[HISTOLOGY] Endocrine System

7/25/2019 [HISTOLOGY] Endocrine System

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Histology: Endocrine System | 1

Endocrine SystemSubject: Anatomy

Lecturer: Eduardo Gonzales, MD

Major integration and control systems of the body

1. nervous system

2.

endocrine system

two systems work parallel but independent of each

other

but overlaps exist both anatomically and functionally

both receive and respond to stimuli

but response of endocrine system is

slower

more diffuse

longer-lasting

Endocrine System

comprised of all cells and glands that elaborate

o cells

occur singly or in clusters in various

organs in the body

e.g., enteroendocrine cells of GIT

o glands (endocrine glands)

no excretory duct (ductless glands)

richly supplied with capillaries

Endocrine glands

distinct organs

1.

pituitary gland

2. pineal gland

3.

thyroid gland

4. parathyroid gland

5.

adrenal glands

component of organs

1.

endocrine portions of hypothalamus

2. islets of Langerhans

Hypothalamus part of diencephalon

at base of brain behind optic

chiasm

forms floor and part of wall of 3rd

ventricle

consists of:

nuclei

nuclear

areas

tracts

Hypothalamus: functions

controls many body

functions (e.g.,

thirst, hunger,

satiety,

temperature, sexual behavior, circadian rhythms,

etc.)

elaborates hormones

Hormones

I.

posterior pituitary hormones

1. oxytocin

2.

anti-diuretic hormone (ADH)

II. hypophyseotrophic hormones (neurohormones)

1.

corticotropin-releasing hormone (CRH)

2.

thyrotropin-releasing hormone (TRH)3. growth hormone-releasing hormone (GRH)

4. growth hormone-inhibiting hormone (GHIH;

somatostatin; SS)

5. gonadotrophin-releasing hormone

(leutinizing hormone-releasing hormone;

GnRH;LHRH)

6. prolactin-inhibiting hormone (PIH)

I. posterior pituitary hormones

o magnocellular secretory neurons

o in supraoptic and paraventricular nuclei

II.

hypophyseotrophic hormones (neurohormones)

o parvocellular secretory neurons

o widely dispersed in hypothalamus but

mostly in:

arcuate nucleus paraventricular nucleus

periventricular nucleus

Pituitary gland

a.ka. hypophysis cerebri

size:

o 12 mm transverse & 8 mm in AP

diameters

weight:

o 500 mg

location:o attached to inferior surface of

hypothalamus

o lodged in hypophyseal fossa of sella

turcica of sphenoid bone


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Hypothalamus and Pituitary Gland

key organs involved in interplay of nervous and

endocrine systems

extensive neural and vascular connections exist

between these organs

Parts:

1. neurohypophysis

2. adenohypophysis

2 parts differ developmentally, structurally and

functionally

1.

Neurohypophysis from neural ectoderm

downgrowth of diencephalon

connection with brain persists & becomes

infundibulum (pituitary stalk)

a)

median eminence

b) pituitary stalk (infundibulum; infundibular stem;

infundibular stalk; hypophyseal stalk)

c) pars nervosa (posterior lobe; infundibular process)

2. adenohypophysis

from oral ectoderm derived from an outgrowth of oral mucosa

(Rathkes pouch) connection of Rathkes pouch with oral cavity

severed later

a) pars distalis (anterior lobe)

b) pars tuberalis (pars infundibularis)

c) pars intermedia (intermediate lobe)

Neurohypophysis

a)

median eminence

portion attached to hypothalamus

axons of parvocellular neurons terminate

here

b)

pituitary stalk

downward extension of median eminence

expands inferiorly to form pars nervosa

1. hypothalamo-hypophyseal tract

o axons of cells insoand pv nuclei on

their way to pars nervosa

2. neuroglial cells (pituicytes)

o stellate; processes interconnects with

other pituicyte

o supportive functions to secretory

neurons

3. capillaries

c) pars nervosa

distal portions and terminations of axons of

neurons in soand pvnuclei

pituicytes

capillaries

Neurohypophysis

not really a gland; does not produce hormones

stores two hormones produced by cells of so and pv

nuclei

secretions stored in axon terminals in pars nervosa

Herring bodies

o aggregation of secretions

o deeply-staining

o basophilic structures.


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Neurohypophysis: Hormones

a.k.a. posterior pituitary hormones

1. oxytocin

o stimulates contraction of smooth muscles in

myometrium; aids in parturition

o stimulates contraction of myoepithelial cells

in mammary gland; aids in ejection of milko in males, facilitate sperm transport within

male genital tract.

2. vasopressin (anti-diuretic hormone; ADH)

o increases permeability of collecting ducts of

kidney; concentrates urine

oxytocin is produced by one cell type

vasopression is produced by another cell type

both cell types are present in both so and pv nuclei

Adenohypophysis part of gland that

synthesizes hormones

Sub-parts:

o pars distalis

(anterior lobe)

o pars tuberalis

(pars

infundibularis)

o pars intermedia

(intermediate

lobe)

a) pars distalis (anterior lobe)

o biggest (sub)part of gland

o comprises about 70% of gland

o produces nearly all the hormones secreted by

pituitary gland

o hormones collectively

referred to as anterior

pituitary hormones

Histology

o epithelial cells

cords

clusters

(note: anastomosing and

irregularly arranged)

o capillaries

o connective tissue

minimal

mostly reticular

fibers.

Epithelium

o types (based on staining of cytoplasm under LM)

A.

chromophils

affinity for acid dyes

acidophils (alpha cells) - cytoplasm

stains red

basophils (beta cells) - cytoplasm stains

blue or purple

B. chromophobes

pale-

staining

with acid

dyes

comprise65% of

epithelial

cells

o types (based on staining of cytoplasm under LM)

A. chromophils

1.

acidophils (alpha cells)

a. somatotrophs

most abundant of chromophils 50% of epithelial cells

secrete somatotropin (growth

hormone)

affects practically all cells

b. mammotrophs

20% of epithelial cells

scattered singly all over lobe

larger secretory granules than

somatotrophs

secrete prolactin stimulates growth and

activity of mammary

glands during pregnancy

& lactation

in males, helps regulate

testicular function

increase in size and number in

pregnancy

most acidophils secrete only one type of

hormone

a few (somatomammotrophs) secrete both

somatotropin and prolactin

2. basophils (beta cells)

c.

thyrotrophs

% of epithelial cells

polygonal cells with long

processes

secretory granulessmallest of

5 cell types

produce thyrotropin (thyroid

stimulating hormone; TSH)

TSH stimulates thyroid gland

to produce thyroid hormones

Note: names

are based on

hormones

that cell type

secretes


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d. Corticotrophs


few secretory granules and

only slightly larger than those

in thyrotrophs

secrete corticotropin (ACTH;

adrenocorticotropin; adreno-corticotropic hormone) that

stimulates adrenal cortex.

e. Gonadotrophs


large, round cells

distributed singly throughout

pars distalis

secretory granules moderate &

variable in size

produce gonadotropins luteinizing hormone (LH)

follicle stimulating

hormone (FSH)

not known yet whether there

are 2 types (one producing LH;

another FSH) or just one type

producing both hormones

B.

chromophobes

o

pale-staining with acid dyeso comprise 65% of epithelial cells

o actually consist of three (3) types of

cells

chromophils (majority & mostly

corticotrophs)

o resting

o have just released their secretory

granules

o in process of producing secretory

granules

o few granules that dont manifest in

LM

folliculostellate cells (FS cells)

o nonsecretory with branching

processes

o form supporting network for other

cells

undifferentiated stem cells.

b)

pars tuberalis (pars infundibularis)

o forms sleeve around pituitary stalk of

neurohypophysis

o more vascular than anterior lobe

o contains hypophyseoportal system

o sometimes with follicles that contain colloids

o parenchymal cells arranged in cords or clusters

around blood vessels

o cells, mostly

1. gonadotrophs

2. thyrotrophs

c)

pars intermedia (intermediate lobe)

o separates anterior from posterior lobe

o boundary with anterior demarcated by groove that

represents original lumen of Rathkes poucho better developed in fetus; rudimentary in adults

o has follicles (Rathkes cysts) that contain eosinophiliccolloid material

o cells

form irregular clusters

synthesize

melanocyte stimulating hormone (MSH)

in adults, production is minimal to

nil

physiologic action in humans is

unknown

may also produce bendorphins


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Hypothalamic control on anterior lobe of pituitary

gland

hormones of anterior lobe of pituitary

1. somatotropin

2.

prolactin

3. thyrotropin

4.

corticotropin5. FSH

6.

LH

hypophysiotropic hormones (neurohormones)

1. growth hormone releasing hormone (GRH)

2. growth hormone inhibiting hormone (GIH;

somatostatin; SS)

3.

prolactin inhibiting hormone

4. thryotropin releasing hormone (TRH)

5.

corticotropin releasing hormone (CRH)

6.

leutinizing hormone releasing hormone(LHRH; gonadotropin releasing hormone;

GnRH)

Note:

each hypophysiotropic hormone exerts control over more

than one pituitary hormone, e.g.

TRH stimulates production of thyrotropin and

prolactin

GnRH stimulates secretion of both FSH and LH

axons of nerve cells that produce hypophysiotropic

hormones end in median eminenence hormones brought to anterior pituitary by

hypophyseoportal system

Pineal Gland

(epiphysis cerebri)

small; cone

shaped

o length = 8mm

o weight = 120 mg

arises as evagination of roof of diencephalon

base attached to roof of 3rd

ventricle by two stalks

well-developed in children

at puberty, starts to involute

capsule

o thin connective tissue; derived from the pia

mater

o septae incompletely divide organ into

lobules.

Cells

1.

pinealocytes(chief cell)

modified

neurons

95% of cell

population

large nucleus

poorly

defined cell

borders

in cords or

clusters surrounded by fenestratedcapillaries

2.

interstitial cells (glial cells)

comprise 5 % of cell population

similar to astrocytes morphologically

3. mast cells

few

explains organs high histamine content.

brain sand (acervulus; psammoma bodies;corpora

arenacea)

o

distinctive feature of glando calcified, extracellular bodies

o concentric, lamellar structures

o increase in number with age

o radiopaque

o gland sometimes used as a landmark in X-

ray studies of brain.

melatonin

o

hormone elaborated by pinealocyteso

secretion is stimulated by darkness and

inhibited by light

o in animals that breed seasonally

regulates sexual development

regulates reproductive cycle

(seasonal breeding), hibernation

and other metabolic processes.


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o in humans

blood level has diurnal pattern;

higher at night than during day

blood level much higher in children

than adults

physiologic function not known yet

it may affect circadian rhythms andsleep patterns.

Thyroid gland

largest endocrine

gland

25-40 g in weight;

slightly bigger in

women than inmen

arises as

epithelial

invagination at

base of tongue

parts:

o two lateral lobes (right and left)

o isthmus

remains connected for a time to base of tongue by

thyroglossal duct that later disappears

foramen cecum

o indicates point of origin of thyroid gland

o apex of the V-shaped furrow (sulcus

terminalis) that separates anterior 2/3 from

posterior 1/3 of tongue.

Thyroid gland: Histology

capsule

o two capsules

o outer capsule - derived from pretracheal

layer of the deep cervical fascia

o true capsule

closely invests gland

septae divides organ into poorly-defined lobules

Lobules

o follicles

several comprise each lobule

spherical, cystic structures

wall formed by simple cuboidalepithelium (usually)

colloid-

homogenous, gel-like

material in cavity of

follicles.

Cells

o follicular (principal) cells

comprise overwhelming majority

round nucleus that contains fine

chromatin material

cytoplasm is slightly basophilic

luminal surfaces are provided with

numerous microvilli not discernible

under LM

the taller the cells and the more

basophilic the colloid, the more

active the follicle

if epithelial cells are low (i.e.,

squamous) and colloid is

acidophilic, follicle is

hypofunctional.

o parafollicular cells

a.k.a., mitochondria-rich cells;

C cells; clear cells

0.1% of cell population

scattered singly or in small groups

in epithelium

much bigger & lighter-staining than

follicular cells

they form part of follicular

epithelium (as per EM).

Thyroid gland: hormones

1. thyroid hormones

thyroxine (T4)

triiodothyronine (T3)

2. calcitonin (thyrocalcitonin)


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thyroid hormones: synthesis

follicular cells

1. synthesize thyroglobulin, a glycoprotein,

which is then discharged by exocytosis into

colloid

2.

collect iodine from blood and transport this

to lumen of follicle in the colloid,

1. some tyrosine residues in thyroglobulin are

iodinated and condensed to form T3 & T4

with aid of enzyme thyroid peroxidase

2. T3 and T4 remain bound to thyroglobulin

until they are to be secreted

to secrete hormones, the follicular cells

1. ingest colloid by endocytosis

2. hydrolyze peptide bonds binding thyroid

hormones to thyroglobulin

3.

release thyroid hormones into capillaries.

thyroid hormones

Function:

regulate the metabolism of

proteins, carbohydrates, fat

and some vitamins

control of secretion

thyrotropin (TSH) from

anterior pituitary; in response

to thyrotropin-releasing

hormone (TRH) from

hypothalamus.

Calcitonin

synthesized and secreted by parafollicular cells

function:

o lowers blood calcium levels

o inhibits bone resorption by directly

suppressing osteoclasts

control of secretion:

o

blood calcium levels directly regulate

secretion of calcitonin.

Parathyroid gland

usually 2

pairs

(superior

and

inferior)

yellowish-brown,

tiny, ovoid

bodies

attached to posterior surface of thyroid gland

each is about 6 mm in length, 3-4 mm in width and

1-2 mm thick, and weighs about 50 mg

lie within capsule of thyroid gland.

origin:

o inferior parathyroid glands arise from third

pharyngeal pouch together with thymus

o superior parathyroid glands arise from

fourth pharyngeal pouch and attach

themselves to thyroid glands.

Parathyroid gland: histology

capsule

o thin connective tissue

o septae incompletely subdivide gland into

lobules

parenchyma

o epithelial cells

in cords and clusters

o capillaries

numerous

o adipose cells

at age 25, comprise about 30% of

volume of gland

o follicles

occasionally present in older

individuals

resemble those found in the

thyroid gland.

Parathyroid gland: Epithelial cells

1. chief (principal) cells

majority of the cells

relatively small (8-10 m in diameter)

polyhedral; homogeneous cytoplasm is faintly

eosinophilic

elaborate and secrete parathyroid hormone

(PTH; parathormone)


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2. oxyphil cells (acidophil cells)

appear shortly before puberty

increase in number with age

occur singly or in clusters

bigger than chief cells but nuclei slightly smaller

cytoplasm with many acidophilic granules and

hence, intensely eosinophilic

nonsecretory and function is unknown

maybe chief cells that are in a different

physiological state.

Parathyroid gland: hormone

parathyroid hormone (PTH; parathormone)

o only hormone produced by parathyroid

gland

o secreted by chief cells

o

most important regulator of blood calciumlevel

o increases circulating blood level of calcium

by

indirectly increasing number and

activity of osteoclasts

inhibiting bone formation by

osteoblasts

enhancing calcium reabsorption in

renal tubules

increasing conversion of vitamin D

to its active form increasing excretion of phosphate

by kidneys

promoting absorption of calcium in

digestive tract.

o control of secretion

secretion of PTH dictated by blood

levels of ionized calcium

high calcium level inhibits

secretion and calcium is

deposited in bone

low calcium level

stimulates secretion

Adrenal Gland

a.k.a, suprarenal

gland; adrenals

paired (left and

right), flat,

pyramidal organs

on upper pole of kidneys

each weighs about 5 g and 50 mm long or high, 30

mm wide and 10 mm thick.

hilus

indentation at middle of anteromedial aspect

where adrenal vein leaves gland

(note: adrenal arteries enter gland through

capsule).

Adrenal gland: histology

capsule

o relatively thick

o collagenous connective tissue; rich in

reticular fibers

o elements penetrate gland up to medulla.

parts:

o differ embryologically, structurally and

functionally

o cortex

outer area

completely surrounds medulla

mesodermal origin

essential for life

some of its hormones play vital

roles in metabolic activities

o medulla

ectodermal origin

not essential for life

hormones help individual cope

with emergencies.

Cortex

80-90% of adrenal gland

produce steroid hormones (adrenocortical

hormones)

produces numerous hormones, but only a few are

important

1. mineralocorticoids

aldosterone

2. glucocorticoids

cortisol

corticosterone

3. androgens

dehydroepiandrosterone (DHEA)

androstenedione.

Layers:

1. zona glomerulosa

2. zona fasciculata

3.

zona reticularis


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zona glomerulosa

15% of cortex

rounded or

pyramidal cells

arranged in

irregular ovoid

clusters

cell clusters

separated by

sinusoids that are

supported by fine

connective tissue

septae

cells have

deeply-

staining

nucleus with one or two nucleoli

cytoplasm is scanty and eosinophilic.

mineralocorticoids, mainly aldosterone

hormone produced by cells of this zona

increases Na+reabsorption by collecting

tubules of kidney

control of aldosterone secretion

mainly by renin-angiotensin system

of kidneys

secondarily by corticotropin (ACTH)

from anterior pituitary.

zona fasciculate thickest layer

(78%) of adrenal

cortex

cells form long,

thin (usually one-

cell thick), straight

cords arranged

perpendicular to

capsule

cords separated by

sinusoids that are

supported by fine

connective tissue

septae.

cells (also called spongiocytes)

large, polyhedral

vesicular nucleus with prominent nucleolus

abundant, faintly-basophilic cytoplasm

cytoplasm vacuolated because of many lipid

droplets so the name.

glucocorticoids

hormones produced by cells of this zona

mainly cortisol and corticosterone

regulate carbohydrate, lipid and proteinmetabolism

primary regulator of the activity of cells of

zona fasciculata is corticotropin (ACTH)

from anterior pituitary.

zona reticularis

innermost and

thinnest layer (7% of

volume of cortex)

cells small and

arranged in shortanastomosing cords

between cords are

sinusoids

cells histologically

similar to cells of

zona fasciculata but

less

vacuolated

(less lipid droplets)

nucleus stain more intensely.

Hormones1. a small quantity of glucocorticoids (cortisol and

corticosterone)

2. androgens dehydroepiandrosterone (DHEA) and

androstenedione

activity less than 20% those of

testicular androgens

hardly any physiological effect on

normal people

not enough to induce masculinization

of women

primary regulator of activity of cells of this zoneis corticotropin (ACTH)

gonadotropins do not affect cells of zona

reticularis.


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Medulla

comprises only 10-20% of adrenal gland

thin region completely surrounded by cortex

central part with large medullary veins that drain

entire gland.

Cells:

1.

chromaffin cells most of adrenal medulla consist of

these cells.

arranged in groups or thick cords that

are surrounded by sinusoids and richly

supplied with nerves

all are associated with endings of

preganglionic sympathetic neurons

polyhedral parenchymal cells

large, darkly-staining nucleus

basophilic ctyoplasm

so-called because of secretory granules

that turn brown when treated with an

oxidizing agent, like chromate

(chromaffin reaction)

2.

ganglion cells (neurons)

neurons scattered among chromaffin

cells

Secretions: three kinds of cathecolamines

o epinephrine (adrenaline)

secreted by 90% of chromaffin cells

o norepinephrine (noradrenaline)

secreted by 10% of chromaffin cells

stronger chromaffin

reaction

granules more electron

dense

o dopamine

cells that secrete this have not

been identified yet

chromaffin cells also synthesize a wide-variety of:

o bioactive amines

o peptides.

Islets of Langerhans

aggregations of pale-staining cells (in H & E

preparations) scattered throughout darker staining

cells of exocrine pancreas

100-200 m in diameter

islet is surrounded by thin layer of fine reticular

fibers; with rich supply of capillaries.

over a million in number

combined volume = only 2% of pancreas

more numerous in tail than in body or head of gland.

Cells:

each islet

has 2 to 3

thousand

cells that

form a

compact

mass

polygonal

polarized

toward the

capillaries

into which they discharge their secretions.

cells types

1.

a cell (A cell)

about 20% of islet cells

large cell and most occupy

peripheral areas of islet

electron-dense secretory granules

of uniform size

secretes glucagon.

2. cell (B cell)

most numerous, 60-75% of islet

cells

most are in central area of islets

smallest of the cells of islet


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secretory granules smaller and less

electron dense than A cell

secretes insulin.

3. cell (D cell)

only about 5% of islet cell

population

scattered singly all over islets largest of islet cells

secretory granules similar to A cells

but less electron dense

secretes somatostatin

4.

F cell (PP cell)

rare

widely scattered and sometimes

occurs among the pancreatic acini

secretory granules irregular in

shape and variable electron

density

secretes pancreatic polypeptide.

not distinguishable in H & E

distinguished from each other by employing special

staining, immunocytochemistry techniques and EM

(by structure of secretory granules)

each cell type secretes a different hormone.

Hormones:

1. glucagon

secreted by a cell (A cell)

2.

insulin

secreted by b cell (B cell)

3.

somatostatin

secreted by cell (D cell)

also produced by some cells of

digestive tract and hypothalamus

but, physiologic effect of

hypothalamic somatostatin

different

4.

pancreatic polypeptide

secreted by F cell (PP cell).

[HISTOLOGY] Endocrine System

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