Water Balance & Excretion

9.4 & 9.5

Osmoregulation

• active regulation of the osmotic pressure of bodily fluids and cells

• osmotic pressure = pressure resulting from a difference in solute concentration across a selectively permeable membrane

Osmoregulation

• hyperosmotic

• hypoosmotic

• isoosmotic

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

• wastes are eliminated 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

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

Review Kidney Structure…

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 every 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 (increasing concentration gradient…more water reabsorbed)

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

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

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