Anatomical Basis of Homeostasis II: Endocrine glands Flashcards
List characteristics of peptide/protein hormone cell
- Lots of RER
- Golgi
- Secretory vesicles – vary in size
List characteristics of Steroid-secreting cells
Lots of smooth ER
Abundant mitochondria
Lipid droplets
What is function of pituitary gland?
Major interface between brain and the endocrine system.
Describe anatomy of pit gland
- rounded body, about 1 cm dia.
- connected to floor of III ventricle by the infundibulum (pituitary stalk), just posterior to the optic chiasma
- lies in a depression in the body of the sphenoid bone = pituitary (hypophyseal) fossa - also called the sella turcica
What is the pit fossa lined and covered over by?
- dura
- covered over by a sheet of dura (diaphragma sellae), pierced by the pituitary stalk
Name the 2 parts of the pit gland
- Adenohypophysis (Anterior pituitary)
2. Neurohypophysis (Posterior pituitary)
Name parts of ant. pit
- pars distalis
- pars tuberalis
- pars intermedia
Name parts of pos. pit
- pars nervosa
- infundibulum (neural stalk)
Where does the ant. pit dev from?
- an upgrowth of ectoderm/ endoderm from the embryonic oral cavity (remnant of Rathke’s Pouch).
Where does post. pit dev from?
- downgrowth from floor of the diencephalon in brain.
What does post. pit consist of?
- axons of modified neurones, supported by a population of glial-like cells = pituicytes.
- Cell bodies of these neurones lie in the supraoptic and paraventricular nuclei of the hypothalamus - Hormones syn in nuclei travel down axons
List functions of ADH/vasopressin
- increases water retention in kidney.
- raises blood pressure by contracting vascular smooth muscle cells (at high concentrations).
List functions of oxytocin
- contraction of smooth muscle cells, esp. of uterus during childbirth; and myoepithelial cells of mammary gland during lactation.
- bonding both socially and sexually
What types of hormones are ADH and oxytocin and how many aa?
- peptides
- 9
Where are ADH + oxytocin made and how are they released?
- made in cell bodies of neurones (in hypothalamus) initially as a larger protein, subsequently cleaved to yield the hormone and a binding protein (neurophysin).
- transported down axons to terminals
- released from terminals into fenestrated capillaries on stimulation of the cell bodies in the hypothalamus
– fenestrations allow plasma in blood to come into contact with cells lying underneath capillary endo.
What are Herring bodies?
- accumulations of hormone within the axons
– secretory granules containing hormone
What is in the pars distalis region?
Cords of cuboidal/polygonal epithelial secretory cells clustered around large, fenestrated sinusoids.
What are the cells in the pars distalis region trad classed into and how do they stain?
- Acidophils (stain pink/orange with H & E)
- Basophils (stain blue with H & E)
- Chromophobes (stain poorly)
List 2 types of acidophils and hormones they secrete
- Somatotrophs - Growth Hormone
- Mammotrophs - Prolactin
List 3 types of basophils and hormones they secrete
Thyrotrophs - Thyroid Stim. Hormone (TSH)
Corticotrophs - Adrenocorticotrophic hormone (ACTH)
Gonadotrophs - Follicle Stim. Hormone (FSH), Luteinizing hormone (LH)
What is function of chromophobes?
- either reserve cells/stem cells or resting cells that have lost their secretory granules
– replace acidophils and basophils when they die
Describe characteristics of somatoptrophs in EM
packed with granules of moderate size
Describe characteristics of thyrotrophs in EM
have smaller granules mostly at the periphery of the cell
Describe characteristics of Gonadotrophs in EM
larger cells, variable sized granules
Describe characteristics of Corticotrophs in EM
- paler cytoplasm under e.m.
- sparse granules located at periphery.
What is located in pars tuberalis?
Thin layer of cuboidal cells, mostly gonadotrophs.
What is located in pars intermedia?
- Cells (basophilic) secrete Melanocyte stimulating hormone
– increases skin pigmentation, but physiological role in man is uncertain.
Describe reg of secretion of ant. pit
- regulated by neuroendocrine cells of the hypothalamus whose axons project to the median eminence.
- discharge releasing hormone into capillaries of the pituitary portal vessels.
- these in turn end in capillaries bathing the cells of the anterior pituitary
– RH stim release of hormones from acidophils and basophils.
What can happen as a result of trauma to the stalk?
loss of hormonal control of pit
What hormones do the hypothalamic hormones stimulate release of?
- Thyrotropin releasing hormone (TRH) – stim release of thyroid hormone
- Gonadotropin releasing hormone (GnRH) – LH + FSH release
- Growth hormone releasing hormone (GRH) - GH
- Corticotropin releasing hormone (CRH) - ACH
What hormones do the hypothalamic hormones inhib release of?
- Somatostatin (blocks GH and TSH release)
- Dopamine (blocks prolactin release)
Why is it a portal system?
- Need less releasing hormone – short distance between hypo and pit – no need for circ around body before it arrives at destination
- More immediate response
- Can use the same hormone again locally elsewhere for other purposes. e.g. somatostatin from Islets of Langerhans blocks release of insulin and glucagon
Describe anatomy of thyroid
- 2 pear-shaped lateral lobes connected by a midline isthmus
- intimately associated with the trachea
- isthmus lies at level of 2nd-4th tracheal rings
- isthmus may be joined to the hyoid bone by a fibrous cord, a remnant of the embryological thyroglossal duct
Describe dev of thyroid
Arises from a diverticulum (outpouch) in floor of the primitive pharynx just caudal to the site of the future tongue
– thyroglossal duct
- opens at base of tongue as the foramen caecum
- connection to pharynx eventually lost, isolating the gland
Describe cells of the thyroid
- Thyroid epithelial cells are organized into follicles.
- secrete thyroglobulin (large glycoprotein, mw 660Kd)
- accumulates in the follicles as “colloid”
Describe storage of iodine in thyroid
- oxidized to Iodine
- covalently attached to the tyrosines of thyroglobulin within the lumen of the follicle
Describe how iodine is released from thyroid
- On stimulation by TSH (from the anterior pituitary)
- follicular cells endocytose (Take up) the iodinated thyroglobulin
- break it down in lysosomes
- release the iodinated tyrosine derivatives as tetra- iodothyronine (thyroxine) (T4) or tri-iodothyronine (T3)
Describe structure and location of Thyroid C cells/Parafollicular cells
- scattered cells found within the follicular epithelium or as clusters between the follicles.
- larger, more rounded than the follicle cells
Describe function of Thyroid C cells/Parafollicular cells
secrete calcitonin (inhibits Ca++ mobilization) = release Ca from bone
What is the neural crest?
- all NS pop of cells derived from it
- migrate to thyroid during development
Describe anatomy of parathyroid glands
- 2 pairs of parathyroid glands, each about the size of a pea
- Usually found on or embedded in the posterior border of the lateral lobes of the thyroid gland, but position is somewhat variable (esp. inferior parathyroids)
- No functional significance in the association between thyroid and parathyroid glands
Describe cells of parathyroid glands
- Densely-packed, small Chief (or principal; P) cells arranged in irregular cords around blood vessels (C).
- secrete parathyroid hormone (parathormone)
stimulates calcium mobilization. - There is a second, minor population of larger, eosinophilic oxyphil cells (O), of unknown function (lack secretory granules)
Describe anatomy of adrenal glands
- Pyramidal (right) or crescent- shaped (left) bodies in contact with the upper poles of the kidneys
Separated from kidneys by connective tissue but surrounded by the renal fascia.
Describe development of adrenal glands
- 2 distinct parts with different embryonic origins:
- Cortex - derived from the coelomic epithelium (mesothelium) lining the posterior abdominal wall
- Medulla - derived from an adjacent sympathetic ganglion, which was itself derived from neural crest
Describe cells of adrenal cortex
- Cells secrete steroids - have lots of smooth endoplasmic reticulum (SER) and lipid droplets (containing cholesterol) so appear pale and “frothy” in histological sections.
- Cells are organized into 3 zones:-
1) Zona glomerulosa (G)
2) Zona fasciculata (F)
3) Zona reticularis (R)
Describe cells of zona glom
- cells arranged in rounded clusters, surrounded by capillaries
- secrete mineralocorticoids – mainly aldosterone (95%)
- target : Kidney (Na+ retention by distal convoluted tubule) regulated by renin/anigiotensin system
Describe cells of zona fasciculata
- cells arranged in straight cords, running radially
- secrete glucocorticoids – mainly cortisol (95%)
- regulate : general glucose, lipid and protein metabolism
- secretion regulated by ACTH
Describe cells of Zona reticularis
- cells arranged in irregular cords
- secrete some glucocorticoids and small quantities of sex steroids (mostly weak androgens)
- functionally insignificant (?)
Describe structure of adrenal medulla
- modified sympathetic ganglion
- large, polyhedral cells arranged in clumps or cords
- resemble “axon-less” ganglion cells
Describe islets of Langerhans
- Small, rounded clusters of cells,
- 100-200 µm dia.,
- embedded within the exocrine pancreas
- The cells are smaller and more-lightly stained than the exocrine cells, and arranged in irregular cords around capillaries.
List cells of IOL and what they secrete
- A or alpha cells (~20%) secrete glucagon
- B or beta cells (~70%) secrete insulin
- D or delta cells (5-10%) secrete somatostatin
- F or PP cells (1-2%) secrete pancreatic polypeptide
- Other, minor cell types secrete vasoactive- intestinal peptide (VIP), substance P, motilin, serotonin, etc.
Describe cells of Diffuse neuroendocrine system
- Scattered cells found especially in the gut and respiratory system
- Secrete amines or peptides with hormone-like (promote homeostasis) or neurotransmitter activity (promote sm contraction) e.g. gastrin, CCK, secretin, enteroglucagon, serotonin etc
- Often secrete locally (paracrine)
What do cells of Diffuse neuroendocrine system have ability to do and how?
- Cells often have ability to take up and decarboxylate amines
– Old name – APUD cells (amine precursor uptake and decarboxylation) - Possess synaptic vesicle-like structures or neurosecretory-type granules (dense core granules)
– released by exocytosis in response to external stimuli - Derived from neural crest
- Produce hormones in vesicles
