• Chemical– Autocrine & Paracrine: local signaling– Endocrine system: distant, diffuse target

• Electrical– Gap junction: local– Nervous system: fast, specific, distant target

Cell to Cell Communication:

Paracrines and Autocrines

• Local communication • Signal chemicals

diffuse to target• Example: Cytokines

– Autocrine–receptor on same cell

– Paracrine–neighboring cells

Figure 6-1c: Direct and local cell-to-cell communication

• Signal Chemicals

• Made in endocrine cells

• Transported via blood

• Receptors on target cells

Long Distance Communication: Hormones

Figure 6-2a: Long distance cell-to-cell communication

• Neurons– Electrical signal down axon– Signal molecule (neurotransmitter) to target cell

• Neurohormones– Chemical and electrical signals down axon– Hormone transported via blood to target

Long Distance Communication: Neurons and Neurohormones

Figure 6-2 b: Long distance cell-to-cell communication

Long Distance Communication: Neurons and Neurohormones

Figure 6-2b, c: Long distance cell-to-cell communication

Gap Junctions and CAMs• Protein channels -

connexin

• Direct flow to neighbor– Electrical- ions (charge)– Signal chemicals

• CAMs – Need direct surface

contact– Signal chemical

Figure 6-1a, b: Direct and local cell-to-cell communication

Signal Pathways

• Signal molecule (ligand)

• Receptor

• Intracellular signal

• Target protein

• Response

Figure 6-3: Signal pathways

Endocrine Reflex Pathways: Overview

Figure 7-9: Hormones may have multiple stimuli for their release

Receptor locations• Cytosolic or Nuclear

– Lipophilic ligand enters cell

– Often activates gene

– Slower response

• Cell membrane– Lipophobic ligand

can't enter cell

– Outer surface receptor

– Fast response Figure 6-4: Target cell receptors

• Membrane associated enzymes– External reactions– Internal reactions

• Receptors bind specific ligand– Example:

Hormones– Cell recognition

moleculesFigure 5-6: Cell membrane receptor

Homeostasis & Controls

• Successful compensation– Homeostasis

reestablished

• Failure to compensate– Pathophysiology

• Illness• Death

Figure 1-5: Homeostasis

ENDOCRINE SYSTEM

• Uses chemical signals for cell to cell communication

• Coordinates the function of cells

• Response to an endocrine signal occurs within minutes to hours

Chemical Regulating Systems: Overview

• Pheromones: organism to organism communication

• Hormones: cell to cell communication molecules– Made in gland(s) or cells– Transported by blood– Distant target tissue receptors– Activates physiological response

HORMONE CLASSIFICATION

• Protein and polypeptide

• Amine

• Steroid

PEPTIDE HORMONES

• Consist of specific amino acids

• Synthesized as large precursor proteins

• Stored in membrane-enclosed compartments

• Hydrophillic

• Surface receptor• Hormone binds• Transduction• Enzyme activation• Open channels• Second messenger

systems• Synthesis

Protein and Polypeptide Hormone Receptors

Figure 7-5: Membrane receptors for peptide hormones

Receptors– Surface– Intracellular

• Small size, OH group

• Benzine ring

• Examples– Thyroxin– Epinephrine

Amine Hormones

STEROID HORMONES

• Precursor: Cholesterol

• Lipophillic

• Immediately released from the cell following synthesis

• Cytoplasmic or nuclear receptors (mostly)

• Activate DNA for protein synthesis

• Slower acting, longer half-life

• Examples: cortisol, estrogen & testosterone

Steroid Hormones

Steroid Hormones: Action

Figure 7-7: Steroid hormone action

Summary of the Endocrine System

Figure 7-2-1: ANATOMY SUMMARY: Hormones

HYPOTHALAMUS

• Integrates functions that maintain chemical and temperature homeostasis

• Functions with the limbic system

• Controls the release of hormones from the anterior and posterior pituitary

HYPOTHALAMUS

• Synthesizes hypophysiotropic hormones in cell bodies of neurons located in the hypothalamus

• Transports hormones down the axon and stored in the nerve endings

• Secretion of hormones is in pulses

HYPOTHALAMUS: Secretion of Hypophysiotropic Hormones

• Is influenced by emotions

• Can be influenced by the metabolic state of the individual

• Delivered to the anterior pituitary via the hypothalamic-hypophyseal portal system

• Usually initiates a three-hormone sequence

Figure 11-3: Autonomic control centers in the brain

HYPOTHALAMUS

Synthesizes & releases hypophysiotropic hormones:– Thyrotropin-releasing hormone (TRH)– Corticotropin-releasing hormone (CRH)– Gonadotropin-releasing hormone (GnRH)– Growth hormone-releasing hormone (GHRH)– Growth hormone-inhibiting hormone (GHIH)– Prolactin-releasing factor (PRF)– Prolactin-inhibitn hormone (PIH)

Endocrine Control: Three Levels of Integration

Figure 7-13: Hormones of the hypothalamic-anterior pituitary pathway

Negative Feedback Controls: Long & Short Loop Reflexes

Figure 7-14: Negative feedback loops in the hypothalamicanterior

pituitary pathway

Negative Feedback Controls: Long & Short Loop Reflexes

Figure 7-15: Control pathway for cortisol secretion

ANTERIOR PITUITARY HORMONES

Growth Hormone (GH, Somatotropin): primary hormone responsible for regulating body growth, and is important in metabolism

Thyroid-stimulating Hormone (TSH): stimulates secretion of thyroid hormone & growth of thyroid gland

Adrenocorticotropic Hormone (ACTH): stimulates cortisol secretion by the adrenal cortex & promotes growth of adrenal cortex

ANTERIOR PITUITARY

Follicle-stimulating Hormone (FSH): Females: stimulates growth & development of ovarian follicles, promotes secretion of estrogen by ovaries. Males: required for sperm production

Luteinizing Hormone (LH): Females: responsible for ovulation, formation of corpus luteum in the ovary, and regulation of ovarian secretion of female sex hormones. Males: stimulates cell in the testes to secrete testosterone

Prolactin: Females: stimulates breast development and milk production. Males: involved in testicular function

• Hypothalamic stimulation–from CNS • Pituitary stimulation–from hypothalamic trophic Hs• Endocrine gland stimulation–from pituitary trophic

Hs

Endocrine Control: Three Levels of Integration

Pathologies: Over or Under Production

Figure 7-19: Negative feedback by exogenous cortisol

POSTERIOR PITUITARY

Comprised of the endings of axons from cell bodies in the hypothalamus (supraoptic and paraventricular)

Axons pass from the hypothalamus to the posterior pituitary via the hypothalamohypophysial tract

Posterior pituitary hormones are synthesized in the cell bodies of neurons in the supraoptic and paraventricular nuclei

POSTERIOR PITUITARY

Hormones synthesized in the hypothalamus are transported down the axons to the endings in the posterior pituitary

Hormones are stored in vesicles in the posterior pituitary until release into the circulation

Principal Hormones: Vasopressin & Oxytocin

Figure 7-12: Synthesis, storage, and release of posterior pituitary hormones

POSTERIOR PITUITARY

Oxytocin:

Synthesized as the precursor hormone: prepro-oxyphysin

Action primarily on the breasts and uterus

Increases contraction of smooth muscle of Vas Deferens

POSTERIOR PITUITARY

Vasopressin

Plasma osmolality is monitored by osmoreceptors in the hypothalamus

Increases in plasma osmolality stimulates secretion of vasopressin

Small changes above normal plasma osmotic pressure ( 285 mosm/kg) stimulate release of vasopressin

POSTERIOR PITUITARY

Vasopressin secretion also stimulated by:

1. Large decreases in blood volume

2. Decreases in blood pressure

POSTERIOR PITUITARY

Vasopression Action:

Decreases water excretion by kidneys (V2 receptors)

Constricts blood vessels (V1 receptors)

Increases adrenocorticortropin Hormone (V1B receptors)