Hypothalamus and pituitary gland .pdf

07/11/23 Hypothalamus and the pituitary: Learning objective: brief over view of anatomy and functional organisation of hypothalamus and pituitary gland. Learning objective: connection bet ween the hypothalamus and the pituitary gland. Learning objective: to distinguish bet ween the t wo different pa...

07/11/23 Hypothalamus and the pituitary: Learning objective: brief over view of anatomy and functional organisation of hypothalamus and pituitary gland. Learning objective: connection bet ween the hypothalamus and the pituitary gland. Learning objective: to distinguish bet ween the t wo different parts of the pituitary and the hormones they produce, using structure and function. Learning objective: to de ne and illustrate what hormones are produced by the hypothalamus that then act on the pituitary. Learning objective: distinguish bet ween direct and indirect effects of growth hormones and its regulation. Learning objective: understand the functions of each of the main pituitary hormones. Anatomy: What is the hypothalamus: Processes inputs and produces outputs making it a master control centre. Anatomically it is a collection of neurones. Pituitary gland: Pea sized structure. Sits within a saddle-shaped depression of the sphenoid bone of the skull called the pituitary fossa or sella turcica. Connected to the hypothalamus by the pituitary stalk, and via a blood vessel net work ( hypothalamo-hypophyseal-portal system ). Composed of t wo distinct structures that differ in embryological development and anatomy. Anatomy of the pituitary gland: The pituitary stalk descends from the central region of the hypothalamus, and is termed as the median eminence. a surrounds Infundibulum The anterior pituitary lobe is divided into 3 parts: pars tuberalis, pars intermedia, pars distalis. The posterior pituitary lobe is divided into 2 parts: infundibular stalk and the pars ner vosa ( main lobe ). Pituitary gland and Cavernous sinus: PEGEary The important of being aware’ of the surrounding nerves is that if there is a growth of the pituitary it may squash these ner ves and effect things like eye movement. Embryology of pituitary gland: Anterior pituitary: derived from the ectoderm of rathke’s pouch. Posterior pituitary: originates from downward extension of neural ectoderm from the oor of the diencephalon. What hormones are produced by the hypothalamus that then act on the pituitary: The hypothalamus is the master control centre and communicates with the pituitary gland through releasing hormones. Pituitary then secretes further hormones to the peripheral glands to produce de nitive endocrine hormones, which then act on target tissues. Growth hormone secretion: Growth hormone is produced by cells called somatotrophs in the pituitary. The production of growth hormone begins very much in early foetal life and continues throughout life. As age progresses, the quality of growth hormone produced decreases. Growth hormone secretion is regulated by t wo essential hormones coming from the hypothalamus. One is the growth hormone releasing hormone, which stimulates secretion. The other is somatostatin which inhibits secretion. What is IGF-1: IGF-1 is a protein secreted from the liver stimulated by GH. Most of the effects of GH on the peripheral tissue are mediated by IGF-1. It has a long half life and it is a stable marker to measure in blood sample unlike pulsatile secretion of GH. Plasma levels of IGF-1 are helpful in diagnosis of GH abnormalities. Growth hormone regulation: Growth hormone communicates to the hypothalamus directly through a short loop. if there is an excess of growth hormone, then there should be a negative signal going to the hypothalamus asking it to shut down the GHRH. There is a long loop wherein growth hormone generates the production of IGF-1, and this IGF-1 along with free fatty acid from adipose tissue, which are released due to the effects of growth hormone and due to the breakdown of lipids. These both give a negative feedback to the hypothalamus by the long loop, for example, it has the hypothalamus to produce more somatostatin or less GHRH. There is an open loop, wherein growth hormone is also called the stress hormone. If you have hypoglycaemia that is increased growth hormone to generate glucose and the ghrelin in the stomach can also induce growth hormone secretion. Prolactin secretion and function: It has direct effects on the target tissues, but does not necessarily stimulate on another gland in the periphery. It stimulates breasts to produce milk. Increased prolactin levels will have a negative effect on the gonadotropins ( which is the sex hormones ). regulation Cortisol secretion and function: Cortisol is secreted from the adrenal glands. It’s secretion is regulated by a mechanism through which the hypothalamus, pituitary and adrenal glands form an axis and communicate with each other. Corticotropin releasing hormone stimulates the pituitary gland. CRH is released by the hypothalamus in response to stimulus such as stress. This them stimulates a hormone called adrenocorticotropic hormone which acts on the t wo adrenal glands causing cortisol to be released. When cortisol is secreted in excess, it has a direct feedback to the anterior pituitary gland, asking the pituitary to shut down the ACTH levels, and also has a feedback directly to the hypothalamus shut down corticotropin releasing hormone. Function of cortisol: Thyroid hormone secretion and function: Thyrotropin releasing hormone stimulates the hypothalamus to secrete thyroid. This stimulates the anterior pituitary gland to release thyroid stimulating hormone. This stimulates the thyroid to release T3 and T4. These are essential for body metabolism. Sex hormones: females Gonadotropin releasing hormone acts on the anterior pituitary gland which then releases luteinizing hormone and follicle stimulating hormone. These act on ovaries which produce oestrogen and progesterone. Sex hormones: male FSH Posterior pituitary gland: unlike the anterior pituitary gland, the posterior pituitary gland is not composed of any speci c secretary cells and they themselves do not secrete any hormones. Terminals, which arise from the supraoptic and paraventricular nuclei are found in the posterior pituitary. The neurones from these nuclei transverse through the pituitary stalk and end up in the posterior pituitary. Therefore the hormones secreted from the hypothalamus are stored in the posterior pituitary gland. ADH/AVP secretion and control: ADH action is at the level of kidneys. It conser ves a body water and regulates overall body volume status. Secretion of ADH is regulated by stimuli from osmotic and uid volume status and baroreceptors. Reduction in body volume/ uid state increases plasma osmolality which activates hypothalamic Osmoreceptors to release ADH. Note: blood osmolality is the same as blood viscosity ( thickness ). Oxytocin: This has a role in child birth and lactation. Stimulates myoepithelial contractions: in uterus during child birth. Milk ejection from lactating mammary gland ( suckling major stimulus for release ).