Homeostasis and Response

What is homeostasis?

the maintenance of a constant internal environment

mechanisms are in place to keep optimum conditions despite internal and external changes.

this is needed for enzyme action and all cell functions.

What does homeostasis control?

● Blood glucose concentration

● Body temperature

● Water levels

What kind of communication is involved in the automatic control systems which detect changes and respond to them?

Nervous and hormonal

What do all control systems have?

Receptors, Coordination Centres & Effectors

What is a receptor?

A cell that detects stimuli (change in environment)

What is a coordination centre?

Something that processes the information received from receptors e.g brain, spinal chord and pancreas

What is an effector?

Brings about responses to bring the conditions in the body back to optimum levels e.g muscles or glands

What does the nervous system do?

Allows us to react to our surroundings, and coordinate actions in response to stimuli

Process of nervous system

1. Receptor cells convert a stimulus into an electrical impulse

2. Electrical Impulse travels along cells called sensory neurons to the central nervous system

3. Information is processed and appropriate response is coordinated, resulting in an electrical impulse being sent along motor neurons to effectors

4. Effectors carry out response (may be muscles contracting, glands secreting hormones)

What are reflexes?

Automatic responses which take place before you have time to think

Why are reflexes important?

They prevent the individual from getting hurt

Why do reflexes stop the individual from getting hurt?

Information travels down a pathway called a reflex arc, allowing vital responses to take place quickly

Why is the reflex arc different from the usual response to stimuli ?

The impulse does not pass through the conscious areas of your brain

Process of reflexes

1. A stimulus is detected by receptors

2. Impulses are sent along a sensory neuron

3. In the CNS the impulse passes to a relay neuron

4. Impulses are sent along a motor neuron

5. The impulse reaches an effector resulting in the appropriate response

What are some examples of reflex arcs?

-Pupils getting smaller to avoid damage from bright lights

-Moving your hand from a hot surface to prevent damage

What are synapses?

The gaps between two neurons

What happens when the impulse reaches the end of the first neuron?

A chemical is released into the synapse

This chemical diffuses across the synapse

When the chemical reaches the second neuron, it triggers the impulse to begin again in the next neuron

What is reaction time?

How long it takes you to respond to a stimulus

Can be measured with the ruler drop test

THE BRAIN - info (excluding components)

Made of many connected neurons

Controls complex behaviour

Part of central nervous system along with spinal chord

Diff. regions controll diff. functions

What are the components of the brain?

Cerebral Cortex

Cerebellum

Medulla

What is the cerebral cortex

-controls consciousness

-intelligence, memory, language

-outer part of the brain

What is the cerebellum

-controls fine movement of muscles

-rounded structure towards the bottom/back of the brain

What is the medulla

-Controls unconscious actions such as breathing and heart rate

-found in the brain stem in front of the cerebellum

Why is investigation of brain function and treating brain damage/disease difficult?

-It is complex & delicate

-It is easily damaged

-Drugs given to treat diseases cannot always reach the brain because of the membranes that surround it

-It is not fully understood which part of the brain does what

How can neuroscientists map out the regions of the brain?

Studying patients with brain damage

Electrically stimulating diff. parts of brain

Using MRI scanning techniques

How can studying patients with brain damage help map out the regions of the brain?

Observing changes in an individual following damage on a certain area of the brain can provide information on the role this area has.

How does electrically stimulating diff. parts of the brain help map out the regions of the brain?

By pushing an electrode into the brain, mental and physical damage can be caused providing information on the role of the area of the brain

How can using MRI scanning techniques help map out the regions of the brain?

A magnetic resonance imaging scanner can be used to create an image of the brain.

This can be used to show which part of the brain is affected by a tumour, or which part is active during a specific task.

What is the eye?

A sense organ containing receptors sensitive to light intensity and colour.

It has many different structures within it

How are the structures of the eye adapted?

to allow the eye to change it's shape in order to focus on near or distant objects (accommodation), and to dim light

What is the retina?

Layer of light sensitive cells found at the back of the eye

When light hits, cells are stimulated. Impulses are sent to the brain, which interprets the information to create an image.

What is the optic nerve?

A nerve that leaves the eye and leads to the brain.

It carries the impulses from the retina to the brain to create an image

What is the Sclera?

White outer layer which supports the structures inside the eye

It is strong to prevent some damage to the eye

What is the Cornea?

The see-through layer at the front of the eye

It allows light through and the curved surface bends and focuses light onto the retina

What is the iris?

Muscles that surround the pupil

What happens to the iris in bright light?

In bright light, the circular muscles contract and radial muscles relax to make the pupil smaller - avoiding damage to the retina

What happens to the iris in dim light?

In dim light, the circular muscles relax and the radial muscles contract to make the pupil larger - so more light can enter to create a better image

What are the ciliary muscles and suspensory ligaments?

Hold the lens in place

Control it’s shape

What is the process of accommodation to focus on a near object?

The ciliary muscles contract

The suspensory ligaments loosen

The lens is thicker and more curved - this refracts the light more

What is the process of accommodation to focus on a distant object?

The ciliary muscles relax

The suspensory ligaments tighten

The lens then becomes thinner - light is refracted less

When do eye defects occur?

When light cannot focus on the retina

What is myopia?

Short sightedness

The lens is too curved, so distant objects appear blurry

What is hyperopia?

Long sightedness

The lens is too flat, so it cannot refract light enough

How to treat eye defects with spectacle lenses

Concave lenses to spread out the light to treat myopia (near sightedness)

Convex lenses to bring the rays together to treat hyperopia (long sightedness)

How to use contact lenses to treat eye defects

Works the same as glasses but allow sport to be carried out

Hard/Soft contact lenses last for different lengths of time

How to use laser eye surgery to treat eye defects

Can be used to either reduce the thickness of the cornea (refracts light less) to treat myopia

Or change it’s curvature (so it refracts light more strongly) to treat hyperopia

How to use replacement lenses to treat eye defects

Hyperopia can be treated by replacing the lens with an artificial one made of clear plastic (or adding plastic on top of natural lens)

Risks - damage to retina, cataracts developing

What is the thermoregulatory centre?

Monitors and controls body temp

Found in the brain

Has receptors that monitor temp of blood

Has receptors in skin that send impulses to the thermoregulatory centre

What is the human body temp?

37.5 degrees celcius

What happens if human body temp becomes too high?

Sweat (evaporates from skin surface resulting in increased energy transfer away from body) is produced from sweat glands

Vasodilation means more blood flows closer to the surface of the skin, resulting in increased energy transfer from the body

What happens if human body temp becomes too low?

Sweating stops

Skeletal muscles contract rapidly (shivering) to generate heat from respiration

Hairs stand on end to create an insulating layer, trapping warm air

Vasoconstriction means blood does not flow so close to the surface, resulting in less heat lost

What are the human body’s two communication systems?

The nervous system

The endocrine system

What does the endocrine system do?

sends hormones (chemical messengers) around the body

when they reach a target tissue they produce a response

What is the endocrine system made up of?

glands which secrete hormones directly into the bloodstream

What is the pituitary gland in the endocrine system?

The master gland

Secretes hormones into the blood to either have an effect on the body or act on other glands to simulate them to produce different hormones

What is the pancreas in the endocrine system?

Secretes insulin

Controls blood glucose levels

What is the thyroid in the endocrine system?

secretes thyroxine

controls metabolic rate, heart rate and temperature

What is the adrenal gland in the endocrine system?

Secretes adrenaline

involved in the ‘fight or flight’ response (the body’s response to stressful situations)

What is the ovary in the endocrine system?

Secretes oestrogen

Is involved in menstrual cycle and development of female secondary sexual characteristics (different features that develop during puberty that distinguish a female from a male)

What are the testes in the endocrine system?

Secretes testosterone

Is involved in the production of sperm and the development of male secondary sexual characteristics

What does the blood do in the endocrine system?

Transports the hormone to a target organ or tissue where it has an effect

Comparison of nervous system to endocrine/hormonal system

Hormonal system is much slower but acts for longer

Why does the concentration of glucose in your blood need to be kept within a certain limit?

Because glucose is needed by cells for respiration

Controlled by the pancreas

What does eating foods that contain carbohydrates do?

Increases glucose levels in the blood

What happens if the glucose levels in your blood are too high?

-Pancreas produces hormone insulin

-Insulin binds to cell in target organs (muscles and liver). This causes:

1) Glucose move from blood into muscle cells for respiration

2) Excess glucose converted into glycogen which is stored in the liver

-Blood glucose concentration reduced

What does vigorous activity (exercise) use glucose for?

Respiration

Therefore there is less in the blood

What happens if glucose levels decrease due to exercise?

-Pancreas produces hormone glucagon

-Glucagon binds to the liver cells causing glycogen to be broken down into glucose

-Glucose released into blood to increase conc.

How is blood glucose conc. kept constant?

Through glucagon and insulin

They work in a negative feedback loop

What is a negative feedback loop? (insulin and glucagon)

When blood glucose levels increase/decrease hormone is secreted to oppose the change

Action of this hormone cannot occur continually because when the blood arrives at a certain glucose concentration the other hormone is produced resulting in the opposite effect

What is diabetes?

You cannot control your blood glucose level

What is type 1 diabetes?

The pancreas cannot produce enough insulin

What are the risks of type 1 diabetes?

Blood glucose level can rise to a fatal amount

Glucose is excreted with urine and lots of urine produced - individual very thirsty

How is type 1 diabetes treated?

Insulin injections at meal times: glucose taken up from bloodstream

Limited intake of simple carbohydrates which contain lots of glucose

Doctors are attempting to cure diabetes with pancreas and pancreatic cell transplants

and genetically engineering pancreatic cells from mice to make insulin

What is type 2 diabetes?

The body cells no longer respond to insulin

What are the risks of type 2 diabetes?

Blood glucose levels can rise to fatal amount

Obesity is a risk factor for this disease

What are the treatments for type 2 diabetes?

Reducing number of simple carbohydrates in diet

Losing Weight

Increasing exercise

There are also drugs to make insulin more effective on body cells, help pancreas make more insulin or reduce the amount of glucose absorbed from the gut

What is osmosis?

The process by which water molecules move from a place where they are in high concentration to a place where they are in low concentration

If water concentration of the blood increases what happens?

Cells in the body take up water because concentration of water in blood is higher than concentration of water in cells, so water moves to the cells by osmosis

Cells then expand as they take up more water and could burst

What happens if water concentration of the blood decreases?

Cells in the body lose water because concentration of water in bloodstream is lower than in cells, so water moves out of cells by osmosis

Cells shrink as they lose water

What happens if body cells lose or gain too much water by osmosis?

They do not function properly

What do the kidneys do to maintain balance of water and other substances in the body?

As blood moves through the body, it makes urine by:

Filtering out waste products

Selectively reabsorbing useful substances: glucose, ions, water

What are examples of waste products that are processed at the kidney?

Water, ions, urea

Water as a waste product processed by the kidney

-Can also leave body at lungs as a result of exhalation or from skin in sweat (no control of amount lost)

-Depending on conc. of water in blood, a certain amount of water lost as urine

Examples of ions as waste products of the kidney

-Taken into body via food

-If ion conc. incorrect, too little or too much water may enter body cells because water potential of blood would be altered

-Lost in sweat (no control of amount lost)

-In kidneys, certain amounts of ions reabsorbed into blood after it’s been filtered to insure maintained conc.

Urea as a waste product in the kidney

-Amino acids are products of digestion in proteins. Amino acids deaminated in liver to form ammonia. As ammonia = toxic, it’s converted into urea

-Lost in sweat (no control of amount lost)

-In kidneys, filtered out of blood

What is anti-diuretic hormone (ADH)?

A hormone involved in control of loss of water as urine

It’s released into pancreas by pituitary gland when a receptor in the brain detects that the blood is too concentrated

What happens when Anti-diuretic hormone (ADH) has been released into the pancreas?

It travels the bloodstream to the kidney tubules

An increased amount of ADH reaching tubules increases their permeability to water, so more moves out of the tubule and back into the bloodstream

This results in a smaller volume of more concentrated (yellow) urine

What is the thermoregulatory centre?

Monitors and controls body temperature
Found in the brain

What are the receptors of the thermoregulatory centre?

-Has receptors that monitor the temperature of the blood

-Has receptors in the skin that send impulses to the thermoregulatory centre

What is human body temperature?

37.5 degrees celcius

What happens if human body temp becomes too high?

• Sweat is produced from sweat glands

• Vasolidation means more blood flows closer to the surface of the skin, resulting in increased energy transfer away from the body

What does sweat do?

Evaporates from skin surface resulting in increased energy transfer away from body

What happens if body temp decreases too much?

• Sweating stops

• Skeletal muscles contract rapidly (shivering) to generate heat from respiration

• Hairs stand on end to create an insulating layer, trapping warm air

• Vasoconstriction means blood doesn’t flow so close to surface, resulting in less heat lost

What do the kidneys do?

Maintain balance of water and other substances in the body

How does blood make urine?

As it moves through the body:

• Filters out waste products

• Selectively reabsorbs useful substances - glucose, ions, water

What are some examples of waste products that are processed the kidney?

Water, Ions and Urea

Water as a waste product that is processed at the kidney

• Can also leave body at lungs as a result of exhalation, or from skin in sweat (there is no control over amount lost)

• Depending on the concentration of water in blood, certain amount of water is lost as urine

Ions as a waste product processed at the kidney

• Taken into the body via food

• If ion conc. incorrect, too little or too much water may enter body cells, as water potential of the blood would be altered

• Lost in sweat (no control of amount lost)

• In kidneys, certain amount of ions reabsorbed into the blood after it has been filtered to ensure conc. in blood is maintained

Urea as a waste product in the kidney

• Amino acids are products of digestion of proteins. Amino acids are deaminated in the liver to form ammonia. As ammonia is toxic, it is converted into urea

• It is lost in sweat (no control of amount lost)

• In the kidneys, it’s filtered out the blood

What is ADH?

A hormone involved in the control of the loss of water as urine