Endocrine System – Hypothalamus-Pituitary Axis & Related Glands

These flashcards review the key structures, hormones, feedback loops, and physiological effects discussed in the lecture on the hypothalamus–pituitary axis, adrenal and thyroid glands, calcium regulation, and the roles of cortisol and thyroid hormone.

What are the only signaling molecules of the endocrine system?

Hormones

Which region of the brain contains the hypothalamus?

The diencephalon

What alternative name is given to the anterior pituitary and why?

Adenohypophysis, because it is made of epithelial (glandular) tissue

What alternative name is given to the posterior pituitary and why?

Neurohypophysis, because it is composed of nervous tissue

Which two hormones are released from the posterior pituitary?

Antidiuretic hormone (ADH) and oxytocin

What is the primary function of ADH?

Regulation of fluid volume (water reabsorption) in the body

What is a major function of oxytocin?

Inducing uterine contractions during childbirth

Name the six major hormones released by the anterior pituitary.

Thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), follicle-stimulating hormone (FSH), luteinizing hormone (LH), growth hormone (GH), and prolactin

What is a tropic hormone?

A hormone that stimulates another endocrine gland to release its hormone

Which hypothalamic hormone triggers GH release?

Growth hormone-releasing hormone (GHRH)

Which hypothalamic hormone triggers FSH and LH release?

Gonadotropin-releasing hormone (GnRH)

Which hypothalamic hormone triggers TSH release?

Thyrotropin-releasing hormone (TRH)

Which hypothalamic hormone triggers ACTH release?

Corticotropin-releasing hormone (CRH)

Why must hypothalamic neurohormones travel through capillaries to reach the anterior pituitary?

Because diffusion across the physical gap would be too slow and inefficient for microscopic molecules

Where are the adrenal glands located?

On top of (superior to) the kidneys; hence also called the suprarenal glands

What two main regions make up an adrenal gland?

The outer adrenal cortex and the inner adrenal medulla

Which tissue type composes the adrenal medulla and what does it secrete?

Nervous tissue; it secretes catecholamines (epinephrine, norepinephrine, dopamine)

Which tissue type composes the adrenal cortex and what broad classes of hormones does it secrete?

Epithelial tissue; it secretes sex steroids, mineralocorticoids, and glucocorticoids

What is the predominant glucocorticoid produced by the adrenal cortex?

Cortisol

What molecule is the precursor for all steroid hormones produced in the adrenal cortex?

Cholesterol

Which mineralocorticoid is chiefly discussed and what is its primary action?

Aldosterone; it regulates sodium and water balance (in kidneys)

Which two sex steroids are secreted by the adrenal cortex?

Testosterone and estrogen

Which axis describes CRH → ACTH → cortisol?

The hypothalamic–pituitary–adrenal (HPA) axis

Which axis describes TRH → TSH → thyroid hormone?

The hypothalamic–pituitary–thyroid (HPT) axis

What kind of molecule is thyroid hormone and where are its receptors located?

Amphipathic; receptors are inside the cytoplasm or nucleus

List four metabolic effects of thyroid hormone.

Increases mitochondrial size/number, raises Na⁺/K⁺-pump numbers, enhances glucose absorption, boosts protein synthesis and gluconeogenesis

Name three classic symptoms of hypothyroidism.

Lethargy, feeling cold, and weight gain

Which hormone lowers elevated blood calcium levels?

Calcitonin

From which thyroid-related cells is calcitonin secreted?

Parafollicular (C) cells on the anterior thyroid

Which hormone raises low blood calcium levels?

Parathyroid hormone (PTH)

List three actions of PTH that increase blood calcium.

(1) Increases calcium reabsorption in kidneys, (2) increases bone resorption, (3) increases intestinal calcium absorption (via calcitriol)

What opposite renal effect does calcitonin have compared to PTH?

Stimulates excretion of calcium in urine

How does the parathyroid gland detect low calcium to release PTH?

Calcium-sensing G-protein coupled receptors lose bound Ca²⁺, activating a cascade that triggers exocytosis of PTH

Give two major metabolic effects of cortisol on nutrients.

Stimulates gluconeogenesis and mobilizes amino acids/fatty acids

Why can prolonged high cortisol produce "adrenal diabetes"?

Because persistent gluconeogenesis and glucose sparing lead to chronically elevated blood glucose

How does cortisol reduce inflammation?

Decreases vasodilation, reduces capillary permeability, and limits white-blood-cell mobilization

Why is cortisol administered to transplant patients?

Its immunosuppressive effect (atrophy of lymphoid tissue) helps prevent rejection of the transplanted organ

What hematologic effect can excess cortisol cause, and what is a downside of it?

Polycythemia (high RBC count) which thickens blood and increases viscosity

Explain the long-loop negative feedback in the HPT axis.

High thyroid hormone in blood inhibits TRH release from hypothalamus and TSH release from anterior pituitary

Explain the short-loop negative feedback in the HPA axis.

Elevated ACTH in blood feeds back to inhibit CRH release from the hypothalamus

Which two feedback loops help terminate excess cortisol secretion?

Short loop: ACTH → hypothalamus; Long loop: cortisol → hypothalamus & anterior pituitary