The Urinary System
Chapter 16
Waste Excretion
• Chemical reactions in the body result in
waste products that may be potentially
harmful, therefore must be eliminated.
– Examples of metabolic waste products:
• Carbon dioxide, Urea, Salts
– Methods of elimination:
• Respiratory system, urinary system, digestive
system, sweat
• The urinary system is the most important
route of waste-product removal in the body.
It removes nearly all the soluble waste
products from blood and transports out of the
body.
– Also removes excess water from the body.
Parts of urinary system:
The Urinary System
• Two kidneys
– Make urine and carry out
other vital functions.
• Two ureters
– Carry urine to the urinary
bladder.
• Urinary bladder
– Collects, stores and releases
urine.
• Urethra
– Carries urine from the body to
the external environment.
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Terminology
• nephro/reno = kidney
• Nephrology- the study of the kidney.
• Diuresis- producing and passing large amounts of urine
• Oliguria- passing small amounts of urine
• Anuria- no urine is passed from the body
• Dysuria- difficult urination
• Hematuria- blood in urine
• Polyuria- increased urine volume.
Kidney Function
•
Must maintain homeostasis through a variety of processes.
– Blood filtration, reabsorption, and secretion
• Blood is filtered, useful substances are returned to circulation and
waste products are secreted.
– Fluid balance regulation
• Makes sure body has enough water to maintain healthy environment.
– Acid-base regulation
• Ability to remove hydrogen and bicarbonate ions from blood.
– Electrolyte regulation
• Na+, K+, Cl• can be fatal outside of normal levels
– Hormone production
• Kidneys produce erythropoietin- necessary for red blood cell
production
• Produce some prostoglandins
• Influenced by Antidiuretic Hormone (posterior pituitary) and
Aldosterone (adrenal cortex)
Location of
the kidneys
• In dorsal part of abdomen, ventral to and
on either side of first few lumbar
vertebrae.
• Are retroperitoneal to the abdominal
cavity and are considered outside
abdominal cavity.
• In most domestic animals, right kidney is
slightly more cranial than left.
• Perirenal fat surrounds and helps
protect from exertion from other organs.
• Move somewhat with the movement of
the diaphragm
Gross Anatomy of the Kidney
• Bean shaped and covered by fibrous connective tissue capsule.
• Reddish brown in color
• Generally a smooth surface
– Cattle have multiple lobed kidney which gives it a lumpy appearance
• Hilus: indented area on medial side of kidney
– Ureters, nerves, blood and lymph vessels enter/leave kidney
• Renal Pelvis: funnel-shaped area inside hilus
– Forms beginning of ureter
– Lined with stretchable transitional epithelium
– Cattle lack a renal pelvis
Gross Anatomy of the Kidney
• Cortex- outer portion of the kidney.
– Rough granular appearance,
reddish brown in color
• Medulla- inner portion around the
renal pelvis.
– Smooth appearance
– Dark purple outer area and grayred inner area.
– Varies with species can be
multipyramidal (multilobar) or
unipyramidal (unilobar).
• Calyx- funnel-like extension of the
renal pelvis that the medullary
pyramids drain into.
– Calyces funnel fluid into renal
pelvis
• Nephron- basic functional unit of
the kidney whose job is to filter,
reabsorb and secrete.
Microscopic Anatomy
of the Kidney
– Smallest part of the kidney
– Number varies per kidney and
species
• 1 million in human, sheep, pigs
• 200,000 in cat
– Composed of:
• Renal Corpuscle
– Bowman’s capsule and
glomerulus
• Proximal Convoluted Tubule
(PCT)
• Loop of Henle
• Distal Convoluted Tubule (DCT)
• Located in cortex of kidney.
Renal Corpuscle
• Function is to filter blood in first
stage of urine production.
– This filtrate is called glomerular
filtrate
• Made up of Glomerulus (tuft of
glomerular capillaries), and
Bowman’s capsule (double walled
capsule that surrounds the
glomerulus).
– Bowman’s capsule has inner
visceral layer and outer parietal
layer.
• Space between these two
layers is known as the
capsular space and is
continuous with the proximal
convoluted tubule.
Proximal Convoluted
Tubule (PCT)
• Continuation of the capsular
space of the Bowman’s
capsule.
• Longest part of the tubular
system of the nephron.
– Glomerular filtrate becomes
tubular filtrate (primitive urine).
• Epithelial cells are cuboidal
and have a brush border on
lumen side that increases the
surface area.
Loop of Henle
• Continued from PCT
• Descends into medulla of the
kidney and the ascends back to
cortex.
• Descending portion
– Epithelial cells like PCT and
brush border
• At bottom of loop, epithelium
flatten to simple squamous
epithelial cells and loses brush
border
• Ascending loop wall becomes
thicker again
– No brush border
Distal Convoluted
Tubule (DCT)
and
Collecting Ducts
• DCT is a continuation of
ascending portion of Loop of
Henle
– Not as twisted as PCT
• The DCT from all nephrons
empty into a series of collecting
ducts which carry tubular filtrate
through medulla and eventually
empty it into renal pelvis that
becomes ureter.
• The DCT and Collecting Ducts
are the sites of action for:
– Antidiuretic Hormone (ADH)
– Regulation of K+
– Acid-base balance
Nerve Supply to the Kidneys
• Supplied by sympathetic portion of
autonomic nervous system.
– Sympathetic stimulation decreases the
diameter of blood vessels leading to the kidney
• Controls the blood flow through the
glomerular capillaries.
• Is not essential for kidney function,
– Why transplanted kidneys will work.
Blood Supply to the Kidneys
• Kidneys have very large blood
supply.
• All circulating blood passes
through kidney every 4 or 5
minutes.
• Composed of:
–
–
–
–
–
–
Renal artery
Afferent glomerular arterioles
Glomerular capillaries
Efferent Glomerular arterioles
Peritubular capillaries
Renal vein
• Renal artery
– Branches off of aorta and enters kidney at hilus
– Divides smaller and smaller until becomes afferent glomerular arterioles
• Afferent glomerular arterioles
– Carry blood into the glomerular capillaries of the renal corpuscle.
• Glomerular capillaries
– Continuation of afferent glomerular arterioles.
– Filter plasma from blood in capsular space – called glomerular filtrate.
– Only place in body where blood that enters and leaves capillaries is still
oxygenated blood.
Blood Supply
• Efferent Glomerular arterioles
– Receive (arterial) blood from glomerular capillaries
– Divide into peritubular capillaries
• Peritubular capillaries
–
–
–
–
Surround nephron and converge to form venules the become renal vein.
Oxygen transfer occurs here.
Usable substances are removed from tubular filtrate and reabsorbed.
Other waste substances are secreted into filtrate here as well.
• Renal vein
– Leaves kidney at hilus and joins abdominal portion of the caudal vena cava.
• Purest blood in body.
Blood Supply