 Hello everyone, welcome back to another session in dentistry M1. So today we have a small topic in physiology that is HPA axis or HTP axis. So which is Hypothalamic Pituitary Adrenal axis. So it is a central nervous system arrangement and which acts mainly on the stress response. When there is a stress, this axis of hypothalamus pituitary adrenal will be activated and there will be production of hormones and facing that peculiar stress situation. So HPA axis or Hypothalamic Pituitary Adrenal axis. It is a complex set of direct influences and feedback interactions. So hope you understand what is a feedback mechanism and direct influences. There is a hormone releasing from this and it influences pituitary and it in turn influences adrenal cortex. And again if there is a deficiency of if there is a excess the cortisol will negatively act on hypothalamus or any other gland and which will reduce the secretion of the hormones that is negative feedback mechanism. There is a mechanism or there is a message giving back to the original position so that there will be a balance at the end product that is feedback mechanism. So it is a complex set of direct influences and feedback interaction among three components. So which are the components one is hypothalamus anterior pituitary and adrenal cortex. So hypothalamus we know it is a structure in brain then anterior pituitary which is a P shaped structure located below the thalamus and adrenal gland which are the minor glands which is present above the kidneys. So these are three structures. So now let us see what is happening in HPA axis. So the para ventricular nucleus of hypothalamus. So there is many nucleus and particularly para ventricular nucleus of hypothalamus which contains neuro endocrine neurons which synthesize and secrete two hormones that is vasopressin and corticot tropin releasing hormone. So CRH and vasopressin. So these are released from para ventricular nucleus of hypothalamus. So these two hormones which regulate the anterior lobe of pituitary gland in particular these two hormones stimulate the secretion of adrenocorticotropic hormone. So CRH and vasopressin which regulate the adrenocorticotropic hormone secretion which is also known as corticotropin. This is earlier known as corticotropin. So what happens? This ACTH which in turn acts on the adrenal cortex. Those are the glands which is present above the kidney. So it acts on adrenal cortex. So CRH acts on pituitary to release of ACTH, ACTH act on adrenal cortex which produces glucocorticoids that is cortisol. Adrenal cortex release many hormones, glucocorticoids, mineralocorticoids so the glucocorticoids is cortisol which is a basic hormone for stress response. So sometimes what happens is this cortisol will act on anterior pituitary and hypothalamus as I mentioned in a negative feedback. So there is some imbalances happening in the production of cortisol. Cortisol will give feedback to these two to produce lesser amount of CRH and ACTH so that there will be a balance happens here in the production of cortisol. That is a negative feedback mechanism. So cortisol is a hormone which is helping us to face the stress or a stress response hormone. So since it is a stress related hormone so stress managing hormone when there is over production or more than normal production of cortisol happens there is increased availability of glucose. So why this glucose is coming? It is to facilitate the response of the person to fight or fleeing so this responses needs more glucose that is done by the production of cortisol. So at the same time there is increased glucose availability. The cortisol also suppress the highly demanding metabolic process of the immune system which in turn result in further availability of glucose. So that is how it makes the glucose available for all these stress response. So other than that this HPA axis is influenced by physical activity, illness, blood levels of cortisol and also by this sleep wakes cycle which is known as circadian rhythm. So the HPA axis which has a central role in regulating many homeostatic systems in the body such as metabolic system, cardiovascular system, immune system, reproductive system and central nervous system which basically this HPA axis basically integrates physical and psychosocial influences in order to allow an organism to adapt effectively to its environment. So that is about HPA axis it is basically a stress response hormone and it is starting from hypothalamus by corticotropic releasing hormone and t-repetutory adenocorticotropic releasing hormone and ultimately it releases cortisol to face stress and also many functions it has. So when there is over production there will be a negative feedback mechanism happens and there will be a balance. So that is all about HPA axis it is a commonly asked short not and physiology. So I will come up with a new topic in human physiology. Thank you.