Gas Exchange and Smoking Part 1

Gas Exchange Unicellular Multicellular O2 diffuses across cell membrane from fluid around cell into cytoplasm CO2 diffuses out of cytoplasm, across cell membrane, out of organism Plants & Animals respire Specialized gas exchange surface in Humans Alveoli in the lungs

Adaptations of Human Respiratory System Clean, warm air enters during breathing Increase surface area for diffusion of O2 and CO2 b/t blood and atmosphere Minimize distance for this diffusion Maintains diffusion gradients

1. Clean, warm air enters during breathing Air warmed to body temp Moistened by evaporation from lining Protects lung tissue from desiccation (drying out) Hair and mucus provide protection Catch particles larger than 5-10 um Goblet cells Produce mucus in trachea and bronchi (more about this in a bit…)

Alveoli tiny but numerous 2. Increase surface area for diffusion of O2 and CO2 b/t blood and atmosphere Alveoli tiny but numerous Collectively large surface area for gas exchange (70 m2) Increases # of O2 and CO2 molecules that diffuse across surface at any moment Speed up rate of gas exchange

3. Minimize distance for this diffusion Capillaries surround each individual alveoli Enables RBC carrying CO2 to get very close to gas exchange surface (alveoli) Enables oxygen in alveoli to diffuse across capillaries to haemoglobin in RBC Diffusion across alveoli wall and across the capillary epithelium is NOT the same as considering diffusion across membranes of individual epithelial cells

4. Maintains diffusion gradients by: Breathing movements draws air in from outside of the body into lungs and then push it out again Maintains a relatively high concentration of O2 and low concentration of CO2 Blood flow past alveolus Deoxy blood brought TO alveoli Oxy blood carried AWAY from lungs

DIAPHRAGM muscle that contracts and relaxes during respiratory cycle

Terms and Structures to Know Cartilage Ciliated epithelium Goblet cells Smooth muscle cells Elastic fibers Ciliated Epithelial cell Cilia Goblet cell Basement membrane Mucus Lungs Trachea Bronchus Rib External intercostal muscle Internal intercostal muscle Bronchiole Alveolus

pseudostratified ciliated columnar epithelium relatively avascular and almost wholly cellular (i.e., having little or no connective tissue associated with it) aggregation of cells which are in apposition over a large part of their surfaces, and which are specialized for absorptive, secretory, protective, or sensory activities. PCCE = pseudostratified ciliated columnar epithelium

Lungs Thoracic cavity Surrounded by pleural membranes (air tight) small amount of fluid Prevents friction between lungs, ribs, and diaphragm Air enters lungs through airways

Airways (from largest to smallest) Trachea Regular C-shaped rings of cartilage 2 Bronchi (bronchus) Irregular blocks of cartilage Bronchioles (many small branches) Smooth muscle contract/relax to adjust diameter of airways No cartilage = allow muscles to relax during exercise to allow more O2 in Terminal bronchioles Respiratory bronchioles (smaller branches of terminals, hold bunches of grapes/alveoli Alveoli

Overview Cartilage Ciliated epithelium Goblet cells Trachea and Bronchi support Ciliated epithelium Trachea, bronchi, some bronchioles Move mucus Goblet cells In ciliated epithelium Produce mucus Smooth muscle cells Trachea, bronchi, bronchioles Widen or narrow tubes Elastic Fibres Trachea, bronchi, bronchioles, alveoli Elasticity

Cartilage Found in trachea and bronchi Provide support Prevents collapse of airway tubes when air pressure is low C-shaped in trachea Irregular in bronchi

Smooth Muscle Cells Found in walls of Trachea Bronchi Bronchioles Contracts slowly, over long periods of time, does NOT tire Contraction reduces diameter of tubes During exercise, it relaxes, widening tubes, move Oxygen into lungs

Elastic Fibers Found in walls of ALL tubes AND between alveoli Breathing in  fibers stretch to allow alveoli and airways to expand Breathing out  fibers recoil to help reduce volume of alveoli and expand air out of lungs

Goblet cells On ciliated epithelium of trachea and bronchi Very FEW goblet cells in bronchioles. Why? Mucus would hinder gas exchange in the alveoli Upper portion of cell swollen with MUCIN droplets Mucin (glycoproteins) makes up mucus Slimy solution (water, proteins, lipids) Traps inhaled particles Made also made by mucus glands beneath epithelium

Ciliated epithelium Structure Function Sneezing and coughing Single layer of cells Outer surface covered with many thin extensions (cilia) that move Function Move mucus upwards towards mouth to prevent dust and particles from reaching lungs Carry mucus upward toward larynx and pharynx (1 cm/min) Nasal cavity Move mucus in down respiratory tract, into throat so it can be broken down by enzymes in the stomach and pathogens destroyed by acid in stomach Trachea and Bronchi Move mucus up to pharynx to be swallowed Sneezing and coughing When large particles are caught in mucus OR build up of mucus in bronchi and trachea

Trachea Lining made of ciliated epithelium resting on basement membrane (basal cells) of protein fibers Goblet cells in between ciliated cells Loose tissue and glands beneath epithelium

Bronchus Fewer Goblet cells per cm2 than trachea Epithelial cells not as tall as epithelial cells in trachea Elastic fibers beneath epithelium Irregular blocks of cartilage

Bronchiole No cartilage Terminal bronchiole Respiratory bronchiole No Smooth muscle surrounding epithelium of Connect to alveoli

Alveoli Thin epithelial lining squamous epithelial cells 0.5 um thick Surrounded by many blood capillaries carrying deoxy. Blood Oxygen& Carbon dioxide diffuse down their concentration gradients Walls contain elastic fibers

Gas Exchange at Alveolar Surface Air in alveoli = high Oxygen concentration, low concentration of Carbon Dioxide High partial pressure of oxygen Low partial pressure of carbon dioxide Blood brought to lungs by pulmonary artery = low concentration of oxygen, high concentration of carbon dioxide Oxygen diffuses through the thin walls of the alveoli and into the capillary Carbon dioxide diffuses from capillary into alveoli and is breathed out of body

Volume of Lungs Tidal Volume (normal) Vital Capacity (max) Volume of air moved into and out of lungs in one breath About 0.5 dm3 Vital Capacity (max) Maximum amount of air that can move in/out of lungs during deepest breath 3-5 dm3

Inhale/Exhale Inhalation Exhalation Contraction of external intercostals and diaphragm Increases volume of thoracic cavity Draw in air through trachea through bronchi into bronchioles Exhalation Relaxation of external intercostals and diaphragm Air flows out, down pressure gradient