Embryology and anatomy Flashcards
Which glands have an entirely endocrine function?
- Thyroid
- Pituitary
- Pineal
- Parathyroids
- Adrenals
What are the medulla and cortex of the adrenal glands formed from?
The Medulla is from the neuroectoderm and the cortex is from the mesoderm (mesonephros)
What forms the thyroid and parathyroids?
The thyroid is formed from the floor of the mouth.
The parathyroids from the pharyngeal arches
Where is the hypothalamus located?
Beneath the thalamus, at the floor of the 3rd ventricle
Describe the hypophysis
Link between the CNS and the hormonal activity of the body
Has 2 regions= Adenohypophysis and neurohypophysis
Where is the hypophysis located?
Ventral to the hypothalamus
- It is in a bony recess = hypophyseal fossa. (Sella turcica= the fossa and surrounding processes)
- Dura forms the diaphragm through which the hypophyseal stalk projects to connect between hypothalamus and hypophysis
- NO subarachnoid space in the fossa as it needs to be outside the BBB
What are the different regions of the adenophypophysis?
Pars tubercularis= monitors melatonin levels and it located around the stalk
Pars intermedia= Surrounds neurohypophysis in equidae and carnivores
Pars Distalis= main secretory region, collection of cells with each secrete a different hormone
What part of the adenohypophysis is absent in horses?
The cleft of hypophysis
Describe the anatomy of the neurohypophysis
- Infindubulum= the stalk. It attaches to the tuber cinereum of the hypothalamus (nerves run through it)
- Neural lobe= contains projections from neurons in the hypothalamus
How is the adenohypophysis linked to the hypothalamus?
- Hormonally
- Has a capillary portal system
- Capillaries go down into adenophypophysis where hormones are released into bloodstream.
Describe how the neurohypophysis is linked to the hypothalamus
- Neurologically
- Cell bodies located in the hypothalamus, axons extend down the stalk into the neurophypophysis
Describe the pars intermedia
- Produces MSH in the fetus
- In ages horses tumours here= PPID: excess production of both MSH and ACTH as they both have the same precursor- pro opiomelanocortin.
What happens in Rathke’s pouch doesn’t differentiate into glandular tissue?
- Adenohypothysis doesn’t develop and instead pituitary cysts develop
- This is what causes pituitary dwarfism in German shepherds
What causes pituitary dwarfism in German shepherds?
The failure of Rathke’s pouch to differentiate into glandular tissue
Describe GnRH cell migration
-They start in the olfactory bud-> migrate to the hypothalamus
Describe the development of the neurohypothysis
- Downgrowth of ectoderm of the forebrain
- Retains its connection with the brain via the infindibulum
Describe the capillaries around the hypophysis
- They are fenestrated allowing free flow of molecules (espesh hormones) into the circulation
- No tight jundctions
- Results in BBB being absent from these parts of hypothalamus and hypophysis
Where are releasing factors produced? Give two examples
- in the hypothalamus
- CRF= Cortisol releasing factor
- TRF= Thyroid stimulating hormone
Where is the pineal gland located?
In the caudo dorsal area of the diencephalon
What is the epithalamus?
The pineal gland
What does the pineal gland control?
- Circadian rhythms
- Controls breeding season
- Varies in size between species
What does the pineal gland produce and how does it get its information?
- Gets information about day length from visual tracts
- Produces and secretes melatonin
What are the affects of melatonin?
- Moderates sleep patterns
- Important in annual breeders ( inhibits/ stimulates repro cycles dependant on whether long or short day breeders)
What measures the melatonin levels?
Pas tuberalis
