No body system works alone. A muscle cell in your leg needs glucose from the digestive system and oxygen from the respiratory system, and it depends on the circulatory system to deliver both and carry away carbon dioxide. Because the systems are linked, a problem in one quickly affects the others: damaged lungs make the heart work harder, and narrowed arteries can starve the heart muscle itself of oxygen. This topic uses the anatomy from the previous three lessons to explain what goes wrong in some common disorders, and how medical technologies let us see inside the body and support it.
Three systems, one team
- Digestive to circulatory: glucose, amino acids, vitamins and minerals are absorbed through the villi into capillaries and carried to the liver and then the whole body.
- Respiratory to circulatory: oxygen diffuses from the alveoli into lung capillaries and binds to hemoglobin; carbon dioxide diffuses the other way and is exhaled.
- Circulatory to every cell: capillaries deliver glucose and oxygen to cells for cellular respiration and remove carbon dioxide and other wastes.
- Working together during exercise: muscles use more glucose and oxygen and produce more carbon dioxide, so breathing rate and depth increase, heart rate and stroke volume increase, and blood flow shifts toward the muscles and away from the digestive tract.
Educational content only
This lesson describes disorders and technologies so you can understand the biology. It is not medical advice and cannot be used to diagnose anyone. Symptoms can have many causes; anyone concerned about their health should speak with a doctor, nurse or other qualified health professional.
Respiratory disorders
| Disorder | What goes wrong | Effect on gas exchange |
|---|---|---|
| Asthma | The airways are chronically inflamed and sensitive. During an asthma attack, the smooth muscle around the bronchioles tightens, the lining swells and extra mucus is made. Triggers can include pollen, dust mites, smoke, cold air, exercise and respiratory infections. | Narrowed bronchioles let less air reach the alveoli, causing wheezing, coughing and shortness of breath. Inhaled medications can relax airway muscle (relievers) or reduce inflammation (controllers). |
| Emphysema | The thin walls between alveoli break down, so many small air sacs merge into fewer, larger ones. The lungs also lose elasticity. The main cause is long-term cigarette smoking. It is one form of chronic obstructive pulmonary disease (COPD). | Less total surface area means less oxygen can diffuse into the blood. Air is trapped because the lungs no longer recoil well, making exhalation hard. The damage cannot be reversed, but stopping smoking slows it. |
| Pneumonia | An infection, often bacterial or viral, inflames the alveoli, which can fill with fluid. | Fluid-filled alveoli cannot exchange gases, so less oxygen reaches the blood. |
Digestive disorders
| Disorder | What goes wrong | Link to anatomy |
|---|---|---|
| Peptic ulcer | An open sore in the lining of the stomach or duodenum. Most are linked to infection by the bacterium Helicobacter pylori or to long-term use of anti-inflammatory pain relievers such as ibuprofen or ASA. Stress and spicy food are not the main causes, although they may worsen discomfort. | When the protective mucus layer is weakened, stomach acid and pepsin damage the tissue underneath. |
| Colitis | Inflammation of the colon (large intestine). It can be caused by infection or by long-term inflammatory bowel diseases such as ulcerative colitis. Symptoms can include abdominal pain and diarrhea. | An inflamed colon cannot absorb water properly, so feces stay watery. |
| Constipation | Feces move through the colon too slowly and become hard and difficult to pass. Low fibre, too little fluid and inactivity can contribute. | The longer material stays in the colon, the more water is absorbed from it. |
| Heartburn (acid reflux) | The sphincter at the bottom of the esophagus lets stomach acid flow back up, causing a burning feeling. Frequent reflux is called gastroesophageal reflux disease (GERD). | Unlike the stomach, the esophagus has no thick protective mucus layer against acid. |
Circulatory disorders
| Disorder | What goes wrong | Consequence |
|---|---|---|
| Arteriosclerosis | Artery walls thicken, harden and lose their elasticity. Its most common form, atherosclerosis, is the build-up of fatty deposits called plaque (containing cholesterol and other materials) inside artery walls. Risk factors include smoking, high blood pressure, high LDL cholesterol, diabetes, physical inactivity and age. | Narrowed arteries carry less blood, blood pressure rises, and plaque can rupture and trigger a blood clot. |
| Hypertension (high blood pressure) | Blood pressure stays higher than typical over long periods. It often causes no symptoms, so it is found by measuring blood pressure. | The heart must work harder, and vessel walls are damaged over time, raising the risk of heart attack and stroke. |
| Heart attack (myocardial infarction) | A coronary artery becomes blocked, usually by plaque plus a clot. | Heart muscle beyond the blockage is starved of oxygen and begins to die. |
| Cardiac arrest | The heart's electrical system malfunctions and the heart suddenly stops pumping effectively. | Blood stops reaching the brain and body; the person collapses. CPR and an automated external defibrillator (AED) are used to try to restore a normal rhythm. |
| Stroke | A blood vessel supplying the brain is blocked by a clot or bursts. | Brain cells in the affected area are deprived of oxygen and can be damaged. |
Heart attack vs cardiac arrest
A heart attack is a plumbing problem: a blocked coronary artery stops blood from reaching part of the heart muscle, but the heart usually keeps beating. Cardiac arrest is an electrical problem: the heart's rhythm fails and it stops pumping blood altogether. A heart attack can lead to cardiac arrest, but they are not the same event.
Technologies for seeing and supporting the body
| Technology | How it works | What it is used for | Trade-offs |
|---|---|---|---|
| Endoscope | A thin, flexible tube with a light and camera, passed through the mouth or anus | Viewing the lining of the esophagus, stomach, duodenum or colon; taking tissue samples; removing small growths | Less invasive than open surgery, but still enters the body |
| MRI (magnetic resonance imaging) | A strong magnetic field and radio waves; a computer builds detailed images, including 3-D views | Detailed images of soft tissues such as the heart, blood vessels, brain and joints | No ionizing radiation; expensive, slow and loud; not suitable for some metal implants |
| CT (computed tomography) | X-ray images taken from many angles and combined by a computer into cross-sectional slices | Fast imaging of lungs, bones, blood vessels and internal bleeding | Quick and detailed, but uses ionizing radiation |
| Ultrasound (echocardiogram for the heart) | High-frequency sound waves reflect off tissues to form moving images | Watching heart valves and chambers in action; imaging abdominal organs | No ionizing radiation, portable and cheaper; less detail than MRI or CT |
| Spirometer | Measures how much air a person can exhale and how fast | Studying lung function in conditions such as asthma and COPD | Simple and non-invasive; depends on the person's effort |
| Insulin pump | A small wearable device that delivers programmed doses of insulin through a thin tube placed under the skin | Managing diabetes, in which the pancreas makes too little insulin or the body responds poorly to it | More flexible than repeated injections, but costly and needs careful monitoring |
| Pacemaker | An implanted device that sends electrical pulses to keep the heart beating at a steady rate | Supporting a heart whose natural pacemaker or electrical conduction is faulty | Requires surgery and periodic battery replacement |
| Angioplasty and stents | A tiny balloon is inflated inside a narrowed artery, and a mesh tube (stent) is often left to hold it open | Restoring blood flow through narrowed coronary arteries | Less invasive than bypass surgery; arteries can narrow again |
| Organ transplant | A failed organ (e.g. kidney, liver, heart, lung) is replaced with one from a donor | Replacing an organ that can no longer function | Donors must be matched; recipients take anti-rejection (immunosuppressant) drugs for life; donor organs are in short supply |
Technology develops in response to what society needs. Canada has a notable place in this story: insulin was first isolated for treating diabetes in Toronto in the early 1920s by Frederick Banting and Charles Best, working with J. J. R. Macleod and James Collip. As diabetes has become more common, partly because of more sedentary lifestyles and an aging population, insulin pumps and continuous glucose monitors have made management more convenient. Other technologies raise hard social questions. MRI and CT scanners are expensive to buy, operate and maintain, so they are concentrated in larger urban centres, and people in rural and northern communities may have to travel far or wait longer. The shortage of donor organs has driven organ donor registries, living donation of a kidney or part of a liver, and research into artificial organs, while also raising ethical questions about how scarce organs should be allocated fairly.