David Sadava David M Hillis H Craig Heller

David Sadava, David M. Hillis, H. Craig Heller, May R. Berenbaum La nuova biologia. blu Anatomia e fisiologia dei viventi S

Physiology, Homeostasis, and Temperature Regulation

What Are the Relationships between Cells, Tissues, and Organs? Physiological systems are made up of organs that serve specific functions, e. g. , heart, lungs, kidneys. Organs are made up of tissues—assemblages of similar cells. Organs consist of more than one type of tissue. Four types of tissue: • Epithelial • Muscle • Connective • Nervous

What Are the Relationships between Cells, Tissues, and Organs? Epithelial tissues: sheets of tightly connected cells that create boundaries between the inside and the outside of the body. Skin, blood vessel linings, ducts and tubules, gut lining. Controls movement of molecules between body compartments by selective transport.

What Are the Relationships between Cells, Tissues, and Organs? Epithelial cells have many specialized roles: • Secretion of hormones, milk, mucus, digestive enzymes, and sweat • Some have cilia that move substances over surfaces or through tubes • Some provide information to the nervous system (e. g. , smell and taste receptors)

What Are the Relationships between Cells, Tissues, and Organs? Muscle tissues consist of elongated cells with protein filaments called actin and myosin that work together to generate force and cause movement. There are three types of muscle tissues: • Skeletal muscle—attached to bones; responsible for locomotion and movement • Cardiac muscle makes up the heart; responsible for heartbeat and blood flow • Smooth muscle makes up the walls of many organs (e. g. , gut, bladder, blood vessels)

Muscle Cells Contain Protein Filaments

What Are the Relationships between Cells, Tissues, and Organs? Connective tissues: cells are dispersed in an extracellular matrix secreted by the cells. The matrix varies, but protein fibers are always present: • Collagen is dominant— fibers are strong and resistant to stretch, strengthens skin and connections between muscles and bones; • Elastin stretches and recoils— abundant in tissues that are regularly stretched (e. g. , lungs, arteries).

Connective Tissues • Cartilage and bone provide firm structural support • Blood consists of cells dispersed in a liquid extracellular matrix, the blood plasma • Adipose tissue stores lipids, cushions organs, and reduces heat loss

What Are the Relationships between Cells, Tissues, and Organs? Nervous tissues contain two basic cell types: • Neurons encode and conduct information as electrical signals to other cells. Chemical signals from a neuron are received by target cells, which can be other neurons, muscle cells, or cells secreting hormones. • Glial cells, or glia, provide a variety of support functions for neurons. One type creates a barrier between blood vessels and neural tissue that protects the nervous system from potentially harmful chemicals in the blood.

Tissues Form Organs consist of more than one tissue type; most contain all four types. The wall of the gut is an example. Individual organs are part of an organ system, a group of organs that work together (e. g. , the digestive system). Organizational hierarchy: Cells → Tissues → Organ systems→ Individual organism

How Do Multicellular Animals Supply the Needs of Their Cells? Homeostasis is the maintenance of stable physical and biochemical conditions in the internal environment. If homeostasis is compromised, cells can be damaged and can die. Maintenance of homeostasis is a central theme of physiology.

How Do Multicellular Animals Supply the Needs of Their Cells? Physiological systems are controlled by actions of the nervous and endocrine systems. To regulate these systems and maintain homeostasis, information are required. A thermostat is an analogy for this.

How Do Multicellular Animals Supply the Needs of Their Cells? Components of physiological systems: Effectors effect changes in the internal environment, (e. g. , muscles). Effectors are controlled systems because they are controlled by neural or hormonal signals from regulatory systems.

How Do Multicellular Animals Supply the Needs of Their Cells? Regulatory systems: • Obtain, integrate, and process information • Issue commands to controlled systems • Have sensors to provide feedback information to compare to set points

How Do Multicellular Animals Supply the Needs of Their Cells? Types of information necessary for physiological systems: • Set point—a reference point • Feedback information—information that is compared to the set point • Error signal—any difference between the set point and feedback information

How Do Multicellular Animals Supply the Needs of Their Cells? Negative feedback is information that corrects an error signal. Whatever force is pushing the system away from its set point must be “negated”. Positive feedback amplifies a response and increases deviation from a set point. Responses tend to reach a limit and terminate rapidly. Examples: sexual behavior and the birth process.

How Do Animals Alter Their Heat Exchange with the Environment? Both ectotherms and endotherms can influence body temperature by altering four avenues of heat exchange: • Radiation—heat transfer via infrared radiation • Convection—heat transfer through a surrounding medium • Conduction—heat transfer by direct contact • Evaporation—heat transfer through evaporation of water from a surface (e. g. , sweating)

Animals Exchange Heat with the Environment

How Do Animals Alter Their Heat Exchange with the Environment? Controlling blood flow to the skin helps maintain body temperature. Increased blood flow to the skin increases heat loss and lowers body temperature. Constriction of blood vessels to the skin results in less heat loss. In mammals the hypothalamus in the brain is the major control center for temperature. Experiments show that cooling of the hypothalamus causes restriction of skin blood vessels and increases metabolic heat production.

How Do Endotherms Regulate Their Body Temperatures? Fever is an adaptive response that helps the body fight pathogens. Fever is a rise in body temperature caused by pyrogens. Pyrogens can be exogenous—foreign proteins (e. g. , bacteria and viruses) or endogenous—produced by immune cells in response to infection.

How Do Endotherms Regulate Their Body Temperatures? Pyrogens cause a rise in the hypothalamic set point. Shivering and getting under blankets results in increase of body temperature to match the new set point. Moderate fevers help the body fight infections, but extreme fevers can be dangerous.

Adapted from Life: The Science of Biology, Tenth Edition, Sinauer Associates, Sunderland, MA, 2014 Inc. All rights reserved