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This filtrate then flows along the length of the nephron, which is a tubular structure lined by a single layer of specialized cells and surrounded by capillaries. The major functions of these lining cells are the reabsorption of water and small molecules from the filtrate into the blood, and the secretion of wastes from the blood into the urine.
Creatinine is removed from the blood chiefly by the kidneys, primarily by glomerular filtration, but also by proximal tubular secretion. Little or no tubular reabsorption of creatinine occurs. If filtration in the kidney is deficient, blood creatinine concentrations rise.
Reabsorption is a two-step process beginning with the active or passive extraction of substances from the tubule fluid into the renal interstitium (the connective tissue that surrounds the nephrons), and then the transport of these substances from the interstitium into the bloodstream.
Examples of substances reabsorbed are solute-free water, sodium, bicarbonate, glucose, and amino acids. Examples of substances secreted are hydrogen, ammonium, potassium and uric acid. The nephron is the structural and functional unit of the kidney. Each adult human kidney contains around 1 million nephrons, while a mouse kidney contains only ...
Renal corpuscle showing glomerulus and glomerular capillaries Figure 2: (a) Diagram of the juxtaglomerular apparatus: it has specialized cells working as a unit which monitor the sodiujuxtaglomerular apparatus: it has three types of specm content of the fluid in the distal convoluted tubule (not labelled - it is the tubule on the left) and adjust the glomerular filtration rate and the rate of ...
One of these is cystatin C, a ubiquitous protein secreted by most cells in the body (it is an inhibitor of cysteine protease). [14] Cystatin C is freely filtered at the glomerulus. After filtration, Cystatin C is reabsorbed and catabolized by the tubular epithelial cells, with only small amounts excreted in the urine.
The juxtaglomerular apparatus consists of three types of cells: the macula densa, in the distal straight tubule (thick ascending limb of the loop of Henle), after which the distal convoluted tubule begins [2] [3] juxtaglomerular cells, (also known as granular cells) which secrete renin; extraglomerular mesangial cells
This process is called ultrafiltration; the resulting fluid, virtually free of large proteins and blood cells, is referred to as glomerular filtrate, or ultrafiltrate. [1] Further modification of ultrafiltrate, by reabsorption and secretion, transforms it into urine. Glomerular pressure is about 75 millimeters of mercury (10 kPa). It is opposed ...