Micturition And GFR Flashcards
When does micturition contractions occur?
When the Bladder FILLS
Once the bladder stretches, where does the signal travel to?
Sacral region of the spinal cord via the PELVIC nerves
The reflex of the micturition occurs via what pathway?
Parasympathetic nerves
What happens as the bladder continues to fill?
The micturition reflexes occur MORE and are often more POWERFUL
What happens when the reflex is powerful enough
It Causes a second reflex
Characteristics of the Pudendal nerves
Inhibit the External sphincter
How does the body inhibit urination when the Pudendal nerves are firing?
Higher Brain centers ( Pons) keep micturition inhibited until desired
Major function of the nephrons
To get rid of waste materials
Urea, creatinine, Uris acid, and Bilirubin
Other NON-regulatory functions of the Nephrons?
Secretion, Metabolism, and excretion of HORMONES
&
Gluconeogenesis
Regulatory functions of the nephron
Regulates:
- Arterial pressure
- Acid base balance
- Bodily fluid osmolarity
- Water and Electrolyte balance
What are the processes that deer in the rate at which different substances are excreted in the Urine?
- Filtration
- Reabsorption
- Secretion
What is the mathematical calc of Urinary Excretion Rate?
UER = Filtration rate - (Reabsorption rate + Secretion rate)
What particles cannot be filtered?
NEGATIVELY charged
What is the first step in urine formation?
Filtration
Components of the glomerular filtrate.
Water
Urea
Glucose
Ions
(WUGI)
Filtration Fraction
The fraction of the renal plasma flow that is filtered
FF = GFR/Renal Plasma Flow
- approx 20%
Concentration of ___ is NOT the same in the Plasma as it is in the Filtrate.
Proteins
What happens to the filter ability as the radius increases?
The filter ability DECREASES
The layers of the Filtration Barrier
- Endothelium
- Basement Membrane
- Podocytes
Components of the Endothelium in the Filtration Barrier
Fenestrae and Negative Charge
Components of the Basement Membrane in the Filtration Barrier
Collagen
Proteoglycan fibers
STRONG negative charges
Components of the Podocytes in the Filtration Barrier
Negative Charge
What is the Normal GFR?
125ml/min
180L/day
What determines GFR?
The balance of the Hydrostatic and Colloid Osmotic forces acting across the capillary membrane
What is the filterability of Water?
1.0
Characteristics of Albumin
6nm in length
- slightly SMALLER than the filtration pores (8nm)
Has a NEGATIVE charge that repels it
What are some diseases that Lower the Glomerular capillary Filtration coefficient?
- Chronic uncontrolled HTN
- Diabetes Mellitus
(Increases Urine Output and “Sweet Pee”)
What is Minimal change Nephropathy?
Loss of NEGATIVE charges on the basement membrane
What is Hydronephrosis?
Distension and Dilation of the renal PELVIS and CALYCES
GFR equation
GFR = K1 * Net Filtration Rate
GFR = K1*(Pg - Pb - πg + πb)
Glomerular Hydrostatic pressure
- Symbol
- Quantity
Pg
60mm Hg
Bowman’s Capsule Hydrostatic Pressure
- Symbol
- Quantity
Pb
18mm Hg
Glomerular Capillary colloid osmotic pressure
- Symbol
- Quantity
πg
32mm Hg
Colloid osmotic pressure of Bowman’s capsule
- Symbol
- Quantity
πb
0 mm Hg
What is K1?
Capillary Filtration coefficient
- the product of permeability and filtering surface area of capillaries
- typically a fixed number
Typical Net Filtration Pressure quantity?
10 mm Hg
K1 Equation
Typical K1 value
K1 = GFR/Net Filtration Pressure
K1 = (125ml/min)/(10mm Hg)
= 12.5 mm Hg
What happens to the GFR is K1 Increases? Decreases?
K1 is DIRECTLY proportional to the GFR
If K1 increases then GFR will Increase and vice versa
Relationship between Glomerular hydrostatic pressure and GFR
They are DIRECTLY proportional
What happens to the Pg and GFR when arterial Pressure Increases?
Leads to and increase in Pb —> increase in GFR
What happens to the Pg and GFR when Afferent arteriolar RESISTANCE increases?
Leads to a Decrease in Pg —> decrease in GFR
What happens to the Pg and GFR when Efferent arteriolar resistance Increases?
Leads to an increase in Pg —> Increase in GFR
- Just slightly
Much of the O2 consumption by the kidneys are related to what?
The high rate of active Sodium Reabsorption
Renal Blood flow Equation
RBF = (Renal Art. Pressure - Renal Vein Pressure)/(Total vascular RESISTANCE)
Nervous regulation of the GFR
ALL blood vessels of the kidneys are Richly innervated by SYMPATHETIC system
Effects of strong activation of Sympathetic nerves to the kidneys?
- Constrict renal arterioles
Which leads to…..
- Decrease renal blood flow
- Decrease GFR
Hormones Controlling GFR
- Epi and Norepinephrine
- From the adrenal MEDULLA - Endothelin
- Angiotensin II
- NO
- Prostaglandins and Bradykinin
Role of Endothelin in controlling GFR?
- Released by DAMAGED endothelial cells of the kidneys
- May contribute to Renal Constriction
- Decrease GFR
Role of Angiotensin II in controlling GFR?
- Constricts EFFERENT Arterioles
- Formed usually in situation of decrease blood volume
Role of NO in controlling GFR?
- Maintains Vasodilation
Role of Prostaglandins and Bradykinin in controlling GFR?
- Vasodilators that may offset the effects of the Sympathetic & Angiotensin II vasoconstriction
Think “2 for 2”
What is the normal daily fluid excretion
1.5L/day
What are the Macula Densa cells sensitive to?
The concentration of sodium in the blood
What happens if the Macula Densa senses a decrease in NaCl?
- Activates the Renin/Angiotensin Pathway
- Increase in EFFERENT arteriolar resistance - Decrease AFFERENT arteriolar resistance
- to allow more blood flow
The effects of GFR on the Macula Densa
Directly Proportional
- the lower the GFR, the less Sodium sensed by the Macula Densa.
