BIOM1002: Topic 3.1 - Homeostasis

homeostasis - def

maintenance of a relatively stable internal environment not withstanding changes int he external environment 

geared towards optimal protein function  

homeostasis involves ___ regulatory systems

two

endocrine → hormones are chemical signalling molecules of endocrine system

nervous system → autonomic (ANS)

golden rules of biology (3)

cells are great big protein factories

proteins do all the work inside the cell

protein shape = protein function 

features we homeostatically regulate (4)

same as those that can disrupt hydrogen bonds of proteins

temp

pH

ions and therefore salts

solvents (polar molecules)

heterotherms

may use either strategy depending on their biology

ectotherms

depend on environment for their heat source

endotherms

vary metabolic heat production, compensation for heat loss to the environment 

negative feedback loop - general steps

1. Stimulus produces change in variable

2. Change detected by receptor

3. Input -> information sent along afferent pathway to control centre

4. Output -> information set along efferent pathway to activate effector

   1. Response of effector feeds back to influence magnitude of stimulus and returns variable to homeostasis

positive feedback loop

amplifies 

eg. blood clotting

blood glucose level homeostasis - high BGL

1. cells in pancreas detect high BGL

2. beta islet cells in pancreas secrete insulin

3. insulin acts on liver cells which remove glucose from the blood and stores it as glycogen

4. lowered BGL

blood glucose level homeostasis - low BGL

1. cells in pancreas detect low BGL

2. alpha islet cells in pancreas secrete glucagon

3. glucagon acts on liver cells which break down glycogen and release  glucose into the blood

4. increased BGL

blood pressure homeostasis - too high

1. stimulus = increased mean arterial pressure

2. effect = decreased HR, decreased force of heart muscle contraction, blood vessel dilation

3. response = decreased mean arterial pressure

blood pressure homeostasis - too low

1. stimulus = decreased mean arterial pressure

2. effect = increased HR, increased force of heart muscle contraction, blood vessel constriction

3. response = increased mean arterial pressure

sensory - visceral

info from internal organs of the body that we’re not consciously aware of

eg. heart blood vessels, lung, bladder

sensory - somatic

info from body wall → are or can be consciously aware of

eg. skin, skeletal muscle, bones and joints

motor - visceral

smooth and cardiac muscle related activity → involuntary

autonomous nervous system

typically associated with homeostasis

motor - somatic 

movement of joints and limbs and respiration → voluntary

eg. skeletal muscle activity

autonomous nervous system (ANS)

responsible for involuntary control of the internal organs, smooth muscle, cardiac muscle, and glands to maintain homeostasis

divided into 2 components: sympathetic and parasympathetic

ANS - sympathetic 

regulates reflexes associated with flight or fight responses 

changes in thermoregulatory reflexes involves changes in activity of sympathetic nervous system

ANS - parasympathetic

rest and digestive processes

tend to things that occur when we are not under threat

endocrine system - chemical signalling

chemical signalling molecules (hormones) travel from the cell that secreted them to the target cell with the specific receptor for the ligand via the circulatory system

nervous system - chemical signalling

neurones communicate with their target cell via neurotransmitters released in small packets across the synaptic cleft 

effects are typically restricted to adjacent cells (action discreet)

thermoregulation - neurotransmitter for chemical signalling 

noradrenaline 

released by neurons of the sympathetic nervous system to evoke fear, flight or fight responses

activates class of receptors called adrenergic receptors 

activation of adrenergic receptors by sympathetic pathway leads to increased heat production inside the cell 

thermoregulation - hormones for chemical signalling overview (2)

adrenaline

thyroid hormone

circadian rhythm - overview

24-hour cycles that are part of the body’s internal clock → run in background to carry out essential functions and processes

changes over lifetime 

circadian rhythm - decrease in body temp

associated with sleep cycle

circadian rhythm - rise in body temp

associated with waking cycle

circadian rhythm - subjective alertness

linked to oscillations in core body temp

decrease in core body temp correlates with decrease in subjective alertness

ways to exchange heat with the environment (4)

radiation → Sun, infrared radiation from fires 

evaporation → heat trasnfer when water evaporates 

convection → heat exchange with surrounding medium

conduction → heat exchange with another object 

changes in blood flow helps with using these systems

physiological thermoregulatory responses - metabolism

non-shivering thermogenesis → primarily mediated by sympathetic regulation, endocrine system

shivering thermogenesis → primarily mediated by somatic regulation, endocrine system

physiological thermoregulatory responses - skin blood flow 

mediated by sympathetic nervous system → vasoconstriction and active vasodilation

physiological thermoregulatory responses - sweating

sympathetic nervous system

elements of reflex pathway (4)

1. variable under regulation activates a sensor

2. sensor activates afferent which is transmitted to the control centre or integration centre

3. efferent pathway conveys response tot he effectors 

4. effectors initiate the response which restores homeostatic control

reflex response to changes in environmental temperature - core body temp

changes in core body temp = detected by thermoregulatory sensors in hypothalamus 

evoke reflex response to protect and return core body temp to homeostasis

reflex response steps to changes in environmental temperature - visceral response (5)

1. change in core temp

2. homeostatic regulatory centres of the brain 

3. integrate with core temperature target

4. visceral responses to regulate core temp

5. change in core temp

reflex response to changes in environmental temperature - ambient temp

changes in ambient temp detected by thermoreceptors in the skin

large changes will cause thermal discomfort

reflex response to changes in environmental temperature - ambient temp (steps)

1. change in ambient temp detected by skin temp sensors

2. afferent pathway from sensors feed into homeostatic regulatory centres to make the body aware that the environmental conditions have changed

3. efferent pathway includes behavioural responses like putting a jumper on

4. thermal comfort restored without any disruption to core temp

summary of somatic and visceral system - thermoregulation

there is a cross-over such that changes in ambient temp sensitises the visceral system and evokes responses to protect the core body temp in anticipation of changes to ambient environment 

fever - def

physiological alteration of set point to be higher than normal

initiation of fever

infectious agents activate immune response → immune cells release inflammatory mediators

mediators stimulate production of prostaglandin → alters neuronal activity in hypothalamus leading to altered set point

causes prevent heat loss and increase heat production via shivering and vasoconstriction

fever - pyrogen

something that cases a fever

fever - aspirin

blocks production of prostaglandin

initiation of fever - steps (4)

1. Infection leads to active inflammatory signals

2. Inflammatory signals result in production of PGE2

3. PGE2 signals the thermostat to increase body temp

4. Increase in body temp acts on effectors resulting in shivering, thermogenesis and decreased blood flow to skin -> rise in core body

physiological benefits of fever

some bacterial protein optimal operating range is impacted

slows viral replication rate → shifting body temp away from normal reduces efficiency of own cells at replicating virus cells 

helps activate or enhance immune response to infection

heat sensitive activation of immune response

certain proteins within the immune system operate better at higher than normal body temp

immune response has low activity during normal temp → selectively activated during infection

fever - sepsis

sepsis = uncontrolled inflammatory response

excess high temps can lead to organ damage → fever’s benefits are limited

Thermoregulation hormones - adrenaline

secreted by adrenal gland under sympathetic control → activates class of receptors called adrenergic receptors

Thermoregulation hormones - thyroid hormone

secreted by thyroid gland under hypothalamic regulation → increases energy expenditure 

T3 and T4 = thyroid hormones that activate pathways inside the cell that lead to increased heat production