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bright red blood per rectum. SEE: hematochezia.

BRCA1 gene

SEE: under gene.

BRCA2 gene

SEE: under gene.


(brāk) 1. In orthopedics, a fracture. 2. To interrupt the continuity in a tissue or electric circuit or the channel of flow or communication.


(brāk′ă-wā″) In orthodontics, a device to apply tension or force to a facebow.


(brāk′poynt″) 1. A cut off level. 2. An end point. 3. The threshold that defines the failure of a process or a material. 4. A lesion in a nucleic acid sequence in which there is a locus of chromosomal damage.

breakthrough disease

(brāk′throo″) Any disease that occurs in spite of adequate vaccination to prevent it, e.g., "breakthrough varicella" or "breakthrough influenza" .


(brest) 1. The upper anterior aspect of the chest. 2. The mammary gland, a compound alveolar gland consisting of 15 to 20 lobes of glandular tissue separated from each other by interlobular septa. Each lobe is drained by a lactiferous duct that opens onto the tip of the nipple. The mammary gland secretes milk used for nourishment of the infant. For purposes of description, the female breast is divided into four quadrants: upper inner (the top medial quarter), lower inner (the bottom medial quarter), upper outer (the top lateral quarter), and the lower outer (the bottom lateral quarter). The tail of the breast extends up and away from the upper outer quadrant. SEE: illus.; mammary gland; milk.




Structure of mammary glands


DEVELOPMENT: During puberty, estrogens from the ovary stimulate growth and development of the duct system. During pregnancy, progesterone secreted by the corpus luteum and placenta acts synergistically with estrogens to bring the alveoli to complete development. After parturition, prolactin in conjunction with adrenal steroids initiates lactation, and oxytocin from the posterior pituitary gland induces ejection of milk. Sucking or milking reflexly stimulates both milk secretion and discharge of milk.

CHANGES IN PREGNANCY: During the first 6 to 12 weeks, there is fullness and tenderness, erectile tissue develops in the nipples, nodules are felt, pigment is deposited around the nipple (primary areola) (in blondes the areolae and nipples become darker pink; in brunettes they become dark brown and sometimes even black), and a few drops of fluid may be squeezed out. During the next 16 to 20 weeks, the secondary areola shows small whitish spots in pigmentation due to hypertrophy of the sebaceous glands (glands of Montgomery).


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