Flashcards in Chapter 13 - Endocrine system Deck (117):
Endocrine system consists:
- Of ductless glands
- Endocrine cells, isolated in the epithelial lining of the digestive tract and in the respiratory system
- Richly vascularized so that the hormones easily can enter the blood stream
- Regulates metabolic activities in certain organs and tissues of the body, thereby helping to bring about homeostasis
- Produces slow and diffused effect via hormones, whoch are released into the blood stream to influence target cells at remote site
Endocrine glands are:
- Pineal body
- Pituitary gland
- Thyroid gland
- Parathyroid glands
- Suprarenal glands
Endocrine glands are ductless, while the exocrine glands
Empty their secretions in a duct system and exert only local effect
Chemical messngers that are produced by endocrine glands and deliverd by the blood stream to target cells or organs
Most homones elicit several effects on their target cells:
- Short-term effects
- Long-term effects
Hormones are classified into 3 types based on their composition:
1. Proteins and polypeptides
2. Amino-acid derivates
3. Steroid and fatty acid derivates
Proteins and polypeptides
- Mostly water-soluble
> Follicle-stimulating hormone (FSH)
- Mostly water-soluble
Steroid and fatty acid derivates
- Mostly lipid-soluble
- The hormons binds on specific receptors on (or in) the target cell.
- The binding of a hormone to its receptor communicates a message to the target cell innitiatingsignal transduction, or translation of the signal into biochemical reaction.
Where does the thyroid and steroid hormons binds to on the cell?
They bind to the cytoplasmicsurface
- Cyclic guanosine 3',5'-monophosphate (cGMP)
- Metabolites of phosphatidylinositol
- Caclium ions
- Sodium ions (in neurons)
Which receptors use G proteins to activate a second messenger, which elicites a metabolic response?
> Thyroid-stimulating hormone (TSH)
Which hormones use catalytic receptors taht activate protein kinase to phosphorylate target proteins?
- Growth hormone
Positive feedback mechanism
Travels to the endocrine gland, and initiates an increase in hormone secretion
Regulation of the endocrine glands maintains homeostasis
What happens with the hormone when they reach their target cells?
They become permanently inactivated in their target tissue; additionally they may be degraded and destroyed in the liver and kidneys
Pituitary gland, or hypophysis.
- Endocrine glad
- Composed of portions derived from the oral ectoderm and from neuronal ectoderm
- Produces hormones that regulates growth, metabolism, and reproduction
Subdivions of the pituitary gland:
Develops from an rvagination of the oral ectoderm (Rathke's pouch) that lines the primitive oral cavity (stomadeum)
Develops from neural ectoderm as a downgrowth of the diencephalon
The cellular constituens and the function of the adenohypophysis and neurohypophysis is
Different, because of the different embryological origin
Location of the pituitary gland
- Below the hypothalamus
- Sits in the hypophyseal fossa, a bony depression in the sella turcica of the sphenoid bone that is lined by the dura mater, called diaphragma sellae
What controls the secretion of nearly all of the hormones produced by the pituitary?
Subdivision of the pituitary gland, hypophysis:
> Pars distalis (pars anterior)
> Pars intermedia
> Pars tuberalis
> Median eminence
> Pars nervosa
Blood supply of the pituitary gland
- The hypophyseal poratl system of veins delivers neurosecretory hormones from the primary capillary plexus of the median eminence to the secondary capillary plexus of the pars distalis
- The arterial supply is provided from two pairs of vessles that arise from the internal carotid artery
Superior hypophyseal arteries
- Supply the pars tuberalis and the infundibulum
- Form a capillary network, the primary capillary plexus, in the median eminence
Inferior hypophyseal arteries
- Primarly supply the posterior lobe
- Send a few branches to the anterior lobe
Hypophyseal portal veins
- Drain the primary plexus of the median eminence, which delivers it blood into the secondary capillary plexus, located in pars distalis
Primary capillary plexus and Secondary capillary plexus
- Both are fenestrated
Hypothalamic neurosecretory hormones
- Manufactured in the hypothalamus
- Stored in the median eminence
- Enter the primary capillary plexus
- Drained by the hypophyseal portal veins
- Course: goes through the infundibulum and connect to the secondary capillary plexus in the anterior lobe. Here the neurosecretory hormones leave the blood to stimulate or to inhibit the parenchymal cells
From where does the anterior lobe develop from?
A diverticulum of the oral ectoderm
What does the adenohypophysis consist of?
It consist of pars distalis, pars intermedia, and the pars tuberalis
What does the parenchymal cells of the pars distalis consis of?
What is another word for the anterior lobe of the pituitary gland?
What is the anterior lobe of the pituitary gland composed of?
cords of parenchymal cells that are surrounded by reticular fibers
> these fibers are surrounded by large sinusoids of the secondary plexuses
How is the endothelial lining of the sinusoid in the pars distlis, anterior lobe of the pituitary gland?
it is fenestrated
Parenchymal cells of the pars distalis that have an affinity for dyes are called chromophils
Parenchymal cells of the pars distalis that have not an affinity for dyes are called chromophobes
Acidophils and basophils
What types of cell are the acidophils and the basophils?
They are chromophils
Where are the acidophils and the basophils?
They are in the pars distalis, or the anterior lobe of the pituitary gland
- Secrete: somatotrophin (growth hormone)
- Stimulated by: SRH
- Inhibited by: Somatostatin
- Release: prolactin
> Estrogen and progesteron inhibit prolactin
> The release of prolactin is stimulted by Prolactin-releasing Factor (PRH) and oxytocin
What stimulates the release of prolactin from mammotrophs?
The release of prolactin is stimulted by:
- Prolactin-releasing Factor (PRH)
Granules of basophils:
Where are basophils ususally located?
at th periphery of the pars distalis, or the anterior lobe of the pituitary gland
- Secrete: Adrenocorticotropic hormone (ACTH) and lipotropic hormone (LPH)
> The secretion is stimulated by CRH
Adrenocorticotropic hormone (ACTH)
Stimulates cells of the suprarenal cortex to release their secretory products
- Embedded in the cords of the parenchymal cells at a distance from the sinusoids.
- Have secretory granules containing thyrotropin (TSH)
- Secretion is stimulated by: TRH
- Secretion is inhibited by: T4 and T3 in the blood
- Situated near the sinuses
- Secrete FSH and LH
- Secretion is stimulated by LHRH
- Secretion is inhoboted by various hormones that are produced by ovaries and testes
Who have less cytoplasm:
Answer: a. Chromophobes.
Chromophobes generally have less cytoplasm than the chromophils
Represent either nonspecific stem cells or partly degranulated chromophils
- Nonsecretory cells
- Unknown function
- Location: pars distalis
- Form gap junction with other folliculostellate cells
Where does the pars intermedia lie?
the pars intermedia lies between the pars distalis and the pars nervos
What contains cysts that are remants of Rathke´s pouch?
pars intermedia of adenohypophysis
- cuboidal, cell-lined, containing cyst
- remants of the ectoderm of the evaginating Rathke´s pouch
The pineal gland is
responsive to diurnal light and dark periods and is thought to inluence gonadal activity
Pineal gland =
What type of gland is the pineal gland (pineal body)?
What influence the secretion of the pineal gland (pineal body)?
the light and dark periods of the day
Where is the pineal gland (pineal body)?
it is a cone-shaped, midline projection from the roof of the diencephalon, within a recess of the third ventricle extending to the stalk that is attached to it.
The pineal gland (pineal body) measurements:
- 5-8 mm long
- 3-5 mm wide
- 120 mg
What covers the pineal gland?
the gland is coverd by pia mater, forming a capsule from which septa extend, dividing the pineal gland into incomplete lobules
How does blood vessels enter the pineal gland?
blood vessels enter the gland via the connective tissue septa
What types of cells are in the pineal gland and what are they composed of
the parenchymal cells of the gland are composed primarily of pinealocytes and interstitial cells
Pinealocytes (general definition):
pinealocytes are the parenchymal cells of the pineal gland that are responsible for secreting melatonin
- slightly basophilic
- contain synaptic ribbons
- they synthesize melatonin from tryptophan
- well developed cytoskeleton, composed of microfilaments, microtubules and synaptic ribbons
- have SER and RER
- numerous of mitochondria
Where are synaptic ribbons observed?
- pineal gland (pinealocytes)
- inner ear
When is melanocytes released?
- inhibits the release of growth hormone and gonadotropin y the hypophysis and hypothalamus, respectively
Melatonin´s effect on feelings:
it induces the feeling of sleepiness and, therefore, some individuals use it as a supplement to combat sleep disorders, mood disorders, and depression.
Interstitial cells (general def.):
interstitial cells of the pineal gland are believed astroglia-like/astrocyte-like cells
Where are corpora arenacea found?
(=brain sand) pineal gland
Corpora arenacea =
Corpora arenacea (brain sand)
- concreations of calcium phosphates and carbonates, which are deposited in concentric rings around an organic matrix
- appear in early childhood and increase in size with age
What innervates the pineal body?
postganglionic sympathetic nerves from the superior cervical region. as the axon enters the gland the myelin is lost and they synapse on the pinealocytes
norepineprine, released at the pinealocytes, controls production of melatonin
What controls production of melatonin?
norepineprine, released at the pinealocytes, controls production of melatonin
Which glands absence would be incompatible with life? and why
The absence of parathyroid gland is incompatible with life because parathyroid hormone (PTH) regulates the blood calcium levels
How many parathyroid glands do most people have?
Where is the parathyroid gland located?
on the posterior surface of the thyroid gland
Is the parathyroid gland enveloped?
yes. each parathyroid gland is enveloped in its own, thin, collagenous connective tissue capsule
What does PTH act on? and why?
- intestines (indirectly)
* to maintain the optimal concentrations of calcium within blood and interstitial tissue fluid
What does the parathyroid gland develop from?
the parathyroid gland develop from the third (becomes inferior parathyroid glands. they descend with thymus) and fourth (becomes superior parathyroid glands) pharyngeal pouches during embryogenesis
What does the parenchyma of the parathyroid gland consist of?
- chief cells
- oxyphil cells
- intermediate cells
Parathyroid gland measurements:
- 5 mm in length
- 4 mm wide
- 2 mm thick
- 25-50 mg
What does the septa of the parathyroid gland serve as?
the septa serve mainly to support the parenchyma and consist of cords or clusters of epithelial cells surrounded by reticular fibers, which also support the parenchyma and a rich capillary network
What does the connective tissue stroma of the parathyroid gland in older adults contain?
it can contain up to 60% adipose tissue
What does chief cells synthesize?
parathyroid hormone (PTH)
Parathyroid hormone manufacturing:
- its precusor, preproparathyroid hormone, is synthesized on ribosomes of the RER and rapidly cleaved as it is transported to the lumen of the RER to form proparathyroid hormone
Oxyphil cells (general def.):
are believed to be the inactive phase of chief cells
Where does the PTH bind?
PTH binds to the receptors on the osteoblast, signaling the cells to increase their secretion of osteoclast-stimulating factor = increasing bone resorption
What does the PTH controls when it comes to the gastrointestinal tract?
PTH controls the rate of calcium uptake in the gastrointestinal tract by indirectly regulating the production of vitamin D in the kidneys; vitamin D is necessary for intestinal uptake of calcium
Suprarenal (adrenal) gland (general def.):
suprarenal gland produce two different groups of hormone; steroids and catecholamines
Where are the suprarenal glands located?
- located at the superior poles of the kidneys and are embedded in adipose tissue
- they are retroperitoneal, located behind the peritoneum, and surrounded by connective tissue capsule that contains large amounts of adipose tissue
Which suprarenal gland is pyramid-shaped and sits on top of the kidney?
the right suprarenal gland
Which suprarenal gland is more crescent-shaped and lies along the medial border of the kidney?
the left suprarenal gland
Does the suprarenal cortex and medulla have the same origin?
- the suprarenal cortex arises from mesoderm
- the suprarenal medulla arises from the neutral crest
What does the suprarenal cortex produce?
- hormone called corticosteroids (cortisol and corticosterone), which are synthesized from cholesterol. The corticosteroids are regulated by ACTH
What secretes ACTH?
the anterior pituitary gland
What does the suprarenal medulla produce?
Blood supply to the suprarenal gland is provided by:
arteries from three separate sources:
* inferior phrenic arteries
* aorta, from which the middle suprarenal arteries originate
* renal arteries
what forms the subcapsular plexus?
- inferior phrenic arteries
- aorta, from which the middle suprarenal arteries originate
- renal arteries
Where does the superior renal arteries originate?
inferior phrenic arteries
Where does the inferior suprarenal arteries originate?
Where does the short cortical arteries arise from?
the subcapsular plexus
Where can we fins the short cortical arteries and the long cortical arteries?
Long cortical arteries:
pass unbranched through the cortex and into the medulla, where they form a network of capillaries. Thus the suprarenal medulla recieves dual blood supply:
- an arterial supply from the long cortical arteries
- numerous of vessels from the cortical capillary beds
Short cortical arteries:
- form a network of sinusoidal fenestrated endothelial walls
How is the suprarenal cortex divided:
the suprarenal cortex is divided into three zones (three classes of adrenocortical hormones) that produce three classes of steroids (without storing them)
What are the zones that the suprarenal cortex is divided in to:
- zona glomerulosa
- zona fasciculata
- zona reticularis
What are the three classes of adrenocortical hormones:
*all are synthesized from cholesterol, the major component of low-density lipoprotein