Histology of endocrine organs Flashcards
Describe the embryologic origins of the pituitary gland.
The anterior lobe is derived from ectoderm while the posterior lobe is derived from neuroectoderm. Both fold and grow in toward one another in the sphenoid bone during development. This ultimately results in the formation of the pituitary gland inside of the sella turcica in the sphenoid bone.
Label the images. Also, where are these images from in the body?
Anterior pituitary
Growth Hormone
- Produced by what cell type?
- How do these cells stain?
- What factors stimulate the release of GH?
- What factors inhibit the release of GH?
- Somatotrope
- Acidophil/PAS-
- GHRH, dopamine
- Somatostatin, GH, IGF-1
Prolactin
- Produced by what cell type?
- How do these cells stain?
- What factors stimulate the release of prolactin?
- What factors inhibit the release of prolactin?
- Lactotrope
- Acidophil/PAS-
- PRH
- Dopamine
ACTH
- Produced by what cell type?
- How do these cells stain?
- What factors stimulate the release of ACTH?
- What factors inhibit the release of ACTH?
- Corticotrope
- Basophil/PAS+
- CRH
- Cortisol
LH and FSH
- Produced by what cell type?
- How do these cells stain?
- What factors stimulate the release of LH and FSH?
- What factors inhibit the release of LH and FSH?
- Gonadotrope
- Basophil/PAS+
- GnRH, Estrogen
- Inhibin, testosterone, estrogen
TSH
- Produced by what cell type?
- How do these cells stain?
- What factors stimulate the release of TSH?
- What factors inhibit the release of TSH?
- Thyrotrope
- Basophil/PAS+
- TRH
- Somatostatin, T3
LH, FSH and TSH have the same […] subunit but specificity is conferred by the […] subunit
Alpha
Beta
Describe the origins of the thyroid gland.
originates from endoderm as part of tongue. Migrates down into neck during development.
Why is the thyroid gland unique from other endocrine glands?
It stores its hormones extracellularly in the follicular fluid bound to thyroglobulin whereas most endocrine organs stores hormones intracellularly.
What is the epithelium of the thyroid gland?
Simple cuboidal.
What is released from the cells staining in brown in this image? What organ is this image from?
Calcitonin
Thyroid
What organ is this slide from?
Thyroid.
Describe how the thyroid stores its hormones.
- Follicular epithelial cell synthesizes thyroglobulin (rER –> posttranslationally glycosylated in rER and Golgi –> packaged into vesicles –> secreted into the lumen of the follicle)
- Follicular epithelial cells actively transport iodide from the blood into their cytoplasm using ATPase-dependent sodium/iodide symporters (NIS). Iodide ions then diffuse rapidly toward the apical cell membrane. From here, iodide ions are transported to the lumen of the follicle by the iodide/chloride transporter called pendrin located in the apical cell membrane. Iodide is then immediately oxidized to iodine, the active form of iodide. This process occurs in the colloid and is catalyzed by membrane-bound thyroid peroxidase (TPO).
- One or two iodine atoms are then added to the specific tyrosine residues of thyroglobulin. This process occurs in the colloid at the microvillar surface of the follicular cells and is also catalyzed by thyroid peroxidase (TPO). Addition of one iodine atom to a single tyrosine residue forms monoiodotyrosine (MIT). Addition of a second iodine atom to the MIT residue forms a diiodotyrosine (DIT) residue.
- Thyroid hormones are formed by oxidative coupling reactions of two iodinated tyrosine residues in close proximity. For example, when neighboring DIT and MIT residues undergo a coupling reaction, T3 is formed; when two DIT residues react with each other, T4 is formed. After iodination, T4 and T3 as well as the DIT and MIT residues that are still linked to a thyroglobulin molecule are stored as the colloid within the lumen of the follicle.
- In response to TSH, follicular cells take up thyroglobulin from the colloid by a process of receptor-mediated endocytosis. After endocytosis, thyroglobulin follows at least two different intracellular pathways.
● In the lysosomal pathway, thyroglobulin is internalized and transported within endocytic vesicles to early endosomes. They eventually mature into lysosomes or fuse with existing lysosomes. Thyroglobulin is then degraded by lysosomal proteases into constituent amino acids and carbohydrates, leaving free T4, T3, DIT, and MIT molecules. Under physiologic conditions, this is the major pathway of colloid resorption.
● In the transepithelial pathway, thyroglobulin is transported intact from the apical to the basolateral surface of follicular cells. To enter this pathway, thyroglobulin binds to its receptor, megalin, which is a transmembrane protein expressed at the apical surface of follicular epithelial cells directly facing colloid. Thyroglobulin internalized by megalin avoids the lysosomal pathway, and endocytic vesicles are delivered to the basolateral membrane of follicular cells. In pathologic conditions of high TSH or TSH-like stimulation, megalin expression is increased, and large amounts of thyroglobulin follow the transepithelial pathway. This pathway may reduce the extent of T4 and T3 release by diverting thyroglobulin away from the lysosomal pathway. Individuals with Graves disease and other thyroid diseases have detectable amounts of circulating thyroglobulin that contains portions of megalin receptor.
- Release of T4 and T3 from follicular cells into the circulation. Follicular cells predominately produce T4 in a T4 to T3 ratio of 20:1. Most of the T4 and T3 produced is liberated from thyroglobulin in the lysosomal pathway, and only negligible amounts of T4 and T3 are released bound to thyroglobulin. Both T4 and T3 cross the basal membrane and enter the blood and lymphatic capillaries. Most of the released hormones are immediately bound to a specific plasma protein, thyroxine-binding globulin (TBG) (~70%), or a protein called transthyretin (~20%). T4 has a stronger bond to TBG, whereas T3 has a stronger bond to transthyretin. Less than approximately 10% of released hormones are bound to a nonspecific fraction of albumin, leaving only small amounts (~1%) of free circulating hormones that are metabolically active. One-third of circulating T4 is converted to T3 in peripheral organs, such as the kidney, liver, and heart. T3 is five times more potent than T4 and is mainly responsible for biologic activity by binding to the thyroid nuclear receptors in the target cells.
What tissue is slide from?
Label image.
Which is cortex and medulla in image?
Cortex = outer
Medulla = inner
What organ is this image from?
Label image.
Adrenal Cortex
Where in body is slide from?
Label image.
When you see these special kinds of mitochondria, you know you are looking at tissue from the […]
Adrenal cortex –> tubular mitochondria
What organ is tissue from?
Label image.
Adrenal medulla
How can you tell the difference between cells that secrete NE and cells that secrete E in adrenal medulla?
NE cells have dark granules with clear area in vesicles as well
Epi are just dark
Using the image below, explain why it is so important that the blood flow in the adrenal gland is from cortex –> medulla.
In order to produce epinephrine from norepinephrine, cortisol is needed to stimulate the cells to do so –> cortisol flows from zona fasiculata to medulla and is high concentration so available to make Epi when needed
What organ is this from?
Label image.
B
C
This is a herring body in the posterior pituitary, and is located at the end of nerve fibers. It stores Oxytocin and Antidiuretic Hormone (ADH, or Vasopressin)
- C
- Endoderm, Thyroglossal duct from base of the tongue/pharynx (Foramen Cecum)
- B
B
FSH; LH; TSH
These are parafollicular cells, which produce calcitonin. Calcitonin plays a role in calcium homeostasis by antagonizing the actions of parathyroid hormone (PTH). It plays an important role in lower vertebrates, but a minor role in humans.
Mesodermal mesenchyme; neural crest
B
