Renal Physiology

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Renal Physiology

• The kidneys 5 functions
• Regulation of body fluid volume
• Regulation of Osmolarity Ion Balance
• Regulation of pH
• Excretion of Wastes
• Synthesis of Hormones

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Kidney Anatomy
Blood enter/leaves via Renal artery/vein
Urine leaves via Ureter
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Nephron
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Nephron 4 ways substances move
Blood
Filtrate
Urine
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Filtration
Bowmans Capsule
Efferent Arteriole
Podocyte
Glomerulus
Proximal tubule
Glomerular capillary
Afferent Arteriole
20 PLASMA entering Glomerulus enter NEPHRON by
BULK FLOW!
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What is filtered?
VIDEO
Filtrate in Nephron contains Plasma (ions,
waters, small molecules) It SHOULD NOT contain
large proteins or blood cells (they cant fit
through Pores/Slits)
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How much is filtered?

• Normal 125 ml/Min 180 L/day Glomerular
  Filtration Rate
• Your plasma is filtered 60 times per day!
• Blood flow to kidney MUST be HIGH

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Control of Filtration Rate

• Local mechanisms alter the diameter of the
  afferent arteriole

Bowmans Capsule
Efferent Arteriole
Podocyte
Macula Densa (Ascending LOH)
Glomerulus
Proximal tubule
Glomerular capillary
Afferent Arteriole
Macula Densa releases local control chemicals
(ATP, ADP, NO)
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Control of Filtration Rate

• Sympathetic ANS vasoconstriction of afferent
  efferent arterioles
• REDUCED FLOW, decreased Filt. Rate
• Hormones Angiotensin II gt vasoconstriction gt
  decreased Filt. Rate
• Prostaglandins gt vasodilation gt increased
  Filt. Rate

Angiotensin II Prostoglandins also affect the
size of the filtration slits!
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Reabsorption What is reabsorbed?
99 of molecules entering renal tubule are
reabsorbed into peritubular capillaries! Na,
K, Ca2, Glucose, Water, Cl-, Urea, small
proteins
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ReabsorptionActive Transport of Na DRIVES
REABSORPTION!!!!!!!Everything else is DIFFUSION
(electrical or concentration gradient)
Na reabsorbed by Active Transport!
Na Electrical Gradient Anions (-) reabsorbed
Na
hypertonic
Anions
Osmotic gradient (high ISF) Water reabsorbed
Water
High Renal Tubule Conc. Other molecule
diffuse down conc. gradients
Ca2 K Urea
Renal Tubule
ISF
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Glucose Reabsorption
100 of Glucose is reabsorbed _at_ normal blood
glucose levels Diabetes mellitus gt elevated
blood glucose gtgt glucosuria
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Secretion

• FROM Peritubular Capillary TO Renal Tubule

Organic molecules (too big for Filtration), K,
H are key molecules SECRETED
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Penicillin (Antibiotic) Secretion
Penicillin is filtered secreted
_at_ 4 hours plasma conc. of penicillin 0
100 of Penicillin is EXCRETED by 4 hours
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Excretion
180 L/Day - 178.5 L/Day 0
1.5 L/Day
Water
200 mg/min - 200 mg /min 0 0
mg/min
Glucose
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Fluid and Electrolyte Balance
Why does your body maintain fluids and
electrolytes in a balanced state? Na Water
determine blood volume and pressure K is
essential for resting membrane potential in
excitable cells H and HCO3- are key in
maintaining pH Ca2 is a key signaling ion
Integrative, multisystem task kidney,
cardiovascular, respiratory, neural
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Water Homeostasis
8 8oz waters 9 oz from food
Living in DRY Places can INCREASE
Diarrhea can INCREASE
You body maintains water homeostasis, PRIMARILY,
by altering urine volume!
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Water Reabsorption
Important Water reabsorption in the LOH is
ALWAYS on (unless drugs are present)
Your body ONLY alters water reabsorption in the
distal tubule collecting duct!
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Variable Water Reabsorption

• Antidiuretic Hormone (ADH) Vasopressin

Vasopressin (ADH) Aquaporins
Vasopressin (ADH) Aquaporins
Antidiuresis little concentrated urine
Diuresis lotsa dilute urine
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What drives ADH release?

• Blood Osmolarity
• High OSM gt Increase ADH
• Low OSM gt Decrease ADH
• 2) Blood Volume
• 3) Blood Pressure
• Low BPgt Increase ADH
• High BPgt Decrease ADH

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• Sodium Homeostasis

Na balance is intimately tied to blood pressure
and volume homeostasis!
25 of Adult Americans are Hypertensive Hypert
ension Leading Cause of Cardiovascular Death!
Excess SALT Intake is Major contributing
Factor Americans consume 3.5 - 8 grams per
day NAS recommended 2 grams per day
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Effect of ingested Sodium on Kidney Function
ASSUME Each day you consume 2 grams of
salt This could increase you blood osmolarity to
307 mosm/L
Cardiovascular Atrial natriuretic peptide (ANP)
Aldosterone Pathway Renal
Renin-Angiotensin-Aldosterone Pathway
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Sodium Reabsoption is variable ONLY in the distal
tubule and collecting duct
Aldosterone Adrenal hormone that regulates Na
reabsorption
Aldosterone more Na-K ATPase pumps more
K and Na channels
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Aldosterone Release controlled by Osmolarity
Adrenal Cortex
Reduce Aldosterone Synthesis
Sodium Excretion
Aldosterone Release is also controlled by Blood
pressure Renin-Angiotensin-Aldosterone Pathway
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constantlyproduces
Angiotensinogenin the plasma
Liver
produce
Renin
Low Blood Pressure
Kidney
ANG I in plasma
contains
ACE(enzyme)
Blood vesselendothelium
ANG II inplasma
Sympathetic Activation Heart Vasculature
Adrenal Cortex
Hypothalamus
ADH Synthesis
Aldosterone Synthesis
Vasoconstrict
Thirst
enhances
Sodium Reabsorption
Water Reabsorption
Increase Blood Volume
Increase Blood Pressure
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Aldosterone Release controlled by Osmolarity
Adrenal Cortex
Reduce Aldosterone Synthesis
Sodium Excretion
Aldosterone Release is also controlled by Blood
pressure Renin-Angiotensin-Aldosterone Pathway
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Angiotensinogenin the plasma
constantlyproduces
Liver
ACE inhibitor drug for HYPERTENSION
Renin
produce
High Blood Pressure
Kidney
ANG I in plasma
contains
ACE(enzyme)
Blood vesselendothelium
ANG II inplasma
Sympathetic Activation Heart Vasculature
Adrenal Cortex
Hypothalamus
Reduce ADH Synthesis
Reduce Aldosterone Synthesis
Vasodilation
Thirst
enhances
Water Excretion
Sodium Excretion
Reduce Blood Volume
Lower Blood Pressure
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Adrenal Cortex
Reduce Aldosterone Synthesis
Cardiovascular
Reduce ANG II
Sodium Excretion
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Atrial Natiuretic Peptide (ANP)
BP Blood Volume
Atrial Stretch
ANP secretion
Increase GFR
Decreased ADH
Decreased Sympathetic
Decreased Renin
Decreased Aldosterone
Increase Water Excretion
Increase Na Excretion
Lower Blood Volume
Lower Blood Pressure
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General Pathways for Sodium, Blood Volume, and
Blood Pressure Homeostasis
Adrenal Cortex
Increase ANP Decrease Symp.
Reduce Aldosterone Synthesis
Reduce ANG II
Sodium Excretion
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pH Review
More H ions Few H ions
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Acid-Base Homeostasis pH

• pH is affected by the concentration of H
• Your body maintains pH at 7.38-7.43, precisely!
• Low pH acidosis (reduced CNS function)
• High pH alkalosishyperexcitable membranes
  (diaphragm arrest!)

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Where do acids (H ions) come from?
H is always being produced .so H always
needs to be excreted
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3 mechanisms of pH homeostasis

• Buffering systems
• Lungs
• Kidneys 25

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Loss of any mechanism can lead to ACIDOSIS gt
lowered blood pH
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The buffer of H is HCO3-

• CO2 H2O ? H2CO3 ? H HCO3-

Law of Mass Action
CO2 H2O H2CO3 H HCO3-
H combines with HCO3- to BUFFER the effect of
increase H
CO2 H2O ? H2CO3 ? H HCO3-
More CO2 H2O are produced by buffering action
HCO3- is used up
HCO3- is 600,000 x more concentrated than H in
blood
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Respiratory Regulation of pH
CO2 H2O ? H2CO3 ? H HCO3-
Carotid Aortic chemoreceptors
Brainstem chemoreceptors
Increased Ventilation Rate and Volume
CO2 H2O ? H2CO3 ? H HCO3-
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Renal Regulation of pH- 25

• Reabsorbtion of HCO3- indirect excretion of H
  Always ON

Filtered HCO3- cannot be directly reabsorbed
Most Filtered H is not directly excreted
Hydrogen Phosphate Ion HPO42-
H
HCO3-
HCO3-
HCO3-
H
ATPase
REABSORBTION
H2CO3
H2CO3
C.A.
C.A.
H2O CO2
H2O CO2
REABSORBTION
Amino Acids
NH3
HCO3-
HCO3-
NH4 Ammonium Ion
H2PO4- Phosporic Acid
Peritubular Capillaries
PROXIMAL Renal Tubule
Nephron Cell
Renal ISF
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Skeletal System Functions

• Support
• Movement
• Calcium Homeostasis!

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Parathyroid Gland
Ca2 receptors are linked to G-protiens that
control the release of PTH (parathyroid hormone)!
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Calcium Homeostasis

• Ca2 Receptors in Parathyroid gland monitor
  blood Ca2 levels
• If Ca2 Low PTH released
• Bone breaks down releasing Ca2
• Kidney reabsorbs Ca2
• Intestines uptake more Ca2
• If Ca2 High PTH syn. inhibited
• Bone building, incorporating Ca2
• Kidney does not reabsorb Ca2
• Intestines do not uptake Ca2

Bone accounts for 99 of the calcium reserves in
your body!
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Osteoporosis
Osteoporosis is linked to long-term low
dietary intake of Ca2
Bone Loss gt Bone Building so that
Ca2 levels are maintained
Ca2 is a key ion everywhere!!!!
Women are more susceptible than men.lower bone
mass menopausal estrogen decrease