Lecture 15: Micturition and glomerular filtration-Exam 3

Question 1

Function of nephrons

Answer 1

Get rid of waste materials such as urea, uric acid, creatinine and bilirubin
Regulate water and electrolyte balance
Regulate body fluid osmolarity
Regulate arterial pressure long term by excretion of variable amounts of sodium ions and water, short term by secretion of hormones and vasoactive factors such as renin
Regulate acid base balance by eliminating acids such as sulfuric acid and phosphoric acid and regulate body fluid buffers stores
Secretion, metabolism and excretion of hormones such as erythropoietin and active form of vitamin D
Gluconeogenesis

Question 2

Processes that determine the rate at which different substances are excreted in the urine

Answer 2

Filtration: First step in urine formation
Reabsorption
Secretion

Question 3

Urinary excretion rate

Answer 3

= Filtration rate-Reabsorption rate+ secretion rate

Question 4

Component of the glomerular filtrate

Answer 4

Ions,glucose, water and ions
Concentration of most substances except for proteins is the same in the filtrate as it is in the plasma
Some small molecules not filtered due to being proteins bound

Question 5

Filtration fraction

Answer 5

Fraction of renal plasma flow filtered

=GFR/Renal plasma flow

Question 6

Layers of filtration barrier

Answer 6

Endothelium with fenestrae and negative charges
Basement membrane with collagen and proteoglycan fibers and strong negative charges
Podocytes with negative charges

Question 7

Glomerular Filtration Rate (GFR)

Answer 7

Determined by balance of hydrostatic and colloid osmotic forces acting across capillaries membranes
GFR= 125 mL/min=180 mL/day
GFR= K1 x net filtration rate
K1= coefficient filtration rate

Question 8

Coefficient filtration rate K1

Answer 8

Product of permeability and filtering surface area of capillaries
Increase of K1—> Increase of GFR
Decrease of K1 –> Decrease of GFR

Question 9

Net filtration rate

Answer 9

=Pg-Pb-Pig+Pib
Pg=glomerular hydrostatic pressure=60 mm Hg
Pb=Bowman’s capsule hydrostatic pressure= 18 mm Hg
Pig=glomerular capillary colloid osmotic pressure= 32 mm Hg
Pib=Bowman’s capsule colloid osmotic pressure = 0 mm Hg

Question 10

Diseases that lower coefficient filtration rate

Answer 10

Chronic uncontrolled hypertension
Diabetes mellitus
Minimal change nephropathy: loss of negative charges on basement membrane
Hydronephrosis: distention and dilation of renal pelvis and calyces

Question 11

Factors that influence glomerular capillary colloid osmotic pressure

Answer 11

Arterial plasma colloid osmotic pressure

Filtration fraction: Increase causes increase glomerular capillary colloid osmotic pressure

Question 12

Variables that determine glomerular hydrostatic pressure

Answer 12

Arterial pressure: increase causes increased Pg which increases GFR
Afferent arteriole resistance: increase causes decreased Pg which decreases GFR
Efferent arteriole resistance: Increase causes increased Pg which slightly increases GFR

Question 13

Factors that determine renal blood flow

Answer 13

Blood flow in kidney 7 times more than blood flow in brain
Oxygen consumption in kidney 2 times more than oxygen consumption in brain
Much of oxygen consumption due to high rate of active sodium reabsorption
Tubular sodium reabsorption closely related to GFR and rate of sodium filtered

Question 14

Renal blood flow

Answer 14

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

Question 15

Nervous regulation of GFR

Answer 15

All blood vessels of kidney richly innervated by sympathetic system
Strong activation of renal sympathetic nerves constricts renal arterioles and decreases renal blood flow and GFR
Moderate sympathetic activation has little effect

Question 16

Mechanisms controlling GFR consistency

Answer 16

Sympathetic
Hormones: Norepinephrine and epinephrine, angiotensin II, endothelial derived nitric oxide, prostanglandin and bradykinin

Question 17

Effects of endothelin

Answer 17

Released by damage endothelial cells of kidney and other tissues
Contribute to vasoconstriction which reduces GFR
Contribute to hemostasis when blood vessel is severed
Plasma levels increase in certain diseases state associated with vascular injury ( toxemia of pregnancy, acute renal failure, chronic uremia)

Question 18

Effects of angiotensin II

Answer 18

Preferentially constricts efferent arterioles
Formed usually in situations with decreased arterial pressure and/or volume depletion
Afferent arterioles protect against effects

Question 19

Effects of nitric oxide

Answer 19

Derived from endothelial cells

Basic level helps maintain renal vasodilation

Question 20

Effects of prostaglandin and bradykinin

Answer 20

Protect afferent arterioles against effects of sympathetic and angiotensin II

Question 21

Autoregulation

Answer 21

Refers to relative constancy of GFR and renal blood flow

Question 22

Primary function of autoregulation

Answer 22

Maintain a relatively constant GFR
Allow precise control of renal excretion of water and solutes
Prevent relatively changes in GFR and renal excretion that would otherwise occurs with changes in blood pressure

Question 23

Tubuloglomerular feedback mechanisms

Answer 23

Afferent arterioles feedback mechanisms

Efferent arterioles feedback mechanisms

Question 24

Juxtaglomerular (JG) complex feedback mechanisms

Answer 24

Macula densa in distal tubule

JG cells in afferent and efferent arterioles

Question 25

Autoregulation feedback

Answer 25

⬇️AP->⬇️ Pg->⬇️ GFR-> slow flow rate in loop of Henle ->⬆️ reabsorption of NaCl in ascending limb->⬇️ NaCl in macula densa->⬇️ resistance in afferent arterioles(1)
⬇️ NaCl in macula densa->JG cells -> ⬆️ renin->⬆️ angiotensin II->⬆️resistance in efferent arterioles (2)
1 and 2–> ⬆️ glomerular hydrostatic pressure (Pg)–>⬆️GFR

Question 26

Micturition reflex

Answer 26

Superimposed micturition complex appears as bladder fills
Sensory signals from bladder stretch receptors conducted to the sacral region of spinal cord via pelvic nerves and conducted reflexively back to bladder via parasympathetic nerves
Micturition stops as bladder is partially filled
Once initiated reflex is self regenerative and fatigue after a few seconds and bladder relaxes
As bladder filled reflex occurs more often and more powerful
When powerful enough reflex causes secondary reflex
Second reflex conducted to pudendal nerves and inhibit external urinary sphincter
Higher brain centers in pons inhibit micturition unless desired
when it is time to urinate, brain centers help micturition centers to facilitate initiation of reflex and also inhibit external urinary sphincter and urination occurs