Organisation

• Multicellular organisms have many levels of organisation
• Cells


  The basic building blocks of all living organisms
• Unicellular organisms


  Made from one cell
• Multicellular organisms


  Made up of collections of cells
• Complex multicellular organisms


  • Cells are specialised to carry out particular functions
  • Specialised cells form tissues
  • Tissues form organs in organ systems
• Examples of organ systems in humans

  • Digestive system (provides the body with nutrients)
  • Respiratory system (provides the body with oxygen and removes carbon dioxide)
• Gas exchange surfaces


  • Large surface area to allow faster diffusion of gases across the surface
  • Thin walls to ensure diffusion distances remain short
  • Good ventilation with air so that diffusion gradients can be maintained
  • Good blood supply (dense capillary network) to maintain a high concentration gradient so diffusion occurs faster
• Gas exchange occurs by the process of diffusion; breathing is essential in maintaining high concentration gradients between the air in the alveoli and the gases dissolved in the blood
• Organ systems


  Provide dissolved materials that need to be moved quickly around the body in the blood by the circulatory system
• Breathing keeps the oxygen level in the alveoli high and the carbon dioxide level low
• The role of the stomach is to start protein digestion
• Alveoli


  The site of gas exchange where oxygen diffuses into the blood and carbon dioxide diffuses out
• Proteases


  Enzymes that digest proteins into amino acids
• Structures involved in ventilation of the lungs

  • Trachea
  • Bronchus (plural: bronchi)
  • Bronchiole
  • Alveoli
• Acid produced by the stomach

  • Aids protein digestion by helping proteins unravel so enzymes can break the bonds holding amino acids together
  • Inhibits many microorganisms that may be present in food, reducing the chance of infection
• Ventilation of the lungs

  Air passes through the trachea, bronchus, bronchiole, and alveoli
• The stomach is one of a number of organs that make up the digestive system
• Diaphragm


  • A thin sheet of muscle that separates the chest cavity from the abdomen; it is ultimately responsible for controlling ventilation in the lungs
  • When it contracts it flattens and this increases the volume of the chest cavity (thorax), which causes a decrease in air pressure inside the lungs relative to outside the body, drawing air in
  • When it relaxes it moves upwards back into its domed shape and this decreases the volume of the chest cavity (thorax), which causes an increase in air pressure inside the lungs relative to outside the body, forcing air out
• Role of the digestive system

  To break down large insoluble molecules into smaller, soluble food molecules to provide the body with nutrients
• Intercostal muscles


  • External intercostal muscles contract during inhalation to pull the ribs up and out, increasing the volume of the chest cavity and decreasing air pressure to draw air in
  • Internal intercostal muscles contract during forced exhalation to pull the ribs down and in, decreasing the volume of the chest cavity and increasing air pressure to force air out
• Types of tissue found in the stomach

  • Muscular
  • Epithelial
  • Glandular
• There is a greater need to rid the body of increased levels of carbon dioxide produced during strenuous activity, which allows a greater volume of gases to be exchanged
• These tissues work together to allow the stomach to carry out its role
• Inhalation and inspiration, exhalation and expiration, are synonymous terms for breathing in and out
• Digestion


  A process in which relatively large, insoluble molecules in food are broken down into smaller, soluble molecules that can be absorbed into the bloodstream and delivered to cells in the body
• Double circulatory system


  The human heart is part of a double circulatory system, with the right side pumping blood to the lungs for gas exchange (pulmonary circuit) and the left side pumping blood under high pressure to the body (systemic circulation)
• Small soluble molecules


  Used to provide cells with energy (via respiration) or with materials to grow, repair and function
• Benefits of a double circulatory system

  • Blood travelling through the small capillaries in the lungs loses a lot of pressure which reduces the speed at which it can flow
  • By returning oxygenated blood to the heart from the lungs, the pressure can be raised before sending it to the body, meaning cells can be supplied with oxygenated blood more quickly
• CHD


  Coronary Heart Disease
• Alimentary canal


  The channel or passage through which food flows through the body, starting at the mouth and ending at the anus
• Heart structure


  • The right side of the heart receives deoxygenated blood from the body and pumps it to the lungs where oxygen diffuses in and carbon dioxide diffuses out
  • The left side of the heart receives oxygenated blood from the lungs and pumps it to the body
  • Blood is pumped towards the heart in veins and away from the heart in arteries
  • The chambers at the top are the atria, the chambers at the bottom are the ventricles
• Pathway of blood through the heart

  1. Deoxygenated blood enters the right atrium via the vena cava, flows to the right ventricle, then to the lungs via the pulmonary artery

  2. Oxygenated blood returns to the left atrium via the pulmonary vein, flows to the left ventricle, then to the body via the aorta
• 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
• Components of the human digestive system

  • Organs that form the alimentary canal
  • Accessory organs
• Adaptations of the heart

  • The walls of the ventricles are much thicker than those of the atria as they are responsible for pumping blood out of the heart and so need to generate a higher pressure
  • The wall of the left ventricle is much thicker than that of the right ventricle as it has to pump blood at high pressure around the entire body, whereas the right ventricle is pumping blood at lower pressure to the lungs
  • There are two sets of valves inside the heart - the atrioventricular valves and the semilunar valves - which prevent the backflow of blood
  • The septum separates the two sides of the heart, preventing the mixing of deoxygenated and oxygenated blood
  • The heart is made of cardiac muscle tissue which does not fatigue like skeletal muscle
  • The coronary arteries supply the heart tissue with oxygenated blood
• The large intestine is home to hundreds of species of bacteria
• Pacemaker


  A group of cells located in the right atrium that coordinate the contraction of the heart muscle and regulate the heart rate
• Role of bacteria in the large intestine

  • Break down substances we can't digest (like cellulose)
  • Supply essential nutrients
  • Synthesise vitamin K
  • Provide competition with any harmful bacteria to restrict their growth
• Cardiac muscle tissue


  • Does not fatigue like skeletal muscle
• Causes of CHD


  • Buildup of fatty material (mainly cholesterol) in the coronary arteries
  • Narrowing of the lumen of the coronary arteries