MR WEST MOD 3

• as size increases, the surface area to volume ratio decreases
• animals must:

  • maintain a supply of materials that they need for respiration and growth:
  • nutrients
  • oxygen
  • remove the waste products of metabolism
  • carbon dioxide
  • ammonium
  • urea
• in small organisms needs can be easily met by diffusion across their body surface (exchange surface)

  • distances are short (less than 0.5 mm)
  • surface area relatively large
• large active organisms cannot rely upon their body surface:

  • surface area relative to volume is insufficient for exchange
  • distances are too great
• Large organisms need:

  • specialist exchange surfaces to satisfy the demands created by high activity levels
  • transport system to deliver materials to / from exchange surfaces
• Features of exchange:

  • increased surface area to volume ratio - small organisms / folding of surface
  • thin - diffusion efficient only over short distance
  • moist - O2, CO2 and nutrients diffuse in solution. rate is inversely proportional to square of distance
  • mechanism to maintain diffusion gradients transport system ventilation mechanism or creation of currents across surface
• Mammalian gaseous exchange system:

  • The lungs are a pair of structures with a large surface area located in the chest cavity with the ability to inflate.
  • The lungs are surrounded by the rib cage which serves to protect them.
  • A lubricating substance is secreted to prevent the friction between rib cage and lungs during inflation and deflation.
  • External and internal intercostal muscles between the ribs which contract to raise and lower the ribcage respectively.
  • A structure called the diaphragm separates the lungs from abdomen area.
• Mammalian Gas Exchange System

  • The air enters through the nose, along the trachea, bronchi and bronchioles which are structures well adapted to their role in enabling passage of air into the lungs.
  • The gaseous exchange takes plance in the walls of alveoli, which are tiny sacs filled with air.
  • The trachea, bronchi and bronchioles enable the flow of air into and out of the lungs.
  • The airways are held open with the help of rings of cartilage, incomplete in the trachea to allow passage of food down the oesophagus behind the trachea.
• Mammalian Gas Exchange System

  • Trachea and bronchi are similar in structure, with the exception of size – bronchi are narrower.
  • They are composed of several layers which together make up a thick wall.
  • The wall is mostly composed of cartilage, in the form of incomplete C rings.
  • Inside surface of the cartilage is a layer of glandular and connective tissue, elastic fibres, smooth muscle and blood vessels.
  • This is referred to as the ‘loose tissue’.
  • The inner lining is an epithelial layer composed of ciliated epithelium and goblet cells.
• Mammalian Gas Exchange System

  • The bronchioles are narrower than the bronchi.
  • Only the larger bronchioles contain cartilage.
  • Their wall is made out of smooth muscle and elastic fibres.
  • The smallest of bronchioles have alveoli clusters at the ends.
• Lungs

  A) cut end of rib

  B) intercostal muscle

  C) bronchioles

  D) alveoli / air sacs

  E) pleural membranes

  F) muscle of diaphragm

  G) diaphragm

  H) position of heart

  I) bronchus (bronchi)

  J) left lung

  K) trachea

  
• alveolar wall is squamous (pavement) epithelium

  • very thin
  • short diffusion path
• mammalian gas exchange system:

  • Cartilage - support trachea and bronchi, role in preventing lungs collapsing if pressure drops in exhalation
  • Ciliated epithelium – bronchi, bronchioles and trachea, moves mucus - prevent lung infection, move it towards throat
  • Goblet cells – trachea, bronchi and bronchioles. Mucus secretion trap bacteria and dust, reduce risk of infection then lysozyme digests bacteria
  • Smooth muscle – can contract so can constrict the airway, control its diameter and control air flow to and from alveoli
  • Elastic fibres – stretch on inhale and recoil on exhale, control air flow
• Alveoli

  • the air spaces are divided up by the alveolar walls:
  • single layer of squamous epithelium
  • flattened cells
  • adjacent capillaries are also squamous epithelium
  • combined thickness 1 µm
  • elastic fibres present
  • moist film into which gases dissolve before diffusion:
  • surfactant (detergent) present reduces cohesion of water molecules and so prevents collapse of alveoli
• Ventilation

  • The flow of air in and out of the alveoli is referred to as ventilation and is composed of two stages; inspiration and expiration. This process occurs with the help of two sets of muscles, the intercostal muscles and diaphragm.
• During inspiration, the external intercostal muscles contract, the internal ones relax, causing the ribs to raise upwards. The diaphragm contracts and flattens. In combination, the intercostal muscles and diaphragm cause the volume inside the thorax to increase, lowering the pressure. The difference between the pressure inside the lungs and atmospheric pressure creates a gradient, causing the air to enter the lungs
• During expiration, the internal intercostal muscles contract whereas the external ones relax therefore lowering the rib cage. The diaphragm relaxes and rises upwards. These actions in combination decrease the volume inside the thorax, increasing the pressure, forcing the air out of the lung
• The volume of air which is always in the lungs is the residual volume. The tidal volume can be exceeded, eg: during exercise where the inspiratory reserve volume is reached in an attempt to increase amount of air breathed in. Similarly, the expiratory reserve volume is the additional volume of air that can be exhaled on top of the tidal volume
• Spirometer

  • A spirometer is used to measure lung volume. A person using a spirometer breathes in and out of the airtight chamber, causing it to move up and down, leaving a trace on a graph
• • Vital capacity – the maximum volume of air that can be inhaled or exhaled in a single breath. Varies depending on gender, age, size, height
  • Tidal volume – the volume of air we breathe in and out at each breath at rest
  • Breathing rate – the number of breaths per minute, can be calculated by counting the number of peaks or troughs in a minute
• Spirometer Trace

  A) expiratory reseve volume

  B) tidal volume

  C) vital capacity

  D) inspiratory reserve volume

  E) total lung volume

  F) residual lung volume

  
• PV = TV X BR

  • PV - total air breathed per minute (pulmonary ventilation)
  • TV - tidal volume
  • BR - breathing rate (breaths / minute)
• Insects:

  • along the thorax and abdomen of most insects are small openings (spiracles)
  • air enters and leaves via spiracles but water is also lost
  • can be opened or closed by sphincters
  • spiracle sphincters are closed as much as possible to minimise water loss
• Insects:

  • Tracheae
  • up to 1 mm in diameter
  • lined by spirals of chitin (relatively impermeable to gas) which keep them open
  • Branch into many narrower tracheoles (0.6 - 0.8 µm) which give a large surface area
  • freely permeable to gas - not lined by chitin
  • moist inside
• Insects:

  • Tracheole
  • oxygen dissolves in the moisture in the walls of the tracheoles and diffuses into the surrounding cells
  • towards the end of the tracheoles there is tracheal fluid which limits the penetration of air for diffusion
  • when oxygen demands build up, lactic acid increases in the tissues resulting in water moving out of tracheoles. This exposes more surface area for gas exchange
• beetles, locusts and grasshoppers have high energy demands

  • The supply of more oxygen is carried out by alternative methods like:
  • mechanical ventilation
  • collapsible enlarged tracheae or air sacs
• Fish:

  • Gills
  • Fish:
  • large surface area (4 gills ; pairs of lamellae ; each lamella is folded)
  • short diffusion path
  • vascularised (good blood supply)
  • ventilated
  • Tadpoles have external gills:
  • highly branched
  • short diffusion path
  • vascularised
  • movement provides water current
• • gill filaments - provide large surface area; filled with blood; short diffusion path
  • gill arch - bony structure to support the gill filaments and gill rakers
  • gill rakers - filter water and trap prey (small zooplankton)

  
• • gills have numerous folds that give them a large surface area
  • the rows of gill filaments have many protrusions called gill lamellae. The folds are kept supported and moist by the water that is continually pumped through the mouth and over the gills
• Stages of the Ventilation of Gills:

  1. Mouth opens (operculum closed)
  2. buccal cavity floor lowered
  3. increases the volume and decreases the pressure of buccal cavity compared to outside
  4. water rushes in the mouth down a pressure gradient
  5. opercular cavity expands
  6. buccal cavity floor is raised
  7. pressure in the buccal cavity is now higher than in the opercular cavity
  8. water moves from buccal cavity over the gills into opercular cavity
  9. mouth is now closed and operculum opens
  10. the sides of the opercular cavity move inwards, increasing the pressure
  11. water rushes out of the fish through the operculum
• why do animals need a specialised transport system?

  • low surface area to volume ratio
  • high metabolic demands
  • remove waste products
  • transport hormones
  • products of digestion required in different locations
• invertebrates have an open circulatory system
• vertebrates have a closed circulatory system
• Open system:

  • transport medium (haemolymph) is pumped at low pressure directly into the main body cavity (haemcoel) where it slowly flows about the cells
  • inefficient circulatory system limits the size of invertebrates
  • low pressure
  • haemolymph is collected by open vessels like drains, which carry the blood back to the heart
  • system is supplemented with a seperate open system for gas exchange
  • flow cannot be altered to meet demand
• Closed system:

  • Transport medium (blood) remains within the blood vessels and materials diffuse in and out of the blood through the walls of capillaries
  • flow can be altered to meet demand
  • carries nutrients, gases and waste products
  • under high pressure
• elastic fibres in blood vessels allow elastic recoil to control blood flow
• Arteries

  • adapted to carrying blood away from the heart to the rest of the body, thick walled to withstand high blood pressure, contain elastic tissue which allows them to stretch and recoil thus smoothing blood flow, contain smooth muscle which enables them to vary blood flow, lined with smooth endothelium to reduce friction and ease flow of blood
• Arterioles

  • branch off arteries, have thinner and less muscular walls, their role is to feed blood into capillaries
• Capillaries

  • smallest blood vessels, site of metabolic exchange, only one cell thick for fast exchange of substances
• Venules

  • larger than capillaries but smaller than veins