Endocrine Development and Functional Histology

Question 1

What are the precursors of the different types of hormones?

Answer 1

• Protein and glycoprotein molecules, e.g. insulin, growth hormone, parathyroid hormone (PTH).
• Small peptide molecules, e.g. vasopressin, products of enteroendocrine cells.
• Amino acid derivatives, e.g. thyroxine, adrenaline (epinephrine) and noradrenaline (norepinephrine).
• Steroids derived from cholesterol, e.g. adrenal cortical hormones, ovarian and testicular hormones.

Question 2

What hormones come from small peptides?

Answer 2

vasopressin, products of enteroendocrine cells.

Question 3

What hormones come from amino acids directly?

Answer 3

thyroxine, adrenaline (epinephrine) and noradrenaline (norepinephrine).

Question 4

What hormones are derived from cholesterol?

Answer 4

• Steroids derived from cholesterol, e.g. adrenal cortical hormones, ovarian and testicular hormones.

Question 5

what visual clues might distinguish an endocrine cell that produces amino acid, protein, or peptide hormones?

Answer 5

Endocrine cells which produce hormones based on amino acids, peptides and proteins often have characteristic membrane-bound secretory vacuoles with electron-dense central cores ( dense core granules).

Question 6

What are the three functional divisions of the endocrine system?

Answer 6

The endocrine system can be divided into three parts:

• The major endocrine organs in which the sole or major function of the organ is the synthesis, storage and secretion of hormones (e.g. thyroid and adrenal glands)
• Endocrine components within other solid organs , for example, the endocrine components of the pancreas, ovary, testis and kidney, in the form of clusters of endocrine cells within other tissues
• The diffuse endocrine system , scattered individual hormone cells (or small clumps), usually within an extensive epithelium (e.g. gastrointestinal and respiratory tracts). The major function of these cells is probably paracrine (i.e. acting on adjacent non-endocrine cells, rather than entering the bloodstream and producing systemic effects).

Question 7

The hormones from the pituitary system are differentiated how? (general classification)

Answer 7

The pituitary hormones fall into two functional groups:

• Hormones which act directly on non-endocrine tissues: growth hormone ( GH ), prolactin , antidiuretic hormone ( ADH , vasopressin ), oxytocin and melanocyte stimulating hormone ( MSH ).
• Hormones which modulate the secretory activity of other endocrine glands ( trophic hormones ): thyroid stimulating hormone ( TSH ), adrenocorticotrophic hormone ( ACTH ) and the gonadotrophic hormones, follicle stimulating hormone ( FSH ) and luteinising hormone ( LH ).

Question 8

Describe (super general) the embryonic origins of the posterior pituitary

Answer 8

The posterior pituitary , also called the neurohypophysis or pars nervosa, is derived from a downgrowth of nervous tissue from the hypothalamus, to which it remains joined by the pituitary stalk.

Question 9

Describe (super general) the embryonic origins of the ANTERIOR pituitary.

Answer 9

The anterior pituitary arises as an epithelial upgrowth from the roof of the primitive oral cavity known as Rathke’s pouch . This specialised glandular epithelium is wrapped around the anterior aspect of the posterior pituitary and is often called the adenohypophysis .

*The adenohypophysis may contain a cleft or group of cyst-like spaces which represent the vestigial lumen of Rathke’s pouch. This vestigial cleft divides the major part of the anterior pituitary from a thin zone of tissue lying against the posterior pituitary known as the pars intermedia . An extension of the adenohypophysis surrounds the neural stalk and is known as the pars tuberalis .

Question 10

Describe the process of NEUROSECRETION that occurs in the posterior pituitary

Answer 10

(pay attention to the fact that the posterior pituitary has a completely different way of secretion than the anterior pituitary)

• The type and mode of secretion of the posterior pituitary differs greatly from that of the anterior pituitary.
• The posterior pituitary secretes two hormones:
• antidiuretic hormone (ADH = vasopressin = arginine vasopressin), + oxytocin
• both of which act directly on non-endocrine tissues.

*ADH is synthesized in the neuron cell bodies of the supraoptic nucleus , and oxytocin is synthesised in those of the paraventricular nucleus of the hypothalamus. Bound to glycoproteins, the hormones pass down the axons of the hypothalamopituitary tract through the pituitary stalk to the posterior pituitary where they are stored in the distended terminal parts of the axons. Release of posterior pituitary hormones is controlled directly by nervous impulses passing down the axons from the hypothalamus, a process known as neurosecretion .