Chapter 8: Chemical Signals and Homeostasis

The Endocrine System

Hormones and the Endocrine System• Hormones are chemical regulators produced by

cells in one part of the body that effect cells in another part of the body.

• The word hormone comes from the Greek hormon that means “to excite or set into motion”

• Chemicals that are produced by endocrine glands and secreted directly into the blood are called the endocrine hormones.

• Circulatory system carries them to various parts of the body.– Examples: Growth hormone or somatotropin, insulin,

epinephrine (adrenaline) are all nontarget hormones– Examples: parathyroid, gastrin are target hormones

and act on one specific site in the body.

Endocrine Hormones

• chemicals secreted by endocrine glands directly into the blood

• classified according to their activation site• Non-target hormones: affect many cells

throughout the body; ex. insulin, epinephrine

• target hormones: affect specific cells or target tissues; ex. parathyroid hormone, gastrin

Chemical Control Systems

• the endocrine system maintains control over a long duration (nervous system adjusts to short term more on this later)

So… How does it work?• the hypothalamus regulates the pituitary gland through

nerve stimulation, but it is the pituitary gland that stimulates the glands of the endocrine system to release hormones

• How did scientists find out about the hormones that are in very low concentration in the blood?

• A lot of trial and error and “oops!” moments (often removing an organ and seeing what goes wrong)

Types of Hormones• There are two types of hormones: steroid and protein• Steroid hormones: made from cholesterol

– soluble in fat– eg. sex hormones– Eg. Cortisol: hormone that stimulates the conversion of amino

acids to glucose by the liver

• These hormones act by diffusing directly into the target cell and activating specific genes to illicit response. *see fig.4 pg. 374 for more detail.

• Protein hormones: made from amino acid chains (water soluble )– eg. Insulin hormone that helps regulate blood sugar levels;– and GH (somatotropin) hormone that stimulates growth of the

body

Chemical Signals

• How do hormones signal cells?

• Hormones can only affect the cells that contain the right type of receptor capable of recognizing and interacting with the hormone

• There are two types of hormones that differ in their structure as well as how they act upon target cells. (see page 374)

Steroid hormones

• enter the target cell by passing through the target cell membrane and binding to a receptor protein in the cytoplasm of the cell (see figure 4, p. 374)

• the binding of the hormone to the regulatory sites (site other than active site) to induce or suppress the expression of specific genes in that cell

Peptide (protein) hormones• Along with most hormones that are derived from amino

acids, peptide hormones are not able to pass through the plasma membrane, thus they bind to specific receptors embedded on the outer side of the target cell’s plasma membrane.

• Creates a signal transduction pathway that converts the extracellular signal to intercellular signals that alter the target cells behaviour. (see figure 5, p. 375)

• In many cases the binding of the hormone to its receptor on the outside of the target cells activates a G protein which binds to an enzyme called adenylyl cyclase, activating it.

• Adenylyl cyclase catalyzes the conversion of ATP into cyclic AMP

• The production of cyclic AMP can be stopped by a second type of G protein which inhibits the activity of Adenylyl cyclase

Major Glands of the Endocrine System Pituitary Gland “master gland” (See

section 8.1)• pea sized gland located at the base of the brain

that controls other endocrine glands and regulates body growth; functions as a control centre, coordinating the endocrine and nervous systems

• connected by a stalk to the hypothalamus• composed of the posterior lobe and the anterior

lobe• produces and stores hormones; hormones

stored in the pituitary gland are secreted when stimulated by the hypothalamus via nerve impulses

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Posterior lobe

• stores and releases hormones which are produced in the hypothalamus

an H-shaped gland in the front of the neck that secretes a hormone that controls the speed at which the body cells work (Section 8.3)

• Secretion of thyroid hormones is under negative control (feedback) from the hypothalamus: via TSH. • *See fig. 3 pg. 385 for diagram.

• See table 1, pg. 387 for a summary of thyroid hormones

Thyroid Gland

Parathyroid Glands

4 small glands located behind (in) the thyroid gland that regulate the Ca2+ (important in muscle function and much more) content in the blood (Section 8.3)

• See fig. 5 pg. 385 for diagram.

• See table 1, pg. 387 for a summary of parathyroid hormones

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Adrenal Glands located above each kidney – they regulate the

use of carbohydrates and salts and prepare body for emergency by producing adrenaline (p. 381-382)

• Two glands; each gland is made of two glands encased in one shell: the adrenal cortex (outer), and the adrenal medulla (inner)

• Adrenal medulla: produces epinephrine (adrenaline) and norepinephrine (noradrenaline)

• Adrenal cortex: three different hormones: glucocorticoids, mineralocorticoids, sex hormones (androgens) in small amounts.

• See fig. 5 pg. 382 for diagram.• See table 1, pg. 382 for a summary of adrenal hormones

• Inner gland (adrenal medulla) produces two hormones: – Epinephrine (adrenaline)– Norepinephrine (noradrenaline)– Produced in times of stress: blood sugar rises, glycogen is

converted into glucose, increases heart rate, breathing rate, and cell metabolism. Blood vessels dilate for more oxygen to go through the body.

• The outer gland (adrenal cortex) produces three hormones: – Glutocorticoids: example is cortisol that increases the level of

amino acids in the blood to help recover from stress because they are converted into glucose by the liver, raising the level of glucose for greater energy source.

– Mineralocorticoids: regulate the salt-water balance. Example: aldosterone.

– Small amounts of sex hormones.

Epinephrine

Action of Epinephrine on liver

Questions: pp. 387, # 1-8

8.4: Adjustment to Stress

Prostaglandins involved in stress response (among other things – there are 16 different types) by increasing blood flow, and relaxing smooth muscle in paths to lungs.

• * more localized response • See table 1, pg. 388 for a summary • See table 2, pg. 389 for Problems associated

with long-term stress• See table 3, pg. 391 for a list of banned

performance enhancing drugs

Pancreas

a digestive gland that secretes pancreatic juice to small intestine and insulin into the blood stream. (See section 8.2)

• has two cell types: produces hormones AND enzymes in islets of Langerhans: produce insulin and glucagon

• β cells: produce insulin (when glucose ↑) : makes cells more permeable to glucose, therefore, blood glucose decreases

• * in liver, glucose is turned into glycogen (store

• α cells: produce glucagon (when glucose ↓): causes blood glucose to increase as glycogen is converted from the liver.

• See fig. 1 pg. 378 for diagram of feedback system involved.

• *Additional info on diabetes: see pg. 379

Diabetes

• A chronic disease that has no cure and when left untreated it can cause death, blindness, kidney failure, nerve damage, and limb amputation.

• It is when the patient has an inefficient production or use of insulin.

• Without enough insulin, blood sugar levels rise and causes hyperglycemia.– Kidneys cannot reabsorb all the blood glucose that is

filtered through and them, so glucose ends up in the urine.

– Because there is a lot of glucose in the urine, quite a bit of water follows it, so that makes diabetics thirsty and they usually have large volumes of urine.

Three types of diabetes: • Type I: pancreas us unable to produce insulin

because of an early degeneration of the beta cells in the islets of Langerhans. Patients must take insulin to live.

• Type II: is when patients have a decreased insulin production or ineffective use of the insulin that the body does produce. Usually diagnosed in adults and can be controlled with diet, exercise, and oral drugs that stimulate the islets of Langerhans

• Gestational Diabetes: is a temporary condition that happens during pregnancy. Questions, pp. #1-8,

10, 11

8.5 : Sex Hormones

Ovaries female sex glands – estrogen and progesterone

• Estrogen and progesterone are involved in the complex female sexual cycle in which one egg matures aprox. every 28 days.

• Changes in these pituitary hormones cause changes in ovarian hormones: estrogen and progesterone throughout the cycle and through pregnancy if it occurs.

Testes male sex glands – testosterone

• Testosterone stimulates spermatogenesis, devel. of male secondary sex characteristics, and is also associated w sex drive

• * see pg. 389-90 for more detail on anabolic steroids

Endocrine System Review Hormones in the Endocrine system review