L17 - Renal I - structure and function

What is the function of the urinary system?

To maintain homeostasis within the internal environment of the body

Name 7 aims of the urinary system

1. 1. Excretion (removing of organic metabolic waste

2. 2. Water balance

3. 3. Electrolyte balance (OH-, H+, Cl-, Na2+)

4. 4. Conservation of valuable nutrients (glucose)

5. 5. Control of blood cell formation (erythropoietin)

6. 6. Regulation of blood pressure (renin)

7. 7. 1ml/min urine production

What is the primary function of the kidney?

Regulation of extracellular fluid (plasma and interstitial fluid)

While filtering plasma to make urine, kidneys also regulate what?

Volume of blood, conc. of waste products, conc. of electrolytes and pH of plasma

Glucose → by products

Via cellular respiration → CO2 and H2O

Lipids (CH3(CH2)nCOOH) → by products

Via cellular respiration → CO2, H2O, and energy

Proteins → by products

By-products are nitrogenous waste products: urea, creatinine (N cannot be exhaled, must come out in urine)

BUN normal levels

15 ml/dL urea in blood

Normal creatinine levels in blood

1ml/dL

What is the name for increased level of urea and creatinine in blood caused by renal failure?

Uremia

What is BUN used for?

To measure urea in blood samples to assess renal function/failure

How much does a typical kidney weigh?

100g

What is the renal cortex?

Outer regions of the kidney, granular, reddish-brown

What is the renal medulla?

Inner regions of kidney, composed of renal pyramids with striped appearance, 5-10 per kidney

What are renal columns?

Separations of the renal pyramids

What are the major and minor calyces?

A pyramid surrounding cortical tissue that collect urine from renal lobes

What is the renal pelvis?

Where the urine drains within the kindey

Features of the ureters

Carry urine out of kidneys to bladder, connect bladder at an angle to prevent backflow, capable of peristalsis

What happens to the ureters when the bladder gets fuller and fuller?

Bladder filling compresses the distal end of the ureter, further preventing backflow

Normal urine production rate

1 ml/min

What is oliguria?

< 1ml/min urine

What do diuretics do?

Increase urine production rate, BP medication

What solidifies to form kidney stones?

“Casts”; Ca2+, minerals, acid salts)

What can cause kidney stones?

Oliguria

Where do kidney stones form?

In minor and major calyces of kidney, can move into ureter

What is hydronephrosis?

Kidney stone in ureter (unilateral) or urethra (bilateral) blocking urine drainage

Normal Renal Blood Flow (RBF)

1L/min, cardiac output = 5L/min → kidneys receive 50% of cardiac output

Where does the renal artery enter in the kidney?

Hilum

Renal vasculature

Renal artery at hilum → segmental arteries → interlobar arteries → arcuate arteries → cortical radiate arteries → afferent arterioles (1 mil/kidney)

What is a nephron?

Structural and functional unit of urine formation in kidney

Where to afferent arterioles drain into?

Glomerulus (1 mil/kidney), all in the cortex

What is the glomerulus?

Filtration site for blood, composed of ~50 loops of fenestrated capillaries, giving cortex granular look

Where does the filtrate go from the glomerulus?

Tubule system called nephron

What is the nephron composed of (simple)?

Renal corpuscle and renal tubules

What is the Renal Corpuscle?

Site of filtration, located in cortex, glomerulus + Bowman’s capsule

How much fluid passes through the Renal Corpuscle?

180L, but no blood cells

Why does filtration occur in the renal corpuscle?

Fluid and solutes are forced from blood in glomerulus → Bowman’s capsule

What drains blood from glomerulus?

Efferent arterioles

What are the renal tubules?

Site of re-absorption and secretion into blood, give pyramid look to medulla

What makes up the renal tubules?

1. 1. Proximal convoluted tubule

2. 2. Descending tube

3. 3. Loop of Henle

4. 4. Ascending tube

5. 5. Distal convoluted tubule

6. 6. Collecting tubule

7. 7. Collecting duct

PCT structure

entirely within cortex, simple cuboidal epithelium with microvilli

DT structure

Descends into medulla, alternates between thick and thin segments

LH structure

Connects AT and DT

AT structure

Alternates between thick and thin segments

DCT structure

Simple cuboidal epithelium without microvilli

RBC as a compound in blood

Don’t filter out of glomerulus and into ultra filtrate to become urine

Plasma proteins as compound in blood

Don’t filter out of glomerulus and into ultra filtrate to become urine

Blood compounds that do filter out of glomerulus

Water, sodium (134-145 mmol), glucose, urea, creatinine, urobilin (yellow)

Reabsorption of ultra filtrate: Cl-

Passive transport in renal tubules

Reabsorption of ultra filtrate: Na+

Active transport in renal tubules

Reabsorption of ultra filtrate: H2O

Follows salt by osmosis

How much ultra filtrate is left after reabsorption?

1/3, but still isosmotic

What does isosmotic mean?

A solution with the same osmotic pressure as another solution, indicating equal concentrations of solutes.

Glomerular filtration summary

Water and solutes smaller than proteins are forced through capillary walls and pores of GC into the RT

Tubular reabsorption summary

Water, glucose, amino acids and needed ions transported out of filtrate into the tubule cells and then enter capillaries

Tubular secretion summary

H+, K+, creatinine and drugs are removed from the peritubular blood and secreted by the tubule cells into the filtrate

What is damage to glomerulus causing bloody urine called?

glomerular hematuria

What is blood in urine caused by kidney stone/UTI/bladder cancer called?

Non-glomerular haematuria

How can you tell if the blood is from glomerular or non-glomerular hematuria?

Dysmorphic RBC = glomerular, normal RBC = non-glomerular

What can also cause blood in urine?

Anemia (breakdown of RBCs)

What is proteinuria?

Damage to glomerulus causing plasma proteins to come out in urine

What can cause proteinuria?

Hypertension or edema