Water Balance & Excretion
9.4 & 9.5
Osmoregulation
• process of actively regulating the osmotic pressure of bodily fluids and cells
• hyperosmotic (hypertonic)
• hypoosmotic (hypotonic)
• isoosmotic (isotonic)
Homework: p.445
#11. Explain the difference between the terms “hypertonic” and “hyperosmotic”.
Unicellular Organisms
• water balance is often maintained by contractile vacuoles
• video of Paramecium:
http://www.youtube.com/watch?v=mTXRcbjuYGU
Excretion
• eliminating waste is important for all living organisms
Types of Waste
• Our bodies eliminate wastes through various organs:
• lungs (CO2)
• large intestine (solid wastes)
• liver (transforms toxins for removal)
• kidneys (soluble wastes)
Nitrogenous Wastes
• mostly from deamination
• animals that live in water can remove ammonia with lots of water
• mammals, some reptiles, most amphibians form urea
• birds and some invertebrates produce uric acid
Homework: p.445
#4. Explain the advantages & disadvantages for terrestrial animals of creating urea rather than other forms of nitrogenous waste.
#5. Why is it an advantage for birds to create uric acid as their nitrogenous waste compound? (Think of flight.)
Human Excretory System
Renal Blood Flow)
• blood is brought to the kidneys by the renal arteries
• filtered blood leaves the kidneys through the renal veins
The Urinary System
• kidneys can hold up to 25% of the body’s blood at a time
• kidneys filter the blood
• urine (with wastes and toxins) is conducted to the bladder through the ureters
Kidney Structure
Basic structure:• cortex• medulla• renal pelvis
Kidney Kiwi
Kidney Kiwi Dissection
Nephron
• the functional unit of the kidney is the nephron
• there are about 1 million nephrons in each kidney
Other links…
• Khan academy…this video starts off with the structure of the kidney & nephron, then goes into detail about the formation of urine (covered in 9.5)
• http://www.khanacademy.org/video/the-kidney-and-nephron?playlist=Biology
How is urine formed?
Urine Formation
• filtration
• reabsorption
• secretion
• Simple overview of urine formation:• http://www.pennmedicine.org/encyclopedia/em_DisplayAnimatio
n.aspx?gcid=000136&ptid=17
Filtration
• higher blood pressure in glomerulus• water, ions, smaller dissolved molecules
(glucose, amino acids, urea) can move through the walls of the glomerulus
• your kidneys filter your entire blood plasma 65 times a day
Reabsorption
• ion pumps reabsorb Na+, K+, Cl- (active)
• active transport proteins reabsorb amino acids, glucose
• filtrate becomes hypoosmotic to interstitial fluid, so water is reabsorbed by osmosis and through aquaporins
Where?
• a lot of reabsorption occurs in the proximal convoluted tubule
• filtrate with high concentration of urea and other wastes enters loop of Henle and then distal convoluted tubule:– more water and ions (Na+& Cl-)are
reabsorbed
Where (cont’d)?
• collecting ducts are permeable to water but not salt ions, so more water is reabsorbed
• at bottom of medulla, urea is reabsorbed through passive urea transporters
Secretion
• H+ ions (active) to adjust blood pH (HCO3
- is also reabsorbed to balance)• products of detoxified poisons (passive)• water-soluble drugs (passive)• nitrogen-containing wastes (such as
small amounts of NH3)• in the proximal and distal convoluted
tubules
Animations
• Narrated animation on urine formation; good amount of detail:
• http://davisplus.fadavis.com/scanlon6e/Animations/animations.cfm?exercise=NephronFiltration&title=Nephron%20Filtration
• Narrated animation of structure & function; quite detailed:
• http://bcs.whfreeman.com/thelifewire/content/chp51/51020.html
Kidney Disorders
Urinalysis
• can be used to detect many metabolic and kidney disorders as well as urinary tract infections
• urine can be assessed using a dipstick or at a laboratory
Multiple Test Dipstick
Diabetes Mellitus
• Type 1 - body cannot produce insulin
• Type 2 - cells fail to use insulin properly
• gestational - hormones of pregnancy interfere with action of insulin
• urinalysis would show high levels of glucose (and greater volumes of urine)
Kidney Stones
• caused by precipitation of minerals, can be alkaline or acidic
• VERY painful
Kidney Stones - Treatment
• time…• lithotripsy (shock-
wave therapy)• ureteroscopy (and
placement of stent or surgical removal of stone)
Dialysis
• for low-functioning kidneys, dialysis machine can filter blood
Homework: p.454
#2. What may be the reasons that the body normally uses two kidneys?
#3. Describe the flow of blood into and out of the kidneys. Compare the contents of the blood when entering and exiting the kidneys.
#9. What would be the result on the body if Na+, K+, and Cl- were not reabsorbed in the kidneys?