1/26/99

Physiology II

 

Selectivity of the sections:

proximal tubule

descending loop--water permeable

ascending loop--Na+ permeable

distal tubule--diluting segment

collecting duct--final concentration of urine

 

Control of nephron:

     -Na+ and water are the molecules

     -glomerulus flow rate--at a slower rate, greater absorption

                           at a faster rate, less absorption

          -only site in nephron that has filtration

          -2 types

          1. cortical nephron longer, thicker loop of Henle

          2. 20%, juxtaglomerular cells

     -Pressure filtration--blood pressure forces small molecules from the glomerulus into Bowman's capsule--water, glucose, aa, salts, urea, uric acid, creatine

     -concentration gradients--active transport to set up gradients

     -hematuria--glomerulus damage-should never see blood in the urine

     -should never find cells or protein in the filtrate

 

Glomerulus

-large surface area of capillary

-Fenestra--widely spaced cells, space is wide enough for albumin could pass through with no problems

-backed by a basement membrane, repels proteins due to negative charge

-Nephrosis--non-inflammatory, problem w/basement membrane, spill protein into filtrate, first symptom because protein deficient

-slit pore

-inulin, large MW, filtered completely, Glomerulus filtrate rate

-plasma flow--Paraaminopuritic Acid (PAH)-filtered and secreted

     GFR/PF = 125/650 = 19%

-pressure is dissipated rapidly, input from an arteriole (afferent), leaving the glomerulus is the efferent arteriole leading to venule called peritubular capillaries

-control of filtration

     -glomerulus affected by central circulation

-juxtaglomerular Apparatus--tubules are drawn

     -distal tubule as a specific group of cells--maccula densa-monitor ionic concentration of the tubular fluid ([salt])

     -important for regulation to tell you how good fxn has been up to that point

     -Na+ is what it looks at along w/ analogue Cl-

     -flow is fast w/high pressure, have high [Na+] at maccula densa, slow down flow

     -flow is slow w/low pressure, have low [Na+] at maccula densa, speed up flow

     -feedback mechanism

     -release renin from maccula densa

          1.  acute--at on juxtaglomerular cells causing them to shrink which pulls them away from capillary (afferent arteriole), increase flow rate

2.  renin is hormone, goes to liver to activate angiotension 1 to lungs to activate angiotension 2, increase pressure by increasing vascular rigidly

          3.  efferent arteriole is involved by constricting it which allows for the blood to be in glomerulus to increase pressure, eventually stops b/c water will be decreased b/c to much water will be lost

     -if control flow, control absorption

 

Diabetes

1.  polydipsia (craving for water, elevated glucose in plasma)

2.  polyurea (only reabsorb glucose to a certain, keep water in tubule)

3.  polyphagia (crave food b/c cells are deprived)

-do not monitor blood glucose in urine

 

-site of maximum absorption-proximal tubule-65%

-osmolarity remains the same b/c salt and water move at the same time

-set up a gradient, virgin nephron-never has been used

     -use active transport to set up gradient

     -charge gradient and concentration gradient

     -Na+ is an osmotic agent so we also absorb a water

 

Tubular Fluid

          Filtration

glucose            320mg/min

PO4                .1mM/min

SO4                .06mM/min

AA                 1.5mM/min

urate              15mg/min

plasma protein     30mg/min

Hb                 1mg/min

lactate            75mg/min

acetacetate        variable

 

Secretion

Creatinine

PAH                80mg/min

Penicillin

 

Tubular Load

     -GF=125ml/min w/100mg glucose/dl

     100mg/dl x 1.25dl/min = 125mg glucose/min --tubular load

-will reabsorb all of this

-Tubular Transport Maximum-those that require a transport carrier

-co-transport

     -carrier

     -substrate

     -secondary substrate

-tubular glomerulus balance--system adapts w/in a small range

-penicillin--secretion from vaso rectum, active transport, not filtered, strong negative charge

 

Composition of Urine

water

Na+

Cl-

Ca2+

K+

PO3

SO3

urea

uric acid--gout

Creatinine

ammonia

 

-collecting duct-only active transport, no diffusion

-any glucose, aa, or proteins not absorbed by proximal tubule is a part of the urine-after that point, only move water and Na+

 

Descending Loop

-controlled by other parts of the kidney

-relationship b/w descending and ascending loop--counter current mechanism

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