kidney #1

Question 1

What is the major job of the kidney

Answer 1

kidney regulates composition of body fluids and removes metabolic waste (ensure homeostasis)

Question 2

—What is the functional unit of the kidney?

Answer 2

nephron

Question 3

What is the glomerulus?

Answer 3

group of capilaries (does exchange and filtration) surronded by a special type of basement membrane

Question 4

What happens in the glomerulus?

Answer 4

water, small molecules are filtered into bowmans capsule

Question 5

Is the composition of the filtrate the same as that of urine?

Answer 5

no- reabsorption and secreation in specialized tubules

Question 6

—What happens in the specialized tubules?

Answer 6

—Unwanted substances don’t get reabsorbed ⇒ pass out into urine. —Wanted substances reabsorbed back into plasma of surrounding capillaries. —Unwanted substances secreted from plasma directly through epithelial cells into the tubules

Question 7

Thus, 3 processes in urine formation

Answer 7

1. filtration
2. reabsorption- from tubules to blood vessels
3. secretion- from blood vessels to tubules

Question 8

Some Major Kidney Functions

Answer 8

1. Fluid-Electrolyte Balance – e.g. water, K, Na, PO4, Ca 2. Excretion of Metabolic Wastes 3. Excretion of Drugs and Toxins 4. Regulation of Acid-Base Balance 5. Role in Regulation of Blood Pressure (renin-angiotensin system ) 6. Erythropoiesis (via erythropoietin) 7.Vitamin D Activatio

Question 9

1.Fluid-Electrolyte Balance

Answer 9

—Kidney conserves or excretes water, depending on needs e.g. depend on drinking and sweating
—Reabsorption varies. —⇓ total blood volume ⇒ hypothalamus stimulates release of antidiuretic hormone from posterior pituitary gland ⇒ ⇑ water reabsorption (more concentrated urine)

Question 10

Electrolytes

Answer 10

—Kidney regulates electrolyte balance and excretes excess amounts e.g. Na, K
Sodium —Most Na filtered by kidney reabsorbed —Majority of Na reabsorbed is not regulated (basal) - in proximal tubules. —The portion of Na reabsorption that can be regulated - distal convoluted tubules (regulated
step)
—Allows conservation or increased excretion of Na, depending on need: —e.g. ⇓ reabsorption when NA intake is very high (need to get rid of the Na)
—e.g. ⇑ reabsorption with excessive sweating
—Regulation is by aldosterone [adrenal cortex] which ⇑ Na reabsorption.
Potassium —Approximately all K filtered is reabsorbed (in proximal tubule). —Any K in the urine is secreted in the distal tubules in exchange for Na (+ other specialized transport).
Calcium and Phosphate …….We will review when we get to kidney disease.

Question 11

aldosterone regulates what

Answer 11

Na

—Regulation is by aldosterone [adrenal cortex] which ⇑ Na reabsorption.

Question 12

2.Excretion of Metabolic Wastes

Answer 12

examples: urea, creatinitne, uric acid
how can diet increase urea production? where does urea com from?
- high protein intake-ammonia group on amino acid needs to get excreated; converted to urea in teh liver (urea cycle)
- not enough non-protein energy sources (low CHO, low fat)
- very poor protein quality (imcomplete protein that lack all teh amino acids)
first priority for protein is energy - need good protein to energy ratio

Question 13

Screening and Diagnostic Tests for kidney disease

Answer 13

1.Blood pressure 2.Urinalysis —Urine examined for presence of materials that should not be present —e.g. erythrocytes, leucocytes & large proteins (e.g. albumin)
a) Random urine protein or albumin —ACR - Urine albumin to creatinine ratio or
3
—PCR - Urine protein to creatinine ratio
b) Urine Osmolality —Ability of kidney to concentrate or dilute urine —e.g. water reabsorption capacity
3. Serum [urea] —Normally, ammonia ⇒ urea (liver) ⇒ urine —If kidney unable to excrete urea, then serum urea ⇑
4. Serum [Electrolytes] —e.g. Na, K —Another measure of kidney’s filtering & reabsorbing capacity
5.Radiological procedures
6. Assessment of Glomerular Filtration Rate (GFR)(decreases with chronic kidney disease •the volume of fluid filtered from the renal glomerular capillaries into Bowman’s space per unit time. •Currently done by serum creatinine and calculation of the eGFR (NOT serum creatinine alone)

Question 14

2.Urinalysis
what is it
ACR and PCR

Answer 14

—Urine examined for presence of materials that should not be present —e.g. erythrocytes, leucocytes & large proteins (e.g. albumin)
a) Random urine protein or albumin —ACR - Urine albumin to creatinine ratio or

—PCR - Urine protein to creatinine ratio increases with chronic kidney disease

Question 15

b) Urine Osmolality

Answer 15

—Ability of kidney to concentrate or dilute urine —e.g. water reabsorption capacity

Question 16

3. Serum [urea] —sometimes BUN blood urea nitrogen- makes up most of the nitrogen

Answer 16

Normally, ammonia ⇒ urea (liver) ⇒ urine —If kidney unable to excrete urea, then serum urea ⇑ concentration in blood

Question 17

. Serum [Electrolytes]

Answer 17

—e.g. Na, K —PO4 often tend to rise with chronic kidney disease

Another measure of kidney’s filtering & reabsorbing capacity

Question 18

—What is creatinine?

Answer 18

breakdown product of phosphocreatine (high energy reserve) in muscle

Question 19

—What factors determine how much Creatinine is in serum? Where does creatinine come from

Answer 19

muscle mass- fairly constatn if well
- certain amount in serum but can kidney get rid of excess?
produced in amounts proportioned to muscle mass
concentration in blood depends on GFR
concentration in serum increases if kidney unable to excrete nitrogenous waste products

Question 20

Methods to assess GFR

Answer 20

—Serum creatinine -gives us an idea but shouldnt be used on its own—Timed urine collections – 24 hr —Creatinine clearance —Inulin clearance —*Calculated GFR calculations (eGFR) —based on serum creatinine —many formulas including Cockcroft Gault and MDRD —Nuclear medicine methods
The ideal marker would be: —Endogenous —Freely filtered —Not secreted or reabsorbed —Inexpensive to measure —No marker meets all criteri

Question 21

Making the Estimate of Glomerular Filtration Rate (eGFR)
1) Canadian Society for Nephrology recommends estimating glomerular function rate (eGFR) using equations.
—Normal eGFR:

Answer 21

— varies according to age, sex, and body size —In young adults - approximately 120-130 mL/min/1.73 m2 and declines with
age.

Equations (commonly used) 1) Cockcroft-Gault equation:
CrCl (ml/min)= (140-age) x actual weight (kg) x 1.2 (if male) /
SCreat (µmol/L)

2) MDRD (Modification of Diet in Renal Disease) 6 variable or abbreviated version GFR (ml/min/1.73m2)=170 (PCr)-0.999 x (Age)-0.176 x (0.762 if female) x (1.21 if African American) x (serum urea)-0.170 x (Albumin)+0.318
2) If eGFR not available, tables based on serum creatinine and other variables are available to provide approximations of eGFR. See attached

Question 22

Renal/Kidney Failure Acute Failure:

Answer 22

—Days - several weeks/months —Can resolve without ↓ function —Can progress to chronic —Common causes: —Severe dehydration —Toxicity (drugs, contrast agents) —Obstruction —Infection —↓ blood flow to the kidneys

Question 23

Chronic Kidney Disease (CKD):

Answer 23

—Progressive decline in kidney function —Occurs over mo/years —Irreversible, but may be able to slow progression with treatment
5
—Dialysis and kidney transplants extend life in kidney failure.

Question 24

—CKD –Etiology:

Answer 24

—Diabetes mellitus —Uncontrolled hypertension —Glomerulonephritis —Vascular disease, polycystic kidney disease, lupus erythematosus

Question 25

CKD: Pathophysiology

Answer 25

—Progressive loss in function: —gradual ⇓ in # of functioning nephrons —Cause may initially adversely affect either glomeruli or tubules - eventually effects
the whole nephron
—Fewer remaining functional nephrons ↑ in size and function (compensatory) —eGFR gradually ⇓ —Often onset not obvious until a large % of renal function lost

Question 26

Stages of CKD (Canadian Society of Nephrology)

Answer 26

—Stage 1 - > 90 ml/min
—Stage 2 – 60 – 89 ml/min
Stage 3 - 30 – 59ml/min malnutrition potential begins —
Stage 4 - 15 – 29 ml/min —Stage 5 - < 15 ml/min —Stage 5 = end-stage renal disease →kidney transplantation or dialysis is required for life. dont always wait until stage 5 to start dialysis, can start before
normal GFR is 130-150ml/min

Question 27

CKD: Signs and Symptom

Answer 27

—Early on, may be polyuria or nocturia (depends on cause), but progresses to oliguria/anuria/dysuria —Foamy urine/tea coloured —fatigue —itching —anemia —swelling of hands and feet —shortness of breath —bad taste in mouth (can be imporatnt in nutrition)—cold intolerance —nausea, vomiting, anorexia (uremia = buildup of urea / other byproducts of protein metabolism)
—Untreated uremia ⇒ CNS (abnormal behavior, coma)

Question 28

Renal osteodystrophy: (bone pain, fractures)

Answer 28

Contributors are- 1) acidosis 2) excess PTH 3) altered vit D metabolism

Question 29

Treatment for Chronic Kidney Disease Modifiable Risk Factors for Chronic Kidney Disease Progression

Answer 29

—Control blood pressure —Detect microalbuminuria, and treat with drug therapy to slow progression —Control HbA1c —Cease smoking, reduce dyslipidemia
Treatments we will discuss: —Nutritional care —Also relate to medications and supplements —Dialysis —(Renal Transplants)

Question 30

Dialysis

Answer 30

—2 types: —Hemodialysis —Peritoneal dialysis

Question 31

Hemodialysis

Answer 31

—an “artificial kidney machine” or dialyzer removes unwanted substances from the blood stream. —the blood from an artery in an arm or leg circulates through the machine (and membrane) and is then returned to the parallel vein. i.e. permanent access to bloodstream is needed.
—Figure 18.5, 18.6
Different forms of vascular access.
—The semi-permeable membrane is permeable to water and compounds of low MW, such as potassium, sulfate, urea, creatinine, uric acid. —Substances of higher MW cross the membrane more slowly. —The membrane is impermeable to blood cells and most plasma proteins.
—The rates & amounts of fluid and waste products removed can be varied by using different: a) membranes b) blood flow rates c) dialysate concentration
—Commercial solutions, and their composition can be modified as needed. —Many substances will need to diffuse along a concentration gradient. —For example, the dialysate will have lower K than serum. —Glucose is often included in the dialysate to prevent hypoglycemia. —Excess fluid is removed (by ultrafiltration). —A hydrostatic pressure gradient across the membrane is increased with pumps to get rid of excess fluid.
-Goal of hemodialysis : clear waste products and fluid down to nearly normal levels by the end of treatment → these will gradually return to ↑ levels between treatments. —Usually done at hospital centers —Some at home. —Usually dialysis 2-3x/week for ~ 3-6 hours each time.

Question 32

The rates & amounts of fluid and waste products removed can be varied by using different:

Answer 32

a) membranes b) blood flow rates c) dialysate concentration

Question 33

Peritoneal Dialysis

Answer 33

—Uses the peritoneum as the selective, semipermeable membrane for dialyzing. —What is the peritoneum?
—Dialysate enters the peritoneal space through a catheter penetrating the abdominal wall → clamped so that the fluid remains in the peritoneum → drain it after a given amount of time. —Fig 18.7
—Relies on exchange with plasma circulating in the capillaries that are perfusing the peritoneal wall. —Principles similar to hemodialysis except that the dialysate contains enough glucose to make it hypertonic relative to plasma. —→ causing fluid to flow into the peritoneal cavity ( a way to rid excess fluid). —Efficiency of dialysis determined by: a) concentrations in the dialysate b) dwell time
Two major types: 1) Continuous Ambulatory Peritoneal Dialysis (CAPD) —Uses repeated infusions of dialysate into the peritoneal space. —The dialysate stays in the peritoneal space for 4-6 hours at a time (waste products diffuse into the dialysate). —Then drained by gravity, and the procedure is repeated (continuously). —A long dwell time overnight.
2) Continuous Cycling Peritoneal Dialysis (CCPD) —a machine does repeated timed cycles of infusion, dwell, and drain at night (automatically). —Dialysate left in the peritoneal cavity during the day.

Question 34

Efficiency of dialysis determined by:

Answer 34

a) concentrations in the dialysate b) dwell time

Question 35

Two major types: o fperitoneal

Answer 35

1) Continuous Ambulatory Peritoneal Dialysis (CAPD) —Uses repeated infusions of dialysate into the peritoneal space. —The dialysate stays in the peritoneal space for 4-6 hours at a time (waste products diffuse into the dialysate). —Then drained by gravity, and the procedure is repeated (continuously). —A long dwell time overnight.
2) Continuous Cycling Peritoneal Dialysis (CCPD) —a machine does repeated timed cycles of infusion, dwell, and drain at night (automatically). —Dialysate left in the peritoneal cavity during the day.