How to Study the Structure and Function of Human Skin

25 November, 2019

Nurses need to understand the skin and its functions to identify and manage skin problems. This article, the first in a two-part series, looks at the skin’s structure and key functions. This article comes with a self-assessment enabling you to test your knowledge after reading it

Abstract

Skin diseases affect 20-33% of the population at any one time, and around 54% of the UK population will experience a skin condition in a given year. Nurses observe the skin of their patients daily and it is important they understand the skin so they can recognise problems when they arise. This article, the first in a two-part series on the skin, looks at its structure and function.

Citation: Lawton S (2019) Skin 1: the structure and functions of the skin. Nursing Times [online]; 115, 12, 30-33.

Author: Sandra Lawton, Queen’s Nurse and nurse consultant and clinical lead dermatology, The Rotherham NHS Foundation Trust.

• This article has been double-blind peer reviewed
• Scroll down to read the article or download a print-friendly PDF here (if the PDF fails to fully download please try again using a different browser)
• Assess your knowledge and gain CPD evidence by taking the Nursing Times Self-assessment test
• Read part 2 of this series here

Introduction

Skin diseases affect 20-33% of the UK population at any one time (All Parliamentary Group on Skin, 1997) and surveys suggest around 54% of the UK population will experience a skin condition in a given year (Schofield et al, 2009). Nurses will observe the skin daily while caring for patients and it is important they understand it so they can recognise problems when they arise.

The skin and its appendages (nails, hair and certain glands) form the largest organ in the human body, with a surface area of 2m2 (Hughes, 2001). The skin comprises 15% of the total adult body weight; its thickness ranges from PDF, Size 16.00 KB

Skin structure and function

Skin structure and function

The skin is an organ that provides the outer protective wrapping for all the body parts. It is the largest organ in the body. It is a waterproof, airtight and flexible barrier between the environment and internal organs. It keeps the internal environment of our body stable. The skin is divided into 3 layers, the epidermis, the dermis and the subcutaneous layer.

The diagram below shows how the different layers and parts of the skin are arranged.

Image reproduced with permission of Department of Dermatology St Vincent’s Hospital Melbourne

Epidermis

The epidermis is the outer layer of the skin. It is a mosaic of cells glued together and its thickness depends on the location on the body. On the palms and soles the epidermis is thick, flexible and resists mechanical injury. On the eyelids it is very thin and allows maximum movement. The epidermis prevents loss of water and body fluids, resists mechanical and chemical injury and protects against bacteria, viruses and parasite infections. The pigment in the epidermis plays an important role in protecting the skin from ultraviolet radiation.

The hair follicles, sweat glands, sebaceous (oil) glands and apocrine glands develop from the epidermal cells, but their deeper parts extend into the dermis. The glands open onto the surface of the skin via small ducts.

Hair grows from the hair follicle, which is found in all skin except the palms and soles.

Nails are specialised plates of hard keratin that develop from the epidermis overlying the small bones at the ends of the fingers and toes.

There are 3 main groups of cells in the epidermis:

1. Keratinocytes (skin cells)
2. Melanocytes (pigment cells)
3. Langerhans cells (immune cells).

The main cell in the epidermis is the keratinocyte, which develops from the bottom or basal layer and then migrates upwards over a period of about four weeks to the outer surface (stratum corneum) where it is shed.

Langerhans cells are specialised immune cells that are an important part of the body’s immune response to foreign materials and infections.

The melanocytes produce pigment. All humans have the same number of melanocytes. The difference in skin colour occurs because in darker skin melanocytes produce more pigment. The melanin pigment protects the cells of the epidermis and the tissues in the dermis from sun damage. Lighter skinned people are more susceptible to developing sun damaged skin because their melanocytes produce less melanin (skin pigment).

Dermo-epidermal junction

This is a complex region where the dermis and epidermis are attached to each other via specialised cells and molecules. It contains the basement membrane.

Dermis

The dermis lies beneath the epidermis and is 20 to 30 times thicker than the epidermis. It is composed of a dense network of specialised proteins (collagen and elastin) organised into fibres of differing sizes and properties. A complex gel of different proteins surrounds these fibres. All together this is known as the extracellular matrix.

Within the extracellular matrix are blood and lymphatic vessels, nerves, the bottom part of the hair follicles and sweat glands.

Subcutis (subcutaneous layer)

This is a specialised area under the dermis, which contains a network of collagen fibres and fat cells (adipocytes). It protects the body from external trauma and insulates from cold. It acts as a main storage site for fat and therefore energy. There are many blood and lymphatic vessels and nerves passing through the subcutis.

The thickness of the subcutaneous layer varies according to the location on the body and from person to person.

This information has been written by Dr Rashi Minochi and Dr James Choi

Details about the body’s largest organ

Heather L. Brannon, MD, is a family practice physician in Mauldin, South Carolina. She has been in practice for over 20 years.

Casey Gallagher, MD, is board-certified in dermatology and works as a practicing dermatologist and clinical professor.

The skin is the largest organ, and it’s one of the most complicated. It’s ever-changing, and it contains many specialized cells and structures. The skin’s primary function is to serve as a protective barrier that interacts with a sometimes-hostile environment.

It also helps regulate body temperature, gathers sensory information from the surrounding environment, and plays an active role in the immune system to protect the body from disease.

Learning how the skin functions begins with an understanding of the structure of the three layers of skin: the epidermis, the dermis, and subcutaneous tissue.  

The Epidermis

The epidermis is the outermost layer of the three layers of skin. Its thickness depends on where it is located on the body. For example, it’s thinnest on the eyelids (half a millimeter). It’s thickest on the palms of the hands and soles of the feet (1.5 millimeters).

• Stratum basale: This bottom layer, which is also known as the basal cell layer, has column-shaped basal cells that divide and push older cells toward the surface of the skin. As the cells move up through the skin, they flatten and eventually die and shed.
• Stratum spinosum: This layer, which is also known as the squamous cell layer, is the thickest layer of the epidermis. It contains newly formed keratinocytes, which are strengthening proteins. It also contains Langerhans cells that help prevent infection.  
• Stratum granulosum: This layer contains more keratinocytes moving toward the surface.
• Stratum lucidum: This layer exists only on the palms of the hands and soles of the feet.
• Stratum corneum: This is the outermost or top layer of the epidermis. It’s made of dead, flat keratinocytes that shed approximately every two weeks.

The epidermis contains three specialized cells:

• Melanocytes that produce pigment (melanin)
• Langerhans cells that act as the first line of defense in the skin’s immune system
• Merkel cells that have a function that is not yet fully understood.  

The Dermis

The dermis is the middle layer of the three layers of skin. It’s located between the epidermis and the subcutaneous tissue. It contains connective tissue, blood capillaries, oil and sweat glands, nerve endings, and hair follicles.

The dermis is split into two parts—the papillary dermis, which is the thin, upper layer, and the reticular dermis, which is the thick, lower layer.  

The thickness of the dermis varies depending on its location on the body. On the eyelids, it’s 0.6 millimeters thick. On the back, the palms of hands, and the soles of feet it’s 3 millimeters thick.

The dermis is home to three different types of tissues that are present throughout:

• Collagen
• Elastic tissue
• Reticular fibers  

The dermis contains several specialized cells and structures, including:

• Hair follicles
• Sebaceous glands
• Apocrine and endocrine glands
• Blood vessels and nerve endings
• Meissner corpuscles and lamellar corpuscles that transmit the sensations of touch and pressure.  

The Subcutaneous Tissue

Subcutaneous tissue is the deepest and innermost layer of the three layers of skin. It’s mostly made up of fat, connective tissue, and larger blood vessels and nerves.  

The thickness of this layer varies depending on where it’s located on the body—for example, it’s thickest on the buttocks, the soles of the feet, and the palms of the hands.

Subcutaneous tissue is a vital component of body temperature regulation. It also acts as a cushion, so if you ever fall or hit something with your body, it protects your insides and makes the injury hurt less.

The skin is one of the most important organs of a human. It is the outer layer of a person’s body and performs a lot of very important functions for the body.

The skin is divided into three main parts. These parts are as follow:

• The epidermis: This is the protective layer of the skin.
• The dermis: This is a layer that is made up of connective tissues and fibers.
• Subcutaneous fat: This contains fat cells which store fat.

Functions of the skin

Below are the five major functions of the skin:

1. Protects the body: The first function of the skin is give protection to the body tissues. The skin protects the tissues of the body from mechanical damage and from bacteria. It also protects the body from losing too much water through evaporation. Had it not been for our skin, the body will lose water excessively through evaporation.
2. A sense organ: The skin also functions as a sense organ. Thanks to the skin, we are able to detect pain, pleasure, changes in pressure and temperature. This is another very important function of the skin.
3. Excretes waste products: The skin is one of the four major excretory organs of the body. The skin excretes waste products from the body in the form of sweat. In the absence of the skin, these waste products or harmful products will remain in the body and cause great damage to our health. Some of the waste products that the skin excretes from the body include: excess water, mineral salts, and urea.
4. Produces Vitamin D: The skin produces Vitamin D. How does the skin help the body produce Vitamin D? This happens when the skin gets direct contact with sunlight – especially morning sunlight.
5. Regulates temperature in the body: The last but not least function of the skin is the fact that it helps to regulate temperature in the body in order for the body to maintain a constant body temperature.

The above are the major reasons are why the skin is important to us.

, MD, Harvard Medical School

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The skin is the body’s largest organ. It serves many important functions, including

Protecting the body against trauma

Regulating body temperature

Maintaining water and electrolyte balance

Sensing painful and pleasant stimuli

The skin keeps vital chemicals and nutrients in the body while providing a barrier against dangerous substances from entering the body and provides a shield from the harmful effects of ultraviolet radiation emitted by the sun. In addition, skin color, texture, and folds (see Descriptions of Skin Marks, Growths, and Color Changes) help mark people as individuals. Anything that interferes with skin function or causes changes in appearance (see Effects of Aging on the Skin) can have major consequences for physical and mental health.

Many problems that appear on the skin are limited to the skin. Sometimes, however, the skin provides clues to a disorder that affects the entire body. Consequently, doctors often must consider many possible diseases when evaluating skin problems. They may need to order blood tests or other laboratory tests to look for an internal disease in people who come to them with a skin problem (see Diagnosis of Skin Disorders).

Layers of the Skin

The skin has three layers:

Fat layer (also called the subcutaneous layer)

Each layer performs specific tasks.

Getting Under the Skin

The skin has three layers. Beneath the surface of the skin are nerves, nerve endings, glands, hair follicles, and blood vessels.

Epidermis

The epidermis is the relatively thin, tough, outer layer of the skin. Most of the cells in the epidermis are keratinocytes. They originate from cells in the deepest layer of the epidermis called the basal layer. New keratinocytes slowly migrate up toward the surface of the epidermis. Once the keratinocytes reach the skin surface, they are gradually shed and are replaced by newer cells pushed up from below.

The outermost portion of the epidermis, known as the stratum corneum, is relatively waterproof and, when undamaged, prevents most bacteria, viruses, and other foreign substances from entering the body. The epidermis (along with other layers of the skin) also protects the internal organs, muscles, nerves, and blood vessels from injury. In certain areas of the body that require greater protection, such as the palms of the hands and the soles of the feet, the stratum corneum is much thicker.

Scattered throughout the basal layer of the epidermis are cells called melanocytes, which produce the pigment melanin, one of the main contributors to skin color. Melanin’s primary function, however, is to filter out ultraviolet radiation from sunlight (see Overview of Sunlight and Skin Damage), which damages DNA, resulting in numerous harmful effects, including skin cancer.

The epidermis also contains Langerhans cells, which are part of the skin’s immune system. Although these cells help detect foreign substances and defend the body against infection, they also play a role in the development of skin allergies.

Dermis

The dermis, the skin’s next layer, is a thick layer of fibrous and elastic tissue (made mostly of collagen, with a small but important component of elastin) that gives the skin its flexibility and strength. The dermis contains nerve endings, sweat glands and oil glands (sebaceous glands), hair follicles, and blood vessels.

The nerve endings sense pain, touch, pressure, and temperature. Some areas of the skin contain more nerve endings than others. For example, the fingertips and toes contain many nerves and are extremely sensitive to touch.

The sweat glands produce sweat in response to heat and stress. Sweat is composed of water, salt, and other chemicals. As sweat evaporates off the skin, it helps cool the body. Specialized sweat glands in the armpits and the genital region (apocrine sweat glands) secrete a thick, oily sweat that produces a characteristic body odor when the sweat is digested by the skin bacteria in those areas.

The sebaceous glands secrete sebum into hair follicles. Sebum is an oil that keeps the skin moist and soft and acts as a barrier against foreign substances.

The hair follicles produce the various types of hair found throughout the body. Hair not only contributes to a person’s appearance but has a number of important physical roles, including regulating body temperature, providing protection from injury, and enhancing sensation. A portion of the follicle also contains stem cells capable of regrowing damaged epidermis.

The blood vessels of the dermis provide nutrients to the skin and help regulate body temperature. Heat makes the blood vessels enlarge (dilate), allowing large amounts of blood to circulate near the skin surface, where the heat can be released. Cold makes the blood vessels narrow (constrict), retaining the body’s heat.

Over different parts of the body, the number of nerve endings, sweat glands and sebaceous glands, hair follicles, and blood vessels varies. The top of the head, for example, has many hair follicles, whereas the soles of the feet have none.

Fat layer

Below the dermis lies a layer of fat that helps insulate the body from heat and cold, provides protective padding, and serves as an energy storage area. The fat is contained in living cells, called fat cells, held together by fibrous tissue. The fat layer varies in thickness, from a fraction of an inch on the eyelids to several inches on the abdomen and buttocks in some people.

Annual Review of Anthropology

Vol. 33:585-623 (Volume publication date 21 October 2004)
First published online as a Review in Advance on June 21, 2004

Nina G. Jablonski

Department of Anthropology, California Academy of Sciences ,

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Abstract

▪ Abstract Humans skin is the most visible aspect of the human phenotype. It is distinguished mainly by its naked appearance, greatly enhanced abilities to dissipate body heat through sweating, and the great range of genetically determined skin colors present within a single species. Many aspects of the evolution of human skin and skin color can be reconstructed using comparative anatomy, physiology, and genomics. Enhancement of thermal sweating was a key innovation in human evolution that allowed maintenance of homeostasis (including constant brain temperature) during sustained physical activity in hot environments. Dark skin evolved pari passu with the loss of body hair and was the original state for the genus Homo. Melanin pigmentation is adaptive and has been maintained by natural selection. Because of its evolutionary lability, skin color phenotype is useless as a unique marker of genetic identity. In recent prehistory, humans became adept at protecting themselves from the environment through clothing and shelter, thus reducing the scope for the action of natural selection on human skin.

• Contributed by CK-12: Biology Concepts
• Sourced from CK-12 Foundation

How is the human body similar to a well-tuned machine?

Many people have compared the human body to a machine. Think about some common machines, such as drills and washing machines. Each machine consists of many parts, and each part does a specific job, yet all the parts work together to perform an overall function. The human body is like a machine in all these ways. In fact, it may be the most fantastic machine on Earth.

The human machine is organized at different levels, starting with the cell and ending with the entire organism (see Figure below). At each higher level of organization, there is a greater degree of complexity.

The human organism has several levels of organization.

Cells

The most basic parts of the human machine are cells—an amazing 100 trillion of them by the time the average person reaches adulthood! Cells are the basic units of structure and function in the human body, as they are in all living things. Each cell carries out basic life processes that allow the body to survive. Many human cells are specialized in form and function, as shown in Figure below. Each type of cell in the figure plays a specific role. For example, nerve cells have long projections that help them carry electrical messages to other cells. Muscle cells have many mitochondria that provide the energy they need to move the body.

Different types of cells in the human body are specialized for specific jobs. Do you know the functions of any of the cell types shown here?

Tissues

After the cell, the tissue is the next level of organization in the human body. A tissue is a group of connected cells that have a similar function. There are four basic types of human tissues: epithelial, muscle, nervous, and connective tissues. These four tissue types, which are shown in Figure below, make up all the organs of the human body.

The human body consists of these four tissue types.

• Connective tissue is made up of cells that form the body’s structure. Examples include bone and cartilage.
• Epithelial tissue is made up of cells that line inner and outer body surfaces, such as the skin and the lining of the digestive tract. Epithelial tissue protects the body and its internal organs, secretes substances such as hormones, and absorbs substances such as nutrients.
• Muscle tissue is made up of cells that have the unique ability to contract, or become shorter. Muscles attached to bones enable the body to move.
• Nervous tissue is made up of neurons, or nerve cells, that carry electrical messages. Nervous tissue makes up the brain and the nerves that connect the brain to all parts of the body.

Organs and Organ Systems

After tissues, organs are the next level of organization of the human body. An organ is a structure that consists of two or more types of tissues that work together to do the same job. Examples of human organs include the brain, heart, lungs, skin, and kidneys. Human organs are organized into organ systems, many of which are shown in Figure below. An organ system is a group of organs that work together to carry out a complex overall function. Each organ of the system does part of the larger job.

Many of the organ systems that make up the human body are represented here. What is the overall function of each organ system?

Your body’s 12 organ systems are shown below (Table below). Your organ systems do not work alone in your body. They must all be able to work together. For example, one of the most important functions of organ systems is to provide cells with oxygen and nutrients and to remove toxic waste products such as carbon dioxide. A number of organ systems, including the cardiovascular and respiratory systems, all work together to do this.

Female: uterus; vagina; fallopian tubes; ovaries

Male: penis; testes; seminal vesicles

Summary

• The human body is organized at different levels, starting with the cell.
• Cells are organized into tissues, and tissues form organs.
• Organs are organized into organ systems such as the skeletal and muscular systems.

Review

1. What are the levels of organization of the human body?
2. Which type of tissue covers the surface of the body?
3. What are the functions of the skeletal system?
4. Which organ system supports the body and allows it to move?
5. Explain how form and function are related in human cells. Include examples.
6. Compare and contrast epithelial and muscle tissues.

Anatomy is the study of the structure of living organisms. This subdiscipline of biology can be further categorized into the study of large-scale anatomical structures (gross anatomy) and the study of microscopic anatomical structures (microscopic anatomy.)

Human anatomy deals with anatomical structures of the human body, including cells, tissues, organs, and organ systems. Anatomy is always linked to physiology, the study of how biological processes function in living organisms. Therefore it is not enough to be able to identify a structure, its function must also be understood.

Why Study Anatomy?

The study of human anatomy provides a better understanding of the structures of the body and how they work.

Your goal in a basic anatomy course should be to learn and understand the structures and functions of the major body systems. Remember that organ systems don’t just exist as individual units. Each system depends on the others, either directly or indirectly, to keep the body functioning normally.

It is also important to identify the major cells, tissues, and organs and know how they function.

Make the Most of Study Time

Studying anatomy involves lots of memorization. For instance, the human body contains 206 bones and over 600 muscles. Learning these structures requires time, effort, and good memorization skills.

Perhaps you can find a study partner or group that will make it easier. Be sure to take clear notes and ask questions in class about anything you are unclear on.

Know the Language

Using standard anatomical terminology ensures that anatomists have a common method of communicating to avoid confusion when identifying structures.

Knowing anatomical directional terms and body planes, for instance, enables you to describe the locations of structures in relation to other structures or locations in the body. Learning the common prefixes and suffixes used in anatomy and biology is also helpful.

If you are studying the brachiocephalic artery, you can figure out its function by knowing the affixes in the name. The affix brachio- refers to the upper arm and cephal refers to the head.

If you have memorized that an artery is a blood vessel that carries blood away from the heart, you can determine that the brachiocephalic artery is a blood vessel that carries blood from the heart to the head and arm regions of the body.

Use Study Aids

Believe it or not, anatomy coloring books are one of the best study aids to learn and memorize structures and their location. The Anatomy Coloring Book is a popular choice, but other coloring books work as well.

Anatomy flashcards, like Netter’s Anatomy Flash Cards and Mosby’s Anatomy & Physiology Study and Review Cards are recommended as well. Flashcards are valuable for reviewing information and are not meant to be a substitute for anatomy texts.

Acquiring a good complementary text, such as Netter’s Atlas of Human Anatomy, is a must for higher-level anatomy courses and those interested in or already attending medical school. These resources provide detailed illustrations and pictures of various anatomical structures.

Review, Review, Review

To really make sure you comprehend the material, you must constantly review what you have learned. It is vital that you attend any and all anatomy review sessions given by your instructor.

Be sure to always take practice quizzes before taking any test or quiz. Get together with a study group and quiz each other on the material. If you are taking an anatomy course with a lab, be sure that you prepare for what you are going to be studying before lab class.

Stay Ahead

The main thing you want to avoid is falling behind. With the volume of information covered in most anatomy courses, it is important that you stay ahead and know what you need to know before you need to know it.

Know the Body

Organisms, including humans, are arranged in a hierarchical structure.

Tissues

Cells compose tissues of the body, which can be categorized into four primary types.

• epithelial tissue
• muscle tissue
• connective tissue
• nervous tissue

Organs

Tissues in turn form organs of the body. Examples of body organs include

• brain
• heart
• kidneys
• lungs
• liver
• pancreas
• thymus
• thyroid

Organ Systems

Organ systems are formed from groups of organs and tissues working in conjunction to perform necessary functions for the survival of the organism.

Introduction:

The most important and perhaps the most complex organ of human body is the brain. It controls all senses and functions of the body. Human brain weighs about 3 lbs. and is enclosed in a hard bony shell for protection, called skull. Interpreting information collected from different parts of the body and preparing the body for the generation of an appropriate response are some of the physiological tasks of the brain. Cerebrum, cerebellum, diencephalon and brainstem are the primary brain divisions.

For centuries, researchers and scientists have been trying their best to thoroughly explore the human brain structure, but until recently they have been unable to examine it completely and think it something very hard to accomplish. In fact, many of its functions still remain least understood, such as thinking.

This fact sheet is an introduction to the basic structure and functions of human brain.

Human Brain Structure and Functions:

Based on their placement in the front, middle or back areas of skull, the human brain can be divided into three major parts, namely, forebrain, midbrain and hindbrain. These broad divisions are comprised of different smaller divisions, with each having a specific role to play. It oft happens that different parts share responsibility for the completion of the same task. In this way, the overall job of the brain is done in a beautiful manner. In case of a disorder or malfunctioning of any of the structures, the diagnosis is usually a very complex and demanding task. So, you should take special care of this organ. A knowledge of the structure and function of various brain divisions will help you in this regard.

Forebrain – Center for Processing Sensory Information:

The forebrain is considered as the most important part of brain because, on account of its functioning, it distinguishes human from other animals. This part is responsible for processing sensory information, collected by different sensory organs, such as eyes, nose, ears, tongue and skin. It is further divided into two parts, namely, diencephalon and telencephalon. The diencephalon contains thalamus and hypothalamus which control sensory and autonomic processes. Telencephalon contains the biggest part of brain, called cerebrum.

Midbrain – Mediating between Hindbrain and Forebrain:

The midbrain acts as a bridge to transmit signals from hindbrain and forebrain. These signals mostly come from the senses of touch and hearing, collected by the specialized organs, i.e. skin and ears, respectively. The upper part of the midbrain is called optic tectum, which serves to integrate visionary and auditory data.

Hindbrain – Control Center for Visceral Functions:

The hindbrain can be further divided into 3 parts: medulla oblongata, pons and cerebellum. The main function of this human brain structure is to control certain visceral functions in body (including heart rate, breathing and blood pressure). Looking at the tasks assigned to pons, it serves to monitor the sleep and waking up functions while working in coordination with other parts of the nervous system. The cerebellum co-ordinates the movements of arms and legs and also plays a role in processing the sensory information that it receives from visual and auditory systems.

Other Brain Divisions and Their Functions:

Apart from the basic divisions of forebrain, midbrain and hindbrain, the master organ of your body can also be divided along other dimensions. Here follows a precise description of some structurally and functionally important parts of the brain.

The Cortex – Regulation of Voluntary Movements:

Also known as the cerebral cortex, it is the outermost layer of the neural tissues in the cerebrum. The medial longitudinal fissure divides the cortex into two major components, that is, right cerebral hemisphere and left cerebral hemisphere. On the basis of function, it is said to be comprised of motor areas, sensory areas and association areas. Located in both the hemispheres of the cortex, the motor areas are concerned with the regulation of voluntary movements. The right side of your body is controlled by the left half of this area and vice versa. As the name indicates, the sensory areas are associated with the processing of data received from the senses. The primary function of the association areas, on the other hand, is to assist abstract thinking and language. They also help you in producing a meaningful perceptual experience of the world around you.

Brainstem – Regulation of Sleep & Breathing:

Comprised of hindbrain, medulla and pons, the brainstem is the posterior most part of the brain that extends backward to join the spinal cord. This small structure carries much importance in the brain as it provides passage for the nerve connections of sensory and motor systems. The basic functions of brainstem include the control of sleep and breathing.

Lobes of Brain:

The human brain structure can also be divided into several different types of lobes, including parietal, occipital, frontal and temporal lobes. The management of body position, handwriting and sensation falls under the domain of parietal lobes. The occipital lobes house the visual processing system of the brain. The motor function, judgement and problem solving is accomplished in the frontal lobes. The temporal lobes of the brain are associated with the processing of memory and hearing.

The Anatomy and Physiology of the Subcutaneous Layer of the Skin

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William Truswell, MD, is board-certified in otolaryngology and facial plastic and reconstructive surgery. He is president of the American Board of Facial Plastic and Reconstructive Surgery.

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What is the hypodermis or subcutaneous layer of the skin? What type of tissue is this (anatomy and structure) and what is its purpose (physiology or function)? How is this layer important in aging, and what medical conditions affect the hypodermis? What plastic surgery procedures are done on this layer to reduce the signs of aging?

Overview

The hypodermis is the innermost (or deepest) and thickest layer of skin. It is also known as the subcutaneous layer or subcutaneous tissue.

The layers of the skin include the epidermis (the outermost layer), the dermis (the next layer which is loaded with blood vessels and nerves), and then the hypodermis.  

Anatomy and Structure

The hypodermis contains the cells known as fibroblasts, adipose tissue (fat cells), connective tissue, larger nerves and blood vessels, and macrophages, cells which are part of the immune system and help keep your body free of intruders.

The thickness of the hypodermis varies in different regions of the body and can vary considerably between different people. In fact, the thickness of the hypodermis plays an important role in distinguishing between males and females. In men, the hypodermis is thickest in the abdomen and shoulders, whereas in women it is thickest in the hips, thighs, and buttocks.  

Function (Physiology)

The hypodermis may at first be viewed as tissue which is used primarily for the storage of fat, but it has other important functions as well. These functions include:

• Storing fat (energy storage)
• Protection (think buttocks and sitting on a hard chair)
• Attaching the upper skin layers (dermis and epidermis) to underlying tissues such as your bones and cartilage, and supporting the structures within this layer such as nerves and blood vessels
• Body temperature regulation: This layer functions as an insulator, offering protection against the cold, and protects the body against heat as well through sweating.
• Hormone production: The hormone leptin is secreted by fat cells to tell the body it is time to stop eating.  

Conditions Which Affect the Hypodermis

There are several medical disorders and medical procedures which are related to this unique layer of the skin:

Hypothermia and Overheating: The thinning of the hypodermis with age is one of the reasons that older people are more prone to hypothermia. If you are ordinarily hot, this news is not necessarily so good. The thinning of the hypodermis also may mean that you sweat less, and a lack of sweating is important in conditions such as heat exhaustion and heatstroke.  

Injections: While many medications are given intravenously, some are injected into the hypodermis (subcutaneous layer). Examples of medications which may be given by subcutaneous (subQ) injection include epinephrine for allergic reactions, some vaccinations, insulin, some fertility drugs, some chemotherapy medications, growth hormone, and anti-arthritis drugs such as Enbrel. Medications given by subcutaneous injections are absorbed more slowly than drugs given by intravenous injection, making subQ injections an ideal route for many drugs.  

Obesity: Excess body fat is located in the hypodermis, a layer that has received a lot of attention in recent years due to the growing rate of obesity, and the thought that not all body fat is equal, at least with respect to the role it may play in metabolic syndrome and heart disease.  

The Hypodermis and Aging

While the hypodermis is not visible, it can have a dramatic effect on the appearance of the skin and the way aging impacts the skin, specifically in the area of the face and neck. With aging, the volume of facial fat decreases and there is less supportive tissue to support the normal turgor and elasticity of the skin. The facial skin begins to droop and sag resulting in a look that can be interpreted as appearing tired. The bones and muscles of the face also lose volume.  

Hyaluronic Acid Fillers for Aging

To correct the loss of facial volume and counteract the effects of aging, hyaluronic acid fillers, used specifically for volume replacement, can be injected.   Hyaluronic acid is compatible with the body and may be a good choice for facial filler. It is found naturally in the body with high concentrations in soft connective tissue and the fluid that surrounds the eyes. It is also found in cartilage and joint fluids.  

An injection of hyaluronic acid filler will support facial structures and tissues that have lost volume and elasticity. It acts as a volumizer by bringing water to the surface of the skin, making it look more supple and fresh. It plumps and lifts cheeks, jawlines, and temples. The filler can also fill out thin lips and plump hands that have begun to sag.

While side effects are rare, there are risks to injections of hyaluronic acid. There is a risk of allergic reactions, and of course, the cosmetic result may not be what you had hoped.  

Bottom Line on the Hypodermis

While many people think of the hypodermis as simply a layer of the skin which stores fat, it is also very important in maintaining body temperature and other functions.  

1. Introduction

• Structure refers to something’s form, makeup or arrangement.
• Function refers to something’s job, role, task, or responsibility.
• Determine means to cause, direct, govern.

In biology, a key idea is that structure determines function. In other words, the way something is arranged enables it to play its role, fulfill its job, within an organism (a living thing). Structure-function relationships arise through the process of natural selection. But before explaining how that process works, let’s get our heads around the structure-function connection.

Structure determines function is also a key idea in engineering. In this human realm, structure/function relationships are often more obvious and easier to grasp than they are in the biological realm. Let’s use a hammer as an example:

Hammer

Function: This tool has two functions. Pounding nails in, and pulling them out.

Structure to Function Relationship:

The handle allows the tool to be easily grasped. The length of the handle allows for a swing that increases the speed of the head of the hammer. The head is composed of hard metal. When the head hits the nail, the metal transmits the force of the swinging hammer into the nail, driving it into the wood .

The claw allows the user to grab a nail. The rounded head acts as the fulcrum of a lever. The long handle allows for leverage to pull the nail out of the wood.

2. Apply the idea: Human Artifacts

[qwiz style = “width: 528px; min-height:0px; border: 3px solid black; ” qrecord_id=”sciencemusicvideosMeister1961-structure and function quiz 1 (artifacts)”]

[h]Application: Structure and Function in Human Artifacts
[q]Describe the function of the tool shown below, and explain how the structure relates to the function.

[c*] show the answer

[f] ANSWER (adapted from Wikipedia)

Function: needle-nose pliers are both cutting and holding pliers, used to bend, re-position and cut wire.

Structure to function relationship: The long nose gives fine control while the cutting edge near the pliers’ joint provides leverage for cutting wires. Because of their long shape they are useful for reaching into small areas, unreachable with fingers or other tools.

[q] Describe the function of this tool , and explain how the structure relates to the function.

[c*] show the answer

Function: A hand saw is used to cut wood.

Structure to function relationship: The wooden handle allows the user to firmly grasp the tool. The length allows for a long stoke. The sharp teeth are harder than the wood that the saw is cutting through.

[q]D escribe the function of this tool , and explain how the structure relates to the function.

[c*] show the answer

Function: A wrench is used to turn nuts and bolts.

Structure to function relationship: The ends are shaped to fit nuts and bolts of specific sizes. The angle allows for easy movement in enclosed spaces. The long handle enables the user to generate considerable force, which is used to turn the nut or bolt.

3. Structure and Function in Biology

Biological structures come about as a species adapts to its environment. The result is an adaptation: a trait that helps the members of a species to survive and reproduce. Adaptation comes about through evolution, which we’ll study later in this course. But for now, let’s look at some structure function relationships in living things.

3a. Structure and function in the human hand

Function: The human hand has many functions, but we’ll focus just on two: grasping things for fine control (such as a pencil), and grabbing objects for power (as in the example of the hammer above).

Structure to function relationship: the opposable thumb (the ability to touch the thumb to the fingers) makes fine control possible. The ability to touch the fingers to the base of the hand and to wrap the thumb on top makes the power grip possible.

3b. Structure and function in human teeth

Function: The overall function is tearing and grinding food down into tiny pieces that can be easily swallowed, and later absorbed into the body.

Structure to function relationship: The sharp incisors (the teeth in front) can tear food; while the molars (the flat teeth in back) can grind food into tiny pieces. The molars are also closest to the hinge of the jaw, so that’s where chewing can occur with the most force (especially useful for grinding up harder-to-digest plant foods).

3c. Structure and function in biology

[qwiz style = “width: 528px; min-height:0px; border: 3px solid black; ” qrecord_id=”sciencemusicvideosMeister1961-structure and function 2 (biology)”]

[h]Application: Structure and Function in Biology

[q]D escribe the function of the adaptation below, and describe how the structure is related to the function (note: focus on the wings).

[c*] show the answer

Function: Flight

Structure to function relationship: Between each of the bat’s fingers there’s a flat, thin, flap of skin. The skin provides lift as the bat flaps its wings, enabling the bat to fly.

[q]D escribe the function of the adaptation below, and describe how the structure is related to the function (note: focus on the ears)

[c*] show the answer

Function: Echolocation (locating objects though echoes). Bats can “see” with sound. They emit high frequency squeaks, which bounce off objects and back into the bat’s ears. The bat’s brain can turn the sound into the equivalent of an image, and use that image to track and catch flying prey (such as moths).

Structure to function relationship: The huge ears catch the echoes of the bat’s squeaks, and direct the sound to the inner ear.

[q]D escribe the function of the adaptation below, and describe how the structure is related to the function.

[c*] show the answer

Function: Grasping Prey, Perching on branches

Structure to function relationship: The powerful fingers and sharp claws enable these talons to firmly grasp and carry prey; or allow the bird to grasp the branches it perches upon.

[q]D escribe the function of the adaptation below, and describe how the structure is related to the function.

[c*] show the answer

Function: Swimming

Structure to function relationship: The webbing between the toes acts as a fin, enabling the duck to efficiently kick in the water, moving it forward.

4. Next steps

If you need more practice, please scroll up to the top and work through this tutorial again. Otherwise, follow the links below:

• Levels of Biological Organization (the last tutorial in this series)
• Biology Key Concepts main menu