Biology - Homeostasis

Homeostasis

Maintenance of the body’s constant internal environment

Detecting Change

• In order to maintain homeostasis the body must be able to detect changes or variations in the internal and external environments

• A change from the ideal condition is called a stimulus

• A stimulus is detected by a receptor

• The ideal condition for the body is called the set point

Receptors

• Smell – chemoreceptors in the nose detect smells

• Sight – photoreceptors in the retina detect light

• Taste – chemoreceptors on the tongue detect different tastes

• Touch – mechanoreceptors (pressure, vibration and pain) and thermoreceptors (heat)  detect changes in the skin

• Hear – mechanoreceptors in the cochlear detect vibrations

• Pain – pain receptors throughout the body excluding brain, liver and lungs

Effectors

•When a stimulus is detected by a receptor an action need to occur to bring the body back to homeostasis

•This response is done by an effector.

•Effectors can be muscles or glands.

Controlling receptors and effectors

• Receptors send information to the control centre.

• The control centre processes it and directs effectors.

• Receptors and effectors must be coordinated by a control centre.

• The control centre is the brain or the spinal cord

Stimulus Response Model

The stimulus response model shows how the body can direct a stimulus and coordinate a response

Responses

•The action that the body takes to return to homeostasis is called the response. 

Examples:

•Shivering if cold

•Sweating if hot

•Releasing insulin if blood sugar is too high

Systems Working Together

Each body system is made up of organs with specific functions such as:

•Supply the cells with nutrients and energy

•Remove waste

Nervous and Endocrine Systems

-Control and coordinate stimuli and responses from all systems

Respiratory System:

• Respiratory system: brings in oxygen, removes carbon dioxide

• Main organ: lungs

• Gas exchange happens in alveoli (tiny air sacs)

Circulatory System:

• Circulatory system (cardiovascular): transports oxygen & nutrients to cells, removes wastes like carbon dioxide

• Involves heart, blood, and blood vessels (arteries, veins, capillaries)

Digestive System:

Digestive system: breaks down food, supplies nutrients to body, absorbs them into tissues and cells

Excretory System:

• Excretory system: removes waste products from chemical reactions, maintains balance of water, nutrients, and salts

The Nervous System:

The nervous system is composed of the:

•central nervous system (CNS) — contains brain and spinal cord

•peripheral nervous system (PNS) — contains the nerves connecting CNS to the rest of the body

Communication:

•The nervous system sends messages as an electrical impulse along a neuron

• Then as a chemical message (neurotransmitters) across the gaps (synapses) between neurons.

Central Nervous System:

• CNS: receives & processes environmental information

• Consists of brain and spinal cord

• Brain functions: intelligence, creativity, perception, conscious reactions, emotions, memories

Peripheral Nervous System:

• PNS: consists of all nerves outside CNS

• Divided into:

  • Somatic nervous system: voluntary actions

  • Autonomic nervous system: involuntary actions

Neurons:

• Nervous system made of neurons (nerve cells), grouped as nerves

• Three types of neurons:

  • Sensory neurons

  • Interneurons

  • Motor neurons

Sensory Neutrons:

•carry the impulse generated by the stimulus to the CNS

Interneurons:

•carry the impulse through the CNS

Motor Neurons:

take the impulse to effectors such as muscles or glands

Synapses and Neurotransmitters

• Message path: electrical impulse → synapse → neurotransmitter → next neuron

• Synapse: gap between axon and dendrite, prevents all neurons from firing at once

• Neurotransmitters: chemicals that fill the synapse to pass message

• Examples of neurotransmitters: serotonin, dopamine

Reflex Arc:

• Reflex arc: spinal cord acts as control centre instead of brain

• Allows for much quicker reactions

Endocrine System:

• Controls body functions by releasing hormones (chemical messengers) into the bloodstream.

• pituitary gland = master gland that is responsible for producing many hormones that regulate other endocrine system glands

Glands:

An organ that releases chemical signalling molecules

Hormones:

Signalling molecules that travel through the bloodstream.

Hormones (Signalling Molecules):

• Hormones ONLY act on those cells that have the specific receptor.

• The hormone will cause a change in the cell’s activity.

Comparing the Nervous and Endocrine Systems:

• Nervous system: Fast-acting, controls short-term changes (seconds–minutes).

• Endocrine system: Slow-acting, controls long-term changes (minutes–years).

Functions controlled by the nervous and endocrine systems

Why systems must work together:

• Multiple systems can respond to a single stimulus

Feedback Loops:

• Feedback loops are the co-ordination of the body's response to a stimulus.

• They can be positive or negative 

Negative Feedback Loops:

• A negative feedback loop is when the response is in the opposite direction to the stimulus.

• Most feedback in the body will be negative

Positive Feedback Loops:

• A positive feedback loop is when the response is in the same direction to the stimulus.

Medical Applications:

• Medicine is about keeping the body in homeostasis

Case Study: Contraceptives

• Hormonal contraceptives: Prevent or reduce fertilisation by altering menstrual cycle hormones.

• Future methods: May block sperm or trick the egg into thinking it’s fertilised.

• Research: A male contraceptive pill is being developed.

Sports Applications:

• •Sports scientists use their knowledge of homeostasis to improve elite athlete abilities, through:

  • Thermoregulation – managing body temperature.

  • Wearable tech – monitoring body functions.

  • Glucose control – regulating energy supply.

What is a disease?

• A body condition that disrupts homeostasis

Diseases can be:

•Infectious/Communicable (covid-19, flu gastro,cold) – caused by pathogens

•Non-Infectious/Non-Communicable (cancer, diabetes) –caused by genetic, physiological, environmental and behavioural factors.

Non- Communicable Diseases

•Cannot be passed from person to person

•They are caused by a combination of genetic, physiological, environmental and behavioural factors.

Infectious/Communicable Diseases

•Infectious diseases are caused by pathogens.

•Pathogens are disease causing agents

•Pathogens can be cellular or non-cellular

Infectious diseases

• Cellular pathogens = Animals, Fungi, Protozoa, Bacteria

• Non-cellular pathogens = Viruses, Prions

Modes of Transmission:

• Sneezing

• Vectors

• Contaminated Objects

• Water Supply

• Physical Contact

• Coughing

Portals of Entry

Pathogens usually need to enter the body to cause disease

• The mouth

• The eyes

• The nose

• The ears

• The urogenital openings

• Broken skin

Disruption of Homeostasis:

The body works within narrow limits to maintain homeostasis

Pathogens or NCDs disrupt this balance by:

• Damaging cells, tissues, organs or systems

• Disrupting Negative and Positive Feedback Loops

• Building up or introducing  toxins

Pathogens:

• •Pathogens are disease causing agents

• Pathogens can be cellular or non-cellular.

Non-Cellular

• Non-cellular pathogens include prions, viruses, and viroids.

• They are considered non-living.

• They cannot replicate independently

• Must infect a host cell to reproduce

Virus:

a diverse group of non- cellular pathogens

Viroid:

non-cellular pathogen

Prion:

an abnormal infectious protein

Cellular Pathogens

•Pathogens that are made up of one or more cells

e.g:

•Bacteria

•Fungi

•Protozoa (Protists)

•Worms (helminths)

Bacteria