ex. 27: the endocrine system - fau.pearlashes.comfau.pearlashes.com/anatomy/sharon/sharon ex 27...

Copyright 2009, John Wiley & Sons, Inc.

Ex. 27: The Endocrine System


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


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


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


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


Hypothalamus and pituitary gland


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


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


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


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


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)


Hypothalamohypophyseal tract

Osmoreceptors

High blood osmoticpressure stimulateshypothalamicosmoreceptors

1

Osmoreceptors


Osmoreceptorsactivate theneurosecretory cellsthat synthesize andrelease ADH

Hypothalamus

1

2Osmoreceptors


Nerve impulsesliberate ADH fromaxon terminals inthe posteriorpituitary intothe bloodstream


Hypothalamus

ADH

1

2

3

Osmoreceptors




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


Low blood osmoticpressure inhibitshypothalamicosmoreceptors



Hypothalamus




ADH

Target tissues

1

2

3

4

5

Osmoreceptors


Low blood osmoticpressure inhibitshypothalamicosmoreceptors



Hypothalamus

Inhibition of osmo-receptors reduces orstops ADH secretion




ADH

Target tissues

1

2

3

4

5

6


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)


Thyroid gland


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


Parathyroid glands


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


Adrenal glands


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


Pancreas


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


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


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

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