Adenohypophysis

^ Cell types

• Chromophils

♦ Acidophils. Hormone-containing granules in the cytoplasm stain with acidic dyes, e.g., eosin

■ Somatotropes. Secrete somatotropin, (growth hormone, GH) which promotes growth (anabolic)

■ Mammotropes. Secrete prolactin which stimulates milk production

♦ Basophils. Hormone-containing granules in the cytoplasm of these cells stain with basic dyes, e.g., hematoxylin

■ Thyrotropes. Secrete thyroid stimulating hormone (TSH) which stimulates thyroid hormone synthesis and release

■ Gonadotropes. Secrete luteinizing hormone (LH) and follicle stimulating hormone (FSH); both hormones are present in males; however, in males, LH can be referred to as interstitial cell stimulating hormone (ICSH); regulate egg and sperm maturation and sex hormone production.

■ Adrenocorticotropes. Secrete adrenocorticotropic hormone (ACTH) which regulates glucocorticoid secretion by adrenal gland

• Chromophobes

♦ Cells with sparse granule content that do not stain with either hematoxylin or eosin

♦ May be degranulated cells or reserve, undifferentiated cells

Hormone(s)

General Cell Type

Specific Cell Type

GH

Acidophil

Somatotrope

Prolactin

Acidophil

Mammotrope

TSH

Basophil

Thyrotrope

FSH/LH

Basophil

Gonadotrope

ACTH

Basophil

Adrenocorticotrope

^ Distribution of cell types in the adenohypophysis

• Pars distalis contains all five cell types

• Pars tuberalis contains gonadotropes only

• Pars intermedia contains basophils; however, their function in humans is unclear.

^ Regulation of adenohypophyseal secretion

• Adenohypophyseal hormone secretion is regulated by factors produced by neurons in the hypothalamus. These factors either stimulate or inhibit hormone secretion from their target cells in the adenohypophysis.

• The releasing or inhibitory factors (neurohormones) are transported down their axons which terminate in a capillary bed located at the base of the hypothalamus in a region called the median eminence. Activity in these neurons causes release of the neurohormones from the terminals and their uptake into the capillaries.

Median Eminence
figure 16.1. Comparison of the structure and regulation of secretion of pituitary gland subdivisions.

• The capillaries anastomose into the hypophyseal portal vessels which travel down the infundibulum and end in a second capillary network within the adenohypophysis.

• Hypothalamic factors exit this second capillary plexus and either stimulate or inhibit the secretion of hormones from their target acidophil or basophil cells.

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    What is the purpose for hypothalamic hypophyseal portal system?
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