Sect 4 PPI - Renal Function

Kidneys

Reddish brown, bean shaped, 4-5in long

- 0.5% of adult body weight

- 25% of blood is being filtered

- 1,200ml/min

25%

What percent of blood is being filtered by the kidney?

1200ml/min

How much blood is being filtered by the kidney per min?

Both located slightly above the waistline in the posterior wall of the abdominal cavity, in a retroperitoneal position

Location of kidneys

true

T or F:

You only need 1 functioning kidney to perform all filtration

Renal Cortex, Renal Medulla, Renal Pelvis

3 parts of the kidney

Formation and Flow of urine

1. Bloodstream (Aorta/Renal artery/Renal afferent arterioles)

2. Glomerulus

3. Glomerular capsule

4. Renal tubules

5. Collecting ducts

6. Renal pelvis

7. Ureter

8. Urinary bladder

9. Urethera

10. Urinary meatus: urine is expelled

Renal Pyramids

Cone shaped structure containing straight parallel segments of nephrons

- 27 per kidney

Nephron

Functional unit of the kidney

- filters blood & produces urine

Renal Corpuscle

Consists of glomerulus and glomerular capsule

Glomerulus

Tangled blood capillaries (tuft)

Substances are pushed through multiple small pores in the capillaries into the glomerular capsule (Bowman's capsule) by hydrostatic pressure based on size and charge

Glomerular capsule

Thin-walled structure that surrounds the glomerulus and collects the substances filtered through the glomerulus

Renal Tubules

Composed of proximal convoluted tubules, the nephron loop (Loop of Henle), and distal convoluted tubules

located in medulla of kidneys

Collecting tubules and ducts

What other 2 structures are located in the medulla of the kidneys

Renal Calyces

System of drainage sinuses the connect the inner part of the kidney to the ureter (Major & Minor)

Minor → Major → Renal Pelvis → Ureters

Ureters

Slender muscular tubes apprx 10-12in long

Carries urine formed in the kidney to the urinary bladder

Urinary bladder

A hollow muscular organ that holds the urine until it is expelled

Uretha

The tube that carries urine outside the body

8-10in

How long is a male urethra?

1.5in

How long is a female urethra?

Urinary meatus

An external opening from which urine is expelled

Filtration, Reabsorption, Secretion

What are the 3 steps of urine formation?

Filtration

1st step of urine formation:

- fluids and dissolved substances are forced through the glomerulus by hydrostatic pressure into the glomerular capsule

- creates "glomerular filtrate"

RBCs and proteins

2 substances are too large to be filtered and remain in the blood

water, Na+, K+, glucose, urea

Most common constituents of GF

100-125ml/min

What is the normal Glomerular Filtrate Rate (GFR)?

Reabsorption

2nd step in urine formation:

- substances that body needs are reabsorbed by renal tubule system (some cross back into blood)

- ex: Glucose, Water, Electrolytes

- any other excess or unwanted substances remain to form urine

Renal Threshold

blood levels of a substance that are too high to allow any more to be reabsorbed

- if it exceeds, spills over into urine

175 mg/dL

What is the renal threshold of glucose?

Secretion

3rd step in urine formation

- substances are transferred from the blood (peritubular capillaries) back into renal tubules for excretion as urine

- fine-tuning before excretion

water

solvent that makes up 95% of substances in urine

95%

Water makes up ________% of the substances in urine

800-2000 ml/day

What is considered the normal range of daily output of urine?

Oliguria

too little urine production (

Diuresis

too much urine production due to a kidney disease (>3000 ml/day)

Anuria

absence of urination

Dysuria

difficult or painful urination

Nocturia

increased urination at night

Polyuria

too much urine production NOT due to a kidney disease (>3000 ml/day)

- due to: excess drinking, diabetes (due to increase water ingestion)

Azotemia

retention of nitrogen retaining products in the blood

- normally are filtered out if filtration working

- due to: medical condition OR high protein diet OR kidney problems

- not as severe

Uremia

urine in the blood

- all waste & toxins that should be expelled through urine is not being retained in blood

- very severe = end of stage renal failure

- see in pts on dialysis or kidney transplant

1. Glomerular Filtration

2. Renal blood flow and urine output

3. Tubular function

Assessment of renal function can be divided into 3 categories:

Assessment of Glomerular Filtration

Essential because this function best correlates with the ability of the kidneys to maintain the composition of body fluids (homeostasis)

Renal blood flow and urine output

- Kidneys receive 25% of cardiac output = 1200ml/min

- Blood flow must be sufficient for kidneys to maintain adequate homeostasis

- Daily output apprx. 800-2000ml/day (N: 1200-1500ml/day)

Tubular function

Measuring the concentration of the renal handling of substances normally secreted by the tubules can pinpoint any abnormalities in this system

Glomerular Filtration Rate (GFR)

the rate at which a substance is filtered from the blood of glomerular capillary into the urine filtrate of Bowman's space

overall renal disease

GF is a measurement of:

diminishing renal function & increasing severity of disease

Progressively decreasing GFR is an indicator of:

1 ml/min/year

As we age, GFR decreases by:

Clearance

a measurement of the excretion or removal of a chemical from the body

defined as the volume of plasma at which a measured amount of substance can be completely eliminated into the urine per unit of time

plasma concentration and its excretory rate

The clearance of a substance depends on (2):

GFR and renal plasma flow

The clearance of a substance depends on the plasma concentration and its excretory rate, which depends on (2):

filtered completely through the glomerulus and not reabsorbed through the nephron tubule

The best substance to use as a reference for glomerular clearance would be a chemical that is:

1. Constant production

2. Very tiny amounts reabsorbed

3. ~100% filtered out

3 criteria used for determining which analytes should be used for renal clearance testing

Clearance tests

the best lab tests currently available to detect mild to moderate glomerular damage

Creatinine

Common substance used for clearance tests used in the lab?