Physiological Homeostasis Flashcards by An Nakamura

Definition of homeostasis

Dynamic maintenance of physiological variables within a predictable range

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Definition of dynamic

Variable fluctuates, still within normal range, average value will be predictable over longer periods of time

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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

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Definition of feed forward

Anticipation of change brings about the response to that change before the change can be detected by negative feedback sensors

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Definition of positive feedback

Change in variable triggers response that causes further change in variable. Amplification of change

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Definition of sensors

Detect changes in physiological variable

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Definition of afferent pathway

Carry signals from sensors to integrating center

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Definition of integrating center

Compare inputs from sensors against physiological set point and elicit a response

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Definition of efferent pathway

Carry signals from integrating center to effectors

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Definition of effectors

Produce response that tends to normalize physiological variable

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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

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Effects of homeostasis

Short term and medium long term

Immediate survival

Health, wellbeing, reproductive capability

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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

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What is a negative feedback

Change in variable compared set point, causes normalization response
When physiological circumstances change, set points can change

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Types of negative feedback

Neuronal
Endocrine
Local (chemical/physical)

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What is feed forward

Anticipation of change, brings about response before change detected by negative feedback sensors

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What is positive feedback

Change in variable triggers response that amplifies change

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Where is the neuronal integrating center in nervous negative feedback

Midbrain and brain stem

Hypothalamus, pons, medulla

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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)

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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