Download The Kidney

Excretion
 The removal from the body of the waste products of
metabolism
 Includes removal through the lungs, skin, urinary
system and kidney
 Done through osmoregulation
 The maintenance of a proper balance of water and
dissolved substances in the organism
Types of Nitrogenous Waste
Type of Waste
Organism
Advantages
Disadvantages
Ammonia
Fish
Little energy
required
Toxic; must be
removed from the
animal quickly
Urea
Mammals
Medium energy to
produce; only toxic
in abnormal
amounts
Requires water for
dilution and
removal from the
body
Uric acid
Birds
Insoluble and can
be easily stored;
little to no water
required
Requires a lot of
energy to produce
Malpighian Tubes
 Found in insects
 Selectively permeable
 Open in the insects guts
and closed at the other end
 Reabsorption of non-
excess water and nutrients
 Waste and excess water are
released into the gut
 Waste is released with the
feces
Osmoregulators vs
Osmoconformers
 Osmoregulators
 Internal solute concentration is different than the
environment
 Mechanisms are in place to regulate water balance
 High energy cost
 Osmoconformers
 Internal and external solute concentration is almost
identical
 No need to regulate water
 Restricted to one environment
Diagram of the Kidney
The explanation
 Humans have two kidneys near the lower back
 Each kidney has a renal artery leading to it and a renal
vein and ureter leading away from it
 Renal vein removes clean blood from the kidney
 Ureter takes urine to the bladder
Annotated Glomerulus
The explanation
 The functional unit is the
nephron
 Renal artery
 Takes blood to the kidney for
filtration
 Renal vein
 Removes clean blood from
the kidney
 Afferent vessel
 Takes blood to the
glomerulus
 Efferent vessel
 Takes blood away from the
glomerulus
 Vasa recta
 Blood vessels around the
nephron
 Takes away reabsorbed
materials
The explanation
 Glomerulus
 Extensive capillary bed
 Provides ultra-filtration
 Bowman’s capsule
 First part of the nephron
 Receives filtrate from the glomerulus
 Proximal convoluted tubule
 Most reabsorption of glucose, salt,
and water takes place here
 Loop of henle
 Reabsorption of salt
 Reabsorption of water
 Distal convoluted tubule
 Reabsorption of salt
 Collecting duct
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


Reabsorption of urea
Reabsorption of salt
Reabsorption of water
Regulated by ADH
Ultra-filtration
 The fluid of the blood is pushed out of the glomerulus into
the nephron
 The substances that the body doesn’t want to lose (glucose) are
reabsorbed into the blood
 Waste substances (ammonia) are secreted into the filtrate to be
removed by the urine
 Diameter of the afferent vessel is larger than the efferent
vessel
 Puts the blood under high pressure allowing ultra-filtration
 Pushes some of the liquid and small dissolved molecules
into the bowman’s capsule for filtration
 All the blood circulates through the kidney every 5 minutes
and 15%-20% goes through the bowman’s capsule
Reabsorption of water
 Bowman’s capsule
 Where the filtrate of the glomerulus enters the nephron
 Joins the proximal convoluted tubule


Fluid here is similar to plasma
Contains glucose, amino acids, vitamin, hormones, urea, salts and water
 Most of the glucose, amino acids, vitamins, hormones and most salt
and water is reabsorbed here into blood vessels
 Driven by osmosis for water and active transport for everything else
 Has microvilli to increase the surface area for absorption
 Lots of mitochondria to provide energy for active transport
Roles of the different parts
 Loop of Henle
 In the descending loop water is
removed through osmosis
 Some salt diffuses here as well
 The ascending loop is
impermeable to salt and water
 Helps maintain the
concentration gradients
 Medulla
 Concentration gradient is
maintained by a countercurrent
 No direct exchange between the
filtrate and the blood
 Collecting Duct
 Wall is permeable and water can
pass from the ultra-filtrate into
the blood vessels to be carried
away
 ADH
 Anti-diuretic hormone
 Increases the permeability of the
walls of the distal convoluted
tubule and the collecting duct
 Released from the posterior lobe
of the pituitary gland when the
amount of solutes in the blood
is too high
 When absent no water can be
absorbed
Osmoregulation
 The regulation and control
of water balance of the
blood, tissue and
cytoplasm
 Maintains homeostasis
 Evens out:
 The amount of water
ingested
 Sweating
 Ventilation (water is
actually lost while
breathing)
Hydration Levels
Dehydration
Overhydration
Sleepiness
Change in behavior
Constipation
Blurred vision
Dry mouth/skin
Muscle cramps
Dizziness/headache
Nausea/vomiting
The liquids
 Blood plasma
 In the renal artery is rich in oxygen and contains more urea, more
salt and possibly more water than what the body requires
 In the renal vein contains carbon dioxide, less urea and the
optimum amounts of water and salts
 No change in proteins and no glucose
 Glomerular filtrate
 Found in the bowman’s capsule
 Similar to the plasma but no large molecules
 Urine (compared to glomerular filtrate)
 Contains less water, less salt, no glucose, no proteins or amino acids
 Lots of urea
Urine Testing
 Glucose
 In diabetics with insulin deficiency will have higher blood glucose
when it arrives at the kidney
 If the blood glucose is too high it is not all reabsorbed into the
blood and spills out into the urine
 Blood Cells
 Sign of infection or internal bleeding
 Proteins
 Usually too large to fit through the glomerous
 In pregnancy it is a sign of preeclampsia
 Drugs
 Often filtered out into the urine
Kidney Failure
 Dialysis
 External filtration of the blood
 Takes several hours
 Must be done every 1-3 days
 Kidney transplant
 New kidney must have correct protein matches so the
immune system does not attack it
 Possible to live with 1 healthy kidney