Biology – Premed Windsor University School of Medicine Gaseous Exchange

Pre Med – Biology Chapter Gaseous Exchange There is more to lectures than the power point slides! Engage your mind

gills alveoli elephant seals Gas Exchange Respiratory Systems

Why do we need a respiratory system? O2O2 food ATP CO 2 respiration for respiration

Gas exchange O 2 & CO 2 exchange between environment & cells Atmospheric Gases: Oxygen -- 21% Nitrogen -- 78% CO % Diffusion from area of [High partial pressure] to [Low partial pressure]

Optimizing gas exchange Why high surface area? – maximizing rate of gas exchange – CO 2 & O 2 move across cell membrane by diffusion [High concentration] to [Low concentration] rate of diffusion proportional to surface area Why moist membranes? – moisture maintains cell membrane structure – gases diffuse only dissolved in water High surface area? High surface area! Where have we heard that before?

Gas exchange in many forms… one-celledamphibiansechinoderms insectsfishmammals endotherm vs. ectotherm size cilia water vs. land

Large & Thin Surface Area Respiratory Surfaces: Lung alveoli in mammals Gill lamellae in fish Leaf in Plants Cell membrane in Protozoa Skin in Amphibians

Evolution of gas exchange structures external systems with lots of surface area exposed to aquatic environment Aquatic organisms moist internal respiratory tissues with lots of surface area Terrestrial

Gas Exchange in Water: Gills

Counter current exchange system Water carrying gas flows in one direction, blood flows in opposite direction just keep swimming…. Why does it work counter current? Adaptation!

Blood & water flow in opposite directions – maintains diffusion gradient over whole length of gill capillary – maximizing O 2 transfer from water to blood water blood How counter current exchange works front back blood 100% 15% 70%40% water counter- current concurrent

Gas Exchange on Land Advantages of terrestrial life – air has many advantages over water higher concentration of O 2 O 2 & CO 2 diffuse much faster through air – respiratory surfaces exposed to air do not have to be ventilated as thoroughly as gills air is much lighter than water & therefore much easier to pump – expend less energy moving air in & out Disadvantages – keeping large respiratory surface moist causes high water loss reduce water loss by keeping lungs internal Why don’t land animals use gills?

Terrestrial adaptations air tubes branching throughout body gas exchanged by diffusion across moist cells lining terminal ends, not through open circulatory system Tracheae

Lungs Exchange tissue: spongy texture, honeycombed with moist epithelium Why is this exchange with the environment RISKY?

Breathing footprints breathing

The lungs organs that allow gas exchange oxygen in / CO 2 out trachea - has rings of cartilage bronchi (bronchus) bronchioles alveoli (alveolus) computer animation

Alveoli (air sacs) provide large surface area for gas exchange one lung equivalent to a tennis court of surface area using alveoli footprints alveoli

air sac in lungs deoxygenated blood oxygenated blood body cells air in air out

Features of Alveoli for efficient gas exchange large surface area to absorb oxygen. moist surface to allow oxygen to dissolve. thin lining to allow easy diffusion of gases. dense network of blood capillaries for easy gas exchange.

Features of capillaries for efficient gas exchange dense network to carry CO 2 and O 2 Large surface area to transport gases Lining is one cell thick so gases can pass through quickly and easily.

Alveoli Gas exchange across thin epithelium of millions of _________________ – total surface area in humans ~100 m 2

Negative pressure breathing Breathing due to changing pressures in lungs – air flows from higher pressure to lower pressure – pulling air instead of pushing it

Mechanics of breathing Air enters nostrils – filtered by hairs, warmed & humidified – sampled for odors Pharynx  glottis  larynx (vocal cords)  trachea (windpipe)  bronchi  bronchioles  air sacs (alveoli) Epithelial lining covered by cilia & thin film of mucus – mucus traps dust, pollen, particulates – beating cilia move mucus upward to pharynx, where it is swallowed

don’t want to have to think to breathe! Autonomic breathing control Medulla sets rhythm & pons moderates it – coordinate respiratory, cardiovascular systems & metabolic demands Nerve sensors in walls of aorta & carotid arteries in neck detect O 2 & CO 2 in blood

Medulla monitors blood Monitors CO 2 level of blood & cerebrospinal fluid bathing the brain CO 2 + H 2 O  H 2 CO 3 (carbonic acid) if pH decreases then increase depth & rate of breathing & excess CO 2 is eliminated in exhaled air

Breathing and Homeostasis Homeostasis – keeping the internal environment of the body balanced Exercise need more ATP bring in more O 2 & remove more CO 2 Disease need to work harder to bring in O 2 & remove CO 2 O2O2 ATP CO 2

Diffusion of gases Concentration gradient & pressure drives movement of gases into & out of blood at both lungs & body tissue bloodlungs CO 2 O2O2 O2O2 bloodbody CO 2 O2O2 O2O2 capillaries in lungscapillaries in muscle

Hemoglobin Why use a carrier molecule? – O 2 not soluble enough in H 2 O for animal needs blood alone could not provide enough O 2 to animal cells hemocyanin in insects = copper (bluish/greenish) hemoglobin in vertebrates = iron (reddish) Reversibly binds O 2 – loading O 2 at lungs or gills & unloading at cells cooperativity heme group

Heme Group of Hemoglobin

Cooperativity in Hemoglobin Binding O 2 – binding of O 2 to 1 st subunit causes shape change to other subunits conformational change – increasing attraction to O 2 Releasing O 2 – when 1 st subunit releases O 2, causes shape change to other subunits conformational change – lowers attraction to O 2

O 2 dissociation curve for hemoglobin Bohr Shift  drop in pH lowers affinity of Hb for O 2  active tissue (producing CO 2 ) lowers blood pH & induces Hb to release more O 2 P O 2 (mm Hg) More O 2 delivered to tissues pH 7.60 pH 7.20 pH 7.40 % oxyhemoglobin saturation Effect of pH (CO 2 concentration)

O 2 dissociation curve for hemoglobin Bohr Shift  increase in temperature lowers affinity of Hb for O 2  active muscle produces heat P O 2 (mm Hg) More O 2 delivered to tissues 20°C 43°C 37°C % oxyhemoglobin saturation Effect of Temperature

Transporting CO 2 in blood Tissue cells Plasma CO 2 dissolves in plasma CO 2 combines with Hb CO 2 + H 2 OH 2 CO 3 H+ + HCO 3 – HCO 3 – H 2 CO 3 CO 2 Carbonic anhydrase Cl– Dissolved in blood plasma as “bicarbonate ion” carbonic acid CO 2 + H 2 O  H 2 CO 3 bicarbonate H 2 CO 3  H + + HCO 3 – carbonic anhydrase

Releasing CO 2 from blood at lungs Lower CO 2 pressure at lungs allows CO 2 to diffuse out of blood into lungs Plasma Lungs: Alveoli CO 2 dissolved in plasma HCO 3 – Cl – CO 2 H 2 CO 3 Hemoglobin + CO 2 CO 2 + H 2 O HCO 3 – + H +

Adaptations for pregnancy Mother & fetus exchange O 2 & CO 2 across placental tissue Why would mother’s Hb give up its O 2 to baby’s Hb?

Fetal hemoglobin (HbF) What is the adaptive advantage? 2 alpha & 2 gamma units HbF has greater attraction to O 2 than HbA – low % O 2 by time blood reaches placenta – fetal Hb must be able to bind O 2 with greater attraction than maternal Hb

Lungs Can you? Label the internal structures of the lungs State the features of the alveoli which allow efficient gas exchange Explain the role of diffusion in gas exchange State the features of the capillary network that allow efficient gas exchange

Smoking  Cilia: Hair-like extensions lining the trachea  Traps dust and particles  Traps microorganisms  Mucus secretion  Cigarette smoking prevents cilia from beating in wave-like pattern, moving the microorganisms upward  Effects ---- Bronchitis, Emphysema

Bronchitis Inflammation of the lung airways Mucus accumulation

Emphysema Damage to alveoli in lungs, lose elasticity Reduced surface area for gas exchange