Respiration
Respiratory organs
1. Skin
o Mostly amphibians use this strategy, and to varying extents (Fig. 48.3)
2. Gills
o External gills (Fig.48.4)
§ Delicate
§ Attract predators
§ Require energy to move around
o Internal gills Fig. 48.5) (fish)
§ Covered by hard plate (operculum)
§ usually four gill arches on each side
o one gill arch is a vessel entering gills with deoxygenated blood from body and one leaving gills with oxygenated blood
o also gill filaments, flat
o filaments have lamellae, where gas exchange happens
o gills perfused by blood and water moves over gill filaments
§ water goes in through mouth and out through gills unidirectionally
o some fish must keep moving to ventilate gills (ram ventilators)
§ some sharks, tuna
o most can move mouth muscles to push water across (buccal pumping)
§ countercurrent flow of blood and water
o water moves unidirectionally across gill filaments and past lamellae
o blood flows across lamellae in opposite direction
o countercurrent flow maximizes gas exchange by maximizing P2-P1 at each point along the gas exchange surface
How does a fish gill maximize Q?
- large A
- small D – cells lining lamellae are flattened
- P2-P1 is kept at maximum by countercurrent flow of water and blood
3. Insect tracheae (Fig. 48.7)
o system of tubes in insect
o open to outside via spiracles
o highly branched inside body
o no cell is very far away from an air capillary
- oral and nasal air passages meet in the pharynx
- air moves through larynx (where vocal cords are)
- moves into trachea (front tube) (rings of cartilage keep open)
- splits into bronchi
- then bronchioles
- then alveoli
o these are sacs where air exchange takes place
o very thin cell walls and capillary beds completely surround alveoli
o very large surface area in total (70m2) even though each alveolus is very small
o surfactant coats the alveoli
§ this reduces surface tension in water
§ keeps the alveoli from collapsing
§ surfactant does not begin to be produced until relatively late in gestation, so premature babies often born with collapsed lungs and cannot get a breath (respiratory distress syndrome of the newborn)
Ventilation (Fig. 48.10)
- Lungs are a closed cavity, lined by the pleural membranes
o Fluid between lungs and pleural membranes
o Lungs stick to pleural membranes via this fluid
- Rib cage around, big muscle (diaphragm) underneath
- When cavity enclosed by pleural membranes increases in size, negative pressure and air sucked in
- Can increase cavity size by muscle contraction
o Diaphragm
o Intracostals, which pull ribs up and out
- when muscles at rest, pressure is still slightly negative, keeps alveoli inflated
- if chest cavity punctured, pressure inside and outside equalizes and lungs collapse
- a system of dead-end sacs
- air goes in and out through a system of tubes by same route
- P2-P1 is not maximized in tidal breathing
o air is not completely exchanged in normal breathing
o not replacing entire volume of air, so new air mixing with stale air
§ typically, tidal volume is 500ml, mixes with 2L of stale air in lungs
§ tidal volume is average volume of air moved in and out in a breath
o cannot do countercurrent exchange when you are a tidal breather – not anatomically possible
- have a unique lung structure that allows them to be very efficient breathers
- all other animals lungs is a series of dead-end pouches. Air goes in and out through same system of tubes
- birds are unique, they do not have a system of pouches, rather air flows unidirectionally through the bird lung by using air sacs as reserves to push air one way (Fig. 48.13-5)
- air goes in through trachea from mouth, into tubes called bronchi
- this brings fresh air to posterior air sacs
- air then moves through lung in tubes (parabronchi) (Fig. 48.11)
- birds maximize P2-P1
o because air flow only one way, always a continuous supply of new air to air capillaries
o also air is kept continuously flowing through parabronchi, whether the bird is inhaling or exhaling
- breathing controlled in the medulla and pons of the brainstem under “normal” conditions
- homeostatic control of breathing
o what is monitored?
o Seems like it is usually CO2 and pH that is monitored
o How?
§ Actually sensory neurons in medulla monitor pH of cerebrospinal fluid
§ pH of blood goes DOWN when PCO2 goes UP
§ because CO2 is carried in blood mostly as H+ + HCO3-
§ CO2 + H2O -> H2 CO3 -> H+ + HCO3-