CHAPTER 45

Joey Nolan, Mallory Parsons, Hailey Kuehl, Jaclyn Mizdrak

Hormones (Endocrine Signals) Hormones – mediate

responses to environmental stimuli and regulate growth, development, and reproduction

Hormones are secreted into extracellular fluids and travel via the bloodstream

Neurohormones – hormones that originate from neurons in the brain and diffuse in the blood stream

Ex. Vasopressin, Oxytocin Neurohormones travel through blood vessels by diffusion

to reach the target cell

Local Regulators

Local Regulators – chemical signals that travel over a short distances by diffusion

Help regulate blood pressure, nervous system function, and reproduction

Two Types of Local Regulators Paracrine Signals - cells near the

secreting cell Autocrine Signals – the secreting cell itself

The Local Regulator sends chemical signals to nearby cells.

Molecules Function as Hormones

Three Major Classes Polypeptides Amines Steroid Hormones

Researchers studied the accumulation of radioactive steroid hormones Only in target cells that were responsive Receptors for steroid hormones are located

inside the target cells

The receptors on target cells allow for cell response to the secreting cell.

Signal Transduction Pathways Water-soluble hormones bind to signal receptor proteins

Activation of an enzyme Change in uptake or secretion

of specific molecules Rearrangement of the

cytoskeleton Ex. Stress – Epinephrine binds

to G-protein coupled receptor, which triggers synthesis of cAMPas a secondary messenger, which activates kinase A, which activates the breakdown of glycogen and inactivates glycogen synthesis, pumping glucose into the bloodstream.http://www.youtube.com/watch?v=-gUC7ZQTp34

Signal transduction pathway

Different Responses to Same Hormone Different target cells respond in

various ways to the same hormone if they have different signal transduction pathways and/or effector proteins Ex. Epinephrine – in a β

receptor on a skeletal muscle blood vessel it causes the vessel to dilate, but in an α receptor on an intestinal blood vessel it causes the vessel to constrict

One hormone, two different effects

Lipid Soluble Hormones

Lipid soluble hormones pass easily through the cell.

Receptors for these hormones are located within the cell; therefore, these hormones pass through the plasma membrane of cell in order to bind to these receptors.

Contrastingly, signal transduction pathways bind to receptors located on the plasma membrane in order to activate these types of reactions. Lipid soluble

hormone structures

Comprehension Check

cAMP activates protein kinase A. Epinephrine binds to G protein-coupled receptor in the plasma membrane. Glucose is released into the bloodstream. Protein kinase A activates breakdown of glycogen and prevents glycogen synthesis. G protein-coupled receptor stimulates the synthesis of cAMP to serve as a second messenger.

3

1

5

4

2

Paracrine Signaling

Paracrine signaling links neighboring cells which secrete local regulators

Several types of chemical compounds function as local regulators. Cytokines – polypeptides that play a role in immune

responses Nitric Oxide – activates an enzyme that relaxes the

neighboring smooth muscle cells, resulting in vasodilation, which improves blood flow to tissues

Prostaglandins – fatty acids Growth Factors –

polypeptides which stimulate cell proliferation and differentiation

Paracrine signaling

Simple Endocrine Pathways

A change in some internal or external variable (the stimulus) causes the endocrine cell to secrete the hormone.

After reaching its target cell via the bloodstream, the hormone binds to its receptor, triggering signaling transduction that results in a specific response.

Simple endocrine pathway

Pancreatic Alpha and Beta Cells Alpha cells make glucagon and beta cells make insulin These antagonistic hormones (insulin and glucagon)

help regulate carbohydrate metabolism by having opposite effects Insulin triggers the uptake of glucose from blood, decreasing blood glucose levels Glucagon promotes release of glucose from blood, increasing blood glucose levels

These opposite effects balance the blood glucose levels; there won’t be too much or too little

Maintenance of glucose homeostasis by insulin and glucagon

Diabetes and Invertebrate Hormones Type 1 diabetes(Insulin-dependent): The immune system

destroys beta cells within the pancreas. Appears during childhood and requires several insulin injections per day.

Type 2 diabetes(Non-insulin-dependent): Target cells no longer respond properly to insulin. Increased risk with heredity, excess weight and lack of exercise. Usually appears after 40.

Invertebrate Hormones: In Aplysia, specialized nerve cells secrete egg-laying hormones that also inhibit feeding and locomotion.

In the development of butterflies, ecdysone is produced from the corpora allata along with juvenile hormone to determine when the caterpillar will molt and develop a pupae.

Diagram of Pancreas

Hypothalamus and Pituitary Glands Hypothalamus: located near the base of

the brain. Receives info. from nerves throughout the body and other parts of the brain. Sends signals to the pituitary , which is located at the base of the hypothalamus.

The hypothalamus gives directions to the pituitary about the specific hormones to be produced and in turn those hormones are central to endocrine signaling throughout the body.

Diagram of the Hypothalamus and the

Pituitary Gland

Hormones Produced by the Pituitary Gland Posterior Pituitary: extension of the hypothalamus that grows

downward toward the mough during embyonic development. Stores and secretes two hormones made by the hypothalamus.

Oxytocin: (peptide) Regulated by the nervous system. Used to regulate mammary glands and uterine contractions during labor.

Oxytocin regulates the mammary glands through positive feedback. Stimulation of the sensory nerves in the nipples send signals to the hypothalamus that triggers the release of oxytocin, which signals the secretion of milk. The more oxytocin produced, the more milk, and the more suckling of the baby.

Antidiuretic hormone (ADH): (peptide) AKA vasopressin promotes the retention of water by the kidneys and is regulated by the water and salt balance within the body. Also decreases urine volume.

Oxytocin molecule

Anterior Pituitary Gland

Tropic hormones are hormones that regulate the function of endocrine cells or glands. Examples include:

Thyroid stimulating gland(glycoprotein): Regulates thyroid gland.

Follicle-Stimulating Hormone(glycoprotein): Stimulates production of ova and sperm.

Luteinizing hormone(glycoprotein): Stimulates ovaries and testes.

Adrenocorticotropic hormone(peptide): Stimulates the adrenal cortex to secrete glucocorticoids.

Growth Hormone uses both tropic and non-tropic means to regulate growth and metabolic functions.

Prolactin(protein): Non-tropic and stimulates milk production and secretion.

Diagram of the processes of hormones controlling

the glands of the endocrine system

Hormones of the Thyroid and Parathyroid Thyroid Triiodothyronine (T3) and thyroxine (T4) Required for the normal functioning of bone-forming

cells and branching of nerve cells during development of the brain

Mainly T4 is secreted, but target cells remove an iodine to make T3 Parathyroid• When calcium in the blood

falls below a set point (about 10mg/100mL), glands release PTH• A negative-feedback

loop inhibits further release of PTH

• If blood calcium rises above set point, calcitonin is released

Hormones of the Adrenal Glands Adrenal Medulla

Catecholamines Epinephrine (adrenaline) and norepinephrine

Response to stress; increases heart rate and respiration rate, glycogen breakdown and release

Nerve signals from the brain via autonomic neurons regulate secretion

Adrenal Cortex Corticosteroids

Glucocorticoids Promote glucose synthesis from noncarb sources Can suppress components of the immune system at high levels

Mineralcorticoids Maintain salt and water balance

Sex Hormones

Primarily come from testes and ovaries, controlled by feedback relationships and gonadotropins from the anterior pituitary gland

Androgens Testosterone, which first functions before birth and is

responsible for male secondary sex characteristics Estrogens

Estradiol, responsible for maintenance of female reproductive system and female secondary sex characteristics

Progestins Progesterone, primarily involved in preparing and

maintaining tissues of the uterus

The Pineal Gland

A small mass of tissue near the center of the brain Synthesizes and secretes melatonin, a modified

amino acid Regulates functions related to light and to seasons

marked by changes in day length May affect skin pigmentation, but primarily relates

to biological rhythms associated with reproduction The main target of melatonin is the

suprachiasmatic nucleus (SCN), the biological clock Depending on species, contains light-sensitive

cells or has nervous connections from the eyes to control secretory activity

Comprehension CheckA. Oxytocin B. Adrenocorticotropic Hormone (ACTH)

C. Luteinizing Hormone (LH) D. Thyroid-Stimulating Hormone (TSH)

E. Prolactin (PRL) F. Follicle-Stimulating Hormone (FSH)

G. Androgens H. Estrogens

I. Progestins

1. Stimulates ovaries and testes.

2. Estrodiol.

3. Stimulates milk production and secretion.

4. Stimulates production of ova and sperm.

5. Progesterone.

6. Stimulates thyroid gland.

7. Stimulates adrenal cortex to secrete glucocorticoids.

8. Used to regulate mammary glands and uterine contractions during labor.

9. Testosterone.

C

H

E

F

I

D

B

A

G