Chapter 32 Notes General Biology

Homeostasis ● French physiologist Claude Bernard recognized the “internal constancy” of animal bodies in the 19th century ● Walter Cannon (1920) coined the term homeostasis (meaning “to stay the same”) ● The ability of an organism to maintain its internal environment within the narrow limits that allow optimal cell functioning ● The maintenance of stable conditions (a dynamic equilibrium) in the body for optimal cell functioning ○ Body temperature and pH ○ Oxygen, CO2, water, salt, and glucose concentration Why Homeostasis is Needed? ● Homeostasis allows enzymes to function ○ Most enzymes are proteins whose ability to function depends on their threedimensional structure maintained by hydrogen bonds ○ Temperature, salt, and pH can affect hydrogen bonds and therefore affect protein structure and function ○ Enzyme can tolerate narrow range of temperature, salt, and pH Temperature Regulation ● Two groups of animals depending on how they regulate body temperature 1. Ectotherms (cold blooded) ● Reptiles, amphibians, most fish, and invertebrates 2. Endotherms (warm blooded) ● Birds and mammals Ectotherms ● Ectotherms derive most of their heat from the environment ○ The body temperatures of most ectotherms vary quite a bit as the external temperature changes over the course of hours, days, or weeks ○ Through behavior or by occupying a very constant environment, some ectotherms can maintain quite stable body temperatures Endotherms ● Endotherms produce most of their heat through metabolic reactions ● Most endotherms maintain a fairly constant body temperature between about 95ºF and 106ºF ○ Benefit: A warm body usually can sense its environment better, respond more quickly, and move faster than a cold body ○ Cost: Energy required to maintain a high body temperature Regulation of Internal Conditions ● Feedback Systems regulate internal conditions ● There are two types of feedback systems 1. Negative Feedback Systems: The Main System 2. Positive Feedback Systems Negative Feedback Reverses the Effects of Changes ● Negative feedback systems maintain many physiological parameters within narrow limits ● Components of a negative feedback systems: 1. The sensor detects the current condition 2. The control center compares that condition to a desired state called the set point 3. The effector produces an output that restores the desired condition Negative Feedback Maintains Internal Temperature ● Hypothalamus in the brain is the key homeostatic regulator in birds and animals ● It coordinates signals to maintain body temperature despite large fluctuations in environmental temperature ● Nerve endings in the abdomen, skin, large veins, and hypothalamus itself act as temperature sensors and transmit this information to the hypothalamus ● Hypothalamus is the control center for temperature regulation ● If the body temperature falls below the set point, the hypothalamus activates effector mechanisms that raise body temperature ○ These mechanisms include shivering, blood vessel constriction, and increased metabolic rate ○ When body temperature is restored, the sensors signal the hypothalamus to switch off the actions that generate and conserve heat ● The body’s temperature control system can also act to reduce body temperature if it rises over the set point ○ The hypothalamus sends out signals that cause the blood vessels leading to the skin to dilate, allowing warm blood to flow to the skin, where some heat can be radiated out to the air ○ Sweat glands secrete fluid, cooling the body by evaporating water from the skin ○ Fatigue and discomfort cause the body to slow down, so the body generates less heat Positive Feedback ● In positive feedback, a change produces a response that intensifies the initial change ● Positive feedback is rare. Example: During the birth of babies: ○ The early contractions of labor push the baby’s head against the cervix, causing it to stretch and open ○ Nerve cells in the cervix react to the stretching by signaling the hypothalamus ○ The hypothalamus responds by triggering the release of a hormone called oxytocin ○ Oxytocin stimulates more and stronger uterine contractions ○ Stronger contractions cause the baby’s head to stretch the cervix even more How Is the Animal Body Organized? ● Animals maintain homeostasis by: ○ Performing numerous functions simultaneously ○ Coordinating the activity of various structures in the body ● This coordination of body functions relies on a hierarchy of structures Cells → tissues → organs → organ systems Cells, Tissues, Organs, and Organ Systems ● Cells are the fundamental units of all living organisms ● Tissues are composed of similar cells that work together to carry out a particular task ● Organs are structures that perform complex functions and include two or more interacting tissue types ● Organ Systems consist of groups of organs that act in a coordinated manner Tissues ● Some tissues may include both cells and extracellular matrix (ECM) produced by its cells. The ratio of cells to ECM varies among those tissues ● ECM is a network of extracellular macromolecules that provide structural and biochemical support of surrounding cells. ECM can be ○ Thin and watery (in blood and lymph) ○ Gelatinous (in connective tissue) ○ Stretchy (in skin) ○ Tough and flexible (in cartilage) ○ Rigid (in bone) ● There are four major categories of animal tissues 1. Epithelial tissue forms both epithelial membranes and glands 2. Connective tissue 3. Muscle tissue 4. Nerve tissue Epithelial Membranes ● Where ○ Cover external body surfaces (forming the epidermis of skin) ○ Line the ducts and hollow organs (lung, uterus, bladder, heart and blood vessels) ○ IN SKIN AND HOLLOW ORGANS ● Functions ○ Provide protection ○ Facilitate gas exchange ○ Regulate the movement of nutrients and wastes across the walls of internal structures ○ Secrete substances such as mucus ● General Characteristics ○ Have a free surface that usually faces a cavity inside the body ○ Are anchored to and supported by an underlying basement membrane ■ A thin, non-cellular layer composed primarily of fibrous proteins ○ Are thin and lack blood vessels ■ Their cells acquire nutrients, exchange gases, and eliminate wastes by diffusion ○ Can usually regenerate ○ Are firmly attached to one another by connections such as desmosomes and tight junctions ● Classification ○ Made of one cell or more ■ Simple epithelium is only one cell thick ■ Stratified epithelium contains more than one cell layer ○ Cell Shape ■ Squamous cells are flat and thin ● SQUASHED ■ Cuboidal cells are cube-shaped ■ Columnar cells are elongated ○ These cells could be ciliated ■ Bring cilia on their upper surfaces ● Squamous Epithelium ○ The lining of the lung air sacs ○ Allow rapid diffusion of gases between the lungs and the bloodstream ● Cuboidal Epithelium ○ The lining inside of ducts. These ducts carry secretions from glands ○ Lines the kidney tubules, where it contributes to urine formation ● Simple Columnar Ciliated Epithelium ○ Line the trachea (windpipe) ○ Bearing cilia ○ Have cells that secrete mucus ● Simple Columnar Non-Ciliated Epithelium ○ Line the digestive tract ○ Secrete digestive material and help in absorbing nutrition ● Stratified Epithelium ○ Two or more cells thick and can usually withstand considerable wear and tear ○ Stratified epithelium is mostly found in the esophagus, skin, and just inside body openings that are continuous with the skin, such as the mouth and anus ● Glands are clusters of epithelial cells specialized for secretion ○ Epithelial tissues form glands ● Exocrine Glands: They secrete substances into a body cavity or onto the body surface, usually through a duct ○ Examples include sweat glands, mammary glands, and salivary glands ● Endocrine Glands: They do not have a duct. They secrete hormones into the interstitial fluid, from which the hormones diffuse into the nearby capillaries ○ Such as the ovaries, testes, thyroid, and pituitary ○ Hormones are chemicals that are produced in small quantities and are transported in the bloodstream to regulate the activity of other cells Connective Tissue ● Forms a diverse group of tissues ● Support and strengthen other tissues ● Help bind the cells of other tissues together in coherent structures ● Has a large amount of ECM relative to cells ○ ECM is made of protein fibers (such as collagen and elastin) ○ These protein are secreted by cell within the tissue ○ Collagen is the main structural protein of connective tissues, with the exception of blood and lymph 3 Categories 1. Loose connective tissue 2. Dense connective tissue (Tendon and Ligament) 3. Specialized connective tissue (Cartilage, Bone, and Blood and Lymph) Loose Connective Tissue ● Is the most abundant form of connective tissue ● Consisting of a thick fluid containing scattered cells that secrete protein ● It supports, surrounds, and cushions other tissue types ● Fat, or adipose tissue, is a form of loose connective tissue that acts as a cushion under the skin, stores fats, and cushions and insulates the body Dense Connective Tissue ● Is packed with collagen fibers ● In tendons (which connect muscles to bones) and ligaments (which connect bones to bones), the collagen fibers are arranged parallel to one another ● Tendons and ligaments have tremendous strength, but only in the direction in which the collagen fibers are oriented Specialized Connective Tissues ● Includes... ○ Cartilage - consists of cartilage cells surrounded by a thick matrix composed of collagen secreted by the cartilage cells ○ Bone - Resembles cartilage, but its matrix is hardened by deposits of calcium phosphate ○ Blood and lymph → ECM if blood and lymph has no collagen. Consists of mostly watery extracellular matrix, cells, and proteins. ● Blood contains… ○ Red blood cells → Transport oxygen ○ White blood cells → Fight infection ○ Platelets (are cell fragments): Help in blood clotting ○ The blood cells are suspended in a fluid called plasma ● Lymph consists largely of liquid that has leaked out of blood capillaries, plus white blood cells Muscle Tissue ● Muscle tissue has the ability to contract ● There are 3 types of muscle tissue ○ Skeletal Muscle ○ Cardiac Muscle ○ Smooth Muscle Skeletal Muscle ● Is stimulated by the nervous system ● Is generally under voluntary, or conscious, control ● Appears striped (striated) ○ The regular arrangement of fibrous proteins makes it appear striped (striated) ● Its main function is to move the skeleton Smooth Muscle ● Smooth muscle, named because its cells do not appear striated ● Is found throughout the body ● Embedded in the walls of the digestive and respiratory tracts, uterus, bladder, and larger blood vessels ● Produces slow, sustained, involuntary contractions that may be stimulated by the nervous system, by stretch, or by hormones or other chemicals Cardiac Muscle ● Is located in the heart ● Is spontaneously active under involuntary control ● In cardiac muscle , the cells are interconnected by intercalated discs, through which electrical signals spread through the heart, stimulating the cardiac muscle cells to contract in a coordinated fashion Nerve Cells ● Is specialized to produce and conduct electrical signals ● Makes up the brain, spinal cord, and nerves in all body parts ● Is composed of 2 types of cells… 1. Neurons or Nerve Cells 2. Glial Cells Neurons ● A typical nerve cell consists of… ○ Dendrites - Specialized to receive signals from other neurons or from the environment ○ A cell body - Contains the nucleus and carries out most of the neuron’s metabolism ○ An axon - Carries the neuron’s electrical signal to a muscle, gland, or other neuron ○ The terminals - Transmit information to the other cells Glial Cells ● Surround, support, electrically insulate, and protect neurons ● Regulate the composition of the interstitial fluid in the nervous system Organs ● A organ is an organized group of tissues (structures) that act in a coordinated manner ● Most organs consist of all four tissue types, with different kinds and proportions of epithelial, connective, muscle, and nerve tissues ● Most organs function as part of an organ system Skin Is an Organ ● The skin is an important barrier against the evaporation of water and the entry of disease-causing microorganisms ● Epidermis: Outer layer of the skin Specialized stratified epithelial tissue ● Dermis: Beneath the epidermis ○ A layer of loose connective tissue ○ Contains numerous blood vessels and sensory nerve endings ○ Specialized epithelial cells dip down from the epidermis into the dermis, forming hair follicles ○ Contains glands derived from epithelial tissue ○ Sweat glands produce watery secretions ○ Sebaceous glands secrete an oily substance (sebum) ● Adipose Tissue: Below the dermis (hypodermis)(Technically not part of the skin) ○ Is a layer of adipose tissue interspersed with fibrous proteins produced by connective tissue cells ○ The fat helps to insulate the body, preserving heat and making it easier to maintain a constant body temperature in cool weather Organ Systems ● Organ systems consist of two or more individual organs (in some cases, located in different regions of the body) that work together, performing a common function What does homeostasis mean? ● The maintenance of the same exact conditions in every cell in a body ● The maintenance of identical conditions in a cell at all stages in the cell cycle ● The maintenance of stable conditions in the body for optimal cell functioning ● The maintenance of identical conditions on the inside and outside of a cell How will a fever of 105ºF affect metabolic reactions in a person’s body? ● It will speed up metabolic reactions, making the use of glucose more efficient. ● It will slow down metabolic reactions, making the use of glucose less efficient. ● Heat denatures the catalysts’ three-dimensional structure, which will shut down metabolic reactions. ● Heat denatures the catalysts’ three-dimensional structure, speeding up metabolic reactions. Why do you get “goose bumps” when you are cold and shiver? ● The skin fills with blood to warm the outer surface, making a bumpy appearance. ● The skin fills with tiny warming air pockets, causing the bumpy appearance. ● Adipose collects in pockets under the skin to warm the outer surface, making the hairs stand up on end, causing the bumpy appearance. ● Muscles surrounding skin hairs contract. This generates heat, making the hairs stand up on end, causing the bumpy appearance. Where would a single layer of ciliated, mucus-secreting epithelial cells be found? ● Stomach ● Mouth ● Skin ● Trachea A structure that is made of more than one kind of tissue is _____. ● Mutated ● Damaged ● An organ ● Undergoing mitosis