concept 3a Flashcards
neurons
specialized cells capable of transmitting electrical impulses and then translating those electrical impulses into chemical signals
anatomy of the neuron
have a nuclei located in the cell body (soma)
dendrites branching off of the soma
axon hillock is the narrowing of the soma as it enters the axon, signal is integrated
axon is long appendage that terminates near target cell, carries the action potential
myelin sheath and Schwann cells surround the axon to help transmit the action potential
action potential jumps between the myelin sheath to areas called nodes of Ranvier
nerve terminal at the end of the axon to transmit signal to next cell
cell body
location of the nuclei, endoplasmic reticulum, and the ribosomes
dendrites
appendages of the soma
receive incoming messages from other cells
this info is transmitted to the cell body before reaching the axon hillock where the signal is integrated
myelin sheath
insulation around the axon
prvent signal loss or crossing of signals
increase the speed of conduction in the axon
myelin is produced by oligodendrocytes in the CNA and Schwann cells in the PNS
nodes of Ranvier
small breaks in the myelin sheath with exposed areas of axon membrane
critical for rapid signal conduction
action potentials jump from one break to the next for conduction of signal
nerve terminal
synaptic bouton (knob)
end of the axon
enlarged and flattened to maximize neurotransmission to the next neuron and proper release of neurotransmitters
these are the chemicals that transmit info b/w neurons
synaptic cleft
space b/w neurons where terminal portion of the axon releases neurotransmitters which bind to the dendrites of the postsynaptic neuron
synapse
the nerve terminal, synaptic cleft, and postsynaptic membrane
neurotransmitters released from the axon terminal traverse the synaptic cleft and bind to receptors on the postsynaptic neuron
nerve
multiple neurons bundled together in the peripheral nervous system
nerves may be sensory, motor, or mixed and these are related to the type of info they carry
cell bodies are clustered into ganglia
tracts
axons bundled together in the central nervous system
only carry one type of information
cell bodies are grouped into nuclei
neuroglia
glial cells
support cells for neurons
responsible for function such as holding neurons in place, supplying neurons w/ oxygen and nutrients, insulating neurons from other neurons, destroying pathogens, and removing dead neurons
astrocytes
nourish neurons and form the blood-brain barrier, which controls the transmission of solutes form the bloodstream into nervous tissue
ependymal cells
line the ventricles of the brain and produce cerebrospinal fluid, which physically supports the brain and serves as a shock absorber
microglia
phagocytic cells that ingest and break down waste products and pathogens in the central nervous system
oligodendrocytes
in the CNS
produce myelin around the axons
Schwann cells
in the PNS
produce myelin around the axons
action potential
an abrupt change in the membrane potential of a nerve or muscle cause by changes in the membrane ionic permeability
results in conduction of an impulse in nerves or contraction in muscle
all-or-nothing
relay electrical impulses down the axon to the axon terminal
ultimately release neurotransmitters into the synaptic cleft
resting membrane potential
exhibited by all neurons
there is an electric potential difference b;/w the inside of the neuron and the extracellular space
about -70 mV
inside of neuron being negative relative to outside
inside has more K+ and outside has more Na+
Na+/K+ ATPase
neurons have selective permeability to Na+ and K+ ions
this structure is used to maintain the negative internal environment
important for restoring gradient after action potential has been fired–> it transports 3 Na+ out of the cell for every 2 K+ into the cell using 1 ATP
depolarization
raising the membrane potential from its resting potential
makes neuron more likely to fire an action potential
happens when neuron receives excitatory input
hyperpolarization
lowering the membrane potential from its resting potential
makes neuron less likely to fire an action potential
happens when neuron receives inhibitory input
threshold
the lowest magnitude of stimulus strength that will induce a response
usually around -55 to -40 mV
when axon hillock receives enough excitatory input to be depolarized
once this is reached an action potential will be triggered
summation
additive effects of multiple signals that can reach threshold and create and action potential
2 types: temporal and spatial
temporal summation
multiple signals are integrated during a relatively short period of time
a number of small excitatory signals firing at nearly the same moment could bring cell to threshold
spatial summation
multiple signals are integrated from a number of different locations on one neuron
action potential generation
cell reaches threshold and voltage-gated Na+ channels open and permit passage of Na+ into the membrane bc of electrochemical gradient
as Na+ moves into cell it becomes more positive and rapidly depolarizes
when cell reaches +35 mV Na+ channels are inactivated
positive potential opens voltage-gated K+ channels and gradient moves K+ out of cell
this restores the negative potential of the cell as it is repolarized
efflux of K+ is overshot and causes hyperpolarization this the the refractory period
voltage-gated sodium channels
can exist in 3 states
closed- before cell reaches threshold and after inactivation has been reversed
open- from threshold to approximately +35 mV
inactive- from approximately +35 mV to the resting potential where it is deinactivated and returns to closed state
repolarization
when K+ is driven out of the cell restoring the negative potential
refractory period
when efflux of K+ is overshot and potential goes below -70 mV (hyperpolarization)
this is a period when an action potential can not be fired
resting period for the membrane
2 types: absolute and relative
absolute refractory period
no amount of stimulus can cause another action potential to occur
relative refractory period
there must be a greater than normal stimulate not cause an action potential because the membrane is starting from a potential that is more negative than the resting value
impulse propagation
movement of an action potential down an axon
resulting in neurotransmitter release at the synaptic bouton and transmission of the impulse to the target neuron or organ
depolarization of one segment of the axon will bring subsequent segments to threshold which will result in an action potential
speed of impulse
depends on length and cross-sectional area of the axon
longer axon results in higher resistance and slower conduction
greater cross sectional area results in after propagation and decrease resistance
effects of area are more significant than length
myelin insulates axon and increases the speed of conduction
saltatory conduction
process by which an electric single jumps across the nodes of Ranvier to travel down the axon
presynaptic neuron
the neuron preceding the synaptic cleft
release neurotransmitters into the synaptic cleft
postsynaptic neuron
neuron after the synaptic cleft
neuron that the neurotransmitters bind to
effector
neuron signals to a gland or muscle (target organ) rather than another neuron the postsynaptic cells is called effector
neurotransmitters in nerve terminal
before release they are stored in membrane-bound vesicles in nerve terminal
when action potential reaches this area voltage-gated calcium ions open allowing calcium to flow into cell
this triggers fusion of vesicles with membrane at synapse causing exocytosis of neurotransmitter
neurotransmitter in synapse
neurotransmitters are exocytized from the nerve terminal into the synapse
they diffuse accrues the cleft and bind to receptors on the postsynaptic membrane
this allows message to be passed from one neuron the the next
neurotransmitter regulation
neurotransmitters must be removed from the synapse after they transmit the signal
3 mechanisms to remove them: breakdown, reuptake, or diffuse out of cleft
breakdown of neurotransmitters
neurotransmitters are broken down by enzymatic reactions
break down of acetylcholine (ACh) by acetylcholinesterase (AChE)
reuptake of neurotransmitters
neurotransmitters are brought back into the presynaptic neuron using reuptake carriers
reuptake carriers for serotonin, dopamine, and norepinephrine
diffusion of neurotransmitters
neurotransmitters diffuse out of the synaptic cleft
nitric oxide is a gaseous signaling molecule that diffuse out of cleft
nervous system
collection of cells that govern involuntary and voluntary behavior
role in maintaining homeostasis
many different functions
over 100 billion cells that communicate, coordinate, and regulate signals for the body
actions occur when body reacts to stimuli using the nervous system
functions of the nervous system
sensation and perception motor function cognition (thinking) and problem-solving executive functioning and planning language comprehension and creation memory emotion and emotional expression balance and coordination regulation of endocrine organs regulation of heart rate, breathing rate, vascular resistance, temperature, and exocrine glands
3 types of nerve cells
sensory neurons
motor neurons
interneurons
sensory neurons
afferent neurons
transmit sensory information from receptors to he spinal cord and brain
ascend in the spinal cord toward the brain
motor neurons
efferent neurons
transmit motor information form the brain and spinal cord to muscles and glands (target organs)
exit the spinal cord on way to rest of the body
interneurons
found b/w the neurons
most numerous of the 3 types
located predominantly in the brain and spinal cord
often linked to reflexive behavior
divisions of the nervous system
Central nervous system and Peripheral nervous system
CNS consists of the brain and spinal cord
PNS is divided into somatic NS and autonomic NS
Autonomic NS is divided into sympathetic NS and parasympathetic NS
central nervous system
consists of the brain and spinal cord
brain in CNS
white matter- consists of axons encased in myelin sheaths, lies deeper than grey matter
grey matter- consists of unmyelinated cell bodies and dendrites
spinal cord in CNS
extends downward from the brainstem
divided into 4 divisions: cervical, thoracic, lumbar, and sacral
protected by the vertebral column
like brain has white and grey matter but white is on the outside and grey is deep within it
axons of motor and sensory neurons are in the spinal cord
dorsal root ganglia
contains cell bodies of sensory neurons
sensory info enters the spinal cord here where it can be synapsed with motor neurons in the grey matter of the spinal cord
ventral root
motor root
on the side closest of the front of the body
where motor neurons exit the spinal cord where they can then transmit info to the rest of the body
peripheral nervous system
made up of nerve tissue and fibers outside the brain and spinal cord
12 pairs of cranial nerves and 31 pairs of spinal nerves
connects the CNS to the rest of the body
subdivided into the somatic and autonomic NS
somatic NS
consists of sensory and motor neurons distributed throughout the skin, joints, and muscles
governs all voluntary actions
autonomic NS
regulates heartbeat, respiration, digestion, and glandular secretions–> manages involuntary muscles of internal organs and glands
helps regulate body temp but activating sweating or piloerection
automatic function
differences b/w somatic and autonomic
motor neuron in somatic goes directly from spinal cord to muscle w/out synapsing
in autonomic 2 neurons work in series to transmit messages from spinal cord
2 neurons of the autonomic NS
first is the preganglionic neuron
seconds is the postganglionic neuron
soma of the preganglionic neuron is in the CNS and its axon travels to a ganglion in the PNS
this is where it synapses on the soma of the postganglionic neuron which affects the target organ
divisions of the autonomic NS
sympathetic NS- fight or flight
parasympathetic NS- rest and digest (feed or breed)
act in opposition to each other, antagonistic
parasympathetic NS
rest and digest (or feed or breed)
main role is conserve energy
associated w/ resting and sleeping states
act to reduce heart rate and constrict bronchi
manage digestion by increasing peristalsis and exocrine secretions
neurotransmitter is acetylcholine-released by pre and post ganglionic neurons
innervated by the vagus nerve (cranial nerve X)
function of parasympathetic NS
constrics pupils stimulates flow of saliva constricts bronchi slows heart beat stimulates peristalsis and secretion stimulates bile release contracts bladder
sympathetic NS
fight or flight
activated by stress
closely associated with rage and fear reactions
preganglion neurons release acetylcholine and post ganglionic neurons release norepinephrine
function of sympathetic NS
increase heart rate
redistributes blood to muscles of locomotion
dilates pupil (to maximize light intake)
inhibits salivation
relaxes bronchi
accelerates heartbeat
stimulates sweating or piloerection
decreases digestion and peristalsis (inhibits peristalsis and secretion)
stimulates glucose production and release
secretion of adrenaline and noradrenaline (epinephrine and norepinephrine)
inhibits bladder contraction
stimulates orgasm
reflex
an involuntary nervous pathway consisting of sensory neurons, interneurons, motor neurons, and effectors
it occurs in response to a specific stimulus
reflex arcs
neural circuits that control reflexive behavior
sensory neurons transmit signal to the spinal cord
they connect w/ interneurons send signal to the brain and also send signal to the effector w/out waiting for the brain to respond–> leading to a much faster reaction (a reflex)
by the time signal arrives to the brain the muscles have already responded
2 types: monosynaptic and polysynaptic
monosynaptic reflex arc
single synapse b/w the sensory neuron that receives stimulus and the motor neuron that responds to it
knee-jerk reflex
relex is simply a feedback loop in response to potential injury
knee-jerk reflex
patellar tendon is stretched (knee bent)
when it is tapped with a hammer info travels up the sensory neuron to the spinal cord
here it synapses with the motor neuron that sends signal to the quadriceps muscle
the net results is contraction of this muscle causing extension of the leg which lessens the tension on the patellar tendon
feedback loop in response to potential injury
if patellar tendon or quadriceps muscles are stretched too far they may tear causing damage to the knee joint–> reflex protects the muscle
polysynaptic reflex arc
at least one interneuron b/w the sensory and motor neurons
withdrawal reflex
withdrawal reflex
reaction to stepping on a nail
leg that septs on nail is stimulated to flex, using hip and hamstring muscle, pulling the foot away from the nail (this step is monosynaptic)
to maintain balance the other food must be planted on the ground
the motor neuron controlling the quadriceps muscle in the opposite leg are stimulated, extending the leg
interneurons provide connection from sensory info to motor neurons in supporting leg
glands
organs of the endocrine system
secrete hormones
hormones
signaling molecules that are secreted directly into the bloodstream to travel to distant target tissues or organs
at tissue they bind to receptors inducing a change in gene expression or cellular functioning
classifications of hormones by structure
classified by their chemical identity
peptide hormones
steroid hormones
amino acid derivative hormones
peptide hormones
made up of amino acids
range in size from very small to very large
derived from polypeptides that are cleaved during post translational modifications
these are transported to the Golgi apparatus for modifications that activate the hormone and direct to location in cell
released by exocytosis after packaged into vesicles
charged–> cannot pass the plasma membrane
generally water soluble and can travel freely thought the bloodstream, don’t require carriers
first messenger
the peptide hormone that binds to the receptor on the plasma membrane
triggers transmission of a second signal, the second messenger
many receptor subtypes, the type determines what happens once the hormone has stimulated the receptor
signaling cascade
the connection b/w the hormone at the surface and the effect brought about by second messengers within the cell
at each step there is a potential for amplification
amplification
characteristic of a signaling cascade
the binding of a single peptide hormone to a membrane-bound receptor results in a signal that increases in strength thought the signaling cascade
common second messengers
cyclic adenosine monophosphate (cAMP)
inositol triphosphate (IP3)
calcium
G protein-coupled receptor
binding of a peptide hormone triggers the receptor to either activate or inhibit an enzyme called adenylate cyclase
this raises or lowers the level of cAMP
cAMP
second messenger in G protein-coupled receptors
binds to intracellular targets, such as protein kinase A
protein kinase A
phosphorylates transcription factors like cAMP response element-binding protein (CREB) to exert the hormone’s ultimate effect
can modify other enzymes as well as transcription factors
can have rapid or slow effect on the cell
effects of peptide hormones
rapid but short-lived bc act through second messenger systems
effects do not last without relatively constant stimulation
steroid hormones
derived from cholesterol
produced primarily by the gonads and adrenal cortex
can cross the plasma membrane, receptors are usually intracellular or intranuclear
upon binding the hormone-receptor complex undergo conformational changes
function by binding to DNA to alter gene transcription
not water soluble, carried by proteins in the bloodstream, generally inactive when attached to the protein must dissociate to function
dimerization
common conformational change
pairing of 2 receptor-hormone complexes
effects of steroid hormones
slower but longer-lived than peptide hormones
bc steroid hormones cause alterations in the amount of mRNA and protein present in a cell
amino acid-derivative hormones
derived from one or two amino acids, usually with modifications
less common type
epinephrine, norepinephrine, triiodothyronine, thyroxine
mechanism is less predictable
catecholamines
epinephrine and norepinephrine bind to G protein-coupled receptors have extremely fast onset but are short lived like peptide hormones adrenaline rush
thyroid hormones
thyroxine and triiodothyronine bind intracellularly have slower onset and longer duration like steroid hormones regulate metabolic rate over a long period of time
hormone nomenclature
peptide and amino acid-derivative hormones have names that end in -in and -ine
steroid hormones have names that end in -one, -ol, and -oid
classifications of hormones by target tissue
direct hormones
tropic hormones
direct hormones
are secreted and then act directly on a target tissue
insulin released by the pancreas causes increased uptake of glucose by muscle
tropic hormones
hormone that is secreted and travels to a target cell or organ where it triggers release of another hormone
this causes changes in the physiological activity of target cells
usually originate in the brain and anterior pituitary gland
endocrine glands
hypothalamus pituitary (anterior and posterior) thyroid parathyroid glands adrenal cortex adrenal medulla pancreas gonads (testes and ovaries) pineal gland
hypothalamus
bridge b/w the nervous and endocrine systems
regulates the pituitary thought tropic hormones
capable of having organism-wide effects
located in the forebrain directly about the pituitary gland and below the thalamus
hypothalamus hormones
gonadotropin-releasing hormone (GnRH) growth hormone-releasing hormone (GHRH) thyroid-releasing hormone (TRH) corticotropin-releasing factor (CRF) the release of these hormones is regulated by negative feedback
hypothalamus interactions w/ anterior pituitary
hypothalamus secrets tropic hormones into the hypophyseal portal system
the hormones travel directly to the anterior pituitary which stimulates the release of other hormones
gonadotropin-releasing hormone (GnRH)
secreted from the hypothalamus
stimulates the release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from the anterior pituitary
growth hormone-releasing hormone (GHRH)
secreted from the hypothalamus
stimulates the release of growth hormone (GH) from the anterior pituitary
thyroid-releasing hormone (TRH)
secreted from the hypothalamus
stimulates the release of thyroid-stimulating hormone (TSH) from the anterior pituitary
corticotropin-releasing factor (CRF)
secreted from the hypothalamus
stimulates the release of adrenocorticotropic hormone (ACTH) from the anterior pituitary
prolactin-inhibiting factor (PIF)
dopamine
secreted by the hypothalamus
causes a decrease in prolactin secretion from the anterior pituitary
hypothalamus interactions w/ posterior pituitary
neurons in the hypothalamus send their axons down the pituitary stalk directly into the posterior pituitary
this causes release of oxytocin and antidiuretic hormone
oxytocin
hormone that stimulates uterine contractions during labor
stimulates milk letdown during lactation
involved in bonding behavior
released when the posterior pituitary is stimulated by the hypothalamus
antidiuretic hormone (ADH)
aka vasopressin
increases reabsorption of water in the collecting ducts of the kidneys by increasing permeability of collecting duct
secreted in response to increased plasma osmolarity or increased concentrations of solutes within the blood
products of the anterior pituitary
FLAT PEG Follicle-stimulating hormone (FSH) Luteinizing hormone (LH) Adrenocorticotropic hormone (ACTH) Thyroid-stimulating hormone (TSH) Prolactin Endorphins Growth hormone (GH) FLAT: all tropic hormone PEG: all direct hormones
follicle-stimulating hormone (FSH)
stimulated by gonadotropin-releasing hormone (GnRH) from the hypothalamus
act on the gonads (testes and ovaries)
peptide hormone
stimulates follicle maturation in females; spermatogenesis in males
luteinizing hormone (LH)
stimulated by gonadotropin-releasing hormone (GnRH) from hypothalamus
act on the gonads (testes and ovaries)
peptide hormone
stimulates ovulation in females; testosterone synthesis in males
adrenocorticotropic hormone (ACTH)
stimulated by corticotropin-releasing factor (CRF) from the hypothalamus
acts on the adrenal cortex
peptide hormone
stimulates the adrenal cortex to synthesize and secrete glucocorticoids
thyroid-stimulating hormone (TSH)
stimulated by thyroid-releasing hormone (TRH) from the hypothalamus
acts on the thyroid
peptide hormone
stimulates the thyroid to produce thyroid hormones
prolactin
stimulates milk production in the mammary glands and secretion
peptide hormone
high levels of estrogen and progesterone allow for development of milk ducts in preparation
after expulsion of placenta, estrogen, progesterone, and dopamine levels drop, block on milk production is removed and lactation begins
endorphins
decrease the perception of pain
peptide hormone
can promote euphoria
many pharmaceutical agents, morphine, mimic the effects of these natural painkillers
groth hormone (GH)
promotes the growth of bone and muscle
release is stimulated by growth hormone-releasing hormone (GHRH) by hypothalamus
peptide hormone
raises blood glucose levels
giantism
caused by excess of GH released in childhood before closer of epiphyseal plates
dwarfism
caused by a deficit of GH in childhood before closer of epiphyseal plates
acromegaly
affects bones in the hands, feet, and head
patients tend to present this to doctors bc they need larger shoes, cannot wear their rings, and can no longer fit into their hats
posterior pituitary
contains nerve terminals of neurons with cell bodies in hypothalamus
receives and stores 2 hormones that are produced in the hypothalamus: ADH and oxytocin
positive feedback of oxytocin
the release of oxytocin promotes uterine contractions
which promotes more oxytocin release
then promotes stronger uterine contractions, and so on.
thyroid
vertebrate endocrine gland located in the neck
synthesizes triiodothyronine, thyroxine, and calcitonin
controlled by thyroid-stimulating hormone from the anterior pituitary
2 major functions: setting basal metabolic rate and calcium homeostasis
triiodothyronine (T3)
produced by the iodination of the amino acid tyrosine in the follicular cells of the thyroid
T3 refers to number of iodine atoms attached to tyrosine
amino acid-derivative hormone
stimulates metabolic activity
increased amounts lead to increased cellular respiration
thyroxine (T4)
produced by the iodination of the amino acid tyrosine in the follicular cells of the thyroid
T4 refers to the number of iodine atoms attached to tyrosine
amino acid-derivative hormone
stimulates metabolic activity
increased amounts lead to increased cellular respiration
hypothyroidism
deficiency of iodine or inflammation of the thyroid
theyroid hormones are secreted in insufficient amounts or not at all
characterized by lethargy, decreased body temp, slowed respiratory and heart rate, cold intolerance, and weight gain
cretinism
deficiency in thyroid hormones in children will lead to this disease
characterized by mental retardation and developmental delays
reason children are tested at birth for deficiencies
hyperthyroidism
caused by an excess of thyroid hormone, may result from tumor or thyroid overstimulation
opposite of hypothyroidism
characterized by heightened activity level, increased body temp, increased respiratory and heart rate, heat intolerance, and weight loss
calcitonin
produced by C-cells (parafollicular cells) in the thyroid
peptide hormone
decreases blood calcium concentrations; increased calcium excretion from the kidneys, decreased calcium absorption from gut, and increased storage of calcium in bone
high levels of calcium in blood stimulate secretion of calcitonin from C-cells
Why is calcium and important ion?
has critically important functions:
bone structure and strength
regulation of muscle contraction
clotting of blood (calcium is a cofactor)
also plays a role in cell movement, exocytosis, and neurotransmitter release
parathyroid glands
4 small pea-sized structures that sit on the posterior surface of the thyroid
produced parathyroid hormone (PTH)
parathyroid hormone (PTH)
peptide hormone
increases blood calcium concentration–> antagonist of calcitonin
affects phosphorus homeostasis by resorbing phosphate from bone and reducing reabsorption of phosphate in kidney
activates vitamin D, required for absorption of calcium and phosphate in the gut
adrenal glands
located on top of the kidneys
each gland has a cortex and a medulla
each part is responsible for the secretion of different hormones
adrenal cortex
secretes corticosteroids
these are steroid hormones that are divided into 3 functional classes: glucocorticoids, mineralocorticoids, and comical sex hormones
glucocorticoids
steroid hormones that regulate glucose levels
affect protein metabolism
cortisol and cortisone are types of this hormone
increase blood glucose concentrations
decrease protein synthesis
can decrease inflammation and immunologic responses
release under control of ACTH
mineralocorticoids
used in salt and water homeostasis
aldosterone
increases sodium reabsorption in distal convoluted tubule and collecting duct, increasing water reabsorption
promote potassium and hydrogen ion excretion
controlled by renin-angiotensin-aldosterone system
renin-angiotension-aldosterone system
controls aldosterone
- decreased blood pressure causes the juxtaglomerular cells of kidney to secrete renin
- renin cleaves an inactive plasm protein, angiotensinogen, to active from, angiotensin I
- Angiotensin I is converted to angiotensin II by angiotensin-converting enzyme (ACE) in lungs
- Angiotensin II stimulates adrenal cortex to secrete aldosterone
- once blood pressure is restored, there is decreased drive to stimulate renin release
cortical sex hormones
androgens and estrogens
males secrete large quantities of androgens in testes so adrenal testosterone plays small role in male physiology
females are more sensitive to disorders of cortical sex hormone production
functions of corticosteroids
the 3 S’s
Salt (mineralocoritcoids)
Sugar (glucocorticoids)
Sex (cortical sex hormones)
adrenal medulla
inside of adrenal cortex
responsible for the production of epinephrine and norepinephrine
specialized nerve cells are capable of secreting compounds directly into circulatory system
catecholamines
epinephrine and norepinephrine secreted from the adrenal medulla amino acid-derivative hormone increase blood glucose concentration and heart rate dilate bronchi alter blood flow patterns
pancreas
has both exocrine and endocrine functions
exocrine tissues secrete substance directly into ducts
endocrine tissues are small groups of hormone-producing cells grouped into islet of Langerhans
islet of Langerhans
contains 3 types of cells alpha, beta, and delta cells each cell type secretes a different hormone alpha cells secrete glucagon beta cells secrete insulin delta cells secrete somatostatin
glucagon
secreted from alpha cells in the pancreas
peptide hormone
stimulates glycogen breakdown
increases blood glucose concentrations
secreted during times of fasting–> glucagon levels are high when glucose is gone
insulin
secreted from beta cells in the pancreas
peptide hormone
lowers blood glucose concentrations and increases anabolic processes
antagonist to glucagon, secreted when blood glucose levels are high
induces muscle and liver cells to take up glucose ands tore it as glycogen
counterregulatory hormones
insulin decreases plasma glucose
glucagon increases plasma glucose
growth hormone, glucocorticoids, and epinephrine all increase plasma glucose
hypoglycemia
excess insulin
characterized by low blood glucose concentration
hyperglycermia
excess glucose in the blood
underproduction, insufficient secretion, or insensitivity to insulin results in diabetes mellitus
diabetes mellitus
often report polyuria (increased frequency of urination) and polydipsia (increased thirst)
2 types: type I (insulin-dependent) and type II (non-insulin-dependent)
type I diabetes
insulin-dependent
caused by autoimmune destruction of the beta cells of the pancreas
produce little to no insulin
require regular injections of insulin to prevent hyperglycemia and permit entry of glucose into cells
type II diabetes
non-insulin-dependent
result of receptor-level resistance to the effects of insulin
partially inherited and partially due to environmental factors, obesity or diet
require insulin only when bodies can no longer control glucose levels
somatostatin
inhibitor of both insulin and glucagon secretion
secreted by the delta cells of the pancreas
peptide hormone
stimulated by high blood glucose and amino acid concentrations
produced by the hypothalamus, where it functions to decrease growth hormone secretion
gonads
testes secrete testosterone in response to stimulation by gonadotropins (FSH and LH)
ovaries secrete estrogen and progesterone in response to gonadotropins
testosterone
secreted by the testis and adrenal cortex
steroid hormone
develops and maintains male reproductive systems and secondary sex characteristics
estrogen
secreted by the ovaries and placenta
steroid hormone
develops and maintains female reproductive systems and secondary sex characteristics
govern the menstrual cycle and pregnancy
progesterone
secreted by the ovaries and placenta
steroid hormone
promotes maintenance of the endometrium
govern the menstrual cycle and pregnancy
pineal gland
located deep within the brain
secretes melatonin
melatonin
secreted by the pineal gland
peptide hormone
involved in circadian rhythms
blood levels of melatonin are partially responsible for sensation of sleepiness
erythropoietin
secreted from the kidney
peptide hormone
stimulates bone marrow to produce erythrocytes
secreted in response to low oxygen levels in the blood (high altitude)
atrial natriuretic peptide (ANP)
secreted from the heart (atria)
peptide hormone
promotes salt and water excretion
when atria is stretched from excess blood volume, they release ANP
antagonistic to aldosterone bc it lowers blood volume and pressure
thymosin
secreted from the thymus
peptide hormone
stimulates T-cell development, important for development and differentiation
thymus atrophies by adulthood and thymosin levels drop
