Lecture 11

Question 1

6 functions of the kidneys

Answer 1

1) excretion of waste : creatinine, urea, uric acid, toxins -> in urine

2) ECF regulation and blood pressure ; if ECF low = blood pressure low

3) regulation of osmolarity (290 mOsM) : adjust urine volume, filtration / reabsorption of salts

4) maintenance of ion balance : Na+, K+, Ca2+

5) regulation of pH : H+ and HCO3- (not as fast as lungs)

6) production of hormones : erythroprotein, renin

Question 2

4 components of urinary system

Answer 2

kindey, ureters, urine bladder, urethra

Question 3

what is critical to renal function ?

Answer 3

high rate of blood flow through kidneys (20% of CO)

Question 4

2 layers of the kidney, where the urine is stored, functional unit of kidney ? 2 types

Answer 4

outer cortex and inner medulla.
Urine stored in renal pelvis.

Unit is the nephron : cortical nephron and juxtamedullary nephron

Question 5

name the different regions of a nephron (5) and their main function

Answer 5

1) glomerulus : connection with arterioles, filtration of blood
2) proximal tube : reabsorption (mostly water and glucose) and secretion of molecules from blood
3) loop of henle : reabsorption, mainly osmolarity compounds
4) distal tube : reabsorption and secretion
5) collecting duct : branches from different nephrons join

Question 6

distribution of the two types of nephrons. To what capacity can a kidney go ?

Answer 6

80% cortical : glomerulus, proximal and distal tubes

20% juxtamedullary : loops of henle and collecting ducts

kidney can go up to 130% of its capacity

Question 7

main function of the 2 nephron types, one difference between the two (blood related)

Answer 7

cortical : filtration of about 20% of plasma, waste clearance

juxtamedullary : urine concentration.

Diff : cortical have a peritubular capillary network around their tubes (for secretion). Juxta only have that around the part located in the cortex.

Question 8

what does the urinary excretion depend on (formula) ? how many liters per day do we filter in the glomerulus ?

Answer 8

amount secreted = filtered + secreted - reabsorbed
-> about 0.5 to 2 liters a day

glomerulus : around 180L filtered per day

Question 9

renal corpuscule : three layers of the filtration barrier, what are mesangial cells ?

Answer 9

barrier : capillary endothelium - basal lamina (negatively charged) - bowman’s capsule epithelium (podoctyes).
-> Slits between the feet of podocytes. Small enough that blood cells can’t cross.

Mesangial cells between capillaries can contract to alter blood flow. They are also immunocompetent

Question 10

two types of capillaries ? where would you find them ?

Answer 10

Continuous : leaky junctions but not very permeable. -> in brain

Fenestrated : large pores -> in kidney

Question 11

three pressures that are involved in the filtration process

Answer 11

driving force : hydrostatic blood pressure

resistance : colloid osmotic pressure (plasma proteins attract water) and fluid pressure from fluid in bowman’s capsule

net pressure is about 10 mmHg

Question 12

what is the glomerular filtration rate ? influenced by what ? how can it be regulated ?

Answer 12

Volume of fluid that filters into bowman’s capsule per unit of time : average GFR = 125 mL/min or 180L/day.

Influenced by blood flow, surface area and permeability.

• increase resistance in efferent arteriole -> GFR increases
• increase resistance in afferent arteriole -> decreased GFR

Question 13

definition of renal clearance, what is one assumption ?, formula for clearance

Answer 13

volume of blood plasma which is cleared from a specific compound in mL/min

assumption that substance X is completely transferred in urine (nothing in venous output)

c = UxV/P

Question 14

difference between inulin and glucose clearance ?

Answer 14

inulin clearance = GFR because nothing is reabsorbed or secreted.

In healthy patients, glucose is 100% reabsorbed -> clearance is zero

Question 15

clearance of inulin, creatinine, glucose

Answer 15

inulin and creatinine : 120 ~ GFR
glucose = 0

Question 16

what are the two sphincters made of ?

Answer 16

internal -> smooth muscle
external -> skeletal muscle

Question 17

what is micturition ?

Answer 17

spinal reflex (conscious and unconscious control from higher brain cenetrs) :
- bladder fills and walls expand -> stretch receptors send signals
- full bladder -> parasympathetic neurons -> smooth muscle contracts. At the same time, somatic motor neurons to external sphincter are inhibited.

Question 18

how do the kidneys react when blood pressure increases or decreases ?

Answer 18

increases -> excrete salts and water in urine
decreases -> conserve water to minimize volume loss

Question 19

what is the response to salt ingestion ?

Answer 19

osmolarity increases (not volume) -> increased renal water reabsorption -> later on the kidneys excrete salt and water

In other words, salt is first diluted with more water and then both are excreted

Question 20

how is ANG II produced ? when is the pathway activated ?

Answer 20

liver produces angiotensinogen. Renin transforms it to ANG I in plasma. ACE enzyme transforms it to ANG II.

Activated when decrease of blood pressure