Bio Chapter 45 - Hormones and the Endocrine System

Animal hormones

chemical signals that are secreted into the circulatory system and communicate regulatory messages within the body

Hormones reach all parts of the body, but only target...

cells that have receptors for that hormone

nervous system

is a network of specialized cells—neurons—that transmit signals along dedicated pathways

The nervous and endocrine systems often overlap in function (True or False)

True :)

Communication between animal cells through secreted signals can be classified by two criteria:

The type of secreting cell
The route taken by the signal in reaching its target

Endocrine signaling

Endocrine signaling maintains homeostasis, mediates responses to stimuli, and regulates growth and development

Paracrine signaling and Autocrine signaling

Local regulators are molecules that act over short distances, reaching target cells solely by diffusion

Paracrine and Autocrine signaling play roles in processes such as...

blood pressure regulation, nervous system function, and reproduction

prostaglandins

Local regulators that mediate such signaling, function in the immune system and blood clotting.

Synaptic signaling

neurons form specialized junctions with target cells, called synapses

What happens at synapses?

secreted molecules called neurotransmitters diffuse short distances and bind to receptors on target cells

neuroendocrine signaling

specialized neurosecretory cells secrete neurohormones that diffuse from nerve endings into the bloodstream

pheromones

Members of some animal species may communicate with pheromones, chemicals that are released into the environment

Pheromones serve many functions, including...

marking trails leading to food, defining territories, warning of predators, and attracting potential mates

Hormones fall into three major classes

polypeptides, steroids, and amines

Water-soluble hormone classes:

Polypeptides and most amines

lipid-soluble hormone classes:

Steroid hormones and other largely nonpolar hormone

epinephrine (or adrenaline)

regulates many organs in response to stressful situations
Binds to receptors on the plasma membrane of liver cells
This triggers the release of messenger molecules that activate enzymes and result in the release of glucose into the bloodstream

In female birds and frogs...

estradiol, a form of estrogen, binds to a cytoplasmic receptor in liver cells
The estradiol-bound receptor activates transcription of genes needed to produce egg yolk

Endocrine cells are often grouped in ductless organs called...

endocrine glands (Inside)and exocrine glands (Outside), such as salivary glands, have ducts to carry secreted substances onto body surfaces or into body cavities

secreted substances onto body surfaces or into body cavities

Salivary
Lacrimal
Sebaceous
Mammary
Mucus
Ceruminous

hypothalamus

coordinates endocrine signaling
- It receives information from nerves throughout the body and initiates appropriate neuroendocrine signals

pituitary gland

At the base of the hypothalamus, composed of the posterior pituitary and anterior pituitary

posterior pituitary

tores and secretes hormones that are made in the hypothalamus by neurosecretory cells

anterior pituitary

makes and releases hormones under regulation of the hypothalamus

thyroid hormone

regulates many functions
- If thyroid hormone level drops in the blood, the hypothalamus secretes thyrotropin-releasing hormone (TRH), causing the anterior pituitary to secrete thyroid-stimulating hormone (TSH)

TSH stimulates release of thyroid hormone by the...

thyroid gland

Thyroid hormone is the only...

odine-containing molecule synthesized in the body

With low levels of thyroid hormone, due to insufficient iodine, the...

pituitary continues to secrete TSH
This causes the thyroid to enlarge, resulting in a goiter

Growth hormone (GH)

secreted by the anterior pituitary gland.
- The liver is a major target and responds to GH by releasing insulin-like growth factors (IGFs)

insulin-like growth factors (IGFs)

stimulate bone and cartilage growth

An excess of GH can cause____, while a lack of GH can cause ______.

gigantism, dwarfism

parathyroid hormone (PTH)

is released by the parathyroid glands when Ca2+ levels fall below a set point

Calcitonin (produced by the thyroid)

decreases the level of blood Ca2+

The adrenal glands are located...

atop the kidneys

Each adrenal gland consists of two glands:

the adrenal medulla (inner portion) and adrenal cortex (outer portion)

adrenal medulla

secretes epinephrine (adrenaline) and norepinephrine (noradrenaline)
- They coordinate a set of physiological responses that comprise the “fight-or-flight” response

adrenal medulla 3 functions:

- Trigger the release of glucose and fatty acids into the blood
- Increase oxygen delivery to body cells
- Direct blood toward heart, brain, and skeletal muscles and away from skin, digestive system, and kidneys

The same hormone may have different effects on target cells that have...

Different receptors for the hormone
Different signal transduction pathways

adrenal cortex

becomes active under stressful conditions including low blood sugar, decreased blood volume and pressure, and shock

corticosteroids

A series of hormonal signals lead to production and secretion of a family of steroids

Glucocorticoids

such as cortisol, influence glucose metabolism and the immune system

Mineralocorticoids

such as aldosterone, affect salt and water balance

The gonads, testes and ovaries, produce most of the sex hormones:

androgens, estrogens, and progesterone

All three sex hormones are found in both males and females (True or false)

TRUE, but in different proportions.

The testes primarily synthesize...

androgens, mainly testosterone, which promote development of male reproductive structures
- Testosterone is responsible for male secondary sex characteristics

Estrogens

most importantly estradiol, are responsible for maintenance of the female reproductive system,

progesterone

is primarily involved in preparing and maintaining the uterus

pineal gland

located in the brain, secretes melatonin
- Primary functions of melatonin appear to relate to biological rhythms

The endocrine system relies on __________ that __________ all of the cells of the body.

hormones; reach

A cell releases a cytokine, which binds to and acts on a neighboring cell. This represents an example of __________.

paracrine signaling

Because most chemical signals are unable to pass through the plasma membrane, the cellular action they initiate results from __________.

the activation of a signal transduction pathway

What is the role of a second messenger in hormone action?

It relays a hormone's message inside a target cell.

a role of the local regulator nitric oxide (NO):

When oxygen levels fall, nitric oxide activates an enzyme that relaxes smooth muscle. This dilates blood vessels and improves blood flow.

Ibuprofen is known for its pain-relieving and anti-inflammatory properties because it inhibits the synthesis of __________.

prostaglandins

In insects, ecdysteroid is released __________.

in response to prothoracicotropic hormone

The major tropic action of growth hormone is to signal the __________ to release __________.

liver; insulin-like growth factors (IGFs)

How is the level of thyroxine in the blood regulated?

High levels of T3 and T4 inhibit the secretion of TRH and TSH.

A goiter may form because __________.

low blood levels of T3 and T4 inhibit the negative feedback loop and an overload of TSH causes enlargement of the gland

What endocrine organ only stores hormones produced by the hypothalamus?

Posterior pituitary

A doctor might give an expectant mother __________ to stimulate uterine contractions and induce labor.

oxytocin

The regulation of water volume in the blood involves which hormone?

ADH

How does the hypothalamus control the secretion of growth hormone (GH) from the anterior pituitary?

The hypothalamus produces a releasing hormone that stimulates the pituitary to secrete GH.

What is a neurohormone secreted by the posterior pituitary?

Oxytocin

Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) are tropic hormones that are also known as __________.

gonadotropins

prolactin

It controls fat metabolism and reproduction in birds.

How does parathyroid hormone affect levels of Ca2+ in the blood?

When Ca2+ levels fall, PTH stimulates bone cells to decompose the matrix of bone and stimulates reabsorption of Ca2+ in the renal tubules.

The adrenal medulla is the gland is stimulated by nerve signals carried from the brain. (True or False)

True

What endocrine gland releases steroid hormones?

Adrenal cortex

What is a problem with the long-term use of glucocorticoids, such as cortisone, to treat inflammation?

Suppression of the immune system

In the winter, the __________ of vertebrates is apt to produce __________ than in summer months.

pineal gland; more melatonin

Hormones secreted by the posterior pituitary gland are made in the…

hypothalamus

When a person drinks alcohol, the rate of urination increases. Which of the following best accounts for the increase in urination above normal rates?

Alcohol inhibits the release of ADH.

A cell with membrane-bound proteins that selectively bind a specific hormone is called that hormone's…

target cell

Fight-or-flight reactions include activation of the…

adrenal medulla, leading to increased secretion of epinephrine

The primary difference between estrous and menstrual cycles is that…

the endometrium shed by the uterus during the estrous cycle is reabsorbed with no extensive fluid flow out of the body. whereas the shed endometrium of menstrua cvcles is excreted from the body.

Melatonin is secreted by the ______.

pineal gland during the night