Dominic Stone
The breast is a secondary sex characteristic that distinguishes females from males. It is a mammary gland that produces and secretes milk to feed infants. The breast overlies the pectoralis major muscle and extends from the collarbone to the armpit, covering a large area of the chest. The breast is composed of differing layers of tissue, including adipose tissue and glandular tissue, which affect lactation functions. The shape and position of the breast are influenced by various factors, including the underlying muscle and bone structures of the chest.
| Characteristics | Values |
|---|---|
| Location | The breasts lie over the pectoralis major muscle on the chest |
| Coverage | From the collarbone to the armpit and across the ribcage |
| Composition | Glandular tissue, connective tissue, fatty tissue, ligaments, and milk ducts |
| Function | The primary function of the breasts is to produce milk for nourishment during lactation |
| Lymphatic System | Lymph vessels and lymph nodes are present in the breast area, helping to fight infections |
| Nipples | Contain muscle fibres that contract to make the nipple erect or pointed outward |
| Areola | Circular area around the nipple with glands that secrete an oily substance acting as a lubricant |
| Cancer Risk | Breast cancer usually develops in the upper outer quadrant, closest to the armpit, due to the presence of glandular tissue |
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What You'll Learn
Breasts are connected to the chest by the pectoralis major muscle
The pectoralis major is a thick, fan-shaped or triangular convergent muscle of the human chest. It is the largest muscle in the chest area and lies underneath the breast tissue. The pectoralis major arises from parts of the clavicle (collarbone) and sternum (breastbone), costal cartilages of the true ribs, and the aponeurosis of the abdominal external oblique muscle. It is active in deep or forced inspiration, assisting in breathing.
The pectoralis major is responsible for the movement of the shoulder joint and has four primary actions: flexion, adduction, horizontal adduction, and internal rotation of the humerus. This muscle is targeted in exercises such as the flat barbell bench press and the flat dumbbell bench press, where individuals lie supine and use their arms to lift and lower weights.
In rare cases, the pectoralis major may be absent due to Poland Syndrome, a congenital condition that results in the malformation of the chest. This absence does not typically cause functional loss as other surrounding muscles compensate. However, it can create aesthetic concerns, leading some individuals to seek surgical implants for modification.
Injuries to the pectoralis major are uncommon but can occur in high-impact contact sports or weight-lifting, particularly during the bench press. Tears or ruptures of this muscle can result in pain, weakness, and disability, requiring surgery and physical therapy for recovery.
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The pectoralis major muscle is a large muscle on the chest
The pectoralis major muscle is a large, fan-shaped muscle located on the chest. It is the most superficial muscle in the pectoral region, lying underneath the breast tissue in females and covered by a deep layer of fascia, subcutaneous tissue, and skin in males. This muscle is responsible for the adduction and internal rotation of the arm at the shoulder joint. It also assists in pulling the trunk forward or upward when the humeral attachment is fixed, which is important for activities like climbing.
The pectoralis major has three parts: the clavicular part, the sternocostal part, and the abdominal part. All three parts originate from different sites and converge laterally, inserting onto the greater tubercle of the humerus. The clavicular part, which originates from the anterior surface of the medial clavicle, helps to flex the extended arm up to 90 degrees. The sternocostal part, which is larger and originates from the anterior surface of the sternum, superior six costal cartilages, and external oblique muscle aponeurosis, facilitates the extension of the flexed arm by pulling it downwards.
The pectoralis major is a popular muscle group to target in gym workouts, with exercises such as the flat barbell bench press and flat dumbbell bench press commonly utilising this muscle group. In these exercises, the individual lies supine on a bench with their feet flat on the ground and uses either a barbell or dumbbells to extend their arms, lowering the weight slowly towards the nipple line before bringing it back up.
The pectoralis major muscle is innervated by the lateral and medial pectoral nerves, which stem from the brachial plexus. It receives vascular supply from the pectoral branches of the thoracoacromial artery and the internal thoracic artery's perforating branches. While rare, rupture of the pectoralis major tendon can occur, most commonly in weight lifters performing exercises such as the bench press.
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The pectoralis minor muscle is located under the pectoralis major
The pectoralis minor muscle is one of the most superficial muscles on the anterior aspect of the chest or thoracic wall. It is located deep only to the pectoralis major muscle. It is one of the anterior axioappendicular (thoracoappendicular) muscles, along with the pectoralis major, subclavius, and serratus anterior. Together, these muscles produce various movements of the scapula and can be used as accessory muscles of respiration.
The pectoralis minor muscle arises as three separate heads from the anterior surface of the 3rd, 4th, and 5th ribs near the corresponding costal cartilages. The muscle extends superolaterally to form a flat tendon, which inserts into the medial border and coracoid process of the scapula. The pectoralis minor is also used as a reference point for the three divisions of the axillary artery.
The primary nerve supply to the pectoralis minor muscle comes via the medial pectoral nerve (C8, T1), a minor branch of the brachial plexus that arises from the cervical portion of the spinal cord. Innervation to the pectoralis minor is also received from the lateral pectoral nerve, via a communicating branch known as the 'ansa pectoralis'. This results in the pectoralis minor receiving innervation from the spinal roots of C5-T1.
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The breast covers a large area of the chest
The breasts are two prominences located on the upper ventral region of the torso. They are composed of differing layers of tissue, predominantly two types: adipose tissue and glandular tissue. Adipose tissue is a type of fat tissue that gives the breast its distinct size and globular shape. Glandular tissue, also known as lobules, produces milk for lactation. Each breast has between 15 to 20 lobes, or sections, that surround the nipple. The breast covers a fairly large area of the chest, extending from the collarbone to the armpit and across the rib cage. At the front of the chest, the breast tissue can extend from the collarbone to the middle of the sternum (breastbone). On the sides of the chest, the breast tissue can extend into the armpit and reach as far back as the latissimus dorsi muscle, which extends from the lower back to the upper arm.
The base of each breast is attached to the chest by the deep fascia over the pectoralis major muscles. The pectoralis major muscle is a large muscle on the chest that lies underneath each breast. The space between the breast and the pectoralis major muscle is called the retromammary space, which gives mobility to the breast. The breast is divided into four quadrants by an invisible line running up and down and right to left through the nipple. Most breast cancers develop in the upper outer quadrant, closest to the armpit, as this area has a lot of glandular tissue.
The breast has many blood and lymph vessels. Lymph vessels are thin tubes similar to blood vessels that transport lymph, a fluid that helps the body's immune system fight infections. Lymph vessels connect to lymph nodes, which are found under the armpits, in the chest, and in other places. Axillary lymph nodes are located under the arms and help filter lymph fluid from the breast. The breast also contains ligaments, which are dense bands of connective tissue that support the breast. They run from the skin through the breast and attach to muscles on the chest.
The nipple is the area at the centre of the areola and contains muscle fibres. When these muscle fibres contract, the nipple becomes erect or pointed outward. The areola is the circular darker-coloured area of skin surrounding the nipple. It contains small glands that secrete an oily substance that acts as a lubricant for the nipple and areola during breastfeeding. The primary function of the breasts is to produce milk for nourishing infants. Milk is produced in milk-secreting cells in the alveoli and flows through ducts to the nipple when the mother's brain secretes oxytocin, triggering the contraction of muscle cells surrounding the alveoli.
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The breast is made up of fat, connective tissue, glands and ducts
The breast is a complex organ with a unique structure that primarily serves the function of milk production for lactation. The breast is made up of several components, including fat, connective tissue, glands, and ducts, each playing a crucial role in its anatomy and physiology.
Fat, also known as adipose tissue, is a significant constituent of the breast. It fills the spaces between the glandular and connective tissues, contributing to the overall breast size. The amount of fat in the breast influences its density and volume. As women age, the breast undergoes changes, with glandular and ductal tissues gradually being replaced by fat, leading to a decrease in breast density.
Connective tissue forms another essential component of the breast. It provides structural support and surrounds the breast like a thin layer of tissue called fascia. This connective tissue extends from the skin, running through the breast, and attaching to the muscles on the chest, known as ligaments. Ligaments are dense bands of connective tissue that provide additional support to the breast.
Glands, specifically the lobules, are small sections of tissue found within the lobes of the breast. These lobules contain tiny bulb-like glands responsible for milk production. During pregnancy and breastfeeding, hormones stimulate these glands to produce milk. The number of lobules can vary, typically ranging between 15 to 25 lobules in each breast.
Ducts, or milk ducts, are small tubes that form a network within the breast. They carry milk from the lobules to the nipple, enabling breastfeeding. Estrogen plays a crucial role in duct development, stimulating their growth and the formation of side branches to accommodate increased milk production.
In summary, the breast is a multifaceted organ with a unique composition. The interplay between fat, connective tissue, glands, and ducts contributes to the breast's structure, function, and overall health. Understanding the anatomy of the breast is essential for comprehending its role in lactation and for detecting and treating breast-related conditions, such as cancer.
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Frequently asked questions
The breasts overlie the pectoralis major muscles and extend from the second rib to the sixth rib in the front of the rib cage.
The pectoralis major muscle is a large muscle on the chest.
The pectoralis major muscle gives mobility to the breast.
The breast is made of fatty tissue (adipose tissue), connective tissue, glands, and ducts.
The primary function of the breasts is to nourish infants with breast milk.
