Endocrine Regulation: Pancreatic Control, HPA Axis, and HPT Axis

Comprehensive vocabulary flashcards covering the anatomical components, regulatory hormones, feedback pathways, and autonomic controls of the endocrine pancreas, the hypothalamic-pituitary-adrenal (HPA) axis, and the hypothalamic-pituitary-thyroid (HPT) axis.

Pancreas

Islet of Langerhans

B-cell

a-cell

Sympathetic

Parasympathetic

Hypothalamus (HPA axis)

A brain region that integrates environmental and internal stimuli to release ACTH-RH, while receiving negative feedback ($-$) from both ACTH and glucocorticoids.

ACTH-RH

Adrenocorticotropic hormone-releasing hormone secreted by the hypothalamus that delivers a stimulatory ($+$) signal to the anterior lobe of the pituitary gland.

Anterior lobe (Pituitary gland)

The anterior glandular division of the pituitary gland that synthesizes and releases tropic hormones such as ACTH and TSH in response to hypothalamic releasing factors.

ACTH

Adrenocorticotropic hormone produced by the anterior pituitary that stimulates ($+$) the adrenal cortex and exerts short-loop negative feedback ($-$) on the hypothalamus.

Adrenal cortex

The outer layer of the adrenal gland that responds to ACTH stimulation ($+$) by synthesizing and secreting androgens and glucocorticoids.

Glucocorticoids

Adrenal cortex hormones that stimulate ($+$) target organs and mediate long-loop negative feedback ($-$) by suppressing both the anterior lobe of the pituitary gland and the hypothalamus.

Androgens (adrenal)

Steroid hormones synthesized by the adrenal cortex under ACTH stimulation ($+$) that act downstream on peripheral target organs.

Target organs (HPA axis)

Peripheral tissues and organs that receive stimulatory ($+$) inputs from circulating androgens and glucocorticoids.

Internal stimuli (HPA axis)

Endogenous signals from inside the body that convey physiological state to the brain and hypothalamus to modulate HPA axis activation.

Hypothalamus (HPT axis)

The neuroendocrine center that processes environmental and internal stimuli to release TRH, subject to negative feedback ($-$) from thyroid hormones ($T_4$ and $T_3$).

TRH

Thyrotropin-releasing hormone released by the hypothalamus that delivers a stimulatory ($+$) signal to the anterior lobe of the pituitary gland.

Pituitary gland (HPT axis)

The endocrine structure receiving hypothalamic TRH signals ($+$) to regulate TSH production, subject to negative feedback ($-$) from circulating thyroid hormones.

TSH

Thyroid-stimulating hormone secreted by the anterior pituitary lobe that delivers a stimulatory ($+$) signal to the thyroid gland.

Thyroid gland

A follicular endocrine gland that synthesizes and releases $T_4$ and $T_3$ when stimulated ($+$) by TSH.

$T_4$ and $T_3$

Thyroxine ($T_4$) and triiodothyronine ($T_3$), hormones secreted by the thyroid gland that act on target organs and exert negative feedback ($-$) on both the anterior pituitary lobe and the hypothalamus.

Target organs ($T_4 \rightarrow T_3$)

Peripheral tissues that respond to thyroid hormones and metabolically convert circulating thyroxine ($T_4$) into active triiodothyronine ($T_3$).

Environmental stimuli (HPT axis)

External environmental conditions that feed into the brain and hypothalamus to regulate TRH output and thyroid activity.

Internal stimuli (HPT axis)

Endogenous signals acting upon the brain and hypothalamus to influence the hypothalamic-pituitary-thyroid regulatory axis.