Micturition and Glomerular Filtration Flashcards
Describe the steps that are involved in the micturition reflex
- micturition contractions begin as the bladder fills
- sensory signals are sent from the bladder stretch receptors
- as the bladder fills, the micturition reflexes get more often and powerful
- passes through the pudendal nerves to inhibit the external sphincter
- higher brain centers keep micturition partially inhibited until it is desired
- when it is time to urinate the cortical centers facilitate the sacral micturition centers to initiate the reflex and the external urinary sphincter so that urination can occur
Describe the path of the sensory signals from the bladder to the stretch receptors
They are conducted to the sacral region of the spinal cord via the pelvic nerves
come back to the bladder via the parasympathetic system
True or false: The micturition is not self regenerative
False: it is…
Where are the higher brain centers located that are involved in regulating micturition?
pons
What are the functions of nephrons?
- get rid of waste materials
- regulate water and electrolyte balance
- regulate fluid osmolarity
- regulate arterial pressure
- regulate acid and base balance
- secretion, metabolism, and excretion of hormones
- gluconeogenesis
WOW PAGES
waste, osmolarity, water and electrolytes, Pressure, Acid-base, Gluconeogensis, Excretion, Secretion
What are the three processes that determine the rates at which different substances are excreted in the urine?
Filtration, Reabsorption, and Secretion
What is the equation for the urinary excretion rate?
Filtration rate-reabsorption rate + secretion rate
What are the 4 processes that occur in the kidney?
- filtration
- reabsorption
- secretion
- excretion
What is the first step in urine formation?
filtration
What are the components of the glomerular filtrate?
Water
ions
glucose
urea
What is the equation for the filtration fraction?
GFR/renal plasma flow
What percent and or decimal of the plasma flowing through the kidney is filtered?
0.2 or 20%
Why are certain low molecular weight substances not freely filtered in the kidney?
Because they are partially bound to the proteins
What is the relationship between the molecular radius and the relative filterability?
As the effective molecular radius increases, the filterability decreases
What are the 3 layers of the filtration barrier?
endothelium (fenstrae and negative charges) basement membrane (collagen and proteoglycan fibers and strong negative charges) podocytes (with negative charges)
What is the GFR determined by?
- Balance of the hydrostatic and the colloid somatic forces acting across capillary membrane
- capillary filtration coefficient
What is the average GFR?
125ml/min=180 L a day
What is the filterability of water?
1.0
What are some of the diseases that lower glomerular capillary filtration coefficient?
Chronic uncontrolled hypertension and diabetes mellitus
Define minimal change nephropathy
loss of negative charges on the basement membrane
Define hydronephrosis
Distension and dilation of the renal pelvis and calyces
What is the equation for GFR?
GFR=K1 x(Pg −Pb −πg +πb)
Pg = glomerular hydrostatic pressure = 60 mm Hg
• Pb = Bowman’s capsule hydrostatic pressure = 18 mm Hg
• πg = glomerular capillary colloid osmotic pressure = 32 mm Hg
• πb = colloid osmotic pressure of Bowman’s capsule = 0
What is K1 in the GFR equation?
K1 is the capillary filtration coefficient= product of permeability and filtering surface area of capillaries
How would an increase in K1 effect the GFR?
it would increase the GFR
How would a decrease in k1 effect the GFR?
It would decrease the GFR
What are the factors that influence the glomerular capillary colloid osmotic pressure?
arterial plasma colloid osmotic pressure
filtration fraction
What are the factors that increase the glomerular colloid osmotic pressure?
Increasing the filtration fraction
What are the variables that determine the glomerular hydrostatic pressure?
Arterial pressure
Afferent arterial resistance
efferent arteriolar resistance
What happens to your GFR and glomerular hydrostatic pressure when you increase arterial pressure?
Increase Pg and increase GFR
What happens to your GFR and glomerular hydrostatic pressure when you increase afferent arteriolar resistance?
Decreased PG and decreased GFR
What happens to your GFR and glomerular hydrostatic pressure when you increase efferent arteriolar resistance?
increased Pg and slightly increased GFR
What are the factors that determine the renal blood flow?
- Kidneys have 7X the blood flow of the brain but only 2X the o2 consumption
- most of the o2 consumed by the kidneys is related to the high rate of active sodium reabsorption
- tubular sodium reabsorption is closely related to the GFR and the rate of sodium filtration
What is the equation for the renal blood flow?
(renal artery pressure-renal vein pressure)/(total vascular resistance)
What is the effect of the kidneys if there is a strong activation of the renal sympathetic system?
renal arterioles are constricted and there is a decrease in the renal blood flow and the GFR
What is the role of endothelin in the kidney?
released by the damaged vascular endithelial cells of the kidneys and other tissues
may contribute to renal vasoconstriction leading to reduced GFR
What are the 3 disease states that are associated with an increase in plasma levels associated with vascular injury?
- toxemia of pregnancy
- acute renal failure
- chronic uremia
What is the purpose of Angiotensin II?
- constricts efferent arterioles
- formed in situations associated with decreased arterial pressure or volume depletion
- increase GFR
- afferent arterioles are protected by the effects of angiotensin 2 (bc vasodilators)
Describe nitric oxide
- derived from endothelial cells
- basic levels help maintain the renal vasodilation
What do prostaglandins and bradykinin do?
they are vasodilators that may offset the effects of sympathetic and angiotensin 2 vasoconstriction effects (afferent)
Describe auto regulation
relative constancy of GFR and renal blood flow
- maintain a relatively constant GFR
- precise control of renal excretion of water and solutes
- prevent large changes in GFR and renal excretion that would otherwise occur with changes in blood pressure
What is the normal GFR?
180 L/day
What is the normal daily fluid excretion?
1.5L/day
If there was no auto regulation, what would the GFR and urine flow potentially increase to a day?
GFR 225 L a day
urine flow 46.5L a day
Describe the juxtaglomerular complex
- macula densa in the distal tubule
- juxtaglomerular cells in the afferent and efferent arterioles
What happens in the kidney if there is a decrease in the GFR?
There is a slow flow rate in the loop of Henle
increase reabsorption of sodium and chloride ions in the ascending limb
decrease in sodium chloride at the macula densa
What happens in the nephron if there is a decrease in NaCl
results in a signal from the macula densa
decreased resistance to blood in the afferent arterioles
increased renin release from the JG cells (major storage site of renin
increased angiotensin 2
Increased efferent arteriolar resistance
