Clinicals case of heart failure

1. THYROID f0llicle
By :
saikalyan
Ug : 2101945

2. Introdction :
• The thyroid gland is a vital butterfly-
shaped endocrine gland situated in the
lower part of the neck
• The thyroid gland, located anterior and
inferior to the larynx, consists of two
lobes united by an isthmus.
• Each lobule contains a cluster of
follicles, which are the structural and
functional unit..
• It synthesizes the thyroid hormones
thyroxine (tetra-iodothyronine or T4)
and tri-iodothyronine (T3),

3. Microscopic structure of
thyroid follicle
• Follicle consist of layer of simple
epithelium, enclosing cavity called the
follicular cavity.
• The cavity is usually filled with gel-like
viscous iodine-rich material called
colloid.
• Interfollicular spaces are filled by
reticular connective tissue, adipose
tissue and blood vessels.

4. HISTOLOGY & COMPOSTION :
• The parenchyma of the thyroid is composed of
millions of rounded epithelial thyroid follicles
of variable diameter, each with simple
epithelium
• thyroid follicle is surrounded by thin
connective tissue stroma rich in fenestrated
capillaries
• The colloid stains pink with haematoxylin and
eosin (H&E) staining, while the follicular cells
have a purple appearance.
• Among endocrine glands, thyroid is unique as
it stores large quantity of its hormonal
secretion extracellularly as colloid.

5. State of the follicle Linning epithelium Amount of collid
Inactive /resting squamous abundant
active cuboidal moderate
Highly active Low columnar scanty
Thyroid follicle at different levels of activity

6. Synthesis of Thyroid Hormone
• Thyroid hormone synthesis begins with the
recognition of thyroid-stimulating hormones
(TSH) by TSH-receptors at the basolateral
region of the follicular cells.
• iodine is taken into the cell via Na+/I-
symporters.
• Iodine is used in the organification of tyrosine
in the follicular lumen to form
monoiodotyrosine (MIT).
• MIT can then be organified to form
diiodotyrosine (DIT). The enzyme thyrosine
peroxidase (TPO), can subsequently link a MIT
and a DIT molecule to form triiodothyronine
(T3) or two DIT molecules to form thyroxine
(T4).

7. Graves' Disease :
• Graves disease is an autoimmune disorder
that leads to an overactive thyroid gland
(hyperthyroidism).
• Due to the production of autoantibodies
against the TSH receptor on the follicular
epithelial cells.
• These antibodies mimic the effects of TSH
and cause overproduction and release of
thyroid hormone.
• The epithelial cells in this patient no longer
surround round follicles of colloid.
• these follicles are disappearing and the
colloid is becoming depleted. Compare to
normal thyroid.
.

8. hypothyroidism
• Hypothyroidism happens when the thyroid gland
doesn't make enough thyroid hormone. This
condition also is called underactive thyroid.
• The thyroid parenchyma extensive infiltration of
lymphocytes, leading to the destruction of thyroid
follicles.
• lymphocytes form aggregates, leading to the
development of lymphoid follicles with germinal
centers, which are a hallmark of the autoimmune
response
• phagocytose the degenerating thyroid follicular
cells resulting destruction of the follicular
architecture and impaired hormone synthesis.

9. References :
• Histology, thyroid gland - statpearls - NCBI bookshelf.
(n.d.-b).
https://www.ncbi.nlm.nih.gov/books/NBK551659/
• Professional, C. C. medical. (n.d.-a). Hypothyroidism:
Symptoms, causes, treatment & medication. Cleveland
Cleveland Clinic.
https://my.clevelandclinic.org/health/diseases/12120-
hypothyroidism
• Loscalzo J, et al., eds. Hypothyroidism. In: Harrison's
Principles of Internal Medicine. 21st ed. McGraw Hill;
2022. https://accessmedicine.mhmedical.com
• Hypothyroidism. National Institute of Diabetes and
Digestive and Kidney Diseases.
https://www.niddk.nih.gov/health-
information/endocrine-diseases/hypothyroidism .
• Ross DS. Diagnosis of and screening for hypothyroidism in
nonpregnant adults.
https://www.uptodate.com/contents/search .