Human Respiration Notes

Human Respiration

Respiration in Cells

• Respiration is a chemical process: It involves the breakdown of nutrient molecules, specifically glucose, to release stored energy.
• Respiration is enzyme-controlled: It relies on enzymes to facilitate the chemical reactions.
• Respiration vs. Breathing: Respiration is a chemical reaction, while breathing is the physical movement of air into and out of the body (ventilation).
• Types of Respiration:
  • Aerobic: Occurs with oxygen.
  • Anaerobic: Occurs without oxygen; releases less energy per glucose molecule than aerobic respiration.
• Location: Respiration occurs in all living cells, with most aerobic respiration reactions taking place in the mitochondria.

Using Energy

• Energy is essential for all living cells. In humans, cells require energy for:
  • Contracting Muscles: Enables body movement.
  • Protein Synthesis: Production of protein molecules by linking amino acids.
  • Cell Division: Repairs damaged tissues and facilitates growth.
  • Active Transport: Moves substances across cell membranes against concentration gradients.
  • Growth: Building new cells that divide to form more cells.
  • Transmitting Nerve Impulses: Transfers information rapidly throughout the body.
  • Producing Heat: Maintains a constant body temperature.

Energy Source

• Food Digestion: Energy originates from the food we consume.
• Nutrient Absorption: Digested food is broken down into smaller molecules and absorbed from the small intestine into the bloodstream.
• Nutrient Transport: Blood carries nutrients to all body cells.
• Glucose Utilization: Glucose is the primary nutrient for energy provision.
• Respiration Process: Cells break down glucose molecules through metabolic reactions, releasing energy with the help of enzymes.

Aerobic Respiration

• Stepwise Process: Aerobic respiration occurs in a series of small steps, each controlled by enzymes.
• Mitochondrial Location: Most steps take place within the mitochondria.

Aerobic Respiration - Word and Symbol Equations

• Word Equation: $GLUCOSE + OXYGEN \rightarrow CARBON DIOXIDE + WATER$
• Balanced Symbol Equation: $C<em>6H</em>{12}O<em>6 + 6O</em>2 \rightarrow 6CO<em>2 + 6H</em>2O$

Aerobic Respiration - Examiner Tips

• Relationship to Photosynthesis: The aerobic respiration equation is the reverse of the photosynthesis equation.
• Mark Allocation: In exams, marks are awarded for:
  • Correct formula for glucose and oxygen.
  • Correct formula for carbon dioxide and water.
  • Correctly balancing the equation.

Anaerobic Respiration

• Definition: Chemical reactions in cells that break down nutrient molecules to release energy without using oxygen.
• Incomplete Breakdown: It involves the incomplete breakdown of glucose, yielding a smaller amount of energy compared to aerobic respiration.
• Varied Products: Produces different breakdown products depending on the organism.
• Key Equations: It is important to know the equations for anaerobic respiration in humans (animals) and in yeast.
• Location: Anaerobic respiration occurs in the cytoplasm, not in the mitochondria.

Anaerobic Respiration in Animals

• Occurrence: Primarily takes place in muscle cells during vigorous exercise.
• Energy Demand: Muscles require more energy during intense activity.
• Oxygen Limitation: The heart and lungs can only supply a limited amount of oxygen to muscle cells.
• Process: Some glucose is broken down with oxygen, while the rest is broken down without it, producing lactic acid.
• Energy Yield: Less energy is released due to the energy remaining stored in the lactic acid molecules.
• Equation: $GLUCOSE \rightarrow LACTIC \ ACID$

Anaerobic Respiration in Yeast

• Yeast: Single-celled fungi often respire anaerobically, breaking down glucose into alcohol and carbon dioxide.
• Plants: Can also respire anaerobically for short periods.
• Equation: $GLUCOSE \rightarrow ALCOHOL + CARBON \ DIOXIDE$
• Balanced Chemical Equation: $C<em>6H</em>{12}O<em>6 \rightarrow 2C</em>2H<em>5OH + 2CO</em>2$

Aerobic vs Anaerobic Respiration

• Aerobic Respiration:
  • Complete breakdown of glucose.
  • Uses oxygen.
  • Takes place in mitochondria.
  • Large amount of energy released.
  • Products: Carbon dioxide and water.
• Anaerobic Respiration:
  • Incomplete breakdown of glucose.
  • Does not use oxygen.
  • Takes place in cytoplasm.
  • Small amount of energy released.
  • Products: Lactic acid in animal cells; alcohol and carbon dioxide in yeast and plant cells.

Aerobic Respiration - Products

• The purpose of any form of respiration is to release energy stored in the chemical bonds
  of molecules like glucose, so all types of respiration release energy

• The overall equation for aerobic respiration is (energy released is not shown)
  $GLUCOSE + OXYGEN \rightarrow CARBON \ DIOXIDE + WATER$

Aerobic Respiration - Equation

• In a balanced equation for aerobic respiration in any cell; one molecule of glucose reacts
  with 6 molecules of oxygen, forming 6 molecules of carbon dioxide and 6 molecules of
  water. Energy is also released but this is not shown in an equation.

• $C<em>6H</em>{12}O<em>6 + 6O</em>2 \rightarrow 6 CO<em>2 + 6 H</em>2O$

Aerobic respiration

• Aerobic respiration is a chemical reaction that takes place in cells of living organisms
• It uses oxygen as part of the reaction to release energy

Anaerobic respiration

• The word equation for anaerobic respiration in yeast is:
  $glucose \rightarrow alcohol + carbon dioxide$

• The word equation for anaerobic respiration in animals is:
  $glucose \rightarrow lactic acid$

Aerobic Respiration

• Aerobic Respiration requires sugar such as glucose from carbohydrates which animals eat. Plants make glucose by photosynthesis.
• Both Animal and plants get oxygen directly from their surroundings – either from air for terrestrial (land-living) organisms, or from oxygen dissolved in water for aquatic (water-living) organisms.
• The waste products are carbon dioxide and water which must be removed from the organism’s body.

Gas Exchange

• Gas Exchange is the diffusion of oxygen and carbon dioxide into and out of an organism’s body.

• Gas Exchange Surface is the part of the body where the gas exchange between the body and the environment takes place.

• The gas exchange surfaces have to be permeable, so that oxygen and carbon dioxide can move easily through them.

• The gas exchange surfaces have to be permeable

• They are thin to allow gases to diffuse across them quickly.

• They are close to an efficient transport system to take gases to and from the exchange surface.

• They have a large surface area, so that a lot of gas can diffuse across at the same time.

• They have a good supply of oxygen.

The Human Breathing System

• The structures involved in gas exchange in a human are the two lungs
• Each lung is filled with many tiny air spaces called air sacs or alveoli
• It is here that oxygen diffuses into the blood, so that the surface of the alveoli is the gas exchange surface.
• The lungs are supplied with air through the windpipe or trachea.

The nose and mouth

• Air can enter the body through either the nose or mouth.
• Hairs in the nose trap dust particles in the air.
• Inside the nose are some thin bones which are covered with a thin layer of cells.
• Some of these cells, called goblet cells, make a liquid containing water and mucus
• The water in this liquid evaporates into the air in the nose and moistens it.
• Other cells have very tiny hair-like projections called cilia. The cilia are always moving, and bacteria or particles of dust get trapped in them and in the mucus.
• Cilia are found all along the trachea and bronchi, too.
• They sweep the mucus, containing bacteria and dust particles, up to the back of the throat, so that it does not block the lungs.

The trachea

• From the nose or mouth, the air then passes into the windpipe or trachea. Just below the epiglottis is the voice box or larynx.
• This contains the vocal cords. The vocal cords can be tightened by muscles so that they make sounds when air passes over them.
• The trachea has rings of cartilage around it
• As you breathe in and out, the pressure of the air in the trachea increases and decreases.
• The cartilage helps to prevent the trachea collapsing at times when the air pressure inside is lower than the pressure of the air outside it.

The bronchi

• The trachea goes down through the neck and into the thorax
• In the thorax, the trachea divides into two. The two branches are called the right and left bronchi (singular: bronchus).
• One bronchus goes to each lung and then branches out into smaller tubes called bronchioles.
• Thorax: the chest; the part of the body from the neck down to the diaphragm
• Bronchus: one of the two tubes that takes air from the trachea into the lungs
• Bronchiole: a small tube that takes air from a bronchus to every part of the lungs

Alveoli

• There are many tiny air sacs or alveoli at the end of each bronchiole

• The walls of the alveoli are the gas exchange surface. Tiny capillaries are closely wrapped around the outside of the alveoli

• Oxygen diffuses across the walls of the alveoli into the blood.

• Carbon dioxide diffuses the other way.

• The walls of the alveoli have several features which make them an efficient gas exchange surface:

  • They are very thin. They are only one cell thick. The capillary walls are also only one cell thick.
  • They have a good supply of oxygen. Your breathing movements keep your lungs well supplied with oxygen. This is called ventilation.
  • They have an excellent transport system. Blood is constantly pumped to the lungs along the pulmonary artery.
  • They have a large surface area. In fact, the surface area is enormous. The total surface area of all the alveoli in your lungs is over $100 m^2$.

Alveoli - Adaptations

• Alveoli are specifically adapted to maximise gas exchange
• Layer of moisture
• High $O_2$
• Low $CO_2$
• Capillary wall that is 1 cell thick gives a short diffusion distance
• Alveolar wall that is 1 cell thick gives a short diffusion distance
• Good blood supply creates a steep concentration gradient for $CO<em>2$ and $O</em>2$
• Ventilation creates a steep concentration gradient for $CO<em>2$ and $O</em>2$

Key Words

• Alveoli - Tiny air-filled sacs in the lungs where gas exchange takes place.
• Trachea - The tube through which air travels to the lungs; it has rings of cartilage in its walls; to support it.
• Goblet cells - Cells found in the lining (epithelium) of the respiratory passages and digestive system, which secrete mucous.
• Cilia - Tiny hair-like projections in the lining of the respiratory passage that traps dust, mucus and bacteria
• Thorax - The chest; the part of the body from the neck down to the diaphragm.
• Bronchus - One of the two tubes that takes air from the trachea into the lungs.
• Bronchiole - A small tube that takes air from a bronchus to every part of the lungs
• Ventilation - The movement of air into and out of the lungs, by breathing movements

Air Pathway

• Air containing oxygen is inhaled through the mouth or nose, moving down the trachea which branches into the left bronchus and right bronchus (plural bronchi), the bronchi then divide into smaller branches (or airways) called bronchioles which eventually lead to a cluster of alveoli (singular alveolus).

Differences Between Inspired & Expired Air

• Inspired air contains around 20 - 21% oxygen. Expired air contains around 16% oxygen as some is absorbed.
• The carbon dioxide content of inspired air is around 0.04%. The carbon dioxide content of expired air is around 4% as carbon dioxide diffuses into the alveoli from the blood
• The percentage of nitrogen in inspired and expired air is around 79 - 80% and does not change as nitrogen is not able to be utilized by the body in the form of nitrogen gas

Breathing movements

• To make air move in and out of the lungs, you must change the volume of your thorax.
• Muscles in two parts of the body help you to breathe. Some of them, called the intercostal muscles, are between the ribs. The others are in the diaphragm.

Inspiration

• When breathing in, the muscles of the diaphragm contract. This pulls the diaphragm downwards, which increases the volume in the thorax

• At the same time, the external intercostal muscles contract. This pulls the rib cage upwards and outwards. This also increases the volume of the thorax

• As the volume of the thorax increases, the pressure inside it falls below atmospheric pressure. Air therefore flows in along the trachea and bronchi into the lungs.

Expiration

• When breathing out, the muscles of the diaphragm relax. The diaphragm springs back up into its domed shape because it is made of elastic tissue. This decreases the volume in the thorax.

• The external intercostal muscles also relax. The rib cage drops down again into its normal position. This also decreases the volume of the thorax.

• Sometimes the internal intercostal muscles contract strongly, making the rib cage drop down even further. The muscles of the abdomen wall also contract, helping to squeeze extra air out of the thorax.

Reason for Differences Between Inspired & Expired Air Table

Exercise and breathing rate

• All the cells in your body need oxygen for respiration and all of this oxygen is supplied by the lungs. The oxygen is carried by the blood to every part of the body.

• The muscles in your legs contract much harder and more frequently than usual, so they require more energy.

• The cells in the muscles combine oxygen with glucose as fast as they can, to release extra energy for muscle contraction.

• Extra energy can be provided by anaerobic respiration.

• The muscle cells continue to respire aerobically with the oxygen they have, but they also break down some glucose without combining it with oxygen.
  $glucose \rightarrow lactic \ acid + energy$

• This lactic acid must be broken down by combining it with oxygen in the liver. This is done by aerobic respiration in the liver cells.

• While you were running, you built up an oxygen debt. You 'borrowed' some extra energy, without paying for it with oxygen. Now, as the lactic acid is combined with oxygen, you are paying off the debt.

• Oxygen debt: extra oxygen that is needed after anaerobic respiration has taken place, in order to break down the lactic acid produced

Control of breathing rate

• The rate at which your breathing muscles work - and therefore your breathing rate is controlled by the brain.
• The brain constantly monitors the pH of the blood
• If there is a lot of carbon dioxide or lactic acid in the blood, this causes the pH to fall.
• When the brain senses this, it sends nerve impulses to the diaphragm and the intercostal muscles, stimulating them to contract harder and more often. The result is a faster breathing rate and deeper breaths.