Chemical coordination and integration 1 Flashcards
why do we have chemical coordination in addition to neural
the neural system provides a
point-to-point rapid coordination among organs. The neural
coordination is fast but short-lived. As the nerve fibres do not innervate
all cells of the body and the cellular functions need to be continuously
regulated; a special kind of coordination and integration has to be
provided. This function is carried out by hormones. The neural system
and the endocrine system jointly coordinate and regulate the
physiological functions in the body.
what are hormones
The classical definition of hormone as a
chemical produced by endocrine glands and released into the blood and
transported to a distantly located target organ has current scientific
definition as follows: Hormones are non-nutrient chemicals which
act as intercellular messengers and are produced in trace amounts.
explain the human endocrine system
The endocrine glands and hormone
producing diffused tissues/cells located
in different parts of our body constitute
the endocrine system. Pituitary, pineal,
thyroid, adrenal, pancreas, parathyroid,
thymus and gonads (testis in males and
ovary in females) are the organised
endocrine bodies in our body
(Figure 22.1). In addition to these, some
other organs, e.g., gastrointestinal tract,
liver, kidney, heart also produce
hormones.
hypothalamus:
where is it located
which cells secrete hormones
the hypothalamus is the
basal part of diencephalon, forebrain
(Figure 22.1) and it regulates a wide
spectrum of body functions. It contains
several groups of neurosecretory cells
called nuclei which produce hormones.
These hormones regulate the synthesis
and secretion of pituitary hormones.
types of hormones secreted by hypothalamus
the hormones produced
by hypothalamus are of two types, the releasing hormones (which
stimulate secretion of pituitary hormones) and the inhibiting hormones
(which inhibit secretions of pituitary hormones). For example a
hypothalamic hormone called Gonadotrophin releasing hormone (GnRH)
stimulates the pituitary synthesis and release of gonadotrophins. On the
other hand, somatostatin from the hypothalamus inhibits the release of
growth hormone from the pituitary.
how do hypothalamis hormones reach pituitary
These hormones originating in the
hypothalamic neurons, pass through axons and are released from their
nerve endings. These hormones reach the pituitary gland through a portal
circulatory system and regulate the functions of the anterior pituitary.
The posterior pituitary is under the direct neural regulation of the
hypothalamus
explain the structure and location ot pfituiatary gland
The pituitary gland is located in a bony cavity
called sella tursica and is attached to
hypothalamus by a stalk (Figure 22.2). It is
divided anatomically into an adenohypophysis
and a neurohypophysis. Adenohypophysis
consists of two portions, pars distalis and pars
intermedia. The pars distalis region of pituitary,
commonly called anterior pituitary, produces
growth hormone (GH), prolactin (PRL),
thyroid stimulating hormone (TSH),
adrenocorticotrophic hormone (ACTH),
luteinizing hormone (LH) and follicle
stimulating hormone (FSH). Pars intermedia
secretes only one hormone called melanocyte
stimulating hormone (MSH). However, in
humans, the pars intermedia is almost merged
with pars distalis. Neurohypophysis (pars
nervosa) also known as posterior pituitary,
stores and releases two hormones called
oxytocin and vasopressin, which are actually
synthesised by the hypothalamus and are transported axonally to
neurohypophysis.
explain the function of hormes released by pars distalis
Over-secretion of GH stimulates abnormal growth of the body leading
to gigantism and low secretion of GH results in stunted growth resulting
in pituitary dwarfism.
Prolactin regulates the growth of the mammary
glands and formation of milk in them.
TSH stimulates the synthesis and
secretion of thyroid hormones from the thyroid gland.
ACTH stimulates
the synthesis and secretion of steroid hormones called glucocorticoids
from the adrenal cortex.
LH and FSH stimulate gonadal activity and hence
are called gonadotrophins.
In males, LH stimulates the synthesis and
secretion of hormones called androgens from testis. In males, FSH and
androgens regulate spermatogenesis.
In females, LH induces ovulation
of fully mature follicles (graafian follicles) and maintains the corpus
luteum, formed from the remnants of the graafian follicles after ovulation.
FSH stimulates growth and development of the ovarian follicles in females.
what is msh
MSH acts on the melanocytes (melanin containing cells) and regulates
pigmentation of the skin.
what are the hormones released by pars nervosa
Oxytocin acts on the smooth muscles of our
body and stimulates their contraction. In females, it stimulates a vigorous
contraction of uterus at the time of child birth, and milk ejection from the
mammary gland. Vasopressin acts mainly at the kidney and stimulates resorption of water and electrolytes by the distal tubules
and thereby reduces loss of water through urine
(diuresis). Hence, it is also called as anti-diuretic
hormone (ADH).
what is the pineal gland
The pineal gland is located on the dorsal side of
forebrain. Pineal secretes a hormone called melatonin.
Melatonin plays a very important role in the regulation
of a 24-hour (diurnal) rhythm of our body. For
example, it helps in maintaining the normal rhythms
of sleep-wake cycle, body temperature. In addition,
melatonin also influences metabolism, pigmentation,
the menstrual cycle as well as our defense capability.
what does thyroid gland anatomy
The thyroid gland is composed of two lobes which are
located on either side of the trachea (Figure 22.3). Both
the lobes are interconnected with a thin flap of connective
tissue called isthmus. The thyroid gland is composed of
follicles and stromal tissues. Each thyroid follicle is
composed of follicular cells, enclosing a cavity.
what hormones are released by the thyroid gland
These
follicular cells synthesise two hormones,
tetraiodothyronine or thyroxine (T4
) and
triiodothyronine (T3
).
what will happen if the iodine is low
Iodine is essential for the normal
rate of hormone synthesis in the thyroid. Deficiency of
iodine in our diet results in hypothyroidism and
enlargement of the thyroid gland, commonly called
goitre. Hypothyroidism during pregnancy causes
defective development and maturation of the growing baby leading to stunted growth (cretinism), mental retardation, low
intelligence quotient, abnormal skin, deaf-mutism, etc. In adult women,
hypothyroidism may cause menstrual cycle to become irregular.
what is hyperthyroidism
Due to
cancer of the thyroid gland or due to development of nodules of the thyroid
glands, the rate of synthesis and secretion of the thyroid hormones is
increased to abnormal high levels leading to a condition called
hyperthyroidism which adversely affects the body physiology.
Exopthalmic goitre is a form of hyperthyroidism, characterised by
enlargement of the thyroid gland, protrusion of the eyeballs, increased
basal metabolic rate, and weight loss, also called Graves’ disease
