On the right is a body outline with the main endocrine glands placed where they really sit — pituitary in the head, thyroid in the neck, adrenals on the kidneys, the pancreas below the stomach, and the gonads. Each is a ductless gland that pours a hormone straight into the blood. ⏭ Step to light up each gland in turn and read the hormone it makes.
Keep stepping until the pituitary lights up. It is the master gland: its hormones — GH, TSH, ADH, oxytocin, FSH and LH — include several that switch other glands on, like TSH driving the thyroid. Yet the pituitary is itself commanded by the hypothalamus just above it, the bridge between nerves and hormones. ▶ Play to sweep through every gland, or ↻ Reset to start the tour again.
Switch to the Glucose feedback tab. The graph plots blood glucose over time; the dashed green line is the set point, about 90 mg per 100 cm³. Eat a meal and the line climbs above it; fast or exercise and it drops below. ▶ Play and watch the live line rise after the meal — the body cannot leave it there. Two opposite hormones will drag it back.
Watch the feedback loop beneath the graph. When glucose is high, the pancreas (its β cells) releases insulin. Insulin tells the liver and muscles to take up glucose and lock it away as glycogen. As they do, the glucose line falls back toward the set point — and insulin switches off. ⏭ Step through to see each arrow of the loop light up in order.
Now the opposite. When glucose drops below the set point, the pancreas (its α cells) releases glucagon. Glucagon tells the liver to break glycogen back down into glucose and release it, so the line rises back to normal. Insulin and glucagon are antagonistic — opposite — and together they hold the line steady. ↻ Reset and ▶ Play to watch a full meal-and-fast cycle correct itself.
Open the Hormone action tab. A hormone molecule is carried along the blood vessel and reaches two cells. Only the target cell carries the matching receptor — the hormone binds it like a key in a lock and switches on a response inside the cell. The other cell has no receptor, so it ignores the hormone completely. ▶ Play to send the hormone to its target; that specificity is why one chemical in the blood can change just one tissue. Revisit the detail in the Lecture.