Animals

• Unifying themes in physiology:

  • Obey physical and chemical laws
  • Shaped by evolution
  • Usually regulated
  • Integrative
• Animals are eukaryotes that share key traits:

  • Multicellularity with cells that :
  • Lack cell walls
  • Have an extensive extracellular matrix
  •  Heterotrophy
  • They obtain carbon from other organisms
  • Most ingest their food rather than absorbing it
  •  Motility
  • They move under their own power at some point in their life
• Adaptations:

  • Heritable traits that make individuals more likely to survive and reproduce in a certain environment better than individuals that lack those traits
  • Genetic change in a population in response to natural selection exerted by the environment
  • Results from evolution by natural selection
• Acclimatization:

  • Phenotypic change that occurs in an individual in response to environmental fluctuations
  • Short term and reversible
• Homeostasis:

  • Stability in chemical and physical conditions within an organism's cells, tissues, and organs
  • 2 different approaches to maintaining homeostasis:
  • Regulate --> actively maintain relatively constant internal conditions even when the environment fluctuates
  • Conform to their external environment
• Homeostasis is important because:

  • It's dependent on enzyme function
  • Temperature, pH, and other physical and chemical conditions have a dramatic effect on the structure and function of enzymes
  • We function at an optimal level when homeostasis occurs
• Most animals have regulatory systems that constantly monitor internal conditions such as:

  • Temperature
  • Blood pressure
  • Blood pH
  • Blood glucose

  Each variable has a set point (a normal or target value for that variable)
• A homeostatic system is based on 3 general components:

  • A sensor
  • A structure that senses some aspect of the external or internal environment
  • An integrator
  • Evaluates the incoming sensory information by comparing it to the set point and determining whether a response is necessary
  • An effector
  • Any structure that helps restore the internal condition being monitored
• Homeostatic systems are based on negative feedback

  • Effectors reduce or oppose the direction of change in internal conditions
  • 3 common features:
  • Redundancy
  • Antagonistic pairs (ex. sweating + shivering)
  • Continuous feedback
• Physiology is integrative.

  Atoms -> molecules -> cells -> tissues -> organs -> organ systems
• An adaptive structure will have its size, shape, or composition correlate with its function.

  Mechanism:

  • If a mutant allele alters the size and shape of a structure to make its function more efficient:
  • Individuals with that allele produce more offspring
  • Allele will increase in frequency over time
• Correlations between form and function begin at the molecular level.

  Similar correlations between structure and function occur at the cellular level.

  Cell shape and function correlate.
• Tissue:

  • A group of siilar cells that work together as a unit to perform the same function
  • 4 types:
  • Connective
  • Nervous
  • Muscle
  • Epithelial
• Connective tissues:

  • Cells are loosely arranged in a liquid, jellylike, or solid matrix
  • Matrix comprises extracellular fibers and other materials
  • Secreted by the connective tissue cells themselves
  • Nature of the matrix determines the nature of the connective tissue
• 4 types of connective tissues:

  • Loose connective tissue -- contains an array of fibrous proteins in a soft matrix
  • Dense connective tissue -- contains a matrix dominated by tough collagen fibers that are secreted by fibroblasts
  • Supporting connective tissue -- has a firm extracellular matrix
  • Fluid connective tissue -- cells surrounded by a liquid extracellular matrix
• Nervous Tissue:

  • Consist of nerve cells (neurons) and several types of supporting cells
  • Transmit electrical signals by changes in permeability of the cell's plasma mebrane to ions (action potentials)
  • Most neurons have 2 distinct types of projections from the cell body, where the nucleus is located:
  • Dendrites - short branches that transmit electrical signals from adjacent cells to the neuronal cell body
  • Axons - long branches that carry electrical signals from the cell body to other cells
• Muscle tissue:

  • Functions in movement-related physiological activities
  • 3 types of muscle tissue:
  • Skeletal muscle: attaches to bones and exters force on them when it contracts (responsible for most body movements)
  • Cardiac muscle: makes up the walls of the heart and is responsible for pumping blood throughout the body
  • Smooth muscle: lines the walls of the digestive tract and blood vessels controlling movement through those systems
• Epithelial tissues (epithelia):

  • Cover the outside of the body, lines the surfaces of organs, and form glands
  • Provide protection
  • Act as "gatekeepers" for the selective movement of water and nutrients across their inner and outer surface
• Organ: a structure that serves a specialized function and consists of several tissues
• Gland: a group of cells that secrete specific molecules or solutions
• Epithelial tissues:

  • Typically form layers of closely packed cells
  • All epithelial tissue has a polarity
  • Apical side
  • Faces away from other tissues
  • Lines organs and secretes mucus
  •  Basolateral side
  • Faces the animal's interior
  • Cements the apical to the basil lamina
  • Basal lamina: connects the epithelial to the connective tissue
• Body size has pervasive effects on how animals function

  • Large animals need more food than smaller animals do, produce more waste, take longer to mature, reproduce more slowly, and tend to live longer
  • Smaller animals lose heat and water more rapidly
• The cell surface area determines the rate at which nutrients diffuse across the membrane into a cell and the rate at which waste products diffuse out
• The cell volume determines the rate at which nutrients are used and waste is generated

  • As a cell gets larger, its volume increases much faster than its surface area does
• The ratio of surface area to volume affects the animal's overall physiology
• Larger animals have smaller surface area/volume ratio compared to smaller animals --> less relative surface area compared to smaller animals
• Metabolic rate is the overal rate of energy consumption measured by the rate of oxygen consumption.

  Basal metabolic rate (BMR) is the rate at which an animal consumes oxygen while at rest with an empty stomach, under normal temperature and moisture conditions.

  "Mass-specific" BMR is a function of body
• Small animals have higher BMRs than large animals do --> a gram of elephant tissue consumes much less energy than a gram of mouse tissue
• As an organism's size increases, its mass-specific metabolic rate decreases
• Effective ways for structures to have a high surface area/volume ratio:

  • Flattening
  • Folding
  • Branching
• Endotherms produce adequate heat to warm its own tissue

  Ectotherm relies on heat gained from the environment
• Homeotherms keep their body temperature constant

  Poikilotherms allow their body temperature to change depending on environmental conditions
• Small mammals in cold climates lose heat rapidly because their surface area is large relative to their volume. To survive in colder temperatures, they reduce their metabolic rate and allow their body temperature to drop (a form of poikilothermy)
• Poikilothermy:

  • Torpor - a temporary drop in body temperature
  • Hibernation - a longer drop in body temperature
• Endotherms can warm themselves because their basal metabolic rates are extremely high

  • Heat given off by high rate of chemical reactions is enough to warm the body
  • Mammals and birds retain this heat because they have elaborate insulating structures such as feathers or fur
• Ectotherms gain heat directly from the environment and only generate a small amount of heat as a by-product of metabolism

  • Most heat gain is by radiation or conduction
• Endotherms have higher metabolic rates and thus can be more active at all times, but this costs a lot of energy and focuses that energy on producing heat vs. other energy-demanding processes.

  Ectotherms are able to thrive with much lower intakes of food and can use a greater proportion of their total energy intake to support reproduction, but muscle acitivity and digestion slow as body temperature drops, making them vulnerable in the cold.
• Heat exchange is critical in animal physiology:

  • Overheating can cause proteins to denature and cease functioning
  • High temperatures can lead to excessive water loss and dehydration
  • Low body temperatures can slow down enzyme function and energy production
• Conduction: the direct transfer of heat between 2 physical bodies that are in contact with each other
• Convection: a special case of conduction in which heat is exchanged between a solid and a liquid or gas rather than between two solids