#17. The endocrine system - Overview - In response to sights, sounds and other sensory stimuli, an animal’s nervous system sends rapid messages, in the form and action potentials, to precise locations in the body - In response to changes in external or internal conditions, cells in the CNS or the endocrine system release certain molecules. These molecules produce longer-term responses in a broad range of tissues and organs - The endocrine system is a collection of organs and cells that secrete chemical signals into the bloodstream. A chemical signal that circulates through body fluids and affects distant targets cells is called a hormone - A hormone may reach all parts of the body, but only specific target cells respond to specific hormones - A given hormone traveling in the bloodstream elicits specific responses from its target cells, while other cell types ignore that particular hormone - Hormones are broadcast throughout the body via the bloodstream, but they act only on cells that express the appropriate receptor. Target cells respond to a particular hormone because they contain a receptor for that hormone - The presence of an appropriate receptor dictates which cells will respond to a particular hormone (this is key in physiological studies) - Cell-to-cell signaling: An overview (Ch 49, pp 992-997) - Major categories of chemical signals (5 types, Ch 49, Summary table 49.1) - Autocrine signals: act on the same cell that secretes them - Paracrine signals: diffuse locally and act on nearby cells - Endocrine signals: are hormones carried between cells by blood or other body fluids - Neural signals: diffuse a short distance between neurons (i.e., neurotransmitters) - Neuroendocrine signals: are hormones released from neurons (i.e., neurohormones) - Hormone signaling pathways (3 types, Ch 49, pp 993-994, Figure 49.1) - The endocrine system and the nervous system act individually and together in regulating an animal’s physiology - Three types of hormone signaling pathways - 1. Endocrine pathway (direct from an endocrine cell): hormones are sent directly from endocrine cells to effector cells in response to stimulus-This is found in plants and some animals. There is not involvement of the CNS - In most of the cases, information about external or internal conditions is gathered by sensory receptors an then integrated by neurons in the CNS before the production of an hormonal signal - 2. Neuroendocrine pathway (direct from the CNS): Neurons in the CNS respond by releasing neuroendocrine signals that act on effector cells directly - 3. Neuroendocrine-to-endocrine pathway (CNS-to-endocrine system): Neurons in the CNS respond by releasing neuroendocrine signals that stimulate cells in the endocrine system, which respond by producing a hormone - All three types of signaling pathway are regulated by negative and positive feedback inhibition - In animal cell-to-cell signaling, feedback inhibition reduces production or secretion of the hormone, or both - What makes up the endocrine system? - Endocrine gland, organs that secrete a hormone into the bloodstream - Exocrine gland, organ that deliver secretion through outlets called ducts into a space other than circulatory system - Chemical characteristics of hormones - Three major classes of chemical that can act as hormones in animals - Polypeptides - Amino acid derivatives - Steroids - Steroids are lipid soluble, while polypeptides and amino acid derivatives are not (with the exception of T3 and T4)- see Figure 49.3 (Ch 49, pp 995) - What do hormones do? (Ch 49, 997-1003) - A single hormone can have multiple functions (e.g., PRL) - Different hormones may affect the same aspect of physiology - Hormones coordinate the activities of cells the three areas: - 1. Development, growth and reproduction - 2. Response to environmental challenges (stress) - 3. Maintenance of homeostasis - Some examples: - 1. Development, growth and reproduction - Metamorphosis (we can use examples of flatfishes) - Sexual development - 2. Response to environmental changes - How do hormone coordinate responses to stressors? - Short-term response to stress (fight-or-flight): epinephrine or adrenaline - Long-term response to stress: cortisol (glucocorticoid) - Long-term stress response is a compromise (e.g., reproductive dysfunction in captive fishes) - 3. Maintenance of homeostasis - Leptin and energy reserved - EPO and oxygen availability - Signal reception (Ch 11, pp210) - The presence of an appropriate receptor dictates which cell will respond to a particular hormone - Receptors are dynamic - Receptors can be blocked - Signal processing: how do hormones act on target cells? (Ch 11 pp2010-214; Ch 49, pp 1006-1010) - The important point about a signaling molecule is its ability to pass through lipid bilayer - Processing lipid-soluble hormones: - When lipid-soluble signals enter a cell, the information they carry is processed directly-without intermediate steps - Most lipid-soluble signaling molecules are able to diffuse across the hydrophobic region of the plasma membrane ad enter the cytoplasm of the target cells (Ch 11, pp 211, Figure 11.12) - Steroid hormones bind intracellular receptors (see figure 49.15 for steroid hormone action) - Steroid hormone-receptors complexes bind to specific sites in DNA called hormone-response elements (ERE) located in the 5’ direction from the start of the target genes - Because each hormone-receptor complex leads to the production of many copies of the gene product, the signal form the hormone is amplified - Warning: steroid may also mediate rapid non-genomic actions through membrane receptors (see links of interest) - Processing lipid-insoluble signals: - Large or hydrophilic signaling molecules are lipid insoluble and do not cross the plasma membrane. To affect a target cell, they have to be recognized at the cell surface (Ch 11, pp 211, Figure 11.13) - When a signaling molecule binds at the cell surface, it triggers signal transduction –the conversion of a signal from one form to other. A Long and often complex series of events ensues, collectively called a signal transduction pathway - The two major types of signal transduction and amplification systems are: - Signal transduction via G-protein-coupled receptors - When G protein are activated by a signal receptor, they trigger a key step in signal transduction: the production of a messenger inside the cell. They link the receipt of an extracellular signal to the production of an intracellular signal (second messenger, Fig. 11.14, pp 212) Examples of second messenger table (Table 11.2, Ch 11, pp 213) - Signal transduction via Enzyme-linked receptors - Enzyme-linked receptors transduce hormonal signals by directly catalyzing a reaction inside the cell (Fig. 11.15, Ch 11, pp 213) - Signal transduction pathways form a network. This complexity is important: it allows cells to respond to many different signals in an integrated way (Fig. 11.16, Ch 11 pp215) - The same chemical messenger can trigger different responses in cells from different organs or in cells at different developmental stages. The reason for that is that the cells contain different receptors, second messenger, protein kinases, enzymes or transcriptionally active genes (Ch 49, pp 1010) - Endocrine disruptors (Ch 49, pp 999-1000): Introduction to guest speaker (Jim West) - Links of interest - Fight or flight response by Bozeman Science https://www.youtube.com/watch?v=m2GywoS77qc - Steroid-hormone rapid actions, membrane receptors and a conformational ensemble model http://www.nature.com/nrd/journal/v3/n1/pdf/nrd1283.pdf - Signal transduction pathways by Bozeman Science-he ONLY explains the functioning of the G-protein-coupled receptors https://www.youtube.com/watch?v=qOVkedxDqQo - G-protein coupled hormone signal transduction https://www.youtube.com/watch?v=A3AUhMCE9n0 - Common second messengers http://www.ncbi.nlm.nih.gov/books/NBK21205/figure/A2051/?report=objectonly -Physiological changes in fish from stress in aquaculture with emphasis on the response and effects of corticosteroids http://www.sciencedirect.com/science/article/pii/095980309190019G #18. Guest Speaker: Jim West / Lyndal L. Johnson on endocrine disrupters in Puget Sound #19. Case studies: Physiological and behavioral mechanisms in the intertidal zones - Overview (Book: Marine Biology: An Ecological Approach, pp 266-334) - Environmental conditions in intertidal zones - The intertidal zone accounts for the smallest area of the world’s ocean, but it is the best known (most accessible to humans) - The intertidal zone has the greatest variation in environmental factors of any marine area -1. Tides - Tides have two direct effects on organisms - The first effect involves the duration of exposure to the air. Since the organisms are primarily marine, the longer the organism is exposed to the air, the greater is the chance that they will become desiccated beyond their limits of tolerance. Intertidal organisms differ in their tolerance to exposure, and this difference contributes to their patterns of distribution - The second effect is the result of the time of day that exposure air occurs. Exposure to air during midday in the tropics could lead to lethal temperatures; exposures at night in the cold temperate zones in winter could lead to the organism’s freezing to death - We might expect a greater diversity of organisms in the intertidal zone of a tropical area where low tides regularly occur during the night of during the early morning than in an area where they occur at mid-day - In cold-temperate zones, the reverse would be true - In addition, the greater predictability of tides induces certain rhythms, such as feeding and reproduction, in intertidal organisms -2. Temperature - Air temperatures always have a greater range that water temperatures, and extremes may either kill organisms or weaken them, making them susceptible to death by other factors, such as desiccation - Daily exposure to temperature fluctuations of as much as 20C is not uncommon in many rocky intertidal habitats - The temperatures experiences by intertidal organisms differ dramatically among habitats types: organisms on open rock surfaces face the largest temperature fluctuation, while organisms living under seaweeds or marsh grasses are buffered from extreme temperature fluctuations (Figure 6.4 –The influence of intertidal habitats on the temperature experienced in the intertidal zone) Ice can have significant effect on intertidal organisms on far northern or southern shores - It has been proposed that this disturbance might explain the absence from New England rocky shores of long-lived organisms otherwise common on intertidal shores unaffected by ice -3. Wave action - Wave action directly affect organisms in two ways - First, on sedimentary shores it moves the entire substrate around, in the process smashing organisms and tearing them apart. Hence, any creatures that live there must be adapted to this force in some way - Second, waves throw water higher on the shore than the water level due to tides; therefore, wave action allows marine organisms to live higher than the tides would permit them to. These organisms experience temperatures extremes and effect of desiccation - 4. Salinity - Salinity may change in the intertidal zone in two ways - First, the intertidal zone may be exposed at low tide and subsequently flooded with fresh water from runoff of heavy rains - The second concerns to tide pools –areas that retain SW at low tide. Tide pools may be flooded with freshwater runoff and thus increase their salinity, or may show increase of salinity due to evaporation during the day. - General physiological and behavioral adaptations of intertidal organisms - 1. Resistance to water loss (dehydration tolerance) - When intertidal organisms are exposed to air during low tides, they begin to lose water by evaporation Mechanisms to reduce water loss until an external supply of water become available again (see Figure 6.7, pp 273) - The simplest mechanism for avoiding water loss is seen in mobile animals. These animals simply move from the expose surface areas of the intertidal zone into moist crack, crevices, or burrows where eater is available -actively selecting suitable micro-habitats - Living in dense groups decrease decreases water loss - Living in association with seaweed canopies that buffer individual from water loss - Closing shells - Some anemones cover themselves with shell fragments - Production of mucus that reduces water loss (anemone Actinia, and hydroid Clava squamata)-See a very interesting paper on the applications of the mucus of Actinia equina on links of interest. Burrow in the substrate - Body systems that tolerate considerable water loss during hours - Most high intertidal animals can withstand a remarkable amount of desiccation - Chitons can tolerate a 75% water loss - Intertidal algae Porphyra, Fucus and Enteromorpha cannot move and have no mechanisms for avoiding water loss. They can tolerate as much as 60-90% loss of water. See Tolerance to oxidative stress induced by desiccation in Porphyra columbina, in links of interest-We can use some time to explain this paper in class, or use it as a complementary activity - Effect of desiccation in seaweed (see Seaweed ecology and Physiology book, Ch 7, pp 333-336) - During emersion photosynthesis rate drops –This is because the inorganic carbon supply is greatly restricted; a small amount of bicarbonate in the surface film of water on the seaweed is available for photosynthesis but it is not quickly replenished (CO2 in air 10-fold lower than bicarbonate in water) - 2. Maintenance of heat balance - Intertidal organisms that are exposed to extremes of heat and cold show behavioral and structural adaptations to maintain their internal heat balance - Avoid high temperatures by reducing heat gain from the environment: - Have a relatively large body size compared to similar species either lower in the intertidal zone or in the subtidal zone –A large body size means less surface to volume and less area for gaining heat (large snails commonly live at higher shoreline elevation than smaller individual that are more vulnerable to gain heat - Reduce the area of body tissue in contact with the substrate –This is hard for many species, as they need attachment to the substrate (waves) - Increase heat loss from their bodies: - In mollusks greater elaboration of ridges and other sculpturing on the shell –Ridges and sculpturing act as a radiators and facilitate heat loss by convection. In Tectarium muricatus and Nodilittorina tubercular, both of which have strongly sculptured shells, the shell temperatrure is approximately 0.5 C lower than that of the substratum. In contrast, the difference between the shell surface temperature and that of the substratum in weakly ribbed forms such as Littorina lineata is significantly less - Dark-colored bodies gain and lose heat by radiation more rapidly than light-colored ones –Many tropical and subtropical snails of the high intertidal zone, are much lighter in color that their lower-level relatives; presumably their coloring slows the heat gain - 3. Mechanical stress - Wave action reaches its maximum in the intertidal zone. As a result, it is necessary for any organism that live intertidally to adapt to resist the smashing and tearing effect of waves. - Animals: - Limitation of size and shape: small, squat bodies with streamlined shapes that minimize their exposure to the lift and drag of wave forces - Bigger animals can compensate it with additional means of attachment - Byssal gland in bivalve mollusks - Enlarge foot that clamps to the substrate - Sponges develop a denser body walls in wave-exposed than in wave-protected habitats - Motile organisms have no structural mechanisms to resist being swept away and survive because they seek shelter form the waves in crevices or under rocks - Seaweed - In contrast, intertidal algae are often large and cope with wave stress by being flexible and bending toward the substrate as the waves pass over, thereby minimizing their surface area that is contact with the waves (Figure 6.9) - 4. Respiration - Since most of animals inhabiting the intertidal zone are marine, they have respiratory surfaces or gills to extract O2 from the water - These respiratory structures are highly susceptible to desiccation in air and do not function well unless they are submerged in water - Among intertidal organisms there is a tendency to enclose the respiratory surfaces in a protective cavity to prevent them from drying - Other adaptation is the reduced-size gill and the formation of a mantle cavity which serves a lung-like structure for aerial respiration Protect respiratory structures by close up or clamp down - Many intertidal fishes often are specialized for cutaneous respiration through the reduction if gills and the proliferation of blood vessels in the skin - Some studies suggest that many fishes may satisfy over half their O2 needs by gas exchange through the skin - 5. Feeding - All internal animal must expose the fleshy parts of their bodies in order to feed - For those on hard substrate, this means exposing those parts most susceptible to desiccation –As a result, most diurnal rocky intertidal animals are active only during the time the tide is in and they are covered with water - Organisms living in soft substrates are often protected by water saturated substrates and may be active feeders during low tides - 6. Salinity stress - Osmotic stress, either low salinities (heavy rains) or high salinity (evaporation during low tides) - Very stressful environment - The vast majority of the organisms in the intertidal zone are invertebrates and therefore osmoconformers. Many osmoconformers, such as starfishes and sea urchin, that inhabit intertidal habitats cannot tolerate large fluctuations in salinity and die in masse after heavy rains - 7. Reproduction - Because so many intertidal organisms are sedentary or sessile, many rely on external fertilization and have planktonic larvae or free-floating eggs that disperse and live in the water column - To increase their chances of fertilization they form aggregations before releasing their gametes - Many of the mobile intertidal organisms, such as crabs and snails, reproduce by internal fertilization - Other reproductive adaptation is include breeding cycles that are synchronized with the tides –An example is Mytilus edulis, is which gonads mature during periods of spring tides and spawning occurs on subsequent neap tide. In this case synchronized spawn increase chances of fertilization - Links of interest - Tolerance to oxidative stress induced by desiccation in Porphyra columbina http://jxb.oxfordjournals.org/content/62/6/1815.full.pdf+html - The mucus of actinia equine (Anthozo, cnidaria): An unexplored resource for potential applicative purposes –This is an easy-to-read, pretty interesting paper http://www.ncbi.nlm.nih.gov/pubmed/26295400