BIO 1108 Exam 3 Study guide October 11 16 2013 The forms of communication between animal cells differ in the type of secreting cell and the route taken by the signal to its target Endocrine signals or hormones are secreted into extracellular fluids by endocrine cells or ductless glands and reach target cells via circulatory fluids Paracrine signals act on neighboring cells whereas autocrine signals act on the secreting cell itself Neurotransmitters also act locally but neurohormones can act throughout the body Pheromones are released into the environment for communication between animals of the same species In insects molting and development are controlled by PTTH ecdysteroid whose release is triggered by PTTH and juvenile hormone Coordination of signals from the nervous and endocrine systems and modulation of one hormone activity by another bring about the precise series of developmental stages that lead to an adult form Distinct cellular responses are associated with water soluble and lipid soluble hormones Polypeptide hormones and most amine hormones are water soluble and bind to receptor embedded in the plasma membrane Binding to water soluble hormones to the cell surface receptors triggers intracellular signal transduction leading to specific responses in the cytoplasm or changes in gene expression In contrast steroid and thyroid hormones are lipid soluble and readily enter target cells There they bind to specific protein receptors in the cytosol or nucleus These complexes of a lipid soluble hormone and its receptors act in the nucleus to regulate transcription of specific genes The same hormone may have different effects on the target cells that different receptors for the hormone or different signal transduction pathways Local regulators which carry out paracrine and autocrine signaling included cytokines and growth factors proteins peptides nitric oxide gas NO and prostaglandins modified fatty acids Hormone pathways may be regulated by negative feedback which dampens the stimulus or positive feedback which amplifies the stimulus and drives the response to completion Negative feedback pathways sometimes occur in antagonistic pairs such as the maintenance of glucose homeostasis by glucagon from alpha cells of pancreas and insulin from beta cells of the pancreas Insulin reduces blood glucose levels by promoting cellular uptake of glucose glycogen formation in the liver protein synthesis and fat storage The disorder diabetes mellitus which is marked by elevated blood glucose levels results from inadequate production of insulin type 1 or loss of responsiveness of target cells to insulin type 2 BIO 1108 Some neurosecretory cells in the hypothalamus produce hormones secreted by the posterior pituitary Other hypothalamic cells produce hormones that are transported by portal vessels to the anterior pituitary where they stimulate or inhibit the release of a particular hormones The two hormones released from the posterior pituitary act directly on non endocrine tissue Oxytocin induces uterine contractions and release of milk from mammary glands and antidiuretic hormone ADH enhances water reabsorption in the kidneys Often anterior pituitary hormones act in a cascade In the case of thyrotropin or thyroid stimulating hormone TSH TSH secretion is regulated by thyrotropin releasing hormone TRH TSH in turn induces the thyroid gland to secrete thyroid hormone a combination of the iodine containing hormones T3 and T4 Thyroid hormone stimulates metabolism and influences development and maturation Hormones sometimes acquire distinct roles in different species over the course of evolution Prolactin stimulates milk production in mammals but has a diverse effect in different vertebrates Melanocyte stimulating hormones MSH influences skin pigmentation in some vertebrates and fat metabolism in mammals Although prolactin and MSH act on non endocrine targets most anterior pituitary hormones are tropic acting on endocrine tissues or glands to regulate hormone secretion Tropic Hormones of the anterior pituitary include TSH follicle stimulating hormone FSH luteinizing hormone LH and adrenocorticotropic hormone ACTH Growth hormones GH has both tropic and non tropic effects It promotes growth directly has diverse metabolic effects and stimulates the production of growth factors by other tissues Parathyroid hormone PTH secreted by the parathyroid glands causes bone to release Ca2 into the blood and stimulates reabsorption of Ca2 in the kidneys PTH also stimulates the kidneys to activate vitamin D which promotes intestinal uptake ofCa 2 from food BIO 1108 Calcitonin secreted by the thyroid has the opposite effects in the bones and kidneys as PTH Calcitonin is important for calcium homeostasis in adults of some vertebrates but not humans In response to stress neurosecretory cells in the adrenal medulla release epinephrine and norepinephrine which mediate various flight or fight responses The adrenal cortex releases glucocorticoids such as cortisol which influences glucose metabolism and the immune system as well as mineralocorticoids primarily aldosterone which helps regulate salt and water balance Although the adrenal cortex produces small amounts of sex hormones the gonads testes and ovaries produce most of the body s sex hormones All three types androgens estrogens and progestin are produced in males and females but in different proportions The pineal gland located within the brain secretes melatonin which functions in biological rhythms related to reproduction and sleep Release of melatonin is controlled by the SCN the region of the brain that functions as a biological clock October 18 21 2013 Animal reproduce either asexually or sexually Sexual reproduction requires the fusion of male and female gametes forming a diploid zygote Asexual reproduction is the production of offspring without gamete fusion Fission budding fragmentation with regeneration and parthenogenesis are mechanisms of asexual reproduction in various invertebrates Facilitating selection for or against sets of genes may explain why sexual reproduction in various vertebrates Although most animals reproduce exclusively sexually or asexually some alternate between the two Variations on these two modes are made possible through parthenogenesis hermaphroditism and sex reversal Hormones and environmental cues control reproductive cycles Fertilization can occur externally or internally with regard to the mother s body In either case