Lecture 8 Flashcards
What is a hormone
A chemical, usually secreted by an endocrine gland, that is conveyed by the bloodstream and regulates distant target organs and tissues. These are slow, non-precise, but have more substantial effects on biology. Neurotransmission is precise. Endocrine gland: a gland that secretes hormones into the bloodstream to act on distant targets. Endocrine go into bloodstream. Exocrine go into ducts. Biphasic stress: slow hormonal response and fast neural response.
Four types of chemical communication
Endocrine communication: going into bloodstream to target cell. Pheromone: odor-based communication between two members of the same species. Allomone communication: odor-based communication between members of different species. Synaptic communication - same as before.
Major endocrine glands and their functions
Hypothalamus: control of hormone secretions. Pineal gland: reproductive maturation, body rhythms. Anterior pituitary: hormone secretion by thyroid, adrenal cortex, and gonads; growth. Posterior pituitary: water and salt balance. Thyroid: growth and development, metabolic rate. Pancreas: sugar metabolism. Gut: digestion and appetite control. Gonads: body development, maintenance of reproductive organs in adults.
Major classes
Amine, peptide, and steroid. Peptide and amine are fast.
Behavioral endocrinology
1) remove gland: finding that the central mechanism in the chicken/rooster was not in CNS but in the gland. 2) knockout - delete a gene for a given hormone. 3) Individual differences analyses via blood: not a lot of relationship between hormones and behavior. Autoradiography: inject radioactively labeled hormone, place tissue on photographic film to index which brain regions accumulated most labeled hormone. Immunocytochemistry: detects a particular protein in tissues, antibody recognizes and binds to protein, chemical methods localize proteins in tissue.
Hypothalamus, pituitary gland, and neuroendocrine cells
Hypothalamus - neural region central to homeostasis that links nervous system to endocrine system. Does thermoregulation, sex, stress, reproductive cycles, hunger. Pituitary gland - central endocrine gland, serves as a bridge between hypothalamus and periphery. All hormones in the body are modulated by this system. Neuroendocrine cell: neuron that releases hormones into local or peripheral circulation. They release hormones instead of neurotransmitters, bridge between nervous system and hormonal system.
Posterior pituitary
Releases oxytocin and vasopressin. The anterior pituitary drives a lot like sex and stress. Paraventricular - bind to neuroendocrine cells, posterior releases into capillaries that go into periphery.
Oxytocin
Implicated in a large range of maternal, social, and affiliative bonding. Lactation and the letdown reflex and uterine contractions during childbirth. Released during orgasm. In animals, it facilitates monogamy. Fuels trust and romantic attachment (in contrast to dopamine). Intranasal oxytocin elevates empathy, generosity, bonding, and in-group affiliation. It may elevate out-group distancing.
The regulation of hormones - a negative feedback circuit
Hypothalamus helps mediate the release of hormones, hormone released into bloodstream, hormone binds with hypothalamus and tells it there is enough hormone, so don’t need to release more. There are other nuclei involved in hormone regulation - hippocampus and cortisol.
Anterior pituitary
Front division of pituitary gland - secretes 6 tropic hormones. Neuroendocrine cell bodies in hypothalamus produce releasing hormones. Releasing hormones traverse the hypothalamic-pituitary portal system (set of veins between hypothalamus and pituitary gland) to control pituitary’s release of tropic hormones. Cells in anterior pituitary respond to releasing hormones by releasing/inhibiting release of their own hormones, known as tropic hormones. Tropic hormones travel through the bloodstream to regulate endocrine glands throughout the body. These are second hormones released.
Anterior pituitary order of events
Hypothalamus - releasing hormone (hypothalamic pituitary portal veins) - pituitary gland - tropic hormone - target endocrine gland - target hormone.
Two anterior pituitary hormones act on gonads
Gonads - testes or ovaries. Gonadotropin releasing hormone (GnRH) - hypothalamic hormone controlling release of FSH and LH from pituitary. This is the first hormone released. Gonadotropins (FSH and LH) - anterior pituitary hormone stimulates cells of gonads to produce sex steroids and gametes. Oral contraceptives. In males - sex steroids are androgens (testosterone) and gametes are sperm produced in testes. Sex steroids in women are progestins (progesterone) and estrogens (estradiol) and gametes are ova (eggs) produced in ovaries. Ovarian hormones produced in cycles - menstrual cycle (28 days in humans). Birth control is piggybacking on negative feedback loop, so you’re not releasing GnRH and not initiating the ovulatory cycle.
Neural circuits for reproduction in rodents
These are interesting to study when looking at sexual responsivity. Androgens act on hypothalamic medial preoptic area (mPOA) and medial amygdala in male rats. Estrogens affect neurons in ventromedial hypothalamus and periaqueductal gray (site of endogenous opiods) in female rats. Basal ganglia/ventral striatum is relevant to processing reward cues and dopamine transmission. Lordosis - female receptive posture in four-legged animals.
Human sexuality
In addition to areas activated in rodents, areas activated in humans include much of the cortex including the orbitofrontal cortex (reward sensitivity), ventromedial prefrontal cortex (reward sensitivity), parietal cortex, anterior cingulate cortex, and insular cortex (somatotopographic map of the body). Amygdala and prefrontal cortex shut down during orgasm (deactivation of amygdala in both men and women, deactivation of prefrontal cortex in women). Switch from parasympathetic to sympathetic during orgasm.
Male orgasm
Activation in mesolimbocortical dopamine circuit (ventral tegmental area, nucleus accumbens). Comparable to that induced by heroin. Male orgasm associated with deactivation of the amygdala.