1. Chapter 44 – Osmoregulation and Excretion

2. Homeostasis 2 key homeostatic processes:
Osmoregulation – how animals regulate their solute concentrations and balance the gain and loss of water
Excretion – how animals get rid of the nitrogen-containing waste products of metabolism

3. Osmotic Challenges: Aquatic
Osmoconformer: no active adjustment of internal osmolarity (marine animals); isoosmotic to environment, no tendency to lose or gain water, expend little energy
Osmoregulator: adjust internal osmolarity because body fluids are not isoosmotic (freshwater, marine, terrestrial); costs energy
Marine fishes (hyperosmotic)- keep water, lose salt; excretes large amounts of urine salt
Freshwater fishes (hypoosmotic)- lose water, keep salt; drinks large amount of water

4. Osmotic Challenges: Terrestrial
Terrestrial organisms must also regulate their water levels
Adaptations include:
Waxy cuticle in plants
Shells of land snails
Waxy layers of insect exoskeleton
Layers of dead skin
Being nocturnal
Most lose water from moist surface areas of gas exchange, urine, feces, and skin
Must gain water from diet or through metabolism

5. Nitrogenous Wastes
Nitrogenous wastes: breakdown products of proteins and nucleic acids; can be very toxic
Ammonia (NH3): very toxic; most aquatic animals, many fish
Urea: lower toxicity; mammals, most amphibians, sharks, bony fish (in liver; combo of NH3 and CO2)
Uric acid: lower toxicity, paste-like, little water loss; birds, insects, many reptiles, land snails

6. Excretory Process
Filtration – excretory tubule collects a filtrate from blood, water and solutes forced into excretory tubule
Reabsorption – transport epithelium reclaims valuable substances from filtrate
Secretion – waste substances, toxins and excess ions, are extracted from body fluids and are added to the filtrate
Excretion – filtrate leaves the system and the body

7. Excretory Systems Protonephridia – flatworms (“flame-bulb” systems)
Metanephridia – annelids (ciliated funnel system)
Malpighian tubules – insects (tubes in digestive tract)
Kidneys – vertebrates

8. Mammal Excretory System
Renal artery/vein: kidney blood flow
Ureter: urine excretory duct
Urinary bladder: urine storage
Urethra: urine elimination tube
Renal cortex (outer region)
Renal medulla (inner region)
Nephron: functional unit of kidney, approx. 1 million per kidney)
Cortical nephrons (confined to renal cortex; 80%)
Juxtamedullary nephrons (extend into renal medulla; 20%; only in mammals and birds, important in water conservation – hyperosmotic urine)

9. Nephron Structure
Afferent arteriole: supplies blood to nephron from renal artery
Glomerulus: ball of capillaries
Efferent arteriole: blood from glomerulus
Bowman’s capsule: surrounds glomerulus
Proximal tubule: secretion & reabsorption
Peritubular capillaries: from efferent arteriole; surround proximal & distal tubules
Loop of Henle: water & salt balance
Distal tubule: secretion & reabsorption
Collecting duct: carries filtrate to renal pelvis

10. Basic Nephron Function

11. Proximal Tubule, Loop of Henle, Distal Tubule
PT – reabsorb HCO3-, NaCl, water, nutrients, and K+ ions; secrete H+ and NH3
Decending L of H – reabsorb water
Ascending L of H – reabsorb NaCl
DT – reabsorb NaCl, water, and HCO3-; secrete K + and H +

12. Collecting Duct
Carries filtrate through the medulla to the renal pelvis
Reabsorbs NaCl, urea, and water

13. Water Conservation in Kidney
Creates hyperosmotic urine
Conserves water through both active and passive processes
Review

14. Kidney regulation: hormones
Antidiuretic hormone (ADH) ~ secretion increases permeability of distal tubules and collecting ducts to water (H2O back to body); inhibited by alcohol and coffee
Juxtaglomerular apparatus (JGA) ~ reduced salt intake--->enzyme renin initiates conversion of angiotensinogen to angiotensin II increase blood pressure and blood volume by constricting capillaries
Angiotensin II also stimulates adrenal glands to secrete aldosterone; acts on distal tubules to reabsorb more sodium, thereby increasing blood pressure (renin-angiotension-aldosterone system; RAAS)
Atrial natriuretic factor (ANF) ~ walls of atria; inhibits release of renin, salt reabsorption, and aldosterone release