ENODCRINE SYSTEM PART 1 - ENGLISH
Nursing Notesclick here to subscribe My Student Support System
ENDOCRINE SYSTEM PART – 1
• The
endocrine system consists of glands widely separated from each other with no
physical connections. Endocrine glands are groups of secretory cells surrounded
by an extensive network of capillaries that facilitates diffusion of hormones
(chemical messengers) from the secretory cells into the bloodstream.
• The
endocrine glands are also known as ductless glands because they have no
duct to carry their secretions, hormones diffuse directly into the bloodstream.
Hormones are then carried in the bloodstream to target tissues and organs
that may be quite distant, where they influence cellular growth and
metabolism.
HORMONES
• Hormones
are chemical messengers that are secreted into the blood or the extracellular
fluid by one organ (endocrine gland) and have an effect on the functioning of
other organ (target organ).
• When
a hormone arrives at its target cell, it binds to a specific receptor,
where it acts as a switch influencing chemical or metabolic reactions inside
the cell. The receptors for peptide hormones are situated on the cell membrane
and those for lipid-based hormones are inside the cell.
HYPOTHALAMUS-
• The
hypothalamus is a portion of the brain with a variety of functions. It is a
small (about 4 g), cone‐like structure that is directly connected to the
pituitary gland by the pituitary stalk . It is an extremely complex part of the
brain containing many regions with highly specialised functions.
• One
of the most important functions of the hypothalamus is to link the nervous
system to the endocrine system via the pituitary gland. Almost all hormone
secretion by the pituitary gland is controlled by either hormonal or electrical
signals from the hypothalamus. Hypothalamic hormones reach the anterior
pituitary through a portal system known as Hypophyseal Portal System
• There
are two sets of hormones released by the
hypothalamus . One set of hormones
reaches to posterior lobe of the pituitary gland. These hormones
are anti-diuretic hormone and oxytocin. Anti-diuretic
hormone causes water reabsorption at the kidneys and
oxytocin stimulates contraction of the uterus in childbirth and is important in
breastfeeding.
• The
other set of hormones are stimulating and inhibiting hormones that reach
the anterior lobe of the pituitary gland. These hormones are
following-
• Growth hormone-releasing
hormone (GHRH)- It stimulates cells in the anterior lobe of the pituitary
to secrete growth hormone (GH).
• Growth hormone-release
Inhibiting hormone (GHRIH)- It is also known as somatostatin. Somatostatin
acts on the anterior lobe of the pituitary to inhibit the release
of growth hormone (GH) and inhibit the release
of thyroid-stimulating hormone (TSH)
• Thyrotropin-releasing hormone
(TRH)- When it reaches the anterior lobe of the pituitary it stimulates the
release of thyroid-stimulating hormone (TSH) and prolactin (PRL)
• Corticotropin-releasing
hormone (CRH)- It’s actions on cells in the anterior lobe of the
pituitary stimulate the release of
adreno- corticotropic hormone (ACTH; also known as corticotropin)
• Prolactin-releasing hormone
(PRH)- It stimulates the anterior lobe of the pituitary it stimulates the
release of prolactin Hormone (PRL)
• Prolactin-inhibiting hormone
(PIH)- It is also known as dopamine. It inhibit the production of prolactin
hormone from anterior pituitary gland.
• Gonadotropin-releasing
hormone (GnRH)- GnRH stimulates the anterior pituitary to release follicle
stimulating hormone (FSH) and luteinizing hormone (LH), which work together to
ensure normal functioning of the ovaries and testes.
PITUTARY GLAND-
• The
pituitary gland is also known as master gland of our body as it’s hormones
controls almost all other glands. The pituitary gland lies in the hypophyseal
fossa of the sphenoid bone below the hypothalamus, to which it is attached by a
stalk .
• The
pituitary gland is functionally and anatomically divided into two parts:
(posterior and anterior lobes)
• The
posterior lobe (Neurohypophysis) is
made up mostly of nerve fibres that originate in the hypothalamus and terminate
on the posterior lobe. The posterior
lobe releases two hormones – Oxytocin and ADH (these are produced by
hypothalamus and released by posterior pituitary)
• Oxytocin-
Oxytocin has an effect on uterine contraction in childbirth and is
responsible for the ‘let down’ response in breastfeeding mothers (the release
of milk in response to suckling).
• Antidiuretic
hormone (ADH)- The effects of ADH are that it increases water retention by
the kidneys by increasing the permeability of the collecting ducts in the
kidneys.
• The
anterior lobe (Adenohypophysis) is
made up mostly of secretary cells. The Anterior lobe releases following
hormones-
• Growth
hormone (GH)- This is the most abundant hormone synthesised by the anterior
pituitary. It stimulates growth and division of most body cells but especially
those in the bones and skeletal muscles. Body growth in response to the
secretion of GH is evident during childhood and adolescence, and thereafter
secretion of GH maintains the mass of bones and skeletal muscles. It also
regulates metabolism in many organs
(liver, intestines and pancreas)
• Thyroid
stimulating hormone (TSH)- This hormone is synthesised by the anterior
pituitary and its release is stimulated by thyrotrophin releasing hormone (TRH)
from the hypothalamus. It stimulates
growth and activity of the thyroid gland, which secretes the hormones tri-iodothyronine
(T3) and thyroxine (T4).
• Adrenocorticotrophic
hormone (ACTH, corticotrophin)- Corticotrophin releasing hormone (CRH) from
the hypothalamus promotes the synthesis and release of ACTH by the anterior
pituitary. This increases the concentration of cholesterol and steroids within
the adrenal cortex and the output of steroid hormones, especially cortisol.
• Prolactin-
This hormone is secreted during pregnancy to prepare the breasts for lactation
(milk production) after childbirth. The blood level of prolactin is
stimulated by prolactin releasing hormone (PRH) released from the hypothalamus
and it is lowered by prolactin inhibiting hormone (PIH, dopamine) and by
an increased blood level of prolactin. Immediately after birth, suckling
stimulates prolactin secretion and lactation.
• Gonadotrophins-
Just before puberty two gonadotrophins are secreted in gradually increasing
amounts by the anterior pituitary in response to luteinising hormone
releasing hormone (LHRH), or gonadotrophin releasing hormone (GnRH).
Theses gonadotrophin hormones are-
• Follicle
stimulating hormone (FSH)
• Luteinising
hormone (LH).
• Follicle
stimulating hormone (FSH)- In females, the ovaries are the targets for
follicle-stimulating hormone (FSH). Each month FSH initiates the development of
several ovarian follicles, saclike arrangements of secretory cells that
surround a developing oocyte. FSH also stimulates follicular cells to secrete
estrogens (female sex hormones). In males, FSH stimulates sperm production in
the testes.
• Luteinising
hormone (LH)- In females, luteinizing hormone (LH) triggers ovulation, the
release of a secondary oocyte (future ovum) by an ovary. LH stimulates
formation of the corpus luteum (structure formed after ovulation) in the ovary
and the secretion of progesterone (another female sex hormone) by the corpus
luteum. In males, LH stimulates cells in the testes to secrete testosterone
• Melanocyte-stimulating
hormone (MSH)- It increases skin pigmentation
and produce a darkening of the skin. It acts on cells in the skin
to stimulate the production of melanin. Melanin is the pigment which is
responsible for dark color of the skin.
THYROID GLAND-
• The
thyroid gland is a butterfly‐shaped gland located in the front of the neck on
the trachea just below the larynx. It is made up of two lobes joined by an
isthmus. The upper extremities of the lobes are known as the upper poles and
the lower extremities the lower poles.
• The
thyroid gland produces hormones that regulate the body's metabolic rate controlling
heart, muscle and digestive function, brain development and bone
maintenance. Its correct functioning depends on a good supply of iodine
from the diet. The thyroid hormones are synthesised as large precursor
molecules called thyroglobulin. The release of T3 and T4 into the blood
is stimulated by thyroid stimulating hormone (TSH) from the anterior
pituitary.
• T3
(tri-iodothyronine) and T4 (thyroxin) affect most cells of the body by
increasing the basal metabolic rate and heat production, regulating metabolism
of carbohydrates, proteins and fats. T3 and T4 are essential for normal growth
and development, especially of the skeleton and nervous system. Most other
organs and systems are also influenced by thyroid hormones .
• Calcitonin-
Calcitonin hormone is also secrteted by thyroid gland. It acts on bone cells
and the kidneys to reduce blood calcium (Ca2+) levels when they are raised. It
promotes storage of calcium in bones and inhibits reabsorption of calcium by
the renal tubules. Its effect is opposite to that of parathyroid hormone, the
hormone secreted by the parathyroid glands. Release of calcitonin is stimulated
by an increase in the blood calcium levels.
PARATHYROID GLANDS-
• There
are four small parathyroid glands, two embedded in the posterior surface of
each lobe of the thyroid gland. They are surrounded by fine connective tissue
capsules. Usually, one superior and one inferior parathyroid gland are attached
to each lateral thyroid lobe
• Parathyroid
glands produce parathyroid hormone (PTH), also called parathormone. Secretion
is regulated by blood calcium levels. When they fall, secretion of PTH is
increased and vice versa. The main function of PTH is to increase the blood
calcium level when it is low. This is achieved by indirectly increasing the
amount of calcium absorbed from the small intestine and reabsorbed from the
renal tubules.
No comments:
Post a Comment