Page 5

LSS Urinary System

Alexandra Burke-Smith

The functional unit of urine production is called a nephron (below) – there are millions within the parenchyme of the kidney. Glomerulus supplied by afferent arteriole from arcuate arteries (branched from renal artery from aorta). The afferent arteriole is of much higher pressure than the efferent arteriole, creating a pressure gradient which drives ultrafiltration. The glomerulus is surrounded by the glomerular capsule; also known as BOWMAN’S CAPSULE.

Renal corpuscle  Structure composed of the glomerulus + Bowman’s capsule  The glomerulus consists of capillaries with associated podocytes (visceral epithelial cells); these “wrap” around the capillaries, with long processes/feet that leave slits/gaps between them = fenestrations  Blood supply: from afferent to efferent arteriole, the blood supply enters at the vascular pole of the corpuscle  Filtration barrier: the fenestrae between the processes of the podocytes have a specialised basal lamina which allows the passage of ions and molecules <~50,000m weight to pass from the blood (i.e. first step in producing urine)  The filtrate then drains into the proximal convoluted tubule at the urinary pole of the corpuscle Mechanism of urine production 1) Ultrafiltration  Blood passing through glomerulus is filtered  Filtrate consists of all components of <~50,000 m weight, then drains into proximal convoluted tubule (look at notes above on renal corpuscle for more detail) 2) Selective Reabsorption  Material that needs to be retained in the blood is then reabsorbed in the proximal convoluted tubule (70% reabsorbed)  This includes ions, glucose, amino acids, small proteins, water etc  Methods of uptake: o Na+ uptake by basolateral Na+ pump. Water and anions then follow the Na+ (along osmotic + electrochemical gradient) o Glucose uptake is via Na=/glucose co-transporter o Amino acids by Na+/amino acid co-transporter o Protein uptake by endocytosis 5

Alex's Urinary  

Alex's Urinary