Question

Think about the formation of urine. Imagine that you are describing the journey of a drop of blood, from the hepatic artery, to the production of glomerular filtrate, to the excretion of urine. What are the structures that the blood/GFR/urine will pass through, and what processes is the product exposed to? In other words - how is urine produced from the vantage point of a single drop of blood in the hepatic artery? Once you have described the normal process for this, pick one of the pathologies below and describe how the process of urine formation would be different in an individual with your chosen pathology:

Diabetic kidney disease

Answer 1

PROCESS OF URINE FORMATION

   urine formation in 3 processes

1. Glomerular filtration
2. Tubular Reabsorbtion
3. tubular secretion

• When blood passes through glomerular capillaries , the plasma is filtered into the Bowman capsule.This process is called glomerular filtration.
• Filterate from Bowman capsule passes through the Tubular portion of the nephron.while passing through the tubule,the filtrate undergoes various changes both in quality and quantity.
• Many unwanted substances like glucose ,amino acids,water and electrolytes are reabsorbed from the tubules.This process is called Tubular reabsorption.
• And ,some unwanted substances are secreted into the tubule from peritubular blood vessels. This process is called Tubular secretion or excretion.
• Events of Urine Formation
• 

1 GLOMERULAR FILTRATION

• This is 1st process of urine formation
• It is a process by which the blood is filtered while passing through the glomerular capillaries by filtration membrane.
• Filtration membrane is formed by 3 layers
• Glomerular capillary membrane
• basement membrane
• visceral layer of Bowman's capsule

2 TUBULAR REABSORPTION

• It is a process by which water and other substances are transported from the renal tubules back to the blood.
• when the glomerular filterate flows through the tubular portion of nephron,both qualitative and quantitative changes occur.
• Large quantity of water (more than 99%) ,electrolytes and other substances are reabsorbed by the tubular epithelial cells.
• The reabsorbed substances move into the interstitial fluid of renal medulla.
• And ,from here the substances move into the blood in peritubular capillaries.
• Since the substances are taken back into the blood from the glomerular filtrate,the entire process is called tubular reabsorbtion.
• It is a selective reabsorption ,because the tubular cells reabsorb only the substances necessary for the body.
• Essential substances such as glucose,amino acids and vitamins are completely reabsorbed from renal tubule
• Whereas the unwanted substances like metabolic waste products are not reabsorbed and excreted through the urine

3 TUBULAR SECRETION

• It is the process by which the substances are transported from the blood into renal tubules.
• Also called tubular excretion
• In addition to reabsorption from renal tubules ,some substances are also secreted into lumen from peritubular capillaries through the tubular epithelial cells.

WITH ALL THESE CHANGES,THE FILTRATE BECOMES URINE.

DIABETIC KIDNEY DISEASE

• Structural changes occurs, including thickening of the glomerular basement membrane,fusion of foot processess,loss of podocytes with denuding of the glomerular basement membrane ,and mesangial matrix expansion.
• Renal involvement is an important complication of Diabetes Mellitus.
• Clinical symptoms in Diabetic Nephropathy are  asymptomatic proteinuria ,nephrotic syndrome,progressive renal failure and hypertension.
• Morphologic Features : Diabetic Glomerulosclerosis,Vascular lesions,diabetic pylonephritis and tubular lesions (Armanni -Ebstein lesions)
• Glomerulosclerosis :

• 2 forms Diffuse or nodular
• In diffuse Form thickening of GBM and diffuse increase in mesangial matrix with mild proliferation of mesangial cells can be seen.
• Vascular lesions :
• Atheroma of renal arteries.
• Hyaline arteriosclerosis affecting the afferent and efferent arterioles of the glomeruli
• It is also causes Renal ischaemia
• Diabetic pyelonephritis ; it causes due to bacterial infections
• Tubular lesions ;
• In high blood sugar patients,the epithelial cells of the proximal convoluted tubules develop extensive glycogen deposits appearing as vacuoles
• these are Armanni -Ebstein Lesions

Afferent arteriole Filtsation Efferent arteriole Arterial blood L- peritubular capillary | Reabsort Ption Glomerulus secretion Tubular portionat Venous blood urine

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