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Copyright 2009, John Wiley & Sons, Inc.
Ex. 27: The Endocrine System
Copyright 2009, John Wiley & Sons, Inc.
Nervous and endocrine systems Act together to coordinate functions of all body systems Nervous system
Nerve impulses & neurotransmitters (some neurotransmitters are hormones) Faster responses Briefer effects Specific targets
Endocrine system Hormone = mediator molecule
Released in 1 part of the body but regulates activity of cells in other parts
Slower responses Longer-lasting effects Broader influence
Copyright 2009, John Wiley & Sons, Inc.
Endocrine glands/organs 2 kinds of glands/organs
Exocrine – ducted Secretions to body cavities … lumen of an organ … outer body surface
Endocrine – ductless Hormones secreted into interstitial fluid Diffuse into blood; bind to target receptors Include:
Exclusive endocrine glands/organs: Pituitary Thyroid Parathyroid Adrenal Pineal glands
Nonexclusive glands/organs: Hypothalamus Thymus Pancreas Ovaries Testes Kidneys Stomach Liver Small intestine Skin Heart Adipose tissue Placenta
Copyright 2009, John Wiley & Sons, Inc.
Copyright 2009, John Wiley & Sons, Inc.
Hormone types Circulating (majority) Circulating in blood
throughout body Last a relatively long
period Local Act locally
Paracrine Act on neighboring cells
Autocrine Act on the same cell that
secreted them E.Gs.: IL-2, NO
Inactivated quickly
Copyright 2009, John Wiley & Sons, Inc.
Hypothalamus and pituitary gland Hypothalamus
The major link between nervous and endocrine system Master control gland Nine known hormones secreted from cells targeted to the pituitary gland
Releasing hormones (‘-RH’) Inhibitory hormones
Neurons Pituitary gland
Attached to hypothalamus by infundibulum (neck or stalk) Seven hormones secreted Anterior pituitary (adenohypophysis)
Pars distalis: larger portion Pars tuberalis: forms sheath around infundibulum
Posterior pituitary (neurohypophysis) Pars nervosa: larger portion Infundibulum: axons travel through
Pars intermedia Atrophies during fetal development Some cells migrate to anterior pituitary & persist
Copyright 2009, John Wiley & Sons, Inc.
Hypothalamus and pituitary gland
Copyright 2009, John Wiley & Sons, Inc.
Anterior pituitary Release of hormones stimulated by releasing
and inhibiting hormones from the hypothalamus Also regulated by negative feedback Anterior pituitary hormones: tropic Act on other endocrine cells, glands, organs
5 types of cells: Somatotrophs Thyrotrophs Gonadotrophs Lactotrophs Corticotrophs
Copyright 2009, John Wiley & Sons, Inc.
Hormones of the anterior pituitary Somatotroph secretions:
Human growth hormone (hGH) or somatostatin Stimulates secretion of insulin-like growth factors (IGFs)
Promote growth, protein synthesis
Thyrotroph secretions: Thyroid-stimulating hormone (TSH) or thyrotropin
Stimulates synthesis and secretion of thyroid hormones by thyroid Gonadotroph secretions:
Follicle-stimulating hormone (FSH) Ovaries: initiates development of oocytes Testes: stimulates testosterone production
Luteinizing hormone (LH) Ovaries: stimulates ovulation Testes: stimulates testosterone production
Copyright 2009, John Wiley & Sons, Inc.
Hormones of the anterior pituitary Lactotroph secretions: Prolactin (PRL)
Promotes milk secretion by mammary glands
Corticotroph secretions: Adrenocorticotropic hormone (ACTH) or
corticotropin Stimulates glucocorticoid secretion by adrenal cortex
Melanocyte-stimulating Hormone (MSH) “Unknown” role in humans Probable role in stimulating melanocytes but mechanism
is not understood Corticotrophs are remanants from pars intermedia
Copyright 2009, John Wiley & Sons, Inc.
Other anterior pituitary hormones Gonadotrophs: stimulated by GnRH (more later)
FSH Ovaries:
Monthly stim. of follicular development Monthly stim. of E2 secretion by follicular cells
Testes: Stim. sperm production
LH Ovaries:
Monthly stim. of E2 secretion by follicular cells Monthly triggering of ovulation
Monthly stim. of CL formation & P4 secretion Testes:
Stim. of testosterone secretion Prolactin: more later ACTH: more later MSH
Increased melanin secretion in amphibians Presence of receptors in brain but little circulating MSH in blood
Increased MSH does lead to skin darkening Possibly has brain metabolic regulatory function of some kind in humans
Copyright 2009, John Wiley & Sons, Inc.
Posterior pituitary Does not synthesize hormones
Stores and releases hormones made by the hypothalamus Transported along hypothalamohypophyseal tract Intersection with nervous system
Produced in neurosecretory cells Packaged in secretory vesicles Moved by fast axonal transport to axon terminals in post. pit. Axon terminals associated with specialized neuroglia (pituicytes)
Blood flow: Internal carotid arteries – inferior hypophyseal arteries – capillary plexus of infundibular process
– posterior hypohyseal veins – general circulation Examples
Oxytocin (OT) Synthesized in paraventricular nucleus (neurosecretory cells) During and after delivery of neonate Effects uterus and breasts
Enhances smooth muscle contraction in wall of uterus Stimulates milk ejection from mammary glands
Antidiuretic hormone (ADH) or vasopressin Synthesized in supraoptic nucleus (neurosecretory cells) Decreases urine production by causing the kindeys to return more water to the blood Also decreases water lost through sweating and constriction of arterioles which increases blood
pressure (vasopressin)
Copyright 2009, John Wiley & Sons, Inc.
Hypothalamohypophyseal tract
Osmoreceptors
High blood osmoticpressure stimulateshypothalamicosmoreceptors
1
Osmoreceptors
High blood osmoticpressure stimulateshypothalamicosmoreceptors
Osmoreceptorsactivate theneurosecretory cellsthat synthesize andrelease ADH
Hypothalamus
1
2Osmoreceptors
High blood osmoticpressure stimulateshypothalamicosmoreceptors
Nerve impulsesliberate ADH fromaxon terminals inthe posteriorpituitary intothe bloodstream
Osmoreceptorsactivate theneurosecretory cellsthat synthesize andrelease ADH
Hypothalamus
ADH
1
2
3
Osmoreceptors
High blood osmoticpressure stimulateshypothalamicosmoreceptors
Nerve impulsesliberate ADH fromaxon terminals inthe posteriorpituitary intothe bloodstream
Osmoreceptorsactivate theneurosecretory cellsthat synthesize andrelease ADH
Hypothalamus
Sudoriferous(sweat) glandsdecrease waterloss by perspirationfrom the skin
Arterioles constrict,which increasesblood pressure
Kidneys retainmore water,which decreasesurine output
ADH
Target tissues
1
2
3
4
Osmoreceptors
High blood osmoticpressure stimulateshypothalamicosmoreceptors
Low blood osmoticpressure inhibitshypothalamicosmoreceptors
Nerve impulsesliberate ADH fromaxon terminals inthe posteriorpituitary intothe bloodstream
Osmoreceptorsactivate theneurosecretory cellsthat synthesize andrelease ADH
Hypothalamus
Sudoriferous(sweat) glandsdecrease waterloss by perspirationfrom the skin
Arterioles constrict,which increasesblood pressure
Kidneys retainmore water,which decreasesurine output
ADH
Target tissues
1
2
3
4
5
Osmoreceptors
High blood osmoticpressure stimulateshypothalamicosmoreceptors
Low blood osmoticpressure inhibitshypothalamicosmoreceptors
Nerve impulsesliberate ADH fromaxon terminals inthe posteriorpituitary intothe bloodstream
Osmoreceptorsactivate theneurosecretory cellsthat synthesize andrelease ADH
Hypothalamus
Inhibition of osmo-receptors reduces orstops ADH secretion
Sudoriferous(sweat) glandsdecrease waterloss by perspirationfrom the skin
Arterioles constrict,which increasesblood pressure
Kidneys retainmore water,which decreasesurine output
ADH
Target tissues
1
2
3
4
5
6
Copyright 2009, John Wiley & Sons, Inc.
Thyroid gland (Table 18.6) Located inferior to larynx
2 lobes connected by isthmus Thyroid follicles produce thyroid hormones
Spherical sacs of follicular cells; surrounded by basement membranes Functions of thyroid hormones:
Increase BMR Stim. use of cellular O2 to produce ATP Increase use of glucose and fatty acids for ATP production Tetraiodothyronine (T4) = thyroxin Triiodothyronine (T3)
Stim. synth. of additional NA+/K+ pumps which use more ATP Stim. protein synth. & increase use of glucose & f.a.s for ATP prod. Enhanced action of catecholamines Synergistic w/GH & insulin
Parafollicular cells (C cells) produce calcitonin Between follicles Lowers blood Ca2+ by inhibiting bone resorption (inhibit osteoclasts)
Copyright 2009, John Wiley & Sons, Inc.
Thyroid gland
Copyright 2009, John Wiley & Sons, Inc.
Parathyroid glands Embedded in lobes of thyroid gland
Usually 4: superior & inferior posteriorly on ea. lateral thyroid lobe
Two epi. cell types Chief cells: parathyroid hormone (PTH) = parathormone Oxyphil cell: unk. func.
Parathyroid hormone (PTH) or parathormone Major regulator of Ca2+, Mg 2+, and HPO4
2- ions in the blood
Blood calcium level directly controls secretion of both calcitonin and PTH via negative feedback
Copyright 2009, John Wiley & Sons, Inc.
Parathyroid glands
Copyright 2009, John Wiley & Sons, Inc.
Adrenal glands Superior to each kidney; retroperitoneal cavity 2 structurally and functionally distinct regions
Adrenal cortex (peripheral layer); 80-90% of gland 3 zones
Zona glomerulosa Mineralocorticoids effect mineral homeostasis
Aldosterone Homeostasis of Na+ & K+ BP & blood V
Zona fasciculata Glucocorticoids effect glucose homeostasis
Cortisol Zona reticularis
Weak androgens Masculinizing effects (testosterone-like hormones) Dehydroepiandrosterone (DHEA): only important in females: libido, conversion to E2 masked in males by T after puberty
Adrenal medulla (deep layer); central core Modified sympathetic ganglion of ANS
Epinephrine (adrenaline) and norepinephrine (NE; noradrenalin) from chromaffin cells Intensify sympathetic responses
Copyright 2009, John Wiley & Sons, Inc.
Adrenal glands
Copyright 2009, John Wiley & Sons, Inc.
Pancreatic islets Both exocrine and endocrine gland Roughly 99% of cells produce digestive enzymes Pancreatic islets (Islets of Langerhans)
Alpha (A) cells Glucagon
Raises blood sugar Beta (B) cells
Insulin Lowers blood sugar
Delta (D) cells Somatostatin
Inhibits both insulin and glucagon F cells
Pancreatic polypeptide Inhibits somatostatin Gallbladder contraction Secretion of pancreatic digestive enzymes
Copyright 2009, John Wiley & Sons, Inc.
Pancreas
Copyright 2009, John Wiley & Sons, Inc.
Ovaries and testes Gonads – produce gametes and hormones
Ovaries Oocytes & follicles Hormones:
Estradiol (E2) and estrone (E1) Progesterone (P4; also from placenta) Roles of E2 & P4:
Regulate menstrual cycle with FSH & LH (E2 & P4) Maintain pregnancy w/ hCG (P4) Prepare mammary glands for lactation (E2 & P4) Maintain female secondary sex characteristics (E2 & P4)
Inhibin: inhibit FSH Relaxin (also from placenta) produced at highest levels during later pregnancy:
loosens ligaments; allows some softening of bone Testes
Sperm & seminal fluid Testosterone
Regulates sperm production Maintains male secondary sex characteristics
Inhibin: inhibit FSH FSH stimulates testosterone production
Copyright 2009, John Wiley & Sons, Inc.
Pineal gland Attached to roof of 3rd ventricle of brain at
midline Masses of neuroglia and pinealocytes Melatonin
Amine hormone Derived from serotonin
Appears to contribute to circadian rhythm More melatonin liberated during darkness than light Sleepiness
Copyright 2009, John Wiley & Sons, Inc.
Thymus Thymus
Located behind sternum between the lungs Hormonal secretions are involved in T-cell maturation:
Thymosin Thymic humoral factor (THF) Thymic factor (TF) Thymopoietin