Histología de Sistema Urinario

The urinary system consists of two kidneys, which are solid organs surrounded by a connective tissue capsule. The capsule has two layers: the inner layer made up of myofibroblasts and the outer layer consisting of denser fibroblasts and collagen. The renal parenchyma is divided into the cortex, which contains glomeruli and proximal and distal tubules, and the medulla, which has the loop of Henle and collecting tubules.

The nephron is the functional and structural unit of the kidney, consisting of a glomerulus, which filters urine, and a tubule with various segments. The glomerulus contains an afferent arteriole that leads to a network of capillaries and is drained by an efferent arteriole, surrounded by Bowman's capsule, which has parietal and visceral layers with podocytes that filter blood into the urinary space.

The glomerular filtration barrier selectively allows certain proteins to pass while blocking others based on size and charge. The mesangial cells support the glomerular structure and help regulate filtration, forming part of the juxtaglomerular apparatus. The distal convoluted tubule connects back to the glomerulus and is involved in filtration and regulation of electrolytes and water balance.

In the proximal convoluted tubule, reabsorption occurs, especially of glucose, which gets entirely reabsorbed at normal levels. The loop of Henle plays a crucial role in creating a hyperosmotic renal medulla due to its countercurrent mechanism, allowing for the regulation of water and solutes, preserving water while allowing solutes like sodium and chloride to remain in the interstitial space.

In the collecting duct, water can be reabsorbed or excreted based on the presence of antidiuretic hormone (ADH). Aquaporin channels in the collecting duct cells allow water to move out into the hyperosmotic medulla, concentrating the urine. If ADH is not present, the water remains in the duct, leading to dilute urine.