Chapter 41: Osmotic Regulation and Excretion

Osmoregulation

The process of maintaining salt and water balance (osmotic balance) across membranes within body fluids

What happens to cells placed in a hypertonic environment?

They tend to shrink due to the loss of water.

What happens to cells placed in a hypotonic environment?

They tend to swell due to the intake of water.

Osmoregulators

Actively maintain internal osmotic balance at an energy cost

Osmoconformers

Maintain an internal environment that is isotonic to their external environment, expending less energy

What are the three ways water can enter an animal's body?

Drinking, food consumption, and metabolism.

How do cartilaginous fishes (like sharks) achieve isotonicity with seawater?

They maintain high concentrations of urea in their blood to match the tonicity of the sea water.

Glomerulus

Proximal covered tubule*  

The filtrate after this point flows into a collecting duct*, eventually, urine moves through the ureter, urinary duct, and urethra

A part of the nephron that is a tuft of capillaries

Bowman's capsule

The initial site of blood filtration in the nephron, surrounding the glomerulus to collect filtrate (water, ions, waste) while retaining blood cells and large proteins

Renal corpuscle

Part of the nephron that is the glomerulus + bowman's capsule

Proximal covered tubule

Part of the nephron that extends off of the bowman's capsule

Collecting duct

The filtrate in the nephron eventually flows into this

What are the three distinct processes of urine formation?

Glomerular filtration, tubular reabsorption, and tubular secretion.

What is the function of Antidiuretic Hormone (ADH) in the kidneys?

It plays a key role in water reabsorption and is released by the posterior pituitary gland.

Name three types of excretory organs found in invertebrates.

Flame cells (planarians), nephridia (earthworms), and Malpighian tubules (insects).

How do terrestrial animals reduce water loss during nitrogen excretion?

By converting ammonia into relatively insoluble uric acid, which requires less water to excrete.

How is blood pH regulated in the kidneys?

By the reabsorption of bicarbonate ions or the secretion of hydrogen ions

Hemodialysis

The clinical purification of blood by dialysis, acting as a substitute for normal kidney function

Ammonia

The primary nitrogenous waste product resulting from the catabolism of amino acids and nucleic acids

Why can aquatic animals excrete ammonia directly?

Because ammonia is highly soluble in water, allowing it to be easily diluted and excreted.

The three layers/regions of the human kidney

Renal cortex (outer), renal medulla (middle), and renal pelvis (innermost).

What is the role of the renal medulla in urine concentration?

It maintains an osmotic gradient that causes water to leave the descending limb of the loop of the nephron.

Antidiuretic hormone (ADH)

A hormone that influences the absorption of water by kidney tubules

Where is ADH produced?

The posterior lobe of the pituitary gland in the brain

Ureter

Conducts urine from the kidney to the urinary bladder.

Urethra

The tube that carries urine from the bladder to the outside of the body.

The first process of urine production

Glomerular filtration(in the glomerular capsule)

The second process of urine production

Tubular reabsorption(at the proximal convoluted tubule)

The third process of urine production

Tubular secretion(at the distal convoluted tubule)

Why do terrestrial animals often need to drink more water than aquatic animals?

Because they lose water through respiration and the excretion of nitrogenous wastes like urea.

What is the benefit of excreting uric acid for birds and reptiles?

It allows them to inhabit drier environments far from standing water because it requires very little water to excrete.