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Biology 2nd Baccalaureate

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6.2.1. Kidneys

The kidneys

The kidneys are two bean-shaped excretory organs, about the size of a closed fist, located at the back of the abdomen, one on each side of the spine.

The right kidney is located below the liver and the left below the diaphragm, next to the spleen. The asymmetry of the abdominal cavity produced by the liver makes the right kidney slightly lower than the left.

Above each kidney is an adrenal gland, with endocrine functions.

In the kidney three parts can be distinguished:

  • The cortex, the outermost part, and contains the glomeruli .
  • The medulla, the innermost part. It has six triangular areas, the renal pyramids , with their vertices directed towards the renal pelvis .
  • The renal pelvis, a cavity that collects urine formed in the cortex and medulla.

The blood reaches the kidney with lots of debris through the artery renal (a branch of the aorta), filtered, and leaves no debris through the renal veinwhich result in the vena cava.

Anatomía del riñón

By Jose Luis Zafra Díaz (Provienes de Jose Luis Zafra Díaz) [GFDL or CC BY-SA 4.0-3.0-2.5-2.0-1.0], via Wikimedia Commons

The functional units of the kidney are the nephrons, and there are approximately one million nephrons in each kidney. The main parts of a nephron are:

  • Glomerulus of Malpighi or Malpigio: a packed network of capillaries from the renal artery, where the blood plasma is filtered.
  • Bowman's capsule: end of the nephron, shaped like a double-walled cup that surrounds the glomerulus and collects the substances that have been filtered.
  • Proximal convoluted tubule: very tortuous tube located at the exit of Bowman's capsule. Its wall has many villi that increase the surface of the exchange of substances. It ends in a straight area that constitutes the first part of the loop of Henle.
  • The loop of Henle has two branches: the descending branch and the ascending branch, so it is U-shaped.
  • The distal convoluted tubule begins at the loop of Henle and empties into the collecting tubule.
  • The collecting tubule: each collecting tube is common to several nephrons and runs from the cortex to the medulla, always parallel to the loops of Henle. They join with other collecting tubules in the renal pelvis, which empties into the ureters.

Partes de una nefrona


Answer in your notebook

6.4.- Draw a nephron indicating the name of its parts.


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Biology and Geology teaching materials for Compulsory Secondary Education (ESO) and Baccalaureate students.