Chapter 11: Urinary System
11.1 Urinary System Overview
- ___________________________________ is created as food is broken down from energy
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The role of the urinary system is to remove that waste
- Waste in the digestive system is eliminated in the feces
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When the products of digestion get into tissues, wastes accumulate and diffuse into the bloodstream, including ammonia, acids, and salts
- These must be eliminated to maintain homeostasis
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Most metabolic wastes are eliminated by urinary system resulting in ___________________________
- ______________________________ are the primary organs of the urinary system
- Kidneys regulate salt excretion in order to maintain water balance between tissues and the blood
- Kidneys keep pH levels of the blood within normal levels by adjusting ion levels
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The major organs of the urinary system:
- ________________________ filter and cleanse blood brought by renal arteries
- ________________________ carry waste from kidneys to the __________________, which stores the waste for excretion via the ______________________________
- Blood that has passed through the kidneys returns to the circulation via renal veins
- The paired, fist-sized kidneys sit in the upper abdominal cavity behind the liver
- A tough, connective tissue renal capsule protects the kidney
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The kidney is made up of three layers:
- Outer _________________________________
- Inner _________________________________
- A hollow center, the _______________________________
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Within the cortex and medulla are ______________________________, do the actual filtering
- Each kidney has about 1.25 nephrons
- Each kidney filters 1,000 liters of blood daily with the end product of _________
- The urine moves via muscular contractions of the ureters to the bladder, which can store about 1 liter
- The bladder walls are made of muscle, which contracts to expel urine through the __________________________________, a ring muscle at the top of the urethra
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The __________________________________ controls urine flow out of the urethra
- The urethra in females is 3-4 cm long and carries only urine
- The urethra in males is 18-20 cm long and carries both urine and sperm
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_________________________ relies on a positive feedback loop
- Urine flow through the urethra stimulates muscle contractions to fully empty the bladder
- Once empty, urine flow ceases and muscle contractions stop
11.2 Excretion
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______________________ is a water-based solution including ________________, a waste product of protein metabolism
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Ammonia is produced when proteins are used from cellular respiration
- The liver converts it to urea
- Toxic to cells
- Uric acid results from DNA metabolism and is found in low levels in urine
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Ammonia is produced when proteins are used from cellular respiration
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Urine also contains sodium, potassium, chloride, calcium and hydrogen ions
- Kidneys excrete these ions to maintain homeostasis of blood volume and acidity
- Trace amounts of other materials are also found in urine, e.g., toxins and drugs
- Urine’s yellow color comes from bilirubin (degraded hemoglobin) waste products
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Creatinine is also found in urine and comes from intense muscle activity
- Creatinine forms when creatine phosphate is used to make ATP to power muscles, a process which generates ADP
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There are three phases to the processing of waste by the kidney:
- ______________________________________________________
- ______________________________________________________
- ______________________________________________________
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______________________________ is the first step of urine formation
- Blood pressure forces plasma from the capillaries into the glomerulus
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The _________________________________ (Bowman’s capsule) is the nephron’s receiving end
- The capsule surrounds a capillary mass, the ___________________________
- Fluid filtered from the glomerulus into the capsule flows through the proximal convoluted tubule which is embedded in the renal cortex
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20% of nephrons have a long _________________________ (loop of Henle) which brings the tubule into the renal medulla
- The other 80% stays in the cortex
- Each nephron ends in a _______________________________
- The distal tubules drain into a common ___________________________________, shared by several nephrons
- The collecting ducts empty waste into the renal pelvis
- __________________________________ is the second step of urine formation
- The glomerular filtrate contains wastes to be excreted and essential materials to be reabsorbed
- Most of the water, sodium, glucose and amino acids are reabsorbed, along with 50% of the urea
- ___________________________________ is the third step in urine formation
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The proximal and distal tubules permit secretion of some low concentration substances in the plasma, such as creatinine
- These wastes move from capillaries into nephrons via active transport
- Tubular secretion is used to remove many drugs, food additives, inorganics and even hydrogen ions from the body
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The proximal tubules are lined with microvilli, finger-like projections that greatly increase surface area to facilitate reabsorption
- The process uses ATP to actively transport sodium from the nephron into the renal cortex
- This causes chloride, water, glucose and amino acids to be removed from the filtrate
- Since sodium is positively charged, its transport into the renal cortex creates an electrical gradient between the nephron lumen (inside space) and the outside
- As a result, chloride (negatively charged) diffuses out to equalize the charge on both sides of the nephron cell membrane
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The sodium and chloride ions in the renal cortex create an osmotic gradient
- Fluids in the nephrons are hypotonic to the renal cortex
- Water diffuses out of the nephron into the cortex
- Aquaporines (membrane proteins) facilitate the water’s movement, making for the rapid reabsorption of two-thirds of the water in the filtrate
- The active transport of sodium from the tubule cells creates a difference in sodium concentration between the tubule epithelial cells and the filtrate in the lumen
- This results down its concentration gradient into the epithelial cells
11.3 Water, pH, and Salt Balance
- The loss of too much water results in a decline in blood volume and a decrease in blood pressure, which impairs metabolic processes
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Water loss also makes the blood hypertonic to tissues, which lose water to the blood
- _________________________ is the loss of too much water, resulting in dry mouth, sunken eyes and lethargy as a result of brain cell shrinkage
- ___________________________________ permeability determines the final urine concentration that is excreted into the renal pelvis
- A slightly dehydrated person recaptures much of the water in the filtrate by increasing the permeability of the collecting ducts to water
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Water conservation at this level occurs because the collecting ducts pass into the solute-rich medulla interior on the way to the renal pelvis
- This is a hyperosmotic environment, so any water in it diffuses out, leaving a highly concentrated urine
- Metabolic activities produce acid, which is measured as an increase in hydrogen ions or a decrease in pH
- Blood must be in the range of pH 7.35 – 7.45
- Acid produced by metabolism must be neutralized
- ____________________ in the blood are the main mechanism for pH maintenance
- The bicarbonate ion is the main buffer
- Absorbs excess hydrogen ions when the pH is low and releases it into the bloodstream when pH is high
11.4 When Kidneys Fail
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A number of issues can affect normal kidney function; many can be corrected
- ________________________________ (masses of crystals of calcium, phosphorus, uric acid and proteins) may block a ureter
- Nephrons can be destroyed by urinary tract infections and by chronic high blood pressure
- Diabetes causes nearly 50% of kidney failures
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Protein in the urine is a first sign of kidney failure
- The protein has slipped through the glomerulus
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If kidney damage continues, the results is ________________________________________
- ESRD suffers have less than 10% normal kidney function
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The demand for kidney transplants far exceeds the supply, so __________________ is used as a measure to keep the patient alive
- The most effective form of dialysis circulates a patient’s blood through an artificial kidney machine
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The machine has membranous tubes bathed in clean fluid
- Metabolic wastes diffuse from the blood through the membranes and into the fluid
- A single dialysis treatment may take 3-6 hours and may be needed 3-4 times a week