Renal System

Question 1

organization of renal system

Answer 1

• right and left kidneys
• ureters leave kidneys and enter urinary bladder
• urethra is the tube connecting urinary bladder to external environment

Question 2

functions of kidney

Answer 2

• regulates extracellular fluid volume and blood pressure
• regulation of osmolarity
• maintenance of ion balance
• regulation of pH
• excretion of wastes
• production of hormones

Question 3

nephrons

~ how many /kidney

Answer 3

• functional units of the kidney
• approx 1 million per kidney
• found in the medulla (pink triangles) and cortex (outermost region) of the kidney

Question 4

anatomy of nephron

Answer 4

look at slides pg 9 and 10 of slides

Question 5

microvilli

Answer 5

increases surface area of epithelial cells of the nephron, important for absorption

Question 6

glomerular filtration

Answer 6

amount of solute excreted = amount filtered from blood to urine - amount reabsorbed + amount seccreted

Question 7

loss of plasma

Answer 7

20% of volume gets filtered, and 19% is reabsorbed
–> 99% of plasma entering kidney returns to systemic circulation

Question 8

filtration barriers

Answer 8

1. glomerular capillary endothelium
2. basal lamina
3. epithelium of Bowman’s capsule

Question 9

main components of filtrate

Answer 9

• urea
• glucose
• ions
• creatinine
• H20

Question 10

what is GFR and what is it influenced by

Answer 10

• glomerular filtration rate
• volume of fluid that filters into Bowman’s capsule/time
• approx 180 L/day
• is influenced by pressure: hydrostatic, colloid osmotic

Question 11

resistance changes in renal arterioles

Answer 11

1. increased resistance in efferent (above, e comes later than a) arteriole –> increases GFR
2. increased resistance in afferent (below, a comes first) arteriole –> decreases GFR

Question 12

regulation of GFR

Answer 12

autoregulation
- myogenic response to bp changes: stretch due to increased pressure causes vasoconstriction of afferent arterioles
- tubuloglomerular feedback:

extrinsic regulation
- hormones
- sympathetic neurons

Question 13

juxtaglomerular apparatus

Answer 13

macula densa cells on the ascending loop of Henle are in contact with the arterioles, and send paracrine signals that affect afferent arteriole diameter

Question 14

tubuloglomerular feedback

Answer 14

1. GFR increases
2. flow through loop of henle increases
3. flow pas macula densa increases
4. paracrine signal from macula densa to afferent arteriole
5. afferent arteriole constricts –> pressure changes lead to GFR decrease!!

Question 15

reabsorption

Answer 15

• most reabsorption happens in the proximal tubule
• transepithelial transport: substances cross apical membrane and basolateral membrane
• paracellular pathway: substances pass through tight junctions

Question 16

what is reabsorption primarily driven by?

Answer 16

Na+ movement

Question 17

glucose reabsorption

Answer 17

1. Na+ moving down its electrochemical gradient uses SGLT protein to pull glucose against its concentration gradient
2. glucose diffuses out basolateral side of cell using GLUT protein
3. Na+ is also pumped out basolateral membrane

Question 18

what mechanism is responsible for the BULK of Na+ reabsorption

Answer 18

• mechanism for glucose transport
• also applicable to amino acids and ions

Question 19

Na+ reabsorption in the collecting duct

Answer 19

1. Na+ enters cell via ENac = epithelial Na+ channel
2. pumped out basolateral side
   –> hormonal regulation of this mechanism is responsible for FINE TUNING Na+ reabsorption

Question 20

net filtration pressure equation

Answer 20

hydrostatic pressure (in blood) - colloid osmotic pressure (pi) - fluid pressure (in proximal tubule) = net filtration pressure from glomerulus to tubule

Question 21

maintaining water balance

Answer 21

• kidneys conserve or remove body fluid by regulating amount of H2O reabsorbed

Question 22

arginine vasopressin (AVP)

Answer 22

• hormone released by posterior pituitary gland to influence H2O reabsorption
• released when: high plasma osmolarity, low blood volume, low blood pressure
• results in increased water reabsorption and concentrated urine via adding water pores into the apical membrane of collecting duct cells
  + AVP = collecting duct is permeable to water
• AVP = collecting duct is impermeable to water

Question 23

aldosterone

Answer 23

• steroid hormone
• synthesized in and released from adrenal cortex
• acts on distal tubule and collecting duct
• results in: increased Na+ reabsorption

Question 24

stimuli of aldosterone release

Answer 24

• angiotensin II (when low blood pressure)
• hyperkalemia (high K+ in plasma)

Question 25

renin secretion stimulated by low blood pressure - three routes

Answer 25

1. reduce GFR: detected by reduced Na+ at macula densa 2. reduced BP: detected by atrial stretch receptors 3. reduced BP: detected directly by afferent arterioles

Question 26

3 mechanisms for maintaining pH homeostasis

Answer 26

1. buffers 2. regulation of ventilation 3. kidneys: H+ secreted and HCO3- reabsorbed at proximal tubule

Question 27

can respiratory and renal systems balance out each other's pH?

Answer 27

yes, but respiratory system functions faster in doing so

Question 28

lower urinary tract

Answer 28

- urinary bladder, urethra, and periurethral striated muscles roles: 1. continence: urine storage in the bladder 2. micturition: effective voiding at an appropriate time --> controlled by sympathetic, parasympathetic and somatic nervous system

Question 29

goals and approaches for bladder management

Answer 29

goals: 1. protect upper UT 2. improve urinary incontinence 3. restore LUT function approaches 1. pelvic floor muscle training 2. catheterization 3. drugs for overactive bladders --> but these can cause leakage 4. electrical stimulation of bladder --> but, body can get used to problem (desensitized), or pathology can change

Question 30

novel approaches to bladder problems!!

Answer 30

- optical stimulation of bladder - drug delivery from within: slow release of drug within bladder (but how do we remove it?) - tissue engineering approach - tissue produced must be mechanically flexible

Question 31

how would we test bladder grafts?

Answer 31

- mechanical testing: uniaxial tensile, biaxial tensile, ball burst - imaging to determine shape and dynamics - mathematical modeling - computational simulations to predict stress distribution

Question 32

gut-brain axis

Answer 32

- includes afferent and efferent neural, endocrine, and nutrient signals between CNS and GI tract -

Question 33

gut microbiota-brain axis

Answer 33

- microbiota: bacteria, archaea, fungi, and viruses - gut is host to more than 500 microbial species - important for metabolism