Reabsorption and Secretio

How does blood flow

Counter flow to the loop of henle

Filtered load of substances equation

W=GFR * plasma concentration

Net seqretion

Excretion rate- filtered load

Net reabsorption equation

Filered load- excretion rate

Reabsorption

• high variable and selective

• Most electrolytes and nutritional substances are almost completly reabsorbed and waste poorly rabsorbed

Secretion

• Highly variable

• important for rapidly exreting some waste products and foreign substances

  • Drugs and toxins

PAH

Secretion

• Alll removed from blood

• freely filtered rest is secreted

Glucose

Reabsorption

• All reabsorbed and none in the urine

Amino acids

Reabsorption

• All reabsorbed and none in the urine

Inulin

None

• Neither reabsorbed or secreted

Creatinine

None

• Slightly secreted but not much

Sodium

Reabsorbed but is highly regulated

• Hormone regulated

Water

Reabsorbed but is highly regulated as well

• Homrone regulated

Glucose reabsportion

Gets transported from tubular fluid into the cell by secondary active transport using the sodium molecule which brings glucose in with it. This is through an SGLT transporter, moving from the cell to the blood a GLUT transporter is used

What happens when there is too much glucose in the blood

The nephrons get overworked and hits their macimal transport load which then stimulates glucose in the urine

Why is the threshlold for glucose apperence in blood lower than TM

Becuase TM is different for differing nephrons

Where is most of the sodium reabsorbed in the kidney

The proximal tubule

Where is sodium reabsorbed without water

Thick ascending limb of loop of henle

Where is fine tuning of sodium excretion and reabsportion take place

Distal convoluted tuble and collecting duct

What is tubular fluid

The urine to be at any point along the nephron

What happens when we only reabsorb water

urine is more concentrated

What happens when we only reabsorb solutes

Urine is more dilute

TF/P

The ration of tubular fluid concentration of X at any point along nephron relative to plasma concentrations of X

=1.0 (TF/P)

No reabsorption or secretion or reabsorption occurs with water

< 1.0 (TF/P)

Reabsorption more than water

>1.0 (TF/P)

More water reabsoption than solute or net secretion

Proximal tubule

• most of the sodium reabsorption

• isosmotic

• Co transport with glucose amino acids and phosphates

• Counter transport linked to bicarbonate buffering

Late proximal Tubule

• High Cl- concentrations

• Largelyu reabsorbes NaCL

  • Sodium hydrogen exchanger

  • CL formulate exchanger

3 segements of the loop of henle

• Thin descending limb

• Thin ascending limb

• Thick Ascending limb

What is the loop of henle responsible for

countercurrent multiplication and concentration and dilution of urine managment

Thin Descending

• Permable to water and small solutes like salt and urea

• Tubulkar fluid progressivly more concentrated as it descends

Thin Asending

• permable to NaCL but impermeable to water

• Solute moves out so tubular fluid becomes more hyposmotic but does not increase fluid concentration

Thick Ascending limb

• Reabsorbs 25% of filtered sodium

• load dependent on how much it will reabsorb (more= more)

• Loop diretics inhibit transporters in this section keeping sodium and water in the urine

  • Impermeable to water

Early distal tubule

Similar to thick ascending

Not permable to water

tubular fluidn becomes more dilute

Late distal tubule and collecting duct

• Water permability depends on presence of ADH

• 2 cell types found in these areas

  • Alpha intercalcalated cells

  • Principle cells

Alpha intercalcalated cells

Acid base and poatasium balance

• proton secretion occurs in exchange for reabsorbed potasium in hypokalmia

Principle cells

Site of aldosterone action to increase sodium reabsorption

What does an increase in sodium intake stimulate

• Decrease in sympathetic activity

• Increase in ANP

• Decrease in oncotic pressure

• Renin-angiotensin aldosterone pathway

What does an increase in sympathetic activity cause in regards to increase sodim intake

• Decrease in BP

• Dialation of afferent arterioles

• Decrease in sodium reabsorption in the proximal tubule

What does an increase in ANP stimulate when sodium intake increases

• Constriction of efferent arterioles

• Decrease in sodium reabsorption in collecting ducts

What does a decrease in oncotic pressure stimulate in regards to increase sodium intake

Decrease in sodium reabsorption in the proximal tubule

What does a decrease in renin angiotensin pathway stimulate with increase sodium intake

Decrease in sodium reabsorption in the proximal tuble and collecting duct

What is the over solution to an increase in sodium intake

Increase in sodium excretion

What happens when we have a decrease in sodium intake

• Decrease sodium excretion

• Transfer water from external to intracellular fluid

What are some factors that cause a shift of potasium out of the cell

• Acidosis

• Exercise

Hyperkalemia

High potasium

What causes potasium to shift into the cell

• Insulin

• Alkilosis

Hypokalemia

Low potasium levels

Renal potasium regulation

• Absorbed in the proximal tubule and thick ascending limb

  • 
    

What determines net absorption of potasium

What happens in the distal tubule and collecting duct

Intercallated cells do what with potasium

Reabsorb

Principle cells do what with potasium

Secrete it

How does potasium reabsorption take place

• Hydrogen potasium atpase pump hydrogen ions into the tubule and potasium is reabsorbed

How does potasium secretion take place

• Goverened by diffusion based on sodium potasium gradient

  • magnitude of gradient governs amount of secretion

What does parathydroid hormone do?

Is seccreted when blood calcium levels are low and brings back calcium, while it dumps phosphates

Which part of the nephron does aldosterone target

Late distal tubule

What is the action of aldosterone in the nephron

• increase sodium reabsorption- principle cells

• increases potasium secretion- principle cells

• increase proton secretion- intercalated cells

Excess aldosterone- (primery aldosteronism or conns syndrom)

• Sodium retention

• Hypokalemia

• Alkalosis

• Hypertension

Aldosterone diffinciy- (addisons disease)

• sodim wasting

• Hyperkalemia

• Hypotension- dumping water

Excess ADH secreation

• Decreases plasma osmolarity

• Hyponatremia

Central diabetes insipidus

• Insufficient ADH

• Increased plasma osmolarity

• hypernatremia

• excess thirst

• Dump water into urine concntrating blood

Atrial Natriuretic Peptide- ANP

• Released from cardiac atria in response to destention

• Directly inhibit reabsorption of soidum and water at collecting ducts

• Inhubits renin secretion

Where is parathydroid hormone secreted from

Cheif cells in the parathyroid gland

What part of the nephron does parathyroid hormone stimulate to increase sodium reabsorption

Distal tubules