B3.2.15 Adaptations of the mammalian heart for delivering pressurized blood to the arteries (HL) Notes

Adaptations of the Mammalian Heart for Delivering Pressurized Blood to the Arteries

The mammalian heart is a highly specialized muscular organ adapted to efficiently pump oxygenated blood to the body and deoxygenated blood to the lungs under high pressure.

Form–Function Adaptations of the Mammalian Heart

1. The structure of the heart is a direct reflection of its function.
2. Each component is adapted to ensure that blood is pumped efficiently and with the necessary pressure.

1. Cardiac Muscle

Structure

1. Cardiac muscle is composed of specialized muscle fibers that are striated (striped) but unlike skeletal muscle, they are interconnected by intercalated discs.
2. These discs allow for the rapid transmission of electrical impulses between heart cells, enabling coordinated contractions.

Function

1. The heart’s muscle fibers contract in a synchronized manner, which is essential for pumping blood.
2. The heart muscle is also highly aerobic, containing many mitochondria to supply the energy needed for constant contraction.
3. This adaptation allows the heart to work continuously without tiring.

2. Pacemaker (Sinoatrial Node)

Structure

Located in the right atrium, the pacemaker consists of specialized cells that generate electrical impulses.

Function

1. The pacemaker initiates electrical impulses at regular intervals, stimulating the atria to contract.
2. These impulses then travel to the atrioventricular node (AV node) and down to the ventricles, ensuring that the heart beats in a coordinated rhythm.

Adaptation

The pacemaker’s natural ability to control the heart rate allows it to adjust the heart’s function based on the body's demands, such as increasing the heart rate during exercise and decreasing it during rest.

3. Atria

Structure

The atria are the upper chambers of the heart, with thinner walls compared to the ventricles.

Function

1. The primary function of the atria is to collect blood returning to the heart from the body (right atrium) and from the lungs (left atrium).
2. They then contract to push blood into the ventricles.

Adaptation

The thin walls of the atria allow for a larger volume of blood to be collected without requiring significant pressure to move it to the ventricles.

4. Ventricles

Structure

The ventricles are the lower chambers of the heart, with the left ventricle having a thicker muscular wall than the right.

Function

1. The ventricles are responsible for pumping blood to the lungs (right ventricle) and to the rest of the body (left ventricle).
2. The left ventricle is particularly important as it pumps oxygenated blood through the systemic circulation at high pressure.

Adaptation

1. The left ventricle’s thick muscular wall provides the strength required to pump blood throughout the entire body.
2. The right ventricle, with a thinner wall, pumps blood only to the lungs, which require lower pressure.

5. Atrioventricular Valves (AV Valves)

Structure

1. The AV valves consist of two main valves: the bicuspid valve (left side) and the tricuspid valve (right side).
2. These valves are made of fibrous tissue and are located between the atria and ventricles.

Function

1. The AV valves prevent the backflow of blood from the ventricles into the atria during ventricular contraction.
2. They ensure that blood moves in a single direction, from the atria to the ventricles.

Adaptation

The cusps of the valves are anchored by chordae tendineae (fibrous cords) to prevent the valves from inverting under pressure, ensuring they function efficiently.

6. Semilunar Valves

Structure

1. The semilunar valves consist of the pulmonary valve (between the right ventricle and the pulmonary artery) and the aortic valve (between the left ventricle and the aorta).
2. These valves have a half-moon shape and are positioned at the exits of the ventricles.

Function

The semilunar valves prevent the backflow of blood from the arteries back into the ventricles after blood is pumped out during contraction.

Adaptation

Their half-moon shape allows for efficient closure under pressure, ensuring that blood moves only in the intended direction, into the arteries.

7. Septum

Structure

The septum is a thick, muscular wall that divides the heart into two halves: the right and left sides.

Function

1. The septum ensures that oxygenated and deoxygenated blood do not mix.
2. This division is crucial for maintaining the efficiency of gas exchange and ensuring that oxygenated blood is directed to the body and deoxygenated blood to the lungs.

Adaptation

The septum is muscular and thick to withstand the high pressure from the ventricles without allowing any blood to leak between the chambers.

8. Coronary Vessels

Structure

1. The coronary arteries and veins form the vascular system that supplies the heart muscle (myocardium) with oxygen and nutrients.
2. These vessels run along the surface of the heart.

Function

1. The coronary vessels ensure the heart muscle itself receives adequate blood supply.
2. Since the heart works continuously, it requires a large and constant supply of oxygen and nutrients to function effectively.

Adaptation

The coronary vessels are large enough to supply blood to the entire heart and are branched to ensure the entire myocardium is well-perfused.