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1

6 functions of urinary system

o Filter blood to remove wastes/toxic substances
o Production, storage and elimination of urine
o Regulates fluid and electrolyte balance
o Regulates blood PH
o Regulates blood volume and blood pressure
o Regulates erythropoiesis

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kidney functions

filter blood and produce urine

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ureter

move urine from kidneys to bladder

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urethra

moves urine from bladder to exterior

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urinary bladder

stores urine

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Kidney location and structure

retroperitoneal-outside/behind abdominal cavity
Renal cortex
Renal Medulla

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kidneys surrounded by three external layer

 renal fascia
 adipose capsule
 renal capsule

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Nephron: definition and structure

major functional unit of the kidney. Urine production begins here. Empties into collecting system.
o Renal corpuscle: filters blood
o Renal tubule: collects filtrate

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Collecting system

series of tubules that receive filtrate from nephron and further modify it

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parts of collecting system

Cortical and medullary collecting ducts and papillary collecting ducts and papilla and minor calyx

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Types of nephrons

Cortical nephron and Juxtamedullary nephron

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what’s the difference between the types of nephrons

Cortical nephron: primarily in cortex. Branch into peritubular capillaries. And Juxtamedullary nephron: extend into medulla. Peritubular capillaries connected to long straight capillaries

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which nephron is more abundant

Cortical nephron

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Urine production

eliminates metabolic waste products while minimizing loss of water and nutrients

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urea

most abundant organic waste from protein catabolism

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creatinine

product of creatine phosphate catabolism

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uric acid

product of nucleic acid catabolism

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renal failure

results in buildup of toxic wastes

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dialysis

medical process for those who have lost kidney functions. Machine that filters blood.

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Filtration

kind of transport: passive movement of fluid and solutes direction of movement: blood in glomerular capillaries to filtrate inside renal corpuscle (blood to filtrate). Driven by hydrostatic pressure

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Reabsorption

active or passive movement of water solute from filtrate in renal tubule back to blood in peritubular capillaries

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Secretion

active transport of water and solutes from blood in peritubular capillaries to filtrate in renal tubule

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Paracellular route

substances pass between adjacent tubule cells

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Transcellular route

substances must move through tubules cells

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diffusion and osmosis are examples of

passive transport

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active transport requires

an energy input

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facilitated diffusion and active transport are examples of

carrier-mediated transport and require protein pumps

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Carriers (channels) are specific and can be saturated (what happens if channels get saturated

all binding sites are filled and can start seeing the substance in urine

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transport maximum

maximal blood solute levels that can be transported

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renal threshold

plasma concentration at which a specific compound appears in urine because the TM has been reached

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Renal corpuscle

Glomerular (Bowman’s) capsule and the glomerulus

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What are podocytes

cells that form the visceral layer of the capsule of the renal corpuscle

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what are filtration slits

between podocytes and part of filtration membrane. Must fit in these area in order to filter.

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how filtration works

it is only selective based on size: only small particles filtered (proteins and cells are not filtered)

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Components of filtration membrane

made of pores of fenestrated capillaries, basal lamina, and filtration slits of podocytes

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Hydrostatic pressure

pressure in glomerulus

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GHP and filtration

favors filtration

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CHP and filtration

opposes filtration

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GCOP

osmotic pressure and pulls water into capillaries, so it opposes filtration

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Net filtration pressure equation

= GHP – CHP-GCOP
o 0 or negative =no filtration
o Positive number = filtration

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What is GFR

amount of filtrate produced by both kidneys per minute

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what does GFR depend on

GFR depends on blood pressure (higher BP means higher GFR)

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Autoregulation

ability of neprhons to adjust their own blood flow and GFR

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myogenic

stretch receptors in afferent arteriole detect pressure changes and respond to adjust GFR

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tubuloglomerular mechanisms

the glomerulus receives feedback on the status of downstream tubular fluid and adjusts filtration rate accordingly

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changes in the afferent and efferent arterioles control

blood pressure in the glomerulus and therefore GFR

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 BP low/GFP low

= dilate arteriole/constrict efferent arteriole. Goal: high BP and high GFR

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 BP high/GFP high

= constrict afferent arteriole/dilate the efferent arteriole. Goal: low BP/low GFR

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JGA

macula densa of DCT + smooth muscle of arterioles

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JGA Hormonal regulation

JGA cells secrete rennin and EPO

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Renin-angiotensin-aldosterone system

renin converts angiotensinogen to angiotensin I and then ACE converts angiotensin I to Angiotensin II

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renin is released in response

low BP (low GFR) and low filtrate concentration in DT

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low BP causes

low GFR, causes release of renin, causes activation of angiotensin II, causes increase in blood volume, causes increase in BP and therefore increase in GFR.

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ANP

released in response to high BP and GFR

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high BP causes

ANP/ BNP release, which causes an increase in GFR, which leads to more fluid loss and therefore less blood volume and less blood volume means lower BP.

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recycling urea

helps pull water by osmosis

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the countercurrent exchanger in the vasa recta

blood and filtrate go in opposite directions. Descending vasa recta absorbs NaCl, and the ascending vasa recta absorbs water

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DT and collecting duct secretion

depending on needs substances can be secreted. Potassium, HCO3, and ammonium ions

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DT and collecting duct selective reabsorption

body has a choice (selective based on needs). Na+, Ca2+, HCO3, water, urea. 85% of water and 90% of sodium reabsorbed.

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aldosterone causes

more Na reabsorption and K loss

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ADH causes

more water reabsorption (by increasing the number of aquaporins in membrane of DT and collecting duct

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in collecting duct urine gets?

concentrated and its volume is reduced

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Obligatory water reabsorption

85% in Proximal tubule and loop, through osmosis driven by medullary concentration

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Facultative water reabsorption

(15 %, controlled by ADH, in Distal Tubule and collecting duct and requires aquaporins) more aquaporins means more reabsorption, which produces a smaller amount of concentrated urine. No ADH= no aquaporins, which means no water reabsorption and large amounts of diluted urine.

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slit like opening in ureter

prevents back flow

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rugae

series of ridges produced by folding of the wall the bladder

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detrusor muscle

around the bladder

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urethra is longer in

males

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pH scale

low H+=high PH=basic. High H+=low PH=acidic

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acid

dissociates to release H+

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base

reduces the amount of free hydrogen in solution

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Strong acid

completely dissociates in solution

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Weak acid

does not dissociate completely

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Strong base

dissociates completely

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Weak base

do not dissociate completely

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Volatile acids

can move from liquid to gas

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carbonic acid is a

volatile acid

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Fixed acids

only stay in solution. Remain in body until excreted

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Organic acids

byproducts of metabolism

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Normal range of ECF pH

7.35-7.45

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Sources of H+ gains

from GI tract and metabolism

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Sources of H+ losses

kidneys and lungs

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Chemical Buffer systems

combination of weak acid and its anion. Are the first response, but a temporary solution

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Protein buffer systems

know that amino group accepts H (base) and carboxyl group can donate H (acid) and act as buffer; know that only free or terminal amino acids can do that; know that hemoglobin is a buffer

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Phosphate buffer systems

you only need to know that it’s the major ICF (intracellular fluid) buffer

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Carbonic-acid bicarbonate buffer system

most important ECF buffer

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how does the Carbonic-acid bicarbonate buffer system work?

prevents PH changes caused by fixed and organic acids

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the 2 limitations to the Carbonic-acid bicarbonate buffer system

only works if respiratory system works and need enough bicarbonate

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Carbonic-acid bicarbonate buffer system equation

CO2+H2O --- H2CO3 --- H+ + HCO3-

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what will drive forward reaction? what will drive reverse?

too basic- forward reaction. too acidic= reverse reaction.

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most important factor affecting pH

pCO2

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relationship between H+, pH and pCO2

high pCO2=high H+=low ph. low pCO2=low H+=high Ph

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Acute phase

ph moves rapidly out of normal range/ no compensation

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compensated phase

adjusted back to normal pH but constant compensation

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normal phase

normal pH and no compensation, source of problem is removed

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what happens to ph and pCO2 during Respiratory acidosis

low Ph, high CO2.

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causes of respiratory acidosis

respiratory problems, emphysema, CNS injury, heart failure

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compensation for acidosis

respiratory compensation- increase RR; renal compensation- excretion of H+; reabsorption of HCO3-

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what happens to ph during metabolic acidosis

low ph

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causes of metabolic acidosis

diarrhea, loss in bicarbonate, unable to get rid of acid, producing too much acid

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what happens to Ph and CO2 during respiratory alkalosis

high Ph and low CO2

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causes of respiratory alkalosis

hyperventilation, pain, anxiety

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compensation for alkalosis

decreased RR, excretion of HCO3-; reabsorption of H+

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what happens to Ph during metabolic alkalosis

high ph

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causes of metabolic alkalosis

vomiting, diuretics, too much bicarbonate

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compensation for metabolic alkalosis

decreased RR, excretion of HCO3-; reabsorption of H+

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what fluids make up the ECF

fluid outside cells. Includes plasma of blood, interstitial fluid, and other body fluids

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ICF

intracellular fluid (cytosol)

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how ECF and ICF are different

more than half fluid is inside cells and ICF contains more water

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Major ICF ions

potassium, magnesium, proteins, sulfate, hydrogen phosphate

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major ECF ions

sodium, chloride, calcium, bicarbonate

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basic principles of regulation

o All receptors in ECF not ICF
o Receptors monitor plasma volume and osmotic concentration
o Cells cannot move water by active transport only passively by osmosis – water follows salt

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Main sources of water gains

from drinking, eating, and metabolism

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water losses

urine, feces, exhaled air, insensible and sensible perspiration

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fluid shifts

rapid movement of water between ECF and ICF

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hypertonic ECF

(low fluid, high concentration), shift is out of cells (from ICF to ECF)

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hypotonic ECF

(high fluid, low concentration), shift is into cells (from ECF to ICF)

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Osmoreceptors

in the hypothalamus respond to angiotensin 2 and rise in osmolarity of ECF. Regulates thirst and urination sensation

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ADH

secreted by posterior pituitary upon stimulation from osmoreceptors. Stimulates you to drink more/excrete less

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Aldosterone

secreted by adrenal cortex in response to too much potassium or not enough sodium or in presence of Ang 2. Stimulates to drink more/excrete less

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Angiotensin II

Activated after renin is released by kidneys in response to low BP and blood volume. Stimulates us to drink more/excrete less

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ANP/BNP

secreted by cardiac muscle excreted in response to high BP and increased volume. drink less/excrete more

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how to get Dehydration

Sweating too much, diarrhea, vomiting, diabetes, too many diuretics

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Dehydration results in

hypertonic ECF (hypernatremia), low plasma volume and low BP

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Response mechanisms to dehydration

water shift out of cells (from ICF to ECF); roles of renin-angiotensin, ADH, aldosterone: increase volume (increase thirst and decrease excretion)

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What is the difference between hypovolemia and dehydration

hypovolemia is loosing water and solute (bleeding) no fluid shift because no change in concentration and dehydration is only losing is water. Concentration goes up.

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causes of overhydration

Renal failure, too much IV fluid, too much water, low or no ADH

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over hydration results in

hypotonic ECF (hyponatremia), increased plasma volume and BP

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Response mechanisms to overhydration

water shift into cells (from ECF to ICF); role of ANP/BNP (decrease thirst and increase excretion)

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What is the difference between hypervolemia and over hydration

hypervolemia is both water and electrolytes gained. Results in edema. No fluid shift because no change in concentration and overhydration is water gain and concentration change

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difference between total amount and the concentration of an ion

o Total amount of ions= how much solute
o Concentration of ions = total amount/ amount dissolved in

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o fluid balance is critical factor that determines

electrolyte balance

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Sodium imbalance is, while potassium imbalance is

sodium balance is more common while potassium balance is more dangerous

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sources of Na gains

absorption though GI tract

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sources of Na losses

excretion by kidneys and perspiration

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water follows

salt

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fluid loss and gain affects the concentration of electrolytes

fluid gains lower concentration and fluid losses increases concentration

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Hypernatremia

higher than normal concentration of sodium. caused by fluid loss. Detected by osmoreceptors stimulates same mechanisms as response to dehydration

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Hyponatremia

lower than normal concentration of sodium caused by overhydration or rapid loss of sodium. Detected by osmoreceptors in brain and stimulates same mechanisms as response to overhydration.

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sources of K gains

absorption through GI

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sources of K losses

excretion by kidneys

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Hyperkalemia

lower than normal potassium concentration. caused by- inadequate intake, diuretics causes more negative resting membrane potential, which leaves cells less responsive to stimuli

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Hypokalemia

higher than normal potassium levels caused by pH or ECF, renal failure, burns. Results in more positive resting membrane potential or excitable cells, such as cardiac arrhythmias.

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Calcium balance. what is it important for and what hormones do you need to stay in balance?

important for muscle contractions. PTH and Vit. D are important for balance

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what causes hypercalcemia

higher than normal calcium concentration. caused by hyperparathyroidism, excess vitamin D, bone disorders, and renal failure

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hypocalcemia

lower than normal calcium concentration. caused by Ca and Vitamin D dietary deficiency, PTH deficiency, chronic renal failure

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where is the JGA located

between the renal corpuscle and the afferent/efferent arteriole

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what does the JGA do?

regulates blood flow to the glomerulus and secretes EPO and renin

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effects of low level neural stimulation

causes increase in GFR

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effects of high level neural stimulation

causes constriction of afferent arterioles and decrease in GFR. Ex: warm weather and exercise

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parts of renal tubule

proximal tubule, nephron loop, and distal tubule

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what happens to the filtrate as it travels through the tubule?

the filtrate changes as it travels through the tubule.

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proximal tubule function

some secretion but mainly reabsorption.

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what is reabsorbed in the proximal tubule

sodium, potassium, Cl-, PO4-, HCO3-

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difference between thick and thin nephron loop

thick: reabsorption of ions: sodium chloride, calcium, and magnesium. thin: reabsorption of water

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during Medullary concentration gradient concentration is higher in

medulla, because of countercurrent mechanisms and urea

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what needs to be present for urine concentration at the collecting duct

ADH