Homeostasis refers to the body’s ability to maintain relatively stable internal conditions even while continually subjected to external changes. Body temperature, blood volume and heart rate are just a few examples of the hundreds of conditions the body regulates to maintain homeostatic balance. This internal equilibrium is so important that virtually every disease or disorder in the body can be traced to a homeostatic imbalance.
The maintenance of homeostasis includes:
Control of the water balance of the blood
Control of blood sugar level
Control of body temperature
Control of blood urea level
Each of the internal factors are maintained by a separate mechanism that is specific for that factor. However, all the mechanisms for homeostasis share common features:
A specific sensor is able to detect the value of the factor being monitored
Any deviation from the desired value (norm)is corrected so that the norm is more or less maintained
The corrective mechanism involves negative feedback.
For the body cells to survive and function properly, the composition and temperature of the fluids around the cells (intestinal fluid) must remain much the same.
Corrective mechanism
Rise above norm
Norm
Norm
Corrective mechanism
Fall below norm
Various organ systems of the body act to maintain homeostasis through a combination of hormonal and nervous mechanisms. In everyday life, the body must regulate respiratory gases, protect itself against agents of disease (pathogens), maintain fluid and salt balance regulate energy and nutrient supply, and maintain a constant body temperature. All these must be coordinated and appropriate responses made to incoming stimuli. In addition, the body must be able to repair itself when injured and be capable of reproducing (leaving offspring). The human body must maintain homeostasis in order to function properly and aid in growth and development, disruptions to homeostatic functions can have triggered effects on the growth and development.
Normal blood temperatureRegulation of body temperature by Homeostasis:
Cold receptors in skin
Warm receptors in skin Decrease increase
Hypothalamus
Heat gain
Heat loss
Vasodilation of superficial arterioles onset of sweating hair lowered as hair erector muscles relax and decreased metabolic rate.
Vasoconstriction of superficial arterioles onset of shivering hair raised by contraction of hair erector muscles and increased metabolic rate.
Feedback Feedback
Negative feedback in the control of body temperature:
Skin vasodilation sweating lowering hairs
Heat loss centre in the hypothalamus
Thermoreceptors in the hypothalamus
Rise in blood temp Nerve impulse Nerve Impulse normal blood temp
Blood at original temperature turns off corrective mechanisms
Positive feedback occurs when the feedback causes the corrective measures to remain turned on, this causes the system to deviate more from the norm. One example is of neurones when a stimulus causes a small influx of sodium ions. Positive feedback occurs when there is a breakdown of control systems. In Certain diseases like typhoid fever, breakdown of temperature regulation resulting in a rise in body temperature leading to hypothermia, and vice versa if the body gets too cold (hypothermia).
The human body systems, all play a part in maintaining homeostasis; they all have their own specific roles and parts. The human body systems work together in order to function effectively, no system would be able to work effectively on its own.
Organ system
Homeostatic function
Cardiovascular
Transports oxygen, nutrients and hormones secreted by the endocrine glands to tissue cells and transports wastes away from cells; defends against disease; helps control temperature, fluid, and pH balance.
digestive
Absorbs soluble nutrients after ingesting food and digesting it, eliminates nondigestible remains.  Supplies blood with nutrients and water for tissue cells.
respiratory
Captures oxygen and exchanges gasses at lungs and tissues, maintains breathing, helps control pH balance.  Supplies blood with oxygen for tissue cells and rids blood of carbon dioxide.  Helps regulate the acid-base balance of the blood.
Skeletal
Protects the body and provides support for locomotion and movement, stores minerals, produces blood cells.
endocrine
Coordinates and integrates the activities of other systems by secreting hormones, responding to stress, regulating fluid, pH balance and metabolism.  Works more slowly, with longer-lasting effects than the nervous system.
muscular
Produces body and internal movement, maintains posture, and produces heat that maintains body temperature.  Protects and supports internal organs.
urinary
Removes nitrogenous and other metabolic wastes from the bloodstream by excretion, helps control fluid balance, as well as the water-salt, and acid-base balance of the blood.
nervous
Receives sensory input, integrates and stores input, directs the body, and helps coordinate the activities of all the other organ systems.  It responds quickly to internal and external stimuli.
The circulatory system is built up the heart, blood and blood vessels, which services all the cells in the body. Wastes are taken away and exchanged with oxygen and food nutrients. All cells in the body require oxygen and nutrients and they need they’re wastes removed. These are the main roles of the circulatory system. The heart, blood and blood vessels work together to service the cells of the body. Using the network of arteries, veins and capillaries, blood carries carbon dioxide to the lungs (for exhalation) and picks up oxygen. From the small intestine, the blood gathers food nutrients and delivers them to every cell.
Components of the cardiovascular system
Heart
Blood vessels
Blood
Heart is a muscular pumping organ located in the medial to the lungs. The top of the heart, known as the hearts base, connects to the great blood vessels of the body; the aorta, vena cava, pulmonary trunk, and pulmonary veins.
Blood vessels are the highways that allow blood flow quickly and efficiently from the heart to regions of the body.
Three types of blood vessels, arteries and arterioles, capillaries, and veins and venules.
Blood as a connective tissue, transports many substances through the body and helps maintain homeostasis of nutrients, wastes, and gases.
Blood is made up of red blood cells, white blood cells, platelets, and liquid plasma.
All of the organ systems in the body contribute to homeostasis, but the cardiovascular system, the heart and blood vessels is especially important. Without the cardiovascular system none of the other systems can function. The muscular system requires large amounts of oxygen from the cardiovascular system. Muscles cramp and freeze up when they do not get adequate oxygen supply. If in the case the cardiovascular system cannot pump enough oxygen rich blood to the muscles the body is unable to move. The cardiovascular system also helps in maintaining blood volume; it works in conjunction with the kidneys to maintain blood volume and composition. The cardiovascular system provides the blood pressure that the kidneys use to filter waste out of the body. The cardiovascular system and the skin help maintain homeostasis by regulating body temperature. When the body over heats, the blood vessels that serve the skin dilate. The cardiovascular system rushes warm blood to the superficial capillaries of the skin. Heat from the blood radiates off of the skin’s surface, cooling the body.
When body temperature drops too low, skin capillaries constrict. This prevents warm blood from reaching the surface of the skin. The heart pumps extra blood to the deeper vital organs.
Nasal passage
Air entering from the nostrils is led to the nasal passages. The nasal cavity that is located behind the nose comprises the nasal passages that form an important part of the respiratory system in human beings. The nasal cavity is responsible for conditioning the air that is received by the nose. The process of conditioning involves warming or cooling the air received by the nose, removing dust particles from it and also moistening it, before it enters the pharynx
Pharynx
It is located behind the nasal cavity and above the larynx. It is also a part of the digestive system of the human body. Food as well as air passes through the pharynx
Larynx
Consists of two pairs of membranes. Air causes the vocal cords to vibrate, thus producing sound. The larynx is situated in the neck of mammals and plays a vital role in the protection of the trachea.
Trachea
Airway through which respiratory air travels
bronchi
The trachea divided into two main bronchi. The bronchi extend into the lungs spreading in a tree-like manner as bronchial tubes. The bronchial tubes subdivide and with each subdivision, their walls get thinner. This dividing of the bronchi into thin-walled tubes results in the formation of bronchioles. The bronchioles terminate in small air chambers, each of which contains cavities known as alveoli. Alveoli have thin walls, which form the respiratory surface. The exchange of gases between the blood and the air takes place through these walls.
lungs
Lungs form the most vital component of the human respiratory system. They are located on the two sides of the heart. They are responsible for transporting oxygen from the atmosphere into blood and releasing carbon dioxide from blood to the atmosphere.
The respiratory system is made up of the nasal passage, the pharynx, larynx, the trachea, bronchi and lungs. It is responsible for the process of respiration that is vital to the survival of living beings. Respiration is the process of obtaining and using oxygen, while eliminating carbon dioxide.
Breathing occurs when air passes into and out of the lungs; it’s an involuntary process but can be controlled consciously. Breathing involves the movement of air in and out of the lungs in generated by differences in pressure inside and outside the body. The most important muscle used in breathing is the diaphragm, a muscular sheet between the base and the abdominal cavity. The diaphragm is assisted by the internal and external intercostal (which lie between the ribs) and by the neck and abdominal muscles. A person normally breathes in and out about 500ml (1pt) of air 12-17 times a minute. Breathing involves inhalation followed by exhalation, during inhalation the diaphragm and external intercostal muscles contract to expand the chest cavity. During forceful inhalation the neck muscles also contract. However during exhalation the chest cavity decreases, and the diaphragm and external intercostal muscles relax. In order to function, the body cells need oxygen. The respiratory system, which consists of air passages, pulmonary vessels, and the lungs, as well as breathing muscles, supplies fresh oxygen to the blood for distribution to the rest of the body tissues.

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In addition, respiration removes carbon dioxide, a waste product of body processes. Alveoli which are tiny air sacs of the lungs, they are elastic, thin-walled structures that are supplied with air by respiratory bronchioles. Tiny blood capillaries surrounding the alveolar walls allow oxygen to be carried into the bloodstream. In exchange, carbon dioxide diffuses from blood into the alveoli, from where it is exhaled. Gas exchange takes place in the lungs, where carbon dioxide from the blood passes into the alveoli through the respiratory membrane, a thin barrier that has several layers. Oxygen crosses the membrane in the opposite direction, from the alveoli to the blood capillaries.
Homeostasis is hence maintained by the respiratory system in two of the following ways: gas exchange and regulation of blood pH. Gas exchange is performed by the lungs by eliminating carbon dioxide, a waste product given off by cellular respiration. As carbon dioxide exits the body, oxygen needed for cellular respiration enters the body through the lungs. ATP, produced by cellular respiration, provides the energy for the body to perform many functions, including nerve conduction and muscle contraction. Lack of oxygen affects brain function, sense of judgment, and a host of other problems.
The body’s complex anatomical systems work closely together to support movement, blood circulation, digestion and other basic requirements of life. The muscular system consists of three types of muscle, each with a separate function. The functions of the muscular and skeletal systems are so intricately interconnected that they are often referred to by the single term, the musculoskeletal system. This system consists of bones, joints, tendons, ligaments, skeletal muscles, nerves, cartilage and the voluntary or striated muscles. They work together to protect the brain and internal organs, posture, blood cell formation, and fat storage. Smooth muscles make up important internal organs, like the bladder, arteries and veins. They interact with the digestive system, reproductive system and circulatory system. Smooth muscles control and regulate blood pressure and blood flow. The cardiac muscle is the heart itself, an involuntary muscle that interacts with the circulatory system to supply oxygen to all the tissues of the body. Skeletal muscles are under voluntary control, meaning we can choose to move them. Movement of smooth muscles and the cardiac muscle is involuntary, under control of the autonomic nervous system. The muscular system also plays an essential role in homeostasis, which is the regulation of internal body temperature. Homeostasis is maintained by the hormones that increase osteoblast activity to build bone, called calcitonin which is released by the thyroid gland, and the release of parathyroid hormone which increases osteoclast activity and is released by the parathyroid glands. As long as both of these function normally, the bone mass stays the same, this is a homeostatic state of bone. If it goes out of balance you will either build too much bone or loose bone mass and develop osteoporosis.
The nervous system is the body’s decision and communication centre. The central nervous system (CNS) is made of the brain and the spinal cord and the peripheral nervous system (PNS) is made of nerves. Together they control every part of a person’s daily life, from breathing and blinking to helping people to memorize facts for a test. Nerves reach from the brain to the face, ears, eyes, nose, and spinal cord, and from the spinal cord to the rest of your body. Sensory nerves gather information from the environment; send that info to the spinal cord, which then speed the message to the brain. The brain then makes sense of that message and fires off a response. Motor neurons deliver the instructions from the brain to the rest of your body. The spinal cord, made of a bundle of nerves running up and down the spine, is similar to a superhighway, speeding messages to and from the brain at every second. The CNS controls homeostasis as well as depends on it. The CNS controls homeostasis by using its receptors to sense changes in the body’s internal environment. E.g., certain receptors in the aorta monitor carbon dioxide and oxygen concentration in the blood. This information is relayed to the brain (most functions are controlled by the hypothalamus), and again through the CNS, the effector organs are signalled. Eg To increase or decrease the rate of breathing in response to carbon dioxide/oxygen concentration. The CNS comprises of nerve cells that depend on a very stable internal environment, especially in terms of sodium and potassium concentrations, without which it cannot function properly.
Book References
Author
date
title
origin
Publisher
Oxford college
CC unit 2 material
Saffery and Stewart (eds)
2008,
Maintaining the whole: human biology and health book3, The open university
Web References
Author
Title of article or page
online
Web address
Date accessed
Kevin Berman, MD, PhD, Atlanta Center for Dermatologic Disease, Atlanta, GA. Review provided by VeriMed Healthcare Network. Also reviewed by A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, David R. Eltz, Stephanie Slon, and Nissi Wang.
Circulatory system
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14/02/13
Respiratory system
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http://www.medical-exam-essentials.com/respiratory-system-diagram.html
20/02/13
Central nervous system
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20/02/13
Journal References
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