Download Excretion Lecture 1

Excretory System!
New Song!
 https://www.youtube.com/watch?v=K3Z-Lt58H0s
Homeostasis
 Excretory system maintains homeostasis by balancing
the amount of water, salt, and metabolite
concentrations within the blood.
Not just the Kidney’s!
 Lungs: Remove CO2
 Skin: Removes heat
 Liver: Removes metabolic wastes and creates bile and
urea
 Kidney: Removes metabolic wastes
Mammalian Kidney
inferior
vena cava
aorta
adrenal gland
kidney
nephron
ureter
bladder
urethra
renal vein
& artery
microvilli on
epithelial
cells
 http://handsonscience.jimdo.com/online-games-andactivities/unit-4-breathing-circulation-and-excretion/
Mastering biology
 http://www.youtube.com/watch?v=8UVlXX-9x7Q
Mammalian System
blood
filtrate
 Filter solutes out of blood & reabsorb
H2O + desirable solutes
 Key functions
 filtration
 fluids (water & solutes) filtered out
of blood
 reabsorption
 selectively reabsorb (diffusion) needed
water + solutes back to blood
 secretion
 pump out any other unwanted solutes to
urine
 excretion
 expel concentrated urine (N waste +
solutes + toxins) from body
concentrated
urine
Nephron
 Functional units of kidney

1 million nephrons
per kidney
 Function


filter out urea & other
solutes (salt, sugar…)
blood plasma filtered
into nephron
 high pressure flow

selective reabsorption of
valuable solutes & H2O
back into bloodstream
 greater flexibility & control
why
selective reabsorption
& not selective
filtration?
“counter current
exchange system”
How can
different sections
allow the diffusion
of different
molecules?
Mammalian kidney
 Interaction of circulatory &
excretory systems
 Circulatory system
Bowman’s
 glomerulus =
ball of capillaries
capsule
Proximal
tubule
Distal
tubule
Glomerulus
 Excretory system
 nephron
 Bowman’s capsule
 loop of Henle




proximal tubule
descending limb
ascending limb
distal tubule
 collecting duct
Glucose
Amino
acids
H2O
Mg++ Ca++
H2O
Na+ ClH2O
H2O
Na+ Cl-
H2O
H2O
Loop of Henle
Collecting
duct
Nephron: Filtration
 At glomerulus
 filtered out of blood
H2O
&
solutes




H2O
glucose
salts / ions (Na+ / Cl–)
urea
 not filtered out
cells &
large
molecules
 cells
 proteins
high blood pressure in kidneys
force to push (filter) H2O & solutes out
of blood vessel
BIG problems when you start out with
high blood pressure in system
hypertension = kidney damage
Nephron: Re-absorption
 Proximal tubule
 reabsorbed back into blood
 NaCl
 active transport
of Na+
 Cl– follows
by diffusion
 H2O
 glucose
 HCO3-
 bicarbonate
 buffer for
blood pH
Nephron: Re-absorption
 Loop of Henle
descending limb
 reabsorbed
 H2O
 structure

 many aquaporins in
cell membranes
 high permeability
to H2O
 no Na+ or Cl– channels
 impermeable
to salt
structure fits
function!
Nephron: Re-absorption
 Loop of Henle
ascending limb
 reabsorbed
 Na+ & Cl–
 structure

 many Na+ / Cl– channels in cell
membranes
 high permeability
to Na+ & Cl–
 no aquaporins
 impermeable to H2O
structure fits
function!
Nephron: Re-absorption
 Distal tubule

reabsorbed
 salts
 H2 O
 bicarbonate
 HCO3 regulate blood pH
Nephron: Reabsorption & Excretion
 Collecting duct

reabsorbed
 H2O = through aquaporins

excretion
 concentrated urine
 to bladder
 impermeable lining
= no channels in cell
membranes
Osmotic control in nephron
 How is all this re-absorption achieved?
 tight osmotic
control to reduce
the energy cost
of excretion
 use diffusion
instead of
active transport
wherever possible
the value of a
counter current
exchange system
why
selective reabsorption
& not selective
filtration?
Summary
 Not filtered out of blood
 cells
 proteins
 remain in blood (too big)
 Reabsorbed back to blood: active transport
 Na+
 glucose

amino acids
 Reabsorbed back to blood: diffusion
 H2O

Cl–
 Excreted out of body
 urea
 excess H2O
 excess solutes (glucose, salts)
 toxins, drugs, “unknowns”