WEEK 2: PITUITARY GLAND Flashcards
State the anatomical position of the pituitary gland
It is found in the sella turcica ( hypophyseal fossa) of the sphenoid bone
Name the main parts of the pituitary gland
*anterior pituitary gland ( adenohypophysis)
*Posterior pituitary gland ( neurohypophysis)
*Infundibulum ( Pituitary stalk)
What is the other name for pituitary gland?
Hypophysis cerebri or hypophysis
Describe the blood supply to the pituitary gland
Superior and Inferior hypophyseal arteries which are branches of the internal carotid artery
Describe the embryology of the pituitary gland
A glandular diverticulum grows upwards from the ectoderm of the primitive buccal cavity and meets with a similar neural outgrowth from the floor of third ventricle.The stalk of the Rathke’s pouch disappears but the neural outgrowth persists at 6-8 weeks.
Where does the ectodermal diverticulum originate from that forms the Anterior pituitary gland?
Primitive buccal cavity
Between the anterior and posterior part of the Rathke’s pouch, which one proliferates more
Anterior part which forms the pas distalis
Describe the vascular link between the hypothalamus and the anterior pituitary
How the hypophysiotropic hormones reach pituitary gland and pituitary hormones reach target organs
1.Hypophysiotropic hormones produced by neurosecretory neurons in the hypothalamus enter the hypothalamic capillaries
2.These hypothalamic capillaries rejoin to form the hypothalamic - hypophyseal portal system, a vascular link to the anterior pituitary
3. The portal system branches into the capillaries of the anterior pituitary
4. The hypophysiotropic hormones,which leave the blood across the anterior pituitary capillaries, control the release of anterior pituitary hormones
5.When stimulated by the appropriate hypothalamic releasing hormone,the anterior pituitary secretes a given hormone into these capillaries
6. The anterior pituitary capillaries rejoin to form a vein, through which the anterior pituitary hormones leave for ultimate distribution throughout the body by the systemic circulation
List the cell types under the acidophils, basophils and chromophobes
Acidophils:lactotropes( Prolactin secreting cells)
Somatotropes( Growth Hormone secreting cells)
Basophils: Gonadotropins( FSH and LH secreting cells)
Thyrotropes (TSH secreting cells)
Corticotropes( ACTH releasing cells)
Which part of the pituitary gland is an extension of the hypothalamus?
Pas nevosa/ posterior pituitary gland
What parts of the pituitary gland are formed by the neural outgrowth?
Infundibulum,Pas nevosa and median eminence
Which cells found in the Anterior pituitary gland have long projections and with gap junctions?
Folliculostellate cells
What part of the anterior pituitary gland contains numerous colloid containing cysts( Rathke’s cysts), lined with cuboidal epithelium and are remnant of Rathke’s pouch?
Pas intermedia
What parts of the pituitary gland is formed by the Rathke’s pouch?
Anterior pituitary (Pas distalis,pas intermedia,pas tuberalis)
Where does the neuro ectodermal diverticulum that forms the posterior pituitary gland originate from?
Hypothalamus ( diencephalon)
All the hormones of the anterior pituitary gland are tropic hormones except which one?
Prolactin
Describe how the hypothalamus and posterior pituitary act as a unit to secrete vasopressin and oxytocin
The Pars nevosa contains axons which originate from cell bodies in the hypothalamus and pass to the posterior pituitary by the hypothalamo- hypophyseal tract and the infundibulum stalk.These nerve fibers carries the secretory granules consisting of oxytocin and vasopressin which are synthesized by the neural bodies in the hypothalamus. Both of these hormones are produced in the supraoptic and paraventricullar nuclei, but a single neuron can produce only one of these hormones.
The secretory granules are stored in the neuronal terminals in the posterior pituitary.
*Each neuronal terminal can only store one either oxytocin or vasopressin at a time ,thus allowing each hormone to be released independently as needed.
*The secretory granules are release via exocytosis after stimulating by the hypothalamus
Describe the stimulatory pathway for oxytocin or vasopressin secretion by the hypothalamus
The hormonal release is triggered in response to action potentials that originate in the hypothalamus cell body and sweep down the axon to the neuronal terminals in the posterior pituitary.As in any other neuron,action potentials are generated in these neurosecretory neurons in response to synaptic input to their cell bodies.
How can one different the 3 cell types in histology diagram of the anterior pituitary gland?
Acidophils: more pinkish
Basophils: blueish/ purplish
Chromophobes: no staining
How is the hypothalamic- hypophyseal portal system unique?
It involves an unusual capillary to capillary connection.
1.Internal carotid artery ( artery)
2.Superior hypophyseal arteriole ( arteriole)
3.capillary plexus. ( Capillary)
4. Hypophyseal portal vein ( vein)
5. Capillary plexus( capillary)
6. Venule. ( Venule)
7. Normal circulation
What is a portal system?
Is a vascular arrangement in which venous blood flows directly from one capillary bed through a connecting vessel to another capillary bed.
State the functions of Vasopressin
*It conserves water during urine formation by the kidney nephrons( antidiuretic effect)
*It causes contraction of arteriolar smooth muscles in regulating blood pressure (increase blood pressure)
State the functions of oxytocin
- Stimulates contraction of uterine smooth muscles to expel the infant during birth
*Promotes ejection of milk from mammary glands during breastfeeding - Facilitates bonding between mother and infant (love hormone)
NoTE: folliculostellate cells have a phagocytic and supporting functions
Chromophobes are also supporting cells
# They are both non secretory
State the 6 hormones produced by the anterior pituitary gland
TSH(Thyroid stimulating hormone)
FSH(Follicle stimulating hormone)
LH (Luteinizing hormone)
ACTH( Adrenocorticotropic hormone)/ corticotropin
GH(Growth hormone)
Prolactin
Name the 3 main cell types found in the pituitary gland ( Pars distalis) and their %
Acidophils(. 40%)
Basophils (10%)
Chromophores(50%)
Folliculostellate cells
NOTE: Acidophils+ Basophils together are collectively referred to as Chromophils
State the functions of FSH
*Stimulates sperm production in males
* Plays a role in growth and development of ovarian follicles / egg development
*Stimulates secretion of estrogen hormone by the ovaries
Name the two hormones which are stored and secreted in the Pars nevosa
Vasopressin (ADH)
Oxytocin
State the functions of Luteinizing hormone
- control sex hormone secretion in both male and female
- Responsible for ovulation
*Stimulates formation of the corpus luteum
Lists the pituitary gland disorders?( Not anomalies)
Dwarfism- more genetic and can be inability to use growth hormone
Gigantism - high cortisol
Cushing’s disease- high GH
Acromegaly -high GH
Where are ADH and oxytocin produced?
In the hypothalamus supraoptic and paraventricullar nuclei by the neurosecretory neurons
What are FSH and LH collectively referred to as?
Why?
Gonadotropins
Because they control the secretion of the sex hormones by the gonads
What is the function of prolactin?
Enhances breast development
*Enhances milk production ( lactation) after giving birth
What are functions of pituicytes?
They are supporting cells in the posterior pituitary
State the functions of Adrenocorticotropic hormone (ACTH)
*stimulates the adrenal gland to release cortisol which
Regulates blood glucose, maintains blood pressure and regulates metabolism as a stress hormone
* Plays a role in how the body respond to stress
NOTE: Sinusoidal capillaries are found within the clusters of the basophils and acidophils in the anterior pituitary gland
How are the 3 components of POMC produced?
ACTH: in response to UV light from the sun
Alpha MSH: keratinocytes in the skin
* Alpha MSH promotes dispersal from nearby melanocytes of the pigment melanin to cause tanning
* Appetite suppressing neurons in the hypothalamus secretes alpha MSH control food intake
Endorpin: are endogenous opiate that suppress pain
* Opiate
State the functions of TSH
*stimulates secretion of thyroid hormone
*Stimulates growth of thyroid gland
Name 2 hormones that regulate the synthesis and secretion of Growth hormone
GHRH
GHIH( Somatostatin)
How does GH promotes growth of soft tissues?
Stimulating hyperplasia and hypertrophy
How does stress results in stunted growth and weight loss?
Prolonged stress induced cortisol exerts potent antigrowth effects such as promoting protein breakdown, inhibiting growth in the long bones and block growth hormone secretion
The Rathke’s pouch has 3 parts(anterior, posterior and cleft in between).State specifically what part of the Anterior pituitary gland are formed from which part?
Anterior -Pas distalis
Posterior -Pas intermedia
cleft- interglandular cleft
State the function of Pars intermedia
Secretes POMC( Pro-opiomelanocortin)
Has: ACTH, alpha MSH, beta endorpin and beta- lipotropic
Alpha MSH stimulates prolactin release
Name the abnormal growth patterns associated with growth hormone release
*Deficiency: dwarfism
*GH excess: Acromegaly -disproportioned growth usually due to hypersecretion of Growth Hormone after adolescence ( thick bones and soft tissues especially connective tissue and skin , proliferate)
*Gigantism: rapid growth in height without distortion of the body in childhood before epiphyseal plates close.
Name the large precursor in which ACTH is synthesized as a part of
Pro- opiomelanocortin(POMC)
Page 698-699 Major Hormone Summary
What are the functions of herring bodies in the posterior pituitary
Contain neurosecretory granules
State the two main hormones produced by the Pars Tuberalis
FSH and LH
NOTE: it has cuboidal basophilic cells
Relations to the pituitary gland
Anterior: sphenoid sinus
Posterior: posterior intercarvernous, dorsum sellae, basilar artery and the pons
Superior: Diaphragm sellae. Optic chiasm
Inferior: sphenoid sinus
What structure forms at 4 weeks of foetal development via thickening of cells in the oral ectoderm which forms the Rathke’s pouch?
hypophyseal placode
Name the structures that form the Pars Nevosa
Axons
Capillaries
Herring bodies
Pituicytes
