The Endocrine System and Hormones PDF

Topic 6 The Endocrine System and Hormones • Endocrine Glands and Hormones • The Posterior Pituitary • The Anterior Pituitary • The HPG Axis Glands are another output of the nervous system Glands – organs that secrete substances for use in the body or discharge into the surroundings Endocrine gl...

Topic 6 The Endocrine System and Hormones • Endocrine Glands and Hormones • The Posterior Pituitary • The Anterior Pituitary • The HPG Axis Glands are another output of the nervous system Glands – organs that secrete substances for use in the body or discharge into the surroundings Endocrine glands Release hormones within body Hormones – signaling molecules • • travel via bloodstream act on target tissues Exocrine glands Secrete fluid outside the body • Examples: sweat, saliva, milk, tears Forms of chemical communication Synaptic (neurocrine)— chemical release and diffusion across a synapse. Endocrine—a hormone is released into the bloodstream to act on target tissues Forms of chemical communication Autocrine — released chemical acts on the releasing cell • Autoreceptor – receptor on a neuron that detects NTs it has released to monitor its own activity Paracrine — the released chemical diffuses to nearby target cells • Volume transmission – Herzog, 2017 extrasynaptic NT binding/activity caused by “spillover” Forms of chemical communication Pheromone—hormones used to communicate between individuals of the same species • released into the environment. Allomone — chemicals released by one species to affect the behavior of another species. General principles of hormone function 1. Hormones act gradually, not instantaneously. 2. Hormones act by changing the probability or intensity of a behavior. 3. The relationship between behavior and hormones is reciprocal. General principles of hormone function 4. One hormone may have effect multiple behaviors, and one behavior can be affected by several hormones. 5. Hormones often have a pulsatile secretion pattern. Woller et al (2009) General principles of hormone function 6. Hormone levels change through the day controlled by circadian clocks in the brain. 7. Hormones can interact with other hormones and change their effects. 8. Hormones can only affect cells with a receptor protein for that hormone. Feedback control mechanisms regulate the secretion of hormones Negative feedback — system’s output feeds back and directly inhibits further secretion • • Autocrine Target cell – biological response to hormone inhibits endocrine secretion The pituitary gland Body’s “primary” gland • • releases important hormones regulates other glands Directly connected to hypothalamus via the pituitary stalk (infundibulum) Special neural/endocrine hybrid cells Neuroendocrine cell - hybrid neuron/endocrine cell • • Receive synaptic input, produce APs Release hormones The pituitary gland Posterior pituitary (PP) stores and releases only two hormones • Posterior 25% of pituitary • Input only from supraoptic and paraventricular nuclei of the hypothalamus Anterior pituitary (AnP) many different endocrine cells, each with own hormone • Anterior 75% of pituitary • Input from several hypothalamic nuclei Posterior pituitary Hormone release directly into bloodstream via axons that travel through the pituitary stalk Two hormones: • Oxytocin (OXT) • Arginine vasopressin (AVP) Oxytocin OXT –important for reproductive and parenting behavior. • “Love hormone” – somewhat problematic OXY neurons in supraoptic, paraventricular nuclei send direct projections to brain areas in addition to PP • Includes nucleus accumbens, amygdala Milk letdown reflex Milk letdown reflex – reflexive milk release by mammary glands in response to suckling • • Triggered by OXT release from PP Reflex that can be conditioned! OXT and attachment Triggers uterine contractions during childbirth Released upon skin-to-skin touch between baby/mom OXT in mother’s milk  attachment bond formation in baby OXT antagonists prevent baby rats from recognizing mother’s smell, prevent mother rats from showing maternal behavior OXT goes beyond parental bonds OXT levels  in both human and dog after petting session (Handlin et al, 2011, 2012) Giving OXT to rodents  physical contact with each other (Carter et al, 2020) OXY Released during orgasm in both men and women  formation of pair bonds (Cera et al, 2021) Studying bond formation Pair-bonds – durable and exclusive relationships between two individuals Prairie voles (PV)  monogamous (single-mate) pair-bonds Meadow voles (MV)  polygamous (more than one mate) OXY and pair-bonds Female PVs (mono)  high OXT receptor expression Female MV (poly)  low OXT receptor expression OXY facilitates pair-bond formation in female PVs OXT agonist  formation of pair bond with nearby male OXT antagonist  prevents pair-bond formation in sexual partners. AVP  pair-bond functions in males Male MVs (poly) show fewer AVP receptors than male PVs (mono). Forcing expression of AVP receptors  male MVs form strong pair-bonds Nair & Young, 2006 OXT increases affiliation for the familiar Problem: in all examples, OXT administered to animals familiar with each other! In humans, OXT nasal spray  positive attitudes towards those seen as similar, but  acceptance of “outsiders” • OXY  likelihood of lying when beneficial to in-group members (Shalvi & De Dreu, 2014)  OXT levels in women in distressed/insecure relationships The anterior pituitary (AnP) More complex, but versatile release mechanism Multi-stage hormone release process featuring 3 structures • Hypothalamus • Pituitary • [Target gland] Six hormones Hormone release via the AnP is much more complex Hypothalamic releasing hormone AnP tropic hormone Remote endocrine gland target hormone AnP hormone secretion Releasing hormones synthesized by neuroendocrine neurons in various hypothalamic nuclei • Axons converge onto the median eminence – connection between hypothalamus and infundibulum Releasing hormones secreted into hypothalamic-pituitary portal system (HPPS) or hypophyseal portal system • dense web of blood vessels leading through AnP AnP hormone secretion AnP endocrine cells respond to incoming releasing hormones by secreting tropic hormones into general blood circulation AnP hormone secretion Tropic hormones reach endocrine glands throughout the body Each endocrine gland only has receptors for 1-2 tropic hormones Final target hormone released by affected endocrine gland Hypothalamic neuroendocrine cells influenced by both circulating and synaptic inputs Example axis: Hypothalamicpituitary-thyroid (HPT) axis 1. Hypothalamus  thyroid releasing hormone (TRH) into HPPS 2. Triggered by TRH, AnP  thyroid stimulating hormone (TSH) into bloodstream 3. Triggered by TSH, thyroid gland  thyroid hormones (T3 and T4) Negative feedback limits overall release Hormones released by the AnP 1. Thyroid-stimulating hormone (TSH) increases thyroid hormone release. 2. Adrenocorticotropic hormone (ACTH) controls production and release of adrenal cortex steroid hormones. • More on this later! Hormones released by the AnP 8 Gonadotropins influence the gonads: 3. Follicle-stimulating hormone (FSH) 4. Luteinizing hormone (LH) More on this in a bit Hormones released by the AnP Final two AnP hormones act directly on tissue and lack final gland/hormone 5. Prolactin stimulates milk production in females and is involved in parental behavior. 6. Growth hormone (GH) (somatotropin) influences growth, mostly during sleep. Anterior pituitary hormones Hypothalamic-pituitary-gonadal (HPG) axis Releasing hormone = gonadotropin releasing-hormone (GnRH) Tropic hormones – Two gonadotropins: follicle-stimulating hormone (FSH) luteinizing hormone (LH) Target gland  gonads Gonads Gonads (AKA sex glands or reproductive glands) Female gonad  ovary Male gonad  testis Gonadotropin actions in gonads Gonadotropins perform two main functions in the gonads • Gamete (sex/reproductive cell) production • • ova (female) or sperm (male) Sex hormone production and release • androgens, estrogens, progestins Gonadotropin actions in the testes FSH  governs sperm production in Sertoli cells LH  stimulates production of testosterone (T) from Leydig cells Sex-specific effects of testosterone Promotes development of male secondary sex characteristics Can trigger changes in appearance and behavior Gonadotropin actions in the ovary FSH  stimulates ovacontaining follicles, secretion of estrogens (most importantly estradiol) LH  triggers rupture of follicles, releasing ovum • Follicles form corpora lutea  secrete progestins (primarily progesterone) Estrogen Promotes development of female secondary sex characteristics Progesterone “hormone of pregnancy”, prepares and maintains uterus for pregnancy In primates, without implantation of fertilized egg, progesterone levels fall • Triggers menstruation – discharge of blood/tissue from uterus lining Ovulatory/menstrual cycles Female gonadal hormones produced in tightly regulated ovulatory cycles • • Vary in length by species (humans – 4 weeks, rats – 4 days) Ovulation – release of the ovum Overview of the menstrual cycle Follicular phase – growth of follicles (controlled by FSH). Estrogen levels increase over time Ovulation – follicles rupture (triggered by LH), releasing ovum • Only time you can pregnancy can occur* Luteal phase – corpus luteum secretes progesterone, uterine wall thickens to support implantation of the ovum, pregnancy Menses/menstruation – uterine lining is shed Hormonal and neural systems interact to produce integrated behavior Ringdove courtship behavior shows four types of system interactions • Neural to neural • Neural to endocrine • Endocrine to endocrine • Endocrine to neural End of material for Exam 1 Your action items (9/19) PRA2 due at the start of lab this week! Exam 1 is next Thursday Covers Topics 1-6 (2 covered, but de-emphasized) • Neuroanatomy Exam grades posted this evening at 5 pm Final make-ups today • Coming Up: Thursday: T7 - Sensory Systems • Tuesday, 9/26: T8 – The Motor Hierarchy • Thursday, 9/28: Exam 1 • Your action items (9/21) Thursday lab: PRA2 due at the start of lab Exam 1 is in one week! Covers Topics 1-6 (2 covered, but de-emphasized) • Quiz 2 grades coming (hopefully) tomorrow Tuesday would be a great time for one last quiz before Thursday’s exam! Coming Up: • • • Tuesday: T7 - Sensory Systems (not covered on Exam 1) Thursday: Exam 1 Tuesday 10/3: T8 – The Motor Hierarchy