Physiology, Homeostasis, and Temperature Regulation

29

Homeostasis

• the maintenance of stable conditions in an internal environment.

• Cells are specialized for maintaining the internal environment

• such as temperature, pH, and ion concentration.

• Specialized cells evolve into tissues, organs, and physiological systems that serve specific functions to maintain homeostasis

Concept 29.1 Multicellular Animals Require a Stable Internal Environment

Multicellular organisms need a stable fluid environment

Intracellular fluid – within the cells (mostly water)

extracellular fluid

•which includes blood plasma and interstitial fluid that bathes each cell.

Figure 29.1 The Internal Environment

Four types of tissue:

• Epithelial

• Connective

• Nervous

• Muscle

Cells make up tissues

Epithelial Tissue

•are sheets of tightly connected epithelial cells that cover inner and outer body surfaces.

•Some line blood vessels and hollow organs.

•Some secrete substances such as hormones or sweat, or serve transport functions for nutrients.

•Others serve sensory functions of smell, taste, and touch.

•are dispersed cells in a secreted extracellular matrix.

•The composition of the matrix differentiates the types of connective tissues.

•Collagen and elastin provide strength and elasticity to cartilage.

•Bone matrix is mineralized for strength while the matrix of blood cells—plasma—is liquid.

•Adipose tissue, made of fat cells, has little matrix.

Connective Tissue

Nervous Tissue

•contain two basic cell types—neurons and glial cells.

•Neurons generate and conduct electrical signals, or nerve impulses, throughout the body.

• They are units of the central and peripheral nervous systems and communicate via chemicals, neurotransmitters.

•Glial cells provide support for neuronal function.

Muscle Tissues

•consist of elongated cells that generate force and cause movement.

•Three types of muscle tissues: • Skeletal—responsible for locomotion and movement• Cardiac—makes up the heart and generates heartbeat and blood

flow• Smooth—involved in movement and generation of forces in internal

organs

To maintain homeostasis:

Set point – a referenceFeedback – what is happeningError Signal – any difference between set pt. and feedback

SensorEffectors

Negative FeedbackPositive FeedbackFeedforward Information

Figure 29.3 Control, Regulation, and Feedback

Feed forward – changes set point!

Concept 29.2 Physiological Regulation Achieves Homeostasis of the Internal Environment

Regulatory systems:

• Obtain, integrate, and process information

• Issue commands to controlled systems

• Contain sensors to provide feedback information that is compared to the set point

• Regulatory systems then issue commands to effectors that effect changes in the internal environment.

• Effectors are controlled systems because they are controlled by regulatory systems.

Concept 29.2 Physiological Regulation Achieves Homeostasis of the Internal Environment

Sensory information in regulatory systems includes:

• Negative feedback

• Positive feedback

• Feedforward information

Concept 29.2 Physiological Regulation Achieves Homeostasis of the Internal Environment

Negative feedback:

• Causes effectors to counteract the influence that creates an error signal

• Results in a movement back to set point

• Example: driving too fast – causes you to slow down!

Positive Feedback

Positive feedback:

• Amplifies a response

• Increases deviation from a set point

• Examples: sexual behavior – little stimulation increases behavior response

Feedforward Information

Feedforward information:

• Anticipates internal changes and changes the set point.

• Example: seeing deer changes set point to lower speed

29.3 Living Systems are Temperature Sensitive

Concept 29.3 Living Systems Are Temperature-Sensitive

Physiological processes are temperature-sensitive and increase their rate at higher temperatures.

Q10 describes temperature-sensitivity as the quotient of the rate of a reaction at one temperature divided by the rate of the same reaction at a lower temperature (10 degrees)

Q10 = RT/RT–10

Figure 29.4 Q10 and Reaction Rate

if Q10 < 1 the rate drops with an increase in T

if Q10 > 1 then the rx rate increases with temperature

• Calculate the Q10 for the following scenario

• A rate of an enzyme worked at a rate of 76 at 10 degrees Celsius and it worked at a rate of 145 at 20 degrees Celsius.

• 145/76 = 1.91 (the exponent cancels out 10/(20-10)

• The temperature for these calculations do NOT always have to be 10 apart. See formula.

• Animals can acclimatize to seasonal temperature changes

• Animals can regulate their body temperature

• Ectotherms – depends on temperature of environment

• Endotherms – maintain constant body temperature independent of external temperatures

Animals

Figure 29.5 Ectotherms and Endotherms React Differently to Environmental Temperatures (Part 1)

• Mammals and Birds (Endotherms) have high rates of metabolic heat production

• expend most of their energy pumping ions across membranes.

• Cells are “leakier” to ions than cells of ectotherms.

• Endotherms spend more energy and release more heat to maintain ion concentration gradients.

Concept 29.4 Animals Control Body Temperature by Altering Rates of Heat Gain and Loss

If environmental temperature (Ta) falls below an endotherm’s lower critical temperature, animal must produce heat or body temperature (Tb) will fall.

Mammals produce heat in two ways:

Shivering —skeletal muscles contract and release energy from ATP as heat.

Nonshivering heat production—in adipose tissue called brown fat. –

*hibernation

Figure 29.7 Brown Fat

Brown fat has lots of mitochondria and a rich blood supply!

Concept 29.4 Animals Control Body Temperature by Altering Rates of Heat Gain and Loss

Reducing heat loss is important in cold climates.

Some cold-climate species have a smaller surface area than warm-climate relatives.

Rounder body shapes and shorter appendages reduce surface area-to-volume ratios.

Figure 29.9 Anatomical Adaptations to Climate (Part 1)

•Short Fur•Limited body insulation•Large ears and long limbs allow heat to radiate out

Figure 29.9 Anatomical Adaptations to Climate (Part 2)

•Thick coat of insulating fur•Small ears, short limbs, rounded body shape give it a smaller surface area to volume ratio – so less heat can be lost

Concept 29.4 Animals Control Body Temperature by Altering Rates of Heat Gain and Loss

Other adaptations to reducing heat loss include:

• Increased thermal insulation with fur, feathers, or fat

• Ability to decrease blood flow to the skin by constricting blood vessels

Concept 29.4 Animals Control Body Temperature by Altering Rates of Heat Gain and Loss

Some ectotherms are able to raise their body temperature by producing heat:

• Insects contract their flight muscles

• Honeybees regulate temperature as a group, adjusting individual heat and position in the cluster so that larvae are kept warm

Concept 29.4 Animals Control Body Temperature by Altering Rates of Heat Gain and Loss

Both endotherms and ectotherms may use behavioral regulation to maintain body temperature.

Examples: Lizard moving into sun or shade, or elephant spraying itself with water or dust

Thermostat in Mammals

In vertebrate brains, the hypothalamus is the major center of the thermostat.

The temperature of the hypothalamus can be the main feedback to the thermostat.

Concept 29.5 A Thermostat in the Brain Regulates Mammalian Body Temperature

Cooling the hypothalamus can cause body temperature to rise by:

• Constricting blood vessels to the skin

• Increasing metabolic rate

Warming the hypothalamus can lower body temperature by:

• Dilating blood vessels to the skin

• Sweating or panting

Concept 29.5 A Thermostat in the Brain Regulates Mammalian Body Temperature

The temperature of the hypothalamus is a negative feedback signal—variability from its set point can trigger thermoregulatory responses.

Other factors can change hypothalamic set points:

• Change in skin temperature

• Wakefulness or sleep

• Circadian rhythm—a daily internal cycle

Concept 29.5 A Thermostat in the Brain Regulates Mammalian Body Temperature

Fever is a an adaptive response to help fight pathogens. The rise in body temperature is caused

by a rise in the set point for metabolic heat production.

As a response, we shiver and get under a blanket. Body temp. rises until it matches the higher set point.

At the higher body temp. you no longer feel cold, but someone touches your forehead – “you are burning up”, take aspirin which lowers set point to normal.

Some animals lower their temperature during inactive periods to conserve energy—daily torpor.

Long-lasting regulated hypothermia— hibernation