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The breast is a part of the anatomy of both males and females. However, the female breast has milk ducts and glandular tissue that aid breastfeeding. The breast lies on top of and is loosely attached to the pectoral muscles on the front of the chest. While there are no muscles in the breast, the pectoralis major muscle forms the base of the breast. The nipple, which is the area at the centre of the areola, contains muscle fibres.
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What You'll Learn
- Breasts are not made of muscle, but lie on top of them
- The pectoralis major muscle forms the base of the breast
- Nipples contain muscle fibres that cause them to point outward when contracted
- Breasts are made of milk ducts, blood vessels, lymph vessels, and different types of tissue
- Breasts are attached to the chest muscles by ligaments
Breasts are not made of muscle, but lie on top of them
The breasts are primarily made up of fatty and glandular tissue, with no muscle tissue. However, they lie on top of and are loosely attached to the pectoralis major muscle on the chest. This muscle forms the base of the breast and extends from the breastbone to the collarbone and into the armpit. The pectoralis major muscle is also utilised in reconstructive plastic surgery, as it can provide good coverage for a breast implant.
The breasts contain mammary glands, which produce milk for breastfeeding. Milk is carried from these glands to the nipples through milk ducts. The nipples are surrounded by the areola, a circular area of darker-coloured skin. The areola contains small glands that secrete an oily substance, acting as a lubricant for the nipple and areola during breastfeeding.
In addition to fatty and glandular tissue, the breasts also contain connective tissue, which holds the glandular and fatty tissue in place. Blood vessels and lymph vessels are also present in the breasts. Lymph vessels are thin tubes similar to blood vessels that transport lymph fluid, which helps the body's immune system fight infections.
The breasts are divided into four quadrants by an invisible line running vertically and horizontally through the nipple. Each breast lies over a large muscle and covers a fairly large area, extending from below the collarbone to the armpit and across to the breastbone.
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The pectoralis major muscle forms the base of the breast
The breasts contain no muscles, but they lie over a large muscle called the pectoralis major. This muscle forms the base of the breast and is the superior-most and largest muscle of the anterior chest wall. It is a thick, fan-shaped muscle that lies underneath the breast tissue and forms the anterior wall of the axilla. The pectoralis major is the most superficial muscle in the pectoral region.
The pectoralis major has its origin in the anterior surface of the medial half of the clavicle, the anterior surface of the sternum, the first seven costal cartilages, the sternal end of the sixth rib, and the aponeurosis of the external oblique of the anterior abdominal wall. It inserts onto the lateral lip of the intertubercular sulcus of the humerus. There are two heads of the pectoralis major, the clavicular and the sternocostal, which reference their area of origin.
The clavicular head of the pectoralis major can be tested by transversely adducting the arm at the glenohumeral joint against resistance, during which it can be seen and palpated. The sternocostal head can be tested by adducting the arm at the glenohumeral joint against resistance, and it can also be seen and palpated. The pectoralis major is active in deep or forced inspiration, but not expiration. When the diaphragm and intercostal muscles are insufficient for proper breathing, the pectoralis major can assist in inspiration.
The pectoralis major is responsible for four actions, primarily responsible for the movement of the shoulder joint. The first action is flexion of the humerus, as in throwing a ball underhand or lifting a child. The second action is adduction, and the third is internal rotation of the humerus. The fourth action is keeping the arm attached to the trunk of the body. The two heads of the pectoralis major have different functions. The clavicular part is close to the deltoid muscle and contributes to flexion, horizontal adduction, and inward rotation of the humerus. The sternocostal part is antagonistic to the clavicular part, contributing to downward and forward movement of the arm and inward rotation when accompanied by adduction.
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Nipples contain muscle fibres that cause them to point outward when contracted
The breasts of women and men contain no muscles. However, breasts lie over a large muscle called the pectoralis major muscle on the chest. While breasts do not contain muscles, the nipples do. The nipple is the small structure at the centre of each breast and contains muscle fibres. When these muscle fibres contract, the nipple becomes erect and points outward. This is known as the "let-down reflex".
The nipple is surrounded by the areola, a pink or brown, circular area on the surface of the breast. The areola contains small glands that release an oily substance to lubricate the nipple and areola. The nipple itself is made up of smooth muscle fibres, connective tissue, and milk ducts (tubes that carry milk). Each nipple has about nine small openings where milk is released. It also has hundreds of nerves that provide sensation.
The physiological purpose of nipples is to deliver milk, produced in the female mammary glands during lactation, to an infant. In males, nipples do not have the same level of function or prominence. Nipples can be categorised into three types based on their appearance: protruding, flat, and inverted. Protruding nipples are the most common type, sticking outward from the areola. Flat nipples are even with the skin of the areola, neither sticking out nor pointing inwards. Inverted nipples point inward and look tucked inside the areola.
During breastfeeding, nipple stimulation by an infant stimulates the release of oxytocin from the hypothalamus. Oxytocin is a hormone that increases during pregnancy and acts on the breast to help produce the milk-ejection reflex. The release of oxytocin from nipple stimulation causes the uterus to contract even after childbirth, helping to prevent postpartum haemorrhage.
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Breasts are made of milk ducts, blood vessels, lymph vessels, and different types of tissue
While breasts are commonly associated with femininity and sexual attraction, they serve a vital reproductive function in lactation. Breasts are composed of various structures, including milk ducts, blood vessels, lymph vessels, and different types of tissue.
Milk ducts are an essential component of the breast, facilitating the transport of milk produced in the mammary glands to the nipple for breastfeeding. These ducts begin to develop and branch out during puberty, marking the onset of breast growth. Alongside the ducts, the breasts contain lobules, which are small structures that produce milk. The number and size of these lobules increase under the influence of the hormone progesterone, which also plays a role in enlarging blood vessels and breast cells.
Blood vessels are another crucial aspect of breast anatomy. They circulate blood throughout the breasts, chest, and body, providing essential nutrients and oxygen to the tissues. The breasts also contain lymph vessels, which are part of the lymphatic system. These vessels are similar in appearance to blood vessels but serve a different function. They collect and transport lymph fluid, a clear liquid that helps the body's immune system fight infections. The lymph vessels lead to small, bean-shaped structures called lymph nodes, which are located in clusters under the arms, above the collarbone, and in the chest.
The composition of breast tissue varies between individuals and changes throughout a woman's life. During pregnancy and breastfeeding, the breasts contain predominantly glandular tissue responsible for milk production. As women age, this glandular tissue is gradually replaced by fatty tissue, resulting in a decrease in the overall density of the breasts. Dense breasts, characterised by a higher proportion of glandular and fibrous tissue, can pose challenges in detecting breast cancer through mammograms.
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Breasts are attached to the chest muscles by ligaments
While breasts do not contain muscles, they are attached to the chest by ligaments. The pectoralis major muscle forms the base of the breast, extending from the breastbone to the collarbone and into the armpit. This muscle is responsible for much of the upper arm and shoulder movement. The breasts lie on top of and are loosely attached to the pectoralis muscle by suspensory ligaments, also known as Cooper's ligaments (named after the physician who first identified them). These ligaments are dense bands of connective tissue that provide support and structure to the breasts. They run from the skin through the breast and attach to the pectoralis muscles on the chest.
Cooper's ligaments are not taut, allowing for natural mobility in the breasts. However, with age, these ligaments can lose their elasticity and become stretched, leading to changes in breast shape and a condition called breast ptosis. The shape and firmness of the breasts are influenced by the proportion of fibrous tissue to fatty tissue. A higher proportion of fibrous tissue results in stronger ligaments and firmer breasts, while a higher proportion of fatty tissue leads to softer and more pendulous breasts.
The breasts themselves are composed of mammary glands, fat, connective tissue, and ducts. The mammary glands, or lobules, produce milk during pregnancy and breastfeeding. The ducts then carry the milk to the nipple for release. The nipples contain muscle fibres that contract to make the nipple erect or pointed outward.
In addition to the pectoralis major muscle, the breasts also lie over the serratus anterior and external oblique muscles on the lateral and medial walls of the chest. These muscles contribute to the overall structure and support of the breasts.
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Frequently asked questions
The breasts themselves are not muscles, but they lie on top of and are connected to the pectoralis major muscle.
The breasts are made up of fat, connective tissue, glands, and ducts.
In females, the breasts serve as mammary glands that produce and secrete milk to feed infants. They are also a source of sexual pleasure. In males, breasts do not have a physiological function but can still provide sexual pleasure.
Both males and females develop breasts from the same embryological tissues. However, female breasts have milk ducts and glandular tissue that aid in breastfeeding. Female breasts also contain more breast tissue than male breasts.
The size and shape of breasts are influenced by hormonal changes, medical conditions, and the underlying muscle and bone structures of the chest.
