Homeostasis
Homeostasis is a process of where our body has to be able to control certain things such as body temperature and the water level so that they don’t change, therefore it is when it keeps things the same. It is how the body keeps the conditions inside, and some scientists refer to it as a constant internal environment; two examples of this is:
• Keeping the body temperature at 37 degrees,
• The amount of water in our body.
Our bodies are always making adjustments to be able to carry out normal bodily functions, but fortunately for us the adjustments are done automatically, if this wasn’t the case then we would all be very busy and would regulate our internal environment very frequently. Homeostasis is controlled by the Automatic nervous system and the Endocrine system (hormones).
Negative feedback system
Homeostasis is quite often referred to as the negative feedback, which means that the system is able to take suitable action to maintain the constant environment. The main responsibility of homeostasis is that it has to maintain constant levels of many body functions e.g. body temperature, heart rate, breathing rate, and also blood sugar levels.
Body temperature
The term used for monitoring the body temperature is called thermoregulation. An adult’s body temperature is usually close to 37 degrees. There are temperature detectors in the skin and the internal organs monitor it and feedback to the hypothalamus in the brain to take the correct action when the temperature rises or falls. Monitoring of body temperature: the body temperature is controlled by the thermoregulatory centre in the hypothalamus which is in the brain. It receives input from two sets of the thermos receptors:
• Receptors that are in the hypothalamus itself are able to monitor the temperature of the blood which passes through the brain; this is the core temperature.
• Receptors which are in the skin (especially in the trunk) are the ones which monitor the external temperature of the body.
Controlling body temperature:
Our bodies have two different mechanisms which control our bodies being too hot or too cold. When we are feeling really hot, the blood vessels which are supplying blood to the skin can swell or dilate, and this is known as Vasodilation. During this process, your body carries a lot of the heat energy around your body, there are also capillaries under the skin which can be filled with blood if you get too hot. This allows more warm blood to flow near the surface of the skin, where the heat can be lost to the air; this is why a lot of individuals look red when they’re too hot. Being too hot isn’t good for us, and many individuals can fall ill from being too hot, and many pass out, and this is why we have to cool ourselves down; this is done by sweating. When your body is too hot, the sweat glands are stimulated to release sweat, the sweat liquid turns into a gas and then evaporates, but to be able to do this, it needs to be warm, as it gets the heat from your skin; as your skin loses the heat, it also cools down. When we are feeling too cold, the blood vessels which are supplying warm blood to the skin become narrow or they get constricted which means they get shut off, this is known as Vasoconstriction, and is the opposite of vasodilation. During this process when the capillaries are ‘shut off’, it takes the blood away from the surface of the skin so that less heat is lost. Hairs on the skin also stand up, which is referred to as Goosebumps, but the technical term for it is piloerection. Also, this reduces the flow of warm blood near the surface of the skin, and reduces heat loss; this is why some individuals may looks pale/purplish when they feel too cold.
Breathing rate
Breathing rate or also known as respiration is controlled by the nerve impulses from the respiratory centre in the brain which is called medulla. This centre also follows some of the principles of the negative feedback system and stimulates a change in the respirations when the chemo-receptors in the blood senses a fall or increase in the amount of carbon dioxide which is circulating the body, e.g. when exercising the receptors sense a high level of carbon dioxide in the blood stream and they send messages to the brain to increase and deepen the breathing rate so that the individuals is able to expel carbon dioxide and replenish oxygen. This is done by sending nerve impulses to the diaphragm, which then causes them to contract (when contacting it'll reduce size). The diaphragm will flatten and it goes lower, this then increasing the space for the lungs to be able to inflate so air is going into the lungs; this is called inspiration. The nerve impulses also affect the intercostal muscle, the intercostal music is between the ribs, these muscles are able to contract and life the ribs up and outwards, again to let the air into the lungs.
Glucose levels
Everyone has cells within their body and there are tons of them, and the cells in our body's need to exact same level of glucose in the blood. Sometimes there can be an excess of glucose and that will get turned into glycogen in the liver, this is regulated by 2 hormones which are from the pancreas know as: Insulin and Glucagon. Controlling the level of blood sugar within the blood also follow the same rule, the negative feedback system. The control centre of this is the pancreas, and this so where the receptors monitor the concentration of glucose which is in the blood stream and the hormones control the right balance. The hormones are mainly responsible for maintaining a control of: insulin - lowers blood sugar levels and also Glucagon - raises blood sugar levels. In a normal health individual, blood sugar levels if they are measured are usually around 4-8 mmol/l (millimoles per litre). After a meal, sugar levels will go high which is known as hyperglycaemia and when they're hungry, sugar levels will go low which is known as hypoglycaemia.
Heart rate
Heart rate can be changed for many different reasons, but the main reason for heart rate increasing is exercise, fear and also excitement. The heart rate is controlled by the autonomic nervous system. Hormones also affect this, therefore it is also controlled by the endocrine system. Heart rate just like the others follow the rules of the negative feedback system, we do not in any way tell our heart to speed up or slow down. There is a pacemaker in the heart which is located I the right atrium and is known as the sino atrial node; this sends nerve impulses across the heart muscle to the other nerves around the body, which then in turn stimulate the other areas of the heart to beat in a rhythm. There are other nerve centres which are known as the atrioventricular node and the bundle of HIS (group of nerves).
(Picture on the right). This is known as the cardiac cycle, the medulla (cardio centre in the brain) adapts the heart beat according to the messages it is being sent from the sympathic and parasympathic nervous system. Messages are sent through the sympathic nervous system, if the heart needs to speed up, and is then increased (heart rate). On the flip side, if the heart rate needs to be slowed down, a message will get sent through the parasympathic nervous system, and it shall be decreased (heart rate). The detectors which are in control of sending these messages back and forth are chemical receptors which are located in the heart, blood and brain, they regularly measure the acidity of the blood and normal heart rate of an individual. The hormone which is known as adrenaline comes from the adrenal glands (located on top of the kidneys) and is secreted when in stress or exercising; this also prepares our bodies for actions and also the rate. An example of this is fight or flight, e.g. if an individual is walking down a dark snicket, and a random individual is stood against the wall, they shall get frightened, and shall think about whether they should walk past the individual (fight), or turn back around and walk away (flight); in both situations, heart rate will increase rapidly.