Lecture: Endocrinology

Question 1

autocrine

Answer 1

affects the producing cell

Question 2

paracrine

Answer 2

affects neighboring cells

Question 3

neurocrine

Answer 3

secretion from a neuron to a cell

Question 4

“true” endocrine

Answer 4

affects distant cells
secretes basally towards CT
secretion goes into the vasculature to be carried to a distant organ

Question 5

Common endocrine features

Answer 5

always have fenestrated capillaries in endocrine organs in order to pick up the endocrine compound
‐ even in pituitary, despite BBB

disturbed cell polarity, lack of an “apical” domain

‘carrier proteins’ that facilitate transmission in blood which happens for lipid soluble hormones
Examples:
‐ SHBG (sex hormone binding globulin)
‐ corticosteroid binding globulin
‐ GHBP (growth hormone)
‐ thyroxine‐binding globulin
‐ transthyretin

Question 6

Types of hormones

Answer 6

protein (peptide, amino acid)
‐ from epithelial‐origin glands

steroid (derived from cholesterol)
‐ from mesenchymal origin glands

T3 and T4 are in between steroid and protein, on a continuum

Question 7

Types of receptors

Answer 7

cell membrane
intracellular
nuclear membrane

If a steroid hormone is made, it will just diffuse out of the cell that made it. So if you want to control how much of it is in the circulation, you control how much of it is made as opposed to other hormones that control how much is released. Rate limiting enzymes at each step of pathway control how much steroid hormone is produced

For a protein hormone, the receptor has to be located on the extracellular surface. For a steroid hormone, if you want to affect DNA transcription, steroid hormones are good because it can cross the nuclear and cell membranes so the receptor can be in the nucleus.

Question 8

Steroid hormones

Answer 8

Intracellular cholesterol is the precursor for all steroid hormones. It can come from…
- extracellular uptake
- intracellular mobilization:
- synthesis
They need binding proteins
- albumin
- sex‐hormone binding globulin
- corticosteroid binding globulin

Question 9

Control of hormones

Answer 9

releasing factors ‐ positive feedback
inhibiting factors ‐ negative feedback

Endocrine axes: 3 separate organs that control the amount of circulating hormones. They communicate chemically by + or - feedback

1. Hypothalamus: secretes hormones that affect the pituitary
2. Pituitary: secretes hormones that affect the target hormone
3. Target organ:

Question 10

Endocrine Axes

Answer 10

Hypothalamus: CRH (cortisol -)
Pituitary: Corticotroph (cortisol -) (CRH+)
Trophic hormone: ACTH
Target organ: Adrenal glands (ACTH +)
Target hormone: cortisol
Action: Cell homeostasis and function

Hypothalamus: Somatostatin, TRH
Pituitary: Thyrotroph
Trophic hormone: TSH
Target organ: Thyroid gland
Target hormone: T3, T4
Action: Thermogenesis, protein synthesis

Hypothalamus: GnRH
Pituitary: Gonadotroph
Trophic hormone: LH and FSH
Target organ: Ovaries, testes
Target hormone: Estradiol, progesterone and testosterone, inhibitin
Action: Ovulation, spermatogenesis

Hypothalamus: GHRH
Pituitary: Somatotroph, somatostatin
Trophic hormone: GH
Target organ: Liver –> chondrocytes
Target hormone: IGF-I
Action: Linear and organ growth

Hypothalamus: Dopamine
Pituitary: lactotroph
Trophic hormone: PRL
Target organ: breast
Target hormone: ??
Action: Lactation

___troph = the cell in pituitary that targets ____ organ

Question 11

Nucleus (in brain)

Answer 11

a region of the brain that has cells of a given type.
ex: paraventricular nucleus, supraoptic nucleus

Question 12

2 types of hypothalamic projections

Answer 12

Magnocellular system: sends axons to neurohypophysis (posterior pituitary) and those axons secrete hormones.
- ParaVentricular Nucleus (PVN)
- Supra‐Optic Nucleus (SON)

Parvocellular system: secretes releasing hormones that affect adenohypophysis (anterior pituitary). Secretes its hormones right there in the hypothalamus
- ParaVentricular Nucleus (PVN)
- arcuate nucleus
- pre‐optic nucleus

Google:
Magnocellular neurons are large cells that primarily project to the posterior pituitary gland to release hormones like oxytocin and vasopressin into the bloodstream, while parvocellular neurons are smaller cells that project to other brain regions to regulate various physiological processes through releasing hormones locally within the central nervous system

Magnocellular - bloodstream directly
Parvocellular - released in CNS

The adenohypophysis and neurohypophysis are two distinct parts of the pituitary gland, or hypophysis, that differ in their embryonic origin, anatomy, and function:

Adenohypophysis
Also known as the anterior pituitary, this part of the gland is made up of glandular tissue and is responsible for releasing hormones like growth hormone, prolactin, and thyroid-stimulating hormone. The adenohypophysis is controlled by hormones released from the hypothalamus.

Neurohypophysis
Also known as the posterior pituitary, this part of the gland is made up of neural tissue and is responsible for storing and releasing hormones like oxytocin and antidiuretic hormone. The neurohypophysis is controlled by nerve stimulation from the hypothalamus.

Question 13

Function of Growth Hormone Releasing Hormone (GHRH), somatostatin

Answer 13

control release of growth hormone

Question 14

Function of Corticotropin Releasing Hormone (CRH)

Answer 14

control release of ACTH

Question 15

Function of Gonadotropin Releasing Hormone (GnRH)

Answer 15

control release of LH and FSH

Question 16

Function of Thyroid Releasing Hormone (TRH)

Answer 16

control release of TSH

Question 17

Pituitary hormones

Answer 17

GHRH, CRH, GnRH, TRH

Question 18

Pituitary anatomy

Answer 18

If you pick up brain out of skull, you will cut the stalk to the pituitary because it sits separately in a bony cavity

Neurohypophysis:
- pars nervosa (posterior lobe, synonymous with posterior pituitary): bottom bulb part, where hormones are produced, magnacellular axons descend here
- infundibular stalk: connecting part
- median eminence: upper part of pituitary that connects it to hypothalamus

Adenohypophysis: looks like ball of cells
- pars distalis (anterior lobe, synonymous with anterior pituitary) : anterior bulbous part, ball of cells located here
- pars intermedia: part of anterior lobe that hugs the posterior lobe
- pars tuberalis: part that hugs/wraps around the stalk

Question 19

Pituitary - portal circulation

Answer 19

we have a microcirculation between the hypothalamus and the pituitary

Portal veins convey blood from capillaries near the hypothalamus to the pituitary pars distalis capillaries.

Hypothalamic “releasing hormones”:
reach the pituitary in relatively high concentration & cause release of pituitary hormones, which then circulate to the body.

Consequence of this: the concentration is high the first time around, but low the second time around because it gets diluted by the bloodstream

Question 20

Pars Distalis Hormones

Answer 20

growth hormone (GH, somatotropin)- acidophil

prolactin (PRL)- acidophil

adrenocorticotropin (ACTH)- basophil

gonadotropins: follicle stimulating hormone (FSH), luteinizing hormone (LH)- both are basophils

thyroid stimulating hormone (TSH) - basophil

chromophobes are not seen

Question 21

Components of the neurohypophysis:

Answer 21

neuropil ‐ descending axons from hypothalamic neurons

capillaries ‐ sinusoidal by anatomical size ‐ walls are fenestrated

pituicytes ‐ resident glial cell, controls blood‐brain barrier

Herring bodies ‐ dilated endings of axons, containing hormones for release into circulation

The way to tell you are in the neurohypophysis is to see that the protein hormones pile up at the end of the axon (in Herring bodies) until they are told to be released

Question 22

Neurohypophysis hormones and their function

Answer 22

anti‐diuretic hormone (ADH): water retention in kidneys

oxytocin: milk “let‐down”

Question 23

Pituitary embryology

Answer 23

The pituitary is formed from
two separate tissues:
- neural ectoderm generates the neurohyphphysis and
- oral ectoderm generates the adenohypophysis

Question 24

Adrenal Gland

Answer 24

Has two parts with different embryonic derivations. Adventitial gland- sits in CT, has capsule that separates it from surrounding CT.

Cortex has 3 layers (ZG, ZF, and ZR) which contains cholesterol drops
- Zona glomerulosa
- Zona fasciculata: most amount of cholesterol, frothy root beer float appearance, many white vacuoles which are the cholesterol containing droplets
- Zona reticularis

Cortex- steroid hormones
Medulla- epinephrine and nor epinephrine which are NTs in the brain, but hormones in the body (fight/flight)

Question 25

Adrenal gland - embryology

Answer 25

Adrenal cortex forms out of mesenchymal tissue

Medulla origin is the same as that of the sympathetic ganglia which is ectomesenchyme/neural crest cells

Question 26

Adrenal gland - blood supply

Answer 26

Arteries (suprarenal) come through the capsule. two things can happen to the blood. 1) gets dumped into capillary bed that feeds the cortex which will percolate through the cortex and then the medulla and will get picked up by the centromedullary vein. 2) blood can go straight to the medulla so that the first time it hits a capillary bed is in the medulla

The reason for this is because the medulla is controlling the fight/flight response so there needs to be a way to get blood there quickly

Question 27

Adrenal cortex - corticosteroids

What are the principal hormones, layers, and functions?

Answer 27

Principal Hormone (class): aldosterone (mineralocorticoids)
Layer: zona glomerulosa
Function: blood pressure, Na
resorption

Principal Hormone (class): cortisol (glucocorticoids)
Layer: zona fasciculata
Function: fat, carbohydrate, protein mobilization, ACTH influence

Principal Hormone (class): dihydroepiandrostenedione (DHEA), (androgens)
Layer: zona reticularis
Function: secondary sex characteristics

Question 28

Adrenal medulla - “chromaffin cells”

What are the hormones produced?

Answer 28

epinephrine (adrenaline)
norepinephrine (noradrenaline)

• catecholamine products from precursor tyrosine
• increase HR & BP during stress, mediate fight‐or‐flight response

Question 29

Thyroid gland

Which hormones are produced and what are the functions?

Answer 29

It is planes of sections through spheres

Hormone: T3 (triiodothyronine), T4 (thyroxine)
Cell: follicular cells
Function: protein synthesis and degredation, glycogenesis, lipolysis, heart rate, general growth and metabolism

Hormone: calcitonin
Cell: C‐cell (minority cell)
Function: lowers blood Ca++
*Located at the junctions/corners of the thyroid spheres/follicular cells

Question 30

Embryonic origins of the medulla and cortex

Answer 30

Medulla- neural crest/exctomesenchyme

Cortex- intermediate mesoderm

Question 31

What is the name of the substance in the middle of the spheres of the thyroid gland?

Answer 31

Colloid

Question 32

Thyroid - production of T3, T4

Answer 32

T3 and T4 are necessary hormones that have iodine at their core

Thyroid synthesizes a molecule that binds iodine. Body sucks up all iodine eaten from seafood and stores it for several months.

Iodine is taken up by a Na/I symporter on the basal surface of follicular cells. Pendrin moves I into colloid.

Thyroglobulin is a molecule made by the follicular cell that stores Iodine.

Either 1 or 2 Iodines bind to thyroglobulin which is endocytosed back into the follicular cell. Thyroxine (T4) is made from two 2’s while triiodothyronine (T3) is made from a 1 and a 2. T3 and T4 and then released into the blood. They have carrier proteins because they are half lipid soluble.

Question 33

Thyroid pathologies

Answer 33

iodine deficiency (goiter): Why enlargement? Stores thyroglobulin to have it ready when I comes (Toth’s reason)

Graves’ disease (autoimmunity to TSH receptor): Thyroid does not produce T3/T4 unless it sees TSH from the pituitary. If the body deletes the TSH receptor, thyroid gland is not responsive to pituitary and does not produce T3/T4.

Question 34

Parathyroid
Which hormones are produced and what are the functions?

Answer 34

Hormone: PTH principal (chief) cells
Cell: parathormone (PTH)
Function: calcium regulation (antagonist of calcitonin). This is the “pull” part of Calcium regulation. (C cells in thyroid are the “push” part)

Hormone: oxyphil cells (minority ~5%)
Cell: ? (unknown)
Function: ? (unknown)

Question 35

Pineal gland
Which hormones are produced and what are the functions?

Answer 35

Hormone: melatonin
Cell: pinealocytes
Function: circadian rhythms

It is located right in the middle of the brain. So it has to sense light indirectly through the retina and sets up circadian rhythm. It is in the midline normally, so if it is not in the midline in an image, it means a swollen brain.

Question 36

What are the 3 items/cells found in the pineal gland?

Answer 36

• pinealocytes (may contain lipofuscin pigment which is a dark brown endogenous pigment, in older brains, metabolic waste products bc the brain cells do not regenerate)
• glial cells
• brain sand (corpora arenacea): mineralized concretions giving a white appearance to pineal gland. More is seen in older brains as opposed to younger brains.

There is lots of CT septa in the pineal gland which is unique because you do not expect to see CT in the brain

Question 37

Pancreatic islets

Answer 37

Hormone: glucagon
Cell: alpha
Function: raise blood glucose

Hormone: insulin
Cell: beta
Function: lower blood glucose

Hormone: somatostatin
Cell: delta
Function: inhibit pancreatic secretions

Hormone: pancreacic polypeptide, vasoactive intestinal peptide
Cell: PP
Function: appetite regulation

Hormone: ghrelin
Cell: epsilon
Function: appetite regulation

Question 38

The Adipose Organ - Fat Depots

Answer 38

Fat is also an endocrine organ

It produces leptin and adiponectin which informs the body about levels of satiety.

Different kinds of fat
* subcutaneous
* visceral
– omental
– mesenteric
– organ-specific
muscular
pericardial
renal

There is a level of complexity within the fat depot

Question 39

Adipose Tissue hormones

Answer 39

Hormone: leptin
Function: satiety

Hormone: adiponectin
Function: glucose regulation/insulin sensitivity

Adipocytokines can control the inflammatory response
- leptin produces inflammatory response
- adiponectin produces antiinflammatory response

These two hormones affect the immune system. Important because this is the difference between having fat and being obese. Adipocytes are so big

Question 40

Adipose tissue inflammation

Answer 40

This determines obesity.

Obesity- the fat cells are so big that they are metabolically unable to sustain their own metabolism and they cry out for help which takes the form of cytokines which signal the immune system.

Adipose tissue has low grade inflammation and is infiltrated with immune cells.

From Lecture Syllabus:
Adipose tissue also forms an important, often under-appreciated source of hormones. Adipose tissue is distributed throughout the body in various depots, which differ in their pharmacological properties. The major fat depots are: subcutaneous, and visceral fat which includes omental, mesenteric, and organ-specific fat depots. The two major hormomes produced by adipose tissue are leptin and adiponectin, which are satiating and anorexigenic respectively, although in a complex way. These hormones also have an influence on the production of inflammatory and anti-inflammatory cytokines, respectively.

Chronic low-grade inflammation of adipose tissue is a strong predictor of the morbidities associated with obesity, including insulin-resistance. Adipose depots include an adipose-specific set of macrophages, which is seeded during fetal development. With aging, more of the organs’ macrophages are derived from blood. These macrophages behave differently in controlling fat storage and inflammation

Question 41

Endocrine functions of other organs

Answer 41

Organ: heart
Hormone: atrial natriuretic factor
Function: blood pressure regulation

Organ: kidney
Hormone: erythropoietin
Function: RBC production

Organ: kidney
Hormone: renin
Function: blood pressure

Organ: skin
Hormone: Vitamin D3
Function: calcium absoprtion

Organ: liver
Hormone: angiotensinogen
Function: blood pressure

Question 42

Reproductive System

Answer 42

Organ: testis
Hormone: testosterone STEROID HORMONE
Function: male sex characteristics

Organ: testis
Hormone: inhibin
Function: feedback hormone

Organ: ovary
Hormone: estrogen STEROID HORMONE
Function: uterine maturation

Organ: ovary
Hormone: progesterone STEROID HORMONES
Function: uterine receptivity

Organ: placenta
Hormone: human chorionic gonadotropin (hCG) STEROID HORMONE
Function: maintenance of pregnancy

Question 43

Hormonal regulation of male reproductive system

Answer 43

Hypothalamus: GnRH
Pituitary: LH (acts on Leydig cells) and FSH (acts on Sertoli cells)
Gonads: Leydig cells and Sertoli cells

Question 44

Female reproductive (menstrual) cycle

Answer 44

The hormones oscillate throughout the reproductive cycle

1. pituitary produces FSH (pituitary), its level rises
2. FSH produces estrogen (produced by ovaries) which is a negative feedback for FSH, so FSH shuts off as estrogen rises. The target hormone is making a substance that is a negative
3. After estrogen gets to a certain level, the pituitary produces LH (produced by pituitary) which surges and is a negative feedback for estrogen whose level falls
4. Estrogen and progesterone (produced by ovaries) rise

Question 45

Development of Reproductive Tract

Answer 45

Genetic development:
* Ovary / Testis derive from bi potential tissue in the germ ridge. (mesonephric mesenchyme)
* Testis development requires testis‐determining factor (TDF), a protein coded on the sex‐determining region of the Y‐chromosome (SRY)
* mesonephric (Wolffian) duct ‐> epididymis, vas deferens
* paramesonephric (Mullerian) duct ‐> oviduct, uterus

Hormonal development:
* External genitalia are driven towards male pattern by di‐hydro testosterone (DHT)

Question 46

Hormones in Brain Development

Answer 46

Sex hormones also affect brain development. Has a genetic component and a hormonal component.
- proof: one bird that has half male chromosomes and half female chromosomes

Lecture Slide:
Differences in brain development are driven both by chromosomes and hormones

Zebra finches show chromosome‐dependent sex differences in body, gonads and brain.

Chromosome‐dependent differences in human brains are more subtle.

Rodents and humans (LeVay (1991) Science) show sexually dimorphic hypothalamic nuclei, affected by
hormones during critical period
& correlated with gender identity.

Question 47

Endocrine organ embryology

Answer 47

endocrine cells come from all germ‐disc layers

surface ectoderm- anterior pituitary
neural ectoderm- hypothalamus, posterior pituitary, pineal

endoderm- pancreas, thyroid, parathyroid

mesoderm- ovary, testis, adrenal cortex

ectomesenchyme/neural crest cells- adrenal medulla

Question 48

Endocrine organs and aging

Answer 48

fibrosis is a normal age‐related finding in many organs

fibrosis = accumulation of collagen fibers where you don’t want them, but also from different component of ECM

• anterior pituitary (GH declines)
• adrenal cortex (cortisol & aldosterone decline)
  … and importantly, lung, heart, liver, kidney

ex: fibrosis of the uterus

Question 49

Endocrine Consequences of Aging

Answer 49

diabetes
- T2DM ‐ insulin deficiency, or insulin resistance

osteoporosis
- chronic bone loss (regulated by levels of estrogen)

menopause
- depletion of all ovarian follicles

metabolic syndrome
- high blood pressure, obesity, high cholesterol, high blood sugar

inflammaging
- age‐related inflammation

Question 50

evaluating an endocrine disorder

Answer 50

Determining the locus of the disease is crucial.

A “primary disease” means the target organ is the origin.

A “secondary disease” means the pituitary and/or hypothalamus is causing a dysregulation of the target organ. Secondary disease may also be caused “off-axis”, for example by an endocrine-secreting tumor. This is especially common in tumors of cells of endocrine origin.

Question 51

Difference between protein and steroid hormones

Answer 51

Most hormones that we discuss fall into the general classes of either proteins or steroids.

Generally, protein hormones are actively stored and released from a cell, diffuse via fenestrated capillaries into the blood, and affect their target organs via cell-surface receptors.

Steroids (or more generally, lipid-soluble compounds) rely on binding to carrier proteins in blood and sometimes in target tissues. They may act via cell-surface receptors, intracellular receptors, or nuclear receptors. Steroid hormones are formed from the precursor cholesterol. The classical steroid hormones are the corticosteroids produced by the adrenal cortex and the sex hormones produced by ovaries and testis.

Question 52

neurohypophysis

Answer 52

The neurohypophysis is derived from neuroectoderm and consists of the median eminence, infundibular stalk and pars nervosa. It contains descending axons that originate in the supraoptic and paraventricular nuclei of the hypothalamus. The dilated ends of the axons form Herring bodies, and release antidiuretic hormone (ADH) and oxytocin. Resident glia are known as pituicytes, and serve to control the release of hormones into the surrounding capillaries.

Question 53

adenohypophysis

Answer 53

The adenohypophysis is derived from oral ectoderm and forms a donut-shaped ring of tissue around the infundibular stalk, consisting of the pars tuberalis, pars intermedia and pars distalis. Cells of the pars distalis may be characterized by their staining properties as acidophils (producing growth hormone (somatotropin) or prolactin), basophils (producing adrenocorticotropic hormone (ACTH), thyroid-stimulating hormone (TSH), follicle-stimulating hormone (FSH), luteinizing hormone (LH), and beta-endorphin), and chromophobes (not well understood).

Question 54

The name of the cavity of the skull in which the pituitary sits

Answer 54

sella turcica

The sella turcica is a saddle-shaped depression in the skull that houses the pituitary gland

Question 55

Thyroid gland

Answer 55

The thyroid gland contains numerous thyroid follicles which are spherical epitlelial-enclosed accumulations of colloid composed of thyroglobulin contained by follicular cells. Occasional interposed parafollicular cells or C-cells represent a minority cell type that exists basal to the follicles.[5] Follicular cells produce T3 and T4. These hormones function in a complex way to control metabolism and homeostasis. (In frogs, they control the tadpole-to-frog tdevelopmental ransition.) [6] Parafollicular cells produce calcitonin, which has the general function of decreasing blood calcium levels.

Question 56

Parathyroid gland

Answer 56

The majority cell type in the parathyroid gland is the chief cell, producing parathormone (PTH) and the minority cell type is the oxyphil cell. PTH has the general function of increasing blood calcium levels and is the major hormone controlling Ca++ balance, affecting the processes of gut absorption (by promoting the production of the active form of vitamin D), kidney excretion, and bone remodeling (by promoting osteoclast formation and function). Although the function of oxyphil cells is unknown, their presence is clinically relevant because they are able to retain the radioactive tracer molecule Tc-99m sestamibi[7] and thus can be used to distinguish parathyroid tissue in CT scans. The parathyroid is otherwise difficult to distinguish separately from the thyroid.

Question 57

pineal gland

Answer 57

The pineal gland sits within the brain. Its parenchymal cells are pinealocytes, producing melatonin, a regulator of circadian rhythms throughout the body. The gland accumulates concretions known as corpora arenacea or brain sand. Unlike typical brain tissue, the pineal gland includes a significant connective tissue component, and only a minority of the cells are glial cells.

Question 58

pancreas

Answer 58

The pancreas contains groups of endocrine cells known as islets of Langerhans. They contain, in decreasing order of frequency, β (beta) cells that produce insulin, α (alpha) cells that produce glucagon, PP (or γ) cells that produce pancreatic polypeptide, δ (delta) cells that produce somatostatin, and possibly other cell types in small minority including ghrelin, a “hunger hormone”.

Question 59

adrenal gland

Answer 59

The adrenal gland consists of two embryologically distinct parts, adrenal cortex and adrenal medulla.

The adrenal cortex produces corticosteroids and is organized in 3 layers; zona glomerulosa, producing mineralocortociods, primarily aldosterone, zona fasciculata producing glucocorticoids, primarily cortisol, and zona reticularis producing androgens.[10] Mineralocorticoids control salt balance and are critical to life.[11] Glucocorticoids have complex functions, generally involving control of the immune response and inflammation, and are widely used as pharmaceuticals. Adrenal-produced androgens have secondary (i.e. non reproductive) functions.

The adrenal medulla contains two types of chromaffin cells[12] producing epinephrine and norepinephrine. When produced by the nervous system, these are neurotransmitters acting in a paracrine fashion across a synaptic cleft. But here, they are hormones, acting to produce a fast “fight-or-flight” response in structures throughout the body.[13] Because the adrenal medulla is derived from neural crest cells, it is developmentally considered to be a “modified sympathetic ganglion”.[14]. The adrenal medulla receives a dual blood supply, with some blood arriving through the cortical capillary bed and some bypassing that bed via long cortical arteries (also called medullary arteries, actually arterioles).

Question 60

diffuse neuroendocrine system (DNES)

Answer 60

Endocrine cells also occur as minority cell types in other endodermal-derived epithelia, and are particularly important to the control of the gastrointestinal and respiratory systems. These cells collectively form the diffuse neuroendocrine system (DNES). Many (but not all) of these cells secrete polypeptide hormones (for example, cholecystokinin (CCK)) from amine precursors.

Question 61

endocrine cell, by definition, is one that secretes a product__________

Answer 61

basally, i.e. into surrounding connective tissue

Because endocrine secretions work by diffusing into the bloodstream, endocrine cells generally have a prominent basal surface, and are surrounded by a close and extensive capillary network. Usually (but with one prominent exception) endocrine cells lack a lumenal (apical) surface

Question 62

pancreatic islets (islets of Langerhans)

Answer 62

These islands of endocrine tissue are called pancreatic islets, or islets of Langerhans. They consist of four types of intermixed cells, producing the hormones glucagon, insulin, somatostatin, and pancreatic polypeptide. These products do not stain in H&E nearly as well as the zymogen granules found in cells of the exocrine pancreas, and thus the islets, clusters of cells 100-200 microns in diameter, are relatively easy to identify by their pale cytoplasm.

Though it is not easy to demonstrate, and not apparent in slides, the pancreas also has a unique circulation. Blood enters the islets via arterioles, and leaves via capillaries that then enter the exocrine tissue. In this manner, the exocrine pancreas sees islet-produced hormones at higher concentrations than are found in the circulation generally.

Question 63

Parathyroid

Answer 63

It sits amidst the thyroid.

he remainder of the cells present are endocrine cells. The most numerous cell is the chief cell (sometimes called principal cell). The minority cell type, constituting maybe 5% of this organ in this slide, is the oxyphil cell. Generally, oxyphil cells are a small minority of the cells, but realize (1) they may be clustered, and (2) they are known to increase in number with aging. What morphological features allow you to recognize the oxyphil cells? EOSINOPHILIC CYTOPLASM

Question 64

Pineal gland

Answer 64

The principal product of the pineal gland is melatonin, the production of which is inhibited by light. Melatonin regulates circadian rhythms throughout the body

In the pineal, look for the presence of CT, or the absence of proper neurons and axons. A separate easy way to recognize the pineal gland is to look for the presence of a unique metabolic byproduct that accumulates throughout life as microscopic calcified particles. These are known as corpora arenacea (or, less poetically, brain sand).

The parenchymal cell of the pineal gland is the pinealocyte.

Question 65

Thyroid gland

Answer 65

The thyroid gland is the source of hormones T3 and T4, which incorporate iodine in their structure. Because iodine is a trace element, often rare in the diet, the thyroid gland has developed a secondary function of sequestering and storing iodine. The follicular cells of the thyroid represent the rare example of endocrine cells with an apical surface. Here, the apical lumen forms a sealed compartment in which is stored iodine bound to its carrier molecule thyroglobulin. The follicular cells completely surround this compartment such that the only way out is back through the follicular cell.

Follicular cells of the thyroid connect to each other via tight junctions that also create the apical and basal polarity in these cells. The (roughly) uniform, prominent eosinophilic material (colloid) is the thyroglobulin filling the lumen of each thyroid follicle.

There are two types of endocrine cells in the thyroid, and the less frequent of the two, the parafollicular cell (also known as the C-cell after its principal product calcitonin) is well-demonstrated in lead hematoxylin by its dark-staining cytoplasm.

Question 66

Pituitary

Answer 66

Part II - Pituitary
The pituitary is an endocrine gland that sits at the base of the brain, surrounded and protected by an indentation in the base of the skull known as the sella turcica (“Turkish saddle”, after its shape). The pituitary gland is derived from two separate embryonic tissues that come to be apposed in the adult: one is oral ectoderm (i.e. roof of the mouth) and the other is neural ectoderm (i.e. part of the brain). The part derived from neural ectoderm is known as the neurohypophysis. Remember, it consists of the axons of neurons whose cell bodies lie in the hypothalamus. These axons secrete antidiuretic hormone (ADH) and oxytocin. The remainder of the pituitary has a similar organization to the parathyroid, in that it is a collection of basally secreting cells surrounded by an extensive capillary network. This portion is called the adenohypophysis. Examine slide buh401.

The adenohypophysis (MORE CELLS) consists of three morphologically distinguishable parts, all of which have secretory cells that look somewhat similar to the peripheral endocrine organs you have already examined: the pars distalis comprising the bulk of the structure, the pars intermedia lying immediately adjacent to the neurohypophysis, and the pars tuberalis surrounding the stalk of the pituitary. (The stalk itself is part of the neurohypophysis.) Despite these divisions, the adenohypophysis is often considered together as one functional unit.

The neurohypophysis (NEURAL TISSUE, LESS CELL) is readily distinguishable due to the absence of cells that look secretory. The bulk of it is the pars nervosa, but the infundibular stalk and median eminence are similarly appearing anatomical portions. You might be tempted to mistake the dense neuropil for collagenous connective tissue, but on fine inspection, the neuropil has a different texture and appearance from collagen. The secretory units of this tissue are the terminals of these axons, which descend from the hypothalamus.[1] Axon terminals that are especially dilated with product can often be seen as Herring bodies, which are rounded in appearance. The only other novel structure in neurohypophyseal regions are the pituicytes, which are the resident glial cells. Though not obvious in the section, pituicyte processes are situated between the axons and the local vasculature. Annoyingly, pituicyte nuclei can be alternately very euchromatic or very heterochromatic depending on their activity. Which are these?

Cells of the adenohypophysis produce many different hormones, though each individual cell is thought to produce only one specific hormone. In an H&E stained section, the intracellular hormone-containing granules stain either acidophilic, basophilic, or not at all depending on their product. Thus, the cells of the adenohypophysis can be classed as acidophils, basophils, or chromophobes, and this is a useful way to identify the pituitary.

Question 67

Adrenal Glands

Answer 67

Unlike the other endocrine glands, the adrenal gland has a layered organization. Yet, the cells still secrete basally into (a small amount of) connective tissue and from there into the circulation.

The adrenal gland is surrounded by a capsule of dense sheet-like connective tissue. Within the gland, the outermost portion is referred to as the adrenal cortex, and the inner portion is the adrenal medulla.

Question 68

suprarenal artery and vein

Answer 68

hree suprarenal arteries supply blood to the gland, and one suprarenal vein (visible in this section) carries blood away.

In the adrenal gland, blood flows from periphery to center. The suprarenal artery branches within the capsule, and contributes blood to both arterioles and capillaries. These vessels travel radially through the cortex, and thus supply the medulla with two separate sources of blood. Find clear examples of arterioles and venules/veins within the adrenal gland.

Question 69

three layers of adrenal cortex

Answer 69

The adrenal cortex is divided into three layers. All three of these layers produce steroid hormones, referred to as “corticosteroids” because they come from the adrenal cortex. From superficial to deep, these three layers are the zona glomerulosa, zona fasiculata, and zona reticularis. They are easily distinguishable. Examine the middle layer, the zona fasciculata. These cells have the canonical appearance of steroid-producing cells. Their bubbly, (frothy, foamy) cytoplasm is due to intracellular cholesterol, which, being a lipid, sequesters itself in tiny droplets