Circulation & Respiration

Question 0

Diffusion is sufficient for organisms measuring…

Answer 0

<0.5mm

Question 1

Respiratory organs

Answer 1

Skin, gills, lungs

Question 2

Vertebrates that respire via skin are…

Answer 2

Lungless salamanders 100% - low metabolism and moist environment
Lake titicaca frog 100% - bottom of lake, skin folds increase SA

Most amphibians, some fish and some snakes

Question 3

Why do organisms living in water need gills

Answer 3

Respiration in water is challenging, low solubility

1L of air contains ~210cm O2
1L of water contains ~10cm O2

Question 4

Adaptations of the gills

Answer 4

1) continuous steady water flow = more energy efficient
2) large SA
3) countercurrent exchange

Question 5

Dual pump overview

Answer 5

Using buccal and opercular cavities via lowering and raising the floor of the buccal cavity, and movement of the operculum allows continuous flow throughout the cycle to avoid O2 depletion at gill surface and minimise acceleration/deceleration of water

Question 6

Counter current system

Answer 6

O2 of blood exiting lamellae approaches that of incoming water

Efficient - 90% extraction

Question 7

Ram ventilation

Answer 7

Used when an organism is swimming with mouth open at high swim speeds

Question 8

Gas bladders

Answer 8

Mainly bony fish

Dorsal out pouch of gut

Mainly buoyancy but sometimes respiratory

Question 9

Aspiration pump/lungs overview

Answer 9

Reptiles mammals birds

Air is drawn into the lung, not forced

Allows feeding and respiration to be functionally uncoupled

Question 10

Avian respiration

Answer 10

Resting metabolic rate is similar to other vertebrates, flight requires higher O2 consumption

1. Ventilation
   Paired lungs in thoracic cavity
   Anterior and posterior sacs among viscera and within bones
   movement of sternum causes compression/expansion of rib cage which acts on air sacs
   Lungs themselves don’t change shape
2. Gas exchange
   Parabronchus contains air capillaries
   Air flows through
   Very thin air-blood interface minimises diffusion barrier
   (Mechanical strength from air capillaries)
   Capillaries arranged in parallel = cross current system - more efficient as respiratory air always meets deoxygenated blood

High fliers require a higher metabolic rate as air is thin and po2 low so...
Enhanced hypoxic response 
Larger lungs increase SA 
Haemoglobin has higher infinity 
Mitochondria closer to capillaries

Question 11

Water to land transition & evolution of respiratory systems

Answer 11

Evolved independently
Mainly in freshwater pools prone to seasonal hypoxia

Ventral lungs evolved prior to dorsal gas bladders

Most fishes = dual pump
Air-breathing fishes = buccal pump
Amphibians = modified buccal pump
Reptiles birds mammals = aspiration pump

Question 12

Dual pump description

Answer 12

Water ventilation, water breathing fishes
Gnathostome system
Buccal & opercular pumps work in a synchronous pattern
Unidirectional flow
Gill curtain between the two pumps

Question 13

Dual pump, muscular mechanisms

Answer 13

1) first stroke/suction phase:
- buccal and opercular valves compressed with closed oral and opercular valves
- buccal cavity expands = low intraoral pressure
- oral valves open, outside water rushes in following the pressure gradient
- at the same time, the opercular cavity expands but the valve is still closed = pressure lower than buccal cavity
- water crosses gill curtain into the opercular cavity

2) second stroke/force phase
- oral valves close, opercular valves open
- simultaneous muscle compression of both cavities raises pressure
- opercular pressure is lower as the valve is open and water exits

Question 14

Buccal pump description

Answer 14

Air ventilation, used by air breathing fishes and amphibians
Ventilates lungs
Mouth cavity expands to fill with fresh air

Question 15

Buccal pump - air breathing fishes - muscular mechanisms

Answer 15

Four stroke, with 2 main phases

1) inhalation phase
- mouth opens to intake (expansion [1]) atmospheric air
- compression [2] forces the bubble of fresh air from the buccal cavity into the lungs
2) exhalation phase
- transfer (expansion [3]) of spent air from the lungs into the buccal cavity -permitted by relaxation of the sphincter around the glottis in some fishes
- expulsion (compression [4]) of air from the buccal cavity to the outside either through the mouth or operculum

Bidirectional/tidal exchange
Helped by hydrostatic pressure?
- increases with depth
-fish rises to the surface with its head tipped upward = greater pressure on the body than the buccal cavity, so helps air be forced out in exhalation
-after fish has gulped atmospheric air and turned down, there is greater pressure on the buccal cavity than the lung = helps move air into the lung

Question 16

Buccal pump - amphibians - muscular mechanisms

Answer 16

• pulse pump to ventilate lungs
• bidirectional flow
• two stroke (primitive and found in most)
• raises head above water, means there is hydrostatic pressure on the lung
• hypaxial muscles contact to actively aid exhalation (not inhalation)
• mouth closes and air exits through nostrils

Question 17

Agnathans - lamprey - respiration

Answer 17

The feeding-ventilation current of water is produced by:

(1) pumps composed of muscular folds - velum
(2) compression and expansion of the brachial apparatus

Closure of velum and muscular contraction of the brachial apparatus forces water across the gills and out the pharyngeal slits

Pharyngeal openings are small and round - 7 pairs, covered by flaps of skin (valves)
Valves prevent retrograde flow as inward water movement forces them closed
Lie medial to the gills/brachial apparatus
- primary lamellae = gill filaments
- secondary lamellae = respiratory capillary beds

Countercurrent system

Question 18

Agnathans - hagfishes - respiration

Answer 18

No major contributions of expansion and contraction of the brachial apparatus
Instead provided via scrolling/unscrolling of the velum and synchronised contraction/relaxation of the brachial pouches

Water enter via the nostril
Unidirectional flow

Question 19

Elasmobranchs - sharks - respiration

Answer 19

Gills lie lateral to the brachial arch (as in all gnathostomes)
Primary lamellae on interbrachial septum
Dual pump

Maintain a nearly constant pressure difference between buccal (medial to gills) and parabrachial (lateral) cavities
Relatively lower in parabrachial = smooth, almost continuous unidirectional irrigation

Cross current

Spiracle - allows passage of water for gill irrigation, embryologically the first gill slit

Sharks in open water have ram ventilation that aids/replaces the dual pump

Question 20

Bony fishes (teleostomi) - Osteichthyes - respiration

Answer 20

Operculum - bony or cartilaginous

Countercurrent

Adductor muscles cross between filaments to control the flow of water across the secondary lamellae

Gas bladders/lungs