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Acid Base Homeostasis Blood Loss Notes

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Semester 2 Case 9: Negative Consequences

* What is the blood supply to the lower limbs?

[1]

Blood Supply to the Anterior & Medial Thigh Artery Origin Course Femoral. Continuation of Descends through femoral external iliac artery triangle bisecting it; then distal to inguinal courses through adductor ligament canal; terminates as it transverses adductor hiatus, where its name becomes popliteal artery Deep Femoral artery 1Passes deeply between femoral 5cm inferior to pectineus and adductor

Distribution in leg Branches supply anterior
& anteromedial aspects of thigh

3-4 perforating arteries pass through adductor

artery.

inguinal ligament

longus; descending posterior to latter on medial side of femur

Medial circumflex femoral.

Deep artery of thigh; may arise from femoral artery

Passes medially and posteriorly between pectineus and iliopsoas; enters gluteal region &
gives rise to posterior retinacular arteries; then terminates by dividing into transverse & ascending branches Passes laterally deep to sartorius & rectus femoris, dividing into ascending, transverse, & descending arteries

Lateral circumflex femoral.

Obturator.

Internal iliac artery or (in about 20%) as an accessory or replaced obturator artery from the inferior epigastric artery

Passes through obturator foramen; enters medial compartment of thigh &
divides into anterior &
posterior branches, which pass on respective sides of adductor brevis

magnus muscle, winding around femur to supply muscles in medial, posterior, & lateral part of anterior compartments Supplies most of blood to head & neck of femur; transverse branch takes part in cruciate anastomosis of thigh; ascending branch joins inferior gluteal artery Ascending branch supplies anterior part of gluteal region; transverse branch winds around femur; descending branch joins genicular periarticular anastomosis Anterior branch supplies obturator externus; pectineus, adductors of thigh, and gracilis; posterior branch supplies muscles attached to ischial tuberosity

Femoral Vein This is the continuation of the popliteal vein proximal to the adductor hiatus. As it ascends through the adductor canal, the femoral vein lies posterolateral and then posterior to the femoral artery. The femoral vein enters the femoral sheath lateral to the femoral canal and ends posterior to the inguinal ligament, where it becomes the external iliac vein. In the inferior part of the femoral triangle, the femoral vein receives the deep vein of the thigh, formed by the union of 3 or 4 perforating veins, enters the femoral vein approximately 8cm inferior to the inguinal ligament and approximately 5cm inferior to the termination of the great saphenous vein. Blood Supply to the Leg Artery Origin Course Distribution in leg Popliteal. Continuation of Passes through popliteal Superior, middle, and femoral artery in fossa to leg; ends at lower inferior genicular arteries adductor hiatus in border of popliteus muscle to both lateral and medial adductor magnus by dividing into anterior &
aspects of knee posterior tibial arteries Anterior Popliteal Passes between tibia &
Anterior compartment of tibeal. fibula into anterior leg compartment through gap in superior part of interosseous membrane &
descends this membrane between tibialis anterior &
extensor digitorum longus Dorsalis Continuation of Descends anteromedially to Muscles on dorsum of pedis anterior tibeal first interosseous space and foot; pierces first dorsal

(Dorsal artery of foot).

artery distal to inferior extensor retinaculum

divides into plantar &
arcuate arteries

Posterior tibial.

Popliteal

Fibular.

Posterior tibeal

Passes through posterior compartment of leg and terminates distal to flexor retinaculum by dividing into medial & lateral plantar arteries Descends in posterior compartment adjacent to posterior intermuscular septum

interosseous muscles as deep plantar artery to contribute to formation of plantar arch Posterior & lateral compartments of leg; circumflex fibular branch joins anastomosis around knee; nutrient artery passes to tibia Posterior compartment of leg; perforating branches supply lateral compartment of leg

The lateral compartment of the leg doesn't have an artery coursing through it. Instead, perforating branches and accompanying veins supply blood to & drain blood from the compartment. Proximally, perforating branches of the anterior tibeal artery penetrate the anterior intermuscular septum. Inferiorly, perforating branches of the fibular artery penetrate the posterior intermuscular septum, along with their accompanying veins.

* What neurovascular structures pass from the neck to the thorax?
Arteries

Arteries in Lateral Cervical Region: Lateral Branches of Thyrocervical Trunk - The thyrocervical trunk is a branch of the subclavian artery. It gives rise to a suprascapular artery & a cervicodorsal trunk (AKA: transverse cervical artery) from its lateral aspect; its terminal branches are the ascending cervical & inferior thyroid artery.

* The suprascapular artery passes inferolaterally across the anterior scalene muscle &
phrenic nerve. It also passes the subclavian artery & the brachial plexus, then posterior to the clavicle.

* The cervicodorsal trunk bifurcates into branches that run superficially & laterally across the phrenic nerve and anterior scalene muscle, 2-3cm superior to the clavicle. They then pass through the trunks of the brachial plexus. Third Part of the Subclavian Artery - Supplies blood to the upper limb. It begins slightly superior to the clavicle, opposite the lateral border of the anterior scalene muscle. This is the longest & most superficial part of the artery, and lies on the first rib. It lies posterior to the anterior scalene muscle, and directly anterior to the inferior trunk of the brachial plexus. Part of the Occipital Artery Arteries in Anterior Cervical Region: The common carotid artery & the external carotid artery are the main arterial vessels in the carotid triangle. Branches of the external carotid also originate in the carotid triangle. Each common carotid artery ascends within the carotid sheath with IJV & vagus nerve to the level of the superior border of the thyroid cartilage. Here, each common carotid terminates by dividing into the internal & external common carotid arteries. The internal carotid artery has no branches in the neck; the external carotid has several. Right Common Carotid Artery - This begins at the bifurcation of the brachiocephalic trunk. (The right subclavian artery is the other branch of this trunk). Left Common Carotid Artery - This ascends into the neck from the arch of the aorta. Therefore, it also has a course of about 2cm in the superior mediastinum. Internal Carotid Arteries - These are direct continuations of the common carotids superior to the origin of the external carotid artery, at the level of the superior border of the thyroid cartilage. The proximal part of each internal carotid artery is the site of the carotid sinus. The carotid body is located in the cleft between the internal & external carotid arteries. No named branches arise from the internal carotid arteries in the neck. External Carotid Arteries - These supply most structures external to the cranium. Each external carotid artery runs posterosuperiorly to the region between the neck of the mandible
& the lobule of the auricle, where it is embedded in the parotid gland & terminates by dividing into 2 branches; the maxillary artery & the superficial temporal artery. Before these terminal branches, there are 6 other arteries that arise: the ascending pharyngeal artery, occipital artery, posterior auricular artery, superior thyroid artery, lingual artery, & the facial artery. Remember: 1-2-3 - 1 artery arises medially, 2 arise posteriorly, and 3 arise anteriorly. Veins Veins in Lateral Cervical Region: External Jugular Vein - Begins near the angle of the mandible by the union of the posterior division of the retromandibular vein with the posterior auricular vein. It crosses the sternocleidomastoid obliquely, deep to the platysma. The EJV terminates in the subclavian vein. It drains most of the scalp & side of the face. Subclavian Vein - This is the major venous channel draining the upper limb. It curves through the inferior part of the lateral cervical regions. It passes anterior to the anterior scalene muscle & phrenic nerve and unites at the medial border of the muscle with the IJV to form the brachiocephalic vein. Just superior to the clavicle, the EJV receives the cervicodorsal, suprascapular, & anterior jugular veins. Veins in Anterior Cervical Region: Most veins in this region are tributaries of the IJV, typically the largest vein in the neck. The IJV drains blood from the brain, anterior face, cervical viscera, and deep muscles of the

neck. It commences at the jugular foramen in the posterior cranial fossa as the direct continuation of the sigmoid sinus. From its origin, the vein descends in the carotid sheath, accompanying the internal carotid artery superior to the bifurcation and the common carotid artery & vagus nerve inferiorly. The inferior end of the vein passes deep to the gap between the sternal and the clavicular heads of the sternocleidomastoid. Posterior to the sternal end of the clavicle, the IJV merges with the subclavian vein to form the brachiocephalic vein. The inferior end of the IJV has a bicuspid valve that permits blood to flow toward the heart while preventing backflow into the vein, as might occur if inverted. The tributaries of the IJV are the inferior petrosal sinus and the facial & lingual, pharyngeal, and superior & middle thyroid veins. Occasionally, the occipital vein may drain into the IJV.

Sympathetic Chains The cervical sympathetic trunk lies posterior to the carotid sheath. Although closely-related, the trunk is not within the sheath; instead, it is embedded in the prevertebral layer of deep cervical fascia.
[2] The sympathetic chain is each of the pair of ganglionated longitudinal cords of the sympathetic nervous system, situated on either side of the vertebral column. The sympathetic trunk travels from the base of the skull to the coccyx, just lateral to the vertebral bodies. The superior end of the sympathetic chain is continued into the skull through the carotid canal, in the form of a plexus on internal carotid artery. The inferior end travels in front of the coccyx and converges with the trunk of other side to form a structure known as ganglion impar. It has 4 parts: cervical part, thoracic part, abdominal part, & pelvic part. Vagus Nerve (Cranial Nerve X)
[3] The vagus nerve runs throughout the body and is responsible for the function & regulation of several bodily systems such as the heart & digestive tracts. Upon leaving the medulla, it extends through the jugular foramen, then passes into the carotid sheath between the internal carotid artery & the internal jugular vein down below the head, to the neck, chest and abdomen, where it contributes to the innervation of the viscera. Besides output to the various organs in the body, the vagus nerve conveys sensory information about the state of the

body's organs to the central nervous system. 80-90% of the nerve fibers in the vagus nerve are afferent (sensory) nerves communicating the state of the viscera to the brain. The motor division of the vagus nerve is derived from the basal plate of the embryonic medulla oblongata, while the sensory division originates from the cranial neural crest. The right vagus nerve gives rise to the right recurrent laryngeal nerve, which hooks around the right subclavian artery & ascends into the neck between the trachea & oesophagus. The right vagus nerve then crosses anteriorly to the right subclavian artery & runs posterior to the superior vena cava and descends posterior to the right main bronchus and contributes to cardiac, pulmonary, & oesophageal plexuses. It forms the posterior vagal trunk at the lower part of the oesophagus and enters the diaphragm through the oesophageal hiatus. The left vagus nerve enters the thorax between left common carotid artery & left subclavian artery and descends on the aortic arch. It gives rise to the left recurrent laryngeal nerve, which hooks around the aortic arch to the left of the ligamentum arteriosum & ascends between the trachea & oesophagus. The left vagus further gives off thoracic cardiac branches, breaks up into pulmonary plexus, continues into the oesophageal plexus, and enters the abdomen as the anterior vagal trunk in the oesophageal hiatus of the diaphragm. The vagus nerve supplies motor parasympathetic fibers to all of the organs except the suprarenal (adrenal) glands, from the neck down to the second segment of the transverse colon. The vagus also controls a few skeletal muscles. This means that the vagus nerve is responsible for such varied tasks as heart rate, gastrointestinal peristalsis, sweating, and quite a few muscle movements in the mouth, including speech and keeping the larynx open for breathing. Phrenic Nerve
[4] The phrenic nerve originates in the neck (C3-C5) & passes down between the lung and heart to reach the diaphragm. It is important for breathing as it passes motor information to the diaphragm & receives sensory information from it. (Remember: C3, 4, & 5 keeps the diaphragm alive). There are 2 phrenic nerves: a left and a right one. It originates mainly from C4, but also receives contributions from C3 and C5. Thus, the phrenic nerve receives innervation from parts of both the cervical plexus & the brachial plexus of nerves. The phrenic nerves contain motor, sensory, & sympathetic nerve fibers. These nerves provide the only motor supply to the diaphragm as well as sensation to the central tendon. In the thorax, each phrenic nerve supplies the mediastinal pleura & pericardium. The phrenic nerve descends obliquely with the internal jugular vein across the anterior scalene, deep to the prevertebral layer of deep cervical fascia & the transverse cervical &
suprascapular arteries. On the left, the phrenic nerve crosses anterior to the first part of the subclavian artery. On the right, it lies on the anterior scalene muscle and crosses anterior to the 2nd part of the subclavian artery. On both sides, the phrenic nerve runs posterior to the subclavian vein and anterior to the internal thoracic artery as it enters the thorax where it runs anterior to the root of the lung and into the pericardium between the fibrous & parietal layers. Pain arising from structures served by the phrenic nerve is often "referred" to other somatic regions served by the spinal nerves C3-C5.

* What is acid-base balance & how is it maintained?
= Excess addition of H+ ions from the body fluids. Alkalosis = Excess removal of H= ions from the body fluids. Remember: A strong acid is one that rapidly dissociates & releases especially large amounts of H+ in solution. Weak acids have less tendency to dissociate their ions, and therefore, release H+ with less vigour. A strong base is one that reacts rapidly & strongly with H+, and therefore, quickly removes these from a solution. A weak base binds H+ much more weakly. Most of the acids and bases in the extracellular fluid that are involved in normal acid-base regulation are weak acids & bases. Normal blood [H+] = 4x10-8Equivalents/L, and this has very little variation. As H+
concentration is so low, it is expressed on a logarithm scale as pH. pH = -log[H+]. Therefore,
[5] Acidosis

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