Circulation and Respiration

• Physiological processes

  • food, water intake
  • oxygen intake
  • elimination of carbon dioxide
  • nutrients, water, salts
  • oxygen
  • carbon dioxide
  • elimination of food residues
  • rapid transport to and from all living cells
  • elimination of excess water, salts, wastes
• Digestive system

  Processes food, water, nutrients, salts
• Respiratory system

  Processes oxygen intake and carbon dioxide elimination
• Circulatory system

  Rapid transport of substances to and from all living cells
• Urinary system

  Processes elimination of excess water, salts, wastes
• Aerobic respiration

  Oxygen is needed, carbon dioxide is produced
• Human respiratory system

  • Trachea is lined by ciliated, pseudostratified columnar epithelium
  • Epithelium rests on connective tissue which may include blood vessels, that provide heat-exchange to help condition the air
  • Incomplete rings of hyaline cartilage encircle the trachea

  
• Concentration gradients for gases

  • Gases diffuse down their pressure gradients
  • Gases enter and leave the body by diffusing down pressure gradients across respiratory membranes
• Atmospheric pressure

  • Pressure exerted by the weight of the air on objects on Earth's surface
  • At sea level = 760 mm Hg
  • Oxygen is 21% of air; its partial pressure is about 160 mm Hg

  
• Boyle's law

  Pressure of a gas in a closed container is inversely proportional to the volume of the container

  
• Inspiration and expiration

  1. Diaphragm flattens

  2. External intercostal muscles contract

  3. Volume of thoracic cavity increases

  4. Lungs expand

  5. Air flows down pressure gradient into lungs
• Boyle's law and respiration

  When the pressure increases, the volume decreases, and vice versa. This allows air at atmospheric pressure to rush in and fill the lungs during inspiration, and be expelled during expiration.

  
• Alveolus

  • Air space inside
  • Pore for airflow between alveoli
  • Alveolar epithelium
  • Capillary endothelium
  • Fused basement membranes of both epithelial tissues

  
• Alveoli are lung air sacs made of simple squamous epithelial cells for easy diffusion of gases
• Capillaries and alveoli form the respiratory membrane for the exchange of gases between the blood and the lungs

  
• Exchange of respiratory gases (external and internal respiration)

  1. O2 diffuses from alveolus to blood to cell

  2. CO2 diffuses from cell to blood to alveolus
• Partial pressures involved in respiration

  • External (atmospheric air)
  • Internal (blood and tissue cells)
• The PO2 of blood pumped into systemic capillaries is higher (105 mmHg) than the PO2 in tissue cells (40 mmHg at rest) because the cells constantly use O2 to produce ATP. Due to this pressure difference, oxygen diffuses out of the capillaries into tissue cells and blood PO2 drops to 40 mmHg by the time the blood exits systemic capillaries.
• While O2 diffuses from the capillaries into tissue cells, CO2 diffuses in the opposite direction. Because tissue cells are constantly producing CO2, the PCO2 of cells (45 mmHg at rest) is higher than that of capillary blood (40 mmHg). As a result, CO2 diffuses from tissue cells through interstitial fluid into capillaries until the PCO2 in the blood increases to 45 mmHg. The deoxygenated blood then returns to the heart and is pumped to the lungs for another cycle of external respiration.
• Transportation of respiratory gases in respiration

  • External (lungs to blood, blood to tissues)
  • Internal (tissues to blood, blood to lungs)
• Role of erythrocytes in the transportation of oxygen and carbon dioxide

  • 97% of O2 is bound to hemoglobin in RBCs, only 3% is dissolved
  • Hemoglobin has higher affinity for O2 at higher partial pressures (in lungs) and lower affinity at lower partial pressures (in tissues)
  • Most CO2 is transported as bicarbonate, some binds to hemoglobin, small amount dissolves in blood
• Lung volumes

  Tidal Volume (VT), Expiratory Reserve Volume (ERV), Inspiratory Reserve Volume (IRV), Residual Volume (RV)
• Lung capacities


  Inspiratory Capacity (IC), Functional Residual Capacity (FRC), Vital Capacity (VC), Total Lung Capacity (TLC)
• Tidal volume is the amount of air that moves in and out of the lungs during normal quiet breathing. Expiratory Reserve Volume (ERV) is the amount of air that can still be exhaled after normal quiet breathing. Inspiratory Reserve Volume (IRV) is the amount of air that can still be inhaled after normal quiet breathing. Residual Volume (RV) is the amount of volume that cannot be exhaled and is always trapped in the lungs.
• Fick's 1st Law of Diffusion

  Rate of diffusion across a membrane is proportional to the surface area (A), difference in partial pressures (P2-P1), and inversely proportional to the distance (D) over which diffusion must take place
• The enormous number of alveoli (approx 300 million in per lung), the extremely thin respiratory surfaces, and the concentration gradients allow for efficient gas exchange during respiration.

  
• Factors influencing gas exchange

  • Surface area to volume ratio
  • Ventilation
  • Transport pigments
• Advantages and disadvantages of water and air as a medium for gaseous exchange

  • Air contains more oxygen than water
  • Water has higher viscosity than air, increasing work required to pump fluid
  • Diffusion of oxygen in air is 10,000 times faster than in water
• Gills


  • Thin tissue filaments that are highly branched and folded
  • Dissolved oxygen in water rapidly diffuses across the gills into the bloodstream
  • Most efficient of all respiratory surfaces
• Countercurrent exchanger


  Used in gills to maximize gas exchange across the length of the entire respiratory surface
• Adaptations of humans at high altitude

  • More vascularized lungs and more alveoli
  • Larger ventricles in heart
  • More mitochondria in muscle
  • Increased rate of breathing, heart output
  • Kidney secretes erythropoietin, increasing red cell production
• Control of breathing


  • Medulla oblongata sets main rhythm, pons fine-tunes it
  • Breathing rate depends on concentrations of oxygen and H+
  • Chemoreceptors detect drop in oxygen and increase breathing
• Carbon monoxide (CO)


  • Colorless, odorless gas
  • Competes with oxygen for binding sites in hemoglobin
  • Binding capacity is at least 200 times greater than oxygen's
  • Exposure impairs oxygen and CO2 delivery
• The bends


  • Pressure increases with depth, increasing N2 dissolved in blood
  • Can bubble out if diver ascends too fast, causing pain, impaired vision, paralysis
• Adaptations of marine mammals

  • Blood is directed preferentially to heart and central nervous system
  • Conserve O2 by using decreased muscular effort - gliding
  • Able to store O2 in the blood and in the spleen
  • High concentration of oxygen-storing protein (myoglobin) in muscles
• Circulation/Respiration


  • Typical vert. circ. system: Heart → 2 circuits: (i) pulmonary (lungs)/ branchial (gills) & (ii) systemic
  • Pulmonary circulation: moves blood between the heart and the lungs
  • Systemic circulation: moves blood between the heart and the rest of the body

  
• Circulation on right side

  1. Oxygen-poor blood enters right atrium

  2. Tricuspid valve opens to let blood travel to right ventricle

  3. Right ventricle squeezes, closes tricuspid valve, opens pulmonary valve

  4. Blood flows through pulmonary artery, branches to lungs, where it gets oxygen and releases carbon dioxide

  
• Circulation on left side

  1. Oxygen-rich blood travels from lungs to left atrium through pulmonary veins

  2. Mitral valve opens to send blood from left atrium to left ventricle

  3. Left ventricle squeezes, closes mitral valve, opens aortic valve

  4. Heart sends blood through aortic valve to aorta, where it flows to the rest of body

  
• Major component of circ. system

  • Blood
• In highly organized animals (almost all verts), the blood can bind larger quantities of O2 reversibly