Why Can't Humans Drink Salt Water? A Seagull Can

Why can't humans drink salt water? Your kidneys top out at about 2% salt in urine, and seawater is 3.5%. So drinking seawater leaves you with less water than you started with. We follow one gulp to see why. It's osmosis, vasopressin and the loop of Henle against the ocean. Then we meet the animals that can drink seawater: a kangaroo rat, gulls with salt glands, crying sea turtles and sharks full of urea. And we bust a few myths, like whales drinking the sea and blood being leftover ancient ocean. 00:00 Adrift in a lifeboat 00:22 Water, water, every where 00:44 The wartime lifeboat records 01:06 Follow one gulp 01:24 What's in a gulp of seawater 01:46 How salty your blood is 02:18 Osmosis: water follows salt 02:38 Into your gut and blood 02:57 Your cells start to shrink 03:15 Your brain sounds the alarm 03:36 Your kidneys save water 03:57 The loop of Henle 04:22 The 2% salt limit 04:43 The desert rat that can 05:10 Seagulls and their salt glands 05:39 Turtle tears and iguanas 06:04 Fish and sharks 06:28 Myth: whales drink seawater 06:51 Why seawater drains you 07:15 Magnesium, sulfate and the loop 07:35 Hypernatremia 08:05 Why evolution never fixed it 08:30 A salt vault, not a salt pump 08:53 Myth: a little is fine 09:17 Myth: blood is ancient ocean 09:45 Back to the lifeboat Sources: NOAA, Can humans drink seawater?: https://oceanservice.noaa.gov/facts/d... NOAA, Why is the ocean salty? (35 parts per thousand; ion shares): https://oceanservice.noaa.gov/facts/w... StatPearls, Hypernatremia: https://www.ncbi.nlm.nih.gov/books/NB... StatPearls, Physiology, osmoreceptors: https://www.ncbi.nlm.nih.gov/books/NB... Sands & Layton 2009, The physiology of urinary concentration (Semin Nephrol): https://pmc.ncbi.nlm.nih.gov/articles... Schmidt-Nielsen B. 1979, Urinary concentrating processes in vertebrates (Yale J Biol Med): https://pubmed.ncbi.nlm.nih.gov/538955/ Schmidt-Nielsen K. 1959, Salt glands (Scientific American 200(1):109–116): https://www.wkbpic.com/wkbx/SA/1959/1... Widdowson 1957, Water equilibrium in health (Proc Nutr Soc 16:118–123): https://www.cambridge.org/core/servic... Medical Aspects of Harsh Environments, Vol. 2 (Borden Institute), WWII lifecraft mortality table: https://upload.wikimedia.org/wikipedi... Ortiz 2001, Osmoregulation in marine mammals (J Exp Biol): https://pubmed.ncbi.nlm.nih.gov/11441... INTERSALT Cooperative Research Group 1988, 24-hour urinary sodium in 52 centres (BMJ): https://pubmed.ncbi.nlm.nih.gov/3416162/ Narration voice: Qwen3-TTS (synthetic). All animation, music and sound are original. This video explains physiology and is not medical advice. #saltwater #kidneys #humanbody