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To date order effexor xr 75mg on-line anxiety symptoms nail biting, myocardial cells produced within the patient (in situ) by cardiac stem cells seem to be nonfunctional order 150mg effexor xr amex anxiety 4 hereford bull, although those grown in Petri dishes (in vitro) do beat. Conduction System of the Heart If embryonic heart cells are separated into a Petri dish and kept alive, each is capable of generating its own electrical impulse followed by contraction. When two independently beating embryonic cardiac muscle cells are placed together, the cell with the higher inherent rate sets the pace, and the impulse spreads from the faster to the slower cell to trigger a contraction. A fully developed adult heart maintains the capability of generating its own electrical impulse, triggered by the fastest cells, as part of the cardiac conduction system. The components of the cardiac conduction system include the sinoatrial node, the atrioventricular node, the atrioventricular bundle, the atrioventricular bundle branches, and the Purkinje cells (Figure 19. The relative importance of this pathway has been debated since the impulse would reach the atrioventricular node simply following the cell-by-cell pathway through the contractile cells of the myocardium in the atria. In addition, there is a specialized pathway called Bachmann’s bundle or the interatrial band that conducts the impulse directly from the right atrium to the left atrium. Regardless of the pathway, as the impulse reaches the atrioventricular septum, the connective tissue of the cardiac skeleton prevents the impulse from spreading into the myocardial cells in the ventricles except at the atrioventricular node. The wave of depolarization begins in the right atrium, and the impulse spreads across the superior portions of both atria and then down through the contractile cells. The contractile cells then begin contraction from the superior to the inferior portions of the atria, efficiently pumping blood into the ventricles. This delay in transmission is partially attributable to the small diameter of the cells of the node, which slow the impulse. Also, conduction between nodal cells is less efficient 850 Chapter 19 | The Cardiovascular System: The Heart than between conducting cells. This pause is critical to heart function, as it allows the atrial cardiomyocytes to complete their contraction that pumps blood into the ventricles before the impulse is transmitted to the cells of the ventricle itself. Damaged hearts or those stimulated by drugs can contract at higher rates, but at these rates, the heart can no longer effectively pump blood. Since the left ventricle is much larger than the right, the left bundle branch is also considerably larger than the right. Portions of the right bundle branch are found in the moderator band and supply the right papillary muscles. Because of this connection, each papillary muscle receives the impulse at approximately the same time, so they begin to contract simultaneously just prior to the remainder of the myocardial contractile cells of the ventricles. This is believed to allow tension to develop on the chordae tendineae prior to right ventricular contraction. Both bundle branches descend and reach the apex of the heart where they connect with the Purkinje fibers (see Figure 19. The Purkinje fibers are additional myocardial conductive fibers that spread the impulse to the myocardial contractile cells in the ventricles. They extend throughout the myocardium from the apex of the heart toward the atrioventricular septum and the base of the heart. The Purkinje fibers have a fast inherent conduction rate, and the electrical impulse reaches all of the ventricular muscle cells in about 75 ms (see Figure 19. Since the electrical stimulus begins at the apex, the contraction also begins at the apex and travels toward the base of the heart, similar to squeezing a tube of toothpaste from the bottom. Membrane Potentials and Ion Movement in Cardiac Conductive Cells + Action potentials are considerably different between cardiac conductive cells and cardiac contractive cells. Conductive cells contain a series of sodium ion channels that allow a normal and slow influx of sodium ions that causes the membrane potential to rise slowly from an initial value of −60 mV up to about –40 mV. The resulting movement of sodium ions creates spontaneous depolarization (or prepotential depolarization). At this point, the calcium ion channels close and K channels open, allowing outflux of + + K and resulting in repolarization. When the membrane potential reaches approximately −60 mV, the K channels close and + Na channels open, and the prepotential phase begins again. The prepotential accounts for the membrane reaching threshold and initiates the spontaneous depolarization and contraction of the cell. This phenomenon accounts for the long refractory periods required for the cardiac muscle cells to pump blood effectively before they are capable of firing for a second time. These cardiac myocytes normally do not initiate their own electrical potential but rather wait for an impulse to reach them. Contractile cells demonstrate a much more stable resting phase than conductive cells at approximately −80 mV for cells in the atria and −90 mV for cells in the ventricles.

This greater omentum extends from the lower border of the stomach into the pelvic part of the abdomen and then loops back up to the transverse colon discount effexor xr 75 mg on-line anxiety disorder 3000. There is also a smaller membrane effexor xr 37.5 mg lowest price anxiety symptoms 6 dpo, called the lesser omentum that extends between the stomach and the liver. It is composed of several parts: the mouth, pharynx, esophagus, stomach, small intestine, and large intestine. The digestive tract is sometimes called the alimentary tract, derived from a Latin word that means "food". It is more commonly referred to as the gastrointestinal (Gl) tract because of the major importance of the stomach and intestine in the process of digestion. In to this space projects a muscular organ, the tongue, which is used for chewing and swallowing, and is one of the principal organs of speech. The tongue has on its surface a number of special organs, called taste buds, by means of which taste sensations (bitter, sweet, sour, or salty) can be differentiated. Among these, the cutting teeth, or incisors, occupy the front part of the oral cavity, whereas the lager grinding teeth, the molars, are in the back. Usually, the 20 baby teeth have all appeared by the time a child has reached the age of 2 or 21/2 years. During the first 2 years the permanent teeth develop within the jawbones 317 Human Anatomy and Physiology from buds that are present at birth. Because decay and infection of adjacent deciduous molars may spread to and involve new, permanent teeth, deciduous teeth need proper care. After the 6-year molars have appeared, the baby incisors loosen and are replaced by permanent incisors. Next, the baby canines (cuspids) are replaced by permanent canines, and finally, the baby molars are replaced by the bicuspids (premolars) of the permanent teeth. Now the larger jawbones are ready for the appearance of the 12-year, or second, permanent molar teeth. In some cases the jaw is not large enough for these teeth or there are other abnormalities, so that the third molars may have to be removed. This watery mixture contains mucus and an enzyme called salivary amylase, which begins the digestive process by converting starch to sugar. It is manufactured mainly by three pairs of glands that function as accessory organs: 319 Human Anatomy and Physiology 1. In swallowing, a small portion of chewed food mixed with saliva, called a bolus, is pushed by the tongue into the pharynx, swallowing occurs rapidly by an involuntary reflex action. At the same time, the soft palate and uvula are raised to prevent food and liquid from entering the nasal cavity, and the tongue is raised to seal the back of the oral cavity. The entrance of the trachea is guarded during swallowing by a leaf-shaped cartilage, the epiglottis, which covers the opening of the larynx. The swallowed food is then moved by peristalsis 320 Human Anatomy and Physiology into esophagus, a muscular tube about 25cm (10 inches) long that carries food into the stomach. If there is a weakness in the diaphragm at this point, a portion of the stomach or other abdominal organ may protrude through the space, a condition called hiatal hernia. The Stomach The stomach is an expanded J-shaped organ in the upper left region of the abdominal cavity (Figure 11-6). In addition to the two muscle layers already described, it has a third, inner oblique (angled) layer that aids in grinding food and mixing it with digestive juices. The left-facing arch of the stomach is the greater curvature, whereas the right surface forms the lesser curvature. Each end of the stomach is guarded by a muscular ring, or sphincter, that permits the passage of substances in only one direction. This valve has also been called cardiac sphincter because it separates the esophagus from the region of the stomach that is close to the heart. We 321 Human Anatomy and Physiology are sometimes aware of the existence of this sphincter; sometimes it does not relax as it should, produce a feeling of being unable to swallow past that point. The region of the stomach leading into this sphincter, the pylorus, is important in regulating how rapidly food moves into the small intestine. The semi-liquid mixture of gastric juice and food that leaves the stomach to enter the small intestine is called chyme. It is known as the small intestine because, although it is longer than the large intestine, it is smaller in diameter, with an average width of about 2. Beyond the duodenum are two more divisions: the jejunum, which forms the next two fifths of the small intestine, and the ileum, which constitutes the remaining portion.

Gross anatomy of a typical long bone You can take Tibia (in the leg) one of the longest bones in the body buy 37.5mg effexor xr with amex anxiety symptoms lasting all day. The red marrow also known as myeloid tissue Endosteum is the lining the medullary cavity of compact bone tissue and covering the trabeculae of spongy bone tissue purchase effexor xr 75 mg amex anxiety symptoms when not feeling anxious. It is more rigid than other tissues because it contains inorganic salts mainly calcium phosphate & calcium carbonate. Osteons are made up of concentric layers called lamellae, which are arranged seemingly in wider and wider drinking straws. In the center of the osteons are central canals (haversion canal) , which are longitudinal canals that contains blood vessels, nerves and lymphatic vessels. Central canals, usually have branches called perforating canals /valkmann’s canal that run at right angle to central canal extending the system of nerves and vessels out ward to periosteum and to endosteum. Radiating from each lacuna are tiny canaliculi containing the slender extensions of the osteocytes where nutrients and wastes can pass to and from central canal. Spongy (cancellous) Bone tissue Is in the form of an open interlaced pattern that withstands maximum stress and supports in shifting stress. They are able to synthesize and 63 Human Anatomy and Physiology secrete un-mineralized ground substance, act as pump cell to move calcium and phosphate in and out of bone tissue. Bone in embryo develops in two ways: Intra-membranous ossification, If bone develops directly from mesenchymal tissue. The 64 Human Anatomy and Physiology cartilage it self do not converted into bone but the cartilage is replaced by bone through the process. Endochondrial ossification produces long bones and all other bones not formed by intra-membranous ossification. These are surface markings where muscles, tendons and ligaments attached, blood & lymph vessels and nerves pass. Example: External auditory meatus Groves and sulcus: are deep furrow on the surface of a bone or other structure. Example Medial condyle of femur Head, expanded, rounded surface at proximal end of a bone often joined to shaft by a narrowed neck. The upper part of the lower extremity, between the pelvis and knee, is the thigh; the leg is between the knees an ankle. Made up of horizontal, cribriform plate, median perpendicular plate, paired lateral masses; contains ethmoidal sinuses, crista galli, superior and middle conchae. Forms roof of nasal cavity and septum, part of cranium floor; site of attachment for membranes covering brain. Shaped like large scoop; frontal squama forms forehead; orbital plate forms roof of orbit; supraorbital ridge forms brow ridge; contains frontal sinuses, supraorbital foramen. Slightly curved plate, With turned- up edges; made up of squamous, base, and two lateral parts; contains foramen magnum, occipital condyles, hypo-glossal canals, atlanto-occipital joint, external occipital crest and protuberance. Protects posterior part of brain; forms foramina for spinal cord and nerves; site of attachment for muscles, ligaments. Wedge-shaped; made up of body, greater and lesser lateral wings, pterygoid processes; contains sphenoidal sinuses, sella turcica, optic foramen, superior orbital fissure, foramen 71 Human Anatomy and Physiology ovale, foramen rotundum, foramen spinosum Forms anterior part of base of cranium; houses pituitary gland; contains foramina for cranial nerves, meningeal artery to brain. Made up of squamous, petrous, tympanic, mastoid areas; contain zygomatic process, mandibular fossa, ear Ossicles, mastoid sinuses. Form temples, part of cheekbones; articulate with lower jaw; protect ear ossicles; site of attachments for neck muscles. Fontanels The skeleton of a newly formed embryo consist cartilage or fibrous membrane structures, which gradually replaced by bone the process is called ossification. Function • They enable skull of the fetus to compress as it pass through the birth canal • Permit rapid growth of brain during infancy • Serves as a landmark (anterior fontanel) for withdrawal of blood from the superior sagital sinus • Aid in determination of fetal position prior to birth. In the skull of the fetus there are 6 prominent fontanels: a) The Anterior (frontal) fontanel, between angle of two parietal bones & segment of the frontal bone. They are irregular in shape and begin to close at 1 or 2 months after birth and completed by 12 months. Largest, strongest facial bone; horseshoe-shaped horizontal bony with two perpendicular rami; contains tooth sockets, coronoid, condylar, alveolar processes, mental foramina. Made up of zygomatic, frontal, palatine, alveolar processes; contain infraorbital foramina, maxillary sinuses, tooth sockets. Horizontal plate forms posterior part of hard palate; vertical plate forms part of wall of nasal cavity, floor of orbit. Curved lateral part of (molar) cheekbones; made up of temporal process, zygomatic arch; contain zygomatico-facial and zygomatico-temporal foramina.