Lecture 8 – Animal Structure and Function

Lecture 8 – Animal Structure and Function Exchange with the Environment • Materials such as nutrients, waste products, and gases must be exchanged across the cell membranes of animal cells • Rate of exchange is proportional to a cell’s surface area while amount of exchange material is proportional to a cell’s volume • A single-celled protist living in water has a sufficient surface area of plasma membrane to service its entire volume of cytoplasm • Multicellular organisms with a saclike body plan have body walls that are only two cells thick, facilitating diffusion of materials • In flat animals such as tapeworms, the distance between cells and the environment is minimized • More complex organisms have highly folded internal surfaces for exchanging materials • In vertebrates, the space between cells is filled interstitial with fluid, which allows for the movement of material into and out of cells • A complex body plan helps an animal living in a variable environment to maintain a relatively stable internal environment The hierarchy of multicellular organisms: cells ® tissues® organs® organ systems Organ systems: Several organs with separate functions that act in a coordinated manner (digestive, respiratory systems, etc.) Tissues: Groups of cells with common structure and function. Four main types: 1. Epithelial Tissue: Formed from sheets of tightly packed cells, epithelial tissue covers the outside of the body and lines organs and body cavities. Characteristics of epithelium include: - Cells are closely joined and are riveted by tight junctions in some tissue types. - It functions as a barrier against mechanical injury, invading microbes, and fluid loss. - Its free surface is exposed to air or fluid. Cells at the base are attached basement to a membrane, which is a dense layer of extracellular material. Epithelial tissue cells are categorized by the number of layers and shape of the free surface cells: - Simple epithelium is one layer of cells. Stratified has multiple layers. - Pseudostratified epithelium is one layer of cells that appear to be multiple because the cells vary in length. - Cell shapes are cuboidal (like dice),columnar (bricks on end), orsquamous (like flat floor tiles). 2. Connective tissue: is characterized by a sparse cell population scattered through an extensive matrix. Functions to bind and support other tissues. - Matrix is a web of fibers embedded in a homogenous ground substance. Three types of fibers: - Collagenous, to resist stretching and have great tensile strength; Elastic, to allow tissue to return to original shape; Reticular, join connective tissue to adjacent tissues. - Connective tissue contains cells, including - Fibroblasts that secrete the protein of extracellular fibers - Macrophages that are involved in the immune system Major types of connective tissue include: - Loose connective tissue - Adipose tissue - Fibrous connective tissue - Cartilage - Bone - Blood Loose connective tissue holds organs in place and attaches epithelia in underlying tissue. - Has all three fiber types. Adipose tissue is specialized to store fat in adipose cells. - Insulates the body and stores fuel molecules. - Each adipose cell has one large fat droplet which can vary in size as fats are stored or utilized. Fibrous connective tissue is dense due to the arrangement of a large number of collagenous fibers in parallel bundles, which impart great tensile strength. - Found in tendons (attach muscles to bones) and ligaments (attach bones together at joints). Cartilage is composed of collagenous fibers embedded chondroitin in sulfate, a proteincarbohydrate ground substance. - Chondrocytes (cells) secrete both collagen and chondroitin sulfate, which make cartilage both strong and flexible. - Cartilage compromises the skeleton of all vertebrate embryos. - Some vertebrates (e.g., sharks) retain the cartilaginous skeleton in adults. Most vertebrates eventually replace most of the cartilage with bone. Cartilage is retained in areas such as the nose, ears, trachea, and intervertebral discs. Bone is mineralized connective tissue. - Osteoblasts, bone-forming cells, deposit a matrix of collagen and calcium phosphate, which hardens into the mineral hydroxyapetite. Blood is connective tissue composed of: - Liquid extracellular matrix of plasma that contains water, salts, and proteins. - - Cellular component that contains: - Leukocytes, white blood cells that function in immune defense. - Erythrocytes, red blood cells that transport oxygen. - Platelets, cell fragments that function in blood clotting. Blood cells are made in the red marrow near the ends of long bones. 3. Nervous tissue senses stimuli and transmits signals from one part of the animal to another. - Neuron: Nerve cell specialized to conduct an impulse or bioelectric signal; consists of: - cell body, dendrites (extensions that conduct impulses to the cell body), and axons (extensions conducting impulses away from the cell body) 4. Muscle tissue consists of long excitable cells capable of contraction. Three types of vertebrate muscle tissue: - Skeletal, cardiac, andsmooth muscle. Feedback control maintains the internal environment in many animals • Animals manage their internal environment by regulating or conforming to the external environment • A regulator uses internal control mechanisms to moderate internal change in the face of external, environmental fluctuation • A conformer allows its internal condition to vary with certain external changes • Animals may regulate some environmental variables while conforming to others Homeostasis: Dynamic state of equilibrium in which internal conditions remain relatively stable; steady state. Homeostasis depends on feedback circuits. Homeostatic control systems have three functional components: 1. Receptor detects internal change. 2. Control center processes information from the receptor and directs the effector to respond. 3. Effector provides the response. Negative feedback: Homeostatic mechanism that stops or reduces the intensity of the original stimulus and consequently causes a change in a variable that is opposite in direction to the initial change. - Most common mechanism in animals. - Example of hormonal control of blood glucose. Positive feedback: Homeostatic mechanism that enhances the initial change in a variable. - Rare in animals. - Examples include blood clotting and the heightening of labor contractions during childbirth. Thermoregulation is the process by which animals maintain an internal temperature within a tolerable range • Endothermic animals generate heat by metabolism; birds and mammals are endotherms. Many are also homeothermic, that is, their body temperature must be maintained within narrow limits. • Ectothermic animals gain heat from external sources; ectotherms include most invertebrates, fishes, amphibians, and nonavian reptiles • In general, ectotherms tolerate greater variation in internal temperature, while endotherms are active at a greater range of external temperatures • Endothermy is more energetically expensive than ectothermy Basal metabolic rate (BMR): An endothermic animal’s metabolic rate measured under resting, fasting and stress-free conditions. Average human male BMR is 1600-1800, female is 1300-1500kcal/day. Metabolic rate: Total amount of energy an animal uses per unit time; usually measured in calories or kilocalories. Metabolic rate influenced by: - Age, sex, and size - Body temperature - Environmental temperature - Food quality and quantity - Activity level Amount of available oxygen Hormonal balance Time of day