Mega BIO TEST 2 Study Cards

Homeostatic regulation

Keeping the body's internal conditions within a workable range even when the outside environment or the body's activity changes.

Two main systems that regulate homeostasis

The nervous system and the endocrine system.

Nervous system vs. endocrine system

The nervous system usually sends fast, targeted electrical signals along neurons and chemical signals across synapses; the endocrine system releases hormones into blood, so effects are usually slower to begin and longer lasting.

What do the nervous and endocrine systems have in common?

Both detect information, process or integrate it, send a signal, and cause a target cell or organ to respond.

Sensor / receptor in a homeostatic system

Detects a change or stimulus.

Integrating center

Receives information, processes it, and determines an appropriate response.

Effector

The cell, tissue, or organ that carries out the response.

Transducer

Something that converts one form of information or energy into another form the system can use.

First messenger

The original chemical signal outside a target cell, such as a hormone or neurotransmitter.

Target cell

A cell that can respond to a signal because it has the appropriate receptor and internal machinery.

Why doesn't every cell respond to every hormone?

Only cells with the correct receptor and the machinery to carry out the response can respond to that signal.

What determines the specific effect of a chemical signal?

The signal itself, the receptor it binds, the signal-transduction pathway, and the enzymes or other molecules inside the target cell.

Signal transduction

The process that converts a signal received at a cell into changes inside that cell.

Autocrine signaling

A cell releases a chemical signal that acts on the same cell that released it.

Paracrine signaling

A cell releases a chemical signal that affects nearby cells; the signal does not need to travel through the whole bloodstream.

Endocrine signaling

Endocrine cells release hormones into the bloodstream so they can reach target cells farther away.

Neural signaling

Neurons transmit electrical signals along their membranes and commonly release neurotransmitters onto nearby target cells.

Neurohormone

A chemical released by a neuron into the blood to act on distant target cells.

Neurosecretory cell

A neuron-like cell that releases chemical signals into nearby blood vessels rather than only communicating across a synapse.

Pheromone

A chemical signal released by one organism that affects other members of the same species.

Eicosanoids

Lipid-derived chemical signals that can act locally, including as paracrines, and can participate in more than one signaling system.

Endocrine secretion

Releasing a chemical signal into the blood without using a duct.

Exocrine secretion

Releasing a substance through a duct onto a surface or into a body cavity, such as digestive enzymes entering the gut.

Hormone: classical definition

A chemical made by living cells, released into the blood, carried some distance, and able to cause a response in specific target cells.

Why are some hormone-like signals exceptions to the classical hormone definition?

Some act locally, are made in unusual locations, or reach their targets by pathways that do not fit every part of the traditional definition.

Prostaglandins

Eicosanoid signals that often act locally and can influence processes such as inflammation, smooth-muscle activity, and other tissue responses.

Growth factors

Signals that influence cell growth, division, survival, or differentiation; some can also be involved in abnormal growth when their regulation is disrupted.

APUD cells

Cells that take up precursor molecules and decarboxylate them; they commonly produce biogenic amines and can also make peptide signals.

APUDoma

A tumor of APUD-type cells that may release hormones or hormone-like chemicals inappropriately, sometimes causing disease.

Renin-angiotensin system: overall purpose

A hormone-related pathway that helps regulate blood pressure, blood volume, and salt-water balance.

Renin

An enzyme released by the kidneys that converts angiotensinogen into angiotensin I.

ACE (angiotensin-converting enzyme)

Converts angiotensin I into angiotensin II.

Angiotensin II

Raises blood pressure and helps conserve sodium and water, including by promoting aldosterone release.

Vitamin D activation pathway

Vitamin D is modified through steps involving the skin, liver, and kidneys; the kidney produces active calcitriol, which helps increase calcium absorption.

Calcitriol

The active form of vitamin D; increases calcium absorption from the gut and helps the kidneys retain calcium.

Four major hormone chemistry groups in this outline

Peptides/proteins/glycoproteins, biogenic amines, steroids, and iodinated amino acids.

Peptide/protein hormones

Hormones made from amino-acid chains; they are generally water-soluble and bind to receptors on the target-cell surface.

Glycoprotein hormone

A protein hormone with attached carbohydrate groups.

Biogenic amines

Signals made from amino acids; examples include epinephrine, norepinephrine, dopamine, and melatonin.

Steroid hormones

Hormones derived from cholesterol; examples include cortisol, aldosterone, testosterone, estrogens, and progesterone.

Iodinated amino-acid hormones

Thyroid hormones T3 and T4, made by adding iodine to tyrosine residues in thyroglobulin.

Which hormone group is derived from cholesterol?

Steroid hormones.

Which gland makes T3 and T4?

The thyroid gland; these hormones are modified, iodine-containing forms of tyrosine.

Hormone family

A group of related hormones with similar structure or evolutionary origin, often made from related genes.

Glycoprotein hormone family examples

TSH, FSH, LH, and hCG.

Growth hormone family examples

Growth hormone (GH), prolactin (PRL), and human placental lactogen (hPL).

Gastrin family examples

Gastrin and cholecystokinin (CCK).

Insulin family examples

Insulin, IGF-I, IGF-II, and relaxin.

AVP and oxytocin relationship

They are related peptide hormones in the same hormone family.

Hydrophilic hormone

A water-attracting hormone that usually cannot cross the lipid membrane easily and therefore commonly uses a cell-surface receptor.

Hydrophobic hormone

A lipid-attracting hormone that can often cross the cell membrane and bind to an intracellular receptor.

Typical action of peptide and many amine hormones

They bind transmembrane receptors and activate signaling inside the cell, often using second messengers.

Typical action of steroid and thyroid hormones

They enter cells and bind intracellular receptors; their effects often involve changing gene expression and usually develop more slowly but last longer.

Second messenger

A molecule or ion inside the target cell that carries the message from an activated receptor to other cell machinery.

Examples of second messengers

cAMP, cGMP, calcium ions (Ca2+), IP3, and DAG.

Adenylate cyclase

An enzyme that converts ATP into cyclic AMP (cAMP).

Phosphodiesterase

An enzyme that breaks down cyclic nucleotides such as cAMP and cGMP, helping end or regulate their signals.

Protein kinase

An enzyme that adds phosphate groups to proteins; phosphorylation can activate or inhibit a protein.

Tyrosine kinase receptor

A cell-surface receptor whose enzyme activity adds phosphate groups to tyrosine residues on proteins.

JAK pathway

A receptor-linked signaling pathway that uses Janus kinases to activate intracellular proteins and alter cell responses, often gene expression.

IP3/DAG pathway: key enzyme

Phospholipase C acts on a membrane phospholipid to produce IP3 and DAG.

IP3

A second messenger that promotes calcium release from intracellular stores, especially the smooth endoplasmic reticulum.

DAG

Diacylglycerol, a second messenger that helps activate protein kinase C.

Calmodulin

A calcium-binding protein that changes activity when it binds Ca2+ and then helps regulate target proteins.

Nitric oxide (NO)

A gaseous chemical signal that can act inside or between cells; it is often linked to cGMP signaling.

How can the same hormone cause different responses in different tissues?

Different tissues may have different receptors, signaling pathways, enzymes, and target proteins.

What does an agonist do?

Binds to a receptor and activates it, mimicking or increasing the effect of the natural signal.

Competitive antagonist

Competes with the natural signal for the same receptor-binding site but does not activate the receptor normally.

Noncompetitive antagonist

Reduces a signal's effect without simply competing for the same binding site; it may interfere with receptor function or a later step.

Synergism

Two signals work together to produce a larger effect than either would produce alone, often more than an additive effect.

Permissiveness

One hormone allows another hormone to produce its full effect, often by increasing receptor availability or supporting the other hormone's pathway.

Additive hormone effect

Two hormones produce effects that add together.

Up-regulation of receptors

A target cell increases the number of receptors, often making it more responsive to a signal.

Down-regulation of receptors

A target cell decreases the number of receptors, often making it less responsive to a signal.

Desensitization

A target cell becomes less responsive after prolonged or excessive stimulation; this is related to, but not exactly the same as, down-regulation.

Hormone half-life

The time needed for the amount or concentration of a hormone in the body to fall by half.

Why do hormone-binding proteins matter?

They carry poorly water-soluble hormones, can increase total hormone concentration in plasma, protect hormones from rapid breakdown or excretion, and extend half-life.

Free vs. protein-bound hormone

Free hormone is generally the portion able to leave the blood and bind to target-cell receptors; bound hormone acts as a circulating reserve.

Why can total thyroid hormone be high while a person has normal thyroid function?

If most of the extra measured hormone is protein-bound, the free active amount may still be normal.

How are peptide hormones cleared?

Proteases break them into smaller peptides or amino acids; breakdown occurs in target cells, blood, and the liver, and fragments may be excreted by the kidneys.

How are amines cleared?

Enzymes break them down, often in target tissues, and breakdown products are excreted by the kidneys.

How are thyroid hormones cleared?

Deiodinase enzymes remove iodine as part of their breakdown and processing.

How are steroid hormones made easier to excrete?

They can be modified or linked to glucuronides or sulfates, making them more water-soluble so the kidneys can excrete them more readily.

Endogenous rhythm

A biological cycle generated within the body, such as a daily rhythm.

Circadian rhythm

An endogenous rhythm with a cycle of about 24 hours.

Ultradian rhythm

An endogenous rhythm that repeats more than once in a 24-hour period.

Circannual rhythm

An endogenous rhythm with a cycle of about one year.

Substrate-level regulation of hormone secretion

A substance being regulated directly influences hormone release; for example, high blood glucose stimulates insulin secretion.

Endocrine regulation of hormone secretion

One hormone stimulates or inhibits the secretion of another hormone.

Negative feedback

A response reduces the original stimulus, helping bring a regulated variable back toward its normal range.

Positive feedback

A response strengthens the original stimulus; it usually continues until a specific event ends the loop.

Long-loop negative feedback

A hormone from a downstream endocrine gland feeds back to inhibit the pituitary and/or hypothalamus that stimulated it.

Short-loop negative feedback

A pituitary hormone feeds back to reduce the release of the hypothalamic hormone that stimulated it.

Pineal gland: melatonin

Melatonin helps regulate daily and annual biological rhythms and can influence hormones such as gonadotropins.

Anterior pituitary: GH

Growth hormone stimulates body growth, cell division, and related growth processes.

Anterior pituitary: prolactin (PRL)

Stimulates milk production in mammary glands.

Anterior pituitary: ACTH

Stimulates the adrenal cortex to produce and release steroid hormones, especially cortisol.

Anterior pituitary: TSH

Stimulates thyroid growth and thyroid hormone synthesis and secretion.

Anterior pituitary: FSH

A gonadotropin involved in ovarian follicle development and egg production, or sperm production in the testes.

Anterior pituitary: LH

A gonadotropin involved in ovulation and gonadal sex-steroid production; in testes it stimulates testosterone production.