Homeostasis Flashcards
Define homeostasis
Maintenance of internal body conditions within an optimum range
Describe what is meant by dynamic equilibrium
The fluctuation of internal conditions around a specific normal level; occurs due to negative feedback loop
Describe examples of homeostatic mechanisms in the body
Temperature —> core at 37.5°C, ensures optimal conditions for enzyme action + cell function, lower temps would mean reactions occur too slowly but higher would denature enzymes, changing shape of active site
Blood glucose —> cells need constant supply of energy from ATP, gained by glucose respired so must be carefully monitored by cells in the pancreas
Water —> makes up cytoplasm in cells and used in metabolic reactions, important to maintain amount of water in blood; kidneys responsible for monitoring this
Describe cooling mechanisms in thermoregulation
• Vasodilation of blood vessels supplying skin capillaries —> allows heat loss to environment via radiation, muscles in walls of arterioles relax allowing more blood flow to skin capillaries
• Sweating —> secreted by sweat glands, cools skin by evaporation as heat energy used to convert water into vapour
• Flattening of hairs —> hair erector muscles in skin relax, causes hairs to lie flat, stops hair from trapping air + allows air to circulate over skin so heat leaves via radiation
Describe warming mechanisms in thermoregulation
• Vasoconstriction of blood vessels supplying skin capillaries —> minimises heat loss to environment via radiation; muscles in arteriole walls contract, causing constriction so less blood flow to skin capillaries
- blood diverted through shunt vessels (deeper in skin so no heat loss)
• Boosting metabolic rate —> most metabolic reactions exothermic so in cold thyroxine released from thyroid increasing BMR and so heat production in body
• Shivering —> muscles contract rapidly; metabolic reactions to power this generate heat warming the blood
• Erection of hairs —> hair erector pili muscles contract, causing hairs to stand on end; forms insulating layer which traps air between hairs and reduces heat loss
• Less sweat —> sweat glands secrete less sweat, reduces heat loss from evaporation of sweat
How is thermoregulation controlled?
Hypothalamus, changes in external temperature detected by thermoreceptors in skin
- communicate with hypothalamus along sensory neuro es which the. Pass impulses along motor neurones to effectors to bring about a response
How is homeostasis an example of negative feedback?
Receptor detects stimulus I.e. change from norm, nervous or endocrine system transfers info across body, effectors (muscle/gland) act to return conditions to normal —> reverses any change to return to normal
What is positive feedback?
Stimulus produces a response causing the factor to be enhanced (either increase or decrease)
What is a transcription factor?
Proteins which control transcription of a gene by binding to a specific region of DNA; may either activate (activators) or suppress (repressors) transcription
How do hormones control transcription generally?
Bind to receptors on target organs and act as stimulus for target cells –> T.F activated, transcription of certain gene activated so mRNA made and translated so protein can be exocitosed/used
Describe difference between two types of hormone
Peptide hormones —> work outside cells, made from protein chains; charged so cannot pass through cell surface membrane, must instead bind to receptors
Steroid hormones —> formed from lipids, not charged so able to move through CSM and bind to to T.Fs directly; lipid soluble so can pass through phospholipids
Describe how hormones work inside cells
Repressing transcription
- transcription factor binds to section of DNA at start of a gene coding for a protein with a specific function (e.g. increasing metabolic rate)
- gene will not be expressed as can not be transcribed –> gene switched off
Activating transcription
- stimulus triggers release of hormone, binds to transcription factor
- T.F allows RNA polymerase to bind to start of gene, allowing transcription –> gene switched on
Describe how hormones work outside cells
- bind to receptors on cell surface membrane
- triggers process activating messenger molecules (secondary messengers)
- these activate enzymes called protein kinases
- which triggers chain of reactions which result in changes to activity of T.Fs which then affect gene expression
