OSMOREGULATION AND

EXCRETION

Key Concepts Osmoregulation balances the uptake and loss of

water and solutes An animal’s nitrogenous wastes reflect its

phylogeny and habitat Diverse excretory systems are variations on a

tubular theme Nephrons and associated blood vessels are the

functional units of the mammalian kidney The mammalian kidney’s ability to conserve

water is a key terrestrial adaptation Diverse adaptations of the vertebrate kidney

have evolved in different environments

Key Words homeostasis excretion uric acid filtration renal vein urethra nephron proximal

tubule collecting duct efferent

arteriole antidiuretic

hormone (ADH)

secretion (selective reabsorption)

renal artery urinary

bladder renal medulla Bowman's

capsule distal tubule afferent

arteriole vasa recta

ammonia filtrate ureter renal cortex glomerulus loop of Henle cortical

nephrons peritubular

capillaries aldosterone osmoregulatio

n urea

Types of metabolic waste produced by living systems

1. Digestive waste (elimination)

2. Respiratory waste

3. Excess water and salts (osmoregulation)

4. Nitrogenous waste (excretion)

Osmoregulation

Balance of uptake and loss of water and solutes

Controlled movement of solutes between internal fluids and environment Osmoconformer

(marine animals isoosmotic with environment)

Osmoregulator (freshwater, marine, and terrestrial animals that adjust internal osmolarity)

Types of nitrogenous wastes

Deamination – protein and nucleic acid metabolism

Three main types differing in terms of:1. Toxicity2. Amount of water

needed for excretion

3. Energy needed for synthesis

300 – 500 mL/gN

1 step rxn

50 mL/gN4 step

rxn

10 mL/gN15 step

rxn

Type of Organism

Structure Product of

excretion

Other features

Plants

Stomata, lenticels for gas exchange Insoluble

crystals Crystals are kept inside plant cells

Cnidarians and

echinoderms

No excretory organ-

Osmoconformers, isoosmotic with environment

Freshwater protists, sponges

Contractile vacuole Porocytes and flagella

Excretory Systems Dispose of metabolic wastes Regulate solute concentrations in

the body Transport epithelia arranged in

tubes 4 major processes

1. Filtration, pressure-filtering of body fluids producing a filtrate (water, salts, sugars, amino acids, N-wastes)

2. Reabsorption, reclaiming valuable solutes (glucose, salts, amino acids) from the filtrate

3. Secretion, addition of larger molecules like toxins and other excess solutes from the body fluids to the filtrate

4. Excretion, the filtrate leaves the system

Flatworms Flame cells

Unsegmented roundworms

Protonephridia, closed network of dead-end tubes lacking openings

Annelids

Metanephridia, open-ended network of tubes with internal openings that collect body fluids

Type of Organism

Structure Product of

excretion

Other features

MolluscsMetanephridia

Crustaceans

Antennal/green gland

Insects

Malpighian tubules and digestive tract

Uric acid

Type of Organism

Structure Product of

excretion

Other features

Marine fishes Gills for

osmoregulation, kidneys

Ammonia

Elasmobranchs (sharks,

skates, rays)

Kidneys Urea

Rectal glands – excrete excess NaCl

Freshwater fishesGills for

osmoregulation, kidneys

Ammonia or urea

Amphibians and mammals

Kidneys UreaLiver converts ammonia to urea

Reptiles and birds

Kidneys Uric acid Salt glands

Type of Organism

Structure Product of

excretion

Other features

From Blood Filtrate to

Urine: A Closer Look

Two solutes: NaCl and urea, contribute to the osmolarity of the interstitial fluid

Cause the reabsorption of water in the kidney and concentrates the urine

Nervous system and hormones regulate kidney functions

Antidiuretic hormone (ADH)

Stimulated by a rise in the blood’s osmolarity (>300 mosm/L)

Enhances fluid retention by making the kidneys reclaim more water

Increases water reabsorption in the distal tubules and collecting ducts of the kidney

The renin-angiotensin-aldosterone system (RAAS) Responds to a loss of salt

and water in the blood Stimulated by low blood

volume or pressure Increases water and

sodium ion reabsorption in the proximal and distal tubules

Leads to an increase in blood volume and pressure

Opposed by the hormone atrial natriuretic factor (ANF)

Released by atria Inhibits release of

renin

Some medical aspects concerning the excretory system

Urinary tract infection (UTI) bacterial infection cystitis/pyelonephritis treated by antibiotics and prevented

through proper hygiene

Kidney stones solidified crystals in kidneys or ureters

Calcium oxalate Uric acid

nephrolithiasis/urolithiasis prevention:

Drinking adequate water Proper diet low in protein, N, and Na Avoid excess Vitamin C intake

Dialysis Hemodialysis Peritoneal dialysis