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Y2S2 VETS2012 anatomy > L2 endocrine anatomy > Flashcards

L2 endocrine anatomy Flashcards

1
Q

Endocrine organs of the neck region

A

Thyroid
Parathyroid
Thymus

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2
Q

Embryology of the glands of the neck region

A

Neck endocrine organs are derived from the pharynx
Series of pharyngeal pouches form thymus, para-thyroids & part thyroid
Main part thyroid from median out-growth pharygeal floor

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3
Q

The early embryonic pharynx gives rise to a series of pouches

A
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4
Q
A
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5
Q

Function of the thyroid gland

A

Thyroid hormones increase metabolic rate, generating heat
2 hormones produced by follicular cells:
Thyroxine (T4)
Tri-iodothyronine (T3)
Hormone produced by follicular cells, then stored until required
Parafollicular (thyroid type C) cells produce calcitonin which increase uptake of Ca++ by the skeleton, thus lowering blood Ca++

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6
Q

Thyroid production of Formation & release of hormones

A

T3 (10%) & T4 (90%) are formed from iodinised tyrosine molecules in cuboidal follicular cells
They are stored outside the follicular cells in the follicular lumen as inactive form “thyroglobulin” which forms “colloid”
When required, released into circulation by follicular cells splitting off T3 or T4
If deficient in TSH or iodine, get build up of thyroglobulin in follicles & enlarged thyroids known as goitre in humans

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7
Q

Anatomy of the thyroid gland

A

Paired lobes, on lateral trachea, just caudal to larynx
Dark red in colour
May be connected via isthmus on ventral trachea
Species variation

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8
Q

Blood and nerve supply

A

Blood supply is species dependent
Usually from common carotid a.
Cranial thyroid a.
Caudal thyroid a. in some species (may have different origin)
Drains to internal jugular vein
Parasympathetic nerve supply via vagus
Sympathetic through cranial cervical ganglion (mostly vasomotor)

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9
Q

Histology of the thyroid gland

A

Consists of follicles lined by simple cuboidal epithelium which produces thyroid hormones
Cells stimulated by TSH (from anterior pituitary)
Active cells are tall cuboidal, with the follicular lumen small as hormone is secreted into the blood stream
Inactive cells are low cuboidal and lumen will be distended with colloid

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10
Q

, parafollicular or ‘C’ (clear) cells

A

Also, parafollicular or ‘C’ (clear) cells occur either singly, between follicular cells or clumped between follicles
Outer CT capsule and inner fibro-elastic capsule divides thyroid into lobules and contains blood and nerve supply

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11
Q

Thyroid histology

A
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12
Q

B. Parathyroid Glands

A

2 pairs small glands
On, or embedded in, thyroid tissue
Referred to as parathyroid III & IV from embryological origin (pharyngeal pouches) or external & internal parathyroid
Small pale pink structures , contrast against brick red of thyroid

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13
Q

Function of Parathyroid Glands

A

Produce parathyroid hormone (= parathormone) which raises blood calcium levels (opposite effect of calcitonin) by:
Osteoclastic resorption
↑ reabsorption of Ca++ & ↓ reabsorption of phosphate ions in kidneys
↑ Ca++ absorption from intestine
Parathormone is the main regulator of blood calcium levels while calcitonin provides fine adjustment

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14
Q

Dog, cat, small ruminants parathyroid

A

Recessed or embedded within the thyroid
Dog: parathyroid III may be in fascia of cranial pole of thyroid gland, parathyroid IV usually buried in thyroid parenchyma
Cat: parathyroid III in caudal thyroid, parathyroid IV in cranial thyroid
Watch out for them during surgery!
`

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15
Q

Ox parathyroid

A

Ox

Parathyroid III usually cranial to thyroid; parathyroid IV usually embedded in thyroid or between it & tracheal wall

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16
Q

Horse parathyroid

A

Parathyroid III much further caudal, near thoracic inlet

Parathyroid IV close to thyroid

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17
Q

Histology of the Parathyroid Gland

A 
Thin CT capsule
Dense plexus of sinusoidal capillaries
2 cell types:
Chief cells (=C)
synthesize & secrete parathormone
prominent nucleus, little cytoplasm
Oxyphil cells (=O)
less numerous
large & clumped
dense nucleus & eosinophilic cytoplasm with fine granules
(Fibrous septa = S)
18
Q

Thymus Gland

A

Large lymphoid organ, regresses with age
Thoracic and cervical parts
Produces immunocompetent T lymphocytes
Produces several hormones inc. thymosine, a hormone which stimulates lymphopoiesis

19
Q

Histology of thymus gland

A 
Capsule (C)
Cortex (Cx)
Packed with maturing T cells
Medulla (M)
Lobes & lobules
Interlobular septa (S)
Hormone producing epithelial cells line capsule, coat septa & capillaries
20
Q

Ox: thymus gland

A

extensive in calf, both cervical and thoracic component

21
Q

horse thymus

A

less extensive than calf, may have small cervical portion

22
Q

Dog thymus

A

in precardial mediastinum

23
Q

Pig thymus

A

extensive cervical and thoracic portions

24
Q

lis the endocrine organs of the abdomen (7)

A 
Adrenal glands
Pancreas
Ovaries
Testes 
Placenta
Gastrointestinal tract
Kidneys
25
Q

A. Adrenal glands

A

Embryology
Dual origin
Cortex from coelomic epithelium, secretes steroids inc. mineralocorticoids, glucocorticoids & some sex hormones (similar origin to gonads)
Medulla from neural crest cells, secretes adrenaline (= epinephrine) and noradren-aline (= norepinephrine

26
Q

Anatomy of the Adrenal Glands

A

Small white/yellow bodies, flattened dorsoventrally
Lie in retroperitoneal space close to thoracolumbar junction
Usually craniomedial to kidneys, on either side of aorta, hence R adrenal often more cranial than L adrenal
Phrenico-abdominal vein bisects the adrenal gland ventrally

27
Q

Anatomy of the Adrenal Glands 2

A

Blood supply from nearby vessels
Venous drainage via hilum & into vena cava
Nerves mainly sympathetic into medulla
Cortex controlled by ACTH from adenohypophysis (glucocorts.) & renin-angiotensin system (mineralocorts.)
Accessory masses occur, usually on surface cortex but can be separate on nearby vessels or in organs

28
Q

Histology of the adrenal glands

A 
Dense fibrous capsule
Support for delicate collagenous framework supporting secretory cells
Cortex
Medulla
Large vein centre of medulla
29
Q

Histology of the adrenal glands Cortex with 3 layers (from outer to inner)

A

Zona glomerulosa
Zona fasciculata
Zona reticularis
(Sometimes 4th layer, zona intermedia, containing undifferentiated cells)

30
Q

Zona glomerulosa

A

Rounded clusters of cells

Mineralocorticoids, esp. aldosterone

31
Q

Zona fasciculata

A

Parallel cords secretory cells

Glucocorticoids, esp. cortisol

32
Q

Zona reticularis

A

Irregular branching cords & clusters, large capillaries

Small amounts androgens & glucocorticoids

33
Q

Adrenal medulla

A

Clusters of cells around capillaries & venules
Venules drain cortex to central medullary vein
Secretory cells also known as chromaffin cells
Secrete adrenaline > noradrenaline
Nerves to medulla pre-ganglionic sympathetic nn. & cells of medulla functionally equivalent to post-ganglionic neurons

34
Q

Ox comparative anatomy adrenal glands

A

Left adrenal gland C-shaped

Right adrenal gland heart-shaped with caudal vena cava running over it

35
Q

Horse adrenal glands

A

Close to kidneys

V compressed dorso-ventrally

36
Q

Brown marsupial mouse or Antechinus

A

Males die after single breeding season
Sexual rampage for two weeks then overcome by a range of infections & starvation
Deficit in glucocorticoid feedback mechanism results in very high free cortisol levels
This impairs immunocompetency (but results in lots of matings)

37
Q

B. Endocrine pancreas

A

Review Digestion notes for gross anatomy
Canine pancreas has 2 lobes, one in mesoduodenum and other in greater omentum near greater curvature of stomach
Larger component is exocrine pancreas, which opens via ducts into duodenum
Embryologically develops as out-pouching of gut
Endocrine cells migrate away from ducts & cluster around capillaries as Islets of Langerhans

38
Q

Pancreas functions

A

Endocrine
Islets of Langerhans
Insulin & glucagon

Exocrine
Enzymes, electrolytes & water
From pancreatic acini  duodenum

39
Q

Anatomy of the pancreas

A

Diffuse, lobulated,pink

40
Q

Islets of Langerhans

A 
Small masses of pale endocrine cells
Scattered through the exocrine pancreas
Demarcated by 
	reticular fibres
About 1 million 
	islets per pancreas
41
Q

Islet cells

A 
Rich blood and nerve supply
With special stains, different cell types can be distinguished
Alpha
Peripheral
25%, glucagon
Beta
Throughout
60%, insulin
Delta
10%, somatostatin

Y2S2 VETS2012 anatomy (8 decks)

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