Endocrine Flashcards
The Endocrine System
The endocrine system (endo-, inside, and krinein, -to secrete)
- comprises several glands (pituitary, thyroid, parathyroid, adrenals) and
- Scattered cells in the gonads, pancreas, intestine, and other organs
Primary function of endocrine cells
produce hormones
- the endocrine organs do not have ducts and so are called the “ductless” glands. Hormones are secreted into the blood or extra cellular spaces
Hormones that are released into the circulation act on distant organs (endocrine effect)
For example, pituitary hormones exert an endocrine effect on the thyroid, adrenals, or gonads
Four major endocrine glands:
: the pituitary, thyroid, parathyroid, and adrenals
The pituitary, thyroid, parathyroids, and adrenals are unrelated to each other and have distinct anatomic locations
gynaecomastia
men gets breasts
Pituitary
- located intracranially in an indentation of the base of the cranium called the sella turcica (a Latin term -Turkish saddle)
- consists of two parts (anterior and posterior), which are connected to the hypothalamus via a stalk that contains extensions of neurons and the vessels of the pituitary portal system
The blood vessels transport-from the hypothalamus into the pituitary
-the neuroendocrine releasing factors that regulate the function of the pituitary cells
highly vascular- lots of blood vessels
The Anterior Pituitary ( adenohypophysis )
consists of five distinct cell types, each of which is named according to the hormone it secretes. These hormones are:
growth hormone (GH) prolactin (PRL ) adrenocorticotropic hormone (ACTH) the gonadotropins (luteinizing hormone [LH] and follicle-stimulating hormone [FSH])- teste or ovary, testosterone- ova,estro and progesterone thyrotropic hormone (thyroid-stimulating hormone [TSH])
Growth Hormone (GH) action and target
Somatomedin Synthesis º Growth Simulation
targets liver and other
prolactin
action and target
lactation- targets breast
Thyroid Stimulating Hormone (TSH)
action: Thyroid Hormone Synthesis &
Release
targets thyroid
Follicle-Stimulating Hormone (FSH)
action -spermatogenesis, estrogen synthesis oogenesis
organ: testi
ovary
Adrenocorticotropic Hormone (ACTH)
action Glucocorticoid Synthesis & Release
target adrena cortex
Luteinizing Hormone (LH)
action:
Ovulation
Corpus Luteum, hence Progesterone Production
target ovary
action:
Testosterone Synthesis
target testi
Regulation!!
The secretion of hormones of the anterior pituitary is regulated by
positive stimulation -exerted by the cells in the hypothalamic centers and
negative feedback inhibition -created by the hormones produced by the target endocrine cells in the thyroid, adrenals, and gonads
The Posterior Pituitary (neurohypophysis)
which comes from anterior vs posterior
- release oxytocin (pitressin) and the antidiuretic hormone (ADH)
In contrast to the hormones of the anterior pituitary, which are trophic and stimulate the functions of other endocrine glands, the hormones of the posterior pituitary have no trophic functionsThese hormones act on nonendocrine cells; - oxytocin stimulates the contraction of the pregnant uterus and
- ADH promotes the reabsorption of water from the renal tubules
THE THYROID GLAND
weight : 15-25 g
• derived from primitive gut
• function: storage & release of thyroid hormones
• 2 “butterfly-shaped” lobes connected by narrow band of tissue called the isthmus
-ant to lower part larynx &. Above clavicle
an endocrine gland located in the neck
- consists of two types of cells: follicular cells and C cells
Follicular cells secrete thyroid hormones (thyroxine [T4] and triiodothyronine [T3])- essential for maintaining the intermediate metabolism.
The secretion of T3 and T4 is regulated by TSH
The C cells secrete calcitonin, a polypeptide - involved in the maintenance of calcium homeostasis
The secretion of calcitonin is influenced by the concentration of calcium in serum
Overview of Major Diseases
The most important diseases involving the endocrine glands present as:
- Hyperfunction
- Hypofunction
- Tumors
hypo
– low or deficient; Hyper- high or excessive
endocrine
- secretion into the circulation
exocrine
– secretion via duct into GI system
syndrome
– group of symptoms common to several diseases
disease
specific cause known
benign tumor
one that does not spread (metastasize)
hypertrophy
– grow in size due to constant stimulus
autonomous
– with no feedback control
primary
– disease caused within the gland
secondary
– caused by something external
tertiary
– 2ndary becomes autonomous
hyposecreation
agenesis, atrophy, destruction
hypersecreation
tumor, hyperplaisia
(1 of 6 comandement)
A.The Function of the endocrine gland is tightly regulated by positive and negative stimuli
dont need to know in detail
The function of the thyroid, adrenals, and gonads is regulated by the anterior pituitary, which secretes the trophic hormones TSH, ACTH, LH, and FSH.
The function of the pituitary is, in turn, regulated by the hypothalamic releasing factors (e.g., gonadotropin-releasing hormone [GnRH]).
The hormones of the peripheral target glands released into the blood have a negative inhibitory influence on the hypothalamus and the pituitary
2 of 6
B. Prolonged hyper stimulation by trophic hormones or metabolic signals leads not only to hyper function, but also to physical enlargement of the peripheral endocrine glands
The thyroid, when over stimulated by TSH, enlarges and becomes nodular
ACTH stimulation leads to adrenocortical hyperplasia
C. Hyper functioning endocrine glands may be hyperplastic or neoplastic
Hyperfunctioning endocrine glands are usually enlarged. -The enlargement may be attributable to hyperplasia (i.e., a reactive increase in cell number) or to benign or malignant tumors
D. Hypo function of the endocrine glands is usually attributable to the destruction of secretory cells
Destruction and loss of endocrine cells or the entire gland may be caused by several mechanisms, the most important of which are inflammation, tumors, and medical interventions
Inflammation may be caused by infectious organisms or autoimmune processes
E. Neoplastic or hyperplastic enlargement of the endocrine glands results in mass lesions that compress adjacent structures
Local symptoms caused by endocrine gland enlargement are most evident in diseases of the pituitary and the thyroid
Enlargement of the pituitary, which is in close proximity to the optic nerve
decussation, produces defects in the visual field (so-called bitemporal hemianopsia, or bilateral loss of peripheral [temporal] sight).
Thyroid tumors may produce a bulge on the anterior side of the neck or compress the larynx, trachea, and the nerves or blood vessels of the neck
F. Tumors of one endocrine gland may be associated with neoplasia and/ or hyperplasia of other glands
Multiple endocrine neoplasia (MEN) is a hereditary syndrome that occurs in at least three forms: MEN-l, MEN-2A, and MEN-2B
In MEN-l, the tumors originate from the pituitary , parathyroids, and pancreatic islets of langherhans
-
In MEN-2A,
the tumors include medullary carcinoma originating from C cells of the thyroid, pheochromocytoma originating from the medulla of the adrenal, and parathyroid adenoma or hyperplasia
MEN-2B,
, which resembles MEN-2A and has the same endocrine lesions, also includes additional multiple skin and mucosal nerve tumors. The occurrence of these familial tumors has been related to defects in tumor suppressor genes
Pituitary Diseases
Diseases of the pituitary are uncommon, but may present as:
Pituitary hyperfunction
Pituitary hypofunction
A localized mass lesion causing compression of the optic chiasm or the basal portion of the brain
Pituitary hyperfunction
Pituitary hyperfunction may present in several forms depending on which one of the five cells is hyperfunctioning. The pituitary is usually, enlarged
The enlargement may be attributable to macroscopic or microscopic adenomas, which are composed of a single cell type or several cell types
Most common are tumors composed of
Less common are
which is the most rare
!!!
Most common are tumors composed of lactotropic cells (also known as prolactinomas)
Less common are somatotropic and corticotropic adenomas
Tumors composed of TSH-, LH-, or FSH-secreting cells are extremely rare
Pituitary Hypofunction
Endocrine insufficiency of the pituitary causes hypofunction of secondary organs, which depend on trophic stimuli from the pituitary.
Pituitary hypofunction is rare, but it may be encountered in any age group.
It may involve all pituitary cells panhypopituitarism) or it may be selective-i.e., limited to one subset of anterior pituitary cells (e.g., hypogonadism secondary to the deficiency of gonadotropic cells) or posterior pituitary cells (e.g., diabetes insipidus)
The causes of pituitary hypofunction include:
congenital developmental defects, as in pituitary dwarfism or hypogonadism
tumors that destroy the pituitary (e.g., nonfunctioning pituitary adenoma) or the hypothalamus (e.g., craniopharyngioma or glioma)
ischemia, as in postpartum necrosis (Sheehan’s syndrome )
The diagnosis of pituitary insufficiency may be suspected clinically but must be confirmed by appropriate biochemical tests, which will show hormone deficiency
Panhypopituitarism of adults (Simmonds’disease)
Panhypopituitarism of adults (Simmonds’disease) is marked by general weakness, cold intolerance, poor appetite, weight loss, and hypotension. Women affected by this disease do not menstruate and men suffer from impotence and loss of libido. Pituitary insufficiency of childhood results in dwarfism
Diabetes insipidus is marked by
diabetes mellitus is cause by sugar
Diabetes insipidus is marked by a lack of ADH secondary to destructive lesions of the hypothalamus, pituitary stalk, or posterior pituitary. It may be caused by tumors, infection of the brain or meninges, intracranial hemorrhage, or trauma involving the bones of the base of the skull. Patients with diabetes insipidus secrete large amounts (5 to 6 L/day) of hypotonic urine
Growth Hormone
Deficiency Syndromes:
Children: Pituitary Dwarfism
Adults: Single deficiency – None
Multiple: Hypopit Syndrome