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Relationships between major body systems
Circulatory and Respiratory Systems
The respiratory system is responsible for supplying the oxygen that the circulatory system delivers to all parts of the body.
The cardiovascular system's main organ is the heart, which pumps blood to the different parts of your body. The blood travels from the heart to the lungs, where the respiratory system supplies the blood with oxygen. You inhale air through your nose or mouth; it passes through your pharynx, larynx, trachea and finally to the lungs, where it diffuses into the red blood cells in the capillaries from the alveoli. The oxygen is then delivered to all cells of the body via the circulatory system, which is essential for survival.
The Waste product, carbon dioxide, produced from the cells passes into the blood plasma and is transported back to the lungs via the circulatory system. Here it diffuses from the capillaries into the alveoli and is eventually breathed out through the mouth.
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Digestive and Endocrine Systems
The digestive and endocrine systems need to work together to control blood sugar levels. Glucose is produced when carbohydrates are digested by enzymes in the mouth and small intestine. This is absorbed into the blood where it can pass into the body tissues where it is used to provide energy. When glucose passes into the blood, the blood sugar level rises. The brain identifies this rise in blood sugar level and sends a message to the pancreas to produce the hormone insulin. The insulin changes the permeability of the cell membranes, allowing it to pass into the cells where it is required for energy.
If we have enough glucose, insulin helps control its storage in the liver as glycogen until required. If blood sugar levels are low, the brain will tell the pancreas to secrete the hormone glucagon instead, which causes the liver to convert the stored glycogen in the liver to glucose.
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Control of Oxygen Levels by Homeostasis
The respiratory system provides another example of homeostatic regulation by the nervous system.
In normal breathing there is a state of homeostasis.
During exercise the respiratory system must work faster to keep the oxygen levels in the cells within normal limits and preventing excessive build-up of carbon dioxide.
It is the level of carbon dioxide in the blood rather than the level of oxygen that triggers a change in our breathing rate.
Oxygen and carbon dioxide are carried in the blood and their concentrations all have an effect on your breathing rate.
There are two key structures involved in the homeostatic mechanism of breathing rate:
• The respiratory centre controls rate and depth of breathing
• Carbon dioxide sensors located in the aorta of the heart and the internal carotid arteries.
carbon dioxide
A slight increase in carbon dioxide concentration leads to a marked increase in breathing rate.
There are receptors (sensors) in the aorta, carotid arteries and heart that are sensitive to changes in levels of carbon dioxide.
If levels of carbon dioxide increase the receptors will send messages to the respiratory centre of the brain (medulla oblongata) to tell it to increase rate and depth of breathing.
In summary
Carbon dioxide and oxygen changes are detected in receptors (sensors), which send messages to the cardio-respiratory centre in the medulla oblongata in the base of the brain
The brain sends a message to the heart to increase its pumping action (heart rate) to take on more oxygen and enable the blood to give up excess carbon dioxide
Respiratory muscles also receive instructions from the brain to contract faster, enabling a rise in both oxygen delivery and carbon dioxide removal
Musculoskeletal and Nervous Systems
One of the main functions of the musculoskeletal system is to produce movement. Movement in the body is the result of muscle contraction, which is controlled by the nervous system. Muscles that control the movements of our arms and legs are known as skeletal muscles and are controlled voluntarily, i.e. we control them. Our brain will send a message via the motor neurones to receptors in our muscles telling them to contract and cause the movements we want.
Some of our muscles such as our heart muscle work involuntary, i.e we have no control over it but are still controlled by our nervous system in certain areas of our brain.
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Reproductive and Endocrine Systems
The reproductive system is dependent on the endocrine system to control puberty, trigger production of sperm and ova for reproduction and preparing for and maintaining pregnancy.
The Pituitary Gland
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Produces the hormone prolactin which is responsible for milk production
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Produces Luteinising hormone (LH), which is responsible for triggering ovulation, controlling menstruation and controls the production of the hormone testosterone from the testes
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Produces Follicle-stimulating hormone (FSH), which controls menstruation, starts ripening of ova and assists in the control of sperm production
Testes
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Produces the hormone Testosterone, which controls the development and growth of sperm and the development of male features during puberty
Ovaries
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Produces the hormone Progesterone, which helps control pregnancy and menstruation
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Produces Oestrogen, which is responsible for the development of female features during puberty and helps control menstruation
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Produces Placental hormones, which help control normal pregnancy
HOMEOSTASIS
Conditions in which cells can function properly are narrow, and even small changes inside the cell can disrupt biochemical activities and in extreme cases may kill the cell altogether. The physiological processes, and the mechanisms that regulate them exist primarily to maintain homeostasis.
Homeostasis is the process by which the body maintains a stable environment in which cells, tissues and systems can function. This involves different body systems work together to make sure that the body functions efficiently as a whole.
When changes start to happen, sensory information induces physiological responses that act to defend the internal environment against the changes. If there is a change in the body, these processes can stop, slow down or speed up.
Why is homeostasis important?
If there was not a constant internal environment, our enzymes would not work properly. That would mean that nothing would operate correctly and we would die.
The most important features of the internal environment that must be kept constant are:
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Its chemical constitutes e.g. glucose
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Its osmotic pressure (determined by the relative amounts of water and solutes)
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The level of carbon dioxide
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Temperature
Other examples of activities that take place in the body that are controlled by homeostatic mechanisms include blood pressure and heart rate
Why is homeostasis important clinically?
When doctors and nurses are assessing our vital signs they are basically assessing our internal environment to see if we are maintaining homeostasis
They expect these measurements and observations to be within a normal range and include:
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Body Temperature (36.5 – 37.2)
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Heart/Pulse Rate (Adult: 60-100 beats per minute)
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Respiratory/Breathing Rate (Adult: 12-16 breaths per minute)
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Blood pressure (Between 90/60 and 120/80)
If one or more of these measurements is outside of the normal range, it indicates that homeostasis is not being maintained, and therefore something has gone wrong and we are not healthy
Homeostatic Mechanisms
Conditions in the body are maintained almost constant by homeostatic reflexes; automatic fixed responses to a stimulus (stress). These reflexes are both innate (built in) or learned e.g. bladder reflex to control water balance.
The majority of homeostatic reflexes in the body involve negative feedback responses; responses that correct/reverse any stimulus that causes a change in the internal environment, returning it to normal.
The components of a homeostatic reflex include:
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Stimulus (environmental change)
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Receptors: The body has sensors; sensory neurones sensitive to particular stimuli e.g. pH, oxygen, temperature etc. all over the body monitoring levels
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Control centre: located either in the nervous system (brain) or the endocrine system
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Maintains a particular condition of the body by establishing a ‘set point’ e.g. temperature 37⁰C
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The control centre COMPARES the actual condition of the body with the DESIRED condition of the body
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If the actual condition doesn’t match the desired condition, the control centre sends messages down the motor pathways of the nervous system to the effectors; compensating for the change and returning the actual condition back to the desired condition
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Effectors: These are the organs of the body that correct the changes in the body
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Muscular organs (contract/relax)
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Glands (secrete)
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A positive feedback loop would cause the change to become greater and greater, like an avalanche. An example of this would be blood clotting.
