Loop of Henle/DCT Flashcards by Cal Schiller

In the entire LOH, unlike the PCT, solute and water reabsorption are ___ regulated

independently

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mostly water reabsorption and solute secretion (concentrates the filtrate)

Descending limb (of LOH)

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no water reabsorption, but reabsorption of solutes occurs (dilutes the filtrate)

ascending limb (of LOH)

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This region is passively permeable to water and solutes

Descending Limb LoH

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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)

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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

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Urea, Na+, and Cl- are ___ into tubule

in the descending LOH

secreted

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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

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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

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Reabsorbs 10-15% of filtered water that is left

Early portion of the DCT

reabsorbs sodium and chloride as well

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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

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Specialized cells found intermixed in the DCT and throughout the collecting ducts

Principal cells

Intercalated cells

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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)

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DCT is similar to PCT in that Na+ reabsorption occurs via ___ transport

active

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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)

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ADH targets principal cells in the

DCT and collecting ducts

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ADH triggers these cells to generate ___ in the apical membrane of the cells lining the tubule

aquaporin-2 channels

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The more ADH that is present, the more aquaporin-2 channels will be _____

generated

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In general, in the presence of ADH, we produce a small quantity of ____ urine

highly concentrated

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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

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The addition of ___ in the interstitial fluid from the collecting duct assists in increasing the high osmolarity in the interstitial fluid

(ADH effects)

urea

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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

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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

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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

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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+)

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+)

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)

Loop of Henle/DCT Flashcards

(92 cards)