Hormones n Homeostasis WADY EDT

8/13/2019 Hormones n Homeostasis WADY EDT

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Hormones, Endocrine System

& Homeostasis


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LOs

Describe hormones and endocrine system in

human

List several examples of hormones and their

functions

Explain the concept of homeostasis


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What are hormones?

Hormones are 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

have receptors for that hormone


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How do cells communicate?

Two systems coordinate communication throughout the body:

the endocrine system and the nervous system

The endocrine system secretes hormones that coordinateslower but longer-acting responses including reproduction,

development, energy metabolism, growth, and behavior

The nervous system conveys high-speed electrical signalsalong specialized cells called neurons; these signals regulate

other cells


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Endocrine Signaling

Hormones secreted into extracellular fluids by endocrine cells

reach their targets via the bloodstream

Endocrine signaling maintains homeostasis, mediatesresponses to stimuli, regulates growth and development


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Endocrine Tissues and Organs

In some tissues, endocrine cells are grouped together in

ductless organs called endocrine glands

Endocrine glands secrete hormones directly into surrounding

fluid

These contrast with exocrine glands, which have ducts and

which secrete substances onto body surfaces or into cavities


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Major endocrine glands:

Hypothalamus

Pineal gland

Pituitary gland

Thyroid gland

Parathyroid glands(behind thyroid)

Adrenal glands

(atop kidneys)

Pancreas

Ovaries (female)

Testes (male)

Organs containingendocrine cells:

Thymus

Heart

Liver

Stomach

Kidneys

Smallintestine


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Hormone Actions

Affects parts distant from gland

May affect numerous parts of the body

Effects take longer than nervous system

Effects may be long lasting


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Hormone Activity

Affect only target cells

Hormone must bind to a receptor

Receptor activates chain of events


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Classes of Hormones

Peptide hormones (most common) Steroid hormones (gonads & adrenal cortex)


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Feedback Regulation

A negative feedback loop inhibits a response by reducing theinitial stimulus, thus preventing excessive pathway activity

Positive feedback reinforces a stimulus to produce an even

greater response

For example, in mammals oxytocin causes the release of milk,

causing greater suckling by offspring, which stimulates the

release of more oxytocin


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Growth Hormone

Controls normal growth

Hypersecretion

Gigantism

Acromegaly

Bones of hands & face

thicken


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Growth Hormone

Acromegaly

Bones of hands & face thicken


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Pineal Gland

Embedded within brain

Produces melatonin

Increase in secretion at night

Helps set circadian rhythms

physical, mental and behavioral changes that follow

a roughly 24-hour cycle, responding primarily to

light and darkness in an organisms environment can influence sleep-wake cycles, hormone release,

body temperature and other important bodily

functions


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Thyroid Gland

Below level of voice box

Hormones that regulate metabolism

Most body cells have receptors

Negative feedback loop regulates release


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Thyroid Disorders

Graves disease

Hyperthyroidism

Rapid heart rate

Nervousness

Protrusion of eyes


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Thyroid Disorders

Goiter

Hypothyroidism

Slow growth Caused by insufficient

iodine in diet

Thyroid enlarges


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Pancreas

Endocrine portion in islets of Langerhans

Hormones that regulate levels of glucose


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Diabetes

High levels of glucose in blood

Lack of insulin

Inability of tissue to respond to insulin

Two types

Type I = insulin dependent

Pancreas does not produce enough insulin

Type II

Often occurs later in life


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Gonadal Sex Hormones

The gonads, testes and ovaries, produce most of the

sex hormones: androgens, estrogens, and progestins

All three sex hormones are found in both males and

females, but in significantly different proportions


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Sex hormones

The testes primarily synthesize androgens, mainly

testosterone, which stimulate development and

maintenance of the male reproductive system

Testosterone causes an increase in muscle and bone

mass and is often taken as a supplement to cause

muscle growth, which carries health risks


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Sex hormones

Estrogens are responsible for maintenance of the

female reproductive system and the development of

female secondary sex characteristics

In mammals progesterone are primarily involved in

preparing and maintaining the uterus

Synthesis of the sex hormones is controlled by FSH

and LH from the anterior pituitary


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Effects of anabolic steroid


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Homeostasis

Copyright 2009 Pearson Education, Inc.


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Homeostasis is an internal steady state

Animals regulate their internal environment



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Externalenvironment

Homeostaticmechanisms

Internal

environment

Smallfluctuations

Largefluctuations


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Humans promote homeostasis by

Adding clothing when we are cold

Drinking water when we are dehydrated

Eating when our calories are running low Urinating when our bladders are full


Animals regulate their internal environment


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Sweat glands secrete sweat


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Sweat glands secrete sweat

that evaporates, cooling body

Blood vessels inskin dilate and

heat escapes

Temperaturedecreases

Thermostat shuts offcooling mechanisms

Temperature risesabove normal

Temperature fallsbelow normal

Thermostat shuts offwarming mechanisms

Homeostasis:Internal body temperature

of approximately 3638C

Temperatureincreases

Blood vessels in skinconstrict, minimizingheat loss

Skeletal muscles

rapidly contract,

causing shivering,

which generates heat

Thermostat inbrain activateswarming mechanisms

Thermostat in brainactivates coolingmechanisms


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Hormones n Homeostasis WADY EDT

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