Cardiovascular System: Anatomy and Physiology
Cardiovascular System
Sympathetic System
The sympathetic system increases conduction velocity and heart rate (FC), leading to increased force of contraction. It is predominant during physical activity and stress.
Hormone System
Hormones, such as epinephrine and norepinephrine (catecholamines), exert their action through the liver, producing similar effects as sympathetic activity.
Excitoconductor System
This system is responsible for cardiac automaticity and consists of:
- Sinoatrial (SA) node
- Atrioventricular (AV) node
- Bundle of His (AV bundle)
- Purkinje fibers
Sinoatrial Node (Pacemaker)
Located in the right atrial wall near the entry point of the superior vena cava, the SA node initiates normal cardiac contractions. Action potentials spread rapidly through the atria, causing both to contract.
Atrioventricular Node
Situated between the atria and ventricles, the AV node can depolarize spontaneously under abnormal conditions, acting as a backup pacemaker crucial for survival.
Bundle of His
This bundle transmits action potentials slowly initially, then rapidly through specialized fibers. It divides into two branches, reaching the ventricular apex and forming the Purkinje fiber network.
Purkinje Fibers
These fibers rapidly conduct action potentials along the inner ventricular walls, ensuring near-synchronous contraction of ventricular fibers.
Blood Vessels
The vascular tree comprises arteries, arterioles, capillaries, venules, and veins. Blood return is facilitated by respiratory mechanics, the muscle pump, and venous valves. At rest, the venous sector holds 64% of blood volume, while the head and neck sector holds 36%.
Arteries
Arteries are elastic, cylindrical tubes carrying blood away from the heart. Their walls consist of three layers: tunica intima (endothelial lining), tunica media (smooth muscle), and tunica externa (connective tissue).
Capillaries
Capillaries are endothelial tubes connecting arterial and venous circulation, allowing for exchange of gases and nutrients.
Veins
Veins return blood to the heart from capillaries. They are formed by the union of venules and have thinner, less elastic walls. Veins possess valves, membranous folds preventing backflow of blood.
Anastomosis
Anastomoses are connections between adjacent arteries. Types include inosculation (end-to-end), convergence (e.g., basilar artery), confluence (e.g., cerebral arteries), and network/plexiform (e.g., periarticular).
Veins of Head and Neck
The internal jugular vein is the main vein, accompanied by five smaller ones: external jugular, anterior jugular, inferior thyroid, vertebral, and posterior jugular.
Inferior Vena Cava
The inferior vena cava carries blood to the right atrium from the lower body. It originates from the union of common iliac veins and receives tributaries from parietal (lumbar, phrenic) and visceral (testicular/ovarian, renal, adrenal, hepatic) veins.
Veins of the Pelvis
These include external and internal iliac veins.
External Iliac Vein
A continuation of the femoral vein, it joins the internal iliac vein to form the common iliac vein.
Internal Iliac Vein
A short trunk receiving parietal veins.
Veins of the Lower Limb
These include superficial and deep venous systems.
Deep Venous System
Deep veins accompany arteries and have corresponding names (e.g., tibial veins).
Deep Veins of the Foot and Leg
These include dorsal and anterior (tibialis anterior) systems, as well as plantar and posterior (tibialis posterior and fibular) systems.
Deep Veins of the Inferior Member
The popliteal vein is formed by the union of anterior and posterior tibial veins. The femoral vein is a continuation of the popliteal vein, extending from the adductor hiatus to the inguinal ligament.
Superficial Venous System
Located in subcutaneous tissue, the main superficial veins are the great saphenous vein (medial) and the small saphenous vein (lateral).
Vascularization of the Heart
The heart is supplied by coronary arteries.
Right Coronary Artery
Originating from the aorta near the right semilunar valve, it has three segments (preauricular, intra-atrial, posterior interventricular) and supplies the right atrium, right ventricle, and interventricular septum.
Heart Vessels
Venous drainage does not mirror arterial supply. Most blood flows into the right atrium via the great cardiac vein and coronary sinus, with some drainage through the small cardiac vein and independent veins.
Innervation of the Heart
The heart is innervated by sympathetic and parasympathetic systems.
Parasympathetic System
Acting through the vagus nerve (cranial nerve X), the parasympathetic system predominates at rest, decreasing heart rate. Vagus nerve stimulation can significantly lower heart rate.