Lecture 16: Micturition And GFR Flashcards
Describe the steps that occur during the micturition reflex
- Contractions begin to appear more as bladder fills more.
- Sensory signals: sacral region- pelvic nerves, reflexively back to bladder-parasympathetic nerves
- Reflex contractions relax when only partly filled.
- Micturition is self-regenerative…it fatigues after a few seconds and the bladder relaxes.
- When powerful enough, it causes 2nd reflex.
- pudendal nerves inhibit external sphincter.
- Pons keeps partly inhibited when needing to micturate.
- cortical centers can facilitate sacral micturition centers to help initiate a micturition reflex and at the same time inhibit external urinary sphincter.
Be able to list the various functions of the nephrons
Rid of wastes
Regulate water and electrolytes, body fluid osmolarity, arterial pressure (excrete electrolytes (long term) and hormones- renin(short term))
Regulate acid-base balance
Secretion, metabolism, and excretion of hormones
List and describe the 3 processes carried out by nephrons that determine the composition of the urine.
Filtration
Reabsorption
Secretion
Express the above filtration, reabsorption, and secretion mathematically:
Urinary excretion rate=
Filtration rate-Reabsorption rate+ secretion rate
List the major components of the glomerular filtrate
Water
Ions
Glucose
Urea
Define filtration fraction and express mathematically:
Fraction of renal plasma flow that is filtered.
GFR / Renal plasma flow
20% of plasma flowing through kidney is filtered.
List the major characteristics that determine whether or not a substance is filtered by the nephron.
Neutral and positive charges are filtered by the nephron better because the layers of the filtration barrier are negative.
Radius is a factor in filterability as well.
Describe the 3 components of the filtration barrier.
Endothelium: w/ fenestrae and NEGATIVE charges
Basement membrane: w/ collagen and proteoglycan fibers and strong NEGATIVE charges.
Podocytes: w/ NEGATIVE charges
List the factors that determine glomerular filtration rate
Balance of hydrostatic and Colloid osmotic force acting across capillary membrane
—the same as the CV system starling forces.
Capillary filtration coefficient
Define capillary filtration coefficient.
Product of permeability and filtering surface area of capillaries (K1)
Know that the GFR is:
125ml/min = 180L /day
Recognize and define: minimal change nephropathy and hydronephrosis
Minimal change neuropathy: loss of negative charges on the basement membrane
Hydronephrosis: dissension and dilation of renal pelvis and calyces
Be able to mathematically express the glomerular filtration rate in terms of starling forces:
GFR= K1 (glomerular hydrostatic pressure - bowman’s capsule hydrostatic pressure - glomerular capillary colloid osmotic pressure + colloid osmotic pressure -bowmans capsule)
Describe how changes in the capillary filtration coefficient affects GFR
Increased K1 = increased GFR
Decreased K1 = decreased GFR
List and describe factors that affect GFR:
Arterial pressure
Afferent arteriolar resistance
Efferent arteriolar resistance
Misc. factors: arterial plasma colloid osmotic pressure, filtration fraction, increasing filtration fraction
Increased A pressure= increased glomerular hydrostatic pressure= INCREASES GFR
Increased afferent arteriolar resistance= decreases glomerular hydrostatic pressure= DECREASES GFR
Increase in efferent arteriolar resistance= increase in glomerular hydrostatic pressure = slightly INCREASES GFR
Explains the effect of the sympathetic system on GFR.
Sympathetic activation of kidney leads to strong activation of:
- constriction of renal arterioles
- decrease renal blood flow and GFR
Moderate activation has little effect.
List and describe hormones that control GFR and how they effect GFR:
Norepinephrine and Epinephrine: sympathetic-(less GFR)
Angiotensin II:constrictor-more GFR d/t efferent constriction
Endothelin: constrictor-less GFR
NO:dilator
Prostaglandins and Bradykinin: dilator
List source of the previous hormones:
Norepi and epi: adrenal medulla
Endothelin: damaged vascular endothelial cells of the kidneys and other tissue
Angiotensin II: from liver
NO: endothelial cells
Prostaglandins and bradykinins: EFAs
Kidney autoregulation overview
Autoregulation assists in decreasing flow rate in loop of henle leading to:
- decreased GFR
- increased reabsorption of Na+ and Cl- in the ascending limb
- decreased NaCl at macula densa
[this decrease in NaCl results in signal from macula densa that:
- decreases resistance to blood in afferent arterioles
- increases renin release from JG cell (major storage of renin)
- increases angiotensin II
- increased efferent arteriolar resistance—-increasing GFR! Balance!]
Define autoregulation as it r/t kidneys:
Trying to maintain appropriate blood flow at all times.
Precise control of renal excretion of water and solutes
Prevents large changes in GFR and renal excretion that would otherwise occur w/ changes in blood pressure
Describe the functions of autoregulation and explain why it is important
SLight increases in BP w/o autoregulation could increase GFR to 225L/ day from 180L/day. Urine flow would increase from 1.5L/day to 46.5L/day.
2 components to the autoregulation:
- tubuloglomerular feedback mechanism (afferent/efferent feedback)
- juxtaglomerular complex
List and describe the 2 compartments of the autoregulation feedback mechanism:
tubuloglomerular feedback mechanism 2 components:
afferent/efferent feedback mechanism
Relate the macula densa to the JG complex
Macula densa is in distal tubule which is adjacent to JG cells in afferent and efferent arterioles.
Describe in detail the role of the JG complex in autoregulation:
JG cells release Renin-angiotensin II cascade when the [NaCl] decreases at the macula densa.
Understand the concept of GFR, renal clearance and determine their values
GFR: estimates how much blood passes through glomeruli / min
Renal clearance: The volume of plasma that is completely cleared of the substance by the kidneys per unit time
Values: GFR >60, Clearance=625 ml/min
