Microanatomy 1 Flashcards
what do endocrine cells do
- they produce hormones and release them into the surrounding interstitial spaces from which they may enter the circulatory centres
what do hormones act as
- they act as chemical messengers that affect nearby or distant target tissues and coordinate and integrate the functions of all the physiological symptoms of the body
what is the pituitary gland
- it is an appendage of the brain
how is the pituitary glad attached to the brain
- connected to it by the pituitary stalk
where does the pituitary gland sit
- situated int he pituitary fossa or (sella tunica) of the sphenoid bone
what type of hormones does the pituitary gland release
control directly the functions of target tissues (eg. growth hormone, vasopressin, oxytocin)
regulate the hormonal output of other endocrine glands (ie. trophic hormones such as corticotrophin and thyrotrophin).
what is the structure of the pituitary gland
comprised of the anterior and posterior pituitary
- originate from different embryological sources and this is reflected in there structure and function
what is secretion of the pituitary hormones controlled by
Secretion of pituitary hormones is controlled by hormonal and neural (posterior pituitary) input from the hypothalamus of the brain and is under feedback regulation by the circulating levels of hormones produced by target organs.
what is the hypothalamic control of the anterior pituitary mediated by
- mediated by releasing and releasing inhibiting hormones
how do the hypothalamic hormones reach the pituitary by
reaches the pituitary via the hypothalami-hypophyseal portal system
what epithelium is in the anterior pituitary
- typical glandular epithelium
name the 5 types of cells in the anterior pituitary gland
- somatotropin
- mammotrophs (lactotrophs)
- corticotrophs
- thyrotrophs
- gonadotrophs
describe the 5 types of cells in the anterior pituitary and what they produce
- Somatotrophs - cells responsible for GH (growth hormone) secretion, most abundant making up about 50% of the gland
Mammotrophs (lactotrophs) - prolactin secreting cells, make up about 20% of anterior pituitary, increase in numbers during pregnancy; prolactin controls milk production during lactation
Corticotrophs - secrete ACTH (adrenocorticotrophic hormone also known as corticotrophin), make up about 20% of the gland
Thyrotrophs - secrete TSH (thyroid stimulating hrmone also known as thyrotrophin) and make up about 5% of the pituitary gland
Gonadotrophs - responsible for secretion of FSH (follicle stimulating hormone) and LH (luteinising hormone) and make up the final 5% of the gland
what is the blood supply of the anterior pituitary gland
- most of the blood supply is derived from the hypophyseal portal vessels
- present of fenestrate in the sinusoidal capillaries of the pituitary gland facilitated the exchange of hormones in the tissues
what is the posterior pituitary
- does not contain glandular epithelium
- instead it is a down growth of nervous tissue from the hypothalamus
how is the posterior pituitary attached to the hypothalamus
- it is attached to the hypothalamus via the pituitary stalk
what does the posterior pituitary contain
- it contains axonal processes and terminals of hypothalamic neurosecretory neurones
what are the axons in the pituitary stalk and posterior pituitary supported by
the axons in the pituitary stalk and posterior pituitary are supported by a glial-type cell called the pituicyte.
what are the neurosecretory products of the posterior pituitary
ADH and oxytocin
what is the blood supply of the posterior pituitary
- rich network of fenestrated capillaries is present in the posterior pituitary that facilitate the passage of the hormones into circulation
name the three major components of the pituitary stalk
portal vessels
axons of neurosecretory neurones passing to the posterior pituitary
pituicytes
what is the function of most of the cells intrinsic to the pituitary stalk
Pituicytes are the most abundant intrinsic cell type and they support the axons in the stalk performing functions akin to other types of glia.
where are the thyroid and parathyroid glands located
- they are located in the neck and to the front of the upper trachea
- usually consist of 2 or three pairs
describe what the parathyroid glands look like
- they are small oval glands embedded in the capsule of the thyroid glands on its posterior surface
what does the parathyroid gland do
- produces parathyroid hormones that regulates serum calcium and phosphate levels - decreases in blood calcium levels stimulate the secretion of parathyroid hormone
- contains a variable amount of adipose tissue, the amounts increase with age
- contains oxyphil cells which are homogeneously stained cells with a small central nuclei whose function is unknown
what cell in the parathyroid gland produces the hormone that regulates serum calcium and phosphate levels
chief cells
what does the parathyroid hormone act on
Parathyroid hormone acts on bone, kidney and the small intestine to increase calcium levels.
What does the thyroid gland produce
- produces the iodine-containing hormone T4 (tetra-iodothyronine;thyroxine)
- some T3 (tri-iodothyronine;
synthesis and secretion of these hormones is dependent on thyrotrophin which is released from the anterior pituitary
contain scattered clear staining cells called parafollicular or C cells that produce the hormone calcitonin
what does T4 (tetra-iodothyronine) do
the active metabolite of T4 mainly produced from it in peripheral tissues) which act to regulate the basal metabolic rate and influence growth and maturation.
what is thyroid follicles lined by
are lined by simple epithelium that is usually cuboidal in nature but can vary in appearance depending on its secretory activity.
what cells are responsible for the production of T4 and T3
thyroid follicles
what do thyroid follicles contain in there lumina
contain in their lumina thyroid colloid, consisting mainly of the glycoprotein complex thyroglobulin involved in the synthesis, storage and release of thyroid hormones.
what do parafollicular or C cells do
These cells secrete calcitonin in response to raised blood calcium levels
- it aims to decrease blood calcium levels
what do thyroid follicles do
Thyroglobulin involved in the synthesis, storage and secretion of T4 and T3.
where is the adrenal gland
they are on top of kidneys
describe the structure of the adrenal glands
- composed of an outer adrenal cortex
- composed on an inner adrenal medulla
what does the adrenal cortex do
produce steroid hormones
what are the three regions of the adrenal cortex
zona glomerulosa
zona fasciata
zona reticularis
describe the three regions of the adrenal cortex
- arrangement of cells
- major hormones
Zona glomerulosa
- rounded clumps
- mineralocorticoids such as aldosterone
zona fasciculata
- parallel cords
- glucocorticoids such as cortisol
zona reticularis
- irregular cords
- androgenic steroids
name an example of a mineralocorticoids
aldosterone
name an example of a glucocorticoids
cortisol
what is the main cell in the adrenal medulla
- chromaffin cells
what do chromaffin cells secretion
that secrete the catecholamine hormones adrenaline and noradrenaline in response to direct nervous input from sympathetic preganglionic fibres.
what is the blood supply of the adrenal medulla
- has a dual blood supply
- one half comes form the sinusoids of the adrenal cortex and then the other half comes from the medullary arterioles that only supply the medulla, these both originate from capsular arteries
- blood from the arterioles passes through he cortex where it becomes rich in adrenocorticosteroids and eventually enters the capillary network of the medulla.
what do corticosteroids modulate in the medulla
- they modulate the production of adrenaline in the medulla
how long is the human adrenal gland
2-3cm in length
when in the medulla stains slightly lighter
. The central medulla stains slightly lighter than the adjacent zona reticularis of the cortex
why do many cells in the medulla of the adrenal glands have a foamy unstained appearance
Triglycerides are the main substrate for steroid synthesis and form lipid droplets in the cytoplasm. These are removed from the cell during processing (similar to lipid in adipocytes) leaving unstained ‘holes’
what is pancreases comprised of
- spherical clusters of endocrine tissue embedded within the exocrine acini - these structures are named the islets of langerhans
what are the major hormones produced by the islets of langerhans
- insulin
- glucagon
what is diabetes mellitus
- common disorder of the inulin secretion or responsiveness causing impaired metabolism, vascular and neurologic disease
what does somatostatin do
-acts locally to inhibit inulin and glucagon secretion
what does pancreatic polypeptide have a role in
- has a role in inhibition of pancreatic enzyme secretion from the surrounding acing cells
name the cell types that make up the islet of langerhnas
a (A)
b (B)
d (D)
pp (F)
Name what the cell produce in the islet of langherans and there percentage that they make up of endocrine cells
A
- glucagon
- 20%
B
- insulin
- 70%
D
- somatostatin
- 5-10%
pp(F)
- pancreatic polypeptide
- 1-2%
what can adenomoas of the pituitary gland be
- these can either be function or nonfunctional
describe non function adenomas
- these tend to be larger at the time of diagnosis then functional ones
- present with symptoms due to local mass effects such as visual disturbances or signs and symptoms of elevated intracranial pressure
what do functional adenomas present with
- these interfere with normal endocrine functions so present line this
describe the histology of a normal anterior pituitary gland
= number of different cell types are obvious
- fine reticular network of connective tissue organises the tissue into rough acing groups
- immunohistochemical staining for growth hormones revels cells making this hormone scattered within the gland
describe the histology for pituitary adneoma
- mainly composed of fairly uniform small to medium sized cells with moderate amounts of cytoplasm
- reduction in the supporting reticulin network
- patient presented with features of excess growth hormone secretion
- stains positive for growth hormone
what is acromegaly
- this is abnormal group of the viscera, skin, soft tissues and skeleton occurs in adults
what does adenoma stain positive for
growth hormone
what happens in early hashimotors thyroiditis
- patients may be euthyroid or hyperthyroid as immune processes destroy and cause release of increased amounts of thyroid hormones
- when almost all thyroid follicles are destroyed the patient becomes hypothyroid and the immune reaction subsides
- fibrosis occurs along with reduction in the size of the gland
what can hypothyroidism cause
- it can cause coarsening of the skin with puffiness due to accumulation of glycosaminoglycans
- this is called myxoedmic face
what is thyrotoxicosis
- this is the clinical syndrome resulting from excess of circulating thyroid hormones acting upon the tissues
what are the symptoms of thyrotoxicosis
- anxiety
- hair loss
- weight loss
- menstural irregularities
- osteoporosis
- diarrhoea
- warm moist palms
- tremor
what is the commonest cause of pathological thyroid hyperplasia
graves disease - it accounts for approximately 85% of cases of hyperthyroidism
what is graves disease
- an autoimmune disease characterised by a triad of clinical features such as hyperthryoidism, exophthalmos (protruding eyes) and non pitting oedema of the lower limbs (pretibila myxoedema)
what are the clinical features of hyperthyroidism
= related to increased basal metabolic rate
- increased sympathetic nervous system activity
what antibodies are produced in graves disease
- circulating antibodies to the TSH receptor
- one of these is an immunoglobulin called thyroid stimulating immunoglobulin which binds to the TSH receptor on the thyroid follicular cells and mimics it
- this results in excess secretion of thyroxine
- the microscopic appearance of the gland is called thyrotoxic hyperplasia
how is thyrotoxic hyperplasia called
- in graves disease there is an antibody called thyroid stimulating immunoglobulin which binds to the TSH receptor on the thyroid follicular cells and mimics it
- this results in excess secretion of thyroxine
- the microscopic appearance of the gland is called thyrotoxic hyperplasia
describe the histology of thyrotoxic hyperplasia as a result of graves thyroiditis
- follicular cells are taller and have larger nuclei
- colloid shows scalloping - reflecting increased use of the stored colloid to provide thyroxine
- follicles are also smaller reflecting reduced remaining colloid due to the higher utilisation
- increased numbers of follicular cells can sometimes bunch up into papillae projecting into the colloid
- lymphoid aggregates will also be present
name some disorders of the adrenal gland
- cortical atrophy
- cortical hyperplasia
- cortical adenoma
- pheochromocytoma
- neuroblastoma
- paraganglioma
what is cortical atrophy
- response to stress or long term corticosteroid administration
what is cortical hyperplasia
may be diffuse or more commonly nodular
- diffuse hyperplasia is a response to pituitary to ectopic ACTH
- nodular is idiopathic
what is cortical adenoma
- independent of ACTH secretion
- solitary nodule in cortex often multiple cell types
what is phaeochromyocytoma
- arise from medullary chromatin cells
- symptoms of catecholamine secretion
- nests of plump cells with granular cytoplasm
what is neuroblastoma
adrenal embryonal tumour
- highly malignant
what is paraganglioma
tumor of extra adrenal paragnalgion system,
equivalent of adrenal phaeochromocytoma
- carotid body tumours is one example
describe the shape of the adrenal cortical adenoma
- form a circumscribed, spherical mass within the cortex
- must be composed of one type of cortical cell or a mixture of cells
what are functional adenomas most associated with
- hyperaldosteronism
- bushings syndrome
not all adrenocrotical neoplasms are ..
functional
what is the most common cause of cushions syndrome
pituitary adenoma
what are the characteristics of Cushing syndrome
moon facies
abdominal striae
tzruncal central obesity
what is the function of most cells in the pituitary stalk
- Pituicytes are the most abundant cell
- they support the axons in the stalk
- they perform functions akin to other glial cells
what does thyroid colloid consist of
thyroglobulin
