Consider the role of feedback loops in the biological mechanisms that control at least two different human behaviours. Critically evaluate the evidence and assess whether disruption of the process can account for the corresponding `abnormal` human


Bodily functions are regulated with the help of central nervous system and endocrine system. Hormones and neurological functions regulate eating and sleeping behavior in humans. Hormones play very important role in well-being of a person. In bad mood or high temper hormones level fluctuates that can affect psychological behavior due to alteration in inner biological mechanisms. It can affect person’s mood, ovulation, sexual desire, fertility, and other psychological behaviors. Hence, imbalance of hormones can lead to several psychological disorders and can affect bodily functions negatively. In females estrogens and progesterone are very important in control of various physiological functions. Estrogen and progesterone disbalance can dramatically affect woman’s health. Another important hormone is gonadotrophin releasing hormone that can affect hypothalamus and pituitary functions. Hormonal functions in body are affected by various factors including diet, lifestyle, stress, work stress, exercise, emotions, sleeping habits, ovulation and age.

The Role Of Feedback Loops In The Biological Mechanisms That Control Eating Behavior

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Serotonin (5-HT) is a neurotransmitter that is responsible for controlling the normal patterns of eating. It may enhance food repulsion, and functions by the hypothalamic receptors in the body. If this macronutrient is consumed, a negative feedback loop occurs, which in turn reduces the amount of carbohydrates a person consumes (Leibowitz, 1998). Studies have suggested role of hypothalamic serotonergic receptor mechanisms in regulation of food intake. 5-HT receptors mediate these responses. Derivatives of serotonin reduce weight gain and food intake, hence, drugs that stimulates serotonin release interfere in carbohydrate ingestion. However, fat and protein ingestion is not much affected. With excessive consumption of carbohydrates the negative feedback loop triggers increasing 5-HT receptors. Thus carbohydrates in diet can enhance the synthesis and release of 5-HT receptors in hypothalamus. Hormones and glucose play vital role in this feedback loop. Hormones in this loop are insulin, hormones derived from adipose tissue, corticosterone, and leptin, all of them affect satiety, appetite, natural feeding cycle and serotonergic function (Leibowitz, 1998).

What we eat in our diet also affects the type of hormones stimulated in that feedback loop. Circulating hormones and glucose level in blood affect the feedback loop in eating behavior. Drugs can alter feedback loop and stimulate certain other hormones in the chain (Leibowitz, 1998).

A negative feedback occurs when body is deprived of nutrition. The body will automatically respond and will slow down its metabolic processes. Due to this those who start dieting to loose weight, do loss weight initially but not later as body re-adjusting its metabolic rate to. With physical activity and exercising will change body’s need and set metabolic rate to higher level. Studies have suggested that in clinical studies that eating and other bodily disorders cause disturbances of 5-HT receptors.

The Role Of Feedback Loops In The Biological Mechanism That Control Sleeping Behavior

In certain brain regions sleep response is actively stimulated. Studies have identified specific sites in brain that are basal forebrain including hypothalamus and pons that are actively involved in NREM sleep control and REM sleep control and initiation respectively. Signals are generated from pons and conveyed to thalamus and cerebral cortex and even to spinal cord causing temporary paralysis. Sleep patterns change from person to person depending upon lifestyle and age of a person (Sleep and the brain).

Biological clocks have genetically been designated for physiological mechanisms that enable living beings to live in harmonious state with in accordance with nature, like day and night cycles and the seasonal changes. The significant role of a biological clock is to control open biological rhythms such as the cycles of sleep and wake. The biological clock also has a role in managing reproductive cycles in different seasons in many animals as it has a capability to sense the altering lengths of daylight and darkness throughout a year. The generation of melatonin, a hormonal signals coming out from the pineal gland of the endocrine system, is managed by the circadian clock in the SCN. Its intensity increases when night and decreases at day. This has been observed in both nocturnal and diurnal kinds of living beings. Melatonin is also named as the hormone of darkness due to the pattern it displays. The SCN determines the time of occurrence and duration of melatonin release; melatonin further feeds back on the SCN to control its process (Biological Clock).

4) Critically evaluate the evidence and assess whether disruption of the process can account for the corresponding “abnormal” human behaviours.

Abnormal behavior for eating

Eating i.e. food intake is a normal human behavior which is consciously controlled. However, individuals with obesity and weight-gain problems report that they cannot control habit of eating. There are several biological, behavioral and environmental factors controlling food intake

Despite the action of eating being one that is wholly under one’s control, many obese people claim that they are unable to have power over what they eat (Blundell & Gillett, 2001). The liberty of choosing one’s own diet is present, but studies have shown that biological and environmental factors also lay an effect on a person’s dietary intake. If the environmental factors are such that food consumption is encouraged, there is then no way in which the individual can make corrective behavior to maintain body weight. The energy that is used in obese individuals is lesser as compared to the intake, which results in misbalanced weight.

In a study by Turek et al (2005) “The CLOCK transcription factor is a key component of the molecular circadian clock within pacemaker neurons of the hypothalamic suprachiasmatic nucleus. We found that homozygous Clock mutant mice have a greatly attenuated diurnal feeding rhythm, are hyperphagic and obese, and develop a metabolic syndrome of hyperleptinemia,hyperlipidemia, hepatic steatosis, hyperglycemia, and hypoinsulinemia. Expression of transcripts encoding selected hypothalamic peptides associated with energy balance was attenuated in the Clock mutant mice. These results suggest that the circadian clock gene network plays an important role in mammalian energy balance (Turek et al., 2005).”

Anorexia due to disruption of feedback loop and hormonal Imbalance

Anorexia nervosa is an eating disorder in which an individual wishes to eat lesser than the normal body requirement, for fear of weight gain. It is an illness, and mostly females are affected by it. Anorexia may lead to life threatening conditions due to malnutrition and other health complications. Anorexic individuals are seen to be very thin, and face severe weight loss.

Hormonal changes play an imperative role in causing this disorder. If there is an imbalance of hormones in the body, it may result in anorexia, for example, low reproductive hormones such as estrogen and dehydroepiandrosterone, low thyroid hormones, high stress hormones, and low growth hormones. Some other consequences of anorexia may be loss of bones, infertility, and in women, amenorrhea.  Blood pressure is dropped, and anorexics may die of heart failure. Apart from that, anemia is prevalent in anorexics, bloating and constipation is present, and all the vital organs gradually fail.

Abnormal behavior for sleeping

The disturbances in sleep and wake schedules are considered to be a major reason behind number of health issues, like greater risk for obesity, type II diabetes, and high blood pressure. Its role for increasing risk of malignancy and premature aging is not much obvious. We will discuss here some of the epidemiological and experimental proofs that give evidence that changes in sleep and wake schedules have links with health problems like malignancy and aging before time. Epidemiological evidence indicates that changes in sleep and wake practices, for example when a person is engaged in doing night time shifts or rotating shifts job, can cause increasing risk of breast, prostate, in leukemia, endometrial, and colorectal cancers. Excessiveness in both ways is not good; extra long or extra short sleeps cause and increase mortality.

These facts are then affirmed by experimenting on animal systems where it is found that depriving from sleep results in dying in Drosophila cycle01 mutants. The actions of light-dark pattern in rodents or mutations that destroy many DNA segments in the circadian nerve fibers boost up aging and development of neoplastic. Melatonin , hormone of darkness secreted by the pineal gland seems to have developed in part to render shield from mutagenesis. It coordinates and adjusts cellular growth, differentiation, and caspase-mediated cell death to the circadian peaks and troughs of genotoxic depression. A model that is based on circadian-controlling of sleep and wake periods connects the circadian nerve fibers to the mutational concepts of aging and neoplasia (Shadan, 2008).

Insomnia due disruption of normal feedback loop and imbalance of hormones

Numerous families face sleep problems. It is only that the intensity of the sleeplessness varies. The condition of sleeplessness, also known as insomnia may be due to genetic factors, or other factors such as emotional instability and the like. Many people have to take sleeping pills in order to get sufficient sleep through the night, to wake up fresh the next morning. Lack of sleep not only causes distress, but in the long term may also be associated with lung diseases, heart conditions, digestive disorders, and even AIDS (Blaivas, 2007).

Insomnia may be short-term, due to some prevailing conditions, or chronic. Chronic insomnia may be a result of hormonal imbalance in the body. A shortage of melatonin, a hormone secreted by the pineal gland, may result in chronic insomnia. The excessive release of cortisol, a stress hormone, may contribute to chronic insomnia, especially in people with psychiatric disorders. The release of growth hormones may also impair sleep, because they are released at night time. Sleep mediators are present to change the feedback loops. An example is adenosine, which balances between metabolism and sleep control.


It is apparent that if we go against the rules of nature, nature will automatically take its course against us. Any disruptions in the natural hormonal regulations may result in impaired sleep, causing insomnia, short-term or chronic, as well as anorexia nervosa, a severe and serious eating ailment, which could result in death. Feedback loops are essential to keep the human body healthy, but attention needs to be rendered when there is a malfunction in the body, or when something is not normal. Therefore it is necessary to pay medical attention if the normal biological mechanisms of the body seem to be in trouble. God has made the natural behaviours of mankind for some good reason or the other. In this paper, we intend to discuss the natural behaviours of sleeping and eating, and how a disruption in both of these necessary acts may cause negative effects to the body, leading to abnormal actions at times.

Sleeping is a behavioural state that is necessary for the body to function normally. It is not just keeping the eyes closed for a number of hours, but is essential to rest the body and mind both, and to build up energy levels for the activities to be performed after waking. Similarly, normal eating patterns are crucial for an individual’s body to meet needs for carrying out the regular functions. The body is like a machine, and food is the fuel to keep it working. It is not just food that is required for proper functioning, but a balance of all the activities undertaken by the body, that make it run best. If anything goes out of balance, the machine will begin creating problems. Sleeping and eating disorders play a pivotal role in the disturbance of the system and behavior of the individual. We will now take an insight into how this occurs.

A normal functioning body needs to meet specific requirements for it to continue with its processes. There are some processes that are controllable, and others that are not in our control, but are still carried out within the body. We can alter our lifestyles or make amendments according to our health status.

The internal elements that are not in our control in our bodies, usually involve hormones, which are chemicals that are released by tissues, and transported through the blood stream, to carry out necessary functions. There are hormones associated with every activity that we perform, and affect specific body organs according to need. A person’s eating disorder is related with the extremes to which he or she may reach. It is either in excessive eating, or in insufficient food consumption. These actions are normally practiced.


Leibowitz, S. (1998) Hypothalamic serotonin in control of eating behavior, meal size, and body weight. Biological Psychiatry, Volume 44, Issue 9, Pages 851-864. Retrieved from

Shadan, F. F. (2008) Sleep-wake cycle, aging and cancer.  Journal of applied biomedicine. Volume 6 (2008), No 3, p 131-138. Retrieved

Blundell, J.E. and Gillett, A. (2001) Control of Food Intake in the Obese. Obesity Research (2001) 9, s263–S270; doi: 10.1038/oby.2001.129. Retrieved

Fred W. Turek,1,3 Corinne Joshu,3,4* Akira Kohsaka,3,4* Emily Lin,3,4* Ganka Ivanova,2,4Erin McDearmon,3,5 Aaron Laposky,3 Sue Losee-Olson,3 Amy Easton,3 Dalan R. Jensen,6 Robert H. Eckel,6Joseph S. Takahashi,1,3,5 Joseph Bass2,3,4 Obesity and Metabolic Syndrome in Circadian Clock Mutant Mice
Science Express on 21 April 2005. Science 13 May 2005: Vol. 308. no. 5724, pp. 1043 – 1045.

Reviewed By: A.D.A.M. Editorial Team: Greg Juhn, M.T.P.W., David R. Eltz, Kelli A. Stacy. Previously reviewed by Harvey Simon, M.D., Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital (7/18/2006).

Biological Clock. Information about sleep. Retrieved from


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