Lecture 5: Gas Exchange

need of oxygen

to generate ATP, which is needed for cellular function and metabolism. as a result of cellular activity, high levels of CO2 is generated, which must be expelled.

cellular respiration

oxidative processes within cells

external respiration

exchange of O2 and CO2 between an organism and its environment

factors for effective gas-exchange surfaces

• moist

• thin

• relatively large surface area

vascularization

formation/presence of blood vessels; helps enhance the effectiveness of diffusion

Types of Respiratory Organs

1. cutaneous respiration

2. tracheal systems

3. gills or brachia

4. lungs

cutaneous respiration

respiratory organ that refers to direct diffusion of respiratory gasses to skin

• paramecium, marine sponge, jellyfish, flat worms, amphibians

tracheal systems

respiratory organ referring to a branching system of tubes, with openings called spiracles (usually no well-defined circulatory system)

• in insects

gills or brachia

respiratory organ that retain its shape in the presence of water, and possess papulae (extension of the fluid-filled coelom)

• in fish, starfish, axolotl, ragworms, etc.

way in which a fish ventilates its gills

gills are given its shape from counterflow of water

1. when mouth open, water enters and a structure called the operculum is closed & water collects in gills

2. when mouth is closed, the operculum opens, pushing water across gills to exit

gill filaments

part of gill that help filter oxygen out of the water

blood vessels in gills mechanism

countercurrent flow/exchange:

1. as oxygen-rich water enters the filaments, oxygen is filtered in and distributed to blood vessels in the gill for these to be oxygenated (arteries)

2. as water exits the gill filaments in the form of de-oxygenated water, this is where unoxygenated blood residues (veins)

lungs

respiratory organ that are invaginations, and are more suited for terrestrial animals

air gives lungs its structure

lung mechanism in frogs

positive-pressure breathing

• pressure in the buccal cavity increases (more air) = inflation

lung mechanism of birds

possess air sacs attached to the lung proper, since birds are suited for flight

1. inspiration 1: oxygen-rich air goes to posterior air sac

2. the pressure pushes air to the more thoracic component, once it reaches the cervical component, it becomes deoxygenated

3. second inspiration: repeat steps 1-2

4. the second batch of air that enters the anterior air sac pushes the previous air outwards (cycle repeats)

component of lungs in mammals

passage of air: trachea → bronchus → bronchioles → alveoli

• associated with arteries and veins (capillary network in alveoli, where gas exchange occurs)

lung mechanism of mammals

negative pressure breathing

• upon inhale, diaphragm contracts (moves downward) = ribcage expands, but “stomach” area is sucked in

• upon exhale, diaphragm relaxes (moves up)- rib cage smaller

altitude and oxygen content

higher altitude - less saturation of oxygen

• alveoli open up more for more efficient exchange

forms of lung capacity/volume

1. tidal volume

2. vital capacity

tidal capacity

refers to the volume of air that an animal inhales and exhales with each breath (normal breathing in and out)

~500 ml in resting humans

vital capacity

refers to the maximum tidal volume during forced breathing (total amount of air you can inhale)

~3.4L female, 4.8L male

residual volume

needed amount of air for lungs to retain shape; left-over air when you force exhale

inspirational reserved volume capacity (IRV)

maximum volume of air that can be inhaled

expiratory reserve volume capacity (ERV)

maximum volume of air that can be exhaled

• when you exhale, you don’t exhale all of air content of lungs (since without air, lungs will collapse)

respiratory pigments

proteins where oxygen is bound to for transport

types of respiratory pigments

1. hemacyanin

2. hemoglobin

appearance of hemoglobin

reddish because of iron presence (where oxygen binds to)

excess CO2 in body

drop in pH = increased depth & rate of breathing = excess CO2 is eliminated in exhaled air

determinant of pH level in blood

gas concentration

• more oxygen = basic (blood alkalosis)

• more carbon dioxide = acid (blood acidosis)

pons and medulla

region in the brain that detects shifts in blood pH, which relays impulses to the brain and instructs the diaphragm and ribs accordingly

pulmonary capillaries

• where oxygen diffuses into

• where carbon dioxide diffuses out of

oxyhemoglobin

oxygen + hemoglobin (in RBCs)

carbaminohemoglobin

carbon dioxide + hemoglobin (in RBCs)

bicarbonate ion

most CO2 is transported in this form (not yet combined with hemoglobin)

oxygen dissociation curve

a graph that tells us how fast any typical tissue can be saturated with oxygen, and reflective of how long a particular tissue can hold onto oxygen

factors of oxygen dissociation curve:

• metabolic activity

• temperature

• altitude

• thoughts

increase of the following: acidosis

decrease of the following: alkalosis

components of the oxygen dissociation curve

x axis → oxygen pressure

y axis → oxygen saturation of hemoglobin

more oxygen saturation = more oxygen pressure

high oxygen pressure & high saturation point

results in slow oxidation of oxygen (since full already)

• usually takes place in the Lungs

low oxygen pressure and low saturation point

takes place when tissues are active (e.g. calf muscles)

• because always active, saturation point will be a lot faster & oxygen in red blood vessel is detached a lot quickly because of how utilized this is (muscles needing O2)

average pressure and saturation of oxygen

takes place when tissues are at rest

• red blood cells can hold on to oxygen longer

implication if dissociation curve flattens earlier (but same slope)

assume that saturation is faster, and more metabolic activity

implication if dissociation curve has a steeper slope (but same area where it flattens; longer area how its flattened)

assumes that body holds onto more oxygen

Bohr shift

refers to a drop in pH that lowers the affinity of hemoglobin for O2 (shift to the right)

• RBC gives more oxygen to sustain metabolic activity going on

• results in higher CO2 concentration

haldane effect

refers to increase in pH, when blood holds onto O2 more (shift to left)

• implies you do not have good metabolism

relation of activity to O2/CO2 levels

• increase activity = increase metabolism = increase respiration = faster oxygen tends to dissociate = faster saturation of oxygen = decrease oxygen = increase carbon dioxide

  • acidosis (shift of diss. curve to right)

• decrease activity = decrease metabolism = decrease respiration = increase oxygen = decrease carbon dioxide

  • alkalosis (shift of diss. curve to left)

temperature and oxygen content

higher temperature favors faster dissociation of oxygen, thus more acidified blood