Endocrine glands & its Regulation - PowerPoint Presentation

Slide1

Endocrine glands & its Regulation

Dr.

Shreya R.

Patil

Assistant Professor in

Zoology

Slide2

General Organization of Mammalian Endocrine System

9/5/2017

2

Endocrine Glands & its Regulation

Slide3

Category # 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

Slide4

Category # 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

Slide5

Category # 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

Slide6

Category # 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

Slide7

Category # 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

Slide8

Hormones 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

Slide9

The 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

Slide11

Formation 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

Slide13

9/5/2017

13

Endocrine Glands & its Regulation

Slide14

The 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

Slide18

Steroid 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

Slide19

Mechanism # 2: Mode of Steroid Hormone Action through Intracellular Receptors

9/5/2017

19

Endocrine Glands & its Regulation

Slide20

Role of Hormones as Messengers and Regulators (Role of Hormones in Homeo­stasis):

9/5/2017

20

Endocrine Glands & its Regulation

Slide21

Hypothalamus 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

Slide22

Homeostasis 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

Slide24

Hormones of Hypothalamus and Pituitary

9/5/2017

24

Endocrine Glands & its Regulation

Slide25

Secreted 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

Slide26

Secreted 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

Slide27

The 

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

Slide28

Histology of Pituitary Gland

9/5/2017

28

Endocrine Glands & its Regulation

Slide29

Secreted 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

Slide30

Secreted 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

Slide31

Stored 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

Slide32

Hypersecretion

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

Slide33

Hyper 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

Slide34

Hypo 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

Slide35

Thyroid Gland

(Histology)

9/5/2017

35

Endocrine Glands & its Regulation

Slide36

Secreted 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

Slide37

The 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

Slide38

Hypothyroidism:

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

Slide39

Hypothyroidism

:

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

Slide40

Hypothyroidism

:

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

Slide41

Hyperthyroidism:

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

Slide42

Parathyroid 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

Slide43

Parathyroid 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

Slide44

The 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

Slide45

Hyperparathyroidism

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

Slide46

Hypoparathyroidism

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