Blood circulation that starts in capillaries and ends in capillaries is called

In the general (systemic) circulation, blood leaves the heart through arteries, reaches a capillary bed in a tissue, and returns to the heart through veins. A portal circulation is the specific exception to this pattern: it is any circulatory pathway that begins in one capillary bed and drains into a second capillary bed through a portal vein, without first returning to the heart. This capillary-to-capillary link is the defining structural feature of a portal system.

The stem describes exactly this capillary-to-capillary route, so the correct classification is portal circulation. Two well-known examples illustrate it: the hepatic portal system carries blood from the capillaries of the stomach and intestines through the hepatic portal vein into the capillary-like sinusoids of the liver before it returns to the heart; the hypophyseal portal system similarly links capillaries in the hypothalamus to capillaries in the anterior pituitary.

Contrasting the other terms offered:

• Renal circulation names the kidney's own blood supply, the vessels from the renal artery to the renal vein; it identifies the organ supplied rather than describing this particular capillary-to-capillary-through-a-portal-vessel structural pattern.

• Lymphatic circulation carries lymph, not blood, through lymphatic vessels and nodes back into the venous system; it is a separate fluid-transport system altogether.

• Hepatic circulation is the broader term for the liver's entire blood supply, arterial blood plus the venous blood arriving from the digestive tract, draining via the hepatic vein back to the heart; it names the organ supplied rather than the specific capillary-to-capillary structural pattern the stem asks about.

Because the pathway begins and ends in capillary beds without an intervening pass through the heart, portal circulation is the term that fits.