Women with defective cilia and flagella often have a fertility problem. Fusion of more than one sperm with the egg plasma membrane is blocked by hardening of the zona pellucida, the layer of extracellular matrix that coats the egg cell. The acrosomal reaction of the sperm results in the digestion of the egg cell plasma membrane. The descending limb has a higher water permeability than the ascending limb. The length of the loop of Henle is approximately the same for all nephrons.
Urea concentration is higher in the ascending limb than the descending limb.
The osmolarity outside the loop of Henle increases as it gets closer to the medulla. Insulin and glucagon are made by separate cells in the pancreas. The liver is the major target of glucagon. Diabetes is a disease due to insulin deficiency or reduced responsiveness to insulin. Anti-diuretic hormone is released by neuroendocrine cells of the hypothalamus that extend into the pituitary.