Chapter 36 endocrine system

endocrine glands

Glands of the endocrine system that release hormones into the bloodstream

hypothalamic-pituitary axis

Goes from the hypothalamus to the anterior pituitary gland, and then from the anterior pituitary gland to target glands or tissues in the body

How can one hormone exert its effects on one cell type and another hormone exert its effect on a different cell type?

Hormones circulating in the bloodstream bind to receptors located either on the surface or inside target cells. Therefore, it is the presence or absence of a receptor for a given hormone that determines which cells respond and which do not.

Explain positive feedback during birth

In response to uterine contractions (the stimulus), the pituitary gland releases the hormone oxytocin. The release of oxytocin causes the uterine muscles (the effector) to contract more forcefully. The uterine contractions in turn stimulate (positive feedback) the pituitary gland to secrete more oxytocin, causing the uterine muscles to contract still more forcefully and frequently

How does the body, and in particular the endocrine system, maintain homeostasis?

Maintaing homeostasis depends on feedback from the target organ to the endocrine gland that secretes the hormone

Neurosecretary cells

a neuron in the vertebrate hypothalamus and the posterior pituitary gland that secretes hormones into the bloodstream

Explain Basics of positive feedback

a stimulus causes a response in the same direction of the initial stimulus, which leads to a further response, and so on. In the endocrine system, positive feedback to a stimulus leads to the secretion of a hormone that causes a response, and the response causes the release of more hormone. The result is an escalation of the response

Several hours after a meal as blood glucose levels fall, a different population of cells in the pancreas, called _______ cells secrete the hormone ________

alpha cells, glucagon

peptide hormones and amine hormones are both derived from

amino acids

The endocrine system does not regulate growth and development t/f

f

T/f Hormones do not act on specific cells

f hormones act on specific cells that bind that hormone

T/f hormones only are important in growth and development

false, hormones can regulate an organisms physiological response to the environment and help maintain stable physiological conditions within cells or within the animal as a whole

Organisms face constant changes in their environment, these changes often present physiological challenges or stresses that the organism must respond to by altering the _____________ of its body

functional state

glucose levels rise after a meal why

glucose is absorbed into the bloodstream from the intestine

Why do glucose levels lower

glucose is taken up by cells to meet their energy needs

insects produce a rigid exoskeleton which must be periodically shed and replaced by a larger one to enable the insect to ______

grow

homeostasis typically depends on what type of feedback

negative feedback

two general types of feedback are

negative feedback and positive feedback

Environmental cues activate the _____ system which can relay signals to the ______ system triggering a _______

nervous endocrine response

changes in light, temperature, the threat of a predator, or presence of a mate stimulate responses to the _______ system and _______ system

nervous system endocrine system

can steroid hormones evolve through changes in amino acid sequence

nope, they rely on changes in their synthetic enzymes or changes in the receptors they bind and the cellular response they trigger

In both cases (either high or low blood glucose levels) is sensed by cells of the _______ either being _____ cells for high glucose levels or _______ cells for low glucose levels and triggers a response (secretion of ______ or _______ ) that brings blood glucose levels back to a set point

pancreas beta alpha insulin glucagon

the hydrophilic hormones are

peptide hormones and amine hormones

Neurosecretary cells involvement with insects

peptide hormones are released from neurosecretary brain cells that act on the corpora alla and prothoracic gland, at appropriate times the neurosecretory brain cells secrete the peptide hormone PTTH which stimulates the release of ecdysone from the prothoracic gland, triggering the transition from larval to pupal and adult forms. Other neurosecretory brain cells also stimulate the corpora alla to produce juvenile hormones

Growth hormones are produced by the

pituitary gland

in some instances, it is necessary to accelerate the response of target cells for a period of time. That is the role of ________________

positive feedback

many physiological parameters such as blood glucose and calcium levels are maintained at relatively steady levels by negative feedback, explain this (Little detail)

A change in glucose or calcium levels cause a response that brings the level back to the starting point called the set point. In these cases, a change in level(stiumlus) is detected by a sensor in the endocrine organ. The endocrine organ (effector) releases a hormone, and the hormone causes a response that opposes the initial stimulus so that glucose or calcium levels move back to the set point

After the Pituitary gland releases ACTH what happens

ACTH acts on cells of the adrenal cortex, stimulating their secretion of cortisol

subsequent work showed that cells in a specialized region of the insect brain secrete the peptide now known as

prothoracicotropic hormone (PTTH)

in each case the response feeds back to the cells (negative feedback) to ______ further hormone secretion

reduce

In Rhodnius, Wigglesworth was able to show that paired endocrine glands, called corpora allata, in a certain region of the head release a hormone that does what

releases a hormone that normally prevents the earlier larvae stages from molting into the adult form, this hormone called juvenile hormone is released in decreasing amounts during each successive molt after the fifth and final stage, the level of juvenile hormone is so low that it no longer blocks maturation; thus, at the final molt the insect undergoes its final growth into the adult form

The target gland in turn, then does what

releases another hormone that acts on a second gland or tissue in the pathway and so on

In negative feedback the stimulus produces as _________ which then ________ the initial stimulus

response counteracts

peptide hormones are ___________ of amino acids , whereas amine hormones are

short chains derived from a single aromatic amino acid such as tyrosine

The second set is

signal transduction in the target cell

peptide and amine hormones alter the activity of the target by initiating _____________ within the target cell

signaling cascades The bound receptor activates an enzyme or other molecule within the cell and it in turn activates another, and so on. These signaling cascades can alter metabolism by activating or inhibiting enzymes, or they can lead to changes in gene expression

Hormones are typically released in _____ amounts

small

The amount of glucose in the blood of animals is maintained at a _____ level

steady

the hydrophobic hormones are

steriod hormones

In rhodnius you would expect PTTH to be released after a blood meal and acts to trigger the animals molt by

stimulating the release of a second hormone from the prothoracic gland called ecdysone

PTTH triggers molting by

stimulating the release of ecdysone, a steroid hormone that coordinates growth and reorganization of body tissues during a molt.

T/f Hormones also regulate growth in humans and other vertebrate animals

t

The brains of insects similar to the nervous systems of other invertebrates and vertebrate animals contain neurosecretory cells t/f

t

some hormonal signaling pathways involve the release of a hormone by one gland that acts on another gland as its target t/f

t

t/f Constant feedback between the response and the sensor maintains a set point, the maintenance of homeostasis is an active process

t

t/f in some insects however, the animal grows larger with every molt, but with little change in body form

t

t/f peptide hormones and amine hormones are more abundant than steriod hormones and are more diverse in their actions

t

t/f peptide hormones are sometimes long enough to be considered proteins

t

t/f relatively few hormone molecules can have a large effect on an organism

t

t/f steroid horomones typically have profound and long lasting effects on the cells and tissues they target, on a timescale of days to months, whereas peptide and amine hormones act on a timescale of minutes to hours

t

t/f the action of ecdysone is a good example of how a hormone can precisely coordinate broad changes in body organization and function, in contrast to the specific regulation that nerves provide

t

t/f the endocrine system has slower and more prolonged signaling

t

t/f because hormones are transmitted through the blood stream, this feedback can occur over varying distances within the body, coordinating the functions at several organs at any one time.

t/f

Why does oxytocin only affect uterine muscle cells and secretory cells in breast tissue

the cells of other organs do not express the receptor, so the hormone can exert its effect only on these specific tissues and no others

What happens in response to this feedback

the endocrine gland modifies its own subsequent production of hormone, either increasing or decreasing it.

what underlies homeostasis

the endocrine system

Since hormones are typically released in small amounts, why can they have large effects on physiology

they can exert strong effects on the overall physiology of an organism by amplification

shedding of the exoskeleton is known as

molting

What do releasing hormones do?

Bind to receptors on cells in the anterior pituitary gland, leading that organ to release a much larger amount of the associated hormones. For example, the hypothalmus secretes a corticotropin-releasing hormone, which stimulates the anterior pituitary gland to release a larger amount of adrenocorticotropin hormone (ACTH)

in some insects such as moths, the animals body also changes dramatically undergoing _______ at a key stage in development

metamorphosis

Glands

Organs or tissues in the body that create chemicals that control many of our bodily functions

British physiologist Vincent Wigglesworth studied the effects of hormones on the blood-sucking insect Rhodnius, explain his experiment

Rhodnius goes through five juvenile stages before developing into its final adult body form. It does not undergo metamorphosis, each of the developmental stages is triggered by a blood meal Wigglsesworth showed that he could prevent molting if the head of the insect were removed shortly after a blood meal, if the insect takes a blood meal and the head is removed a week later, the animals body undergoes a molt and grows its adult form (Insect can live w/o head) wigglsesworth hypothesized that a substance diffusing from the animals head controls its molt. If the head is removed shortly after a blood meal this substance does not have time to reach the insects body to trigger a molt but if the removal is delayed, than it does

Amplification occurs during two steps which happens ________ the hormone binds a cell receptor and _________ the cell afterward

before inside

positive feedback in mammals occurs during ________

birth

German endocrinologist alfred kuhn obtained a similar result in his experiments performed on moth caterpillars, tying the caterpillars head off from the rest of its body prevented molting. Wigglseworth and kuhn considered the diffusing substance to be a

brain hormone

What are some examples of cellular responses resulting from the binding of a hormone

can alter ion flow across a cell membrane change the biochemical activity of target cell initiate changes in gene expression

what can happen if the pituitary gland contains a tumor

can cause an overproduction of growth hormones leading to gigantism, whereas tumors that result in too little growth hormone cause pituitary dwarfism

the binding of a hormone to its receptor triggers _________ in the target cell resulting in ________

changes cellular response

steroid hormones are derived from

cholesterol

Most hormones have an ancient evolutionary history and evolutionary __________

conserved

cortisol function

cortisol acts on many different cells and tissues in the body, causing an acute stress response. Among its effects, it causes the liver to convert glycogen and amino acids to glucose. This action yields a weight of glucose that is 56k times heavier than the initial weight of releasing hormones secreted by the hypothalamus

if glucose levels are too high for too long they can ___________ organs

damage

WIthout some way to maintain a stable internal environment, changing environmental conditions would lead to what

dangerous shifts in an animals physiological function For example, an animals body weight depends on the regulation of its energy intake relative to energy expenditure. Disruption of hormones that regulate appetite and food intake can lead to obesity on the one hand or to weakness and lethary on the other hand.

As levels return to set point, secretion of the hormone _________ and there is a limit to further change

decreases

Diabetes mellitus is a disease characterized by high blood glucose levels. Given what you know about how insulin usually prevents high blood glucose levels, can you think of two different ways that diabetes can result?

diabetes can result either from decreased insulin production by the pancreas (type 1 diabetes) or a decreased effect of insulin on target cells (type 2 diabetes)

when insulin fails to control blood glucose levels, a disease called _______________ results

diabetes mellitus, diabetes causes cardiovascular and neurological damage, including loss of sensation in the extremities, particularly the feet

glucagon function

effects are roughly opposite to those of insulin, glucagon stimulates the breakdown of glycogen and its release from muscle and liver cells , the result is that blood glucose levels rise

Hormone signaling pathways between endocrine glands and tissues are often referred to as

endocrine axes

if glucose levels are too low cells of the body do not have a ready source of

energy

growth hormone controls

growth of the skeleton and many other tissues in the human body

In this way, insulin _____ against high levels of glucose in the blood

guards

Hormones that regulate the concentrations of key ions in the body such as K+ or Na+ are fundamental to

healthy nerve and muscle function, and fluid balance within the body

endocrine control of internal body functions is also central to __________ the macitence of a steady physiological state within a cell or an organism

homeostasis

T/f some receptors are located on the cell surface; others are located inside the cell. Where a receptor is located depends on characteristics of

hormone molecules themselves

when an animals body requires coordinated changes in multiple organ systems, _______________ by the endocrine system plays a critical role

hormone regulation

Growth and development require broad changes in many different organ systems. The release of circulating ___________ from the endocrine system accomplishes these changes, regulating how animals develop and grow

hormones

molting and metamorphosis are regulated by

hormones released from tissues inside the insects head

Hormones can be grouped into two general classes:

hydrophilic molecules, which cannot diffuse across the plasma memrbane, and hydrophobic molecules which can

In vertebrates , hormonal signals are amplified along a pathway called the

hypothalamic-pituitary axis

A positive feedback loop reinforces itself until it is

interrupted or broken by some sort of external signal outside the feedback loop but from within the body.

The endocrine system helps to regulate an organisms response to

its environment

each molting produces a new ____ stage

larval

The first set of signaling steps is

the passing of a signal from one endocrine gland to the next in a hormonal pathway

because most peptide and amine hormones are hydrophilic where must these hormones bind

to receptors on the surface of the cell

The hypothalamus initially releases _____ amounts of peptide hormones called

trace releasing hormones

hormone-receptor complexes that form in the cytoplasm are transported into the nucleus of the cell, these complexes most commonly act as

transcription factors, they stimulate or repress gene expression, thereby altering the proteins produced by the target cell

What does the presence of insulin do

triggers muscle cells and liver cells to take up glucose from the blood and either use it or convert it to a storage form called glycogen.

What happens following after eating a meal, when blood glucose levels rise

when blood glucose levels rise beta cells of the pancreas secrete the hormone insulin, which circulates in the blood

because steroid hormones are hydrophobic where would you expect they bind

with receptors in the cytoplasm or nucleus

can peptide hormones evolve?

yes through evolutionary changes in their amino acid sequence