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The Endocrine System. Endocrine System. Function: Regulates Coordinates Integrates Works cooperatively with the nervous system No ducts: Reactions not immediate -last longer than N.S. responses. Hormones.

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The Endocrine System

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endocrine system
Endocrine System
  • Function:
    • Regulates
    • Coordinates
    • Integrates
    • Works cooperatively with the nervous system
    • No ducts:
    • Reactions not immediate -last longer than N.S. responses
  • Substances secreted by cells that regulate the activity of another tissue or organ
  • Most produced by glands
  • Some produced by clusters of cells
  • Some produced by neurons (neurohormones)
  • Types of Hormones
    • Amino Acid Derivatives
      • Simple amines, thyroxin, peptides and proteins
      • Examples:
        • Thyroid hormones, epinephrine and NE, insulin, glucagon
      • Most hormones this type
  • Types of hormones
    • Steroid hormones
      • Derived from cholesterol
      • Includes gonadal hormones (sex hormones) and adrenal hormones (cortex only)
      • Examples:
        • Progesterone, testosterone, cortisol, aldosterone
  • Types of hormones
    • Eicosanoids
      • Are paracrine hormones (local hormone = produced by cells and released to effect cells in the same area)
      • Examples:
        • Prostaglandins, leukotrines
  • On the target cell -bind hormone
  • Determine the effect the hormone will have on the target cell
  • Binding may cause:
    • Change in membrane permeability or potential
    • Synthesis of substances such as proteins or enzymes
    • Activation or deactivation of enzymes
    • Secretion of substances
    • Stimulation of mitosis
hormone actions
Hormone Actions
  • Alter the activity of target cells
  • Decrease or increase cellular activity in target cells
  • Only affect cells with receptors for that hormone
hormone action

Where are the receptors?

  • On the cell membrane (AA hormones)

intracellular second messenger

  • In the nucleus (steroid hormones & thyroxine)

direct gene activation

hormone action second messenger
HORMONE ACTION-Second Messenger

Intracellular second messenger

  • Hormone
  • Receptor
  • G protein
  • Adenylate cyclase system
  • Cyclic AMP
  • Protein kinases
hormone mechanisms
Hormone Mechanisms
  • Second Messengers
    • Hormone binds to a receptor on plasma membrane
    • Series of reactions initiated within the cell
    • Example:
      • Cyclic AMP
second messengers
Second Messengers
  • Cyclic AMP (cAMP)
    • Formed from ATP when a hormone binds to receptor
    • Hormone/receptor binding
      • ‘G’ protein activates or inhibits adenyl cyclase
      • ATP converted to cAMP
      • May activate protein kinases
      • Initiates cascade of enzymes within the cell
      • Effect depends upon target cell
second messengers1
Second Messengers
  • PIP Mechanism
    • PIP2 split into diacylglycerol and IP3
    • Both act as second messengers
    • IP3 triggers the release of calcium from the ER
    • Ca2+ acts as a third messenger
    • Diacylglycerol may activate protein kinases
direct activation of genes
Direct Activation of Genes
  • Steroid hormones can pass through the plasma membrane
  • Bind to receptors inside cell
  • Hormone/receptor binding stimulates genes on the DNA to begin protein production
hormone regulation
Hormone Regulation
  • Nervous System
    • Ultimate control of hormone mechanisms belongs to the nervous system
      • Mainly hypothalamus and sympathetic nervous system
hormone regulation1
Hormone Regulation
  • Stimulation or inhibition of endocrine glands comes from THREE sources:
    • Other hormones
    • Humoral stimuli
    • Neural stimuli
hormone regulation2
Hormone Regulation
  • Hormonal Regulation (by other Hormones)
    • Hormones may stimulate or inhibit the release of other hormones
      • Hypothalamus-
        • Regulates anterior pituitary gland
      • Pituitary hormones-
        • Stimulate release of hormones from other glands
hormone regulation3
Hormone Regulation
  • Regulation by Humoral Stimuli
    • Changing ion or nutrient levels in the blood may inhibit or stimulate the release of hormones
    • Example:
      • Low blood calcium (Ca2+)
      • PTH released from the parathyroid glands
      • Ca2+ released from bone
      • Increase in blood Ca2+
hormone regulation4
Hormone Regulation
  • Regulation by Neural Stimuli
    • Nerve impulses may stimulate the release of hormones
    • Example:
      • Sympathetic neurons stimulate release of epinephrine and norepinephrine from the adrenal medulla
feedback mechanisms
Feedback Mechanisms
  • Negative Feedback System
    • Rising hormone or ion levels inhibit further hormone release from the gland
  • Positive Feedback System
    • Rising hormone levels cause an increase in the hormone being secreted
hypo or hypersecretion
Hypo or Hypersecretion
  • May result in a disorder
  • Examples:
    • Diabetes
    • Grave’s disease
    • Addison’s disease
    • Cushing’s disease
major endocrine glands
Major Endocrine Glands
  • Pituitary Gland(Hypophysis)
      • Posterior lobe (Neurohypophysis)
        • Releases 2 hormones produced in the hypothalamus

posterior lobe

anterior lobe

posterior pituitary gland
Posterior Pituitary Gland
  • Posterior Lobe
    • Derived from hypothalamus
    • Posterior lobe + infundibulum = neurohypophysis
    • Neuron axons to pituitary = hypothalamic hypophyseal tract

hypothalamic hypophyseal tract

posterior pituitary gland1
Posterior Pituitary Gland
  • Two hormones released here
  • Both produced in nuclei of the hypothalamus
  • Both secreted into capillaries in posterior pituitary for distribution to the body

Oxytocin & ADH

  • SON/PVN – produce ADH & oxytocin
  • Released from posterior pituitary
  • Posterior lobe:
    • Pituicytes
      • ADH
      • Oxytocin
posterior pituitary gland2
Posterior Pituitary Gland

Paraventricular nuclei

  • Supraoptic Nucleus
    • ADH (Vasopressin)
      • Stimulates increased reabsorption of water by kidney tubules
      • Decreases urine volume
      • Increases blood volume
      • React to Osmoreceptors

Supraoptic nuclei

  • Paraventricular Nucleus
    • Oxytocin
    • Uterine contractions
    • Milk release (Contraction of mammary gland smooth muscle

ADH & oxytocin

ventral hypothalamus
Ventral Hypothalamus
  • Releasing and inhibiting hormones
  • Thru portal system
  • Target = anterior pituitary
anterior pituitary gland
Anterior Pituitary Gland
  • Hypophyseal Portal System

neurons in ventral hypothalamus

primary capillary plexus

hypophyseal portal veins

secondary capillary plexus

secretory cells

anterior pituitary gland1
Anterior Pituitary Gland

Ventral hypothalamus

  • Anterior Lobe = Adenohypophysis
    • Derived from roof of mouth
    • Produces hormones
    • Release of hormones is controlled by hormones from neurons of the ventral hypothalamus = releasing or inhibiting hormones

anterior lobe

pituitary hypophysis
Pituitary (Hypophysis)
  • Location and relationships
  • Densely packed cells (anterior)
  • Anterior lobe:
    • TSH
    • ACTH
    • FSH
    • LH
          • GnRH
    • Growth h.
    • Prolactin
    • MSH
anterior pituitary gland2
Anterior Pituitary Gland
  • The following four anterior pituitary hormones are tropic hormones
  • Tropic Hormones:
    • TSH
    • ACTH
    • FSH
    • LH
tropic hormones
Tropic Hormones
  • Hormones Secreted
    • Thyroid Stimulating Hormone (TSH)
      • Stimulates production and release of thyroid hormones by the thyroid gland
      • Release stimulated by TRH
      • Inhibited by rising blood levels of thyroid hormone
tropic hormones1
Tropic Hormones
  • Hormones Secreted
    • Adrenocorticotropic Hormone (ACTH or Corticotropin)
      • Stimulates secretion of corticosteroid hormones (esp. cortisol) from the adrenal cortex
      • Release stimulated by CRH, fever, hypoglycemia and stress
      • Inhibited by rising cortisol levels
tropic hormones2
Tropic Hormones
  • Hormones Secreted
    • Follicle Stimulating Hormone (FSH)
      • Not present until puberty
      • Stimulates gamete production and maturation in both males and females
      • Release stimulated by GnRH
      • Inhibited by rising gonadal hormones
anterior pituitary gland3
Anterior Pituitary Gland
  • Hormones Secreted
    • Luteinizing Hormone (LH)
      • Promotes production of gonadal hormones
      • Controlled by the same hormones as FSH
      • Triggers ovulation in females
non tropic hormones
Non-tropic Hormones
  • Hormones Secreted
    • Growth Hormone (GH) or Somatotropin
      • Produced in response to growth hormone releasing hormone (GHRH from hypothalamus)
      • Also secreted in response to hypoglycemia or decreased blood GH or Increased amino acid levels
      • Inhibited by GHIH (somatostatin from hypothalamus)
      • Stimulates cell growth and division in most cells (esp. bone and muscle)
      • Mobilizes fat to conserve glucose
      • Hyposecretion results in pituitary dwarfism
      • Hypersecretion results in gigantism or acromegaly
non tropic hormones1
Non-tropic Hormones
  • Hormones Secreted
    • Prolactin (PRL)
      • Release stimulated by PRH
      • Inhibited by PIH (dopamine)
      • Both are influenced by estrogen
      • Stimulates milk production by breasts
the thyroid gland
The Thyroid Gland
  • Two lateral lobes
  • Composed of follicles
  • Cuboidal follicle cells produce thyroglobulin
    • Thyroglobulin stored in lumen of follicle
    • Iodine attaches
    • Molecule is split into T3 and T4 (mostly T4)
    • Hormones enter circulation, more T3 formed

thyroid gland

thyroid gland histology
Thyroid Gland - histology
  • Follicular cells




T3 – triiodothyronine

T4 – thyroxine

  • Parafollicular cells


thyroid gland hormones
Thyroid Gland - hormones
  • Follicular cells


T3 – triiodothyronine

T4 – thyroxine

        • + BMR (glucose oxidation)
        • maintains bp
        • tissue growth & development
  • Parafollicular cells


        • decreases blood calcium
        • + osteoblasts
thyroid gland t3 t4 production
Thyroid Gland – T3/T4 production
  • Follicles – colloid, follicular cells
  • Cells make thyroglobulin
  • Thyroglobulin moves into follicle
  • Iodine pumped into follicle
  • Iodine used to make subunits
    • 1 OR 2 IODINE
  • Subunits moved into follicle cells
  • Subunits join to make T3 or T4
  • T3/T4 released from follicle cells
thyroid hormone
Thyroid Hormone
  • T4 converted to T3 once in tissues
  • Secreted in response to TSH
  • Inhibited by rising blood thyroid hormone levels
  • Effects:
    • Increases metabolic rate
    • Increases heat production
    • Promotes protein synthesis and enhances the affect of GH
    • Promotes uptake of glucose by cells
    • Promotes lipid metabolism
    • Speeds up actions of nervous system
thyroid hormone1
Thyroid Hormone
  • Hyposecretion
    • Can result in cretinismin children
    • Myxedema in adults
  • Hypersecretion
    • Grave’s Disease


thyroid gland pathology
Thyroid Gland - pathology
  • Myxedema – adult hypothyroid
  • Goiter – enlarged thyroid due to lack of iodine
  • Cretinism – infantile hypothyroid
  • Grave’s disease – hyperthyroidexophthalmos

parafollicular cells

  • Secreted by parafollicular or Ccells by the thyroid
  • Released in response high blood calcium
  • Stimulates uptake of calcium by bone
parathyroid glands
Parathyroid Glands
  • 4 to 8 on posterior thyroid gland
  • Secrete Parathyroid Hormone (PTH)
    • Secreted in response to low blood calcium
    • Stimulates bone resorption
    • Released calcium enters blood
    • Increases absorption of calcium by intestines and reabsorption by kidneys

parathyroid glands

parathyroid hormone
Parathyroid Hormone

Chief cells

  • Hypersecretion
    • Depletes calcium from bones
    • Depresses nervous system activity
    • Skeletal muscle weakness
  • Hyposecretion
    • Over excitability of neurons
    • Muscle spasms
    • Convulsions
adrenal suprarenal glands
Adrenal (Suprarenal) Glands
  • Two glands--one on top of each kidney
  • Outer cortex, inner medulla
  • Cortex
    • Produces over 2 dozen corticosteroids from cholesterol
    • Increased hormone output in response to ACTH or stress

adrenal gland



adrenal cortex
Adrenal Cortex
  • Three Regions:
    • Zona Glomerulosa
      • Outer region
      • Production of mineralocorticoids (aldosterone)
      • Regulation of electrolyte & fluid balance
  • 95% of mineralocorticoids
  • Sodium reabsorption (and water) by kidney tubules
  • Increases blood volume and pressure
  • Stimulated by angiotensin
    • Renin secreted by kidneys
    • Activates angiotensin hormones in blood
    • Stimulates release of aldosterone
  • Inhibited by Atrial Natriuretic Factor (ANF)
    • Secreted by heart cells when B.P. rises
    • Blocks secretion of renin and aldosterone
adrenal cortex1
Adrenal Cortex
  • Zona Fasciculata
    • Middle region
    • Secretes glucocorticoids (cortisol)
    • Cortisol
      • Released in response to ACTH
      • Inhibited by increased cortisol
      • Promotes gluconeogenesis (production of glucose from non-carbohydrate sources)
      • Causes a rise in B.P.
      • Anti-inflammatory if given in higher doses
  • Hypersecretion
    • Cushing’s Syndrome
    • Depressed bone and cartilage formation
    • Depressed inflammatory response and immune system
    • Edema, hypertension, loss of muscle and bone, ‘moon face’
  • Hyposecretion
    • Addison’s disease
    • Drop in blood plasma volume
    • Inability to cope with stress or regulate blood sugar levels
    • Increased skin pigmentation
adrenal cortex2
Adrenal Cortex
  • Zona Reticularis
    • Inner region
    • Produces glucocorticoids & gonadocorticoids (androgens and estrogen)
adrenal medulla
  • Chromaffin Cells
    • Secrete epinephrine and norepinephrine (Catecholamines)
    • Release stimulated by sympathetic neurons
    • Prolongs the fight or flight response
the pancreas
The Pancreas
  • Mixed endocrine and exocrine function
  • Acinar Cells
    • Secrete digestive enzymes into small intestine
  • Islets of Langerhans
    • Contain alpha cells
      • Glucagon
    • Contain beta cells
      • Insulin
endocrine and exocrine

Islets of Langerhans

Cell Types:

  • Stimulated by high blood sugar
  • Inhibited by decrease in blood sugar or somatostatin (GHIH)
  • Lowers blood sugar
  • Enhances glucose transport into cells (esp. muscle)
  • Stimulates glycogen formation
  • Promotes conversion of glucose to fat
  • Stimulates protein synthesis in muscle

Islet of Langerhans

  • Released in response to low blood sugar
  • Mobilizes fatty acids, glucose and amino acids from storage
  • Promotes release of fat from adipose tissue
  • Promotes:
    • Gluconeogenesis (production of glucose from non-carb. sources)
    • Glycogenolysis (breakdown of glycogen into glucose)
  • Raises blood sugar levels
  • Diabetes Insipidus
    • Caused by ADH deficiency
    • Large quantities of urine
    • Dehydration
    • No blood sugar accumulation
  • Diabetes Mellitus
    • Results from Hyposecretion of insulin or hypoactivity of insulin
  • Diabetes Mellitus
    • Two types:
      • Type 1 (Juvenile Onset)
        • Usually before age 20
        • Decreased amount of beta cells in pancreas
        • Possibly autoimmune cause
        • Long term vascular and neural problems
      • Type 2 (Adult Onset)
        • Insulin is produced but receptors are resistant to it
        • Family tendencies
        • Influenced by weight, diet and exercise
  • Lack of insulin or response to it
  • Inability of glucose to enter body cells
  • High blood sugar
  • Fat stores are mobilized for fuel
  • Blood sugar and fatty acid levels rise higher
  • Ketone bodies build up from breakdown of fatty acids
  • Ketosis or acidosis results (lowered blood pH)
  • Crisis, coma or death
  • Symptoms
    • Polyuria
      • Large urine output
    • Polydipsia
      • Excessive thirst
    • Polyphagia
      • Excessive hunger caused by the inability to use glucose as an energy source
the pineal gland
The Pineal Gland
  • Secretes melatonin
  • May affect responses to light cycles
  • May inhibit gonad activity in humans until puberty

“brain sand”

the thymus gland
The Thymus Gland
  • Shrinks with age
  • Produces thymopoietin and thymosin
  • Aids in development of the immune response (development of T- lymphocytes)
the gonads
  • Produce gametes and reproductive hormones
    • Testosterone in males
      • Maturation of reproductive organs
      • Secondary sex characteristics
      • Sex drive
    • Estrogens and progesterone in females
      • Estrogens cause maturation of reproductive organs and appearance of secondary sex characteristics
      • With progesterone, promote breast development and cyclic changes in uterine lining