Caption

Kidney & adrenal gland. Artwork of a human kidney (red) with an adrenal gland (orange, upper right) and a ureter (orange, lower right). A person's two kidneys filter blood to remove excess water, salts & waste products. These are excreted as urine and pass along the ureter to the bladder. The kidneys regulate the balance between the blood's fluid and salts, and its acidity level. The kidneys regulate blood pressure by secreting the enzyme renin. The adrenal gland's inner portion (medulla) secretes the hormone adrenalin (epinephrine) in times of times of stress to prepare it for physical exert- ion. The outer portion (cortex) produces about 30 steroid hormones that regulate metabolism.