8 - Renal Physiology IV Flashcards
Which substance is excreted more than is filtered?
a. Sodium
b. Potassium
c. Chloride
d. Glucose
b. Potassium
Filtered = initially filtered into tubule Secreted = actively pumped into tubule Excreted = leaves body in the urine
The only one that is secreted is potassium
Re-absorption of glucose occurs in the:
a. Thin descending limb of the loop of Henle
b. Thick ascending limb of the loop of Henle
c. Distal tubule
d. Proximal tubule
e. Collecting duct
d. Proximal tubule
You want to reabsorb this quickly so you donβt lose it, donβt want to lose energy
Amino acids are also reabsorbed here
Define renal clearance
The renal clearance of a substance is the volume of plasma that is completely cleared of the substance by the kidney per unit of time
How do you measure renal clearance?
Renal clearance is measured in volume (of plasma). Volume of plasma totally cleared of the substance in a certain period of time. It is a theoretical concept since there is no single volume of plasma that is completely cleared of a substance
What is the function of clearance by the kidneys?
Clearance provides a useful way of quantifying the excretory function of the
kidneys. It can be used to quantify the rate at which blood flow through the
kidneys as well as basic function of the kidneys
Give an example of renal clearance
Example: if the plasma passing thought the kidneys contains 1 milligram of a substance in each milliliter of plasma.
If 1 milligram of this substance is also excreted into the urine each minute, then 1 ml/min of the plasma is βclearedβ of the substance
What is the equation for renal clearance?
πΆπ₯Γππ₯=πx ππ₯
πΆπ₯=(π x ππ₯)/ππ₯
πΆπ₯= clearance of substance X ππ₯= plasma concentration of X πΜ= urine flow rate ππ₯= urine concentration of X
What is the best overall index of kidney function?
GLOMERULAR FILTRATION RATE ***
How can you use clearance to estimate GFR (glomerular filtration rate)?
. If a substance is freely filtered and is not re-absorbed or secreted by the renal tubules, then the rate at which the substance is excreted in the urine (πΜΓππ₯) is equal to the filtration rate of the substance by the kidney (πΊπΉπ Γππ₯)
What is the equation for GFR?
πΊπΉπ = (πΜΓππ₯)/ππ₯
What substances fit these criteria?
- Inulin, a polysaccharide molecule. It is not produced by our body and must be administrated intravenously to a patient to
measure GFR - Creatinine, a by-product of muscle metabolism It is cleared from the body almost entirely by glomerular filtration
What is the approximate relationship between GFR and plasma creatinine concentration?
Decreasing GFR by 50
percent will increase
plasma creatinine to twice
normal if creatinine production by the body remains constant
How do you estimate the GFR from serum creatinine?
Using the Cockccroft & Gault Equation
What is the CG equation for males?
πΆπΆπ=((140βπ΄ππ)Γ(π΅πππ¦ ππππβπ‘, ππ))/(72Γπππ, ππβππ)
What is the CG equation for females?
πΆπΆπ=((140βπ΄ππ)Γ(π΅πππ¦ ππππβπ‘, ππ))/(72Γπππ, ππβππ) Γ 0.85
MULTIPLY BY 0.85***
What is another recommended equation you can use for estimating GFR?
Another recommended equations for estimating GFR from serum creatinine include the Modification of Diet in Renal Disease (MDRD) Study equation (can find online at NIH website)
Which one should you use?
You can use either, but it will not change the diagnosisβ¦ Just sate which one you are using when you report it in the patientβs chart
What is acute kidney injury (AKI) or acute renal failure (ARF)?
Same thing
- A syndrome that results in a sudden decrease in kidney function or damage from few hours to few days
- It is one of the most serious and common health problems in the US. It occurs in up to 1 in 5 patients in the hospital and twice as often in a critical care setting
- It is defined as a rapid decline in glomerular filtration rate accompanied by accumulation of waste products in the blood and inability to keep the body balance of fluid and electrolytes
What are the three different groups of etiologies of AKI?
Etiology of AKI has been categorized anatomically into:
- Pre-renal
- Renal (intrinsic, intra-renal)
- Post-renal
Describe pre-renal etiologies of AKI
It results from kidney hypoperfusion
List the specific pre-renal etiologies of AKI
Intravascular volume depletion
- Hemorrhage, diarrhea, vomiting
Cardiac failure
- Myocardial infarction
Peripheral vasodilation (hypotension) - Anaphylactic shock, sepsis
Renal hemodynamic abnormalities
- Thrombosis of renal artery
Describe renal (intrinsic, intra-renal) etiologies of AKI
Renal etiologies are classified based on the site of injury in:
1. Vascular 2. Glomerular 3. Tubular 4. Interstitial
List the specific renal etiologies of AKI
Vessel and glomerular injury
- Vasculitis, glomerulonephritis
Tubular epithelial injury
- Ischemia, toxins (insecticides, poison)
Renal interstitial injury
- Pyelonephritis
Describe post-renal etiologies of AKI
It occurs from urinary tract obstruction
List the specific post-renal etiologies of AKI
Bilateral obstruction of ureters or renal pelvises
- Kidney stones
Uretic obstruction
Bladder/urethral obstruction
So, what is the physiological effect of AKI?
- Water and sodium overload due to decreased filtration rate (edema and hypertension)
- Increase in plasma potassium concentration also due to decreased filtration rate (hyperkalemia)
- Metabolic acidosis due to a decreased amount of urine
- Anuria (in severe AKI)
Describe chronic kidney disease (chronic renal failure)?
Same thing
- It results in progressive and IRREVERSIBLE loss of large number of functioning nephrons
- 26 million American adults have Chronic Kidney Disease
- Clinical symptoms often do not occur until the number of functional nephron fall to at least 70 to 75 % below normal
- It occurs because of disorders of blood vessels, glomeruli, tubules, renal interstitium and lower urinary tract
What are all the different causes of chronic kidney disease (CKD)
Metabolic disorders
- Diabetes mellitus***
- Obesity***
Hypertension***
Immunologic disorders
- Glomerulonephritis
- Lupus erythematosus
Infection
- Pyelonephritis
Congenital Disorders
- Polycystic disease
What is an important factor in the progression of chronic kidney disease?
AGE
What is the disease that chronic kidney disease progresses to?
End-stage renal disease
What are the stages of chronic kidney disease (CKD)?
Stage 1 = kidney damage with normal or increased GFR (>90)
Stage 2 = kidney damage with mild decrease in GFR (60-89)
Stage 3 = moderate decrease in GFR (30-59)
Stage 4 = severe decrease in GFR (15-29)
Stage 5 = kidney failure (
How do you define kidney damage?
Kidney damage is defined as pathologic abnormalities or markers of damage, including abnormalities in blood and urine tests or imaging studies
Describe glomerulonephritis
- Glomerulonephritis can be acute or chronic
- Acute glomerulonephritis can cause Acute Kidney Injury
- Chronic glomerulonephritis can result in Chronic Kidney Disease and nephrotic syndrome
- Patient can develop hematuria, proteinuria, azotemia (elevated blood nitrogen) and renal sodium and water retention
Describe nephrotic syndrome
- Increased glomerular permeability to large proteins such as albumin
- GFR is decreased (many glomeruli may become nonfunctional)
- Sodium and water retention
- Edema and decrease in plasma volume
Describe the relationship between hypertension and kidney disease
- Hypertension can exacerbate injury to the kidney and abnormalities of kidney function can cause hypertension
- Renal lesions that reduce the ability of the kidney to excrete
sodium and water promote hypertension
1 - Increased renal vascular resistance
2 - Decreased glomerular capillary filtration fraction
coefficient
3 - Excessive tubular sodium re-absorption
