LH stimulates leydig cells of the testes to synthesize testosterone. Heart cells contain mitochondria but lack sarcomeres. Blood CO2 is carried primarily dissolved in the plasma. The capillary endothelium represents the primary restrictive barrier to filtration in the glomerulus. The collecting ducts runs from the outer cortical region through to the papillary region of the kidney.
Water is reabsorbed passively in the kidney.
The length of the loop of Henle has no affect on the ability to concentrate urine. The filtrate leaving the distal tubule maybe isosmotic but never hyperosmotic compared to plasma. The macula densa cells of the distal tubule release renin. Tubular cells can increase the production of NH3 in the face of an increased acid load. The respiratory system and the kidney are both important in controlling the acid-base balance of the blood.