Lecture 17: Micturition and glomerular filtration

Question 1

Micturition reflex

Answer 1

Superimposed micturition contraction begins to appear as bladder fills
Sensory signals from bladder stretch receptors
Reflex contractions relax spontaneously when bladder is only partially filled
Once initiated, the micturition is self-regenerative
The self-regenerative reflex fatigues after a few seconds and the bladder relaxes
As bladder continues to fill, micturition reflexes occur more often and more powerful
When reflex is powerful enough, it causes a second reflex, passes through pudendal nerves to inhibit external sphincter
Higher brain centers (in pons) keep micturition partially inhibited except when it is desired
When it is time to urinate, cortical centers can facilitate the sacral micturition centers to help initiate reflex and at the same time inhibit external urinary sphincter

Question 2

Sensory signals from bladder stretch receptors

Answer 2

Conducted to sacral region of spinal cord via pelvic nerves

Conducted reflexively back to bladder via parasympathetic nerves

Question 3

Nephron functions

Answer 3

Get rid of waste material
Regulate water/electrolyte balance
Regulate body fluid osmolarity
Regulate arterial pressure- long/short term mechanisms
Regulate acid-base balance
Secretion, metabolism, excretion of hormones
Gluconeogenesis

Question 4

Three processes that determine the rates at which different substances are excreted in the urine

Answer 4

Filtration
Reabsorption
Secretion

Question 5

Urinary excretion rate

Answer 5

UER= Filtration rate - reabsorption rate + secretion rate

Question 6

Components of glomerular filtrate

Answer 6

Water
Ions
Glucose
Urea

Question 7

Filtration fraction equation

Answer 7

FF= GFR/Renal plasma flow

Question 8

% of plasma flowing through kidney that is filtered

Answer 8

20%

Question 9

Low-molecular weight substances filtration

Answer 9

Some low-molecular weight substances are not freely filtered because they are partially bound to proteins

Question 10

What is the glomerular filtration rate

Answer 10

125ml/min= 180L per day

Question 11

Layers of filtration barrier

Answer 11

Endothelium- w/fenestrae and negative charges
Basement membrane- w/collagen, proteoglycan filaments and strong negative charges
Podocytes- w/negative charges

Question 12

GFR determined by

Answer 12

Balance of hydrostatic and colloid osmotic forces acting across capillary membrane
Capillary filtration coefficient

Question 13

Water has a filterability of

Answer 13

1.0

Question 14

Capillary filtration coefficient

Answer 14

Product of permeability and filtering surface area of capillaries

Question 15

Diseases that lower glomerular capillary filtration coefficient

Answer 15

Chronic uncontrolled hypertension and diabetes millitus

Question 16

Define minimal change nephropathy

Answer 16

Loss of negative charges on the basement membrane

Question 17

Define hydronephrosis

Answer 17

Distension and dilation of renal pelvis and calyces

Question 18

GFR equation

Answer 18

GFR= K1 x Net filtration pressure

Question 19

K1 is the

K1 equation

Answer 19

Capillary filtration coefficient

K1= GFR/Net filtration pressure

Question 20

Net filtration pressure is

Answer 20

Glomerular hydrostatic pressure- 60mm Hg
Bowmans capsule hydrostatic pressure- 18mm Hg
Glomerular capillary colloid osmotic pressure- 32mm Hg
Colloid osmotic pressure of bowmans capusle- 0

Question 21

Effects of increasing/decreasing K1

Answer 21

Increase K1- raises GFR

Decrease K1- reduces GFR

Question 22

Factors that influence glomerular capillary colloid osmotic pressure

Answer 22

Arterial plasma colloid osmotic pressure

Filtration fraction

Question 23

Factors that increase glomerular colloid osmotic pressure

Answer 23

Increasing filtration fraction

Question 24

Increase in arterial pressure causes

Answer 24

Increases glomerular hydrostatic pressure which increases GFR

Question 25

Increase in afferent arteriolar pressure causes

Answer 25

Decrease in glomerular hydrostatic pressure which decreases GFR

Question 26

Increase in efferent arteriolar pressure causes

Answer 26

Increase in glomerular hydrostatic pressure which increases GFR (slightly)

Question 27

Kidneys have __x the blood flow of the brain and __x the oxygen consumption of the brain

Answer 27

7x the blood flow of the brain but only 2x the oxygen consumption

Question 28

Much of the oxygen consumed by the kidneys is related to

Answer 28

The high rate of active sodium reabsorption

Question 29

Tubular sodium reabsorption is closely related to

Answer 29

GFR and rate of sodium filtered

Question 30

Renal blood flow equation

Answer 30

RBF= (Renal artery pressure- Renal vein pressure) / (Total vascular resistance)

Question 31

Blood vessels in kidney are richly innervated by

Answer 31

Sympathetic nervous system

Question 32

Strong activation of renal sympathetics causes

Answer 32

Constrict renal arteries Decrease renal blood flow and GFR Moderate sympathetic activation has little effect

Question 33

Hormones controlling GFR consistency

Answer 33

``` Norepinephrine/epinephrine- parallel the sympathetic system Endothelin Angeiotensin II Endothelial-derived NO Prostaglandins and bradykinin ```

Question 34

Endothelin

Answer 34

Released by damaged vascular endothelial cells May contribute to renal vasoconstriction May contribute to hemostasis Plasma levels increase in certain disease states associated with vascular injury

Question 35

Angiotensin II

Answer 35

Constricts efferent arterioles-- increases GFR Formed in situations associated w/decreased arterial pressure or volume depletion Does not constrict afferent arterioles

Question 36

How are afferent arterioles protected against effects of angiotensin II

Answer 36

Due to release of prostaglandins and NO (both vasodilators)

Question 37

NO derived from

Answer 37

Endothelial cells

Question 38

Prostaglandins/bradykinin

Answer 38

Vasodilators that may offset effects of sympathetic and angiotensin II vasoconstrictor effects (especially on afferent arterioles)

Question 39

Definition/function of autoregulation

Answer 39

Refers to relative consistency of GFR and renal blood flow Maintain relatively constant GFR Precise control of renal excretion of water/solutes Prevent relatively large changes in GFR and renal excretion that would otherwise occur w/changes in blood pressure

Question 40

Tubuloglomerular feedback mechanisms for autoregulation

Answer 40

Afferent and efferent arteriolar feedback mechanisms

Question 41

Juxtaglomerular complex

Answer 41

Macula densa in distal tubule | Juxtaglomerular cells in afferent and efferent arterioles

Question 42

Decrease GFR causes

Answer 42

Slow flow rate in loope of henle Increased reabsorption of Na/Cl ions in ascending limb Decrease in sodium chloride at macula densa

Question 43

Decrease in NaCl results in a signal from ___

Answer 43

``` Macula densa which causes Decreased resistance to blood in afferent arterioles Increases renin release from JG cells Increase angiotensin II Increase efferent arteriolar resistance ```