digestive system

Question 1

What is the main structure of the digestive system?

Answer 1

Mouth
Pharynx (Throat)
Oesophagus
Peristalsis
Stomach
Small Intestine
Large Intestine
Rectum
Anus

Question 2

Digestion in the Mouth (and Peristalsis)

Answer 2

Digestion begins in the mouth where food is mechanically broken down by teeth and is chemically broken down by amylase (an enzyme in saliva).

The tongue forms a bolus out of the food which is passed to the pharynx and into the oesophagus with aid from the epiglottis.

The peristalsis pushes the bolus down the oesophages to the stomach (through the lower oesophageal sphincter, via muscle contractions.

Question 3

Digestion in the Stomach

Answer 3

The stomach is a large muscular with folds called rugae which mechanically digests the bolus and mixes it with gastric juice (stomach acid, mucus, and enzymes). The stomach also does slight absorption (alcohol/medicine)

The acid kills bacteria/viruses, the enzymes chemically digest proteins and lipids, and the mucus protects the lining of the stomach.

The digested bolus becomes Chyme and leaves the stomach to the small intestine through the pyloric sphincter.

Question 4

What are the 3 parts of the Small Intestine and what do they do?

Answer 4

1. Duodenum
   Uses bile (produced in the liver and stored in the gall bladder) to break down fats and oils and uses pancreatic juice (secreted from the pancreas) to reduce the acidity of the Chyme.
2. Jejunum
   The functional unit of the digestive system, Villi, absorbs nutrients. Due it the large surface area this is where most of the absorption occurs.
3. Ileum
   The last portion of the small intestine. Has less villi and absorbs the remaining nutrients.

Question 5

What does the Large Intestine do?

Answer 5

Absorbs water from the waste material leftover and produces vitamin K and B using bacteria.

All leftover waste is compacted and stored in the rectum. When full, the anal sphincter loosens, and the waste gets shat out through the anus.

Question 6

What is the structure of the Digestive System’s functional unit?

Answer 6

The Epithelium:
- one cell thick to increase diffusion rate
- microvilli increase surface area for absorption

Lacteal:
- tiny lymphatic vessels
- absorbs fatty acids and glycerol

Blood Capillary:
- absorbs glucose and amino acids

Question 7

Hindgut Fermenters

Answer 7

Fermentation occurs in the caecum (start of large intestine).
Small absorbable products of fermentation are unable to be absorbed until they come out as feces as they are already in the large intestine.
Some hindgut fermenters eat their own shit, allowing it to pass through the small intestine and be absorbed.
(e.g. horses, rabbits, possums, koalas)

Question 8

Foregut Fermenters

Answer 8

Fermentation occurs in the rumen (before the stomach).
Breaks down cellulose into small absorbable products which are absorbed along the length of the small intestine.
Some ruminants regurgitate and re-swallow their food to give it more mechanical digestion and allow for more bacterial fermentation.
(e.g. cows, sheep, kangaroos)

Question 9

Digestion of Cellulose

Answer 9

Cellulose is a complex carbohydrate which needs to be broken down into smaller sub-units before it can pass through cell membranes.
Cellulose digestion is done by the cellulase enzyme (found in fungi, protozoa, and bacteria).

Cellulose digestion by bacteria is Fermentation.