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Difficulty: MediumVertebrates: Poikilothermic Classes (Pisces, Amphibia, Reptilia)

Arrange the heart chambers and associated structures of a typical bony fish (Class Pisces) in the correct sequence through which deoxygenated blood flows, starting from the chamber that receives venous blood from the body to the vessel leading to the gills.

  1. 1Sinus venosus
  2. 2Atrium
  3. 3Ventricle
  4. 4Bulbus arteriosus

Answer

The correct sequence of deoxygenated blood flow through a fish heart is: Sinus venosus → Atrium → Ventricle → Bulbus arteriosus.
In fish (Class Pisces), deoxygenated blood flows through a single-circuit heart in a strict linear pathway: it enters the sinus venosus from the body, moves to the atrium, passes into the thick muscular ventricle, and exits via the bulbus arteriosus toward the ventral aorta and gills.

Step-by-Step Solution

1
Identify the initial collecting chamber for venous blood returning from body tissues.
Deoxygenated blood first enters the thin-walled sinus venosus.
The sinus venosus functions as the primary receiving reservoir for systemic venous blood in fish.
2
Trace blood movement from the initial collecting reservoir into the first main heart chamber.
Blood passes from the sinus venosus into the atrium.
Contraction of the sinus venosus propels blood across the sinoatrial valve into the atrium.
3
Follow blood flow from the atrium into the main pumping chamber.
Blood moves from the atrium into the muscular ventricle.
Atrial contraction drives blood across the atrioventricular valve into the heavy-walled ventricle.
4
Determine the exit pathway out of the heart toward the respiratory surfaces.
Blood is pumped from the ventricle through the bulbus arteriosus into the ventral aorta leading to the gills.
The elastic bulbus arteriosus maintains continuous forward blood flow and buffers pressure fluctuations prior to entering delicate gill capillaries.

Key Concept

Single-circuit cardiac blood flow sequence in Class Pisces
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Topics

Vertebrates: Poikilothermic Classes (Pisces, Amphibia, Reptilia)

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