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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 + Bowman’s capsule

glomerulus is tuft of capillaries

afferent arteriole

efferent arteriole

Bowman’s 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 Starling’s 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