homeostasis and the organization of the animal body chapter 31 pages 604 - 618
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Homeostasis and the Organization of the Animal Body
Chapter 31pages 604 - 618
Hierarchy of Structures
Tissues are composed of similar cells that perform a specific function
Organs perform complex functions and include two or more interacting tissue types
Organ systems consist of two or more interacting organs that function in a coordinated manner
Cells, Tissues, Organs, Organ Systems
How Is the Animal Body Organized?
Animal tissues are composed of similar cells that perform a specific function There are four categories of animal tissues
Epithelial tissue Connective tissue Muscle tissue Nerve tissue
Epithelial Tissue
Covers the body, lines cavities, and forms glands
All body surfaces — skin, digestive, respiratory, and urinary tracts, and circulatory system
Epithelial tissue is sheets of cells firmly attached to one another by connections such as desmosomes and tight junctions
Attached to an underlying layer of fibrous proteins or basement membrane - provides support, flexibility, and strength
Cells are continuously lost and replaced
Types of Epithelium
Simple epithelium is one cell thick and lines the respiratory, urinary, reproductive, and circulatory systems
Stratified epithelium is found in the skin and just inside body openings that are continuous with the skin (mouth and anus) and are continuously lost and replaced
Several cells thick and can withstand considerable wear and tear
Epithelial Tissue
(a) Lining of the lungs (simple epithelium)
basementmembrane
mucus
cilia
mucus- producing cells
flattenedcells
basementmembrane
(b) Lining of the trachea (simple epithelium)
basementmembrane
(c) Skin epidermis (stratified epithelium)
flatteneddyingcells
deadcells
dividingcells
differentiatingcells
Skin - Epithelial Tissue
Glands Glands are cells or groups of cells specialized to secrete
large quantities of substances outside the cell
Two categories Exocrine glands secrete substances into a body cavity or
onto the body surface, usually through a duct Sweat glands, mammary glands, salivary glands, and
glands that secrete digestive enzymes
Endocrine glands lack ducts, and release hormones into the extracellular fluid, diffuses into capillaries Hormones are chemicals produced in small quantities and
transported thru the bloodstream to regulate the activity of other cells
Connective Tissues
Diverse structures and functions Support and strengthen other tissues, binding the cells
of other tissues into coherent structures, such as skin or muscle
They consist of fluid containing proteins, especially collagen
Three categories of connective tissue Loose connective tissue Dense connective tissue Specialized connective tissue
Loose Connective Tissue
The most abundant form of connective tissue, consisting of a thick fluid containing scattered cells that secrete protein
Flexible tissue connects, supports, and surrounds other tissue types, forming a framework for organs such as the liver
Dense Connective Tissue
Packed with collagen fibers that provide flexibility and strength, but only in the direction in which the collagen fibers are arranged
Tendons, which connect bones to muscles
Ligaments, which connect bones to bones
Specialized connective tissues
Diverse functions and structures
Cartilage Bone Fat (adipose tissue) Blood Lymph
Cartilage
Widely spaced cells surrounded by thick, nonliving matrix composed of collagen
It covers the ends of bones at joints, provides the supporting framework for the respiratory passages, supports the ear and nose, and forms shock-absorbing pads between the vertebrae
Flexible, but can break if bent too far
Bone
Bone resembles cartilage, but its matrix is hardened by deposits of calcium phosphate
It forms in concentric rings around a central canal, which contain blood vessels
Adipose
Adipose tissue is made up of fat cells that are modified for long-term energy storage
Can serve as insulation for animals living in a cold environment
Blood and Lymph Blood and lymph are specialized forms
of connective tissue because they are composed largely of extracellular fluids in which proteins are suspended
The cellular portion of blood - Red blood cells transport oxygen White blood cells fight infection Platelets are cell fragments that aid in
blood clotting
The blood cells are suspended in a fluid called plasma
Lymph
Lymph is fluid that has leaked out of blood capillaries, it enters the lymph vessels and is carried back to the circulatory system
Muscle Tissue
Have the ability to contract The long, thin cells of muscle tissue contract when
stimulated and then relax when the stimulation stops
There are three types of muscle tissue Skeletal muscle Cardiac muscle Smooth muscle
Skeletal Muscle
Skeletal muscle is stimulated by the nervous system and is under voluntary, or conscious, control
Its main function is to move the skeleton
Cardiac Muscle
Cardiac muscle spontaneously active, not under conscious control
Interconnected by gap junctions, through which electrical signals spread, stimulating cardiac muscles cells to contract in a coordinated fashion
Smooth Muscle
Found throughout the body, in the walls of the digestive and respiratory tracts, uterus, bladder, and larger blood vessels
Produces slow, sustained, involuntary contractions that are stimulated by the nervous system, by stretch, or by hormones or other chemicals
Nervous Tissue
Specialized to produce and conduct electrical signals
Brain, spinal cord, and nerve cells (neurons) Neurons are specialized to
generate electrical signals and conduct signals to other neurons, muscles, or glands
Glial cells surround, support, insulate, and protect neurons
How Is the Animal Body Organized?
Organs are formed from at least two types of tissues that function together; most consist of all four tissue types
Function as part of an organ system
The skin illustrates the properties of organs Outer layer of epithelial cells underlain by connective
tissue that contains a blood, nerve supply, muscle, and glandular structures derived from the epithelium
Structural Components of Skin
Epidermis, or outer layer, is specialized stratified epithelial tissue
Immediately beneath the epidermis lies a layer of loose connective tissue, the dermis, which contains blood vessels
Specialized epithelial cells dip down from the epidermis into the dermis, forming hair follicles
Below the dermis is a layer of adipose tissue
Skin is an Organ
sensory nerve endings
living epidermalcells
dead cell layer
sebaceous gland
arterioles
venules
hair follicle
muscle(pulls hair upright) sweat gland
hair shaft
epidermis
dermis
subdermalconnective and adiposetissue
capillary bed
lymph vessels
pore
Organ Systems
Two or more interacting organs, located in different regions of the body, that work together to perform a common function
Digestive system - in which the mouth, esophagus, stomach, intestines, liver and pancreas, all function together to convert food into nutrient molecules that can be absorbed into the bloodstream
Homeostasis
Animal cells need a narrow range of conditions to survive
Homeostasis is the process by which an organism maintains its internal environment, within that narrow range
How does it work?
The internal environment is maintained in a state of dynamic constancy
The internal environment is in a state of dynamic constancy
The body adjusts to ongoing internal and external changes to maintain constant conditions
Examples of Regulated Conditions
Temperature
Water and salt concentrations
Glucose concentrations
pH (acid-base balance)
Oxygen and carbon dioxide concentrations
Why is this Important?
Animal cells are constantly generating and using large quantities of ATP to sustain life processes
Continuous supplies of high-energy molecules and O2 are required to carry out the reactions that generate ATP
Energy production helps explain the importance of glucose and oxygen levels
Each of the reactions for producing ATP is catalyzed by a protein whose ability to function depends on its three-dimensional structure
This structure is maintained by hydrogen bonds, which can be disrupted if the environment is too hot, salty, acidic, or basic
The need to maintain these bonds helps explain the requirement for a narrow range of temperature, pH, and salt
Animals vary in their homeostatic abilities
Birds and mammals are efficient at maintaining homeostasis for all the internal conditions listed above
Other animals have reduced or absent homeostasis
for one or more aspects of their internal environment For example, many marine invertebrates, including
snails, crabs, and worms, cannot regulate the overall concentration of their bodily fluids
Classification
Scientists classify animals according to their major source of body warmth
Endotherms generate heat through metabolic reactions - birds and mammals Warm blooded
Ectotherms derive body heat from the environment, and maintain it by occupying a constant environment or by behavioral activities - reptiles, amphibians, fishes, and invertebrates Cold blooded
Warm-Blooded or Cold-Blooded?
Regulation
Feedback systems regulate internal conditions Homeostatic mechanisms that maintain internal
constancy are called feedback systems
Two types Negative feedback - counteracts the effects of
changes in the internal environment to maintain homeostasis
Positive feedback, - drives rapid, self-limiting changes, such as those that occur when a mother gives birth
Negative Feedback
Works by reversing the effect of a change The most important feedback mechanism A change in the environment causes responses that “feed back” to
counteract the change The overall result of negative feedback is a return to the original
condition
Three components A sensor detects the current condition A control center compares that condition to the desired state,
called the set point An effector produces an output that restores the desired condition
Animation: Elements of a Feedback System
Home temperature is regulated by negative feedback Negative feedback systems that control body temperature are similar
to those used to heat a home
The sensor is a thermometer, the control center is a thermostat, and the effector is the heater
The thermometer detects the room temperature and sends that information to the thermostat, where it is compared to the set point of the desired temperature
If the temperature is below the set point, the thermostat signals the heater to turn on and generate heat
The heater warms the room, restoring the temperature to the set point, causing the thermostat to turn off the heater
Animation: Temperature Control in Your House
Negative feedback maintains body temperature The temperature control center is located in the hypothalamus,
a part of the brain
Set point is between 97º- 99º F
Nerve endings act as temperature sensors and transmit information to the hypothalamus
If the body temperature falls below the set point, the hypothalamus activates effector mechanisms that raise body temperature Shivering, blood vessel constriction, increased metabolic rate When body temperature is restored, the sensors signal the hypothalamus
to switch off these actions
Negative Feedback Maintains Homeostasis
The body’s temperature controls system can also act to reduce body temperature if rises above set point Blood vessels leading to the skin to dilate, allowing
warm blood to flow to the skin, where heat can be radiated into the air
Sweat glands secrete fluid, cooling the body as it evaporates from the skin
Fatigue and discomfort cause the body to slow down, so the body generates less heat
Animation: The Control of Body Temperature
Positive Feedback
Positive feedback enhances the effects of changes A change produces a response that intensifies the
initial change Positive feedback is relatively rare in biological
systems, but occurs during childbirth and blood clotting
Childbirth
Labor contractions force the baby’s head against the cervix at the base of the uterus, causing it to stretch and open
Stretch-receptor neurons in the cervix signal the hypothalamus
The hypothalamus releases oxytocin, a hormone which stimulates more and stronger contractions
Stronger contractions cause the baby’s head to stretch the cervix even more, causing the release of more oxytocin
Delivery of the baby relieves the pressure on the cervix, halting the positive feedback cycle
Animation: The Control of Labor
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