Digestion 1

Question 1

What is the primary function of the digestive tract?

Answer 1

To break down food into constituent parts and absorb nutrients for use by the body.

Question 2

How is the digestive tract structurally organized?

Answer 2

It is a long tube open at both ends (mouth to anus) with specialized regions that carry out unique digestive functions.

Question 3

What role does the oesophagus play in digestion?

Answer 3

Mainly transit of food from the mouth to the stomach; secretes mucus to protect the lining.

Question 4

What are the key functions of the stomach in digestion?

Answer 4

Storage, mechanical disruption (milling), and chemical breakdown (acid and pepsin) of proteins.

Question 5

Where does the majority of chemical digestion and nutrient absorption occur?

Answer 5

In the small intestine.

Question 6

What is the role of the large intestine?

Answer 6

: Storage, control of fluid and electrolyte absorption, and preparation of waste for excretion.

Question 7

What is peristalsis?

Answer 7

The coordinated muscular contractions that propel food along the digestive tract in one direction.

Question 8

How does the digestive system regulate activity based on food presence?

Answer 8

It uses communication between organs to activate processes only when food is present, avoiding constant full activity.

Question 9

What is the function of saliva in digestion?

Answer 9

Moistens food, begins chemical digestion (especially of polysaccharides via salivary amylase), and protects the mouth.

Question 10

What adaptations do ruminants have for digestion?

Answer 10

A large fermenting chamber (the rumen) for microbial breakdown of tough plant matter before it reaches the true stomach

Question 11

Why do animals like rabbits re-consume certain fecal pellets?

Answer 11

To digest nutrients further by fermenting in the hindgut and reabsorbing them.

Question 12

Why is the small intestine so long and coiled?

Answer 12

To maximize nutrient absorption by increasing contact surface area with digested food.

Question 13

What digestive enzymes does the pancreas secrete?

Answer 13

The exocrine pancreas secretes enzymes into the small intestine that break down proteins, fats, and carbohydrates.

Question 14

How does the stomach of a crocodile differ from humans?

Answer 14

: Crocodiles swallow large chunks and use swallowed rocks (gastroliths) to mechanically break down food over months.

Question 15

What is the importance of mechanical breakdown in digestion?

Answer 15

: It increases the surface area of food for enzymes to act on and prepares food for chemical digestion.

Question 16

What are the main functions of the mouth in digestion?

Answer 16

Food apprehension, mechanical breakdown (chewing), initial chemical digestion via saliva, and food manipulation.

Question 17

Why is chewing important in digestion ?

Answer 17

Chewing breaks food into tiny particles, increasing surface area to volume ratio, allowing enzymes and digestive processes to act more efficiently on the food.

Question 18

How does the nervous system control chewing?

Answer 18

Chewing is a rhythmic, automatic action coordinated by a neural pattern generator in the brain, usually a voluntary but often automatic process.

Question 19

How do teeth types relate to diet?

Answer 19

Incisors: biting and cutting
Canines: gripping and puncturing
Premolars: cutting and grinding
Molars: grinding
Different species have teeth adapted to their specific diet (e.g., lions have sharp carnassial teeth for shearing meat).

Question 20

How are whale teeth adapted to their diet?

Answer 20

Baleen whales have bony plates (baleen) instead of teeth to filter small prey like krill from water.

Question 21

What are the three major salivary glands?

Answer 21

Parotid (near the ears)
Submandibular or Submaxillary (under the jaw)
Sublingual (under the tongue)

Question 22

What different types of saliva do the salivary glands produce?

Answer 22

Parotid: watery, protein-rich saliva
Sublingual: mucous-rich saliva
Submandibular: mixed watery and mucous saliva, important for lubrication during swallowing

Question 23

What are the main components and functions of saliva?

Answer 23

Mostly water
Enzymes like amylase (starch digestion)
Lysozyme and other antimicrobials
Ions such as sodium chloride, bicarbonate, and iodide
Mucus for lubrication
Buffers to neutralize acids and protect teeth

Question 24

How does bicarbonate in saliva protect teeth?

Answer 24

It neutralizes lactic acid produced by bacteria digesting sugars, preventing dental caries (tooth decay).

Question 25

What antimicrobial role does iodide in saliva play?

Answer 25

Iodide combines with reactive oxygen species to form iodine or hypoiodous acid, which has strong antimicrobial effects.

Question 26

What is the structure in salivary glands responsible for secretion?

Answer 26

Acini — blind-ending sacs of secretory cells connected to ducts where saliva is produced and then passed down.

Question 27

How is saliva secretion initiated at the cellular level?

Answer 27

Plasma leaks from capillaries (hyperfiltration), and secretory cells release enzymes from granules via exocytosis into the acinar lumen.

Question 28

: What happens to saliva as it passes through the ducts?

Answer 28

Some components are reabsorbed to prevent loss of nutrients like glucose and to maintain an optimal composition.

Question 29

How does the composition of saliva vary between species or diets?

Answer 29

Variations depend on diet and lifestyle; for example, herbivores have saliva suited to processing fibrous plant material, while carnivores have saliva adapted to their meat diet.

Question 30

What role does saliva play in taste?

Answer 30

Saliva dissolves food components so taste receptors can detect them, making eating pleasurable.

Question 31

What are the main functions of saliva?

Answer 31

Facilitates swallowing, begins digestion, antimicrobial, solvent for taste buds, lubricates mouth for talking, and washes away food residue.

Question 32

How does salivary secretion vary throughout the day?

Answer 32

Lowest in the morning (~0.2-0.3 ml/min), about 0.5 ml/min during the day, and increases up to 5 ml/min when eating.

Question 33

What is the Pavlov’s dogs experiment related to saliva?

Answer 33

Dogs were trained to salivate when hearing a bell, demonstrating the reflex of saliva production triggered by anticipating food.

Question 34

How many muscles coordinate the process of swallowing?

Answer 34

25 different muscles coordinate swallowing to propel food into the oesophagus.

Question 35

: What mechanism moves food down the oesophagus?

Answer 35

Peristalsis, an involuntary wave of muscle contractions triggered by stretching the oesophagus walls.

Question 36

What prevents stomach acid from refluxing into the oesophagus?

Answer 36

The lower oesophageal sphincter (cardiac sphincter), which is usually closed to protect the oesophagus from acidic gastric juice.

Question 37

What triggers the lower oesophageal sphincter to open?

Answer 37

The presence of a food bolus reaching the bottom of the oesophagus stimulates the sphincter to relax and allow food into the stomach.

Question 38

What is the function of the stomach in digestion?

Answer 38

Stores food, mechanically breaks it down, exposes it to acidic gastric juice, and initiates protein digestion with pepsin.

Question 39

What pH level does pepsin require to function effectively?

Answer 39

Pepsin works best at very low pH, around 2, but can function up to about pH 5.

Question 40

How does the stomach mechanically break down food?

Answer 40

Through muscular contractions of the oblique, circular, and longitudinal muscle layers and rough ridges on the stomach lining.

Question 41

What is the role of the pyloric sphincter?

Answer 41

: Controls the release of stomach contents into the small intestine by relaxing briefly to allow small amounts to pass.

Question 42

Why is acid reflux harmful?

Answer 42

Gastric acid damages the oesophagus lining, causing pain, ulcers, and potentially tumours if exposure is frequent.

Question 43

What is the main acid in the stomach that creates a very acidic environment?

Answer 43

Hydrochloric acid (HCl), secreted by parietal cells.

Question 44

What is the primary role of hydrochloric acid in the stomach?

Answer 44

Denatures proteins, disrupts molecules, and acts as an antimicrobial antiseptic.

Question 45

Why is pepsin secreted in an inactive form (pepsinogen)?

Answer 45

To prevent it from digesting the cells that produce it.

Question 46

What is the role of intrinsic factor secreted by the stomach?

Answer 46

It binds vitamin B12, enabling its absorption later in the ileum.

Question 47

What protects the stomach lining from the acidic environment?

Answer 47

: A protective mucus layer secreted by mucus cells.

Question 48

Which cells secrete hydrochloric acid and intrinsic factor?

Answer 48

Parietal cells (located in the upper and middle parts of the stomach, not the antrum).

Question 49

How do parietal cells produce hydrochloric acid?

Answer 49

: Using proton pumps that actively pump hydrogen ions into the stomach lumen.

Question 50

What enzyme catalyzes the formation of carbonic acid inside parietal cells?

Answer 50

Carbonic anhydrase.

Question 51

What happens to bicarbonate ions produced in parietal cells?

Answer 51

They are secreted into the bloodstream, causing the "alkaline tide."

Question 52

What are proton pump inhibitors (PPIs)?

Answer 52

Drugs that block proton pumps to reduce stomach acid production, used to treat acid reflux and ulcers.

Question 53

What can result from damage to the stomach mucosal layer?

Answer 53

Gastric ulcers, which can lead to tumors if untreated.

Question 54

What type of cells secrete hormones that regulate stomach acid production?

Answer 54

Enteroendocrine cells (e.g., G cells that secrete gastrin).

Question 55

What triggers the initial neural stimulation of acid secretion?

Answer 55

Anticipation of food (sight, smell, taste) causing quick but brief acid release.

Question 56

What sustains acid secretion during digestion?

Answer 56

Hormonal signals like gastrin and histamine from enteroendocrine and mucosal cells.

Question 57

: Why is only a small amount of acidic gastric fluid released into the duodenum at a time?

Answer 57

Because the duodenum is alkaline, and excess acid would denature its enzymes.

Question 58

How does the duodenum handle acidic fluid from the stomach?

Answer 58

It neutralizes the acid to maintain a pH around 4–7.5 before digestion continues.

Question 59

What is chyme?

Answer 59

Chyme is a very thin, watery, acidic fluid with tiny particles of partially digested material (proteins, polysaccharides, fats) ready for final digestion phases.

Question 60

What role does intrinsic factor play in digestion?

Answer 60

Intrinsic factor combines with vitamin B12 in the stomach to enable its absorption in the ileum.

Question 61

How long does it typically take for the stomach to empty after a meal?

Answer 61

Usually 2 to 4 hours, but this varies by individual and meal composition.

Question 62

: How does meal composition affect stomach emptying?

Answer 62

Rich carbohydrates empty quickly causing rapid glucose spikes, while proteins and fats slow emptying to allow proper digestion.

Question 63

Which hormones regulate gastric emptying and secretion in response to food breakdown?

Answer 63

Secretin (released in response to acid) and cholecystokinin (CCK, released in response to fats) regulate pancreatic activity and slow stomach emptying.

Question 64

What is the primary function of the stomach?

Answer 64

Acts as a storage vessel, mechanically breaks down food with acid and muscular contractions, and coordinates digestion via neural and hormonal signals.

Question 65

What is the rumen and its role in ruminants?

Answer 65

The rumen is a large fermentation chamber housing bacteria that break down fibrous plant material into absorbable nutrients and volatile fatty acids.

Question 66

How does the rumen process food?

Answer 66

Food is sorted by density; fibrous material floats on top, digestible material sinks and moves through compartments (reticulum, omasum) for further digestion.

Question 67

What is rumination?

Answer 67

The process where ruminants regurgitate, re-chew, and swallow food to increase breakdown and surface area for digestion.

Question 68

: Why do ruminants produce methane gas?

Answer 68

Methane is a byproduct of bacterial fermentation in the rumen and is expelled through burping to prevent bloating.

Question 69

: How do hindgut fermenters differ from ruminants?

Answer 69

Hindgut fermenters ferment food in the large intestine and may re-ingest certain fecal pellets to extract more nutrients, unlike ruminants who ferment in the rumen.

Question 70

Why do ruminants have a large stomach capacity?

Answer 70

To house the massive bacterial population needed to break down nutrient-poor, fibrous plant material efficiently.