Murdoch Endocrine System Review Flashcards
Make sure you know the names of the abbreviated hormones. Drop the hormones at their origins on the diagram below.
What are the anatomical and histological differences between exocrine and endocrine glands (excluding location)?
Ducts: Exocrine glands usually produce secretions that are released into ducts opening onto an epithelial surface. These, or their openings, may be macroscopically visible, such as the bile ducts and pancreatic ducts.
Lobes and lobules: Exocrine glands are often divided into lobes and lobules, visible by the naked eye (see salivary gland and pancreas as examples). Histologically, exocrine glands will also show various hierarchical levels of interlobular or intralobular ducts, characterized often by a lining of cuboidal epithelium.
Acini: Endocrine glands are ductless organs that secrete their molecular products directly into the blood stream. Unlike exocrine glands, the secretory cells of endocrine glands are not arranged into acini, with cellular apices discharging into a central duct, but instead have a more random and less polarized arrangement (compare the Islets of Langerhans and the exocrine pancreas).
Vascular supply: A common feature of endocrine glands is that they often have a prominent blood/capillary network distributed throughout the gland
The correct answer is: Glucocorticoids , aldosterone, adrenaline, noradrenaline and androgens
= Placenta
Human chorionic gonadotrophin is made in the fetal membranes, specifically the chorion. False negatives arise in early tests, because the hormone is not made until implantation around day 6-12. Note also that spermatozoa may survive a few days prior to ovulation, which could push the delay between intercourse and detection of pregnancy to 17 days or so, plus longer depending on the threshold of the test for hCG detection (levels rise progressively after implantation). Urine is typically used in home-based tests, although it appears they work also on saliva.
The molecular structures of the hormones are of three main types. This affects their properties (e.g. lipid solubility, surface or intracellular receptor, etc.) Drop each hormones onto its appropriate structural category.
There are also the eicosanoid hormones, such as prostaglandin and thromboxane. These are the membrane-derived products of cycloxygenase and lipoxygenase pathways.
Peptide hormones e.g. prolactin (anterior pituitary), insulin (pancreas), glucagon (pancreas). Receptor at the cell surface (because water soluble and unable to cross the cell membrane by itself)
Steroid hormones e.g. progesterone (ovaries/placenta), testosterone (testes), estradiol (ovaries). Lipid soluble and readily penetrate the membrane, exert effect from within the cells via an intracellular receptor
Amino acid derivatives e.g. epinephrine/adrenaline (adrenal medulla), thyroxine, triiodothyronine (thyroid). Lipid soluble and readily penetrate the membrane, exert effect from within the cells.
This is a transmission electronmicrograph (x25,000) of two adjacent cells from the adrenal cortex. It has abundant lipid droplets (with cholesterol esters), mitochondria for energy production, smooth endoplasmic reticulum (SER) for steroid synthesis, and autophagosomes which remove mitochondria and SER between periods of active steroid synthesis. You can also see the nucleus, Golgi apparatus, rough ER and lysosomes.
Match the letter with the correct organelle: Golgi apparatus, Nuclues, Mitochondria, Lipid droplet, Autophagosome
- A → Lipid droplet
- B → Autophagosome
- C → Golgi apparatus
- D → Nucleus
- E → Mitochondria
This is a parafollicular cell from the thyroid (TEM x 5000). It has abundant electron-dense secretory granules, along with prominent Golgi apparatus and rough endoplasmic reticulum, typical of busy protein-producing cells. Match the letters with the organelles, and choose the secretory product of this cell.
Label from the following: Tri-iodothyronine, Nucleus, Secretory granules, Thyroxine, Golgi body, Calcitonin, Rough ER, Thyroglobulin
- A → Golgi body
- B → Secretory granules
- C → Nucleus
- D → rough ER
- Secretion? → calcitonin
Because this is a parafollicular cell (or C-cell) from the thyroid, it secretes the peptide hormone calcitonin, and not one of the other thyroid hormones (which are associated with the follicular cells).
Identify the hypothalamus and pituitary gland in this image from Acland’s video atlas. (Note the pituitary may not be present in some isolated brain specimens as it is easily detached when the brain is removed from the skull).
Describe the size, shape and location of the pituitary gland.
The pituitary gland is a pea shaped structure measuring 1-1.5cm. It is located in the sella turcica, inferior to the hypothalamus, and caudal/posterior to the optic chiasm. The pituitary fossa lies in the sphenoid bone, superior to the sphenoid sinus.
The hypothalamus produces eight hormones, six of these regulate hormone release from the anterior pituitary and two are stored in the posterior pituitary ready to be released on demand.
You should know the six regulating hormones produced by the hypothalamus that regulate the anterior pituitary. Match the regulatory hormones from the hypothalamus with their corresponding regulated anterior pituitary hormone.
CRH, GnRH, GHRH, Dopamine, TRH, Somatostatin
- CRH → ACTH
- GnRH → FSH & LH
- GHRH → Somatotropin
- Dopamine → Prolactin
- TRH → TSH
- Somatostatin → GH inhibition
- Two hormones are produced from the posterior pituitary, which is also called Neurohypophysis.
- The posterior pituitary does not synthesize these hormones but rather stores and secretes them. The hormones are oxytocin and vasopressin (ADH).
- Oxytocin acts on breast myoepithelial cells to cause milk letdown and also on uterine muscle
Most general staining methods simply allow the parenchymal cells of the pars distalis to be subdivided into acidophil cells (A), basophils (B), and chromophobes (C) in which the cytoplasm is poorly stained. X400. H&E.
Immunohistochemistry identifies specific cell types, such as these somatotropes, which secrete GH.
Look at the microscopic images provided of the anterior pituitary. It is packed full of several types of secretory cells among which are many sinusoidal blood capillaries. Name the endocrine cells that secrete the 7 hormones of the gland (you do not need to be able to identify different types histologically, that is now typically done by immunohistochemistry, using antibodies directed against the specific hormone). Use this information to help complete the table below.
How do hormones such as GHRH reach the anterior pituitary?
The correct answer is: Portal tract
Hormones (ADH and oxytocin) produced in the supraoptic and paraventricular nuclei of the hypothalamus reach the posterior pituitary via axonal transport via the infundibulum.
Anterior pituitary cells are stimulated via inhibitory or releasing hormones from the hypothalamus, which travel via the hypothalamo-hypophyseal portal tract. n.b. a portal system conveys blood from one capillary network to another, rather than back to heart: the other example is the hepatic portal vein, carrying blood from intestinal capillary beds to the hepatic sinusoidal network.
- What nonapeptide is synthesised in the supraoptic nucleus of the hypothalamus, is stored for release in the posterior pituitary, and causes insertion of aquaporin channels into the target cell membrane? → Vasopressin
- What substance, from the arcuate nucleus of the hypothalamus, inhibits prolactin release? → Dopamine
- What substance, from the paraventricular nucleus of the hypothalamus, inhibits growth hormone release from the anterior pituitary? → Somatostatin
- What substance, stimulated by hypoglycaemia, is released from the hypothalamus, runs in hypophyseal portal veins, and causes the release of an anterior pituitary hormone responsible for generally anabolic effects, including stimulating IGF production and elevation of blood glucose? → GHRH
- What substance, from the anterior pituitary, is released in response to low cortisol, and stimulates glucocorticoid production? → ACTH
- What is the key central regulator of GnRH secretion? → KIsspeptin
= A
What structure lies above and anterior to the pituitary gland, and below the hypothalamus, and is vulnerable to compression by pituitary tumours?
Optic Chiasm
Identify the pituitary gland and optic chiasm on the image of the head, by dragging and dropping the labeled markers.
The pituitary gland and optic chiasm are closely related to one another, such that pituitary enlargement may impinge upon the optic chiasm.
Locate the pituitary on the MRI image, by dragging and dropping the marker.
In addition to the synthesis and release of neurosecretions that have endocrine roles (either directly via the posterior pituitary, or indirectly via actions upon the anterior pituitary), state four other functions of the hypothalamus.
Regulation of body temperature, hunger, thirst, sleep (suprachiasmatic nucleus), as well as emotions such as fear.
Mammillary bodies are important in memory.
How does vasopressin reach the posterior pituitary gland?
= Via axonal projections from hypothalamic nuclei (supraoptic nucleus).
Vasopressin (antidiuretic hormone - ADH) is synthesised in the neurones of the supraoptic nucleus in the hypothalamus, and passes via axonal transport into the posterior pituitary, where it is stored in the axonal terminals until release.
Describe the location and shape of the adrenal glands.
The adrenals are paired, pyramid shaped glands located on the superior surface of each kidney. The right adrenal is close to the inferior vena cava, medially, and is close to the liver and right hemidiaphragm. The left adrenal is close to the left crus of the diaphragm, medially, and is also proximal to aorta, spleen and the tail of the pancreas.
The adrenal has a distinct (pale) cortex and (darker) medulla on cut section.
The encapsulated adrenal gland has an outer cortex derived from [mesoderm] and an inner medulla derived from [neural crest]. The medulla is effectively a [sympathetic] ganglion (note that the myenteric ganglia of the intestinal tract are [parasympathetic] ganglia). The outermost zone of the adrenal cortex is the zona [glomerulosa]. It produces [mineralocorticoids], specifically [aldosterone]. The middle zone is the zona [fasciculata], producing [cortisol] (amongst others), which is a member of the [glucocorticoids]. The middle zone also produces small amounts of [androgens]. The inner cortical zone is the zona [reticularis], producing primarily [androgens] and precursors to [oestrogens].
The adrenocortical hormone [aldosterone], causes increased renal tubular retention of [Na+] and excretion of [K+]. Water is osmotically retained as a result, which increases blood volume.
All the adrenal cortical hormones are [steroids], derived from [cholesterol], unlike the adrenal medulla hormones which are [catecholamines], derived from [amino acids]. The adrenal hormones are therefore water-soluble, and approximately 50% are bound to plasma proteins in the blood.
The adrenal cortex consists of three histological zones which are named according to the arrangement of the secretory cells: zona glomerulosa, zona fasciculata and zona reticularis. The zona glomerulosa contains secretory cells arranged in rounded clusters (resembling glomeruli perhaps - hence the name). The zona fasciculata consists of parallel cords (hence the name: a fascicle is a bundle) of secretory cells disposed at right angles to the capsule. The zona reticularis consists of small closely packed cells arranged in irregular cords or networks (reticular means like a network). Often the borders of the zones are less regular and often less easily recognised than in this specimen. Inferior to the zona reticularis lies the adrenal medulla.
The adrenals are physically adjacent to the kidneys, and also have a close functional relationship via a multistep hormonal circuit. Complete the circuit below by adding in the appropriate labels.
What enzyme facilitates the conversion of androstenedione to oestrogens within the granulosa cells?
= Aromatase
Androstenedione from the thecal cells cannot form oestrogen (but can become testosterone) because the thecal cell has no aromatase. Androstenediones diffuce across into the granulosa cells where they are converted by aromatase into oestrogen.
Aromatase is also called oestrogen synthetase. It catalyses the transformation (aromatisation) of androstenedione into oestrone, and of testosterone into oestradiol. Aromatase is also expressed in other tissues.
What are the effects of oestrogen in the late follicular phase?
Effect of high levels of oestrogen on:
- GnRH
- LH levels
- FSH levels
- What other hormones are affecting feedback in this stage?
At higher levels in mid to late follicular phase, oestrogen has a positive feedback effect on the release of GnRH. GnRH promotes release of more LH and FSH (and oestrogen rises), but FSH is later inhibited by inhibin, whereas LH continues in a positive feedback cycle to give the LH surge. Low levels of progesterone production from granulosa cells contribute to positive feedback and promote LH and GnRH release.
Oestrogen is responsible also for the proliferative phase of the uterus.
High progesterone levels from the corpus luteum suppress release of FSH and LH from the anterior pituitary. Progesterone also stimulates the secretory phase of the endometrium, and viscous cervical mucus.
LH from the anterior pituitary causes proliferation of thecal cells, and increases their secretion of progesterone. LH also acts on granulosa cells to increase their secretion of progesterone. Both these cells become mainly progesterone-secreting under the influence of LH and hence oestrogen falls a day or so before ovulation and progesterone rises. In addition to the LH surge causing this rise in progesterone (and fall in oestrogen) from the follicle, it also causes collagenase secretion, which weakens the follicle wall. The simultaneous increase in fluid volume contributes to follicular rupture.
The corpus luteum produces progesterone, oestrogen and inhibin, but has a limited life span of around 12 days.
What hormone rescues the corpus luteum in pregnancy?
= hCG
Human chorionic gonadotropin, from the placenta (hence the name) rescues the corpus luteum and acts as an LH analogue, binding to receptors on the luteal cells.
