H & E: 2:00 - 3:00
Tuesday, November 3, 2009
Dr. Cotlin
The Endocrine System: Hypophysis (or Pituitary Gland)
Scribe: Caitlin Cox
Proof: Marjorie O’Neil
Page 1 of 6
**She altered the order of the slides during lecture, and she skipped around a lot at the beginning due to
technical difficulties. To minimize confusion, I kept the order of the slides the same as the original ppt we
received, and I have indicated when she talked about a slide out of order.
I.
II.
III.
IV.
V.
VI.
VII.
Introduction [S1]:
a. Skipped.
The Endocrine System [S2]:
a. The endocrine system is the communication system of the body regulating all of our metabolic activities.
Hormones [S3]:
a. Hormones are the mediators.
b. They are proteins, polypeptides, small amino acids, or steroids.
c. Most will have short term and long term effects.
d. They will bind to specific hormone receptors. The nature of their chemical composition will dictate. The
hydrophilic molecules (proteins, amino acids) will have cell surface receptors. Steroid hormones will be able to
go inside and have cytoplasmic or nuclear receptors.
e. We can think of this as a signal transduction system for the body. If you think of what a cell does on a single
basis, we have signal transduction and 2nd messengers. Hormones are like the 2nd messengers of the body.
The Development of Exocrine and Endocrine Glands [S4]:
a. The endocrine glands do NOT have a duct. All of their contents will be secreted directly into capillary beds,
directly into the vasculature.
b. All glands, whether endocrine or exocrine, are of epithelial origin. These cells will orient in cords or circular
patterns and have tight junctions. They will also sit on basement membrane, just like any other epithelium
tissue would do.
Hypophysis (or Pituitary Gland) [S5]:
a. Historically, the mucous in the nose was thought to be derived from the pituitary gland, so that is how it got its
name. Currently, it is more commonly called the hypophysis.
b. It is an undergrowth of the hypothalamus.
c. It is considered the master organ because all of your other endocrine organs are going to respond to hormones
secreted by the hypothalamus. This organ is under neural control. It will stimulate secretions from adrenal
glands, thyroid, all of our reproductive, as well as mammary glands, muscle, bone eliciting growth.
d. This system is referred to as the hypothalamo-hypophysial system. The hypothalamus is going to secrete
neurohormones that are going to directly stimulate cells in the hypophysis.
e. Hypophysis is suspended from the hypothalamus by a little stalk; it is continuous with the brain.
f. The pituitary is sometimes referred to as the neuroendocrine system. The nervous system is directly altering
the endocrine system; the two are physically connected at this point.
g. It sits in a bony structure called the sella turcica.
h. As you will see with all endocrine tissues, there is very rich vasculature because our hormones are going to be
secreted directly into those vessels.
i. Two major subdivisions of the hypophysis are the: Adenohypophysis (anterior hypophysis) and
Neurohypophysis (posterior hypophysis).
Regions of the Hypophysis [S6]:
a. The Adenohypophysis, or the anterior lobe, is direct epithelial secreting tissue. It consists of these regions:
pars distalis, tuberalis, and intermedia. Cells are actively secreting. It is epithelial in origin.
b. The Neurohypophysis, or the posterior lobe, is NOT epithelial in origin. Also, it is not endocrine secreting cell
tissue. There are no endocrine secreting cells in this tissue. It is the place where the tracts of the nerves from
the hypothalamus go in and secrete. It is just neurosecretory tissue. The bulk of that is going to be the pars
nervosa, and then infundibulum.
c. In histology sections, in the anterior, you will see lots of cells, lots of secretory granules, and staining material.
In the posterior lobe, it will look a lot like nervous tissue because it is.
Subdivisions of the Hypophysis [S7]:
a. The major portion of the Adenohypophysis is going to be the pars distalis. This makes up the bulk of the
anterior hypophysis. She pointed out the pars distalis, intermedia, and tuberalis.
i. There are specific cells in the pars intermedia, and the pars intermedia makes up little follicles, which are
NOT related to the follicles found in the thyroid that we will discuss later.
b. This is the Neurohypophysis. The bulk of it is the pars nervosa. The infundibulum, the stalk, is a direct
downgrowth. The hypothalamus is up here and some of our nuclei, some of the nerve cell bodies are located in
the hypothalamus. Their axons are going to extend through the stalk region to terminate in a capillary bed. This
H & E: 2:00 - 3:00
Scribe: Caitlin Cox
Tuesday, November 3, 2009
Proof: Marjorie O’Neil
Dr. Cotlin
The Endocrine System: Hypophysis (or Pituitary Gland)
Page 2 of 6
is the hypothalamo-hypophysial tract. You will have neuron cell bodies in the hypothalamus; their axons will go
down the stalk and terminate in the capillary beds.
c. The anterior lobe is the secretory material; the neural secretory tissue is in the posterior lobe.
VIII. Development of the Pituitary Gland [S8]:
a. These two lobes are so different because they have different developmental origins. The glandular epithelial
tissue of the Adenohypophysis is a direct outgrowth from oropharynx ectoderm; see in the picture how the
pouch evaginates up. Neural ectoderm invaginates down. The two come together and wrap around
themselves. So very different developmental origins: one is epithelium, one is nerve tissue.
IX. Sella Turcica Radiograph[S9]:
a. This depression is where the pituitary gland sits. The pituitary gland is pea-shaped.
X. The Pituitary Gland and its target organs [S10]:
a. Here are the target organelles of the anterior and posterior lobes. We will not go through them; it is just to show
you we can classify cells as acidophils or basophils.
XI. Arterial and Venous Portal System [S11]:
a. A normal capillary bed goes from: artery  capillary bed  vein. Sometimes we see multiple capillary beds
where the blood goes through a primary bed and then a secondary bed. We saw this in the kidney where the
primary capillary bed was the glomerulus and the secondary capillary bed was the vasculature in the cortex and
the medulla. The liver is a portal system. We see this portal system in the hypophysis also.
b. She talked about Slide 17 & 18 right here for a minute. See [S17-18], and then come back to this slide.
c. In the hypophysis, we will see the two capillary bed system. We will see arteriole going to a primary capillary
bed, which is where gas exchange will occur. Then, when I say a portal vein, we are going to have a vein taking
that direct material to a secondary capillary bed. Neurohormones are going to be secreted in the primary and
then carried to a secondary capillary bed. Keep that orientation in mind.
XII. Blood Supply to the Hypophysis [S12]:
a. This is the written form of what she will explain on the next slide in picture form.
XIII. Blood Supply to the Hypophysis [S13]:
a. There’s a superior hypophyseal artery and an inferior hypophyseal artery.
b. The superior is going to feed the tissue right at the stalk, that median eminence or infundibulum, and enter that
primary capillary bed. The primary capillary bed is located at the base of the hypothalamus in the stalk region.
Then the portal veins (the hypophyseal portal veins) will carry blood from the primary capillary bed down to the
secondary capillary bed in the anterior lobe. All of that is going to drain by the hypophyseal veins. So the blood
going to the anterior lobe is directly from the primary capillary bed.
c. The inferior hypophyseal artery will feed the posterior lobe and, to some degree, the anterior lobe because the
anterior lobe will get venous blood from that primary capillary bed. When we talk about portal veins, we are
talking about those veins going from the primary capillary bed to the secondary capillary bed. The hypophyseal
veins are draining the pituitary as a whole.
XIV.
Blood Supply to the Hypophysis [S14]:
a. Here are our anterior and posterior lobes and hypothalamus.
b. The axons coming from the hypothalamus will have two different points of where they drop their hormones.
i. One set will deliver their hormones at the primary capillary bed; those will be the ones in controlling and
regulating the secretions from the anterior lobe. The axons will terminate at the primary bed and secrete
hormones. The hormones will be carried down these portal veins, released here, and their target organs
are the cells here. They have a very short life span because they only have to travel from the stalk down
here. These cells will be triggered/ stimulated to release their hormones, which will then go into systemic
circulation.
ii. The neurohormones are going to be released into the pars nervosa. Nerves are the cells generating the
neurohormones. The neurohormones are packaged and made in the cell bodies. They will be stored in
the axon terminals and secreted in the capillary bed in the pars nervosa. These also will be secreted
directly in the hypophyseal vein.
c. So there are two blood systems going on. Keep that orientation in mind.
XV. Interaction between the Hypothalamus, Adenohypophysis and Thyroid Gland [S15]:
a. We have this kind of expansion/amplification system. The hypothalamus is releasing hormones that will directly
stimulate cells of the pars distalis. This example is thyroid releasing hormone, which will tell these cells to
secrete thyroid hormone, which will trigger the thyroid to do its job. We usually see a feedback loop where the
thyroid will secrete T3 and T4. T3 and T4 will go on to stimulate other organelles and also be involved in the
feedback loop of turning this system off.
b. Throughout the endocrine system, we will see these feedback loops of secretion and inhibition.
XVI.
Hypothalamic derived Releasing and Inhibiting Factors [S16]:
a. The releasing and inhibiting factors will regulate the pars distalis.
H & E: 2:00 - 3:00
Scribe: Caitlin Cox
Tuesday, November 3, 2009
Proof: Marjorie O’Neil
Dr. Cotlin
The Endocrine System: Hypophysis (or Pituitary Gland)
Page 3 of 6
b. These are going to be the hormones released in the primary capillary bed and carried through the portal veins.
The secondary capillary system will be fenestrated or sinusoidal, meaning there are lots of gaps. We want to
flood those cells with those hormones; we can facilitate that by having this discontinuous capillary network.
c. Thyroid-stimulating hormone releasing hormone will tell the cells in the pars distalis to release thyroid hormone.
d. Adrenocorticotropine hormone releasing hormone will tell cells to release hormones that are going to affect the
cortex of the adrenal glands.
e. Growth hormone releasing hormone, signal to some of our bone and liver. Somatostatin will inhibit the release
of growth hormone. These work in opposition.
f. Gonadotropin releasing hormone tells those cells to release gonadotropins.
g. Prolactin inhibiting factor/hormone will tell cells NOT to secrete prolactin.
h. All of these releasing/inhibiting factors are going to be secreted by the hypothalamus. Therefore, they are
neurohormones carried to the portal vein, and then they stimulate cells of the Adenohypophysis.
XVII. Histology [S17-18]:
a. She pointed out the pars distalis, nervosa, intermedia, tuberalis, and infundibulum. It is very easy to distinguish
between the pars nervosa and the pars distalis. She likes using these terms instead of anterior and posterior
lobe because, as you can see, the bulk is the distalis versus the nervosa.
XVIII. Adenohypophysis (the anterior pituitary gland) [S19]:
a. It is an evagination of the oral ectoderm.
b. The tissue looks like cords of cells. They arrange in cords or circular arrays. Again, epithelial in origin, so that is
what you would expect structurally. Minimal connective tissue. Lots of fenestrated capillaries in that area.
c. Three distinct regions: distalis, intermedia, and tuberalis.
XIX.
Cells of the pars distalis [S20]:
a. There are two main types of cells in the pars distalis: chromophils or chromophobes.
b. We are really only concerned about the chromophils, which DO stain. The chromophobes do NOT stain; they
show up clear, and we are not sure if they represent immature cells or cells that have lost their secretory
granules (degranulated).
c. We can label the chromophils based on their staining patterns:
i. Acidophils will stain orange and red with an acidic dye. These are the most abundant cell in the pars
distalis.
ii. Basophils will stain bluish with basic dyes. These are less numerous and located at the periphery.
XX. Acidophils [S21]:
a. There are two main types of acidophils: somatotrophs and mammotrophs.
i. Somatotrophs will secrete somatotropin (growth hormone). The release will be stimulated by somatotropin
releasing hormone. Somatotrophs are inhibited by somatostatin. Growth hormone will increase general
metabolic and growth rate.
ii. Mammotrophs will secrete prolactin. The release is stimulated by prolactin releasing hormone and
oxytocin. Mammotrophs are inhibited by inhibitory factor and dopamine. This is the one that will promote
mammary gland development and lactation. The number increases following birth and drops off after
nursing stops.
iii. All of these that we see during regular resting situations are under releasing hormone effect except the
mammotrophs. Mammotrophs are always under inhibitory effect. Everyone secretes the inhibitory factor,
even males. The normal resting in a non-pregnant person is to inhibit the release of prolactin. It is
reversed in the situation where we need mammary gland development and lactation, so during pregnancy
and following birth while the woman is lactating.
XXI.
Basophils [S22]:
a. There are three main types of basophils:
i. Corticotrophs secrete adrenocorticotropic hormone. It is stimulated by corticotrophin releasing hormone
and is inhibited by high plasma cortisol levels. The adrenal gland produces a lot of steroids, and those will
have an inhibitory effect as well. It stimulates synthesis and release of hormones in the adrenal or
suprarenal cortex.
ii. Thyrotrophs is stimulated by thyroid stimulating hormone. Notice the pattern: all of these releasing
hormones stimulate a specific cell that is going to release a specific hormone that has a target. In this
case, the target is the thyroid. It is stimulated by thyrotropin releasing hormone and is inhibited by its
products: T3 and T4.
iii. Gonadotrophs are going to secrete FSH (follicle stimulating hormone) and LH (luteinizing hormone).
Secretion is under the control of gonadotropin releasing hormone and can be inhibited by hormones
produced in the target organelles. These will stimulate ovarian follicle growth, estrogen secretion, and
steroid hormones in the testes.
XXII. Cells of the Adenohypophysis [S23]:
H & E: 2:00 - 3:00
Scribe: Caitlin Cox
Tuesday, November 3, 2009
Proof: Marjorie O’Neil
Dr. Cotlin
The Endocrine System: Hypophysis (or Pituitary Gland)
Page 4 of 6
a. Acidophils stain reddish. Basophils stain bluish. Chromophobes are light and indistinguishable.
XXIII. Pars distalis – Cells arranged in cords [S24]:
a. You see cords of cells and cords of cells wrapped around themselves.
b. What are the spaces? They are the capillary sinuses. You are seeing a group of cells surrounded by sinusoids.
There are blood vessels all over because all of these cells are directly secreting right in their space, and it is
going to be picked up and carried in the vasculature.
XXIV. Pars distalis – Mallory-Azan stain [S25-27]:
a. Mallory-Azan is a specific stain used sometimes. It really distinguishes between acidophils (the red ones) and
basophils (blue).
XXV. Adenohypophysis continued [S28]:
a. Pars intermedia lies between the pars distalis and the pars nervosa. The cells in here specifically secrete
prohormones.
b. She switched to the next slide [S29] for a moment.
c. Pars tuberalis is the stretch that wraps around the stalk. The infundibulum is that region of the Neurohypophysis
that contains all the unmyelinated axons of the hypothalamus. The tuberalis is the part of the Adenohypophysis
that wraps around that stalk. Mainly composed of basophilic cells that secrete FSH and LH.
XXVI. Pars intermedia [S29]:
a. There are follicles. Cuboidal cells generate these follicles. The follicles are described as being colloidcontaining, but this is not the same as thyroid follicles which contain true colloid that has a function (it stores
hormones). This colloid does not have function. It is thought that it is simply a remnant of the two tissues
wrapping around each other. She switched back to [S28] to talk about the pars tuberalis.
XXVII. Neurohypophysis (the posterior pituitary gland) [S30]:
a. The Neurohypophysis is a downgrowth of the hypothalamus.
b. It is neural tissue NOT endocrine tissue.
c. It is composed of unmyelinated axons of neurosecretory cells.
d. In the Neurohypophysis, we do NOT see the nerve cells themselves. The cell bodies of these are located in the
hypothalamus. It is just the axons and the axon terminals. The axons in the infundibulum make up this tract
that we see. The nerve terminals reside in the pars nervosa.
e. The neurohormones are produced in the hypothalamus. They are transported along the axon and stored in
Herring bodies. So remember that the hormones are in the Neurohypophysis, but the nerve cell bodies are in
the hypothalamus.
f. The secretions are: vasopressin (antidiuretic hormone) and oxytocin. These will be released into the
bloodstream directly from the axon terminals. The cell bodies have the potential to start and generate an action
potential down the length of the axon. Nerve terminal is probably involved, calcium signaling, and regulated
secretion of those molecules.
g. The only supporting cells we see are these pituicytes. They are neuroglial cells. They support the pars
nervosa, but are not secretory cells themselves.
h. So, if we looked at a cell in the pars nervosa, you would know that it wouldn’t be a neuron; it would be a pituicyte
or a supporting connective tissue cell. Again, it does NOT consist of endocrine tissue; it is just a storage site.
XXVIII. The Neurohypophysis [S31]:
a. We have talked about two sets of neurons extended from the hypothalamus: some that terminate at the primary
capillary bed and some that extend all the way to the pars nervosa.
XXIX. Diagram [S32]:
a. These are the ones that will come and extend and secrete their material right here at this capillary bed in the
pars nervosa and then to systemic circulation.
XXX. Pars Nervosa [S33]:
a. When we do see cells, we will see these Herring bodies, which are just collections of the secretory granules.
b. Read this yourself, but she said she has basically already said all of this.
XXXI. Hormones of the Neurohypophysis [S34]:
a. The two hormones of the Neurohypophysis are:
i. Vasopressin, also called antidiuretic hormone (ADH). Its primary mode of action is in the kidney on the
collecting ducts and distal tubules to modulate permeability. The whole point of ADH is to conserve water
by resorption of water in the kidney. ADH will decrease urine volume and increase urine concentration.
ii. Oxytocin’s target is the smooth muscle of the uterus and myoepithelial cells in the mammary glands.
Oxytocin will cause muscle contraction during orgasm and labor, primarily to help get the baby out during
labor. And contractions of the mammary glands to help with milk ejection. This has a positive feedback
mechanism, so as it is produced, it will stimulate more to be secreted.
XXXII. Effects of ADH and Oxytocin [S35]:
a. You can read this on your own.
H & E: 2:00 - 3:00
Scribe: Caitlin Cox
Tuesday, November 3, 2009
Proof: Marjorie O’Neil
Dr. Cotlin
The Endocrine System: Hypophysis (or Pituitary Gland)
Page 5 of 6
XXXIII. Cells of the Neurohypophysis [S36]:
a. This is a picture of the Neurohypophysis.
b. This gray structure (indicated by the arrows) is a Herring body.
c. Neurohypophysis looks a lot like nervous tissue. There are the pituicytes and all of the axon terminals.
XXXIV. Pars Nervosa [S37-39]:
a. All of the cells are pituicytes. The black-grayish-brownish material is the Herring bodies.
XXXV. Clinical Correlations [S40]:
a. Lots of different effects because there are so many target organelles.
i. Problem in excess growth hormone causes gigantism.
ii. Problems in our gonadotropin releasing hormone where we a altering the FSH and LH; it might cause
infertility issues.
iii. Hypothyroidism caused by deficiencies in thyroid secreting hormone, deficiencies in the effects of thyroid.
iv. Cushing’s disease is a result of cortisol secretion in the adrenal cortex.
v. Diabetes is when you have alterations in ADH production leading to renal dysfunction.
XXXVI. The Endocrine System: Thyroid and Parathyroid Glands [S41]:
a. We will finish this on Friday, but she wants to give us the gist of what the thyroid and parathyroids do.
XXXVII. Thyroid and Parathyroid Glands [S42]:
a. They are located in the upper throat around the trachea. Thyroid has left and right lobes joined by a narrow
isthmus. All of the purple is the thyroid gland.
b. The parathyroid gland consists of two pairs of glands that are embedded into the lobes of the thyroid gland.
They will be capsulated and embedded into the thyroid.
XXXVIII.
Blood Supply to the Thyroid [S43]:
a. Blood supply is simple. The superior thyroid arteries will extend off the carotid. Drainage through the thyroid
veins.
XXXIX. The Thyroid Gland [S44]:
a. There are two types of cells in the thyroid: follicular cells and parafollicular cells.
b. Follicular cells will secrete thyroxine (T4) and triiodothyronine (T3). T3 and T4 stimulate metabolism.
c. Calcitonin will regulate calcium levels.
XL. Thyroid Follicle [S45]:
a. This is what the tissue looks like.
b. The functional unit is the thyroid follicle. The material inside the follicle is called colloid. Colloid is a
FUNCTIONAL storage spot for thyroid hormones.
c. Follicular cells are the cells that line the follicle. You can see their epithelial nature: they are sitting on a
basement membrane and their apical region (the secreting region) is facing the colloid.
d. The parafollicular cells are situated between the follicles. They do not touch the colloid, so they are not involved
with T3 and T4 synthesis. These cells are sometimes called C cells.
e. There is also thyroglobulin, which is a scaffold for building T3 and T4. It will be stored in the thyroid follicle.
XLI.
Thyroid Gland [S46]:
a. A picture of the thyroid gland. The size of the follicles will vary. The shrinkage of the colloid is just an artifact of
dehydration; the colloid would fill the entire follicle. The gland is also very vascularized.
XLII.
Follicular Cells [S47]:
a. The follicular cells are the ones that secrete T3 and T4.
b. They are going to range from low squamous (squatty cells) to columnar. They are the tallest when they are
stimulated and actively turning out the hormones.
c. Typical of a columnar epithelial cell, it is sitting in a basement membrane, the receptors for the thyroid
stimulating hormone will sit at the basolateral region, very active RER, and there is a need for iodine.
d. Iodine is a critical component for T3 and T4 synthesis.
XLIII. Parafollicular Cells [S48]:
a. These will secrete calcitonin. They will be found individually or in small groups. Are not associated with the
follicle at all. Calcitonin will decrease calcium concentration. Their major target is osteoclasts, which degrade
bone and release calcium to increase blood calcium levels. Therefore, these will inhibit the calcium
concentrations in the blood.
XLIV. The Parathyroid Glands [S49]:
a. They produce parathyroid hormone (PTH), which also acts to regulate calcium levels. PTH and calcitonin both
act to regulate calcium concentrations. You absolutely need PTH, and thus parathyroid glands, to live.
XLV. Histology of Parathyroid Glands [S50]:
a. These will be very small and embedded in the thyroid tissue. Usually the cells are organized into clusters or
cords. Very vascular. Tends to collect adipose tissue; a fatty parathyroid gland indicates it is from an older
individual.
H & E: 2:00 - 3:00
Scribe: Caitlin Cox
Tuesday, November 3, 2009
Proof: Marjorie O’Neil
Dr. Cotlin
The Endocrine System: Hypophysis (or Pituitary Gland)
Page 6 of 6
XLVI. Histology [S51]:
a. Two types of cells:
i. Oxyphil cells look large, puffy, and clear. They don’t appear to secrete any detectable hormone.
ii. Chief cells look like normal secretory cells (you see granules); they secrete PTH.
XLVII. Thyroid and Parathyroid Glands [S52]:
a. Usually you can’t see parathyroid gland without thyroid because of the way they are embedded.
[end 42:06 min]