15. the endocrine system

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The Endocrine SystemThe Endocrine System


Describe the negative feedback system that Describe the negative feedback system that controls production of hormones.controls production of hormones.

List the major endocrine glands and the hormones List the major endocrine glands and the hormones they produce.they produce.

Describe the structure and functions of the Describe the structure and functions of the pituitary gland.pituitary gland.

Describe the effect(s) of growth hormone, Describe the effect(s) of growth hormone, prolactin, thyroid-stimulating hormone, prolactin, thyroid-stimulating hormone, adrenocorticotropic hormone, follicle-stimulating adrenocorticotropic hormone, follicle-stimulating hormone, luteinizing hormone, melanocyte-hormone, luteinizing hormone, melanocyte-stimulating hormone, antidiuretic hormone, and stimulating hormone, antidiuretic hormone, and oxytocin.oxytocin.

Learning ObjectivesLearning Objectives


Describe the structure of the thyroid gland.Describe the structure of the thyroid gland. Describe the effects of thyroid hormone, Describe the effects of thyroid hormone,

calcitonin, and parathormone.calcitonin, and parathormone. Differentiate between TDifferentiate between T33 and T and T44.. List the three categories of hormones produced List the three categories of hormones produced

by the adrenal cortex.by the adrenal cortex. List the hormones produced by the pancreatic List the hormones produced by the pancreatic

islet cells and describe the effect(s) of each.islet cells and describe the effect(s) of each. Describe the effect(s) of androgens, estrogens, Describe the effect(s) of androgens, estrogens,

and progestins.and progestins. List the hormones produced by the kidneys, List the hormones produced by the kidneys,

stomach, small intestine, placenta, thymus, and stomach, small intestine, placenta, thymus, and pineal body.pineal body.

Learning ObjectivesLearning Objectives


Endocrine SystemEndocrine System Works together with Works together with

nervous system to nervous system to maintain maintain homeostasishomeostasis

Primary function: Primary function: produces hormonesproduces hormones

Hormones act on Hormones act on specific target cells specific target cells to produce specific to produce specific effectseffects..


Chemical messengers produced by Chemical messengers produced by endocrine glands and secreted directly into endocrine glands and secreted directly into blood vessels blood vessels

Produce effects when they find their Produce effects when they find their specific receptors in or on cells specific receptors in or on cells

A cell that has receptors for a particular A cell that has receptors for a particular hormone is referred to as a hormone is referred to as a targettarget of that of that hormonehormone..

HormonesHormones


Control of Hormone SecretionControl of Hormone Secretion

Negative feedback systems Negative feedback systems When the level of a specific hormone When the level of a specific hormone

drops below needed levels, the drops below needed levels, the appropriate endocrine gland is stimulated appropriate endocrine gland is stimulated to produce more hormone.to produce more hormone.

Once the proper hormone level is present Once the proper hormone level is present in the bloodstream, stimulation of that in the bloodstream, stimulation of that endocrine gland is reduced and production endocrine gland is reduced and production of that hormone is reduced.of that hormone is reduced.


Control of Hormone SecretionControl of Hormone Secretion Direct stimulation from the nervous system Direct stimulation from the nervous system Secretion of some hormones is stimulated Secretion of some hormones is stimulated

by sympathetic nerve impulses when an by sympathetic nerve impulses when an animal feels threatened.animal feels threatened. ““Fight or flight" responseFight or flight" response


Major Endocrine GlandsMajor Endocrine Glands Anterior pituitaryAnterior pituitary Posterior pituitaryPosterior pituitary ThyroidThyroid ParathyroidParathyroid Adrenal cortexAdrenal cortex Adrenal medullaAdrenal medulla Pancreas (islets)Pancreas (islets) TestisTestis OvaryOvary


HypothalamusHypothalamus Part of diencephalon section Part of diencephalon section

of the brainof the brain Controls activities of the Controls activities of the

pituitary glandpituitary gland Portal system of blood Portal system of blood

vessels links hypothalamus vessels links hypothalamus with anterior portion of with anterior portion of pituitary glandpituitary gland


HypothalamusHypothalamus Modified neurons in the Modified neurons in the

hypothalamus secrete hypothalamus secrete releasing and inhibiting releasing and inhibiting factors into portal blood factors into portal blood vesselsvessels Specific for a particular Specific for a particular

anterior pituitary hormoneanterior pituitary hormone


Modified neurons in Modified neurons in hypothalamus also secrete hypothalamus also secrete antidiuretic hormone and antidiuretic hormone and oxytocin oxytocin

Transported to posterior Transported to posterior pituitary for storagepituitary for storage

Released into the bloodstream Released into the bloodstream by nerve impulses from the by nerve impulses from the hypothalamus hypothalamus

HypothalamusHypothalamus


Pituitary Gland (Hypophysis)Pituitary Gland (Hypophysis) Two separate glands with different Two separate glands with different

structures, functions, and embryological structures, functions, and embryological originsorigins

Anterior pituitary - adenohypophysis; Anterior pituitary - adenohypophysis; rostral portionrostral portion Stimulated by hypothalamus and direct Stimulated by hypothalamus and direct

feedback from target organs and tissues to feedback from target organs and tissues to produce its hormonesproduce its hormones

Posterior pituitary - neurohypophysis; Posterior pituitary - neurohypophysis; caudal portioncaudal portion Stores and releases hormones produced in Stores and releases hormones produced in

hypothalamushypothalamus


The Anterior PituitaryThe Anterior Pituitary Known anterior pituitary hormones:Known anterior pituitary hormones:1. Growth hormone1. Growth hormone

2. Prolactin2. Prolactin

3. Thyroid-stimulating hormone3. Thyroid-stimulating hormone

4. Adrenocorticotropic hormone4. Adrenocorticotropic hormone

5. Follicle-stimulating hormone5. Follicle-stimulating hormone

6. Luteinizing hormone6. Luteinizing hormone

7. Melanocyte-stimulating hormone7. Melanocyte-stimulating hormone


Growth Hormone (GH)Growth Hormone (GH) Also known as somatotropin and Also known as somatotropin and

somatotropic hormonesomatotropic hormone Promotes body growth in young animalsPromotes body growth in young animals Helps regulate the metabolism of proteins, Helps regulate the metabolism of proteins,

carbohydrates, and lipids in all the body's carbohydrates, and lipids in all the body's cellscells


ProlactinProlactin Helps trigger and maintain lactationHelps trigger and maintain lactation

Secretion of milk by the mammary glandsSecretion of milk by the mammary glands Prolactin production and release continues Prolactin production and release continues

as long as the teat or nipple continues to as long as the teat or nipple continues to be stimulated by nursing or milking. be stimulated by nursing or milking.

When prolactin stimulation stops, milk When prolactin stimulation stops, milk production stops, and the mammary gland production stops, and the mammary gland shrinks back to its nonlactating size.shrinks back to its nonlactating size.


Thyroid-Stimulating Hormone (TSH)Thyroid-Stimulating Hormone (TSH)

Also known as Also known as thyrotrophic hormone thyrotrophic hormone Stimulates growth and development of Stimulates growth and development of

thyroid gland and causes it to produce its thyroid gland and causes it to produce its hormoneshormones

Secretion is regulated by feedback from Secretion is regulated by feedback from the thyroid glandthe thyroid gland Has direct effects on anterior pituitary gland Has direct effects on anterior pituitary gland

through changes in TSH-releasing factor through changes in TSH-releasing factor produced by the hypothalamusproduced by the hypothalamus


Adrenocorticotropic Hormone (ACTH)Adrenocorticotropic Hormone (ACTH) Stimulates growth and development of the Stimulates growth and development of the

adrenal cortex and release of some of its adrenal cortex and release of some of its hormoneshormones

Regulated by feedback from the hormones Regulated by feedback from the hormones of the adrenal of the adrenal

ACTH can also be released quickly as a ACTH can also be released quickly as a result of stimulation of the hypothalamus by result of stimulation of the hypothalamus by other parts of the brain.other parts of the brain. Hypothalamus sends a burst of ACTH-releasing Hypothalamus sends a burst of ACTH-releasing

factor to the anterior pituitary through the portal factor to the anterior pituitary through the portal system causing ACTH to be released quicklysystem causing ACTH to be released quickly


Follicle-Stimulating Hormone (FSH)Follicle-Stimulating Hormone (FSH)

In female, stimulates growth and In female, stimulates growth and development of ovarian follicles - development of ovarian follicles - oogenesisoogenesis Also stimulates cells lining the follicles to Also stimulates cells lining the follicles to

produce and secrete estrogensproduce and secrete estrogens In the male, stimulates spermatogenesisIn the male, stimulates spermatogenesis


Luteinizing Hormone (LH)Luteinizing Hormone (LH) Completes process of follicle development Completes process of follicle development

in ovary in ovary Increasing amounts of estrogens feedback Increasing amounts of estrogens feedback

to the anterior pituitary and cause reduced to the anterior pituitary and cause reduced production of FSH and increased production of FSH and increased production of LH production of LH

LH levels reach a peak when follicle is fully LH levels reach a peak when follicle is fully maturemature Usually causes ovulationUsually causes ovulation


Luteinizing Hormone (LH)Luteinizing Hormone (LH) After ovulation, LH stimulates cells in the After ovulation, LH stimulates cells in the

empty follicle to multiply and develop into empty follicle to multiply and develop into the corpus luteum.the corpus luteum. Corpus luteum produces progestin hormones Corpus luteum produces progestin hormones

necessary for the maintenance of pregnancy necessary for the maintenance of pregnancy In the male, LH stimulates interstitial cells In the male, LH stimulates interstitial cells

to develop and produce testosterone.to develop and produce testosterone.


Melanocyte-Stimulating Hormone (MSH)Melanocyte-Stimulating Hormone (MSH)

Associated with control of color changes in Associated with control of color changes in the pigment cells (melanocytes) of reptiles, the pigment cells (melanocytes) of reptiles, fish, and amphibiansfish, and amphibians

Administration of artificially large amounts Administration of artificially large amounts of MSH to higher mammals can cause of MSH to higher mammals can cause darkening of the skin from melanocyte darkening of the skin from melanocyte stimulationstimulation


The Posterior PituitaryThe Posterior Pituitary Stores two hormones produced in the Stores two hormones produced in the

hypothalamus hypothalamus Antidiuretic hormone and oxytocin Antidiuretic hormone and oxytocin Transported from hypothalmus to posterior Transported from hypothalmus to posterior

pituitary and stored in nerve endingspituitary and stored in nerve endings Periodically released into the bloodstream Periodically released into the bloodstream

in response to nerve impulses from in response to nerve impulses from hypothalmushypothalmus


Antidiuretic Hormone (ADH)Antidiuretic Hormone (ADH) Helps prevent diuresisHelps prevent diuresis Receptors in hypothalamus detect Receptors in hypothalamus detect

changes in osmotic pressure of blood that changes in osmotic pressure of blood that result from dehydration/hemoconcentration result from dehydration/hemoconcentration

Generates nerve impulses - causes Generates nerve impulses - causes release of ADHrelease of ADH ADH travels to the kidney - causes kidneys to ADH travels to the kidney - causes kidneys to

reabsorb more water from the urine and return reabsorb more water from the urine and return it to the bloodstream it to the bloodstream

ADH deficiency causes diabetes insipidus.ADH deficiency causes diabetes insipidus.


OxytocinOxytocin Effects on uterus - causes contraction of Effects on uterus - causes contraction of

the myometrium at the time of breeding the myometrium at the time of breeding and at parturitionand at parturition Induces uterine contractions that aid transport Induces uterine contractions that aid transport

of spermatozoa to the oviductsof spermatozoa to the oviducts Stimulates uterine contractions that aid in the Stimulates uterine contractions that aid in the

delivery of the fetus and the placentadelivery of the fetus and the placenta


OxytocinOxytocin Effect on active mammary glands - causes Effect on active mammary glands - causes

movement of milk down to the lower parts movement of milk down to the lower parts of the gland (milk letdown)of the gland (milk letdown) Stimulation of the teat or nipple by nursing or Stimulation of the teat or nipple by nursing or

milking causes oxytocin to be released into the milking causes oxytocin to be released into the bloodstream. bloodstream.

Causes contraction of the myoepithelial cells Causes contraction of the myoepithelial cells around the mammary gland alveoli and small around the mammary gland alveoli and small ducts ducts

Forces milk into the lower parts of the glandForces milk into the lower parts of the gland


The Thyroid GlandThe Thyroid Gland Consists of two lobes on Consists of two lobes on

either side of larynxeither side of larynx Lobes may be connected by Lobes may be connected by

isthmusisthmus Thyroid hormone is produced Thyroid hormone is produced

in folliclesin follicles Simple cuboidal glandular cells Simple cuboidal glandular cells

surrounding globule of thyroid surrounding globule of thyroid hormone precursorhormone precursor


Thyroid HormonesThyroid Hormones TT33 (triiodothyronine) and T (triiodothyronine) and T44

(tetraiodothyronine, or thyroxine)(tetraiodothyronine, or thyroxine) Produced when TSH from anterior pituitary Produced when TSH from anterior pituitary

reaches the thyroid glandreaches the thyroid gland TT44 produced in greater abundance than T produced in greater abundance than T33

but is mostly converted to Tbut is mostly converted to T33 before before

producing effects on target cellsproducing effects on target cells


Effects of Thyroid HormonesEffects of Thyroid Hormones Influences development and maturation of Influences development and maturation of

CNS; growth and development of muscles CNS; growth and development of muscles and bonesand bones

Calorigenic effect - regulates the metabolic Calorigenic effect - regulates the metabolic rate of all the body's cellsrate of all the body's cells

Allows animal to generate heat and Allows animal to generate heat and maintain constant internal body maintain constant internal body temperaturetemperature


Effects of Thyroid HormonesEffects of Thyroid Hormones

Production increases with exposure to cold Production increases with exposure to cold and then increases metabolic rate to and then increases metabolic rate to generate more heatgenerate more heat

Affects metabolism of proteins, Affects metabolism of proteins, carbohydrates, and lipids much like GH carbohydrates, and lipids much like GH doesdoes


CalcitoninCalcitonin

Produced by C cells located between Produced by C cells located between thyroid folliclesthyroid follicles

Helps maintain blood calcium levelsHelps maintain blood calcium levels Prevents hypercalcemia by encouraging Prevents hypercalcemia by encouraging

excess calcium to be deposited in the excess calcium to be deposited in the bonesbones

Calcium is involved in muscle contraction, Calcium is involved in muscle contraction, blood clotting, milk secretion, and blood clotting, milk secretion, and formation and maintenance of the skeletonformation and maintenance of the skeleton


Parathyroid Hormone (PTH)Parathyroid Hormone (PTH) Also called parathormone Also called parathormone Produced by the parathyroid glandsProduced by the parathyroid glands

Small, pale nodules in, on, or near the thyroid Small, pale nodules in, on, or near the thyroid glandsglands

Helps maintain blood calcium levelsHelps maintain blood calcium levels Prevents hypocalcemiaPrevents hypocalcemia

Causes kidneys to retain calcium and intestine Causes kidneys to retain calcium and intestine to absorb calcium from food; withdraws to absorb calcium from food; withdraws calcium from bonescalcium from bones


The Adrenal GlandsThe Adrenal Glands Located near the Located near the

cranial ends of the cranial ends of the kidneys kidneys

Consist of two Consist of two glands:glands:

1.1. Adrenal cortex Adrenal cortex

2.2. Adrenal medullaAdrenal medulla


Adrenal CortexAdrenal Cortex Produces numerous Produces numerous

steroid hormones steroid hormones classified into three classified into three main groups: main groups: 1.1. GlucocorticoidsGlucocorticoids

2.2. Mineralocorticoids Mineralocorticoids

3.3. Sex hormonesSex hormones


Adrenal CortexAdrenal Cortex

1.1. Glucocorticoids: cortisone, cortisol, and Glucocorticoids: cortisone, cortisol, and corticosteronecorticosterone

Hyperglycemic effectHyperglycemic effect Also help maintain blood pressure and help Also help maintain blood pressure and help

the body resist the effects of stressthe body resist the effects of stress Mineralocorticoids (e.g., aldosterone)Mineralocorticoids (e.g., aldosterone) Regulate the levels of important electrolytes Regulate the levels of important electrolytes

(mineral salts) in the body(mineral salts) in the body

2.2. Sex hormones - androgens and Sex hormones - androgens and estrogensestrogens


Adrenal MedullaAdrenal Medulla Produces epinephrine and norepinephrineProduces epinephrine and norepinephrine Secretion is controlled by the sympathetic Secretion is controlled by the sympathetic

portion of the autonomic nervous systemportion of the autonomic nervous system ““Fight or flight" responseFight or flight" response

Increases heart rate and output, increases Increases heart rate and output, increases blood pressure, dilates air passageways in blood pressure, dilates air passageways in the lungs, and decreases GI functionthe lungs, and decreases GI function


PancreasPancreas

Located near the duodenum Located near the duodenum Has both exocrine and endocrine functionsHas both exocrine and endocrine functions Endocrine component - small percentage of Endocrine component - small percentage of

the total volume of the organthe total volume of the organ Pancreatic islets (islets of Langerhans): Pancreatic islets (islets of Langerhans):

groups of cells scattered throughout the groups of cells scattered throughout the pancreaspancreas Alpha cells - produce glucagonAlpha cells - produce glucagon Beta cells - produce insulinBeta cells - produce insulin Delta cells - produce somatostatinDelta cells - produce somatostatin


Pancreatic HormonesPancreatic Hormones

Insulin: lowers blood glucose levels by Insulin: lowers blood glucose levels by causing glucose, amino acids, and fatty causing glucose, amino acids, and fatty acids to be absorbed into body cellsacids to be absorbed into body cells

Glucagon: lowers blood glucose levels by Glucagon: lowers blood glucose levels by stimulating liver cells to convert glycogen stimulating liver cells to convert glycogen to glucose and by stimulating to glucose and by stimulating gluconeogenesis gluconeogenesis

Somatostatin: inhibits secretion of insulin, Somatostatin: inhibits secretion of insulin, glucagon, and GH; diminishes GI activityglucagon, and GH; diminishes GI activity


TestesTestes Interstitial cells: clumps Interstitial cells: clumps

of endocrine cellsof endocrine cells Produce androgens Produce androgens

when stimulated by LHwhen stimulated by LH

Interstitial cell stimulating Interstitial cell stimulating hormone (ICSH) in the malehormone (ICSH) in the male

Testosterone: primary Testosterone: primary androgenandrogen

Provides for development of Provides for development of male secondary sex male secondary sex characteristics and characteristics and accessory sex glandsaccessory sex glands

Activates spermatogenesisActivates spermatogenesis


OvariesOvaries Produce ova and hormones in cyclesProduce ova and hormones in cycles Controlled by follicle stimulating hormone Controlled by follicle stimulating hormone

(FSH) and luteinizing hormone (LH)(FSH) and luteinizing hormone (LH) Hormone groups produced in the ovaries:Hormone groups produced in the ovaries:

1.1. Estrogens Estrogens

2.2. ProgestinsProgestins


EstrogensEstrogens FSH stimulates ovarian follicles to developFSH stimulates ovarian follicles to develop

Cells of follicles produce and release Cells of follicles produce and release estrogensestrogens

Amount of estrogen produced increases as Amount of estrogen produced increases as

follicle growsfollicle grows Increasing estrogen levels accelerate Increasing estrogen levels accelerate

physical and behavioral changesphysical and behavioral changes


EstrogensEstrogens Feedback to anterior pituitaryFeedback to anterior pituitary

Cause anterior pituitary gland to reduce the Cause anterior pituitary gland to reduce the production of FSH and increase the production production of FSH and increase the production of LHof LH

When follicle is fully mature, LH level When follicle is fully mature, LH level

peakspeaks In most animal species, ovulation occurs when In most animal species, ovulation occurs when

LH level peaksLH level peaks


ProgestinsProgestins Group of hormones produced by corpus Group of hormones produced by corpus

luteumluteum High LH level stimulates cells of empty High LH level stimulates cells of empty

follicle to multiply and develop into corpus follicle to multiply and develop into corpus luteum luteum

Progesterone - principal progestinProgesterone - principal progestin Helps prepare uterus to receive the fertilized Helps prepare uterus to receive the fertilized

ovum; needed to maintain pregnancyovum; needed to maintain pregnancy


ProgestinsProgestins In pregnant female, hormone signal is sent In pregnant female, hormone signal is sent

from uterus, and corpus luteum is from uterus, and corpus luteum is maintainedmaintained

If no pregnancy occurs, lack of hormone If no pregnancy occurs, lack of hormone signal causes corpus luteum to shrink and signal causes corpus luteum to shrink and disappeardisappear


KidneysKidneys Produce erythropoietin - stimulates red Produce erythropoietin - stimulates red

bone marrow to increase production of red bone marrow to increase production of red blood cells blood cells

Production of erythropoietin stimulated by Production of erythropoietin stimulated by hypoxiahypoxia

As red blood cell production increases, As red blood cell production increases, more oxygen feeds back to kidneys and more oxygen feeds back to kidneys and slows the production of erythropoietinslows the production of erythropoietin


StomachStomach Gastrin: produced by cells in the wall of Gastrin: produced by cells in the wall of

the stomach the stomach Secretion stimulated by presence of food Secretion stimulated by presence of food

in the stomach in the stomach Stimulates gastric glands to secrete Stimulates gastric glands to secrete

hydrochloric acid and digestive enzymeshydrochloric acid and digestive enzymes Encourages muscular contractions of the Encourages muscular contractions of the

stomach wallstomach wall


Small IntestineSmall Intestine Secretin and cholecystokinin produced by Secretin and cholecystokinin produced by

cells in lining of small intestine cells in lining of small intestine Secretion occurs in response to presence Secretion occurs in response to presence

of chyme in duodenumof chyme in duodenum Secretin stimulates pancreas to secrete Secretin stimulates pancreas to secrete

fluid to neutralize acidic chyme after it fluid to neutralize acidic chyme after it passes out of the stomachpasses out of the stomach

Cholecystokinin stimulates pancreas to Cholecystokinin stimulates pancreas to release digestive enzymes into the release digestive enzymes into the duodenumduodenum


PlacentaPlacenta Surrounds a developing fetus during Surrounds a developing fetus during

pregnancy pregnancy Acts as an interface with the maternal Acts as an interface with the maternal

circulation circulation Produces hormones to help support and Produces hormones to help support and

maintain pregnancymaintain pregnancy Estrogen and progesterone Estrogen and progesterone Chorionic gonadotropin (some species)Chorionic gonadotropin (some species)


ThymusThymus Extends cranially from the level of the Extends cranially from the level of the

heart up into neck region along both sides heart up into neck region along both sides of the tracheaof the trachea

Large in young animals, atrophies later in Large in young animals, atrophies later in lifelife

Function involves hormones or Function involves hormones or hormonelike chemical substances (e.g., hormonelike chemical substances (e.g., thymosin and thymopoietin)thymosin and thymopoietin)

Seems to cause certain cells to be Seems to cause certain cells to be transformed into T-lymphocytestransformed into T-lymphocytes


Pineal BodyPineal Body Located at caudal end of the cleft that Located at caudal end of the cleft that

separates the two cerebral hemispheres separates the two cerebral hemispheres Influences cyclic activities in the bodyInfluences cyclic activities in the body Melatonin - hormonelike substance called Melatonin - hormonelike substance called

that seems to affect moods and wake-that seems to affect moods and wake-sleep cyclessleep cycles May also play a role in the timing of seasonal May also play a role in the timing of seasonal

estrous cycles in some speciesestrous cycles in some species


ProstaglandinsProstaglandins Hormonelike substances derived from Hormonelike substances derived from

unsaturated fatty acidsunsaturated fatty acids Produced in a variety of body tissues (skin, Produced in a variety of body tissues (skin,

intestine, brain, kidney, lungs, reproductive intestine, brain, kidney, lungs, reproductive organs, and eyes)organs, and eyes)

Nine main groups - designated A through INine main groups - designated A through I Subscript numbers and Greek letters designate Subscript numbers and Greek letters designate

subgroupssubgroups Influence blood pressure, blood clotting, Influence blood pressure, blood clotting,

inflammation, GI, respiratory, reproductive, inflammation, GI, respiratory, reproductive, and kidney functionand kidney function

15. the endocrine system

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