CHAPTER 47: ENDOCRINE SYSTEM

AND CELLULAR SIGNALING

AP BIOLOGY

I) HORMONESA)Hormones are chemical messengers that affect

cellular metabolism1) Metabolism includes: 2) Protein synthesis3) Enzyme activation4) Changes in membrane permeability5) Mitotic division6) Release of enzymes, hormones, or other secretions

B)Endocrine signals are produced by endocrine cells that release signaling molecules, which are specific and can travel long distances through the blood to reach all parts of the body.

C)Hormones that target other glands are known as tropins (topic hormones)

II) HORMONES AND SIGNAL TRANSDUCTIONA)Signal transduction pathways link signal reception

with cellular response1) Signaling begins with the recognition of a chemical

messenger, a ligand, by a receptor protein.2) Different receptors recognize different chemical

messengers, which can be peptides, small chemicals or proteins, in a specific one-to-one relationship.

B)In multicellular organisms, signal transduction pathways coordinate the activities within individual cells that support the function of the organism as a whole.1) Hormones are involved in signal transduction pathways

C) A receptor protein recognizes signal molecules, causing the receptor protein’s shape to change, which initiates transduction of the signal.1) Protein hormones interact with receptors to initiate second messengers

2) Second messengers permit signals to reach targets inside cells

D)Signal transduction is the process by which a signal is converted to a cellular response.1) Signaling cascades relay signals from receptors to cell targets,

often amplifying the incoming signals, with the result of appropriate responses

2) Second messengers are often essential to the function of the cascade.

3) Many signal transduction pathways include: i. Protein modifications

ii. Phosphorylation cascades in which a series of protein kinases add

a phosphate group to the next protein in the cascade sequence

III) TYPES OF HORMONESPROTEIN

• Can not enter cell• Not lipid soluble• Proteins are large and charged

• Hydrophilic, ionic

• Bind to receptors

• Trigger second messenger activity

• Second messengers:• Cyclic AMP (cAMP)• Inositol TriPhosphate (IP3)

STEROID (LIPID)• Enter cells directly

• Bind to a nuclear hormone receptor (NHR)

• NHR carries protein into nucleus and binds to DNA

• Regulates gene expression• Control RNA synthesis• Function as repressors or activators

STEROID (LIPID) HORMONE ACTIVITY

III) PROTEIN HORMONES AND SECOND MESSENGERS

A) Second messengers are molecules that relay signals from receptors on the cell surface to target molecules inside the cell, in the cytoplasm, or nucleus.

B) Since protein hormones cannot enter the cell they must utilize these complex second messenger molecules.

C) Cyclic AMP  (cAMP)1) When a protein hormone binds to a receptor it activates a G-protein, such as

Ras.a) G-proteins are Guanosine Nucleotide Proteins (GTPase) that interact

with GTP, forming GDP and phosphate2) The G-protein will then bind to and activate the membrane-bound

enzyme adenylyl cyclase 3) Adenylyl cyclase reacts with ATP to form cyclic AMP.4) The cyclic AMP then goes on the activate specific proteins. 5) Some ion channels, for example, are gated by cyclic AMP. 6) An important protein activated by cyclic AMP is protein kinase A, which goes

on the phosphorylate certain cellular proteins.D. Hormones that use cAMP: Adrenalin, glucagon

ANIMATION

PROTEIN HORMONES AND SECOND MESSENGERSCYCLIC AMP

PROTEIN HORMONES AND SECOND MESSENGERS

INOSITOL TRIPHOSPHATE (IP3)

http://www.phschool.com/science/biology_place/biocoach/biomembrane2/surface.html

III) PROTEIN HORMONES AND SECOND MESSENGERSA) Inositol Tri-phosphate

1) When a protein hormone binds to a receptor it activates a G-protein, such as Ras.

a) G-proteins are Guanosine Nucleotide Proteins (GTPase) that interact with GTP, forming GDP and phosphate

2) The G-protein will then bind to and activate the membrane-bound enzyme phospholipase-C

3) Phospholipase-C produces inositol tri-phosphate (IP3)

4) Inositol Tri-Phosphate diffuses through the cytoplasm to the endoplasmic reticulum

5) The ER releases calcium ions in response to the IP3 binding.

6) The calcium ions activate calcium-sensitive proteins in the cytoplasm

Animation

IV) HUMAN GLANDS AND HORMONESA) Pituitary Gland1) Located at the bottom of the brain under the hypothalamus

a) Contains two lobesI. Anterior (front) Lobe

a) Secretes the following hormonesi. TSH (Thyroid Stimulating Hormone): stimulates thyroid glandii. ACTH (Adreno Corticotropic Hormone): stimulates the cortex of adrenal

glandsiii. HGH (Human Growth Hormone): stimulates bone/muscle growthiv. LH (Luteinizing Hormone): stimulates ovulation/sperm maturationv. FSH (Follicle Stimulating Hormone): stimulates egg/sperm developmentvi. Prolactin: stimulates milk ejection

II. Posterior LobeI. Secretes the following hormones:

I. Oxytocin : labor contractionsII. ADH (Anti-diuretic hormone): stimulates kidney tubules to retain water in

the body

B) Hypothalamus 1. Located just above the pituitary gland 2. Secretes releasing factors to regulate pituitary 3. Integrates nervous and endocrine systems

C) Thyroid 1. Located in neck 2. Secretes three hormones: a) Thyroxine (T4): increases metabolism and cellular respiration, cell growth, differentiation b) Triiodothyronine (T3): increases metabolism,cellular respiration, cell growth, differentiation c) Calcitonin: lowers blood calcium levels (absorbs calcium into bones) 3. Thyroxine and triiodothyronine contain iodine Iodine is essential for proper thyroid functioning.

D) Parathyroid 1. Located next to thyroid gland 2. Secretes Parathormone: Raises blood calcium levels; releases calcium from bone and absorbs from kidneys and intestines

E) Pancreas1. Located under stomach2. Endocrine and exocrine gland

a ) exocrine: secretes into ducts3. Contains two sets of cells that secrete hormones

A) Islets of Langerhans1. alpha cells: secrete glucagon to hydrolyze

glycogen into glucose2. beta cells : secrete insulin to lower blood

glucose levels

F) Adrenal Gland1. Located on top of each kidney2. Two parts to each gland

a) Adrenal Cortex – outer part of the gland1) Secretes: a. Cortisol: reduce inflammation; increase glucose

metabolism b. Aldosterone: increase sodium absorption from

kidney tubules c. Androgens: testosterone

b) Adrenal Medulla – inner part of the gland1) Secretes hormones involved in the fight-or-flight

response a. Epinephrine b. Norepinephrine2) Functions: increase heart rate, blood pressure, muscle

contraction

G) Gonads1. Testes: secrete testosterone2. Ovaries: secrete estrogen and progesterone

Estrogen: Female secondary sex characteristics Regulates menstrual cycle

> Occurs at high concentrations near the end of the follicular phase, estrogen

becomes a positive inducer of the anterior pituitary > Positive feedback triggers the anterior pituitary to release more FSH and

LH more FSH and LH cause the ovary to produce more estrogen > The ensuing LH surge is responsible for ovulation

Progesterone: > Stimulates secretory and vascular activity of the endometrium, (thickens

uterine lining) preparing for implantation of an embryo > Secreted by the corpus luteum (empty follicle) after ovulation

IV) OTHER REGULATORY MECHANISMSA) Circadian Rhythms “biological clocks”

1) Biological processes that oscillate within a 24 hour perioda) One dark and one light periodb) Regulated by the Pineal Gland (secretes melatonin) which controls sleep

patternsB) Other Hormone-related Compounds

2) Prostaglandinsa) Compounds that exert an effect on a small group of cells in one areab) No widespread effects

I. Blood clotting; dilation of cervix3) Pheromones

a) Compounds used to attract mates; for recognition of resourcesI. Ex: trailing of terminates

FEEDBACK INHIBITION

INSULIN AND GLUCAGON NEGATIVE FEEDBACK

REGULATION OF BLOOD CALCIUM LEVELS BY PTH

Menstrual Cycle – Hormones & Feed Back A) 28 day cycle of Pituitary and Ovarian hormones 1. Hypothalamus – secretes GnRH (Gonadotropin Releasing Hormone) 2. Pituitary secretes FSH and LH - follicle begins to form in ovary 3. Ovary secretes estrogen in response to FSH - estrogen stimulates more FSH - - - - - more FSH stimulates more estrogen 4. Follicle grows, and LH causes follicle to rupture, releasing egg (ovulation) 5. LH causes cells in the ruptured follicle to produce progesterone (cells turn yellow in response to progesterone – this is the corpus luteum) - progesterone thickens endometrium - progesterone inhibits LH - as LH levels drop, progesterone production decreases - as progesterone decreases, endometrium begins to degrade 6. Progesterone secretion stops 7. Hypothalamus – secretes GnRH and LH and FSH begin to increase 8. Ovary secretes estrogen in response to FSH

Pituitary Hormones

VII) CHANGES IN SIGNAL TRANSDUCTION PATHWAYS CAN ALTER CELLULAR RESPONSE.A) Conditions where signal transduction is blocked or defective can be

deleterious, preventative or prophylactic (using medicines to prevent disease).

1. Diabetes Islets cells malfunction

Type I: Insulin production stopsTreatment: insulin injections to lower blood glucose levels

Type II: insulin produced is not effective - cell receptors do not bind insulin

Treatment: medications that make cells more responsive 2. Hypothyroidism

Abnormally low thyroxine levelsSymptoms: extreme fatigue, weight gain, cold intolerance,

muscle cramps, feeling of not enough sleep