Osmoregulation:

The process of maintaining an internal balance of water and solutes, which is vital for cell function and homeostasis

Excretion:

The elimination of metabolic waste products from the body, helping to regulate water and solute levels

Why are nitrogenous wastes associated with nucleic acids and proteins, but not with lipids or
carbohydrates

• Nitrogenous wastes are byproducts of the metabolism of proteins and nucleic acids, which contain nitrogen. Lipids and carbohydrates don’t produce nitrogenous waste because they lack nitrogen in their molecular structures.

Explain water movement in an isoosmotic condition. When two solutions separated by a
membrane differ in osmolarity, in which direction does water flow?

In an isoosmotic condition, water movement across a membrane is balanced, with no net gain or loss of water on either side. When solutions differ in osmolarity, water flows from the hypoosmotic (lower solute concentration) to the hyperosmotic (higher solute concentration) side

An animal can maintain water balance in two ways. Explain the difference between
osmoconformers and osmoregulators

• Osmoconformers match their internal osmolarity with their environment, common in many marine animals.
• Osmoregulators actively control their internal osmolarity, common in freshwater and terrestrial animals.

explain osmoregulation in saltwater (marine) and freshwater fish.

• Saltwater fish lose water to their salty environment and must drink seawater, excreting excess salts through gills and small amounts of urine.
• Freshwater fish gain water and lose salts, so they excrete large amounts of dilute urine and take up salts through their gills.

Why do many organisms have a body fluid composition adapted to the salinity of their
environment?

Many organisms adapt their body fluid composition to the salinity of their environment to reduce energy use in osmoregulation, as maintaining homeostasis requires less energy when body fluids closely match the environment.

explain why an albatross can
consistently drink seawater and still maintain homeostasis but a human cannot

Albatrosses use countercurrent flow in salt glands to excrete excess salts, enabling them to drink seawater. Humans lack this efficient salt-excreting adaptation, so seawater consumption would disrupt human electrolyte balance

What are the three forms in which animals excrete nitrogenous wastes?

ammonia , urea, uric acid

Ammonia

Highly toxic, excreted by aquatic animals fish, where it’s diluted.

Urea

Less toxic, used by terrestrial animals, allowing for water conservation.

Uric acid

Least toxic, excreted by birds and reptiles to conserve water, especially beneficial for egg-laying species.

Why do many egg-laying animals excrete uric acid as their nitrogenous waste?

Uric acid’s low toxicity and water insolubility make it suitable for egg-laying animals, where it can accumulate without harming the developing embryo.

Explain why endotherms produce more nitrogenous waste than ectotherms, and why predators excrete more than herbivores.

• Endotherms have higher metabolic rates, producing more nitrogenous waste. Predators, consuming protein-rich diets, excrete more waste than herbivores.

Filtration

Blood plasma is filtered into the excretory tubule.

Reabsorption

Valuable solutes and water are reabsorbed into the blood.

Secretion

Additional waste substances are added to the filtrate.

Excretion

The remaining filtrate (urine) is expelled.

Protonephridia

Network of tubules for filtration in flatworms Flatworms

Metanephridia

Tubules in segmented worms for filtration Earthworms

Malpighian tubules

Remove waste and conserve water in insects Insects

Kidneys

Complex filtering organs in vertebrates Mammals, reptiles

Mammalian Kidney Anatomy

The mammalian kidney includes excretory organs (renal cortex, renal medulla, nephrons) and blood vessels (renal artery, renal vein).

Kidney

Filters blood, produces urine.

Ureters

Transport urine from kidneys to bladder.

Bladder

Stores urine.

Urethra

Expels urine.

Nephron

The functional unit of the kidney, where filtration occurs.

What is the functional difference between a cortical nephron and a juxtamedullary nephron?

• Cortical nephrons are mainly in the renal cortex, involved in general filtration.
• Juxtamedullary nephrons extend deep into the medulla, concentrating urine.

The first step of excretion is filtration. Carefully read the information accompanying the
figure of a nephron on p. 987. Describe how filtration occurs

Blood pressure forces plasma into Bowman’s capsule, filtering out large molecules and cells, retaining only small molecules and ions

Processing Blood Filtrate

As blood filtrate passes through each nephron region, processes like reabsorption and secretion refine urine composition and concentration.

Filtration

Glomerulus, Blood filtered into nephron

Reabsorption

Proximal tubule, Reclaims valuable solutes

Secretion

Distal tubule, Adds waste to filtrate

Excretion

Collecting duct, Final urine exits to ureter

Countercurrent Multiplier System

This system in the loop of Henle allows for water reabsorption and urine concentration by creating a gradient, reducing water loss

Explain how urine can be isoosmotic to the inner medulla’s interstitial fluid but hyperosmotic
to blood and interstitial fluid elsewhere in the body

Urine can be isoosmotic to the medullary interstitial fluid but hyperosmotic to blood due to concentrated solutes in the medulla, enhancing water reabsorption.

Among mammals, differences in nephron structure have evolved that reflect the habitat of the
species. Explain why the loops of Henle of desert mammals are very long, whereas those of
beavers are very short

Desert mammals have longer loops of Henle to maximize water reabsorption, while aquatic mammals like beavers have shorter loops, as they don’t face water scarcity.

explain the general, systemic role of antidiuretic hormone (ADH) in
maintaining blood osmolarity

ADH helps maintain blood osmolarity by increasing water reabsorption in the kidneys, thus concentrating urine when hydration is low.

What type of feedback regulation is illustrated in the preceding question?

• ADH operates through negative feedback, responding to blood osmolarity changes to maintain stable water balance.