Animal Form and Function Lecture 2

Muscle Tissue  Muscle tissue was a key innovation in the evolution of animals—like nervous tissue, it appears in no other lineage – Muscle tissue functions in movement  There are three types of muscle tissue 1. Skeletal muscle 2. Cardiac muscle 3. Smooth muscle Figure 42.5 Skeletal muscle 10 m Long cells, voluntary movement Cardiac muscle 10 m Branched cells, involuntary movement Smooth muscle 10 m Tapered cells, involuntary movement Epithelial Tissue  The epithelial tissues (epithelia) are tissues that cover the outside of the body, line the surfaces of organs, and form glands  An organ is a structure that serves a specialized function and consists of several tissues  A gland is a group of cells that secrete specific molecules or solutions  Epithelia carry out several functions – Protection – Transport of water and nutrients Epithelial Tissue  Epithelial cells typically form layers of closely packed cells  All epithelial tissue has a polarity – The apical side faces away from other tissues – The basolateral side faces the animal’s interior – The basal lamina connects the epithelial to the connective tissue  The apical and basolateral sides of an epithelium have distinct structures and functions Figure 42.6 Faces outer environment Apical side of epithelium Epithelium Basal lamina connects epithelium to other tissues Basolateral side of epithelium 10 m Organs and Organ Systems  Cells with similar functions are organized into tissues  Tissues are organized into specialized structures called organs  Organs are part of larger units called organ systems, which consist of groups of tissues and organs that work together to perform one or more functions Figure 42.7 (b) Organs are organized into organ systems. (a) Tissues are organized into organs. DIGESTIVE SYSTEM: TISSUES: Epithelial tissue Connective tissue Nervous tissue Muscle tissue ORGAN: Small intestine Salivary glands secrete enzymes that begin to digest food. The esophagus is a long, muscular tube that transports food to the stomach. The stomach is a thick, muscular sac whose contractions help break up food. The liver and pancreas contain cells that secrete enzymes and other molecules that aid digestion. The small intestine is a long, coiled tube where enzymes digest food and nutrients are absorbed. The large intestine is a large tube where water is reabsorbed and wastes are compacted. Surface Area/Volume Relationships: Theory  The cell surface area determines the rate at which gases and nutrients diffuse across the membrane  The cell volume determines the rate of diffusion – As a cell gets larger, its volume increases much faster than its surface area does  The area/volume affect the animal’s overall physiology – The physiological activity can be measured as the metabolic rate Figure 42.9 (a) What are the surface area and volume of each cube? (b) Surface area and volume of a cube versus length of a side 4l Volume 2l l Surface 6l 2 area Volume l3 Ratio 6:1l (surface area/volume) 6(2l)2  24l2 6(3l)2  54l2 6(4l)2  96l2 (2l)3  8l3 (3l)3  27l3 (4l)3  64l3 3:1l 2:1l 1.5:1l Volume (cm3) and surface area (cm2) 3l Volume increases more rapidly than does surface area Surface area Length (cm) Surface Area/Volume Relationships: Data  Metabolic rate is the overall rate of energy consumption – The consumption of energy is measured as the basal metabolic rate (BMR)  The BMR is the rate at which an animal consumes oxygen while at rest with an empty stomach, under normal temperature and moisture conditions  The BMR is measured in mL of O2 consumed per gram of body mass per hour Comparing Mice and Elephants  On a per-gram basis, small animals have higher BMRs than do large animals – An elephant has more mass than a mouse – But a gram of elephant tissue consumes much less energy than a gram of mouse tissue does  As an organism’s size increases, its mass-specific metabolic rate must decrease – Or the surface area available for exchange of materials would fail to keep up with the metabolic demands of the organism Adaptations That Increase Surface Area  Increases in surface area relative to its volume are achieved in three ways: 1. Flattening – Example: Fish gills have flattened, sheetlike structures called lamellae 2. Folding – Example: The mammal small intestine has folds called villi 3. Branching – Small blood vessels called capillaries are highly branched Figure 42.12 (a) Flattening: fish gill lamellae (b) Folding: intestinal folds and villi (c) Branching: capillaries Villi Lamellae 10 m 100 m 25 m Homeostasis: General Principles  Homeostasis is the maintenance of relatively constant internal environment – Internal chemical and physical states are kept within a tolerable range  Constancy of physiological state can be achieved by two processes: 1. Conformation 2. Regulation Two Approaches to Achieving Homeostasis  Conformational homeostasis is homeostasis that occurs by conformation to the external environment – For example, the body temperature of Antarctic rock cod closely matches that of the surrounding seawater  Regulatory homeostasis requires a physiological mechanism that adjusts the internal state to keep it within limits that can be tolerated, regardless of the external conditions – For example, a dog maintains a body temperature of about 38C whether it’s cold or hot outside