ANATOMY & PHYSIOLOGY

The Skeletal System

The skeletal system is the foundation of the body. The system is composed of bones and cartilage that hold everything together, all united by moveable and immovable joints.

We are going to focus on the bones of the head and face only. The skull supports the structures of the face and forms a cavity for the brain. Functions of the skull include protection of the brain, fixing the distance between the eyes to allow stereoscopic vision, and fixing the position of the ears to help the brain use auditory cues to judge direction and distance of sounds.

The skull is composed of two parts: the cranium (skull) and the mandible (jaw).

The braincase (neurocranium) consists of 14 bones:

1.         Occipital Bone: Forming the lower back part of the cranium

2.         2 x Parietal Bones: Forming the sides and crown of the cranium.

3.         Frontal Bone: Forming the forehead.

4.         2 x Temporal Bones: Forming the side of the head in the ear region.

5.         Ethmoid Bones: These are the light and sponge like bones between the eye sockets.

6.         Sphenoid Bones: These join all the bones of the cranium.

The Facial Skeleton

1.         2 x Nasal Bones: Forming the bridge of the nose.

2.         2 x Lacrimal Bones: Forming the front part of the inner wall of the eye sockets.

3.         2 x Zygomatic Bones: (or molar bones) Forming the prominent cheekbones.

4.        2 x Maxillae Bones: The upper jawbones.

5.         Mandible: Lower jaw bone.

The Muscular System

The Muscular System is the anatomical system that allows movement. The muscular system in vertebrates is controlled through the nervous system, although some muscles (such as cardiac muscle) can be completely autonomous. There are approximately 639 skeletal muscles in the human body.

The facial muscles are a group of striated muscles innervated by the facial nerve that, among other things control facial expression. These muscles are also called mimetic muscles. Many of the muscles located in the face are small and are attached to (insert into) another small muscle of the facial skin. When the muscles contract, they pull the facial skin in a way; this creates facial expressions.

The Circulatory System

The circulatory systems main function is transportation to help the body to fight infection and stabilise the body temperature and function properly. The blood carries oxygen and nutrients such amino acids and electrolytes to the cells of the body. It carries waste products and carbon dioxide from the cells and tissues for elimination from the body. The blood carries various cells and substances which allow the body to prevent disease and heal injuries. It also transports hormones, the body’s chemical messengers to their target organs to cause a response.

Arteries of the head, face and neck

The common carotid artery is the artery that supplies the head and neck with oxygenated blood: it divides in the neck to form the external and internal carotid arteries which are located on either side of the neck. The internal carotid passes the temporal bone and enters the head, taking the blood to the brain. The external carotid stays outside the skull, and divides into branches:

1.         The occipital branch – supplies the back of the head and scalp

2.         The temporal branch– supplies the sides of the face, the head, the scalp and the skin.

3.         The facial branch – supplies the muscles and the tissues of the face.

The Lymphatic System

The lymphatic system is closely connected to the circulatory system and can be considered as supplementing it. Its primary function is defence: to remove bacteria and foreign materials thus preventing infection. It also drains away excess fluids for elimination from the body. The lymphatic system consists of the lymph fluid, lymph vessels, lymph nodes (glands). You may have experienced swelling of the lymph nodes when you have been ill.

Unlike the circulatory system the lymphatic system has no muscular pump equivalent to the heart. Instead, the lymph moves through the vessels and around the body because of the contractions of the larger muscles during movement. Contractions of the body muscles move the lymph through the one-way valves to the lymph ducts where they are filtered for waste before returning into the circulatory system.

The Skin

The skin is the largest organ in the body, and contains glands, hair and nails. It completely covers the body and is continuous with the mucous membranes which line the body orifices. The skin has a network of blood vessels which help with regulation of body temperature, and a network of sensory nerves, which enable us to sense and feel different textures on the skin.

Functions of the Skin

Sensation      S – determines pain, touch, hot and cold

Heat regulation       H – regulates the body temperature

Absorption   A – absorption of products to maintain supple skin

Protection    P – protects from bacterial invasion and UV rays

Elimination   E – elimination of waste and toxins

Secretion      S – secretion of sebum to lubricate the skin

The Epidermis is composed of 5 layers

1.         The Stratum Corneum is the outermost layer consisting of several layers of flat hardened cells, which are constantly being replaced.  The cells contain a fatty material, which keeps them waterproof and prevents cracking and the entry of bacteria.

2.         The Stratum Lucidum is a clear layer of cells found on the palms of the hands and the soles of the feet but not in other parts of the body.

3.         The Stratum Granulosum can be a single or several layers of cells. The cells are made of keratohyalin, which reflects the light and gives the skin its white appearance.  This layer is where keratinisation begins, which is the change from living cells to dead cells with no nucleus.  The cells dry out and become horny and hard and form the protein keratin.

4.         The Stratum Spinosum or prickle layer has several layers of fibrous cells.  Some melanin is present in this layer.

5.         The Stratum Germinativum is a single row of cells, which produce the epidermis. Mitosis (cell division) takes place here. This layer also produces melanin to protect the skin from sunlight, by darkening and thickening the skin. Melanin is formed from the amino acid tyrosine, which produces melanocytes, which then become melanin.

The epidermis contains no nerve endings or blood vessels and takes about 6 weeks to renew itself completely.

The Dermis or true skin is made up of the following:

1.         Blood Vessels, which have several functions:

1.         Dilating and contracting to control body temperature.

2.         To supply nourishment to the hair, nails etc.

3.         To fight disease (histiocytes and mast cells).

4.         To carry away waste products.

2.         Nerves, which detect pain, changes in temperature, pressure and itching.  There are sensory nerves, which carry messages to the brain and motor nerves, which carry messages from the brain.  Some nerves are both motor and sensory.

3.         Sweat Glands – there are 2 types of sweat glands:

1.         Apocrine:  found in the groin, chest and underarms.  The glands secrete salt water and waste products.  This sweat has no smell when fresh but if left to mix with bacteria and sebum on the skin’s surface it will become odorous.  The apocrine glands are larger than eccrine glands and have a more extensive blood supply.  They open into the hair follicle, just above the sebaceous glands.

2.         Eccrine:  found all over the body and open directly onto the skin’s surface via a coiled duct.  They are more numerous on the palms of the hands and soles of the feet.  They have a liberal nerve and blood supply.  The palms and soles react to emotional stimulus and the forehead and body react to thermal stimulus.

Functions of Sweat

1.         Sweat is excreted onto the skin; it evaporates and helps to cool the body down.

2.         Sweat is an important source for the excretion of waste products.

1.         Connective Tissue:  Elastin and collagen are long fibrous molecules with transverse bands.  They give skin its elastic property.  Collagen is made from cells called fibroblasts and is white.  Elastin is yellow.

2.         Lymphatics:  Lymph is a watery, clear fluid which is derived from plasma.  It aids the body by helping to combat infection.  Lymph nodes are situated all over the body and act as filters for bacteria etc.  Lymph is not pumped round the body but is carried by muscle contraction.

3.         Arrector Pili Muscle:  is attached to the base of the hair follicle and terminates at the epidermis.  When this muscle contracts, it pulls the hair upright and bunches the skin (goose bumps).  This action means that air is trapped between the hairs and helps to insulate the body.  The muscle contracts automatically when the body is cold.

4.         Sebaceous Gland:  Opens into the hair follicle.  It secretes sebum (oil) which lubricates and waterproofs the skin and hair.  Sebaceous glands are found all over the body except for the soles of the feet, palms of the hands, lips and eyes.

5.         Hair Follicles:  These are natural openings in the skin which produce hairs.  They hold the hairs in place and protect them.

The Subcutaneous Layer

This is situated below the dermis and contains fat cells (subcutaneous fat) and connective tissue.

Subcutaneous fat has the following functions:

1.                     Protection of the internal organs

2.                     Insulation against heat loss

3.                     Energy store

The coils of some of the sweat glands, blood vessels and the base of some follicles are also present in the hypodermis.

The Acid Mantle

This is protective acid film over the epidermis, which helps prevent the entry of bacteria.  It is made from a mixture of sweat and sebum on the skin’s surface and has a pH of between 4.5 and 5.5.  pH means the potential hydrogen ions and refers to the pH scale which runs from 0-14.  0-6 if acidic, 7 is neutral and 8-14 is alkali.

It is important therefore to keep the skin acidic. Soap is made from alkalis and should therefore not be used frequently on the skin as it will break down the protective acid mantle.