Human Anatomy/Printable version

Human Anatomy

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What is anatomy?

In its broadest sense, anatomy is the study of the structure of an object, in this case the human body. Human anatomy deals with the way the parts of humans, from molecules to bones, interact to form a functional unit. The study of anatomy is distinct from the study of physiology, although the two are often paired. While anatomy deals with the structure of an organism, physiology deals with the way the parts function together. For example, an anatomist may study the types of cells in the cardiac conduction system and how those cells are connected, while a physiologist would look at why and how the heart beats. Thus, anatomy and physiology are separate, but complementary, studies of how an organism works.

History

A complete article on the history of anatomy can be found here.

Terminology and Organization

Anatomy is "the science of the structure of living organisms" so human anatomy is the science of the structure of the human body. This wikibook will hopefully give you a good understanding of what your body is made of and of how it develops. Strictly speaking, how the body functions is physiology. Despite this fact, it is almost impossible to explain anatomy without going into some physiology and vice versa so some physiological concepts will be introduced in this book.

There are two types of anatomy: gross, or macroscopic, and microscopic. Gross anatomy deals with things that can be viewed by the unaided eye. Microscopic anatomy is the study of structures on the cellular level. There are, in turn, 3 fields of study within the topic of gross anatomy. These are surface anatomy, the study of external anatomical forms and markings; regional anatomy, which focuses on a certain region of the body (both internal and external); and systemic anatomy, which focuses on a given organ system. Within microscopic anatomy, there are two topics of study which are of great importance: cytology, the study of cells; and histology, the study of tissue.

Standard Anatomical Position

For positional terminology to make sense, a standard anatomical position has to be established. In human anatomy, the standard anatomical position is supine (lying down face up). The legs are straight and together, or slightly separated. The arms are straight out along the torso with the palms of the hands upward. The arms are separated slightly from the torso. The thumbs point away from the body.

Terminology

Diagram of Anatomical Terms

In order to talk about anatomy, some terms need to be understood. The terms can be divided into positional terms and descriptive terms. Positional terms help in locating structures by giving precise descriptions of relations (which eliminates the need to specify in what position the subject is). An easy example is superior, which means above or on top of when the subject is upright: The human head is superior to the torso. It cannot be said that the head is above the torso if the person is lying down. Descriptive terms can give varied information.

Descriptions of General Position

Superior and Inferior

The terms superior and inferior are used when referring to parts of the body which are toward an end of the body. Superior meaning toward the head and inferior meaning toward the feet. Toward an end does not necessarily mean close to the end. For example, the bowels are inferior to the lungs. This does not mean that the bowels are close to the feet nor does it mean the converse (that the lungs are close to the head). It simply means that the lungs are closer to the head than the bowels. Cranial and caudal have the same meaning as superior and inferior, respectively, but are used in reference to animal, rather than human, anatomy.

Anterior and Posterior

Anterior refers to the side of the body facing up in the standard anatomical position. Posterior refers to the bottom side. Like superior and inferior, these do not necessarily mean that the parts they are describing are close to the front or back of the body, they simply explain relative positions. Dorsal and ventral are sometimes used in place of anterior and posterior, respectively. These are mostly used with animal anatomy, but can be used in human anatomy as long as they are describing the side of an appendage.

Lateral and Medial

Lateral is a word used to describe anything which is closer to the outside (toward the arms, in the standard anatomical position) while medial is used to describe anything toward the center of the body.

Superficial and Deep

Superficial is a used to describe structures that are closer to the exterior surface of the body. Deep refers to structures closer to the center of the body region. For example, skin is superficial to bones, and bones are deep to skin.

Proximal and Distal

Proximal and distal are terms that describe one point relative to another. Proximal refers to a point closer to the reference point while distal refers to a point farther away. For example, the metacarpals are distal to the carpus.

Dorsal and Ventral

Dorsal refers to a structure closer to the back of an organism while ventral refers to a point closer to the abdomen; these descriptors are generally used in animal anatomy in place of posterior and anterior, respectively.

Other Directional Terms

Ipsilateral and Contralateral

Ipsilateral refers to two parts that are on the same side of a given reference point. For example, it could be said that the left arm and left leg are ipsilateral to one another with respect to the midsagittal plane. Contralateral is the inverse; the left arm and right leg are contralateral to one another with respect to the midsagittal plane.

Axial and Abaxial

Axial refers to a point close to the midsagittal plane while abaxial refers to a point farther away from the midsagittal plane.

Intermediate

Between two points. For example, the knee is intermediate between the gluteal and the foot.

Visceral

The term visceral refers to any system or point that contacts organs. For example, the visceral peritoneum is in direct contact with the abdominal organs.

Parietal

Conversely, parietal refers to the outer membrane of a system. For example, the parietal pericardium lines the pericardial cavity.

The Skeletal System

The skeletal system is composed of bones, cartilage, and ligaments. It supports muscles in order to enable movement, protects internal organs, produces red blood cells, and stores minerals such as calcium and phosphate.

Osteology

Front view of a skeleton of an adult human

Back view of a skeleton of an adult human

Structure

The Axial Skeleton

• Skull
• Vertebral Column
• Thorax

The Appendicular Skeleton

• Upper Extremities
• Lower Extremities

Gross Anatomy

posterior muscle view

'abs'

Arm muscles front superficial

Sartorius muscle

Arm muscles front superficial

Leg muscles

Gluteus maximus muscle

Arm muscles front deep

Serratus anterior

Extensor pollicis longus muscle

microscopic human muscle structure

The Heart

Angiology

The circulatory system in man.

Angiology is the medical specialty which studies the diseases of circulatory system and of the lymphatic system, i.e., arteries, veins and lymphatic vases, and its diseases.

Angiology/Arteries

Arteries are by definition vessels carrying blood from the heart to other organs.

Arteries have three layers - the tunica interna (intima), tunica media, and tunica externa.

Angiology/Veins

Veins are by definition vessels that bring back to the heart, either from the capillaries within the systemic circuit or from the capillaries in the lungs (pulmonary circuit). Veins consist of three layers; the tunica adventitia (or tunica externa) is the outer layer, the tunica media is the middle layer, and the tunica intima is the inner layer. Large veins such as those in the legs contain bicuspid (two leaflets) valves that prevent the back flow of blood. The valves increase in number the further away from the heart.

Angiology/Lymphatic System

< Human Anatomy

The lymphatic system includes lymph nodes, lymph vessels, and lymph. The lymph contains many lymphocytes, which are a type of leukocyte, white blood cell, or immune cell. The lymphatic system contributes greatly to ridding an organism of foreign invasion. The invader can be bacteria, viruses, parasites, fungi, or toxins. If an invasion gets out of control, it can lead to an infection, which the lymphatic system then plays a roll in subduing.

The lymph nodes will swell when combating an infection, often being one of the confirming signs of illness in the same time of the lateral due to a foreign organism.

Lymph drains through the lymph system in the direction of venous blood flow (towards the heart). It is pumped by the gross muscular movement of the body as it squeezes the intercellular spaces where the lymph moves.

People who have had cancerous tissue removed will often have lymph nodes removed as well to check for spreading of the cancer. After such removal the person must be careful to avoid injury to the body along that route of lymph as the immune response to infection is impaired (e.g. a mastectomy on the left side with removal of lymph nodes means that arm needs to be treated with caution).

The Neuron

The neuron

The Neuron is a fundamental unit in the brain and a specialized cell intended to transmit information to muscle, gland cells and other nerve cells. Depending on the species, the brain could contain anywhere between 1 billion and 100 billion neurons. A neuron consists of dendrites, an axon, a cell body and synaptic terminals. Axons transmit information from the neuron on to other neurons to which it is interconnected. To speed up the transmission of electrical signals along the axon, many axons are covered in a myelin sheath. Dendrites receive information transmitted by the axons of other neurons. Both axons and dendrites partake in specialized contact points called synapses.

There are 3 main kinds of neurons. Motor neurons control the activity of muscles and are in control of all forms of behavior. Sensory neurons are entwined with receptors to detect and also respond to changing attributes of the internal and external environment. For example receptors sensitive to changes in light would subserve the modality of vision, and so on. Interneurons not only arbitrate simple reflexes but are responsible for highly complex functions of the brain.

Action potential

Neural Interactions

The place that nerves meet in signal transduction is called a synapse. Synaptic connections are the basis for...

Positions

The human body can adjust to a variety of positions.

Human positions refer to the different physical configurations that the human body can take.

Basic positions

• Standing
• Sitting
• Squatting
• Lying
• Kneeling
• Crouching
• All-Fours

Stress positions

• Hands Up