Physiology, Homeostasis, and Temperature Regulation 29 Physiology, Homeostasis, and Temperature Regulation

Homeostasis such as temperature, pH, and ion concentration. 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

Multicellular organisms need a stable fluid environment 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. APPLY THE CONCEPT Multicellular animals have an internal environment of extracellular fluid

Figure 29.1 The Internal Environment

Four types of tissue: Epithelial Connective Nervous Muscle Cells make up tissues Four types of tissue: Epithelial Connective Nervous Muscle

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.

Connective Tissue 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.

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

consist of elongated cells that generate force and cause movement. 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: Information Control Set point – a reference Feedback – what is happening Error Signal – any difference between set pt. and feedback Negative Feedback Positive Feedback Feedforward Information Regulation Sensor Effectors

Figure 29.3 Control, Regulation, and Feedback Feed forward – changes set point! Set point feedback Regulatory system

Obtain, integrate, and process information 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.

Sensory information in regulatory systems includes: Negative feedback Concept 29.2 Physiological Regulation Achieves Homeostasis of the Internal Environment Sensory information in regulatory systems includes: Negative feedback Positive feedback Feedforward information

Stabilizes Negative feedback: 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! Stabilizes

Reach limit, then terminate Positive Feedback Positive feedback: Amplifies a response Increases deviation from a set point Examples: sexual behavior – little stimulation increases behavior response Reach limit, then terminate

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 Rxn rates are doubled Or tripled as temp. Increases by 10 =1, not temp. sensitive

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

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

Figure 29.5 Ectotherms and Endotherms React Differently to Environmental Temperatures (Part 2) In the thermoneutral zone the metabolic rate is low and independent of temperature. The basal metabolic rate (BMR) is the metabolic rate of a resting animal at a temperature within the thermoneutral zone.

Concept 29.4 Animals Control Body Temperature by Altering Rates of Heat Gain and Loss Metabolism—conversion of ATP to do work produces heat Radiation—warmer objects lose heat to cooler objects by radiation Convection—heat is lost when wind is cooler than body surface temperature Conduction—heat is transferred when objects of different temperatures come into contact Evaporation—heat is lost and body is cooled when water leaves the body

expend most of their energy pumping ions across membranes. 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. LINK Review the mechanisms of ion transport described in Concepts 5.2 and 5.3

Mammals produce heat in two ways: 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 See Chapter 6, p. 104

Brown fat has lots of mitochondria and a rich blood supply! Figure 29.7 Brown Fat Brown fat has lots of mitochondria and a rich blood supply!

The BMR per gram of tissue increases as animals get smaller. Concept 29.4 Animals Control Body Temperature by Altering Rates of Heat Gain and Loss The basal metabolic rate (BMR) is correlated with body size and environmental temperature. The BMR per gram of tissue increases as animals get smaller. Example: A gram of mouse tissue uses energy at a rate 20 times greater than a gram of elephant tissue.

Reducing heat loss is important in cold climates. 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

Other adaptations to reducing heat loss include: 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

Insects contract their flight muscles 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. See Figure 30.7 A

Cooling the hypothalamus can cause body temperature to rise by: 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 See Figure 30.7 A

Figure 29.13 The Hypothalmus Regulates Body Temperature (Part 1)

Other factors can change hypothalamic set points: 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 ANIMATED TUTORIAL 29.1 The Hypothalamus

Fever is a an adaptive response to help fight pathogens. 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. Some animals lower their temperature during inactive periods to conserve energy—daily torpor. Long-lasting regulated hypothermia— hibernation