Digestion

Question 1

What are the stages of food processing? (4)

Answer 1

1. Ingestion – voluntarily taking food through the mouth
2. Digestion – food is broken down into small molecules
3. Absorption – small molecules move into the blood
4. Egestion – undigested material is excreted

Question 2

Components of the Digestive System =

Answer 2

Gastrointestinal Tract (GIT) / Alimentary canal + Accessory glands

Question 3

Gastrointestinal tract = (8)

Answer 3

mouth → pharynx → oesophagus → stomach → small
intestine → large intestine → rectum → anus

Question 4

Accessory glands = (4)

Answer 4

salivary glands + liver + gallbladder + pancreas

Question 5

What are sphincters?

Answer 5

Regulate the passage of material between components and slow processes down to aid digestion and absorption

Question 6

How is food digested? (6)

Answer 6

1. Upper oesophageal sphincter (UOS) → after swallowing, food goes through UOS and then goes through Lower oesophageal sphincter (LOS) 5 – 8 s later.

Malfunction of LOS → heartburn/gastric reflux → acidic content of stomach pushes up into oesophagus if LOS does not close properly → acidic content reacts with sensitive lining of oesophagus causing pain

2. Stomach → food stays in stomach for 2 -6 h after ingestion → small amounts of food exist from Pylorus slowly to allow small intestine to digest content
3. Sphincter of Oddi → regulates digestive enzymes + bile from gallbladder
4. Ileocecal valve → food exits small intestine from this sphincter into the large intestine → 5 – 12 h after ingestion before food moves into large intestine/colon
5. Food moves through colon → takes 7 – 72 h until it reaches rectum
6. Expelled after 24 – 72 h after ingestion from internal + external sphincters

Question 7

What is mechanical digestion?

Answer 7

Mastication: grinding of bolus by teeth to breakdown food into smaller pieces → helps increase SA for enzymatic activity

Question 8

What is chemical digestion?

Answer 8

→ enzymatic hydrolysis → breakdown of larger food into simpler molecules by enzymes in presence of water

Question 9

Starch →

Answer 9

Glucose [Amylase]

Question 10

Protein →

Answer 10

Amino acids [Protease]

Question 11

Fat →

Answer 11

Fatty acids + glycerol [Lipase]

Question 12

Chemical digestion of starch →

Answer 12

Salivary amylase in the mouth helps breakdown/hydrolyse starch into maltose + dextrins

Question 13

What are salivary glands?

Answer 13

→ exocrine glands (glands with ducts) that produce
saliva

Question 14

What are the types of salivary glands? (3)

Answer 14

1. Parotid gland
   - Location: back of the cheek
   - Produces: amylase for chemical digestion
2. Submandibular gland
   - Location: jaw
3. Sublingual gland
   - Location: under the tongue

Question 15

What do the Submandibular + Sublingual glands produce?

Answer 15

Submandibular + Sublingual gland produce mucus to lubricate food to facilitate swallowing → forms bolus

Question 16

What are the stages of Swallowing/Deglutition? (3)

Answer 16

During mechanical and chemical digestion, nasal cavity is open, allowing for air to go down the trachea into the lungs
1. Oral phase
2. Pharyngeal phase
3. Oesophageal phase

Question 17

What is the oral phase? (4)

Answer 17

• Voluntary
• Tongue presses food against roof of the mouth, triggering pressure receptors which causes swallowing centre, that initiates reflexes preventing food entry into nasal passages
• As you prepare for swallowing, soft palate/uvula at the back of the throat, blocks nasal cavity, preventing bolus going into nasal cavity
• Tongue blocks the oral cavity

Question 18

What is the Pharyngeal phase? (2)

Answer 18

• Involuntary
• Larynx elevates and glottis closes by the epiglottis to ensure bolus of food does not go down trachea and cause choking

Question 19

What is the Oesophageal phase? (2)

Answer 19

• Involuntary
• Food passes through UOS, which then closes, allowing for the nasal cavity to open again

Question 20

What is peristalsis? (2)

Answer 20

→ part of the oesophageal phase
- Wave-like motions of the alimentary canal, moving food bolus forwards
- Contraction of smooth muscle in the walls of the oesophagus, forcing bolus down the oesophagus

Question 21

What is the stomach? (3)

Answer 21

Stores: Rugae → gastric folds → allow stretching of the stomach (can stretch to store 2 L)

Fundus actively expands with the amount of food taken in

Disinfects food: Has acidic content not allowing microorganisms to survive

Question 22

What are the 3 muscle layers of the stomach?

Answer 22

= oblique + circular + longitudinal → contraction aids mechanical digestion and mixing of food with secreted gastric juices

Question 23

Chyme =

Answer 23

Ingested food + gastric juices

Question 24

Gastric juices =

Answer 24

Hydrochloric acid (HCL) denatures proteins + Pepsin (protease enzyme) breaks down proteins into smaller peptides

Question 25

Rugae have ___ ____ which are the openings of the gastric glands which are lined with cells.

Answer 25

gastric pits

Question 26

What are the Cells in Stomach lining that protect stomach underlying tissues from getting digested? (4)

Answer 26

- Parietal cells - Chief cells - Mucus cells - Epithelial cells

Question 27

What are parietal cells?

Answer 27

→ produce H+ and CL- ions into lumen of stomach where they combine to form HCL

Question 28

What are Chief cells? (3)

Answer 28

→ release pepsinogen (inactive form of pepsin) so that it doesn’t attack cell itself Pepsinogen is converted into Pepsin (process activated via HCL) Positive feedback loop → pepsin production causes more activation of pepsinogen leading to more pepsin being produced so that there is enough to digest food in stomach pH: 1.5 – 3.0

Question 29

What are mucus cells? (3)

Answer 29

→ produces thick coat of mucus → physical barrier from gastric juices Mucus contains Bicarbonate ions (alkaline) → chemical barrier to neutralize the acid

Question 30

What are epithelial cells?

Answer 30

→ have tight junctions which are frequently replaced

Question 31

What is Gastric Ulcers formation?

Answer 31

Normally gastric juices are only released when food is present, but smoking + stress can lead to gastric juices being released in the absence of food. These gastric juices start eroding the stomach lining, leaving a open sore (ulcer) which can bleed. Bacteria (Helicobacter pylori) also cause ulcers as they are acid-tolerant, produce alkaline to neutralize acid in stomach to make environment suitable for habitat.

Question 32

What is the small intestine? (2)

Answer 32

- Acidic chyme moves into the small intestine via the pyloric sphincter. - Where most digestion + absorption occurs.

Question 33

What are the 3 parts of the small intestine?

Answer 33

- Duodenum: shortest, 25 cm, pancreatic enzymes + bile mixed with chyme to aid digestion - Jejunum: 2.5 m, majority for nutrients are absorbed - Ileum: 3.5 m, remaining nutrients are absorbed until they move into larger intestine

Question 34

What is the duodenum?

Answer 34

Acid food (chyme) from stomach mixes with digestive juices from accessory glands.

Question 35

What are the accessory glands? (3)

Answer 35

1. Pancreas → pancreatic juice rich in enzymes 2. Liver → produces bile 3. Gall bladder → stores bile

Question 36

What is bile? (3)

Answer 36

Neutralizes (pH=8) and dilutes the content of the stomach, creating an optimal pH for pancreatic enzymes Bile = water + bile salts + bile pigments + fats Bile does not have any enzymes, its bile salts emulsify fats, increasing the surface area for the enzyme lipase to work

Question 37

Micelles =

Answer 37

bile salts + cholesterol + lecithin

Question 38

What are the two glands of the pancreas?

Answer 38

Endocrine gland and Exocrine gland.

Question 39

What is the endocrine gland of the pancreas?

Answer 39

- Islets of Langerhans cells secrete hormones (beta cells = insulin [when glucose gets too high], alpha cells = glucagon [when glucose gets too low]) into blood vessels

Question 40

What is the exocrine gland of the pancreas? (3)

Answer 40

- Acinar cells secrete digestive enzymes into pancreatic duct - Pancreatic juices = H2O, HCO3 -, digestive enzymes - Bicarbonate ions (HCO3-) neutralize acidic chyme thereby providing optimal environment for pancreatic enzymes

Question 41

The pancreas secretes digestive pancreatic enzymes: (4)

Answer 41

1. Lipase → digests fats 2. Amylase → digests carbohydrates 3. Proteases → digests proteins → trypsin, chymotrypsin, carboxypeptidase 4. Nucleases → digests nucleic acids

Question 42

How are proteins digested? (5)

Answer 42

1. Proteases (digest proteins to form smaller polypeptides) are released in inactive form called ‘zymogens’ so that pancreas is not digested itself - Trypsinogen (inactive form) is activated by enzyme, Enterokinase found at brush border of enterocyte cells lining the small intestine, forming Trypsin (active form) - Trypsin then further activates zymogens + inactive proteases to create active proteins to digest proteins in small intestine - Gall stone or if trypsin is activated in pancreatic duct → pancreatitis, digestion of pancreas - Trypsin has positive feedback on Trypsinogen

Question 43

How are amino acids digested? (5)

Answer 43

2. Peptidases (further breakdown polypeptides into amino acids) - Peptidases are known as membrane-bound enzymes → bound to brush border of enterocytes (columnar epithelial cells) lining the small intestine → ensures amino acids are broken away close to site where they can be absorbed + ensures peptidases are not excreted with chyme - Dipeptidases → breaks peptide bonds into 2 amino acids - Carboxypeptidases → cutting off amino acid off carboxy end of the peptide - Aminopeptidases → cutting off amino acid off amino end of the peptide

Question 44

How are disaccharides broken down? (3)

Answer 44

3. Disaccharidases (break down disaccharides into monosaccharides) - Sucrase, maltase lactase → located on brush border of enterocyte cells - enzyme, lactase breaks down lactose into glucose + galactose which then enter bloodstream

Question 45

Lactase breaks down ____ to form Galactose + Glucose Maltase breaks down ____ to form Glucose + Glucose Sucrase breaks down _____ to form Glucose + Fructose

Answer 45

Lactose Maltose Sucrose

Question 46

_____ helps break down nucleotides.

Answer 46

Nuclease

Question 47

Nucleotidase → Nucleosidase →

Answer 47

→ removes the phosphate group from the nucleotide → cleaves or breaks off the nitrogenous base

Question 48

Left with 3 separate components: pentose sugar, phosphate group, nitrogenous base which can be used by the cell to ______ its own DNA.

Answer 48

synthesise

Question 49

How are carbohydrates digested? (4)

Answer 49

Salivary amylase in the mouth breaks down starch molecules into smaller molecules which then travel down the oesophagus into the stomach in the form of bolus where the salivary amylase becomes deactivated. When bolus reaches duodenum, pancreas releases pancreatic juice via exocrine ducts which contain pancreatic amylase. This enzyme further breaks down the glucose chains and then enzymes on the brush border (micro villi) finish the breakdown of the chain into monosaccharides. The glucose, fructose and galactose are absorbed into the enterocyte cells and then out of the cells into the blood stream where they travel into the liver. In the liver: - fructose + galactose is converted into glucose

Question 50

Sucrose = glucose + _____ Maltose = glucose + ______ Lactose = glucose + _______

Answer 50

fructose glucose galactose

Question 51

The actual glucose is converted to: (4)

Answer 51

- stored as liver glycogen - becomes part of blood glucose - stored as muscle glycogen - converted/stored as fat.

Question 52

What happens once proteins enter the stomach?

Answer 52

1. Once proteins enter the stomach, chief cells in the stomach release pepsinogen (inactive enzyme). HCl activates the pepsinogen into pepsin. Pepsin breaks the proteins into small polypeptides. The alkaline pH of the small intestine inhibits pepsin’s function. Pancreas release trypsinogen, chymotrypsinogen and procarboxypeptidase. These are inactive when released. An enzyme called Enteropeptidase activates the enzymes trypsinogen into trypsin. This trypsin activates chymotrypsinogen into chymotrypsin and procarboxypeptidase into carboxypeptidase. 2. Trypsin and chymotrypsin act on specific bonds between specific amino acids (dipeptides or small fragments), while carboxypeptidase can only act on specific end of fragment, releasing one amino acid at a time (free amino acids). 3. The brush border microvilli contain peptidases which complete the breakdown of the dipeptides and small fragments. 4. The free amino acids and the dipeptides are absorbed by the enterocyte cells via membrane transporters. The dipeptides further break down into separate amino acids when entering the enterocytes. The amino acids are exported out of the cells into the blood where they travel to the liver.

Question 53

In the liver, amino acids are: (4)

Answer 53

- taken up by liver cells - used by cells throughout the body - converted to glucose - be used for cellular respiration

Question 54

Triglyceride =

Answer 54

glycerol unit + 3 fatty acid chains

Question 55

How are fatty acids digested? (5)

Answer 55

- Lingual lipase if released in the saliva in the mouth however it is not active in the mouth. The lingual lipase + triglyceride travel down to the stomach. The acidic pH activates the lingual lipase. Chief cells release gastric lipase. These lipases break the triglycerides into diglycerides and fatty acid chains. - When entering the small intestine, since they are hydrophobic, enter the small intestine in large lipid masses, which must be broken down into smaller fragments → emulsification via bile salts + phospholipids. Bile salts and phospholipids are amphipathic molecules. The hydrophobic regions enclose the hydrophobic fats forming emulsion droplets. - Pancreatic lipase released by the pancreas breaks down the molecules into monoglycerides and 3 fatty acids. Form micelles, much smaller than emulsion droplets. These transport monoglycerides + fatty acids to the enterocyte cells membranes, where they absorb the fatty acids + monoglycerides. - In the cells, the fatty acid s+ monoglycerides reform triglyceride. These are wrapped in proteins forming lipoprotein = chylomicron. The chylomicrons are transported through the lymphatic vessels eventually entering the bloodstream. - They are transported to liver, fat, muscle tissue where they can be stored or used by cells.