Histology of endocrine glands Flashcards
(40 cards)
Explain what hormones are and how they differ from neurotransmitters
Chemical signalling system, complementary to the nervous system
Resemble neurotransmitters
but:
Hormones - widespread action via blood - some hormones are simple amino acids like neurotransmitters or are produced by neurones.
Neurotransmitters - local via synapses
Explain the difference between an exocrine and endocrine gland
Exocrine = internal and external body surfaces via ducts Endocrine = hormones via blood
Exocrine gland has a central duct and the secretory granules collect and are released from apical surface of cell.
Endocrine gland released hormones from the basal part of the cell. These are delivered into sinusoids and blood capillary. Blood capillaries have fenestrated epithelium so the hormones come into direct contact with the blood.
What are the 4 classes of hormones and give an example of each?
- Amino acid derivatives e.g. adrenaline
- Small peptides e.g. ADH
- Proteins e.g. growth hormone, insulin
- Steroids e.g. cortisol, oestrogen
Give the characteristics of peptide and steroid secreting cells
Peptide:
- lots of rER
- golgi
- secretory vesicles
Steroid:
- smooth ER (steroids are lipid soluble so are collected from secreted as lipid droplets =)
- abundant mitochondria
- lipid droplets
Explain the anatomy of the pituitary gland
- rounded body about 1cm dia
- connected to floor of III ventricle by the infundibulum (pituitary stalk), just posterior to the optic chiasma
(The third ventricle is one of four connected fluid-filled cavities comprising the ventricular system within the mammalian brain.
Very small organ siting being the optic chiasma (where the brain sides swap over))
Where is the pituitary gland found?
- lies in a depression in the body of the sphenoid bone
- the pituitary fossa (hypophyseal)
What is the pituitary gland lined by?
Lined by dura and covered over by a sheet of dura, pierced by the pituitary stalk
Stalk hanging down is not surrounded by bone and the stalk can be sheered in trama. This has an affect on hormone production.
Give the two distinct parts of the pituitary and each part of this
Adenohypophysis (Anterior pituitary)
– pars distalis (major component)
– pars tuberalis (extension of the anterior pituitary in the stalk)
– pars intermedia (comes from the embryonic origin)
Neurohypophysis (Posterior pituitary)
– pars nervosa (major part)
- infundibulum (pituitary/neural stalk)
How does the anterior and posterior pituitary form?
Anterior =
Adenohypophysis - an upgrowth of ectoderm/endoderm from the embryonic oral cavity (Rathke’s Pouch - a cleft formed from the invagination of the anterior pituitary)
Posterior =
Neurohypophysis - downgrowth from floor of the diencephalon. This is the posterior part which grows downwards).
The two meet and fuse together.
Posterior pituitary:
- What does it consist of?
- Where does this originate from?
- Where do all these lie?
Consists of axons of modified neurones, supported by a population of glial-like cells, called pituicytes. The axons originate from two nuclei found in the hypothalamus shown below.
Cell bodies of these neurones lie in the supraoptic and paraventricular nuclei of the hypothalamus.
What are the two hormones produced in the pituitary gland?
➢antidiuretic hormone (ADH, vasopressin)
• increases water retention in kidney.
• raises blood pressure by contracting vascular smooth muscle cells (at high concentrations).
➢oxytocin
• contraction of smooth muscle cells, esp. of uterus during childbirth; and myoepithelial cells of mammary gland during lactation.
may also be involved in enhancing trust between individuals.
Give the anatomical aspect of ADH and oxytocin
- Both have 9 amino acids each and 2 are different
• made in cell bodies of neurones (in hypothalamus) as a larger protein, subsequently cleaved to yield the hormone and a binding protein (neurophysin). Binds when moving the hormones down the axon. When an action potential goes down the axon they are released.
• transported down axons to terminals
• released from terminals into fenestrated capillaries on stimulation of the cell bodies in the hypothalamus.
accumulations of hormone within the axons exist, called Herring bodies
Give details on the pars distils of the anterior pituitary
• Cords of cuboidal/polygonal epithelial secretory cells clustered around large, fenestrated sinusoids. Cords are a long chain of cells lying alongside a capillary. • Traditionally classified into: – Acidophils (red stain) – Basophils (stain blue) – Chromophobes (dont stain)
What are the hormones produced from cells of acidophils, basophils and chromophobes?
Acidophils:
- Somatotrophs producing growth hormone
- Mammotrophs producing prolactin
Basophils:
- Thyrotrophs producing thyroid stimulating hormone
- Corticotrophs producing adrenocorticotrophic hormones
- Gonadotrophs producing FSH and LH
Chromophones:
- either reserve cells or resting cells that have lost their secretory granules (stem cells for pituitary)
What is the pituitary the master gland?
Its products control many other endocrine glands.
Explain these two parts of the anterior pituitary:
Pars tuberalis:
• Thin layer of cuboidal cells, mostly gonadotrophs (producing LH and FSH.
Extension of the anterior pituitary around the outside of the stalk.
Pars intermedia:
- Region sitting between the anterior and posterior pituitary contains remanence of the Rathkes pouch
- Cells secrete melanocyte stimulating hormone which increases skin pigmentation, but physiological role in man is uncertain
Explain the regulation of secretion in the anterior pituitary
• Anterior pituitary is regulated by neuroendocrine cells of the hypothalamus whose axons project to the median eminence.
– discharge into capillaries of the pituitary portal vessels.
– these in turn end in capillaries bathing the cells of the anterior pituitary.
Network starts in base of hypothalamus and passes blood into lower part of anterior pituitary. This carries hormones called releasing factors which regulate the release of hormones from the anterior pituitary.
Give 6 hypothalamic hormones that either stimulate or inhibit the release of hormones from the anterior pituitary
Thyrotropin releasing hormone (TRH) Gonadotropin releasing hormone (GnRH) Growth hormone releasing hormone (GRH) Corticotropin releasing hormone (CRH) Somatostatin (blocks GH and TSH release) Dopamine (blocks prolactin release)
How is the hypothalamus key to the anterior pituitary?
Anterior pituitary is controlled by releasing hormones synthesised in the hypothalamus.
Why do we have a portal system with hormones?
- Need less releasing hormone (as transferred directly from the hypothalamus into pituitary)
- More immediate response (short distance to travel)
- Can use the same hormone again elsewhere for other purposes (hormones not released at high conc into general circulation)
Give the 4 anatomy points of the thyroid
- 2 pear-shaped lateral lobes connected by a midline isthmus (the midline)
- intimately related to the trachea
- isthmus lies at level of 2nd- 4th tracheal rings (vertebrae)
- isthmus may be joined to the hyoid bone by a fibrous cord, a remnant of the embryological thyroglossal duct
How does the thyroid develop?
• Arises from a diverticulum in floor of the primitive pharynx just caudal to the site of the future tongue (arises as a down growth from the throat)
– thyroglossal duct
– opens at base of tongue as the foramen caecum
– connection to pharynx eventually lost, isolating the gland
What is the cellular organisation of the thyroid?
– oxidized to Iodine
– covalently attached to the tyrosines of thyroglobulin within the lumen of the follicle
• On stimulation by TSH (from the anterior pituitary)
– follicular cells endocytose the iodinated thyroglobulin
– break it down in lysosomes
– release the iodinated tyrosine derivatives as tetra- iodothyronine (thyroxine) (T4) or tri-iodothyronine (T3). The name is determines by the number of iodine residues.
How does the tyro work to release tyrosine?
Cells take up and oxide iodine, iodine is released separately to thryoglobuin from the cell together with enzymes which attach the iodine resides to the tyrosine on the thyroglobulin. Some cells are taking up iodide and releasing it into the space and the immature thyroglobulin protein. Enzymes couple the iodine to the tyrosine resides in the thyroglobulin protein (many tyrosine residues in the protein). When the cell wants to secrete thyroid hormone, it takes up some thyroglobulin and fused the thyroglobulin with lysosomes to chop it up into amino acids and then if those are tyrosine they are released into the blood.
