Section 7: Renal Physiology Flashcards by Justin Wong

Homeostatic roles of the kidney (6):

1.Fluid balance / plasma volume 2. regulation of osmolarity 3. electrolyte balance 4. plasma pH 5. waste excretion 6. hormone production

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hormones produced in the kidney (2)

erythropoetin (EPO) calcitriol (active vitamin D3)

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Yellow colour of urine comes from :

billirubin

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typical total water composition of human body

0.6 (60%) (Male) 0.5 (50%) (Female)

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Total body water (TBW) is distributed into 2 categories: ECF and ICF. What are the % distributions of the water ?

Extracellular fluid (ECF) is 1/3 total body water Intracellular fluid (ICF) is 2/3 TBW

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ECF consists of 2 parts :

interstitial fluid (ISF) and plasma

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water distribution of ECF into interstitial fluid and plasma

Extracellular fluid is 3/4 interstitial fluid and 1/4 plasma

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osmolarity definition

concentration of particles in osmol/L

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osmolality defintion

concentration of particles in osmol/kg

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ECF osmolarity (typical)

300 mOsmol / L

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osmolarity of 150 mM NaCl solution

300 osmol (NaCl dissociates into two particles)

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type of solutes that do not contribute to osmotic pressure (do not affect osmolarity)

penetrating solutes eg EtOH, urea

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If a cell is placed into a solution with a lower osmolarity than the cell, water will

enter the cell

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Forces governing fluid movement between intersitial fluid and plasma (across capillaries)

capillary blood pressure osmotic pressure tissue pressure

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Normal saline

150 mM NaCl

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Renal process (4 steps)

Filtration
Re absorption
Secretion
Excretion

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role of podocytes

epithelial cells that surround capillaries

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What is GFR ?

glomerular filtration rate, volume of plasma filtred over time

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What forms kidney stones ?

Calcium buildup in the kidney or uriter

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intrinsic myogenic control of glomerular blood flow

high blood pressure activates stretch sensitive channels and lets calcium in, activating muscles that constrict blood vessels

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intrinsic tubloglomerular feedback control system of glomular flow

macula densa senses paracrine constriction of afferent arteriole

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extrinsic control of glomerular flow

sympathetic innervation (α1) decreases glomerular permiability and causes afferent arteriole constriction

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role of mesangial cells

reduce permeability by constricting and bringing podocytes close together. Contract when stimulated by sympathetic NS and angiotensins

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clearance

filtred volume from which a solute is excreted

(volume returns to blood without solute, so that volume is cleared)

if 100 ml afferent blood is 50 mg/ml and 100 ml efferent blood is 40 mg/ml, how much is cleared ?

20 ml

What substance is used to measure clearance ?

Insulin was once used, but creatine is more practical

Substance used to measure renal plasma flow

P-aminohippuric acid (PAH) is totally cleared, so it is used in renal plasma flow measurements

Renal blood flow equation

RBF = RPF / (1-Hct) where: RBF = renal blood flow RPF = renal plasma flow Hct = haematocrit (% of blood that is RBC)

Characteristics of the tubular epithelium

- one cell thick-have polarity (luminar and basal sides) - brush borders

Re absorption of glucose: a) uses antiports b) is transcellular c) causes solvent decay d) occurs down a gradient into a tubular cell

b) is transcellular

solvent drag

when a solvent (water) is reabsorbed, small particles are dragged along with it (eg Na, K)

solutes reabsorbed in the proximal tubule (6)

Na, Cl, K, glucose, amino acids, Bicarbonate (HCO3)

Organic ion secretion

addition of COO- to an organic molecule in order to actively secrete into filtrate

Na/K pump limitation

can only pump against 200 mM gradient (why we need countercurrent system)

Permeability in the loop of Henle

descending loop is permeable to water, but not saltascending loop is permeaple to salt, but not water

ADH role

ADH is a peptide hormone that makes membrane more permeable to water (more absorption)

ADH mechanism of action

causes release of cAMP and promotes release of aquaporins

ADH released from :

posterior pituitary gland

potential cause of diabetes insipidus (ADH related)

absence or nonfunctional ADH/ADH receptors

effects of angiotensin II (3)

- arteriolar constrtiction - promotes Na reabsorption on proximal tubule - stimulates aldesterone release

aldosterone effects (2)

increases Na reabsorption by distal tubule regulates potassium

Atrial natriuretic hormone (2)

-released by atrial muscle, -inhibits Na reabsorption (Natri -\> sodium (Na))

possible causes of ECF hypertonicity (6)

- decreased water intake - sweating - vomiting, osmotic diarrhea - diabetes insipidus - diabetes mellitus

possible causes of cellular hypotonicity (2)

excessive water ingestion (compulsive (?)) excessive vasopression (ADH)

isotonic ECF disturbances (2)

loss: haemorrage, diarrhea gain: isotonic IV saline

Which IV solution would est correct a hypertonic ECF: a) normal saline (.15M) b) 1/2 normal saline (.075M) c) 0.3 M glucose d) a hypertonic solution e) a hypotonic solution

a) is incorrect because very little will enter cell b) only ~1/2 will go in c) is correct2/3 will go into cell (see ECF/ICF distribution)

Sweat 1L, drink 1L water, ECF will be :

hypotonic, as sweat contains electrolytes etc.Note the sweat is slightly hypotonic to interstitial fluid

pH formula

pH = -log[H⁺] = log¹/[_H+]

Average plasma pH

7.35 - 7.45 | (7.4)

Methods body uses to regulate pH (3)

1) buffers 2) H⁺ secretion 3) HCO^- reabsorption (#2 and 3 are done by the kidneys)

buffers in blood (2)

bicarbonate / carbonic acid Haemoglobin / Oxyhaemoglobin | (pKa 6.1)

buffers in urine

phosphate (H₂PO₄^- / HPO₄^2-) ammonium (NH₄⁺/ NH₃) pKa = 6.8

Henderson Hasselbach equation

pH = pK + log(^products/_reagents)

in addition to buffering, these molecules can affect pH

CO₂ / HCO₃^-

urine pH

~6 (slightly acid)

Can you judge H⁺excretion from urine pH?

No, it is buffered, so H⁺ excretion has a minimal effect on urine pH

Polarity of renal cells

Brush border faces the renal tubule (laminal side), Basolateral side faces the bloodstream

enzyme that combines carbonate with hydrogen

carbonic anhydrase catalyses H⁺ + HCO₃^- --\> CO₂ + H₂O

How is H+ secreted into the proximal tubule ? (5 steps)

1) Na⁺ concentration is created with a Na/K pump 2) H⁺ moved out of cell with Na/H antiport 3) H⁺ combines with bicarbonate to form water and CO₂ 4) CO₂ diffuses back into cell and converted back into HCO₃^- 5) HCO₃^- is transported into bloodstream