General characteristics of the circulatory system
The class Mammals (Mammalia) has a highly organized closed circulatory system. The evolutionarily fixed presence of two circulatory loops allows for the complete separation of arterial and venous blood. This very factor is key to maintaining a constant high body temperature — homeothermy (warm-bloodedness), which aligns mammals with the class of birds.
Anatomically, the mammalian heart is located on the ventral side of the body. During its development, it shifts in such a way that in its formed state it is situated predominantly in the left part of the thoracic cavity.
Major vessels of the heart
The architectonics of the vascular bed directly connected to the mammalian heart is strictly determined. The outgoing and incoming main pathways are distinguished:
- Outgoing (arterial) vessels: exactly 2 major arterial trunks depart from the heart, distributing blood throughout the body.
- Incoming (venous) vessels: 6 large venous collectors approach the heart. These include two venae cavae (collecting blood from the systemic circulation) and four pulmonary veins (carrying oxygenated blood from the lungs).
Embryogenesis of the mammalian and human heart
The process of heart specification and formation in mammalian ontogeny represents a complex cascade of morphogenetic events. It includes several key stages:
- Specification: the formation of cardiac structures begins with the appearance of paired primordia, originating from the mesoderm.
- Tube formation: paired mesodermal primordia approach each other and fuse. As a result, a single heart tube is formed, which initially localizes in the neck region of the embryo.
- Migration: as the embryo grows and develops, the heart tube undergoes caudal displacement, descending from the cervical region and ultimately occupying a position in the left part of the thoracic cavity.
Stages of morphogenesis and recapitulation
During intrauterine development, the heart tube grows intensively and differentiates. This process is a classic example of phylogeny recapitulation — meaning that in its individual development (ontogeny), the mammalian heart briefly repeats the main stages of the historical development of the vertebrate circulatory system.
Sequence of heart morphogenesis stages:
- Two-chambered heart (resembles the heart structure of lower aquatic vertebrates).
- Three-chambered heart.
- Three-chambered heart with an incomplete interventricular septum.
- Four-chambered heart (the final, mature form characteristic of all members of the class Mammalia).
Briefly: answers to topical questions
From which germ layer and which specific structures of it does the mammalian heart develop?
The mammalian heart develops from paired mesodermal primordia, specifically from its lateral unsegmented part — the splanchnotome. The specific source for the development of the myocardium and epicardium is the visceral layer of the splanchnotome (splanchnopleura), which lies adjacent to the entoderm and forms the myoepicardial plate during embryogenesis. Meanwhile, the parietal layer (somatopleura) serves as the source of the mesothelium of the serous membranes, including the pericardium.
Which specific major arterial trunks depart from the mammalian heart?
Two major arterial trunks depart from the mammalian heart, formed by the division of the common arterial trunk (truncus arteriosus).
- Left aortic arch — departs from the left ventricle and carries arterial blood.
- Pulmonary trunk — departs from the right ventricle and carries venous blood.
What anatomical structures ensure the complete separation of blood flows in the four-chambered heart?
The complete separation of arterial and venous blood flows in the four-chambered heart is ensured by anatomical septa and valves. The right and left halves of the heart are completely separated by a muscular wall septum (septum), including the interventricular septum (septum interventriculare). Strictly unidirectional blood movement, preventing the mixing of flows, is ensured by the valvular apparatus of the heart.
What vestigial structures remain in the adult mammalian heart after the closure of embryonic circulatory pathways?
In the adult mammalian heart, after the closure of embryonic circulatory pathways, a vestigial structure remains on the interatrial septum.
- Fossa ovalis (fossa ovalis) — represents the obliterated foramen ovale (foramen ovale), which directed blood into the left atrium in the fetus. It is located on the septum and surrounded by the limbus (limbus fossae ovalis).
Which circulatory loops function in adult mammals and from which heart chambers do they originate?
In adult mammals, two circulatory loops function, originating from different ventricles of the heart.
- Pulmonary circulation (lesser loop) — begins from the right ventricle, which pumps venous blood through the pulmonary valve into the lungs for oxygenation.
- Systemic circulation (greater loop) — begins from the left ventricle, which pumps arterial blood through the aortic valve into the aorta to supply blood to the entire body.
What changes does the mammalian circulatory system undergo immediately after birth?
Immediately after birth, the circulatory system undergoes restructuring triggered by the onset of pulmonary circulation function. There is a sharp drop in pressure in the pulmonary vessels and an increase in systemic vascular resistance.
- Ductus arteriosus (ductus arteriosus Botalli) — spasms under the influence of oxygen.
- Foramen ovale (foramen ovale) — functionally closes.
- Ductus venosus (ductus venosus) — gradually obliterates, turning into the round ligament of the liver.
To remember the number of incoming (venous) vessels of the mammalian heart, use the formula: "2+4=6" (2 venae cavae + 4 pulmonary veins = 6 vessels carrying blood to the heart).
Class and exam questions
From which embryonic source does the heart develop in mammals?
The mammalian heart develops from paired mesodermal (middle germ layer) primordia.
Where is the heart tube initially formed?
Initially, the paired primordia unite into a single heart tube in the neck region, and only then does it migrate into the left part of the thoracic cavity.
What is the principle of recapitulation in heart development?
In ontogeny, the heart sequentially passes through stages characteristic of vertebrate evolution: from two-chambered through three-chambered (including with an incomplete septum) to the final four-chambered one.
How many vessels originate from the mammalian heart and how many empty into it?
2 arterial vessels depart from the heart, and 6 venous vessels bring blood (two venae cavae and four pulmonary veins).
What else to study on this topic
- Phylogeny of the vertebrate circulatory system in a comparative aspect
- Mechanisms of formation and closure of the interventricular septum
- Comparative characteristics of the circulatory systems of mammals and birds
- Topographic anatomy of the venae cavae and pulmonary veins
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