Chapter 40 – Physiology, Homeostasis, and Temperature Regulation
40.1 Why Must Animals Regulate Their Internal Environments? (855)
- Single-celled organisms and some multi-cellular organisms meet needs of nutrients, oxygen, and waste excretion by
direct exchange with the external environment. These animals are common in the sea and tend to be small and flat, or, as
in sponges, perforated with channels through which seawater can flow.
An Internal Environment Makes Complex Multi-cellular Animals Possible (855)
- Homeostasis is the maintenance of stable conditions (within a narrow range) in the internal environment.
- If a physiological system fails to function properly, homeostasis is compromised, and as a result cells are damaged and
Homeostasis Requires Physiological Regulation (856)
- Activities of all physiological systems are controlled (speeded up or slowed down) by actions of the nervous and
endocrine systems. But to regulate the internal environment, information is required.
- Ex. You control the speed of a car with an accelerator and brakes; you need to know how fast you want to go and how
fast you are going to think which one to apply. The desired speed is a set point (reference point), and the reading of your
speedometer is the feedback information. The difference between the feedback information and set point is an error
signal – suggestive corrective actions, which you make by using the accelerator or brake.
- Some components of physiological systems are called effectors – because they effect changes in the internal
environment. Effectors are controlled systems because their activities are controlled by commands from regulatory
systems – obtain, process, and integrate information, then issue commands to controlled systems. A sensor is an
important component of a regulatory system; it provides the feedback information that is compared to the internal set
- Negative feedback is the common use of sensory information in regulatory systems. This indicated that the feedback
causes the effectors to reduce or reverse the process or counteract the influence that created an error signal.
- Positive feedback amplifies a response (i.e. empty body cavities, such as urination, defecation, sneezing, and vomiting).
- Feedforward information changes the set point.
Physiological Systems are made up of Cells, Tissues, and Organs (857)
- A tissue is an assemblage of cells and a piece of an organ will almost always consist of more than one of the four kinds
1. Epithelial Tissues are sheets of densely packed, tightly connected epithelial cells that cover inner and outer
body surfaces. They act as barriers and provide transport across those barriers. Epithelial tissues form the skin and line the
hollow organs of the body, such as the gut. Epithelial tissues secrete hormones, milk, mucus, digestive enzymes, or sweat;
others have cilia that move substances over surfaces or through tubes. Smell and taste receptors are epithelial cells. They
create boundaries between the inside and outside of the body; they line the blood vessels and make up the various ducts
and tubules. Filtration and transport are important functions of the epithelial cells. Dandruff is discarded skin cells.
2. Muscle Tissues consist of elongated cells that can contract to generate forces and cause movement. They are
the most abundant tissues in the body, and when animals are active, muscles use most of the energy produced in the body.
Three types of muscle tissues: skeletal (responsible for locomotion and other body movements such as facial expressions,
shivering, and breathing; these muscles are under both conscious and unconscious control), cardiac (make up the heart
and is responsible for the heart beat and the pumping of blood), and smooth (responsible for movement and generation of
forces in vessels; cardiac and smooth muscles are not under conscious control, but are controlled by physiological
3. Connective Tissues are generally dispersed populations of cells embedded in an extracellular matrix that they
secrete. The composition and properties of the matrix differ among types of connective tissues. Protein fibres are an
important component of the extracellular matrix of connective tissue cells (collagen is the most abundant protein in the
human body). Cartilage and bone are connective tissues that provide rigid structural support. Cartilage is resistant to