U1vi / 21A13: List the cell types in the anterior pituitary gland. Outline their secretions, control and target organ effects

21A13: Exam Report

List the cell types in the anterior pituitary gland. Outline their secretions, control and target organ effects.

40% of candidates passed this question.

Few candidates described cell types as chromophils and chromophobes. There were many errant references to chromaffin cells which are found mainly in the adrenal medulla, and to staining on H&E. Chromophil cells stain by absorbing chromium salts. Few candidates mentioned that the hormones secreted by the anterior pituitary are peptides. Most candidates outlined the hypophyseal-portal system well. Knowledge of TSH and ACTH control and target organ effects were good. Similar knowledge for LH, FSH, PRL and GH was much more sporadic.

U1vi / 21A13: List the cell types in the anterior pituitary gland. Outline their secretions, control and target organ effects

The Anterior Pituitary Gland is the anterior lobe of pituitary gland which sits in the Sella Turcica and connects to the Hypothalamus via the Pituitary Stalk. The APG is a major organ of the endocrine system essential for growth, development, homeostasis, metabolism & reproduction

Anterior Pituitary

The hypothalamic-hypophyseal portal system connecting the Hypothalamus to the Anterior Pituitary

Cell Types

There are 5 major cell types

Cell Type

Corticotropes

Popn

10%

Stain

Basilic

Hormone Produced

ACTH & MSH

Cell Type

Thyrotropes

Popn

10%

Stain

Chromophobic

Hormone Produced

TSH

Cell Type

Gonadotropes

Popn

10%

Stain

Chromophobic

Hormone Produced

LH, FSH

Cell Type

Somatotropes

Popn

50%

Stain

Acidic

Hormone Produced

GH

Cell Type

Lactotropes

Popn

10-25%

Stain

Acidic

Hormone Produced

PRL

Hormones

⦁ Hormones secreted by the anterior pituitary are peptides

  • Mnemonic: FLAT PEG (FSH, LH, ACTH, TSH, Prolactin, [endorphins], growth hormones)

Hormonal Secretions

FSH
LH

Control

↑ secretion with GnRH
↓ secretion with negative feedback

Target Organ Effects

  • LH → Ovulation and luteinisation of ovarian follicles (females); testosterone secretion (males)
  • FSH → Ovarian follicle development (females); spermatogenesis (males)

Hormonal Secretions

ACTH

Control

  • ↑ secretion → by (i) ↑ corticotrophin releasing factor (CRF ↑ with stress, ↓ BGL, infection, injury, exercise, Etc.), (ii) catecholamines, and (iii) ADH
  • ↓ secretion → -ve feedback with ↑ GC and androgen levels

Target Organ Effects

  • (i) ↑ glucocorticoid synthesis and release (from all 3 layers of cortex → esp zona fasciculata and reticularis)
  • (ii) ↑ androgen (cholesterol & steroid) synthesis and release (from zona fasciculata and reticularis)
  • (iii) +ve trophic actions on adreno-cortical cells

Hormonal Secretions

TSH

Control

  • ↑ secretion → (i) ↑ TRH levels (via Gq) 2° to cold exposure in neonates, (ii) oestrogen
  • ↓ secretion → (i) -ve feedback with ↑ free thyroid hormones levels (esp FT3), (ii) ↓ TRH levels 2° to trauma/stress, (iii) Glucocorticoids, (iv) Somatostatin, (v) Dopamine

Target Organ Effects

  • (i) ↑ synthesis and secretion of thyroid hormone (T4 [90%] and T3 [10%])
  • (ii) ↑ size (hyperplasia and hypertrophy of follicular cells) and vascularity of thyroid gland → facilitates further thyroid hormone synthesis

Hormonal Secretions

Prolactin

Control

under tonic inhibitory control by DA from hypothalamus → PRL secretion occurs with (i) PRF release (due to suckling response), or (ii) TRH release

Target Organ Effects

  • (i) During pregnancy → promotes mammary gland and ductal development
  • (ii) Following delivery → (a) promotes lactation (↑ production of fat and lactose) and (b) causes amenorrhoea (PRL suppresses LH secretion)

Hormonal Secretions

Growth Hormone

Control

  • ↑ secretion → GHRH, nutritional factors (starvation, ↓ BGL, ↓ plasma FFA), stress, excitement, trauma
    • Alpha adrenergic, dopaminergic, serotoninergic agonist, opiod and aa stimulate GH release
    • ↓ secretion → GHIH, -ve feedback by somaomedins (IGF-1)

Target Organ Effects

  • Releases somatomedins (IGF-1 from liver) → anabolic actions on skeletal/cartilage growth → causes proliferation of chondrocytes and osteoblasts and protein uptake by osteogenic cells → epiphyseal growth or periosteal growth(if epiphyses fused)
  • Protein metabolism → ↑ a.a. uptake into cells and ↑ protein synthesis
  • Fat metabolism → ↑ lipolysis in adipose tissue, ↑ utilisation of FFA for energy in peripheral tissues (via β-oxidation), ↑ ketogenesis
  • CHO metabolism → anti-insulin effect via ↑ glycogenesis and ↓ glucose uptake by tissues (\↑ BGL)

Author: Huiling Tan