Renal System Flashcards
organization of renal system
- right and left kidneys
- ureters leave kidneys and enter urinary bladder
- urethra is the tube connecting urinary bladder to external environment
functions of kidney
- regulates extracellular fluid volume and blood pressure
- regulation of osmolarity
- maintenance of ion balance
- regulation of pH
- excretion of wastes
- production of hormones
nephrons
~ how many /kidney
- functional units of the kidney
- approx 1 million per kidney
- found in the medulla (pink triangles) and cortex (outermost region) of the kidney
anatomy of nephron
look at slides pg 9 and 10 of slides
microvilli
increases surface area of epithelial cells of the nephron, important for absorption
glomerular filtration
amount of solute excreted = amount filtered from blood to urine - amount reabsorbed + amount seccreted
loss of plasma
20% of volume gets filtered, and 19% is reabsorbed
–> 99% of plasma entering kidney returns to systemic circulation
filtration barriers
- glomerular capillary endothelium
- basal lamina
- epithelium of Bowman’s capsule
main components of filtrate
- urea
- glucose
- ions
- creatinine
- H20
what is GFR and what is it influenced by
- glomerular filtration rate
- volume of fluid that filters into Bowman’s capsule/time
- approx 180 L/day
- is influenced by pressure: hydrostatic, colloid osmotic
resistance changes in renal arterioles
- increased resistance in efferent (above, e comes later than a) arteriole –> increases GFR
- increased resistance in afferent (below, a comes first) arteriole –> decreases GFR
regulation of GFR
autoregulation
- myogenic response to bp changes: stretch due to increased pressure causes vasoconstriction of afferent arterioles
- tubuloglomerular feedback:
extrinsic regulation
- hormones
- sympathetic neurons
juxtaglomerular apparatus
macula densa cells on the ascending loop of Henle are in contact with the arterioles, and send paracrine signals that affect afferent arteriole diameter
tubuloglomerular feedback
- GFR increases
- flow through loop of henle increases
- flow pas macula densa increases
- paracrine signal from macula densa to afferent arteriole
- afferent arteriole constricts –> pressure changes lead to GFR decrease!!
reabsorption
- most reabsorption happens in the proximal tubule
- transepithelial transport: substances cross apical membrane and basolateral membrane
- paracellular pathway: substances pass through tight junctions
what is reabsorption primarily driven by?
Na+ movement
glucose reabsorption
- Na+ moving down its electrochemical gradient uses SGLT protein to pull glucose against its concentration gradient
- glucose diffuses out basolateral side of cell using GLUT protein
- Na+ is also pumped out basolateral membrane
what mechanism is responsible for the BULK of Na+ reabsorption
- mechanism for glucose transport
- also applicable to amino acids and ions
Na+ reabsorption in the collecting duct
- Na+ enters cell via ENac = epithelial Na+ channel
- pumped out basolateral side
–> hormonal regulation of this mechanism is responsible for FINE TUNING Na+ reabsorption
net filtration pressure equation
hydrostatic pressure (in blood) - colloid osmotic pressure (pi) - fluid pressure (in proximal tubule) = net filtration pressure from glomerulus to tubule
maintaining water balance
- kidneys conserve or remove body fluid by regulating amount of H2O reabsorbed
arginine vasopressin (AVP)
- 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
aldosterone
- steroid hormone
- synthesized in and released from adrenal cortex
- acts on distal tubule and collecting duct
- results in: increased Na+ reabsorption
stimuli of aldosterone release
- angiotensin II (when low blood pressure)
- hyperkalemia (high K+ in plasma)
renin secretion stimulated by low blood pressure - three routes
- reduce GFR: detected by reduced Na+ at macula densa
- reduced BP: detected by atrial stretch receptors
- reduced BP: detected directly by afferent arterioles
3 mechanisms for maintaining pH homeostasis
- buffers
- regulation of ventilation
- kidneys: H+ secreted and HCO3- reabsorbed at proximal tubule
can respiratory and renal systems balance out each other’s pH?
yes, but respiratory system functions faster in doing so
lower urinary tract
- 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
goals and approaches for bladder management
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
novel approaches to bladder problems!!
- 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
how would we test bladder grafts?
- mechanical testing: uniaxial tensile, biaxial tensile, ball burst
- imaging to determine shape and dynamics
- mathematical modeling
- computational simulations to predict stress distribution
gut-brain axis
- ## includes afferent and efferent neural, endocrine, and nutrient signals between CNS and GI tract
gut microbiota-brain axis
- microbiota: bacteria, archaea, fungi, and viruses
- gut is host to more than 500 microbial species
- important for metabolism
