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Chemical Signals in Animals or The Endocrine System

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Basic Definitions

1. Hormone: a chemical signal that . . .

2. Target Cells: have receptors such that hormones have a specific place to cause an effect.

3. Endocrine glands vs. exocrine glands

a) Endo: these are ductless glands because they secrete their hormones directly into the blood stream

b) Exocrine: secrete chemicals (sweat, mucus, dig. enzymes) into ducts that then carry the chemical to their location

4. Neurosecretory cells: special nerve cells that secrete hormones.

a) Example: hypothalamus and ADH

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Figure 45.1 Feedback Mechanisms

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The Diversity of Cellular Regulators

1. Growth Factors

a) Peptides or proteins

b) Stimulate cell division

c) Examples:

(i) nerve growth factor (although it can stimulate other types of cells)

(ii) insulinlike growth factor which stimulates bone growth.

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Growth Factors (cont’d)

2. Nitric Oxide (NO)

a) when secreted by neurons, it acts as a neurotransmitter

b) when secreted by wbc’s, it kills bacteria and cancer cells

c) when released by cells that line blood vessels it causes vasodilation by causing smooth muscle that lines the vessels to relax.

-1998 Nobel Prize in Medicine

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Growth Regulators, cont’d

• Prostaglandins

a) first discovered in semen produced by the prostate gland

b) stimulate uterine contraction which helps get the sperm cells to the egg.

c) secreted by the placenta and makes uterine contract during labor

d) intensify the sensation of pain; inhibited by aspirin and ibuprofen

e) one kind of prostaglandin causes blood vessels in lungs to relax, while another kind causes vasoconstriction.

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Figure 45.3 Mechanisms of chemical signaling: a review

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Same Chemical Signal. . . Different Cellular Response

BECAUSE

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Table 45.1 Major Vertebrate Endocrine Glands and Some of Their Hormones (Hypothalamus–

Parathyroid glands)

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Table 45.1 Major Vertebrate Endocrine Glands and Some of Their Hormones (Pancreas–Thymus)

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Figure 45.6a Hormones of the hypothalamus and pituitary glands

The posterior pituitary gland is an extension of the nervous tissue of the hypothalamus

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Figure 45.6b Hormones of the hypothalamus and pituitary glands

Hypothalamus controls the ant. pituitary secretions by substances called “releasing factors.”

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Figure 45.7 Two thyroid hormones (thyroxine)

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Figure 45.8 Feedback control loops regulating the secretion of thyroid hormones T3

and T4

Thyroid Releasing Hormone or Factor

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Figure 45.9 Thyroid and Parathyroid Glands in Calcium Homeostasis

Know these three effects

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Interaction of PTH and Vitamin D

1. Helps to convert an inactive form of Vit. D to active form in the liver and kidneys

2. Vit D is a steroid hormone

3. Once the active form of Vit D is made it helps calcium reabsorption in the intestines

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The Regulation of Blood Glucose Levels

Pancreas

•Both an exocrine (mostly) and an endocrine gland

•Islets of Langerhans are clusters of cells throughout the pancreas

•these islets produce two hormones: insulin and glucagon

•each islet has two types of cells: alpha and beta

•Alpha Cells: secrete glucagon (peptide hormone)

•Beta Cells: secrete insulin

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Actions of Insulin

1) stimulates all cells except brain to take up glucose; brain

cells take up glucose without insulin.

2) Slows breakdown of glycogen in liver

3) Inhibits conversion of amino acids and fats to sugar

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Actions of Glucagon

Only liver cells are sensitive to glucagon

• Increases glycogen hydrolysis

• Converts amino acids to glucose

• Converts fats (glycerol) to glucose

• Releases glucose into the bloodstream

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Figure 45.10 Glucose homeostasis maintained by insulin and glucagon

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Diabetes:

excess sugar in the blood stream

appears in the urine

excess thirst hence drinking of lots of water

fats are used in metabolism resulting in a lowering of pH of blood.

Type I Diabetes Mellitus (insulin-dependent diabetes)

•body is producing insulin but the body attacks its own beta cells and destroys them.

•occurs at a young age

•treated with insulin injections

•insulin is now made by genetic engineering

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Type II Diabetes Mellitus

•deficiency of insulin or target cells won’t respond

•occurs at the ripe old age of 40

•exercise and diet!!!!

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Stress Related Hormones

Adrenal glands

•Location

•Two Glands in One

•Adrenal medulla: cells of the medulla are derived from the nervous system so here is another connection between the NS and endocrine systems

Secretes epinephrine and norepinephrine (different molecules, same effect.

Short term stress

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•Adrenal cortex and ACTH (adrenocorticotropic hormone ( steroid hormones)

Secretes mineralocorticoids and glucocorticoids

Long term stress

Mineralocorticoids (aldosterone)

Retention of sodium and water

Increase in blood volume and pressure

Glucocorticoids (cortisol)

Proteins and fats are converted to sugars

Immune system may be suppressed (cortisone injections will cause this)

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Figure 45.12 The synthesis of catecholamine hormones

•occurs in adrenal medulla

•tyrosine is an amino acid

(Also called adrenaline)

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Figure 45.14 Stress and the adrenal gland

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Figure 45.13 Steroid hormones from the adrenal cortex and gonads

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Figure 45.2 Hormonal regulation of insect development (Layer 3)