Animal Physiology

• What is physiology?

  The study of processes and functions in living organisms.

  In depth: The study of the integrated functions of the body and the functions of all its parts, including biophysical and biochemical processes.
• What is the goal of physiology?


  To explain the physical and chemical factors that are responsible for the origin, development and progression of life.
• How can climate change affect physiology and health of animals?

  • Lead to changes in feed availability
  • Heat stress
  • Can cause change in prevalence of diseases
  • Can cause changes in distribution/abundance of disease vectors
  • Can cause emergence of new diseases
• How can domestication affect the physiology and health of animals?

  • Selection for milk production in cattle can lead to mastitis, lameness, or ketosis
  • Brachycephalic obstructive airway syndrome in dogs
  • Obesity
• What are the three sentences that describe homeostasis?

  The property of a system In which variables are regulated so that internal conditions remain stable and relatively constant.

  
  

  Refers to the physiological mechanisms that maintain relatively constant the variables related to the internal milieu of an organism.

  
  

  The steady-state interval environment that is required for the maintenance of life.
• Key components of homeostatic circuits: Controlled Variable


  Physiological variable that is manipulated in order to maintain the regulated variable within normal values (i.e. set point)
• Key components of homeostatic circuits: Regulated Variable


  Physiological variable for which sensors are present in the homeostatic circuit and is maintained at a stable level (i.e. set point) by a negative feedback system.

  
  

  The regulated variable is maintained within a range (i.e. set point) that is compatible with the viability of the organism.

  E.g.

  Controlled variable: Heart rate

  Regulated variable: Blood Pressure (baroreceptors)
• Key components of homeostatic circuits: Sensor

  A "device" that measures the magnitude of a physiological variable by generating an output signal that is proportional to the magnitude of the stimulus.
• What can a sensor be?

  Specialised sensory cells: Thermoreceptors/osmoreceptors

  Cellular components: e.g. Ca2+ sensing receptor, a G protein-coupled receptor that senses blood Ca2+ in the parathyroid gland
• Key components of homeostatic circuits: Set Point

  The range of values of the regulated variable that the homeostatic circuit attempts to maintain.

  
  

  Set points are changeable, either physiologically or as the result of a pathological.
• Key components of homeostatic circuits: Error Component

  Determines the difference between the set point value and the actual value of the regulated variable: error signal
• Key components of homeostatic circuits: Controller

  It receives information (error signal) from the error detector and sends output signals (instructions or commands) to increase or decrease the activity of effectors.

  
  

  Controllers are typically endocrine cells and sensory neuron's of the automatic nervous, lower brainstem (medulla), and hypothalamus. They generate signals (hormones and neurotransmitters) that are used by effectors.
• Key components of homeostatic circuits: Effector


  A component of the homeostatic circuit that is activated by the controller to change the value of the regulated variable.

  The term 'effector' should only be applied to a physical entity such as a cell, tissue, or organ.
• What is an external disturbance?


  Any change in the conditions of the external environment that result in a change to the internal environment.
• What is an internal disturbance?


  Any change in the structure or function of the organism that results in a change of the magnitude of the regulated variable.
• Homeostatic regulation is a constant, continuous process and does not ordinarily operate as an on/off switch that results in an all or nothing response.

  
• What is negative feedback?


  A reaction in which the system response in such a way as to reverse the direction of change.

  A process in which the body sense a change and activates mechanisms that negate or reverse it.

  By maintaining stability, negative feedback is the key mechanism for maintaining health.
• An example of negative feedback:

  • An increase in BG conc above its homeostatic range (hyperglycaemia) promotes processes that will increase it
  • A decrease BG conc below its homeostatic range (hypoglycaemia) promotes processes that will decrease it

  In both situations, the result is that the level of BG is kept relatively constant over periods of time.
• What is positive feedback?


  A self-amplifying cycle in which physiological change leads to even greater change In the same direction.

  Less common In naturally occurring systems, however in some cases has positive effects.

  
  

  Can quickly change a regulated variable far from its homeostatic set point.
• Example of positive feedback: (Birth)

  During birth pressure on the cervix induces release of oxytocin, which stimulates the uterus to contract.

  The more the cervix is stimulated the more oxytocin released, increasing the intensity of uterine contractions until the baby is expelled.
• Example of positive feedback: (Blood Clotting)

  1. Damaged cells in blood vessel release chemicals that begin blood clotting process.
  2. Chemicals start chain reactions where cells, cell fragments and proteins in blood begin to clot.
  3. As clotting continues, each step releases chemicals, accelerating the process.
  4. This continues until the formation of a blood clot, patching the vessel and stopping the bleeding.
• Example of positive feedback: (Fever)

  A fever can cause a positive feedback loop resulting in continuous increase of temperature. This becomes fatal at 45°C.
• Homeostatic circuits: 'Sticky Points' (1)

  The same regulated variable can have a different dynamic range in different tissues.

  e.g. The brain has low tolerance to deviations in many physiological variables, while adipose tissue is usually less demanding.
• Homeostatic circuits: 'Sticky Points' (2)


  A regulated variable can also be a controlled variable under some circumstances.

  e.g. CO2 pp in the ECF is maintained within defined limits by a regulatory system that that senses CO2 pp, operating by negative feedback.

  During compensatory adjustments in the acid-base balance (i.e. H+ homeostasis) CO2 pp becomes the controlled variable that is manipulated to maintain a normal pH.
• Extracellular Fluid: The internal environment

  
• What is the structure and function of the cell membrane?

  Composed of the phospholipid bilayer and proteins. Has the important function of determining what enters and leaves the cell.
• Common cell shapes:

  
• Transport across cell membranes: Simple diffusion

  • High>Low
  • Down concentration gradient
  • Passive
  • Extracellular>Intracellular
• Transport across cell membranes: Osmosis

  • High>Low
  • Across cell membrane using aquaporins
  • Passive
  • Extracellular>Intracellular
• Transport across cell membranes: Filtration

  • Water(and its solutes) driven through membrane by hydrostatic pressure
  • Down pressure gradient
  • Passive
  • What passes through is dependent on size of pores
  • Extracellular>Intracellular
• Transport across cell membranes: Facilitated diffusion

  • Carrier-mediated transport of a solute
  • Down concentration gradient
  • Passive
  • Uses transmembrane protein
  • Extracellular>intracellular
• Transport across cell membranes: Active transport

  • Carrier mediated transport of a solute
  • Against concentration gradient
  • Using energy provided by ATP
  • Extracellular>intracellular
• Transport across cell membranes: Sodium-potassium pump

  (Na+/K+ pump) Pumps 3 Na+ out for every 2 K+ in.

  
• Transport across cell membranes: Vesicular transport

  Movement of large particles, droplets or fluids or lots of molecules at once through the membrane , contained in bubble like vesicles of membrane

  
• Types of endocytosis: Phagocytosis


  The process of engulfing particles such as bacteria, dust, and cellular debris
• Types of endocytosis: Pinocytosis


  The process of taking in droplets of ECF containing molecules of some use to the cell
• Types of endocytosis: Receptor-mediated endocytosis

  phagocytosis or pinocytosis where specific modules bind to specific receptors on the cell membrane and are then taken into the cell in clathrin-coated vesicles with minimal ECF
• Cell Signalling: (1)

  
• Cell Signalling: (2)

  
• Cell Signalling: (3)