homeostasis – regulation of internal conditions patterns of internal regulation in animals...
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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
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
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