Endocrine System

HormonesSection 1

Endocrine system made of glands that transmit chemical messengers through the body

Hormones chemical messengers

Types of Glands Gland organ made of cells that secrete materials

into other areas of the body

Body has two types:

1. Exocrine glands

2. Endocrine glands

Exocrine glands secrete nonhormonal chemicals into ducts which transport chemicals to specific locations inside and outside the body

Ex. Sweat, mucous, salivary glands

Endocrine glands ductless glands located throughout body – secrete hormones into bloodstream

Types of Hormones Grouped into 2 categories based on structure

Amino acid-based hormones include proteins, peptides, amino acids, other forms derived from amino acids

Ex. Epinephrine (adrenaline)

Steroid hormones lipids that body makes from cholesterol

Ex. Estrogen, testosterone

Classes of hormones differ in physical/chemical properties

Mechanisms of action on body also different

Hormone Action Body makes many hormones

Each hormone affects only specific cells called target cells

Have receptors that recognize and bind to specific hormones

Receptors are proteins inside cytoplasm and on surface of target cell

When hormone binds to receptor it triggers events that make changes in cell

Amino Acid-Based Hormones Because they cannot diffuse passively across cell

membrane a two-messenger system is required for action

Hormones identify target cells by attraction to receptor proteins

Hormone acts as first messenger by binding to receptor

First messenger binding to protein receptor forms hormone-receptor complex which activates a second messenger on inside of cell

Second messenger relays and amplifies hormone signal

In many cases the hormone-receptor complex indirectly activates an enzyme that converts ATP to cyclic AMP (c-AMP)

c-AMP acts as second messenger by indirectly activating other enzymes and proteins in target cell

c-AMP starts chain of events that leads to functional changes in cell

Steroid Hormones Do not act through cell

surface receptors

Diffuse through membranes of target cells

Bind to receptors in cytoplasm

Hormone-receptor complex causes cell to activate existing enzymes or start making new enzymes or proteins

Figure shows how hormone-receptor complex binds to DNA inside nucleus

Once bound, hormone-receptor complex activates transcription of mRNA

By activating transcription, hormones stimulate production of new proteins (cause changes in cell)

Prostaglandins Are a group of hormonelike lipids

Also regulate cell activities

Not made by specific endocrine glands

Made in small amounts by cells throughout body

Act locally instead of being transported through blood

Effects:

Relaxation of smooth muscles in air passageways and blood vessels

Regulation of blood pressure

Contraction of intestinal walls and uterus

Stimulation of inflammatory response

Endocrine glandsSection 2

Located throughout body

Regulate many processes

Pituitary Gland Secretes hormones that

affect other glands and organs

Has 2 lobes regulated by hypothalamus

Hypothalamus links nervous system to endocrine system

Neurosecretory cells of hypothalamus make hormones that are either stored in pituitary gland or regulate its activities

hypothalamus and pituitary are primary regulators of endocrine system

Posterior Pituitary Two amino acid-based hormones are made by

neurosecretory cells

Hormones transported down axons from hypothalamus to posterior pituitary

There they are stored for eventual release into blood

Oxytocin (ahk-see-TOH-sin) stimulates contraction of uterus during childbirth and flow of milk from mammary glands during nursing

Antidiuretic hormone (ADH) helps regulate concentration of solutes in blood by controlling amount of water excreted by kidneys

When concentration of solutes in blood increases the hypothalamus signals posterior pituitary to secrete ADH

ADH causes tubules in kidneys to reabsorb water into blood

Kidneys produce urine with high solute concentration

Hypothalamic receptors detect decrease in concentration of solutes in blood

Stop signaling posterior pituitary to release ADH

Anterior Pituitary Neurosecretory cells also make and secrete releasing

hormones which stimulate endocrine cells in anterior pituitary to make and secrete hormones

Other NS cells make release-inhibiting hormoneswhich inhibit production and secretion of anterior pituitary hormones

Releasing hormones and release-inhibiting hormones are made in response to stimuli processed by nervous system

There is at least 1 releasing hormone for each anterior-pituitary hormone

Specialized system of blood vessels connects hypothalamus and anterior pituitary

Some anterior pituitary hormones are regulated through releasing and release-inhibiting hormones

Growth hormone (GH) controls skeletal and muscular growth

Prolactin (PRL) stimulate and sustains production of breast milk during lactation

PRL-releasing hormone stimulates PRL production and secretion

PRL release-inhibiting hormone stops PRL secretion

Releasing hormones also regulate production and secretion of other hormones in anterior pituitary that stimulate other endocrine glands

Thyroid Gland 2 lobes located near lower part

of larynx

Thyroid stimulating hormone (TSH) regulates thyroid gland

Release of TSH from anterior pituitary regulated by releasing and release-inhibiting hormones of hypothalamus

When stimulated by TSH thyroid produces and releases 2 hormones

Thyroxine (thie-RAHK-sin)

Triiodothyronine (trie-ie-oh-doh-THIE-roh-neen)

Both hormones made from same amino acid

Both made with iodine atoms

Thyroid hormones help maintain normal heart rate, blood pressure, and body temp

Stimulate enzymes that are associated with glucose oxidation and oxygen consumption, generating heat and increasing metabolic rates

Also promote carbohydrate usage over fat for energy

Thyroid important for human development

Produces calcitonin (kal-sih-TOH-nin) which stimulates the transfer of calcium ions from blood to bone

Used to generate bone tissue

Abnormal thyroid activity can harm body’s metabolism

Overproduction of hormones is called hyperthyroidism

Symptoms: weight loss, high blood pressure, heart rate and body temperature

Can be treated with meds or surgical removal of part of thyroid gland

Thyroid-hormone deficiency is called hypothyroidism

Symptoms: growth retardation, exhaustion, weight gain, low heart rate and body temperature

Can also cause cretinism (KREET-uhn-iz-uhm) (form of mental retardation) during fetal and childhood development

If caused by iodine deficiency, then goiter results (swelling of thyroid)

Treated with supplementary thyroxine

Adrenal Glands One adrenal gland is located above each kidney

Each has inner core (medulla) and outer layer (cortex)

Medulla and cortex function as separate endocrine glands

Medullary hormones controlled by nervous system

Anterior pituitary regulates cortical hormones

Adrenal Medulla Produces 2 amino acid-based hormones

Epinephrine (EP-i-nef-rin) (a.k.a. adrenaline)

Norepinephrine (NE) (a.k.a. noradrenaline)

These orchestrate nervous system’s reaction to stress (“fight-or-flight”)

When person stressed, medulla secretes epinephrine and NE into blood

Cause liver to break down glycogen to glucose

Raises level of glucose in blood – oxidized for additional energy

Result: enlargement of bronchial tubes, dilation of pupils, increased heart rate

As heart beats faster surface blood vessels constrict, BP rises, more blood to muscles, brain and heart

Adrenal Cortex Responds to adrenocorticotropic hormone (ACTH)

Secreted by anterior pituitary

Stress causes hypothalamus to release ACTH-releasing hormone

ACTH stimulates adrenal cortex to make steroid hormones, cortisol and aldosterone

Cortisol regulates metabolism of carbohydrates and proteins

Aldosterone helps maintain salt-and-water balance in body by affecting kidneys

Gonads Ovaries and testes

Gamete-producing organs that also produce group of steroid sex hormones

Sex hormones regulate body changes that start with puberty

Puberty – adolescent stage where sex organs mature and secondary sex characteristics (facial hair, etc.) appear

In females:

Menstrual cycle begins, breasts grow, hips widen

In males:

Sperm production begins, voice deepens, chest broadens, hair grows on body and face

Anterior pituitary secretes:

Luteinizing (LOO-tee-in-ize-ing) hormone (LH)

Follicle-stimulating hormone (FSH)

Both stimulate secretion of hormones from gonads

In females LH and FSH stimulate secretion of estrogenand progesterone from ovaries

Prepare for possible pregnancy by causing monthly release of egg by ovary and buildup of uterine lining

Estrogen regulates female secondary sex characteristics

In males LH stimulates testes to secrete androgens

Testosterone is an androgen that regulates male secondary sex characteristics

Along with FSH, testosterone stimulates sperm production

Pancreas Contains mostly exocrine cells

Also has islets of Langerhans which are specialized cells that function together as endocrine gland

Secrete 2 amino acid-based hormones that regulate sugar level in blood

Insulin lowers blood sugar level by stimulating body cells to absorb glucose

Glucagon stimulates release of glucose into bloodstream by liver cells

Insulin deficiency causes diabetes mellitusabnormally high blood glucose concentration

Type 1 diabetes: childhood disorder where insulin-producing islet cells die

Usually treated with daily injections of insulin

Sometimes islet cell transplant

Type II diabetes usually happens over 40 years old

More common, less severe than type I

Caused by insufficient insulin or unresponsive target cell receptors

Type II is hereditary

Onset also related to obesity

Can control through exercise and diet

With diabetes, excess glucose inhibits water reabsorption by kidneys

Large amounts of urine produced

Dehydration and kidney damage result

Lack of insulin causes nausea and rapid breathing

Possibly leads to oxygen deficiency, circulatory and nervous system failure, coma, death

Too much insulin causes hypoglycemia

Disorder where glucose is stored instead of being delivered to body cells

Leads to lowered blood glucose concentration and release of glucagon and epinephrine

Symptoms: lethargy, dizziness, nervousness, overactivity

Extreme cases: unconsciousness, death

Thymus Gland Thymus gland consists mostly of T-cells and plays

role in development of immune system

Located beneath sternum between lungs

Secretes thymosin amino acid-based hormone that stimulates formation of T-cells

Pineal Gland Located near base of brain

Secretes melatonin

Concentrations of melatonin increase at night and decrease during day

Thought to help regulate sleep patterns

Parathyroid Glands Four embedded at back of thyroid (2 in each lobe)

Secrete parathyroid hormone which increases concentration of Ca+ in blood

Proper balance of Ca+ needed for normal bone growth, muscle tone, neural activity

Endocrine cells in walls of digestive organs secrete variety of hormones to help digest food

When food eaten, endocrine cells in stomach lining secrete gastrin which stimulates other stomach cells to release digestive enzymes and HCl

Endocrine cells of small intestine release secretin which stimulates release of digestive fluids from pancreas and bile from liver

Feedback mechanismsSection 3

Endocrine system uses feedback mechanisms to respond/adjust to changes in/out of body

In feedback mechanism, last step in series controls the first step

Homeostasis Endocrine system plays important part in maintenance

of homeostasis

Affects activities of cells, tissue, organs

Ex. Glucagon and insulin together maintain balanced blood glucose levels

Antagonistic hormones actions of 2 hormones having opposite effects (fig. 51-10)

Insulin secretion

Blood glucose level decreases

Glucagon secretion

Blood glucose level increases

To maintain homeostasis hormone secretion must be regulated

Ex. ADH secretion controlled by hypothalamic receptors that detect concentration of solutes in blood

More common: feedback mechanisms

Most hormone systems use negative feedbackrelease of initial hormone stimulates release/production of other hormones that then inhibit release of initial hormone

Positive feedback release of initial hormone stimulates release/production of other hormones that stimulate further release of initial hormone

Example:

LH regulates estrogen production by ovaries

Increased estrogen concentrations stimulate surge in LH secretion before ovulation

Negative Feedback Mechanisms Involve interactions of nervous, endocrine, and

circulatory systems

Final step of events inhibits initial signal in series

Ex. Thermostat at home

When room temp drops below certain point, thermostat activates to produce heat

When room temp at set point, thermostat shuts off heater

NFM help maintain hormone concentrations at certain range

Hypothalamus – anterior-pituitary – testis system

Hypothalamus releases LH-releasing hormone which stimulates secretion of LH from anterior pituitary

LH released and transported through body

Binds to target cells in testes, forming hormone-receptor complexes that stimulate c-AMP production which leads to testosterone secretion into blood

Testosterone binds to target cells

Some target cells are hypothalamic neurosecretorycells that produce LH-releasing hormone

If testosterone concentration higher than normal, secretion of LH-releasing hormone will be inhibited

Regulation of concentration of thyroid hormones in blood

When hypothalamus detects low concentration of thyroxine and triiodothyronine it secretes TSH-releasing hormone into anterior pituitary

Anterior pituitary secretes TSH into blood

TSH stimulates thyroid to secrete thyroxine and triiodothyronine whose target cells include hypothalamic neurosecretory cell that make TSH releasing/inhibiting hormone

When hypothalamus detects increasing levels of thyroid hormones it stops secreting TSH-releasing hormone and starts secreting TSH-inhibiting hormone into anterior pituitary

Anterior pituitary stop secreting TSH

Thyroid stops secreting thyroxine and triiodothyronine

Plant hormones

Growth and development of plants influenced by:Genetic factorsExternal environmental factorsChemicals

Plants respond to chemicals that are naturally inside them and to synthetic chemicals

Groups of Hormones Hormone chemical messenger that

affect plant’s ability to respond to environment

Organic compounds

Effective even at low concentrations

May be made in one part of plant and transported to another (similar to endocrine system)

Hormones interact with specific target tissues to cause physiological (physical) responsesGrowth Fruit ripening

Each response may be two or more hormones acting together

b/c hormones stimulate or inhibit plant growth, they are referred to as growth regulators

Many can be made in the lab –increases quantity of hormones available for commercial use

Botanists recognize 5 groups of hormones

1.Auxins2.Giberellins3.Ethylene4.Cytokinins5.Abscisic acid

Auxins hormones involved in plant-cell

elongation, shoot and bud growth, and rooting

IAA (indolacetic acid) is well-known natural auxin

Stimulates development of fleshy structures like fruit

Experiment on strawberries shows evidence about role of IAA in plants

Removing seed-containing parts from strawberry prevents fruit from enlargingIf IAA is then applied,

strawberry (without seeds) enlarges normally

IAA is made in actively growing shoot tips and developing seeds

Before cell can elongate, cell wall must be less rigid so it can expand

IAA triggers increase in plasticity (stretchability) of cell walls

Synthetic Auxins Auxins have variety of possible

effects, so used for several reasons in gardening, commercial agriculture, research

Napthalene acetic acidsynthetic auxin used to promote root formation on stem and leaf cuttings

When NAA sprayed on young fruits of apple and olive trees some fruits drop off so that rest of fruit grows larger

Other like pears and citrus –several weeks before picking –NAA prevents fruits from dropping off trees before they mature

So, auxins can have opposite effects – cause fruit to drop or prevent dropping – proves important point:

Effects of hormone on plant often depend on stage of plant’s development

NAA used to prevent undesirable sprouting of stems from base of ornamental trees

Stems contain lateral bud at base of each leaf

Buds fail to sprout as long as shoot tip is intact – apical dominance

If shoot tip removed lateral buds grow

If IAA or NAA applied to cut tip of stem, lateral buds stay dormant

NAA used commercially to prevent buds from sprouting on potato tubers during storage

Another important synthetic auxin is 2,4-D, a weed killerAt certain concentrations it kills

dicots without hurting monocotsFood crops are mostly

monocots

Agent Orange – mixture of 2,4-D and another auxin – used to defoliate jungles in Vietnam war

A nonauxin contanimant in Agent Orange throught to have caused health problems in people exposed

Giberellins In 1920s Japanese scientists

discovered substance produced by fungi of genus Gibberella caused fungus-infected rice plants to grow abnormally tall

Giberellin later found to be produced in small quantities by plants themselves

Have many effects on plants, but primarily stimulate elongation growth

Spraying plants may cause them to grow larger than normal

Like auxins, giberellins have important commercial applications

Many seedless grapes sprayed to increase size of fruit

Increases alcohol content of beer by increasing amount of starch converted to sugar during brewing

Also used to treat seeds, because they break seed dormancy and promote uniform germination

Ethylene Plays role in ripening of fruits

Unlike other hormones it’s gas as room temp

Diffuses easily through air

“one bad apple spoils the barrel”One rotting apple will make

ethylene, which stimulates others to ripen then spoil

Commercially ethylene applied in solution of ethephon

Breaks down to release ethylene gas

Used to ripen bananas, honeydew melons, tomatoes

Oranges, lemons, grapefruit often stay green when ripeTaste good, people won’t

buyEthylene turns them

desirable colors – orange, yellow, etc.

In some plant species, ethylene promotes abscission –detachment of leaves, flowers, fruits

Growers can use mechanical tree shakers if fruit sprayed with ethylene before harvest

Leaf abscission advantage

Dead, damaged, infected leaves drop to prevent spreading disease or blocking light of healthy leaves

Minimize water loss in winter

CytokininsPromote cell divisionMade in developing shoots,

roots, fruit, and seedsImportant in culturing plant

tissues in lab

High ratio of auxins to cytokininsin tissue culture stimulates root formation

Low ratio promotes shoot formation

Other cytokinins used to promote later bud growth of flower crops

Abscisic Acid Generally inhibits other hormones

Originally thought to promote abscission

Brings about dormancy in buds

Maintains dormancy in seeds

Causes stomata to close in response to drought

Too expensive to make commercially

Other Growth Regulators Many used on ornamental plants

Do not fit into five categories

Ex. Utility (electric, water, etc.) apply growth retardants – prevent plant growth

Sometimes less expensive than prune (cut) trees