4.2.2.1 The Human Digestive System Flashcards
What does the human digestive system provide the body with?
Nutrients
What is the digestive system an example of?
An organ system in which serval organs work together to digest and absorb food
What is the function of the mouth?
- The mouth is the beginning of the digestive system - digestion starts here
- The smell of food triggers the salivary glands in your mouth to secrete saliva (contains the carbohydrase enzyme amylase) which chemically breaks down starch in food to maltose (which ultimately is broken down into glucose)
- Chemical digestiontakes place therefore with the enzyme amylase
- Mechanical digestion (mastication)also takes place: chewing breaks down the food into smaller pieces to increase surface area
What chemicals (inc.enzymes) are produced in the mouth?
Amylase
What is the function of the oesophagus?
- The oesophagus carries food to the stomach
- The oesophagus is a muscular tube
- Food is pushed through the oesophagus and into the stomach by means of a series of muscular contractions called peristalsis
- The mass of chewed food that passes from mouth of stomach (down the oesophagus is called thebolus
What is the function of the stomach?
- The stomach contains hydrochloric acid which kills any ingested bacteria
- It also produces protease enzymes which digest protein (chemical digestion)
- The muscular walls of the stomach contract to churnthe food, breaking it into smaller pieces and increasing its surface area (mechanical digestion)
- The mass of partially digested food + gastric juices that leave the stomach is called chyme
What chemicals are produced (inc.enzymes) in the stomach?
- The stomach contains hydrochloric acid which kills any ingested bacteria
- It also producesprotease enzymeswhich digest protein (chemical digestion)
What is the function of the liver?
- It processes absorbed food and detoxifies the blood
- It makes bile
- Bile is alkaline to neutralisehydrochloric acid from the stomach
- Bile emulsifies fat globules to form small droplets which increases the surface area
What chemicals are produced in the liver?
Bile - an alkaline substance
What is the function of the gall bladder?
The gallbladder stores excessbilebefore it is released into the small intestine
What is the function of the pancreas?
- It is a gland like the salivary gland and both provide digestive juices (enzymes)
- Among other functions, the pancreas producesdigestive enzymes
- Carbohydrate enzyme –carbohydrase
- Fat enzyme –lipase
- Protein enzyme –pancreatic protease
- These are secreted into the first segment of thesmall intestine
- These enzymes break downproteins, fats, and(chemical digestion)
- The pancreas also makes insulin, secreting it directly into the bloodstream. Insulin is the chief hormone for metabolising sugar
What chemicals are produced (inc.enzymes) in the pancreas
- Among other functions, the pancreas producesdigestive enzymes.
- Carbohydrate enzyme –carbohydrase (amylase)
- Fat enzyme –lipase
- Protein enzyme –pancreatic protease
What is the function of the small intestine?
- The small intestine produces protease, amylase and lipase that continue digestion (chemical digestion)
- Soluble products of digestion areabsorbedinto the blood through the walls which are covered in projections called villi (increases surface area)
What chemicals are produced (inc. enzymes) in the small intestine?
The small intestine producesprotease, amylaseandlipasethat continue digestion (chemical digestion)
What is the function of the large intestine?
- The large intestine connects the small intestine to the rectum. The large intestine is a highly specialised organ that is responsible for processing waste
- Bacteria break down anything that was not fully digested in the small intestine
- As material passes through the large intestine, water is absorbed into the blood
- It can then be referred to as faeces
- The faeces itself is mostly food debris (fibre) and bacteria
What is the function of the rectum?
The rectum is an eight-inch chamber that connects the intestines to the anus
The rectum:
- Receives faeces from the large intestine
- Lets the person know there is a stool which needs to be evacuated
- Holds the stool until evacuation happens
What is the function of the anus?
The anus is the last part of the digestive tract
What are some adaptations of the small intestine?
- 7m long - Ample time for absorption of soluble molecules as food travels along
- Very thin cell wall (one cell thick) - easy diffusion, shorter diffusion pathway
- Villi and microvilli - provide larger surface area for absorption
- Capillaries, good blood supply - Maintains a steep concentration gradient to aid diffusion
What are some adaptations of villi?
- Good blood supply, capillaries – maintains a steep concentration gradient
- Thin walls (one cell thick) – short diffusion distance
- Large surface area - finger like projections, has microvilli, larger SA for diffusion
Where in the digestive system does active transport take place?
- During digestion, the villi in the small intestine absorb the soluble nutrients. Over time, the concentration of nutrients in the villi reach an equilibrium with the concentration in the gut
- Active transport is used to continue the transport of the small amounts of remaining nutrients against the concentration gradient
What are products of digestion used for?
- Used to build new carbohydrates, lipids and proteins
- Some glucose is used in respiration
Why don’t vitamins or minerals need digesting?
Vitamins and minerals don’t need digesting as they are either fat soluble or water soluble
What do large multicellular organisms develop systems for?
Large multicellular organisms develop systems for exchanging materials
What happens during the development of a multicellular organism?
During the development of a multicellular organism, cells differentiate, so that they can perform different functions
What are three tissues found in the digestive system?
- Muscular tissue
- Glandular tissue
- Epithelial tissue
What is the function of muscular tissue?
Can contract to bring about movement
What is the function of glandular tissue?
Produces substances such as enzymes and hormones
What is the function of epithelial tissue?
To cover the outside and inside of the stomach
What is the function of muscular tissue in the stomach?
To churn the contents
What is the function of the glandular tissue in the stomach?
To produce digestive juices
What is the function of the epithelial tissue in the stomach?
To cover the outside and inside of the stomach
What are carbohydrates made up of?
Units of sugar
What are simple sugars?
Carbohydrates that contain only one or two sugar units
What do complex carbohydrates contain?
Long chains of simple sugar units bonded together
What do lipids consist of?
Three molecules of fatty acids bonded to a molecule of glycerol
What are protein molecules made of?
Made of long chains of amino acids
Enzyme:
- Enzymes proteins that are biological catalysts in living organisms - help speed up metabolism
- Theyspeed up the rate at whichchemical reactionsproceed without being altered in the process
- catalyse the break down of large molecules into smaller molecules
- They are specific (have specific shaped active sites) – only certain substrates can fit into the active site of an enzymes e.g. only starch can be broken down by amylase
- Enzymes catalyse specific reactions in living organisms due to the shape of their active site
- Digestive enzymes convert food into small soluble molecules that can be absorbed into the bloodstream
- Responsible for various metabolic reactions in our body
Enzyme-substrate complex:
when a substrate is bound to the active site - complementary to each other
Enzyme-product complex:
the enzyme converts the substrate into product forming an enzyme-product complex
Catalyst:
substance that increases the rate of a chemical reaction without being chemically changed
Substrate:
the substance on which an enzyme acts
Active site:
the region on an enzyme that the substrate fits into
Product:
the end result of a chemical reaction
Denaturation:
- The process of modifying the molecular structure of a protein
- If enzymes are exposed to extremes of pH or high temperatures the shape of their active site may change
- If this happens then the substrate will no longer fit into the enzymes - no longer complementary
- the enzymes will have denatured
Where are enzymes produced?
- Some enzymes work outside the body cells
- The digestive enzymes are produced by specialised cells in glands and in the lining of the gut
- The enzymes then pass out if the cells into the gut where they come into contact with food molecules
- Catalyse the break down of large molecules into smaller molecules
What can enzymes do to substrates?
Enzymes can join or break down substrates
What is the enzyme for digestion of food type (substrate) starch and where is it made?
- Carbohydrase e.g. amylase
- Made in salivary glands, small intestine, pancreas
What are the products of digestion of starch?
- Glucose/maltose
- Simple sugars
Where does the digestion of starch take place?
- Mouth
- Small intestine
What is the enzyme for the digestion of food type (substrate) protein and where is it made?
- Protease e.g. pepsin
- Produced in the stomach, pancreas and small intestine
What are the products of digestion for protein?
Amino acids
Where does the digestion of protein take place?
- Stomach
- Small intestine
What is the enzyme for the digestion of the food type (substrate) fat and where is it made?
- Lipase
- Produced in pancreas and small intestine
Where does the digestion of fat take place?
Small intestine
What are the products of digestion for fat and what are their uses?
- Products are fatty acids and glycerol
- Fatty acids and glycerol are used for making hormones, making cell membrane and act as an energy store
- Fat is important in our diet as fats help to increase the absorption of some vitamins
What are conditions that increase the rate of fat breakdown by lipase?
- Alkaline conditions caused by bile
- A large surface area
- Increasing temperature to optimum temperature (up to around 40 ºC) increases the rate of reaction, by increasing the collision rate between the enzyme and substrate molecules (as in any chemical reaction)
Explain the Lock and Key Hypothesis:
- Substrate collides with the active site of the enzyme, the 2 molecules temporarily bind
- Active site has a complementary shape to the substrate – this makes the enzyme specific (complementary means they fit perfectly together)
- The substrate fits perfectly into the active site – like a lock and key. We call this an enzyme-substrate complex
- Once the product has been formed (could be by breaking or making bonds), the products can now leave the active site
- As the enzyme molecule is unchanged, and has not been used up or altered by the process, it can be used again
Explain the Induced Fit Hypothesis:
- The substrate has a very similar shape to the active site
- When it binds to the active site, the active site changes shape to make a more complementary fit.
- When the product has been formed, it can leave the active site.
- The active site returns to its original shape to be used again
How does an increasing temperature affect enzyme activity?
- As temperature increases (towards the optimum), kinetic energy increases. This means that the substrate and enzymes are more likely to collide – there will be more frequent successful collisions
- This increases rate of reaction
- Optimum rate = highest rate of reaction
- Above optimum temperature, the kinetic energy is too high (the particles move too much
And have too much kinetic E) and the bonds that hold the active site in the correct shape break - The shape of the active site is altered – no longer complementary to the substrate. The substrate can no longer bind to the active site, so rate of reaction falls until it reaches 0
- The enzyme is denatured
Temperature coefficient formula:
Q1 = rate at a higher temperature/rate at a lower temperature
What is the temperature coefficient a measure of?
A measure of the rate of reaction as a consequence of increasing the temperature by 10°C
What do most enzymes have a temperature coefficient of?
Most enzymes have a Q10 of around 2 (rate doubles with 10°C increase)
How does pH affect rate of reaction (digestion)?
- Like with temperature, enzymes have an optimum pH. This is the pH at which the rate of reaction is quickest
- If the pH becomes more acidic or more alkaline than the optimum, the rate of reaction will decrease
- This is because the incorrect pH will break the bonds that hold the active site in the correct shape
- Away from optimum pH the bonds that hold the active site in shape breaks
- The enzyme will be denatured - it will change the shape of the active site so the enzyme and substrate can no longer bind
- Further away from the optimum, more bonds break, reduced rate of reaction
What is optimum pH of pepsin (protease in stomach)
approx. pH 2.0
What is the optimum pH of salivary amylase?
approx pH 6.4
What is the optimum pH of trypsin (protease in small intestine)?
approx pH 8.0
What is the optimum pH of lipase?
approx pH 7.0
What chemicals create the optimum pH for enzymes in some parts of the digestive system and how?
- The acidic HCl makes the environment perfect for pepsin (protease in the stomach)
- Bile (alkaline which neutralises acid on food creates optimum pH for lipase and trypsin (both found in small intestine)
Method for investigation to see how changing the concentration of the enzymes catalase affects the rate of reaction
- Use half hydrogen peroxide, half water.
- Starting with the most dilute concn of Catalase.
- Use tweezers to pick up disc and soak in the correct concentration of catalase.
- Place the disc just under the surface of the hydrogen peroxide. Start the timer as you let go.
- The disc will sink and then rise. Stop the timer when the disc reaches the top again.
- Wash tweezers and move onto the next concn.
- Share results with at least one other group so you can calculate an average.
How does increasing enzyme concentration affect the rate of reaction?
- As the enzyme concentration increases so does the rate of enzyme activity
- Here, enzyme concentration is the limiting factor
- A maximum rate is reached when increasing the enzyme concentration does not increase the rate of reaction anymore (the graph plateaus)
- A continued increase in enzyme concentration results in the same activity as there are not enough substrate molecules to be catalysed
- Now, substrate concentration is the limiting factor
How does increasing substrate concentration affect the rate of reaction?
- As the substrate concentration increases so does the rate of reaction
- Here, substrate concentration is the limiting factor
- A maximum rate is reached when increasing the substrate concentration does not increase the rate of reaction anymore (the graph plateaus)
- A continued increase in substrate concentration results in the same rate of reaction, as there are not enough enzymes to break down the excess substrate molecules
- Now, enzyme concentration is the limiting factor
Where is bile made?
In the liver
Where is bile stored?
In the gall bladder
Graph to show how pH affects the rate of digestion:
Graph to show how substrate concentration affects the rate of digestion:
Graph to show how temperature affects the rate of digestion:
Graph to show how enzyme concentration affects the rate of digestion:
Diagram of the digestive system:
How are enzymes related to metabolism?
- they are proteins that speed up metabolism
What do digestive enzymes do?
- Digestive enzymes convert food into small soluble molecules that can be absorbed into the bloodstream
