Hi everyone ! These notes will definitely help you with Histology. All the notes are precise and contain all the points you should know about these topics. So, you can use them as class notes, as well as summaries to get prepared well for your exams. Hope you guys will love these !
▪ Endocrine cells are typically epithelial, at least in origin, and aggregated as cords or clusters.
▪ Characteristics of Endocrine organs ;
a. No duct
b. Fenestrated or Sinusoidal capillaries — higher permeability than continuous capillaries
c. Cells are arranged in 4 ways — groups , cords , networks , follicles ( arranged circularly )
d. Secrete hormones
▪ 3 ways of endocrine secretion ;
1) Autocrine signaling - cells may produce molecules that act on themselves or on cells of the same type
2) Paracrine signaling - produce hormones that act on adjacent target cells or only a short distance away
3) Endocrine signaling - hormones secreted into blood to act on target cells with receptors for those
hormones at a distance from the site of their secretion
▪ Endocrine cells secrete hormones stored in secretory vesicles to act on a target cell
▪ Neuro cell secrete neurotransmitters to another neuro cell to pass ( conduct ) a nerve impulse
▪ Neuro – secretary cells = secrete hormones into blood to act on a target cell
▪ Hormones, like neurotransmitters, are frequently hydrophilic molecules such as proteins, glycoproteins, peptides, or
modified amino acids with receptors on the surface of target cells.
▪ There are 2 types of endocrine cells ;
1) Nitrogen - secreting cells
2) Steroid - secreting cells
▪ located anterior and inferior to the larynx , extending from 2nd – 4th cartilages of trachea
▪ Small gland consists of two lobes united by an isthmus - with four parathyroid glands attached to the posterior
surface
▪ Structure ;
a) Capsule - DCT
b) Parenchyma - follicles + reticular tissue
▪ The thyroid gland is covered by a fibrous capsule from which septa extend into the parenchyma , dividing it into
lobules and carrying blood vessels, nerves, and lymphatics.
▪ The parenchyma of the thyroid is composed of millions of rounded epithelial thyroid follicles of variable diameter,
each with simple epithelium and a central lumen densely filled with gelatinous acidophilic colloid .
▪ Secretary storage is outside the cells , in the colloid of the follicle lumen.
▪ Thyroid colloid contains the large glycoprotein thyroglobulin , the precursor for the active thyroid hormones.
▪ Follicles are densely packed together, separated from one another only by sparse reticular connective tissue ,
although this stroma is very well vascularized with fenestrated capillaries for transfer of released hormone to the
blood.
1
, a) Follicle cavity = colloid — a jelly-like substance
• Inactive - much
• Active - less
b) Simple follicular epithelium cells ;
• Inactive - squamous
• Active - cuboidal or columnar
• Less CT - rich in fenestrated capillaries
▪ Follicular cell - Microvillus , RER , Golgi complex , secreting granules , Pinocytosis vesicles , lysosome
▪ Follicular cells is a Nitrogen - secreting cell
▪ Follicular cells function - production of thyroid hormone
c) Parafollicular cells ;
▪ Between the follicles
▪ Cells are bigger and lightly stained
▪ Secrete calcitonin — Calcitonin functions to reduce calcium levels in the blood by actively reducing breakdown
of bone and inhibiting re-absorption of calcium in digestive system
▪ Well-developed organelles :- Golgi complex , RER , Secreting granules with calcitonin
✓ The follicular cells or thyrocytes , range in shape from squamous to low columnar , their size and other features
varying with their activity, which is controlled by thyroid-stimulating hormone (TSH) from the anterior pituitary.
✓ Active glands have more follicles of low columnar epithelium; glands with mostly squamous follicular cells are
hypoactive.
✓ Thyrocytes have apical junctional complexes and rest on a basal lamina .
✓ Another endocrine cell type, the parafollicular cell or C cell, is also found inside the basal lamina of the follicular
epithelium or as isolated clusters between follicles .
✓ Parafollicular cells are usually somewhat larger than follicular cells and stain less intensely.
✓ Secretion of calcitonin is triggered by elevated blood Ca2+ levels, and it inhibits osteoclast activity , but this function
in humans is less important than the roles of parathyroid hormone and vitamin D in the regulation of normal calcium
homeostasis.
Production of Thyroid Hormone - promoted by TSH
① Production of thyroglobulin ;
* synthesis in the rough ER and glycosylation in the Golgi apparatus , then the glycoprotein is released from
thyrocytes into the follicular lumen
② Uptake of iodide ;
* from blood by Na/I symporters (NIS) in the thyrocytes’ basolateral cell membranes. Decreased levels of
circulating iodide trigger synthesis of NIS , increasing iodide uptake and compensating for the lower plasma
concentration. An apical iodide/chloride transporter (also called pendrin) pumps I – from thyrocytes into the
colloid
③ Iodination of tyrosyl residues ;
2
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller mandarachalangi. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $9.49. You're not tied to anything after your purchase.
