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Urinary System
Overall Functions
• Excretion – remove nitrogenous wastes from
blood
• Osmoregulation – maintain proper balance of
ions
• Volume regulation – maintain proper balance
of water
• Regulation of pH
• Detoxify superoxides, free radicals and some
types of drugs.
Why are nitrogenous wastes a
problem?
• Ammonia is a moderately strong base
(elevates blood pH).
• Urea is a weaker base made from ammonia
and carbon dioxide in the liver – less toxic
than ammonia (NH3)
• Uric Acid is a waste produced from the
metabolism of nucleic acids
• Creatinine is a waste product from creatine
metabolism.
The kidneys only comprise about
0.5% of the total body weight, but
they receive 1,200 mL of blood
per minute; about 20% of the
Total cardiac output.
Kidneys are constantly cleaning,
balancing ions and water, and adjusting the
pH of the blood.
Inferior Vena Cava
Renal Vein
Aorta
Renal Artery
Kidney
Ureter
Urinary Bladder
Urethra
Tubule system
(produces urine)
Calyx
(funnel-like
Structure that
Collects urine from
Tubules)
Cortex
Pelvis of the
Kidney
ureter
Medulla
The Nephron is the Functional Unit of the Kidney
Glomerulus
Afferent
Arteriole
Bowman’s
Capsule
Proximal
Convoluted
tubule
Collecting Duct
Efferent
Arteriole
Distal
Convoluted
Tubule
Urine is carried to Calyx,
Pelvis and then the Ureter
Loop of Henle
Functions of the Nephron
1. Filtration
The glomerulus is made of “fenestrated
capillaries” that are unusually permeable.
All of the following substances can easily filter
out of the glomerulus and into Bowman’s
capsule.
water
glucose (and other sugars)
amino acids
small organic molecules
ammonia, urea, uric acid
salts, H+, HCO3
The only substances that are not usually
filtered out are blood cells, proteins and larger
organic molecules.
Notice that several important nutrients are filtered out of the blood during
the filtration process.
Functions of the Nephron
2. Reabsorption
Reabsorption is a process that
1. Utilizes active transport pumps
2. Occurs in the proximal and distal tubules
3. Reclaims nutrients that were lost
during the filtration process.
4. Returns the nutrients to the blood
Examples of reabsorbed substances
1. glucose
2. amino acids
3. NaCl
NOTE: water is reabsorbed passively by
osmosis.
Functions of the Nephron
3. Tubular secretion
Secretion is a process that
1. Utilizes active transport pumps
2. Occurs in the proximal and distal tubules
3. Adds wastes from the blood that were not
effectively filtered at the glomerulus.
4. Increases the concentration of wastes in
the urine
Examples of secreted substances
1. Ammonia, H+ (smaller ionic)
2. histamine, creatinine (larger, organic)
3. penicillin
Glomerular Filtration Rate
The two kidneys produce nearly 45
gallons (180 liters) of filtrate per
day.
Glomerular Filtration Rate (GFR)
depends almost completely on
hydrostatic pressure in the
glomerulus.
* dilation or constriction of
afferent and efferent arterioles.
* overall blood pressure
What happens in exercise when
blood pressure may increase up to
200 mm Hg or more?
During exercise, the sympathetic nervous system comes into play. Symp.
Nerves stimulate the afferent arteriole and it constricts.
Regulation of Na+ Reabsorption
If blood pressure is low for an extended period of time, the kidney
reacts by releasing an enzyme called renin.
Renin is involved in a series of reactions that ultimately lead to the
release of a hormone called Aldosterone from the adrenal gland.
Aldosterone is a steroid that acts on the distal convoluted tubule and
increases the rate of NaCl reabsorption.
As the concentration of NaCl increases in the blood, water is
reabsorbed at a faster rate (osmosis).
With more salt and water in the blood, the volume of blood goes up
and blood pressure goes up.
Impact of diet and strenuous exercise . . . .
Regulation of Urine Volume
coordinate function of Loop of Henle and the Collecting Duct
Na+
Na+
Na+
Na+
Na+
Four Times Saltier
Than the Blood