Ch. 48: Osmoregulation and Disposal of Metabolic Wastes

Name the principle metabolic waste products produced by most animals.

CO2 (respiratory excretion)
Nitrogenous wastes

List some kinds of nitrogenous wastes

uric acid
� insects, reptiles, birds
� amphibians, mammals

During the metabolism of amino acids, the nitrogen-containing amino group is removed and converted to....

ammonia (which is highly toxic)

Uric acid is produced both from...

the breakdown of nucleotides from nucleic acids.

Describe the physical properties of uric acid.

? insoluble in water
? forms crystals that are excreted as a crystalline paste, so little fluid loss results. (This is an important water conserving adaptation in many terrestrial animals).

Where is urea synthesized?
From what?

Urea is synthesized in the liver from ammonia and CO2 by a sequence or reactions known as the urea cycle.

Why do animals convert ammonia to uric acid or urea?

Ammonia is highly toxic. Both uric acid and urea are less toxic forms of ammonia.
Uric acid is water insoluble and forms crystals that can be excreted without much water loss.
Urea is water soluble and requires more water to excrete.

Uric acid is produced from...

the breakdown of nucleic acids


Animals whose body fluid concentration varies along with changes in their environmental fluids (usually seawater).


Animals having homeostatic mechanisms that maintain an optimal salt concentration in their tissues regardless of changes in the salt concentration of their surroundings.

What are
Nephridial organs

Structures that function in osmoregulation and excretion in many invertebrates.

What are
Malpighian tubules

Tubules which comprise the excretory system of insects and spiders.

Describe osmoregulation in freshwater fish.

Freshwater fish must rid themselves of excess water.

What percentage of wastes are eliminated via sweat, in mammals?

5% - 10%

The outer portion of the kidney is called the...

renal cortex

The inner portion of the kidney is called the...

renal medulla

What is the name for the cone-shaped structures within the renal medulla?
How many of theses structures are present in each kidney?

renal pyramids
Each kidney comprises 8 to 10 renal pyramids.

The tip of each renal pyramid is called a...

renal papilla

Each papilla has several pores, the openings of...

collecting ducts.

Trace the path of urine from production to excretion

? collecting ducts
? renal pelvis
? ureters
? urinary bladder
? urethra

Why are bladder infections more common in females than males?

The length of the male urethra discourages bladder infections.
Female urethrae are shorter.

What enzyme is produced by the kidneys?

� helps regulate fluid balance and blood pressure

What hormones are produced by the kidneys?

? Erythropoietin
? 1,25-dihydroxy-vitamin D3
� stimulates calcium absorption by the intestine

The functional unit of the kidney is called a...


How many nephrons are present in each kidney?

Up to one million

Describe the structure of a nephron

A nephron consists of ...
� a cuplike Bowman's capsule
� connected to a long, partially coiled renal tubule

Within Bowman's capsules are a cluster of capillaries called...

a glomerulus

LIst the three main regions of the renal tubule...

� proximal convoluted tubule
� the loop of Henle
� distal convoluted tubule

Trace the path of filtrate through a nephron

� Bowman's capsule
� proximal convoluted tubule
� loop of Henle
� distal convoluted tubule
� collecting duct

The human kidney has two types of nephrons.
Name these...

? cortical nephrons
� more numerous (85% of nephrons)
� relatively small glomeruli
� located almost entirely within the cortex or outer medulla
? juxtamedullary nephrons
� large glomeruli
� long loops of Henle extend deep into the medulla
� contribute to

Trace the path of blood through the kidneys

� Renal artery
� an afferent arteriole
� capillaries of a glomerulus
� an efferent arteriole
� peritubular capillaries
� small veins
� renal veins

Urine is produced in a three step process.
List the steps of this process.

? Filtration
� Glomerulus
? Reabsorption
� convoluted tubules
? Tubular Secretion
� distal convoluted tubule (mostly)

What is the filter flow rate of the kidneys?

About 1200 mL per minute
(About 1/4 the entire cardiac output)
� 45 gallons per day

How much filtered fluid is returned by the kidneys to the bloodstream?


How much urine is produced per day?

about 1.5 L

Describe reabsoption

Wastes remain in urine
Needed substances (such as Glucose and amino acids) are returned to the blood

Urine becomes concentrated as it passes through...

the renal tubule
(particularly: the loop of Henle)

Describe the composition of urine...

? 96% water
? 2.5% nitrogenous wastes (mainly urea)
? 1.5% salts
? traces of other substances (such as bile pigments)

Healthy urine is so sterile...

it has been used to clean battlefield wounds when clean water was not available.

What causes the diaper rash of infants?

When exposed to bacterial action, urine quickly decomposes to form ammonia and other products.
Ammonia causes diaper rash.

ADH is created by the...


ADH is stored and secreted by...

the posterior pituitary

Describe ADH function...

makes the kidney's collecting ducts more permeable to water so that more water is reabsorbed when blood osmolarity rises (i.e. when fluid levels are low).

Aldosterone is secreted by...

the cortex of the adrenal glands

Describe the function of aldosterone...

stimulates the distal convoluted tubules and collecting ducts to increase sodium reabsorption.

Atrial Natriuretic Peptide is produced by...

the heart

Describe the function of ANP

increases sodium exretion and decreases blood pressure.

Trace the Renin-Angiotensin-Aldosterone pathway

? blood volume decreases
? blood pressure decreases
? cells of juxtaglomerular apparatus secrete renin
? renin catalyzes conversion of angiotensinogen to angiotensin I
? ACE catalyzes conversion of angiotensin I to angiotensin II
? Angiotensin II constric

Trace the function of ANP

? Blood volume increases
? Blood pressure increases
? Atria of heart stretched
? atria release ANP
? directly inhibits sodium reabsorption and inhibits aldosterone secretion (which also inhibits sodium reabsorption)
? larger urine volume
? blood volume de