Lecture Outline : Urinary System
I. Overall Function of The Urinary System:
A) Maintain homeostasis of blood composition, volume & pressure
II. Identify The Major Organs of The Urinary System and Their Function:
A) Kidneys
B) Ureters
C) Urinary bladder
D) Urethra
III. Identify The Major Structures of The Kidney:
A) Hilum - entrance to renal sinus
B) Renal pelvis - expansion of ureter
C) Calyces (major & minor) - tubes emanating from renal pelvis
D) Inner medullary region - contains renal columns & pyramids (site of nephrons)
E) Outer cortex - forms outer cover & renal colums
F) Renal columns - portion of cortex extending between renal pyramids
G) Renal pyramids - ~ 8-18 regions per kidney
H) Renal arteries & veins
IV. Identify The Major Functions of The Kidney:
A) Regulate blood volume & composition
1) H2O, solutes, metabolic wastes & H+ removal
B) Regulate blood pressure
1) monitor renal blood pressure
2) secretion of renin (begin renin-angiotensin pathway)
C) Regulate certain aspects of metabolism
1) perform gluconeogenesis
2) secrete erythropoeitin in response to hypoxia
3) synthesize calcitriol in response to PTH
V. Overview Of The Nephron ("functional unit of the kidney"):
A) Two principle types of nephrons:
1) cortical nephron
2) juxtamedullary nephron
B) Two major portions of the nephron:
1) renal corpuscle
2) renal tubule
C) Basic function of nephron:
1) filter blood and produce filtrate via three-step process...
VI. Filtrate Production:
A) Three-step process:
1) glomerular filtration
a) filter fluid & waste solutes out of blood
2) tubular reabsorption
a) return important solutes back to blood
3) tubular secretion
a) selective secretion of more solutes into filtrate
VII. Identify The Major Structures and Functions of The Renal Corpuscle:
A) Two major parts:
1) glomerulus
2) glomerular (Bowman's) capsule
B) Characteristics:
1) acts a site of glomerular filtration
2) contains highly fenestrated capillaries
3) incoming blood via afferent artery
4) outgoing blood via efferent artery
VIII. Identify The Major Structures and Functions of The Renal Tubules:
A) Three main portions:
1) proximal convoluted tubule
2) nephron loop
a) descending portion
b) ascending portion
3) distal convoluted tubule
i) contains maculae densa cells
B) Characteristics:
1) acts as site of reabsorption and secretion
2) collects filtrate from glomerular capsule
3) empties filtrate into collecting ducts
4) collecting ducts unite to form papillary ducts
5) papillary ducts drain into minor calyx
IX. Identify The Major Factor Affecting Glomerular Filtration Rate (GFR):
* Approx. 180 Liters of filtrate produced/day
A) Major factor affecting GFR == Glomerular Blood Pressure (Glomerular Hydrostatic Pressure (HPg)
1) diameter of afferent/efferent arterioles
a) constriction of afferents == decreased GFR
b) constriction of efferents == increased GFR
* Similar pressures affect GFR that are seen in bulk fluid flow in other capillary beds
* Net Filtration Pressure (NFP) = HPg - (OPg + HPc)
where: OPg == "oncotic" (colloid) pressure of glomerular blood
HPc == capsular hydrostatic pressure
NFP == 10mmHg (fairly low pressure)
* Because NFP is quite low, filtration is VERY sensitive to glomerular blood pressure
X. Identify The Major Mechanisms In Regulating GFR:
A) Renal autoregulation:
1) Describe The Function and Structures of The Juxtaglomerular Apparatus (JGA):
a) juxtaglomerular cells of the afferent (and some efferent) arterioles
i) smooth muscle cells that control (constriction & dilation) glomerular blood flow
ii) also secrete renin in response to decreased renal blood pressure (see hormonal control below)
b) maculae densa region of the distal convoluted tubule close to JG cells
i) cells that detect & respond to decreased Na+ , Cl- , and H2O in filtrate
ii) triggers relaxation (dilation) of afferent arteriole to increase glomerular blood flow
B) Hormonal regulation
1) renin-angiotensin pathway
2) aldosterone
3) antidiuretic hormone (ADH)
4) atrial natriuretic peptide (ANP)
C) Neuronal regulation
1) sympathetic innervation of afferent & efferent arterioles
2) increased symp. Activation == decreased GFR (more afferent than efferent constriction )
XI. Identify The Solutes Involved In Tubular Reabsorption:
A) 99% of filtrate is recovered
B) Reabsorption mostly occurs in PCT, but also some in DCT
C) Na+ reabsorbed via active processes
1) Na+ is "central" ion involved in solute reabsorption
2) H2O follows Na+ by osmosis
3) K+, Cl-, HCO3- follow H2O via diffusion
4) Na+ reabsorption uses approx. 6% body energy at rest.
D) HCO3- important to buffer H+ in blood
1) passive reabsorption and generation of HCO3-
E) Glucose reabsorption via active transport
1) transport maximum of 375mg/min
2) diabetic hyperglycemia results in overloading transport maximum == glucosuria
XII. Identify The Solutes Involved In Tubular Secretion:
A) Last step where more solutes actively added to filtrate
B) K+, H+, NH4+, and HCO3- main solutes involved
1) H+ and HCO3- secretion is pH dependant to help buffer blood