microbes, digestion

Question 1

What are the main types of microbe-host interactions?

Answer 1

Pathogen/Parasite (harms host), Commensal (host unaffected), Mutualist (both benefit).

Question 2

Where do microbes reside permanently in the human body?

Answer 2

Skin, oral cavity, gut, urogenital tract.

Question 3

What sites in the human body are microbe-free?

Answer 3

Internal organs and systemic tissues.

Question 4

What happens to microbes that fail to colonise?

Answer 4

They are cleared quickly and have no meaningful interaction with the host.

Question 5

What distinguishes long-term microbial residents?

Answer 5

They don’t cause disease and contribute to normal function, such as occupying available niches.

Question 6

How can some short-term residents affect long-term microbes?

Answer 6

They may displace or outcompete them.

Question 7

What are specialist pathogens?

Answer 7

Microbes that subvert host defences to reproduce and cause disease.

Question 8

What is the difference between pathogens and parasites?

Answer 8

Pathogens cause short-term disease; parasites harm the host’s growth over the long term.

Question 9

What is a commensal microbe?

Answer 9

A microbe that benefits without affecting the host.

Question 10

What is mutualism?

Answer 10

A relationship where both host and microbe benefit.

Question 11

Why is classifying microbes difficult?

Answer 11

Due to the scale, complexity, and dynamic nature of their interactions.

Question 12

How does microbe scale differ from human cells?

Answer 12

Microbial cells outnumber human cells due to their smaller size.

Question 13

Why does the microbial metagenome matter?

Answer 13

It is larger than the human genome and plays a role in health and disease.

Question 14

What protects internal tissues from microbial colonisation?

Answer 14

A tight gut barrier formed by mucin and epithelial tight junctions.

Question 15

What are Koch’s simplified postulates for pathogens?

Answer 15

1. Absent in healthy people, 2. Causes disease when introduced, 3. Cleared after recovery.

Question 16

What is amensalism in microbiology?

Answer 16

The microbe never establishes a sustained population in or on the human body.

Question 17

How are chronic diseases linked to microbes?

Answer 17

Often associated with shifts in microbial community rather than single pathogens.

Question 18

What does the DOHaD framework propose?

Answer 18

Early microbiome development influences lifelong health and disease risks.

Question 19

How is the gut microbiome established after birth?

Answer 19

Microbes colonize skin and gut; stable colonization begins in ileum, densest in colon.

Question 20

What are the major bacterial phyla in the human gut?

Answer 20

Bacteroidetes, Firmicutes, Proteobacteria, Actinobacteria, Verrucomicrobia.

Question 21

What are common microbial contributions to nutrition?

Answer 21

Digestion of fiber and production of SCFAs: acetate, propionate, butyrate.

Question 22

How much of our energy can come from microbial fermentation?

Answer 22

10–15% of human calories via colon fermentation.

Question 23

Where does most microbial fermentation occur?

Answer 23

In the colon, especially non-starch polysaccharides.

Question 24

Which bacterial phyla ferment fiber?

Answer 24

Bacteroidetes and Firmicutes.

Question 25

What does Methanobrevibacter (an Archaea) do?

Answer 25

Performs methanogenesis by converting hydrogen and carbon to methane.

Question 26

What are Short Chain Fatty Acids (SCFAs)?

Answer 26

Metabolites like acetate, propionate, and butyrate used for energy and signalling.

Question 27

What is colonization resistance?

Answer 27

Normal microbes preventing pathogen colonization via competition and environmental control.

Question 28

How does the gut immune system tolerate microbes?

Answer 28

By maintaining a mucin barrier and regulating immune responses to avoid overreaction.

Question 29

What can overactivation of the immune system lead to?

Answer 29

Chronic inflammatory diseases like IBD and allergies.

Question 30

What is the difference between pathogen-induced and immune-mediated diseases?

Answer 30

Pathogen-induced = direct damage (e.g., cholera); immune-mediated = damage from host response (e.g., Lyme disease).

Question 31

What is dysbiosis?

Answer 31

Imbalance in the microbiome leading to loss of beneficial functions and inappropriate immune activation.

Question 32

Why is nutrient control important for microbiome health?

Answer 32

It shapes microbial composition and function.

Question 33

How is “health” defined in terms of microbiome?

Answer 33

Not absence of disease, but balance and symbiosis between host and microbes.

Question 34

What are the primary functions of the digestive system?

Answer 34

Ingestion, secretion, motility, digestion, absorption, elimination, protection.

Question 35

What are the four main layers of the GI tract?

Answer 35

Mucosa, submucosa, muscularis externa, serosa/adventitia.

Question 36

What are the accessory organs of digestion?

Answer 36

Salivary glands, liver, gallbladder, pancreas.

Question 37

What did Dr. Beaumont discover from Alexis St. Martin?

Answer 37

Foundational insights into stomach digestion through a gastric fistula.

Question 38

What are the absorbable units of carbohydrates, proteins, lipids, and nucleic acids?

Answer 38

Carbs: monosaccharides, Proteins: amino acids, Lipids: fatty acids + monoglycerides, Nucleic acids: nucleotides.

Question 39

What is the function of saliva?

Answer 39

Lubricates, digests (amylase), and protects (lysozyme); mostly water.

Question 40

What enzymes are found in saliva?

Answer 40

Salivary amylase (starch to maltose), lysozyme (breaks bacterial walls).

Question 41

What is peristalsis?

Answer 41

Wave-like contractions that propel food through the GI tract.

Question 42

What are the stomach's main anatomical regions?

Answer 42

Cardia, fundus, body, pylorus.

Question 43

What are the stomach’s two sphincters?

Answer 43

Gastro-oesophageal sphincter and pyloric sphincter.

Question 44

What is the role of rugae in the stomach?

Answer 44

Mucosal folds that increase surface area and allow expansion.

Question 45

What are the three layers of stomach muscle?

Answer 45

Oblique, circular, and longitudinal muscle layers.

Question 46

What are the major gastric secretions and their functions?

Answer 46

Gastrin (stimulates secretions), HCl (activates pepsinogen), Pepsin (digests protein), Mucus (protects mucosa), Intrinsic factor (B12 absorption).

Question 47

Where does most digestion occur in the small intestine?

Answer 47

Duodenum.

Question 48

Where does most absorption occur in the small intestine?

Answer 48

Jejunum.

Question 49

What is absorbed in the ileum?

Answer 49

Lipids, fat-soluble vitamins, bile salts.

Question 50

What structural features increase absorption in the small intestine?

Answer 50

Villi and microvilli (brush border).

Question 51

What are the main enzymes for digestion in the small intestine?

Answer 51

Pancreatic enzymes (amylase, lipase, proteases) and brush border enzymes.

Question 52

Why is slow chyme release important?

Answer 52

Prevents overload, ensures neutralisation, supports enzyme function and absorption.

Question 53

What are the digestive functions of the liver?

Answer 53

Secretes bile, bilirubin, and bile salts.

Question 54

What is the role of the gallbladder?

Answer 54

Stores and concentrates bile.

Question 55

What does the pancreas secrete?

Answer 55

Pancreatic juice (enzymes + bicarbonate), insulin, glucagon.

Question 56

What are the regions of the large intestine?

Answer 56

Caecum, colon, rectum, anal canal.

Question 57

What functions occur in the large intestine?

Answer 57

Fermentation by bacteria, water and vitamin absorption, motility, elimination.

Question 58

What is haustral contraction?

Answer 58

Slow segmenting movements every 30 mins in the colon.

Question 59

What are mass peristalsis movements?

Answer 59

Large movements toward the rectum 3-4 times per day.

Question 60

What is bilirubin and where is it excreted?

Answer 60

A hemoglobin breakdown product; excreted in bile.

Question 61

What are the components of faeces?

Answer 61

Undigested food, bacteria, dead GI cells, bile pigments.