Textbook Chapter 33

Regulation: Endocrine System and Hormones

Regulatory Systems: Nervous and EndocrineNervous System Endocrine SystemFast actingShort-lived effectsMessages are

electrochemical (action potential and neurotransmitters)

Messages travel along neurons

Slower activityLonger-lasting

effectsMessages are

chemical (hormones)

Messages travel through the bloodstream

Endocrine System and HormonesThe endocrine system is made up of glands

that secrete hormones into the bloodstream

The exocrine system is made up of glands that make secretions that are released out of the body

Hormones are the endocrine chemical messengers:They are usually carried in the bloodThey effect the metabolic activity and cause

specific changes in target cells or glandsThey attach to receptors on/in target cells

and either activate or oppress protein synthesis in that cell OR activate enzymes already present in the cytoplasm

Hormone Release and Specificity Hormones are released by glands into the

blood stream, which carries the hormone throughout the body

Hormones then diffuse out of capillaries into the interstitial fluid

Hormones only affect cells with matching receptors and cannot bind to cells with different receptors

The target cell action in response to a hormone is based on two things: type of receptors and intracellular proteins based on the target cell

Example of Different Target Cell Reaction

Hormone Release is Regulated by Positive or Negative FeedbackThe release of most hormones are regulated by

negative feedback mechanisms (ie. ADH, thyroxine)In endocrine negative feedback mechanisms, the

effects or release of a hormone usually inhibits the gland that produces “the source” of the hormone.

The release of some hormones are regulated by positive feedback mechanisms (ie. oxytocin)In endocrine positive feedback mechanisms, the

effects or release of a hormone usually excites the gland to produce more of that hormone

However, all positive feedback mechanisms eventually stop by the use of a negative feedback mechanism

Classes of HormonesPeptide Hormones: chains of amino acids (ie. insulin)Amino-Acid Derivative Hormones: hormones derived

from one or two amino acids (ie. epinephrine)Peptide hormones and amino acid derivatives usually bind to

receptors on cell membranesSteroid Hormones: lipid-based hormones synthesized

from cholesterol made of complex rings of carbon and hydrogen atoms (ie. testosterone)Steroid hormones usually bind to receptors located in the cell

cytoplasm or nucelusProstaglandins: made of two fatty acid carbon chains

attached to a five carbon ringMade by every cellAct locally

Types of Hormones

Peptide-hormone

Amino-acid derivative

Steroid hormone

Peptide and Amino Acid Hormone Effect on Cells Peptide and amino-acid derivative hormones

cause the activation or inhibition of enzyme activity already present in the cell

Peptide and amino-acid derivative hormones cannot enter the cell because the plasma membrane is hydrophobic

These hormones rely on a second messenger system to produce effects on the cell

The most common second messenger is cyclicAMP

1. The hormone binds to a receptor on the cell membrane

2. The binding activates a G protein attached to the receptor

3. The G protein stimulates adenylyl cyclase to produce cAMP from ATP through phosphorlysis

4. cAMP binds to and activates other enzymes, such as α-kinase, that catalyze specific reactions

Peptide and Amino Acid Hormone Effect on Cells

Peptide and Amino Acid Hormone Effect Animation

Steroid Hormone Effect on CellsSteroid hormones cause proteins to be produced or

not produced by interacting with the cellular DNA of target cells

Steroid hormones are hydrophobic like the plasma membrane, so they diffuse through the plasma membrane

1. The steroid hormone diffuses through the cell membrane

2. The hormone binds to a receptor in the cytoplasm that carries it into the nucleus, or just to a receptor in the nucleus directly

3. The hormone-receptor complex binds to a specific part of the DNA

4. This causes RNA polymerase to bind to a promoter cite

5. RNA polymerase transcribes DNA into mRNA6. The mRNA leaves the nucleus, binds to a

ribosome, and causes the synthesis of the protein instructed by the promoter site

Steroid Hormone Effect on Cells

Steroid Hormone Effect on Cells

Endocrine Glands and their Hormones Hypothalamus: ADH, oxytocin, releasing hormones Pituitary Gland: (anterior) ACTH, TSH, GH, PRL, FSH, LH

(posterior) oxytocin and ADH Pineal Gland: melatonin Thyroid Gland: thyroxine, calcitonin Parathyroid Glands: parathyroid hormone Thymus Gland: thymosins Heart: atrial natriuretic peptide hormone Adrenal Glands: (medulla) epinephrine, norepinephrine

(cortex) glucocorticoids, aldosterone, testosterone Kidney: erythropoietin Fat: leptin Pancreas: glucagon, insulin Testes: androgens (testosterone) Ovaries: estrogen, progesterone

Endocrine Glands and their Hormones

The HypothalamusThe hypothalamus: perceives impulses

from the brain, scans the chemical composition of the blood, and sends chemical signals to the pituitary gland

It is the connection between the two regulatory systems

Controls body temperature, blood pressure, emotions

Secretes hormones called releasing factors that control the secretions of the anterior pituitary gland

Creates two hormones: oxytocin and ADH, that are released via the posterior pituitary gland

The Pituitary Gland The anterior pituitary gland produces its own hormones, the

posterior pituitary gland releases hormones produced by the hypothalamus

The pituitary gland produces hormones that controls most of the other glands

Releasing hormones delivered from the hypothalamus by neurosecretory cells either cause or inhibit the anterior pituitary to secrete its own hormones

Hormones of the anterior pituitary gland:Thyroid-stimulating hormone (TSH)Growth hormone (GH):Follicle-stimulating hormone (FSH)Luteinizing hormone (LH)Prolactin (PRL)Adrenocorticotropic hormone (ACTH)Endorphins:

Hormones of the posterior pituitary gland (produced in hypothalamus):OxytocinAntidiuretic hormone (ADH)

Pituitary Gland Hormones

Oxytocin and ProlactinOxytocin stimulates the contraction of

smooth muscles in the uterus and the production of milk during and after childbirth

Oxytocin binds to milk gland muscles, and causes them to contract, pushing out milk

Prolactin stimulates milk production and breast development

Both hormones are regulated by positive feedback mechanisms during breast-feeding and childbirth

Hormones in Breastfeeding

Metabolism HormonesThyroxine is released by the thyroid glandThe hypothalamus produces thyroid-releasing hormone

(TRH), which stimulates the anterior pituitary to release thyroid-stimulating hormone (TSH), which stimulates the thyroid gland to produce and release thyroxine.

Thyroxine is an iodine containing hormone that regulates and controls cellular metabolism: it regulates the rate of fat, protein, carbohydrate metabolism and the rate of cellular respiration

Thyroxine is regulated by a negative feedback mechanismHyperthyroidism

High blood pressure, weight loss, overheating, irritabilityHypothyroidism

Leads to low blood pressure, overweight, often cold, lethargy

Iodine Deficiency

Stress ResponseThe sympathetic nervous system stimulates the adrenal

medulla to secrete epinephrine and norepinephrine, which trigger the “fight-or-flight” response

Stress triggered by epinephrine and norepinephrine is “short-term stress” and is not bad for you

Epinephrine and norepinephrine carry out the functions of the sympathetic nervous system and increase blood glucose levels through the breakdown of glycogen

“Long-term stress” is triggered by the release of adrenocorticotropic hormone (ACTH) from the anterior pituitary gland. Long-term stress is unhealthy if prolonged

ACTH stimulates the release of glucocorticoids and androgens (mineralcorticoids) from the adrenal cortexGlucocorticoids break down fats and proteins to increase blood

glucose levels; they also suppress immune responseAndrogens (minearlcorticoids) increase sodium ion and water

retention and increase blood pressure and blood volume

Short vs. Long Term Stress Response

Reproductive Hormones: MalesThe male reproductive glands are the testes, which are

responsible for spermatogenesis and testosteroneGonadotropin-releasing hormone (GnRH) is made in the

hypothalamus and stimulates the release of FSH and LH Luteinizing hormone (LH) from the anterior pituitary

stimulates Leydig cells to produce testosteroneTestosterone helps regulate sperm, and stimulates

secondary male sex characteristics, development, and growth spurts.

Follicle stimulating hormone (FSH) from the anterior pituitary, with the help of testosterone, stimulates Sertoli cells to produce sperm cells

Reproductive hormones are regulated through negative feedback

Spermatogenesis and Testosterone

Reproductive Hormones: FemalesThe female reproductive hormone glands are the ovaries,

which are responsible for the production of egg cells and the hormones estrogen and progesterone

Gonadotropin-releasing hormone (GnRH) is made in the hypothalamus and stimulates the release of FSH and LH

Luteinizing hormone (LH) stimulates the production of the corpus lutem, which produces estrogen and progesterone

Estrogen stimulates the production of secondary female sex characteristics, breast development, and menstruation

Progesterone is important in the regulation of the menstrual cycle, as it stimulates the shedding of the uterine lining

Follicle-stimulating hormone (FSH) stimulates follicle cells to mature into egg cells

Glucose HomeostasisThe pancreas is both an exocrine and endocrine organ:

Cortical (cortex) cells release digestive enzymesIslet cells produce endocrine hormones

The main islet of Langerhan cells: produce endocrine hormones, are:α islet cells produce glucagonß islet cells produce insulin

Glucagon and insulin work together with a negative feedback mechanism to maintain glucose homeostasis

Insulin targets liver and muscle cells and causes increased glucose uptake and metabolism

Glucagon targets liver and muscle cells and causes increased glycogenolysis (breakdown of glycogen into glucose) and gluconeogenesis (production of glucose)

Glucose Homeostasis

Calcium HomeostasisCalcium homeostasis is regulated by a

negative feedback mechanism involving calcitonin and parathyroid hormone

Calcitonin is produced in the thyroid gland, and lowers calcium levels in the blood by depositing calcium in the bones and reducing sodium ion reabsorption during excretion

Parathyroid hormone (PTH) is produced in the parathyroid gland, and increases calcium levels in the blood by releasing calcium from the bones, increasing calcium ion reabsoprtion during excretion, and increasing sodium intake through the intestines with the help of vitamin D

Calcium Homeostasis

Sodium and Water Balance Sodium water balance is directly regulated by aldosterone

(mineralcorticoids), which increases the reabsorption of sodium ions and water, leading to increased blood volume and pressure

Antidiuretic hormone (ADH), produced in the hypothalamus and released from the posterior pituitary gland increases the permeability of the collecting ducts in nephrons, increasing water reabsorption and increasing blood pressure

Decreased reabsorption is caused by the lack of aldosterone and ADH Aldosterone is produced by the adrenal cortex A decrease in sodium ion levels in the blood or an increase of potassium

ion levels in the blood directly stimulates the adrenal cortex to produce aldosterone

A decrease in blood volume or blood pressure stimulates the kidney to produce the enzyme renin, which catalyzes angiotensin II, a hormone that stimulates the release of aldosterone from the adrenal cortex

Adrenocorticotropic hormone (ACTH) can also directly stimulate the adrenal cortex to release aldosterone

Increased blood pressure or blood volume causes the heart to release atrial natriuretic peptide (ANP), which inhibits the release of aldosterone from the adrenal cortex

Sodium and Water Balance

Other HormonesGrowth Hormone: controls growth by increasing bone size

and stimulating mitosisEndorphins: suppress pain by blocking receptors in the brainErythropoietin: increases the production of red blood cells in

the bone marrow; produced in the kidneys in response to low oxygen levels

Thymosine: stimulates the maturation of white blood cellsMelatonin: regulates sleeping cycles; produced in the pineal

gland; not fully understoodLeptin: thought to increase appetite; produced in adipose

cells; not fully understoodMelanocyte-stimulating hormone: stimulates the

melanogenesis in melanocytes; produced in the anterior pituitary gland

Review What are the hormones associated with water/sodium balance?

Angiotensin II, ANP, ADH, ACTH, aldosterone The most common second messenger is …

cyclicAMP In males, FSH is responsible for …

Spermatogenesis The hormones that trigger and carry out the “long term stress

response” are … ACTH, glucocorticoids, aldosterone

Osteoporosis can be a result of the excessive secretion of … the parathyroid gland

The dynamic equilibrium produced by glucagon and insulin is controlled by … Negative feedback mechanism

What are all the hormones that the anterior pituitary gland produces? TSH, FSH, LH, GH, PRL, MSH, ACTH, endorphins