Lecture 20, Ch. 45

Lecture #20

Date _______

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Chapter 45 ~ Chemical Signals in Animals

Regulatory systems ◆

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Hormone~ chemical signal secreted into body fluids (blood) communicating regulatory messages Target cells~ body cells that respond to hormones Endocrine system/glands~ hormone secreting system/glands (ductless); exocrine glands secrete chemicals (sweat, mucus, enzymes) through ducts Neurosecretory cells~ actual cells that secrete hormones Feedback mechanisms ~ negative and positive

Local regulators: cells adjacent to or near point of secretion ◆

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Growth factors ~ proteins for cell proliferation Nitric oxide (NO) ~ neurotransmitter; cell destruction; vessel dilation Prostaglandins ~ modified fatty acids secreted by placenta and immune system; also found in semen

Mode of Action: Chemical Signaling ◆

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1- Plasma membrane reception • signal-transduction pathways (neurotransmitters, growth factors, most hormones) 2- Cell nucleus reception • steroid hormones, thyroid hormones, some local regulators

Vertebrate Endocrine System ◆

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Tropic hormones ~ a hormone that has another endocrine gland as a target Hypothalamus~pituitary Pituitary gland Pineal gland Thyroid gland Parathyroid glands Thymus Adrenal glands Pancreas Gonads (ovary, testis)

The hypothalamus & pituitary, I ◆ ◆ ◆

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Releasing and inhibiting hormones Anterior pituitary: Growth (GH)~bones √gigantism/dwarfism √acromegaly Prolactin (PRL)~mammary glands; milk production Follicle-stimulating (FSH) & Luteinizing (LH)~ovaries/testes Thyroid-stimulating (TSH)~ thyroid Adrenocorticotropic (ACTH)~ adrenal cortex Melanocyte-stimulating (MSH) Endorphins~natural ‘opiates’; brain pain receptors

The pituitary, II ◆ ◆

The posterior pituitary: Oxytocin~ uterine and mammary gland cell contraction

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Antidiuretic (ADH)~ retention of water by kidneys

The pineal, thyroid, & parathyroid ◆

Melatonin~ pineal gland; biological rhythms

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Thyroid hormones: Calcitonin~ lowers blood calcium Thyroxine~ metabolic processes

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Parathyroid (PTH)~ raises blood calcium

The pancreas ◆ ◆

Islets of Langerhans Alpha cells: •glucagon~ raises blood glucose levels

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Beta cells: •insulin~ lowers blood glucose levels

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Type I diabetes mellitus (insulin-dependent; autoimmune disorder)

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Type II diabetes mellitus (non-insulin-dependent; reduced responsiveness in insulin targets)

The adrenal glands ◆

Adrenal medulla (catecholamines): •epinephrine & norepinephrine~ increase basal metabolic rate (blood glucose and pressure)

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Adrenal cortex (corticosteroids): •glucocorticoids (cortisol)~ raise blood glucose •mineralocorticoids (aldosterone)~ reabsorption of Na+ and K+

The gonads ◆

Steroid hormones: precursor is cholesterol

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androgens (testosterone)~ sperm formation; male secondary sex characteristics; gonadotropin

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estrogens (estradiol)~uterine lining growth; female secondary sex characteristics; gonadotropin

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progestins (progesterone)~uterine lining growth

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Steroid Hormone Action

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