Notwithstanding the sub-optimal characteristics of reclaimed water, in particular for the high CaCl 2 content, the scarcity of good quality water forces its use as an alternative water supply especially for irrigation. To this aim, being characterized by high adaptability to salinity, ornamental shrub and bush species could provide an interesting model to study the effects of salty wastewater use in plants Acosta-Motos et al.
Ornamental shrubs, naturally present in coastal arid and semiarid areas, as well as in marginal soils, are, in fact, endowed with unique morpho-anatomical, physiological and biochemical traits which allow them to cope with salinity, while maintaining good growth rate and abundant flowering, and therefore preserving their ornamental value Tattini et al.
Notwithstanding several studies have been performed to assess the physiological responses of these ornamental species to NaCl Lippi et al. Indeed, it is difficult to discriminate among plant responses due to osmotic and ionic stresses. Since osmotic stress is always proportional to salt concentration, iso-osmotic solutions of different salt types may trigger the same plant growth and physiological responses due to osmotic unbalance, still causing ion-specific stress effects linked to salt type and genotype-specific sensitivity Pagter et al.
Thus, it is of great importance to elucidate the biochemical, physiological and anatomical mechanisms of adaptation of potted C. The responses of the two species to the two chloride salts were analyzed in terms of growth parameters, leaf gas exchange, photosystem efficiency, water relations and leaf functional anatomical traits. To achieve a comprehensive and integrated interpretation of all data, we applied tools of multivariate statistics, whose usefulness has been recently proved in horticultural species, including ornamentals, in response to salinity concentration Rouphael et al.
The knowledge gained from this study could be used as a meaningful approach to discriminate between osmotic and ionic stresses responses in plants under salt stress conditions, in addition to provide practical specialist skills for the alternative re-use of reclaimed water for xeriscaping of urban, industrial and marginal areas of Mediterranean countries.
Rooted cuttings of 2-year-old Callistemon citrinus and Viburnum lucidum , purchased from a specialized nursery Vivaio Torsanlorenzo, Ardea, Italy , were transplanted on March 12 into 1. The pots were placed on 1. For both ornamental species, the experiment treatments consisted of three nutrient solutions, a basic nutrient solution control non-salt treatment and two saline nutrient solutions obtained by adding 80 mM NaCl or The study was performed in terms of equimolar concentrations of the two different chloride salts, in order to assess the salt-specific influence.
Treatments were arranged in a completely randomized blocks design CRBD with four replicates per treatment. The first and last plant of each experimental unit were considered as guards. The quality of the irrigation water was typical of the area and characterized by a high bicarbonate concentration 5.
Values of the pH and EC of the irrigation water were 7. The composition of the basic nutrient solution non-salt control used to replenish nutrients absorbed by plants was as follows: The irrigation water 0.
The saline nutrient solutions had the same basic composition, plus an additional 80 mM NaCl or The pH in the three nutrient solutions was 6. Saline treatments started on March 25 12 days after transplanting, 12 DAT. The nutrient solutions in all treatments were pumped from independent tanks through a drip irrigation system, with two emitters per plant at a flow rate of 2 L h -1 each.
Irrigation timing varied from 2 to 4 fertigations per day of 1—3 min. For both C. At the end of the trial DAT , four plants per experimental unit were harvested and dissected into leaves, stems and roots.
The total leaf area per plant was measured using an electronic area meter Li-Cor, Li-Cor, Lincoln, NE, United States , and the number of leaves as well as the plant height were also recorded. Dried plant organs were then sampled for ion analyses.
Lastly, the relative growth rate g g -1 day -1 was calculated using the equation reported by De Groot et al. Measurements were made by avoiding major veins, leaflet margins and damaged areas. Twenty leaves were randomly measured and averaged to a single SPAD value per each replicate. On the same date, measurements of leaf gas exchanges and chlorophyll a fluorescence emission were conducted within 2 h across solar noon i.
PAR, R. Fluorescence measurements were also performed on six replicates per each treatment. For the chlorophyll a fluorescence emission measurements, a portable FluorPen FPmax fluorometer, equipped with a light sensor Photon System Instruments, Brno, Czechia was used.
For the fluorescence measurements in the light, the fluorometer FluorPen FPmax was equipped with an open leaf-clip suitable for measurements under ambient light. Stem water potential was measured using the pressure chamber series portable plant water status console, Soil Moisture Equipment Corp. The stem water potential measurement was made at midday i. Nitrogen total N concentration in leaf and root tissues was determined after mineralization with sulfuric acid in the presence of potassium sulfate and a low concentration of copper by the Kjeldahl method Bremner, The mixture was centrifuged at rpm for 10 min R M, Remi Elektrotechnik Limited, India , then filtered through a 0.
Anions and cations in both C. On the same date of the physiological and biochemical measurements DAT , leaves of both C. Each leaf was dissected to remove the apical and basal portions, and dividing the median region of the lamina into two sub-samples: one for stomata analysis, the other for mesophyll characterization through thin sectioning.
Stomata characterization was performed on both adaxial and abaxial lamina surfaces in C. The slides were observed under an epi-fluorescence microscope BX60, Olympus, Hamburg, Germany equipped with a Mercury lamp, band-pass filter — nm, dichromatic mirror nm and above, and barrier filter nm and above.
Such filters allow highlighting stomata among epidermal cells, owing to the different excitation and emission properties of various compounds that make visible the guard cells, especially the thickened inner cell wall at the stomata aperture level Ruzin, ; De Micco et al. Images of the lamina surface, from three separate regions avoiding main veins, were collected by means of a digital camera CAMEDIA C, Olympus , taking care to avoid veins.
The following parameters were measured through the software program AnalySIS Sections were analyzed under a transmitted light microscope BX60, Olympus, Germany and digital images were collected and analyzed, as reported above, to quantify some functional anatomical traits, including: thickness of leaf lamina TLL , palisade and spongy parenchymas TPP and TSP , measured in five positions of the leaf lamina avoiding veins; quantity of intercellular spaces in the spongy parenchyma ISS - expressed as the percentage of tissue occupied by intercellular spaces over a given surface, in six positions of the leaf lamina; De Micco et al.
ISS was not measured in C. Principal component analysis PCA was also conducted using Minitab The PCA outputs included treatment component scores as well as variable loading to each selected component Ciarmiello et al.
The growth parameters plant height and number of leaves per plant and biomass production decreased under salinity independently of the type of salt in both ornamental species, with a particular significant detrimental effect of CaCl 2 on C. Citrinus Table 1. Specifically, in C. The lowest biomass production observed in C.
Moreover, in V. Table 1. Table 2. Similarly to the effects on plant growth parameters, the total leaf area and net CO 2 assimilation rate P n in C. Furthermore, the addition of 80 mM NaCl or Moreover, it is worth noting that no significant difference among the physiological parameters was recorded in V. The chlorophyll a fluorescence analysis evidenced significant differences in photochemistry among salt treatments between C.
Table 3. Table 4. Effects of salt treatment in the nutrient solution on macronutrients, sodium, chloride and potassium-to-sodium ratio of leaves and roots of potted Callistemon citrinus and Viburnum lucidum plants. The application of Similarly, to C. Our results also showed that CaCl 2 elicited a significant increase in Cl - concentration in both leaves and roots, 4.
TLL was decreased by both salinity treatments Table 5. Table 5. The application of 80 mM NaCl or Finally, no significant differences among salt treatments were observed for both SF avg. A heat map providing the morpho-anatomical, biochemical and physiological changes of potted C. The heat-map identified two main clusters in both ornamental species, which, however, divided the analyzed samples differently Figure 1. For instance, in C. Our results indicated that while in C.
In particular, CaCl 2 treatment clustered separated from the other two treatments in C. On the other hand, the two equimolar concentrations of NaCl and CaCl 2 clustered separated from control treatment in V.
Figure 1. Cluster heat map analysis summarizing potted Callistemon citrinus A and Viburnum lucidum B responses to non-saline, NaCl and CaCl 2 salinity treatments performed in terms of equimolar concentrations.
Figure 2. Principal component loading plot and scores of principal component analysis PCA of morpho-anatomical, biochemical, physiological parameters and ion contents and partitioning of potted Callistemon citrinus A and Viburnum lucidum B grown under non-saline, NaCl and CaCl 2 salinity treatments. In the current experiment, the score plot of the PCA superimposed on the above matrix of variables in both species revealed strong clustering of the three nutrient solutions, with C.
Particularly, the C. The lower right quadrant included C. Finally, in V. The two ornamental shrubs, C. In spite of the imposed iso-osmotic salinity of the compared treatments, the effect of To the best of our knowledge, there are no comparative studies on the responses of ornamental shrubs to iso-osmotic saline irrigation with NaCl and CaCl 2 , whereas only few reports on vegetable species are available on the CaCl 2 salinity Colla et al.
In particular, 40 mM CaCl 2 significantly reduced the root, stem and leaf dry weight of saffron plants compared to control Rabhi et al. The two ornamental species differently responded to the salinity treatments in the ratio between below- and above-ground biomass. Indeed, the increase in root to shoot ratio is a frequently detectable response to salt stress, more related to the osmotic effect than to a salt-specific effect Hsiao and Xu, In fact, V.
This suggests the existence of an inclusion mechanism similar to that adopted by other Mediterranean ornamental plants under salinity Navarro et al. Indeed, the compartmentalization of toxic ions as cheap osmotica in the vacuole and the synthesis and accumulation of osmolytes in the cytosol are essential mechanisms of osmotic adjustment and oxidative stress protection in plant cells Carillo, ; Ferchichi et al.
Acosta-Motos et al. The ability of C. Notwithstanding the higher ability of C. Thus, the concentrations of available PO 4 3- tended to strongly decrease in C. Based on our data, dark reactions of photosynthesis might be supposed more sensitive than light reactions to different salt treatments: gas exchanges evidenced a significant decline in net photosynthesis, stomatal conductance and transpiration for both species under NaCl as well as CaCl 2 treatments compared to unstressed controls accompanied by the reduction of SPAD index and leaf area.
Consistently with the data obtained for plant growth, in C. The stronger decline of photosynthesis observed under CaCl 2 treatment was not accompanied by an equally strong reduction in stomatal conductance. This latter, occurring at the same extent in both the saline treatments was not able to explain alone the dramatic reduction in the leaf photosynthetic rate.
The lower photosynthesis induced by salt treatments may be also a direct consequence of the salt-induced reduction of leaf lamina thickness: indeed, the area-based photosynthetic capacity is directly proportional to leaf thickness Wyka et al. However, while C. Indeed, the occurrence of more frequent but smaller stomata, exerting a better control of stomatal aperture, has been recorded also in other ornamental species subjected to salinity stress Carillo et al.
On the contrary, in V. Such common tendency of variation in V lucidum plants in response to the two salt types is maintained also in structural adjustments. The occurrence of thinner lamina under both salt treatments is not due to a reduction in the thickness of the palisade parenchyma, thus indicating the maintenance of the main tissue devoted to photosynthesis.
However, the occurrence of less intercellular spaces at the spongy tissue level would also indicate the occurrence of changes in the mesophyll resistance Sack and Frole, The increase in the amount of intercellular spaces has often been linked with the ability to cope with salinity by improving the CO 2 diffusion in the mesophyll, thus compensating for salinity-induced increased stomatal limitations Acosta-Motos et al. The slightest effects exerted by NaCl on the photochemistry of C.
Gochnatia polymorpha Less. Cabrera Asteraceae changes in leaf structure due to differences in light and edaphic conditions. Acta Botanica Brasilica 24 3 Comparative anatomy of the vegetative organs of the Hedera helix L. Scientific Papers Cooling effect of Sedum sediforme and annual plants on green roofs in a Mediterranean climate. Ceres Publishing House, Bucharest. Green roof plants: a resource and planting guide. Comparative morphological and anatomical studies of leaves, stem, and roots of Selinum vaginatum C.
Clarke and Selinum tenuifolium Wall. Altitudinal changes in leaf hydraulic conductance across five rhododendron species in eastern Nepal. Terashima I, Hikosaka K Comparative ecophysiology of leaf and canopy photosynthesis.
Plant Cell and Environment — Responses of tree species to heat waves and extreme heat events. Plant Cell and Environment Plant survival and growth on extensive green roofs: A distributed experiment in three climate regions. Ecological Engineering Stomatal conductance increases with rising temperature. Plant Signaling and Behaviour 12 8 :e The role of green roof technology in urban agriculture. Renewable Agriculture and Food Systems 27 4 Wolf D, Lundholm JT Water uptake in green roof microcosms: Effects of plant species and water availability.
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Announcements Article numbers instead of traditional pagination Publication frequency quarterly starting from and impact factor Go to previous slide Go to next slide. Homoeothermic animals have a thermo-neutral zone which is the range of ambient temperatures in which animals require minimal energetic expenses that do not compromise body reserves to maintain a constant body temperature basal metabolic rate.
This zone is specific for each species, but varies among breeds and genetic lines 1,2. Another factor is the thermal comfort zone. Unlike in humans in which the concept is very subjective "condition of mind in which it expresses satisfaction with the ambient temperature" 8 , in animals the concept is well defined as the range of temperature and relative humidity in which an animal is comfortable and its metabolic and physiologic processes are stable and directed to storage of carbohydrate, proteins and fat 2,9, There are several indices to predict with some precision whether the environment is a potential heat stress factor for the animal.
The most useful factors are shown in Table 1. Conceived at the beginning as an indicator of thermic comfort in humans, later it was shown to be useful for animals of production as well.
However, some researches, like Silva and collaborators, did not find any correlation between THI, temperature and respiratory rate, whereby it is possible that under some environmental conditions, like in the neotropics, this index might not be useful The BGHI temperature and humidity index also takes into account radiation, being more useful when people are evaluating thermic stress in grazing animals that are in tropical regions This index combines temperature, humidity and wind velocity ETI shows representative results to heat exposition in short time periods, common in summer season in some warm regions.
However, Silva and collaborators in a study on Holstein and Jersey cows in an equatorial region showed that ETI is one of the best indexes for tropical conditions, because it has significant correlations with corporal temperature and respiratory rate Silva and collaborators suggested in that it is important to consider not only temperature and humidity, but also thermic radiation and airflows, to make thermic stress indices suitable to environmental conditions and the kind of animal they are evaluating.
For the evaluation of open air environment, in the case of grazing animals, it should seem that all of the variables are possible, both in environment and in physiological variables. In fact, the animal performance is the combination result of most of those variables. Some of those variables are complex and can change with time.
Temperature values out of the thermo-neutral range zone are defined as superior critical temperature and inferior critical temperature. In these temperatures homoeothermic animals have to adjust their metabolism to regulate their body temperature When early adaptive responses do not compensate for changes in temperature, animals could be affected by thermal stress, also called caloric stress.
Thermal stress is the activation process of physiological mechanisms in order to respond to thermogenic and thermolytic events. These responses are known as physiological responses to stress and they involve the activation of neuroendocrine pathways. If those responses are sustained for extended periods of time chronic stress , the animals' production trait variables can be affected, causing a decrease in the efficiency of the production systems such as milk production, rate of growth and level of physical activity 1.
Physiological responses to thermal stress in animals include the activation of endocrine, autonomic and central nervous systems, as well as cardiovascular mechanisms for redistribution of blood flow.
All of them act in a synergic way depending on the magnitude of the stressor factor and they respond to it by generating physiological mechanisms to suppress or decrease the threat of the adverse effects of thermal stress The objective of this review is to explain the physical and physiological responses of mammals to thermal stress, like biological environment adaptation strategy, identifying the weak points in our knowledge.
Thermal energy in animals is transferred across gradients, i. When ambient temperature increases above the comfort zone, it is transferred to the animal. In response to this, there is an increase in body temperature. On the contrary, when ambient temperature decreases below the comfort zone, the animal will suffer from a loss of caloric energy due to shivering or other responses to maintain body temperature 1, Several routes exist for the loss or gain of thermal energy in animals figures 1 and 2 : conduction, convection, radiation and evaporation.
Conduction is the transfer of heat by direct contact between any surface and the animal. It is characterized by the generation of variations in kinetic energy in cold molecules caused by other molecules. When ambient temperature increases, animals have to cope with thermal discomfort, so they change their behavior by modifying the posture of their bodies to allow direct contact with cooler surfaces like floor or walls in order to transfer thermal energy from themselves to those surfaces; this dissipates heat and decreases body temperature.
It is the transference of thermal energy by the movement of air or water. Air and water can absorb heat by the redistribution of their particles. In animals, convection is carried out between skin and air by evapotranspiration, also known as sweating or panting It is the exchange of thermal energy between two objects or animals which are not in contact through the transference of electromagnetic waves.
Exchange of heat by radiation between an animal and its environment is achieved in accordance to the Stefan-Boltzman law, which establishes that the capacity of a black body to gain thermal energy by radiation is proportional to the fourth power of its absolute superficial temperature T 4 in Kelvin grades.
An example of radiation is thermal energy reflected by the soil and gained by the animal 1, Water has a high specific heat, so when it evaporates as sweat, animals experience a decrease in body thermal energy. This process is favored over convection In the process of caloric transference by evaporation of water molecules, each gram ofwater sweat absorbs 0.
It is the most effective process for thermoregulation when ambient temperature is near body temperature 1, These ways of transference of thermal energy collaboratively participate in the context of environment-animal interaction to generate the thermal ambient of the animal at a given moment Figure 1 and 2.
However, adaptive responses of the animal before thermal stress are very dynamic in nature, as it is explained above. Surface area allows animals to dissipate or gain heat, and the greater the surface the greater the dissipation or gain in thermal energy.
There are differences in adaptation of thermal conditions between children and adults. Smaller blood volumes in children compared with adults, even relative to body size, may limit the potential for heat transfer during heat exposure and may compromise exercise performance in the heat.
Testosterone and prolactin are two hormones that differ in baseline levels between children and adults and may affect the function of sweat glands and the composition of sweat. These possible effects of testosterone and prolactin require further investigation Animals experience constant physiological changes in order to cope with diverse environmental situations thermal, social and location , which can activate neuroendocrine responses.
Stress leads to the activation of physiological mechanisms required to maintain homeostasis. Stress compromises important metabolic functions such as reproduction, immunity and growth 21, Stress can be classified as acute or chronic depending on whether the exposure to drastic changes in temperature is for a short or a long period of time. Both activate neuroendocrine pathways that modify physiological processes in order to maintain homeostasis to ensure survival of the animal Stress hormones, produced in response to an increase in environmental temperature, induce the following effects in animals: Mobilization of energy for maintenance of muscular and neural functions; increase in the perception of the environment; increase in brain perfusion for delivery of glucose; improvements in cardiovascular and respiratory functions; modulation of immune responses; decrease in reproductive and sexual functions; and decrease in appetite Neuroendocrine responses in animals submitted to stress are diverse and include release and activation of several tropic hormones like adrenocorticotropic hormone ACTH , thyrotrophic hormone TSH , somatotropic or growth hormone GH , follicle stimulating FSH and luteinizing LH hormones, and prolactin PRL Some functions of these hormones will be discussed.
Hans Selye 26 was the first person to describe the neuroendocrine responses of the body to stress. He suggested that when individuals were submitted to stressful situations, they activated the sympathetic nervous system SNS and HHAa triggered the so-called "general adaptation syndrome" 5,19,25, Activation of HHAa is initiated in the animal in response to changes in temperature that are outside of the thermal comfort zone of the species.
Those changes are initially perceived by the peripheral nervous system and then assimilated by the central nervous system, wherein the paraventricular nucleus of the hypothalamus is stimulated to release corticotropin releasing hormone CRH CRH is released into the hypothalamus-hypophyseal portal system to induct the synthesis and secretion of ACTH into the blood stream.
ACTH stimulates the zona fasciculata of the adrenal cortex to synthesize and secrete cortisol into blood to exert its physiological actions in target tissues muscle, liver and adipose tissue 17,28, Cortisol is a member of the steroid hormone family whose common precursor is cholesterol. It has been demonstrated that animals submitted to stress noise, physical perturbation or changes in ambient temperature have an increase in circulating concentrations of CBG and free cortisol.
This finding shows that the secretion of cortisol is one of the most important hormonal responses to stress The main physiologic effect of cortisol produced by a thermal stress is the mobilization of energy for the maintenance of muscular and neural functions. Cortisol directly influences metabolism and behavior in animals submitted to thermal stress. It affects glycogenolysis, lipolysis and proteolysis in order to provide the energy required to restore homeostasis figures 1 and 2.
High concentrations of cortisol in serum are associated with an increase in aggressive behavior in some animals 17, ANS is part of the nervous system that regulates body processes related to expenditure and storage of energy.
ANS is anatomically organized into preganglionic and postganglionic neuronal nets and it is physiologically divided into sympathetic and parasympathetic nervous systems The sympathetic nervous system responds to stressful situations. The sympathetic nervous system presents short preganglionic axons, emerging from the thoracolumbar spinal cord, and long postganglionic axons 32, Synapses between these two types of axons are mediated by neurotransmitter acetylcholine AC.
Some effects of AC are to induce vasodilatation of blood vessels in skeletal muscle and to activate sweating Synapses between postganglionic axons and target tissues are mediated by catecholamine, mainly neurotransmitter adrenaline, which induces the following effects: contraction of the spleen, tachycardia, hemodynamic modifications such as vasoconstriction of peripheral blood vessels, and decrease in gastrointestinal contractions 17,19, Liberation of adrenaline occurs in animals faced with acute stressful situations such as thermal changes and pain that lead to behavioral and physiological changes The thyroid gland produces triiodothyronine T3 and tetraiodothyronine or thyroxine T4 in response to stimulation by TSH produced by thyrotropic cells in the anterior hypophysis.
Both T3 and T4 are transported in serum by specific proteins due to their low solubility in blood. T4 is the precursor of T3, and T3 has the highest biological activity Thyroid hormones control cellular metabolism that favors oxygen consumption and energy generation needed for tissue activities.
Oxygen consumption in cells is related to increase in mitochondrial activity and generation of heat. High levels of thyroid hormones increase cellular respiration, ATP generation, cellular growth, cardiac and respiratory rates and catabolic pathways 36, In cases of thermal stress, secretion of releasing and tropic hormones is affected.
When an animal is subjected to high ambient temperatures, secretion of those hormones is inhibited in order to avoid thermogenesis. On the other hand, when an animal is subjected to ambient cold, those hormones are released to promote catabolic pathways that favor body thermogenesis. In this case, secretion of T3 and T4 is stimulated When stress is chronic, physiologic functions of T3 are decreased due to high levels of glucocorticoids that inhibit transformation of T4 in T3 Figure 1 and 2 This is a hormone synthesized and secreted by supraoptic and paraventricular hypothalamic nuclei into the blood stream and transported to target tissues.
It is also known as vasopressin due to its regulatory effect on blood pressure. ADH is a vital hormone for water homeostasis in a thermal stress event as its main function is to reabsorb water in the kidney. However, the pattern of ADH secretion varies in accordance with the type of thermal stress In heat stress, thermolytic routes are activated for sweating and cooling via evaporation. Constant liquid losses stimulate baroreceptors in the atrium and greater blood vessels, as well as hypothalamic osmoreceptors, which induce ADH release to prevent dehydration.
There is an inhibition of ADH during cold stress which favors water loss by urination to avoid heat transference from tissues to water, generating polyuria Figure 1 and 2 These hormones are related to the maintenance of homeostasis for electrolytes.
RAA is activated when blood flow is reduced in the afferent arteriole of glomeruli of the kidney due to hypovolemia. Hypovolemia can result from dehydration as a consequence of high ambient heat.
The decrease in blood flow to the kidney induces secretion of renin from the juxtaglomerular apparatus. Once renin is produced, it stimulates the synthesis and secretion of angiotensin, which induces the synthesis and secretion of aldosterone from the adrenal cortex Aldosterone stimulates reabsorption of water and ions, principally sodium, in the kidney in order to avoid massive excretion of water and to maintain blood pressure.
In cold stress, sensitivity of the juxtaglomerular apparatus is inhibited, favoring water excretion polyuria Figure 1 and 2 22,36, Recent studies suggest that other hormones, like progesterone, insulin, oxytocin, androgens and estrogens, play a role in responses to thermal stress via undefined physiological mechanisms 5. Animals constantly interact with their environment.
Thermoconduction is a process by which animals can lose or gain thermal energy based on fluctuations in ambient temperature Physiological responses to thermal stress in animals depend basically on the nature of the temperature change outside the thermal comfort zone 7, Thus water is very important for thermoconduction and thermoregulation.
Animals are frequently affected by high ambient temperatures, increasing body temperature if the loss of intrinsic heat does not exceed extrinsic heat gain. Once thermal homeostasis is lost, animals activate physiological mechanisms to reestablish a dynamic balance 7. Peripheral vasodilatation of blood vessels. This is an increase in the body's total surface area of peripheral blood vessels to favor dissipation of thermal energy from an animal's body to its environment mediated via increased nitric oxide production 18, Hemodynamic changes.
Increase in cardiac output and blood flow to the skin optimizes caloric interchange with the environment 18, Activation of neuroendocrine responses.
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