A comparative account of heart in different vertebrates such Reptiles, birds, mammals, where number heart chamber is varied to different vertebrates

1. M.G. COLLEGE ARMORI
DIST. GADCHIROLI
Class: B.Sc. II Sem III
Paper: I Unit: IV Comparative Anatomy
Topic: Comparative account of Heart
in Vertebrates
By: Pro. S.B. Kumre
( Dept. Of Zoology )

2. Introduction
• The blood vascular system of lower chordates is similar to non- chordates.
• Single chambered heart: Cephalochordates approach the vertebrate type, but
amphioxus has no definite heart. Vessel carrying the blood the gills and is considered
as valveless single chambered heart.
• 2 chambered heart: Cyclostomes consists of two chambers a receiving chamber
atrium and pumping chamber the ventricle. And two accessory chambers. Sinus
venosus-> blood from the veins into the atrium. Conus arteriosus-> blood from
ventricle and discharging into the aorta.
• 3 Chambered heart: Reptiles have a 3 chambered heart with two atria and one
ventricle, except crocodiles have 4 chambered heart.
• 4 chambered heart: Mammals and birds have four-chambered heart.
• Function: The heart is a hollow muscular organ that rythmically contracts and
relaxes. During each contraction-relaxation cycle, blood is drawn from the veins into a
thin walled collecting chamber, the atrium, and is then passed to a second thick walled
chamber, the ventricle, which forcibly contracts to distribute the blood to the arteries.
Backflow is prevented by one-way valves.
• The heart first appeared in the earliest vertebrates.

3. Embryology and position of the heart
• The heart is a specialized portion of an
embryonic blood vessel which becomes
s-shaped. And is derived from
mesenchyme. Two vessels arise from
mesenchyme and fuse together, and
from then heart tissue formed.
• At first, the heart is tubular with veins
entering posteriorly and the artery
leaving anteriorly.
• The position of the heart in fishes and
amphibians lies immediately posterior
to the head close connection with the
gills.
• In amniotes there is gradual shift to
the posterior with the development of
the lungs and the elongation of the
neck.

4. Heart in Reptiles
heart in various reptiles
crocodilian reptile

5. Heart in reptiles
• The atrium is divided into two portions. The ventricle develops
a septum which partially divides the ventricle into right and
left halves. The aorta and conus are split to the base so that the
pulmonary artery leaves the heart as a separate vessel.
• Except for crocodilians, which have a four-chambered heart,
all reptiles have a three-chambered heart consisting of two
atria and one ventricle. The chamber called the right atrium
receives deoxygenated, or "spent," blood returning from the
body tissues.
• It passes this blood into the ventricle, from where it is pumped
to the lungs for oxygenation. The oxygenated blood from the
lungs returns to the left atrium and once again enters the same
ventricle, from which it is pumped to the body tissues.

6. Heart in Birds
• Birds, like mammals, have a 4-
chambered heart (2 atria & 2
ventricles), with complete
separation of oxygenated and
de-oxygenated blood. The right
ventricle pumps blood to the
lungs, which is a thin walled
while the left ventricle pumps
blood to the rest of the body,
which is thick walled.
• The sinus venosus is completely
incorporated into the right
atrium.
• The heart of birds is a modified
reptilian heart retaining only
the right aortic trunk which
leaves the left ventricle. The left
aortic trunk is absent.

7. Heart in mammals
• The mammalian heart is also 4
chambered .
• Complete separation of blood.
• The sinus venosus has entirely
disappeared.
• From the right atrium, the
blood is sent through tricuspid
valve to the right ventricle
then to the lungs for the
exchange of gases.
• The left atrium receives blood
from the lungs. Then forces the
blood through the aorta to all
parts of the body.
• The outlet through the aorta is
protected by semilunar valves.

8. Comparative account of the Aortic Arches
in the Vertebrates
• • In typical vertebrate embryo 3 arterial
channels- aventral aorta dorsal aorta and 6
pairs of aorti arches, ventral aorta present
beneath the pharynx.
• In head region ventral aorta branches into a
pair of external carotid arteries and 6 pairs of
aortic arches.
• Ventral afferent branchial artery carrying
venous blood And dorsal efferent branchial
artery taking arterial blood.
• The two lateral dorsal aortae unite just behind
the pharynx to form a single dorsal aorta which
continues into tail region as caudal artery.

9. Aortic arches in Reptiles
• Reptiles are terrestrial vertebrates in which
gills disappear and is replaced by lungs.
• 3 functional arches (III, IV, VI) are present
with elongation of neck, posterior shifting of
heart and partial division of ventricle.
• Ventral aorta and conus split into 3 trunks-
two aortic or systemic and 1pulmonary arch.
• Right systemic arch, (IV) arises from left
ventricle- carrying oxygenated blood to the
carotid arch (III ) and sent into head.
• Left systemic arch arises from right ventricle
carrying deoxygenated or mixed blood to the
body through dorsal aorta.
• Pulmonary trunk(VI) arises from right
ventricle carrying deoxygenated blood to the
lungs.
• Ductus caroticus and ductus arteriosus are
absent.

10. Aortic arches in birds and Mammals
External carotid
Internal carotid
Carotid trunk
Subclavian
Pulmonary
artery
Pulmonary trunk
Systemic trunk
Dorsal aorta
Left systemic
aorta
Right systemic
aorta
Pulmonary
trunk
bird mammals
I
II
III
IV
V
VI