Physiological Homeostasis Flashcards
Definition of homeostasis
Dynamic maintenance of physiological variables within a predictable range
Definition of dynamic
Variable fluctuates, still within normal range, average value will be predictable over longer periods of time
Definition of negative feedback
Change in variable being regulated compared against set point causing a response that tends to move the variable back to the set period. Normalization to set point
Definition of feed forward
Anticipation of change brings about the response to that change before the change can be detected by negative feedback sensors
Definition of positive feedback
Change in variable triggers response that causes further change in variable. Amplification of change
Definition of sensors
Detect changes in physiological variable
Definition of afferent pathway
Carry signals from sensors to integrating center
Definition of integrating center
Compare inputs from sensors against physiological set point and elicit a response
Definition of efferent pathway
Carry signals from integrating center to effectors
Definition of effectors
Produce response that tends to normalize physiological variable
What is physiological homeostasis
Dynamic maintenance of physiological variables within a predictable range
Variable may fluctuate, still within a normal range
Average value will be predictable over longer periods of time
Size and frequency of fluctuations depends on variable
Effects of homeostasis
Short term and medium long term
Immediate survival
Health, wellbeing, reproductive capability
Hierarchy of importance of physiological variables
Variable that is of greater immediate importance, maintained at expense of other variables that are of importance in the long term
What is a negative feedback
Change in variable compared set point, causes normalization response
When physiological circumstances change, set points can change
Types of negative feedback
Neuronal
Endocrine
Local (chemical/physical)
What is feed forward
Anticipation of change, brings about response before change detected by negative feedback sensors
What is positive feedback
Change in variable triggers response that amplifies change
Where is the neuronal integrating center in nervous negative feedback
Midbrain and brain stem
Hypothalamus, pons, medulla
Function of nervous control in negative feedback loops
Temperature control (acts on muscles and skin)
Osmolarity control (acts on kidneys)
Blood pressure/flow control (acts on heart, blood vessels)
Blood gas/ventilation control (acts on respiring muscles/lungs)
Uses of the sympathetic and parasympathetic nervous system
Opposing actions on various functions
Results in fine tuning of physiological variables
What does the autonomic nervous system control
Heart rate Blood vessel diameter GI tract motility Salivary secretion Sweat gland secretions Endocrine secretions
What neurotransmitters are being used
Sympathetic, noradrenaline
Parasympathetic, acetylcholine
Describe the negative feedback loop
Stimulus
Receptors, along afferent pathway
Integrating center, sends response along efferent pathway
Effector, elicits response
Example of using negative feedback loops
Control of body temperature
Common features of endocrine control mechanisms
Endocrine gland/tissue secretes hormones
Released into the blood
Transoprted in the blood to distant target tissues
Act on target tissues through specific receptors
Response of target tissue depends on type of hormone receptor expressed
Location of endocrine glands
Hypothalamus Pituitary Thyroid Parathyroid Adrenal (cortex and medulla) Pancreas Ovaries Testes
Endocrine organs
Hypothalamus (neuroendocrine) Posterior pituitary (neuroendocrine) Anterior pituitary (endocrine)
What hormones are released from the hypothalalmus
Releasing hormones Growth hormone releasing (GHRH) Corticotrophin releasing (CRH) Thyrotropin releasing (TRH) Gonadotrophin releasing (GnRH)
Inhibitory hormones
Somatostatin
Dopamine
What hormones are released from the posterior pituitary
Oxytocin
ADH
What hormones are released from the anterior pituitary
Growth hormone (GH) Prolactin FSH LH Thyroid stimulating hormone (TSH) Adrenocorticotrophic hormone (ACTH)
What is the function of releasing hormones
Releasing hormones released from hypothalamus
Encourages release of specific hormones in anterior pituitary
Types of hormones
Peptides Polypeptides glycoproteins Amino acid dericatives Steroids
Examples of peptide hormones
ADH
Oxytocin
Examples of polypeptide hormones
Growth hormone
Insulin (pancreas)
Examples of glycoprotein hormones
LH
FSH
TSH
Examples of amino acid derivative hormones
Derived from tyrosine
Adrenaline (from adrenal medulla)
Thyroxine (from thyroid)
Examples of steroid hormones
Cholesterol, precursor to Pregnolone, precursor to Progesterone Estrogen Androgens Glucocorticoids Mineralcorticoids
Types of hormone receptors
Peptides
Proteins
Glycoproteins
Catecholamines
Steroids
Thyroid hormones
Location of peptide, protein, glycoprotein and catecholamine receptors
Plasma membrane
Mechanism of peptide, protein, glycoprotein and catecholamine receptors and speed of response
2nd messenger, change enzyme activity
Rapid, transient response
Location of steroid and thyroid hormones
Intracellular cytoplasm/nucleus
Mechanism of steroid and thyroid hormones and speed of response
Alter gene transcription
Slow, prolonged response
Endocrine reflex arc
Stimulus
Receptors and integrating center in same cell, sent down efferent pathway
Response, causes negative feedback
Example of a use of the endocrine reflex arc
Control of blood glucose conc
Features of local homeostatic response
Negative feedback reflex operating locally
Independent of neuronal, hormonal response
Sensors, afferent pathway, integrating center efferent pathway, effectors all in same tissue/organ
Local negative feedback reflex arc
Stimulus
Receptors, afferent pathway, integrating center and effector in same cell
Response sent down efferent pathway
Triggers a second response, send down another efferent pathway
Feedforward control mechanism
Instinctive reflex arc in terms of fight and flight response
Threat stimuli
Anticipation of physical exertion
Sympathetic activation
Noradrenaline, adrenaline release
Increased HR, blood flow to skeletal muscles
Preparation for increased O2 and fuel demand from muscles
Feedforward control mechanisms
Conditioned reflexes
Anticipation of meal
Parasympathetic activation
Stimulation of saliva, gastric juive production
Preparation for food intake
Positive feedback arc
Parturition
Pregnancy alters estrogen/progesterone balance
Increases excitability of uterus (hormonal)
Uterine contractions (mechanical)
Fetus presses on cervix (neuronal)
Signal sent to hypothalamus for more oxytocin secretion
Loop continues until birth ends
