1208 Unit 3

ligands

Chemical signals sent between cells. it binds to a receptor during chemical signaling. Examples of ligands include hormones and neurotransmitters

Categories of cell signaling

Direct, autocrine, paracrine, endocrine, pheromones

Direct signaling

communication between cells that are in direct contact with each other. This communication is often mediated by gap junctions in animal cells and plasmodesmata in plant cells

Autocrine signaling

occurs when a ligand acts on the same cell that releases it

Paracrine signaling

occurs when a ligand diffuses in a small area and only acts on neighboring cells

nueral signals

specialized subset of paracrine signals, diffusing a very short distance within the synaptic cleft between adjacent neurons

endocrine signaling

signals are hormones, which are carried throughout the organism’s body via the vascular system (in either plants or animals!) to act on cells that may be very far away from the cells which released the ligand

neuroendocrine

signals are a specialized subcategory of endocrine signals that are released by neurons but travel via the vascular system to act on cells that are far away.

Pheromone signaling

are released into the environment to act on the cells in a different individual

How is a hormone secreted?

A hormone is secreted from a cell or gland into the vascular system (or into the environment, in the case of single-celled organisms).

How do hormones act on distant cells?

Hormones act on distant cells in other locations in the body (or community, in the case of single-celled organisms) by traveling through the circulatory system (or environment).

What is signal amplification in hormones?

Signal amplification allows hormones to cause large effects even with only small amounts of the molecule.

Why do hormones only affect specific target cells?

Hormones only affect specific target cells because only those cells possess a receptor that is capable of binding to that particular hormone.

What is a characteristic response of hormones?

Hormones cause a characteristic response that is always the same in a given set of circumstances due to the activation of the receptor initiating a specific signaling pathway.

What role do hormones play in feedback loops?

Hormones are part of a feedback loop, which can be either positive or negative.

6 classes of hormones

hydrophilic, peptide, amino-acid, hydrophobic, steroid, gas

Hydrophilic

hormones are soluble in water or aqueous solution, meaning that they cannot cross the cell's hydrophobic plasma membrane. The receptor for a hydrophilic hormone must be present on the cell's surface for the hormone to reach it

Peptide-hormones

hydrophilic, small protiens

amino-acid hormones

hydrophilic, which are modified amino acids

Hydrophobic

hormones are typically small nonpolar molecules that are insoluble in water, meaning that they can easily cross the cell's hydrophobic plasma membrane. The receptor for a hydrophobic hormone is located within a cell's cytoplasm or nucleus

steroid hormones

hydrophobic, which are small organic compounds with characteristic carbon ring structures

gas hormones

hydrophobic, gases capable of acting like ligands

Hormone signaling pathway steps

signal reception, signal transduction, signal amplification, signal response and feedback loops

What is the first step in hormone signaling?

The first step is signal reception, where the hormone binds to the receptor.

Where do nonpolar, hydrophobic ligands bind?

They bind to internal receptors, also known as intracellular or cytoplasmic receptors, found in the cytoplasm.

What happens when a hormone binds to its intracellular receptor?

The receptor changes shape, allowing the receptor-hormone complex to enter the nucleus.

What is the role of the hormone-receptor complex in gene expression?

It binds to specific sequences of DNA and activates or represses transcription of certain genes.

How do hydrophilic ligands interact with cells?

They bind to cell-surface receptors, also known as transmembrane receptors, on the cell surface.

What is signal transduction?

It is the process of converting an extracellular signal into an intercellular signal.

What do hydrophilic ligands activate upon binding to their receptors?

They activate chemical or protein 'messengers' to relay the signal from outside to inside the cell.

What is signal transduction?

the process by which a signal is transmitted through a cell via a series of molecular events.

What type of ligands require signal transduction?

Hydrophilic ligands because they must bind to extracellular receptors and cannot cross the plasma membrane.

What happens when a hormone binds to a cell-surface receptor?

The intracellular portion of the receptor changes shape, activating a signaling pathway or signaling cascade.

What is a signaling pathway?

a series of events that occur in a defined sequence, often involving the activation of enzymes and proteins.

What are second messengers?

non-protein signaling molecules, such as calcium or cyclic AMP, that propagate the signal throughout the cell.

What is a phosphorylation cascade?

a series of proteins activated by the addition of phosphate groups, which changes their activity.

What is the ultimate result of signal transduction pathways?

The ultimate result of signal transduction pathways is some type of cellular response, which may include changes in gene expression.

What is signal amplification in hormones?

a phenomenon where a very small amount of a hormone can result in a very strong physiological response.

How do hydrophilic hormones amplify their signal?

via second messengers or phosphorylation cascades.

What is the role of second messengers in signal amplification?

produce or release thousands of molecules in response to a hormone signal.

What is a phosphorylation cascade?

A phosphorylation cascade is a process where thousands of proteins become activated in response to a hormone signal.

How do nonpolar hormones amplify their signal?

amplify their signal during transcription and translation.

What happens during transcription in signal amplification?

hundreds of copies of mRNA are synthesized from a single gene.

What happens during translation in signal amplification?

hundreds of copies of each protein are synthesized from a single mRNA.

Signal response

last stage in hormone signaling

positive feedback loop

occurs when the response to a hormone causes the original signal to be amplified or increase

negative feedback loop

occurs when the response to a hormone causes the original signal to be decreased

signaling cross walks

if signals from two different hormones are received at the same time, the outcome can be different than if they came in separately

quorum sensing

phenomenon where individual single cells monitor the density of their population; once the population reaches a specific density, the cells collectively change their gene expression and behavior at the same time

autoinducer

continuous secretion of a signaling molecule, or a bacterial hormone

Where is the hypothalamus located?

Within the brain

What systems does the hypothalamus integrate?

The endocrine and nervous systems

What type of input does the hypothalamus receive?

Input from the body and other brain areas

What does the hypothalamus initiate in response to environmental changes?

Endocrine responses

Where are the hormones the hypothalamus secretes?

posterior pituitary gland

What type of hormones does the hypothalamus synthesize and secrete to control the anterior pituitary gland?

Regulatory hormones

pituitary gland

the body's "master gland," located at the base of the brain and attached to (and regulated by) the hypothalamus

anterior pituitary gland

regulated by releasing or release-inhibiting hormones produced by the hypothalamus

posterior pituitary gland

receives signals via neurosecretory cells to release hormones produced by the hypothalamus

Where is the thyroid gland located?

In the neck

What regulates the thyroid gland?

The hypothalamus-pituitary axis

What hormones does the thyroid gland produce?

Thyroxine (T4) and triiodothyronine (T3)

What is the role of thyroxine (T4) and triiodothyronine (T3)?

They increase the basal metabolic rate and affect protein synthesis

How do thyroid hormones affect growth?

They help regulate long bone growth

What are the adrenal glands?

Two glands located on each kidney.

What are the two layers of the adrenal glands?

Adrenal cortex (outer layer) and adrenal medulla (inner layer).

What hormones does the adrenal cortex produce?

Mineralocorticoids (e.g., aldosterone) and glucocorticoids (e.g., cortisol).

What is the function of aldosterone?

Increases reabsorption of sodium by kidneys to regulate water balance.

What is the function of cortisol?

Increases blood glucose levels by stimulating glucose synthesis and gluconeogenesis.

What hormones does the adrenal medulla produce?

Epinephrine (adrenaline).

What is the role of epinephrine in the body?

It is a short-term stress response hormone that increases heart rate, breathing rate, and blood glucose levels.

How does epinephrine affect glucose in skeletal muscles?

It accelerates the breakdown of glucose.

What stimulates the release of epinephrine?

Neural impulses from the sympathetic nervous system.

Where is the pancreas located?

Between the stomach and the proximal portion of the small intestine.

What hormone does the pancreas produce to decrease blood glucose levels?

Insulin

What is the function of insulin?

It decreases blood glucose levels by promoting uptake of glucose by liver and muscle cells and conversion to glycogen.

What hormone does the pancreas produce to increase blood glucose levels?

Glucagon

What is the function of glucagon?

It increases blood glucose levels by promoting breakdown of glycogen and release of glucose from the liver and muscle.

gonads

produce sex steroid hormones that promote development of secondary sex characteristics and regulation of gonad function

Insulin

produced by the beta cells of the pancreas, which release insulin when blood glucose levels rise above normal levels

What are the ways insulin lowers levels

-enhances the rate of glucose uptake and utilization by target cells, which use glucose for ATP production

-stimulates the liver to convert glucose to glycogen, which is then stored by cells for later use

-increases glucose transport into certain cells, such as muscle cells and the liver

-stimulates the conversion of glucose to fat in adipocytes and the synthesis of proteins.

How does insulin affect the liver's glucose levels?

Insulin stimulates the liver to convert glucose to glycogen, which is then stored by cells for later use.

Which types of cells does insulin increase glucose transport into?

Insulin increases glucose transport into certain cells, such as muscle cells and the liver.

What effect does insulin have on adipocytes?

Insulin stimulates the conversion of glucose to fat in adipocytes and the synthesis of proteins.

What is the overall effect of insulin on blood glucose concentrations?

These actions together cause blood glucose concentrations to fall, creating a hypoglycemic 'low sugar' effect.

How does the body respond to low blood sugar levels caused by insulin?

The low blood sugar effect inhibits further insulin release from beta cells through a negative feedback loop.

glucagon

raises blood glucose levels, causing a hyperglycemic effect

ways glucagon increases blood sugar

-stimulates the breakdown and release of glucose from glycogen in liver cells

-stimulates absorption of amino acids from the blood by the liver, which then converts them to glucose

-stimulates adipose cells to release fatty acids into the blood

glucagon and insulin are both negative or positive feedback loops

negative

juvenile hormone

promotes retention of larval characteristics

prothoracicotropic hormone

signals to the prothoracic gland to release the hormone ecdysone

Ecdysone

promotes either molting (shedding the exoskeleton) or metamorphosis

Growth and metamorphosis is which system?

crosstalk

glucocorticoids

mobilize lipid and protein reserves, stimulate gluconeogenesis, conserve glucose for use by neural tissue, and stimulate the conservation of salts and water

what does the sympathetic nervous system use to regulate stress response

hypothalamus

adrenal medulla

mediates short-term stress responses via nerve impulses

adrenal cortex

mediates long-term stress responses, via the hormone adrenocorticotropic hormone

adrenocorticotropic hormone is produced by

anterior pituitary gland

short-term stress releases what two hormones

epinephrine and norepinephrine

epinephrine and norepinephrine do what to regulate

-cause glycogen to be broken down into glucose and released from liver and muscle cells

-increase blood pressure

-increase breathing rate

-increase metabolic rate

-change blood flow patterns, leading to increased blood flow to skeletal muscles, heart, and brain; and decreased blood flow to digestive system, skin, and kidneys