Chapter 26 - Guyton (2nd EXAM) Flashcards
Functions of the kidneys.
- Excretion of metabolic waste products and foreign chemicals
- Regulation of water and electrolyte balances
- Regulation of body fluid osmolality and electrolyte concentrations
- Regulation of arterial pressure
- Regulation of acid-base balance
- Secretion, metabolism, and excretion of hormones
- Gluconeogenesis
In people with severe kidney disease or who have had their kidneys removed and have been placed on hemodialysis, severe anemia develops as a result of?
decreased erythropoietin production
How do the kidneys contribute to normal calcium deposition in bone and calcium reabsorption by the gastrointestinal tract?
kidneys produce the active form of vitamin D, 1,25-dihydroxyvitamin D3 (calcitriol)
The kidneys synthesize glucose from amino acids and other precursors during prolonged fasting, a process referred to as?
gluconeogenesis
Are the kidneys located inside or outside the peritoneal cavity?
outside
The renal artery and ureter pass through what?
hilium
Blood flow to the kidneys is about how much of the cardiac output?
22% (or about 1100 mL/min)
Located between the glomerular and peritubular capillaries, this structure helps regulate hydrostatic pressure in both sets of capillaries.
efferent arterioles
Each nephron contains?
a tuft of glomerular capillaries called the glomerulus, through which large amounts of fluid are filtered from the blood, and a long tubule in which the filtered fluid is converted into urine on its way to the pelvis of the kidney
Bowman’s capsule
encases one glomerulus
Efferent arteriole
leads to a second capillary network, the peritubular capillaries
Afferent arterioles
lead to the glomerular capillaries, where large amounts of fluid and solutes (except the plasma proteins) are filtered to begin urine formation
Micturition
process by which the urinary bladder empties when it becomes filled
Contraction of the _______ muscle is a major step in emptying the bladder.
detrusor
Principal nerve supply to the bladder.
pelvic nerves, which connect with the spinal cord through the sacral plexus, S-2 and S-3 (sensory and motor - parasympathetic); skeletal motor fibers transmitted through the pudendal nerve to the external bladder sphincter; sympathetic innervation
through the hypogastric nerves, connecting mainly with L-2
Peristaltic contractions in the ureter are enhanced by ___________ stimulation and inhibited by ___________ stimulation.
parasympathetic; sympathetic
The ureters enter the bladder through the detrusor
muscle in the _______ region of the bladder.
trigone
Vesicoureteral reflux
urine in the bladder is propelled backward into the ureter
This effect is important for preventing excessive flow of fluid into the pelvis of a kidney with a blocked ureter (stone).
ureterorenal reflex (pain impulses cause a sympathetic reflex back to the kidney to constrict the renal arterioles, thereby decreasing urine output from the kidney)
Stretch signals from the _______ ______ are especially strong and are mainly responsible for initiating the reflexes that cause bladder emptying.
posterior urethra
What nerves must be inhibited to cause urination even when you don’t want to?
pudendal nerves to external sphincter (micturition reflex becomes powerful enough it will inhibit voluntary constrictor signals)
The micturition reflex is a completely autonomic spinal cord reflex, but it can be inhibited or facilitated by centers in the brain. These centers include:
strong facilitative and inhibitory centers in the brain stem, located mainly in the pons, and several centers located in the cerebral cortex
What is the cause of overflow incontinence?
damaged sensory fibers from the bladder to the spinal cord preventing stretch signals so urine constantly overflows a few drops at a time into urethra (despite intact efferent fibers from the cord to the bladder and despite intact neurogenic connections within the brain); this would be caused by injury at the sacral region of the spinal cord
How is micturition affected by spinal cord injury above the sacral region?
typical micturition reflexes can still occur but no longer controlled by the brain; periodic (unannounced) bladder emptying
Uninhibited neurogenic bladder.
condition derives from partial damage in the spinal cord or the brain stem that interrupts most of the inhibitory signals; facilitative impulses passing continually down the cord keep the sacral centers so excitable that even a small quantity of urine elicits an uncontrollable micturition reflex (frequent urination)
Urinary excretion rate =
filtration - reabsorption + secretion
What are two advantages to a high GFR?
some waste products depend primarily on glomerular filtration for their excretion, entire plasma can be filtered and processed about 60 times each day
Urine formation begins with filtration of large amounts of fluid through the glomerular capillaries into ________ ________.
Bowman’s capsule
GFR is determined by:
sum of the hydrostatic and colloid osmotic forces across the glomerular membrane, which gives the net filtration pressure; and glomerular capillary filtration coefficient Kf (GFR = Kf x Net filtration pressure)
The glomerular capillaries have a much higher rate of filtration than most other capillaries because?
high glomerular hydrostatic pressure and a large Kf
What prevents plasma proteins from passing through the fenestrations in the glomerular capillary membrane?
endothelial cells, basement membrane, and epithelial cells all have a fixed negative charge (proteoglycans) that prevents the passage of plasma proteins
Kf =
GFR / net filtration pressure
In what ways does chronic hypertension and uncontrolled diabetes mellitus reduce Kf?
increasing the thickness of the glomerular capillary basement membrane and damaging the capillaries so severely that there is loss of capillary function
Bowman’s capsule hydrostatic pressure typically does not change (if it increases, GFR will decrease). What could increase Bowman’s capsule hydrostatic pressure - most commonly?
precipitation of calcium or uric acid in the ureter (stones)
Glomerular hydrostatic pressure is determined by three variables:
arterial pressure, afferent arteriolar resistance, and efferent arteriolar resistance
How would constriction of afferent arterioles affect GFR?
decrease
How would efferent arteriole constriction affect GFR?
depends on the severity of the constriction; modest efferent constriction raises GFR, but severe efferent constriction (more than a threefold increase in resistance) tends to reduce GFR due to increase in colloid osmotic pressure caused by the Donnan effect
Primary determining factor of oxygen consumption in the kidneys?
sodium reabsorption
The outer part of the kidney, the renal ______, receives most of the kidney’s blood flow.
cortex
Flow to the renal medulla is supplied by a specialized portion of the peritubular capillary system called the ____ _____.
vasa recta
Sympathetic nervous system action ________ GFR.
decreases (only when severe as with hemorrhage)
Hormones that decrease GFR?
norepinephrine, epinephrine, endothelin, angiotensin II (prevents decrease)
Hormones that increase GFR?
endothelial-derived nitric oxide, prostaglandins, bradykinin
Adaptive mechanisms in the renal tubules allow them to increase their reabsorption rate when GFR rises, a phenomenon referred to as_____________ balance.
glomerulotubular
Decreased macula densa sodium chloride causes?
dilation of afferent arterioles to decrease resistance to blood flow which raises glomerular hydrostatic pressure and helps return GFR toward normal, and increases renin release from the juxtaglomerular cells of the afferent and efferent arterioles (angiotensin II constricts efferent arterioles)
How would high protein intake and increased blood glucose affect renal blood flow and GFR?
increase (reabsorbed along with sodium in the proximal tubule)
What occurs after GFR drops (tubuloglomerular feedback)?
decreased delivery of sodium chloride to the macula densa activates a tubuloglomerular feedback–mediated dilation of the afferent arterioles and subsequent increases in renal blood flow and GFR
Located in the medulla of the kidney?
loop of Henle (juxtamedullary nephrons have a loop of Henle that extends deep into the medulla), medullary collecting tubule, collecting duct
Urea
waste product from protein/amino acid metabolism
Uric acid
waste product from nucleic acid metabolism
Creatinine
waste product from muscle metabolism
Bilirubin
waste product from hemoglobin metabolism
