slide set 3.2 - chapter 6 and 7 (homeostasis)

  1. regulation of hormone secretion
    usually part negative feedback loop

    • Simplest mechanism
    • when an endocrine gland is sensitive to the physiological changes produced by its target cells
    • ex. PTH = ↑ plasma calcium

    • endocrine secretion may also be regulated by a hormone produced by another gland
    • ex. estrogen form ovary feeds back to Pit to regulate FSH
  2. negative feedback control
    • 1. plasma concentration of thyroid hormones ↓ (ex. T4 AND T3)
    • 2. the anterior pituitary secretes TSH
    • 3. thyroid in turn secretes TH
    • 4. TH inhibits further secretion of TSH
  3. parathyroid hormone
    • PTH controls blood calcium concentration (Ca++)
    • acts to ↑ while calcitonin works to ↓

    • due to lactation, blood Ca concentration is ↓
    • the change is sensed by the parathyroid
    • PTH stimulates osteoclasts in bone to release more Ca++ from storage in bone tissue
    • this ↑ maternal blood Ca++ concentration to set point
  4. hypothalamus
    • 1. integrates functions that maintain chemical and temperature homeostasis
    • function with the limbic system
    • 2. controls the release of hormones form the anterior and posterior pituitary
  5. temperature regulation is a good example of a hypothalamic servo-control system
    • to regulate temperature, integration of autonomic endocrine and skeblemotor must occur
    • the set point for the body is normal temperature
    • the hypothalamus contains "feedback detectors" that come from 2 sources:
    • 1. peripheral receptors: transmit information through temperature pathways to the CNS
    • 2. central receptors : located in the anterior hypothalamus
  6. distinct region of the hypothalamus mediate heat dissipation and heat conservation
    the anterior hypothalamus = mediates decreases ↓ in heat

    lesions = cause hyperthermia

    • Electrical stimulations cause:
    • dilatation of blood vessels in the skin
    • panting
    • suppression of shivering

    the posterior hypothalamus = mediates heat conversion

    lesions = cause hypothermia is an animal is placed in a cold environment

    • Microstimulation causes:
    • shivering
    • constriction of blood vessels in skin
  7. how does the hypothalamus contribute to food intake?
    • the hypothalamus is sensitive ti adiposity signals supplied by hormones leptin (secreted by fat cells) and insulin (secreted by pancreas)
    • leptin plays a role  in establishing a biological set point for body weight  by modifying the strength in synapses onto neurons
  8. a model for energy homeostasis
    • adiposity signals = modulate anabolic and catabolic pathways in the central nervous system (CNS)
    • these pathways control food intake and energy expenditure by influencing behaviour, autonomic activity and metabolic rate
    • satiety signals = terminate feeding
    • energy balance and fat = control the amounts of leptin and insulin circulating in the blood (adiposity signals)
  9. hypothalamic neuropeptides that influence caloric homeostasis
    • 2 adiposity signals, insulin and leptin, are produced in the periphery and travel through the blood to influence neurons in the arcuate nucleus
    • some arcuate neurons synthesize and release peptide y (NPY) and agouti-related protein (AgRP) and are inhibited by adiposity signals
    • other arcuate neutrons make and release alpha-melanocyte-stimulating hormone (alpha-MSH) and cocaine-amphetamine-related-transcript (CART) and are stimulated by adiposity signals
    • NPY/AgRP neurons inhibit the paraventricular nucleus (PVN) and stimulate the lateral hypothalamic area (LHA)
    • alpha-MSH/CART neurons do the opposite
    • the PVN has a net catabolic action, releasing the neuropeptides CRH and oxytocin and thereby ↓ food intake and ↑ energy expenditure
    • the LHA has a net anabolic action, releasing 2 additional neuropeptides, orexin A and melanin-concentrating hormone (MCH), both which will stimulate food intake ↑ and ↓ energy expenditure

  10. hypothalamic releasing hormones
    • 7 hormones are made in the hypothalamus
    • 1. TRH
    • 2. CRH
    • 3. GnRH
    • 4. GHRH
    • 5. GHIH
    • 6. PRF
    • 7. PIH
  11. pituitary gland
    • small but potent
    • located in a well protected location in the brain
    • located on the ventrical surface of the brain within the skull

    • Infundibulum
    • stemlike stalk that connects pituitary to the hypothalamus

    • the pituitary gland is made of 2 separate glands = anterior gland and posterior
    • gland
  12. hypophyseal portal system
    portal systems = 2 capillary networks in serial arrangements

    portal veins = blood vessels that link 2 capillary networks
  13. anterior pituitary glands : 5 secretory cells and their trophic hormones
    adenohypophysis (anterior pituitary)

    • Divided in 2 parts:
    • 1. pars anterior = forms the major portion of the adenohypophysis
    • 2. pars intermedia

    tissue is composed of irregular clumps of secretory cells supported by fine connective tissue fibres and surrounded by a rich vascular network

    • 5 secretory cells exits in the anterior pituitary:
    • 1. Somatotrophs*
    • secrete GH (growth hormones)
    • 2. Corticotrophs
    • secretes ACTH (adrenocorticotropic hormone)
    • 3. Thyrotrophs
    • secrete TSH
    • 4. Lactotrophs*
    • secrete prolactin (PRL)
    • 5. Gonadotrophs
    • secrete LH and FSH

    Growth hormone (GH) , which are produceed by Somatotrophs, promotes growth by stimulating the liver to produce growth factors that accelerate amino acid transport into the cells

    • GH promotes growth of bone, muscle, and other tissues by accelerating amino acid transport into the cells
    • all process involve protein metabolism
    • GH also stimulates lipid metabolism
    • accelerates the mobilization of lipids from cells speeds up lipid catabolism
    • this shifts a cells use of nutrients from glucose catabolism → lipid catabolism

    • Prolactin (PRL)
    • produced by lactotrophs (acidophils) in the anterior pituitary

    • Pregnancy
    • during pregnancy, PRL promotes development of breasts, anticipating milk secretions

    • After birth
    • PRL stimulates the mothers mammary glands to produce milk
  14. Anterior pituitary - Tropic hormones
    • Tropic hormones
    • have a stimulating effect on other endocrine glands
    • stimulates syntesis and secretion of the target hormone

    4 trophic hormones are produced and secreted by the basophils of the pars anterior

    • 1. TSH
    • promotes and maintains growth and development of the thyroid
    • causes the thyroid to secrete hormones T3 and T4
    • the thyroid regulates metabolism

    • 2. ACTH
    • promotes and maintains normal growth and development of cortex of the adrenal gland
    • also stimulates adrenal cortex to secrete some of its hormones cortisol and aldosterone (act on kidneys)

    • 3. FSH
    • in females = acts on ovaries 
    • stimulates follicle cells to grow towards maturity 
    • stimulates follicle cells to secrete estrogen
    • in males = development of testes and maintains spermatogenesis
    • acts on Sertoli cells

    • 4. LH
    • in females = stimulates formation and activity of  ovaries
    • corpus lutenum = secretes progesterone and estrogen when stimulated by LH
    • LH also supports FSH in stimulating maturation of follicle 
    • in males = LH secretes interstitial cells in testes to develop and secrete testosterone

    • FSH and LH = gonadotropins
    • because they stimulate growth and maintenance of gonads

  15. control of the anterior pituitary by releasing hormones from the hypothalamus
    • releasing hormones = influence the secretion of hormones by acidophils and basophils
    • negative feedback= this is how the hypothalamus adjusts secretions of the anterior pituitary → adjust secretions of target glands → adjusts activity of their
    • target tissues
  16. what happens to FSH levels at menopause?
    (estrogen progesterone feedback)
    they rise ↑
  17. Hypophyseal portal system
    • hypothalamus secretes releasing hormones into the blood
    • then are carried directly to the hypophyseal portal system

    the hypophyseal portal system = carries blood from the hypothalamus directly to adenohypophysis where target cells of releasing hormones are located
  18. endocrine control = 3 levels of integration
    • hypothalamus stimulation - from CNS
    • pituitary stimulation - from hypothalamic trophic Hs
    • endocrine gland stimulation - from pituitary trophic Hs
  19. multiple hormones can target a cell/tissue
    • ex.:
    • GH
    • somatomedins
    • thyroxin

    • all have receptors on many tissues
    • stimulate pathways for growth
  20. relationship between the hypothalamus and the posterior pituitary
    • neurosecretory cells have their bodies directly in the hypothalamus and their axon terminals in the posterior pituitary
  21. The big picture : the endocrine system and the whole body
    • neuroendocrine system adjusts nutrient supply
    • calcitonin, a parathyroid hormone, and vitamin D balance calcium ion use
    • nervous system and endocrine system regulate reproduction
Card Set
slide set 3.2 - chapter 6 and 7 (homeostasis)