Skin and body membranes Flashcards
What do body membranes do?
line or cover, protect and lubricate body surfaces
What makes up the membranes?
epithelial cells, these are sheets of epithelial tissue and supported by connective tissue that line internal structures or cavities
Describe the mucous membrane
also known as mucosa. Moist lining of the alimentary respiratory and genitourinary tracts. Covers surface of body cavities open to exterior
Describe the serous membranes
they secrete serous watery fluid
pleura lines the thoracic cavity and lungs
pericardium lines the pericardial cavity and surrounds the heart
peritoneum line the abdominal cavity and surrounding organs
describe the synovial membrane
Lines cavities of moveable joints and surrounds tendons that could be injured rubbing against bones. It consists of areolar connective tissue and elastic fibres. Secrets clear, sticky, oily synovial fluid that nourishes the joints
Describe the structure of the skin
largest organ in the body has a surface area of about 1.5-2 m2. In some areas there are accessory structures like glands, hair, nails. Two main layers : the epidermis which cover the dermis. Between the skin and the underlying structures there is a subcantaneous layer composed of areolar tissue and adipose (fat).
Describe the epidermis
most superficial layer, varies in thickness, thickest being on the palms of hands and soles of feet. No blood vessels or nerve ending.
Surface cells are constantly rubbed off and replaced by those underneath- complete replacement takes about a month
What is melanin?
a natural skin pigment in the deep germinative layer (inner most layer of the epidermis)
What does melanin do?
protects the skin from UV rays in sunlight, exposure to sunlight promotes synthesis of melanin
How is white skin pink?
saturation of haemoglobin and the amount of blood circulating in the dermis.
What can give skin a yellow colour?
excessive levels of bile pigments in the bluff and subcuntaneous fat
What are the two types of sweat glands?
eccrine
apocrine
describe the eccrine sweat glands
major sweat glands open onto skin surface secreting clear watery fluid important in temp regulation
decsribe apocrine sweat glands
open at hair follicles and become active at puberty. Bacterial decomposition of their secretion causes body odour
Where does heir grow from ?
bottom of hair follicles situated in epidermal cells in the dermis
What are arrector pili?
bundles of muscle fibres attached to the hair follicles
what causes good bumps?
contraction makes the hair stand up and raises the skin
Describe sebaceous glands
secretes an oily antimicrobial substance called sebum, into hair follicles. present all over the skin except palms and soles of feet
provides some waterproofing and acts as a bactericidal and fungicidal agent, preventing infection. Also prevents drying and cracking, especially on exposure to heat and sunlight
what are the functions of the skin?
protection - invasion of micro- organisms - chemicals Physical agents - mild trauma, UV light - dehydration regulation of body temp
What is radiation?
the main mechanism, exposed parts of the body radiate heat away from the bosy
What is evaporation?
body heat converts water in sweat to water vapour
What is conduction?
clothes and other objects in direct contact with the skin take up heat
What is convection?
air passing over exposed parts of the body is heated and rises, cool air replaces it and convection currents are set up
describe the control of body temp
regulated by the hypothalamus and is sensitive to the temp of circulating blood. Responds to decreasing temp by sending nerve impulses:
- arterioles in the dermis which constrict decreasing blood flow to the skin
- skeletal muscles stimulating shivering
as body temp rises and in normal range, the negative feedback system switched off
