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THE ENDOCRINE SYSTEM. Kristina C. Erasmo, M.D. ENDOCRINE SYSTEM. System of glands that involve the release of extracellular signaling molecules known as hormones Do not possess any excretory ducts Integration and control system of the body. Hormone. - PowerPoint PPT Presentation
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Kristina C. Erasmo, M.D.
System of glands that involve the release of extracellular signaling molecules known as hormones
Do not possess any excretory ducts
Integration and control system of the body
Substance that is carried by the blood to target organs/tissues whose cells have the appropriate receptors for the substance
Function as “chemical signals”
Hypothalamus Pituitary gland Pineal gland Thyroid gland Parathyroid gland Adrenal gland Pancreas
At base of brain, behind the optic chiasm
Forms the floor and part of the wall of the 3rd ventricle
Part of the diencephalon
Functions:o Control numerous bodily functions
o Thirst, hunger, satietyo Temperatureo Sexual behavioro Circadian rhythms
o Produces several hormoneso Oxytocino Antidiuretic hormone o Neurohormones
The cell bodies of the neurons form numerous aggregations (nuclei)
Supraoptic nucleuso Above and lateral to optic chiasm
Paraventricular nucleuso In the lateral wall of 3rd ventricle
Oxytocino Stimulates contractions of the uterus and ejection of
milk Vasopressin (antidiuretic hormone/ADH)
o Regulates water retention (kidneys)o ↑ urine osmolarity (↑ concentration), ↓ urine excretion
Neurohormones (hypophysiotropic hormones) – secretory neurons
Ovoid body attached to inferior surface of hypothalamus
Lodged in the hypophyseal fossa of the sella turcica of the sphenoid bone
Neurohypophysis (posterior pituitary)o From neural ectoderm
Adenohypophysis (anterior pituitary)o From oral ectoderm
Greater part is formed by the axons of the secretory neurons whose cell bodies are in the SVN and PVN of hypothalamus
Proximal portions of these axons form hypothalamo-hypophyseal tract
Distal portions form bulk of the posterior lobe of pituitary
Not a gland Stores and secretes oxytocin and ADH
(“posterior pituitary hormones”) 2 parts:
o Pituitary stalk (infundibulum, infundibular stem, infundibular stalk, hypophyseal stalk)o Attached to the hypothalamus
o Pars nervosa (posterior lobe, infundibular process)o Expanded inferior continuation of the pituitary stalk
Produces “anterior pituitary hormones”o Somatotropin, prolactin, thyrotropin, corticotropin,
FSH, LH 3 parts:
o Pars distalis (anterior lobe)o Pars tuberalis (pars infundibularis)o Pars intermedia (intermediate lobe)
Forms a sleeve around the pituitary stalk of neurohypophysis
Where vessels of hypophyseoportal system and arteries that supply anterior and posterior lobe run through
Thin, poorly developed region of adenohypophysis
Contain secretory granuleso Melanocyte-stimulating
hormone (MSH)o β-endorphin
Comprises 70% of pituitary gland
Nearly all hormones produced by pituitary gland come from this lobe (“anterior pituitary hormones”)
Consists of anastomosing and irregularly arranged cords and clusters of secretory epithelial cells that surround fenestrated capillaries
2 types of secretory cells:o Chromophils
o Acidophils (alpha cells)
o Basophils (beta cells)o Chromophobes
65 % of epithelial secretory cells in pars distalis Consists of follicular cells and undifferentiated
stem cells
35 % of epithelial secretory cells of pars distalis Acidophils
o Somatotrophso Mammotrophs
Basophilso Thyrotrophso Corticotrophso Gonadotrophs
Secretes Target Organ
Acidophils
Somatotrophs Most abundant (50%)
Growth hormone (somatotropin)
Non-specific
Mammotrophs 20% Prolactin Mammary glands
Basophils
Thyrotrophs 5% TSH (thyroid-stimulating hormone, thyrotropin)
Thyroid gland
Corticotrophs 20% ACTH (adrenocorticotropic hormone, corticotropin)
Adrenal cortex
Gonadotrophs 5% Gonadotropins – luteinizing hormone and follicle-stimulating hormone
LH: Ovary, Leydig cellsFSH: Ovary, Sertoli cells
Hypothalamic control over anterior gland of pituitary glando Corticotropin-releasing hormone (CRH)o Thyrotropin-releasing hormone (TRH)o Growth hormone-releasing hormone (GRH)o Growth hormone-inhibiting hormone (GIH,
somatostatin)o Gonadotropin-releasing hormone (GnRH)o Prolacting-inhibiting hormone (PIH)
Small, conical structure Base is attached to
posterior portion of the roof of the 3rd ventricle of the brain by two short stalks
Well-developed in children
Starts to involute at puberty
Enveloped by thin CT capsule derived from the pia mater
CT septa arise from the capsule and divide the organ into irregular lobules
Lobules contain cells arranged in short cords or clusters surrounded by fenestrated capillaries
CT septa contain blood vessels and unmyelinated nerve fibers
Cells:o Pinealocytes (95 %)
o Modified neuronso Produce melatonin
o Glial cells (Interstitial cells)
Brain sand (Psammoma bodies)o Calcified bodies with a concentric lamellar structureo Increase in number with age
Largest endocrine gland Unpaired gland that lies
on the anterior aspect of the neck
Left and right lateral lobes Isthmus – horizontal
bridge of glandular tissue which connects both lobes
Enclosed by two capsules
CT septa divide the organ into lobules
CT infiltrated with lymphocytes and some lymphoid nodules
Each lobule contains follicles
Follicleso Irregular spherical,
cystic structureso Lined by simple
cuboidal epitheliumo Cavity contains colloid
(homogenous, gel-like material)
Epithelial cells:o Follicular cells (principal cells)
o Majorityo Synthesize thyroglobulin
o Parafollicular cells (C or clear cells)o 0.1 %o Synthesize calcitonin – inhibits bone resorption (directly
suppressing osteoclasts), thus lowering blood calcium levels
Two pairs (superior and inferior), yellowish-brown, tiny ovoid bodies
Attached to the posterior surface of the lateral lobes of the thyroid gland
PARATHYROID GLAND
Chief cells (principal cells)o Majorityo Secrete parathyroid
hormone (PTH) Oxyphil cells (acidophil
cells)o Non-secretoryo Unknown function
Paired, flat, pyramidal organs
Rest on the upper pole of their correspondin kidneys
Enveloped by thick CT capsule
Cortex o Outer layero Completely surrounds
medullao Mesodermal origin
Medullao Inner layero Ectodermal origin
80 – 90 % of the adrenal gland Produce adrenocortical hormones (steroid
hormones)o Zona glomerulosa – aldosterone o Zona fasciculata – cortisol o Zona reticularis – androgens (DHEA and
androstenedione)
Comprises 10-20 % of adrenal gland
Central part: medullary veins that drain the entire gland
Consists of parenchymal cells arranged in groups or cords surrounded by sinusoids and richly supplied with nerves (associated with pre-ganglionic sympathetic neurons)
Chromaffin cells: secrete cathecolamines o Epinephrine (adrenaline)o Norepinephrine (noradrenaline)o Dopamine
Islets of Langerhanso Small aggregations of pale-staining cells scattered
among the dark-staining cells of the exocrine portion of the pancreas
o Each islet surrounded by thin layer of fine reticular fibers
o Provided by rich supply of capillarieso Millions but only 2 % of volume of pancreas
β cellso Secrete insulin
α cellso Secrete glucagon
δ cellso Secrete somatostain – inhibits secretion of glucagon,
insulin and pancreatic polypeptide F cells
o Secrete pancreatic polypeptide – slows absorption of food from the intestines