Maintenance of homeostasis begins in the liver. Describe how the liver maintains the proper blood-sugar level. What happens when the liver's glycogen storage capacity is depleted; when it is saturated?
During digestion, the blood of the intestinal villi picks up simple sugars and, thus, has a much higher concentration of these substances than normal blood. The blood is collected by the portal vein which breaks into a capillary bed in the liver. The liver absorbs most of the glucose, converting and storing it as insoluble glycogen. The blood leaving the liver through the hepatic vein has a blood-sugar level only slightly above the normal blood-sugar level. When this blood mixes with the glucose-depleted blood in the vena cava, a normal blood-sugar level is restored. Obversely, the liver breaks down glycogen and releases it as glucose into the blood stream when blood from the intestine has a low blood-sugar level. If the liver's 24-hour glycogen reserve is depleted, the liver converts amino acids into glucose in order to compensate for the dropping blood-sugar level. When the liver's glycogen storage capacity is saturated, the liver converts the excess glucose into fat which is then stored in adipose tissues.
