Endocrine System Flashcards
endocrine System consists of:
- ductless Glands
- clusters of cells within certain Organs (Langerhans islets in pancreas….)
- Endocrien cells (HI, respiratory, UGS)
endocrine Glands are vascularized by
sinusoidal capillaries
Types of hormonal Action
- Autocrine: Acts on same cell
- Paracrine: on cells nearby
- Endocrine: on distant target Organs
- Synaptic or Neurocrine: invilving neurosecretory neurons
Types of hormones
Polypeptide derivatives: water soluble (Insulin, FSH)
Amino-Acid derivatives: water soluble, receptors located in membrane (thyroxine, epinephrine)
Steroids and fatty Acid derivatives: lipid-soluble, receptors in cytoplasm (progesterone, Cortisol)
Classification of endocrine glands
I. Central Glands
- Hypothalamus
- Pituitary Gland (hypophysis)
- Epiphysis (pineal Gland)
II. Peripheral Glands
- thyroid
- parathroid
- Adrenal
- Pancreas
- Gonads
- DNES
Stroma and Parenchyma of endorcrine glands
stroma: loose CT with reticular fibers
Parenchyma: epithelial tissue or nerve tissue
Parenchymal cells in endocrine glands
in clumps and Cords
except in thyroid: are organized in follicles
Hypothalamus
coordinates most endocrine functions of the body
Neurons of hypothalamus
typical Neurons and neurosecretory cells
accumulation of neurosecretory cells forms the nuclei
N. Supraopticus and n. paraventricularis
- produce Oxytocin and ADH
- transported along axons into neurohypophysis
Other nuclei of the hypothalamus
- produce Hormones and accumulate them in axonal endings near median eminence
- Hormones into the hypothalamohypophyseal Portal System for the adenohypophysis
hypothalamic polypeptides are releasing and inhibiting hormones
Pituitary Gland, hypophysis
- in sella turcica on sphenoid bone
- infunibulum cinnects Gland to hypothalamus
Structure of pituitary gland
Anterior pituitary (adenohypophysis)
- pars distalis
- pars intermedia (sometimes considered separate part)
- pars tuberalis
Posterior pituitary (neurohypophysis)
- pars nervosa
- infundibulum
- median eminence
developmental Sources of the pituitary gland
Adenohypophysis: oral ectoderm (Rathke’s pouch)
Neurohypophysis: neural ectoderm
Capsule and stroma: from head mesenchyme
Adenohypophysis
- cells arranged in Cords
- between Cords are sinusoids
two main populations of cells:
1- Chromophobes
2- Chromophils (acidophils and basophils)
Chromophobes
- few secretory granules
Pathway of secretion in chromophils
- proteins synthesized in rER pass through Golgi –> granules
- Stimulation –> granules released
Acidophils
- round
- centrally located nucleus
- acidophilic granules
- ->somatotropes
- ->mammotropes
Somatotroped
- type of acidophil in adenohypophysis
- large secretory granules
- produce grwoth Hormone
- stimulates epiphyseal plates in Long bones
Mammotropes
- type of acidophil in adenohypophysis
- irregularly shaped granules
- granules increase in number ad size during pregnancy
- produce prolactin
Basophils
- oval or polygonal
- eccentric nucleus
- basophilic granules
- –>corticotropes
- –>Gonatotropes
- –>Thyrotropes
Corticotropes
- type of basophil in adenohypophysis
produces
- Adrenocorticotrophic Hormone (ACTH)
- Melanocyte stimulating Hormone (MSH)
ACTH
- adrenocorticotrophic Hormone
- stimulated zona fasciculata and zona reticularis of adrenal cortex
Gonadotropes
- type of basophil in adenohypophysis
- produce gonadotropins:
- –>FSH: stimulates follicles in ovaries and Sertoli cells
—>LH: stimulates corpus luteum and Leydig cells
Thyrotropes
- Type of basophil in adenohypophysis
- small basophilic granules
- produce TSH –> stimulates follicular cells of thyroid gland
Two functional Groups of Hormones of the anterior pituitary
- trophic Hormones: modulate activity of other endocrine Glands (TSH, ACTH, FSH, LH)
- Hormones acting on non-endocrine tissue
(GH, prolactin, MSH)
Pars intermedia of the pituitary gland
- from Rathle’s pouch
- poorly developed in humans
- doubtful function
- cells are basophilic and chromophobic
- small cavities filles with eosinophilic material
Pars tuberalis
- in adenohypophysis
- parenchymal cells are arranged in Cords of basophilic cells
Regulation of the anterior pituitary
- regulated by neurosecretory Hormones of the Hypothalamus
- releasing and inhibiting Hormones released in median eminence
- pituitary cells are stimulated
Neurohypophysis
- composed of axons of neurosecretory Neurons supraopticus and paraventricularis
- axons are supported by pituicytes (glial cells)
- herring bodies (with Oxytocin and ADH granules)
ADH (antidiuretic Hormone) / vasopressin
- increased blood pressure by promoting contraction of smooth muscle in Arteries and arterioles
- Regulation of water homeostasis:
- –> increased Reabsorption of water in distal convoluted tubules and collecting ducts of kidney
Oxytocin
promotes contraction of:
- uterine smooth muscle in Orgasm, Menstruation, birth
- myoepithelial cells in mammary gland
Regulation of posterior pituitary
- Hormones are made in the nuclei in Hypothalamus
- pass through axons and released into capillaries
Epiphysis / Pineal gland
- at posterior wall of 3rd ventricle
capsule of dense irregular CT
Stroma: loose CT
Parenchyma: neurosecretory Neurons/pinealocytes, glial cells
Developmental Sources of the pineal gland
from neural tube
capsule, Septa, stroma –> from head mesenchyme
Pinealocytes
- round nucleus
- highly branched processes
- axons are associated with blood capillaries
dark cells (type I) with secretory granules pale cells (type II) with few granules
granules contain melatonin
Glial cells of pineal gland
- modified astrocytes
- smaller than pinealocytes
- small and compact nucleus
Calcified secretions of pineal gland
- characterisitc feature of an aging pineal Gland
- presence of round, basophilic bodies
- called CORPORA ARENACA or BRAIN SAND
- concretions are derived from precipitation of Calcium Phosphate and Carbonates on carrier proteins
Melatonin
- induced by Darkness and inhibited by light
- regulates day and night biorythm –> circadian rythm
- Information about light from retina
- pineal Gland has role in adjusting to sudden changes in day length
- pineal Gland Plays role in altering emotional Responses due to reduced day length
- Melatonin regulates reproductive function in mammals by inhibiting activity of gonads
Peripheral endocrine Glands/cells that are dependent on hypophysis
follicular cells of thyroid Gland
zona fasciculata and zona reticularis of adrenal Cortex
GOnads
Peripheral endocrine Glands/cells that are Independent on hypophysis
- parafollicular cells of thyroid Gland
- parathyroid Gland
- zona glomerulosa of adrenal Cortex
- Medulla of adrenal Gland
- pancreas
- DNES
Thyroid gland
- two large lateral lobes connected by an ishtmus (pyramidal lobe)
- capsule of dense iriegular CT with trabelculae
- thyroid follicles
Development of thyroid gland
4th week:
endoderm –> thyroid diverticulum –> connected to tongue by thyroglossal duct
7th week:
Neural crest –> cells of ultimobranchial bodies –> towards thyroid Gland –> parafollicular cells
Thyroid follicle
- single layer of cuboidal epithelial cells on b.m.
- colloid in follicle lumen with THYROGLOBULIN
- capillary bed around follicles
- stores Hormones in an inactive form
folliculae (principal) cells
Parafollicular (C) cells
Follicular cells of thyroid
- cuboidal
- produce T3 and T4/thyroxine
- Tyrosine –> thyroglobulin + iodine –> T3 and T4 into blood
T3 and T4
- iodine containing Hormones
- T3 is metabolically active form
- regulate basal metabolic rate
- influence on growth and maturation of nerve tissue
secretion is regulated by TSH from anterior pituitary
Functional states of thyroid follicles
Hyperactive
- hihgh cuboidal or columnar cells
- decreased colloid
Hypoactive
- low cells
- accumulation of colloid
Parafollicular (C) cells
- small clumps between follicles or as individual cells lining
- never in contact with colloid
- secrete calcitonin
Calcitonin
- secreted by parafollicular cells
- is a polypeptide Hormone
- lowers Calcium blood Levels
- –> inhibiting osteoclastic Resorption
- –> stimulating osetoblastic activity
dependend on blood Calcium level
Parathyroid glands
- located on back of thyroid
- derived from 3rd and 4th branchial pouches (endoderm)
capsule
stroma: loose CT and fat cells!
Parenchyma: epithelial cells in cords
Cells of parathyroid gland
Chief cells
- pale staining (low activity)
- dark staining (secrete parathyroid Hormone)
Oxyphil cells
- differentiate at puberty
- Function unknown
Parathyroid Hormone (PTH)
raises blood Calcium Level
- -> increasing osteoclastic Resorption
- -> increasing renal tubular Reabsorption of Calcium
- -> promoting Absorption of Ca in small inestine
controlled by blood Calcium level
Adrenal glands
- in perirenal fat
capsule
stroma: loose CT
Parenchyma: epithelial cells
Cortex and medulla
Developmental Sources of the adrenal glands
Cortex: Mesoderm
Medulla: neural crest
Zones of the adrenal cortex
von außen nach innen
zona glomerulosa
zona fasciculata
zona reticularis
Zona glomerulosa
- arranged in ovoid clusters and curved columns
- cells are small and columnar
- Cells have sER, Golgi, Mitochondria
- ALDOSTERONE
Aldosterone
- produced on zona glomerulosa
- a mineralcorticoid
- to maintain blood electrolyte balance and blood pressure
- regulated by renin-angiotensin-aldosterone system
Zona fasciculata
- cells are large
- cells are polyhedral
- arranged in Long straight Cords
- cells have sER, mitochondria, Golgi, numerous Lipid droplets!!
- CORTISOL AND CORTICOSTERONE
Cortisol and corticosterone
- produced in zona fasciculata
- Glucocorticoids from Cholesterol
- regulating Glucose and FA metabolism
- Response to stress
controlled by pituitary ACTH
Zona reticularis
- Cells are arranged in anastomosing Cords
- sER, mitochondria, relatively few Lipid dropltes, lipofuscin Pigment granules
- ANDROGEN AND ANDROGENS
Adrenal medulla
- large epithelioid cells
- organized in short interconnecting Cords
- cells are called chromaffin cells
- cells have granules
- granules contain catecholamines
Populations of medullary chromaffin cells
Large dense core vesicles –> secrete norepinephrine
Vescles that are smaller —> Epinephrine
Catecholamines
- acute Response to stress (prepare Body for flight or fight) –> acceleration of heart rate, ling Action, contriction of blood vessels
Control by preganglionic sympathetic innervation
Chromaffin system
- cells of adrenal Medulla
- ->do not have axons or axins
- -> behave like postganglionic sympathetic Neurons
- Neurons of sympathetic ganglia are also chromaffin cells
- Paraganglia
DNES
adrenal Medulla Pancreatic islets Parafollicular cells Renal JUGA cells Leydig cells Endocrinocytes in GI, UGS, respiratory epithelium
DNES cells
- from neural crest or endoderm
- rER, sER, granules
- secrete polypeptides and protein Hormones
- act in paracrine or endocrine way
- no direct Innervation
- no contact with luminar Surface
