Lecture #15: Micturition and Glomerular Filtration Flashcards
What are the 2 different conduction paths of sensory signals from bladder stretch receptors?
1) conducted to sacral region of spinal cord via pelvic nerves.
2) conducted reflexively back to bladder via parasympathetic nerves.
As the bladder continues to fill, micturition reflexes occur more often and are more powerful. Once the micturition reflex is powerful enough, it causes a second reflex. What is the second reflex and what does it do?
The second reflex passes through the pudendal nerves to inhibit the external sphincter.
The nephrons function to get rid of waste materials. What are the 4 waste products secreted?
Urea
Creatinine
Uric Acid
Bilirubin
How does the nephrons function to regulate arterial pressure long term?
By excreting variable amounts of sodium ion and water.
How does nephrons function to regulate arterial pressure short term?
Secrete hormones and vasoactive factors such as renin.
What do all of the many functions of nephrons regulate within the body?
> Get rid of waste materials
- urea, creatinine, uric acid, bilirubin
> Regulate water and electrolyte balance
> Regulate body fluid osmolarity
> Regulate arterial pressure
- Long Term
* excrete variable amounts of sodium ion and water
- Short Term
* Secrete hormones and vasoactive factors such as renin
> Regulate acid-base balance
- excrete acids and regulate body fluid buffer stores - eliminate sulfuric and phosphoric acids
> Secretion, Metabolism, and Excretion of Hormones
- erythropoietin - active form of vitamin D
> Gluconeogenesis
What is the formula to calculate urinary excretion rate?
UER =
Filtration Rate - Reabsorption Rate + Secretion Rate
What is the first step in urine formation?
Filtration
What components make up the glomerular filtrate?
Water
Ions
Glucose
Urea
What formula is used to calculate filtration fraction?
Filtration Fraction = GFR/Renal Plasma Flow
- fraction of renal plasma flow that is filtered = 0.2
(i. e., 20% of plasma flowing through kidney is filtered).
True or False:
The concentration of most substances except for proteins is the same in the filtrate and the plasma.
TRUE
What forms the slit filtration barrier?
Podocytes
- with negative charges
True or False:
The endothelium and basement membrane layers of the filtration barrier have a negative charge and the podocytes of the filtration barrier have a neutral charge.
False - The endothelium, basement membrane, and podocytes of the filtration barrier all have a negative charge.
Albumin is smaller in size then the slit pores made by the podocytes, but why does it not freely pass through?
Because of the negative charge.
In which portion of the filtration barrier are fenestre found?
Endothelium
Does the endothelium, basement membrane, or podocytes of the filtration barrier have the strongest negative charge?
Basement Membrane
What determines the glomerular filtration rate (GFR)?
> the balance of hydrostatic and colloid osmotic forces acting across the capillary membrane
> capillary filtration coefficient
- product of permeability and filtering surface area of capillaries
What are 2 diseases that can lower glomerular capillary filtration coefficient?
> Chronic un-controlled hypertension
> Diabetes mellitus
What is the definition of minimal change nephropathy?
When the basement membrane losses negative charges.
What is hydronephrosis?
Distension and Dilation of Renal Pelvis and Calyces.
True or False:
Reflex contractions relax spontaneously when the bladder is only partially filled.
True
How do you calculate glomerular filtration rate (GFR)?
GFR = (K1) x (Net Filtration Pressure)
*Net Filtration Pressure is the Starling Forces
(Pg - Pb - PIEg + PIEb)
(60 - 18 - 32 + 0) = 10 mmHg
K1 = GFR/Net filtration pressure
= 125 ml/min / 10 mmHg = 12.5 mmHg
What effect does increase the K1 have on GFR?
It raises GFR
What effect does lowering K1 have on the GFR?
It reduces GFR
True of False:
Some low-molecular weight substances are not freely filtered because they are partially bound to proteins.
True
What is the K1?
K1 = capillary filtration coefficient
*product of permeability and filtering surface area of capillaries.
What are 2 factors that influence glomerular capillary colloid osmotic pressure?
1) arterial plasma colloid osmotic pressure
2) filtration fraction
What is a factor that increase glomerular colloid osmotic pressure?
Increasing Filtration Fraction
What effect does increasing arterial pressure have on glomerular hydrostatic pressure and thus, GFR?
An increase in arterial pressure will increase the Pg (glomerular hydrostatic pressure), and thus, will increase the GFR.
What effect does increasing the afferent arteriolar resistance have on glomerular hydrostatic pressure and thus, GFR?
Increasing the afferent arteriolar resistance would decrease the Pg (glomerular hydrostatic pressure) thus, decreasing the GFR.
What effect would increasing the efferent arteriolar resistance have on the glomerular hydrostatic pressure and thus, the GFR?
Increasing the efferent arteriolar resistance would result in an increase in Pg (glomerular hydrostatic pressure) thus, slightly increasing the GFR.
How do you calculate Renal Blood Flow?
RBF =
(renal artery pressure - renal vein pressure)/total vascular resist.
What accounts for most of the oxygen consumed by the kidneys?
Much of the oxygen consumed by the kidneys is related to the high rate of active sodium reabsorption.
Does strong activation of renal sympathetic nerves increase or decrease GFR and renal blood flow?
Decreases renal blood flow and GFR.
Does strong activation of renal sympathetic nerves constrict or dilate renal arterioles?
Constricts renal arterioles.
True or False:
All blood vessels of the kidneys are richly innervated by sympathetic system.
True
True of False:
Moderate sympathetic activation has a large effect on arteriole constriction.
False - moderate sympathetic activation has little effect.
What are the two mechanisms that control GFR consistency?
1) Sympathetic System
2) Hormones:
> norepinephrine and epinephrine (from adrenal medulla)
- parallel the sympathetic system
> endothelin
> angiotensin II
> endothelial-derived NO
> prostaglandins and bradykinin
What is the role of endothelin (hormone) in controlling GFR?
Endothelin is released by damaged vascular endothelial cells of the kidneys and other tissues.
> it may contribute to renal vasoconstriction leading to reduced GFR
> it may contribute to hemostasis when a blood vessel is severed
> plasma levels increase in certain disease states associated with vascular injury
- toxemia of pregnancy
- acute renal failure
- chronic uremia
What 3 diseases increase plasma levels of endothelin?
toxemia of pregnancy
acute renal failure
chronic uremia
Why do afferent arterioles seem to be protected against the effects of angiotensin II?
Because afferent arterioles release prostaglandins and nitric oxide, which are vasodilators. Thus, they counter act the effects of angiotensin II by releasing vasodilators.
What effect does angiotensin II have on efferent arterioles? Also, what does this do to GFR, increase or decrease?
Angiotensin II constricts the efferent arterioles, thus increasing the GFR.
Why is angiotensin II usually released to act upon the efferent arterioles?
Formed usually in situations associated with decreased arterial pressure or volume depletion.
Where is nitric oxide (NO) derived from and what does it do to renal arterioles?
Nitric Oxide is derived from endothelial cells and helps maintain renal vasodilation
What role do prostaglandins and bradykinin play on renal arterioles?
Vasodilators that may offset effects of sympathetic and angiotensin II vasoconstrictor effects (especially on afferent arterioles).
What does autoregulation refer to and what does it function to maintain and control within the kidney?
Autoregulation refers to the relative constancy of GFR and renal blood flow.
Primary Function is to:
- maintain a relatively constant GFR - allow precise control of renal excretion of water and solutes - prevent relatively large changes in GFR and renal excretion that would otherwise occur with changes in blood pressure
True or False:
Autoregulation prevents relatively large changes in GFR and renal excretion that would otherwise occur with changes in blood pressure.
TRUE
True or False:
Autoregulation allows precise control of renal excretion of water and solutes.
TRUE
What is the normal GFR per day?
180 L/day
- tubular reabsorption = 178.5 L/day
- normal daily fluid excretion = 1.5 L/day
What would happen without autoregulation of the kidneys?
Without autoregulation, a slight increase in blood pressure could increase GFR up to 225 L/day.
** This would increase urine flow to 46.5 L/day.
In what structure is the macula densa located?
Distal Tubule
In which arterioles are juxtaglomerular cells found?
Juxtaglomerular cells are in afferent and efferent arterioles.
What are the two components of the tubuloglomerular feedback mechanism for autoregulation?
1) afferent arteriolar feedback mechanism
2) efferent arteriolar feedback mechanism
What happens if autoregulation decreases GFR?
Decrease GFR = slow flow rate in loop of Henle =
>increase reabsorption of sodium and chloride ions in the ascending limb
>decrease in sodium chloride at macula densa
If there is a decrease in NaCl, what will the resulting signal from the macula densa result in?
> decrease resistance to blood in afferent arterioles
increase renin release from JG cells
increase angiotensin II
increase efferent arteriolar resistance
Look over slides 44 and 45 in the lecture 15 handout.
Figure 27-11 in the book
