 Hey everybody, Dr. O here. So in this video, we're going to talk about the function of the parasympathetic activation of the autonomic nervous system. So I'm going to look at it kind of broadly and then we'll get a little more specific. So parasympathetic activation, when this system, when your rest and digest system kicks in, you're basically going to see a decrease in metabolic rate because your body's trying to conserve energy and rebuild. You're going to see a decrease in heart rate and blood pressure. We're not running. We're not fighting. We're not fleeing. You're going to see an increase in secretion by salivary and digestive glands because digestion is going to be a big part of the rest and digest system. You're going to see an increase in movement and blood flow in the GI tract. So that's going to lead to defecation as well. And then like I just said, it's going to stimulate defecation as well as urination. That's going to be the real big picture. We'll look at how it does that in just a moment. So the parasympathetic system really does it focuses on food processing, relaxation, absorption of energy, this rest and digest system. So it's where you're trying to rebuild and conserve energy. That's why some people call this the anabolic system because its job is to increase the amount of nutrients that are in your blood and stored in your body, but not a big deal. So you're storing up energy. So your sympathetic system can mobilize it and use it, I guess. These responses are very short lived and we've talked about that for several reasons compared to the sympathetic system. Remember, the sympathetic nervous system releases norepinephrine and epinephrine, and then in noradrenaline into your bloodstream. So the sympathetic system is going to be very wide reaching and it's going to have a longer effect. But your parasympathetic nervous system only uses really the neurotransmitter acetylcholine. And there's an enzyme called acetylcholine esterase that breaks that down very quickly. So the response of the parasympathetic system is going to be very short lived. The neurotransmitters are going to be released locally and they're going to be broken down or reabsorbed really, really quickly. So the responses are localized for reasons we've talked about and they're only going to last for a few seconds. Whereas the sympathetic system is diffused and the response lasts a lot longer. Okay, let's look at specifically when this entire system kicks in at what happens with parasympathetic activation, the major effects that are occurring. Number one, you see that either at the top, that'd be constriction of the pupil. You're not looking for predators or prey off in the distance. So you're going to be focusing your vision on near vision. So maybe now in the modern world you're watching TV, you're reading a book, reading the paper, these kind of things. So that'd be constriction of the pupils. Increased secretion by your digestive glands, like the salivary glands in the mouth, the gastric glands, the glands in your spalm testin, your pancreas, liver, everything, right? So you're going to be digesting the food that's coming through your body. Number three, be the secretion of hormones that are needed to absorb nutrients. Think about insulin and things like that. So you're going to be absorbing nutrients into your blood and then into your cells, all about storing and absorbing nutrients, as we've said. Number four would be changes in blood flow and glandular activity. So you're going to be associated with sexual arousal. So sexual arousal in both males and females is a parasympathetic response, which is why you need to relax. Parasympathetic nervous system is needed for a man to achieve an erection. Remember, ejaculation is going to be a sympathetic response. Number five, increase in smooth muscle activity along the GI tract. So you're going to be moving food as you digest and absorb it and then eliminate it, which would be number six, the stimulation and coordination of defecation. So defecation is a parasympathetic response along with urination. So seven would be contraction of the urinary bladder so that you can urinate. You do have to relax in order to urinate. Number eight, we're going to see constriction of the respiratory passageways. You don't need to move as much air because you're resting. You're not fighting, you're not fleeing. And number nine, we're going to see a reduction in heart rate and force of contraction and blood pressure. Because again, you're relaxing, you're recuperating, you're not fighting or fleeing. And I already mentioned the last one, number 10, that you're going to sexual arousal and the stimulation of all the sexual glands involved with lubricating the reproductive systems, etc., are going to be under parasympathetic control. Okay, so those are the key functions of the parasympathetic nervous system. I hope this helps. Have a wonderful day. Be blessed.