BIOL 191 | Ch. 32 - Animals: General Features & Homeostasis

Cell differentiation

Happens during development; they become specialized to perform a particular function

Cells are organized into progressively more complex structures including;

Tissues, organs, and organ systems

Tissue

Is an association of many cells having a similar structure and function

Tissues can be classified into 4 types

• Muscle tissue

• Nervous tissue

• Epithelial tissue

• Connective tissue

Each contain subtypes that perform variations of the main function

Muscle tissues

Contain specialized cells that contract (shorten), generating mechanical forces they may

• produce body movements

• decrease the diameter of a tube

• exert pressure on a fluid-filled cavity

The 3 types of muscle tissue

Skeletal, smooth, and cardiac muscle

Nervous tissues

Complex networks of neurons, cells that communicate by initiating and conducting electrical signals (action potentials) from one part of the body to another

Electrical Signal Function

• Stimulate or inhibit another neuron

• Stimulate muscle cells to contract

• Stimulate glandular cells to secrete their products (e.g., sweat or digestive glands)

Epithelial Tissue

Sheets of densely packed cells that cover body surfaces, enclose organs, or line the walls of body cavities

Epithelial cells

Specialized for protection and transport; they are asymmetrical (have district basal and apical surfaces)

Epithelial tissue form

May be;

• simple

• stratified

• pseudo stratified

• transitional

Connective Tissues

A diverse group that connect, surround, anchor, and support the structures of an animal’s body. (e.g., bone, cartilage, blood)

Organ

Composed of two or more tissues arranged in particular proportion/patterns (sheets, tubes, layers, bundles, strips)

Organ System

Different organs function together to perform an overall function

Organ Development

In animals is controlled by a highly conserved family of body-plan genes (Hox genes) with homologs in all animals

Key principle of biology

Structure determines function

Important properties of cells

Surface area and volume; they increase at different rates as cells become larger

Many structural modifications (adaptations) allow increased _____ ____ to facilitate processes of exchange.

Surface area

Ideal for transport, absorption, or direction of environmental stimuli

High surface area/volume (SA/V) ratio

Homeostasis

The process of maintaining a relatively stable internal environment, despite changes in the external surroundings

• Dynamic process

Animal’s typical environment

Variable

Conformers

Describes some animals, features of the internal environment match the external environment

• Energetically, conforming is an inexpensive strategy

Regulators

Describes some animals, features of the internal environment differ from the external environment

• Energetically, regulating the internal environment is an expensive strategy

Animals on conformers vs regulators

Can be both with respect to different variables

Variables maintained in a normal range in a homeostatic environment

• Concentration of nutrients, wastes, and ions in blood

• Concentration of O2 and CO2 in body fluids

• pH of body fluids

• Blood pressure and blood volume

Homeostatic variable fluctuation

May fluctuate within a certain normal range, if a disturbance drives that variable out of range, compensatory mechanisms restore the variable toward normal

Homeostatic control systems

Performs actions that maintain homeostasis

• Consists of a set point, sensor, integrator, and effector

Sensor

Typically a group of neurons, such as temperature-sensitive neurons in the skin

Integrator

Often located in the brain and compares input from the sensor with a set point

Effector

Produces a response that compensates for the change caused by the homeostatic challenge

Set point

The ideal or target value that the system tries to maintain

Negative Feedback Loop

A change in the variable being regulated brings about a response that moves the variable in the opposite direction

• maintains a variable within a normal range

Positive Feedback Loop

Accelerate a process; a change in a variable leads to events that amplify that change

• Is an appropriate response when a potentially dangerous or stressful process must be completed quickly

Feedforward Regulation

Prepares the body for a possible challenge to homeostasis before it occurs

• Often occurs in animals with well-developed nervous systems

Mammals

Survive in a relatively narrow range of body temperatures

• Homeostatic regulatory mechanisms work to prevent your temp from exceeding these ranges

Temperature affects animals’ bodies in three main ways

Chemical reactions, protein functions, and membrane structure

Chemical Reaction and Temp

Rate of the reaction typically increases 2-3 fold for every 10C increase in body temp

Proteins and Temp

High temps can cause denaturing

Membranes and Temp

The plasma membrane and the membranes of intracellular organelles are affected.

Metabolic rate

The amount of energy an organism uses in a given period of time to power its activities

Basal metabolic rate (BMR)

Is the most common measure to compare the metabolic rates of different species

Ectotherms

Rely on heat from the external environment to warm themselves

Endotherms

Generate internal heat through their metabolism

Homeotherms

Maintain their body temperature within a narrow range

Heterotherms

Have body temperatures that undergo considerable variation

Animals exchange heat with the environment in 4 ways

Radiation, evaporation, conduction and convection

Endotherm heat regulation

Can regulate how much heat is gained or lost between the environment and their bodies via;

• Changes in skin blood flow

• Countercurrent exchange

• Evaporative heat loss

• Behavioral adaptations

• Changes in muscle activity

Changes in skin blood flow

Endotherm regulation; hot days vessels dilate = more blood flow, cold days vessels constrict = less blood flow

Countercurrent Exchange

Endotherm regulation; heat is transferred between fluids flowing in an opposite direction

Changes in muscle activity

A major mechanism for the control of heat production in endotherms

• E.g., shivering thermogenesis (muscles contract rapidly without any locomotion)

• Nonshivering thermogenesis occurs in brown adipose tissue

Animal bodies & water

Mostly composed of it, which is distributed within fluid compartments

Extracellular fluid

Primarily present as blood plasma and as interstitial fluid

Intracellular fluid

Contained inside cell walls

Ion Balance

Critical for number of cellular activities, including muscle contraction and communication in the nervous system

• Foods have salts and water; contribute to balance

Vital processes that have the potential to disturb ion and water balance

Eliminating nitrogenous wastes, obtaining O2 and eliminating CO2, consuming and metabolizing food, and regulating body temperature

Nitrogenous wastes

Product of proteins and nucleic acids when broken down and metabolized

Respiration & water loss

Respiration in animals with lungs is associated with significant water loss (“see your breath” in cold weather)

Water-breathing animals

More complex because water and ions can move across gills

Sweating and Panting

Can be used to cool the body of endotherms