Hypothalamic and Pituitary hormones - KSU

Hypothalamic and Pituitary
hormones

Dr. Howaida Nounou

Dr.Howaida Nounou 1

Functional Types of Hormones

• Trophic (tropic)

– Originate from anterior pituitary gland

– Specific for another endocrine gland.( regulate growth and
function of other endocrine glands)

• Direct effector

– Secreted by non-pituitary endocrine glands

– Act directly on peripheral tissue

– Exert a feedback effect on the hypothalamus or anterior
pituitary gland

• Negative feedback- an increase in the product causes a decreased
in the system

• Positive feedback- an increase in the product causes an increase in
the activity of the system

Dr.Howaida Nounou 2

Regulation of Hormones

• Occurs by controlling the rate of synthesis rather
than the rate of degradation

• Primary control= Hypothalamus

– Small gland next to pituitary gland
– Connected to the pituitary by the “pituitary stalk”
– Stores and releases antidiuretic hormone (ADH)

( vasopressin) and oxytocin from the posterior
pituitary gland

• Pituitary Gland

– Releases both tropic and effector hormones

Dr.Howaida Nounou 3

Hypothalamus and Pituitary

• The hypothalamus-pituitary unit is the most
dominant portion of the entire endocrine
system.

• The output of the hypothalamus-pituitary unit
regulates the function of the thyroid, adrenal
and reproductive glands and also controls
somatic growth, lactation, milk secretion and
water metabolism.

Dr.Howaida Nounou 4

Hypothalamus and pituitary gland

Dr.Howaida Nounou 5

Hypothalamus and pituitary gland

Dr.Howaida Nounou 6

Hypothalamus and Pituitary

• Pituitary function depends on the hypothalamus.

• The pituitary gland lies in a pocket of bone at the
base of the brain, just below the hypothalamus to
which it is connected by a stalk containing nerve
fibers and blood vessels. The pituitary is composed
to two lobes-- anterior and posterior

Two distinct portions
• Anterior pituitary (adenohypophysis)
• Posterior pituitary (neurohypophysis)

Dr.Howaida Nounou 7

Pituitary Gland Control

• Hypothalamic releasing hormones stimulate
cells of anterior pituitary to release hormones

• Nerve impulses from hypothalamus stimulate
nerve endings in the posterior pituitary gland
to release hormones

Dr.Howaida Nounou 8

Posterior Pituitary:
neurohypophysis

• Posterior pituitary: an outgrowth of the
hypothalamus composed of neural tissue

• Hypothalamic neurons pass through the
neural stalk and end in the posterior pituitary.

• The upper portion of the neural stalk extends
into the hypothalamus and is called the
median eminence.

Dr.Howaida Nounou 9

Neurosecretory cells of Posterior Pituitary

• Posterior pituitary gland does NOT have cells
that produce hormones

• Neurosecretory cells of hypothalamus release
hormones

– Directly into Posterior pituitary
– Which is released into systemic blood stream
– Rapid response

Dr.Howaida Nounou 10

Hypothalamus and
posterior pituitary

magnocellular neurons
paraventricular and supraoptic
nuclei secrete oxytocin and
vasopressin directly into
capillaries in the posterior lobe

Dr.Howaida Nounou 11

Hypothalamo-hypophyseal portal system

• Carries hypothalamic hormones specifically to the
anterior pituitary without dilution in the systemic
blood.
1. Allows rapid response
2. Little dilution of peptide hormones
3. Peptides have short 1/2 life

Dr.Howaida Nounou 12

Hypothalamus-pituitary

Hypothalamus

Hypophyseal Portal Vessels Pituitary Stalk

Posterior Pituitary
(Neurohypophysis)

Anterior Pituitary Dr.Howaida Nounou 13
(Adenohypohysis)

Hypothalamic Hormones

• Corticotropin releasing hormone (CRH)
• Gonadotropin Releasing Hormone (GnRH)
• Thyrotropin Releasing Hormone (TRH)
• Growth Hormone Releasing Hormone (GHRH)
• Growth hormone release inhibiting hormone (

GHIH) ( Somatostatin, SS)
• Prolactin release factor (PRF)
• Prolactin release inhibiting hormone ( PIH)

• Oxytocin 14
• Vasopressin (VAP) or antidiuretic hormone (ADH)

Dr.Howaida Nounou

Hypothalamus Releasing Hormones:
Secretion

• Is influenced by emotions
• Can be influenced by the metabolic state of

the individual
• Delivered to the anterior pituitary via the

hypothalamic-hypophyseal portal system

Dr.Howaida Nounou 15

Hypothalamic Hormones

Dr.Howaida Nounou 13-16

16

Hypophysiotrophic Hormones

Products produced by the hypothalamus, effecting
pituitary function

Hormone Action
Stimulates release of TSH and prolactin
Thyrotropin releasing hormone (TRH) Stimulates release of LH and FSH
Stimulates release of ACTH
Gonadotropin releasing hormone (GnRH) Stimulates release of GH

Corticotropin releasing hormone ( CRH) Inhibits GH and TSH release

Growth hormone releasing hormone Inhibits prolactin release
(GHRH)
Stimulates prolactin release
Growth hormone-inhibiting hormone
(GHIH) , Somatostatin

Prolactin-inhibiting hormone (PIH),
dopamine
Prolactin release factor (PRF)

Control of Hormonal Secretions

• primarily controlled by negative feedback mechanism

Dr.Howaida Nounou 13-11

18

Feedback Control of Hormone
Production

Feedback loops are used
extensively to regulate
secretion of hormones in the
hypothalamic-pituitary axis.
An important example of a
negative feedback loop is seen
in control of thyroid hormone
secretion

Dr.Howaida Nounou 19

1-Hypothalamic-pituitary adrenal (HPA) axis

Stress Immune
Circadian system:
altered
rhythm
Hypothalamus

CRH Muscle:
Net loss of amino
Anterior Posterior Acids (glucose)
Pituitary Gland Pituitary Gland
Liver:
(-) ACTH Deamination of
proteins into amino
Adrenals Glucocorticoids,
Catecholamines, etc.. acids,
gluconeogenesis
Kidney
(glucose)
Fat Cells:
Free fatty

acid
mobilization

Heart rate:
Increased

Dr.Howaida Nounou 20

Hypothalamic-Pituitary-Adrenal
Axis

• Hypothalamus CRH stimulates
the production of ACTH by
anterior pituitary.

• ACTH stimulates the
production of cortisol
(glucocorticoids) by the adrenal
cortex.

• Coritsol inhibits hypothalamus
and anterior pituitary to secret
CRH and ACTH respectively (
negative feed back inhibition)

Dr.Howaida Nounou 21

• Physiologic stress, surgery, 22
hypoglycemia, fever
increases ACTH production

• ACTH acts on adrenal gland
through CAMP mechanism
resulting in synthesis and
secretion of Cortisol,
Aldosterone and Androgens

• Cortisol feeds back
negatively to inhibit both
CRH and ACTH

Dr.Howaida Nounou

Testosterone

Hypothalamus 2-Hypothalamic-Pituitary-

Gonadal Axis (HPG): Males

GnRH

-

Anterior

Pituitary

FSH
LH

+

-

Testosterone 23

Dr.Howaida Nounou

Hypothalamic-Pituitary-
Gonadal Axis (HPG):
Females

GnRH

-- --

Dr.Howaida Nounou 24

Hypothalamic-Pituitary Gonadal Axis

• GnRH (LHRH) is secreted by hypothalamus then stimulates
synthesis & secretion of LH & FSH by anterior pituitary.

• LH & FSH stimulate the production of testosterone & estrogen and
progesterone from the gonads( Testis & ovaries)

• High levels of estrogens suppress the release of GnRH
providing a negative-feedback control of hormone levels.

• Elevated levels of progesterone control themselves by the
same negative feedback loop used by estrogen (and
testosterone).

Dr.Howaida Nounou 25

3- Hypothalamic- 26
pituitary thyroid

axis (HPT)

- Hypothalamus secrets thyrotropin
releasing hormone (TRH) that stimulates
the production of thyroid stimulating
hormone ( TSH) by anterior pituitary.

- TSH stimulates the production of
thyroid hormones ( T3 & T4) by the
thyroid gland.

- Thyroid hormones feed back
negatively on hypothalamus and anterior
pituitary to inhibit secretion of TRH and
TSH. ( negative feed back inhibition)

Dr.Howaida Nounou