Endocrine embryology and anatomy Flashcards
Describe the process of a Sandwich ELISA
- Immobilise antibody being tested on a solid substrate/plastic well
- Add substrate, antigen (hormone) will bind
- Was to remove substances not bound to antibodies
- Add antibodies that will bind to antigen (hormone) and are already enzyme linked
- Wash to remove excess, unbound antibodies
- Add reagent that will change colour in presence of enzymes
- Measure degree of colour change to assess concentration of antigen (hormone)
Describe the process of radio-immuno assays
- Known concentration of hormone/antigen radiolabelled (iodine) bound by Ab to form Ab-hormone complex
- Unlablleded hormone being tested for added, competes with labelled hormone
- Resulting hormone-Ab-complexes precipitated using secondary Ab
- Radiolabelled measured
- Compare starting amount of radiolabelled to new level, can determine concentration of unknown hormone
What is the coefficient of variation?
SD/mean
What is diagnostic sensitivity?
The proportion of true positives correctly identified by a test
What is assay sensitivity?
The assay’s ability to detect a low concentration of a given substance in a biological sample. Is usually expressed as a concentration
What are the advantages of disadvantages of RIAs?
- Cheap per sample
- But expire quickly
- Use of radioisotopes so not suitable for use in veterinary practice
- Good sensitivity
- But high coefficient of variation
What are the advantages and disadvantages of ELISA?
- Does not require radioisotopes
- Good sensitivity (not as good as RIA)
- Low CV
- More expensive
- Easier to do in practice
- Less kit wastage (do not expire as quickly as RIAs)
What are typical capillary features for endocrine organs?
- Fenestrated epithelium
- Obvious transcytosis
- No pericyte
Describe pericytes
- Cells crucial to blood-brain barrier
- Rounded nucleus vs crescent nucleus of endothelial cells
- Endothelial cells and pericytes share basement memrbanes
- Important in control of molecular transport between blood and CNS
List the glands that are entirely endocrine in function
- Hypophysis (pituitary)
- Pineal
- Thyroids
- Parathyroids
- Adrenals
List the glands that are partly endocrine in function
- Pacreas
- GIT
- Kidneys
- Testes
- Ovaries
- Placenta
- Thymus
- Heart
- Adipose
- Liver
Outline the embryological development of the brain
- Changes in cell shape and number lead to folding
- Neural plate invaginates along axis = neural groove
- Neural folds on each side fuse dorsally = tube
- Neural tube = tissues of CNS (brain rostrally, spinal cord caudally)
- Neuroepithelial cells bipotential = neurons or supporting neuroglial cells
- Closure of tube progresses antero-posteriorly
- Once closed, meninges and vertebral structures develop around it
Outline the development of the ganglia, cranial and spinal nerves
- Some neuroextodermal cells from lateral edges of neural plate not incoporated into tube
- Persist as neural crest dorsal to neural tube
- Separate into right and left columns
- Lots of potential for migration
What is the embryological origin of the pituitary gland?
- Adenohypophysis from roof of mouth
- Neurohypophysis from hypothalamus
What is the origin of the pineal gland?
CNS
What is the origin of the thyroid glands?
Floor of mouth
What is the origin of parathyroid glands?
Pharyngeal arches
What is the origin of the adrenal glands?
- Medulla from neuroectoderm
- Cortex from medoderm (mesonephros)
Describe the embryology of the adenohypophysis
- Upgrowth of ectodermof roof of developing mouth - Rathke’s pouch
- Buds off, hole in middle becomes left, migrates towards growing brain
- Cups around developing neurohypophysis
- Connection with mouth lost
- Differentiation to glandular tissue
- Initially round, flattened as comes into contact with the neurohypophysis
What is the consequence of Rathke’s pouch failing to differentiate into glandular tissue?
- Pituitary cysts instead of adenohypophysis
- Leads to pituitary dwarfism
- Otherwise are completely neurally competent
Outline GnRH cell migration
- Start in olfactory bulb
- Migrate to hypothalamus
Outline the embryology of the neurohypophysis
- Downgrowth of ectoderm of forebrain (diencephalong/future hypothalamus)
- Retains connection with brain via infundibulum
What are the 2 holes in the pituitary and where do they come from?
- Recess of third ventricle, dragged down by neurohypophysis
- Hypophyseal cleft from space in Rathke’s pouch
What are the structures of the diencephalon
- Epithalamus (incl pineal gland)
- Thalamus
- Hypothalamus
Where is the pituitary gland located?
- Hanging off the hypothalamus
- Within “dent” of skull in basisphenoid bone - sella turcica/hypophyseal fossa
- Dura forms diphragma sellae through while hypophyseal stalk conencts between hypothalamus and hypophysis
- Outside the BBB, no subarachnoid space in fossa
What are teh rostral, caudal, lateral and ventral relations of the hypophysis?
- Rostrally: optic chiasma
- Caudally: mammillary bodies
- Laterally: cavernous sinus
- Ventrally: sphenoid bone
Where are the venous sinuses and what is their function?
- Either side of base of skull
- Venous drainage from nasal chambers
What are the regions of the adenohypophysis?
- Pars tuberalis
- Pars distalis
- Pars intermedia
What is the function of the pars tuberalis of the adenohypophysis?
Monitors melatonin levels from pineal gland
Where is the pars intermedia in the adenohypophysis in equidae and carnivores?
Surrounds the neurohypophysis
Briefly outline the function of the pars distalis of the adenohypophysis
- Main secretory regions
- Different cells secreting different hormones
- Hormonally linked to hypothalamus via capillary portal system
Describe the structure of the neurohypophysis
- Infundibulum attached to tuber cinereum of hypothalamus
- Neural lobe
- Outpouching of brain, physically connected by nerve fibres (cell bodies in hypothalamus)
- Ends of axons (telodendria) from hypothalamus in neurohypophysis
What hormones are secreted by the neurhypophysis?
- Oxytocin
- ADH
Describe the structure of the pars intermedia
- Small area of tissue between 2 main parts of hypophysis
- Remnants of Rathke’s pouch
- Poduces MSH in foetus
Describe the location of the pineal gland
- Aka epithalamus/epiphysis
- Caudo-dorsal part of diencephalon
- Between tenecephalic hemispheres, cerebellum, and rostral colliculi
- i.e. small gland on back of thalamus
What is the function of the pineal gland?
- Controls diurnal rhythms
- Controls breeding seasons
- Secretes melatonin
Describe the parietal eye in reptiles
- Direct connection to pineal throguh hole in skull
- Sensitive to light, similar to eye
How are the functions of the pineal gland and the pars tuberalis linked?
Tuberalis receives melatonin from pineal gland and releases hormones in response
What are the 2 cell types found in the thyroid glands
- Follicular cells
- Parafollicular cells/C-cells
Describe the development of the follicular cells of the thyroid glands
- Downgrowth from pharyngeal endoderm of developing tongue
- At site of future foramen caecum
- Starts in middle of tongue, buds down
- Branches into Y shape
- Each arm will become left or right lobe
Describe the development of the parafollicular/ C-cells
- Dragged down with follicular cells
- Originate from ultimobranchial body
- Endoderm os most caudal pharyngeal pouch
- May also be of neural crest origin
What is the consequence of the embryology of the thyroid gland?
2 cells types not functionally linked present
What structeres are formed from the 1st pharyngeal pouches?
Eustachian tube, tympanic cavity
What structures are formed from the 2nd pharyngeal pouches?
Palatine tonsils
What structures are formed from the 3rd pharyngeal pouches?
- External parathyroids (III)
- Thymus
What structures are formed from the 4th pharyngeal pouches?
- Internal parathyroids (IV)
- C cells in thyroid
Describe the development of the parathyroids
- Develop from 3rd and 4th pharyngeal pouches
- Association with thymus leads to variable species location of external
- Parathyroid IV inside thyroid in most mammals
- As thyroid moves down, traps parathyroids but the tissues stay distinct throughout
Outline the development of the adrenal cortex
- From mesoderm between gonadal ridge and mesentery
- Cranial end of mesonephros
Outline the development of the adrenal medulla
From neural cres cells that produce sympathetic gandlia
Describe the foetal adrenal cortex
- Develops first
- Is distinct from adult cortex
- Produces corticosteroids in all species
- Converts placental progesterones to androgens to go back to placenta
- Regresses after birth, replaced by adult cortex
Outline the development of the pancreas
- Develops as outgrowth of foregut (dorsal and ventral)
- Langerhans islets bud off from developing exocrine pancreas
- Made up of glandular tissue from gut, connective tissue from mesenchyme
Describe the location of the thyroid gland
- Around cranial part of trachea
- Just caudal to larynx
What structures are found medially to the thyroid gland?
- Trachea
- Thyroid artery
- Recurrent laryngeal artery
What structures are found dorsally to the thyroid gland?
- Oesophagus
- Parathyroids
- Carotid sheath
Why might a thyroidectomy not remove all thyroid tissue?
Some thyroid tissue dotted all the way down and found in the lwoer neck and thorax in 60% of dogs
Describe the connection between the left and right thyroid gland lobes
- Some spcies have functional tissue
- Others joined by connective tissue
- Connective region called isthmus
What is the function of the follicular cells of the thyroid glands?
Production of thyroid hormones T3 and T4, storeed extracellularly
Describe the parafollicular cells of the thyroid glands
- Produce calcitonin
- Diffusely spread within gland
Describe the histological ppearance of the thyroid glands
- Large pockets of colloid surrounded by follicular cells
- Colloid is storage protein with thyroid hormones attached
- Parafollicular cells spread around gland
What is the function of the colloid in the thyroid gland?
- Extracellular storage of thyroid hormones
- Means there is no need for constant production and secretion of hormones from cells
What species have a functional isthmus in the thyroid gland?
- Pigs
- Humans
- Catte
What species have a connective tissue connection between the lobes of the thyroid glands?
- Dogs
- Cats
- Small ruminants
- Horses
Describe the thyroid gland of horses
- Connective tissue isthmus (non-functional)
- Very mbile gland
- Commonly changes size
Describe the appearance of teh porcine thyroid gland
- Arrowhead shaped
- Not very lobular appearance
- Very small “left” and “right”
Describe the appearance of the boxine thyroid gland
- Bumpy
- Connected by functional isthmus
- Lobes obvious and round
Describe the appearance of the canine thyroid glands
- Smooth
- Connective tissue isthmus
- Elongated lobes (oval rather than round)
Describe the appearance of the equine thyroid glands
- Connective tissue isthmus
- Round lobes
- Smooth
What is the cell type of the parathyroid glands?
Chief/principle cells
Describe the location of the parathyroids in the dog and cat
- IV deep in thyroid
- Exact position of III is variable
- Cranial lobes (dogs) or caudal lobes (cats)
- Often embedded under capsule and difficult to distinguish
Describe the parathyroid gland locations of ruminants
- External parathyroid close to bifurcation of common carotid artery
- Internal associated with thyroid gland
Describe the parathyroid gland locations in horses
- External near trachea ~15cm cranial of thoracic aperture, but very variable
- Internal around cranial part of thyroid or inside it
Describe the location of the adrenal glands
- Medial to cranial pole of kidney
- Some species variations
- Embedded in a little fat
What structures lie close to the adrenal glands?
- Kidneys
- Caudal vena cava (right adrenal)
- Aorta (left adrenal)
- Renal artery and vein
What are the layers of the adrenal cortex?
- Zona glomerulosa (outer)
- Zona fasciculata (middle)
- Zona reticularis (inner)
What is produced by the zona glomerularis of the adrenal cortex?
Mineralocorticoids
What is produced by the zona fasciculata of the adrenal cortex?
Glucocorticoids (and some androgens)
What is produced by the zona reticularis of the adrenal cortex?
Oestrogens, testosterone, some progesterone (and some glucocorticoids)
Describe the adrenal medulla
- Modified nercous tissue
- Arenal and noradrenaline procude here
Describe teh innervation of the adrenal medulla
- Innervated by preganglionic sympathetic fibres
- Post-ganglionic cells have no axons
- Release NT direclty from cell bodies
Describe the endocrine tissue of the pancreas
- Islets of Langerhans
- Alpha: glucagon
- Beta: insulin
- Delta: somatostatin
What is the function of the exocrine pancreas?
Production of digestive enzymes
Which species have a dorsal pancreatic duct?
Dog, horse, ox, pig
Which species do not have a ventral (right, main) pancreatic duct?
Ox, pig
Describe the pancreas in the horse
Right and left lobes fused
Describe the pancreas of the ox
Dorsal lobe fused at end of right, single duct for both “lobes”
Describe the pancreas of sheep and goats
Fused at end of left lobe, single duct for both lobes
Describe the pancrease of the pig
Complex pattern of fusion between right and left lobe
Outline the endocrine function of the GIT
- Produced by enteroendocrine (epithelial) cells in teh gastrointestinal mucosa
- ~20 cell types producing different hormones
List the gastrointestinal hormones
- Gastrin
- Secretin
- Cholecystokinin
- Serotonin
- Gastric inhibitory polypeptide
- Somatostatin
Name the avian endocrine glands
- Hypophysis (similar to mammals)
- Pineal gland
- Pancreas
- Thyroids
- Parathyroids
- Ultimobranchial bodies
Describe the endocrine features of the pancreas
- 3 different types of islets
- Dark islets (alpha cells)
- Light islets (beta cells)
- Mixed islets
Describe the structure thyroid and parathyroid glands of birds
- Not all physically bound together
- All located at thoracic aperture
- Craniolateral to syrinx
How is the blood supply to the thyroid arranged?
Double blood supply and venous drainage
Describe the blood supply to the thyroid
- Cranial thyroid artery (from common carotid)
- Caudal thyroid artery (from brachiocephalic trunk)
- Anastomose inside thyroid gland
Describe the venous drainage of the thyroid gland
- Thyroid veins
- Drain into internal and external jugular vein and brachiocephalic vein
Describe teh innervation of the thyroid gland
- Complete autonomic nerve supply, vasomotor only
- Sympathetic fibres from cranial cervical ganglion
- Parasympathetic fibres leave vagus at distal vagal ganglion
- Sympathetic and parasympthateic, axons travel together in cranial laryngeal nerve
- Only control blood supply, not release of hormones from gland
Describe the innervation of the parathyroids
Same as thyroids
- Autonomic only
- SNS: cranial cervical ganglion
- PSNS: vagus from distal vagal ganglion
- Travel together in cranial laryngeal nerve
- Control blood supply, not release of hormones
Describe the vascularisation of the parathyroid
Blood supply from local vessels
Describe the vascularisation of the adrenal glands
- Small arterial branches from neighboruing arteries (aorta, renal, lumbar cranial mesenteric)
- Enter adrenal, run through cortex
- Comes in radially, converges in middle, into veins and out
- Medullary central vein collects blood, drained into caudal vena cava
What is the consequence of the vascularisation of the adrenal gland
- Hormones in blood stream reach cortex first without having to go through medulla
- Medullary products can leave into circulation quickly and into systemic
Describe the innervation of the adrenal gland
- Sympathetic supply
- Can be considered sympathetic ganglion with post-ganglionic cells rather than post-ganglionic axons
Describe the venous drainage of the pancreas
Portal vein to liver
Describe the blood supply to the pancreas
Pancreatic branches of celiac, superior mesenteric and splenic arteries
