The Mammalian Excretory System Principles of Modern Biology II At Wilkes University Kenneth M. Klemow, Ph.D.

The Mammalian Excretory System

Principles of Modern Biology IIAt Wilkes UniversityKenneth M. Klemow, Ph.D.

One problem:

•Mammalian blood contains metabolic waste products that must be removed - without removing useful materials.

http://mdc.mo.gov/kids/out-in/1998/1/back3.jpg

Another problem:

•Terrestrial mammals must maintain a relatively constant osmotic level.

•Living on land promotes desiccation; thus must retain water.•Occasionally we have excess water and must excrete it. http://www.fairfaxcounty.gov/dpwes/

images/recycling/giraffecolor.jpg

The solution

•Mammals have an excretory system that removes waste products and maintains osmotic balance.

Mammalian excretory system

•Kidneys•Ureters•Urinary bladder•Urethra

http://upload.wikimedia.org/wikipedia/commons/thumb/1/18/Illu_urinary_system.jpg/300px-Illu_urinary_system.jpg

The mammalian kidney

•Cortex•Medulla•Renal pelvis•Renal pyramids•Blood vessels

•Renal artery•Renal vein

•Ureterhttp://research.surgery.wisc.edu/southard/organs/kidney.gif

The mammalian kidney

•Have gradient of increasing salinity from cortex to medulla

http://research.surgery.wisc.edu/southard/organs/kidney.gif

Nephron: basic urine-producing unit of kidney

Each kidney contains about one million nephrons

Spans cortex and medulla

Sac with long tube leading to ureter

http://www.bbc.co.uk/scotland/education/bitesize/standard/img/biology/kidney_function1.gif

Nephron consists of five parts:



Bowman’s capsule



Bowman’s capsule

Proximal tubule



Bowman’s capsule

Proximal tubuleLoop of Henle



Bowman’s capsule


Descending branch



Bowman’s capsule


Descending branch

Ascending branch



Bowman’s capsule


Descending branch

Ascending branch

Distal tubule


Also have collecting duct:

Collects urine from distal tubule

Passes through medulla

Discharges to renal pelvis


And blood vessels


And blood vessels

Afferent arteriole


And blood vessels

Afferent arterioleGlomerulus


And blood vessels

Afferent arterioleGlomerulusEfferent arteriole


And blood vessels

Afferent arterioleGlomerulusEfferent arteriolePeritubular

capillaries


Major processes of nephron

FiltrationSecretionReabsorptionExcretion


At the glomerulus

Blood is filtered 2000 L/day

Raw urine passes into capsule space 180 L/day

Remaining blood flows into efferent arteriole

http://coe.fgcu.edu/faculty/greenep/kidney/glomer3.jpg

At the proximal tubule

Useful molecules (sugars, amino acids, bicarbonate, potassium) are resorbed from filtrate into blood

Na+ is resorbed by active transport

Cl- and water follow passively

Urine is iso-osmotic to blood

http://renux.dmed.ed.ac.uk/EdREN/makingimages/NephronS.gif

Making hyperosmotic urine

Concentrated

Making hyperosmotic urineStep 1

In ascending branch, Na+ is resorbed by active transport

Cl- follows passivelyWater stays behindUrine becomes more diluteMedulla tissue becomes

more salty - giving gradient

Na+Cl-



In descending branch, urine enters salty medulla

Water diffuses from tubuleUrine becomes more

concentrated

H2O

H2O



In descending branch, urine enters salty medulla

Water diffuses from tubuleUrine becomes more

concentrated

H2O

H2O

Opposite flow in loop of Henle magnifies saltiness in tissue, giving “Countercurrent Multiplier” effect.


In distal tubule, urine is hypo-osmotic to blood

H+ and K+ are secreted into tubule

Urine becomes more acidic

H+ K+



In collecting duct, watery urine passes through salty medulla.

H2O leaves, assuming antidiuretic hormone (ADH) is present

Urine becomes more concentrated H2O

H2O



In collecting duct, watery urine passes through salty medulla.

H2O leaves, assuming antidiuretic hormone (ADH) is present

Urine becomes more concentrated H2O

H2O

Note: ADH allows us to retain water under normal circumstances

ADH may not be present

Excessively dilute urine or alcohol in blood cuts off flow of ADH from posterior pituitary

Collecting ducts do not resorb water

Watery urine leaves collecting duct


Finally

Sodium concentrations and blood pressure are regulated by hormones aldosterone and atrial natriuretic hormones

See P. 1035-1036 of your text!

http://www.nlm.nih.gov/medlineplus/images/saltshaker.jpg

The Mammalian Excretory System Principles of Modern Biology II At Wilkes University Kenneth M. Klemow, Ph.D.

Documents

medulla http

zbowmans capsule http

blood vessels http

renal pelvis http

mammalian blood

distal tubule zpasses

medulla zsac

medulla zdischarges