The word ‘anatomy’ derives from the Greek term ‘anatome’ which means ‘cutting apart’. However, anatomy is a broad subject which encapsulates many scientific components of life thus it is an ever developing science (Patton et al, 2007). Human anatomy is the subdiscipline of biology which focuses on the internal structures of the human body including cells, tissues, organs and organ systems. Physiology, on the other hand studies the function of each structure individually and in combination with other structures. Therefore, it could be said that anatomy and physiology are intertwined because in order to fully understand the biological processes in living organisms, it is imperative to identify the structure in order to understand the function (Clark, 2005). This report will discuss the relationship between the various internal systems in the human body and analyse the function of the heart organ.
The hierarchy between different cells, tissue, organs and systems.
Defining a living thing is a hard concept, as is defining the idea of ‘life’ itself. Living things include animals and plants, as well as the invisible world of bacteria and viruses (Bailey, 2014). However, there is a consensual agreement into the main characteristics that differentiate a living thing from a non-living thing. As such, it is a generally accepted view that a thing is alive if it exhibits or is capable if exhibiting the seven characteristics of life (Beckett, 1986). These include movement, reproduction, growth, and response to stimuli, exchange of gases, excretion and nutrition. The human body possesses all 7 characteristics as such; organisms are very complex and unique (Solomon, 2008).
Therefore, it could be said that life is ordered and organisms are essentially determined by the complex hierarchal structure, increasing in complexity from its basis in atoms to molecules and then in sequence to organelles, cells, tissue, organs, organ system and to a functioning organism (Russell et al, 2008) (See Fig.1). Cells are considered the basic building blocks of all living things. They provide structure for the body and serve specific functions within the body for example, blood cells transport materials around the body and protect against disease (Solomon et al, 2010). Cells have diverse parts, most commonly referred to as organelles and have specialised structures that perform certain tasks within a cell. However, as with any living mechanism there are defects and any structural defects in cells can contribute to pathological abnormality (Solomon et al, 2010) (See Fig. 2).
During the process of growth within a multi-cellular organism, cells differentiate into specialised cells in order to perform different functions. Thus, cells associate to form tissue, which is a group or masses of specialised cells that perform common functions (Bitesize, 2014). For instance, the nervous tissue is specialised to react to stimuli and conduct impulses to various organs in the body which in turn bring about a response to the stimulus (Solomon, 2008). Within the human body there are four primary types of tissues which include the epithelial, connective, muscle and nervous tissue (See Fig. 3). Each tissue has a key role within the human body which helps the body function properly and maintain an equilibrium state (Russell et al, 2008).
In most multi-cellular organisms tissues organise to form functional structures called organs, which include the heart, brain, skin etc. Multiplex functions emerge from the organ level as each individual organ performs functions that none of the component tissues can perform alone. For instance, the heart and blood vessels work together by circulating blood throughout the body to provide oxygen and nutrients to cells (Bobick et al, 2004).
Organs that work in union for a common purpose compose an organ system. The human body is a complex series of numerous organ systems (Patton, 2010). The main systems of the human body are the circulatory, digestive, endocrine, excretory, immune, muscular, nervous, respiratory, skeletal and integumentary systems (See Fig. 4). All these systems work in unison and harmony and are vital for survival and well-being and if any function of one the systems cease to work the body will not perform properly (Beckett, 1986).
What is epithelial tissue and its function and where it can be found
The epithelial tissue or ‘epithelial’ consists of tightly packed sheets of cells which are joined with little space between them (See Fig. 5). This close contact can either be in a single layer or multiple layers however; the structure of lining epithelium differs from organ to organ depending on its location and function (Bailey, 2004). For example, epithelium that covers the outer surfaces of the body and serves as a protective layer is different from the epithelium that lines the internal organs (See Fig. 6). Epithelial tissues specialise in covering the body’s external and internal surfaces, line cavities, form various organs and glands and line their ducts (Tortora et al, 2007). Therefore, the key characteristics of epithelial tissue are protection, secretion, absorption and excretion.
Classification of Epithelium
Epithelium is classified according to the number of cell layers and the morphology of the surface cells (KUMC, 1996). The text below details some the several different types of epithelial cells that can be located around the body.
Simple Epithelia: An epithelium with a single layer of cells
Squamous: Cell is thin and flat, in fact it is the thinnest of all epithelial cell types. It can be found in the lungs (alveoli’s) and functions as a mediator of filtration and diffusion (See Fig. 7).
Cuboidal: Roughly square or cuboidal in shape and is found in glands, lining of kidney and within the ducts of glands. Provide a layer of protection from abrasion, secretion of hormones and absorption (See Fig. 8).
Columnar: Longer and wide and connected by tight junctions, the main function of this cell is protection. They also secrete gastric juices and enzymes and microvilli absorb digestive end products (See Fig. 9).
Ciliated: Rectangular in shape and have between 200-300 hair-like protrusions (cilia).Found mainly in trachea, bronchial regions and fallopian tubes. Sweep and propel matter to help in prevention of infection (See Fig. 10)
Stratified Epithelia: Numerous Cell Layers
Squamous: Flat-scale like, found in lining of oesophagus and provide protection from stomach acid and external sources (See Fig. 11).
Columnar: Often found between simple columnar and stratified squamous epithelium. Provide secretion and protection i.e. salivary glands (See Fig. 12).
Cuboidal: This type of tissue is relatively rare in the human body. The cells are cube-shaped and provide protection of larger ducts, cell layers surround and protect gland ducts i.e. salivary glands, sweat glands etc. (See Fig. 13).
Transitional: Are flexible and alternate between relaxed (cuboidal shaped) and tense (squamous shaped) shapes i.e. urinary bladder, specialised to expand as bladder fills, also prevents urine from diffusing back to internal cavity (See Fig. 14).
Pseudo Stratified Epithelium: Falsely-stratified single layer of epithelial
Pseudo Stratified Columnar: Cells appear layered due to positions of nuclei within the row of cells, but are not truly layered. Produce mucus, trap and move dust and other toxins out of the lungs (See Fig. 15).
Pseudo Stratified Columnar Ciliated: Small hair like projections embedded in the membrane and help sweep debris that could harm the underlying tissues or structures i.e. trachea, nasal cavity and bronchi (See Fig. 16).
Explain the types of muscle tissue
All movement through the body is created and stopped by muscles. Muscle tissue contracts in response to stimuli; this contraction lengthens the muscle to create movement (Jones and Bartlett Learning, no date). The tissues of the body are interdependent for instance; muscle tissue cannot generate movement unless it receives oxygen which is carried by red blood cells. Muscle contains three main connective tissue sheets these are called endomysium, perimysium and epimysium, which transmit energy from the contracting muscle to the tendon (Siegfried, 2002).
There are three types of muscle tissue; skeletal, smooth and cardiac (Bobick et al, 2004). Skeletal muscle forms the muscles that are attached to the bones, when it contracts the muscles move the joints that they are attached to. For example, when the legs are flexed and extending during walking. In addition, when the skeletal muscle contracts it generates heat, thus helps maintain body temperature (Solomon, 2008) (See Fig. 17)
Smooth muscle is the component of the walls of many tubes within the body such as the tubes found in the digestive system, blood vessels and bladder. By contracting it propels the contents along the tube it surrounds and regulates the fluid flowing through it (Bobick et al, 2004) (See Fig. 18). The cardiac muscle forms the structure of the heart; by contracting it squeezes the blood out of the heart into the blood vessels and vice versa (See Fig.19). The cardiac muscle and smooth muscle are similar in performance as they work on involuntary impulse (Russell, 2008)
Function of the Heart
The cardiovascular system is a complex system that consists of the heart, blood, blood vessels, capillaries and veins (Tortora et al, 2007). This system allows nutrients such as amino acids, electrolytes, hormones, dissolved gases and blood cells to circulate throughout the body. These all aid in the process of fighting disease, stabilising core body temperature and most importantly maintaining homeostasis (Siegfried, 2002).
The walls of the heart consist mainly of the cardiac muscle, which is a special type of muscle that is only found in the heart. The heart is unique in structure and function, unlike other muscles it never suffers from fatigue (Solomon, 2008). The heart comprises of cardiac muscle which uses the reserve energy of mitochondria, which uses the energy taken in from food to provide energy for the muscle. With such an enormous amount of energy generated, the cardiac muscle in its normal and healthy state never rests because as energy is transferred to the muscle more energy is obtained from calorie intake, thus the process is continuous (Patton et al, 2010). Nevertheless, the heart does not tolerate lack of oxygen or nutrients and soon dies if its supply of blood is cut off.
The three layers comprising the wall of the heart are the outer pericardium, middle myocardium and inner endocardium. The pericardium consists of connective tissue and adipose tissue, which protect the heart by reducing friction (Tortora et al, 2007). The thick myocardium is mostly made up of cardiac muscle tissue which is nourished by blood capillaries, lymph capillaries and nerve fibres. The tissue in particular helps pump blood out of the chambers of the heart (Beckett, 1986). The endocardium is made up of epithelium tissue and connective tissue which has many elastic collagenous fibres and specialised cardiac muscle fibres. The cardiac muscle fibres are shorter and thinner than skeletal muscle, this structure is essential as these muscle fibres continuously contract involuntarily. The cardiac muscle fibres feature a nucleus in the centre of each individual fibre. These fibres are tubes branch out and attach to neighbouring cardiac muscles. Such networking of interconnected fibres form strong muscle tissue that will be able to contract in synchrony (Solomon, 2008).
(See Fig. 20)
In summary, it is quite obvious that the human body is one of nature’s greatest achievements. The smallest elements of human life are constructed from the tiniest of molecules to the most complex structures of, cells, tissue, organs and organ systems. Most importantly it is evident each function from the various systems in the body is dependent on the function of another. Therefore in order for the body to function properly and achieve health and wellbeing; all anatomical structures have to work in union to achieve homeostasis (Jones and Bartlett Learning, no date).