Parathyroid Glands:Parathyroid Glands:

The parathyroid The parathyroid glands are small in glands are small in size and are found size and are found on the posterior on the posterior aspect of the thyroid aspect of the thyroid gland. gland.

Typically, there are Typically, there are four of them but the four of them but the actual number may actual number may vary. vary.

Histology of the Histology of the ParathyroidParathyroid

The endocrine The endocrine cells within these cells within these glands are glands are arranged in thick, arranged in thick, branching cords branching cords containing containing oxyphil cells of oxyphil cells of unclear function unclear function and most and most importantly large importantly large numbers of numbers of chief chief cellscells that secrete that secrete parathyroid parathyroid hormone (PTH)hormone (PTH)..

PTH:PTH: Small proteinSmall protein

Single most important hormone controlling Single most important hormone controlling calcium homeostasis. Its release is calcium homeostasis. Its release is triggered by falling blood calcium levels triggered by falling blood calcium levels and inhibited by hypercalcemia (high blood and inhibited by hypercalcemia (high blood calcium). calcium).

There are three target organs for PTH:There are three target organs for PTH:

skeletonskeleton kidneyskidneys intestineintestine

In humans, the major calcium storage In humans, the major calcium storage organ is bone.organ is bone.

Calcium is stored as CaPOCalcium is stored as CaPO44.. Generally, calcium salts are not very soluble Generally, calcium salts are not very soluble

in aqueous solutions such as plasma.in aqueous solutions such as plasma. Calcium metabolism is virtually Calcium metabolism is virtually

inseparable from phosphate inseparable from phosphate metabolism.metabolism.

The major factors regulating calcium The major factors regulating calcium and phosphate metabolism are and phosphate metabolism are parathyroid hormone (PHT), calcitonin parathyroid hormone (PHT), calcitonin and calcitrol.and calcitrol.

PTH stimulates the PTH stimulates the following on these target following on these target

organs:organs: Osteoclasts (bone absorbing cells) are stimulated to Osteoclasts (bone absorbing cells) are stimulated to

digest bone and release ionic calcium and phosphates digest bone and release ionic calcium and phosphates to the blood.to the blood.

Kidneys are stimulated to reabsorb calcium and Kidneys are stimulated to reabsorb calcium and excrete phosphate.excrete phosphate.

Intestines are stimulated to increase calcium Intestines are stimulated to increase calcium absorption. absorption.

Vitamin D is required for absorption of calcium from Vitamin D is required for absorption of calcium from ingested food. ingested food. For vitamin D to exert this effect, it must first be converted For vitamin D to exert this effect, it must first be converted

by the kidneys to its active formby the kidneys to its active form It is this conversion that is directly stimulated by PTH.It is this conversion that is directly stimulated by PTH.

Pathology of the Pathology of the parathyroid glands:parathyroid glands:

Because calcium is essential for so Because calcium is essential for so many functions, including transmission many functions, including transmission of action potentials, muscle of action potentials, muscle contraction, pacemaker activity in the contraction, pacemaker activity in the heart, and blood clotting, precise heart, and blood clotting, precise control of ionic calcium levels in body control of ionic calcium levels in body fluids is absolutely critical. As a result fluids is absolutely critical. As a result both hyper- and hypoparathyroidism both hyper- and hypoparathyroidism can have severe consequences.can have severe consequences.

Hyperparathyroidism:Hyperparathyroidism: Rare, usually the result of a parathyroid gland tumor.Rare, usually the result of a parathyroid gland tumor.

Results in severe loss of calcium from the bones. Results in severe loss of calcium from the bones.

The bones soften and deform as their mineral salts The bones soften and deform as their mineral salts are replaced by fibrous connective tissue. are replaced by fibrous connective tissue.

Results in hypercalcemia Results in hypercalcemia

Leads to, depression of the nervous system leading to Leads to, depression of the nervous system leading to abnormal reflexes and weakness of the skeletal muscles, and abnormal reflexes and weakness of the skeletal muscles, and formation of kidney stones as excess calcium salts are formation of kidney stones as excess calcium salts are deposited in kidney tubules.deposited in kidney tubules.

Hypoparathyroidism:Hypoparathyroidism:

It is a PTH deficiency, which is a common It is a PTH deficiency, which is a common consequence of parathyroid trauma or consequence of parathyroid trauma or removal during thyroid surgery. removal during thyroid surgery.

The resulting hypocalcemia increases The resulting hypocalcemia increases excitability of neurons and may lead to excitability of neurons and may lead to tetany resulting in uncontrollable muscle tetany resulting in uncontrollable muscle twitches and convulsions, which if twitches and convulsions, which if untreated may progress to spasms of the untreated may progress to spasms of the larynx, respiratory paralysis and death.larynx, respiratory paralysis and death.

Calcitonin in non-Calcitonin in non-mammalian vertebratesmammalian vertebrates

In most non-mammalian vertebrates, In most non-mammalian vertebrates, calcitonin is secreted from a specific calcitonin is secreted from a specific gland called the ultimobranchial gland called the ultimobranchial gland.gland.

In mammals, this tissue has been In mammals, this tissue has been incorporated into the thyroid gland incorporated into the thyroid gland (C- or parafollicular cells).(C- or parafollicular cells).

Bone probably evolved as a calcium Bone probably evolved as a calcium storage organ first, storage organ first, thenthen became became structural.structural.

Calcium availability is not an issue for Calcium availability is not an issue for marine organisms.marine organisms. However, when fish started moving into However, when fish started moving into

fresh water, calcium was in short supply.fresh water, calcium was in short supply. These fish needed to start storing calcium.These fish needed to start storing calcium. This may explain the emergence of the This may explain the emergence of the

jawed fishes.jawed fishes. Believed to have evolved in fresh water.Believed to have evolved in fresh water. Had bonier skeletons than marine fish.Had bonier skeletons than marine fish.

Cartilage was a good starting material Cartilage was a good starting material for calcium storage, since calcium is for calcium storage, since calcium is already a component.already a component.

Having stronger bones would have Having stronger bones would have facilitated jaw evolution by providing facilitated jaw evolution by providing a sufficiently strong substrate.a sufficiently strong substrate. Jaws require strong structural support Jaws require strong structural support

because they can develop great forces.because they can develop great forces. At the same time, fish were At the same time, fish were

developing more robust dermal developing more robust dermal plating from protection.plating from protection. Also from CaPOAlso from CaPO44 deposits in scales. deposits in scales.

Calcium regulation in non-Calcium regulation in non-mammalian vertebrates:mammalian vertebrates:

Fishes in general:Fishes in general: Unlike other vertebrates, fish do not Unlike other vertebrates, fish do not

have parathyroid tissue. However, have parathyroid tissue. However, immunoreactive PTH has been immunoreactive PTH has been demonstrated in trout and goldfish.demonstrated in trout and goldfish.

Many fish lack true bone.Many fish lack true bone. In most teleosts, bone is acellular (no In most teleosts, bone is acellular (no

osteoclasts or osteoblasts).osteoclasts or osteoblasts). Scales may play a major role as calcium Scales may play a major role as calcium

storage organs.storage organs.

In fish, unlike other vertebrates, the In fish, unlike other vertebrates, the principal calcium regulators are principal calcium regulators are calcitonin and stanniocalcin.calcitonin and stanniocalcin.

Stanniocalcin is secreted in response Stanniocalcin is secreted in response to elevated plasma calcium (similar to elevated plasma calcium (similar to PTH in other vertebrates).to PTH in other vertebrates).

Stanniocalcin is secreted by the Stanniocalcin is secreted by the Corpuscles of Stannius.Corpuscles of Stannius.

Parathyroid hormone related Parathyroid hormone related hormone (PTHrH) has been isolated hormone (PTHrH) has been isolated from plasma.from plasma.

Parathyroid Hormone Parathyroid Hormone related Hormone (PTHrH)related Hormone (PTHrH)

PTHrH is a protein with hypercalcemic PTHrH is a protein with hypercalcemic activity.activity.

It was first isolated from a malignant tumor.It was first isolated from a malignant tumor. Has significant sequence overlap with PTH, Has significant sequence overlap with PTH,

particularly at the N-terminal.particularly at the N-terminal. Thought to have evolved from PTH gene.Thought to have evolved from PTH gene.

Has been identified in over 20 different Has been identified in over 20 different tissues in humans (including lactating tissues in humans (including lactating mammary, uterus, and the amnion and fetal mammary, uterus, and the amnion and fetal parathyroid glands.parathyroid glands.

Probably plays a role in CaProbably plays a role in Ca2+2+ accumulation accumulation by the fetus.by the fetus.

Agnathan fishes:Agnathan fishes: These do not appear to have specific These do not appear to have specific

mechanisms for regulating calcium and mechanisms for regulating calcium and phosphate.phosphate.

However, mammalian calcitonin will However, mammalian calcitonin will decrease urinary flow and urinary decrease urinary flow and urinary electrolyte concentration.electrolyte concentration.

Chondrichthyean fishes:Chondrichthyean fishes: Calcium is stored in cartilage, since these Calcium is stored in cartilage, since these

fish lack true bone.fish lack true bone. Ultimobranchial glands contain a potent Ultimobranchial glands contain a potent

hypocalcemic factor (for mammals)hypocalcemic factor (for mammals) Other fish calcitonins are ineffective in sharks Other fish calcitonins are ineffective in sharks

and rays.and rays.

Teleost fishes:Teleost fishes: CT lowers calcium influx across the gill.CT lowers calcium influx across the gill. Salmon CT is very potent at lowering Salmon CT is very potent at lowering

plasma calcium in mammals and birds.plasma calcium in mammals and birds. This may be due to its long half-life This may be due to its long half-life

(compared to mammalian CT).(compared to mammalian CT). Calcitrol (1,25 dihydroxycholecalciferol) Calcitrol (1,25 dihydroxycholecalciferol)

although not absolutely required, will although not absolutely required, will increase calcium uptake across the gut.increase calcium uptake across the gut.

Calcitrol has been shown to increase Calcitrol has been shown to increase plasma calcium in freshwater catfish.plasma calcium in freshwater catfish.

Estrogens also increase plasma Estrogens also increase plasma calcium.calcium.

Sarcopterygean fishes:Sarcopterygean fishes: Lungfish appear to be insensitive to Lungfish appear to be insensitive to

mammalian CT and PTH from other fish mammalian CT and PTH from other fish or from mammls.or from mammls.

There is some evidence that CT and There is some evidence that CT and PTH are diuretic and antidiuretic, PTH are diuretic and antidiuretic, respectively.respectively.

Amphibians:Amphibians: Very little is known.Very little is known. Amphibians possess both an ultimobranchial Amphibians possess both an ultimobranchial

gland and parathyroid glands.gland and parathyroid glands. Specialized structures, the endolymphatic Specialized structures, the endolymphatic

sacs, are involved in calcium metabolism.sacs, are involved in calcium metabolism. These sacs are located at the base of the skull These sacs are located at the base of the skull

and contain large amounts of CaPOand contain large amounts of CaPO44.. May also be involved in plasma buffering.May also be involved in plasma buffering.

Frogs have cellular bone and the effects of Frogs have cellular bone and the effects of CT and PTH are similar to that seen in CT and PTH are similar to that seen in mammals.mammals.

Bovine PTH is effective in amphibians.Bovine PTH is effective in amphibians.

ADRENAL GLANDS:ADRENAL GLANDS:

The two adrenal The two adrenal glands are pyramid-glands are pyramid-shaped organs shaped organs found atop the found atop the kidneys.kidneys.

Each gland is Each gland is structurally and structurally and functionally two functionally two endocrine glands in endocrine glands in one.one.

The inner adrenal medulla is made up of nervous tissue and acts as part of the sympathetic nervous system. The outer adrenal cortex forms the bulk (about 80%) of the gland. Each of these regions produces its own set of hormones.

Adrenal Medulla:Adrenal Medulla: It is made up of chromaffin cells which secrete the It is made up of chromaffin cells which secrete the

catecholamines epinephrine (E) (adrenaline) and catecholamines epinephrine (E) (adrenaline) and norepinephrine (NE) (noradrenaline) into the blood. norepinephrine (NE) (noradrenaline) into the blood.

During the fight-or-flight responses, the sympathetic During the fight-or-flight responses, the sympathetic nervous system is activated, including the chromaffin nervous system is activated, including the chromaffin tissue and large amounts of catecholamines (80% of which tissue and large amounts of catecholamines (80% of which is E) are released.is E) are released.

In most cases the two hormones have very similar effects In most cases the two hormones have very similar effects on their target organs. However, E is the more potent on their target organs. However, E is the more potent stimulator of the heart rate and strength of contraction, stimulator of the heart rate and strength of contraction, and metabolic activities, such as breakdown of glycogen and metabolic activities, such as breakdown of glycogen and release of glucose).and release of glucose).

NE has great effect on peripheral vasoconstriction and NE has great effect on peripheral vasoconstriction and blood pressure.blood pressure.

Adrenal Cortex:Adrenal Cortex:

The cells of the adrenal cortex are The cells of the adrenal cortex are arranged in three distinct zones, each zone arranged in three distinct zones, each zone producing corticosteroids.producing corticosteroids.

The The Zona glomerulosaZona glomerulosa is the outer-most is the outer-most layer of cells and it produces layer of cells and it produces mineralocorticoids, that help control the mineralocorticoids, that help control the balance of minerals and water in the blood. balance of minerals and water in the blood.

The The zona fasciculatazona fasciculata is composed of cells is composed of cells that secrete glucocorticoids. that secrete glucocorticoids.

The The zona reticulariszona reticularis produce small produce small amounts of adrenal sex steroids.amounts of adrenal sex steroids.

Hormones of the Adrenal Hormones of the Adrenal CortexCortex MineralocorticoidsMineralocorticoids

Although there are several Although there are several mineralocorticoids, mineralocorticoids, aldosteronealdosterone is by far the is by far the most potent and accounts for more than 95% most potent and accounts for more than 95% of production. Its main function is to maintain of production. Its main function is to maintain sodium balance by reducing excretion of this sodium balance by reducing excretion of this ion from the body. ion from the body.

The primary target organs of aldosterone are The primary target organs of aldosterone are kidney tubules where it stimulates kidney tubules where it stimulates reabsorption of sodium ions from urine back reabsorption of sodium ions from urine back to the bloodstream. to the bloodstream.

Aldosterone also enhances sodium absorption Aldosterone also enhances sodium absorption from sweat, saliva, and gastric juice. from sweat, saliva, and gastric juice.

Secretion of aldosterone is induced Secretion of aldosterone is induced by a number of factors such as high by a number of factors such as high blood levels of potassium, low blood blood levels of potassium, low blood levels of sodium, and decreasing levels of sodium, and decreasing blood volume and pressure. blood volume and pressure.

The reverse conditions inhibit The reverse conditions inhibit secretion of aldosterone. secretion of aldosterone.

Glucocorticoids:Glucocorticoids: Glucocorticoids influence metabolism of Glucocorticoids influence metabolism of

most body cells, help us resist stress, and most body cells, help us resist stress, and are considered to be absolutely essential to are considered to be absolutely essential to life. life.

The most important glucocorticoid in The most important glucocorticoid in humans is humans is cortisolcortisol, but small amounts , but small amounts of cortisone and corticosterone are also of cortisone and corticosterone are also produced.produced.

The main effect of cortisol is to promote The main effect of cortisol is to promote gluconeogenesis or formation of gluconeogenesis or formation of glucose from noncarbohydrate glucose from noncarbohydrate molecules, especially fats and proteins. molecules, especially fats and proteins.

Cortisol also breaks down adipose (fat) tissue, Cortisol also breaks down adipose (fat) tissue, released fatty acids can be then used by many released fatty acids can be then used by many tissues as a source of energy and "saving" glucose tissues as a source of energy and "saving" glucose for the brain. for the brain.

Blood levels of glucocorticoids increase significantly Blood levels of glucocorticoids increase significantly during stress, which helps the body to negotiate the during stress, which helps the body to negotiate the crisis.crisis.

Interestingly, chronic excess of cortisol has Interestingly, chronic excess of cortisol has significant anti-inflammatory and anti-immune significant anti-inflammatory and anti-immune effects and glucocorticoid drugs are often used to effects and glucocorticoid drugs are often used to control symptoms of many chronic inflammatory control symptoms of many chronic inflammatory disorders, such as rheumatoid arthritis or allergic disorders, such as rheumatoid arthritis or allergic responses.responses.

Regulation of glucocorticoid Regulation of glucocorticoid secretion:secretion:

It is provided by a typical negative feedback It is provided by a typical negative feedback system:system:

increased (hypothalamus) CRH increased (hypothalamus) CRH negativenegative

increased (adenohypophysis) ACTH increased (adenohypophysis) ACTH increased (adrenal cortex) cortisolincreased (adrenal cortex) cortisol

Gonadocorticoids (Sex Hormones)Gonadocorticoids (Sex Hormones)

The amount of sex steroids produced by The amount of sex steroids produced by zona reticularis is insignificant compared zona reticularis is insignificant compared to the amounts secreted by the gonads. to the amounts secreted by the gonads.

These hormones may contribute to the These hormones may contribute to the onset of puberty and the appearance of onset of puberty and the appearance of axillary and pubic hair in both males and axillary and pubic hair in both males and females. females.

In adult women adrenal In adult women adrenal androgens androgens (male (male sex hormones, especially testosterone) may sex hormones, especially testosterone) may be, at least partially, responsible for the sex be, at least partially, responsible for the sex drive.drive.

Pathology of the adrenal cortex Pathology of the adrenal cortex functionfunction:

Hyperadrenalism :Hyperadrenalism : It is referred to as Cushing's disease and can be It is referred to as Cushing's disease and can be

caused by a cortisol-secreting tumour in the caused by a cortisol-secreting tumour in the adrenal glands, ACTH-secreting tumour of the adrenal glands, ACTH-secreting tumour of the pituitary, or ACTH secreted by abdominal pituitary, or ACTH secreted by abdominal carcinoma. carcinoma.

However, it most often results from the clinical However, it most often results from the clinical administration of pharmacological (very high) administration of pharmacological (very high) doses of glucocorticoid drugs. doses of glucocorticoid drugs.

The symptoms include a persistent The symptoms include a persistent hyperglycaemia, dramatic loss of muscle and bone hyperglycaemia, dramatic loss of muscle and bone proteins, and water and salt retention, leading to proteins, and water and salt retention, leading to hypertension and edema - one of its signs is a hypertension and edema - one of its signs is a swollen "moon" face. The only treatment is a swollen "moon" face. The only treatment is a surgical removal of tumour or discontinuation of surgical removal of tumour or discontinuation of the drug.the drug.

Hypoadrenalism :Hypoadrenalism :

It is referred to as Addison's disease It is referred to as Addison's disease and involves significant reduction in and involves significant reduction in plasma glucose and sodium, very high plasma glucose and sodium, very high levels of potassium and loss of weight. levels of potassium and loss of weight. The usual treatment is corticosteroid The usual treatment is corticosteroid replacement therapy.replacement therapy.

Comparative aspects of Comparative aspects of adrenal function:adrenal function:

Anatomy of adrenal tissue:Anatomy of adrenal tissue: In mammals, both cortical tissue and In mammals, both cortical tissue and

chromafin tissue are incorporated into two chromafin tissue are incorporated into two glands (bilateral).glands (bilateral).

In lower vertebrates, these two tissues are In lower vertebrates, these two tissues are not always associated with each other.not always associated with each other.

In amniotes, we see the more traditional In amniotes, we see the more traditional adrenal gland structure, with the gland at adrenal gland structure, with the gland at the apical pole of the kidney.the apical pole of the kidney.

In all vertebrates these two tissues are In all vertebrates these two tissues are always associated with the kidney.always associated with the kidney.

Renin-angiotensin Renin-angiotensin system:system:

Kidney (JGA) secretes renin in Kidney (JGA) secretes renin in response to sympathetic stimulation, response to sympathetic stimulation, hypotension or decreased plasma hypotension or decreased plasma NaNa++ and/or increased plasma K and/or increased plasma K++..

Angiotensinogen is converted to AI.Angiotensinogen is converted to AI. AI is converted to AII by ACE in the AI is converted to AII by ACE in the

lungs.lungs.

AII has a number of direct effects:AII has a number of direct effects: VasoconstrictionVasoconstriction Cardiac and vascular hypertrophyCardiac and vascular hypertrophy Stimulates thirstStimulates thirst Stimulates ADH secretionStimulates ADH secretion Stimulates adrenal cortex to release Stimulates adrenal cortex to release

aldosterone.aldosterone. Aldosterone has direct effects on the Aldosterone has direct effects on the

kidney:kidney: Stimulation of NaStimulation of Na++ recovery. recovery.

Renin-angiotensin system is Renin-angiotensin system is responsible for long-term regulation of responsible for long-term regulation of blood volume and electrolyte balance.blood volume and electrolyte balance. Normal response to decreased blood Normal response to decreased blood

volume or increased blood osmolarity.volume or increased blood osmolarity.

If blood volume is to high, then the If blood volume is to high, then the atrial wall releases Atrial Natriuretic atrial wall releases Atrial Natriuretic Factor (ANF) which will inhibit renin Factor (ANF) which will inhibit renin secretion by kidney.secretion by kidney.

Agnathan fishes:Agnathan fishes: No discreet JGA.No discreet JGA. No identifiable renin-angiotensin system.No identifiable renin-angiotensin system. However, they do have natriuretic However, they do have natriuretic

peptides which are secreted by the gills.peptides which are secreted by the gills. Sea lampreys have detectable elevated Sea lampreys have detectable elevated

corticosteroid levels when in freshwater. corticosteroid levels when in freshwater. Blood is isosmotic to seawater, yet there Blood is isosmotic to seawater, yet there

are specific differences in ion are specific differences in ion concentrations.concentrations.

Injections of aldosterone alter blood electrolyte Injections of aldosterone alter blood electrolyte composition (mainly sodium). Cortisol has no composition (mainly sodium). Cortisol has no effect.effect.

Chondrichthyean fishes:Chondrichthyean fishes: Have one discreet adrenal gland Have one discreet adrenal gland

(probably due to only one kidney).(probably due to only one kidney). Secretes a unique type of cortisol.Secretes a unique type of cortisol.

1-1-hydroxycorticosteronehydroxycorticosterone Secreted mainly in response to stress.Secreted mainly in response to stress. No discreet renin-angiotensin system.No discreet renin-angiotensin system.

However, they do have a a JGA-like structure However, they do have a a JGA-like structure and the cells have secretory granual that are and the cells have secretory granual that are immunoreactive for renin antibodies.immunoreactive for renin antibodies.

Also have an ACE-like enzyme in the Also have an ACE-like enzyme in the gills.gills.

Have natriuretec peptide in heart.Have natriuretec peptide in heart.

These fish have hyperosmotic plasma.These fish have hyperosmotic plasma.

Not due to electrolytes, but to high Not due to electrolytes, but to high circulating levels of urea and circulating levels of urea and trimethylamine oxide.trimethylamine oxide.

No clearly defined role for No clearly defined role for corticosteroids.corticosteroids.

1-1-hydroxycorticosterone does bind to hydroxycorticosterone does bind to gills, rectal gland and kidney nephrons.gills, rectal gland and kidney nephrons.

1-1-hydroxycorticosterone can stimulate hydroxycorticosterone can stimulate salt secretion across rectal gland, but salt secretion across rectal gland, but this effect is minor.this effect is minor.

May stimulate elevated expression of May stimulate elevated expression of CFTR in gills and rectal gland.CFTR in gills and rectal gland.

These fish osmoregulate differently These fish osmoregulate differently than most fishes.than most fishes.

HCT affects NaHCT affects Na++ retention in the retention in the kidney.kidney.

Natriuretic peptides stimulate Natriuretic peptides stimulate HCT HCT secretion.secretion.

Teleost fishes:Teleost fishes: Respond to ACTH and stress with Respond to ACTH and stress with

increased corticosterone levels.increased corticosterone levels. Renin-angiotensis activity has been Renin-angiotensis activity has been

demonstrated in all groups.demonstrated in all groups. Well developed JGA.Well developed JGA. The renin-angiotensin system appears The renin-angiotensin system appears

to be involved in in both osmotic and to be involved in in both osmotic and ionic regulation.ionic regulation.

Corticosteroids may play a major role in Corticosteroids may play a major role in regulating metabolic rate in in regulating metabolic rate in in migratory and spawning fish.migratory and spawning fish.

The principal circulating corticosteroid is The principal circulating corticosteroid is cortisol.cortisol.

Cortisol has been shown to directly stimulate Cortisol has been shown to directly stimulate NaNa++-K-K++ ATPase in epithelial cells of the gill, ATPase in epithelial cells of the gill, gut and kidney.gut and kidney.

As earlier discussed, cortisol is very important As earlier discussed, cortisol is very important in freshwater adaptation.in freshwater adaptation.

Directly stimulates CFTR insertion into the apical Directly stimulates CFTR insertion into the apical membranes of ion transporting cells of gills.membranes of ion transporting cells of gills.

There is secretion of extra-adrenal There is secretion of extra-adrenal corticosteroid secretion (from ovary) in at corticosteroid secretion (from ovary) in at least one species.least one species.

In Rainbow trout, long photoperiod stimulates In Rainbow trout, long photoperiod stimulates elevated corticosteroid levels. May be elevated corticosteroid levels. May be associated with increased activity levels.associated with increased activity levels.

Sarcopterygean fishes:Sarcopterygean fishes: HH22O deprivation stimulates increased O deprivation stimulates increased

corticosteroid levels.corticosteroid levels. Increases air-breathing during dry Increases air-breathing during dry

spells.spells. Interestingly, during the aquatic phase Interestingly, during the aquatic phase

the animals secrete cortisol and during the animals secrete cortisol and during the air phase they secrete the air phase they secrete corticosterone.corticosterone.

Amphibians:Amphibians: Adrenal tissue is rather diffusely distributed Adrenal tissue is rather diffusely distributed

in kidney.in kidney. Larval (aquatic) form secretes cortisol, but Larval (aquatic) form secretes cortisol, but

after metamorphosis the animals secrete after metamorphosis the animals secrete corticosterone.corticosterone.

Aldosterone is the principal electrolyte Aldosterone is the principal electrolyte regulator (like in amniotes), not cortisol regulator (like in amniotes), not cortisol (like in fish).(like in fish).

Well developed renin-angiotensin system.Well developed renin-angiotensin system. The JGA does not contain a macula densa, The JGA does not contain a macula densa,

except in one species of toad (convergent except in one species of toad (convergent evolution).evolution).

Exposure of ranid frogs to seawater Exposure of ranid frogs to seawater causes atrophy of adrenocortical tissue.causes atrophy of adrenocortical tissue.

Adrenalectomy causes a decrease in Adrenalectomy causes a decrease in plasma sodium and increases plasma plasma sodium and increases plasma potassium.potassium.

Aldosterone seems to be the major salt-Aldosterone seems to be the major salt-regulating hormone.regulating hormone. Acts on skin and urinary bladder to increase Acts on skin and urinary bladder to increase

salt transport into the blood (uptake and salt transport into the blood (uptake and recovery, respectively).recovery, respectively).

Salt depleted frogs exhibit elevated renin Salt depleted frogs exhibit elevated renin levels.levels.

ACTH elevates aldosterone in at least one ACTH elevates aldosterone in at least one ranid frog, ranid frog, Rana esculentaRana esculenta..

AII has been shown to stimulate AII has been shown to stimulate aldosterone and corticosterone synthesis aldosterone and corticosterone synthesis in vitroin vitro in adrenocortical tissue from in adrenocortical tissue from Rana Rana ridibundaridibunda..

These results suggest a fair amount of cross-These results suggest a fair amount of cross-talk between the mineralcorticoid and the talk between the mineralcorticoid and the glucocorticoid systems (in ranid frogs at least).glucocorticoid systems (in ranid frogs at least).

Aldosterone stimulates increased plasma Aldosterone stimulates increased plasma sodium in tiger salamanders.sodium in tiger salamanders.

Reptiles:Reptiles: Discreet adrenal glands associated with Discreet adrenal glands associated with

kidney.kidney. Lack of zonation in the adrenal cortex.Lack of zonation in the adrenal cortex. Well developed renin-antiotensin system.Well developed renin-antiotensin system.

AII stimulates the secretion of aldosterone as AII stimulates the secretion of aldosterone as well as corticosterone in most reptiles.well as corticosterone in most reptiles.

In turtles, AII stimulates only aldosterone In turtles, AII stimulates only aldosterone secretion.secretion.

There is a well-developed atrial natriuretic There is a well-developed atrial natriuretic system. system.

Secretory cells are diffusely distributed Secretory cells are diffusely distributed throughout the heart.throughout the heart.

No macula densa in the JGA.No macula densa in the JGA.

Few studies on sodium regulation have Few studies on sodium regulation have been done.been done.

As with the fish and amphibians, there is As with the fish and amphibians, there is no clear distinction between the effects of no clear distinction between the effects of mineralcorticoids and glucocorticoids in mineralcorticoids and glucocorticoids in the regulation of plasma electrolytes.the regulation of plasma electrolytes.

Plasma salt loading depresses plasma Plasma salt loading depresses plasma aldosterone levels in a number of lizard aldosterone levels in a number of lizard species looked at.species looked at.

AII stimulates both aldosterone and AII stimulates both aldosterone and corticosterone secretion in lizards, but corticosterone secretion in lizards, but only stimulates corticosterone secretion only stimulates corticosterone secretion in turtles.in turtles.

Birds:Birds: Structure of adrenal glands is very similar to Structure of adrenal glands is very similar to

reptiles.reptiles. Lack of zonation.Lack of zonation.

Corticosterone is the principal corticosteroid.Corticosterone is the principal corticosteroid. There is a well developed renin-angiotensin There is a well developed renin-angiotensin

system, which functions the same as in system, which functions the same as in mammals.mammals.

Like mammals, there is a distinct macula Like mammals, there is a distinct macula densa in the JGA.densa in the JGA.

In marine birds containing a nasal gland, the In marine birds containing a nasal gland, the gland is sensitive to aldosterone.gland is sensitive to aldosterone. Stimulates expression of the basolateral NaStimulates expression of the basolateral Na++-K-K+ +

ATPase.ATPase. Stress stimulates glucocorticoid Stress stimulates glucocorticoid

secretion in secretion in ALLALL vertebrate groups vertebrate groups