Question

Please help me answer these questions in vivid detail regarding the urinary system:

1) Trace blood flow through the kidney beginning with the renal artery and ending with the renal vein.

2) The nephron is the smallest single functional unit of the kidney. What are the two parts of the nephron? What structures are each of these parts composed of? Why isn't the collecting duct included in the nephron?

3) What is the difference between a cortical nephron and a juxtamedullary nephron? Why do we need juxtamedullary nephrons?

4) Describe the filtration membrane and its function. How is this structure similar to the respiratory membrane? What do you think the "digestive membrane" might be referring to?

Answer 1

1. Blood flow through kidney:

Renal artery => Segmental artery => Lobar artery => Interlobar artery => Arcuate artery => Interlobular artery => Afferent arteriole => Kidney capillaries (Glomerulus) => Efferent arteriole => Peritubular plexus => Interlobular vein => Arcuate vein => Interlobar vein => Lobar vein => Segmental vein => Renal vein.

2. A nephron which is an excretory part consists of two parts.

i) Renal corpuscle or malpighian corpuscle made up of glomerulus with a tuft of capillaries and bowman's capsule.

ii) Renal tubule, which participates in selective reabsorption of substances from glomerular filtrate it is made up of proximal convoluted tubule, ascending and descending limbs of loop of henle, distal convoluted tubule.

Collecting duct forms a a part of collecting apparatus which receives urine filtered by the nephron.

3.

Cortical nephrons	Juxtamedullary nephrons
Located in superficial region of cortex.	Located in the juxtamedullary region of cortex.
85% of nephrons are cortical in location.	15% of nephrons are juxtamedullary in location.
Short loop of henle.	Long loop of henle.
Thin ascending Limb of loop of henle is absent.	Thin ascending Limb of loop of henle is present.
Small glomerulus.	Large glomerulus.
Slow rate of filtration.	Rate of filtration is high.
Peritubular capillaries are formed by efferent arteriole.	Efferent arteriole forms both peritubular capillaries and vasa recta.
Function is urine formation and excretion of waste products.	Function is urine concentration.

Juxtaglomerular nephrons lie close to medulla with a longer glomerulus and loop of henle extending deep into medulla. This nephrons are used for urine concentration by counter current mechanism in between loop of henle and vasa recta.

4.Filtration membrane:

• The filtration barrier of a nephron is composed of capillary endothelial cells, basement membrane and foot process of podocytes.
• This membrane forms a filtration barrier through which blood from glomerular capillaries is filtered to form the tubular fluid and is excreted to outside as urine.
• The structure is similar to respiratory membrane where gaseous exchange takes place and is composed of Type 1 alveolar cells lining alveolar membrane and also called as Type 1 pneumatocytes with their basement membrane, interstitium and the endothelial cells of alveolar capillaries.
• Digestive membrane refers to the mucosal layer of the digestive tract. The digested food from the lumen enters the capillaries in lamina propria of mucosa.

Filtration Bavier of nephron Basement membrane foot process of 'podocyte → podopie F?Hraction Glomerular Capillary End the cell
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