Topic 6.1: The Digestive System Flashcards Preview

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Flashcards in Topic 6.1: The Digestive System Deck (19)
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1

The Purpose of Digestion

The main purpose of the digestive system is to break large molecules down into smaller subunits due to the fact that:
• Large molecules are typically chemically inert and need to be broken down and reassembled into usable products
• Large molecules are typically insoluble and cannot be easily absorbed into cells, whereas smaller subunits are soluble

2

Digestive System Structure

Mouth
Salivary Glands
Oesophagus
Stomach
Liver
Gall bladder
Pancreas
Small Intestine
Large Intestine
Rectum

3

Alimentary Canal (directly transfers food)

• Oesophagus – Food tract from mouth to stomach
• Stomach – Storage tank with low pH (protein digestion)
• Small intestine – Site of nutrient absorption
• Large intestine – Absorbs water and dissolved minerals

4

Accessory Organs

• Salivary glands – Moistens food bolus (starch digestion)
• Pancreas – Secretes key enzymes into small intestine
• Liver – Metabolises absorbed nutrients (produces bile)
• Gall bladder – Stores and secretes bile (emulsifies fats)

5

Digestive Movement and Peristalsis

• Unidirectional movement of food along alimentary canal
• Caused by contraction of sequential longitudinal muscles

6

Digestive Movement and Segmentation

• Bidirectional mixing of food within the small intestine
• Caused by contraction of non-sequential circular muscles

7

Types of Digestion

Mechanical and Chemical Digestion

8

Mechanical Digestion

The breakdown of food via physical actions
• Chewing (grinding food using teeth)
• Churning (squeezing stomach contents)
• Segmentation (intestinal contractions)

9

Chemical Digestion

The breakdown of food via chemical agents
• Stomach acids (low pH environment)
• Bile (emulsification of fats into droplets)
• Enzymes (catalyse hydrolysis reactions)

10

Starch Hydrolysis

Starch is composed of glucose monomers
• Is linear (amylose) or branched (amylopectin)

11

Amylase

Amylase (salivary or pancreatic) digests starch
• It digests amylose into maltose disaccharides
• It digests amylopectin into dextrin chains

12

Pancreas and Glucose Regulation

• Insulin increases glucose uptake by cells
• Glucagon decreases glucose uptake by cells

13

Liver and Glucose Storage

The liver is responsible for glucose storage
• Glucose is stored as glycogen (polysaccharide)

14

Purpose of Absorption

Absorption involves the movement of fluids or dissolved substances (such as nutrients) across a cellular membrane
• The absorbed components then undergo assimilation within the cell in order to become fluid or solid parts of an organism
Nutrient absorption occurs within the small intestine, while water and mineral ions are absorbed within the large intestine

15

Membrane Transport Mechanisms

Secondary Active Transport
• Glucose and amino acids are co-transported across the
epithelial membrane with sodium ions (Na+)
Facilitated Diffusion
• Certain monosaccharides, vitamins and some minerals
may be transported by epithelial channel proteins
Simple Diffusion
• Hydrophobic materials (e.g. lipids) are capable of freely
diffusing across the epithelial membrane
Endocytosis
• Dissolved materials may be rapidly absorbed en masse via the process of pinocytosis (cell ‘drinking’)

16

Small Intestine Structure

Serosa
Longitudinal muscle
Circular muscle
Submucosa
Mucosa

17

Vili

finger-like mucosal projections that
increase the surface area of epithelium over which absorption is carried out

18

Key Features of Villi

• Microvilli (High SA:Vol)
• Rich blood network
• Single layer epithelium
• Lacteals (absorb lipids)
• Intestinal crypts (exocrine)
• Membrane proteins

19

Modelling Absorption

Dialysis tubing can be used to model the
size-specific permeability of a membrane
• Large molecules cannot cross (e.g. starch)
• Smaller molecules can cross (e.g. glucose)