PDA II - Kidneys

Kidneys function

• Excretion of metabolic waste

• H20 and electrolytes balance

• Regulate body fluid osmolarity

• RBC prod (erythropoietin)

• Regulate arterial prod (RAAS)

• Regulate calcium metabolism (calcitriol)

• Secretion, metabolism and excretion of hormones

• Gluconeogenesis

2 capillaries network in kidneys

Glomerulus

Peritubular

Origin point and end of pertibular capillaries

Efferent arteriole → capillaries → become vasa recta in medulla → renal vein

Nephrons parts and role

Glomerulus surround by Bowman’s capsule: Filtration (large prot & cells stay in blood)

Tubular system:

• Proximal tubule (cortex): Reabsorption of water, ions (Na,K,Cl,HCO3-), glucose, AA

• Loop of Henle (medulla)

  • Descending limb: Water

  • Ascending: Limb: Na+ and Cl- (actively)

• Distal convoluted tubule (cortex): Reabsorption of Na+, Cl- (aldosterone), Ca2+ (PTH) + secretion of ions

• Collecting duct: Reabsoprtion of water (ADH), Na+ (aldosterone), urea + secretion of Na+, K+, H+, HCO3-

Reabsorption of urea in collecting duct allow what

To concentrate more urine

Which nephron part birds don’t have

Loop of Henle

3 layers that make glomerular filter

1. Endothelium of capillaries

2. Basement membrane of capillaries

3. Podocytes

GFR

Volume of fluid filtered per min from the glomerular capillaries into Bowman’s space

Constriction of afferent arteriole =

Decrease Hydrostatic pressure in glomerulus, lower renal blood flow = lower GFR

Constriction of efferent arteriole =

Higher hydrostatic pressure in glomerulus

Lower renal blood flow

GFR stay almost the same

3 processes in urine formation

1. Glomerular filtration

2. Tubular reabsorption

3. Tubular secretion

Which substance should be absent in urine

Glucose, AA, RBC, protein

Autoregulation mechanism in kidneys

If arterial BP increase:

• Myogenic feedback: smooth muscle in aff. arter are streched => aff. arteriole constric; resistance increase

• Tubulo-glomerular feedback: macula densa send adenosine to smooth muscle c in afferent arteriole to contract them

Angiotensin action on kidneys

Constrict efferent arteriole = higher pressure

Stimulate tubular reabsorption

SNS effect on kidneys

Fight or flight:

• Contraction of aff & eff arterioles = lower blood flow

  • Lower GFR

  • Increased reabsorption of H20 and salts

Extensive, selective, non-selective link with urine formation

Extensive = in 20min all blood plasma is filtered

Selective = Reabsorptino discriminate btw wastes and valuables molecules

Non-selective: No discrimination in filtration (except RBC and prot)

Differents mechanisms of tubular reabsorption

Paracellular (btw epithelial cell)

Transcellular (through epithelial cell):

• Active

  • Primary active (use ATP)

  • Secondary active

• Passive

Primary active reabsorption

Na+ with Na/K+ pumps

Secondary active reabsorption

Glucose & AA: cotransport with Na+

H+: countertransport with Na+

Kidneys role in acid-base balance

Reabsorption of HCO3- in proximal tubule

Secretion of H+ in distal tubule & collecting duct, coupled with ammonia or phosphate buffer

Production of new HCO3- (when H+ + NH3+ → NH4+ HCO3- is reabsorbed )

Transport maximum is what

When there is too much molecules for the number of carrier so molecules will be excreted in urine

True for all reabsorbed molecules except Na+

Glucoinuria

Glucose level in urine above renal threshold for glucose

Aldosterone effect on Na+ and K+

Increase reabsorption:

• More Na+K+ pumps

• More Na+ channels

Increase secretion of K+

Hormones that increase urination

• ANP: Atrial Natriuertic hormone

• BNP: Brain naturietic hormone (ventricular + brain neuron)

• Urodilatin: produced in distal tubules

And they also decrease Na+ reabsorption

What stimulate aldosterone release

RAAS

High concentration of K+

Counter-current system

Enable kidneys to concentrate urine and conserve water, 2 parts:

• Multiplier in loop of Henle

• Exchanger in vasa recta

Counter-current multiplier function in loop of Henle

Descending limb: permeable to H2O, impermeable to Ions

Ascending limb: opposite, actively pump ions out

Medulla is now hyperosmotic allowing to concentrate urine later

Counter-current exchange function in vasa recta

In fact, due to its high permeability, vasa recta captures H2O and looses solutes as it conducts blood toward cortex.
Result: blood exiting medulla has only slightly higher osmolarity > osmolarity of entering blood so that hyperosmotic medullary interstitium is preserved.

Urine volume is determined by what

• Solute reabsorption: more reabsorption = more water reabsorbed = less volume

• Increase SNS: decrease urine volume

• RAAS: decrease urine volume

• ADH: decrease urine volume

• Arterial BP: increase urine volume