BMS1032 Principles of Physiology

What is Homeostasis

The maintenance of stable internal environment is essential for the normal healthy function of the body's cells, tissues and organs

What are examples of homeostasis

Thermoregulation

Blood Glucose

Osmolarity

Blood pressure

How is blood pressure controlled

If it drops - blood vessels contract (vasoconstriction), there is increased reabsorption in the kidney which increases blood volume

If it increases - blood vessels relax (vasodilation) and there is increased excretion in the urine which decreases blood volume

What are the main components needed to maintain homeostasis

Sensor - detects the variable, tells when something is not within the acceptable range (sometimes called the receptor)

Control centre - decides what to do with the information from the sensor

Signal - transmits information from the control centre as to what to do next can be called the signal particle - often hormones are signals

Effector - target organ where the signal has its effect, this effector carries out the process to adjust the controlled variable

What is the difference between efferent and afferent pathways

Afferent is used to describe things like nerves, blood vessels, and arteries that lead toward or bring things (like blood, in the case of arteries) to an organ, such as the heart or brain. Efferent means the opposite—it's used to describe parts that carry or lead things away from organs or other parts.

What is the comparator

The set level of a variable (physiological range) that it should be

What happens during a homeostasis feedback loop

The sensor obtains current information regarding a given variable, it responds to the stimulus by sending information to the control centre along the afferent pathway

The comparator compares the current value from the afferent pathway to the desired value

The effector modifies parameters to restore the variable back to its physiological range

What is a negative homeostatic feedback loop and what examples are there

When change occurs in the opposite direction to the original stimulus

Acute restoration of blood pressure

Return of plasma osmolality

Temperature regulation

What is a positive feedback loop and give examples of when it is used

A loop that enhances a stimulus so that a reaction can occur at an even faster rate. Can help out body achieve long term homeostasis and physiological mechanisms

Labour and uterine contractions

Micturition (urination)

Describe the positive feedback loop with specificity to childbirth

Increased excitability of the uterus causes the start of uterine contractions

There is a down push of the baby on the cervix which is the stimulus

The stimulus causes an afferent signal to be sent to the hypothalamus

This causes the release of oxytocin by the posterior pituitary

This causes positive feedback onto the uterine contractions until the birth of the baby terminates the feedback loop as there is no longer pressure on the cervix

How does communication occur during feedback loops

Cell to cell communication can happen via: signalling molecules, neurotransmitters, and hormones. These chemical messengers help regulate physiological processes by transmitting information between cells.

Contact dependant (when cells are touching)

Paracrine (cells are near each other)

Synaptic

Endocrine

What are the intercellular signalling pathways used in feedback loops

Chemical signals used to activate a receptor which can then translate chemical signals to cellular signals and create a response

Why do we need homeostasis

Failure to compensate or a disruption of homeostasis can cause pathology

What is an average adult male made of

60% liquid

Of which 2/3 is intracellular fluid and 1/3 is extra cellular

Of the extra cellular fluid 80% is interstitial fluid and 20% is blood plasma

Where is Intracellular fluid found

Inside cells - cytoplasm

Describe the ion distribution in bodily fluid compartments

The concentration of ions is equal across the interstitial fluid and extra cellular fluid. To achieve this there are more ions in the interstitial fluid as it is greater. This is essential to prevent net movement of water between these compartments

Define osmosis

The movement of water molecules from a low solute concentration to a high solute concentration across a semi permeable membrane. This can cause an increase in pressure

Define osmolarity and osmolality. Which is more common?

Osmolality- the total number of dissolved particles per Kg of water

Osmolarity- the total number of dissolved particles per litre of solution

Normally osmolarity is used

What terms effect osmosis in cells

The properties of the membrane determine which solutes are osmotically active. So the cell membrane is nearly impermeable to Na+.

In the extracellular fluid compartment Na+ and Cl- are the major osmolytes and are often referred to as osmotically active ions

Describe water movement during osmosis under dehydration

Water is lost from the extracellular space

This means an increase in extracellular osmolality

Water flows from the intracellular space to extracellular fluid causing cell shrinkage

What problems can osmosis cause during injury

Plasma proteins (clotting factors) move out of the cell and accumulate extracellularly causing an osmotic pressure. Water flows out of cells causing inflammation

What is a Hypotonic solution vs a Hypertonic solution

Hypotonic - A solution that has a lower concentration of solute compared to the cell. Causes cellular swelling

Hypertonic - A solution with a higher concentration of solute compared to the cell. Causes cellular shrinkage

What are the effects of solution tonicity on cell volume

Isotonic solutions - water movement is minimal, tends to maintain intracellular volume

Hypertonic solutions - water movement out of the cell, tends to reduce intracellular volume

Hypotonic solutions - water movement into the cell, tends to increase intercellular volume

Describe the layout of the ANS

Preganglionic cell body (CNS) - Preganglionic neuron (myelinated) - autonomic ganglion - Postganglionic neuron (unmyelinated) - Target tissue

What neurotransmitter to the different neurons of the ANS release

The preganglionic nerve releases neurotransmitter acetylcholine that bind to nicotinic acetylcholine receptors

The post ganglionic nerve releases acetylcholine that binds to muscarinic receptor

Where is the sympathetic ganglion found

Very close to the spinal cord

What is the ANS

The autonomic nervous system is the part of the nervous system that supplies the internal organs, including the blood vessels, stomach, intestine, liver, kidneys, bladder, genitals, lungs, pupils, heart, and sweat, salivary, and digestive glands.

What are the 2 main divisions of the ANS

The autonomic nervous system has two main divisions:

Sympathetic - prepare the body for emergency

Para sympathetic - replenish stores and conserving energy

What is the function of the ANS

Control of involuntary activity and vital functions, It innervates smooth and cardiac muscle and secretory glandular tissue

Is regarded as purely motor (efferent) although includes sensory nerves arising from the viscera

What are the classes of ANS receptor

Alpha - a1, a2

Beta - b1, b2, b3

What receptors target which organs in the ANS

alpha receptors (more selective for Noradreniline)

a1 - dilates the pupil, constricts blood vessels

a2 - decreases gut motility

beta receptors are more selective for adrenaline

b1 - increase of heart rate

b2 - dilates blood vessels, relaxes airways

b3 - relaxes urinary bladder

What is the function of the adrenal gland

It secretes hormones from an outer cortex and an inner medulla

What is a medulla

Part of the brain

a sympathetic ganglion innervarated by preganglionic neuron, it releases catecholamine hormones - adrenaline and noradrenaline

What is a ganglion

a collection of neuronal bodies found in the voluntary and autonomic branches of the peripheral nervous system (PNS)

What are the two parts of the peripheral nervous system

Somatic nervous system - controls voluntary responses, responsible for relaying sensory and motor information between the environment and the CNS

Autonomic nervous system - controls involuntary responses

Describe the structure of the somatic nervous system

Sensory nerves detect sensation

Travels down afferent pathways to the NS then down efferent pathways to the motor neurone which control skeletal muscle

How many neurons are present in different parts of the PNS

Somatic - only one neuron

Autonomic - 2 neurons synapsing at an intermediate ganglion

What does intracellular and extracellular mean?

Intracellular - in the cell

Extracellular - out of the cell

Describe the cell and ion gradients of K+, A-, Cl-, Na+ in and out of the cell

K+, A-: have a lot higher concentration in the cell rather than outside, because of this they move down the concentration gradient

Cl-: higher outside the cell than inside, moves down the concentration gradient

Na+: also higher outside the cell but the gradient requires energy