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THE ENDOCRINE SYSTEM Ch 17, Human Anatomy 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.

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slide1

THE ENDOCRINE SYSTEM

Ch 17, Human Anatomy

Sonya Schuh-Huerta, Ph.D.

slide2

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
slide3

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 neuroendocrineorgan
    • Produces hormones & also has nervous functions
slide4

Location of the Major Endocrine Glands

Pineal gland

Hypothalamus

Pituitary gland

Thyroid gland

Parathyroid glands

(on dorsal aspect

of thyroid gland)

Thymus

Adrenal glands

Pancreas

Ovary (female)

Testis (male)

slide5

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
slide6

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
slide7

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
slide8

(a) Humoral stimulus

(b) Neural stimulus

(c) Hormonal stimulus

1

1

1

Capillary blood contains

low concentration of Ca2+,

which stimulates…

Preganglionic sympathetic fibers

stimulate adrenal medulla cells…

The hypothalamus secretes

hormones that…

Hypothalamus

CNS (spinal cord)

Capillary (low Ca2+

in blood)

2

…stimulate

the anterior

pituitary gland

to secrete

hormones

that…

Thyroid gland

(posterior view)

Parathyroid

glands

Pituitary

gland

Preganglionic

sympathetic

fibers

Adrenal

cortex

Thyroid

gland

Gonad

(Testis)

Medulla of

adrenal gland

Parathyroid

glands

PTH

Capillary

3

2

2

…secretion of parathyroid hormone

(PTH) by parathyroid glands. PTH acts to

increase blood Ca2+.

…to secrete catecholamines

(epinephrine and norepinephrine)

…stimulate other endocrine glands

to secrete hormones

3 Major Types of Stimuli

slide9

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 & negativefeedback loops  usually multiple hormones involved in the pathway
slide10

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
slide11

Corpus

callosum

Thalamus

Pineal

Acidophil

Basophil

Chromophobe cell

Hypothalamus

Mammillary

body

Brain stem

Pituitary (hypophysis)

(b)

Capillary with

red blood cells

Spherical cluster

of cells

(a)

(d)

The Pituitary Gland

Mammillary

body

Optic chiasma

Median eminence

of hypothalamus

Tuber cinereum

Anterior lobe

Posterior lobe

Pars tuberalis

Pars intermedia

Infundibulum

Pars distalis

Pars nervosa

(c)

slide12

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
slide13

Anterior Pituitary

  • GH, PRL, & MSH
    • Act directly on non-endocrine target tissues
slide14

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)
slide15

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
slide16

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
slide17

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)
slide20

Hypothalamic Control of Hormone Secretion from the Anterior Lobe

  • 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
slide21

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
slide22

When appropriately

stimulated, hypothalamic

neurons secrete releasing

and inhibiting hormones into

the primary capillary plexus.

1

Hypothalamic neuron

cell bodies

Hypothalamus

Superior hypophyseal

artery

Hypophyseal

portal system

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.

2

Hypophyseal

portal veins

Secondary

capillary

plexus

Anterior lobe

of pituitary

Anterior pituitary

hormones are secreted into

the secondary capillary

plexus.

3

TSH, FSH, LH,

ACTH, GH, PRL

(a) Relationship between the anterior pituitary & hypothalamus

Hypothalamic Control of Ant. Pituitary Secretion

slide23

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
slide24

Relationship Between Posterior Pituitary & Hypothalamus

Hypothalamic neurons

synthesize oxytocin and

ADH.

1

Hypothalamus

Paraventricular nucleus

Supraoptic nucleus

Oxytocin and ADH are

transported along the

hypothalamic-

hypophyseal tract to the

posterior lobe.

2

Optic chiasma

Infundibulum (connecting stalk)

Inferior

hypophyseal

artery

Hypothalamic-

hypophyseal

tract

3

Oxytocin and ADH are

stored in axon terminals

in the posterior pituitary.

Axon

terminals

Oxytocin and ADH are

released into the blood

when hypothalamic

neurons fire.

Posterior

lobe of

pituitary

4

Oxytocin

ADH

(b) Relationship between the posterior pituitary & hypothalamus

slide25

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
slide26

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
slide28

Pineal Gland

  • Located on the roof of the diencephalon
  • Shaped like a pine cone
  • Pinealocytes secrete melatonin
    • A hormone that regulates circadian rhythms
slide29

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 
slide30

Hyoid bone

Epiglottis

Thyroid cartilage

External carotid

artery

Superior thyroid

artery

Common carotid

artery

Inferior thyroid

artery

Isthmus of

thyroid gland

Right

subclavian

artery

Left subclavian

artery

Left lateral

lobe of thyroid

gland

Trachea

Aorta

(a) Gross anatomy of the thyroid gland, anterior view

Thyroid Gland

slide31

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
slide32

Microscopic Anatomy of Thyroid Gland

Colloid-filled

follicles

Follicular cells

(secrete thyroid hormone)

Parafollicular cell

(secretes calcitonin)

(b) Photomicrograph of thyroid gland follicles (160)

slide33

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...
slide34

Parathyroid Glands: Gross & Microscopic

Pharynx

(posterior

aspect)

Parathyroid

cells

(secrete

parathyroid

hormone)

Thyroid

gland

Parathyroid

glands

Esophagus

Oxyphil

cells

Trachea

Capillary

(a) Location of parathyroid

glands, posterior view

(b) Photomicrograph of

parathyroid gland

tissue (360)

slide35

Adrenal Glands (Suprarenal Glands)

  • 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?
slide36

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
slide37

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
slide38

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
slide39

The Adrenal Gland: Gross & Microscopic

Hormones

secreted

Capsule

Zona

glomerulosa

Aldosterone

Zona

fasciculata

Adrenal gland

Cortex

Cortisol

and

androgens

Medulla

Cortex

Zona

reticularis

Kidney

Adrenal

medulla

Medulla

Epinephrine

and

norepinephrine

(a)Drawing of the histology of the

adrenal cortex and a portion of

the adrenal medulla

(b) Photomicrograph (140X)

slide40

Short-term stress

More prolonged stress

Stress

Nerve impulses

Hypothalamus

CRH (corticotropin-

releasing hormone)

Spinal cord

Corticotroph cells

of anterior pituitary

Preganglionic

sympathetic

fibers

To target in blood

Adrenal cortex

(secretes steroid

hormones)

Adrenal medulla

(secretes amino acid–

based hormones)

ACTH

Catecholamines

(epinephrine and

norepinephrine)

Mineralocorticoids

Glucocorticoids

Short-term stress response

Long-term stress response

1.Increased heart rate

2.Increased blood pressure

3.Liver converts glycogen to glucose and releases

glucose to blood

4.Dilation of bronchioles

5.Changes in blood flow patterns leading to decreased

digestive system activity and reduced urine output

6.Increased metabolic rate

1.Retention of sodium

and water by kidneys

2.Increased blood volume

and blood pressure

1.Proteins and fats converted

to glucose or broken down

for energy

2.Increased blood glucose

3.Suppression of immune

system

Stress & the Adrenal Gland

slide41

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
slide42

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
slide43

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
slide44

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
slide45

Gonads

  • Main sources of sex steroid hormones 
    • Testes & ovaries
  • Male
    • Interstitial Leydigcells secrete androgens
      • Primarily testosterone
        • Promotes development of the testes
        • Promotes the formation & survival of sperm
        • Development & maintenance of secondary sex characteristics
slide46

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
slide47

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)
slide48

2008

2010

Sex Steroid Hormones & Bone

  • Promote bone growth (adolescent growth spurt)
slide49

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!
slide51

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
slide52

Bone & Fertility in Balance

Aging

Fertility Disorders

Metabolic Dysfunction

Genes

Environmental factors

Energy Metabolism

Ocn binding

to receptor

Functional gonad

(testis)

Osteocalcin (Ocn)

Testosterone

(& other factors)

Testosterone/Estrogen

Healthy bones

(bone mass)

Germ cell development

(sperm)

Aging

Fertility Disorders

Metabolic Dysfunction

Genes

Environmental factors

Male Fertility

(Female Fertility?)

slide53

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…)
slide54

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…
slide55

Pituitary Disorders

  • Gigantism
    • Hypersecretion of GH in children
  • Pituitary dwarfism
    • Hyposecretion of GH
  • Diabetes insipidus excessive thirst & urination
    • Hypothalamus does not make enough ADH
slide56

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
slide57

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!
slide58

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!
slide59

Disorders of the Thyroid

  • Myxedema
    • Adult hypothyroidism
    • Antibodies attack & destroy thyroid tissue
    • Low metabolic rate & weight gain are common symptoms
slide60

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
slide62

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
slide64

Adrenal Cortex Disorders

Cushing’s

Addison’s

slide65

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
slide66

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!