Endocrinology II: Axis and systems

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Endocrinology II Axis and systems
Advanced Physiology of AnimalsANSC 3405
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Outline

• Endocrine glands/organs
• Hormones of hypothalamus and pituitary
• HPA axis and adrenals
• Hypothalamic Pituitary Gonadals axis
• Thyroid axis
• Growth axis
• Calcium homeostasis

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Endocrine Tissues
Adrenal Gland
Ovary
Hypothalamus
Kidney
Pituitary
Located at base of brain
Thyroid Parathyroid
(Testis in Male)
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Short Loop
Open Loop
Long Loop
(Figure 9-12)
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(No Transcript)
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Hypothalamus-pituitary
Hypothalamus
Pituitary Stalk
Hypophyseal Portal Vessels
Posterior Pituitary (Neurohypophysis)
Anterior Pituitary (Adenohypohysis)
(STUDY Figure 9-15)
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Hypothalamo-hypophyseal portal system

• Carries hypothalamic hormones specifically to the
  anterior pituitary without dilution in the
  systemic blood.
• 1. Allows rapid response
• 2. Little dilution of peptide hormones
• 3. Peptides have short 1/2 life
• Specific hypothalamic nuclei secrete releasing
  or release
• Receptors to inhibit/control release of
  pituitary hormones.

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Neurosecretory cells of Posterior Pituitary

• Posterior pituitary gland does NOT have cells
  that produce/store hormones
• Neurosecretory cells of hypothalamus release
  hormones
• Directly into Posterior pituitary
• Which is rapidly released into systemic
  bloodstream
• Rapid response

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Hypothalamic Hormones

• Corticotropin releasing hormone (CRH)
• Gonadotropin Releasing Hormone (GnRH)
• Thyroid Releasing Hormone (TRH)
• Growth Hormone Releasing Hormone (GHRH)
• Oxytocin
• Vasopressin (VP, AVP)

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Pituitary Gland
Anterior Pituitary
Posterior Pituitary
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Anterior Pituitary Cell Types and Hormones

• Corticotrophs
• - Adrenalcorticotrophic (ACTH)
• Gonadotrophs
• Release Leutinizing Hormone (LH) and Follicle
  stimulating hormone (FSH)
• Thyrotrophs
• Thyroid Stimulating Hormone (TSH)
• Lactotrophs
• Release Prolactin
• Somatotrophs
• Release Growth Hormone (GH)

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Hypothalamopituitary adrenal (HPA) axis
(Figure 9-40)
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Adrenal Glands
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Adrenals
CORTEX
Zona Glomerulosa Mineralocorticoids (Aldosterone)
Na, K and water homeostasis
Zona Fasciculata Glucocorticoids
(Cortisol) Glucose homeostasis and many others
Zona Reticularis Sex steroids (androgens)
Medulla Catecholamines Epinephrine,
Norepinephrine, dopamine
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Hypothalamic-Pituitary-Gonadal Axis (HPG) Males
Hypothalamus
GnRH

Anterior Pituitary
Sertoli cells
Leydig cells
(Figure 9-46)
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Hypothalamus
Hypothalamic-Pituitary-Gonadal Axis (HPG)
Females
GnRH
AP
LH
FSH
Tonic LH
LH surge
Progesterone
(Figure 9-47)
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Estrous cycle
Menstrual cycle
(STUDY Figure 9-48)
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Female Hormones

• Estrogens
• Somatic growth
• Mammary growth (after puberty)
• Reproductive organs
• Progesterones
• Mammary tissue growth (after fertilization)
• Reproductive organs Uterus lining
• Maintain corpus luteum
• PGF2a from uterus causes regression of corpous
  luteum

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Mammary Function

• Oxytocin
• Smooth Muscle contraction
• During birth
• Causes contraction of myoepithelial cells,
  allowing milk ejection
• Increases after cervical distention and suckling
• High progesterone inhibits
• Prolactin
• Synthesis of milk proteins
• Growth of mammary glands
• Dopamine and PIH inhibits
• Increased estrogen and low PIH causes increase

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Oxytocin
Neural Pathway to Hypothalamus
Hypothalamus
Posterior Pituitary
Spinal Cord
Capillaries
Oxytocin Release in Blood
Calf Stimulation of Mammary Gland
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Gender Developmental Hormones

• Testosterone
• Testosterone does not make the brain masculine
• Testosterone is converted into estrogen
  (aromatase) in the brain, and estrogen makes the
  brain masculine
• Alpha Feto Protein
• In females, AFP binds to the estrogen, preventing
  estrogen from entering the brain
• If a female animal lacks this AFP, or if estrogen
  levels are synthetically too high, then a female
  may develop a masculine brain

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Gender and Hormones

• AVP in males
• male aggression, mating persistence,
  territoriality, jealousy
• Oxytocin in females
• sexual arousal/receptivity and satiety, bonding,
  nurturing behaviors, social memories
•  males and females release oxytocin and opioids
  during copulation which reduces aggression and
  facilitates social bonding

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Hypothalamothyroid axis

• Tissues become sensitive to epinephrine
• Increase cellular respiration, O2 use and
  metabolism
• Heat is generated
• Thermoregulation
• Growth and developement

(Figure 9-42)
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Thyroid Hormones

• Thyroxine (T4) and 3,5,3-triiodothyronine (T3)
• Formed from 2 iodinnated tyrosines precursers
• Lipd soluble

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Thyroid diseases

• Hypothyroidism
• From low iodine during development causes severe
  retardation in growth (cretinism)
• TSH increases, causing hypertrophy of gland
  (goiter)
• Other forms cause obesity, thinning of hair and
  skin and lethargy, and feeling coldness

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Thyroid Diseases

• Hyperthyroidism
• Overactive thyroid (ex. Graves disease)
• T3 and T4 over secretion
• Propotosis, weight loss, hair loss, hot flashes,
  mood swings

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Pancreatic axis

• Insulin
• ß cells secrete due to high blood glucose levels
• Glucose uptake into tissues increases
• Glucagon
• a cells secrete when blood glucose is low
• Glucose is released from tissues back into blood

(Figure 9-43)
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Diabetes mellitus

• Type I
• Childhood diabetes
• Loss of pancreatic ß cells
• Decreased insulin
• Type II
• Adult diabetes
• Defective signal reception in insulin pathway
• Decreased insulin
• Both cause hyperglycemia, glycosuria, lipid
  breakdown because tissues are deficient in
  glucose, ketone bodies

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Growth hormone

• Control of GH
• Stress, exercise nutrition, sleep
• Somatostatin (SS) inhibits
• GH causes inhibition of glucose uptake and
  utilization, increased a.a. uptake and protein
  synthesis

(Figure 9-44)
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Growth Hormones

• Action of several hormones.
• GH primary job is to stimulate the liver
• To secrete IGF-1 (Insulin Growth Factor)

• IGF-1
• stimulates proliferation of chondrocytes
  (cartilage cells), resulting in bone growth.
• differentiation and proliferation of myoblasts
• Stimulates amino acid uptake and protein
  synthesis in muscle and other tissues.

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Giantism
Robert Wardlow 8 11.

• Excessive GH durining childhood
• Growth plate stimulation

• Tumor of somatotrophs

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Acromegaly

• GH late in life
• Causes excessive growth of flat bones

Rondo Hatton
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Calcium Homeostasis

• Parathyroid
• most important endocrine regulator of calcium and
  phosphorus concentration in extracellular fluid
  (PTH)
• Targets receptors on bones and kidneys
• Calcitonin
• C cells of Thymus
• Decreases mobilization
• and uptake of calcium

Study Figure 9.45
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Calcium Homeostasis
(Figure 9-45)
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Calcium Homeostasis
Parathyroid
C Cells
PTH
Calcitonin
Inhibit
Inhibit
Bone Kidney Intestine
Bone Kidney
Stimulate
Stimulate
Ca
Ca
In plasma
In plasma
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More endocrine fun to come!
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