the urinary system removing waste, balancing blood ph, and maintaining water balance
TRANSCRIPT
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The Urinary System
Removing waste, balancing blood pH, and maintaining water balance
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The Importance of Removing Wastes
• The cells of the body obtain energy by converting complex organic compounds into simpler compounds.
• Many of these simpler compounds can be harmful and must be eliminated
• The lungs eliminate carbon dioxide • The large intestine removes toxic wastes from
the digestive system
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Removing Waste
• The liver transforms ingested toxins, such as alcohol and heavy metals, and the hazardous products of protein metabolism into soluble compounds that can be eliminated by the kidneys
• The kidneys play a crucial role in removing waste, balancing blood pH, and maintaining water balance
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Metabolic Waste
• When protein is used for energy, it is deaminated before it can enter the Krebs cycle
• The byproduct of deamination is ammonia• Ammonia is extremely toxic— a buildup of as
little as 0.005 mg can kill humans • In the liver, two molecules of ammonia combine
with carbon dioxide, to form urea.• Urea is 100 000 times less toxic than ammonia.
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The Kidney
• Renal arteries branch from the aorta and carry blood to the kidneys.
• Mass: about 0.5 kg• May hold as much as 25%
of the body’s blood at any given time.
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The Urinary System
• Wastes are filtered from the blood and conducted to the urinary bladder by ureters.
• A urinary sphincter muscle located at the base of the bladder acts as a valve, permitting the storage of urine.
• Urine is voided through the urethra
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• http://www.dnatube.com/video/2754/Function-of-the-Nephron
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Structure of the Kidney• The cross section of the
kidney reveals three structures:– An outer layer of connective
tissue: the cortex– An inner layer: the medulla, – A hollow chamber: the renal
pelvis, joins the kidney with the ureter
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Nephrons• Approximately one million
slender tubules, called nephrons, are the functional units of the kidneys
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Parts of the Nephron• Afferent arterioles: small
branches that carry blood to the glomerulus
• Glomerulus: high-pressure capillary bed that is the site of filtration
• Efferent arterioles: small branches that carry blood away from the glomerulus to a capillary net
• Peritubular capillaries: network of small blood vessels that surround the nephron
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Parts of a Nephron• Bowman’s capsule:
cuplike structure that surrounds the glomerulus
• Proximal tubule: section of the nephron joining the Bowman’s capsule with the loop of Henle
• Loop of Henle: carries filtrate from the proximal tubule to the distal tubule
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Parts of the Nephron
• Distal tubule: conducts urine from the loop of Henle to the collecting duct
• Collecting duct: tube that carries urine from nephrons to the pelvis of a kidney
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Nephron
• Small branches from the renal artery, the afferent arterioles, supply the nephrons with blood.
• The afferent arterioles branch into a capillary bed, called the glomerulus.
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Nephrons• Blood leaves the
glomerulus by way of the efferent arterioles.
• Blood is carried from the efferent arterioles to a net of capillaries called peritubular capillaries that wrap around the kidney tubule.
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The Nephron
• The glomerulus is surrounded by a funnel-like part of the nephron, called the Bowman’s capsule.
• The Bowman’s capsule, the afferent arteriole, and the efferent arteriole are located in the cortex of the kidney.
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The Nephron
• Fluids to be processed into urine enter the Bowman’s capsule from the blood.
• The capsule tapers to a thin tubule, called the proximal tubule.
• Urine is carried from the proximal tubule to the loop of Henle, which descends into the medulla of the kidney.
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The Nephron
• Urine moves through the distal tubule, the last segment of the nephron, and into the collecting ducts.
• As the name suggests, the collecting ducts collect urine from many nephrons that, in turn, merge in the pelvis of the kidney.
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Nephrons
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The Formation of Urine
• Urine formation depends on three functions:– Filtration – Reabsorption – Secretion
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Filtration• Each nephron of the kidney has an
independent blood supply• Blood moves through the afferent arteriole into
the glomerulus which is a high-pressure filter.• Normally, pressure in a capillary bed is about
25 mm Hg • The pressure in the glomerulus is about 65 mm
Hg
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Filtration
• Dissolved solutes and water pass through the walls of the glomerulus into the Bowman’s capsule.
• Plasma protein, blood cells, and platelets are too large to move through the walls of the glomerulus.
• Smaller molecules such as Na+ , H+ glucose, amino acids, vitamins, minerals, urea, and uric acid pass through the cell membranes and enter the nephron.
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Reabsorption
• On average, about 600 mL of fluid flows through the kidneys every minute.
• Approximately 20% of the fluid, or about 120 mL, is filtered into the nephrons.
• Only 1 mL of urine is formed for every 120 mL of fluids filtered into the nephron.
• The remaining 119 mL of fluids and solutes is reabsorbed.
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Reabsorption in the Proximal Tubule
• 85% of the water in the filtrate is reabsorbed here
• Selective reabsorption of nutrients such as glucose and amino acids, vitamins and minerals occurs by active and passive transport.
• pH is controlled by secretion of hydrogen ions (H+) and reabsorption of bicarbonate ions (HCO3
- )
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Reabsorption in the Descending Loop of Henle
• Descending limb of loop of Henle is permeable to water, resulting in loss of water from filtrate by osmosis.
• Salt (NaCl) becomes concentrated in filtrate as descending limb penetrates inner medulla
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Reabsorption in the Ascending Loop of Henle
• The ascending limb of loop of Henle is permeable to salt, resulting in diffusion of salt out of ascending limb.
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Reabsorption in the Distal Tubule
• Selective reabsorption of penicilin and other medications from blood into nephron occurs by active transport.
• Distal tubule helps regulate potassium (K+) and salt (NaCl) concentration of body fluids.
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Reabsorption in the Collecting Tubule
• As water is reabsorbed from the nephron, the remaining solutes become more concentrated.
• Molecules such as urea and uric acid will diffuse from the nephron back into the blood, although less is reabsorbed than was originally filtered.
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Secretion• Secretion is the movement of wastes from the
blood into the nephron.• Nitrogen-containing wastes, excess H+ ions,
and minerals such as K+ ions are examples of substances secreted.
• Even drugs such as penicillin can be secreted. • Tubular secretion occurs by active transport• Molecules are shuttled from the blood into
the nephron
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• http://www.youtube.com/watch?v=cuc5KnnRpIM