


Why modify primary urine?

Primary urine is urine after the filtration step, and nearly all animals modify primary urine by retrieving and secreting solutes through active transport.
The primary urine is iso-osmotic with the body, and full of good solutes. The cells activate K+ Cl- channels in order to recover Sodium and chloride from the primary urine, but doesn't allow water to cross. The remaining urine has half the concentration of the primary urine.


What are the Malpighian tubules?

An osmoregulatory organ (in insects) that can produce hypo-osmotic urine with a high concentration of NaCl (in Rhodnius prolixus, where the blood is 50% plasma [hypo-osmotic], half of body weight is excreted as urine).


What does the Grasshopper do for excretion?

Malpighain tubules produce all the urine and feces (within the gut), and moves ions in a primary urine through the gut to make urine.


What do the Malpighain tubules float in, in insects?

In an open space/fluid. Drinking blood loads the haemolyph with Na+, Cl-. and water. The Malpighain tubules take it up and form urine.


What are the regions of the kidney?

Renal cortex (outer), renal medulla (inner, divided into remal pyramids in larger mammals), and renal pelvis (drainage area in the centre of kidney).


What is a Nephron?

The smallest functional unit of the kidney. There are 1 million in a human kidney, and they consist of a tubule and associated vascular components. It is responsible for the formation of urine.


What is the path of tubes in the human kidney?

1. Starts with the Renal Corpuscle [Cortex - where primary urine is produced]
2. Primary urine goes though Proximal Tubule [Cortex]
3. Primary urine goes through Loop of Henle [Cortex/Medulla - very short, in some nephrons this is long and goes into the medulla but most of the time it is short and stays in the cortex]
4. Distak Tubule [Cortex]
5. Collecting Duct [Medulla]


What are the three basic processes of the nephron?

1. Glomerular Filtration - filtering of blood into tubule forming the primary urine
2. Tubular Reabsorption - absorption of substances needed by body from tubule to blood
3. Tubular Secretion - secretion of substances to be eliminated from the body into the tubule from the blood


What is the Juxtamedullary Nephron?

A long-looped nephron important in establishing the medullary vertical osmotic gradient.


What is involved in Glomerular Filtration?

The glomerular/glomerular corpuscle is where the primary urine is formed. Glomerular filtration is the first step in urine formation, the body reabsorbs what is 'good' and ignores what is 'unknown'. There is the separation of plasma fraction of the blood, and this is drive by blood hydrostatic pressure (ultrafiltration). This contains small plasma solutes and water, waste products, and useful molecules (glucose and ions). No cells enter the ultrafiltrate; very low protein content.


What is important about the Renal Corpuscle?

Contains the glomerulus and glomerular capsule.


What happens in the Glomerulus?

It receives blood from afferent arteriole, and the capillaries are in very close proximity to glomerular capsules. There is a filtration slit between the glomerulus and the glomerular capsule, anything small enough to fit through these holes will enter the urine. The basement membrane is made of proteins and is negatively charged. Separation is due to size and charge (filtration slit and basement membrane).
Glomerular capillaries have large pores (fenestrae, fenestrated capillaries) and high permeability (about 400 times greater than other capillaries).


What is important about the Glomerular Capsule?

Bowman's Capsule. The inner wall is closely associated to the capillaries, and it is made of unique cell type (podocytes).


What forces are involved in glomerular filtration?

1. Glomerular Capillary Blood Pressure (favours filtration; 55 mmHg)
2. Plasma-Colloid Osmotic Pressure (Opposes filtration; -30 mmHg)
3. Bowman's Capsule Hydrostatic Pressure (Opposes filtration; -15 mmHg)
Net Filtration Pressure: favours filtration, 10 mmHg.


What is the Glomerular Filtration rate?

About 115 ml/min, 7.5 L/hr, 180 L/day.
The entire plasma volume of a body is filtered every 45 minutes; 99% of the filtrate is reabsorbed by the nephron tubules.


What is important about the Proximal Convoluted Tubule?

It is the primary area of reabsorption (65% of filtered water, 67% of filtered sodium, glucose and amino acids) and secretion (variable proton secretion for acid/base regulation; organic molecules). It uses active solute transport to return useful solutes. Glucose (and sodium through co-transport) and amino acids are carrier mediate, ions are involved in secretion and reabsorption. Glucose has a saturation level (renal threshold - 200mg/100ml). Glomerular filtration prevents large amounts of proteins (because of size and charge). Filtrated proteins are reabsorbed through receptor-mediated endocytosis instead of active transport/channels.


What is important about the Loop of Henle?

It establishes osmotic gradient in the medulla, which allows water reabsorption in the collecting duct. It reduces the osmotic pressure of the filtrate to about 100 mOsm, and reabsorbs 20% of filtered water and sodium. The descending limb is permeable to water but not to NaCl; filtrate concentrates in the medulla (because water leaves but not ions). The Ascending limb has active NaCl reabsorption, is impermeable to water, and concentrates the interstitial fluid in the medulla; dilutes the ultrafiltrate.


How much of the ultrafiltrate has been reabsorbed by the time it reaches the distal convoluted tubule?

85%; 65% from proximal tubule and 20% from loop of Henle.


What causes the osmotic gradient in the loop of Henle?

The ascending limb; ions from the ascending limb increase the concentration of ions in the medulla, water leaves the descending limb due to osmosis. It's a countercurrent multiplier system that works by positive feedback. The more transport by the ascending limb, the more concentrated the descending limb. This facilitates transport by the ascending limb.


What is Urea?

An excretion product (NH2). Urea contributes to the osmotic gradient, the ascending limb (and distal tube) is impermeable to it. It accumulates in the medulla.


What are Vasa Recta?

Blood vessels; where reabsorbed water goes. Countercurrent exchange within itself maintains osmotic gradient in medulla (blood that just went through filtration in the glomerulus, most of the proteins were left in the blood so this has a very high protein concentration). They draw excess water and solutes from the descending and ascending limb.


What is important about the Distal Convoluted Tubule?

It may dilute the filtrate (the fluid reaching the collecting duct is about 80 mOsm). It regulates sodium and potassium in the blood (variable Na transport controlled by aldosterone, variable permeability to water controlled by antidiuretic hormone (ADH)).


What is important about the Collecting Duct?

It's the last part of urine formation; it concentrates the urine by exploiting the osmotic gradient in the medulla (generated by the loop of Henle). It's permeable to water (regulated by antidiuretic hormone (ADH)).


What happens when vasopressin is present?

The distal and collecting tubules become permeable to water; the concentration of urine may be up to 1,200 mOsm; small volume of concentrated urine is excreted. Reabsorbed water is picked up by peritubular capillaries.


What happens when no vasopressin is present?

The distal and collecting tubules become impermeable to water; concentration of urine may be as low as 100 mOsm. A large volume of dilute urine leaves, no water is reabsorbed.


What does Furosemide do?

Blocks NaCl excretion.


The Vasa recta is arranges as a __ ___ that helps maintain __ __.

Countercurrent system; osmotic gradient.


What are the permeabilities and active transport properties of the descending and ascending limbs?

Descending limb = permeable to water, impermeable to NaCl.
Ascending limb = permeable to NaCl, impermeable to water.