11.3 The Kidney and Osmoregulation

Understandings

• Animals are either osmoregulators or osmoconformers.• The Malpighian tubule system in insects and the kidney

carry out osmoregulation and removal of nitrogenous waste.

• The composition of blood in the renal artery is different from that in the renal vein.

• The ultrastructure of the glomerulus and Bowman’s capsule facilitate ultrafiltration.

• The proximal convoluted tubule selectively reabsorbs useful substances by active transport.

• The loop of Henle maintains hypertonic conditions in the medulla.

• ADH controls reabsorption of water in the collecting duct.

• The length of the loop of Henle is positively correlated with the need for water conservation in animals.

• The type of nitrogenous waste in animals is correlated with evolutionary history.

Applications/Skills• A: Consequences of dehydration and overhydration• A: Treatment of kidney failure by hemodialysis or kidney

transplant.• A: Blood cells, glucose, proteins and drugs are detected in

urinary tests.• S: Drawing and labeling a diagram of the human kidney.• S: Annotation of diagrams of the nephron.

Guidance- ADH will be used in preference to vasopressin- The diagram of the nephron should include the

glomerulus, Bowman’s capsule, proximal convoluted tubule, loop of Henle, distal convoluted tubule; the relationship between the nephron and the collecting ducts should be included.

OsmoregulationThere needs to be a balance between water ingested and water eliminated

In order to maintain homeostatic levels of water, the body must undergo osmoregulation

The amount of water eliminated depends on - amount of water ingested recently- perspiration rate- ventilation rate

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Osmoregulators vs Osmoconformers

Osmoconformers have virtually the same solute concentration as their environmentWater moves in and out freely due to osmotic balanceRestricted to living in environments which they are iso-osmotically matched

Osmoregulators have different solute concentrations than their environmentHave mechanisms to regulate water balance

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Nitrogenous Waste Products

The bloodstream picks up molecular waste products from tissues. As a result, it needs to be continuously filtered in order to remove these products.

Nitrogenous wastes are waste products that result from deamination of amino acids.

Could be ammonia, urea, or uric acid.

Which type of nitrogenous waste is produced depends on the species evolutionary history and habitat.

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Waste Product Example Organism Advantages Disadvantages Evolutionary or habitat relationship

Ammonia Fish Requires little energy to produce

Very toxic; must be diluted and removed quickly by using a great deal of water

Fish have an unlimited water supply to flush out ammonia

Urea Mammals Requires less energy to produce than uric acid; toxic only at high levels

Requires more energy to produce; requires some waterfor dilution and removal

Levels are kept under control by kidneys; requires less waterfor dilution than ammonia; can be stored temporarily in bladder

Uric Acid Birds Insoluble in aqueous solutions (blood/cytoplasm); can be stored in specialized structures in eggs

Requires a great deal of energy to produce

Since it’s not watersoluble, birds have independence from having to find water frequently

Malpighian Tubules

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Small tubes that lie in pools of blood in an insects body cavity

Closed at one end (distal end)

Opens into the insects gut (proximal end)

Components of the insects blood enter the tubules

Nitrogenous wastes, excess water, and salt ions remain in the tubules and move to the proximal end that empties into the gut; gets eliminated

Useful substances are transported back to the blood

Renal medulla- layer of tissue surrounding the renal pelvis

Renal Artery- takes blood into the kidney

Renal vein- drains filtered blood away from the kidney

Ureter- tube that takes urine to the bladder

Renal cortex- layer of tissue to the outside of the renal medulla

Renal pelvis- drains urine into the ureter

The Kidney

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Proximal convoluted tubule Distal convoluted tubuleNephrons

Glomerulus- capillary bed that filters substances from the blood; walls of the capillaries have fenestrations (small slits) that open when blood pressure is increasedBowman’s capsule- surrounds glomerulusAfferent arteriole- brings unfiltered blood to the nephronEfferent arteriole- drains blood from the glomerulus; has a smaller diameter than the afferent arteriole

Afferent arteriole

Efferent arteriole

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Bowman’s Capsule

Afferent arterioleEfferent arteriole

Glomerulus

The afferent arteriole brings unfiltered blood to the nephron.

Branches into a capillary bed inside the Bowman’s capsule (glomerulus)

An increase in blood pressure is caused by the decreased diameter of the efferent arteriole

This causes the fenestrations in the capillaries to open

This leads to the ultrafiltration of the blood

Fluid filtered by the glomerulus passes through the basement membrane into the proximal convoluted tubule; large molecules (like proteins) cannot pass through

Blood carrying proteins and other substances not filtered leaves through the efferent

Basement membrane

Ultrafiltration

Adapted from:http://www.mcatzone.com/uploads/gloss/bowmans_capsule.jpg

ReabsorptionThe filtrate contains some substances that the body needs (water, some ions, glucose, etc)

Most of these are recovered by reabsorption in the proximal convoluted tubule

These substances leave the tubule filtrate and are taken back into the bloodstream via the peritubular capillary bed

- Salt ions leave by active transport; this causes the filtrate to become hypotonic

- Some water follows the salt ions due to osmotic pressure

- Glucose is moved out by active transport

Loop of HenleMuch of the water remains after the filtrate leaves the proximal convoluted tubule

It enters the descending portion of the loop of Henle, which is permeable to water, relatively impermeable to salt ions

Filtrate then enters the ascending portion of the loop of Henle, which is permeable to salt ions, relatively impermeable to water

This makes the interstitial fluid in the renal medulla hypertonic in relation to the fluid in the tubules and collecting ducts

*Despite the fact that water left in the descending portion, the filtrate that moves up the ascending portion and into the distal convoluted tubule is still relatively hypotonic

ADHThe collecting duct is differentially permeable to water

This depends on the presence or absence of antidiuretic hormone (ADH)

If ADH is present, the collecting duct is permeable to water and water moves by osmosis out of the duct into the medulla, enters the capillary bed, and is returned to the bloodstream

If ADH is absent, the collecting duct is impermeable to water

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Water Conservation

A longer loop of Henle = greater water conservation

Shorter loop= reduced ability to conserve water - medulla is not made to be hypertonic - water not reabsorbed from collecting duct

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Changes Made by the Kidney

Blood leaving the renal vein:- Lowered amt of urea- Lowered amt of salt ions- Lowered amt of water- Nearly identical amt of glucose- Nearly identical amt of protein - No change in blood cells

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Kidney Failure

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Hemodialysis (commonly called kidney dialysis) is a process of purifying the blood of a person whose kidneys are not working normally.

Hemodialysis treatment lasts about four hours and is done three times per week. A person can be treated this way for years.

The Dialyser contains a semi-permeable membrane that allows small particles (e.g. urea) to diffuse through, but larger molecules and cells remain in the blood

Used dialysate collects filtered out small molecules such urea

Fresh dialysate contains:•No urea – to encourage

diffusion from the blood•Glucose and other useful

molecules at optimal concentrations – to minimize loss from the blood.•High solute concentration

removes excess water.

Saline solution prevents excessive water loss which could lead to dehydration.

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A transplant is the best long-term treatment.

Donors can be either:• Someone who has recently died• A person who has chosen to give up one of

their two kidneys

Donors and the recipient have to be a close match in both blood and tissues to minimize the chance of rejection*.

*If the match is not close enough the recipient's immune system will react to the new kidney as it would to a pathogen.

The transplanted kidney is grafted in to the lower abdomen with the renal artery, renal vein and ureter connected to the recipient’s blood vessels and bladder.

Kidney Transplant

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Urinalysis

• Presence of blood cells infections, disease and some cancers.

• Glucose is a strong indication of diabetes.• Trace amounts of protein are normal

(some proteins are very small), but larger amounts indicate kidney disease.

• Drugs (or their breakdown products) can often be detected in urine samples

Diagnostic tests of urine samples provide an easy effective way to detect illness and drug abuse.

Processes that affect the metabolism affect the metabolic waste that is produced and then excreted in urine.

Dehydration and Overhydration

Dehydration Overhydration

Sleepiness Change in behavior, confusion

Constipation Blurred vision

Dry mouth/skin Muscle cramps

Dizziness, headache Nausea, vomiting

HomeworkVOCAB

Urea, deamination, excretion, nitrogenous waste, Malpighian tubules, renal artery, renal vein, urine, renal pelvis, ureter, renal medulla, renal cortex, nephron, glomerulus, bowman’s capsule, ultrafiltration, osmoregulation, ADH, osmoregulators, osmoconformers, kidney dialysis, dehydration, overhydration

OTHER

Exercises 9-15, pg 478