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Introduction. Human physiology is the study of the functioning of the normal body, and is responsible for describing how various systems of the human body work. (Seeley R.R., Stephens T.D. and Tate P. Anatomy and Physiology. a: longitudinal section, b: cross section.(Marieb E.N. and Hoehn K. Human Anatomy and Physiology. Figure (): Tracheobronchial Tree.(Seeley R.R., Stephens T.D. and Tate P. Anatomy and Physiology. The Coaching Habit. Essentials of human physiology for pharmacy / by Laurie J. Kelly p. ; cm. — (CRC .

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Textbook of medical physiology / Arthur C. Guyton, John E. Hall.—11th .. the majesty of the human body and its many functions and that it stimulates students to. BiolHuman Anatomy and Physiology-Syllabus/Course Calendar and Physiology PDF textbook is also available for you to access. Both items are free. T W ELF TH EDITION Stuart Ira Fox Pierce College TM i 22/07/10 PM HUMAN PHYSIOLOGY, TWELFTH EDITION Published by.

Oocytes develop within the outer layer of this stroma, each surrounded by supporting cells. This grouping of an oocyte and its supporting cells is called a follicle. The growth and development of ovarian follicles will be described shortly. Beneath the cortex lies the inner ovarian medulla, the site of blood vessels, lymph vessels, and the nerves of the ovary. You will learn more about the overall anatomy of the female reproductive system at the end of this section.

The cycle includes two interrelated processes: oogenesis the production of female gametes and folliculogenesis the growth and development of ovarian follicles. Oogenesis Gametogenesis in females is called oogenesis. The process begins with the ovarian stem cells, or oogonia Figure 3.

Oogonia are formed during fetal development, and divide via mitosis, much like spermatogonia in the testis. Unlike spermatogonia, however, oogonia form primary oocytes in the fetal ovary prior to birth.

The number of primary oocytes present in the ovaries declines from one to two million in an infant, to approximately , at puberty, to zero by the end of menopause. The initiation of ovulation—the release of an oocyte from the ovary—marks the transition from puberty into reproductive maturity for women.

Just prior to ovulation, a surge of luteinizing hormone triggers the resumption of meiosis in a primary oocyte. This initiates the transition from primary to secondary oocyte. However, as you can see in Figure 3 , this cell division does not result in two identical cells. Instead, the cytoplasm is divided unequally, and one daughter cell is much larger than the other.

This larger cell, the secondary oocyte, eventually leaves the ovary during ovulation. The smaller cell, called the first polar body, may or may not complete meiosis and produce second polar bodies; in either case, it eventually disintegrates.

Therefore, even though oogenesis produces up to four cells, only one survives. Figure 3. The unequal cell division of oogenesis produces one to three polar bodies that later degrade, as well as a single haploid ovum, which is produced only if there is penetration of the secondary oocyte by a sperm cell. How does the diploid secondary oocyte become an ovum—the haploid female gamete? Meiosis of a secondary oocyte is completed only if a sperm succeeds in penetrating its barriers.

Meiosis II then resumes, producing one haploid ovum that, at the instant of fertilization by a haploid sperm, becomes the first diploid cell of the new offspring a zygote. Thus, the ovum can be thought of as a brief, transitional, haploid stage between the diploid oocyte and diploid zygote.

The larger amount of cytoplasm contained in the female gamete is used to supply the developing zygote with nutrients during the period between fertilization and implantation into the uterus. Interestingly, sperm contribute only DNA at fertilization —not cytoplasm. Therefore, the cytoplasm and all of the cytoplasmic organelles in the developing embryo are of maternal origin.

This includes mitochondria, which contain their own DNA. Scientific research in the s determined that mitochondrial DNA was maternally inherited, meaning that you can trace your mitochondrial DNA directly to your mother, her mother, and so on back through your female ancestors. We inherit half of our nuclear DNA from our father, and half from our mother. However, mitochondrial DNA mtDNA comes only from the mitochondria in the cytoplasm of the fat ovum we inherit from our mother.

She received her mtDNA from her mother, who got it from her mother, and so on. Each of our cells contains approximately mitochondria, with each mitochondrion packed with mtDNA containing approximately 37 genes. Mutations changes in mtDNA occur spontaneously in a somewhat organized pattern at regular intervals in human history. By analyzing these mutational relationships, researchers have been able to determine that we can all trace our ancestry back to one woman who lived in Africa about , years ago.

Scientists have given this woman the biblical name Eve, although she is not, of course, the first Homo sapiens female. More precisely, she is our most recent common ancestor through matrilineal descent.

Still, all branches eventually lead back to Eve. But what happened to the mtDNA of all of the other Homo sapiens females who were living at the time of Eve? Researchers explain that, over the centuries, their female descendants died childless or with only male children, and thus, their maternal line—and its mtDNA—ended. Folliculogenesis Again, ovarian follicles are oocytes and their supporting cells. They grow and develop in a process called folliculogenesis, which typically leads to ovulation of one follicle approximately every 28 days, along with death to multiple other follicles.

The death of ovarian follicles is called atresia, and can occur at any point during follicular development.

Recall that, a female infant at birth will have one to two million oocytes within her ovarian follicles, and that this number declines throughout life until menopause, when no follicles remain. Folliculogenesis begins with follicles in a resting state. These small primordial follicles are present in newborn females and are the prevailing follicle type in the adult ovary Figure 4. Primordial follicles have only a single flat layer of support cells, called granulosa cells, that surround the oocyte, and they can stay in this resting state for years—some until right before menopause.


After puberty, a few primordial follicles will respond to a recruitment signal each day, and will join a pool of immature growing follicles called primary follicles.

Primary follicles start with a single layer of granulosa cells, but the granulosa cells then become active and transition from a flat or squamous shape to a rounded, cuboidal shape as they increase in size and proliferate. As the granulosa cells divide, the follicles—now called secondary follicles see Figure 4 —increase in diameter, adding a new outer layer of connective tissue, blood vessels, and theca cells—cells that work with the granulosa cells to produce estrogens.

Within the growing secondary follicle, the primary oocyte now secretes a thin acellular membrane called the zona pellucida that will play a critical role in fertilization.

A thick fluid, called follicular fluid, that has formed between the granulosa cells also begins to collect into one large pool, or antrum. Follicles in which the antrum has become large and fully formed are considered tertiary follicles or antral follicles. Several follicles reach the tertiary stage at the same time, and most of these will undergo atresia. The one that does not die will continue to grow and develop until ovulation, when it will expel its secondary oocyte surrounded by several layers of granulosa cells from the ovary.

In fact, roughly 99 percent of the follicles in the ovary will undergo atresia, which can occur at any stage of folliculogenesis. Figure 4. FSH stimulates the growth of a tertiary follicle, and LH stimulates the production of estrogen by granulosa and theca cells.

human physiology

Hair shaft diameters represent little variations and hairs are found to be thicker in androgen dependent areas. Hair follicle density is much more condense in the forehead and follicular infundibular volume is also bigger.

It is important just because of the large follicular infundibular volume that is associated with more follicular reservoir ability [ 1 , 13 ]. Structure of the hair Hair is consisted of two distinct structures: follicle—the living part located under the skin and hair shaft—fully keratinized nonliving part above the skin surface.

The arrector pili muscle, takes place between the hair bulge area and dermoepidermal junction. Above the insertion of the arrector pili muscle, sebaceous glands and, in some certain regions, apocrine glands are opened into the follicle.

Hair shaft is consisted of three layers: cuticle, cortex and in certain cases medulla. Flat and square-shaped cuticle cells are adhered tightly to the cortex cells proximally. Peripheric movements of cuticle cells make the direction of the distal free edge upward and cause extensive overlapping. These imbrications are crucial. By interlocking with the cuticle cells of inner root sheath, they contribute to the follicular anchorage of the growing hair.

These imbricated surfaces also facilitate removal of dirt and desquamated cells from the scalp. Cuticle has also important protective properties and barrier functions against physical and chemical insults [ 14 — 16 ]. During the migration of the cells from the hair bulb to compose the cortex, the shapes of them become more fusiform.

These cells coalesce tightly and are placed parallel to the axis of the shaft. The cortex comprises the bulk of the shaft and also contains melanin [ 2 , 15 , 16 ] Medulla is located in the center of the hair shaft preferably presented in coarser fibers. The hair medulla contains structural proteins that are markedly different from other hair keratins and eosinophilic granules that are filled by an amino acid, citrulline and eventually form internal coatings within the membranes of mature cells [ 14 , 16 , 17 ].

The follicle is the essential growth structure of the hair and basically has two distinct parts: upper part consisting of infundibulum and isthmus whereas the lower part comprising of hair bulb and suprabulbar region.

The upper follicle remains constant, while the lower part has continuous cycles of regeneration [ 1 , 2 , 16 , 18 ]. The infundibulum, the uppermost portion of the hair follicle extending from the opening of the sebaceous gland to the surface of the skin, is a funnel-shaped structure filled with sebum, the product of the sebaceous glands. The isthmus is the lower portion of the upper part of hair follicle between the opening of the sebaceous gland and the insertion of arrector pili muscle.

Mcgraw Hill Connect Human Physiology Quiz Answers

Only few differentiated corneocytes remain and the invagination of the epidermis in this area must be considered as highly permeable for topically applied compounds [ 19 ]. Hair follicle stem cells are thought to reside in the bulge area on the isthmus close to the insertion of the arrector muscle [ 20 ].

Lineage studies have proven that bulge cells are multipotent and that their progeny generate the new lower anagen hair follicle [ 21 ].

One of the most distinguishing features of stem cells is their slow-cycling nature, presumably to conserve their proliferative potential and to minimize DNA errors that could occur during replication. They migrate in a downward direction. On entering the hair bulb matrix, they proliferate and undergo terminal differentiation to form the hair shaft and inner root sheath.

They also migrate distally to form sebaceous glands and to proliferate in response to wounding [ 16 , 20 , 22 ]. Diagram of proximal hair follicle. Outer root sheath ORS extends from the epidermis at the infundibulum and continues to the hair bulb and its cells change considerably throughout the follicle.

In the infundibulum, it resembles epidermis, whereas in the isthmus level, ORS cells begin to keratinize in a trichilemmal mode. Keratinocytes in the ORS form the bulge area at the base of the isthmus. At the lower tip of the hair bulb it consists of a single layer of cuboidal cells, becoming multilayered in the region of the upper hair bulb.

In some follicles, there is a distinct single cell layer interposed between the outer and inner root sheaths, known as the companion layer [ 23 ]. Companion layer cells show numerous intercellular connections to the inner root sheath and are thought to migrated distally along with the inner root sheath to the isthmus region and to form the plane of slippage between the inner and outer root sheaths [ 1 , 3 , 14 , 16 ].

These cells take place in certain functions of the follicle such as acting as a sensory organ and serving as an immunologic sentinel for the skin [ 5 ]. The innermost layer is the cuticle of IRS whose cells interlock with those of the hair cuticle.

This connection, anchoring the hair shaft to the hair follicle, is so tight.

The inner root sheath hardens before the presumptive hair within it, and so it is thought to control the definitive shape of the hair shaft. Each of the three layers of IRS undergoes abrupt keratinization. This occurs at different levels in each layer; however, the patterns of change are similar.


The expanded onion-shaped portion of the lower hair follicle, including the hair matrix and the follicular papilla is known as the hair bulb which is the active reproductive portion of the hair follicle.

The hair bulb encloses folicular dermal papilla, mucopolysaccharide-rich strome, nerve fiber and capillary loop. The matrix cells are localized to the lowermost portion of the follicle and surround all sides of the follicular papilla. The hair shaft and IRS are derived from the matrix cells. The IRS is derived from the lower and laterally located matrix cells, whereas the hair shaft is originated from upper and centrally located cells.

In addition to producing the main structural components of hair, they also produce the hair keratins, and their associated proteins KAPs [ 24 ]. Melanocytes reside among matrix stem cells to produce the pigment of the hair. During their differentiation phase, matrix cells phagocytose melanin or pheomelanin from the dendritic elongations of melanocytes. The hair assumes its color via the amount and the type of the phagocytized major pigment [ 1 , 3 , 16 , 25 ].

Follicular papilla, which is derived from a condensation of mesenchymal cells at the early stages of follicular embryogenesis, is one of the most important players during the induction and maintenance of the follicular epithelial differentiation.

It is responsible for determining the follicle type. The volume and secretory activity of follicular papilla and also the number of matrix stem cells determine the size of the anagen hair bulb, the duration of anagen phase and the diameter of the hair shaft [ 11 , 26 , 27 ].

Moreover the follicular papilla is an essential source of growth factors [ 1 , 3 , 16 , 28 ]. Molecular structure Keratin proteins can be divided into two major families: the type I acidic keratins and the type II basic-neutral keratins.

About 54 functional keratin genes 28 type I and 26 type II keratins have been identified to date. There are 11 type I hair keratins, designated K31—K40, and 6 type II hair keratins, designated K81—K86, and the remainder are epithelial keratins [ 24 ].

human physiology

The keratin-associated proteins KAP , is a large group of proteins which constitutes the matrix of the keratin. The matrix proteins are separated to three major subgroups according to their amino acid compositions [ 29 ].

Different hair and epithelial keratins are expressed in the various concentric layers of the hair follicle, with hair keratins found primarily in the cortex and hair cuticle [ 1 , 2 ].

Hair follicle innervation and vascularization Nerves related to the hair follicle are identical to the dermal nerve network including sensory afferents and autonomic sympathetic nerves. Smaller nerve fibers form a circular layer around the bulge area of terminal follicles and the bulb area of vellus follicles.

There are several types of nerve endings associated with the hair follicle: free nerve endings, lanceolate nerve endings, Merkel cells and pilo-Ruffini corpuscles. Each nerve ending responds to distinct stimulus. Free nerve endings transmit pain, lanceolate nerve endings detect acceleration, Merkel cells responsible of pressure sensation and pilo-Ruffini corpuscles detect tension.

Perifollicular nerves related neuromediator and neuropeptides, that is, substance P, calcitonin gene-related peptide influence follicular keratinocytes and hair follicle cycling [ 1 , 3 , 16 ]. Cutaneous vascularization is provided by arterioles, which are concentrated at the lower portion of the hair follicle and compose vascular network.

During the hair cycle phases, there are some alterations in the density of perifollicular vascularization due to the upregulation of vascular endothelial growth factor expression [ 1 ].

Immunology of hair follicle The immunology of hair is very amazing and complicated. The hair follicle represents an immune privileged IP site, which is defined basically as a location in the body where foreign tissue grafts can survive for longer periods of time without immune rejection. This specialized immune environment of IP is required to prevent destructive immune reactions in critical regions. Other immune privileged sites include the anterior chamber of the eye, testis, brain and placenta.

Hair follicle IP has a unique characteristic of recurring in a cyclic pattern.The average period from submission to first decision in was 40 days, and that from first decision to acceptance was 30 days. These small primordial follicles are present in newborn females and are the prevailing follicle type in the adult ovary Figure 4.

The gamete they produce is called an oocyte. The macro-environment surrounding the hair follicle also takes part in regulating cycle transitions.


The final decision on the acceptance of an article for publication is made by the Editor-in-Chief. Pigmentation of hair follicle Hair shaft pigmentation ensures multiple benefits including UV protection, thermoregulation and sexual perceptions. Therefore, the cytoplasm and all of the cytoplasmic organelles in the developing embryo are of maternal origin. Updating Results. GnRH activates the anterior pituitary to produce LH and FSH, which stimulate the production of estrogen and progesterone by the ovaries.

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