What is the biological purpose for crying when we are "sad"?

Crying or weeping (physic tears): is increased lacrimation due to strong emotional stress, depression or physical pain. This practice is not restricted to negative emotions; many people have been known to cry when extremely happy or when they are laughing. In humans, emotional tears can be accompanied by reddening of the face and sobbing — cough-like, convulsive breathing, sometimes involving spasms of the whole upper body. Tears brought about by emotions have a different chemical make up than those for lubrication. The limbic system is involved in production of basic emotional drives, such as anger, fear, etc. The limbic system also has a degree of control over the autonomic system. This is more specifically the hypothalamus. It is the parasympathetic system that controls the lacrimal glands. Acetylcholine is the neurotransmitter specific to both the nicotinic and muscarinic receptors. It is when the receptors are activated that the lacrimal gland is stimulated to produce tears.

crying or weeping, is increased lacrimation due to strong emotional stress, depression or physical pain. This practice is not restricted to negative emotions; many people have been known to cry when extremely happy or when they are laughing. In humans, emotional tears can be accompanied by reddening of the face and sobbing — cough-like, convulsive breathing, sometimes involving spasms of the whole upper body. Tears brought about by emotions have a different chemical make up than those for lubrication. The limbic system is involved in production of basic emotional drives, such as anger, fear, etc. The limbic system also has a degree of control over the autonomic system. This is more specifically the hypothalamus. It is the parasympathetic system that controls the lacrimal glands. Acetylcholine is the neurotransmitter specific to both the nicotinic and muscarinic receptors. It is when the receptors are activated that the lacrimal gland is stimulated to produce tears.

My thoughts on crying are that it is like a refreshing rain, sometimes we cry when we are happy, sometimes when we are sad. After a storm the sun shines again. Sweet Release!

generally referred to as crying or weeping, is increased lacrimation due to strong emotional stress, depression or physical pain. This practice is not restricted to negative emotions; many people have been known to cry when extremely happy or when they are laughing. its for expressing ourselves and showing great emotion. As I, a young man would only cry if it were a loved one that i lost. It goes like that.

I know that if I try to hold in a cry my head feels like it's going to explode. It feels so good to cry even though I feel like crap while I'm crying. I'd say it's to keep our heads from exploding:-)

It releases stress which in turn will help to heal the body. Stress is one of the factors which make us ill.

My mother says it helps decrease the build up of hormones

We all know how crying gives us relief. I don't think anyone knows for sure why we shed tears.

It is a means of nonverbal communication; it's a way of signalling to people around us that something is wrong.

my mom says it cleans the soul. plus it feels good, makes everyone feel better to get it out somehow.