adjacent cells coordinate cellular activities by exchanging ions and molecules across gap junctions

Direct Communication

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.

Gap Junctions

the use of chemical messengers to transfer information from cell to cell with a single tissue.

Paracrine Communication

chemical messengers that are released in one tissue & transported in the bloodstream to alter the activities of specific cells in other tissues.

Hormones

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.

hormone/factor

specific cells that have receptors needed to bind and "read" the hormonal message when it arrives

Target Cells

the activity of hormones in coordination cellular activities in tissues in distant portions of the body.

Endocrine Communication

• 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)

Synaptic Communication

includes all the endocrine cells & tissues of the body that produce hormones of paracrine factors with effects beyond their tissues of origin

Endocrine System

• 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

Endocrine Cells

secrete their products onto epithelial surfaces, generally by way of ducts.

Exocrine Cells

1. amino acid derivatives
2. peptide hormones
3. 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.

melatonin

1. thyroid hormones, produced by the thyroid gland
2. the compounds epinephrine (E), norepinephrine (NE), & dopamine, which are sometimes called catecholamines

Made from tyrosine & tryptophan:

1. eicosanoids
2. steroid hormones

The two classes of lipid derivatives:

• signaling molecules
• Include: leukotrienes, prostaglandins, thromboxanes, & prostacyclins

Eicosanoids

1. it diffuses out of the bloodstream & binds to receptors on target cells
2. it is absorbed & broken down by cells of the liver or kidneys
3. 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

Hormone Receptor

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

First Messenger

an intermediary molecule that appears due to a hormone-receptor interaction

Second Messenger

1. cyclic AMP (cAMP), a derivative of ATP
2. cyclic GMP (cGMP), a derivative of GTP, another high-energy compound
3. calcium ions (Ca²⁺), focuses on cAMP & Ca²⁺

Important Second Messengers are:

magnifies the effect of a hormone on the target cells

Amplification

the production of a linked sequence enzymatic reactions

Receptor Cascade

• 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

Down-regulation

• 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

Up-regulation

The link between the first messenger & the second messenger generally involves a _____?

G protein

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.

Kinase

inactivates cyclic AMP by converting it to AMP (adenosine monophosphate)

Phosphodiesterase (PDE)

a process that opens the c channels & permits extracellular Ca²⁺ to enter the cell

Phosphorylation

• 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

Calmodulin

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

Testosterone

• are the functional counterparts of neutral reflexes
• endocrine reflexes can be triggered by:
  1. humoral stimuli (changes in the composition of the extracellular fluid)
  2. hormonal stimuli (the arrival or removal of a specific hormone)
  3. neural stimuli (the arrival of neurotransmitters at neuroglandular junctions)

Endocrine Reflexes

• 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

Endocrine Reflexes

1. 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.
2. 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

Regulatory Hormones

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

Define hormone.

the use of chemical messengers to transfer information from cell to cell within a single tissue

Describe paracrine communication

1. direct communication
2. paracrine communication
3. endocrine communication
4. 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

Nueroendocrine Reflexes

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)

Insulin

several hypothalamic & pituitary hormones are released in sudden bursts

Pulses

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

Sella turcica

• the base lies between the optic chiasm & the mammillary bodies
• cradled by the sella turcica

Infundibulum

locks the pituitary gland in position & isolates it from the cranial cavity

Sellar diaphragm

1. the pars distalis- the largest & most anterior portion of the pituitary gland
2. an extension called the pars tuberalis- which wraps around the adjacent portion of the infundibulum
3. 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

Median eminence

allow relatively large molecules to enter or leave the bloodstream

Fenestrated capillaries

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

Adrenal Cortex

hormones that affect glucose metabolism

Glucocorticoids

• 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

Gonadotropins

• 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)

Hypogonadism

1. follicle-stimulating hormone
2. 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

Nurse cells

inhibin

FSH is production is inhibited by:

a peptide hormone released by cells in the testes & ovaries

Inhibin

• also known as lutropin
• induces ovulation
• promotes ovarian secretion of estrogens & progesterone

Luteinizing hormone (LH)

the production of reproductive cells in females

Ovulation

prepares the body for possible pregnancy

Progesterone

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

Androgens

• estrogens
• progesterone
• androgens

inhibit...

GnRH production

• 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

Prolactin (PRL)

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)

• prolactin
• estrogens
• progesterone
• glucocorticoids
• pancreatic hormones
• hormones produced by the placenta

What cooperates in preparing the mammary glands for secretion?

milk ejection

What occurs only in response to oxytocin release at the posterior lobe of the pituitary gland?

• somatotropin
• stimulates cell growth & replication by acceleration the rate of protein synthesis

Growth hormone (GH)

cartilage cells

Chondrocytes

• skeletal muscle cells
• chondrocytes (cartilage cells)

What cells are sensitive to GH?

1. primary mechanism- indirect
2. direct

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

Somatomedins

• 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

Glucose-sparing effect

the elevation of blood glucose levels by GH because, diabetes mellitus (endocrine disorder) is characterized by abnormal high blood glucose concentrations

Diabetogenic effect

• 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

Melanin

1. during fetal development
2. in very young children
3. in pregnant women
4. 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

1. antidiuretic hormone (ADH)
2. 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

Osmoreceptors