Chapter 3d Flashcards
Gut
also known as
the gastrointestinal tract) the long flexible tube from mouth to anus that is the passageway involved in digestion
What is the gut responsible for
The gut is responsible for processing food, absorbing nutrients, and excreting waste
Parts of the gut
Mouth
Oesophagus
Stomach
Small and large intestines
Rectum
Anus
Microorganisms in gut
Within your gut, there are many living microorganisms that help maintain gut health and functioning. These microorganisms typically refer to bacteria, fungi, and viruses.
Gut microbiota v gut micro biome
The gut microbiota refers to all of the microorganisms that live in the gut, whilst the gut microbiome refers to all of the genes of the microorganisms that live in the gut.
Gut health
The health of the gut can change based on the types and amounts of microorganisms present in the gut. For example, the presence of some types of bacteria (often referred to as ‘good’ bacteria) can result in good gut health, whilst the presence of other types of bacteria (often referred to as ‘bad’ bacteria) can result in poor gut health. When the gut microbiota is imbalanced, meaning there is not enough ‘good’ bacteria and too much ‘bad’ bacteria, it is called gut microbiota dysbiosis (Thursby & Juge, 2017). In contrast, when the gut microbiota is balanced, it is called gut microbiota symbiosis. Additionally, a common term used to describe the composition of gut microbiota is whether it is diverse, meaning there are many different kinds of microorganisms present, or not diverse, meaning there are few kinds of microorganisms present. Typically,
a diverse gut microbiota results in better gut health.
Factors effecting gut health
Diet
Stress
Age
Genetics
Meds
Physical activity
Gut Brian axis
The gut-brain axis is a relatively new and emerging area of research. It involves looking at the connection between the gut and the brain, and how they may interact and influence each other. Specifically, the gut-brain axis refers to the bidirectional connection between the gut and the brain through the enteric and central nervous systems.
Enteric and cns connection to gut brain axis
The enteric nervous system refers to the network of nerves in the gut and is a subdivision
of the autonomic nervous system. By contrast, the central nervous system refers to a major division of the nervous system comprising the brain and spinal cord, which receives neural messages from and transmits neural messages to the peripheral nervous system. Nerves within the enteric nervous system communicate with nerves in the central nervous system, therefore reflecting the relationship between the gut and the brain.
• For example, if an individual has a gut-related condition, such as inflammatory bowel disease, it can influence the neural messages the enteric nervous system sends to the brain in the central nervous system.
• In the same way, if an individual has a brain-related condition, such as depression, it can influence the neural messages the central nervous system sends to the gut in the enteric nervous system.
Vagus nerve
The vagus nerve is the longest cranial nerve that connects the gut and the brain, enabling them to communicate. The vagus nerve is responsible for bidirectionally conveying information between the gut and the brain. 10–20% of nerve fibres in the vagus nerve are involved in conveying information from the brain to the gut and 80–90% are responsible for conveying information from the gut to the brain (Breit et al., 2018).
Gut brain axis in psychological processing and behaviour
When we feel anxious, we may experience stomach discomfort, and when we experience stomach discomfort, we may feel anxious. Therefore, having ‘butterflies in your stomach’ reflects the gut-brain connection. I
the gut can impact our psychological processes and behaviour. Research on the gut-brain axis has suggested there are potential links between the gut and experiences of stress, the presence or absence of mental illness, learning, memory, body weight, and behaviour.
The composition of gut microbiota can impact psychological processes and behaviour. Often,
a diverse gut microbiota is associated with greater levels of overall health, therefore having more positive influences on psychological processes and behaviour. Additionally, the presence of ‘good’ bacteria and the absence of ‘bad’ bacteria in the gut microbiota has positive influences on psychological processes and behaviour.
Emerging research
Because the gut-brain axis is an emerging area of research, it is important to understand that this research is constantly evolving and improving, which means it is difficult to make definitive statements and draw conclusions. For example, it is incorrect to say that the composition of
gut microbiota causes an individual to experience stress or to develop a mental illness, rather,
it is more correct to say that emerging research suggests there are some possible connections between these concepts. Additionally, as new research emerges, some gut-brain axis studies have presented contradictory results. For example, a study with one strain of mice indicated that there was less social engagement and interaction in germ-free mice (Mayer et al., 2015), whereas another study with a different strain of mice indicated that there was a normal level
of social engagement and interaction in germ-free mice (Luczynski et al., 2016). This highlights the gut-brain axis is a new and dynamic area of research.
germ-free animal studies
• comparing microbiota composition in humans
• exploring gut-related diseases and their impacts on cognition and emotion.
Germ free animal studies
link between the gut microbiota and the brain can be seen through
studies on germ-free animals. Germ-free animals are animals that have had microorganisms from their gut microbiota removed. Germ-free animal studies compare certain behaviours and psychological processes in germ-free animals with non-germ-free animals (often referred to as regular or conventional animals).
Some findings from germ-free animal studies that indicate the role of gut-brain axis in psychological processes and behaviour include (Mayer et al., 2015):
• significant changes in anxiety-like behaviour and anxiety responses in germ-free mice
• poorer memory function in germ-free mice
• increased secretion of stress hormones in germ-free mice
• less social engagement and interaction in germ-free mice.
One particular study involved implanting microbiota from patients with major depressive disorder (MDD) into germ-free mice and observing the impact of this implantation on mice behaviour. The mice with the implanted microbiota from the patients with MDD began to exhibit depressive-like behaviours (Zheng et al., 2016).
This research does not necessarily suggest that germ-free animals are ‘unhealthier’ or ‘healthier’ than conventional animals, as it is just observing psychological and behavioural differences between them. Additionally, although studies on germ-free animals may show some gut-brain influence on psychological processes and behaviour, they are difficult to generalise to humans.
Microbiota composition in humans
Some studies have compared the microbiota in healthy individuals and individuals with different psychological or behavioural patterns or experiences. Research has suggested that the composition of gut microbiota can influence the likelihood of experiencing:
• autism spectrum disorder (Garcia-Gutierrez et al., 2020)
• mental disorders, including depressive disorders, anxiety disorders,
and psychotic disorders (Kelly et al., 2016; Lee & Kim, 2021)
• cognitive decline (Proctor et al., 2016).
One of the more well-known gut-brain axis topics is the potential link
between the gut microbiota and the stress response. Stress can influence
the gut microbiota and the gut microbiota can also influence the likelihood
of experiencing stress, reflecting the bidirectional relationship between
the gut and the brain. For example, studies show that experiencing stress
can negatively impact the diversity and composition of an individual’s gut microbiota (Molina-Torres et al., n.d.; Madison et al., 2019). Likewise, having an unhealthy gut microbiota is linked to higher stress levels (Dinan et al., 2012). The gut-brain connection can also explain why an individual may experience digestive discomfort when experiencing stress, or on the other hand, may experience stress when experiencing digestive discomfort.
Gut related diseases
Some emerging research focuses on individuals with gut-related diseases and their experiences of anxiety, depression, and other cognitive and/or emotional problems. Two of these gut-related diseases that have been discussed in research are irritable bowel syndrome and inflammatory bowel disease.
There are potential links between the presence of these gut-related diseases and the presence of anxiety and depression symptoms (Abautret-Daly et al., 2017; Whitehead et al., 2002). Therefore, experiencing a gut-related disease may increase the likelihood of experiencing a mental illness.
