---
title: 'Humans Can Regrow an Organ'
source: 'https://youtube.com/watch?v=oNTaHYXQ4MM'
video_id: 'oNTaHYXQ4MM'
date: 2026-09-26
duration_sec: 74
channel: 'Kurzgesagt – In a Nutshell'
---

# Humans Can Regrow an Organ

> Source: [Humans Can Regrow an Organ](https://youtube.com/watch?v=oNTaHYXQ4MM)

## Summary

The video explains the menstrual cycle as a remarkable process of organ regeneration, detailing the hormonal orchestration that rebuilds the endometrium each month. It also touches on the widespread impact of premenstrual syndrome and the hope for new treatments.

### Key Points

- **The Monthly Regeneration** [00:00] — Around 2 billion humans regrow an organ every month. The uterus grows a temporary organ-like structure, the endometrium, to prepare for a possible pregnancy. The cycle begins when tissue from the old endometrium is shed.
- **Hormonal Stimulation** [00:14] — Estrogen from the ovaries stimulates the growth of a new endometrium. Several egg-filled follicles have already started maturing, but usually only one matures fully and releases its egg.
- **Progesterone's Role** [00:30] — The empty follicle starts producing progesterone, which transforms the endometrium into a nutrient-rich home for a possible embryo.
- **The Rollercoaster and PMS** [00:46] — If no embryo implants within two weeks, hormone levels drop, the lining's oxygen supply is cut off, and the tissue is kicked out of the body. This hormonal rollercoaster affects the entire body and brain, and is one reason up to 90% of people with a uterus experience premenstrual syndrome.
- **Understanding PMS and Hope** [01:01] — Some scientists think PMS is caused by changing hormone levels disrupting serotonin signals, contributing to headaches, mood changes, and for some, severe depression. For those with extreme symptoms, treatments that alter the body's response to progesterone offer real hope.

## Transcript

Around 2 billion humans regrow an organ every month. To prepare for a possible pregnancy, the uterus grows a temporary organ-like structure, the endometrium. The cycle begins when the tissue from the old endometrium is shed.
The growth of a new one is stimulated by estrogen from the ovaries where several egg-filled follicles have already started maturing. Usually only one follicle matures fully and releases its egg. Next, the empty follicle starts producing progesterone, which transforms the endometrium
into a nutrient-rich home for a possible embryo. If no embryo implants within two weeks, hormone levels drop, the lining's oxygen supply is cut off, and the tissue is kicked out of the body. This hormonal rollercoaster affects the entire body and brain, and it's one reason up
to 90% of people with a uterus experience premenstrual syndrome. Some scientists think that PMS is caused by changing hormone levels disrupting serotonin signals and contributing to headaches, mood changes, and for some, severe depression.
For those with extreme symptoms, treatments that alter the body's response to progesterone offer real hope. But while billions of people go through this cycle, we're only beginning to fully understand this extraordinary piece of biology.