Homeostasis Flashcards
4 things homeostasis imbalance can result from:
Aging
Genetic mutations
Pathogens
Environment
Definition of homeostasis
The ability of an organism to maintain its internal environment despite change to its internal and external environment
5 sensory receptors in external environment:
Mechanoreceptors Thermoreceptors Electromagnetic receptors Nociceptors Chemoreceptors
Internal environment
Helps efficient cell/organ/system function
What’s included in the internal environment?
EC fluid, IF, intravascular fluid
T/F internal environment is controlled within a narrow range:
T
What does the internal environment detect?
Level of chemicals in blood/tissues
Examples of chemicals in blood/tissues:
Glucose, O2, CO2, H2O, ions
What is the stimulus to response pathway?
Stimulus –> receptor –> control center –> effector –> response
Can the stimulus to receptor response be nervous system or endocrine?
Both!
Characteristics of nervous system response:
APs, transported by neurons, fast, short, voluntary/involuntary, local
Characteristics of endocrine response:
Hormones, transport by blood, slow, short or long, always involuntary, distant, many cells effected
Definition of neurohormones:
Chemicals released by neurons into blood for action at a distant target organ / tissue
Example of neurohormone pathway:
1 hypothalamic neurons make oxytocin/ADH
2 oxy/ADH transported down axons of hypothalamus (hypophyseal tract) to PP
3 stored in PP
4 hypothalamic neurons fire, AP arrives at terminals
5 oxy/ADH released into blood
Autocrine:
Acts on same cell
Paracrine
Acts on adjacent cell
Characteristics of lipid-soluble hormones:
Lipophilic Ex: steroids, calcitriol DO transport proteins Long plasma half life Intracellular receptors Mediator: receptor-hormone complex
Characteristics of water soluble hormones:
Hydrophilic
Ex: polypeptides, glycoproteins, catecholemines
DONT transport proteins
Short plasma 1/2 life
Uses plasma membrane receptors
Mediators: cAMP, cGMP, Ca, kinase cascades
Hormone response model:
Receptor –> integrator (brain) –> effector (muscle/gland) –> response —> feedback
Negative feedback definition:
Body senses change = stimulation = feeds back to reverse the change. MOST COMMON kind of feedback
Ex of negative feedback
Body temp changing, negative feedback brings it back to homeostasis
Mechanism of negative feedback:
Stimulus that homeostasis is not in balance –> integration of signal at hypothalamus (TRH) –> AP releases TSH (effector) –> thyroid gland releases hormones into blood –> NEGATIVE FEEDBACK and homeostasis restored
Definition of positive feedback:
Self-amplifying physiological change that leads to even greater change and builds off of itself. Can be detrimental unless corrected by cessation. LEAST COMMON kind of feedback
Ex of positive feedback
Parturition
Mechanism of parturition as an example of positive feedback:
Stretch receptors in uterus –> signal to brain to release oxytocin into blood –> POSITIVE feedback to uterus to contract more forcefully –>cycle keeps going until cessation
Moderate homeostatic imbalance:
Disorder/abnormality of structure/function disease with specific signs / symptoms, signs and symptoms are subjective (ex fever)
Severe homeostatic imbalance:
Results in death
How is heart failure an example of both negative and positive feedback?
System tries to correct imbalance = negative feedback, but then becomes overwhelmed and destructive positive feedback takes over
