4.4 The Circulatory System and Blood Supply of the Head, Face and Neck

The Circulatory System and Blood Supply of the Head, Face and Neck

Exam Focus: The reliably testable content is the artery-versus-vein distinction, the common carotid as the principal supply to the head, the facial and superficial temporal arteries as the branches a facial massage stimulates, and the connection between the dermal papilla's blood supply and hair growth.

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1. Cardiovascular / Circulatory System Overview

The cardiovascular system (circulatory system) is the continuous transport network of the human body, responsible for pumping blood, distributing oxygen, water, and nutrients to every cell, and collecting metabolic waste products ($CO_2$, lactic acid, urea) for filtration and excretion.

                     CARDIOVASCULAR CIRCULATION

               ┌───────────────────────────────────┐
               │               LUNGS               │
               │   (Oxygen picked up / CO2 expelled)│
               └─────────────────┬─────────────────┘
                   ▲             │
   Pulmonary Artery│             │Pulmonary Vein
   (Deoxygenated)  │             │(Oxygenated)
               ┌───┴─────────────▼───┐
               │        HEART        │
               │  RA ➔ RV │ LA ➔ LV  │
               └─────────┬───▲───────┘
                         │   │
             Systemic    │   │Systemic
             Aorta       │   │Venae Cavae
             (Oxygenated)│   │(Deoxygenated)
                         ▼   │
               ┌─────────────┴─────────────────────┐
               │         BODY TISSUES              │
               │ (Head, Face, Scalp, Extremities)  │
               └───────────────────────────────────┘

Heart Anatomy & Dual Circulatory Pathways

The heart is a hollow, muscular, cone-shaped organ roughly the size of a closed fist, enclosed within a protective pericardial sac. It consists of four distinct internal chambers:

• Right Atrium (RA): Receives deoxygenated blood returning from the body via the superior and inferior venae cavae.
• Right Ventricle (RV): Pumps deoxygenated blood into the pulmonary artery toward the lungs.
• Left Atrium (LA): Receives freshly oxygenated blood returning from the lungs via pulmonary veins.
• Left Ventricle (LV): Thickest, most muscular chamber; pumps oxygen-rich blood through the aorta into the entire systemic circulation.

Blood circulation operates through two continuous loops:

1. Pulmonary Circulation: The loop moving deoxygenated blood from the right side of the heart to the lungs for gas exchange (releasing $CO_2$ and absorbing $O_2$) and returning oxygen-rich blood back to the left atrium.
2. Systemic (General) Circulation: The extensive loop carrying oxygenated blood from the left ventricle through the aorta and arterial branches to all body tissues, then returning deoxygenated, nutrient-depleted blood back to the right atrium.

Blood Composition & Biological Functions

Blood constitutes approximately 1/20th (about 8% to 10%) of total adult body weight (roughly 8 to 10 pints). It is composed of formed cellular elements suspended in liquid plasma:

┌────────────────────────────────────────────────────────────────────────┐
│                         COMPOSITION OF BLOOD                           │
├────────────────────────────────────────────────────────────────────────┤
│ 1. RED BLOOD CELLS (Erythrocytes)                                      │
│    • Produced in red bone marrow; lack nuclei at maturity.             │
│    • Contain Hemoglobin, an iron-rich protein that binds oxygen.       │
│    • Deliver oxygen to active cellular tissues.                        │
├────────────────────────────────────────────────────────────────────────┤
│ 2. WHITE BLOOD CELLS (Leukocytes)                                      │
│    • Mobile defensive cells of the immune system.                      │
│    • Perform phagocytosis: engulf and destroy pathogenic bacteria,     │
│      fungi, and cellular debris.                                       │
├────────────────────────────────────────────────────────────────────────┤
│ 3. BLOOD PLATELETS (Thrombocytes)                                      │
│    • Tiny cellular fragments essential for blood clotting (coagulation)│
│      and sealing microvascular injuries.                               │
├────────────────────────────────────────────────────────────────────────┤
│ 4. BLOOD PLASMA                                                        │
│    • Pale yellow, fluid component of blood (~90% water).               │
│    • Carries dissolved food nutrients, hormones, enzymes, antibodies,  │
│      and carries metabolic waste to excretory organs.                  │
└────────────────────────────────────────────────────────────────────────┘

Blood Vessel Classifications

• Arteries: Thick-walled, highly elastic, muscular vessels that carry oxygenated blood away from the heart under high arterial pressure (with the sole exception of the pulmonary artery, which carries deoxygenated blood).
• Arterioles: Small, branching arterial vessels that deliver blood directly into capillary beds.
• Capillaries: Microscopic, ultra-thin, single-cell-walled vessels connecting arterioles to venules. Capillaries form vast microvascular networks where actual oxygen, nutrient, and metabolic waste exchange takes place between blood and tissue cells.
• Venules: Small vessels that collect deoxygenated blood from capillary networks and merge into veins.
• Veins: Thin-walled, less elastic vessels that carry deoxygenated blood toward the heart. Veins contain internal, cup-like, one-way valves that prevent blood backflow against gravity.

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2. Major Blood Vessels of the Head, Face, and Neck

                        COMMON CAROTID ARTERY
                        ┌─────────┴─────────┐
                        ▼                   ▼
             INTERNAL CAROTID        EXTERNAL CAROTID
             (Brain, Eyes, Forehead) (Face, Scalp, Neck)
                                     ┌──────┴──────────────────────────┐
                                     ▼                                 ▼
                               FACIAL ARTERY               SUPERFICIAL TEMPORAL
                            (Lower Face, Lips)             (Temple, Crown, Scalp)
                               │ Submental                     │ Anterior Temporal
                               │ Inferior Labial               │ Middle Temporal
                               │ Superior Labial               │ Posterior Temporal
                               └ Angular                       │ Transverse Facial
                                                               └ Parietal

The Common Carotid Arteries

The main arterial supply to the head, face, and neck is provided by the paired Common Carotid Arteries (located on the left and right sides of the anterior neck). At the level of the upper thyroid cartilage, each common carotid bifurcates into two major branches:

1. Internal Carotid Artery: Travels deeply into the cranial vault; supplies oxygenated blood to the brain, eye sockets, eyelids, and forehead.
2. External Carotid Artery: Extends upward through the neck to supply the superficial structures of the face, scalp, ears, and neck.

Key Branches of the External Carotid Artery

Venous Drainage: The Jugular Veins

Deoxygenated blood returns from the head and neck primarily via two large paired venous channels:

• Internal Jugular Vein: Located deeply in the neck alongside the internal carotid artery; collects blood from the brain, cranial sinuses, and deep facial structures.
• External Jugular Vein: Located superficially along the side of the neck; drains blood returning from the outer face, scalp, and superficial neck structures into the subclavian vein.

3. Circulation and the Hair Follicle

Chapter 6 covers the anatomy of the hair root; the circulatory link is worth stating here because it drives several exam inferences.

The dermal papilla is a cone-shaped elevation at the base of the follicle that fits into the hair bulb and contains the blood vessels supplying the follicle. Everything the hair matrix needs to build a hair shaft — oxygen, amino acids, iron, zinc, B vitamins — arrives through that capillary loop. Three consequences follow:

• Systemic events show up in the hair. A high fever, major surgery, childbirth, crash dieting or severe stress can push a large proportion of follicles simultaneously into the telogen phase, producing the diffuse shedding known as telogen effluvium two to three months later. The cosmetologist's job is to recognise the diffuse pattern, avoid harsh chemical services on compromised hair, and refer.
• Circulation-boosting manipulations are genuinely useful. Scalp massage during a shampoo, and the manipulations described in Chapter 7, increase local blood flow to the papilla.
• Destroy the papilla and the hair does not return. This is why traction alopecia becomes permanent if sustained tension continues, and it is the boundary between what a stylist can improve and what requires medical referral.

4. Recognising Circulatory Warning Signs

Cosmetologists do not diagnose, but they observe, and 19 NYCRR § 160.27(c) makes the boundary clear.