Download Urinary System

Functions
 Removes wastes
 Regulate normal concentrations of water and
electrolytes
 Regulates pH and body fluid volume
 Helps regulate RBC production
 Helps regulate blood pressure
Part of the System
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Kidneys
Ureters
Urinary bladder
Urethra
Kidney
 Red-brown, bean-shaped organ
 Located on either side of vertebral column high in
abdominal cavity
Kidney Functions
 Regulate composition, volume, and pH of
extracellular fluid
 Formation of urine
 Secrete erythropoietin to control RBC
production
 Role in activation of vitamin D
 Secrete renin to regulate blood volume and
pressure
Kidney Structure
 Concave side leads to hollow cavity called renal
sinus
 Entrance is called the hilum
 Entering through hilum:
 Renal artery and renal vein
 Lymphatic vessels
 Nerves
 Ureter
Kidney Structure
 Ureter expands into renal pelvis in the
renal sinus
 Renal pelvis subdivides into major calyces
 Major calyces subdivide into minor calyces
 Renal papillae - projection of renal sinus wall
with openings into the minor calyces
 Surrounding renal sinus:
 Renal medulla- striated renal pyramids
 Renal cortex- granular shell with renal columns
dipping into renal medulla
Blood flow to Kidneys
 Renal artery carries 15-30% of cardiac output to
kidney
 Blood flow sequence:
 Renal artery  Interlobular arteries  Afferent
arterioles  Glomerular capillaries  Efferent
arterioles  Peritubular capillaries  Enters venous
system  Leaves through renal vein
Nephrons
 Functional unit of
kidney
 About 1 million
nephrons PER kidney
 Composed of renal
corpuscle/cortex
and renal
tubules/medulla
Renal corpuscle/cortex
 Glomerular capillaries
form tangled structure
called glomerulus
 Thin-walled sac,
glomerular capsule, is
surrounded by
capillaries
 Renal tubule is
connected to capsule
Renal Tubule/medulla
 Proximal convoluted tubule  Descending limb of
the loop of Henle  Ascending limb of the loop of
Henle  Distal convoluted tubule  Collecting duct
 Minor calyces
 Kidney animation
Juxtaglomerular Apparatus
 Location of secretion of renin
 Apparatus is composed of two types of cells:
 1) densely packed cells called the macula densa in
the distal convoluted tubule
 2) juxtaglomerular cells in the afferent and efferent
arterioles
Steps of Urine Formation
 1) Glomerular filtration
 Filter substances out of the blood plasma
 2) Tubular reabsorption
 Substances in tubule are reabsorbed into plasma
 3) Tubular secretion
 Substances are secreted into tubule
Glomerular Filtration
 Produced 180 liters of filtrate every 24 hours
 Plasma is forced out of the gomerular capillary due
to blood pressure
 Glomerular capillary is more permeable than other
capillaries due to tiny openings called fenestrae
 Podocytes
 Cells that cover the capillaries and don’t allow plasma
proteins to leave the capillary
 Glomerular capsule receives glomerular filtrate
Filtration Pressure
 Pressure is kept high by the two capillary bed
structure
 Pressure overcomes osmotic pressure and
hydrostatic pressure in the capsule
 Net filtration pressure takes into account all three
factors (usually remains positive favoring filtration)
Rate of Filtration
 Controlled by diameter of blood vessels
 Afferent: Constriction , Dilation 
 Efferent: Constriction , Dilation 
 Controlled by colloid osmotic pressure
 Plasma Protein Concentration: inversely proportional
to filtration rate
 Controlled by hydrostatic pressure
 Fullness of capsule: inversely proportional to
filtration rate
Regulation of Filtration Rate
 Sympathetic nervous system
 Control rate by changing diameter of arterioles
 Atrial natriuretic peptide
 Hormone secreted by heart when blood volume is to
high
 Increases filtration rate
Regulation of Filtration Rate
(cont)
 Renin is secreted when:
 Afferent arterioles sense blood pressure drop
 Response to sympathetic stimulation
 Macula densa senses decrease in Cl, K, and Na in
distal tubule
 Renin converts angiotensinogen to angiotensin I
 Angiotensin I is converted to angiotensin II
 Angiotensin II constricts efferent arteriole and increases
secretion of aldosterone
 Look back at Ch 11 for function of aldosterone! 
Tubular Reabsorption
 Substances are moved out of the tubule by:
 Diffusion, osmosis, and active transport
 Proximal tubule
 Glucose, amino acids, creatine, lactic acid, uric acid,
ascorbic acid, phosphate, sulfate, calcium,
potassium, and sodium moved by active transport
 Water moved by osmosis
Bicarbonate (HCO3-)
- is the most important buffer in the blood
-prevents blood from becoming too acidic
Tubular Reabsorption (cont)
 Sodium is actively transported
 Negatively charged ions are moved using passive
transport
 Water follows by osmosis due to concentration
difference
 Sodium and water reabsorption continues along
sections of the loop of Henle and distal tubule
Tubular Reabsorption (cont)
 Limited transport capacity- only limited number of
carriers for transport
 If concentration is below renal plasma threshold,
carriers can reabsorb all
 If concentration is above renal plasma threshold,
some of the substance will be left in urine
Tubular Secretion
 Secretion of:
 Penicillin
 Creatinine
 Histamine
 Hydrogen ions
 Potassium ions
Regulation of Urine Volume
and Concentration
 Aldosterone:
 Increase Na
reabsorption and K
secretion
 ADH:
 Makes distal tubule
and collecting duct
more permeable to
water
Urea and Uric Acid
 Urea
 Part of filtrate; 50% is
excreted in urine
 Uric acid
 All but a small amount is
reabsorbed
Urine
 Final composition varies:
 Contains urea, some uric acid, some amino acids, and
electrolytes
 Should not contain plasma proteins or blood
 Volume of urine:
 Usually between 0.6 and
2.5 liters PER day
Ureter
 Carries urine from kidney to bladder
 Layers of wall:
 Mucous coat- inner layer
 Muscular layer- smooth muscle
 Fibrous coat- outer layer
 Peristalsis moves urine towards bladder
 Flap of the mucous coat covers opening to
bladder and prevents backflow of urine into
ureter
Urinary Bladder
 Hollow, expandable, muscular organ
 Trigone
 triangular shaped part of the bladder with an opening
at each corner (ureters and neck of bladder leading
to ureter)
 Four layers to walls:
 Mucous coat (transitional epithelium)
 Submucous layer (connective tissue and elastic
fibers)
 Muscular Coat (detrusor muscle and sphincters)
 Serous coat (parietal peritoneum on one side and
connective tissue on the other)
Urethra
 Tube leading from
bladder to outside
 Longer in males than
females
 Urethral glands
 Secrete mucous into
the canal
Micturition
 When bladder becomes full internal urethral
sphincter relaxes
 External urethral sphincter is voluntary muscle
 Micturition reflex- detrusor muscle and muscles in
abdomen and pelvic floor contract forcing urine
into urethra
Kidney/Urinary System review
Seinfeld