Digestion

• What are the stomachs roles?

  • churning food to break it into smaller pieces
  • producing protease enzymes
  • Protease enzymes, e.g. pepsin, digest proteins into amino acids
  • the production of stomach acid
• cells in the stomach?

  • The stomach contains cells that are specialised to, e.g. secrete protease enzymes, stomach acid or mucus which protects the stomach lining from acid
• Tissues in the stomach?

  • Glandular tissue contains cells that secrete substances, e.g. enzymes or stomach acid
  • Muscle tissue contains cells that can contract, allowing the stomach to church food
  • Epithelial tissue lines the stomach
• Organs and organ systems in the stomach

  • The stomach is an example of an organ; it is a group of tissues that work together to carry out part of the process of digestion
  • The stomach works together with a series of other organs in the digestive system to digest food
• stomach diagram


  stomach

  
• Digestion: Basics

  • The digestive system is an example of an organ system in which several organs work together to digest and absorb food
  • Digestion is a process in which relatively large, insoluble molecules in food (such as starch, proteins) are broken down into smaller, soluble molecules that can be absorbed into the bloodstream and delivered to cells in the body
  • These small soluble molecules (such as glucose and amino acids) are used either to provide cells with energy (via respiration), or with materials with which they can build other molecules to grow, repair and function
• Tissues and Organs of the Human Digestive System

  • The human digestive system is made up of the organs that form the alimentary canal and accessory organs
  • The alimentary canal is the channel or passage through which food flows through the body, starting at the mouth and ending at the anus. Digestion occurs within the alimentary canal.
  • Accessory organs produce substances that are needed for digestion to occur (such as enzymes and bile) but food does not pass directly through these organs
• Diagram of digestion

  digestion

  A) A

  B) B

  C) c

  D) D

  
• What's the function mouth/salivary glands?

  the mouth is where mechanical digestion takes place, the teeth chew food to break it into smaller pieces and increase it's surface area to volume ratio, amylase enzymes in saliva start digesting starch into maltose, the food is shaped into a bolus(ball)by the tongue and lubricated in saliva so it can be swallowed quickly
• What's the function of the oesophagus?

  tube that connects the mouth to the stomach where the food bolus goes after being swallowed wave - like contraction will take place to push the food bolus down without relying on gravity
• What's the function of the stomach?

  food is mechanically digested by churning actions while protease enzymes start to chemically digest proteins hydrochloric acid is present to kill bacteria in food and provide the optimum pH for protease enzymes to work
• what’s the function of the small intestine?

  first section is called the duodenum and is where food coming out of the stomach finishes being digested by enzymes produced here and also secreted from the pancreas, pH of the small intestine is slightly alkaline around 8-9, second section is called the ileum and is where absorption of digested food molecules takes place, the ileum is long and lined with villi to increase the surface area over which absorption can take place
• What’s the function of the large intestine?

  water is absorbed from remaining material in the colon to produce faeces, faeces is stored in the rectum and removed through the anus
• What’s the function of the pancreas?

  produced all three types of digestive enzymes: amylase, protease and lipase, secretes enzymes in an alkaline fluid into the duodenum for digestion to raise pH of fluid coming out of the stomach
• What’s the function of the liver?

  Produces bile to emulsify fats to break larger droplets into smaller droplets - mechanical digestion, amino acids not used to make proteins broken down here(deamination) which produced urea
• What’s the function of the gall bladder?

  stores bile to release into duodenum as required
• The importance of bacteria in digestion

  • The large intestine is home to hundreds of species of bacteria
  • These bacteria form a microbial ecosystem (the microbiota, or gut flora) that play an essential role in human digestion of food by:
  • Breaking down substances we can’t digest (like cellulose)
  • Supplying essential nutrients
  • Synthesising vitamin K
  • Providing competition with any harmful bacteria to restrict their growth
  • Taking antibiotics can disrupt the gut microbiota which can cause short-term problems with digestion
• What do digestive enzymes do?

  They digest large food molecules into smaller ones
• What is metabolism?

  It is the sum of all reactions in a cell
• What are enzymes made from?

  Proteins
• How do enzymes affect chemical reactions?

  They speed up reactions at lower temperatures
• What happens when substrates bind to an enzyme's active site?

  A chemical reaction occurs, forming products
• What happens to enzymes after a reaction?

  They remain unchanged
• How quickly can some enzymes process substrates?

  Hundreds or thousands per second
• What are enzymes?

  biological catalysts
• How do enzymes work?

  Enzymes catalyse specific chemical reactions in living organisms – usually one enzyme catalyses one particular reaction:

  • The specificity of an enzyme is a result of the complementary nature between the shape of the active site on the enzyme and its substrate(s)
  • Enzymes have specific three-dimensional shapes because they are formed from protein molecules
  • Proteins are formed from chains of amino acids held together by bonds
  • The order of amino acids determines the shape of an enzyme
  • If the order is altered, the resulting three-dimensional shape changes
• What is the lock and key model?

  • The ‘lock and key theory’ is one simplified model that is used to explain enzyme action
  • The enzyme is like a lock, with the substrate(s) the keys that can fit into the active site of the enzyme with the two being a perfect fit
• how does the lock and key model work?

  1. Enzymes and substrates move about randomly in solution
  2. When an enzyme and its complementary substrate randomly collide – with the substrate fitting into the active site of the enzyme – an enzyme-substrate complex forms, and the reaction occurs
  3. A product (or products) forms from the substrate(s) which are then released from the active site. The enzyme is unchanged and will go on to catalyse further reactions
• What determines the specific shape of an enzyme?

  Amino acids that make the enzyme
• Why is the three-dimensional shape of an enzyme important?

  It ensures substrate fits into the active site
• What is the optimum temperature for enzymes in the human body?

  37°C
• What happens to enzymes when heated beyond their optimum temperature?

  They start to break bonds and distort
• What is the consequence of an enzyme losing its shape due to high temperatures?

  It reduces the effectiveness of substrate binding
• What does it mean when an enzyme is described as 'denatured'?

  The shape of the active site is lost completely
• Can substrates fit into denatured enzymes?

  No, the specific shape is lost
• What are the effects of temperature on enzyme activity?

  • Enzymes work fastest at optimum temperature (37°C)
  • High temperatures break bonds, distorting enzymes
  • Distortion reduces substrate binding effectiveness
  • Complete loss of shape leads to denaturation
• Denaturation

  Denaturation is largely irreversible – once enzymes are denatured they cannot regain their proper shape and activity will stop

  • Increasing temperature from 0°C to the optimum increases the activity of enzymes as the more energy the molecules have the faster they move and the number of collisions with the substrate molecules increases, leading to a faster rate of reaction
  • This means that low temperatures do not denature enzymes, but at lower temperatures with less kinetic energy both enzymes and their substrates collide at a lower rate
• What is the optimum pH for most enzymes?

  7
• What is the optimum pH for stomach enzymes?

  pH 2
• What is the optimum pH for enzymes produced in the duodenum?

  pH 8 or 9