THE ENDOCRINE SYSTEM Ch 17, Human Anatomy Sonya Schuh-Huerta, Ph.D.
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Transcript of THE ENDOCRINE SYSTEM Ch 17, Human Anatomy Sonya Schuh-Huerta, Ph.D.
THE ENDOCRINE SYSTEMTHE ENDOCRINE SYSTEM
Ch 17, Human AnatomyCh 17, Human Anatomy
Sonya Schuh-Huerta, Ph.D.Sonya Schuh-Huerta, Ph.D.
The Endocrine System: An Overview
• A system of ductless glands– Secrete messenger molecules called
hormones
• Interacts closely with the nervous system
• Endocrinology– Study of hormones & endocrine glands
Endocrine Organs
• Scattered throughout the body• Pure endocrine organs
– Pituitary, pineal, thyroid, parathyroid, & adrenal glands
• Organs containing endocrine cells– Pancreas, thymus, gonads, & hypothalamus
• Hypothalamus is a neuroendocrine organ– Produces hormones & also has nervous functions
Location of the Major Endocrine Glands
Pineal gland
HypothalamusPituitary gland
Parathyroid glands(on dorsal aspect of thyroid gland)
Thymus
Thyroid gland
Adrenal glands
Pancreas
Ovary (female)
Testis (male)
Hormones
• Classes of hormones– Amino acid–based hormones– Steroids derived from cholesterol
• Basic hormone action– Circulate throughout the body in the blood– Influences only specific tissues target
cells• A hormone can have different effects on different
target cells
Control of Hormone Secretion
• Secretion triggered by 3 major types of stimuli– Humoral simplest of endocrine control
mechanisms• Secretion in direct response to changing ion or
nutrient levels in the blood• Parathyroid monitors calcium levels
– Responds to decline by secreting hormone to reverse decline
Control of Hormone Secretion
• Secretion triggered by 3 major types of stimuli (cont…)– Neural
• Nerve fibers stimulate hormone secretion• Sympathetic nerve fibers stimulate cells in the
adrenal medulla• Induces release of epinephrine & norepinephrine
– Hormonal• Certain hormones trigger secretion of other
hormones– Hypothalamus secretes hormones stimulates pituitary
to secrete hormones stimulates other glands to secrete hormones
3 Major Types of Stimuli(a) Humoral stimulus (b) Neural stimulus (c) Hormonal stimulus
Capillary (low Ca2+
in blood)
Parathyroidglands
Thyroid gland(posterior view)
PTH
Parathyroidglands
CNS (spinal cord)
Medulla ofadrenal gland
Preganglionicsympatheticfibers
Capillary
Hypothalamus
Thyroidgland
Adrenalcortex
Gonad(Testis)
Pituitarygland
Capillary blood contains low concentration of Ca2+, which stimulates…
Preganglionic sympathetic fibersstimulate adrenal medulla cells…
The hypothalamus secretes hormones that…
…stimulatethe anteriorpituitary glandto secretehormonesthat…
…secretion of parathyroid hormone (PTH) by parathyroid glands. PTH acts to increase blood Ca2+.
…to secrete catecholamines(epinephrine and norepinephrine)
…stimulate other endocrine glandsto secrete hormones
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Control of Hormone Secretion
• Always controlled by feedback loops– Blood concentration declines below a
minimum• More hormone is secreted
– Blood concentration exceeds maximum• Hormone production is halted
• Referred to as positive & negative feedback loops usually multiple hormones involved in the pathway
The Pituitary Gland
• Secretes 9 major hormones
• Attached to the hypothalamus by the infundibulum (= pituitary stalk)
• 2 basic divisions of the pituitary gland:– Adenohypophysis (= anterior pituitary)
• Has 3 major divisions
– Neurohypophysis (= posterior pituitary) has 2 major divisions
The Pituitary Gland
Tuber cinereum
Mammillarybody
InfundibulumPars nervosa
Pars tuberalis Pars intermedia Pars distalis
Median eminence of hypothalamus
Optic chiasma
(c)
Anterior lobePosterior lobe
(a)
(d)
Acidophil Basophil Chromophobe cell
Capillary withred blood cells
Spherical cluster of cells
(b)
Corpuscallosum
Pituitary (hypophysis)
Brain stem
Mammillarybody
Hypothalamus
Pineal
Thalamus
Anterior Pituitary
• The largest division of the anterior lobe:– Makes & secretes 7 different hormones– Tropic hormones regulate the hormone
secretion of other glands• Includes: TSH, ACTH, FSH, LH
Anterior Pituitary
• GH, PRL, & MSH– Act directly on non-endocrine target tissues
Anterior Pituitary
• Growth hormone/GH (= somatotropic hormone)– Produced by somatotropic cells– Stimulates body growth by stimulating
increased protein production & growth of epiphyseal plates
– Stimulates growth directly & indirectly by the liver’s secretion of insulin-like growth factor-1 (IGF1)
Anterior Pituitary
• Thyroid-stimulating hormone (TSH)– Produced by thyrotropic cells– Signals thyroid gland to secrete thyroid
hormones
• Adrenocorticotropic hormone (ACTH)– Stimulates adrenal cortex to secrete
hormones that help cope with stress
Anterior Pituitary
• Melanocyte-stimulating hormone (MSH)– In humans, MSH functions in appetite
supression (“My Stomach’s not Hungry” hormone)
• Gonadotropins FSH & LH – Produced by gonadotropic cells
– they increase sex steroid production by the
gonads & the maturation of gametes
Anterior Pituitary
• Prolactin (PRL) produced by prolactin cells– Targets milk-producing glands in the breast
stimulates milk production after childbirth &
during lactation
– There are prolactin-secreting tumors that result in milk production in both women & men
(galactorrhea; can lead to problems with fertility)
– Prolactin central to milk production in all female mammals (exception – male bats)
Anterior Pituitary
Anterior Pituitary
• The hypothalamus– Controls secretion of anterior lobe hormones– Exerts control by secreting:
• Releasing hormones prompt anterior lobe to release hormones
• Gonadotropin-releasing hormone (GnRH) produced & secreted by specific neurons of hypothalamus cause release of FSH & LH
• Inhibiting hormones turn off secretion of anterior lobe hormones
Hypothalamic Control of Hormone Secretion from the Anterior Lobe
• Releasing hormones– Are secreted like neurotransmitters– Enter a primary capillary plexus– Travel in hypophyseal portal veins to a
secondary capillary plexus• From the secondary capillary plexus, the releasing
hormones trigger the anterior lobe to secrete the specific hormone, which is dumped into the secondary capillary plexus, and enters general circulation & travels to target organs
Hypothalamic Control of Hormone Secretion from the Anterior Lobe
Hypothalamic Control of Ant. Pituitary Secretion
When appropriately stimulated, hypothalamic neurons secrete releasing and inhibiting hormones into the primary capillary plexus.
Hypothalamic hormones travel through the portal veins to the anterior pituitary where they stimulate or inhibit release of hormones from the anterior lobe.
Anterior pituitary hormones are secreted into the secondary capillary plexus.
HypothalamusHypothalamic neuroncell bodies
Hypophysealportal system
Superior hypophysealartery
(a) Relationship between the anterior pituitary & hypothalamus
Anterior lobeof pituitary
TSH, FSH, LH, ACTH, GH, PRL
Primary capillaryplexus
Hypophysealportal veins
Secondarycapillaryplexus
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Posterior Pituitary
• Is structurally part of the brain
• Its axons make up the hypothalamic–hypophyseal tract– Arises from neuronal cell bodies in the
hypothalamus• Supraoptic nucleus• Paraventricular nucleus
Relationship Between Posterior Pituitary & Hypothalamus
Hypothalamic neuronssynthesize oxytocin and ADH.
Oxytocin and ADH are transported along the hypothalamic-hypophyseal tract to the posterior lobe.
Oxytocin and ADH are stored in axon terminals in the posterior pituitary.
Oxytocin and ADH are released into the blood when hypothalamic neurons fire.
Paraventricular nucleus
Supraoptic nucleus
Optic chiasma
Hypothalamus
Inferiorhypophysealartery
OxytocinADH
Infundibulum (connecting stalk)Hypothalamic-hypophysealtract
Axon terminals
Posteriorlobe ofpituitary
(b) Relationship between the posterior pituitary & hypothalamus
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Posterior Pituitary
• Does not make hormones
• Stores & releases hormones made in the hypothalamus!
• Releases 2 very important peptide hormones:– Anti-Diuretic hormone (ADH) –remember this?– Oxytocin
Posterior Pituitary
• ADH (Anti-Diuretic hormone; =vasopressin)– Targets kidneys to resorb water; prevents
diuresis
• Oxytocin– Induces smooth muscle contraction of
reproductive organs, ejects milk during breast feeding, & signals contraction of the uterus during childbirth
Hormones Made by Hypothalamus & Secreted by Posterior Pituitary
Pineal Gland
• Located on the roof of the diencephalon
• Shaped like a pine cone
• Pinealocytes secrete melatonin – A hormone that regulates circadian rhythms
Thyroid Gland
• Located in anterior neck around trachea• Largest pure endocrine gland• Functions in metabolism & metabolic rate; how
quickly the body uses energy; making proteins, etc.• Composed of follicles & areolar
connective tissue
Thyroid GlandHyoid bone
Thyroid cartilage
Common carotidartery
Epiglottis
Superior thyroidartery
External carotidartery
Isthmus ofthyroid gland
Left subclavianartery
Left laterallobe of thyroidgland
Inferior thyroidartery
Trachea
Rightsubclavianartery
Aorta
(a) Gross anatomy of the thyroid gland, anterior view
Thyroid Gland Hormones• Produces 2 types of hormones:
– Thyroid hormones (TH = T3 & T4) – Thyroxine (T4) & triiodothyronine (T3) tyrosine-based
hormones produced by thyroid – Involved in regulation of metabolism act on nearly all
cells of body; increase basal metabolic rate, protein synthesis; long bone growth; increase body’s sensitivity to catecholamines; regulate protein, fat & carb metabolism
– Secreted by follicular cells– Calcitonin Secreted by parafollicular cells; lowers
blood Ca2+ levels (inhibits intestinal Ca2+ absorption & inhibits osteoclast activity in bones; protects against calcium loss from skeleton during pregnancy & lactation
Microscopic Anatomy of Thyroid GlandColloid-filledfollicles
Follicular cells(secrete thyroid hormone)
Parafollicular cell(secretes calcitonin)
(b) Photomicrograph of thyroid gland follicles (160)
Parathyroid Glands
• Lie on the posterior surface of thyroid gland
• Contain 2 types of endocrine cells– Chief cells
• Produce Parathyroid Hormone (PTH)• Functions to increase blood Ca2+
levels by acting on receptors in bone, kidney & intestine all leads to higher plasma calcium levels! (opposite of calcitonin)
– Oxyphil cells• Function unknown...
Parathyroid Glands: Gross & Microscopic
(b) Photomicrograph of parathyroid glandtissue (360)
Capillary
Parathyroidcells(secreteparathyroidhormone)
Oxyphilcells
Pharynx(posterioraspect)
Thyroidgland Parathyroid
glands
Trachea
Esophagus
(a) Location of parathyroid glands, posterior view
• Pyramid-shaped glands located on the superior surface of each kidney
• Supplied by about 60 suprarenal arteries
• Nerve supply is almost exclusively sympathetic fibers!!!
• Functions in…? -remember?
Adrenal Glands (Suprarenal Glands)
Adrenal Glands
• 2 endocrine glands in one!– Adrenal medulla a cluster
of neurons• Part of Sympathetic Nervous System!• Postganglionic nerve fibers
– Adrenal cortex forms the bulk of the gland
• Functions All adrenal hormones help one cope with danger, terror, or stress
Adrenal Medulla
• Chromaffin cells– Are modified ganglionic sympathetic neurons– Secrete amine hormones epinephrine &
norepinephrine (= catecholamines) • Enhance “fight-or-flight” response• Hormones are stored in secretory vesicles
– Are arranged in spherical clusters & some branching cords
Adrenal Cortex
• Secretes lipid-based steroid hormones glucocorticoids, mineralocorticoids, androgens, E2
• Cortex is composed of 3 layers (zones):– Zona glomerulosa cells arranged in
spherical clusters– Zona fasciculata cells arranged in parallel
cords; contains lipid droplets – Zona reticularis cells arranged in a
branching network
The Adrenal Gland: Gross & Microscopic
Cortex
Kidney
Medulla
Adrenal gland
Capsule
Aldosterone
Epinephrineandnorepinephrine
Cortisolandandrogens
Zonaglomerulosa
Zonafasciculata
Zonareticularis
Adrenalmedulla
(a)Drawing of the histology of theadrenal cortex and a portion ofthe adrenal medulla
(b) Photomicrograph (140X)
Hormonessecreted
Cort
ex
Med
ulla
Stress & the Adrenal GlandShort-term stress More prolonged stress
Stress
Hypothalamus
CRH (corticotropin-releasing hormone)
Corticotroph cellsof anterior pituitary
To target in blood
Adrenal cortex(secretes steroidhormones)
GlucocorticoidsMineralocorticoids
ACTH
Catecholamines(epinephrine andnorepinephrine)
Short-term stress response
1.Increased heart rate2.Increased blood pressure3.Liver converts glycogen to glucose and releasesglucose to blood4.Dilation of bronchioles5.Changes in blood flow patterns leading to decreased digestive system activity and reduced urine output6.Increased metabolic rate
Long-term stress response
1.Retention of sodiumand water by kidneys2.Increased blood volumeand blood pressure
1.Proteins and fats convertedto glucose or broken downfor energy2.Increased blood glucose3.Suppression of immunesystem
Adrenal medulla(secretes amino acid–based hormones)
Preganglionicsympatheticfibers
Spinal cord
Nerve impulses
Pancreas
• Located in the posterior abdominal wall
• Functions regulation of blood sugar, metabolism & digestion
• Contains endocrine & exocrine cells– Exocrine cells
• Acinar cells secrete digestive enzymes (remember?..)
– Endocrine cells• Islets of Langerhans• About one million islets scattered throughout the
pancreas
Islets of Langerhans
• Main endocrine cell types:– Alpha cells ( cells) secrete glucagon
• Signal liver to release glucose from glycogen• Raises blood sugar
– Beta cells ( cells) secrete insulin• Signal most body cells to take up glucose from the
blood• Promotes storage of glucose as glycogen in liver• Lowers blood sugar
Pancreas
• Pancreatic islets contain 2 rare cell types– Delta (∂) cells
• Secrete somatostatin– Inhibits secretion of insulin & glucagon
– F (PP) cells• Secrete pancreatic polypeptide (PP)
– May inhibit exocrine activity of the pancreas
Thymus
• Located in the lower neck & anterior thorax
• Function Important immune organ; T-lymphocytes arise from precursor cells here; decreases in size & function after puberty
Gonads• Main sources of sex steroid
hormones – Testes & ovaries
• Male– Interstitial Leydig cells secrete androgens
• Primarily testosterone – Promotes development of the testes– Promotes the formation & survival of sperm– Development & maintenance
of secondary sex characteristics
Gonads
• Female– Ovaries
• Androgens & estrogens secreted by follicular cells
• Estrogen– Dev & maintenance of secondary sex
characteristics
– Dev of eggs– Regulation of menstrual cycle
• Progesterone– Prepares the uterus for Pregnancy
Sex Steroid Hormones
• Critical for normal reproductive function
• Affect many other tissues/organs of the body• Bone• Muscle• Fat• Liver & kidney• Brain (sexual behavior, mood, cognition)
Sex Steroid Hormones & Bone
• Promote bone growth (adolescent growth spurt)
2008 2010
Sex Steroid Hormones & Bone
• Also maintain bone mass• With aging or in diseases that render the gonads
dysfunctional (low T/E2) loss of bone mass & osteoporosis!
Could Skeletal Tissue Exert Reciprocal Effects on Gonads?
gonad
sex steroids
???
bone
Osteocalcin – A Hormone Secreted by Bone
• Secreted by osteoblasts (bone-forming cells of skeleton)• Involved in bone growth & bone remodeling• Roles in energy metabolism & glucose homeostasis -Ocn-/- mice have skeletal & metabolic defects greater bone
density, fat, & insulin resistance
(Lee et al. Cell, 2007; Ducy et al. Nature, 1996)
• Ocn-/- mice – reduced T & reduced fertility (Oury et al. Cell, 2011)
• Osteocalcin – a hormone linking bone with metabolism & reproduction
Bone & Fertility in Balance
Male Fertility(Female Fertility?)
Germ cell development(sperm)
Osteocalcin (Ocn)
Functional gonad (testis)
Healthy bones(bone mass)
Ocn binding to receptor
G s
Ado
GTP
Testosterone
(& other factors)
Energy Metabolism
Testosterone/Estrogen
AgingFertility DisordersMetabolic DysfunctionGenesEnvironmental factors
AgingFertility DisordersMetabolic DysfunctionGenesEnvironmental factors
Other Endocrine Structures…
• Endocrine cells occur within:– The heart
• Atria contain atrial natriuretic peptide (ANP) vasodialator; involved in control of BP
– The GI tract• Enteroendocrine cells (Ghrelin, CCK, gastrin,
secretin, motilin, enterocrinin, etc.…)• Ghrelin the hunger (“belly-growling”) hormone!
– The placenta• Sustains the fetus & secretes several hormones
(human chorionic gonadotropin, progesterone, E2, relaxin…)
Other Endocrine Structures
– The kidneys• Cells of the juxtaglomerular apparatus (JGA)
secrete renin • Endothelial cells & interstitial connective tissue
secrete erythropoietin
– The skin• With sunlight, modified cholesterol molecules
convert to a precursor of vitamin D
– Bone• Osteocalcin, & others…
Pituitary Disorders
• Gigantism – Hypersecretion of GH in children
• Pituitary dwarfism– Hyposecretion of GH
• Diabetes insipidus excessive thirst & urination– Hypothalamus does not make enough ADH
Disorders of the Pancreas: Diabetes Mellitus
• Caused by– Insufficient secretion of insulin – Resistance of body cells to the effects of
insulin
• Type 1 Diabetes– Develops suddenly, usually before age 15– T cell–mediated autoimmune response
destroys beta cells of pancreas no more insulin
Diabetes Mellitus• Type 2 Diabetes
– Adult onset– Usually occurs after age 40– Associated with higher BMI/obesity– Body cells have decreased
sensitivity to insulin– Controlled by dietary
changes & regular exercise!
Disorders of the Thyroid
• Grave’s disease– Most common type of hyperthyroidism – Immune system makes abnormal antibodies
• Stimulates the over-secretion of TH by follicle cells
– Leads to nervousness, weight loss, sweating, & rapid heart rate; protrusion of the eyeballs
– Too much thyroid action metabolism too high!
Disorders of the Thyroid
• Myxedema– Adult hypothyroidism– Antibodies attack & destroy thyroid tissue– Low metabolic rate & weight gain are common
symptoms
Disorders of the Thyroid
• Endemic goiter– Due to lack of iodine in the diet
• Cretinism– Hypothyroidism in children– Short, disproportionate body, thick tongue,
& mental retardation
Thyroid Disorders
Disorders of the Adrenal Cortex
• Cushing’s syndrome– Caused by hypersecretion of glucocorticoid hormones
(cortisol) usually a pituitary tumor– Weight gain on trunk, fat pads, “moon face,” thinning
of the skin, striae, etc.
• Addison’s disease– Hyposecretory disorder of the adrenal cortex– Deficiencies of both mineralocorticoids &
glucocorticoids– Fatigue, weakness, weight loss, mood changes,
hyperpigmentation
Adrenal Cortex Disorders
Adrenal Cortex Disorders
Cushing’s Addison’s
The Endocrine System with Age• Endocrine organs operate effectively until old age
• Anterior pituitary – Increase in connective tissue & lipofuscin – Decrease in vascularization & number of hormone-
secreting cells• Adrenal cortex
– Normal rates of glucocorticoid secretion continue• Adrenal medulla
– No age-related changes in catecholamine secretion
•Gonads– Testes: decline in sperm counts, but can function
throughout life – Ovaries: loss of all eggs/diminished function in mid-life
Congratulations!!!! You made it to the end of Anatomy!
What’s Next?Today’s Lab: Final Lab Exam 5!Mon, May 20, 5:25 pm: Final Exam!