The Endocrine System

By: Meklit Daniel, Camya Robinson, Jordan Montalbo & Vanessa Ruales 4A

The Endocrine System● Endocrine system and nervous system work together to

help regulate activities of the other systems● Both use chemical signals when responding to changes

that may threaten homeostasis● Different ways of delivering signals

Endocrine System

Endocrine vs Nervous SystemEndocrine● Composed of glands● Hormones secreted by glands

into bloodstream to target cells● Takes time to deliver hormones

and for cells to respond● Effect is longer lasting● System organized for

prolonged response

Nervous● Composed of neurons● Sensory receptors detect changes

in internal and external environment

● Communication dependent on nerve impulses

● Axon conduction rapidly occurs as well as neurotransmitter diffusion

● System organized to respond to stimuli quickly

Evolution3. D. 1. : Cell communication processes share common features that reflect a shared evolutionary history.

● Similarities between Endocrine and Nervous System: show closeness evolutionarilyo have similar purposes: internal communication and regulationo function similarly:

some nerve cells (neurosecretory cells) release hormones into the blood (neurohormones)

Epinephrine (fight-or-flight response) is both a hormone and a neurotransmitter Nervous system increase or decrease secretions of specific hormones that affect

day/night cycles and reproductive cycleso share same control pathways

What are Hormones?● Hormones are chemical messengers of the endocrine

system.o They are peptides or steroids that influence the

metabolism of their target cells. Affect endocrine glands.o Responsible for helping maintain homeostasis and

regulating normal bodily functions.o Travel through the blood.

● Endocrine glands secrete hormones into surrounding fluid or bloodstream where they meet target cells

● Endocrine glands contrast with exocrine glands whose ducts carry secreted substances onto body surfaces or into body cavities

● Hormones maintain homeostasis; regulate growth, development, and reproduction

Hormones Secretion

2. E. 2: Timing and coordination of physiological events are regulated by multiple mechanisms.

Examples: menstrual cycle, secretion of leptin, thyroid hormone T4, insulin and glucagon, and melatonin; puberty (primary and secondary sex characteristics)

Control Pathways

Simple Endocrine Pathway

Control Pathways● Negative feedback: when an effector’s (hormone or neurotransmitter) response is inhibiting the

initial stimulus, then the response stopso most common; e.g. dehydration in response to decreased ADH

● Positive feedback: when an effector’s response is to increase the stimulus and create an even larger response by other effectorso Example: Nursing

baby suckles nipple, nerve cells stimulated: give message to hypothalamus (control center)

Hypothalamus signals posterior pituitary gland to secrete effector, neurohormone oxytocin

oxytocin causes the mammary glands to secrete milk: baby suckles more The pathway cycles again until baby is satisfied

Control PathwaysEffector’s response depends on type of hormone:

● Proteins and Peptides- small polypeptides w/ up to 30 amino acids● Steroids-lipids; hydrophobic● Amines- from amino acids

Follow same signaling procedure:● Reception: signal molecule binds to specific receptor protein inside or on target cell (cell that

can recognize hormones)● Signal Transduction: receptor protein being stimulated triggers events within cell

● Response: change in cell’s behavior

o depending on target cell, may cause secretion or uptake of substance, activation of enzyme, rearrangement of cytoskeleton

3.D.3: Signal transduction pathways link signal reception with cellular response.

Cell-surface receptors

Intracellular receptors

Receptor-Hormone Complex● Cell surface receptor: embedded in plasma

membrane● Water-soluble ● Secreted by exocytosis, travel freely in

bloodstream and bind to cell-surface signal receptors

● Causes changes in cytoplasmic molecules and sometimes gene transcription

Receptor-Hormone Complex● Water-soluble hormone to signal receptor protein

triggers events at plasma membrane that result in cellular response

● Signal transduction pathway: Series of changes in cellular proteins that convert extracellular chemical signal to specific intracellular response

Pathway for Water-Soluble Hormones

Cell-Surface ReceptorG-Protein Linked Receptors

● span plasma membrane● works with G Protein

o has two guanine nucleotides, GTP or GDP, attached● used by many hormones for signal transduction: epinephrine

1. hormone signals receptor2. receptor changes shape and binds G protein to it, activating it (GTP or GDP activate it)3. G protein dissociates from receptor, finds enzyme and activates it: can lead to cellular response

which hormone intended

Cell-Surface ReceptorEpinephrine to Glucose

1. Reception: Epinephrine (“first messenger”) binds to plasma membrane of liver cell, where G-protein- linked receptor is located

2. Transduction (steps 2-5): Receptor signals G protein to use GTP in order to bind to enzyme adenylyl cyclase

3. Enzyme is signaled to convert ATP to cAMP4. cAMP acts as “second messenger” and activates protein kinase A5. Protein kinase A activates phosphorylase kinase , which activates glycogen phosphorylase6. Result: Glycogen is broken down by glycogen phosphorylase into glucose

Note: Each hormone can have many different effects, depending on the target cell. This is just one effect of epinephrine on the liver cell.

● also depending on species: thyroxine

Cell-Surface ReceptorSecond Messengers: small ions and molecules that can continue control pathways started by hormones

● cAMP: epinephrine increases concentration of cAMP within cello this pathway used for many other purposes than the ultimate breaking down of glycogen

into glucose secretion of water from cells

● cGMP: signals for the ultimate relaxation of muscle cells in the artery walls (medicine)● Calcium ions (Ca2+): hormones can signal for increase of concentration of these ions in cells

o cause signal pathways that lead to muscle cell contraction, secretion of substances, cell division

Cell Surface ReceptorCalcium ions example:

● Calcium ions constantly going into cells of any eukaryote (especially plant)

o actively transported to cytosol through protein pumps because calcium always needed for pathways

o goes into ER b/c large calcium concentration (concentration gradient)

o gets out of ER via IP3(inositol trisphosphate)

second or third messenger

once formed, diffuses to IP3-gated calcium channel and binds to it, causing channel to open

Intracellular Receptor● small, mostly nonpolar hydrophobic molecules, diffuse easily through hydrophobic membrane

o Steroid hormones: estrogen and progesterone build up up in cells will intracellular receptors responsive to these hormones

o Thyroid hormoneso Hormonal form of Vitamin D

● usually diffuse into nucleus, bind to receptor, change cell transcription ( new mRNA)● Response: change in cell expression through translation

Receptor-Hormone Complex● Lipid-soluble hormones ● Diffuse across membranes of endocrine

cells and travel in bloodstream bound to transport proteins

● Upon diffusing into target cells, they bind to intracellular signal receptors and trigger changes in gene transcription

Pathway for Lipid-Soluble Hormones

Paracrine Signaling● local regulators: convey messages between neighboring cells

o local regulators secreted reach target cells within seconds, milliseconds much faster than hormones, similar effects as hormones

● cytokine: immune responses● growth factors: stimulate cell proliferation and differentiation● nitric oxide: when blood oxygen level is low

o relaxes nearby smooth muscle, vessels dilate and blood flow to tissues improve● prostaglandins: help woman’s uterine wall to contract, allowing sperm to reach egg

Hypothalamus● Hypothalamus regulates internal environment through autonomic system → controls

heartbeat, body temperature, and water balance● Neurosecretory cells produce antidiuretic hormone (ADH) that pass through axons

into posterior pituitary, where stored on axon endings● Certain neurons in hypothalamus sensitive to water-salt balance of blood● When cells determine blood too concentrated → ADH released from posterior

pituitary● ADH causes water to be reabsorbed upon reaching kidneys● As blood become dilute, ADH no longer released → negative feedback● Oxytocin hormone made in hypothalamus causing uterine contractions during

childbirth and milk letdown when baby nursed● More baby suckles, more oxytocin● Release of oxytocin from posterior pituitary controlled by positive feedback

Hypothalamus● Hypothalamus controls anterior pituitary producing

hypothalamic-releasing hormones and hypothalamic-inhibiting hormones

● Former stimulates secretion of thyroid-stimulating hormone and latter prevents anterior pituitary from secreting prolactin

Pituitary Gland● 1 cm in diameter connected to hypothalamus by stalklike structure with two portions:

posterior and anterior● Gonadotropic hormones stimulate gonads (males- testes and females- ovaries) to

produce gametes and sex hormones● Adrenocorticotropic hormone (ACTH) stimulates adrenal cortex to make

glucocorticoid● Thyroid-stimulating hormone (TSH) stimulates thyroid to produce thyroxine and

triiodothyronine● Hormones involved in 3-tier system and blood level of last hormone in sequence

exerts negative feedback control over secretions of first 2 hormones

Pituitary Gland● Prolactin produced after childbirth causing mammary glands in breasts to develop and produce

milk; role in carbohydrate and fat metabolism; Oxytocin● Growth hormone GH (somatotropic hormone) promote skeletal and muscular growth

stimulating rate at which amino acids enter cells and protein synthesis occurs● too little= dwarfism● too much= giantism● can cause balding, acne, smaller testicles, breast enlargement in men, breast reduction in

women, “roid rage”● decreases severity of muscle damage during exercise, allowing people to exercise longer with

short recovery times● Melanocyte-stimulating hormone (MSH) cause skin-color changes in fish, amphibians, and

reptiles having melanophore special skin cells producing color variations; low in humans⇒

Homeostasis2.E.2. : Timing and coordination of physiological events are regulated by multiple mechanisms

● hypothalamus, pituitary (posterior, anterior)● pituitary regulated by tropic hormones in anterior pituitary

o responsible for regulating functions of endocrine organso Examples: FSH, LH, TSH (thyroid-stimulating hormone-normal development of thyroid

gland)● Nontropic hormones-anterior pituitary

o prolactin -mammary gland growth, milk synthesiso MSH (melanocyte-stimulating hormone): regulates activity of pigment containing cells in

fishes, amphibians, reptiles; humans: inhibit hunger● Hormones in posterior pituitary include ADH and Oxytocin

Growth Hormone (GH) ● third type of hormone from anterior pituitary● release insulin-like growth factors: circulate in blood, stimulate cartilage and bone growth

o without it, skeleton of immature animal stops growing● Hypersecretion: gigantism, up to 8 ft, normal proportions, sometimes increased bone growth of

face, hands, feet● Hyposecretion: dwarfism, as small as 4 ft, normal proportions

o Scientists have made GH; therapy for children with pituitary dwarfism Some athletes take it, but no effect on someone with normal level of GH

Dwarfism and Gigantism

Thyroid Hormone● Thyroid hormone secreted by thyroid gland which

regulates homeostasis and development● In humans and mammals thyroid hormone regulates

bioenergetics-- i.e. maintain normal blood pressure, heart rate, and regulated digestive and reproductive functions

● In these species thyroid gland has 2 lobes on ventral surface of trachea

Thyroid Hormone● Thyroid hormone refers to pair of similar hormones derived from amino acid

tyrosine● Triiodothyronine (T₃) and thyroxine (T4)● Thyroid secretes T4 but target cells convert most of it to T₃ by removing one

iodine● Too much or too little of thyroid hormone in blood results in serious metabolic

disorder● Hyperthyroidism (excessive secretion) leads to high body temperature, profuse

sweating, weight loss, irritability, and high blood pressure● Graves’ Disease is most common ● Hypothyroidism (little secretion) causes weight gain, lethargy, and intolerance

to cold● Dietary iodine required

Hyperthyroidism

Hypothyroidism

Insulin and Glucagon● Glucose major fuel for cellular respiration and key source for biosynthesis

and maintaining blood glucose concentrations near set point (at or near 90mg/100mL)

● Two antagonistic hormones, insulin and glucagon, regulate concentration of glucose in blood

● Each operate in simple endocrine pathway regulated by negative feedback● When blood glucose above set point → insulin released to trigger uptake of

glucose from blood → decreases blood glucose concentration● When blood glucose below set point → glucagon released to promote

glucose entering into blood → increasing blood glucose concentration● Since both hormones are opposites, combined activity of them tightly

controls glucose concentration in blood

Insulin and Glucagon● Both hormones produced in pancreas scattered throughout

pancreas in clusters of endocrine cells - islets of Langerhans● Each islet has alpha cells which make glucagon● Beta cells make insulin● Secretion of hormones into interstitial fluid and released into

small ducts that empty into pancreatic duct leading to small intestine

● Pancreas is both endocrine and exocrine gland with functions in endocrine and digestive systems

Islets of Langerhans

Insulin and Glucagon● Insulin lowers blood glucose levels by stimulating all body cells outside brain to take

up nearly all glucose from blood● Also lowers blood glucose levels by slowing glycogen breakdown in liver and

inhibiting conversion of amino acids and glycerol to glucose● Glucagon influences blood glucose levels through effects on target cells in liver● Liver and muscle cells store sugar as glycogen while cells convert sugars to fats in

adipose tissues; only cells in liver are sensitive to glucagon● When blood glucose is below set point, glucagon signals liver cells to increase

glycogen hydrolysis, convert amino acids and glycerol to glucose, and release glucose into bloodstream

● Net effect is to restore blood glucose level to set point● Both hormones vital to liver because within liver, they regulate nutrient processing in

ways that support glucose homeostasis but that relies on responses to glucagon and insulin elsewhere in body

Maintenance of Glucose Homeostasis by Insulin and Glucagon

Peptide Hormones● Hormones that are peptides, proteins, glycoproteins, and modified amino

acids● Actions of peptide hormones can vary● In muscle cells, reception of epinephrine leads to breakdown of glycogen

to glucose providing energy for ATP production● Formation of cyclic adenosine monophosphate (cAMP)● cAMP has one phosphate group attached to adenosine at 2 locations

making molecule cyclic● Cyclic AMP activates protein kinase enzyme● Following enzymatic reactions after cAMP formation called enzyme

cascade → after each enzyme is used repeatedly many molecules of glycogen break down to glucose and enter bloodstream

Leptin● Peptide hormone produced by adipose tissue to control appetite● Crosses the blood brain barrier and connects to receptors in the

hypothalamus● Optimal levels of leptin signal to the brain that the body has enough energy

stored as fat and eating can be stopped● Low levels signal to the brain that there is not enough fat in the body and

the person needs to eat● Arcuate nucleus (ARC) in hypothalamus is key area where leptin exerts

influence● Within ARC are two types of leptin-responsive neurons which stimulate

appetite (AgRP) and curb appetite (POMC)

Leptin and Obesity● When discovered in 1994, leptin was believed to be low in obese people

since studies on mice showed that giving them leptin decreased overeating/obesity

● When leptin was given to people, however, it did not have the desired effects

● Most obese people suffer from leptin resistance● Obesity is not caused by the lack of leptin(hormone is made in fat tissues)● Caused by the brain not responding to leptin, it still thinks that the optimal

level fat storage has not been reached and that the person is starving ● No matter how much leptin is the put into the body, the brain will always

resist it

Diabetes● Every cell needs sugar (glucose) for energy● Insulin is a hormone that allows cells to take in glucose

found in the blood● Diabetes Mellitus results from either a lack of insulin in

the body or a lack a body cells that properly react to insulin

● Type 1● Type 2

Type 1● Juvenile diabetes● Autoimmune disease● Immune system attacks the beta cells of the pancreas● Beta cells produce insulin● Over the years, the decrease in insulin becomes noticeable and blood sugar

levels get extremely high● Thought to be caused by several genes located on chromosome 6● Certain viral infections trigger diabetes: Mumps, German Measles, Rotavirus● These viruses have the same antigens that are present in beta cells● T cells (create antibodies and help fight virus) mistake beta cells for the virus● No known cure, but can be managed with insulin shots, a healthy diet, and

physical activity

Type 2● More common form of diabetes● Cells become insulin resistant.The signal that tells cells

to take in sugar is not responded to● Has genetic causes: minorities have a higher chance of

getting it● Mainly caused by obesity● Treatment is heavily dependent on losing weight and

eating a healthy diet

Steroid Hormones● Only produced by adrenal cortex, ovaries, and testes● Thyroid hormones act like steroid hormones even though they are different

in structure● Steroid hormones do not bind to plasma membrane receptors● Able to enter cell because they are lipids● Once inside, steroid hormone binds to a receptor (in nucleus) but also in

cytoplasm at times● Binds to DNA and activates certain genes● mRNA moves to ribosomes in cytoplasm and protein synthesis follows● Steroids act more slowly than peptides because takes more time to

synthesize new proteins than to activate enzymes already present in cells● Actions last longer

Steroid Hormones● Mader book: steroid hormone is like a courier that has a

pass to enter the factory (cell)● Once inside he makes contact with plant manager

(DNA) who sees if factory (cell) ready for production

Sex linked traits● If a gene is found only on the X chromosome and not the Y

chromosome, it is said to be a sex-linked trait.● Some physiological traits are only expressed depending on the

gender of the individual. o Such as milk production in females and pattern baldness in

males.● Usually sex-linked genes are found on the X chromosome. While

The Y chromosome is missing such genes. The result is that females will have two copies of the sex-linked gene while males will only have one copy of this gene.

Sex linked traits● If the gene is recessive, then males only need one such recessive

gene to have a sex linked trait rather than two recessive genes for traits that are not sex linked. This is why males exhibit some traits more frequently than females.

● Some examples of sex linked traits: Red-green colorblindness, Male Pattern Baldness, Hemophilia, and Duchenne Muscular Dystrophy.

Difference between X and Y chromosomes

Male Sex Hormones● Sex hormones affect growth, development, reproductive

cycles and sexual behavior● Adrenal glands secrete small amounts of these hormones--

testes of males and ovaries of females are principal sources● Gonads produce and secrete 3 major categories of steroid

hormones: androgens, estrogens and progestins● Testes synthesize androgens-- testosterone being main one● Alfred Jost discovered that testosterones functions before

birth and how hormones determine sex of child

Male Sex Hormones● Androgens play major role developing males secondary

sex characteristics during puberty● High concentrations of androgen → lower voice, male

patterns of hair growth, and increased muscle and bone mass

● Primary sex characteristic: sex organ or anatomical part of body involved in sexual reproduction

● Secondary sex characteristic: features that appear during puberty in humans and sexual maturity in animals

Female Sex Hormones● Estrogen, most vital is estradiol, which is responsible for

maintenance of female reproductive system and female development of secondary sex characteristics

● Mammals progestins, including progesterones, involved in preparing and maintaining tissues of uterus required to support growth of embryo

● Androgens, estrogens, and progestins components of hormone pathways whose synthesis is controlled by gonadotropins (FSH & LH) from anterior pituitary gland

● Secretion controlled by releasing hormone from hypothalamus, GnRH

Menstrual Cycle● Menstruation- cyclic shedding of endometrium from

uterus, which occurs in flow through cervix and vagina● Also known as uterine cycle● Ovarian hormones in ovarian cycle controlled by

gonadotropic hormones, FSH and LH● Not present in constant amounts and secreted at

different rates during cycle

Menstrual Cycle● Follicular phase: FSH(follicular stimulating hormone) promotes development of follicle that

secretes estrogen primarily. ● Estrogen level in blood rises minutely with the initial development of follicle, exerts negative

feedback control over anterior pituitary secretion of FSH → follicular phase ends● as the follicle grows more it releases more estrogen ● Ovulatory Phase: When estrogen in blood becomes very high → positive feedback on

LH(luteinizing hormone) and FSH (24-36hrs)● ovulation occurs after this surge● Luteal Phase: remaining follicle turns into a Corpus Luteum and starts to secrete estrogen and

progesterone; hormones used to maintain pregnancy● if egg is not fertilized, then the Corpus Luteum degenerates and also the menstrual cycle

begins

www.youtube.com/watch?v=2_owp8kNMus

In Vitro Fertilization (IVF)● Process of fertilization by manually combining an egg and sperm in a laboratory dish and then

transferring embryo to the uterus● Used to treat infertility with patients that have block/damaged or removed fallopian tubes;

genetic disorders; male factor infertility; or ovulation disorders● Use of drugs to suspend normal secretion of hormones followed by artificial doses of hormones

to induce superovulation and establish pregnancy● pituitary suppression period- take drugs that inhibit the release of FSH and stops normal

menstruation● hormones are injected into the body after in order to produce more than one mature egg● causes potential risks to health E.g. heart attack and ovarian hyperstimulation syndrome● IB asks, “Do you think scientific knowledge should override compassionate

considerations in treating infertile couples?”

William Harvey’s Investigation● Studied sexual reproduction in deer● Took Aristotle’s belief that the embryo formed by

coagulation in the uterus immediately after mating● Using deer that had mated Harvey dissected the uterus

and searched for the embryo unable to find any signs of a developing embryo in the uterus until about six or seven weeks after mating

● Disproved Aristotle’s theories but lack of appropriate scientific equipment hindered further studies

Male Reproductive System

Male Reproductive System

Female Reproductive System

Circadian Rhythms ● Circadian rhythm (24 hour cycle) controls our sleep/wake

cycle● They are affected by signals from the environment. ● Light is the main cue influencing circadian rhythms.● Diurnal/ Nocturnal cycles.● For humans, cortisol present in the blood undergoes diurnal

variation. The level peaks in the early morning (around 8 a.m.) and reaches its lowest level at about midnight-4 a.m., or three to five hours after the onset of sleep.

Circadian Rhythms ● Present in all eukaryotes.● Circadian rhythms will continue even without

external cues.● Ex. The artic circle

Jet Lag● Influenced by sunlight exposure ● When you travel to a different time zone, your sleep schedule

is offset because of the changed daytime/nighttime schedule● i.e. You take a flight to Japan from Jacksonville, FL It is 11

p.m. (usual bedtime) in Japan, but you are wide awake. This is because, at that same moment, it is 10 a.m. in Jax which is the time zone that your body is used to

Melatonin● Pineal gland synthesizes and secretes melatonin● Pineal gland is controlled by the suprachiasmatic nucleus (SCN)- bundle of

20,000 nerve cells in the hypothalamus just above the optic nerves● At night, the dimness of light signals the SCN to increase the release of

melatonin, causing sleepiness ● Stays at high levels for about 12 hours● Suggested that melatonin be taken in no more than 5mg dosages around

the time that you want to go to sleep for the first few days of travel● Your biological clock gets readjusted faster

Videos● Khan Academy https://www.youtube.com/watch?

v=ER49EweKwW8● Bozeman https://www.youtube.com/watch?v=-

S_vQZDH9hY&spfreload=10● Crash Course https://www.youtube.com/watch?

v=WVrlHH14q3o