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 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 components Receptor – 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 regulatory Positive – 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 dominant themes 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

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