3 - Hypothalamus, Pituitary and Adrenal Glands Flashcards
Where is the pituitary gland located?
- Resides in saddle-shaped depression of the sphenoid bone (the depression is called the sella turcica)
- It is a protrusion off the bottom of the hypothalamus at the base of the brain.
What are the neighbors of the pituitary gland?
- Superior: hypothalamus and diaphragma sellae
- Inferior: sella turica, and slightly anterior, sphenoid sinus and optic chiasm
- Lateral: cavernous sinuses
What is the clinical relevance of the location of the pituitary?
It lies in a watershed area of the internal carotids putting it at risk for infarction
What is the surgical approach to the pituitary gland?
Tumor removal is usually accomplished through a transsphenoidal approach
You go in through the nose
What is empty sella syndrome?
Empty sella syndrome is where the pituitary gland shrinks or becomes flattened, allowing cerebrospinal fluid to accumulate
How common is empty sella syndrome symptomatic?
Rarely
What are the two divisions of the pituitary?
- Neurohypophysis
- Adenohypophysis
The two parts are anatomically and functionally distinct
What are the two parts of the neurohypophysis?
Pars nervosa and infundibulum
The infundibulum has two parts as well:
- Medium eminence
- Infundibular process
What are the three parts of the adenohypophysis?
- Pars distalis
- Pars tuberalis
- Pars intermedia
What arteries supply the pituitary gland?
Hypophysial arteries
What are the different hypophysial arteries?
- Superior hypophysial
- Inferior hypophysial
Hypophysial arteries are connected by a trabecular arteries
Which arteries collect the oxytocin and vasopressin from the pituitary gland?
Inferior hypophysial arteries
What arteries receive releasing and inhibitory hormones from hypothalamus
Primary capillary plexus formed by superior hypophysial arteries
What are the type of cells in the pituitary that synthesize both growth hormone (GH) and prolactin?
KNOW THIS
Rare acidophilic stem cells are present in the normal pituitary that are capable of synthesizing and secreting both GH and prolactin
What is the most common cell type in the pituitary?
Somatotropes are acidophils that secrete GH – most frequent cell type
What types of cells in the pituitary that secrete prolactin?
Mammotropes (lactotropes) are acidophils that secrete prolactin
Which type of cells of the pituitary that can secrete both prolactin and GH again?
Rare acidophilic stem cells ***
What happens if there is a tumor of prolactin acidophils in the pituitary?
If there is a tumor in the prolactin acidophils, you can have expression of milk in a non-pregnant woman
What are gonadotropes of the pituitary gland?
Gonadotropes are basophils that secrete LH and FSH. Many gonadotropes synthesize both LH and FSH whereas some gonadotropes synthesize one or the other hormone
Come from the anterior pituitary
What are thyrotropes of the pituitary?
Thyrotropes are basophils that secrete TSH
- First thyrotropin-releasing hormone (TRH) is released which allows for the synthesis and release of TSH (thyroid stimulating hormone) form basophils
What is ACTH or adrenocorticotropin hormone?
A hormone released by the pituitary that acts on the adrenal gland (on top of kidney) which stimulates the release of cortisol
What are Herring bodies?
Herring bodies are found in the neurohypophysis and are dilatations along the axons containing ADH (vasopressin) and oxytocin
What are adrenal glands?
Endocrine glands located above the kidneys that produce a variety of hormones including adrenaline and the steroids aldosterone and cortisol
Describe the blood supply of the adrenal gland
Three arteries supply the gland
- Superior suprarenal artery
- Middle suprarenal artery
- Inferior suprarenal artery
What are the parent arteries of each of the vessels that supply the adrenal gland?
Parent vessels are in parentheses
- Superior suprarenal artery (inferior phrenic)
- Middle suprarenal artery (aorta)
- Inferior suprarenal artery (renal)
How do you remember the three parent arteries?
IPAR I = Inferior P = Phrenic A = Aorta R = Renal
Describe plexus which supply the adrenal gland
There is one plexus which supplies the adrenal gland –> Subcapsular plexus
What are the two sets of arteries of the adrenal gland?
Remember that there are two layers - the cortex (outer) and medulla (inner) sections
- Cortical arteries
- Medullary arteries
Describe the cortical arteries of the adrenal gland
- Cortical arteries form a network of fenestrated capillaries in the cortical parenchyma.
- The capillaries drain into a venous plexus at the corticomedullary junction.
- Venules from this plexus then penetrate the medulla and supply it with venous blood from cortical arteries.
Describe the medullary arteries of the adrenal gland
- Medullary arteries penetrate the cortex and enter the medulla where they form a capillary network.
- Medullary venules are the confluence of the capillaries»_space; medullary veins»_space; suprarenal vein
Describe the appearance of the left adrenal gland in an MRI
Y shaped
The left adrenal gland is demonstrated in this image as a Y-shaped structure within the fat around the kidney. It is posterior to the pancreas and stomach and lateral to the aorta and left crus of the diaphragm.
Describe the appearance of the right adrenal gland in an MRI
The right adrenal gland has the appearance of the Mercedes sign
Describe the development of the adrenal gland
Neural crest cells migrate from the sympathetic ganglia to the adrenal primordia. Cortisol and nerve growth factor are required from the differentiation of precursor cells into chromaffin cells.
Chromaffin cells are neuroendocrine cells found mostly in the medulla of the adrenal glands
What is extra-adrenal tissue located?
- Cortical and/or medullary tissue can be found at ectopic sites
What is the Organ of Zuckerkandl?
Organ of Zuckerkandl – medullary tissue located around the abdominal aorta between its bifurcation and the IMA. Chromaffin cells primarily produce norepinephrine with small amounts of epinephrine
What are the three layers of the adrenal CORTEX (outer)?
- Zona glomerulosa (outermost)
- Zona fasciculata
- Zona reticularis (innermost)
GFR –> from outer to inner
Describe the zona glomerulosa
Zona glomerulosa (15% of total volume of adrenal cortex)
- Cells arranged in cords and clusters
- Secretes mineralocorticoids, principally aldosterone
Describe the zona fasciculata
Zona fasciculata (78% of total volume of adrenal cortex)
- Cells are arranged in columns
- Secretes glucocorticoids, primarily cortisol, and small amounts of androgens
Describe the zona reticularis
Zona reticularis (7% of total volume of adrenal cortex) Cells arranged in cords Secretes chiefly androgens and small amounts of glucocorticoids
What happens when there is hypertrophy of the adrenal cortex?
Zona fasciculata and zona reticularis will thicken, zona glomerulosa will not
Outermost layer of the cortex of the adrenal gland will NOT thicken
Describe aldosterone
- Aldosterone is a steroid hormone (mineralocorticoid family) produced by the outer section (zona glomerulosa) of the adrenal cortex in the adrenal gland
- It plays a central role in the regulation of blood pressure mainly by acting on the distal tubules and collecting ducts of the nephron, increasing reabsorption of ions and water in the kidney
Describe primary hyperaldosteronism
Arenal glands produce too much aldosterone, causing you to lose potassium and retain sodium. The excess sodium in turn holds onto water, increasing your blood volume and blood pressure
Primary hyperaldosteronism (usually the result of a benign, adrenal adenoma)
Describe cortisol
- Cortisol is a steroid hormone, in the glucocorticoid class of hormones, and is produced in humans by the zona fasciculata of the adrenal cortex within the adrenal gland
- It is released in response to stress and low blood-glucose concentration.
What are some of the systems that cortisol effects?
- Carbohydrate metabolism
- Protein metabolism
- Fat metabolism
- Inflammatory processes
Describe the effect cortisol has on carbohydrate metabolism
- Increased hepatic glycogen
- Cellular use of glucose is decreased
- Blood glucose is increased
Describe the effect cortisol has on protein metabolism
- Hepatic proteins and plasma proteins (synthesized by the liver) are increased – this increase is due to enhanced uptake of amino acids by hepatocytes but not other cells and stimulation of liver enzymes that synthesize proteins
- Blood amino acids become elevated
Describe the effect cortisol has on fat metabolism
- Increased mobilization of fatty acids from adipocytes
- Increased beta-oxidation of fatty acids
- The net effect is to shift metabolism from glucose substrates to fatty acids
- Excess cortisol can stimulate food intake leading to a preferential deposition of fat in the chest and face
Describe the effect of cortisol on inflammation
- Lyosomal membranes are stabilized
- Decrease in capillary permeability
- Emigration of leukocytes into inflamed area are decreased and phagocytosis of damaged cells is decreased
- Suppression of lymphocytes
- Reduction in the release if IL-1 which leads to a reduction in fever
A tumor of the organ of Zuckerkandl would be expected to chiefly increase its output of:
a. Epinephrine
b. Norepinephrine
c. Both epinephrine and norepinephrine
Answer: norepinephrine
Describe congenital adrenal hyperplasia
Congenital adrenal hyperplasia
- Increase of ACTH, to try to stimulate the cortex
- ACTH influences the adrenal cortex, so you get an increase in cell mass
- Here you have ambiguous genitalia
- Genotype XX in a female newborn because of increased androgens
- No testes are found
