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 osmoregulation urea

Types of metabolic waste produced by living systems

1. Digestive waste2. Respiratory

waste3. Excess water and

salts (through osmoregulation)

4. Nitrogenous waste (through 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/gN1 step rxn

50 mL/gN4 step rxn

10 mL/gN15 step rxn

Type of Organism

Structure Product of excretion

Other features

Plants

Stomata, lenticels Insoluble crystals

Crystals are kept inside plant cells

Cnidarians and echinoderms

No excretory organ -

Osmoconformers, isoosmotic with

environment

Freshwater protists and sponges

Contractile vacuole

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

MolluscsNephridia or metaphridia

Crustaceans Antennal/green gland

InsectsMalpighian tubules and

digestive tractUric acid

Type of Organism

Structure Product of

excretion

Other features

Marine fishes Gills Ammonia

Elasmobranchs (sharks, skates,

rays)Kidneys Urea

Rectal glands – excrete excess NaCl

Freshwater fishes Gills 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

Proximal tubule – secretion and reabsorption

Filtrate

H2OSalts (NaCl and others)HCO3

–

H+

UreaGlucose; amino acidsSome drugs>> Same concentration of substances in blood plasma

Key

Active transport

Passive transport

CORTEX

OUTERMEDULLA

INNERMEDULLA

Descending limbof loop ofHenle – reabsorption-Permeable to water but not to salt

Thick segmentof ascendinglimb – reabsorption- Impermeable to water but permeable to salt

Thin segmentof ascendinglimb

CollectingDuct – permeable to water but not to salt, bottom portion is permeable to urea

NaCl

NaCl

NaCl

Distal tubule – secretion and reabsorption

NaCl Nutrients

Urea

H2O

NaCl

H2O

H2OHCO3 K+

H+ NH3

HCO3

K+ H+

H2O

1 4

32

3 5

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

H2O

H2O

H2O

H2O

H2O

H2O

H2O

NaCl

NaCl

NaCl

NaCl

NaCl

NaCl

NaCl

300

300 100

400

600

900

1200

700

400

200

100

Activetransport

Passivetransport

OUTERMEDULLA

INNERMEDULLA

CORTEX

H2O

Urea

H2O

Urea

H2O

Urea

H2O

H2O

H2O

H2O

1200

1200

900

600

400

300

600

400

300

Osmolarity of interstitial

fluid(mosm/L)

300

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

Osmoreceptorsin hypothalamus

Drinking reducesblood osmolarity

to set point

H2O reab-sorption helpsprevent further

osmolarity increase

STIMULUS:The release of ADH istriggered when osmo-receptor cells in the

hypothalamus detect anincrease in the osmolarity

of the blood

Homeostasis:Blood osmolarity

Hypothalamus

ADH

Pituitarygland

Increasedpermeability

Thirst

Collecting duct

Distaltubule

Increased Na+

and H2O reab-sorption in

distal tubules

Homeostasis:Blood pressure,

volume

STIMULUS:The juxtaglomerular

apparatus (JGA) respondsto low blood volume or

blood pressure (such as dueto dehydration or loss of

blood)

Aldosterone

Adrenal gland

Angiotensin II

Angiotensinogen

Reninproduction

Renin

Arterioleconstriction

Distal tubule

JGA

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