Align-ju STUDENT
Branch of renal vein
Branch of renal artery
Afferent arteriole
Efferent arteriole
Glomerulus
Distal convoluted tubule
Pressure filtration
Glomerular capsule
Proximal convoluted tubule Flow of filtration
CORTEX MEDULLA
Collecting duct
Blood flow
Descending limb
Urine passes to tip of kidney pyramid
Ascending limb
Blood capillary network
Figure 5 . The flow of blood and urine through a nephron , the filtration part of the kidney . Adapted from Dallas [ 4 ] .
Each kidney consists of a protective capsule , an outer cortex layer that contains Bowman ' s capsules ( also called glomerular capsules ) and convoluted tubules where the blood filtration begins . The medulla contains collecting ducts and loops of Henle , where urine is concentrated . The urine collects in the renal pelvis before draining into the ureters .
The filtration function of the kidney is carried out in the nephrons . A kidney contains thousands of nephrons made up of several parts , with each part playing a different role in the filtration process ( Figure 5 [ 4 ] ).
Blood is pushed under high pressure through a fine filter within the glomerular capsule of the nephron ( a capillary bed ), where water and small molecules such as electrolytes , known as ultrafiltrate , are collected by the Bowman ' s capsule . Larger molecules , such as plasma proteins , remain in the bloodstream as they cannot pass through the fine filters .
The ultrafiltrate passes through the nephron into the proximal convoluted tubule , where sodium and around 75 % of the water are reabsorbed into the bloodstream . The amount of water reabsorbed is controlled by the antidiuretic hormone ( ADH ) produced by the pituitary gland . All glucose and amino acids are also reabsorbed . Some molecules and toxins , such as histamine and drugs , are secreted into the filtrate at this point .
The proximal convoluted tubule also plays a part in the other roles of the kidney , as it is here that most bicarbonate is reabsorbed in exchange for hydrogen ions as part of the acid – base balance , and vitamin D is converted to the active form .
The filtrate then passes into the descending limb of the loop of Henle , which is permeable to water , then to the ascending limb , which actively takes up sodium . By the time the filtrate reaches the distal convoluted tubule , it is about 20 % of its original volume . The distal convoluted
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