Lecture 20: Endocrinology Flashcards
What is an endocrine axis?
A chain of hormones regulating a system, typically contained in the hypothalamus, pituitary, and target organ.
Primary endocrine disease
Originates in the target organ of an endocrine axis
Secondary endocrine disease
Originates the the hypothalamus or pituitary, or is caused off-axis.
General pharmacological endocrine axis features.
- Hypothalamic hormones
- Trophic hormones from pituitary
- Action at target organ(s)
Protein vs steroid hormones
Proteins: actively stored and secreted into fenestrated capillaries, target surface receptors
Steroids: require carrier proteins in the blood, synthesized from cholesterol. Target surface, intracell., or nuclear receptors
How does adipose tissue act as a hormone source?
Adipose tissue itself produces many hormones, primarily leptin and adiponectin which are satiating/anorexigenic, inflammatory/anti-inflammatory.
Parts of the pituitary gland
- Neurohypophysis (posterior)
- Adenohypophysis (anterior)
Neurohypophysis
Neuroectoderm origin. Made of descending axons from supraoptic/paraventricular hypothalamic nuclei. Releases ADH, oxytocin.
Pituicytes
Resident glia of the neurohypophysis. Control hormone release to surrounding capillaries.
Structures of the neurohypophysis
- Median eminence
- Infundibular stalk
- Pars nervosa
- Herring bodies (axonal endings dilated with NTs)
Adenohypophysis
Originates from oral ectoderm. Responds to hypothalamic hormones released to the hypophyseal portal system.
Cells of the adenohypophysis
Pars distalis
1. Acidophils -> somatotropin, prolactin
2. Basophils -> ACTH, TSH, FSH, LH, β-endorphin
3. Chromophobes
Pars intermedia cells -> melanocyte-stimulating hormone
Structures of the adenohypophysis
- Pars tuberalis
- Pars intermedia
- Pars distalis
Where is the pituitary located?
The pituitary is at the base of the brain, encapsulated by sphenoid bone in the sella turcica cavity with an apical stalk to the hypothalamus.
Thyroid gland
Composed of many thyroid follicles, which are epithelial-enclosed accumulations of colloid. Uptakes iodine from blood, sequesters with thyroglobulin (colloid, Tyr-containing). Mono-iodin. Tyr + di-iodin. Tyr (MIT/DIT) sum for T3, T4.
Cells of the thyroid gland
Majority: follicular cells containing thyroglobulin -> T3, T4
Minority: parafollicular cells aka C-cells -> calcitonin
Parathyroid gland
Primarily made of chief cells -> PTH, also contains oxyphil cells
Pineal gland
Gland in brain with pinealocytes producing melatonin. Regulates circadian sleep/wakefulness. Accumulates concretions of corpora arenacea (brain sand)
Endocrine pancreas
Islets of Langerhans. In order of decreasing frequency, cells include:
β cells -> insulin
α cells -> glucagon
γ cells aka PP cells -> pancreatic polypeptide
δ cells -> somatostatin
Other cells -> ghrelin (hunger)
Adrenal glands
Consists of 2 embryological parts: cortex + medulla (mesenchyme + NCCs aka ectoderm). Produces corticosteroids, epi, and NE
Adrenal cortex layers
Outer to inner:
1. Zona glomerulosa -> mineralocorticoids (aldosterone)
2. Zona fasciculata -> glucocorticoids (cortisol)
3. Zona reticularis -> androgens
Adrenal medulla
Derived from neural crest cells. Contains 2 types of chromaffin cells producing epi and NE. Has dual blood supply from cortical capillaries and long cortical aka medullary arteries (arterioles).
DNES
Diffuse Neuroendocrine System. Refers to scattered cells in other organs that release endocrine hormones, especially in the GI system.
APUD cells
Amine Precursor Uptake + Decarboxylation cells. Part of DNES, produce polypeptide hormones from amine precursors via decarboxylases.
