Loop of Henle/DCT Flashcards
In the entire LOH, unlike the PCT, solute and water reabsorption are ___ regulated
independently
mostly water reabsorption and solute secretion (concentrates the filtrate)
Descending limb (of LOH)
no water reabsorption, but reabsorption of solutes occurs (dilutes the filtrate)
ascending limb (of LOH)
This region is passively permeable to water and solutes
Descending Limb LoH
Solute reabsorption occurring simultaneously in the ascending limb creates a ___ concentration (osmolarity) in the interstitial fluid
higher
More solutes and less water causes the “first” concentration of filtrate inside the tubule (hyperosmotic) (from descending limb)
Increased interstitial fluid osmolarity forces the descending limb to attempt to find equilibrium (in the descending LOH), causing water ___ and solute ___ to occur in the descending limb
reabsorption
secretion
Urea, Na+, and Cl- are ___ into tubule
in the descending LOH
secreted
This region is passively permeable to small solutes, but impermeable to water (no water reabsorption occurs here)
Because of this, as solutes move out of tubule (reabsorbed), water is left inside the tubule
This creates the “first” dilution of filtrate inside the tubule (hypoosmotic)
Ascending Limb LoH
thin portion
Active reabsorption (movement out of tubule) of Na+, K+, Cl- occurs here, but this region is still impermeable to water
This means that as filtrate moves up the ascending limb, it dilutes even more
Ascending Limb LoH
thick portion
Reabsorbs 10-15% of filtered water that is left
Early portion of the DCT
reabsorbs sodium and chloride as well
By the time filtrate reaches this portion, 90-95% of filtered solutes/water have been reabsorbed and returned to interstitium/bloodstream
Late portion of the DCT
Specialized cells found intermixed in the DCT and throughout the collecting ducts
Principal cells
Intercalated cells
In the DCT and collecting ducts, the amount of reabsorption of solutes/water is dependent on feedback from the body in general… hormones, osmorecptors?
Hormonal (ADH, Aldosterone, Atrial Natriuretic Peptide)
Osmoreceptors throughout the body (ex: body requires more sodium than what’s already been reabsorbed)
DCT is similar to PCT in that Na+ reabsorption occurs via ___ transport
active
In DCT/Collecting ducts though, the cells are relatively still impermeable to water, so water does not follow Na+ via osmosis BUT…
when the need arises, there is a mechanism that gets activated in these cells that allows them to be able to selectively reabsorb water
(Anti-Diuretic Hormone (ADH) causes principal cells in the DCT and collecting ducts to become permeable to water)
ADH targets principal cells in the
DCT and collecting ducts
ADH triggers these cells to generate ___ in the apical membrane of the cells lining the tubule
aquaporin-2 channels
The more ADH that is present, the more aquaporin-2 channels will be _____
generated
In general, in the presence of ADH, we produce a small quantity of ____ urine
highly concentrated
in the presence of ADH, when more water is reabsorbed, it creates an ___ imbalance when it gets to the distal collecting duct
This forces some of the urea to be reabsorbed in order to correct the interstitial fluid imbalance
osmotic
The addition of ___ in the interstitial fluid from the collecting duct assists in increasing the high osmolarity in the interstitial fluid
(ADH effects)
urea
This helps to keep the osmotic gradient constantly moving
The urea that is reabsorbed at the distal collecting ducts migrates through interstitial fluid and gets secreted in the descending limb of the loop of Henle (Urea recycling)
ADH
When ADH is at it maximal secretion…
Body can produce as little as 400-500mL of very concentrated urine each day
The rest is returned to the interstitium/blood stream instead of being urinated out
When blood pressure/volume stabilizes, ADH levels decline causing …
The aquaporin-2 molecules to be removed from principal cells
Normal volume of normal to dilute urine produced
Aquaporin-2 molecules are only effective in the presence of ADH whereas aquaporin-1 molecules are independently functioning in the ___
PCT/LOH
Under the influence of aldosterone, principal cells cause the following:
Sodium reabsorption (usually brings water with it)
Potassium secretion
What causes aldosterone to be released?
Hyperkalemia
Presence of angiotensin II
This occurs when the renin-angiotensin-aldosterone system is stimulated by low blood volume or pressure
Two types of intercalated cells in this region (DCT)
Type A
Type B
Intercalated Cells Type A
cause?
Causes secretion of hydrogen (H+) ions
Causes reabsorption of bicarb
Causes reabsorption of potassium (K+)
Causes secretion of hydrogen (H+) ions
Causes reabsorption of bicarb
Causes reabsorption of potassium (K+)
Intercalated Cells Type A
cause?
Intercalated Cells Type B
cause?
Causes reabsorption of hydrogen (H+) ions
Causes secretion of bicarb
Causes secretion of potassium (K+)
Causes reabsorption of hydrogen (H+) ions
Causes secretion of bicarb
Causes secretion of potassium (K+)
Intercalated Cells Type B
cause?
When atrial cells are stretched because of increased blood pressure or volume, they release ___
ANP
When ANP is stimulated, it has direct actions on the cells located in the ___
DCT and the Collecting Ducts
Inhibits the reabsorption of sodium and water
If this is inhibited, it means more water (fluid volume) is left in filtrate to be eventually excreted (via urination)
This causes a reduction in blood volume/pressure
Atrial Natriuretic Peptide
Also inhibits the renin-angiotensin-aldosterone system
This further reduces reabsorption of various solutes and water
Atrial Natriuretic Peptide
Activated in response to low renal vascular flow/pressure
Example: Low blood pressure
Renin-Angiotensin-Aldosterone System
System activated when blood volume/pressure is too low, no longer stretching the walls of the afferent arteriole
Renin-Angiotensin-Aldosterone System
This causes the juxtaglomerular cells to secrete the hormone/enzyme renin into the blood stream
At the same time, angiotensinogen is released by hepatocytes into the blood
Renin-Angiotensin-Aldosterone System
Renin finds angiotensinogen and cleaves off a 10-amino acid peptide
This converts angiotensinogen to angiotensin-1
Angiotensin I continues to course through the blood until it reaches the lungs. What happens?
Here, angiotensin-I is converted to angiotensin-II by lung endothelial angiotensin converting enzyme (ACE)
Angiotensin II is the active form of the hormone
Angiotensin II affects renal physiology in three ways:
1.Decreases GFR by causing vasoconstriction of afferent arteriole
2. Enhances Na+, Cl- and water reabsorption in the PCT
3. Stimulates the adrenal cortex to release aldosterone
Aldosterone stimulates the principal cells in the collecting ducts to reabsorb more Na+ and Cl- and secrete more K+
With increased reabsorption of Na+ and Cl-, more water is reabsorbed which causes INCREASED blood volume and blood pressure
Even though fluid intake can vary widely, the total volume of fluid in the body remains relatively ___, largely in part to the kidneys
stable
Body fluid volume homeostasis largely dependent on rate of water ___ in urine
excretion
The regulation of plasma ____ and volume are the responsibility of the Loop of Henle, the DCT, and the collecting ducts
osmolarity
Concentrating urine (initially) Permeable to water mostly, therefore concentrating the filtrate
Descending limb of LOH
Diluting urine (initially) Impermeable to water, therefore diluting the filtrate
Thick ascending limb of LOH
Where final dilution/concentration occurs
Where the majority of ADH has its action
DCT + Collecting Ducts
Dilution/Concentration in the DCT and the collecting ducts is controlled by the presence or absence of ADH
In absence of ADH
Urine is diluted
In presence of ADH
Urine is concentrated
Urine volume?
1-2 liters
Urine color?
yellow or amber, varies with urine concentration and diet (beets, medications [pyridium], kidney stones can cause blood in urine)
Urine turbidity?
transparent when voided, becomes cloudy with time
Urine odor?
mildly aromatic, becomes ammonia-like with time
Bacteria turning urea back into ammonia
Urine pH?
ranges from 4.6-8.0, average is 6.0, varies with diet, high protein increases acidity, vegetarian increases alkalinity
Urine specific gravity?
density (ratio of weight of solutes vs water) usually 1.001-1.035 (the higher the solutes the higher the value)
Solutes account for 5% of urine (electrolytes, solutes derived from cellular metabolism, exogenous substances like drugs)
Urea (from breakdown of proteins) Creatinine (from breakdown of creatine phosphate in muscle) Uric Acid (breakdown of nucleic acids) Urobilinogen (breakdown of hemoglobin) Small amount of fatty acids, pigments, enzymes, and hormones
This urea results from the catabolism and deamination of amino acids (proteins) in the liver
Urea can be reabsorbed from filtrate to help create/maintain an osmotic gradient in the kidneys
When GFR reduces severely (as in renal disease), BUN increases
Blood Urea Nitrogen (BUN)- measures urea (uremia)
Two blood tests can provide kidney function information
Blood Urea Nitrogen (BUN)- measures urea (uremia)
Plasma creatinine- catabolism of creatine phosphate in skeletal muscle
catabolism of creatine phosphate in skeletal muscle
Normally remains steady as the rate of creatinine excretion in urine equals its discharge from muscle
There is NO use for creatinine in the body, so we should excrete much, if not all of it in the urine
Plasma creatinine
The volume of plasma (mL) that can be completely cleared of a substance per unit time (min)
Renal Plasma Clearance
plant polysaccharide, easily passes through the filter and is excreted in urine 100%
Great measure of true GFR
Inulin
Great method but inulin is not produced in the body so this test is difficult to do
As creatinine is filtered, not reabsorbed, its clearance is a good estimate of GFR
Creatinine Clearance
At times, can overestimate GFR by 10-20%
Collecting ducts –-papilla - papillary ducts - minor calyces – major calyces – renal pelvis – ureters – urinary bladder – urethra
urine transport
Urine transport by peristalsis (___ to ___) aided by hydrostatic pressure and gravity
renal pelvis
urinary bladder
Ureters are ___
retroperitoneal
Ureters pass ___ into posterior/inferior aspect of bladder
obliquely
When the bladder fills with urine, it pulls the bladder down which closes these valves so no “backflow” occurs
Called the anti-reflux mechanism
Three layers (superficial to deep) of ureter
Adventitia
Muscularis
Mucosa
anchors ureters to surrounding tissues, contains blood vessels, nerves, lymphatic vessels
Adventitia
(peristalsis)-outer circular, inner longitudinal smooth muscle
Muscularis
transitional epithelium with goblet cells that secrete mucous (to protect mucosa from acidity)
Mucosa
posterior to pubic symphysis anterior to rectum in males anterior to vagina in females inferior to uterus in females held in place by peritoneal folds
Urinary Bladder
Three layers make up the urinary bladder wall
Serosa
Adventitia
Muscularis (Detrusor muscle)
Mucosa
covers superior surface, visceral peritoneum
Serosa:
covers posterior and inferior surfaces, continuous with the ureters
Adventitia
Three layers
Inner longitudinal
Middle circular
Outer longitudinal
Muscularis (Detrusor muscle)
When the detrusor is relaxed, it allows for ___
filling
When the detrusor is ___, it forces urine into the urethra
contracted
Rugae
Trigone
Mucosa ( uroepithelium)
allows bladder to expand when it is filling
Transitional epithelium – shape of these epithelial cells changes with the degree of stretch placed on them
Rugae
smooth, triangular area in bladder floor
ureteral openings in posterior corners
internal urethral orifice in anterior corner
!!!
Trigone
Circular smooth muscle (extension of the detrusor muscle) near internal urethral orifice
Involuntary (controlled by parasympathetic nervous system)
Is just above the prostate in males
Internal urethral sphincter (inferior aspect of bladder)
Skeletal muscle (composed of deep perineal muscles/pelvic floor) Voluntary
Sits just below the prostate (in males)
Is at the opening of the external urethral orifice (in females)
External urethral sphincter
Prostatic
Membranous
Spongy
Male Urethra
circular smooth muscle forms internal urethral sphincter
male urethra
Prostatic
shortest region passing through urogenital diaphragm, circular skeletal muscle forms external urethral sphincter
Membranous
longest region passing through penis
contains bulbourethral (Cowper’s gland)
Spongy
delivers alkaline fluid to help neutralize acidity of urethra
Bulbourethral (Cowper’s gland)
Short tube that conveys urine from bladder to exterior
Female Urethra
Parasympathetic reflex initiates the mechanism for urination which causes
micturition = urination
___ contractions of the detrusor muscle
(micturition)
Internal urethral sphincter to open
This causes urine to move from the bladder into the urethra
This causes the sensation that we perceive as our body telling us we need to urinate soon. But voluntary contraction prevents this.
Involuntary
____ relaxation of this external sphincter allows the flow of urine to occur
Voluntary
Effects of aging on kidneys?
Kidney shrinkage
Renal bloodflow/GFR decreases
Increased incidence of calculi/inflammation/UTIs
Retention (BPH/prostate cancer/hematuria/dysuria)
