Question

Clinical application
Claire Diego is an 11 year old girl living in Los Angeles. She complains of having to urinate more frequently with a large urine volume. She also is very thirsty. She has no previous illnesses, except that 6 weeks ago she developed a sore throat. It persisted for 2.5 weeks until she was seen by her pediatrician. At that time it cleared over the next 2 weeks with antibiotics. She is current on her vaccinations. She has had no travel out of the State of California in her life. The family has no pets or contact with wildlife. Her physical test is unremarkable.
Her blood pressure is 120/77. 
Other lab values:
Blood sugar = 99 
ADH level = normal
Aldosterone level = normal Urinalysis: albumin = 5+
RBC’s = 40-50/HPF Urine culture = negative 
 If I said this was a renal corpuscle problem, what link can you see to the sore throat in her history?

Hint: how could antigen/antibody complexes and complement, then inflammation, from the immune system be involved in the etiology of the abnormality? Look again at filtration pressures in the renal corpuscle. Which one of the pressures would now be abnormal in this patient? _____________. Assign that pressure 14 mmHg. Now draw a picture of the forces effecting filtrate flow through this patient’s renal corpuscle and show why she is she urinating more. Show her NFP.

Answer 1

• The sore throat must have been caused by streptococcus bacteria
• The Streptococcal protease exotoxin B is released and this elicits an immune response.
• The antigen and antibody complexes are formed.
• These complexes then deposit on the glomerular vessels.
• This stimulates the complement system
• This in turn initiates an inflammation.
• This inflammation damages the glomerular capillary membrane and podocytes.
• This leads to leakage of protein and RBC from the glomerular capillaries into the bowman's capsule.
• The end result is a nephritic syndrome.

As there is loss of proteins from the glomerular capillaries, there oncotic pressure inside the glomerular capillaries is reduced and then in the bowman's capsule increases.

The hydrostatic pressure in the glomerular capillaries = mean arterial pressure

Formula for mean arterial pressure = diastolic pressure +1/3( systolic pressure - diastolic pressure)

77 + 1/3 (120 - 77 ) = 77 +14 =91 mmHg

The plasma oncotic pressure inside the glomerular capillaries = 0 as they proteins are leaking into the bowman capsule

The hydrostatic pressure inside the bowman's capsule - 10 mmHg

The plasma oncotic pressure inside the bowman's capsule = 14 mmHg

The net filtration pressure = glomerular hydrostatic pressure + capsular oncotic pressure - capsular hydrostatic pressure + glomerular oncotic pressure

(91 + 14) - ( 10 - 0 )

105 -10 = 95 mmHg

the net filtration pressure = 95 mmHg

Compared to normal ( 24 mmHg) the net filtration pressure has increased as a result there is more filtration taking place in the nephron. Therefore, there is more urine formation.