Lecture 17 - Micturition and Glomerular Filtration Flashcards
Describe the micturition reflex.
L17 S4-5
- sensory signals from stretch receptors in bladder conducted by pelvic nerves
- reflex originates from parasympathetic nerves
Primary reflex
- contraction of the bladder
- a partially fully bladder results in contractions that are weak and die out
- the more full the bladder, the stronger the contractions get
Secondary reflex:
-inhibition of the external sphincter
What are the functions of the nephrons? (7)
L17 S9
Remove waste:
-urea, creatinine, uric acid, bilirubin
Regulate water and electrolyte balance
Regulate fluid osmolarity
Regulate arterial pressure
- long term: excretion of sodium and water
- short term: secretion of hormones and vasoactive factors
Regulate acid-base balance
Secretion, metabolism, and excretion of hormones
Gluconeogenesis
What three processes determine rate of urinary excretion?
What is the formula for urinary excretion?
L17 S10
Filtration:
-release from glomerular capillaries into nephron
Reabsorption:
-return to peritubular capillaries from nephron
Secretion:
-release from peritubular capillaries to nephron
Urinary Excretion Rate = Filtration Rate - Reabsorption Rate + Secretion Rate
What is the fraction of renal plasma flow that is filtered in the glomeruli?
L17 S14
- ~20%
Concentration of most substances are __________ (the same/different) in the filtrate and the plasma.
The most common components of filtrate are __________ (4).
the same
water, ions, glucose, and urea
Increased molecular radius __________ (increases/decreases/has no effect on) filterability of a substance.
Increased negative charge __________ (increases/decreases/has no effect on) filterability of a substance.
Increased positive charge __________ (increases/decreases/has no effect on) filterability of a substance.
Increased size:
-decreases
Negative charge:
-decreases
Positive charge:
-increases
What are the different layers of the filtration barrier?
What import characteristics do they have the effect what is filtered?
L17 S18
Endothelium:
- contain fenestrae
- negatively charged
Basement membrane:
- collagen and proteoglycan fibers
- strong negative charges
Podocytes:
-negative charges
The negatively charged nature of these components are what is responsible for reducing the filterability of negative substances, such as albumin, which are small enough to be filtered.
What factors are used to calculate golmerular filtration rate?
L17 S22
- golmerular hydrostatic pressure (outward)
- Bowman’s capsule hydrostatic pressure pressure (inward)
- golmerular capillary colloid osmotic pressure (inward)
- Bowman’s capsule colloid osmotic pressure (outward but typically 0)
Capillary filtration coefficient:
-product of permeability and filtering surface area of capillaries
What effect does increasing each of the following factors have on glomerular hydrostatic pressure (Pg) and GFR?
- arterial pressure
- afferent arteriolar resistance
- efferent arteriolar resistance
L17 S24
Increased arterial pressure:
- increase Pg
- increase GFR
Increase afferent arteriolar resistance:
- decrease Pg
- decrease GFR
Increase efferent arteriolar resistance:
- increase Pg
- increase GFR
What is the average golmerular filtration rate (GFR)?
L17 S19
-125 mL/min or 180 L/day
What mechanisms are involved in controlling GFR?
L17 S31
Sympathetic stimulation
Hormones:
- epinephrine and norepinephrine
- endothelin
- angiotensin II
- endothelial NO
- prostaglandins and bradykinins
Kidneys have __________ times the blood flow of the brain and __________ times the oxygen consumption.
__________ is largely responsible for the oxygen consumption of the kidney.
L17 S25
7 times the blood flow; 2 times the oxygen consumption
high rate of sodium reabsorption
What factor causes endothelin to be released?
What effect does it have on GFR?
L17 S31
Release:
-endothelial damage of kidneys or other tissues
Effect:
-may contribute to renal vasoconstriction (reduces GFR)
What factor causes angiotensin II to be released?
What effect does it have on GFR?
L17 S31
Release:
-decreased arterial pressure or volume depletion (RAAS)
Effect:
- constriction of efferent arterioles (increases resistance, increases Pg, increases GFR)
- no effect on afferent arterioles
What where is nitric oxide released from?
What effect does it have on GFR?
L17 S32
Release:
-endothelial cells
Effect:
-maintains basic vasodilation
