Eduqas Biology A Level C3 - Nutrition

Draw a labelled diagram of the digestive system, from mouth to anus

Mechanical digestion definition

Physical breakdown of large pieces of food into smaller pieces

Chemical digestion definition

Process by which enzymes break down large food molecules into smaller molecules that the body can use

What enzyme do the salivary glands produce?

amylase

What molecule does amylase target?

Starch

Starch + Amylase =

maltose

What is maltose?

A disaccharide composed of two alpha-glucose units

What kind of digestion occurs in the mouth?

chemical and mechanical

What molecules are digested in the mouth?

Starch only

Why is mechanical digestion important in the mouth?

Because it increases the surface area of the food particles, and makes food easier to swallow so we don't choke

What is a bolus?

Portion of food swallowed at one time

What part of the body does the bolus pass to after the mouth?

The oesophagus

What is the mouth also known as?

Buccal cavity

How does the oesophagus move the food down towards the stomach?

Peristalsis

What are the 4 layers of the oesophagus wall (from the lumen out)?

Mucosa, Sub-mucosa, Muscularis and Serosa

What is the purpose of the mucosa layer in the oesophagus wall?

It secrets mucus to lubricate the oesophagus

What is the purpose of the sub-mucosa in the oesophagus?

It is connective tissue containing the blood vessels and lymph vessels of the oesophagus, as well as nerves that coordinate peristalsis

What is the purpose of the muscularis layer in the oesophagus?

To contract and relax during peristalsis

What is the purpose of the serosa layer in the oesophagus wall?

It protects the oesophagus wall from friction injuries as it moves during food processing

Peristalsis definition

Rhythmic wave of coordinated muscular contractions in the circular and longitudinal muscle of the gut wall, passing food along the gut in one direction only

What is a sphincter?

A circular muscle that constricts or dilates to regulate the passage of materials through an opening

What controls the entrance and exit of the stomach?

The two sphincters at the entrance and the exit

What is the sphincter at the entrance of the stomach called?

The cardiac sphincter

What is the sphincter at the exit of the stomach called?

The pyloric sphincter

What is the purpose of the mucosa of the stomach?

It secretes mucus and digestive enzymes

What is the purpose of the sub-mucosa in the stomach?

It contains blood vessels, lymph vessels, and the nerves that control peristalsis

What types of digestion occur in the stomach?

chemical and mechanical

What molecules are digested in the stomach?

Proteins only

How is the mucosa of the stomach structured?

It has large folds called rugae

What are the large folds in the mucosa of the stomach wall called?

Rugae

How does the muscular wall of the stomach differ from that in the oesophagus?

The stomach has an extra layer of muscle called oblique muscle, to aid with peristalsis

What are the two muscles found in the muscularis layer of all the gut walls?

Circular muscle and Longitudinal muscle

What is the purpose of the muscularis layer in the stomach wall?

To provide contractions during peristalsis

What is the purpose of the serosa layer in the stomach wall?

To protect the stomach against friction injuries caused by movement during food processing

What is the purpose of mucus in the stomach?

It coats and protects the stomach walls from being damaged and digested by the pepsin and HCl

What is a gastric pit?

Gastric pits are found in depressions of the mucosa, and contain the gastric glands

What do the gastric glands contain?

Gastric juices, consisting of pepsinogen, HCl and pepsin

What cell secrets mucus and where is it found?

Goblet cells, found in gastric pits

What are the two important cell types found in the lining of the gastric pits?

Oxyntic cell and chief cells

What is the purpose of an oxyntic cell?

It secrets HCl

Why is HCl required in the gastric glands of the stomach?

HCl is used to activate pepsinogen and convert it to pepsin

What is the purpose of chief cells?

They secret pepsinogen

What is pepsinogen?

Inactive form of pepsin

How is pepsinogen activated?

With the addition of HCl

Why isn't pepsin produced directly as pepsin in the cells instead of pepsinogen?

Pepsin is a strongly hydrolysing enzyme and would hydrolyse the proteins in the cells of the stomach wall

How does the stomach protect itself against auto-digestion?

Pepsinogen, which is non-hydrolysing, is created in the cells, and is activated outside of the cells in the gastric pits.

What is pepsin?

An endopeptidase

What is an endopeptidase?

Enzyme that hydrolysises a polypeptide chain somewhere in the middle (as opposed to at the terminals)

What is an endopeptidase?

Enzyme that hydrolysises a polypeptide chain at the terminals of the chain (as opposed to somewhere in the middle)

What endopeptidases and exopeptidases are found in the stomach?

Only Pepsin, an endopeptidase, is found in the stomach

How long does food stay in the stomach?

An average of 4-6 hours

Why must the contents leaving the stomach be neutralised?

The enzymes in the rest of the gut do not work well at low pH levels

Draw a graph showing mucus depth in each region of the digestive system (mouth, oesophagus, stomach, small intestine, colon)

Why is the mucus level relatively high in the mouth?

To lubricate the mouth and also aid the mechanical digestion of the food

Why does the mucus level decrease from the mouth to the oesophagus?

The mucus is only required for lubrication, so there is less

Why is the mucus level in the stomach very high?

The mucus aids mechanical digestion, lubricated and protects the stomach lining from the low pH and the hydrolysing enzymes

Why does the mucus level decrease from the stomach to the small intestine?

Less protection is needed, as the low pH has been neutralised. In the ileum of the small intestine absorption is occurring and so a small diffusion pathway is favoured

Why does the mucus level increase from the small intestine to the colon?

Water is being absorbed and so more lubrication is needed

What contents are entering the small intestine from the stomach?

Carbohydrates such as starch and maltose, short polypeptides and lipids

What does the small intestine consist of?

The duodenum and the ileum

Which is first, the duodenum or the ileum?

The duodenum

When does the pancreatic juice enter the digestive system?

At the duodenum

How does the pancreatic juices enter the digestive system?

Via the pancreatic duct

Where is pancreatic juice created?

pancreas

Does any absorption occur in the stomach?

No

Does any absorption occur in the duodenum?

No

Does any absorption occur in the ileum?

Yes

Does digestion occur in the ileum?

No

What is contained in the pancreatic juices?

- Trypsinogen

- Enterokinase

- Lipase

- Amylase

- Sodium Hydrogen Carbonate

- Other endopeptidases

Are there exopeptidases present in the stomach?

No

Are there exopeptidases present in the small intestine?

Yes

What is trypsinogen?

An inactive form of trypsin

What is trypsin?

An endopeptidase

What activates trypsinogen?

enterokinase

What is enterokinase?

An enzyme in the small intestine that activates trypsinogen

What is the purpose of amylase in pancreatic juices?

To hydrolyse any remaining starch into maltose

What is the purpose of lipase in pancreatic juices?

To hydrolyse lipids into fatty acids and glycerol

What is the purpose of sodium hydrogen carbonate in the pancreatic juices?

To neutralise the pH of contents leaving the stomach, to provide a suitable environment for enzyme action

How does the function of the duodenum differ from the function of the ileum?

The duodenum is for digestion, and the ileum is for absorption and the last bit of digestion

Where is bile made?

liver

Where is bile stored?

gallbladder

What are the two purposes of bile?

To neutralise pH, and to emulsify fats

Why is it beneficial for fats to be emulsified by bile?

It increases the surface area for enzyme action of lipase

Where do exopeptidases work?

In the epithelial cells of the small intestine

Where do endopeptidases work?

In the stomach and the duodenum

How is the ileum structured to aid absorption?

- It is very long and its lining is folded, increasing the surface area at which absorption can occur

- The folds in the lining are villi, which also have microvilli, further increasing surface area

- The epithelial cells have many mitochondria to respire and produce ATP for active transport

- There is a good blood supply to maintain a constant concentration gradient

Do exopeptidases work in the stomach, along with endopeptidases?

No, they are only found in the small intestine

How are amino acids absorbed into the blood stream in the digestive system?

They are transported into the epithelial cells by active transport and then are transported into the capillaries via facilitated diffusion

How is glucose absorbed into the blood stream from the digestive system?

Glucose is first transported into the epithelial cells by co-transport with sodium ions, or by active transport. Glucose then moves into the capillaries via active transport or facilitated diffusion (depending on the concentration gradient)

How is glycerol absorbed into the blood stream from the digestive system?

Glycerol diffuses into the epithelial cells (simple diffusion) and then into the lacteals

The lacteals lead into the lymphatic system, and eventually the glycerol will enter the blood at the neck

How are fatty acids absorbed into the blood stream from the digestive system?

Fatty acids diffuse into the epithelial cells (simple diffusion) and then into the lacteals

The lacteals lead into the lymphatic system, and eventually the fatty acids will enter the blood at the neck

How are minerals absorbed into the blood from the digestive system?

simple diffusion, facilitated diffusion and active transport

How are disaccharides absorbed into the blood from the digestive system?

The are actively transported from the gut lumen into the epithelial cells, and then broken down into monosaccharides. As monosaccharides, they enter the blood stream via facilitated diffusion

What happens to the lipids absorbed after digestion?

- Used in membranes

- Used to make some hormones

- Excess is stored

What happens to the glucose absorbed after digestion?

- Taken to body cells and respired for energy

- Stored as glycogen in liver and muscle cells

- Excess is stored as fat

What happens to amino acids absorbed after digestion?

- Taken to body cells for protein synthesis

- Excess is deaminated

- NH₂ groups are converted into urea

- The rest of the amino acids are converted to storage

What are the 4 parts of the large intestine?

ceacum, appendix, colon and the rectum

What is the purpose of the colon?

to absorb water and salts

What two things are absorbed by the colon?

water and dissolved minerals/salts

Define autotroph

An organism that synthesises its own complex organic molecules from simpler molecules using light or chemical energy