Integumentary Glands

**Figure 1** The primary skin glands include sebaceous glands and sudoriferous glands (divided into eccrine and apocrine glands).

The integumentary glands help to lubricate the skin, regulate skin temperature (thermoregulation), excrete waste, and secrete antimicrobial properties

The sudoriferous glands are the “sweat glands”, encompassing eccrine, apocrine, and modified apocrine glands (see below)
Sebaceous glands secrete the oily sebum

Secretion methods

Holocrine: rupture of secretory cell releases secretion products
Merocrine*: vesicular products are exocytosed out of cell
Apocrine: loss of cytoplasm along with secretion

Onset of secretion

Eccrine: begin secreting shortly after birth
Apocrine: puberty (due to surge of testosterone/androgens)
Sebaceous: last few months of fetal development, surge at puberty

Gland Comparison

Gland type	Gland characteristics	Secretion method	Secrete onto	Secretion type	Stimulation	Gland location
Eccrine (merocrine)	More common; smaller; coiled tubular	Merocrine	Directly onto skin	Sweat (water, NaCl, urea, dermcidin, moisturizing factors)	Direct, localized cholinergic sympathetic synapses	Palms, soles
Apocrine	Larger/branched; coiled tubular;	Merocrine¹	Secrete onto hair follicle	Sticky, cloudy, odorous (due to ABCC11 variant)	Adrenergic sympathetic fibers (NE): after stress, puberty	Axillae, nipples, pubic region
Sebaceous	Simple branched alveolar	Holocrine	Secrete onto hair follicle	Sebum: triglycerides, esters, cholesterol	Endocrine (androgens)	Face, back, chest, nipples, external genitalia

Table 1 The various glands can be differentiated based on their appearance, secretion characteristics, nervous or endocrine innervation, and most prominent locations .¹While apocrine glands are seemingly named after apocrine secretion, in reality, they secrete via merocrine means (exocytosis).

Secretory cells

Eccrine glands

Ectodermal origins
They consist of a single tubular structure with two types of secretory cells (clear, dark), and myoepithelial supportive cells
Antimicrobial properties: secrete peptides such as dermcidin, cathelicidin, lactoferrin; as well as immune factors (e.g., igA, IL-1, IL-31)

Apocrine glands

They consist of a coiled secretory structure (Figure 1) in the lower dermis/upper hypodermis and a straight duct (enters the infundibulum of hair follicle)
- The coiled cells are a single layer of cuboidal/columnar cells on top of a layer of adjacent myoepithelial cells

Modified apocrine glands

These are the only apocrine glands, or integumentary glands in general, that secrete via apocrine means (i.e., pinching off of cytoplasm)

Ceruminous glands: in external auditory. meatus

Secrete cerumen (“ear wax”): keratin, lipids, ceramides
- Type of cerumen determined by SNP in ABCC11 transporter gene
  - Wet, sticky cerumen (GG, GA): most common in Africans/Europeans
  - Dry, flaky cerumen(AA): most common in East Asians/

Glands of Moll (Ciliary glands): at free margins of eyelids

Secrete oil to lubricate eyelashes and prevent drying at margin

Glands of Zeis: at eyelash follicles

Secrete sebum to lubricate eyelashes

Mammary glands: in breasts

Secrete milk: water, lipids, sugars, antibodies for nourishment of offspring