2.8 Gut microbiome and stress

Stress is the body’s physiological response to a potential internal or external threat that can involve and/or impact several of the body systems and functions. Intense, short-term threats lasting for minutes to hours are categorised as acute stress, while longer periods of stress lasting for weeks to months are categorised as chronic stress. The acute stress response results in immediate changes in the functioning of the body that are beneficial to the survival of the organism, such as increased heart and respiratory rate.

During stress, cortisol is secreted from the adrenal glands. For response to an immediate stressful event, such as threat to life or other danger, raised cortisol is important for preparing the body to respond to the threat, such as increasing energy levels and awareness. Part of the response to cortisol is to redirect blood away from the gut to organs vital for survival, such as muscles for running and heart for delivering oxygen to the muscles. Video 1 contains a brief summary of some of the effects of the acute stress response on the body.

Download this video clip.Video player: Video 1

Show transcript | Hide transcript

Transcript: Video 1 Overview of body systems affected by the acute stress response

NARRATOR

The fight-or-flight response is a body’s adaptive response to acutely stressful situations, both real and imagined. Acute stress causes rapid changes to occur in most body systems. There are changes to the cardiovascular systems, including increases in heart rate and contractility in heart muscle, as well as changes in the perfusion of blood through the organs of the body. There are changes in metabolism to increase the blood levels of glucose, fatty acids and amino acids. There are cognitive changes, including alterations in perception and memory. There are changes in pain perception, including stress-induced analgesia; or in other words, pain relief. There are changes to the immune system, including a short-term enhancement in its activity. Finally, there are decreases in reproductive hormone production. Overall, the response to acute stress is to prepare the body for action. This is achieved by ensuring resources are preferentially delivered to those systems needed for rapid action.

End transcript: Video 1 Overview of body systems affected by the acute stress response

Download

Video 1 Overview of body systems affected by the acute stress response

With prolonged or chronic stress, cortisol levels stay high for prolonged periods of time. As a result, the reduced blood flow to the GI tract can have an impact on the health and diversity of the microorganisms in the microbiome. Typically, there is a reduction in the bacteria of the microbiota and an increase in pathogenic bacteria, leading to a decrease in gut microbiota diversity and dysbiosis. The pathogenic bacteria can contribute to the intestinal lining becoming more permeable, which can trigger inflammation in the gut wall. Figure 17 shows a colonoscopy of healthy, pale pink colon on the left with clear folds in the gut wall, and a swollen, red inflamed colon on the right.

Figure 17 (a) Healthy colon; (b) Inflamed colon

Show description|Hide description

The figure consists of two parts labelled (a) and (b) that illustrate the healthy colon and inflamed colon. Part (a): an endoscopic image of a healthy colon shows the triangular lumen with characteristic colonic haustrations (segmented appearance), clearly visible vascular pattern (blood vessels), and smooth pale pink mucosa. Part (b): an endoscopic image of an inflamed colon shows the round lumen with no colonic haustrations (segmented appearance), loss of vascular markings (blood vessels), oedematous mucosa, and erythema.

Figure 17 (a) Healthy colon; (b) Inflamed colon

The altered blood flow in chronic stress also affects gut motility and is linked to irritable bowel syndrome (IBS). Recent research has shown that there is altered gut diversity in patients with IBS, but whether this is a cause or effect is not yet known (Kim, 2023).

As you may be starting to see, the optimal functioning and health of the human host and gut microbiome are intertwined. In the next few sections you are going to learn about some of the factors affecting the health of the gut microbiome. You will then explore more about how imbalances in the gut microbiome can lead to several common health conditions.