Pituitary gland

1. Pituitary Gland
Dr. Sai Sailesh Kumar G
Associate Professor
Department of Physiology
NRIIMS
Email: dr.goothy@gmail.com

2. Introduction
The pituitary gland, or hypophysis
Small endocrine gland located in a bony cavity at the base of the brain
just below the hypothalamus
The pituitary is connected to the hypothalamus by a thin connecting
stalk.

3. Lobes
The pituitary has two anatomically and functionally distinct lobes, the
posterior pituitary and the anterior pituitary
The posterior pituitary is composed of nervous tissue and thus is also
termed the neurohypophysis
The anterior pituitary consists of glandular epithelial tissue and
accordingly is also called the adenohypophysis (adeno means
“glandular”).

4. Lobes
The posterior and anterior pituitary lobes have only their location in
common.
They arise from different tissues embryonically, serve different
functions, and are subject to different control mechanisms.

5. Lobes
The release of hormones from both the posterior and the anterior
pituitary is directly controlled by the hypothalamus, but the natures of
these relationships are entirely different.
The posterior pituitary connects to the hypothalamus by a neural
pathway,
whereas the anterior pituitary connects to the hypothalamus by a
unique vascular link

7. Posterior pituitary
The actions of vasopressin and oxytocin are briefly summarized here
to make our endocrine story complete.

8. Vasopressin
Vasopressin (antidiuretic hormone, ADH) has two major effects that
correspond to its two names:
(1) it conserves H2O during urine formation by the kidney nephrons
(an antidiuretic effect) and
(2) it causes contraction of arteriolar smooth muscle (a vessel pressor
effect)

9. Vasopressin
The first effect has more physiologic importance.
Under normal conditions, vasopressin is the primary endocrine factor
that regulates urinary H2O loss and overall H2O balance.
 In contrast, typical levels of vasopressin play only a minor role in
regulating blood pressure by means of promoting arteriolar
vasoconstriction.

10. Vasopressin
The major control for hypothalamic-induced release of vasopressin
from the posterior pituitary is input from hypothalamic
osmoreceptors, which increase vasopressin secretion in response to
a rise in plasma osmolarity.
A less powerful input from the left atrial volume receptors increases
vasopressin secretion in response to a fall in ECF volume and arterial
blood pressure

11. Oxytocin
Oxytocin stimulates contraction of uterine smooth muscle to help expel the infant during
childbirth, and it promotes ejection of milk from the mammary glands (breasts) during
breast-feeding.
In addition to these two major physiologic effects, oxytocin influences a variety of
behaviors, especially maternal behaviors.
For example, this hormone fittingly facilitates bonding, or attachment, between a mother
and her infant.
For this reason, oxytocin is sometimes nicknamed the “love hormone” or “cuddle
chemical.”

13. Anterior pituitary hormones
Unlike the posterior pituitary, which releases hormones synthesized by
the hypothalamus, the anterior pituitary synthesizes the hormones it
releases into the blood.
Five different cell populations within the anterior pituitary secrete six
major peptide hormones

14. Anterior pituitary hormones
The anterior pituitary cells known as somatotropes secrete growth
hormone (GH, somatotropin), the primary hormone responsible for
regulating overall body growth (somato means “body”).
GH also exerts important metabolic actions

15. Anterior pituitary hormones
Thyrotropes secrete thyroid-stimulating hormone (TSH,
thyrotropin), which stimulates the secretion of thyroid hormone and
growth of the thyroid gland

16. Anterior pituitary hormones
Corticotropes produce and release adrenocorticotropic hormone
(ACTH, adrenocorticotropin), the hormone that stimulates cortisol
secretion by and promotes growth of the adrenal cortex

17. Anterior pituitary hormones
Gonadotropes secrete two hormones that act on the gonads
(reproductive organs, namely, the ovaries and testes)—follicle-
stimulating hormone and luteinizing hormone.

18. Anterior pituitary hormones
Follicle-stimulating hormone (FSH) helps regulate gamete
(reproductive cells, namely, ova and sperm) production in both sexes.
 In females, it stimulates growth and development of ovarian follicles,
within which the ova, or eggs, develop.
It also promotes the secretion of the hormone estrogen by the ovaries.

19. Anterior pituitary hormones
Luteinizing hormone (LH), also secreted by gonadotropes, helps control sex
hormone secretion in both genders.
 LH regulates ovarian secretion of the female sex hormones, estrogen and
progesterone.
 In males, the same hormone stimulates the testes to secrete the male sex
hormone, testosterone.
 In females, LH is also responsible for ovulation (egg release) and luteinization.

20. Anterior pituitary hormones
Lactotropes secrete prolactin (PRL), which enhances breast
development and lactation (milk production) in females. Its
reproductive function in males is uncertain.

21. Anterior pituitary hormones
GH, TSH, ACTH, FSH, and LH are all tropic hormones because they
each regulate secretion of another specific endocrine gland.
PRL is the only one that does not stimulate the secretion of another
hormone. It acts directly on nonendocrine tissue to exert its effects.

22. Anterior pituitary hormones
TSH, ACTH, FSH, and LH all act at their target organs by binding with
G-protein-coupled receptors that activate the cyclic adenosine
monophosphate (cAMP) second-messenger system.
GH and PRL both exert their effects via the JAK/STAT pathway

23. Hypothalamic releasing and inhibiting
hormones
The secretion of each anterior pituitary hormone is stimulated or inhibited by one or more
hypothalamic hypophysiotropic hormones (hypophysis means “pituitary”; tropic means
“nourishing”).
Depending on their actions, these hormones are called releasing hormones or inhibiting
hormones
For example, thyrotropin-releasing hormone (TRH) stimulates release of TSH (alias
thyrotropin) from the anterior pituitary
This three-hormone sequence is called an endocrine axis, as in the hypothalamus–
pituitary–thyroid axis.

26. Hypothalamic–Hypophyseal Portal System
The hypothalamic regulatory hormones reach the anterior pituitary by
means of a unique vascular link.
In contrast to the direct neural connection between the hypothalamus
and the posterior pituitary
The anatomic and functional link between the hypothalamus and the
anterior pituitary is an unusual capillary-to capillary connection, the
hypothalamic–hypophyseal portal system

27. Hypothalamic–Hypophyseal Portal System
A portal system is a vascular arrangement in which venous blood flows
directly from one capillary bed through a connecting vessel to another
capillary bed, as in the hepatic portal system.

28. Hypothalamic–Hypophyseal Portal System
The hypothalamic–hypophyseal portal system provides a critical link
between the brain and much of the endocrine system.
It begins in the base of the hypothalamus with a group of capillaries
that recombine into small portal vessels, which pass down through the
connecting stalk into the anterior pituitary.
Here, the portal vessels branch to form most of the anterior pituitary
capillaries, which in turn drain into the systemic venous system.

30. Hypothalamic–Hypophyseal Portal System
 Almost all blood supplied to the anterior pituitary must first pass through the
hypothalamus.
Because materials can be exchanged between blood and surrounding
tissue only at the capillary level,
the hypothalamic–hypophyseal portal system provides a “private” route
through which releasing and inhibiting hormones can be picked up at the
hypothalamus and delivered immediately and directly to the anterior pituitary
at relatively high concentrations, bypassing the general circulation.

31. Hypothalamic–Hypophyseal Portal System
 The axons of the neurosecretory neurons that produce the
hypothalamic regulatory hormones terminate on the capillaries at the
origin of the portal system.

32. Hypothalamic–Hypophyseal Portal System
 What happens if the portal system is absent?

33. Hypothalamic–Hypophyseal Portal System
 Once the hypophysiotropic hormones were picked up in the hypothalamus, they
would be returned to the heart through the systemic veins,
pumped through the pulmonary circulation,
then returned to the heart and finally be pumped into the systemic arteries for
delivery throughout the body, including the anterior pituitary.
 Not only would this process take much longer, but the hypophysiotropic hormones
would be considerably diluted before arriving at the anterior pituitary.

34. Hypothalamic–Hypophyseal Portal System
 Where these releasing or inhibitory hormones are produced?

35. Hypothalamic–Hypophyseal Portal System
 The hormone is synthesized in the cell body and then transported in
vesicles by motor proteins to the axon terminal.
 It is stored there until its release by exocytosis into an adjacent
capillary on appropriate stimulation.

36. Hypothalamic–Hypophyseal Portal System
 What is the major difference in the hormone release of anterior and
posterior pituitary glands?

37. Hypothalamic–Hypophyseal Portal System
 The major difference is that the hypophysiotropic hormones are
released into the portal vessels, which deliver them to the anterior
pituitary, where they control release of anterior pituitary hormones into
the general circulation.
 In contrast, the hypothalamic hormones stored in the posterior
pituitary are themselves released into the general circulation.

38. Hypothalamic–Hypophyseal Portal System
 What regulates secretion of these hypophysiotropic hormones?

39. Hypothalamic–Hypophyseal Portal System
 Like other neurons, the neurons secreting these regulatory hormones
receive abundant input of information (both neural and hormonal and
both excitatory and inhibitory) that they must integrate.
Studies are still in progress to unravel the complex neural input from
many diverse areas of the brain to the hypophysiotropic secretory
neurons.

40. Hypothalamic–Hypophyseal Portal System
 One example is the marked increase in secretion of corticotropin-releasing
hormone (CRH) in response to stress
Numerous neural connections also exist between the hypothalamus and the
portions of the brain concerned with emotions (the limbic system).
Thus, The menstrual irregularities sometimes experienced by women who
are emotionally upset are a common manifestation of this relationship.

41. Hypothalamic–Hypophyseal Portal System
 The most common blood-borne factors that influence hypothalamic
neurosecretion are the negative-feedback effects of target-gland
hormones.

43. THANK YOU