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Summary ENDOCRINE 1 USMLE step 1 (USMLE-RX BRICKS)
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A SYSTEM'S BASED APPROACH -USMLE RX BRICKS
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Structure and Function of thePituitary Gland
Last Updated: April 25, 2022
access_time17 min
Learning Objectives (4)
After completing this brick, you will be able to:
● Describe the location and gross appearance of the pituitary gland.
● 1
● Describe the histologic appearance of the anterior and posterior lobes,
and list the hormones produced by each.
● 2
● Discuss the embryologic origins of the anterior and posterior lobes.
● 3
● List the hypothalamic hormones that influence pituitary hormone
release, and describe the vascular system through which these
hormones travel.
● 4
CASE CONNECTION
CJ comes to see you about menstrual irregularity and fatigue. Her free T4 and TSH
are both low. You tell CJ that you suspect a pituitary problem is affecting her
thyroid function and you would like to do more testing. SK, a nurse in your clinic,
asked about the advice you gave CJ; SK herself had similar symptoms and the
same free T4 level, but you told SK that her problem was in her thyroid gland.
“How do you know that my problem is in my thyroid gland and her's isn’t? Does
this have something to do with my TSH being high?”
,What will you tell SK about how her situation differs from CJ’s? Consider your
answer as you read, and we’ll revisit at the end of the brick.
What Is the Pituitary Gland and Where Does
It Come From?
Also called the master gland, the pituitary gland controls a large majority of the
hormones that circulate in our bodies throughout the day. We will begin by talking
about the anatomy and histology, then cover embryology, and finish with some of
the physiology that makes the pea-sized pituitary gland so important in regulating
many of our vital body functions as well as our general well-being. Let’s begin!
Location
The pituitary gland, or, hypophysis (Greek for lying under) cerebri, is roughly the
size of a pea and projects out anteroinferiorly to the hypothalamus. The pituitary is
located just inferior to the optic chiasm (where the optic nerves cross) and sits on
top of the sella turcica. The sella turcica (aka, Turkish saddle) is found within the
sphenoid bone of the skull. More specifically, the sella turcica makes up the lowest
portion of the hypophyseal fossa in the sphenoid bone, where it truly cradles the
pituitary gland.
,Lobes
The pituitary consists of two visibly distinct lobes that hang from the hypothalamus
by a thin stalk called the infundibulum (Figure 1). The two lobes include the
anterior pituitary (adenohypophysis) and the smaller posterior pituitary
(neurohypophysis). The anterior pituitary is larger than its neighbor and is richly
perfused with capillaries (discussed in detail later). The posterior pituitary contains
the hypothalamo-hypophyseal tract that extends from the hypothalamus to the
posterior lobe through a portion of the infundibulum.
, What Is the Histology of the Pituitary
Gland?
As mentioned, the pituitary comprises anterior and posterior lobes. A third area
called the pars intermedia is located between the lobes, but this isn’t very important
to the mature pituitary gland.
Anterior Lobe
The anterior lobe carries out the important task of hormone production. The lobe
can be simply divided based on hematoxylin and eosin (H&E) staining and the
hormones produced. Chromophils are stainable and can be broken into hormone-
producing acidophils and basophils, while chromophobes do not stain and produce
no hormone. The names tell you that acidophils are acid loving and look pink on
H&E, while basophils are base loving and look blue-purple on H&E (Figure 2).
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