BCR 3 - Control of Blood Pressure and Haemorrhage

What is meant by homeostasis in physiology?

Maintenance of a relatively constant internal environment despite changes in the external environment

Why is homeostasis considered a central principle in physiology?

Most physiological systems function to maintain stable internal conditions required for normal cellular activity

What can disruption of homeostasis lead to?

Pathophysiology, disease and potentially death if regulation fails

What is meant by the internal environment in physiology?

The extracellular fluid surrounding cells that provides the conditions required for cellular survival and function

What two main components make up the extracellular fluid?

Plasma and interstitial fluid

What is plasma?

The fluid component of blood that carries cells, nutrients, hormones and waste products

What is interstitial fluid?

Fluid located between cells that bathes and surrounds tissues

Why do most cells not interact directly with the external environment?

Cells are surrounded by extracellular fluid which mediates exchange between the body and the external environment

Why is maintaining a stable extracellular fluid environment important for cells?

It provides optimal conditions for enzyme activity, biochemical reactions and cellular metabolism

What types of processes depend on stable internal conditions?

Enzyme function, biochemical reactions and metabolic pathways

What is meant by a homeostatically regulated variable?

A physiological variable that is maintained within a narrow range by specialised sensors and control systems

Why must certain physiological variables be tightly regulated?

Even small deviations can disrupt cellular function and threaten survival

Which body temperature variable is tightly regulated by homeostasis?

Core body temperature

Which cardiovascular variable is tightly regulated in homeostasis?

Mean arterial blood pressure

Which fluid-related variables are regulated by homeostasis?

Blood volume and blood osmolarity

Which metabolic variable is tightly controlled by homeostatic mechanisms?

Blood glucose concentration

Which acid–base variable is tightly regulated in the body?

Blood pH

Which respiratory gases are regulated through homeostasis?

Oxygen and carbon dioxide levels

Which electrolytes are commonly regulated in extracellular fluid?

Sodium, potassium and calcium ions

What allows the body to detect changes in regulated physiological variables?

Specialised sensors or receptors

What allows correction of deviations from normal physiological values?

Compensatory control systems that activate corrective responses

Why do many medical treatments aim to restore regulated variables?

Returning variables to their normal range helps restore homeostasis and physiological stability

What is a negative feedback system?

A control mechanism where the response opposes the initial change in a regulated variable

What is the main purpose of negative feedback in physiology?

To stabilise physiological systems and return variables toward their normal range

How does negative feedback maintain physiological stability?

Responses counteract deviations from the normal value of a regulated variable

What three basic components make up a negative feedback control system?

Sensor, integrating centre and effector

What is the role of a sensor in a homeostatic system?

Detects changes in a regulated physiological variable

Why are sensors essential for homeostasis?

Without detecting changes in physiological variables the body cannot initiate corrective responses

What is another term for the integrating centre in homeostatic regulation?

Control centre

What is the role of the integrating centre?

Compares incoming sensory information with the desired value and coordinates an appropriate response

Which major systems commonly act as integrating centres?

The nervous system and endocrine system

What is the role of an effector in homeostasis?

Carries out actions that alter the regulated variable and move it toward the normal range

What types of structures can act as effectors?

Cells, tissues or organs that produce physiological responses

What is a set point in physiological regulation?

The desired or normal value for a regulated variable

What is meant by an error signal in a feedback system?

The difference between the actual value of a variable and its set point

Why is the error signal important in homeostatic regulation?

It drives the corrective response that attempts to restore the variable toward its set point

Which physiological process is commonly used as an example of negative feedback?

Regulation of body temperature

What is the approximate normal core body temperature in humans?

Around 37 degrees Celsius

Which receptors detect decreases in body temperature at the body surface?

Peripheral thermoreceptors in the skin

Which receptors detect changes in internal body temperature?

Central thermoreceptors located in the brain

Which brain structure acts as the thermoregulatory centre?

The hypothalamus

What happens to sweating when body temperature falls?

Sweating decreases to reduce heat loss

How do peripheral blood vessels respond to cold exposure?

They constrict to reduce blood flow to the skin and limit heat loss

How does shivering help restore body temperature?

Involuntary skeletal muscle contractions generate heat

What type of responses can also contribute to thermoregulation?

Behavioural responses such as seeking warmth or adding clothing

Why is thermoregulation an example of negative feedback?

The responses oppose the initial temperature change and move body temperature toward the set point

What is meant by variability of set points in physiology?

The normal target value for a regulated variable can shift under certain conditions

Can physiological set points change under different circumstances?

Yes, they can adjust depending on physiological or pathological conditions

What happens to the temperature set point during a fever?

It increases to help the body fight infection

What physiological event in females can slightly raise body temperature?

Ovulation

What is positive feedback in physiology?

A control mechanism where the response amplifies the initial change in a variable

How does positive feedback affect system stability?

It tends to move the system further from the set point and can destabilise regulation

Is positive feedback common in physiological regulation?

No, it is less common than negative feedback

What type of physiological processes commonly use positive feedback?

Processes that require rapid amplification of a response

Which haemostatic process uses positive feedback?

Blood clotting

Which reproductive process uses positive feedback during labour?

Childbirth

Which electrical event in neurons involves positive feedback?

Generation of action potentials

Which genetic process can involve positive feedback loops?

Gene regulation

What pathological situation may involve positive feedback worsening the condition?

Severe haemorrhage

How does blood vessel injury initiate clot formation?

Damage exposes underlying surfaces that activate platelets

What happens when platelets adhere to an injured vessel wall?

They become activated and release signalling chemicals

How do platelet-derived chemicals promote clot formation?

They attract additional platelets to the site of injury

Why does platelet recruitment amplify the clotting process?

Each new platelet releases more signalling molecules that recruit further platelets

How is excessive clot formation prevented during haemostasis?

Inhibitory pathways act to limit clot growth and prevent uncontrolled thrombus formation

What is feedforward control?

A regulatory mechanism where responses occur before a change in the regulated variable happens

How does feedforward regulation differ from feedback control?

It anticipates changes rather than responding after a deviation occurs

Does feedforward control depend on detecting an error signal?

No, it occurs before the regulated variable changes significantly

What is an example of feedforward control during exercise?

Ventilation increases in anticipation of increased metabolic demand

Which digestive responses can occur through feedforward control after eating?

Salivation, gastric acid secretion and insulin release

How can psychological stress trigger feedforward responses?

Central nervous system activity anticipates physiological demand and activates regulatory systems

Which classical behavioural experiment demonstrates feedforward regulation?

Pavlov’s conditioning experiment involving anticipatory salivation

How can mental effort affect cardiovascular variables?

Heart rate and blood pressure can increase during mental tasks

What experimental observation supports central feedforward cardiovascular control?

Paralysed individuals attempting muscle contraction show increased heart rate and blood pressure

What does increased cardiovascular activity during attempted movement demonstrate?

The brain can initiate cardiovascular responses without sensory feedback from muscles

What does central command mean in cardiovascular regulation?

Brain signals anticipate physiological demand and activate cardiovascular responses

What is the autonomic nervous system?

A division of the nervous system that regulates internal organs to maintain homeostasis

Which types of organs are primarily controlled by the autonomic nervous system?

Visceral organs such as the heart, blood vessels, glands and digestive tract

Is autonomic nervous system activity intermittent or continuous?

It is continuously active

What major role does the autonomic nervous system play in physiology?

Maintaining whole body homeostasis through regulation of internal organ function

How does the autonomic nervous system commonly regulate organs?

Through reflex pathways often organised as negative feedback loops

What are the two main divisions of the autonomic nervous system?

Sympathetic nervous system and parasympathetic nervous system

What general physiological state is associated with sympathetic activity?

Fight or flight responses during stress or exercise

What general physiological state is associated with parasympathetic activity?

Rest and digest conditions during relaxed states

What is meant by dual innervation in the autonomic nervous system?

Most organs receive nerve supply from both sympathetic and parasympathetic divisions

How do sympathetic and parasympathetic actions usually relate to each other?

They typically produce opposing physiological effects

What type of physiological situations activate the sympathetic nervous system?

Stress, danger, intense emotion or physical activity

How does sympathetic activation affect heart rate?

It increases heart rate

How does sympathetic activation affect blood pressure?

It increases blood pressure

How does sympathetic activity influence digestion?

Digestive activity decreases

How does sympathetic activity affect urinary function?

Urinary activity decreases

What metabolic change occurs during sympathetic activation?

Energy stores are mobilised

What characterises parasympathetic nervous system activity?

Promotion of energy conservation and routine body maintenance

How does parasympathetic activity influence gastrointestinal function?

Digestive activity increases

How does parasympathetic activity affect bladder function?

It promotes bladder contraction and urination

How does parasympathetic activation affect heart rate?

Heart rate decreases

How does parasympathetic activation affect blood pressure?

Blood pressure decreases

Are sympathetic and parasympathetic systems inactive at rest?

No, both maintain a baseline level of activity

Which autonomic division usually predominates at rest?

Parasympathetic activity

How is a typical autonomic neural pathway organised?

A two neuron chain connecting the central nervous system to the effector organ

What are the two neurons involved in an autonomic pathway?

Preganglionic neuron and postganglionic neuron