The somatotropic axis regulates growth hormone (GH) secretion from the anterior pituitary. This process is controlled by two hypothalamic hormones – growth hormone releasing hormone (GHRH) and somatostatin [1][2]. GHRH is secreted from the arcuate nucleus and stimulates GH release. Somatostatin is secreted from the periventricular nucleus and inhibits GH release [1][3]. Dopamine acts both…
Regulation
Neural control of ACTH
The hypothalamic-pituitary-adrenal (HPA) axis controls the secretion of adrenocorticotropic hormone (ACTH) from the anterior pituitary [1][2]. The hypothalamus secretes corticotropin-releasing hormone (CRH) which stimulates ACTH release [2][3]. CRH is produced by neurosecretory cells in the paraventricular nucleus (PVN) of the hypothalamus [3][4]. The PVN projects axons to the anterior pituitary, releasing CRH at the median…
Neural control of the endocrine pancreas
The endocrine pancreas contains alpha and beta cells that secrete glucagon and insulin, which regulate glucose homeostasis [1][2]. Insulin secretion is stimulated by rising blood glucose levels as well as acetylcholine release from vagal parasympathetic nerves [3][4]. Glucose-sensing neurons in the hypothalamus also modulate insulin secretion by activating sympathetic nerves during hypoglycemia [5][6]. Glucagon secretion…
Neural control of insulin secretion
Insulin secretion from pancreatic beta cells is regulated by both nutrient and neural signals. Vagal cholinergic signaling stimulates insulin release, mediated by muscarinic receptors on beta cells [1][4]. Gastrin and secretin also stimulate insulin secretion [1]. In contrast, sympathetic norepinephrine signaling inhibits insulin release via α2-adrenergic receptors [1][5]. Low blood glucose is sensed by glucose…
Neural control of the subcommissural organ
The subcommissural organ (SCO) is a small ependymal gland located in the posterior part of the third ventricle, beneath the posterior commissure [2][4]. It secretes glycoproteins into the cerebrospinal fluid that aggregate to form Reissner’s fiber, which descends through the aqueduct and central canal [1][3]. The SCO is innervated by serotonergic and noradrenergic fibers from…
Neural control of blood glucose level
The regulation of blood glucose levels involves both neural and endocrine mechanisms. The pancreas secretes insulin and glucagon to control glucose levels [1]. Insulin lowers blood glucose by promoting cellular glucose uptake and storage, while glucagon raises glucose levels by stimulating glycogen breakdown and gluconeogenesis [3][4]. Insulin secretion is stimulated by rising blood glucose as…
Renin-angiotensin-aldosterone system
The renin-angiotensin-aldosterone system (RAAS) is a hormone system that regulates blood pressure and fluid balance [1]. When blood pressure or blood volume drops, juxtaglomerular cells in the kidneys secrete renin into the bloodstream [2]. Renin cleaves angiotensinogen produced by the liver into angiotensin I [1][3]. Angiotensin converting enzyme (ACE) then converts angiotensin I into angiotensin…
Control of upright balance
Maintaining upright balance requires continuous integration of sensory information and motor adjustments [1][2]. The three main sensory systems involved are the visual, vestibular, and somatosensory systems [3][4]. Visual input provides information about the environment and body orientation. The vestibular system senses head motion and position via the semicircular canals and otolith organs. Somatosensory receptors, particularly…
Neural regulation of ACTH release
The hypothalamic-pituitary-adrenal (HPA) axis controls the release of adrenocorticotropic hormone (ACTH) from the anterior pituitary [2][3]. The hypothalamus produces corticotropin-releasing hormone (CRH) in the paraventricular nucleus (PVN) [4][6]. CRH is carried via axons in the median eminence to the anterior pituitary, where it stimulates ACTH secretion into the bloodstream [1][3]. ACTH then acts on the…
Neural Regulation of Parathyroid Hormone
Parathyroid hormone (PTH) is secreted from the parathyroid glands in response to low blood calcium levels [1]. Calcium-sensing receptors on parathyroid cells detect decreases in circulating ionized calcium and trigger increased PTH synthesis and release [2][4]. PTH acts to restore calcium homeostasis by promoting calcium resorption from bone, calcium reabsorption in the kidneys, and calcitriol…