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Renal- Guyton Ch. 26
Terms in this set (54)
Functions of the kidneys (8)
1. Excretion of metabolic waste products & foreign chemicals
2. Regulation of water & electrolyte balances
3. Regulation of body fluid osmolality & electrolyte concentrations
4. Regulation of arterial BP
5. Regulation of acid-base balance
6. Regulation of erythrocyte production
7. Secretion, metabolism, & excretion of hormones
Waste products that the kidneys eliminate from the body (5)
-urea (from metabolism of amino acids)
-creatinine (from muscle creatine)
-uric acid (from nucleic acids)
-end products of Hgb breakdown (such as bilirubin)
-metabolites of various hormones
Intake of water and many electrolytes is governed mainly by a person's eating and drinking habits, requiring the kidneys to...
...adjust their excretion rates to match the intakes of various substances.
How do the kidneys play a dominant role in the regulation of BP (short-term and long-term)
Long-term = excreting variable amounts of sodium & water
Short-term = secreting hormones & vasoactive factors or substances (ex. renin) that lead to the formation of vasoactive products (ex. angiotensin II)
What is the important stimulus for erythropoietin secretion by the kidneys?
Describe the kidneys/their position in the body
-lie on posterior wall of abdomen, outside the peritoneal cavity
-each kidney weighs ~150g and is the size of a clenched fist
-surrounded by a tough fibrous capsule to protect it
indented region on the medial side of each kidney through which the renal artery & vein, lymphatics, nerve supply, and ureter (carries final urine from kidney to bladder) passes
2 major regions of the kidney
divided into 8-10 cone-shaped masses of tissue called renal pyramids. the base of each pyramid originates at the border between the cortex & the medulla & terminates in the papilla (which projects into the space of the renal pelvis)
a funnel-shape continuation of the upper end of the ureter
The outer border of the pelvis is divided into open-ended pouches called...
...major calyces that extend downward & divide into minor calyces which collect urine from the tubules of each papilla
How much blood flows to the kidneys?
about 22% of the cardiac output or 1100mL/min
Steps of renal blood flow
aorta -> renal artery -> interlobar arteries -> arcuate arteries -> interlobular arteries (aka radial arteries) -> afferent arterioles -> glomerular capillaries (large amts of fluid & solutes except plasma proteins are filtered to begin urine formation) -> efferent arteriole -> peritubular capillaries
interlobular vein --> arcuate vein --> interlobar vein --> renal vein
Why is the renal circulation unique?
it has two capillary beds (glomerular & peritubular capillaries) which are arranged in series and separated by the efferent arterioles
What helps regulate the hydrostatic pressure in both sets of capillaries?
High hydrostatic pressure in the glomerular capillaries (about 60mmHg) causes...
...rapid fluid filtration
A much lower hydrostatic pressure in the peritubular capillaries (about 13mmHg) permits...
...rapid fluid reabsorption
By adjusting the resistance of the afferent & efferent arterioles, the kidneys can regulate the hydrostatic pressure in both the glomerular and peritubular capillaries, thereby changing what?
-the rate of glomerular filtration
-the rate of tubular reabsorption
Where does the peritubular capillaries empty into? and where does this go?
-empty into vessels of the venous system
-blood vessels of the venous system progressively form the interlobular vein -> arcuate vein -> interlobar vein -> renal vein
Facts about the nephron
-functional unit of the kidney
-800,000 to 1 million (born with)
-do not regenerate
-After age 40, lose 10% every decade
2 parts of the nephron
1. glomerulus --> tuft of glomerular capillaries; thru which large amounts of fluid are filtered from the blood
2. a long tubule --> the filtered fluid is converted into urine on its way to the pelvis of the kidney
What is the hydrostatic pressure in the glomerular capillaries?
high hydrostatic pressure, about 60mmHg
Total glomerulus is encased in...
Fluid filtered from the glomerular capillaries flows into Bowman's capsule and then into the...
...proximal tubule (which lies in the cortex of the kidney)
From the proximal tubule, fluid flows into the...
...loop of Henle (which dips into the renal medulla)
-consists of descending and ascending limb
Describe the limbs of the loop of Henle
-walls of the descending limb and the lower end of the ascending limb are very thin --> "thin segment of the loop of Henle"
-once the ascending limb goes back into the cortex --> "thick segment of the ascending limb"
End of thick ascending limb is...
the macula densa -- a short segment that has in its wall a plaque of specialized epithelial cells ((macula densa plays important role in controlling nephron fxn))
After the macula densa is the...
distal tubule (lies in the renal cortex)
This is followed by the __________ and the ________, which lead to the _____________ .
connecting tubule; cortical collecting tubule; cortical collecting duct
8-10 cortical collecting ducts run downward into the medulla to become the...
...medullary collecting duct --> they merge to form progressively larger ducts that eventually empty into the renal pelvis through the tips of the renal papillae
nephrons that have glomeruli located in the outer cortex; they have short loops of Henle that penetrate only a short distance into the medulla
nephrons with glomeruli that lie deep in the renal cortex near the medulla; they have long loops of Henle that dip deeply into the medulla
Vascular supply for cortical nephrons
entire tubular system is surrounded by an extensive network of peritubular capillaries
Vascular supply for juxtamedullary nephrons
long efferent arterioles extend from the glomeruli down into the outer medulla and then divide into specialized peritubular capillaries called the VASA RECTA that extend downward into the medulla, lying side by side with the loop of Henle. Vasa recta return toward the cortex and empty into the cortical veins. ((plays an essential role in the formation of concentrated urine))
2 steps of micturition
1. bladder fills progressively until the tension in its walls rises above threshold level
2. this tension elicits the micturition reflex that empties the bladder or gives you a conscious desire to urinate
Is the micturition reflex an autonomic spinal cord reflex?
Yes, but it can be inhibited or facilitated by centers in the cerebral cortex or brain stem
Describe the bladder
-body (urine collects here)
-neck (funnel-shaped extension of the body; connects w/ urethra)
-it's the smooth muscle of the bladder
-contraction of this muscle is a major step in emptying the bladder
-the muscle cells connect & form low-resistance electrical pathways, so an action potential can spread throughout the detrusor muscle, to cause contraction of the entire bladder at once
-posterior wall of bladder; small triangular area
-lowermost apex opens into the posterior urethra
-2 ureters empty at the uppermost angles
-this part is smooth--the rest of the bladder is rugae
-in the bladder neck (smooth muscle)
-its natural tone normally keeps the bladder neck & posterior urethra empty of urine until the bladder pressure rises above a critical threshold
-in the urogenital diaphragm
-voluntary skeletal muscle--under control of the nervous system
The principle nerve supply of the bladder is by way of ________ nerves, which connect with the spinal cord through the ________, mainly connecting with cord segments ____ and ___.
The principle nerve supply of the bladder is by way of PELVIC nerves, which connect with the spinal cord through the SACRAL PLEXUS, mainly connecting with cord segments S2 and S3.
What type of nerve fibers course through the pelvic nerve?
-sensory fibers --> detect degree of stretch
-motor fibers --> innervate the detrusor muscle (parasympathetic)
What other 2 types of innervation are important to bladder fxn?
-skeletal motor fibers --> transmitted thru the pudendal nerve to the external sphincter--they are somatic nerve fibers that control the voluntary skeletal muscle of the sphincter
-sympathetic innervation--> thru the hypogastric nerves, connects with L2 (stimulate blood vessels)
Explain how urine moves through the ureters
-walls of the ureters are smooth muscle innervated by para- and sympathetic nerves
-urine moves through by peristaltic contractions --> parasympathetic stimulation enhances; sympathetic stimulation inhibits
How is vesicoureteral reflux caused?
-ureters course obliquely thru the detrusor muscle; when pressure builds up the detrusor muscle compresses the ureters preventing reflux
-in some ppl, the distance the ureter courses thru the muscle is less so contraction of the bladder does not completely occlude the ureter --> causes reflux
What can vesicoureteral reflux cause?
enlargement of the ureters, and if severe, can increase the pressure in the renal calyces & structures of the renal medulla causing damage
when a ureter is blocked, intense vasoconstriction occurs (severe pain), and pain impulses cause a sympathetic reflex back to the kidney to constrict the renal arterioles which decreases UO from the kidney
A single complete cycle of the micturition reflex
1. progressive & rapid increase in pressure
2. period of sustained pressure
3. return of the pressure to the basal tone of the bladder
person voluntarily contracts abdomen, pressure in bladder increases; extra urine goes into the bladder neck/posterior urethra thus stretching the walls; stretch receptors initiate micturition reflex & simultaneously inhibits the external urethral sphincter
sensory nerve fibers are destroyed; bladder fills to capacity and then leaks (overflows)
-common cause is crush injury to the sacral region of the spinal cord
when spinal cord is damaged above the sacral region causing "spinal shock"; don't have any control over it; periodic catheterization can help regain some control
frequent & uncontrolled micturition from damage in the spinal cord or brain stem--inhibitory signals are interrupted
Urinary excretion rate =
filtration rate - reabsorption rate + secretion rate
(read pg. 331 for explanation & picture)
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