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Flashcards in Physiology Deck (38):

Which segment of the systemic circulation has the greatest resistance to flow?

Arterioles. Arterioles contribute the largest part of the TPR (aka SVR).


compression atelectasis

Occurs with accumulation of blood, fluid, or air within the pleural cavity, which mechanically collapses the lung.


contraction atelectasis + clinical significance

1) Occurs when fibrosis of lung or pleura prevent full expansion.
2) atelectasis type post radiation.


resorption atelectasis

Caused by obstruction. Remaining air in alveoli gets resorbed.


alveolar dead space

Sum of volumes of those alveoli which are ventilated but not perfused.


anatomic dead space

Normal dead space. Portion of airway which conducts gas to the alveoli.


physiologic dead space

Sum of anatomical dead space plus alveolar dead space.


Dead space

Air that is inhaled in gas exchange but does not participate in gas exchange either because it 1) remains in the conducting airways or 2) reaches alveoli that are not perfused or poorly perfused.


Pulmonary shunt

Condition in which alveoli of lungs are perfused as normal but ventilation fails to supply perfused region.


Lab values in mixed metabolic acidosis and respiratory alkalosis (eg late stage salicylate poisoning)

Acidotic with low bicarb, low pCO2.


ACTH stimulation test (adrenocorticotropic stimulation test)

Test used to determine renal functioning.


Diabetic diarrhea pathophys

Autonomic neuropathy, leading to motility disorder.


metabolic acidosis cause

1) Increased production of hydrogen ions or
2) inability of body to form bicarbonate.
Thus, in either case, bicarbonate is LOW.


Lab values in DKA

hyperglycemia + increased hydrogen ions + depleted HCO3- + increased ketones + leukocytosis


Shilling test

used to confirm that parietal cells aren’t producing sufficient IF to support B12 absorption. In first stage, give radiolabeled oral B12 + an injection of unlabeled B12. The single injection temporarily saturates B12 receptors in the liver with enough normal B12 to prevent radioactive B12 binding in body tissues, so that if absorbed from the GI tract, it will pass into the urine. Thus, low excretion suggests poor absorption of B12 (it is passed into feces rather than absorbed and excreted in urine). In second stage, give radiolabeled oral B12 + IF. If this is normal, then person has a lack of intrinsic factor, or pernicious anemia. A low result implies malabsorption.


contraction alkalosis pathophys

a few things contribute
1) renal compensation for volume loss. RAAS--> ang II --> increased Na-H exchange in proximal tubule and increased HCO3- reabsorption
2) Aldosterone induces H+ efflux
3) loss of solvent volume without a proportional loss in bicarb concentration.



Chloride/bicarbonate exchange in the collecting duct.



Vasculitis associated with minimal evidence of hypersensitivity upon immunofluorescence., eg churg straus, wegeners, microscopic polyangiitis.


Formation of brownstones

Bacteria have glucoronidases that can deconjugate biluribin. Conjugated bilirubin isn't a problem because it can dissolve and come out.


Why is BUN/Cr high in prerenal AKI?

Urea is necessary to create a gradient in the collecting tubule for water reabsorption. Thus, with hypovolemia, you have increased ADH production, causing increased urea reabsorption. Creatinine is never absorbed, so relatively the ratio is increased.


Fever mechanism

Pyrogens --> increased IL-1 --> IL-1 acts on anterior hypothalamus to increase prostaglandins --> prostaglandins increase the set-point temperature. This also explains why aspirin reduces fever (by inhibiting COX-1, prostaglandins can't increase the set-point).


inside of cell vs. outside of cell

inside is negative, which is why sodium depolarizes cell.


SGLT-1 expressed where?

gut. That's why you need to give glucose in rehydration solutions.


Difference between SLGT-1 and GLUT-2?

Glucose taken up by SGLT-1. Transported to blood by GLUT-2.


what solutions cause cell lysis?



acetylcholine action at muscle end plate...

Opens BOTH Na and K+ ion channels. Thus, membrane potential is depolarized to a value that is approximately halfway between respective membrane potentials.


How do inhibitory postsynaptic potentials hyper polarize the postsynaptic membrane?

Opening Cl- channels (remember Cl- is concentrated OUTSIDE the cell).


secondary active transport

(cotransport) Indirect ATP. Uses a Na+ gradient as an energy source, and therefore, uses ATP indirectly. eg SGLT-1


What causes rigor?

ATP is depleted --> no ATP bound, thus myosin remains attached to actin and cross-bridge cycle cannot continue.


Why does hyperkalemia cause muscle weakness?

Elevated K+ depolarizes the equilibrium potential and therefore depolarization of the resting membrane potential in skeletal muscle. Sustained depolarization closes the inactivation gates on Na+ channels and prevents the occurrence of action potentials in the muscle.


Why do you get amenorrhea with hyperthyroidism?

Increased SHBG --> leading to decreased estrogen.


Why do you hypocholesteromia in hyperthyroidism?

Thyroid hormone upregulates LDL receptors.


how does acetazolamide cause diuresis? acidosis? hyperventilation?

carbonic anhydrase sits on the apical side of the tubule and converts carbonic acid to H2O and CO2 --> CO2 diffuses into cell combines with H20 in cell to reform carbonic acid --> carbonic acid converted again to release H+ ions, which are exchanged with sodium. Without being able to generate Hydrogen ions inside the cell, sodium can't be reabsorbed and is diuresed. Without being able to reform bicarb inside the cell and transport it to blood, the patient becomes acidotic, this is what explains metabolic acidosis. Similarly, patient hyperventilates, which is why it can be used for altitude sickness.


Why is there a spike in FSH accompanying LH?

Estradiol synthesis has a positive feedback effect on synthesis of FSH and LH.


Magnesium in relation to PTH

Hypo or hypermagnesemia can impair PTH secretion or responsiveness, leading to hypocalcemia. But slightly reduced Mg can increase PTH but really reduced Mg inhibits it.


When does shunt physiology occur?

1) pulmonary edema
2) pneumonia
Lungs are normally perfused but not ventilated because of fluid buildup


NBME explanation for PCOS

Excess adipose causes higher levels of estrogen because estrone is aromatized to estrogen, which inhibits the LH surge.


Positive progestin challenge means...