Endocrine System

1
Endocrine System

• Hormones (horman, to urge on)
• Transport via bloodstream
• Chemical composition
• Proteins, peptides and amines
• Steroids
• Mechanisms of action
• P, P and A membrane receptors (Fig. 3-2)
• Steroids intracellular (nuclear) receptors
  (Fig. 3-3)

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The Master Endocrine Gland

• Pituitary
• Attached to hypothalamus by infundibulum
• Anterior lobe (adenohypophysis)
• Embryonic origin Rathkes pouch (Fig. 3-6)
• Releases 7 hormones (including gonadotropins)
• Posterior lobe (neurohypophysis)
• Embryonic origin extension of hypothalamus
• Releases 2 hormones (including oxytocin)

3
Gonadotropins

• Luteinizing hormone
• Follicle-stimulating hormone
• Effects on ovarian follicles
• LH steroidogenesis
• FSH gametogenesis
• Target cells
• LH thecal cells (androgen synthesis)
• FSH granulosa cells (nurse cells)

4
Ovarian follicles

• Primordial follicle
• Primary follicle
• Secondary follicle
• Tertiary follicle (inc. Graafian)
• Corpus Luteum

5
Hypothalamus

• Relation to posterior pituitary (Fig. 3-7)
• Effects on anterior pituitary
• Hypophyseal portal vasculature
• Releasing and inhibiting factors
• Gonadotropin-releasing hormone (GnRH)
• Pulsatile pattern of secretion
• Sensitivity to sex hormones
• Negative feedback
• Positive feedback
• Role of psychic factors, nutrition

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Puberty

• Prior to puberty, gonadotropin (and GnRH) release
  is insignificant
• At puberty, regular pulses of GnRH, followed by
  gonadotropins, occurs
• Trigger for puberty?
• Gonadostat hypothesis
• Nutrition hypothesis

7
Nutrition

• Critical body weight must be attained before
  activation of the reproductive system.
• even though age of menarche is decreasing, the
  average body weight of menarche remains the same
• obese girls go through early menarche
• malnutrition is associated with delayed menarche
• primary amenorrhea common in lean female athletes
• bodyfat setpoint very noticeable in girls with
  fluctuating body weight due to anorexia nervosa

8
Menstrual cycle

• Rhythmic fluctuations of hormones from
• Hypothalamus
• Anterior pituitary
• Ovaries
• Morphological changes in ovary, endometrium
• ovarian cycle follicular, ovulatory, luteal
  phases
• endometrial cycle proliferative, secretory and
  menstrual phases

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Ovarian cycle Follicular phase

• Secondary, tertiary follicles develop
• began developing in previous cycle
• Require FSH, LH for survival
• E secretion is increasing
• Negative feedback (E, inhibin) is present low
  FSH
• Results in atresia (follicle death) of larger
  follicles
• Graafian survives
• More FSH receptors?
• Better vascular supply?

10
Ovarian cycleOvulation

• Triggered by LH surge from pituitary
• Effects of LH surge
• 1st meiotic division of egg
• Luteinization of granulosa cells progesterone
  secretion
• Rupture of follicle (indirect effect exerted
  through progesterone)
• What causes LH surge?

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Ovarian cycleOvulation

• Graafian follicle secretes E surge
• E surge exerts positive feedback
• GnRH surge
• Increased pituitary sensitivity to GnRH
• LH surge
• Result rupture of follicle
• Egg is swept into oviduct by fimbriae, cilia of
  oviduct

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Ovarian CycleLuteal Phase

• Corpus luteum now present
• P and E secreted
• Unique ratio of PE inhibits GnRH secretion
• LH, FSH at lowest levels
• Lifespan of corpus luteum approx. 14 days
• Demise of CL causes menstruation, start of next
  cycle

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Endometrial CycleProliferative phase

• 2 layers present superficial and basal
• Superficial layer
• constitutes 2/3 of endometrium
• responds to steroids
• Contains glands
• Basal layer doesnt change
• During prolif. phase, lots of cell division
  within superficial layer
• New epithelial cells fill uterine cavity
• Caused by E production during follicular phase of
  ovarian cycle

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Endometrial CycleSecretory Phase

• Glands in superficial layer dilate
• Filled with secretions (glycogen, fat)
• Will serve as nutritive source if embryo appears
• Epithelial cells continue to proliferate (2x
  increase in thickness)

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Endometrial cycleMenstrual phase

• Result of decrease in P, E support
• Superficial layer is broken down, shed
• Menstrual fluid produced
• Endometrial cells
• Glandular secretions
• Blood
• Bleeding is result of spiral arteries that
  originate in basal layer

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Predicting ovulation

• Calendar method
• Cervical mucus
• Ovulatory pain
• Body temperature

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