Histology of Pituitary Gland

Pituitary Gland (aka hypophysis)

• What

• Encapsulated with

• Vascularised?

• Regulated by

What: Master gland

Encapsulated with: Irregular, dense connective tissue

Vascularised: Highly vascularised

Regulated by: Hypothalamus

How is the hypopthalamus connected to the pituitary gland?

Through the hypothalamo-hypophyseal system:

• Hypothalamo-hypophyseal tract (axons) → connects to neurophypophysis (posterior pituitary)

• Hypothalamo-hypophyseal portal system (capillaries) → connects to adenohypophysis (anterior pituitary)

The pituitary gland consist of what 2 components?

• Neurohypophysis (diencephalan floor)

• Adenohypophysis (Rathke’s pouch)

Pituitary Gland: Neurohypophysis

• What

• Function

• Where and what are the cell bodies of neurohypophyseal hormones located

• Which hormones are associated with neurohypophysis

  • Are they produced in the neurohypophysis

• Where are these hormones stored

• What is pars nervosa

  • Contains

• In which animals is the neurohypophysis larger than adenohypophysis

What: The posterior pituitary

Function: Stores and releases hormones made in the hypothalamus

Where and what are the cell bodies of neurohypophyseal hormones located:

• Where: In the hypothalamus

• What:

  • Supraoptic nuclei

  • Paraventricular nuclei

Which hormones are associated with neurohypophysis: ADH (antidiuretic hormone) and oxytocin

• Are they produced in the neurohypophysis: No,

  • They are produced in the hypothalamus and

  • Stored and released from the neurohypophysis

Where are these hormones stored: Neurosecretory granules called Herring bodies

What is pars nervosa: The main part of the neurohypophysis contain

• Contains:

  • Terminal axons

  • Surrounding pituicytes (support cells with lipid droplets & cytoplasmic projections)

In which animals is the neurohypophysis larger than adenohypophysis: Feline and porcine

Pituitary Gland: Neurohypophysis

What is the pathway of signals from hypothalamus → neurohypophysis to release ADH and oxytocin

1. Signals start in the cell bodies of the hypothalamus and they produce ADH and oxytocin

   1. Supraoptic nucleus

   2. Paraventricular nucleus

2. Then nerve impulses travel along the hypothalamo-hypophyseal tract which consist of axons

3. Axons terminate at the pars nervosa of the neurohypophysis

4. Hormones are then stored in Herrring bodies

5. They are released in the bloodstream response to nerve impulses

Pituitary Gland: Neurohypophysis

• Describe the histology cytoplasm staining of pituicytes and Herring bodies

• Pituicytes: Lightly stained but has dark elongated nucleus

• Herring bodies: Esoinophilic (pink/red)

Pituitary Gland: Adenohypophysis

• What

• Function

• Where and what are the cell bodies of adenohypophysis hormones located

  • Function

• How do hypothalamic hormones reach the anterior pituitary

• Species where adenohypophysis is histologically prominent

• 3 components

What: Anterior pituitary

Function: Produce and secrete hormones

Where and what are the cell bodies of adenohypophysis hormones located:

• Located: In the hypothalamus

• What:

  • Infundibular nucleus

  • Ventromedial nucleus

• Function of these cells: Produce releasing or inhibiting hormones that regulate the anterior pituitary

How do hypothalamic hormones reach the anterior pituitary:

• After the hypothalamic production of releasing/inhibiting hormones

• Hormones enter primary capillary plexus (median eminence)

  • Which is at the base of hypothalamus

• Then they are carried by the portal veins to the secondary capillary plexus

  • Which is in the adenohypophysis

• Hormones diffuse to pituitary cells → stimulate or inhibit hormone secretion

Species where adenohypophysis is histologically prominent:

• Equine

• Canine

• Ruminant

3 components:

• Pars distalis (biggest, main part that secretes anterior pituitary hormones) #c9184a

• Pars tuberalis (tip that wraps around pituitary stalk) #f7aef8

• Pars intermedia (between anterior and posterior pituitary) #db00b6

Adenohypophysis: Pars Distalis #c9184a

• What are the 2 types of cells in Pars Distalis

• Chromophobic cells

• Chromphilic cells

Adenohypophysis: Pars Distalis —> Chromophobic Cells #c9184a

• What

• Cytoplasm

• Nucleus

What: Undifferentiated, non secretory stem cells

Cytoplasm: Light colored homogenous

Nucleus: Large

Adenohypophysis: Pars Distalis —> Chromophlic Cells #c9184a

• 2 types

  • What do they secrete

• Acidophilic cells

  • Secrete: Somatotropic and lactotropic

• Basophilic cells

  • Secrete: Gonadotropic, thyrotropic and corticotropic

Adenohypophysis: Pars Distalis —> Chromophlic Cells (acidophilic cells) #c9184a

• Somatotropic cells

  • Size

  • Shape

  • Consist of

  • Secrete

• Lactotropic cells

  • Size

  • Shape

  • Consist of

  • Secrete

  • Prominent during

Somatotropic cells:

• Size: Small

• Shape: Round

• Consist of: Large, densely packed granules

• Secrete: Growth hormone

Lactotropic cells:

• Size: Large, single

• Shape: Polyhedral cells

• Consist of: Larger granules

• Secrete: Prolactin hormone

• Prominent during: Gestation and post partum

Adenohypophysis: Pars Distalis —> Chromophlic Cells (basophilic cells) #c9184a

• Gonadotropic cells

  • Size

  • Shape

  • Consist of

  • Secrete

• Thyrotropic cells

  • Consist of

  • Secrete

• Corticotropic cells

  • Secrete

  • Function

Gonadotropic cells:

• Size: Small

• Shape: Round

• Consist of: PAS positive granules

• Secrete: FSH and LH

Thyrotropic cells:

• Consist of: Smallest granules

• Secrete: Thyroid stimulating hormone

Corticotropic cells:

• Secrete: Adrenocortoropic hormone

• Function: Regulates cortical adrenal gland hormone synthesis

Adenohypophysis: Pars Intermedia #f7aef8

• Staining

• Secrete

• Synthesis

Staining: Basophilic

Secrete: Melanocyte-stimulating hormone

Synthesis: Pro-opiomelanocortin → β-endorphin

Adenohypophysis: Pars Tuberalis #db00b6

• What

• Location

• Arrangement

What: Adenohypophysis projection

Location: Partially surrounds anterior aspect of infundibulum

Arrangement: Cluster