Anatomy and Physiology of Children and Adolescents - M. R. Sapin 2007

Cardiovascular System
Blood vessels of the human body
Regulation of cardiovascular system functions

The Heart's activity, the tone of Blood vessel walls, and the maintenance of constant blood pressure are regulated by the Autonomic Nervous system, which operates beyond our conscious control.

The walls of the aorta, carotid and other Arteries, as well as large Veins, contain specialized sensory nerve endings: baroreceptors, which monitor blood pressure, and chemoreceptors, which detect changes in blood composition. In a healthy Organism, Blood Vessels remain in a state of partial contraction known as vascular tone.

Nerve impulses regarding the state of blood vessels and their tone are transmitted via cardiac nerves to the vasomotor center located in the Medulla Oblongata. Additional vasomotor centers are situated in the Gray matter of the Spinal Cord. All of these centers are regulated by corresponding Regions of the Hypothalamus (part of the Forebrain).

When blood pressure drops, impulses from the vasomotor centers intensify heart contractions and increase the tone of vessel walls, causing the vessels to constrict and blood pressure to normalize.

Conversely, when blood pressure rises, the strength and frequency of heart contractions decrease, vascular tone diminishes, the vessels dilate, and pressure returns to normal. These reflex mechanisms provide autoregulation of vascular tone and blood pressure levels.

Humoral mechanisms also play a key role in regulating vascular tone and blood pressure. Changes in The chemical composition of the blood affect the excitability and conduction of nerve impulses in the heart, as well as the force and rate of cardiac contractions.

During emotional surges (such as joy, fear, or anger), the Adrenal Glands release Hormones—adrenaline and noradrenaline—into the bloodstream, which stimulate heart activity and constrict blood vessels. The pituitary hormone vasopressin also acts as a vasoconstrictor. Conversely, acetylcholine, histamine, and other BIOLOGICALLY ACTIVE SUBSTANCES exhibit vasodilating effects.

In emergency situations, such as massive blood loss, vascular tone is maintained by the release of blood from specialized blood depots (including the Skin and Liver). However, if more than 30% of blood volume is lost, these biological mechanisms fail to maintain continuous blood flow, which can lead to fatal consequences.

REVIEW AND SELF-Control Questions:

1. List the blood vessels that form the pulmonary (lesser) Circulation loop and describe its Functions.

2. What constitutes the systemic (greater) circulation loop? Which blood vessels are part of it?

3. To which PARTS OF THE body do the major Branches of the aorta supply blood?

4. Name the Arteries of the upper and lower extremities and the regions they supply.

5. Name the veins involved in forming the systemic circulation loop.

6. From which veins and in what region of the body are the superior and inferior venae cavae formed?

7. Describe the tributaries of the HEPATIC PORTAL VEIN.

8. Discuss the age-related changes in blood vessels (arteries and veins).

9. Explain the movement of blood through arteries and veins, The formation of the pulse, and the Regulation of The Cardiovascular system.