Introducing the Endocrine System Copyright © 2005 Pearson Education, Inc. publishing as Benjamin...

Introducing the Endocrine System

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

IB Assessment Statement

• State that the endocrine system consists of glands that release hormones that are transported in the blood.

Crash Course Video on the Endocrine System

https://www.youtube.com/watch?v=WVrlHH14q3o




The endocrine system and the nervous system act individually and together in regulating an animal’s physiology

Animals have two systems of internal communication and regulation:

1. the nervous system

2. and the endocrine system

• The nervous system conveys high-speed electrical signals along specialized cells called neurons

• The endocrine system secretes hormones that coordinate slower but longer-acting responses

Overlap Between Endocrine and Nervous Regulation

• The endocrine and nervous systems function together in maintaining homeostasis, development, and reproduction

What is Homeostasis?

• Refers to a state of constancy in a system.

– In its normal, or resting, state, a system often is said to be in homeostasis.

• When events occur that disrupt the normal state, the system is able to respond and restore homeostasis.

• Physiologists use the term homeostasis to refer to maintenance of a constant internal environment despite fluctuations in external conditions.

Examples of physiological conditions requiring homeostasis:

• Temperature

• Concentration of Waste Products (urea, CO2)

• O2 concentration

• pH of blood

• Energy Requirements/Blood glucose concentration

• Water/Ion balance (Na+, K+, Cl-)

• Volume/Pressure of blood

• Metabolic rate (rate of cellular respiration)

Homeostasis – is important for our internal environment

• Internal environment consists of:

– Blood

– Tissue fluid


IB Learning Objective

• Define Homeostasis and explain how it is regulative by a negative feedback system.

Negative Feedback – the mechanism of homeostasis

• Type of control in which conditions being regulated are brought back to a set value (example body temperature)

• Negative feedback requires a detector device that measures the value

• When the value falls below or above the set value an effector device is activated (example sweating when body temperature rises)

Homeostatic Mechanism

Negative-Feedback Regulation

– An external stimuli or activity alters a condition of the internal environment, which triggers a response by the body. This response reverses the altered condition.

70 72 74 76 78 80 82 84 86 88 90 92

Effectors – in Negative Feedback

– Effectors are of 2 types: Muscles & Glands

Rise abovenormal value

Fall below normal value

normal value

Corrective Mechanis

m

Corrective Mechanis

m

NEGATIVE FEEDBACK NEGATIVE FEEDBACK MECHANISMMECHANISM

normal

value

negative

feedback

negative

feedback

Endocrine system

• Animal hormones are chemical signals that are secreted by endocrine glands into the circulatory system and communicate regulatory messages within the body

• Hormones reach all parts of the body, but only target cells are equipped to respond

LE 45-2a

Targeteffectors

Response

Simple endocrine pathway

Glycogenbreakdown,glucose releaseinto blood

Liver

Bloodvessel

Pancreassecretesglucagon ( )

Endocrinecell

Low bloodglucose

Receptorprotein

Stimulus

Pathway Example

LE 45-2b

Targeteffectors

Response

Simple neurohormone pathway

Stimulus

Pathway Example

Suckling

Milk release

Smooth musclein breast

Neurosecretorycell

Bloodvessel

Posterior pituitarysecretes oxytocin( )

Hypothalamus/posterior pituitary

Sensoryneuron

LE 45-2c

Targeteffectors

Response

Simple neuroendocrine pathway

Stimulus

Pathway Example

Milk production

Bloodvessel

Hypothalamus

Sensoryneuron

Mammary glands

Endocrinecell

Bloodvessel

Anteriorpituitarysecretesprolactin ( )

Hypothalamussecretes prolactin-releasinghormone ( )

Neurosecretorycell

Hypothalamicneurohormonereleased inresponse to neural andhormonalsignals

LE 45-3

SECRETORYCELL

Hormonemolecule

Signal receptor

VIABLOOD

VIABLOOD

TARGETCELL TARGET

CELLSignaltransductionpathway

OR

Cytoplasmicresponse

DNA

NUCLEUS

Nuclearresponse

Receptor in plasma membrane Receptor in cell nucleus

DNA

NUCLEUS

mRNA

Synthesis ofspecific proteins

Signaltransductionand response

Signalreceptor

Hormonemolecule

SECRETORYCELL



• Explain the control of body temperature, including the transfer of heat in blood, and the roles of the hypothalamus, sweat glands, skin arterioles and shivering.

• IMPORTANCE OF CONSTANT TEMPERATURE

– enzymes are proteins that are important to all biochemical activities in a living organisms

– Enzymes work best at optimum temperature, and are denatured by deviation from this.

• IMPORTANCE OF CONSTANT TEMPERATURE

– Cell membranes become fragile as temperatures rise

– Diffusion rates across cell membranes increase by higher temperatures and decrease in lower temperatures.

– Liquid such as blood becomes more viscous (thick) as the temperature falls

Mechanism to Maintain Body temperature

• Maintaining constant temperature,

• Generation of Heat:

– Biochemical reactions, such as respiration generate heat.

– Movement generates heat by friction within muscles



• Maintaining constant temperature,

• Losing heat:

– Evaporation of water, from the lungs and sweat from the skin.

– Excretion: Urine and Faeces heat is lost as theses substances are removed from the body.



• Insulation:

– Fat stores under the skin prevent heat loss.



• The hypothalamus as the co-ordinator of temperature regulation:

• Vasoconstriction: is a cold adaptation narrowing of arterioles that reduces blood flow to the surface of the skin is coupled with a dilation of the horizontal shunt vessels. This prevents heat loss from blood near the skin surface and retains heat in the body core for essential organs.

• Vasodilation: is an adaptation to warm conditions in which arterioles dilate sending more blood closer to the skin surface from where heat can be radiated to the surrounding environment. The horizontal shunt vessels are constricted sending most blood closer to the skin surface. Additionally sweat (mainly water) is released onto the surface of the skin where it enters the vapour phase when warmed by the heat carried by blood. Therefore the vapour of sweat carried away heat energy from blood.

Thermoregulation is the regulation of body temperature

• Skin – hot and cold receptors

Thermoregulation is the regulation of body temperature

Hypothalamus in brain

• Control Unit

• Monitors the temperature of the blood and compares it to a set value close to 37 C

– heat gain centre in the posterior part

– heat loss centre in the anterior part

Thermoregulation – Response to overheating

Skin

– Heat exchange between body and surrounding occur through our skin

– Sweat glands produce sweat. Water evaporates off the skin and this has a cooling effect.

– Capillaries will dilate (vasodilation). More blood will flow through the skin. The blood transfers heat from the core to the skin. This heat will be lost to environment

– Hair erector muscles which relax. Allows more air flow on skin, which promotes cooling.

BODY TEMPERATURE DROPS BELOW NORMAL

• If core body temperature drops, the hypothalamus:

• Skin capillaries (vasoconstrict) become narrow and they bring less blood to the skin.

• Hair erector muscles raise hairs and traps a layer of still air, thus reducing convection.

• causes the skeletal muscles to contract involuntarily—to “shiver.”

– This causes the body temperature to increase.

Maintaining Homeostasis

• An Example of Feedback Inhibition

Thermostat senses temperature change and switches off heating system

Thermostat senses temperature change and switches on heating system

Room temperature increases

Room temperature decreases


Thermoregulation

• Cold: when cold the following events occur to reduce heat loss and raise temperature.

• Lower than regulation temperature blood reaches the hypothalamus.

• The hypothalamus signals the vasoconstriction (narrowing) of arterioles

• Muscle effectors are produces the rapid contraction relaxation of muscles known as shivering which produces more body heat.

• Hot:

• Sweat is secreted onto the surface of skin when body temperature is high

• Sweat is largely composed of water which has a high specific heat capacity (absorbs a heat easily)

• Body heat is transferred from skin and blood to the sweat

• The sweat evaporates transferring heat away and in doing so cools the body


Videos/ Tutorials on Thermoregulation of Body Temperature

• http://bcs.whfreeman.com/thelifewire/content/chp41/4101s.swf

• http://www.think-bank.com/iwb/flash/homeostasis.swf

• http://www.phys.unsw.edu.au/biosnippets/

http://bcs.whfreeman.com/thelifewire/content/chp41/4101s.swf

http://bcs.whfreeman.com/thelifewire/content/chp41/4101s.swf

http://www.think-bank.com/iwb/flash/homeostasis.swf

http://www.think-bank.com/iwb/flash/homeostasis.swf

http://www.phys.unsw.edu.au/biosnippets/



• Explain the control of blood glucose concentration, including the roles of glucagon, insulin and α and β cells in the pancreatic islets.


Why blood sugar is regulated

Blood sugar concentration is regulated for a number of reason amongst which:

•Osmosis. content of a tissue is determined by the concentration of the surrounding tissues.

•Respiration: Some tissues are entirely dependent on blood sugar as a respiratory substrate being unable to either store glucose of metabolise fat.

Insulin and Glucagon: Control of Blood Glucose

• The pancreas secretes insulin and glucagon, antagonistic hormones that help maintain glucose homeostasis

• Glucagon is produced by alpha cells

• Insulin is produced by beta cells

LE 45-12

Beta cells ofpancreasrelease insulininto the blood.

Insulin

Liver takesup glucoseand stores itas glycogen.

STIMULUS:Rising blood glucose

level (for instance, aftereating a carbohydrate-

rich meal)

Blood glucose leveldeclines to set point;stimulus for insulinrelease diminishes.

Homeostasis:Blood glucose level

(about 90 mg/100 mL)

STIMULUS:Dropping blood glucoselevel (for instance, after

skipping a meal)

Blood glucose levelrises to set point;

stimulus for glucagonrelease diminishes.

Liver breaksdown glycogenand releasesglucose into theblood.

Body cellstake up moreglucose.

Alpha cells of pancreasrelease glucagon into the blood.

Glucagon

Target Tissues for Insulin and Glucagon

• Insulin reduces blood glucose levels by

– Promoting the cellular uptake of glucose

– Slowing glycogen breakdown in the liver

– Promoting fat storage

• Glucagon increases blood glucose levels by

– Stimulating conversion of glycogen to glucose in the liver

– Stimulating breakdown of fat and protein into glucose


6.5.11 Explain the control of blood glucose concentration, including the roles of glucagon, insulin and α and β cells inthe pancreatic islets.(3

• a) Low glucose concentration is detected by the pancreas.

• b) Alpha cells in the pancreatic islets secret glucagon.

• c)Glucagon flows through the blood to receptors on liver cells.

• d)Liver responds by adding glucose to blood stream.

• h) High blood glucose levels stimulate the beta pancreatic cells

• a) Beta pancreatic cells secrete insulin.

• f)Insulin flows through the blood to the receptors on liver cells.

• g)Insulin stimulates the liver to remove blood glucose and store this as glycogen (insoluble)

Glucose Homeostasis Chart

Liver breaks down glycogen to create

glucose

Raises blood-glucose

Glucose uptake by muscle/fat tissue

Lowers blood-glucoseResult

GlucagonInsulinEffector

-cell of the pancreas

Beta-cell of the pancreasControl Center

Glucose transporterGlucose transporterReceptor

Low Blood SugarDo not meet energy requirements of cell

High Blood SugarToxic

Condition

Liver converts glycogen

to glucose

normal normal blood blood

glucose glucose levellevel

Blood glucose Blood glucose level fallslevel falls

SooSoon n

after after a a

mealmeal

Long Long after after

a a mealmeal

Blood Blood glucose glucose

level riseslevel rises

normal normal blood blood

glucose glucose levellevel

Too Too HigHighh

Too Too LowLow

Pancreas Pancreas secretes secretes insulininsulin

Pancreas Pancreas secretes secretes

less insulinless insulin

Liver coverts glucose

to glycogen



• Distinguish between type I and type II diabetes.

Diabetes Mellitus Type I

• Diabetes mellitus (type I) is perhaps the best-known endocrine disorder

– The onset is usually during childhood

– It is caused by a deficiency of insulin

– beta cells fail to produce insulin

– Requires insulin injections to control glucose levels

Type II Diabetes

– The onset is after childhood

– Target cells become insensitive to insulin

– Insulin injections are usually NOT needed

– Low carbohydrate diet usually controls the condition

-cells release glucagon stimulate glycogen breakdown and gluconeogenesis

-cells release insulin stimulate glucose uptake by peripheral tissues

Glucose Homeostasis

Lower Blood Glucose

Higher Blood GlucoseFood

Between meals

Type 1 Diabetes Mellitus

High blood glucose

Detected by -cells

-cells release insulin

Peripheral cells respond to insulin

by taking up glucose

Lower blood glucose

Normal Glucose Metabolism Type 1 Diabetes

High blood glucose

Detected by -cells

-cells release insulin

Peripheral cells respond to insulin

by taking up glucose

Lower blood glucose

-cells destroyed by autoimmune reaction

These steps do not happen because the - cells have been destroyed

Blood glucose remains high


Blood sugar regulation Animations/ Tutorials

• http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter20/animation__blood_sugar_regulation_in_diabetics.html

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter20/animation__blood_sugar_regulation_in_diabetics.html



6.5.12 Distinguish between type I and type II diabetes. (2)

Type I diabetes (early or juvenile onset):

•Auto-immune disease in which the beta-cells pancreatic are destroyed.

•Unable to produce insulin.

•Responds well to regular injection of insulin probably manufactured as the genetically engineered humulin.

Type II diabetes (Adult onset):

•Reduced sensitivity of the liver cells to insulin.

•Reduced number of receptors on the liver cell membrane.

In both types of diabetes there is:

•a build of glucose in the blood stream and it will then subsequently appear in urine.(test with a Clinistic )

•High concentrations of blood glucose (hyperglycaemia) results in the movement of water from cells by osmosis.

•This extra fluid in the blood results in larger quantities of urine production.

•A lack of glucose in cells means that fats then proteins have to be metabolised in respiration.

•Particularly the breakdown of protein for energy creates organ damage.


Glucose Homeostasis Research Timeline

• 1552 BC: Ebers Papyrus in ancient Egypt. First known written description of diabetes.

• 1st Century AD: Arateus — “Melting down of flesh and limbs into urine.”

• 1776: Matthew Dobson conducts experiments showing sugar in blood and urine of diabetics.

• Mid 1800s: Claude Bernard studies the function of the pancreas and liver, and their roles in homeostasis.

• 1869: Paul Langerhans identifies cells of unknown function in the pancreas. These cells later are named “Islets of Langerhans.”

• 1889: Pancreatectomized dog develops fatal diabetes.

• 1921: Insulin “discovered” — effectively treated pancreatectomized dog.

• 1922: First human treated with insulin. Eli Lilly begins mass production.

• 1923: Banting and Macleod win Nobel Prize for work with insulin.

• 1983: Biosynthetic insulin produced.

• 2001: Human genome sequence completed.

1552BC 1st Century AD 1776 1869 188918th Century 1921-23 1983 2001


Current/Future Research in Diabetes• Current

– Clinical Trials: physiological traits of patients/response to therapeutics

– Genetic Approaches: candidate genes; family-based studies; genome-wide scans

– Animal Models: developing gene-knockout models; large-scale mutagenesis studies to produce diabetic phenotypes

– Microarray Analysis: analysis of gene expression in tissues

• Future

– Continued utilization of human genome sequence data

• Sequencing multiple ethnicities

– Beta-cell transplantation

– Use of stem cells to halt or reverse symptoms

Introducing the Endocrine System Copyright © 2005 Pearson Education, Inc. publishing as Benjamin...

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