Toxicol Open Access 3: J Steroids Horm Sci 8: J Adv Dairy Res 4: J Preg Child Health 3: J Nurs Care 5: Mol Biol 6: J Fisheries Livest Prod 4: J Neurol Disord 3: J Aquac Res Dev 4: J Clin Exp Pathol 7: Anat Physiol 7: Endocrinol Metab Syndr 5: Clinics Mother Child Health Med Chem 5: J Neurol Neurophysiol 6: J Diabetes Metab 2: Pharm Anal Acta 7: J Cytol Histol 5: Effect of Subchronic Fe Overload.
Bioenergetics 5: e J Fund Renew Energ Appl 7: J Environ Anal Toxicol 4: Wakaskar RR, Bathena SPR, Tallapaka SB, Ambardekar VV, Gautam N Peripherally cross-linking the shell of core-shell polymermi celles decreases premature release of physically loaded combretastatin A4 in wholeblood and increases its mean res dence time and subsequent potency against primary murine breast tumors after IV administration.
Biomaterials Share This Article. Open Access Journals. Article Usage. Post your comment. Anti Spam Code: Can't read the image? International Conferences If beyond this range, the body would soon fail to carry out its tasks and become dysfunctional.
In order for the body to keep these variables within efficacious limits, various regulatory mechanisms are employed and each of them is comprised of three general components. The components of homeostasis are: 1 a receptor, 2 a control center, and 3 an effector. The receptor , as the name implies, is the part of a homeostatic system that receives information regarding the status of the body. It monitors and perceives the changes in its environment, both the internal and the external.
It is in the form of a sensory nerve terminal that receives the information i. Examples of receptors in the human body are as follows:. The control centers pertain to the homeostatic component that processes impulses relayed by the receptors. Examples are the respiratory center and the renin-angiotensin system. The effectors are the target of the homeostatic response that would bring about the reversion of conditions to the optimal or normal range.
At the tissue or organ level, they are exemplified by the muscle or the gland. At the cellular level, they are the receptors of a nerve, including the nuclear receptors. These three components work by first detecting and then responding to the information i. They respond to the detected change in the environment by relaying the information to the control center for processing , or directly to a particular target effector. Processing in the control center entails deliberation and determination of the appropriate response to the relayed stimuli.
Then, it sends this message to the effectors. The effectors upon receiving the message would bring about the supposed response that would revert to the normal homeostatic range. At the cellular level, the activated nuclear receptors will act upon by upregulating or by downregulating the expression of certain gene s. The protein produced from the gene expression would then exert its effect on the target organ.
Homeostatic mechanisms that respond to a perturbation may be in the form of a looping mechanism called feedback mechanism that may be positive or negative. Positive feedback maintains the direction of the stimulus. It tends to accelerate or promote the effect of the stimulus. Examples are labor contractions, blood clotting, and action potential generation.
Negative feedback is a self-regulatory system and is employed in various biological systems. It reverses the direction of the stimulus and tends to inhibit the source of stimulus or slow down the metabolic process. Examples include thermoregulation, blood glucose regulation, baroreflex in blood pressure, calcium homeostasis, potassium homeostasis, and osmoregulation.
Labor contraction during childbirth is positive feedback since the initial contraction of the uterine muscle leads to further contractions. Rather than inhibiting the contraction, the body tends to produce more contractions. At labor, the posterior pituitary gland releases oxytocin which stimulates muscle contraction.
At child delivery, oxytocin release is further augmented, intensifying muscle contractions until the neonate is pushed outside the birth canal. The formation of a blood clot is an example of positive feedback. The conversion of blood from a liquid into a solid form entails series activations of clotting factors.
As soon as one clotting factor is activated, the next clotting factor is activated, resulting in the formation of a fibrin clot. In this process, the direction of the stimulus is maintained. In neuron signaling, positive feedback is demonstrated during membrane depolarization. As nerve impulse is relayed along the axon of the neuron, voltage-gated sodium channels open in a series down the axon.
The first set of voltage-gated sodium channels open, resulting in the influx of sodium ions. This, in turn, causes the depolarization of the surrounding area, which means the next set of voltage-gated sodium channels will open. Thermoregulation is an example of negative feedback. It refers to the homeostatic regulation of body temperature.
The human body tends to maintain an internal temperature of about The core temperature is regulated chiefly by the nervous system, particularly the anterior hypothalamus and the preoptic area of the brain. When the ambient temperature is less than the skin temperature, heat loss occurs. This means that in colder surroundings e. As a result, the core temperature falls. This is picked up by the thermoregulatory center of the brain and initiates control mechanisms to return the core temperature to the set point.
One of the homeostatic mechanisms is by shivering to generate heat. The thermoregulatory center in the brain sends signals to the muscles to shiver. Since the body remains still while shivering less heat will be dissipated to the environment. On the other way around, when the ambient temperature is higher than the skin temperature, the body gains heat and consequently, the core temperature rises. This occurs during the hot summer days. The thermoregulatory control center in the brain responds, for example by stimulating the eccrine sweat glands to secrete sweat to cool the body off by evaporative cooling.
As each step of clotting occurs, it stimulates the release of more clotting substances. This accelerates the processes of clotting and sealing off the damaged area. Clotting is contained in a local area based on the tightly controlled availability of clotting proteins. This is an adaptive, life-saving cascade of events. Each organ system performs specific functions for the body, and each organ system is typically studied independently.
However, the organ systems also work together to help the body maintain homeostasis. For example, the cardiovascular, urinary, and lymphatic systems all help the body control water balance.
The cardiovascular and lymphatic systems transport fluids throughout the body and help sense both solute and water levels and regulate pressure. If the water level gets too high, the urinary system produces more dilute urine urine with a higher water content to help eliminate the excess water. If the water level gets too low, more concentrated urine is produced so that water is conserved.
The digestive system also plays a role with variable water absorption. Water can be lost through the integumentary and respiratory systems, but that loss is not directly involved in maintaining body fluids and is usually associated with other homeostatic mechanisms. Similarly, the cardiovascular, integumentary, respiratory, and muscular systems work together to help the body maintain a stable internal temperature. This allows heat to dissipate through the skin and into the surrounding air.
The skin may also produce sweat if the body gets too hot; when the sweat evaporates, it helps to cool the body. Rapid breathing can also help the body eliminate excess heat.
Together, these responses to increased body temperature explain why you sweat, pant, and become red in the face when you exercise hard. Heavy breathing during exercise is also one way the body gets more oxygen to your muscles, and gets rid of the extra carbon dioxide produced by the muscles. Conversely, if your body is too cold, blood vessels in the skin contract, and blood flow to the extremities arms and legs slows. Muscles contract and relax rapidly, which generates heat to keep you warm.
This preemptive measure readies the body for the incoming flood of calories , rather than wrestling to control blood sugar and energy stores in its wake. The ability to shift set points allows animals to adapt to short-term stressors, but they may fail in the face of long-term challenges, such as climate change.
But they're not designed to last for long. Homeostatic systems may have primarily evolved to help organisms maintain optimal function in different environments and situations. The th eory posits that homeostasis makes it easier for organisms to extract important information from the environment and shuttle signals between body parts. Regardless of its evolutionary purpose, homeostasis has shaped research in the life sciences for nearly a century. Though mostly discussed in the context of animal physiology, homeostatic processes also enable plants to manage energy stores, nourish cells and respond to environmental challenges.
Beyond biology, the social sciences, cybernetics, computer science and engineering all use homeostasis as a framework to understand how people and machines maintain stability despite disruptions. Nicoletta Lanese is a staff writer for Live Science covering health and medicine, along with an assortment of biology, animal, environment and climate stories. She holds degrees in neuroscience and dance from the University of Florida and a graduate certificate in science communication from the University of California, Santa Cruz.
0コメント