Unit IV: RegulationEndocrine System

Chapter 16

pp. 541-551; 560

Overview of Cell Communications

Mechanisms:

– gap junctions

• pores in cell membrane allow signaling chemicals to move from cell to cell

– neurotransmitters

• released from neurons to travel across gap to 2nd cell

– paracrine (local) hormones

• secreted into tissue fluids to affect nearby cells

– hormones

• chemical messengers that travel in the bloodstream that exert an influence on target cells

Endocrine Glands

Endocrine vs. Exocrine Glands

• Exocrine glands

– ducts carry secretion to a surface or organ cavity

– extracellular effects

• Endocrine glands

– no ducts, hormones

– intracellular effects

cAMP as 2nd messenger system Ca2+ as 2nd messenger

Hormone Hormone Hormone

G proteinactivated

G proteinactivated

G proteinactivated

cAMP cAMP AMPATP

Opens ionchannels

Activatesenzymes

Reducedenzymeactivity Activates

enzymes

Ca2+

Ca2+Ca2+

Ca2+

Calmodulin

Hormone

Proteinreceptor

G protein(inactive)

G proteinactivated

Endocrine Glands

• Receptors located on cell membrane• Alters activity of enzymes

Endocrine Glands

Nuclearpore

Binds to DNA

Gene activation

Transcription

Receptor

Translation

Alteration of cellularstructure or activity

Target cell response

Diffusion

CYTOPLASM

Receptor

Steroid hormoneThyroid hormone

Target cell response

Alteration of activity

Translation

Transcription

Gene activation

Binds to DNA

Receptor

Receptor

Transport

↑ATPproduction

• Receptors located in ICF• Alters activity of specific genes

Neuron

Nerve impulse

Neurotransmitter

Target cells

Target cells

(b) Endocrine system

(a) Nervous systemEndocrinecells

Hormone inbloodstream

Nervous vs. Endocrine Systems1. Communication

– nervous - electrical– endocrine - only chemical

2. Speed and persistence of response– nervous - reacts quickly; stops quickly– endocrine - reacts slowly

3. Adaptation to long-term stimuli– nervous - response declines– endocrine - response persists

4. Area of effect– nervous - targeted and specific– endocrine - general, widespread effects

Portal vessels

Hypophyseal Portal System

Supraopticnuclei

Paraventricularnuclei

Neurosecretoryneurons

HYPOTHALAMUS

Infundibulum

Posterior lobe ofpituitary gland

Anterior lobe ofpituitary gland

Hypophyseal veins

MEDIAN

EMINENCE

Hypothalamus

• Shaped like a flattened funnel, forms floor and walls of third ventricle of brain

• Regulates primitive functions from water balance to sex drive

• Many functions carried out by pituitary gland– Hypophyseal portal system– Hypothalamo-hypophyseal tract

Hypothalamic Hormones

•Transported to posterior lobe of pituitary–Antidiuretic hormone (ADH)–Oxytocin (OXT)

•Stimulate the anterior pituitary to release its hormones–Thyrotropin-releasing hormone release of TSH & PRL–Corticotropin-releasing hormone release of ACTH–Gonadotropin-releasing hormone release of FSH & LH–Growth hormone-releasing hormone release of GH

•Inhibit the anterior pituitary from releasing its hormones–Prolactin-inhibiting factor inhibits release of PRL–Somatostatin /GH-IH inhibits release of GH & TSH

HypothalamusIndirect Control through Releaseof Regulatory Hormones

Direct Releaseof Hormones

Sensorystimulation

Osmoreceptorstimulation

Posterior lobeof pituitary gland

Kidneys

Males: Smoothmuscle in ductusdeferens andprostate gland

Females: Uterinesmooth muscle andmammary glands

Melanocytes (uncertainsignificance in healthyadults)Ovaries

of femaleTestesof maleMammary

glands

Bone, muscle,other tissues

Thyroidgland

Adrenalglands

Adrenal cortex Anterior lobe ofpituitary gland

ACTH

TSH GH

PRLFSH LH MSH

OXT

ADH

Liver

Somatomedins

Corticosteroids

Thyroidhormones

Inhibin Testosterone Estrogen Progesterone Inhibin

Corticotropin-releasinghormone(CRH)

Thyrotropin-releasinghormone

(TRH)

Growthhormone-releasinghormone(GH-RH)

Prolactin-inhibitinghormone

(PIH)

Gonadotropin-releasinghormone(GnRH)

Pituitary/Hypophysis Hormones

Stimulation

Inhibition

Stimulates growth of skeletal muscle,cartilage, and many other tissues

Epithelia,adipose tissue,liver

Anteriorlobe

GH

GH-IH

GH-RH

Liver

Somatomedins

Growth Hormone (Somatotropin)

Promotes tissue growth– stimulates liver to produce IGF-I and II

• protein synthesis – proteins synthesized– enhances amino acid transport

into cells• lipid metabolism

– stimulates FFA and glycerol release from adipocytes

• CHO metabolism– glucose sparing effect

• Electrolyte balance– promotes Na+, K+, Cl- retention,

Ca 2+ absorption

Growth Hormone and Aging

• Childhood and adolescence

– bone, cartilage and muscle growth

– Stimulates growth at epiphyseal plates

• Adulthood

– increase osteoblastic activity and appositional growth

– aging of tissues

• Levels of GH

– higher during deep sleep, after vigorous exercise, after high protein meals

– lower after high CHO meals

Pineal Gland

• Peak secretion ages 1-5; by puberty 75% lower

• Produces serotonin by day, converts it to melatonin at night

• May regulate timing of puberty in humans

• Melatonin in SAD & PMS by phototherapy

Thymus

• Involution after puberty

• Regulate development and activation of T-lymphocytes– Thymopoietin, thymosins, and thymulin