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  #1  
Old 04-11-2012
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Help ask some conceptual questions

Q1. concept behind respiratory acidosis , respiratory alkalosis , metabolic acidosis and alkalosis
Q2. What are the causes of secondary hypercortisolism?
Q3. How does aldosterone produces metabolic alkalosis?
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Old 04-12-2012
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Originally Posted by CHAKRAM View Post
Q3. How does aldosterone produces metabolic alkalosis?
I will give you very brief explanations--

I'll start with the easiest and shortest to explain:

Aldosterone causes Na+ and H2O retention. It causes excretion of K+ principal cells and H+ ions from the intercalated cells lining the collecting duct. This is because when aldosterone moves the Na+ from the lumen, it makes the lumen more negatively charged. This negative charge of the lumen attracts K+ & H+. Every time a H+ ion is moved into the lumen, a NEW HCO3- produced by the kidney through Carbonic Anhydrase Reaction is moved into the ECF as well. This loss of H+ and gain of a new HCO3- contributes to the Metabolic Alkalosis.

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Originally Posted by CHAKRAM View Post
Q2. What are the causes of secondary hypercortisolism?
First- Cortisolism is increase in serum cortisol levels (gluccocorticoid). Secondary hypercortisolism is ACTH DEPENDENT. This simply means that you have cortisol secretion in response to ACTH levels. For example, a Pituitary adenoma (Cushing's Disease) secreting high levels of ACTH will lead to high levels of Cortisol. It will also result in bilateral hyperplasia of the adrenal fasiculata and reticularis (since they are affected by ACTH secretion). Also, if you have any ectopic secretion of ACTH, as in a paraneoplastic syndrome (Small cell carcinoma of lung), it will lead to high levels of cortisol.

Note that Cushings dx is dexamethasone suppressible whereas ectopic production of ACTH is nonsupressible.

Last edited by Hope2Pass; 04-12-2012 at 12:40 AM.
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Old 04-12-2012
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Originally Posted by CHAKRAM View Post
Q1. concept behind respiratory acidosis , respiratory alkalosis , metabolic acidosis and alkalosis
This is a long answer, but in summary, acidosis and alkalosis are usually caused by imbalance of CO2 (weak acid) and HCO3 (weak base). A good way to remember that is that CO2 + OH --> HCO3 (although that's not actually how it works), and since OH is a strong base, CO2 must be significantly more acidic than HCO3.

Respiratory acidosis - hypoventilation causes increased CO2, thereby decreasing pH
Respiratory alkalosis - hyperventilation causes decreased CO2, thereby raising pH
Metabolic acidosis - long list of reasons (diarrhea, DKA, renal tubular dysfunction, MUDPILES) which can lead to decreased HCO3, thereby decreasing pH
Metabolic alkalosis - long list of reasons which can lead to increased HCO3, thereby increasing pH


Quote:
Q2. What are the causes of secondary hypercortisolism?
Anything that increases ACTH, which stimulates cortisol release.
That might include an ACTH-secreting pituitary adenoma (Cushing's disease), an ACTH-secreting small cell lung cancer, and lots of other paraneoplastic syndromes.

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Q3. How does aldosterone produces metabolic alkalosis?
Aldosterone inhibits the Na/K pump in the collecting duct, thereby causing increased potassium dumping into the urine and increased sodium retention into the plasma. That means that there's more potassium going into the collecting duct, where some of it is exchanged for acid in the H/K pump. So, overall, you get increased dumping of both potassium and hydrogen ions, thereby causing increased urinary acid and decreased plasma acid (i.e. metabolic alkalosis).

All of these answers could have been found in First Aid. If you're planning to take Step 1, you should get yourself a copy.
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Old 04-12-2012
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heh, looks like you beat me to the answer by a few seconds...
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Old 04-12-2012
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Originally Posted by CHAKRAM View Post
Q1. concept behind respiratory acidosis , respiratory alkalosis , metabolic acidosis and alkalosis
This is a HUGE topic so I am not going into ALL the conditions that can cause the acid base disturbances but just a basic brief explanation or what is seen in each condition.

Here is the key -

Alveolar ventilation causes respiratory acid base disturbance.
Hyperventilation leads to decreased levels of CO2 and increased levels of O2. You get Respiratory Alkalosis. The kidneys compensate by decreasing HCO3- reabsorption and increase HCO3- excretion in the urine.

Hypoventilation leads to increased levels of CO2 and decreased levels of O2. You get Respiratory Acidosis. The kidneys compensate by increase HCO3- reabsorption.

Metabolic Acidosis is seen in conditions where you have an increased H+ production or failure to excrete the H+ and/or when you have decreased HCO3- reabsorption or increased excretion. This leads to increased levels of acid, decreasing the metabolic pH. Levels of bicarbonate are depressed. The body compensates by hyperventilating, leading to loss of CO2 and increasing O2.

Metabolic Alkalosis is seen in conditions where you have loss of acid and or increase in plasma bicarbonate by preventing the excretion of HCO3-. The blood pH rises causing alkalosis. The body compensates by hypoventilating and thus retaining CO2 and decreasing levels of O2.
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Old 04-12-2012
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What are you actually looking for???? Is it answer of the questions stated above or to ask you some questions based on this conceptions............??? If it's about getting conceptions clear cut then i suggest you to go through Goljan RR. You will find all these easier to remember and if confusion arise later post the part that you are concerned forum members will definitely help you. But if it's about finding question then go through the search options you would be more benefited from those thread in this forum.
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Old 04-12-2012
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Originally Posted by shan564 View Post
heh, looks like you beat me to the answer by a few seconds...
haha hey every answer is a good answer. I like these conceptual questions because I can really put out the knowledge I have and see how much of it I retained. If i feel like i dont know something it helps me because then i quickly look it up and that helps me out as well
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Old 04-12-2012
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still explanation are being posted earlier........meanwhile i didn't notice that.anyway i thought it would be huge post to reply all 3 questions. It's better to keep it concise.U forum members are really fast......
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