Endocrine Histology

Question 1

Hormonal control mechanisms

Answer 1

Endocrine control
Paracrine control
Autocrine control

Question 2

Water soluble or hydrophobic hormones

Answer 2

Steroid hormones -hydrophobic, can cross cell membrane receptors inside cell
Protein hormones- hydrophilic - cant cross cell membrane receptors on cell membrane

Question 3

Types of capillary

Answer 3

Continuous
Fenestrated
Discontinuous

Question 4

Continuous capillary

Answer 4

Typically found in connective tissue
-cardiac, skeletal, smooth muscle
-skin
-lungs
-CNS
Uninterrupted vascular endothelium that rests on a continuous basal lamina

Question 5

Fenestrated capillary

Answer 5

Typically found in endocrine glands, sites of fluid or metabolite absorption
Numerous openings (Fenestrations) providing channels across capillary wall
A continuous basal lamina across fenestrations on the basal plasma membrane surfaces
May also have thin, non membranous diaphragm, across opening referred to as filtration pores

Question 6

Discontinuous capillary or sinusoids

Answer 6

Typically found in liver, spleen, bone marrow
Larger in diameter, more irregular shaped. Large openings in endothelial cytoplasm, separated by wide, irregular, intercellular gaps.
A discontinuous basal lamina

Question 7

Embryology of the thyroid gland

Answer 7

Originates by cell proliferation between 1st and 2nd pharyngeal pouches near base of tongue
The migrates caudally along midline, division of the thyroid into right and left lobes also occurs during this time
4th week an endodermal proliferation (thyroid primordium) develops at tip of the foramen caecum of developing tongue
Migrates inferiorly to its final site anterior and inferior to larynx
Until the 5th week the thyroid remains connected to the foramen caecum by the thyroglossal duct
The gland reaches its final site in 7th week

Question 8

What does the thyroid gland consist of

Answer 8

Mainly spherical follicles composed of simple epithelium of thyrocytes surrounding a lumen with thyroglobulin (colloid)
Thyroglobulin is a large glycoprotein in which tyrosine residues are iodinated as precursors of the thyroid hormones T3 and T4
Thyroid follicles also contain a few smaller and paler cells called parafollicular cells or C cells which produce calcitonin

Question 9

Process of producing thyroid hormones via stored thyroglobulin
Both phases are promoted by TSH & may occur simultaneously in same cell

Answer 9

In exocrine phase: glycoprotein thyroglobulin made and secreted into follicular lumen, iodide pumped across cells into lumen, iodide converted to iodine by membrane bound thyroid peroxidase
Added to tyrosine residues of thyroglobulin to form monoiodotyrosine or diiodotyrosine which are then covalently coupled to form T3 and T4 still within glycoprotein
In endocrine phase: iodinated thyroglobulin endocytosed by thyrocytes and degraded by lysosomes, free active T3 &T4 released to adjacent capillaries in an endocrine matter

Question 10

Where are the parathyroid glands

Answer 10

On posterior side of thyroid gland

Question 11

Embryology of parathyroid glands

Answer 11

Pharyngeal pouch derivatives
Third pouch: inferior parathyroid glands, thymus
Fourth pouch: superior parathyroid gland and parafollicular cells (produce calcitonin in thyroid)
The inferior and superior parathyroid glands descend with the thymus and come to rest on the posterior surface of thyroid gland low in the neck

Question 12

What do parathyroid glands consist of

Answer 12

Primarily of principal cells (chief cells) that secrete PTH (parathyroid hormone), that raises blood Ca2+ levels

Question 13

What is calcitonin

Answer 13

Hormone thyroid gland secretes to help regulate calcium levels in blood by decreasing it. Produced by C cells in thyroid
Opposes actions of PTH (increases blood calcium levels)

Question 14

What are the pancreatic islets of Langerhans

Answer 14

Small clusters of pale cells (neuroendocrine) embedded within exocrine tissue
They have primarily: B cells making insulin, a cells making glucagon and delta cells making somatostatin (GH inhibiting hormone)
Each islet consists of 2000 to 3000 cells surrounded by a network of fenestrated capillaries and supported by reticular fibres

Question 15

Tissues the pancreas is divided into

Answer 15

Exocrine portion- acinar and duct tissue
Exocrine pancreas- formed by protein secretory acini with apically located zymogen granules
Endocrine portion- islets of Langerhans

Question 16

Difference between exocrine and endocrine tissue

Answer 16

Exocrine glands secrete their substances through ducts onto body’s surfaces
Endocrine glands secrete their substances directly into bloodstream, ductless glands

Question 17

What are adrenal glands

Answer 17

Also known as suprarenal glands
Located on top of kidneys
Left; semi lunar shape, higher T11
Right; pyramidal shape, lower T12
Secrete many hormones including cortisol, aldosterone and adrenaline
Help to regulate several body functions including metabolism, blood pressure and body’s responses to stress
Composed of a cortex and medulla

Question 18

What does the adrenal cortex consist of

Answer 18

3 histologically distinct zones; cells producing steroid hormones, drained by same system of capillaries
Most superficial zona glomerulosa with round cell clusters produce mineralcorticoids such as aldosterone, regulates electrolyte levels
Wider middle zone fasciculata with elongated strands of cells produce glucocorticoids such as cortisol, regulates carbohydrate metabolism. Cells known as spongiocytes
Innermost zona reticularis (largest zone) make a weak androgen DHEA converted to testosterone in men& women.

Question 19

What does the adrenal medulla consist of

Answer 19

Inner region of the glands
Neural crest-derived chromaffin cells synthesising either adrenaline or noradrenaline that regulate the stress response

Question 20

Capillaries of adrenal cortex

Answer 20

Sinusoidal type
Numerous holes and sieve plates
Basal lamina is normally lacking and is patchy if present. This is in contrast to the capsular and medullary capillaries which are uninterrupted

Question 21

Pineal gland

Answer 21

Develops from embryonic neuroectoderm, remains attached to the brain and contains modified neurons called pinealocytes that secrete amine melatonin
Pineal concreations called corpora arenacea
Neural connections from the retina to pinealocytes allow diurnal secretion of melatonin and rhythms in physiological activities
Output of pineal melatonin is modulated by light through nervous pathways which input as sympathetic innervation to gland

Question 22

What are paraganglia

Answer 22

A collection of cells that came from embryonic nervous tissue (neural crest origin) and are found near adrenal glands and some blood vessels and nerves
Associated with autonomic nervous system- parasympathetic and sympathetic

Question 23

What is the diffuse neuroendocrine system

Answer 23

Composed of neuroendocrine cells
Widespread in GI and respiratory tract
Many different products depending upon location
Local paracrine

Question 24

Definition of an endocrine gland

Answer 24

A ductless gland that secretes hormones directly into the blood

Question 25

Structure of thyroid gland

Answer 25

Large unpaired gland in neck formed of two lateral lobes connected by an isthmus It is palpable but often not with ageing Also has a pyramidal lobe All supplied by superior and inferior thyroid arteries Venous drainage occurs via superior, middle and inferior thyroid veins

Question 26

Location & relation of thyroid gland

Answer 26

Located on front of neck just under Adam’s apple Resides within visceral compartment of neck Anteriorly: lies behind strap muscles of neck- sternohyoid, sternothyroid and omohyoid Posteriorly: wraps around cricoid cartilage and tracheal rings

Question 27

Arterial blood supply of thyroid

Answer 27

Supplied by two main arteries- superior and inferior thyroid artery The superior thyroid artery is the first branch of the external carotid artery, this artery supplies the superior anterior and superior posterior portions of gland The inferior artery arises from thyrocervical trunk (branch of subclavian artery), artery travels superomedially to reach inferior pole of thyroid, tends to supply posteroinferior aspect of gland

Question 28

Venous blood supply of thyroid

Answer 28

Venous drainage is carried out by superior, middle and inferior thyroid veins The superior and middle veins drain into the internal jugular veins whereas the inferior drains into the brachiocephalic vein

Question 29

Arterial blood supply of the parathyroid

Answer 29

The posterior aspect of the thyroid gland is supplied by the inferior thyroid artery so its branches also supply the parathyroid glands

Question 30

Venous blood supply parathyroid

Answer 30

Venous drainage is carried out by the parathyroid veins which drain into the superior, middle and inferior thyroid veins

Question 31

Secretomotor

Answer 31

Refers to the capacity of a structure (often a nerve) to induce a gland to secrete a substance

Question 32

Vasomotor

Answer 32

Actions upon a blood vessel which alter its diameter

Question 33

How are the thyroid and parathyroid gland innervated

Answer 33

By the cervical sympathetic ganglion These nerves are vasomotor and not secretomotor. Endocrine secretion of parathyroid hormone/thyroid hormone is controlled hormonally/depended on calcium levels

Question 34

Adrenal gland location and relation

Answer 34

The adrenal glands are located in the posterior abdomen, between kidneys and diaphragm They’re retroperitoneal (located in space behind peritoneum membrane forming the lining of the abdominal cavity) with parietal peritoneum covering their anterior surface only Perinephric fascia (connective tissue) encloses the adrenal glands and kidneys, this fascia attaches glands to crura of diaphragm Separated from kidneys by perirenal fat The adrenal glands sit in close proximity to many other structures in abdomen

Question 35

What is the left adrenal gland anterior and posterior to

Answer 35

Anterior- stomach, pancreas and spleen Posterior- left crus of the diaphragm

Question 36

What is the right adrenal gland anterior and posterior to

Answer 36

Anterior- inferior vena cava, right lobe of liver Posterior- right crus of the diaphragm

Question 37

Adrenal gland embryology

Answer 37

The adrenal cortex is derived from the mesoderm of the posterior abdominal wall The adrenal medulla is of ectodermal origin, arising from neural crest cells

Question 38

Arterial blood supply of adrenal glands

Answer 38

The adrenal glands have a rich blood supply via 3 main arteries Superior adrenal artery- arises from the inferior phrenic artery Middle adrenal artery- arises from the abdominal aorta Inferior adrenal artery-arises from the renal arteries

Question 39

Venous blood supply adrenal arteries

Answer 39

On the left side, the left adrenal vein leaves the left adrenal gland and passes inferiorly to enter the left renal vein On the right side the right adrenal vein leaves the right adrenal gland and almost immediately enters the inferior vena cava

Question 40

Innervation of the adrenal gland

Answer 40

The adrenal medulla is innervated by the sympathetic nervous system from mostly the greater splanchnic nerve (T8-L1) Fibres of the greater splanchnic nerve will enter the adrenal gland to synapse on membranes of chromaffin cells The chromaffin cells release adrenaline and noradrenaline directly into bloodstream when stimulated by sympathetic nervous system

Question 41

What are the splanchnic nerves

Answer 41

Arise from within the sympathetic thoracic trunk to innervate abdomen The greater splanchnic nerve helps with the motility of the foregut and provides sympathetic innervation to the adrenal medulla

Question 42

What is the pancreas

Answer 42

L shaped organ positioned at L1 level With the exception of the tail of the pancreas it is a retroperitoneal organ, located deep within upper abdomen The pancreas is a glandular organ with both digestive (exocrine) and hormonal (endocrine) functions It consists of 2 types of secretory tissue: exocrine (acinar cells, secrete digestive enzymes) and endocrine (islets of Langerhans, releases insulin and glucagon)

Question 43

Embryology of the pancreas

Answer 43

Pancreatic development begins with the formation of a dorsal and ventral pancreatic bud Both join with the foregut through a duct The ventral bud rotates and fuses with the dorsal bud At this point of fusion, the main ducts of the ventral and dorsal pancreatic buds fuse, forming the main pancreatic duct The dorsal pancreatic bud forms the neck, body and tail of the developed pancreas and the ventral pancreatic bud forms the head and uncinate process (hook)

Question 44

Structure of the pancreas

Answer 44

Typically divided into 4 parts Head: widest part, lies within C shaped curve created by duodenum & is connected to it by connective tissue Uncinate process: a projection arising from the lower part of the head and extending medially to lie beneath the body of the pancreas, lies posterior to superior mesenteric vessels Neck: located between head and body, overlies superior mesenteric vessels which form a groove in its posterior aspect Body: centrally located crossing midline of human body to lie behind stomach and to left of superior mesenteric vessels Tail: the left end of pancreas that lies within close proximity to hilum of spleen, contained within splenorenal ligament with the splenic vessels, this is only part of pancreas that’s intraperitoneal

Question 45

Anatomical relations to pancreas

Answer 45

Stomach lies anterior to pancreas, separated from pancreas by lesser sac Duodenum- the c shaped duodenum curves around and outlines head of pancreas Spleen-located posteriorly and laterally, the lienorenal ligament connects spleen to tail of pancreas The aorta and vena cava pass posteriorly to head, the superior mesenteric artery and vein lie behind neck and anterior to uncinate process Posterior to neck the splenic and superior mesenteric veins unite to form hepatic portal vein Splenic artery traverses the superior border pancreas

Question 46

Arterial blood supply of pancreas

Answer 46

The pancreas is supplied by the pancreatic branches of the splenic artery (the celiac trunk). These include the great pancreatic artery which supplies tail and dorsal pancreatic artery which supplies blood Head is also supplied by superior and inferior pancreaticoduodenal arteries The Gastroduodenal artery (branch of common hepatic artery from celiac trunk) branches into anterior superior pancreaticoduodenal artery and posterior superior pancreaticoduodenal artery, both supply the anterior and posterior superior region of head

Question 47

Venous blood supply in pancreas

Answer 47

Pancreatic veins are responsible for draining deoxygenated blood from pancreas The pancreatic veins draining venous blood from body and tail empty into splenic vein The anterior superior pancreaticoduodenal vein empties into superior mesenteric vein, while posterior variant empties into hepatic portal vein Both the anterior and posterior inferior pancreaticoduodenal veins drain into superior mesenteric vein

Question 48

Innervation of pancreas

Answer 48

The pancreas receives involuntary innervation via ANS -it’s sympathetic innervation originates from greater and lesser splanchnic nerves -its parasympathetic innervation originates from vagus nerve Inside the organ they carry nerve impulses to acinar cells and pancreatic islets Parasympathetic fibres induce secretion from acinar cells and pancreatic islets ultimately resulting in release of pancreatic juice insulin and glucagon Sympathetic fibres cause vasoconstriction and inhibition of secretion pancreatic juice but stimulates release of glucagon but inhibits release insulin

Question 49

Why is vision often affected in patients with large pituitary adenomas

Answer 49

Because optic chiasm lies in close proximity above the pituitary gland