1. Osmoregulation and Excretion

2. 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

3. Key Words homeostasis excretion uric acid filtration renal vein
urethra
nephron
proximal tubule
collecting duct
efferent arteriole
antidiuretic hormone (ADH)
ammonia
filtrate
ureter
renal cortex
glomerulus
loop of Henle
cortical nephrons
peritubular capillaries
aldosterone
osmoregulation
urea
secretion (selective reabsorption)
renal artery
urinary bladder
renal medulla
Bowman's capsule
distal tubule
afferent arteriole
vasa recta

4. Types of metabolic waste produced by living systems
Digestive waste (elimination)
Respiratory waste
Excess water and salts (through osmoregulation)
Nitrogenous waste (through excretion)

5. 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)

6. Types of nitrogenous wastes
Deamination – protein and nucleic acid metabolism
Three main types differing in terms of:
Toxicity
Amount of water needed for excretion
Energy needed for synthesis
300 – 500 mL/gN
1 step rxn
50 mL/gN
4 step rxn
10 mL/gN
15 step rxn

7. 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 and sponges
Contractile vacuole
Porocytes and flagella

8. Excretory Systems Dispose of metabolic wastes
Regulate solute concentrations in the body
Transport epithelia arranged in tubes
4 major processes
Filtration, pressure-filtering of body fluids producing a filtrate (water, salts, sugars, amino acids, N-wastes)
Reabsorption, reclaiming valuable solutes (glucose, salts, amino acids) from the filtrate
Secretion, addition of larger molecules like toxins and other excess solutes from the body fluids to the filtrate
Excretion, the filtrate leaves the system

9. Type of Organism Structure Product of excretion Other features
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

10. Malpighian tubules and digestive tract
Type of Organism
Structure
Product of excretion
Other features
Molluscs
Metanephridia
Crustaceans
Antennal/green gland
Insects
Malpighian tubules and digestive tract
Uric acid

11. 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 fishes
Ammonia or urea
Amphibians and mammals
Liver converts ammonia to urea
Reptiles and birds
Uric acid
Salt glands

13. From Blood Filtrate to Urine: A Closer Look
Proximal tubule – secretion and reabsorption
Filtrate
H2O
Salts (NaCl and others)
HCO3– H+
Urea
Glucose; amino acids
Some drugs
>> Same concentration of
substances in blood plasma
Key
Active transport
Passive transport
CORTEX
OUTER
MEDULLA
INNER
Descending limb
of loop of
Henle – reabsorption
Permeable to water but not to salt
Thick segment
of ascending
limb – reabsorption
- Impermeable to water but permeable to salt
Thin segment
limb
Collecting
Duct – permeable to water
and salt, bottom portion is permeable to urea
NaCl
Distal tubule – secretion and reabsorption
Nutrients
HCO3 K+
NH3 1 4 3 2 5

14. Osmolarity of interstitial fluid (mosm/L)
H2O
NaCl
300
100
400
600
900
1200
700
200
Active transport
Passive transport
OUTER MEDULLA
INNER MEDULLA
CORTEX
Urea
Osmolarity of interstitial fluid (mosm/L)
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

15. Nervous system and hormones regulate kidney functions
Osmoreceptors
in hypothalamus
Drinking reduces
blood osmolarity
to set point
H2O reab-
sorption helps
prevent further
osmolarity
increase
STIMULUS:
The release of ADH is
triggered when osmo-
receptor cells in the
hypothalamus detect an
increase in the osmolarity
of the blood
Homeostasis:
Blood osmolarity
Hypothalamus
ADH
Pituitary
gland
Increased
permeability
Thirst
Collecting duct
Distal
tubule
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

16. The renin-angiotensin- aldosterone system (RAAS)
Increased Na+
and H2O reab-
sorption in
distal tubules
Homeostasis:
Blood pressure,
volume
STIMULUS:
The juxtaglomerular
apparatus (JGA) responds
to low blood volume or
blood pressure (such as due
to dehydration or loss of
blood)
Aldosterone
Adrenal gland
Angiotensin II
Angiotensinogen
Renin
production
Arteriole
constriction
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

17. 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