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CHAPTER 5 – PITUITARY HORMONES CHAPTER 7 – NEUROHYPOPHYSIAL HORMONES Last 2 chapters before the test – Sept. 18th , Test 1 Pituitary Generally considered to have up to 3 parts Anterior pituitary (lobe) – adenohypophysis Posterior pituitary (lobe) – neurohypophysis Pars intermedia Not in all species – sort-of in humans Once considered the most important of endocrine organs Associated with several important physiological processes in the body Secretes a number of hormones Pituitary hormones have wideranging effects on endocrine and non-endocrine target tissues Pituitary – general information Once considered the collector of brain mucous Later considered ‘the master gland’ Position within several important physiological responses However, highly regulated Important “upper-level manager” Important connection between hypothalamus and body Pituitary – general information 0.5-1g in adult human male, larger in pregnant female Located within the sella turcica Most inaccessible gland Situated below hypothalamus, near optic chiasm Connected via an infundibular stem or stalk Richly vascularized tissue 2 main parts, different embryological origin Pituitary – general information Size of the pituitary and depends on species and physiological condition Color-changing animals, pars intermedia large Will secrete large amounts of hormones that influence color changes Posterior pituitary larger in land vertebrates than aquatic vertebrates Cell population of anterior pituitary can change in reproductive individuals Sella turcica – cuplike structure where pituitary rests Posterior Pituitary Derived from neural ectoderm of floor of forebrain Collection of nerve endings Sometimes considered part of hypothalamus Nerve bodies located in hypothalamus Nerve endings collected in posterior pituitary (neurohemal organ) Pass through median eminence and axons make up much of infundibular stem Secretes vasopressin (AVP, ADH) and oxytocin (OT) These 2 hormones similar in amino acid sequence Genes both on chromosome 20 May represent a duplication and inversion Posterior pituitary Two hypothalamic nuclei have extensions into the posterior pituitary Large neurosecretory granules found in nerve endings Supraoptic nuclei (SON) Paraventricular nuclei (PVN) Contain hormones for quick release Numerous pituicytes interspersed among nerves Supporting function Posterior pituitary Blood supply from the inferior hypophysial artery Note, neurons end on the capillary network Quick release of hormone products into circulation PVN neurons secrete oxytocin (OT) SON neurons secrete vasopressin (AVP) Two hormones are similar, nuclei of production are close together, genes for hormones close together Different stimuli for release Oxytocin (OT) Induces milk let-down (in mammals) and uterine contractions in labor (major actions) Milk release (let-down) Nerve stimulation of mammary tissue induces release Neural pathways conduct stimulii Although auditory and optic sensory can be influential Uterine contractions Induces myometrium contractions May work in concert with rising estrogen levels to induce OTreceptor upregulation in uterus These effects clearly sex-specific. OT in males does have actions Oxytocin (OT) Contractile actions on smooth muscle Can induce contraction in vascular smooth muscle, unsure how widespread Potential influences on smooth muscle contraction in reproductive organs (during copulation) Effects on maternal behavior Mating behavior May work in concert with estrogen May work in concert with estrogen and progesterone (ovulation) to make females more receptive Social behavior – esp. mate affiliation Vasopressin (AVP) Two major functions – smooth muscle contraction or relaxation, movement of water across epithelial tissue Osmoregulation When osmolality low, AVP decreased and water lost When osmolality high, AVP released and water retained Blood volume regulation Changes in volume/pressure Loss of volume or pressure (hemorrhage and blood loss) AVP released and water retained Baroreceptors in heart monitor pressure Influences on social behavior Suppresses vasopressin (ADH), makes you urinate (contributes to your hangover, which is mostly dehydration) Adenohypophysial and other functions Both posterior pituitary hormones influence the anterior pituitary OT appears to influence stress response Inhibitory OT may also influence prolactin secretion AVP may be stimulatory to the stress response AVP may also stimulate release of hormones that influence thyroid gland Vasotocin (AVT) – a version of vasopressin in non-mammalian vertebrates Strong impacts on reproductive behavior Anterior pituitary Invaginates from oral ectoderm – Rathke’s Pouch Pars intermedia – next to the posterior pituitary Pars distalis – anterior pituitary itself Considerable size in some species Pars tuberalis - forms from dorsal extensions of anterior pituitary, Surrounds infundibular stalk Facilitates connection to hypothalamus Not actually innervated Blood link with hypothalamus Anterior pituitary Vascularized by the hypophysial portal system Portal systems connect organs, blood flows through one then another in quick succession Blood enters high in median eminence Hypothalamic nerve cells connected to capillary bed Blood moves through anterior pituitary Hypothalamic hormones transferred to anterior pituitary Anterior pituitary Variety of cell types, named after type of stain accepted Staining storage vesicles (granules) Cells types further divided by what type of hormone they release Acidophils, basophils, or chromophobes Somatotrophs, lactotrophs, corticotrophs, thyrotrophs, gonadotrophs Pituicytes interspersed among these cell types, can isolate off populations of different types Populations are not static Pituitary-hypothalamus association This is showing both the blood flow through the pituitary (anterior pituitary and hypothalamus have blood link) and neurosecretory nerve cell orientation Anterior pituitary – hormones Hormones from anterior pituitary influence mammary glands, gonads, adrenal glands, and thyroid glands Can be grouped into families Growth hormone & prolactin – similar amino acid sequence Thyroid stimulating hormone (TSH), follicle stimulating hormone (FSH), luteinizing hormone (LH) – all glycoproteins, structurally similar Adrenocorticotrophic hormone (ACTH) & alpha-melanocyte stimulating hormone (αMSH) – similar amino acid sequences, Proopiomelanocortin (POMC) precursor Growth hormone (GH) Secreted by somatotrophs (acidophils) No specific target tissue Induces chondrocytes (cartilagenous growth plates) to produce more extracellular matrix Enhances amino acid incorporation into muscle Influences general somatic growth Source of abuse as performance enhancer Effects on protein metabolism & electrolytes Mediated by somatomedins (IGFs) Lengthening of cartilagenous growth plates induces elongation of long bones and increases in height Growth hormone (GH) Accounts for 4-10% wet weight of anterior pituitary Circulates with a binding protein - protection Levels stable through childhood Decline with age in adults Peak during periods of growth GH is new anti-aging drug Daily secretion fluctuates GHRH and somatostatin control release Similar to prolactin – 161 amino acids similar (both 191 total), 2 sulfide bonds each, in same place Prolactin (PRL) Produced by lactotrophs (acidophils) Mammary growth & development Levels increase at puberty Promotes lactogenesis Lactotroph population changes during lactation Estrogen influence Levels higher in females, but both sexes have daily variation in levels Prolactin (PRL) An important role in mammals is lactation (hence the name) – but not the only role (and in non-mammals) Role in male reproduction PRL may help maintain expression of luteinizing hormone receptors in testes Evolutionarily old – multiple functions other spp. Mostly on integument structures Some influences on reproduction, many not related to reproduction Pituitary hormones – glycoprotein hormones Luteinizing hormone (LH), follicle-stimulating hormone (FSH), thyroid-stimulating hormone (TSH) All have covalently bound carbohydrate moieties All comprised of 2 chains – α and β The α chain is identical to all three The β chains are specific to each hormone Chains made separately and then joined More α chain molecules produced than β chains for each hormone Thyroid stimulating hormone (thyrotropin) Secreted by thyrotrophs (basophils) Acts on thyroid gland Induces release of thyroxine and triiodothyronine Important to temperature regulation in endotherms Has impacts on metamorphosis in ectotherms Luteinizing hormone (LH) Secreted by gonadotrophs (basophils) Has actions on the gonads Ovaries, Females – will induce ovulation Works testes in concert with estrogen Males – will induce testosterone release (Leydig cells) FSH important to receptor regulation Spermatogenesis Follicle stimulating hormone (FSH) Secreted by gonadotrophs (basophils) Note, both FSH and LH come from same cell type Pulses of GnRH from hypothalamus important to what hormone released Populations of gonadotrophs that only release one type Target tissue is the gonad Females – influences early follicle development Males – potentiates LH receptors, induces testicular androgen-binding protein Adrenocorticotropic hormone (corticotropin) Produced in corticotrophs (chromophobes, but these are basophils) Smallest hormone from pituitary (39 amino acids) Acts on the adrenal glands Initiates the stress response – IMPORTANT Derived from proopimelanocortin (POMC) Large precursor that yields other hormones (based on where it’s split Melanocyte-stimulating hormone A. Roulin – coloration and CORT connection Melanocyte-stimulating hormone From pars intermedia, but what if you don’t have this? POMC a large molecule that can produce two hormones ACTH and MSH depending on where it is split Control of pituitary hormone secretion Long-loop and short-loop feedback The number of steps to regulation Autoinhibition Allows organ to ‘fine tune’ hormone production Negative and positive feed back systems Positive feedback in ovulation; LH & estradiol increase until egg released Negative feedback for the thyroid; T3 & T4 suppress TSH production Pathophysiology Can see under- and over-secretion of pituitary hormones Hyposecretion Hypersecretion Due to destruction of pituitary (tumor) or loss of vascular connections, disease to the hypothalamus Due to tumors, disease to the hypothalamus, inhibition of feedback controls Examples GH excess and deficiency TSH excess and deficiency ACTH excess and deficiency