Transcript الشريحة 1

Hypothalamus
&
pituitary gland
The hypothalamus is a region of the brain that controls an immense
number of bodily functions. It is located in the middle of the base of
the brain, and encapsulates the ventral portion of the third ventricle
The pituitary gland, also
known as the
hypophysis, is a
roundish organ that lies
immediately beneath the
hypothalamus, resting in
a depression of the
base of the skull called
the sella turcica
("Turkish saddle").
Careful examination of the pituitary gland reveals that it
composed of two distinctive parts:
The anterior pituitary or adenohypophysis is a
classical gland composed predominantly of cells that
secrete protein hormones.
The posterior pituitary or neurohypophysis is not
really an organ, but an extension of the hypothalamus. It
is composed largely of the axons of hypothalamic
neurons which extend downward as a large bundle
behind the anterior pituitary. It also forms the so-called
pituitary stalk, which appears to suspend the anterior
gland from the hypothalamus
Development and Anatomy of the Pituitary Gland
Adenohypohysis:
Pars distalis - the largest section
Pars tuberalis - a collar of tissue that usually surrounds the
infundibular stalk
Pars intermedia - a narrow band that is usually separated from the
pars distalis by a hypophyseal cleft
Neurohypohysis:
Pars nervosa - the bulk of the posterior pituitary
Median eminence - the upper section of the neurohypophysis above the pars tuberalis
Infundibular stalk - the "stem" that connects the pars nervosa to the base of the brain
Parvicellular
neurons
Magnocellular neurons
Superoptic N.
Paraventricular N.
Overview of Hypothalamic and Pituitary Hormones
•
The pituitary gland is often portrayed as the "master gland" of the body.
Such praise is justified in the sense that the anterior and posterior pituitary
secrete a battery of hormones that collectively influence all cells and affect
virtually all physiologic processes.
•
The pituitary gland may be king, but the power behind the throne is clearly
the hypothalamus. As alluded to in the last section, some of the neurons
within the hypothalamus - neurosecretory neurons - secrete hormones that
strictly control secretion of hormones from the anterior pituitary. The
hypothalamic hormones are referred to as releasing hormones and
inhibiting hormones, reflecting their influence on anterior pituitary
hormones.
•
Hypothalamic releasing and inhibiting hormones are carried directly to the
anterior pituitary gland via hypothalamic-hypophyseal portal veins. Specific
hypothalamic hormones bind to receptors on specific anterior pituitary cells,
modulating the release of the hormone they produce.
•
As an example, thyroid-releasing hormone from the hypothalamus binds to
receptors on anterior pituitary cells called thyrotrophs, stimulating them to
secrete thyroid-stimulating hormone or TSH. The anterior pituitary
hormones enter the systemic circulation and bind to their receptors on other
target organs. In the case of TSH, the target organ is the thyroid gland.
Hormones of the hypothalamus
• Adrenocorticotrophic Hormone-releasing hormone
(ACT-RH)
• Follicle Stimulating Hormone-releasing hormone
(FSH-RH)
• Luteinizing Hormone-releasing hormone (LH-RH)
• Growth hormone- releasing hormone (GH-RH)
• Thyroide Stimulating Hormone-releasing hormone
(THS-RH)
• Prolactin- Inhibiting Hormone (PRl-IH)
Pituitary Hormones
Hormone& Major target organ(s) & Major Physiologic Effects
Anterior Pituitary
Growth hormone Liver, adipose tissue, Promotes growth (indirectly), control of
protein, lipid and carbohydrate metabolism
Thyroid-stimulating hormone Thyroid gland Stimulates secretion of thyroid
hormones
Adrenocorticotropic hormone Adrenal gland (cortex), Stimulates secretion of
glucocorticoids
Prolactin Mammary gland ,Milk production
Luteinizing hormone Ovary and testis ,Control of reproductive function
Follicle-stimulating hormone Ovary and testis Control of reproductive
function
Posterior Pituitary
Antidiuretic hormone Kidney ,Conservation of body water
Oxytocin Ovary and testis ,Stimulates milk ejection and uterine contractions
Histology of the pituitary gland
Histology of the Adenohypophysis
The bulk of the adenohypophysis is pars
distalis. That tissue is composed of
winding cords of epithelial cells flanked
by vascular sinusoids. In sections
stained with dyes such as hematoxylin
and eosin, three distinct cell types are
seen among epithelial cells:
Acidophils have cytoplasm that stains red
or orange
Basophils have cytoplasm that stains a
bluish color
Chromophobes have cytoplasm that
stains very poorly
This figure shows pars distalis from a cat
at two magnifications (H&E stain).
Histology of the Adenohypophysis
The pars intermedia is closely associated with pars nervosa and separated from the
pars distalis by the hypophyseal cleft. This lobe of the pituitary shows considerable
variation in size among species. It is small in man, but much larger in species such
as amphibians. The pars intermedia contains large pale cells that often surround
follicles filled with ill-defined "colloid". Melanocyte-stimulating hormone is the
predominant hormone secreted by the pars intermedia. The images below show pars
intermedia from a cat at low and higher magnification. The hypophyseal cleft is seen
in the middle of the left image. In the right image, the three round, clear areas are
follicles characteristic of this tissue.
Histology of the Neurohypophysis
The neurohypophysis is known also as the pars nervosa. Anatomists
distinguish between three areas of this organ, starting closest to the
hypothalamus:
the median eminence
infundibular stalk
infundibular process
The infundibular process froms the bulk of the neurohypophysis is what
is usually referred to as the posterior pituitary.
The bulk of the neurohypophysis is composed on largely unmyelinated
axons from hypothalamic neurosecretory neurons. These axons
have their cell bodies in the paraventricular and supraoptic nuclei of
the hypothalamus. These neurons secrete oxytocin or antidiuretic
hormone. Roughly 100,000 axons participate in this process to form
the posterior pituitary. In addition to axons, the neurohypophysis
contains glial cells and other poorly-defined cells called pituicytes.
Each lobule of this gland has a darker staining cortex (left A) and a lighter
staining medulla (left B). One outstanding feature of this organ is the
presence of thymic roses/thymic corpuscles (C). This organ, large until
adolescence, is important for the development of the immune system. The
hormone produced by this gland is thymosin.