International A Level Biology / Control of the internal environment
The gross and microscopic structure of the kidney
Edexcel International A Level Biology (YBI11), chapter 22: Control of the internal environment, specification point 7.18. Free lesson.
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The kidney has an outer cortex, an inner medulla and a renal pelvis, with nephrons running through the cortex and medulla. Knowing the structures and their positions helps you interpret kidney micrographs and calculate magnification.
What you find in a kidney section
A kidney cut from top to bottom is a longitudinal section. The outer cortex is where blood is filtered. Inside it, the medulla is arranged in cone-shaped pyramids containing long, straight tubes. Urine collects in the renal pelvis before travelling to the bladder. The ureter carries urine from the renal pelvis to the bladder. It is not the urethra, which carries urine out of the bladder. The renal artery, a branch of the aorta, brings blood containing urea into the kidney. The renal vein carries blood away to the vena cava, with much less urea. Each kidney contains…
How blood and filtrate travel through a nephron
Blood enters the nephron's filtering region through one small blood vessel and leaves through another. Fluid filtered from the blood is called glomerular filtrate. It then travels through the nephron tubules in order, with useful substances returning to the blood in the proximal convoluted tubule. The afferent arteriole carries blood towards the glomerulus. The glomerulus is a knot of capillaries where fluid is filtered out of the blood. Blood leaves through the narrower efferent arteriole, then passes into capillaries around the tubule. The Bowman's capsule surrounds the…
Which nephron parts are in the cortex and medulla
The cortex looks grainy because it contains glomeruli. The medulla looks striped because its tubes run in the same direction through the pyramids. This difference helps you identify where a kidney structure is found. The cortex contains the glomeruli, Bowman's capsules, and both coiled tubules, the PCT and DCT. All filtering happens here. The medulla has no glomeruli or Bowman's capsules. The loops of Henle dip into it. Collecting ducts start in the cortex and continue down through the medulla to the renal pelvis.
How to identify structures in a kidney micrograph
A thin, stained section of kidney cortex shows pink tissue and purple nuclei. A round knot of capillaries inside a clear ring is a glomerulus inside Bowman's capsule. Since the medulla has no glomeruli, this pattern identifies the cortex. A PCT usually has a thick, pink wall and a small, fuzzy lumen, the space inside a tube. A DCT has a paler, thinner wall and a wider, clear lumen.
How to calculate magnification
Magnification compares the size of an image with the actual size of the object. Convert both sizes to the same unit first, so the units cancel in the calculation.