Transcript Chapter 15

Human Biology Concepts and Current Issues
Seventh Edition
Michael D. Johnson
15
The Urinary
System
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Lecture Presentations by
Robert J. Sullivan
Marist College
Figure 15.2
Cortex
Kidney
Renal artery
Renal vein
Nephrons
Aorta
Inferior
vena cava
Ureter
Renal
pelvis
Bladder
Ureter
Cortex
Medulla
Medulla
Collecting
duct
Urethra
The components of the
urinary system.
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Internal structure of the
kidney.
The cortex and medulla of
the kidney are composed
of numerous nephrons.
Table 15.2
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Organs of the Urinary System
 Kidneys
–
–
–
–
Principal organ of urinary system
Cortex: outer portion of the kidney
Medulla: inner region of the kidney
Renal pelvis: hollow space in center of kidney where
urine collects
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Organs of the Urinary System
 Ureters
– Muscular tube that transports urine from kidneys to
bladder
 Urinary bladder
– Thick wall of smooth muscle, lined with epithelium
– Stores urine (600–1,000 ml)
 Urethra
– Carries urine from bladder to outside of body
– Two sphincters control urination
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Figure 15.3
Urinary
bladder
Rectum
Prostate
gland
Internal
urethral
sphincter
Uterus
Vagina
Penis
External
urethral
sphincter
Rectum
Urethra
Testis
The male.
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The female.
Nephrons
 Nephron: functional unit of the kidney; 1 million
nephrons per kidney
 Nephrons have two parts:
– Glomerular capsule: cuplike end of nephron tubule
surrounding glomerulus (network of capillaries)—this
is where filtration occurs
– Tubule with associated capillaries & four distinct
regions
– Role of nephrons: remove approximately 180 liters of
fluid from the blood daily, and return most of it, minus
the wastes that are excreted
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Figure 15.4
Distal tubule
Efferent arteriole
Glomerular
capsule
Glomerulus
Proximal tubule
Afferent arteriole
Cortex
Medulla
Descending
limb
Ascending
limb
Collecting
duct
Renal pelvis
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Loop of
Henle
Formation of Urine: Filtration, Reabsorption, and
Secretion
1. Glomerular filtration: movement of protein-free
solution of fluid and solutes from blood into the
glomerular capsule
2. Tubular reabsorption: return of most of the fluid
and solutes back into the blood
3. Tubular secretion: addition of certain solutes from
the blood into the tubule
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Figure 15.6
3
Glomerular
capsule
Afferent
arteriole
Efferent
arteriole
Glomerulus
1
Glomerular filtration:
Water, ions, glucose,
amino acids, bicarbonate,
and waste products
(urea, creatinine) are
filtered from the
glomerular capillaries
into the space within
the glomerular capsule.
Some drugs, waste products,
and ions (primarily hydrogen,
ammonium, and potassium)
are actively secreted from the
peritubular capillaries primarily
into the distal tubule but also
in other nephron segments.
Proximal tubule
Distal tubule
2
Artery Vein
Tubular secretion:
Collecting
duct
Tubular reabsorption:
Water, amino acids,
glucose, most ions
(including bicarbonate),
and some urea are
reabsorbed back into the
peritubular capillaries,
primarily in the proximal
tubule but also in other
nephron segments.
Urine
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Glomerular Filtration Filters Fluid from Capillaries
 Filters fluid & solutes except large proteins and blood
cells from capillaries into glomerular capsule
 Filtration is driven by high blood pressure in
glomerular capillaries
 Rate of filtration:
 The total volume of filtrate formed per minute by the
kidneys- 120-125ml/min
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Tubular Reabsorption Returns Filtered Water and
Solutes to Blood
 Is the process of returning important substances (“good stuff”)
from the filtrate back into blood vessels... and ultimately back
into the body
§ The “good stuff” is glucose, ions, vitamins, water, amino
acids, and any small proteins that might have escaped
from the blood into the filtrate.
 Ninety nine percent of the glomerular filtrate is
reabsorbed
 100% of filtered glucose, amino acids, and most of
water, ions and 50% of urea are reabsorbed
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Tubular Secretion Removes Other Substances from
Blood
 Involves the movement of materials from the blood
capillaries around tubules to the fluid in the tubule
 Substances secreted:
– Disposing of drugs, metabolites
– Eliminating undesirable substances such as urea, uric
acid, creatinine
– Ridding the body of excess K+ ions
– Controlling blood pH- (secreting H+),
– potassium
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Production of Dilute Urine
 The rate at which water is lost from the body depends
mainly on ADH
 When ADH level is very low, the kidneys produce
dilute urine and excrete excess water
– If blood solute concentration is too low (water
concentration too high): ADH secretion is reduced
– Decrease in water reabsorbed by kidney
– Increase in urine production
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Production of Concentrated Urine
•When ADH level is high, the kidneys secrete
concentrated urine and conserve water; a large volume of
water is reabsorbed from the tubular fluid
•If blood solute concentration high (water concentration
too low): ADH released from pituitary
•ADH causes:
•Increase in water reabsorbed by kidney
•Decrease in urine production
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Kidneys Maintain Homeostasis in Many Ways
 Contribute to maintenance of water balance
 Contribute to maintenance of salt balance
 Secrete an enzyme involved in the control of blood
volume and blood pressure
 Maintain acid-base balance and blood pH
 Regulate red blood cell production via erythropoietin
 Activate an inactive form of vitamin D
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The Kidneys Regulate Nitrogenous Wastes and Other
Solutes
 Protein metabolism produces nitrogenous wastes
 Initially, NH3 (ammonia) is produced during
breakdown of amino acids
 Liver detoxifies NH3, producing urea
 Urea is transported from liver to kidneys for disposal
 Other solutes regulated by kidneys
– Sodium, chloride, potassium, calcium, hydrogen ions,
creatinine
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Table 15.1
Kidneys modify water output based on intake and
loss- urine output varies from 1-2 liter/day
To maintain homeostasis, Water Intake  Water Output
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Aldosterone Regulates Salt Balance
 Blood volume & blood pressure control is dependent
on salt balance
 Aldosterone: the hormone that regulates sodium
excretion
– Mechanism: increases Na reabsorption from tubule
back into blood, followed by water reabsorption
– Increases blood volume & blood pressure
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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
– Secretion & then excretion of acid
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Erythropoietin Stimulates Production of Red Blood
Cells
 Decrease in amount of oxygen is detected by certain
cells throughout the kidney
 O2 sensitive cells in kidney secrete hormone,
erythropoietin, in response to decrease in oxygen
 Erythropoietin triggers increase in red blood cell
production in the bone marrow
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Figure 7.6
O2 availability
Increase
Set point
Decrease
O2-sensitive cells in kidneys
respond to a decline in O2
availability by increasing
erythropoietin production
Increased number
of RBCs returns O2
availability to normal
Erythropoietin
stimulates increased
RBC production by
stem cells in
bone marrow
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Kidneys Activate Vitamin D
 Exposure of skin to sunlight causes production of an
inactive form of vitamin D
 Inactive form of vitamin D is transported to liver,
where it is modified
 Further activation of vitamin D then occurs in the
kidneys
 Conversion to active vitamin D in kidneys is
influenced by activity of PTH (parathyroid hormone)
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Micturition Reflex
– When urine collects in bladder, stretch receptors activated –
nerve impulses relayed along sensory neurons to stimulate
micturition reflex center in the spinal cord
–Parasympathetic stimulation causes bladder muscle to contract and
internal urethral sphincter to open
• Conscious control of urination
• Brain can override the micturition reflex and control the
timing of urination
– If desired the external sphincter ( of skeletal muscle) opens for
urination to take place
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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
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Disorders of the Urinary System
 Acute renal failure
– Short-term impairment, may be reversible
– Potential causes: sustained very low blood pressure,
infections, transfusion reactions, severe injury, toxin
exposure, drug reactions
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Disorders of the Urinary System
 Chronic renal failure
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Also known as end stage renal disease (ESRD)
ESRD: long term, irreversible damage
Reduction in functioning nephrons
Diabetes an important cause of chronic renal failure
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End Stage Renal Disease (ESRD); survival depends on:
 Dialysis Cleanses Blood Artificially:
– Attempts to duplicate function of healthy kidneys
 Kidney Transplants:
– Best hope for many chronic renal failure patients
– Improvements in transplant protocols/processes have
improved outcomes
– Better tissue-matching techniques
– Improved anti-rejection medications
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