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Urinary System
Food,water
Water,salt Water
Digestive tract Skin Respiratory system
Nutrients,water
Water,salt
Waste
Circulatory system
Water, solutes,wastes
Urinarysystem
Metabolicproducts, toxins Waste
Liver
Eliminationof foodresidues
Elimination ofwaste, excesssolutes, andwater
Urinary System
• Kidneys regulate water levels– Excess water excreted– Output varies from 2-1/2 liter/day to 1 liter/hour
• Kidneys regulate nitrogenous wastes and other solutes– Urea from protein metabolism– Other solutes regulated by kidneys• Sodium, chloride, potassium, calcium, hydrogen ions,
creatinine
Organs of Urinary System
• Kidneys– Principal organ of urinary system– Cortex: outer portion of the kidney– Medulla: inner region of the kidney
Organs of Urinary System
• Ureters– Transport urine from
kidneys to bladder
• Urinary bladder– Stores urine (600–1,000
ml)
• Urethra– Carries urine from body– Two sphincters control
urination
Nephrons Produce Urine
• Nephron: functional unit of the kidney
• 1 million nephrons per kidney
• Remove approximately 180 liters of fluid from the blood daily– return most of it, minus
wastes that are excreted
NephronNephron structure• Glomerulus: ball of capillaries– where filtration occurs
• Glomerular capsule: cuplike structure surrounding glomerulus
• Proximal tubule: comes off capsule• Loop of Henle: located in renal
medulla• Distal tubule: connects to collecting
duct• Collecting duct: shared by several
nephrons, empties into renal pelvis
Nephron Blood Supply• Renal artery supplies kidney• Blood vessels associated with
nephron– Afferent arteriole: enters
glomerulus– Efferent arteriole: leaves
glomerulus– Peritubular capillaries:
surround proximal and distal tubule
– Vasa recta: parallels loop of Henle
Formation of Urine1. Glomerular filtration:
movement of fluid and solutes from blood into glomerular capsule– No proteins or cells
2. Tubular reabsorption: return of fluid and solutes into blood– Stuff we want to keep
3. Tubular secretion: addition of solutes from blood into the tubule– Throwing out extra junk
Figure 15.7
a) The outer surface of several glomerular capillaries.
Podocyte
Filtrate
Proximal tubule Capillary wall
Glomerularcapsule
Glomerularspace
Glomerulus Blood flowMovement of glomerular filtrate
Afferent arteriole
Efferent arteriole
b) A highly magnified view of the inner surface of a single glomerular capillary, revealing its porous sievelike structure.
Glomerular filtration: Water, ions, glucose,amino acids, bicarbonate,and waste products(urea, creatinine) arefiltered from the glomerularcapillaries into the spacewithin the glomerular capsule.
Tubular secretion: Some drugs, waste products,and ions (primarily hydrogen,ammonium, and potassium)are actively secreted from theperitubular capillaries primarilyinto the distal tubule but alsoin other nephron segments.
Tubular reabsorption: Water, amino acids,glucose, most ions(including bicarbonate),and some urea arereabsorbed back into theperitubular capillaries,primarily in the proximaltubule but also in othernephron segments.
Glomerularcapsule
Glomerulus
Afferentarteriole
Efferentarteriole
Artery Vein
Proximal tubule
Distal tubule
Collecting duct
Urine
1
3
2
Figure 15.6
Tubular Reabsorption
• 100% of filtered glucose, amino acids, and bicarbonate (buffer)
• 65% of water reabsorbed• Most tubular reabsorption
occurs in proximal tubule
Tubular Secretion
• Movement of materials from peritubular capillaries or vasa recta into the tubule
• Purpose–Regulation of chemical levels in body– Excretion of harmful chemicals
• Substances secreted–Penicillin, cocaine, marijuana, pesticides,
preservatives, hydrogen ions, ammonium, potassium
Producing Concentrated Urine• Too little water can lead to:– lower blood volume– declining blood pressure– dehydration of body cells
• Kidneys can conserve water and produce a more concentrated urine
• Mechanism–ADH (antidiuretic hormone) secreted from
posterior pituitary gland–ADH increases permeability of collecting ducts to
water• More water reabsorbed
Producing Dilute Urine
• Excess water can:– Elevate blood pressure– Cause cells to swell and/or burst
• Kidneys respond to excess water by excreting it• Mechanism– Distal tubule is impermeable to water except when
ADH is present– Large volume of water is excreted
Micturition Reflex• Stretch receptors in bladder wall• Internal urethral sphincter– Smooth muscle, involuntary
• External urethral sphincter– Skeletal muscle, under voluntary control
• Brain can override the micturition reflex – Voluntary control becomes increasingly difficult as bladder
gets very full
Kidneys Maintain Homeostasis in Many Ways
• Maintain water balance– Adjust blood volume and blood pressure
• Aldosterone, renin, ANH help maintain salt balance in order to control blood volume
• Maintain acid-base balance and blood pH• Regulate red blood cell production via erythropoietin• Activate an inactive form of vitamin D
Water Balance Determines Blood Volume and Blood Pressure
• Involves the kidneys, hypothalamus, and posterior pituitary gland– Involves increasing or reducing ADH secretion– Involves increasing or decreasing thirst
• Diruretic: increases formation and excretion of urine– Lasix (furosemide): medication that reduces blood
volume and blood pressure– Caffeine: inhibits sodium reabsorption– Alcohol: inhibits ADH release
ADH
Save water
KidneysSavesalt
Blood volume
Increase
Set point
Decrease
Adrenal cortex
Angiotensin-converting
enzyme
Kidneys
Vasoconstriction, blood pressure
Liver
Angiotensinogen
Lungs
Reni
n
Figure 15.15
Kidneys Help Maintain Acid-Base Balance and Blood pH
• Blood pH must stay between 7.35 and 7.45• pH regulated by kidneys, buffers, lungs• Role of kidneys in pH maintenance– Reabsorption of filtered bicarbonate– Excretion of acid as ammonium
Disorders of the Urinary System
• Kidney stones– Crystallized minerals– Block urine flow
• Urinary tract infections (UTI)– Usually caused by bacteria– More common in women than
men because of shorter urethra– If untreated, bladder infections
may ascend to involve kidneys
Disorders of the Urinary System
• Acute renal failure– Short-term impairment, may be reversible– Potential causes: sustained very low blood pressure,
large kidney stones within renal pelvis, infections, transfusion reactions, severe injury, toxin exposure, drug reactions
Disorders of the Urinary System
• Chronic renal failure– Also known as end stage renal
disease (ESRD)– >70% reduction in functioning
nephrons– Causes:• Diabetes (40% will develop CRF)• Uncontrolled high BP• Glomerulonephritis• Polycystic kidney disease• Overuse of acetaminophen or
ibuprofen
Treatment of Irreversible Kidney Failure
• Dialysis• Problems:– Dialysis cannot achieve complete homeostasis of
ions and wastes– Dialysis does not replace renal hormones
Treatment of Irreversible Kidney Failure
• Kidney transplant
Kidney Transplants
• Best hope for many CRF patients• >65,000 people on waiting list for kidneys• Improvements in transplant protocols/processes
have improved outcomes– Better tissue-matching techniques– Improved anti-rejection medications– National data banks