HOMEOSTASIS – REGULATION OF INTERNAL CONDITIONS

• Patterns of internal regulation in animals

• Principles of regulatory systems

• Signaling in internal regulation

• Animal example: mineral-balance regulation in animals

• Plant example: plant responses to drought

                                                             

-50 F, Body = 98.6 F

+ 119 F, Body = 98.6 F

Homeostasis• = ability of animals to regulate their internal

environment

• Regulator = uses mechanisms of homeostasis to moderate internal change in face of external fluctuation

Fresh

Water

Salt

Water

Constant solute, water concentration in blood, body fluids

Conformers – allow some conditions within their bodies to vary with certain external changes

Homeostasis

• Some constancy

• But also includes regulated change essential for normal function, survival– Hormonal changes in reproductive cycles– Responses to challenges

Homeostasis depends on feedback circuits

• Three componentsReceptor – detects a change in some variable

of the animal’s internal environment

Control Center – process information from receptor, directs signal to the effector

Effector – brings about the change to return conditions toward normal

NEGATIVE FEEDBACK SYSTEM

FEEDBACK SYSTEMS

Negative – a change in one direction fuels response in a control system and effector in the opposite direction

- inherently regulatoryPositive – a change in one direction fuels

response in a control system and effector in the same direction

- non-regulatory

Positive Feedback Systems

• Non-regulatory

• Unstable

• Short-lived, produce radical change– Mammalian birth – Generation of nerve impulse– Swallowing or vomiting

Negative feedback in regulation of mammalian body temperature

Homeostatic Mechanisms

• Communication and signaling between a receptor and a control center

• AND between a control center and an effector

Homeostatic Mechanisms

• Communication and signaling between a receptor and a control center

• AND between a control center and an effector

• Signaling and communication are dominantthemes in biology

Signaling and Communication in Homeostasis

• Nervous system – high-speed, electrical signals along specialized cells (neurons)

• Endocrine system – slower communication, via hormones

= chemical messengers secreted directly into body fluids by endocrine glands (organs)

Cell signaling in nervous and endocrine systems

Produce protein, change in membrane permeability, release of material

Nervous and endocrine systems are closely linked

• Epinephrine (adrenalin)– Produced in adrenal gland (an endocrine

organ)– Hormone: “flight or fight” response– Neurotransmitter – conveys signals between

neurons in the nervous system

• Neurosecretory cells – specialized nerve cells that secrete hormones in endocrine organs and tissues

INSECT

DEVELOPMENT

Mineral balance in herbivorous mammals

Sodium - predominant cation in extracellular fluids, needed for many metabolic purposes

Most plants – do not require sodium, do not accumulate it

-very high potassium levels when growing

High sodium intake from animal flesh

Herbivores face physiological challenges in mineral balance

- how to take in enough sodium?- how to reduce sodium loss?- how to get rid of enough potassium

Very little sodium in urine and feces (sodium retention)

Salt blocks, mineral licks, geophagy (behavioral solution)

High excretion of potassium

Mammalian kidney

Urine

Blood vessel

(Enzyme)

(glycoprotein)

Steroid hormone

High K+ in blood

K+ excretion

High K+ in blood

K+ excretion

STRESS

Hypothalamus

ACTH

Plant responses to external changes (drought stress)

Water is lost through leaves via transpiration (stomates)

Drought: transpiration > water uptake

Processes to control

Plant response to water deficit

• Stomates close due to reduced turgor

Plant response to water deficit

Water deficit increases synthesis of abscissic acid, hormone that keeps stomates closed (changed permeability)

Reduced leaf growth = lower rate of increase in leaf surface = lower transpiration

Leaves wilt, roll, expose less surface area to air

Root growth in deeper, moist soil, inhibited shallow root growth

Bio 103 Home