Introduction to Renal Medicine Flashcards
What other specialties are affected by renal medicine?
- endocrinology - diabetic nephropathy
- hepatology - hepatorenal failure
- cardiology - cardiorenal syndrome
- haematology - myeloma
What is cardiorenal syndrome?
Decreases blood supply to the kidneys
How does myeloma affect the kidney?
Protein is deposited in the kidney
What is a nephron?
How many are in each kidney?
A nephron is a filtering unit
There are around 1 million in each kidney, but the exact number is not known as nephrons are present from birth
What happens to urine produced in the kidneys?
It passes through the ureter into the bladder
What supplies the glomerulus?
Afferent arterioles coming from the renal artery
What happens to blood supply after it has entered venules?
The venules drain into the renal vein to be returned to the heart
How long would it be if nephrons from each kidney were placed end to end?
16 kilometers
What are the 2 broad functions of the kidney?
- homeostasis
2. hormone secretion (endocrine)
What is meant by homeostasis?
Maintenance of “milieu interieur”
This is a constant internal environment in the body
What types of hormones are secreted by the kidneys?
Erythropoietin
What is the role of erythropoietin?
It is secreted by the kidneys to stimulate red blood cell production
When may a patient inject erythropoietin?
To increase their red blood cell count if they are anaemic
How are the kidneys important in fluid and electrolyte balance?
- volume status
- electrolyte levels
- osmolarity
What is meant by volume status?
Kidneys regulate the fluid balance in the body through urine production
What electrolyte levels are the kidneys important in controlling?
- sodium
- potassium
- urea
- creatinine
What can very high potassium levels lead to?
What is this condition called?
It is a medical emergency which can lead to the heart stopping
It is called hyperkalaemia
What is meant by osmolarity?
The concentration of particles exerting an osmotic pressure
e.g. glucose
What is significant about the kidneys controlling osmolarity?
The blood usually runs at a certain osmolarity
That allows cells to function well
Confusion, seizures and coma result if osmolarity is not controlled well
How are the kidneys involved in maintaining acid-base balance?
They maintain an optimum pH for cellular function
The kidneys regenerate bicarbonate and bring it back into the blood stream
They remove acid
What can result from poor kidney function, affecting the pH?
Acidemia/acidosis
This is because not as much bicarbonate is being regenerated
How are the kidneys involved in removal of small molecules?
They remove sugars and amino acids
What may glucose in the urine indicate?
Disease of the kidneys
- diabetes mellitus
(caused by a high sugar concentration which the kidneys cannot deal with)
- tubular disorders
(caused by normal blood sugar level, but dysfunctional kidney)
When does loss of amino acids in the urine occur?
In disease of the proximal tubule
How is the kidney involved in excretion of waste products and drugs?
It is involved in the removal of nitrogenous waste from protein metabolism
- urea
- creatinine from muscle
What is used to measure kidney function?
What is the drawback of this method?
The level of creatinine in the blood
It is not a good way to measure kidney disease as creatinine is not produced by the kidney
What determines how much creatinine someone generates?
It depends on an individual’s muscle mass
What may happen to creatinine when the kidneys aren’t functioning?
It accumulates in the blood as it is not being removed
However, the “normal” creatinine concentration depends on someone’s muscle mass
What types of drugs are removed by the kidneys?
- antibiotics
- digoxin
- opiates
- lithium
What happens when a drug is administered to someone with poorly functioning kidneys?
The drug begins to accumulate in the blood
This may lead to an overdose in the patient
How are the kidneys involved in red blood cell production?
They produce erythropoietin, which stimulates red blood cell production
What stimulates red blood cell production?
Hypoxia (low oxygen levels)
This may be at an increased altitude
Why may recombinant erythropoietin be used?
It decreases the need for blood transfusions as it stimulates RBC production
How are the kidneys involved in calcium and phosphate balance?
- secrete the active form of vitamin D3
2. this increases the absorption of calcium from the gut
What is the activated form of vitamin D?
Where it is produced?
1,25 dihydroxycholecalciferol
The first stage occurs in the liver and the second stage occurs in the kidneys
What happens to calcium absorption in kidney failure?
You cannot produce 1,25 dihydroxycholecalciferol
This means calcium is not absorbed from the gut
Calcium levels fall
What can low calcium levels lead to?
- seizures
2. secondary hyperparathyroidism
What is the action of the parathyroid glands when calcium levels are low?
They cause calcium release from the bones
This leads to bone disease
brittle bone disease
If secondary hyperparathyroidism isn’t treated, what can happen?
The parathyroid hormones become autonomous and no longer respond to drugs that try and correct things
This is tertiary hyperparathyroidism
What can tertiary hyperparathyroidism lead to?
Fibrosis in the bone marrow
This means red blood cells aren’t produced
Patients become anaemic and DO NOT respond to Epo
What are the 3 stages involved in chronic kidney disease?
- decreased activation of vitamin D
- decreased calcium level
- this stimulates secretion of parathyroid hormone
What happens once parathyroid hormone begins to be secreted?
- calcium is released from bones
2. this leads to bone disease and renal osteodystrophy
How are the kidneys involved in blood pressure control?
They secrete renin
This converts angiotensinogen to angiotensin I
What is blood pressure like in patients with kidney disease?
They often have high blood pressure
It is a cycle - as high blood pressure causes kidney disease
What blood tests are used to assess kidney function?
Urea and electrolytes
- sodium
- potassium
- urea
- creatinine
Also bicarbonate and chloride levels
What are normal Na+ levels?
133 - 146 mmol/L
What are normal K+ levels?
3.5 - 5.3 mmol/L
What are normal urea levels?
2.5 - 7.5 mmol/L
What are normal creatinine levels?
Male: 64 - 104 micromol/L
Female: 60 - 93 micromol/L
What are normal bicarbonate levels?
22 - 29 mmol/L
What are normal Cl- levels?
95 - 108 mmol/L
What aspects are looked at when performing a urinalysis test for kidney function?
- pH
- haematuria (blood)
- proteinuria (protein)
- glucose (diabetes)
- nitrites (infection)
- leucocytes (infection)
What do nitrites and leucocytes in the urine indicate?
Urinary tract infection
Must take urine cultures to identify the organism before prescribing antibiotics
What urine tests (other than urinalysis) are performed when looking at kidney function?
- protein/creatinine ratio
- albumin/creatinine ratio
- midstream urine
What is a normal protein/creatinine ratio?
Normal < 13.0
What is a normal albumin/creatinine ratio?
Normal < 3.0
What is midstream urine and when is it used?
It is a clean catch of urine
It is sent off if a urinary tract infection is suspected
What radiological investigations may be performed?
What are you looking for?
Ultrasound is performed
You want to look at the size of the kidneys and whether there is an obstruction
What will the ultrasound look like for a patient with chronic kidney disease?
The kidneys will be small and shrunken due to fibrosis
Normal kidneys are around 10-12 cm
What is a MRA?
Magnetic resonance angiography
Why is a kidney biopsy performed?
How is it performed?
It is required to diagnose some rarer forms of kidney disease
It is performed with ultrasound guidance
What are the complications associated with kidney biopsy?
It is not performed in every patient due to the risks:
Risk of bleeding - 1 in 100
Risk of losing a kidney - 1 in 1000
