Clinical Applications of Human Anatomy and Physiology for Healthcare Professionals. Jassin M. Jouria

which is under conscious or voluntary control. The ANS is also further subdivided into the sympathetic nervous system and the parasympathetic nervous system. A simpler way of appreciating this is through the visual aid of a flow chart:

      Figure 1-13 Structures of the nervous system.

      The CNS and PNS both function to transmit and receive electronic impulses between the central and peripheral divisions of the body. This is accomplished through the use of cells and nerves. Neurons and glial cells comprise the two main types of cells in the nervous system. Neurons, or nerve cells, are responsible for “communicating” with each other through connections known as synapses, or cell-to-cell junctions that rapidly transmit and receive chemical or electrical signals. Types of neurons and respective structures will be discussed in detail in Chapter 14: The Nervous System.

      Glial cells (named from their Greek origin meaning “glue”) are supporting cells in the nervous system. Glial cells maintain nerve cells by gluing them in place, supplying them with nutrients, and removing pathogens and damaged or dead neurons.

      One very important function of a particular glial cell, called an oligodendrocyte in the CNS and a Schwann cell in the PNS, is the production of myelin – a fatty sheath wrapped around the axons of neurons, electrically insulating them and allowing for more rapid and efficient transmission of impulses. The axons, long and slender projections of a neuron, are arranged and travel in bundles, making up the bulk of a nerve. Nerves as well as the individual parts of a nerve cell (the axon, cell body, and dendrites) will also be discussed in greater detail later.

      Figure 1-14 Male reproductive organs.

      Reproductive system

      The reproductive system or genital system is a coordination of structures, glands, and hormones that function to together for the sole purpose of reproduction.

      Human reproduction is a form of sexual reproduction conventionally by way of sexual intercourse, also called copulation or coitus, between a male and female.3

      During sexual intercourse, a man’s erect penis is inserted into a female’s vagina until ejaculation, or the release or semen, takes place. Sperm from the semen travels up the vagina where it reaches the cervix and enters the uterus and eventually the fallopian tubes, where internal fertilization of the female egg cell, or ovum, occurs.

      The process of internal fertilization and embryogenesis will be discussed in greater detail later. Nevertheless, unique from other organ systems, the reproductive systems allow for significant disparity between the two sexes.

      All male sex organs are considered to be external genitalia and include the:

      •testes

      •vas deferens

      •epididymis

      •seminal vesicles

      •prostate

      •penis

      The main male sex hormone associated is testosterone.

      The female sex organs can be classified as either interior or exterior. The interior organs are the:

      •ovaries

      •fallopian tubes

      •uterus

      •cervix

      •vagina

      •mammary glands

      Figure 1-15 Female reproductive system.

      The exterior genitalia (collectively called the vulva) are the introitus, the labia minora and majora, the clitoris, and Bartholin’s glands.

      The major female sex hormones associated with the reproductive system are estrogen and progesterone.

      These respective hormones allow for the development of proper secondary sexual characteristics (to be discussed in greater detail later) for the female and male.

      Organs and functions of the male and female reproductive systems will be discussed in further detail in Chapter 15: The Reproductive System.

      Respiratory system

      The respiratory system is an anatomical assembly of structures, commonly separated into an upper and lower system that are responsible for breathing.

      The structures included are the nose, pharynx, larynx, trachea, bronchi, lungs, and diaphragm. Breathing, more accurately termed respiration and ventilation, is the introduction and release of gases, oxygen and carbon dioxide, respectively, into and out of the body.

      The human body requires oxygen for the survival of all living cells, and the byproduct of each cell’s use of oxygen is carbon dioxide, which must be released as it becomes toxic at certain levels.

      Oxygen is exchanged for carbon dioxide in the respiratory system, hence is given the name – “gas exchange”.

      Gas exchange is responsible for regulating an appropriate acid-base balance in the body, as part of homeostasis.

      Respiration is under the direct control of the autonomic nervous system and is physiologically functional in the medulla oblongata and the pons, parts of the brain stem. Housed in this part of the brain stem is a series of interconnected neurons that make up the body’s respiration regulatory center. Inspiration, also called inhalation, is an active process initiated by the body’s diaphragm.

      Figure 1-16 The respiratory system.

      The organs and processes involving respiration will be discussed in more detail in Chapter 9: The Respiratory System. For now, a brief description provides a foundation for the basic functions of the breathing process.

      When the diaphragm contracts, it forces contents of the abdominal cavity downward, allowing the ribcage to be expanded, which creates room for lung expansion. This generates increased “thoracic pressure” (remember that term for future discussion) and allows air to flow into the lungs from the atmosphere. Oxygen is then passed down through to tiny sacs called alveoli, which allow for the exchange of oxygen with the uptake of carbon dioxide from the surrounding pulmonary capillaries.

      Carbon dioxide is then released from the body via exhalation. Exhalation, also called expiration, is generally a passive process, meaning no muscular contraction is needed in order to it to occur. The lungs have natural elasticity, similar to a rubber band. As the lungs are filled, air stretches the lungs until their natural recoil threshold is met, causing the remaining gases to be exhaled until the lungs reach a state of equilibrium with the atmospheric pressure. Disorders of the respiratory system are studied by a branch of medicine called pulmonology.

      Skeletal system

The skeletal system is an organ system composed primarily of bones responsible for the structural framework and support of the human body. An infant’s structure is not identical to an adult skeleton.13 At birth, an infant has more bones than an adult but over time, some of these bones mature and fuse together.

An adult human body has 206 bones that make up approximately 50% of the body’s total weight.14

      The human skeleton is classified into two units: the axial skeleton and the appendicular skeleton.

The