Dr Shreya R Patil Assistant Professor in Zoology General Organization of Mammalian Endocrine System 952017 2 Endocrine Glands amp its Regulation Category 1 According to Chemical Nature ID: 921316
Download Presentation The PPT/PDF document "Endocrine glands & its Regulation" is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Slide1
Endocrine glands & its Regulation
Dr.
Shreya R.
Patil
Assistant Professor in
Zoology
Slide2General Organization of Mammalian Endocrine System
9/5/2017
2
Endocrine Glands & its Regulation
Slide3Category # 1. According to Chemical Nature:
(a) Steroid Hormones:
These are made up of lipids, which basically derived from cholesterol, e.g. Testosterone,
Estrogen
, Progesterone etc.(b) Amine Hormones:These hormones are made up of amines. Amine hormone is derivative of the amino acid tyrosine.
e.g. T3, T4, epinephrine,
norepinephrine
.(c) Peptide Hormones:These hormones are made up of few amino acid residues only and present as simple linear chain.e.g. Oxytocin and vasopressin both consist of only 9-amino acid residues only.(d) Protein Hormones:These hormones are also made amino acid residues which are much more in numbers. They represent primary, secondary and tertiary configuration.e.g. Insulin, glucagon, STH etc. (e) Glycoprotein Hormones:These hormones are glycoprotein in nature. They are conjugated protein where carbohydrate groups are mannose, galactose, fucose etc.e.g. LH, FSH, TSH etc.
Hormone: Classification
9/5/2017
3
Endocrine Glands & its Regulation
Slide4Category # 2. On the Basis of Mechanism of Action:
(a) Group I hormones:
These hormones bind to intracellular receptors to form hormone-receptor complexes (HRC), through which their biochemical functions are mediated. These hormones are
lipophilic
in nature and are derivatives of cholesterol (except T3 and T4). They are found in circulation in association with transport proteins and possess relatively longer half-lives (hours or day). e.g.
Estrogen, Progesterone, Testosterone, T3
, T
4 etc.(b) Group II hormones:These hormones bind to cell surface (plasma membrane) receptors and stimulate the release of certain molecules, namely the second messengers which in turn, perform the biochemical functions. Thus, hormones themselves are lipophobic in nature, usually transported in the free form and possess short half-lives (in minutes).Group II hormones are subdivided into three categories on the basis of chemical nature of second messengers:(i) The second messenger is cAMP. e.g. ACTH, FSH, LH etc.(ii) The second messenger is phospholipid/inositol
/Ca++. e.g. TRH, GnRH, Gastrin etc.
(iii) The second messenger is unknown. e.g. STH, LTH, Insulin, Oxytocin
etc.
Hormone: Classification
9/5/2017
4
Endocrine Glands & its Regulation
Slide5Category # 3. According to Nature of Action:(a) Local Hormones:
These hormones have got specific local effects by
paracrine
secretion.
e.g. Testosterone.(b) General Hormones: These hormones are transported by circulation to the distal target organ/tissue.
e.g. Insulin, Thyroid hormone etc.
Hormone: Classification
9/5/20175Endocrine Glands & its Regulation
Slide6Category # 4. According to Effect:
(a) Kinetic Hormones:
These hormones may cause pigment migration, muscle contraction, glandular secretion etc.
e.g.
Pinealin, MSH, Epinephrine etc.(b) Metabolic Hormones:
These hormones mainly changes the rate of metabolism and balance the reaction. e.g. Insulin, Glucagon, PTH etc.
(c) Morphogenetic Hormones:
These hormones are involved in growth and differentiation. e.g. STH, LTH, FSH, Thyroid hormones etc.Hormone: Classification9/5/20176
Endocrine Glands & its Regulation
Slide7Category # 5. On the Basis of Stimulation of Endocrine Glands:
(a) Tropic Hormones:
These hormones stimulate other endocrine glands for secretion.
e.g. TSH of pituitary stimulates secretion of thyroid gland.
(b) Non-tropic Hormones: These hormones exert their effect on non-endocrine target tissues.
e.g. Thyroid hormone increases the O2 consumption rate and metabolic activity of almost every cells.
Hormone: Classification
9/5/20177Endocrine Glands & its Regulation
Slide8Hormones are secreted by endocrine cells.
Hormones are chemical messengers.
The are chemical signals that circulate in the body fluids.
The hormones regulate the
behavior of the target cells. Hormones, unlike enzymes do not catalyze any reaction.
They are secreted only when needed, they are not stored prior to requirement.
Hormones may be
proteinaceous or non-proteinaceous in nature (amino-acids or steroids). The secretion of hormones is regulated by the nervous system through the feed back effect. Hormones usually cause long term effects like change in behavior, growth, etc.The hormones function is to stimulate or inhibit the target organs.Properties of Hormones
9/5/2017
8
Endocrine Glands & its Regulation
Slide9The following points highlight the two important mechanisms of hormone action. The mechanisms are:
1. Mode of Protein Hormone Action through Extracellular Receptors
2. Mode of Steroid Hormone Action through Intracellular Receptors.
Mechanism of Hormone Action
9/5/2017
9
Endocrine Glands & its Regulation
Slide10(i
) Formation of Hormone Receptor Complex:
Every hormone has its own receptor.
The number of receptors for each hormone varies.
Insulin receptors for most cells is less than 100 but for some liver cells their number may be more than 1,00,000.
The molecules of amino acid derivatives, peptides or polypeptide protein hormones bind to specific receptor molecules located on the plasma membrane to form the hormone receptor complex.
Mechanism 1: Mode of Protein Hormone Action through Extracellular Receptors:
9/5/201710Endocrine Glands & its Regulation
Slide11Formation of Hormone Receptor Complex
9/5/2017
11
Endocrine Glands & its Regulation
Slide12(ii) Formation of Secondary Messengers—the Mediators:
The hormone-receptor complex does not directly stimulates
adenyl
cyclase present in the cell membrane. It is done through a transducer G protein. Alfred Gilmans has shown that the G protein is a peripheral membrane protein consisting of ∝, β and γ subunits (Fig 22.19).
It interconverts between a GDP form and GTP form. In muscle or liver cells, the hormones such as adrenaline bind receptor to form the hormone-receptor complex in the plasma membrane.
The hormone- receptor complex induces the release of GDP from the G protein. The α- subunit bearing GTP separates from the combined β and у subunits. The β and у subunits do not separate from each other. The activated β and γ subunits of G protein activate
adenyl cyclase. The activated adenyl cyclase catalyses the formation of cyclic adenosine monophosphate (cAMP) from ATP.9/5/2017
12Endocrine Glands & its Regulation
Slide139/5/2017
13
Endocrine Glands & its Regulation
Slide14The hormone is called the first messenger and
cAMP
is termed the second messenger.
The hormones which interact with membrane-bound receptors normally do not enter the
taget cell, but generate second messengers (e.g., cAMP).
Besides, cAMP, certain other intracellular second messengers are cyclic guanosine
monophosphate
(cGMP), diacyl-glycerol (DAG), inositol triphosphate (IP3) and Ca++ responsible for amplification of signal. Earl W. Sutherland Jr (1915-1974) discovered cAMP in 1965. He got Nobel prize in physiology of medicine in 1971 for his discovery, “Role of cAMP in hormone action”.
9/5/2017
14Endocrine Glands & its Regulation
Slide15(iii) Amplification of Signal:
Single activated molecule of
adenyl
cyclase can generate about 100 cAMP molecules. Four molecules of cAMP now bind to inactive protein-
kinase complex to activate protein-kinase A enzyme.
Further steps as shown in involve cascade effect. In cascade effect, every activated molecule in turn activates many molecules of inactive enzyme of next category in the target cell. This process is repeated a number of times.
In the cytoplasm a molecule of protein kinase A activates several molecules of phosphorylase kinase. This enzyme changes inactive form of glycogen phosphorylase into active one.Glycogen phosphorylase converts glycogen into glucose-1 phosphate. The latter changes to glucose. As a result single molecule of ademaline hormone may lead to the release of 100 million glucose molecules within 1 to 2 minutes. This increases the blood glucose level.
9/5/201715
Endocrine Glands & its Regulation
Slide16(iv) Antagonistic Effect:
The effect of hormones which act against each other are called antagonistic effects. Many body cells use more than one second messenger. In heart cells
cAMP
acts as a second messenger that increases muscle cell contraction in response to adrenaline, while
cGMP acts as another second messenger which decreases muscle contraction in response to acetylcholine.
Thus the sympathetic and parasympathetic nervous systems achieve antagonize effect on heart beat. Another example of antagonistic effect is of insulin and glucagon. Insulin lowers blood sugar level and glucagon raises blood sugar level.
9/5/2017
16Endocrine Glands & its Regulation
Slide17(v) Synergistic Effect:
When two or more hormones complement each other’s actions and they are needed for full expression of the hormone effects are called synergistic effects.
For example, the production and ejection of milk by mammary glands require the synergistic effects of oestrogens, progesterone,
prolactin
and oxytocin hormones.
9/5/2017
17
Endocrine Glands & its Regulation
Slide18Steroid hormones are lipid-soluble and easily pass through the cell membrane of a target cell into the cytoplasm. In the cytoplasm they bind to specific intracellular receptors (proteins) to form a hormone receptor complex that enters the nucleus.
In the nucleus, hormones which interact with intracellular receptors (e.g., steroid hormones,
iodothyromines
, etc.) mostly regulate gene expression or chromosome function by the interaction of hormone-receptor complex with the genome.
Biochemical actions result in physiological and developmental effects (tissue growth and differentiation, etc.). In-fact the hormone receptor complex binds to a specific regulatory site on the chromosome and activates certain genes (DNA).
The activated gene transcribes mRNA which directs the synthesis of proteins and usually enzymes in the cytoplasm. The enzymes promote the metabolic reactions in the cell. The actions of lipid soluble hormones are slower and last longer than the action of water- soluble hormones.
Mechanism # 2: Mode of Steroid Hormone Action through Intracellular Receptors
9/5/201718
Endocrine Glands & its Regulation
Slide19Mechanism # 2: Mode of Steroid Hormone Action through Intracellular Receptors
9/5/2017
19
Endocrine Glands & its Regulation
Slide20Role of Hormones as Messengers and Regulators (Role of Hormones in Homeostasis):
9/5/2017
20
Endocrine Glands & its Regulation
Slide21Hypothalamus is a part of the fore brain. Its hypothalamic nuclei— masses of grey matter containing neurons, are located in the white matter in the floor of the third ventricle of the brain. The neurons (
neurosecretory
cells) of hypothalamic nuclei secrete some hormones called
neurohormones
(releasing factors) into the blood.The neurohormones are carried to the anterior lobe of the pituitary gland (
hypophysis) by a pair of hypophysial portal veins. In the pituitary gland (
hypophysis
) the neurohormones stimulate it to release various hormones. Hence the neurohormones are also called “releasing factors”.Hormones as Messengers [Hypothalamus-hypophysial (pituitary) Axis]:9/5/2017
21
Endocrine Glands & its Regulation
Slide22Homeostasis means keeping the internal environment of the body constant.
Hormones help in maintaining internal environment of the body.
When the secretion of hormones is under the control of factors or other hormones it is called feedback control.
The regulation of secretion of
thyroxine from the thyroid gland is an example of such feedback control mechanism.
Hormones as Regulators (Feed Back Control):
9/5/2017
22Endocrine Glands & its Regulation
Slide23(
i
) Positive Feed Back Control:
If the level of
thyroxine is less than normal limits in the blood, thyroxine level stimulates the hypothalamus to secrete more of TRH which results in increased secretion of TSH which in turn stimulates increased secretion of
thyroxine. Such regulatory effect is called positive feedback control.
(ii) Negative Feed Back Control:
The thyrotropin releasing hormone (TRH) from the hypothalamus stimulates the anterior lobe of the pituitary gland to secrete the thyroid stimulating hormone (TSH).The TSH in turn stimulates the thyroid gland to secrete thyroxine. A high amount of thyroxine in the blood exerts an inhibitory effect on hypothalamus in such a way that less of TRH and TSH is produced respectively. This eventually results a decrease in thyroxine. This is called negative feedback control.Types of Feed back control
9/5/2017
23
Endocrine Glands & its Regulation
Slide24Hormones of Hypothalamus and Pituitary
9/5/2017
24
Endocrine Glands & its Regulation
Slide25Secreted hormone
Abbreviation
Produced by
Effect
Thyrotropin
-releasing hormone
TRH
Parvocellular
neurosecretory
neurons
Stimulate
thyroid-stimulating hormone (TSH)
release from
anterior pituitary
(primarily)
Dopamine
(Prolactin-inhibiting hormone)
DA or PIH
Dopamine neurons of the
arcuate
nucleus
Inhibit
prolactin
released from
anterior pituitary
Growth hormone-releasing hormone
GHRH
Neuroendocrine
neurons of the
Arcuate
nucleus
Stimulate
Growth hormone (GH)
release from anterior pituitary
Somatostatin
(growth hormone-inhibiting hormone)
SS, GHIH, or SRIF
Neuroendocrine cells of the
Periventricular nucleus
Inhibit Growth hormone release from anterior pituitary
Inhibit
thyroid-stimulating hormone (TSH)
release from anterior pituitary
Hormones of Hypothalamus
9/5/2017
25
Endocrine Glands & its Regulation
Slide26Secreted hormone
Abbreviation
Produced by
Effect
Gonadotropin-releasing hormone
GnRH
or LHRH
Neuroendocrine cells of the
Preoptic
area
Stimulate
follicle-stimulating hormone (FSH)
release from anterior pituitary
Stimulate
luteinizing hormone (LH)
release from anterior pituitary
Corticotropin-releasing hormone
CRH or CRF
Parvocellular
neurosecretory
neurons
of the
Paraventricular
Nucleus
Stimulate
adrenocorticotropic hormone (ACTH)
release from anterior pituitary
Vasopressin
(antidiuretic hormone)
ADH or AVP or VP
Parvocellular
neurosecretory
neurons,
Magnocellular
neurosecretory
neurons
of the
Paraventricular
nucleus
and
Supraoptic
nucleus
Increases water permeability in the distal convoluted tubule and collecting duct of
nephrons
, thus promoting water reabsorption and increasing blood volume
Hormones of Hypothalamus
9/5/2017
26
Endocrine Glands & its Regulation
Slide27The
pituitary gland
(or
hypophysis) is an endocrine gland about the size of a pea and weighing 0.5 grams (0.018
oz) in humans. It is a protrusion off the bottom of the hypothalamus
at the base of the brain, and rests in a small, bony cavity (sella
turcica) covered by a dural fold.The pituitary is functionally connected to the hypothalamus by the median eminence via a small tube called the infundibular stem or pituitary stalk. The anterior pituitary (adenohypophysis) is connected to the hypothalamus via the hypothalamo
–hypophyseal portal vessels, which allows for quicker and more efficient communication between the hypothalamus and the pituitary.
Pituitary Gland
9/5/2017
27
Endocrine Glands & its Regulation
Slide28Histology of Pituitary Gland
9/5/2017
28
Endocrine Glands & its Regulation
Slide29Secreted hormone
Abbreviation
From cells
Effect
Growth hormone
(
somatotropin
)
GH
Somatotrophs
Stimulates
growth
and
cell
reproduction
Stimulates
Insulin-like growth factor 1
release from
liver
Thyroid-stimulating hormone
(thyrotropin)
TSH
Thyrotrophs
Stimulates
thyroxine
(T4) and
triiodothyronine
(T3) synthesis and release from
thyroid gland
Stimulates iodine absorption by thyroid gland
Adrenocorticotropic hormone
(
corticotropin
)
ACTH
Corticotrophs
Stimulates
corticosteroid
(
glucocorticoid
and
mineralcorticoid
) and
androgen
synthesis and release from
adrenocortical cells
Hormones of Pituitary Gland
Anterior pituitary
lobe
(
A
denohypophysis
)
9/5/2017
29
Endocrine Glands & its Regulation
Slide30Secreted hormone
Abbreviation
From cells
Effect
Follicle-stimulating hormone
FSH
Gonadotrophs
In females: Stimulates maturation of
ovarian follicles
in
ovary
In males: Stimulates maturation of
seminiferous tubules
In males: Stimulates
spermatogenesis
In males: Stimulates production of
androgen-binding protein
from
Sertoli
cells
of the
testes
Luteinizing hormone
LH
Gonadotrophs
In females: Stimulates
ovulation
In females: Stimulates formation of
corpus
luteum
In males: Stimulates
testosterone
synthesis from
Leydig
cells (interstitial cells)
Prolactin
PRL
Lactotrophs
Stimulates milk synthesis and release from
mammary glands
Mediates
sexual gratification
Melanocyte-stimulating hormone
MSH
Melanotropes
in the
Pars intermedia
of the Anterior Pituitary
Stimulates
melanin
synthesis and release from skin/hair
melanocytes
Hormones of Pituitary Gland
9/5/2017
30
Endocrine Glands & its Regulation
Slide31Stored hormone
Abbreviation
From cells
Effect
Oxytocin
OX or OXT
Magnocellular
neurosecretory
cells
In females:
uterine contraction
during birthing,
lactation (
letdown
reflex)
when nursing
Vasopressin
(antidiuretic hormone)
ADH or AVP
Parvocellular
neurosecretory
neurons
Increases water permeability in the distal convoluted tubule and collecting duct of
nephrons
, thus promoting water reabsorption and increasing blood volume
Hormones of Pituitary
Gland
Posterior Lobe (
Neurohypophysis
)
9/5/2017
31
Endocrine Glands & its Regulation
Slide32Hypersecretion
of Anterior Pituitary Hormones
1. Acromegaly: In Adults
Symptoms:
Enlarged lips, nose and tongue Deepening of the voice due to enlarged vocal cords and sinusesThicker
, coarse, oily skin Joint aches Excessive
sweating and skin odour
Skin tags - tiny flesh-coloured finger-like projections on the skin Loss, or lack of libido Headaches, Fatigue and weakness Impaired vision Sleep apnoea - breaks in breathing during sleep due to obstruction of the airway High blood pressureTreatment:Treatment options include surgery, medical therapy and radiotherapy.
Disorders of Pituitary Gland
9/5/2017
32
Endocrine Glands & its Regulation
Slide33Hyper secretion
of Anterior Pituitary Hormones
2. Gigantism
: Gigantism, also known as giantism
is a condition characterized by excessive growth and height significantly above average. In humans, this condition is caused by over-production of growth hormone in childhood resulting in people between 7 feet (2.13 m) and 9 feet (2.75 m) in height
.
Disorders
of Pituitary Gland9/5/201733Endocrine Glands & its Regulation
Slide34Hypo secretion
of Anterior Pituitary Hormones
1. Dwarfism:
Dwarfism, also known as short stature, occurs when an organism is extremely small
. In humans, it is sometimes defined as an adult height of less than 4 feet 10 inches (58 in; 147 cm), regardless of sex, although some individuals with dwarfism are slightly taller. Disproportionate dwarfism is characterized by either short limbs or a short torso. In cases of proportionate dwarfism, both the limbs and torso are unusually small. Normal intelligence and lifespan are usual
.
Treatment:
Hormone disorders can be treated with hormone replacement therapy as well before the child's growth plates fuseDisorders of Pituitary Gland9/5/201734
Endocrine Glands & its Regulation
Slide35Thyroid Gland
(Histology)
9/5/2017
35
Endocrine Glands & its Regulation
Slide36Secreted hormone
Abbreviation
From cells
Effect
Triiodothyronine
T3
Thyroid epithelial cell
(More potent form of
thyroid hormone
)
Stimulates body oxygen and energy consumption, thereby increasing the
basal metabolic rate
Stimulates
RNA polymerase
I and II, thereby promoting
protein synthesis
Thyroxine
(tetraiodothyronine)
T4
Thyroid epithelial cell
s
(Less active form of
thyroid hormone
)
(Acts as a
prohormone
to
triiodothyronine
)
Stimulates body oxygen and energy consumption, thereby increasing the
basal metabolic rate
Stimulates
RNA polymerase
I and II, thereby promoting
protein synthesis
Calcitonin
Parafollicular cell
s
Stimulates
osteoblasts
and thus bone construction
Inhibits
Ca
2+
release from bone, thereby reducing blood Ca
2+
Thyroid Gland
(Hormones)
9/5/2017
36
Endocrine Glands & its Regulation
Slide37The thyroid hormones act on nearly every cell in the body. They act to increase the basal metabolic rate, affect protein synthesis, help regulate long bone growth (synergy with growth hormone) and neural maturation, and increase the body's sensitivity to
catecholamines
(such as adrenaline) by permissiveness.
The
thyroid hormones are essential to proper development and differentiation of all cells of the human body. These
hormones also regulate protein, fat, and carbohydrate metabolism, affecting how human cells use energetic compounds. They
also stimulate vitamin metabolism. Numerous physiological and pathological stimuli influence thyroid hormone synthesis
.Thyroid hormone leads to heat generation in humans. However, the thyronamines function via some unknown mechanism to inhibit neuronal activity; this plays an important role in the hibernation cycles of mammals and the moulting behaviour of birds. One effect of administering the thyronamines is a severe drop in body temperature.Thyroid Gland (Functions)
9/5/2017
37
Endocrine Glands & its Regulation
Slide38Hypothyroidism:
1.
Critinism
:
The most common cause of congenital hypothyroidism is iodine deficiency. Cretinism is therefore most probably due to a diet deficient in iodine.
Symptoms: Mild to severe impairment of both physical and mental growth and development.
Cretinism results in mental deterioration, swelling of the skin, loss of water and hair
. Bone maturation and puberty are severely delayed. Ovulation is impeded, and infertility is common.Thickened skin, enlarged tongue, or a protruding abdomen.Thyroid Gland (Disorders)
9/5/201738
Endocrine Glands & its Regulation
Slide39Hypothyroidism
:
2. Myxoedema/Gull’s Disease:
Myxedema is known to occur in various forms of hypothyroidism, and also in Graves' disease
.Symptoms: Myxoedema is responsible for the thickening of the tongue and the laryngeal and
pharnygeal mucous membranes, which results in thick slurred speech and hoarseness, both of which are seen commonly in hypothyroidism. Low Heart rate, Low B.P. and Low Body
temprature
. Obesity due to low BMR.Thyroid Gland (Disorders)9/5/201739
Endocrine Glands & its Regulation
Slide40Hypothyroidism
:
3. Endemic Goitre:
Endemic
goiter is a type of goitre that is associated with dietary iodine deficiency. Some inland areas where soil and water lacks in iodine compounds and consumption of marine foods is low are known for higher incidence of goitre. In such areas
goitre is said to be "endemic".
This type of
goiter is easily preventable. In most developed countries regulations have been put into force by health policy institutions requiring salt, flour or water to be fortified with iodine.Treatment of endemic goiter is medical with iodine and thyroxine preparations. Surgery is only necessary in cases where complicated by significant compression of nearby structures.Thyroid Gland (Disorders)
9/5/2017
40Endocrine Glands & its Regulation
Slide41Hyperthyroidism:
Exophthalmic Goitre/Graves’ disease:
Graves' disease, also known as toxic diffuse
goiter
, is an autoimmune disease that affects the thyroid.
Sympotms:
protuberance of one or both eyes, insomnia, hand tremor, hyperactivity, hair loss, excessive sweating, shaking hands, itching, heat intolerance, weight loss despite increased appetite, diarrhea, frequent defecation, palpitations, muscle weakness, and skin warmth and moistness. Sinus tachycardia, atrial fibrillation, and premature ventricular contractions, and hypertension.Treatment:
Treatment of Graves' disease includes antithyroid drugs which reduce the production of thyroid hormone or surgical excision of the gland
Thyroid Gland
(Disorders)
9/5/2017
41
Endocrine Glands & its Regulation
Slide42Parathyroid glands are small
endocrine
glands in the neck of humans and other
tetrapods that produce parathyroid hormone. Humans
usually have four parathyroid glands, variably located on the back of the thyroid gland — considerable variation exists.
Parathyroid hormone and calcitonin (one of the hormones made by the thyroid gland) have key roles in regulating the amount of calcium in the blood and within the bones.Parathyroid Gland(Hormones)9/5/2017
42Endocrine Glands & its Regulation
Slide43Parathyroid Gland
(Histology)
The
parathyroid glands are named for their proximity to the thyroid — and serve a completely different role than the thyroid gland.
The
parathyroid glands are quite easily recognizable from the thyroid as they have densely packed cells, in contrast with the follicular structure of the
thyroid
.
Two unique types of cells are present in the parathyroid
gland:
Chief cells
, which synthesize and release parathyroid hormone. These cells are small, and appear dark when loaded with parathyroid hormone, and clear when the hormone has been secreted, or in their resting
state.
Oxyphil
cells
, which are lighter in appearance and increase in number with age
,
have an unknown function
.
9/5/2017
43
Endocrine Glands & its Regulation
Slide44The major function of the parathyroid glands is to maintain the body's
calcium
and
phosphate levels within a very narrow range, so that the
nervous and muscular systems can function properly. The parathyroid glands do this by secreting parathyroid hormone
.Parathyroid hormone (PTH, known as parathormone
) is a small
protein that takes part in the control of calcium and phosphate homeostasis, as well as bone physiology. Parathyroid hormone has effects antagonistic to those of calcitonin.Calcium. PTH increases blood calcium levels by directly stimulating osteoblasts and thereby indirectly stimulating osteoclasts to break down bone and release calcium. PTH increases gastrointestinal calcium absorption by activating vitamin D, and promotes calcium conservation (reabsorption) by the kidneys
.Phosphate. PTH is the major regulator of serum phosphate concentrations via actions on the kidney. It is an inhibitor of proximal tubular reabsorption of phosphorus. Through activation of vitamin D the absorption of Phosphate is increased.
[13]
Parathyroid
Gland
(Functions)
9/5/2017
44
Endocrine Glands & its Regulation
Slide45Hyperparathyroidism
Hyperparathyroidism
is the state in which there is excess parathyroid hormone circulating. This may cause bone pain and tenderness, due to increased bone resorption. Due to increased circulating calcium, there may be other symptoms associated with
hypercalcemia
, most commonly dehydration. Hyperparathyroidism is most commonly caused by a
benign proliferation of chief cells in single gland, and rarely MEN syndrome. This is known as
primary hyperparathyroidism
, which is generally managed by surgical removal of the abnormal parathyroid gland.Renal disease may lead to hyperparathyroidism. When too much calcium is lost, there is a compensation by the parathyroid, and parathyroid hormone is released. The glands hypertrophy to synthesise more parathyroid hormone.This is known as secondary hyperparathyroidism. If this situation exists for a prolonged period of time, the parathyroid tissue may become unresponsive to the blood calcium levels, and begin to autonomously release parathyroid hormone. This is known as tertiary hyperparathyroidism.
Parathyroid Gland
(Disorders)
9/5/2017
45
Endocrine Glands & its Regulation
Slide46Hypoparathyroidism
The
state of decreased parathyroid activity is known as
hypoparathyroidism. This is most commonly associated with damage to the glands or their blood supply during thyroid surgery — it may be associated with rarer genetic syndromes such as
Di George syndrome, which is inherited as an autosomal dominant syndrome. Hypoparathyroidism will occur after surgical removal of the parathyroid glands
.Occasionally, an individual's tissues are resistant to the effects of parathyroid hormone. This is known as
pseudohypoparathyroidism
. In this case the parathyroid glands are fully functional, and the hormone itself is not able to function, resulting in a decrease in blood calcium levels.Pseudohypoparathyroidism is often associated with the genetic condition Albright's hereditary osteodystrophy. Pseudopseudohypoparathyroidism, one of the longest words in the English language, is used to describe an individual with Albright's hereditary osteodystrophy; with normal parathyroid hormone and serum calcium levels.Hypoparathyroidism may present with symptoms associated with decreased calcium, and is generally treated with Vitamin D analogues.
Parathyroid Gland
(Disorders)
9/5/2017
46
Endocrine Glands & its Regulation