8 - Kidney and Blood Pressure Flashcards
How does the kidney respond to hypotension?
There is a decrease in renal flow so myogenic and tubuloglomerular feedback are activated as well as:
- RAAS
- Sympathetic Nervous System
- Prostaglandins
- ADH
What conditions cause a reduction in renal blood flow but a normal ECF (As normally a decline in renal blood flow is due to a decline in ECF)?
- Heart failure
- Liver cirrhosis
- Renal artery stenosis
- Nephrotic syndrome
- Conditions causing salt or water wasting
Can be fluid overload in these conditons
What are two major issues that occur when you have a conditon affecting renal blood flow but your ECF is normal?
- Hypertension
- Oedema due to salt and water retention
The kidneys think that you have hypotension so mechanisms occur to retain ECF leading to these conditions
What are some causes of secondary hypertension relating to the kidney?
- Renal artery stenosis
- Coarctation of the aorta
- Primary hyperaldosteronism (Conn’s)
- Cushing’s
A 50 year old man presents with abdominal pain, vomiting and temperatures, how can you explain his observations?
Acutely the sympathetic nervous system is addressing the hypotension, it will be the kidney later
What effect does the sympathetic nervous system have on the kidney when it is activated during hypotension?
What are the kidneys doing in times of hypotension?
- Baroreceptors in JGA detect and dilate the AA for self preservation. However the increase in sympathetic activity wants to constrict the AA so it is a fight. Myogenic autoreg
- Prostaglandin release to help with vasodilation
- Renin release for RAAS
What causes the kidneys to release renin?
Where is renin released from in the kidneys?
- Juxtaglomerular Apparatus from the granular cells
- Made up of MD, granular and extraglomerular mesangial cells
Summarise the hormones involved in the RAAS system?
AngII then goes on to activate aldosterone (adrenal glands) and ADH (pituitary gland) secretion
What effects does angiotensin II have on the body to raise the blood pressure?
How does aldosterone increase blood pressure?
- Increase Na and water reabsorption
- Retains water so increase blood volume and therefore increased b.p
How does ADH increase blood pressure?
Increased water reabsorption so increased ECF and B.P
Why might somebody present with this after sepsis?
- The drop in blood pressure activated the RAAS system. The negative feedback from angiotensin II on renin release can be slow so excess Na and water retained
- Can also be due to the IV fluids that we give them
How do the kidneys respond to prolonged hypertension?
- Kidney resets its normal so pressure-natriuresis curve shifts to the right
- Need higher pressure to excrete the same amount of sodium
How does hypertension lead to a cycle of micro and macro vascular changes?
What is occuring here and how can this be treated?
- Renal artery stenosis
- Reduced renal blood flow so activates RAAS and wants to raise b.p
- Can explain why a young person has hypertension
Outside of the kidney what effect does ADH have on the body?
Vasoconstriction
Why does water leaving the descending limb of the LOH not dilute the concentration of the interstitial fluid and destroy the concentration gradient?
The vasa recta absorbs the water coming out of out the tubule
What is the diagnosis here?
- Neurogenic diabetes insipidus due to hypothalamus damage
- Increased Na conc in serum as less ADH so less water balance off and less water reabsorbed
What is the most likely underlying cause of this woman’s blood results?
- Low Na so increased ADH
- SIADH due to hypothyroidism
How would you test for neurogenic diabetes insipidus?
Desmopressin following water deprivation
