*Homeostasis

Shie Yu Hao (22)Per Sheng Xiang (19)

*Overall Outline

* The need for Homeostasis

* Structure of Mammalian Skin

* Heat Production and Heat Loss

*Emperor Penguin, largest of all Penguins, live in Antarctica. These birds breed in extremely low temperature that can drop to -40 degree Celsius.

*The egg laid by the female is handed over to the male for incubation, and the egg cannot touch the ground or it will freeze immediately!

*How do they do this?

Small Facts

*Homeostasis*Definition:

Homeostasis is the maintenance of a constant internal environment.

*Why is there a need for this?

Conditions outside our body are constantly changing.

Body cells, however, must be kept at constant temperature and bathed in tissue fluid that is kept at a constant pH and water potential.

*Constant body temperature * Enzymes in our body can only work within

certain temperatures.

*Thus, changes in body temperature too drastically may result in enzyme inactivation or even denaturation.

*An example will be high fever, that is people suffering from high fever must consult doctors as high fever is highly fatal!

Note: Denaturation is a process in which proteins or nucleic acids lose their tertiary structure and secondary structure.

*Constant pH and water potential *Drastic change in the pH of tissue fluid will

affect enzyme reaction in the tissue cells and harm our body.

*Composition of tissue fluid must be kept within very narrow limits, thus, any drastic change in water potential will affect our cells.

* Do you know:

Your kidneys help you regulate the water potential (osmotic pressure) in your blood.

When water potential increases, the osmotic pressure of blood will decrease and vice versa.

*Homeostatic control of water potential Normal water potential in

blood (Norm)

Stimulus Water potential of blood decreases

(Due to loss of water through profuse perspiration)

Receptor (Hypothalamus

stimulated)

Corrective MechanismMore ADH released by

pituitary gland More water reabsorbed by

kidney tubules Less water excreted

Urine is more concentrated Less urine produced

Water potential of blood

increasesNegative Feedback

When water potential decreases

*Homeostatic control of water potential Normal water potential in

blood (Norm)

Stimulus Water potential of blood increases

(Due to large intake of water)

Receptor (Hypothalamus

stimulated)

Corrective MechanismLess ADH released by

pituitary gland Less water reabsorbed by

kidney tubules More water excreted

More dilute urine produced

Water potential of blood

decreasesNegative Feedback

When water potential increases

*Need for homeostasis

*Homeostasis is the process that keeps body temperature constant and ensures that the composition of the body fluids is kept within narrow limits.

*By ensuring a relatively stable internal environment, homeostasis allows an organism:

• To be independent from changes of external environment.

• Changes include blood and tissue fluid (mammals).

*Homeostasis negative feedback

*Homeostasis can help you respond to the drastic changes in your body by a receptor (detector).

*Note: Your body reacts to bring about an opposite effect to changes!

*Therefore, if the system is disturbed, the disturbance sets in motion a sequence of events that tends to restore the system to its original state.

*This is the NEGATIVE FEEDBACK process!!

*Note: A negative feedback response means that your body is gradually going back to normal.

*More Facts*Organs or Structure that detects changes

in body are called receptors/sensors.

*Changes from normal condition is called stimulus.

*Homeostasis Occurrence

There must be:

*A stimulus, change in the internal environment

*A receptor that detects the stimulus

*An automatic/self-regulatory corrective mechanism: Brings about reverse effect of stimulus

*Negative feedback to the receptor

*Principle of homeostasisNormal

condition or set-point (Norm)

Stimulus (Condition rises above

normal)

Receptor (Detects stimulus)

Self-regulatory corrective

Mechanism

Condition decreases

Negative Feedback

Condition rises

*Principle of homeostasisNormal

condition or set-point (Norm)

Stimulus (Condition decreases

below normal)

Receptor (Detects stimulus)

Self-regulatory corrective

Mechanism

Condition increases

Negative Feedback

Condition decreases

*Regulating blood glucose concentration

Body cells need glucose for tissue respiration

Tissue respiration then provides cell with energy for vital activities

A drastic change in the blood glucose concentration can be VERY DANGEROUS!

Do you know:

Glucose levels in your blood rise after a meal and fall during vigorous exercise or starvation.

So, how does our body keep the concentration of glucose in the blood constant?

*Examples of homeostasis in human

*Blood glucose concentration risesNormal condition

or set-point (Norm)

Stimulus (Too much glucose in

blood )

Receptor (Islets of Langerhans are stimulated)

Corrective Mechanism

Pancreas secretes more insulin.

Causes liver to convert glucose to

glycogen

Blood glucose concentration

falls Negative Feedback

*Blood glucose concentration fallsNormal condition

or set-point (Norm)

Stimulus (Too little glucose in

blood )

Receptor (Islets of Langerhans are stimulated)

Corrective Mechanism

Pancreas secretes glucagon

Causes liver to convert glycogen to

glucose

Blood glucose concentration

increases Negative Feedback

*Skin forms a protective coat over our body surface

*Acts as an excretory organ

*As well as a regulator of body functions

*So, how does skin do all these stuffs??? Before you can answer this question, you must first learn about the structure of skin

*Structure of mammalian skin

*Structure of mammalian skin Skin is

composed of 2 different parts:

• An outer part called the epidermis

• An inner thicker part called the dermis

*Upper part of Dermis is thrown into ridges

*Rich supply of nerves and blood capillaries

*These structures allow our skin to:

Detect changes in the temperature of the surrounding

Feel pain E.g. A needle pricks into your skinBlush

*Dermis

*A number of blood vessels are present in the dermis

*Arterioles carries blood to these capillaries

*Arterioles are controlled by nerves (Vasomotor nerves)

*Vasomotor nerves brings about reflex contraction and dilation in Arterioles (Vasodilation)

* When Arterioles dilates, more blood is sent to blood capillaries in your skin

*Contraction of Arterioles, Vasoconstriction, reduces the amount of blood flowed through the capillaries in the skin (Causing you to become pale)

* Do you know:

Your skin will turn red when you blush is because of the numerous blood vessels in you skin dilate

Contraction and Dilation of you Arterioles help you to regulate body temperature!!!

*Blood vessels in skin

*Hairs are embedded in the dermis, but they are produced by the epidermis.

*Malpighian layer of the epidermis sinks into the dermis, forming a hollow tube called hair follicle.

*Each hair grows in a hair follicle.

*Hair papilla (mass of tissue containing blood capillaries and nerves) are found at the base of the hair follicle.

*Covered with epidermal cells that constantly divides (Pushes new cells upwards)

*Cells being pushed upwards soon dies and harden, which form hair

*Hair

*Hair erector muscles are attached to the hair follicles

*These muscles can contract, causing:

The hairs to “stand on its ends”

The skin to be raised around the hair, producing the characteristics “goose pimples” in humans

Do you know:

Hair can be specialized for particular purposes.

The whiskers or vibrissae of cats and dogs can help them sense objects.

The long stiff spines of porcupines are modified hairs used for protection.

*Each sweat gland is a coiled tube formed by a

down-growth of the epidermis

*Forms a tight knot in the dermis

*Richly surrounded by blood capillaries

*Secreted sweat flows through a sweat duct and a sweat pore to the skin surface

*Secreted sweat contains mainly water, dissolved salt (sodium chloride) and small amount of urea

*Sweat contains metabolic waste products such as urea, skin is considered an excretory organ

*Sweat glands

* Sweat secretes continuously

*Amount of sweat produce, however, varies

* It may be produced in very small quantities which evaporates almost immediately

*Or

* When more sweat is produced, it appears as droplets on your skin or as “running streaks” of liquid in extreme cases

*Note: Sweat is a mean by which your skin regulates body temperature

*Parts of body that detect changes in the

environment or stimuli are called sensory receptors

*Nerves ending found in the epidermis and dermis

are simple sensory receptors

*Enable us to sense (PPT)- Thermoreceptors:

PainPressureTemperature changes in the external environment

*Sensory receptors

*Beneath the dermis are several layers of adipose cells, where fats is stored

*Fat in these cells also serves as an insulating layer, preventing heat loss

*Sub-cutaneous fat

*Acts as:

*A Protective outer covering of the body

*A Regulatory of body temperature

*An Excretory organ

*A Sense organ

*Skin contains of an outer epidermis and a thick inner dermis

*In short, JUST REMEMBER: PRESS!

*Skin

*How does your body gain heat?

Definition: Heat is produced within you body as a result of

metabolic activities such as tissue respiration

*Lots of tissue respiration takes place in the muscles and liver

*Thus, large amount of heat are set free in these organs

*Heat is then distributed to all parts of your body by the blood

Do you know:

You can also gain extra heat by eating hot food, exercising, from the sun’s radiation or from warm air on very hot days

If these heat is not lost to the surrounding, you may die of overheating

*Heat Production

*How does your body lose heat?

Heat is lost:

Through you skin by radiation, convection and to a limited extent, conduction

By evaporation of sweat from the surface if your skin

In the faeces, urine and in the air that is exhaled

Do you know:

Certain parts of your skin contain shunt vessels. These vessels connect the skin arterioles with the venules.

They control the amount of blood flowing through your skin capillaries.

When shunt vessels constrict, more blood reaches the capillaries in your skin, which increase the amount of heat loss. When shunt vessels dilate to allow more blood to enter them, less blood flows to the capillaries in your skin, thereby decreasing the amount of heat loss. Hence, shunt vessels affect heat loss through skin surface.

*Heat Loss

*Hypothalamus in our brain monitors and regulates body temperature

*Hypothalamus receives information about temperature changes in the external environment from temperature receptors in skin

*Also monitors temperature of blood passing through it

*Regulating body temperature

*Human body temperature risesNormal condition

or set-point (Norm)

Stimulus (Blood and skin

temperature increases)

ReceptorTemperature in skin detects

change and send nerve impulses to brain

Hypothalamus in brain is stimulated and sends nerve

impulses to relevant body parts

Corrective MechanismArterioles in skin dilate, shunt

vessels constrict, more blood flows to blood capillaries in the skin,

increasing heat lossSweat glands more active, more

sweat produced, sweat evaporated and more latent heat lost

Rapid breathing (helps remove heat)

Metabolic rate decreases (decrease heat produced)

Blood temperature

decreases to the norm

Negative Feedback

*Human body temperature fallsNormal condition

or set-point (Norm)

Stimulus (Blood and skin

temperature decreases)

ReceptorTemperature in skin detects

change and send nerve impulses to brain

Hypothalamus in brain is stimulated and sends nerve

impulses to relevant body parts

Corrective MechanismArterioles in skin constrict, shunt

vessels dilates, less blood flows to blood capillaries in the skin,

decreasing heat lossSweat glands less active, less sweat produced and less latent heat lost Shiver, if very cold (Contraction of

skeletal muscles) Metabolic rate increases (decrease

heat produced)

Blood temperature

increases to the norm

Negative Feedback

*Constant body temperature

Extra heat produced is removed at a faster rate so that there is no appreciable rise in body temperature

Heat is gained at a faster rate when surrounding temperature drops too low

*Results