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• What are the major organs of the urinary system?
• What are the major functions of the urinary system?
Chapter 15
The Urinary System
• Major Organ – Kidneys
• Major Function – filter the blood allowing waste and
excess ions to leave as urine and returning the
needed substances to the blood in the right
proportions
• Other Functions – regulate blood’s volume and
chemical make-up
Other Regulatory Functions
1.
2.
3.
Enzyme renin regulates blood pressure
Hormones from kidneys stimulate RBC production
in bone marrow
Kidneys convert Vitamin D to its useable form
Organs of the Urinary System
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•
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Kidney
Ureters
Urinary bladder
Urethra
The Kidneys
• Located near the elbow, posterior in the body cavity
• 5 in and 2.5 in wide (size of a fist, large bar of soap)
• Right kidney lower than the left because of the liver
Figure 15.1b
• Adrenal Gland – produces hormones
• Hilus - indent
Structure of the Kidneys
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Renal artery – blood from the heart with oxygen
Renal Vein – Blood to heart – no oxygen
Ureter – urine to bladder
Renal cortex – outer region
• Renal Pelvis – area superior to the ureter
– Wastes drain to this area
• Renal pyramid – pyramid shape – made of nephrons
• Nephrons – structural and functional units of the
kidney
– Millions in each kidney
– Form urine
• Renal Medulla – space between cortex and pelvis
Figure 15.2b
Structure of a Nephron
Two Parts
1.
2.
Glomerulus
Renal Tubule (leads to collecting duct)
• Blood comes from the renal artery, into the
glomerulus where it is filtered.
• It then passes through the capillary bed and leaves
through the renal vein.
Urine Formation
Results from 3 processes
1.
2.
3.
Filtration
Reabsoprtion
Secretion
Filtration
• Passive process
• Blood plasma with small molecules goes through
• Proteins and RBC are too big and stay in the blood
stream
Reabsorption
• Occurs in the beginning of the tubule
• Filtrate contains waste and good things (water,
glucose, amino acids and ions)
• Reabsorption – takes back the good things by
selective active transport
• This part of the tubule has lots of mitochondria and
microvilli
Secretion
• Occurs in the capillary net
• Removes “bad” stuff from the blood (H+, K+, drugs
and creatine)
• Regulates blood pH (H+)
• This is added to the tubule and secreted
• The filtrate made of wastes leaves through the
collecting duct to the renal pelvis to the ureter, then
the bladder and the out through the urethra
Control of Blood
Composition by the
Kidneys
Blood composition depends on:
1.
2.
3.
Diet
Cellular metabolism
Urine output
In 24 hours 150-180L of blood is filtered
1-1.8 L of urine is produced
The 4 Roles Kidneys
play in keeping blood
composition constant
1.
2.
3.
4.
Excretion of nitrogen-containing waste
Water balance in the blood
Electrolyte balance in the blood
Ensuring proper blood pH
Nitrogen Waste
1.
2.
3.
Urea – comes from AA when used for energy
Uric Acid – comes from the metabolism of nucleic
acids
Creatinine – associated with creatine metabolism
in muscle tissue
Water/Electrolyte Balance
• Males – 60% water
• Females – 50% water (fat less water)
• Electrolyte – charged particle that conducts electric
currents
• Water is essential for the functioning of the body
and its cells
• Hormones control the reabsorption of water and
electrolytes
Maintaining Acid-Base Balance of
blood
• pH of blood – 7.35-7.45
• Kidneys do most of the regulation
• Blood buffers and respiratory controls do the rest
Characteristics of
Urine
Color
• Clear and pale to yellow
• Yellow due to urochrome (pigment from the
destruction of hemoglobin)
• Deeper yellow – more concentrated
• Sterile when exits the body – then begins to grow
bacteria
pH
• About 6
Density
• Greater that distilled water
• Specific gravity – about 1.001 – 1.035
Solutes in Urine
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Na+
K+
Urea
Uric acid
Creatinine
Ammonia – NH4
Bicarbonate ions
Substances NOT found in Urine
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Glucose – Diabetes
Blood proteins (albumin)
RBC or Erthyrocytes
Hemoglobin
WBC or Leukocytes (pus)
Bile
Crystals – kidney stones
Table 15.1
Organs of the Urinary
System
Ureters
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•
•
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Long slender tubes 10-12 in
From hilus to bladder
Urine moves by peristalsis
Pain from kidney stones occurs here
Urinary Bladder
• Smooth collapsible temporary storage tank
Urethra
• Carries urine by peristalsis from bladder to the
outside
• Females – 1.5” – carries urine
• Males – 8” – carries urine/sperm
Micturition (Voiding)
• Emptying the bladder
• 2 sphincters control the release of urine
• 200 mL – stretch receptors activated – contractions
occur – urine moves to the first sphincters
• Person feels the urge to void
• Person can wait or go
• Another 200-300 mL – person has to go again
• Eventually voiding will happen whether a person
wants it or not
Incontinence
• Unable to control the external sphincter
• Small children
• Emotional, pressure or nervous system problems
Urinary Retention
• Bladder is unable to expel urine
• After surgery before anesthesia wears off
• Enlargement of the prostate
The End