Module 4.1

Question 1

Define homeostasis and explain how whole-body homeostasis maintains optimal environment for cell function.

Answer 1

• Overview:
• Cells are great big protein factories
• Proteins do all the work inside the cell
• Protein shape = protein function
   Change the shape of the protein > alter the function of protein
• Homeostasis is the maintenance of a relatively stable internal environment despite changes in the external (ambient) environment – homeostasis oscillates around a setpoint, has a certain range (hence relatively stable)
   Favours optimal protein function
   Is reflexive (self regulating/unconscious)
   Is regulated by feedback loops (usually negative feedback loops)

Question 2

Distinguish between somatic and visceral sensation.

Answer 2

• Visceral (awareness of internal environment/unconscious awareness/involuntary) :
• Sensory – information from internal organs of the body that we aren’t consciously aware of, e.g. heart, blood vessels, lungs, GI tract and bladder
• Somatic (awareness of external environment/conscious awareness/voluntary):
• Sensory – skin, bones, joints, limb movement

Question 3

Distinguish between somatic and visceral motor response.

Answer 3

• Motor/visceral– involuntary (typically associated with homeostasis), smooth and cardiac muscle-related activity and glandular secretion
• Motor/somatic - Voluntary movement, skeletal muscle activity, e.g. movement of joints and limbs and respiration

Question 4

Explain how chemicals and receptors interact with each other and describe how information is communicated between cells.

Answer 4

• Chemical signalling molecules and receptors
• Chemical signalling molecules are called ligands
• Ligands include neurotransmitters and hormones and inflammatory mediators
   Ligand binds to receptor and activates it
   Receptor binding initiates events inside the cell that produces a response
• Receptor-ligand specificity:
   The receptor is specific for a particular signalling molecule
   The presence of the receptor determines if the cell will respond
• Lock and key model
• The cells expression of the receptor that will determine if it will respond to the ligand

Question 5

Define an endocrine hormone, and explain how hormones act.

Answer 5

In the endocrine system, the endocrine gland releases the hormone into the blood vessel which is then transported to the target cell via the circulatory system

Question 6

Explain the difference between endocrine hormonal and neural signalling.

Answer 6

• Neurotransmitters vs hormones
   Neurotransmitters: released in small packets at the synapse
• Synapse = functional connection between two neurons
• Action discreet – restricted to receptors at the synapse
   Endocrine hormones: released into the circulatory system (bloodstream)
• Actions on any cell in the body with a receptor for the ligand

Question 7

Explain why regulating core temperature is important for all multicellular animals

Answer 7

• Biological molecules function best at specific temperatures
   High temperatures cause membranes to rupture/denaturation
   Denaturation is caused by the disruption of hydrogen bonds between amino acids
   Hydrogen bonds can be disrupted due to: temperature, pH, Ions (salts), solvents (polar molecules)
   We homeostatically regulate temperature, pH, Ions (salts), solvents (polar molecules)

Question 8

Describe what is meant by circadian rhythm, and apply this more broadly to understand of the dynamic nature of homeostasis.

Answer 8

• Definition: Circadian rhythms are 24-hour cycles that are part of the body’s internal clock, running in the background to carry out essential functions and processes
• Daily oscillations in homeostatic regulation (circadian rhythms correlate with a range of biological processes that help synchronize the body with the day-night cycle - body temp, melatonin and hormonal levels, cortisol etc:
• Waking activity: awake at day, asleep at night
• Body Temperature: Higher body temperature during the day, lower during the night
   Subjective alertness is linked with oscillations in core body temperature
• Cortisol (hormone associated with arousal/alertness and stress, blood sugar levels/metabolism): higher cortisol and glucose levels during the day, lower at night
• Blood pressure: high during day, low at night
• Melatonin: greater secretion at night
• Greater fluctuations in the above biological processes in older adults

Question 9

Explain the visceral reflexes involved in regulating core body temperature and describe how both hormonal and neural signalling chemicals are involved.

Answer 9

• Thermoregulatory reflexes involve changes in the activity of the somatic motor and autonomic nervous system – sympathetic NS (visceral)
• Key neurotransmitters and hormones involved in thermoregulation
   Neurotransmitter:
• Noradrenaline: released by neurons of the sympathetic nervous systems to evoke fear, flight or fight responses, activates class of receptors called adrenergic receptors
  o Increases heart rate, increase heat production in body (thermogenesis), increase metabolic rate
   Hormones:
• Adrenaline: secreted by adrenal gland (under sympathetic control), activates a class of receptors called adrenergic receptors
• Thyroid hormone: secreted by thyroid gland, under hypothalamic regulation, increases energy expenditure
  o T4 and T3 are thyroid hormones that activate associated receptors to activate pathways inside the cell that lead to increased heat production
  o can also have sympathetic nervous system activating an adrenergic receptor increasing heat production
  o So both ANS and endocrine pathways can cause heat production/thermogenesis

Question 10

Describe how fever is an adaptive (survival) response to infection. Describe the reflexes involved in elevating core body temperature to produce fever.

Answer 10

The Fever Paradox: Fever may be a strategy to boost immune defences

• Fever
• Altered temperature regulated “set point” higher than normal – not homeostatic dysregulation
• Infectious agent activates immune response
   Releases inflammatory mediator
• Stimulates production of prostaglandin (PGE2)
• Alters neuronal activity in the hypothalamus leading to altered set point
• Fever helps activate or enhance the immune response to infection
   Human cells operate most effectively at 37C
   Viruses infect human cells and co-opt protein manufacturing apparatus to replicate themselves
   Fever slows viral replication rate as it raises the set point of 37C temp in which human cells functions optimally
   Some bacterial optimal operating range is impacted
• Heat sensitive activation of the immune system
• Adaptive advantage to survival
   Immune response is low activity during normal temperature
   Immune response is selectively activated during infection due to higher temp set point
• Note: Certain proteins within the immune system operate better at higher than normal body temperature
• Fever is not always beneficial
• Sepsis – uncontrolled inflammatory response
   Excess high temperature can lead to organ damage

Question 11

Contrast the stages of negative and positive feedback loops

Answer 11

• Feedback loops are abundant in biology
• Have four main stages: stimulus, receptor, control and effector
• Negative feedback (self-regulatory) – a response that occurs to reduce change or output to bring system to stable state
   Steps:
• Stimulus - Produces change in variable that causes imbalance from homeostatic levels
• Receptor – Change is detected – converts the stimulus into a chemical signal (via nervous system) or hormonal signal (via endocrine system)
  o Sensory afferent pathway – information sent from receptor to control centre
• Control Centre – signal is processed to decide a change that needs to occur
  o Motor efferent pathway – information sent by the control centre to activate the effector organ/muscle
• Effector – can be cells, glands, or muscles that oppose the change in stimulus to bring back to stability (negative feedback) or amplify the change (positive feedback)
• Response – effector response influences the magnitude of the stimulus and returns variable to homeostasis

Question 12

Provide examples of the negative feedback loops and use diagrams to explain them

Answer 12

• Body temperature:
  o The hypothalamus in the brain controls body temperature. When the body is too hot, the hypothalamus signals the body to sweat, which reduces the temperature. When the body is too cold, the hypothalamus signals the body to shiver, which increases the temperature.
• Blood pressure:
  o When blood pressure is too high or too low, the kidneys and nerves work together to bring it back to normal. For example, the kidneys may excrete more or less water
• Blood sugar:
  o After eating, the pancreas releases insulin into the bloodstream to signal cells to absorb excess glucose. This lowers blood sugar levels

Question 13

Provide examples of the positive feedback loops and use diagrams to explain them

Answer 13

 Examples:
* Childbirth:
o When the baby’s head pushes against the cervix, the body releases oxytocin, which causes contractions. As contractions increase, more oxytocin is released, which continues the cycle until the baby is born
* Blood clotting
o When tissue is injured, platelets release chemicals that attract more platelets to the site of the injury. This forms a clot that stops the flow of blood
* Lactation
o When a baby feeds, the brain releases prolactin, which stimulates milk production. The baby continues to feed, which stimulates more milk production.
* Ovulation
o The dominant follicle releases estrogen, which stimulates the release of LH and FSH. This promotes further follicular growth

Question 14

Contrast the two regulatory systems

Answer 14

• Regulatory systems:
• The endocrine and autonomic nervous system specifically work together to achieve homeostasis
• Endocrine:
• Hormones are the chemical signalling molecules of the endocrine system
• Receptor – protein bound to a specific hormone (detects hormone changes) – can be membrane receptors
• Control centre - Hypothalamus regulates hormonal release through certain glands
• Effector – organ, tissue or cell that carries out actions to restore balance in the body
• Nervous system:
• Neurotransmitters are the chemical signalling molecules of the nervous system
• Central nervous system – includes the spinal cord, brain (control centre)
• Peripheral nervous system (PNS) – nerves branching out
   Afferent pathway: Sensory (Receptor)
   Carry information from the body to brain and spinal cord
   Different types of receptors include:
• GSA (general somatic afferent) – pain, temperature, touch
• GVA (general visceral afferent) – stretch (chemoreceptors/baroreceptors), hear, GI tract, lung, carotid body
   Efferent pathway: Motor (Effector)
   Carry information from the brain to glands and muscles
• Somatic nervous system:
  o Info related to skeletal muscles, movement of joints and limbs
• Visceral nervous system (ANS):
  o Info related to smooth muscle
   Sympathetic nervous system:
• Fight of flight response
• Involved in negative feedback predominantly
• Mobilises body during activity and when under threat
   Parasympathetic nervous system
• Rest and digest the response
• Involved in negative feedback predominantly
• Conserves energy and promotes housekeeping functions during rest

Question 15

Additional thermoregulation info

Answer 15

• Ways to exchange heat with the environment
• Radiation: heat that’s been given off by infrared radiation
• Evaporation: heat transfer when water evaporates (benefits of sweat)
• Convection: heat exchange with surrounding medium, e.g. air or water
• Conduction: heat exchange with another object
• Changes in blood flow help with using these systems
• Physiological thermoregulatory responses -
• Metabolism
   Non-shivering thermogenesis
• Sympathetic regulation
• Endocrine
   Shivering thermogenesis
• Somatic regulation
• Endocrine
• Skin blood flow
   Sympathetic
   Vasoconstriction
   Active vasodilation
• Sweating
  Sympathetic