TBL 5 Objectives

Question 1

Name the pectoral muscles and cite their bony attachments and innervations

Answer 1

Pectoralis major:
- Innervated by the lateral and medial pectoral nerves
- Composed of clavicular head and sternocostal head
Clavicular head attaches proximally to the clavicle
Sternocostal head attaches proximally to the sternum and the superior 6 costal cartilages
Both heads attach distally to the intertubercle sulcus of the humerus

Pectoralis minor:

• Innervated by the medial pectoral nerve
• Attaches proximally to the coracoid process of the scapula and distally to the 3rd-5th ribs

Question 2

Distinguish actions of the pectoral muscles on the upper limb and scapula

Answer 2

Pectoralis major adducts the upper limb and medially rotates the arm

Pectoralis minor stabilizes the scapula when reaching for something by drawing it against the thoracic wall

Question 3

Define the Poland sequence

Answer 3

Characterized by absence of the pectoralis minor and partial loss of the pectoralis major

Question 4

Compare breast histology in childhood and at puberty

Answer 4

Early embryo: epidermal thickenings (primitive nipples) appear but only one pair, which remains in the pectoral region, invaginates into the underlying dermis. (mammary glands are modified sweat glands)

Childhood: the breasts consist of 15-25 rudimentary lactiferous ducts, which open onto the surface of the nipple.

Puberty: ovarian estrogen and progesterone induce budding of multiple, small terminal ducts from the distal end of each lactiferous duct. These hormones also induce white fat accumulation between the budding terminal ducts.

Question 5

Describe ovarian hormones and breast maturation during pregnancy and lactation

Answer 5

Pregnancy: ovarian hormones (estrogen and progesterone) and prolactin stimulate secretory acini formation from the distal ends of the terminal ducts.

After breast-feeding: breasts return to resting state
After menopause: acini and terminal ducts regress, but remaining lactiferous ducts can transform into fluid-filled cysts

Question 6

Name the pectoral muscles that underlie the breasts

Answer 6

Two-thirds lie on pectoralis major, one-third lies on serratus anterior