Adrenal The Adrenal glands are glands located above the kidneys, that provide a variety of hormones including adrenaline and the steroid hormones , a ,c and t . Each gland has an inner , and an outer , where steroidogenesis occurs. The outer is divided into three zones:
Zona G
.
H:
F:
S:
Zona R
.
H:
F:
S:
Zona F H:
F:
S:
.
Adrenal Insufficiency - Pathophysiology 1) Addison’s disease (primary adrenal insufficiency): It is a potentially fatal condition where there is Destruction of the Adrenal destruction accounts for
% of all cases and affects more
than
. Autoimmune . This destruction occurs as
a result of organ specific autoantibodies. Rarer causes of addison’s disease include malignant infiltration, infection and adrenal haemorrhage. 2) Secondary Adrenal insufficiency: It is sometimes described as Addison’s, but the cause originates in the insufficient release of
, where there is
. It mostly occurs as a result of a pituitary adenoma, but can also result
from autoimmune destruction. Secondary Adrenal Insufficiency:
Primary Adrenal Insufficiency:
ACTH:
K+:
H+:
Glucose:
MSH:
Testosterone:
ACTH:
K+:
H+:
Glucose:
MSH:
Testosterone:
The clinical picture – Cushing’s Syndrome
Diagnosis:
Cushing’s syndrome- Pathophysiology A collection of signs and symptoms caused by prolonged exposure to high levels of glucocorticoids. There are a range of different causes that can be categorised into ACTH dependent and independent causes.
ACTH independent causes 1) Iatrogenic – Chronic corticosteroid therapy = No 1 cause
2) Adrenal Adenoma –
ACTH dependent causes
1) Pituitary adenoma
2) Ectopic
In Summary:
ACTH Iatrogenic Adrenal Adenoma Pituitary Adenoma (Cushing’s disease) Ectopic
CORTISOL
Adrenal Atrophy/Hyperplasia Bilateral Atrophy Unilateral Atrophy Bilateral Hyperplasia
The clinical picture – Cushing’s Syndrome
Diagnosis:
1 U & E’s (Urea and Electrolytes) Objectives 1. What’s included in a U&E’s investigation? 2. Sodium, water and potassium: physiology and abnormalities 3. Urea and creatinine: physiology and abnormalities What’s measured in a routine U&E’s investigation? 1.
4.
2.
5.
3.
6.
1. eGFR is calculated by a computer using serum creatinine – it’s not a direct measurement of anything. 2. Sorry there’s not enough time today to cover calcium – it’s worth a lecture in itself!
Sodium, water and the kidneys
Remember that? Well, there’s an extra step to tell you about, and a couple of points to remember: When coffee is filtered, it doesn’t go straight into the coffee spout.
Before that, it gets taste-tested by George Clooney who actually lives inside the machine. If it’s too watery or there’s too much sugar, he adjusts the coffee before it lands in your cup. He’s got some friends to help, but he’s the main man. Let’s call him your Personal Coffee Tester (PCT).
1. There’s also an important substitution at the Distal Convoluted Tubule
When the blood is filtered, it doesn’t go straight into the collecting duct Before it does, the filtrate gets altered by the cells lining the nephron. Water, sodium, potassium, urea, etc are reabsorbed back into the circulation. The majority of reabsorption is in the Proximal Convoluted Tubule (PCT)
2. A general rule: wherever sodium goes, water follows
Sodium is reabsorbed from the urine back into the circulation Potassium is secreted from the circulation out into the urine
Medsoc teaching – U&Es
01/05/16
Vivek Murthy
2 How does the body regulate its own fluid balance? Site of receptor
Modality of receptor
Hormone (s) released
Mechanism of controlling fluid balance
Almost done with the physiology – just one more thing… Intra-cellular fluid (ICF)
Extra-cellular fluid (ECF) Interstitial Intravascular
Proportion of total body fluid Main cation (positive ion)
Time to see some patients with abnormal U&Es! You’re in the GP surgery, about to see a patient who has incidentally low potassium on a recent blood test. What will you do? ________________________________ You’re the F1 covering the ward at night, and the lab ring to tell you a patient has a raised potassium. What will you do? ________________________________
Medsoc teaching – U&Es
01/05/16
Vivek Murthy
3 Hyponatraemia There are lots of causes, which you will never remember off the top of your head. So instead, ask yourself two golden questions. Then you can classify all the causes and work through them logically. Patient with low sodium Question 1
Answers
Translation of answers
Question 2 Translation of Q2
Answer to Q2
Causes!
Hypovolaemia
Hypervolaemia
Assessing fluid status clinically
*NB* Another cause of hyponatraemia is “pseudohyponatraemia.” This is a rare but really interesting phenomenon; unfortunately I don’t have time to discuss it here, but please look it up if you’re interested
Medsoc teaching – U&Es
01/05/16
Vivek Murthy
4 Hypernatraemia In hypernatraemia, the problem is usually that fluid levels have decreased while sodium levels have stayed the same. Causes are: 1. 2. 3. 4.
Reduced intake of water Reduced intake of water Reduced intake of water Diabetes insipidus
Thirst is an incredibly powerful drive. A thirsty person will only not drink water if something serious is stopping them. What could that be?
Potassium is a bit simpler For both hyper- and hypo-kalaemia, there are 3 questions to ask: 1. Problem with intake/production? 2. Problem with excretion? 3. Imbalance between extra- and intracellular levels? Question no. 1
Hyperkalaemia
Hypokalaemia Intake
2
Production Intake Drugs Endocrine Renal
3
Acid-base
Another cause of hyperkalaemia is “artefactual” – draw your bottles in the right order when taking blood! You can also do a blood gas to double-check a lab reading
Drugs Endocrine Renal GI losses Acid-base Drugs
The main concern with altered potassium levels (both high and low) is conduction disturbance in the heart. This can cause arrhythmias, which can be fatal. Severe hyperkalaemia is an emergency! Urea and Creatinine (please see my teaching session on AKI for more detail. But basically…)
Urea
Sodium
Water
Water and sodium are mainly reabsorbed in the PCT. Urea hangs around them like a bad smell and is passively reabsorbed. When the body is fluid depleted, it will react by reabsorbing water and sodium. Urea will therefore also be reabsorbed more. Thus a raised serum urea measurement is indicative of a dehydrated patient.
Creatinine is filtered at the glomerulus and never re-absorbed. Any creatinine in the blood has not been anywhere near the kidneys. Therefore if plasma creatinine levels rise, it’s a sure sign the kidney are struggling to filter it, not because production has increased or reabsorption is happening. To do when you go home:
http://www.sporcle.com/games/vmurthy/medsoc_teaching-ues
1. Practise interpreting U&Es on the ward, and try to link to the patient’s signs and symptoms 2. Check out this quiz, using the link just above, it’s tailor-made for this session! 3. Have a chat with George Clooney next time you have a coffee. He’s probably really bored.
Medsoc teaching – U&Es
01/05/16
Vivek Murthy
