2. LaPointeSpring ‘12
Slide # 2
Organs of the Urinary System
• The kidneys - produce urine
• The ureters
• The urinary bladder - stores urine
• The urethra
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Slide # 3Functions of the Urinary System
• Excretion (kidney)
• The removal of organic wastes, water, and ions from
body fluids
• Elimination (ureters, bladder and urethra)
• The discharge of waste products into the environment
• Homeostatic regulation (kidney)
• Regulating blood volume and pressure
• Regulating plasma ion concentrations
• Stabilizing blood pH
• Conserving nutrients
• Synthesizing vitamin D and regulating hormones
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Slide # 4The kidneys
• Left kidney is slightly more superiorly than right
• Both kidneys and adrenal glands are retroperitoneal
• Hilus
• Entry for renal artery and renal nerves
• Exit for renal veins and ureter
• Renal capsule- collagen fibers, prevent distension
• Adipose layer and renal fascia
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Slide # 6Sectional anatomy of the kidneys
• Superficial outer cortex and inner medulla
• The medulla consists of 6-18 renal pyramids
• Minor and major calyces connect to form the renal
pelvis which drains urine to the ureters
• Functional unit of the kidney is the nephron
• roughly 1.25 million nephrons per kidney
• Connect together to form collecting ducts
• Two capillary beds intimately work with the nephron
and collecting ducts
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Slide # 13Nephron
• Three functions
• Filtration
• Reabsorption
(back into the blood)
• organic nutrients
• water
• ions
• Secretion
(from the blood into tubular fluid)
• drugs and toxins
• ions
• acids
• nitrogenous wastes
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Slide # 14
• Functional unit of the kidney is the nephron
• The renal corpuscle is composed of
• Bowman’s capsule and the glomerulus
• The renal tubule consists of
• Proximal convoluted tubule (PCT)
• Loop of Henle
• Distal convoluted tubule (DCT)
• Nephrons connect to form collecting ducts
Nephron
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Slide # 16Functional anatomy of the nephron
• Proximal convoluted tubule (PCT)
• Reabsorbs nutrients, plasma proteins and ions from
filtrate
• Secretion of drugs and toxins
• Loop of Henle
• Descending limb
• Ascending limb
• Each limb has a thick and thin section
• Involved in concentration and dilution of urine
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Slide # 17
• Distal convoluted tubule (DCT)
• Secretes ions, acid, drugs
• Reabsorbs sodium ions and water from tubular fluid
• Macula densa - specialized cells that regulate
glomerular filtration
• Juxtaglomerular cells (JG cells)- specialized smooth
muscle cells in the afferent arteriole that release renin
Functional anatomy of the nephron
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Slide # 19Two types of nephron
• Cortical nephrons
• ~85% of all nephrons
• Located high in the cortex
• Juxtamedullary nephrons
• Closer to renal medulla
• Loops of Henle extend deep into renal pyramids
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Slide # 28Glomerular filtration rate (GFR)
• Amount of filtrate produced in the kidneys each minute
(~125 ml/min)
• creatinine clearance
• inulin clearance
• Autoregulation - GFR remains relatively constant
despite changes in blood pressure
• Renal blood flow (21% C.O. - 1176 ml/min)
• Renal plasma flow (650 ml/min)
• Filtration fraction (~19%)
125 x 60 x 24 =180,000 ml /day
Average blood vol 5-6 L
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Slide # 29Calculation of GFR
GFR = Uinulin xV_________________________________
Pinulin
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Slide # 30
Autoregulation of RBF and of GFR
0 25 50 75 100 125 150 200
Renal blood flow
GFR
Blood pressure
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Slide # 31Autoregulation (for decreased blood pressure)
• Changes in blood pressure are sensed and result in
• afferent arteriole relaxation
• efferent arteriole constriction
• change in podocyte and capillary surface area by
relaxation of mesangeal cells
• altered oncoctic and osmotic pressure
Afferent arteriole
Efferent arteriole
Glomerulus
PCT
Note when BP increases the opposite affects occur
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Slide # 32Several levels of control of GFR
• Myogenic control
• Paracrine factors
• Neural reflexes (sympathetic nerves)
• Hormonal
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Slide # 33
Macula Densa and JG Apparatus
Tubulogolmerular
feedback
(See Saladin fig 23.14
for feedback loop)
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Slide # 34Hormonal control of GFR
• A drop in filtration pressure stimulates Juxtaglomerular
apparatus (macula densa & JG cells)
• Releases renin and erythropoietin
• Renin coverts angiotensinogen to angiotensin I which is
converted to angiotensin II via ACE (see fig 23.15)
• Ang II causes
• constriction of systemic arterioles
• constricts efferent arteriole more than the afferent
arteriole
• causes aldosterone and ADH release
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Slide # 35Hormonal control of GFR
• Aldosterone stimulates the reabsorption of sodium
• ADH increases the reabsorption of water and activates
thirst
• ANP and BNP cause afferent arteriole dilation and
efferent arteriole constriction
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Slide # 38Sympathetic activation
• Produces powerful vasoconstriction of afferent
arterioles
• Decreases GFR and slows production of filtrate
• Changes the regional pattern of blood flow
• Alters GFR
• Stimulates release of renin by JG apparatus
