Today I Learned: May 22, 2019
Sinuses. Lactation feedback. War pigs.
1) So Many Sinuses
The human skull has more sinuses than I realized. There are four pairs of them all up and down the front of the skull.
Related: the nasal cavity is huge! And so are tongues!
2) How Lactation Works (And Doesn’t Work)
I learned a couple of crazy facts about human lactation today.
Fact 1: Milk is not (primarily) sucked from the nipple. It is ejected. Milk is stored in little glands called aveoli in the breasts. When a baby suckles, the sensation is registered in the hypothalamus and pituitary glands in the brain, which trigger a release of oxytocin into the blood. Oxytocin triggers contraction of little muscle cells called myoepithelial cells* around the aveoli, squeezing out milk.
At first it seemed crazy to me that a lactation signal would have to go all the way to the brain and then come all the way back (especially via a hormone — that was a real surprise), but I guess it takes some real processing power to discriminate between mundane, non-feeding-baby sensory perceptions and the sensation of a baby actually trying to feed. Which leads me to…
Fact 2: Lactation can be triggered by more abstract signals than direct stimulation of nipples. Anything that signals the presence of a hungry baby, like the sound of a crying baby, can trigger lactation. This may seem like a remarkably specific adaptation on the part of evolution, but the mechanism is actually quite simple — lactation is subject to Pavlovian condition, so anything that happens sufficiently consistently when lactation is triggered will itself become a trigger for lactation.
Fact 3: Lactation completely stops if lactation isn’t triggered within 48 hours of the last event. I guess in nature, if a baby stops suckling for two days, it probably won’t need to suckle again?
*Myoepithelial cells are also responsible for squeezing sweat out of sweat glands, saliva out of salivary glands, and tears out of lacrimal glands in the eye.
3) War Pigs
A mix of historical records and legends suggest that pigs were used as weapons of war by the Romans and possibly some of their contemporaries. Pigs, it seems, were a hard military counter to war elephants.
Roman doctrine held that elephants were terrified of the sound of a squealing pig. Accordingly, there are several stories of pigs being deployed to rout enemy war elephants. In one story, a pig was dangled off the walls of a besieged city to scare off an attacking siege elephant. In another, pigs were coated in oil and lit on fire to act as a sort of incendiary anti-elephant skirmisher force.
I… honestly don’t know how much to believe these tales. Can someone with more historical training help me out here?