ENDOCRINE REGULATION AND CONTROL BIOLOGY HOMEOSTASIS

7/27/2019 ENDOCRINE REGULATION AND CONTROL BIOLOGY HOMEOSTASIS

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UNIT 1 –

REGULATION ANDCONTROL I –

HOMEOSTASIS AND THE ENDOCRINESYSTEM



Homeostasis – Role of regulatory

systems1. Define and cite examples of Homeostasis.

2. Discuss the need for homeostasis in livingorganisms



HomeostasisHomeostasis refers to the appropriate, balanced internal

environment.

Metabolic processes occur continuously in every organism,

and they must be carefully regulated to maintainhomeostasis.

When enough of a cell product has been made, itsmanufacture must be decreased or turned off .

When a particular substance is required, cell processes thatproduce it must be turned on.

These homeostatic mechanisms are self-regulating controlsystems that are remarkably sensitive and efficient.



Stressors (changes in the internal or external environment) that

affect normal conditions within the body, continuously challengehomeostasis.

An internal condition that moves out of its homeostatic range(either too high or too low) causes stress.

An organism functions effectively because homeostaticmechanisms continuously operate to manage stress

Many animals are conformers for certain environmentalconditions.

Some of their internal states vary with changes in their surroundings.

Mammals are superb regulators.

They have complex homeostatic mechanisms that maintainrelatively constant internal conditions despite changes in theoutside environment.

How do homeostatic mechanisms work?



Example

Your cells require a constant supply of glucose molecules,which they break down to obtain energy.

The circulatory system delivers glucose and other nutrients

to all the cells.When the concentration of glucose in the blood rises above

normal limits, glucose is stored in the liver and in musclecells.

When you have not eaten for a few hours, the glucoseconcentration begins to fall.

Your body converts stored nutrients to glucose, bringing theglucose concentration in the blood back to normal levels.

When the glucose concentration decreases, you also feel



Feedback Regulation:

Negative feedback systems restorehomeostasis

3. Describe and provide examples from mammalian biology of

negative and positive feedback reactions.

4. Discuss the role of positive and negative feedback in thefunction of an organism



In a negative feedback system, a change in some

steady state triggers a response that counteracts, orreverses, the change.

A sensor detects a change,( a deviation from the normalcondition), or set point.

The sensor signals a control centre.

Based on the input of the sensor, the control centreactivates homeostatic mechanisms that restore thesteady state

The response counteracts the inappropriate change,thereby restoring the steady state.

Note that in a negative feedback system, the response of

the



Example

v Most homeostatic mechanisms in the body arenegative feedback systems.

1. When the glucose concentration in the blooddecreases below its homeostatic level, negativefeedback systems increase its concentration.

If the glucose concentration in the blood is too low,

alpha cells in the pancreas secrete a hormone thatincreases glucose concentration.

3. When body temperature decreases below normallimits, s ecialized nerve cells (sensors) si nal the



Feedback RegulationA few positive feedback systems operate in

the bodyPositive feedback intensifies the change taking place,

(rather than reverses) moving conditions further awayfrom homeostasis.

Although some positive feedback mechanisms arebeneficial,

they do not maintain homeostasis.

For example, a positive feedback cycle operates duringthe birth of a baby.

As the baby’s head pushes against the cervix (lower part of uterus), a reflex action causes the uterus to contract.

The contraction forces the head against the cervix again,



Comparison of Nervous and Hormonalregulation.

5. Compare nervous and hormonal regulationwith respect to structure and function of each

system.



Nervous system vs, Endocrine

systemNervous system regulates the activities of muscles and glands via electrical impulsestransported through neurons.

Neural control is fast; its effects are short-lived

System of neurons transmits “electrical” signals& release neurotransmitters to target tissue

The magnitude of nervous system effects are

dependent upon the frequency of actionpotentials.



Endocrine System regulates the body’s metabolic

activity via hormones that are transported in theblood.

Hormonal control is slow; its effects areprolonged

System of ductless glands secrete chemicalsignals directly into blood, chemical travels totarget tissue

slow, long-lasting response

the magnitude of endocrine effects aredependent upon the amount of hormone released.



Nervous :Neurotransmitters released by neurons

Endocrine :Hormones release by endocrine glands

These two systems interact and regulate each other

Receptorproteins

Target cell

Endocrinegland

Receptorproteins

Hormonecarried byblood

neurotransmitter

axon



Nervous and hormonal regulation –

rapid and gradual control working together

6. Hormonal and neural control combined inhomeostasis, with respect to anatomy



The endocrine system works closely with thenervous system to maintain homeostasis, thesteady state of the body.

The nervous system helps regulate manyendocrine responses. For example, when the

body is threatened, the hypothalamus signalsthe adrenal glands to secrete the hormoneepinephrine.

Hypothalamus = “master nerve control

centre”

nervous system :receives information fromnerves around body about internal conditions

regulates release of hormones from pituitary



Pituitary

Hypothalamus

Anterior

Posterior



Managing Glucose

Levels

Insulin reduces blood glucose levelsglucose levels rise above set point, pancreas secretes

insulin

promotes transport of glucose into cells & storage of glucose (as glycogen) in liver & muscle cells

drops blood glucose levels

Glucagon increases blood glucose levels

when glucose levels drop below set point, pancreassecretes glucagon

promotes breakdown of glycogen & release of glucose



Human Endocrinesystem.

7. Using a generalized diagram of the human

body, identify the main endocrine organs inthe human body.



The chemical nature of hormones

8. Identify the secretions of the main

endocrine organs, and the actions of thesesecretions



Important HormoneFunctionsReproduction

Growth and development

Immune system response

Maintenance of electrolyte, water, andnutrient balance of the blood

Regulation of cellular metabolism and energybalance



Major Endocrine OrgansPineal gland

Hypothalamus

Pituitary gland

Thyroid gland

Parathyroid gland

Thymus glandAdrenal glands

Pancreas

Gonads (i.e., ovaries and testes)



Major Endocrine Glands and Their Hormones



Major Endocrine Glands and Their Hormones

Gland Hormone Target Tissue Principal Actions

Hypothalamus Releasing and inhibiting hormones Anterior lobe of pituitary Regulate secretion of hormonesby theanterior pituitary

Posteriorpituitary

Oxytocin

Antidiuretic hormone (ADH)

UterusMammary glands

Kidneys (collectingducts)

Stimulates contractionStimulates ejection of milk into

ducts

Stimulates re-absorption of water

Anteriorpituitary

Growth hormone (GH)

Prolactin

Melanocyte-stimulating hormones(MSH)

Thyroid-stimulating hormone (TSH)

Adrenocorticotropic hormone

(ACTH)

Gonadotropic hormones

General

Mammary glands

Pigment cells in skin

Thyroid gland

Adrenal cortex

Gonads

Stimulates growth of skeleton andmuscle

Stimulates milk production

Stimulate melanin production

Stimulates secretion of thyroidhormones; helps regulate bone

remodeling

Stimulates secretion of adrenalcortical hormones

Stimulate gonad function andgrowth

Thyroid gland Thyroxine (T4) andtriiodothyronine (T3)

Calcitonin

General

Bone

Stimulate metabolic rate; regulateenergy metabolism

Lowers blood calcium level

Gland Hormone Target Tissue Principal Actions



g p

Pancreas Insulin

Glucagon

General

Liver, adipose tissue

Lowers blood glucoseconcentration

Raises blood glucoseconcentration

Adrenalmedulla Epinephrine andnorepinephrine Muscle; blood vessels;liver; adipose tissue Help body cope with stress;increase metabolic rate; raiseblood glucose level; increaseheart rate and blood pressure

Adrenal cortex Mineralocorticoids

Glucocorticoids

Kidney tubules

General

Maintain sodium and potassiumbalance

Help body cope with long-termstress; raise blood glucose level

Pineal gland Melatonin Hypothalamus Important in biological rhythms

Ovary Estrogens

Progesterone

General; uterus

Uterus; breast

Develop and maintain sexcharacteristics in female;

stimulate growth of uterine lining

Stimulates development of uterine lining

Testis Testosterone General; reproductivestructures

Develops and maintains sexcharacteristics in males;

promotes spermatogenesis

Parathyroidglands

Parathyroidhormone

Bone, kidneys, digestivetract

Regulates blood calcium level



9. Describe the chemical nature of hormonesand how each main type elicits change at thecellular level



Hormone – A chemical substance secreted by one

cell that affects the functions of another cell.Four Classes of Hormones

1. Fatty Acid Derivatives

Prostaglandins and the juvenile hormone of insects

2. Amino acid-based hormones

Most hormones are this type

Tend to stay in the blood

3. Steroid hormones

Synthesized from cholesterol

Lipid-soluble; able to pass through the phospholipid membrane

Include the gonadal hormones and the adrenal cortical hormones(secreted by the adrenal cortex)



Regulation of hormone

secretion.Negative feedback

mechanisms.10. Using examples from human biology,

describe the regulation of hormone secretionby negative and positive feedback.

11. Discuss the implications of failure of aregulatory system



Thyroid hormones increase metabolic rate

In vertebrates, thyroid hormones are essentialfor normal growth and development. Thesehormones increase the rate of metabolism in

most body tissues.

Thyroid hormones also help regulate thesynthesis of proteins necessary for cell

differentiation.



Thyroid secretion is regulatedby negative feedback systems

The regulation of thyroid hormone secretion depends on a negativefeedback loop between the anterior pituitary and the thyroid gland.

When the concentration of thyroid hormones in the blood rises

above normal, the anterior pituitary secretes less thyroid-stimulating hormone (TSH) Thyroid hormone concentration high inhibits anterior pituitarysecretes less TSH thyroid gland secretes less hormonehomeostasis

•

When the concentration of thyroid hormones decreases, thepituitary secretes more TSH.

Thyroid hormone concentration low anterior pituitary secretesmore TSHthyroid gland secretes more hormone homeostasis



Malfunction of the thyroid glandleads to specific disorders

Extreme hypothyroidism during infancy and childhood results in lowmetabolic rate and can lead to cretinism, a condition characterized byretarded mental and physical development

An adult who feels like sleeping all the time, has little energy, and ismentally slow or confused may be suffering from hypo-thyroidism.

When there is almost no thyroid function, the basal metabolic rate isreduced by about 40% the patient develops myxedema, characterized bya slowing down of physical and mental activity.

Hyperthyroidism does not cause abnormal growth but does increasemetabolic rate. This increase results in the rapid use of nutrients, causingthe individual to be hungry and to eat more. But this does not meet thedemands of the rapidly metabolizing cells, so people often lose weight. Themost common form of hyperthyroidism is Graves’ disease, an autoimmunedisease.



Iodine deficiency is acommon cause of goitre,enlargement of the

thyroid gland.



Consequences of Endocrine MalfunctionHormone Hyposecretion Hypersecretion

Growth hormone Pituitary dwarfism Gigantism if malfunction occurs inchildhood; acromegaly in adult

Thyroid hormones Cretinism (in children); myxedema, acondition of pronounced adult

hypothyroidism; dietary iodine deficiencyleads to hyposecretion and goitre

Hyperthyroidism; increasedmetabolic rate, nervousness,

irritability; goiter; Graves’ disease

Parathyroidhormone

Spontaneous discharge of nerves;spasms; tetany; death

Weak, brittle bones; kidney stones

Insulin Diabetes mellitus Hypoglycemia

Hormones of adrenal cortex

Addison’s disease Cushing’s disease



END

ENDOCRINE REGULATION AND CONTROL BIOLOGY HOMEOSTASIS

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