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 System
Endocrine
● 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
Evolution
3. D. 1. : Cell communication processes share common features that reflect a shared evolutionary
history.
● Similarities between Endocrine and Nervous System: show closeness evolutionarily
o have similar purposes: internal communication and regulation
o 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 cycles
o 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.
Hormones Secretion
● 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
Control Pathways
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)
Simple Endocrine Pathway
Control Pathways
●
●
Negative feedback: when an effector’s (hormone or neurotransmitter) response is inhibiting the
initial stimulus, then the response stops
o 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 effectors
o 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 Pathways
Effector’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 Receptor
G-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 receptor
2. 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 Receptor
Epinephrine to Glucose
1. Reception: Epinephrine (“first messenger”) binds to plasma membrane of liver cell, where Gprotein- 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 cAMP
4. cAMP acts as “second messenger” and activates protein kinase A
5. Protein kinase A activates phosphorylase kinase , which activates glycogen phosphorylase
6. 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 Receptor
Second Messengers: small ions and molecules that can continue control pathways started by
hormones
● cAMP: epinephrine increases concentration of cAMP within cell
o 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 Receptor
Calcium 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 hormones
o 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 hypothalamicinhibiting 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
Homeostasis
2.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 organs
o Examples: FSH, LH, TSH (thyroid-stimulating hormone-normal development of thyroid
gland)
● Nontropic hormones-anterior pituitary
o prolactin -mammary gland growth, milk synthesis
o 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