Tissues, Organs and Systems

• What are tissues

  • In most organisms , cells are arranged into tissues 
  • A tissue is a group of cells with a similar structure and function that work together to do a job 
  • Single-celled organisms do not have tissues  
  • Some simple animals do not have organs, only tissues
• Examples of tissues

  • Muscle tissue contracts to bring about movement 
  • Glandular tissue can produce substances such as enzymes and hormones 
  • Epithelial tissue covers all parts of the body
• What are organs

  • An organ is a group of different tissues working together for a specific function 
  • An example of an organ is the stomach
• What are the roles of the different tissues in the stomach

  • The stomach contains muscle tissue that contracts to churn the contents 
  • The stomach contains glandular tissue that produces digestive juices 
  • The stomach contains epithelial tissue that covers the inside and outside of the stomach

  
• What are organ systems

  • Organs are organised into organ systems 
  • Organ systems are groups of organs that work together to do a particular job 
  • A good example of an organ system is the digestive system
• What is the function of the digestive system

  • In the digestive system, organs work together to digest and absorb food 
  • Food contains 3 main nutrients : carbohydrates, proteins and lipids (fats), but they are too large to be absorbed into the blood stream so have to be digested 
  • During digestion, large food molecules are broken down by enzymes into small food molecules 
  • The small molecules can then be absorbed into the bloodstream

  
• Describe what happens from when food enters to the mouth to when it reaches the stomach

  • First food is chewed in the mouth - where enzymes in the saliva begin to digest the starch in the food into smaller sugar molecules 
  • Food then passes through the oesophagus into the stomach - where enzymes begin to digest proteins in the food . The stomach contains hydrochloric acid to help the enzyme do this
  • The stomach muscles churn to turn the food into a liquid , increasing it’s surface area for enzymes to digest

  
• Describe what happens as food passes into the small intestine


  • After the stomach turns the food into a fluid, the fluid passes into the small intestine - at this point chemical are released into the small intestine from the pancreas and liver 
  • The pancreas releases enzymes which continue the digestion of starch and proteins and start the digestion of lipids 
  • The liver releases bile which helps to speed up the digestion of lipids , and neutralises the acid released from the stomach
• Describe what happens as food passes out of the small intestine and out of the body

  • The walls of the small intestine release enzymes to continue the digestion of proteins and lipids 
  • In the small intestine, food molecules produced by digestion are absorbed into the bloodstream either by diffusion or active transport 
  • The fluid makes its way into the large intestine where water is absorbed into the bloodstream  
  • Finally faeces are released from the body
• Purpose of the digestive system

  • In the digestive system, large food molecules are digested into smaller molecules and then the products of digestion are absorbed into the bloodstream 
  • Now the products of digestion are then used by the body to build new carbohydrates , lipids and proteins 
  • Some of the glucose produced is used in respiration