Homeostasis Within the Nervous System

What is Homeostasis?

Homeostasis is the condition of equilibrium in the body’s internal environment due to the consistent interaction of the body’s main regulatory processes (Tortora and Derrickson, 2009). This process developed by Claude Bernard in 1865 and then named by Walter Cannon in 1926, is used by the endocrine and nervous system in order to maintain a psychological internal environment disregarding external influences. As the environment is always changing the body is constantly trying to regulate factors within it such as water concentration, PH levels, Oxygen levels, nutrients, urea and levels of salt, sugar and electrolytes.

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During homeostatic regulation the body uses negative feedback to move the body back to within its normal range of values. To do this a receptor detects and responds to a stimuli from the internal or external environment , once detected the receptor sends information of the stimuli down the afferent pathway to a controller. Once received the controller then determines an appropriate response to the stimuli and sends a signal down the efferent pathway to the effector. Once received the effector then makes a change in order to balance out the effects of the stimuli and once again create a dynamic equilibrium within the body. Body temperature is regulated by the autonomic nervous system. Once body temperature rises above the norm it stimulates temperature receptors in the skin dermis, information regarding this change is then sent to the controller which in this instance is the hypothalamus within the brain. The hypothalamus then processes the information and sends a signal to the effector to start the process of negative feedback. The effector responds by starting the process of vasodilation which in this case would cause the sweat gland to activate in order to lower the body’s core temperature.

Without homeostasis a homeostatic imbalance could occur, organisms need to be able to maintain nearly constant internal environments in order to survive grow and function properly (Guyton and Hall, 2006). Enzymes within the body operate to their full potential within a specific range of conditions. By maintaining PH levels and body temperature enzyme linked reactions can occur efficiently. By maintaining changes in water potential homeostasis protects essential cells needed for processes within the body. Changes in water potential could possibly affect the amount of water within tissue fluid and cells, this could potentially cause the cells to desiccate or burst. Therefore, failure to maintain this could possibly lead to a positive feedback mechanism taking over and the possibility of further complications or death.

What is the endocrine system?

The endocrine system consists of glands that are present throughout the body and secrete hormones in order to control actions that maintain homeostasis, preparing the body for the process of fight or flight, controlling growth and controlling sexual development and reproduction. The glands which make up the endocrine system are the hypothalamus, pituitary, thyroid, parathyroid, adrenals, the islet of Langerhans in the pancreas, pineal, the ovaries and testes. Hormones are chemical messengers that are released into the bloodstream; they are carried within blood plasma and affect target cells. Target cells have receptors that attach to specific hormones which have their own receptor. The hormones that are secreted are slower acting however are long-lasting and are good for assisting in areas within the internal environment that require constant adjustments. Therefore assisting with homeostasis.

Glucose enters the blood from the small intestine, the body’s blood glucose levels are monitored by a gland called the Islet of Langerhans which is located within the pancreas. A bodies normal range of blood glucose levels are between 4-8mmol/l, these levels frequently change due to eating and exercise. A stable blood glucose level is important within the internal environment as it provides the brain with a strong energy source to enable it to operate and also enables mitochondria to produce Adenosine Triphosphate which is used by cells to perform some of the body’s most important functions such as respiration. Homeostatic regulation of glucose happens when the pancreas detects that the glucose levels become too high or too low as blood passes through it. In the event of Hypoglycemia, where the glucose levels becoming too low the receptor, that is found on the surface of alpha cells within the pancreas stop the production of insulin and start to produce a controller, the hormone glucagon. Glucagon then stimulates the stores of glycogen in the liver and muscles to convert back to glucose, this process is called glycogenesis. If this is not enough to bring the sugar levels back to normal, glucagon begins to convert fatty acids in to glucose using a process called Gluconeogenesis within the effectors. The effectors in this situation are the liver cells, muscles cells and fatty cells. Once converted the glucose is then released into the blood stream causing the bodies glucose levels to rise. In addition to this process, during periods of intense exercise where glucose levels drop the hormone adrenaline will convert glycogen into glucose. In the event of Hyperglycemia, where glucose levels become too high, the receptor which is located on the surface of the beta cells within the pancreas produce a controller to counter act the effects. The controller in this instance is a hormone called insulin. Once insulin is secreted into the bloodstream, glucose levels within the body decrease because the excess glucose is converted into glycogen through a process called Glycogenesis within the effectors, namely the liver cells and muscles cells.

The nervous system

Within the process of homeostasis the nervous system detects and responds to adaptions within the body’s internal and external environments by sending fast electrical impulses through nerves to the brain which instructs an effector and enables them to react quickly and return the body to a state of equilibrium. The nervous system consists of the central nervous system which is subdivided into the spinal cord and the brain and the peripheral nervous system which is subdivided into the somatic nervous system which controls our voluntary muscles and the autonomic nervous system which controls our involuntary muscles which helps to create homeostatic regulation of functions within the body such as heart rate. Nerves within these subdivisions transport impulses between the central nervous system and the body. Blood pressure is the force applied on the inner walls of the blood vessels within the body by blood. Blood pressureis measured in millimeters of mercury (mmHg), A blood pressure reading below 130/80mmHg is considered to be normal (NHS Choices) The first numerical factor within a blood pressure reading is the systolic pressure of the blood which is the amount of beats you heart makes per minutes to pump blood away from the heart. The second numerical factor refers to the diastolic pressure which is the pressure of the blood when tour heart is at rest, in-between beats. During homeostatic regulation of blood pressure if a baroreceptor located in the aortic arch and internal carotid arteries detects a decrease in blood pressure it will send fewer impulses to the controllers, the cardiac centre and the vasomotor centre located in the medulla oblongata of the brain simultaneously. By sending fewer impulses to the cardiac centre it excites the sympathetic impulses and inhibits the parasympathetic impulses. This process excites the effector, Sino-atrial node in order to increase the heart rate, by doing this it causes the hearts cardiac output to increase. Alongside this process the fewer impulses being sent to the controller, the vasomotor centre also excites the sympathetic impulses which cause the effector, the smooth muscle within the arterioles to constrict this results in vasoconstriction and increased peripheral resistance. The combinations of these processes cause the blood pressure to increase back to within a normal range. During the detection of high blood pressure by the baroreceptors it sends more impulses to the controllers, the cardiac centre and the vasomotor centre simultaneously. By sending decreasing impulses to the cardiac centre it decreases sympathetic input and an increase in parasympathetic input which decreases the heart rate and cardiac output. Alongside this process the increase in impulses to the vasomotor centre causes an effector, the smooth muscle in the arterioles to dilate. This results in vasodilation and peripheral resistance decreases causing blood pressure to decrease. In addition to the baroreceptors, the kidneys are also involved in the monitoring of blood pressure. If blood pressure decreases the kidneys release a hormone called renin that caused the adrenal cortex to release aldosterone. The release of aldosterone causes the kidneys to retain sodium and allows water to flow without resistance causing blood volume and pressure to rise.

Nephrotic syndrome

Nephrotic syndrome tends to affect primary school age children. Between two and four children in every 100,000 develop nephrotic syndrome (NHS GOSH)

Nephrotic syndrome is a condition where the glomeruli leak a substantial amount of protein therefore not enough protein remains in the blood to enable it to soak up water. This causes the water to move into body tissues causing oedema which presents itself as severe swelling. Proteins provide the body with antibodies this can cause a child with nephrotic syndrome to have a low immune system which results in an increased risk of infection. Other complications of this condition is difficulties in growth and development and prone to blood clots. If protein continues to leak this can lead to a loss of kidney function and ultimately kidney failure. A treatment option for this condition is a medication called furosemide, a loop diuretic that obstructs the reabsorption of sodium and water in the ascending loop of hele, achieved through competitive inhibition. This causes the osmotic gradient through the nephron to be destroyed due to the lumen becoming more hypertonic. This enables the kidney to secrete sodium onto the collecting ducts, attracting water volume which is then excreted by the bladder by producing more urine. This will result in less water retention in tissue that would be putting pressure on organs such as the lungs.

The Electronic Medicines Compendium States that the pharmacodynamics properties of Furosemide are, it promotes sodium and chloride reabsorption. Furosemide inhibits mechanisms in the epithelial cells in order for sodium and chloride to enter and is transported through the secretory pathway in the proximal tubule. It decreases renal excretion of uric acid and increases loss of potassium in the urine and excretion of ammonia by the kidney.

The dosages available for children with oedema as stated by the BNF for Children are orally.

Neonate 0.5–2mg/kg every 12–24 hours (every 24 hours if corrected gestational age under 31 weeks),Child 1 month–12 years 0.5–2mg/kg 2–3 times daily (every 24 hours if corrected gestational age under 31 weeks); higher doses may be required in resistant oedema; max. 12mg/kg daily, not to exceed 80mg daily, Child 12–18 years 20–40mg daily, increased in resistant oedema to 80–120mg daily.

Through a slow intravenous injection, Neonate 0.5–1mg/kg every 12–24 hours (every 24 hours if corrected gestational age under 31 weeks), Child 1 month–12 years 0.5–1mg/kg repeated every 8 hours as necessary; max. 2mg/kg (max. 40mg) every 8 hours and a Child 12–18 years 20–40mg repeated every 8 hours as necessary; higher doses may be required in resistant cases

Through a continuous intravenous infusion ,Child 1 month–18 years 0.1–2mg/kg/hour (following cardiac surgery, initially 100micrograms/kg/hour, doubled every 2 hours until urine output exceeds 1mL/kg/hour)

The Pharmacokinetic properties as stated by the Electronic Medicine Compendium of Furosemide are that it is a weak carboxylic acid which exists in the gastro-intestinal tract. Furosemide is rapidly absorbed but 60-70% id absorbed on oral administration within the upper duodenum at PH level 5.0. Furosemide binds to albumin proteins and the volume of distribution ranges between 170 – 270 ml/Kg.

69-97% is excreted in the first four hours after the drug is given and 80-90% of Furosemide is excreted through the kidneys.

Reference list

Tortora, G.T. and Derrickson, B.H. (2009) Principles of Anatomy and Physiology: Organisation, Support, Movement, and Control Systems of the Human Body. 12th ed. Asia: John Wiley and Sons.

Guyton, A.C. and Hall, J.E. (2010) Textbook of Medical Physiology. 12th ed. Philadelphia: Saunders Elsevier Inc.

NHS Choices (2014) High Blood Pressure Available from: http://www.nhs.uk/conditions/Blood-pressure-(high)/Pages/Introduction.aspx [Accessed 19.11.2014].

NHS GOSH (2012) Childhood nephrotic syndrome information Available from: http://www.nhs.uk/Conditions/nephrotic-syndrome/Pages/Introduction.aspx [Accessed 22.11.2014]

BNF for Children (2014-2015) FUROSEMIDE Available from: https://www.medicinescomplete.com/mc/bnfc/current/PHP11437-lasix.htm?q=furosemide&t=search&ss=text&p=3#PHP11437-lasix [Accessed 23.11.2014]

Electronic Medicine Compendium (2014) Furosemide 10mg/ml Solution for Injection or Infusion, 20mg in 2ml and 250mg in 25ml Available from: https://www.medicines.org.uk/emc/medicine/20958 [Accessed 23.11.2014]