Homeostasis is the maintenance of internal body conditions within very narrow limits.
The tissue fluid that bathes all the cells in the body has to be kept relatively constantly in terms of composition.
Ensure that metabolic reactions in cells proceed in a predictable way.
Feedback Systems
Based on three components
Receptor - Detects a change in some variable of the animal's internal environment
Control Center - Process information from the receptor and directs signal to effector
Effector - brings about the change to return conditions toward normal
(Control of room temperature)
Negative feedback system
A disturbance triggers processes that change the body's condition. These changes are then detected, reversed to restore the set point
Most Homeostatic mechanisms are working by this system
(Negative feedback in regulation of mammalian body temperature)
Positive feedback system
A disturbance triggers processes that change the body's condition such that the disturbances are intensified or prolonged.
Unstable and non-regulatory
Short-lived and produces radical change:
- Mammalian birth
- Swallowing or vomiting
- Generation of nerve impulse
Skin & Temperature Control
Skin
- Forms a continuous layer over the entire body
- Protects the underlying tissues and organs from mechanical injury
- Minimizes the loss of water through body
- Prevents entry of harmful bacteria and fungi
- Consisting mainly of Outer Epidermis & Inner Dermis
Outer Epidermis
Malpighian Layer
- Innermost layer of the epidermis
- Cells contain melanin which helps to absorb UV light
- Actively dividing cells that push the new cells towards the outer layers of the skin
Granular Layer
- Cells which are produced by the Malpighian layer move into the Granular layer and die.
Cornified Layer
- Consists of dead cells
- Keep bacteria out
- Reduces evaporation of water from the skin
Blood capillaries
- Remove away carbon dioxide and nitrogenous wastes
- Brings oxygen and nutrients to the skin
- Presence of capillary loops close to the surface of the skin which are important in temperature regulation
- Process is mainly diffusion
Sweat Gland
- Coiled tube deep in the dermis
- When temperature is too high, it takes up water from the surrounding blood capillaries around it
- Water collects in the gland, travels up the sweat duct, comes out of the pore in the epidermis
- The body is cooled as evaporation of the perspiration takes away latent heat from the skin
- Sweat consists of water, dissolved salts and tiny amounts of urea
Hair Follicle
- Deep pit lined with Granular and Malpighian cells
- Malpighian cells keep dividing and add on to the base of the hair, causing it to grow
- It is attached to the errector muscle which raises the hair away from the skin surface when contracting
- A thicker layer of air is trapped and this is an insulating layer
- Goose pimples are also produced when the hair errector muscles contract
Sebaceous Gland
- Produces an oily substance, sebum, which lubricates the hair and keeps the skin supple
- During puberty, it may over produce sebum due to hormonal changes, causing the sebum to clog up the pore of the skin
- When bacteria incubate in the sebum deposits, boil and acne occur
Adipose Tissue
- Fat tissue underneath the dermis
- Serves as an insulating layer and reduces heat loss from the body
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