Endocrine System Flashcards
What are the functions of the endocrine system?
- Maintain homeostasis
- Stress reactions
- Regulate growth and development
How is the secretion of endocrine hormones controlled?
Feedback loops
Define paracrine secretion.
Some endocrine cells produce hormones that act very quickly at only a short distance
What is the name for when endocrine cells may produce molecules that act on themselves or on cells of the same type?
Autocrine secretion
What is the typical structure of endocrine glands?
Cords of parenchymal cells closely associated with a very rich vascular supply composed of a network of fenestrated capillaries and a relatively small amount of stroma
List the 6 major endocrine organs.
- Pituitary
- Hypothalamus
- Thyroid
- Parathyroid
- Adrenals
- Pineal
Within other solid organs, there are important endocrine components. What organs contain these?
- Pancreas
- Ovary
- Testis
- Kidneys
What is the diffuse endocrine system?
Scattered individual hormone cells (or clumps of cells)
Where are cells of the diffuse endocrine system typically found?
Within extensive epithelial
Most, but not all, endocrine tissue are of epithelial origin. Which tissues aren’t?
- Adrenal medulla
- Hypothalamus
- Posterior pituitary
What do the glands and tissues of the endocrine system do?
- Synthesis and secretion of hormones
- Regulate, control and coordinate organ and tissue activity
Describe what a hormone is.
Chemical messengers typically released into the blood to act at specific distance receptors
What are the 4 types of hormones?
- Protein and glycoprotein
- Small peptide
- Derivatives of amino acids
- Steroids derived from cholesterol
Why is the pituitary gland called the master endocrine gland?
Its hormones regulate physiological activities of many other endocrine glands and tissues
What is the morphology of the pituitary gland?
Size of a flat pea
500-900 mg in adults
Composed of anterior and posterior part
What is the name of the fossa that the pituitary gland is found in?
Sella turcica
What covers the superior aspect of the pituitary gland?
A thickened extension of the dura mater called the diaphragmatic sella
What 2 endocrine organs make up a complex neuroendocrine circuit?
Pituitary and hypothalamus
What 2 parts of a developing embryo does the pituitary gland develop from?
Oral ectoderm
Developing brain
What does the oral ectoderm form during development of the pituitary gland?
The hypophyseal (Rathke’s) pouch which becomes the anterior pituitary (adenohypophysis)
What is the neurohypophyseal bud in the development of the pituitary gland?
A bud from the diencephalon that becomes the posterior pituitary (neurohypophysis)
What is the pars nervosa of the pituitary gland?
Expanded portion of the posterior part that is continuous with the infundibulum
True or False: The infundibulum is a stalk attached to the hypothalamus above.
True
What is the name for the anterior part of the pituitary gland located around the infundibulum stem like a collar?
Pars tuberalis
What is the pars intermedia?
A narrow band of tissue that lies between the pars nervosa and pars distalis
Describe the pars distalis.
Part of the anterior pituitary
Contains a variety of cell types
Why is the staining of the pars distalis of the pituitary variable in regions?
The cells aren’t uniformly distributed so don’t stain evenly
What percentage of the adenohypophysis is the pars distalis?
75%
What are the 2 cell groups in the pars distalis?
Chromophils and chromophobes
What are chromophils?
Secretory cells in which hormones are found in cytoplasmic granules and can be further distinguished into basophils and acidophils
List examples of basophilic endocrine cells.
Gonadotropic: oval cells with round nuclei that secrete FSH and LH
Corticotropic: polygonal cells with round eccentric nucleus and secretes ACTH
Thyrotropic: large oval cells with round eccentric nucleus and basophilic small granules and secrete TSH
What are mammotropic and somatotropic cells examples of?
Acidophilic endocrine cells
What are the hypothalamic hormones that regulate the anterior pituitary?
- Growth hormone-releasing
- Somatostatin
- Thyrotropin-releasing
- Corticotropin-releasing
- Dopamine
- Gonadotropin-releasing
What segment of the pituitary gland has colloid filled follicles?
Pars intermedia
What cells are present in the neurohypophysis?
Pituicytes
Unmyelinated nerve fibres axons
What are Herring bodies?
Swellings in the terminal portion of the axons containing basophilic, large accumulations of neurosecretory material
What does the neurosecretory material in Herring bodies contain?
Aggregations of oxytocin and/or antidiuretic hormone (vasopressin)
True or False: Axons from the supraoptic nuclei are mainly concerned with oxytocin secretion while fibres from paraventricular nuclei are concerned with vasopressin secretion.
False
Describe the thyroid gland.
Located anterior the the larynx
Dense irregular C.T. capsule encloses the 2 lobes and the connecting isthmus
Aymmetric (right lobe twice as big as left)
What is the thyroid gland’s function?
Synthesis of thyroxine and tri-iodothyronine (important for growth, cell differentiation and control of basal metabolic rate and oxygenconsumption)
When does thyroid development begin in embryological development?
Fourth week
What is the capsule of the thyroid gland derived from?
Cervical fascia
Describe the contents of the thyroid’s glandular parenchyma.
Spherical, cyst-like follicles filed with gelatinous colloid made of thyroglobulin
How many follicles are in the thyroid’s glandular parenchyma?
20-30 million
What is the purpose of the colloid material within thyroid follicles?
Temporary storage form and precursor to main thyroid hormones
What is the lining epithelium of thyroid follicles?
Simple cuboidal epithelium (squamous to low cuboidal = inactive while nearly columnar = active)
Describe follicular epithelial cells.
Central round nucleus with prominent nucleoli
Lightly basophilic cytoplasm
Apical Surface: junctional complexes, microvilli, secretory granules, phagosomes and lysosomes, Golgi apparatus
Basal Surface: abundant RER
What are parafollicular/C cells?
Individual scattered, large pale cells in the follicle basal lamina that secrete calcotonin
What does calcotonin do?
- Lowers plasma calcium levels
- Inhibits bone reabsorption
- Antagonist to parathyroid hormone
Describe the parathyroid glands.
4 small oval masses
Located on posterior of the thyroid
Fibrous capsule with septa conveying vessels
Synthesises and secretes parathyroid hormone
What is the role of parathyroid hormone?
Maintains serum calcium levels
What cells are present in the parathyroid gland parenchyma?
Chief/principal cells
Oxyphil cells
Adipose cells
Describe the ultrastructure and function of chief cells.
Small, lightly stained cells with dark central nuclei
Secrete parathyroid hormone
True or False: Oxyphil cells are large eosinophilic cells with abundant mitochondria.
True
What happens to oxyphil cells and adipose cells with age?
They become more numerous
Where are the adrenal glands located?
Superior pole of each kidney
What is the adrenal gland morphology?
Thick, dense C.T. capsule with trabeculae
Yellow, peripheral cortex
Red-brown, central medulla
What embryological tissues are the adrenal medulla and cortex derived from?
Medulla: neural crest cells
Cortex: mesoderm
True or False: The adrenal cortex is about 10% of the gland.
False, the medulla is about 10%
What are the 3 distinct zones of the adrenal cortex and their percentages?
Zona glomerulosa - 15%
Zona fasciculata - 80%
Zona reticularis - 5-7%
What is the contents of each of the distinct regions in the adrenal cortex?
ZG: Contains columnar/pyramidal cells arranged in rounded clusters
ZF: Consists of parallel cords of secretory cells disposed at right angles to capsule
ZR: Adjacent to the medulla, consists of small closely-packed cells arranged in irregular cords
What does zona glomerulosa secrete?
Mineralcorticoids and aldosterone
Which region of the adrenal cortex secretes glucocorticoids e.g. cortisol?
Zona fasciculata
What is the hormonal secretions of the zona reticularis?
Glucocorticoids
Androgens
Dehydroepiandrosterone (converted to testosterone)
Describe the composition of the adrenal medulla.
Cords/clumps of large, pale-staining polyhedral slightly basophilic cells, supported by a reticular fibre network
What are the products of the adrenal medullary parenchymal cells, Chromaffin cells?
Adrenaline and noradrenaline
How to differentiate adrenaline vesicles from noradrenaline vesicles in Chromaffin cells?
Adrenaline is stored in smaller vesicles with a light/moderately dense core
Noradrenaline is stored in larger vesicles with a high density core
What regulates the secretion of products from Chromaffin cells?
Preganglionic sympathetic neurons
What organ is a mixed exocrine-endocrine gland that produces both digestive enzymes and hormones?
Pancreas
What does the endocrine portion of the pancreas consist of?
About 1 million small, scattered islands of tissue called islets of Langerhans
How much of the pancreas is constituted by islets of Langerhans?
1-2%
Does the exocrine or endocrine portion of the pancreas stain darkly basophilic?
Exocrine pancreas stains dark purple while the endocrine portion stains more lightly
Name the 4 principal cell types in the pancreatic islets.
- B cells (secrete insulin) - 70%
- A cells (secrete glucagon) - 20%
- D cells (secrete somatostatin)
- F/PP cells (secrete pancreatic polypeptide)
What is the name of the cells in the testes that produces testosterone?
Leydig cells
True or False: The theca externa of the ovum in the ovaries produces hormone precursors which is converted to oestrogen by granulosa cells.
False, theca interna produces precursors
