Download Chapter 18 - Urinary System

Chapter 18 Lecture Notes
page 1
A. summary of functions
production of urine is NOT a function of the kidney; urine is the
by-product of the kidney’s functions:
1. regulate body water content, which indirectly regulates blood
volume and blood pressure
2. regulate electrolyte levels (Na, K, Cl, Ca, PO4) - the control of Na
levels in the body also indirectly regulates blood volume and
blood pressure
3. eliminate metabolic wastes (urea, uric acid, creatinine)
4. secrete erythropoietin which controls RBC formation
5. secrete renin which leads to the activation of angiotensin II
(controls aldosterone secretion and controls blood pressure
through vasoconstriction)
6. regulate ECF pH by controlling the amount of H+ in the body fluids
B. gross anatomy
1. kidneys
a. location - lateral to vertebral column against posterior wall of
abdominal cavity between T12 and L3
 right kidney lower than left
 held in place by the peritoneum and adipose capsule
BIOL 2404
Strong/Spring 2007
Chapter 18 Lecture Notes
page 2
b. capsule - outer covering of fibrous c.t.
c. hilus - medial indentation
d. layers
 cortex forms outer layer and contains the renal corpuscles
 medulla consists of renal pyramids
o pyramids made of collecting ducts that end at the
papilla (tip of pyramid that opens into a calyx)
e. collecting system
 calyx = cup-like structure that surrounds a papilla
 pelvis = where all calyces join, connected to ureter
BIOL 2404
Strong/Spring 2007
Chapter 18 Lecture Notes
page 3
2. ureters transport urine from kidneys to urinary bladder
a. location - lateral to vertebral column
 renal pelvis to posterior, inferior urinary bladder
b. enter urinary bladder wall at an angle; prevents backflow
c. peristalsis by smooth muscle pushes urine to urinary bladder
3. urinary bladder stores urine
a.



location - in pelvic cavity
posterior to pubic symphysis
anterior to rectum in males
anterior and inferior to uterus, anterior to vagina in females
b. wall contains smooth muscle (detrussor)
c. trigone - area on inferior floor of urinary bladder between
openings of ureters (posterior) and urethra (anterior)
d. internal urethral sphincter surrounds urethra opening
4. urethra carries urine to exterior of body
a. location - inferior to urinary bladder
 in females, anterior to vagina
o orifice in vestibule anterior to vaginal orifice
 in males, inside corpus spongiosum of penis
o orifice in glans penis
b. external urethral sphincter - skeletal muscle in floor of pelvic
cavity, posterior to pubic symphysis
C. blood supply - renal fraction = 20% of cardiac output
abdominal aorta
renal artery
interlobar artery
arcuate artery
BIOL 2404
Strong/Spring 2007
Chapter 18 Lecture Notes
page 4
interlobular artery
afferent arteriole
glomerulus (capillaries)
efferent arteriole
peritubular capillaries and vasa recta
interlobular vein
arcuate vein
interlobar vein
renal vein
inferior vena cava
D. nephron structure and function
1. components
a. renal corpuscle - glomerular capsule surrounding glomerulus
b. proximal convoluted tubule in cortex
c. loop of the nephron dips into medulla; part of water
conserving process
d. distal convoluted tubule in cortex
 nephron empties into collecting duct (cortex to papilla)
BIOL 2404
Strong/Spring 2007
Chapter 18 Lecture Notes
page 5
2. processes
a. filtration is the movement of about 20% of the plasma
(except the proteins) from the glomerulus into the
glomerular capsule
 filtration is caused by blood pressure
 if blood pressure or cardiac output are too low, filtration will
decrease or stop
b. reabsorption is the transport of materials from the filtrate
back into the blood in the peritubular capillaries
 it occurs primarily in the proximal convoluted tubule
 the cells of these tubules remove the materials we want to
keep and leave the rest inside the nephron
o
o
o
o
glucose
amino acids
sodium
water
c. secretion is the transport of materials from the blood in the
peritubular capillaries into the filtrate
 it occurs primarily in the distal convoluted tubule
 it helps remove materials from the blood that were not
removed during filtration
o
o
o
hydrogen ions
potassium (K)
drugs
d. filtration - reabsorption + secretion = excretion
180 liters / day - 178.5 liters / day = 1.5 liters / day
BIOL 2404
Strong/Spring 2007
Chapter 18 Lecture Notes
page 6
afferent arteriole
glomerular capsule
glomerulus
efferent arteriole
proximal convoluted
tubule
peritubular capillaries
loop of the nephron
vasa recta
distal convoluted tubules
peritubular capillaries
collecting duct
4. regulation of water and electrolytes (Na, K, Cl) *
a. sodium and chloride
 sodium is actively transported out of the filtrate by tubule
cells
 chloride follows passively
 most of the sodium in the filtrate is reabsorbed automatically
 the level of aldosterone affects how much of the remaining
sodium is reabsorbed
o the higher the aldosterone level the more sodium is
reabsorbed and the more potassium is excreted
 sodium reabsorption drives glucose, amino acid, and water
reabsorption
BIOL 2404
Strong/Spring 2007
Chapter 18 Lecture Notes
page 7
b. water
 most water is reabsorbed automatically because it follows
sodium by osmosis
 the level of ADH affects how much of the remaining water is
reabsorbed
 ADH inserts water channels into the cells of the distal
convoluted tubule and collecting duct
o without these channels no extra water can be
reabsorbed
o the higher the level of ADH the more water is
reabsorbed
 ADH is secreted at the posterior pituitary when body fluid
osmolarity is high or volume is low
5. renin-angiotensin mechanism and role of ACE
low Na levels, low blood volume, low blood pressure
kidney secretes renin into blood
renin along with ACE from the lungs activate angiotensin
angiotensin increases aldosterone secretion
aldosterone increases sodium reabsorption and water retention
(ACE = angiotensin converting enzyme)
BIOL 2404
Strong/Spring 2007
Chapter 18 Lecture Notes
page 8
E. micturition reflex
1. stretch receptors in urinary bladder wall at about 200 mL
2. afferent signals to CNS
a. reflex control center in sacral spinal cord causes
parasympathetic signals to urinary bladder to contract
detrussor
b. cerebral cortex allows voluntary decision to relax external
urethral sphincter
F. pH balance
1. normal pH of the ECF is 7.35 to 7.45
changes in pH disrupt membranes, alter protein structure and
change enzyme activity
2. imbalances
a. acidosis occurs below pH 7.35
 more common than alkalosis because the body produces
a lot of acids
 causes depressed CNS activity, heart failure, circulatory
collapse
b. alkalosis occurs above pH 7.45
3. homeostasis
a. buffer systems are chemicals that “soak up” extra acid or
base and reduce the severity of pH imbalances
 the bicarbonate buffer system in the blood
BIOL 2404
Strong/Spring 2007
Chapter 18 Lecture Notes
page 9
b. respiratory compensation adjusts pulmonary ventilation to
reduce the severity of pH imbalances
 acidosis causes increased pulmonary ventilation, which
excretes more carbon dioxide
 alkalosis causes decreased pulmonary ventilation, which
excretes less carbon dioxide
c. renal compensation
 acidosis causes the kidneys to increase hydrogen ion (acid)
secretion
 alkalosis causes the kidneys to decrease hydrogen ion (acid)
secretion
BIOL 2404
Strong/Spring 2007