adjacent cells coordinate cellular activities by exchanging ions and molecules across gap junctions
1. coordinate ciliary movement among epithelial cells, 2. coordinate the contractions of cardiac muscle cells, and 3. facilitate the propagation of action potentials from one neuron to the next at electrical synapses.
the use of chemical messengers to transfer information from cell to cell with a single tissue.
chemical messengers that are released in one tissue & transported in the bloodstream to alter the activities of specific cells in other tissues.
a substance with effects outside its tissue of origin is called a hormone if its chemical structure is known, and a factor if that structure remains to be determined.
specific cells that have receptors needed to bind and "read" the hormonal message when it arrives
the activity of hormones in coordination cellular activities in tissues in distant portions of the body.
- stimulate the synthesis of an enzyme or a structural protein not already present in the cytoplasm by activating appropriate genes in the cell nucleus
- increase or decrease the rate of synthesis of a particular enzyme or other protein by changing the rate of transcription or translation
- turn an existing enzyme or membrane channel "on" or "off" by changing its shape or structure.
A Hormone may?
- electrical activity in the presynaptic neuron is converted into the release of a chemical called a neurotransmitter that binds to receptors located in the plasma membrane of the postsynaptic cell
- can form between two neurons, a neuron & muscle cell (neuromuscular junction), & a neuron & gland cell (neuroglandular junction)
includes all the endocrine cells & tissues of the body that produce hormones of paracrine factors with effects beyond their tissues of origin
- both systems rely on the release of chemicals that bind to specific receptors on their target cells
- the two systems share many chemical messengers. norepinephrine & epinephrine are called hormones when released into the bloodstream, but neurotransmitters when released across synapses
- both systems are regulated mainly by negative feedback control mechanisms
- the two systems share a common goal: to preserve homeostasis by coordinating & regulating the activities of other cells, tissues, organs & systems
Nervous System vs. Endocrine System
glandular secretory cells that release their secretions into the extracellular fluid
secrete their products onto epithelial surfaces, generally by way of ducts.
- amino acid derivatives
- peptide hormones
- lipid derivatives
Hormones can be divided into three groups:
relatively small molecules that are structurally related to amino acids, the building blocks of proteins
Biogenic amines (amino acid)
The primary hormone made from tryptophan is ______, produced by the pineal gland.
- thyroid hormones, produced by the thyroid gland
- the compounds epinephrine (E), norepinephrine (NE), & dopamine, which are sometimes called catecholamines
Made from tyrosine & tryptophan:
- steroid hormones
The two classes of lipid derivatives:
- signaling molecules
- Include: leukotrienes, prostaglandins, thromboxanes, & prostacyclins
- it diffuses out of the bloodstream & binds to receptors on target cells
- it is absorbed & broken down by cells of the liver or kidneys
- it is broken down by enzymes in the blood or interstitial fluids
When is a freely circulating hormone inactivated?
(like a neurotransmitter receptor) -is a protein molecule to which a particular molecule binds strongly
on the plasma membrane or inside the cell
Where are hormone receptors located?
a hormone that binds to a receptor on the plasma membrane surface
an intermediary molecule that appears due to a hormone-receptor interaction
- cyclic AMP (cAMP), a derivative of ATP
- cyclic GMP (cGMP), a derivative of GTP, another high-energy compound
- calcium ions (Ca2+), focuses on cAMP & Ca2+
Important Second Messengers are:
magnifies the effect of a hormone on the target cells
the production of a linked sequence enzymatic reactions
- a process in which the presence of a hormone triggers a decrease in the number of hormone receptors
- cells become less sensitive to high levels of a particular hormone
- process in which the absence of a hormone triggers an increase in the number of hormone receptors
- cells become more sensitive to low levels of a particular hormone
The link between the first messenger & the second messenger generally involves a _____?
When is a G protein activated?
When a hormone binds to its receptor at the membrane surface.
an enzyme that attaches a high-energy phosphate group to another molecule in a process called phosphorylation.
inactivates cyclic AMP by converting it to AMP (adenosine monophosphate)
a process that opens the c channels & permits extracellular Ca2+ to enter the cell
- an intracellular protein
- can activate specific cytoplasmic enzymes
- calmodulin activation is also involved in the responses to oxytocin & to several regulatory hormones secreted by the hypothalamus
the combination of DAG & intracellular calcium ions activates a membrane protein called _______.
Protein kinase C (PKC)
stimulates the production of enzymes & structural proteins in skeletal muscle fibers, causing muscle size & strength to increase
- are the functional counterparts of neutral reflexes
- endocrine reflexes can be triggered by:
- humoral stimuli (changes in the composition of the extracellular fluid)
- hormonal stimuli (the arrival or removal of a specific hormone)
- neural stimuli (the arrival of neurotransmitters at neuroglandular junctions)
- controlled by negative feedback
- a simple endocrine
reflex involves only one hormone
- control hormone secretion by the heart, pancreas, parathyroid glands, & digestive tract
- more complex endocrine reflexes involve one or more intermediary steps & two or more hormones
- The hypothalamus itself acts as an endocrine organ. Hypothalamic neurons synthesize hormones & transport them along axons to the posterior lobe of the pituitary gland, where they are released into the circulation.
- The hypothalamus secretes
The hypothalamus provides the highest level of endocrine control. It integrates the activities of the nervous & endocrine systems in three ways:
special hormones that control endocrine cells in the pituitary gland
the secretory activities of endocrine cells in the anterior lobe of the pituitary gland
What do the hypothalamic regulatory hormones control?
substance secreted by endocrine tissues into the blood that acts on the target tissue to produce a specific response
the use of chemical messengers to transfer information from cell to cell within a single tissue
Describe paracrine communication
- direct communication
- paracrine communication
- endocrine communication
- synaptic communication
Identify four mechanisms of intercellular communication
(E) epinepherine, & (NE) norepinephrine
What does the adrenal medullae secrete?
include both neural & endocrine components because the adrenal medullae secrete both E & NE in response to action potentials rather than to circulating hormones
complex information by varying the frequency & pattern of action potentials in a sensory neuron
Sensory receptors provide:
a hormone that stimulates glucose uptake & utilization (when blood glucose levels climb, the pancreas increases its secretion of insulin)
several hypothalamic & pituitary hormones are released in sudden bursts
changes in the frequency of pulses & in the amount secreted in each pulse
What is the most complicated hormonal instructions from the hypothalamus?
- small, oval gland lies nestled within the sella turcica
- is inferior to the hypothalamus
- connected by slender, funnel-shaped structure called the infundibulum
- held in position by the sellar diaphragm
Pituitary Gland or Hypophysis
a depression in the sphenoid bone
- the base lies between the optic chiasm & the mammillary bodies
- cradled by the sella turcica
locks the pituitary gland in position & isolates it from the cranial cavity
- the pars distalis- the largest & most anterior portion of the pituitary gland
- an extension called the pars tuberalis- which wraps around the adjacent portion of the infundibulum
- the slender pars intermedia- a narrow band bordering the posterior lobe
Anterior lobe of the pituitary gland has three regions:
a swelling near the attachment of the infundibulum
allow relatively large molecules to enter or leave the bloodstream
blood vessels that link two capillary networks
Portal vessels (Portal veins)
stimulates the synthesis & secretion of one or more hormones at the anterior lobe
Releasing hormone (RH)
prevents the synthesis & secretion of hormones from the anterior lobe
Inhibiting hormone (IH)
- also known as thyrotropin
- targets the thyroid gland & triggers the release of thyroid hormones
Thyroid-Stimulating Hormone (TSH)
- also known as corticotropin
- stimulates the release of steroid hormones by the adrenal cortex
- specifically targets cells that produce glucocorticoids
- ACTH release occurs under the stimulation of CRH
Adrenocoricotropic Hormone (ACTH)
the outer portion of the adrenal gland
hormones that affect glucose metabolism
- from the hypothalamus
- as glucocorticoid levels increase, the rates of CRH release & ACTH release decline
Corticotropin-releasing hormone (CRH)
regulate the activities of the gonads
- from the hypothalamus
- stimulates production of gonadotropins
Gonadotropin-releasing hormone (GnRH)
- an abnormally low production of gonadotropins
- children: do not mature sexually
- adults: cannot produce functional sperm (males) or oocytes (females)
- follicle-stimulating hormone
- luteinizing hormone
The two gonadotropins are:
- also known as follitropin
- promotes follicle development in females
- in combination with luteinizing hormone, stimulates the secretion of estrogens by ovarian cells
- estradiol is the most important estrogen
- in males: FSH stimulates nurse cells
Follicle-stimulating hormone (FSH)
specialized cells in the seminiferous tubules where sperm differentiate
FSH is production is inhibited by:
a peptide hormone released by cells in the testes & ovaries
- also known as lutropin
- induces ovulation
- promotes ovarian secretion of estrogens & progesterone
Luteinizing hormone (LH)
the production of reproductive cells in females
prepares the body for possible pregnancy
stimulates the production of sex hormones by the interstitial cells of the testes
Interstitial cell-stimulating hormone (ICSH)
- male sex hormones
- most important is testosterone
- works with other hormones to stimulate mammary gland development
- stimulates milk production by the mammary glands
- in males: PRL helps regulate androgen production by making interstitial cells more sensitive to LH
also known as dopamine
Prolactin-inhibiting hormone (PIH)
- secreted by the hypothalamus
- circulating PRL stimulates PIH release & inhibits the secretion of PRF
Prolactin-releasing factors (PRF)
- pancreatic hormones
- hormones produced by the placenta
What cooperates in preparing the mammary glands for secretion?
What occurs only in response to oxytocin release at the posterior lobe of the pituitary gland?
- stimulates cell growth & replication by acceleration the rate of protein synthesis
Growth hormone (GH)
- skeletal muscle cells
- chondrocytes (cartilage cells)
What cells are sensitive to GH?
- primary mechanism- indirect
The stimulation of growth by GH involves two mechanisms:
- also known as insulin-like growth factors (IGFs)
- liver cells repspond to GH by synthesizing & releasing...
- stimulate tissue growth by binding to receptors on a variety of plasma membranes
- skeletal muscle fibers
- cartilage cells
- other target cells
Somatomedin increases the uptake of amino acids & their incorporation into new proteins in?
GH, acting through the somatomedins
What stimulates protein synthesis & cell growth?
as circulating fatty acid levels rise, many tissues stop breaking down glucose to generate ATP & instead start breaking down fatty acids
the elevation of blood glucose levels by GH because, diabetes mellitus (endocrine disorder) is characterized by abnormal high blood glucose concentrations
- also known as somatocrinin
- production of GH is regulated by...
- somatomedins inhibits _______
Growth hormone-releasing hormone (GH-RH)
- also known as somatostatin
- production of GH is regulated by...
- somatomedins stimulate ______
Growth hormone-inhibiting hormone (GH-IH)
- also known as melanotropin
- the pars intermedia may secrete two forms
- stimulates the melanocytes of the skin (increasing their production of melanin)
- dopamine inhibits the release of ______
Melanocyte-stimulating hormone (MSH)
a brown, black, or yellow-brown pigment
- during fetal development
- in very young children
- in pregnant women
- in the course of some diseases
When does the human pars intermedia secret MSH?
- also called the neurohypophysis
- contains the axons of hypothalamic neurons
Posterior lobe of the pituitary gland
- antidiuretic hormone (ADH)
- oxytocin (OXT)
Neurons of the supraoptic & paraventricular nuclei manufacture what?
- also known as vasopressin (VP)
- is released in response to a variety of stimuli (a rise in the solute concentration in the blood or a fall in blood volume or blood pressure)
Antidiuretic hormone (ADH)
- a rise in the solute concentration stimulates specialized neurons in the hypothalamus
- they respond to a change in the osmotic concentration of body fluids