ENDOCRINE TISSUES
Biomedical Sciences Option 5: Endocrinology
Aims and Objectives
By the end of the class you should:
 Recognise the endocrine tissues of the pituitary, thyroid, adrenal and pancreas
 Understand the way in which different endocrine cells are arranged within these organs, and
their relation to the blood vessels and innervation
 Understand the essential morphological differences between cells producing peptide,
amine, steroid, and thyroid hormones
Safety
NO FOOD AND DRINK IN THE CLASSROOM
S W I T C H A L L MO B I L E P H O N E S O F F
W H I T E C O A T S T O B E W O R N A T A L L T I ME S
Experiment 1: Pituitary gland – general organization
The anterior and posterior lobes of the pituitary originate from different embryological
sources and this is reflected in their structure and function. The posterior pituitary is
derived from a down-growth of nerve tissue from the hypothalamus to which it remains
joined by the pituitary stalk. The anterior pituitary derives from an epithelial up-growth
from the roof of the primitive oral cavity known as Rathke’s pouch. The anterior pituitary
is made up of clusters of nucleated endocrine cells surrounded by capillaries whereas
the posterior pituitary is made up of hypothalamic neurosecretory nerve endings. The
posterior pituitary secretes vasopressin (also called antidiuretic hormone or ADH) and
oxytocin. These hormones are made in the neuron cell bodies in the hypothalamus and
pass down the axons through the pituitary stalk to the posterior pituitary where they are
stored in the nerve terminals. The anterior pituitary comprises five different secretory
cell types – somatotrophs (secrete growth hormone, GH), lactotrophs (secrete
prolactin), corticotrophs (secrete adrenocorticotrophin, ACTH), thyrotrophs (secrete
thyroid stimulating hormone, TSH) and gonadotrophs (secrete follicle stimulating
hormone, FSH and luteinising hormone, LH).
Slide 450: (PAS / alcian blue / orange trichrome) Section of ox pituitary gland.
Examine the slide with the naked eye, with a hand lens and with the lowest power of the
microscope. Draw an idealised section through a pituitary, to show the major lobes and
their relationships, the basic cellular organisation and the blood vessel distribution.
POSTERIOR PITUITARY (NEURAL LOBE)
Examine the neural lobe at slightly higher power, then study the electron micrographs provided.

What forms the major endocrine tissue in the neural lobe?

What are the nucleated (non-endothelial) cells in the neural lobe?

How are the hormones of the neural lobe released?
ANTERIOR LOBE
Study the electron micrographs of the anterior pituitary of a normal animal.
GH
GH
ACTH
N
N = nucleus, GH = somatotroph, ACTH = corticotroph

By what mechanism are the anterior pituitary hormones released?
Experiment 2: Thyroid gland – general organization
The thyroid gland produces hormones of two types: (1) iodine containing hormones
triiodothyronine (T3) and thyroxine (T4). Thyroid hormone regulates the basal metabolic rate
and has an important influence on growth and maturation. The secretion of these hormones is
regulated by TSH secreted by the anterior pituitary. (2) The polypeptide hormone calcitonin; this
hormone regulates blood calcium concentrations in conjunction with parathyroid hormone.
Calcitonin lowers blood calcium by inhibiting the rate of decalcification of bone by osteoclast
resorption and by stimulating osteoblast activity.
The thyroid gland is unique among the
endocrine glands because it stores large amounts of thyroid hormone in an inactive form, in a
glycoprotein complex called thyroglobulin or colloid, within extracellular follicles.
Thyroid
follicles are lined by a simple cuboidal epithelium which is responsible for the synthesis and
secretion of T3 and T4. Calcitonin secreting cells are scattered among the follicular cells or in
the interfollicular spaces.
These ‘parafollicular cells’ synthesise and secrete calcitonin in
response to raised blood calcium concentrations.
Slide 498: (H & E) rat thyroid gland, showing both thyroid and parathyroid tissue.
Identify the follicles of thyroid epithelial cells and the acellular colloid within the follicles. Make a
drawing of a few follicles.

Do all follicles appear the same?

What lies between the follicles?
Experiment 3: Adrenal gland – general organization
The adrenal gland comprises two parts: the adrenal cortex and the adrenal medulla. The
adrenal cortex produces and secretes steroid hormones including mineralocorticoids
(aldosterone), glucocorticoids (cortisol in man), and sex hormones (in small amounts). The
steroids are produced from cholesterol. Glucocorticoid production and release is regulated
mainly by ACTH from the pituitary gland. The adrenal cortex consists of three layers of
secretory cells: the zona glomerulosa (outermost layer, secretes mineralocorticoids), zona
fasciculata (broadest, middle zone of the adrenal, secretes glucocorticoids) and zona reticularis
(thin layer, smaller cells adjacent to medulla, secretes small amounts of androgens). The
adrenal medulla has similar origin to that of the sympathetic nervous system and secretes the
catecholamine hormones adrenaline and noradrenaline from cells termed ‘chromaffin cells’.
0+The secretions from the adrenal medulla are directly controlled by preganglionic sympathetic
fibres. The function of the adrenal medulla is to reinforce the action of the sympathetic nervous
system in stress.
Slide 474: (H & E) Human adrenal gland
Examine the slide with a hand lens and then at very low power. Make a diagram of the whole
organ to illustrate its different parts. Identify the zona glomerulosa, the zona fasciculata, and the
zona reticularis. Illustrate how the cells are arranged in the different zones
Examine the electron micrographs showing the adrenocortical cells and use the table to note
the essential characteristics of these steroid-secreting cells.
Cap = capillary, M = mitochondria, G = Golgi apparatus,
T = triglyceride lipid stores, Nu = nucleolus, N = nucleus
N
M
T

Are the adrenal blood vessels constricted in the "fight or flight" response?
Examine also the electron micrographs of adrenal medullary cells.
NT = nerve terminals; Ep and No= adrenaline and noradrenaline secreting cells

What is the function of the prominent nerve fibre bundles in the adrenal medulla?

How is adrenaline / noradrenaline released from the cell?
Experiment 4: Endocrine pancreas –
Islets of Langerhans
The pancreas has both a major exocrine role and important endocrine functions. During
development the potential endocrine cells migrate from the pancreatic duct epithelium and
aggregate around capillaries to form isolated clumps of cells scattered throughout the exocrine
tissue. The endocrine clumps are termed the islets of Langerhans and are most numerous in
the tail of the pancreas. The main secretory products of the pancreas are the polypeptide
hormones insulin (from beta cells) and glucagon (from alpha cells). Insulin promotes the
uptake of glucose in particular by liver, skeletal muscle and adipose tissue thus lowering
plasma glucose concentration whereas glucagon stimulates glycogen breakdown and increases
the plasma glucose concentration. Other secretory cell types in the islets secrete somatostatin,
vasoactive intestinal peptide (VIP) and pancreatic polypeptide (PP).
Slide 202: Human pancreas
The stain method stains  cells reddish-pink, and  cells bluish-grey. Examine the electron
micrographs showing the different cell types of the islets of Langerhans. Use the table to note
the characteristics of the cell types.
A= glucagon secreting cell, B= insulin secreting beta cell, D = somatostatin secreting cell, n=
nucleus, g= secretory granules, m= mitochondria.
ULTRASTRUCTURAL FEATURES OF ENDOCRINE CELLS
Complete the table below to show the relative abundance of different ultrastructural features
(score 0  + ++ )
MitoTissue
PITUITARY
Posterior
Anterior
THYROID
Follicles
C cells
ADRENAL
Cortex
Zona
glomerulosa
Zona
fasiculata
Zona
Reticularis
Medulla
PANCREAS
Islets
of
Langerhans
Principle
Chemical ER
ER
hormone
type
rough
smooth
Golgi
chon
dria
Granules
Lyso
Lipid
som
drops
es