8/20/20206.2: Physiology of the Endocrine System: Essential Human Anatomy and Physiology I with Lab- Keck2/21The structural and functional relation between the hypothalamus and the posteriorpituitary illustrates the overlap between the nervous and endocrine systems. Theposterior pituitaryis connected to the hypothalamus by means of a stalk-likestructure. There are neurons in the hypothalamus that are calledneurosecretorycells because they both respond to neurotransmitters and produce the hormonesthat are stored in and released from the posterior pituitary. The hormones pass fromthe hypothalamus through axons that terminate in the posterior pituitary(Figure6.6).The axon endings in the posterior pituitary(Figure 6.6)store two major hormones:antidiuretic hormone (ADH), sometimes called vasopressin, and oxytocin.ADHpromotes the reabsorption of water from the collecting ducts, which receive urineproduced by nephrons within the kidneys. As the blood becomes dilute, the hormoneno longer is released until it is needed again.Oxytocinis the other hormone madein the hypothalamus and stored in the posterior pituitary. Oxytocin causes the uterusto contract through a positive feedback system, discussed earlier. Oxytocin can begiven artificially to help induce labor. Oxytocin also stimulates the release of milkfrom the mammary glands for nursing.The Anterior Pituitary
8/20/20206.2: Physiology of the Endocrine System: Essential Human Anatomy and Physiology I with Lab- Keck4/21Adrenocorticotropic hormone (ACTH)Follicle stimulating hormone (FSH)Luteinizing hormone (LH)Figure 6.6 Hormones released by the anterior and posterior pituitaryGrowth hormone (GH), or somatotropic hormone, dramatically affects physicalappearance. The amount of this hormone determines the height and bone structure
8/20/20206.2: Physiology of the Endocrine System: Essential Human Anatomy and Physiology I with Lab- Keck5/21of a person. GH causes cell growth, cell division, and protein synthesis. GH impactschanges on skeletal muscles, liver, and bones. In bones, it promotes growth of thecartilaginous plates and causes osteoblasts to form new bone.If too little GH is produced during childhood, the individual becomes a “pituitarydwarf” because the pituitary gland does not secrete enough growth hormone. If toomuch is produced during childhood, the individual is a “pituitary giant”. On occasion,however, there is overproduction of growth hormone in the adult, and a conditioncalledacromegalyresults. Since only the feet, hands, and face (particularly chin,nose, and eyebrow ridges) can respond, these portions of the body become overlylarge.