Chapter 18Chapter 18

The Endocrine SystemThe Endocrine System

Endocrine system glandsEndocrine system glands

Hormone chemistry and ActionHormone chemistry and Action

Are chemically composed of either: Are chemically composed of either: (p. 516 in Saladin)(p. 516 in Saladin)

– Ring structures = steroidsRing structures = steroids– Polypeptides = ACTH, TSH, FSH, LH, oxytocin, insulin, etc.Polypeptides = ACTH, TSH, FSH, LH, oxytocin, insulin, etc.– Monoamines = dopamine, thryoxine (T3/T4)Monoamines = dopamine, thryoxine (T3/T4)

At their target cell, they may diffuse through the cell At their target cell, they may diffuse through the cell membrane and bind to a receptor site in the cytoplasm membrane and bind to a receptor site in the cytoplasm or nucleus (steroid hormones), or they may they may or nucleus (steroid hormones), or they may they may bind to a receptor site on the cell membrane (water-bind to a receptor site on the cell membrane (water-soluble hormones) and activate a first messenger (e.g. soluble hormones) and activate a first messenger (e.g. adenylate cyclase) which, in turn, activates a second adenylate cyclase) which, in turn, activates a second messenger (cyclic AMP).messenger (cyclic AMP).

Endocrine System vs Autonomic Endocrine System vs Autonomic Nervous SystemNervous System

1. The endocrine system releases 1. The endocrine system releases chemical messengers (hormones) into the chemical messengers (hormones) into the blood. The autonomic nervous system blood. The autonomic nervous system communicates by nerve impulses with communicates by nerve impulses with effectors.effectors.

2. The endocrine system acts relatively 2. The endocrine system acts relatively slowly as compared to the autonomic slowly as compared to the autonomic nervous system.nervous system.

Target cells

Endocrinecells

Neuron Nerve impulse

Neurotransmitter

Hormone in bloodstream

Endocrine System vs Autonomic Nervous System

Comparisons of Nervous and Endocrine SystemsComparisons of Nervous and Endocrine Systems

Types of Endocrine GlandsTypes of Endocrine Glands

Three types of glands:Three types of glands:1. Pure 1. Pure endocrine glandsendocrine glands – thyroid, parathyroid, – thyroid, parathyroid,

adrenal cortex, thymus and pineal.adrenal cortex, thymus and pineal.

2. 2. Endocrine/exocrine glandsEndocrine/exocrine glands – pancreas, – pancreas, ovaries and testesovaries and testes

3. 3. Neuroendocrine glandsNeuroendocrine glands – adrenal medulla – adrenal medulla and hypothalamus (supraoptic nuclei and and hypothalamus (supraoptic nuclei and paraventricular nuclei) to posterior pituitary.paraventricular nuclei) to posterior pituitary.

Endocrine OrgansEndocrine Organs

Hypothalamus- neuroendocrine glandHypothalamus- neuroendocrine gland

Anterior pituitary gland- endocrine glandAnterior pituitary gland- endocrine gland

Posterior pituitary gland- neuroendocrine glandPosterior pituitary gland- neuroendocrine gland

Thyroid gland- endocrine glandThyroid gland- endocrine gland

Parathyroid glands- endocrine glandParathyroid glands- endocrine gland

Adrenal gland (cortex and medulla)- endocrine/neuroendocrine glandAdrenal gland (cortex and medulla)- endocrine/neuroendocrine gland

Pancreatic islets- endocrine/exocrine glandPancreatic islets- endocrine/exocrine gland

Gonads- Ovaries in females; Gonads- Ovaries in females; Testes in males- endocrine/exocrine glandsTestes in males- endocrine/exocrine glands

The HypothalamusThe Hypothalamus

LocationLocation: directly below the thalamus in the : directly below the thalamus in the diencephalon of the brain. It lies between the optic diencephalon of the brain. It lies between the optic chiasm anteriorly and the mammillary bodies chiasm anteriorly and the mammillary bodies posteriorly and is inferior to the third ventricle.posteriorly and is inferior to the third ventricle.

StructureStructure: Composed of several groups of nuclei, : Composed of several groups of nuclei, the hypothalamus controls the endocrine system as the hypothalamus controls the endocrine system as well as the autonomic nervous system and produces well as the autonomic nervous system and produces regulatory hormones that regulate the release of regulatory hormones that regulate the release of numerous pituitary hormones. It also produces the numerous pituitary hormones. It also produces the hormones of the posterior pituitary. hormones of the posterior pituitary.

The HypothalamusThe Hypothalamus

The Pituitary Gland or HypophysisThe Pituitary Gland or Hypophysis

Location: Sits in the sella turcica of the sphenoid bone Location: Sits in the sella turcica of the sphenoid bone

Attached to the hypothalamus by the infundibulumAttached to the hypothalamus by the infundibulum

Consists of two lobes:Consists of two lobes:

1.1. AdenohypophysisAdenohypophysis

Releases 7 different hormonesReleases 7 different hormonesConsists of 3 divisions: pars tuberalis, pars intermedia and Consists of 3 divisions: pars tuberalis, pars intermedia and

pars distalis (anterior lobe).pars distalis (anterior lobe).

2. 2. NeurohypophysisNeurohypophysis

Releases 2 different hormonesReleases 2 different hormonesConsists of 3 divisions: median eminence, infundibular stalk Consists of 3 divisions: median eminence, infundibular stalk

and pars nervosa (posterior lobe)and pars nervosa (posterior lobe)

Pituitary glandPituitary glandAdenohypophysisAdenohypophysis

Pars tuberalisPars tuberalis

Pars intermediaPars intermedia

Pars distalisPars distalis

NeurohypophysisNeurohypophysis

Median eminenceMedian eminence

Infindibular stalkInfindibular stalk

Pars nervosaPars nervosa

Anterior Pituitary HormonesAnterior Pituitary Hormones

There are seven anterior pituitary hormones:There are seven anterior pituitary hormones:– Thyroid stimulating hormone (TSH)*Thyroid stimulating hormone (TSH)*– Growth hormone (GH)Growth hormone (GH)– Adrenocorticotropic hormone (ACTH)*Adrenocorticotropic hormone (ACTH)*– Melanocyte stimulating hormone (MSH)Melanocyte stimulating hormone (MSH)– Follicle stimulating hormone (FSH)*Follicle stimulating hormone (FSH)*– Luteinizing hormone (LH) = ICSH in males*Luteinizing hormone (LH) = ICSH in males*– Prolactin (PRL)Prolactin (PRL)

* indicate trophic hormones* indicate trophic hormones

Hypothalamic releasing hormonesHypothalamic releasing hormonesRelease of anterior pituitary hormones is directed by specific Release of anterior pituitary hormones is directed by specific releasing hormones (factors) from the hypothalamic nuclei.releasing hormones (factors) from the hypothalamic nuclei.

All of these are polypeptide molecules.All of these are polypeptide molecules.

TRH – thyrotropin releasing hormone TRH – thyrotropin releasing hormone → → (TSH and PRL)(TSH and PRL)

GHRH – growth hormone releasing hormone GHRH – growth hormone releasing hormone → → (GH)(GH)

Somatostatin – inhibits release of growth hormoneSomatostatin – inhibits release of growth hormone

CRH – corticotrophin releasing hormone CRH – corticotrophin releasing hormone → → (ACTH)(ACTH)

MRH- melanocyte releasing hormone MRH- melanocyte releasing hormone → → (MSH)(MSH)

MIF- inhibits release of MSHMIF- inhibits release of MSH

GnRH – gonadotropin releasing hormone GnRH – gonadotropin releasing hormone → → (FSH/LH)(FSH/LH)

PRH – prolactin releasing hormone PRH – prolactin releasing hormone → → (PRL)(PRL)

PIH – prolactin inhibiting hormone (dopamine)PIH – prolactin inhibiting hormone (dopamine)

Anterior/Posterior Pituitary CirculationAnterior/Posterior Pituitary CirculationBlood flow to pituitary gland is via a portal circulation theBlood flow to pituitary gland is via a portal circulation thehypophyseal portalhypophyseal portal. Arterial flow is via superior and inferior. Arterial flow is via superior and inferior

hypophyseal artery into capillary beds in serieshypophyseal artery into capillary beds in series

Posterior Pituitary HormonesPosterior Pituitary HormonesADH an Oxytocin are secreted by neurosecretory cells in theADH an Oxytocin are secreted by neurosecretory cells in the

paraventricular and supraoptic nuclei of the hypothalamus and areparaventricular and supraoptic nuclei of the hypothalamus and are

transported to posterior pituitary via hypothalamohypophysealtransported to posterior pituitary via hypothalamohypophyseal

tract.tract.

Neurohypophyseal HormonesNeurohypophyseal Hormones

Antidiuretic hormone (ADH)Antidiuretic hormone (ADH) – produced by supraoptic – produced by supraoptic nuclei in the hypothalamus.nuclei in the hypothalamus.– Consists of 9 amino acidsConsists of 9 amino acids– Reduces the excretion of water by kidney collecting Reduces the excretion of water by kidney collecting

ducts; increases cuddling and grooming behavior.ducts; increases cuddling and grooming behavior.

OxytocinOxytocin – produced by the paraventricular nuclei in – produced by the paraventricular nuclei in the hypothalamusthe hypothalamus– Consists of 9 amino acids, but differs from ADH.Consists of 9 amino acids, but differs from ADH.– Induces smooth muscle contraction; increases Induces smooth muscle contraction; increases

cuddling and grooming behavior.cuddling and grooming behavior.

Adenohypophyseal cell typesAdenohypophyseal cell typesThyrotropic cells secrete TSHThyrotropic cells secrete TSH

Somatotropic cells secrete GHSomatotropic cells secrete GH

Corticotropic cells secrete ACTH and MSHCorticotropic cells secrete ACTH and MSH

Gonadotropic cells secrete FSH and LHGonadotropic cells secrete FSH and LH– Tropic hormones regulate the release of other hormones Tropic hormones regulate the release of other hormones

from the glands that they stimulate (TSH, ACTH, FSH and from the glands that they stimulate (TSH, ACTH, FSH and LH).LH).

MSH, PRL and GH all act directly on non-endocrine MSH, PRL and GH all act directly on non-endocrine target tissues.target tissues.

Thyroid glandThyroid glandLocation:Location: largest pure endocrine gland in adults ~ largest pure endocrine gland in adults ~

20-25 gms. and located adjacent to trachea inferior 20-25 gms. and located adjacent to trachea inferior to larynx.to larynx.

Structure:Structure: Butterfly shaped with two lobes joined by Butterfly shaped with two lobes joined by an isthmus. ~ 50% of people have a pyramidal lobe an isthmus. ~ 50% of people have a pyramidal lobe growing upward off of isthmus. growing upward off of isthmus. Gross Anatomy:Gross Anatomy: Bulbous at inferior end and tapers Bulbous at inferior end and tapers superiorly. superiorly.

- Thyroid is highly vascular via thyroidal arteries - Thyroid is highly vascular via thyroidal arteries ..Cellular Anatomy:Cellular Anatomy: Composed of sacs of thyroid Composed of sacs of thyroid follicular cells and lined with simple cuboidal or follicular cells and lined with simple cuboidal or simple squamous epithelium that is filled with protein simple squamous epithelium that is filled with protein rich colloid (thyroglobulin).rich colloid (thyroglobulin).

Thyroid glandThyroid gland

Follicular cells produce tri-iodo thyronine (T3) and Follicular cells produce tri-iodo thyronine (T3) and thyroxine (T4) which are stored in thyroglobulin.thyroxine (T4) which are stored in thyroglobulin.– Target cells are every cell and tissue in the bodyTarget cells are every cell and tissue in the body

Parafollicular or “C” cells found between follicular cells Parafollicular or “C” cells found between follicular cells in the thyroid gland produce calcitonin which keeps in the thyroid gland produce calcitonin which keeps blood Ca++ levels within the normal range by blood Ca++ levels within the normal range by depositing excess Ca++ in the bones and teethdepositing excess Ca++ in the bones and teeth..– Target cells are osteoblasts in boneTarget cells are osteoblasts in bone– Has no demonstrable function in adults, most active in fetus, Has no demonstrable function in adults, most active in fetus,

infants and adolescents. infants and adolescents.

Thyroid glandThyroid gland

Parathyroid glandParathyroid glandLocated on the posterior lateral margins of the thyroid Located on the posterior lateral margins of the thyroid gland are 4 to 8 small nodules.gland are 4 to 8 small nodules.

Structure is small ovoid nodules ~ 2-5 mm x 3-8 mm.Structure is small ovoid nodules ~ 2-5 mm x 3-8 mm.

Produces parathyroid hormone (PTH) which helps Produces parathyroid hormone (PTH) which helps regulate blood Ca++ levels.regulate blood Ca++ levels.

Target organs of PTH are bone, kidneys and Target organs of PTH are bone, kidneys and intestines.intestines.

Histologically it contains numerous small chief cells Histologically it contains numerous small chief cells and rare large oxyphilic cells.and rare large oxyphilic cells.– Chief cells secrete PTH.Chief cells secrete PTH.– Oxyphilic cells are probably inactive or immature chief cells.Oxyphilic cells are probably inactive or immature chief cells.

Parathyroid glandsParathyroid glands

Adrenal glandsAdrenal glandsLocated in the abdominal cavity attached to superior Located in the abdominal cavity attached to superior pole of each kidney (suprarenal).pole of each kidney (suprarenal).

Two distinct regions: Cortex and MedullaTwo distinct regions: Cortex and Medulla

Adrenal cortex has 3 layers:Adrenal cortex has 3 layers:Zona glomerulosaZona glomerulosa – outer layer – outer layer →→ mineralocorticoids. mineralocorticoids.Zona fasciculataZona fasciculata - middle ¾ of cortex - middle ¾ of cortex →→

glucocorticoids.glucocorticoids.Zona reticularisZona reticularis – innermost layer – innermost layer → androgens→ androgens

Adrenal Medulla is neuroendocrine tissue and is part Adrenal Medulla is neuroendocrine tissue and is part of sympathetic division (postganglionic) of ANS. of sympathetic division (postganglionic) of ANS.

Adrenal glandsAdrenal glands Blood supply is via:Blood supply is via:

Superior suprarenal Superior suprarenal

from Inferior phrenicfrom Inferior phrenic

arteries.arteries.

Middle suprarenal andMiddle suprarenal and

Inferior suprenal offInferior suprenal off

of aorta .of aorta .

Adrenal CortexAdrenal CortexHistologic features of adrenal cortex:Histologic features of adrenal cortex:

Outer layer is a dense fibrous capsule.Outer layer is a dense fibrous capsule.Zona glomerulosaZona glomerulosa (15% ov) looks like little balls (15% ov) looks like little balls or knots densely clustered together.or knots densely clustered together.Zona fasiculataZona fasiculata (78% ov) looks like cords that (78% ov) looks like cords that radiate toward the medulla.radiate toward the medulla.Zona reticularisZona reticularis (7% ov) branching network of (7% ov) branching network of pink staining cells between fasciculata and pink staining cells between fasciculata and medulla. medulla. Adrenal medulla is composed of chromafin cells Adrenal medulla is composed of chromafin cells arranged in spherical clusters. arranged in spherical clusters.

Adrenal gland histologyAdrenal gland histology

PancreasPancreasLocation: Just inferior to the stomach and in the first loop of the Location: Just inferior to the stomach and in the first loop of the duodenum approximately in the middle of the abdomen. duodenum approximately in the middle of the abdomen.

Structure:- mixed gland (endocrine/exocrine); spongy-like Structure:- mixed gland (endocrine/exocrine); spongy-like appearance. Exocrine cells produce digestive enzymes. appearance. Exocrine cells produce digestive enzymes.

Pancreatic “Islet of Langerhans” are endocrine cells.Pancreatic “Islet of Langerhans” are endocrine cells.

Hormones produced by 5 classes of islet cells include:Hormones produced by 5 classes of islet cells include:– αα--cells cells →→ Glucagon-Glucagon- a 29 amino acid molecule which targets a 29 amino acid molecule which targets

the liver to breakdown glycogen the liver to breakdown glycogen and release glucoseand release glucose..– ββ cells → cells → Insulin- Insulin- a 51 amino acid molecule which targets a 51 amino acid molecule which targets

the liver and most body cells except the brain to take up the liver and most body cells except the brain to take up glucose.glucose.

– Delta cells Delta cells →→ SomatostatinSomatostatin ↓↓ release of insulin & glucagon. release of insulin & glucagon.– ““F” cells F” cells →→ Pancreatic polypeptidePancreatic polypeptide ↓↓ gall bladder contraction. gall bladder contraction.– ““G” cells G” cells →→ GastrinGastrin ↑ acid secretion, gastric motility and ↑ acid secretion, gastric motility and

stomach emptying.stomach emptying.

PancreasPancreas

OvariesOvaries

Primary sex organs of femalesPrimary sex organs of females

Located retroperitoneal in the abdominal cavity lateral Located retroperitoneal in the abdominal cavity lateral to the uterus and at the proximal end of the uterine to the uterus and at the proximal end of the uterine tubes (fallopian tubes). tubes (fallopian tubes).

Pair of almond shaped organs ~ Pair of almond shaped organs ~ 3 cm x 1.5 cm x 1 cm.3 cm x 1.5 cm x 1 cm.

Produce female sex hormones (estrogen and Produce female sex hormones (estrogen and progesterone) and contain ova.progesterone) and contain ova.

More about the ovaries in reproduction.More about the ovaries in reproduction.

OvariesOvaries

TestesTestes

Primary male sex organs.Primary male sex organs.

Located in the scrotum outside of abdominal Located in the scrotum outside of abdominal cavity.cavity.

Produce sperm and male sex hormones Produce sperm and male sex hormones androgens (testosterone and inhibin).androgens (testosterone and inhibin).

Size ~ 4 cm Size ~ 4 cm ↑↑ x 3 cm a/p x2.5 cm x 3 cm a/p x2.5 cm →.→.

More about the testes in reproductionMore about the testes in reproduction

TestesTestes

ThymusThymus

Located in mediastinal space of the thoracic Located in mediastinal space of the thoracic cavity deep to sternum and supeficial to the cavity deep to sternum and supeficial to the pericardium.pericardium.

Produces several hormones amongst which are Produces several hormones amongst which are thymosin, thymopoietin, and IGF-1.thymosin, thymopoietin, and IGF-1.

Stimulates the maturation of T- lymphocytesStimulates the maturation of T- lymphocytes

Largest size occurs at puberty and thereafter Largest size occurs at puberty and thereafter diminishes in size as one gets older. By the age diminishes in size as one gets older. By the age of 50 it is ~ ¼ its original size.of 50 it is ~ ¼ its original size.

ThymusThymus

Pineal gland or “epiphysis cerebri”Pineal gland or “epiphysis cerebri”

Part of the epithalamus in the brainPart of the epithalamus in the brain

Contains neurons, glial cells and pinealocytes Contains neurons, glial cells and pinealocytes which produce and secrete which produce and secrete melatonin .melatonin .

Melatonin Melatonin regulates the circadian cycle as well regulates the circadian cycle as well as slows the maturation of sperm and ova by as slows the maturation of sperm and ova by inhibiting FSH and LH release from the inhibiting FSH and LH release from the adenohypophysis.adenohypophysis.

Pineal glandPineal gland

Other endocrine like organsOther endocrine like organs

Heart secretes atrial naturetic peptide (ANP).Heart secretes atrial naturetic peptide (ANP).

Skin initiates synthesis of calcitrol Skin initiates synthesis of calcitrol → vitamin D.→ vitamin D.

Kidneys secrete renin, erythropoietin, and aids in Kidneys secrete renin, erythropoietin, and aids in → → vitamin D synthesis.vitamin D synthesis.

Liver secretes erythropoietin and angiotensinogen. Liver secretes erythropoietin and angiotensinogen. The liver also aids in The liver also aids in → vitamin D and insulin-like GF.→ vitamin D and insulin-like GF.

Placenta secretes human gonadotropin.Placenta secretes human gonadotropin.

Stomach secretes gastrin and cholecystokinin and Stomach secretes gastrin and cholecystokinin and other enteroendocrine hormones that affect digestion.other enteroendocrine hormones that affect digestion.

Hypothalamic releasing and inhibiting Hypothalamic releasing and inhibiting hormoneshormones

Pituitary HormonesPituitary Hormones