Bio 169 Urinary System Study Guide
Spring Semester 2005
Learning Objectives, Topics & Keywords
Readings: Martini, 6th ed. Chapter 26, pp 971 1007
1. Understand the overall function and structure of the urinary system
Overview of Urinary System:
Anatomy
kidneys (adjective: renal; also, nephro- )
ureters
urinary bladder
urethra
Physiology
control of fluid volume
control of body composition (homeostasis of osmotic pressure)
elimination of waste metabolites and excess ions
e.g., uremia (= build up of urea (a waste product of amino acid metabolism) in the blood to toxic levels; blood urea nitrogen (BUN)
regulation of blood pressure
renin --> angiotensin
regulation of metabolism
Vitamin D synthesis
erythropoiesis (RBC formation stimulated by erythropoietin)
2. Know the gross anatomy of the kidney.
External Anatomy of "the beans"
paired
reddish color
(from mitochondrial cytochromes ==> kidney cells do much chemical work)
retroperitoneal (behind peritoneum)
blood supply is from renal arteries (large branches of abdominal aorta)
drainage is to renal vein (then to inferior vena cava)
between last thoracic and third lumbar vertebrae (upper pole protected by ribs)
right lower than left (liver pushes down)
about 10 x 7 x 2.5 cm
hilus on concave surface
blood vessels, ureter are here
renal sinus (the vascular space)
external coverings:
renal capsule (tough connective tissue)
adipose capsule (fatty protection)
renal fascia (CT anchor)
internal anatomy:
cortex
separator is arcuate arteries
medulla
renal pyramids (also called medulllary pyramids)
renal papillae (at apex of pyramid)
renal pelvis (the urine space; feeds into ureter)
major calyx (plural: calyces, feeds into renal pelvis)
minor calyx - collects from renal papilla, feeds into major calyx
3. Know the microscopic anatomy of the nephron.
nephron is the functional unit of kidney
= renal corpuscle + renal tubule
corpuscle = glomerulus + Bowmans capsule
glomerulus is tuft of capillaries
afferent arteriole
efferent arteriole
Bowmans capsule defines capsular space
visceral layer is podocytes
parietal layer is epithelium (simple squamous)
tubular components:
proximal convoluted tubule (PCT)
loop of Henle
humans have both short-loop and long-loop nephrons
distal convoluted tubule (DCT)
collecting duct
papillary ducts
histology of the filter (size filter for blood)
endothelium of glomerulus
basement membrane of glomerulus
filtration slits of podocytes
spaces between the foot processes of podocytes
renal tubule is mostly simple cuboidal or simple squamous epithelium
PCT has microvilli on apical border
juxtaglomerular apparatus (JGA secretes renin)
formed where afferent arteriole and DCT pass each other
macula densa ("dense spot") in DCT cells adjacent to afferent arteriole
4. Know the blood supply to the kidney
renal arteries (~25% of cardiac output!)
segmental arteries
interlobar arteries
arcuate arteries
between cortex and medulla
interlobular arteries
afferent and efferent arterioles
to and from the glomerulus
efferent has smaller diameter
peritubular capillaries
carry water and solutes to and from the nephron after filtration
vasa recta ("straight vessels") follow the loop of Henle
5. Understand the mechanisms of urine formation
overview: filtration (in corpuscle), reabsorption (in PCT), secretion (in DCT), and concentration (in collecting ducts)
glomerular filtration
across endothelial-capsular membrane
net filtration pressure (recall Starlings law of the capillaries)
main outward force = blood hydrostatic pressure ( BHP, ~60 mmHg)
main inward forces = blood colloid osmotic pressure (BCOP, ~27 mmHg)
+ intracapsular hydrostatic pressure (CHP, ~15 mmHg)
size filter (passes small solutes, holds back large molecules, that is, > ~40,000 molecular weight, cells)
~180 liters/day of primary filtrate!
GFR - glomerular filtration rate
~125 ml/min
dependent on adequate BP
hypotension (because it lowers BHP) may lead to oligouria or anuria
glomerular inflammation (glomerulonephritis) because it raises CHP may lead to oligouria or anuria
regulation of GFR
autoregulation of resistance of afferent arteriole
exact mechanism unknown - involves feedback of urine osmolality via JGA
systemic hormonal regulation (renin - angiotensin system)
renin released into circulation by kidney
converts angiotensinogen to angiotensin I (inactive)
angiotensin converting enzyme (ACE) converts I to angiotensin II
actions of angiotensin II
vasocontriction
release of aldosterone
thirst
release of ADH
ACE inhibitors as therapy for hypertension and congestive heart failure
tubular reabsorption (return to peritubular capillaries and vasa recta)
PCT active transport of sodium ion from filtrate
ATP-dependent
uses ~6% of resting metabolic energy!
sodium pump molecules in basal membrane
apical entry of sodium ion from lumen is passive (through sodium channels)
water follows osmotically
anions follow passively
glucose absorption is coupled to sodium gradient
shows a transport maximum (Tmax,in mMoles Glucose/min)
if filtered load excedes Tmax, sugar is dumped in urine (glucosuria)
glucose osmotically takes water with it --> polyuria if glucosuria
sodium-potassium-chloride symporter in thick ascending limb of loop
water impermaeble
sends hypo-osmolar (hypotonic) solution to DCT (review: osmolarity, Osmolar)
tubular secretion
by DCT epithelium
e.g, hydrogen ion, potassium ion, drugs like penicillin
K secretion increased by aldosterone
controls serum potassium ion, important for stability of excitable cells
hydrogen ion:
by PCT epithelium: bicarbonate recovery (Na-H countertransport)
distal and collecting tubules: direct active transport by ATP dependent H pump
DCT cells split ammonia from glutamine --> ammonia + hydrogen ion in lumen -->NH4+
control blood pH (acid-base balance)
6. Understand how the osmotic pressure of urine is controlled and regulated
dilution
hypotonic urine enters the collecting ducts from the DCT and the thick limb of the loop
if water not lost, urine will be hypotonic
concentration
high interstitial sodium chloride concentration in medulla
[mechanism is countercurrent multiplier by loop of Henle, see p. 981]
(you are not responsible for how countercurrent multiplier works, only for what it does)
"loop" diuretics (such as Lasix®) interfere with forming high interstitial [NaCl]
water leaves collecting tubule attracted by the high NaCl ("osmotic suck")
ADH controls water permeability of collecting duct (recall: diabetes insipidus)
by controlling insert/remove water channels (aquaporins)
7. Know the anatomy of the ureters, urinary bladder, and urethra
ureters
smooth muscle in wall
peristalsis transports urine
bladder
transitional epithelium
cuboidal to squamous depending on volume
detrusor (smooth) muscle in wall
extensible
urethra
smooth muscle --> peristalsis (male orgasm)
short in females --> increased risk of cystitis (bladder infection)
8. Understand the control of micturition
micturition = urination (also called voiding)
initiated by visceral (autonomic) motor neurons in sacral spinal cord
reflex control (stretch receptors in bladder--> sacral motor neurons)
under higher control (more or less!)
parasympathetic control - two ouputs (recall "SLUD")
relax urethral sphincters (inhibit motorneurons)
contract bladder smooth muscle (excite motorneurons)
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Last updated 21 April 2005