Physiology, Homeostasis andTemperature Regulation

Bio 11, Week 9

Purves et al., Chapter 41

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Outline

• Tissues, organs, organ systems– 4 types of tissues– Organs consist of multiple tissue types– Organ systems are groups of organs that

function together

• Physiologic regulation & Homeostasis– Ectotherms and Endotherms

• Thermoregulation– Feedback loops

Tissues, Organs, Organ Systems

• Cells organized into tissues

• Tissues are organized into organs

• Organs are organized into organ systems

4 Types of Tissues

• When cells with the same characteristics or specializations are grouped together, they form a type of tissue

– Epithelial– Connective– Muscle– Nervous

Epithelial Tissue

• Covers the body and lines organs

• Sheets of densely packed, tightly connected cells that cover surfaces

• Comprise the skin and line hollow organs (gut)

• Some epithelial cells are secretory (hormones, mucus, sweat, digestive enzymes)

Epithelial Tissue cont.

• Some epithelial cells have cilia to transport substances over surfaces or through tubes

• Some epithelial cells have protective functions (create boundaries bt inside and outside)

• Epithelial cells can also form receptors to provide information to the nervous system (smell and taste receptors)

Epithelial Tissue cont.

• Have distinct inner and outer surfaces

• Inner surfaces = basal ends of the epithelial cells (rests on basal lamina)

• Outer surfaces = apical ends of the epithelial cells

Epithalial Tissue cont.

Connective Tissue

• Support and reinforce other tissues

• Dispersed populations of cells embedded in an extracellular matrix comprised of proteins– Collagen (25% total body protein)– Elastin (wrinkles with aging)

Connective Tissue cont.

• Cartilage provides rigid, structural support– Collagen fibers embedded in flexible matrix

• Bone provides rigid, structural support– Collagen fibers hardened by calcium

phosphate

• Adipose Tissue– Stored energy

• Blood

Connective Tissue cont.

Muscle Tissue

• Contract and cause movement

• Elongated cells

• Most abundant tissue type

• When active (contracting) use most of the energy produced by the body

Silverthorn, Human Physiology, 3rd edition Figure 12-1,2

Nervous Tissue• Process information

• Neurons communicate via electrical and chemical signals

• Glial cells support neurons (outnumber them too)

Organs

• Consist of multiple tissue types

• Ex. Wall of stomach – Inner surface lined with epithelial cells that

secreted mucus and digestive enzymes– Connective tissue underneath epithelial lining– Muscle tissue (smooth) allows stomach to

contract– Neurons control contractions and secretions

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Organ Systems

• Controlled and regulated to achieve constancy in the internal environment of the organism.

• Nervous• Endocrine• Muscles• Skeletal• Reproductive• Digestive

• Respiratory• Circulatory• Lymphatic• Immune• Skin• Excretory

The endocrine system of humansPineal gland

Hypothalamus

Posterior pituitary

Anterior pituitary

Thyroid

Parathyroid

Thymus

Heart

Liver

Stomach and small intestine

Pancreas

Adrenal cortex

Adrenal medulla

Kidney

Skin

Gonads

Silverthorn, Human Physiology, 3rd edition Figure 7-2

Homeostasis

• Single-celled organisms meet all of their needs by direct exchange with the external environment

• Evolution of an internal environment, distinct from external environment, made multi-cellular organisms feasible

• Homeostasis allows for conditions of internal (intracellular) environment to remain constant and optimal even when the external environment fluctuates

The External and Internal Environments

Materials enter and leave the body

The External EnvironmentExchange cells

Protective cells

Extracellular fluid (ECF)(This is the Internal Environment)

Intracellularfluid

Intracellularfluid

ECF is the interface between the external environment and the cells

Stratton with permission

Homeostasis cont.

• Homeostasis depends on the ability to regulate the activities of organs and organ systems to keep the internal environment constant

• Generally, activities of organs/organ systems are controlled by the nervous and endocrine systems

• Failure to maintain homeostasis results in disease or pathology

Claude Bernard

He recognized that an animal’s independence from changing external conditions is related to its capacity to maintain a relatively constant Internal environment.

Claude Bernard (1813 - 1878)Silverthorn, 3rd ed.

Walter Cannon

Recognized that the key to maintaining a relatively stable internal environment is the presence of regulatory mechanisms in the body.

He coined the term homeostasis to describe the maintenance of this stable internal environment.

homeo = similar, stasis = state

Walter Bradford Cannon (1871 - 1945)

Silverthorn, 3rd ed.

Temperature

• External temps vary enormously

• Living cells can function over a narrow (tolerable) range of temps (0-45°C)

• Q10 is a measure of temp sensitivity

Q10 = RT/RT-10

Q10 and Reaction Rate

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Optimal Body Temperature

• Ectotherms depend on external sources of heat, such as solar radiation, to maintain body temperature

• Endotherms can regulate their body temperature by producing heat metabolically (mammals and birds)

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Energy Budgets

• Both ectotherms and endotherms can alter their body temperature by altering 4 characteristics of heat exchange b/t their bodies and the environment– Radiation– Conduction– Convection– Evaporation

Heat Loss Side Depends on Surface Temp/Blood Flow to Skin

Heatin = Heatout

Metabolism + Rabs = Rout + convection + conduction

+ evaporation

Reflex Control Pathways Maintain Setpoints

Response Loop• Input signal• Integration of signal• Output signal or

response

Feedback Loop• Response feeds

back to impact the Input (to correct error signal)

Response Loops

Stimulus

Sensor

AfferentPath

IntegratingCenter

EfferentPath

Effector Response

Negative Feedback Loops

Stimulus

Sensor

AfferentPath

IntegratingCenter

EfferentPath

Effector Response

Thermoregulation in Endoderms

• Thermoneutral zones and basal metabolic rates

• Basal metabolic rates are related to body size

• Endotherms respond to cold by producing heat– Shivering heat production– Nonshivering heat production

Shivering

• Depends on contractile machinery of skeletal muscles to consume ATP

• Tremor results

• Conversion of ATP to ADP results in heat production

Nonshivering Heat Production

• Brown fat

• Thermogenin uncouples proton movement from ATP production, so metabolic fuels are consumed without producing ATP

• Heat is still released

Regulatory Thermostat

• Controls thermoregulatory adaptations and mechanisms (shivering)

• Integrative center is in hypothalamus, which establishes a temperature set point and receives feedback information

• Temperature of external environment is sensed by skin sensors (feedforward)

Hypothalamus

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