Anatomy Lecture 1 PDF

INTRODUCTION TO ANATOMY Block: Foundations Block Director: James Proffitt, PhD Session Date: Monday, July 29, 2024 Time: 10:00 am - 11:00 am Instructor: James Proffitt, PhD Department: Cellular & Molecular Medicine Email: jvproffit...

INTRODUCTION TO ANATOMY Block: Foundations Block Director: James Proffitt, PhD Session Date: Monday, July 29, 2024 Time: 10:00 am - 11:00 am Instructor: James Proffitt, PhD Department: Cellular & Molecular Medicine Email: [email protected] INSTRUCTIONAL METHODS Primary Method: IM13: Lecture ☐ Flipped Session ☐ Clinical Correlation Resource Types: RE18: Written or Visual Media (or Digital Equivalent) INSTRUCTIONS Please read lecture objectives and notes prior to attending session. READINGS Read lecture notes prior to session. LEARNING OBJECTIVES 1. Describe and demonstrate standard anatomical position 2. Describe the planes of anatomical section 3. Apply the planes of anatomical section to medical imaging 4. Apply the following terms to describe the position of anatomical structures: anterior/posterior, rostral/caudal, superior/inferior, medial/lateral, proximal/distal, dorsum/palmar/plantar, deep/superficial/intermediate, external/internal, unilateral/bilateral, contralateral/ipsilateral. 5. Describe the contents of a nerve, including afferent and efferent components 6. Explain the clinical relevance of spinal cord segments, cranial nerves, dermatome, myotome, peripheral nerve territories, and referred pain. 7. Compare and contrast the function and distribution of the central nervous system, somatic peripheral nervous system, visceral peripheral nervous system 8. Describe the structural, functional, and organizational differences between arteries and veins, including route of bloodflow 9. Explain the clinical relevance of anastomosis, collateral circulation, venous drainage, and lymphatic drainage 10. Apply the concepts of deep and superficial to explain fascial layers and structural layers 11. Compare and contrast the structure of a cavity, a bursa, and a potential space 12. Describe how relationships between organ systems can be used to organize knowledge in a somatic example (muscular compartment) and a visceral example (small intestine). 13. Explain the clinical relevance of anatomical variation Block: Foundations | PROFFITT [1 of 27] INTRODUCTION TO ANATOMY CURRICULAR CONNECTIONS Below are the competencies, educational program objectives (EPOs), course objectives, session learning objectives, disciplines and threads that most accurately describe the connection of this session to the curriculum. Related Related Competency\EPO Disciplines Threads COs LOs CO-01 LO-01 MK-02: The normal Gross anatomy N/A structure and function of the body as a whole and of each of the major organ systems CO-01 LO-02 MK-02: The normal Gross anatomy N/A structure and function of the body as a whole and of each of the major organ systems CO-01 LO-03 MK-02: The normal Gross anatomy EBM: Diagnostic structure and function of Imaging/Radiology the body as a whole and of each of the major organ systems CO-02 LO-04 MK-02: The normal Gross anatomy N/A structure and function of the body as a whole and of each of the major organ systems CO-02 LO-05 MK-02: The normal Gross anatomy N/A structure and function of the body as a whole and of each of the major organ systems CO-01 LO-06 MK-05: The altered Gross anatomy N/A structure and function (pathology & pathophysiology) of the body/organs in disease CO-02 LO-07 MK-02: The normal Gross anatomy N/A structure and function of the body as a whole and of each of the major organ systems CO-01 LO-08 MK-02: The normal Gross anatomy N/A structure and function of the body as a whole and of each of the major organ systems CO-01 LO-09 MK-05: The altered Gross anatomy N/A structure and function (pathology & pathophysiology) of the body/organs in disease CO-01 LO-10 MK-02: The normal Gross anatomy N/A structure and function of Block: Foundations | PROFFITT [2 of 27] INTRODUCTION TO ANATOMY Related Related Competency\EPO Disciplines Threads COs LOs the body as a whole and of each of the major organ systems CO-01 LO-11 MK-02: The normal Gross anatomy N/A structure and function of the body as a whole and of each of the major organ systems CO-01 LO-12 MK-02: The normal Gross anatomy N/A structure and function of the body as a whole and of each of the major organ systems CO-01 LO-13 MK-02: The normal Gross anatomy N/A structure and function of the body as a whole and of each of the major organ systems NOTES INTRO All of my lecture notes will contain: (1) a Key Terms list (bolded in the written lecture notes) that focuses on the most important basic vocabulary you will need to understand apply the concepts learned in this lesson (2) a curated list of helpful online resources (3) written lecture notes explaining the major concepts. Focus on applying your knowledge to clinical scenarios presented in lesson materials, AMBOSS, your USMLE practice books, or develop some on your own with friends with tools like UWorld, Sketchy, Boards and Beyond, or Anki. Additional citations are included at the end of the notes when needed. Key Terms: Directional Terms, Anatomical Planes, and Organizational Concepts Standard Anatomical Position Sagittal Median Parasagittal Transverse Frontal Anterior Posterior Rostral Caudal Superior Inferior Lateral Medial Proximal Distal Dorsum Palmar Plantar Block: Foundations | PROFFITT [3 of 27] INTRODUCTION TO ANATOMY Superficial Deep Intermediate External Internal Dermatome Myotome Referred Pain Anastamosis Collateral Circulation Venous Drainage Lymphatic Drainage Myofascial compartment Anatomical Structures Afferent (Sensory) Fiber Efferent (Motor) fiber Cranial Nerve Spinal Nerve Somatic peripheral nervous system Visceral peripheral nervous system Artery Vein Venous plexus Lymph Node Lymphatic Duct Fascial layer Structural layer Small intestine Offline & Online Resources Textbooks No textbook is required, but we recommend a copy of Moore’s Essential Clinical Anatomy. You may want to look into several decent books that you can get used for cheap (some of these, such as Netter's or Moore's textbooks, are easier to find cheap copies of through booksellers). You can also fine online textbooks through the UA Health Sciences Library (see below). It is up to you what resources you use for everyday class activities outside of the notes and slides, but we do provide a copy of Grant’s Dissector in Lab Netter Atlas of Human Anatomy Moore's Clinical Anatomy Thieme Atlas of Anatomy McMinn & Abraham's Clinical Atlas of Human Anatomy A great dissection book that could be a guide for your own dissections is Grants Dissector. Grant's Dissector copies are included with each table in the laboratory. Block: Foundations | PROFFITT [4 of 27] INTRODUCTION TO ANATOMY School-owned Resources You will have access to Acland's Video Atlas of Human Anatomy through UA Libraries. This atlas contains videos of real human tissue preparations that will compliment your dissections. To access the Acland's Atlas visit https://libguides.library.arizona.edu/acland and log in with your UA credentials. Health Science Library Databases and online textbooks: http://ahsl.arizona.edu/top- resources Free Online Resources: University of Michigan's BlueLink website has a wide variety of free resources based on real cadaver dissections, including Youtube videos, instructional dissection videos, self-quizzes, and a picture atlas. Access all BlueLink resources here: https://sites.google.com/a/umich.edu/bluelink/curricula For quick information and quizzes, Teach Me Anatomy is helpful and has a website and free phone app: https://teachmeanatomy.info/ If you are interested in Radiology and its relationship to anatomy, check out Radiopaedia: https://radiopaedia.org/?lang=us Cross sections of a real human body are available to view at the Visible Human Project: https://www.nlm.nih.gov/research/visible/visible_human.html UBC Medicine's Neuroanatomy playlists: https://www.youtube.com/channel/UCE4a1o3GMKCRSgHflXqZs8Q/playlists The Noted Anatomist: https://www.youtube.com/channel/UCe9lb3da4XAnN7v3ciTyquQ If you want to know about anatomical variations, visit this site: https://www.anatomyatlases.org/AnatomicVariants/AnatomyHP.shtml Paid Online Resources & Apps: A popular mobile app for learning anatomy is Visible Body. The apps are not free, but you can keep them forever: https://www.visiblebody.com/en-us/ An additional, very detailed app is Complete Anatomy. This is a subscription-based app but has a lot of information: https://3d4medical.com/ If you have access to VR equipment for gaming or other activities apps such as 3D Organon https://www.3dorganon.com/ can be installed for Oculus and other VR headsets. LO 1 Whenever we use directional terms in anatomy, we imagine our patient to be in standard anatomical position (Fig. 1). This is a pose where the patient is: standing up, looking forward, arms down to the side, palms facing forward, legs parallel, toes facing forward. No matter the position of your patient or donor body in lab, always use directional terms as if the patient is in standard anatomical position. This is to ensure consistent use of directional terminology, even though parts of our body are mobile. LO 2 The body can be divided into parts based on three imaginary planes that intersect the body (Fig. 1). These are the sagittal, transverse (aka axial), and frontal (aka coronal) planes. Block: Foundations | PROFFITT [5 of 27] INTRODUCTION TO ANATOMY Figure 1: Demonstration of the anatomical planes of section in standard anatomical position. Sagittal & Median Planes (A); Frontal Plane (B); Transverse Plane (C). Moore et al., 2015 The sagittal plane divides the body into right and left halves. One individual cut along the sagittal plane that divides the body directly down the middle is known as the median plane. All other sagittal plane cuts on either side of the median plane can be called parasagittal. The transverse plane divides the body into top and bottom halves. The frontal plane divides the body into front and back halves. LO 3 For most clinical disciplines, anatomy outside of surface anatomy will be visualized through the use of medical imaging techniques such as X-Ray radiography, Computed Tomography (CT), Magnetic Resonance Imaging (MRI), and Ultrasound. Each of these techniques will take 3D anatomy and visualize it in 2D, which means that many of you will spend a lot of time extrapolating what is happening to your patient in 3D from 2D images (Fig. 2). This is one reason why it is critical to take advantage of the opportunity to work with our donor bodies, as well as practice interpolating between imaging to 3D anatomy and back. Block: Foundations | PROFFITT [6 of 27] INTRODUCTION TO ANATOMY Figure 2: Visualization of CT image of the abdomen in transverse plane. Note that the image is in inferior view (i.e., looking up toward the head). This is the primary view in transverse sections in radiology, though in neurology brain scans are typically viewed from superior view (i.e. looking at the top of the head down toward the feet). Moore et al., 2015. Because CT and MRI collect information in 3D that is then displayed in 2D slices, anatomy can be viewed in any of the 3 anatomical sections (Fig. 3). These data can then be used by image processing software to render 3D models of anatomical structures and pathologies. Figure 3: CT image slices showing planes of section through a skull. Transverse (A); Frontal (B); Midsagittal/median (C). Angelopoulos, 2008. Dental Clinics of North America Block: Foundations | PROFFITT [7 of 27] INTRODUCTION TO ANATOMY Ultrasound also renders 3D anatomy as 2D slices, although the images are based on interface differences that reflect sound waves rather than material density. Ultrasound images are typically displayed in transverse or sagittal plane, but can image in any true plane or oblique plane based on the position of the transponder (Fig. 4). Figure 4: Schematic of ultrasound transponder placement (blue box) for a nerve block in the neck. The cross section shows a schematic of the transverse anatomical plane of the neck. LO 4 Comparative anatomical relationships are described using an array of paired terms, some of which reference planes of section (Fig. 5). Each of these terms are relative, and depend on the comparisons being offered (e.g., the heart is superior to the stomach, the stomach is inferior to the heart). Anterior (ventral), refers to structures nearer to the front of the body, posterior (dorsal) refers to structures nearer the back (e.g., the sternum is anterior to the esophagus, the vertebrae are posterior to the heart). Within the head (especially the brain), we use rostral to describe structures closer to the nose, caudal to refer to structures closer to the back of the head. Superior (cranial) refers to structures closer to the head, inferior (caudal) refers to structures closer to the foot. Medial refers to structures closer to the median plane, lateral refers to structures farther away from the median plane. Terms can be combined to increase specificity. For example, superomedial means closer to the head and nearer to the midline, whereas inferolateral means closer to the feet and father from the midline. Each of these terms can also be used to refer to parts of individual structures (e.g., Block: Foundations | PROFFITT [8 of 27] INTRODUCTION TO ANATOMY the posterior side of the heart, the medial side of the left lung, the distal end of the quadriceps, the proximal end of the triceps brachii). Within a limb we have terms that indicate proximity to the attachment of the limb to the trunk when comparing structures. Proximal means closer to the attachment to the trunk (e.g., the knee is proximal to the ankle), and distal means farther from the attachment to the trunk (e.g., the elbow is distal to the shoulder). These terms also apply to the position in a feature along a linear structure as a function of distance from its origin (e.g., distal in an artery is further along its length and proximal is closer to its origin). Dorsum refers to superior aspect of structures that protrude from the body, such as tongue or nose. The foot and hand also have a dorsum (superior surface of foot; posterior surface of hand). The hand also has a palmar surface (palm), and the foot has a plantar surface (sole). Figure 5: Demonstration of directional anatomical terms. Moore et al., 2015 Anatomical structures are also positioned in layers, such that some structures are closer to the exterior surface and others are further into the tissue. We use terms such as superficial, intermediate, and deep to refer to proximity to the surface of the body. Superficial means Block: Foundations | PROFFITT [9 of 27] INTRODUCTION TO ANATOMY closest to the surface (i.e., skin), deep means closest to the core of the body or limb, and intermediate means in between these layers. Within a single organ, external means farther from the core of the structure, whereas internal means closer to the core of the structure. Many anatomical structures are paired, possessing left and right members. Structures that are paired in this fashion are called bilateral. Structures from only one side are unilateral. Midline structures lack laterality. We also have terms for whether structures occur on the same side: ipsilateral; or opposite side: contralateral. LO 5 The body is composed of multiple anatomical systems that are organized by both structure and function. Each of these systems is composed of distinct combinations of cell and tissue types which determine their structural properties, and therefore their function. In turn, these systems have a gross structure that determines now they work at the macro-scale and therefore how they can become dysfunctional clinically. You will focus on the micro-scale of these systems in your histology, pathology, and physiology work; we will focus on the macro-scale. Note that many of these systems have some degree of overlap due to multiple functions (e.g., some organs have dual functions such as digestive and endocrine). In this session, rather than going over every system in detail, we are going to work on some foundational principles and organizational features that will help you arrange your knowledge going forward. One of the most important of these involves understanding nerves, because nerves are the control system of the body. Your patients will report pain, numbness, weakness, and other disfunctions that are either due to disfunction of the nerves themselves, or something the nerve is detecting. Therefore, it’s critical that we start with innervation. Nerves are bundles of axons, cells of the nervous system, wrapped in myelin and supportive glial cells (Fig. 6). These axons are arranged in sequential bundles all wrapped in connective tissue, forming a nerve. Axons are cells that can either deliver a signal from the brain or spinal cord to a target structure (motor) or receive sensory input from a target structure like pain, pressure, temperature and deliver it to the brain or spinal cord (sensory). Therefore, most nerves (excepting some from the brain) are both motor and sensory, though some terminal branches of nerves might have primarily sensory components. The details of nerve anatomy will be further explored in histology, but for now I want you to understand two things: (1) nerves contain both sensory and motor axons together; (2) nerves are often associated with blood vessels in wrappings of fascia/fat known as neurovascular bundles. In the lab, nerves appear light in color and are noncollapsible (unlike blood vessels that have a Block: Foundations | PROFFITT [10 of 27] INTRODUCTION TO ANATOMY Figure 6: Summary of the structure of a nerve. Note the myelin from the supporting cells and multiple layers of connective tissue surrounding the axons. Axons within these nerves will be motor and sensory! Moore et al., 2015 lumen). They often feel firm due to their wrappings of perineurium and epineurium; I often liken them to a partially cooked flat or football-shaped pasta noodle. LO 6 The nervous system (Fig. 7) is the control center of the body, controlling and regulating both conscious (such as motion and conscious sensations) and unconscious (such as homeostasis or organ function) processes. The nervous system consists of a central portion that includes the brain and spinal cord, which relays with the peripheral portion formed by nerves (cranial nerves from brain, spinal nerves from the spinal cord). Each of these systems is ultimately made up of neuron fibers that either send out information to the periphery to initiate or augment a function, or bring information back to the central nervous system that relays inputs about the environment or condition of the body. Block: Foundations | PROFFITT [11 of 27] INTRODUCTION TO ANATOMY Figure 7: Summary of the nervous system. Note the number of spinal nerves and cranial nerves Moore et al., 2015 Some of the most critical issues faced by patients are nervous system disorders. Helpfully for you clinicians-in-progress, nerves are not arranged randomly. They have a specific layout that allows you to localize where problems might occur based on the location and type of symptoms reported and signs observed. Furthermore, the arrangement of the nervous system forms an excellent structural framework for learning anatomy because nervous supply is segmental, lending itself to chunks of information for studying. Block: Foundations | PROFFITT [12 of 27] INTRODUCTION TO ANATOMY Figure 8: Summary of spinal nerves. Note that spinal nerves (containing motor and sensory fibers) can recombine to form a plexus, or interconnected network, of nerves. Do not learn the individual nerves now. This leads to functional redundancy; a single spinal nerve lesion usually cannot totally disrupt total motor function, though it can lead to symptoms such as pain, localized numbness and some weakness. Moore et al., 2015 Cranial nerves, of which there are 12 pairs, will be studied in-depth in the neuro block. For now, I want you to recognize that there are 12 pairs of cranial nerves with specific functions that can be motor, sensory, or both and that cranial nerves are the primary peripheral nerves of the head. Spinal nerves, on the other hand, are always both motor and sensory; there are 31 pairs of spinal nerves. Each spinal nerve contributes to a segment of sensory innervation to skin and a particular array of muscles. Furthermore, spinal nerves contribute to segmental innervation of the organs of the body; this arrangement is a helpful tool for localizing problems because of their segmental and location-specific nature. The specifics of spinal nerve anatomy will be studied in greater detail in MSS and Neuro blocks, but I want to establish some key principles now. The first is that spinal nerves exit at levels that we number according to association with vertebrae; in the cervical region spinal nerves exit above the vertebrae, in the thoracic, lumbar, and sacral/coccygeal levels they exit below. A mnemonic to remember the numbers is: eat breakfast at 8 (cervical); eat lunch at 12 (thoracic); go home at 5 (lumbar) eat dinner at 6 (sacral + coccygeal). Block: Foundations | PROFFITT [13 of 27] INTRODUCTION TO ANATOMY As spinal nerves exit (Fig. 8) they can recombine together to form interconnected nerve networks called plexuses. This means that many peripheral nerves are actually composed of neurons from multiple spinal nerves. This enables a degree of functional redundancy; if a single spinal nerve is damaged the structures innervated by that spinal nerve can have some function through the action of other spinal nerves, though your patients will have noticeable symptoms regardless. Figure 9: Schematic of the dermatome and myotome. Note that these are innervated by spinal nerves that are both sensory and motor. For nerves to muscles, motor fibers activate the muscle and sensory fibers detect pain+proprioception; for the skin sensory fibers detect stimuli and motor fibers for glands and smooth muscle. Moore et al., 2015 The reason your patient will still experience functional deficits is because each spinal nerve has what is called a myotome and a dermatome (Fig. 9), which is due to an association between nerves, skin, and muscles formed early in embryonic development. The myotome consists of all muscles innvervated by that spinal nerve level on that side. The dermatome consists of all skin innervated by that spinal nerve on that side. Both collections of axons contain motor and sensory fibers, but clinically we often focus on one or the other because damage to the neurons of the myotome can inflict muscle disfunction (typically weakness) and damage to the neurons of the dermatome can inflict paresthesia (numbness + tingling/shooting pain). It is often trickly to use myotomes clinically because a patient might be resistant to moving and because individual muscles are often part of multiple myotomes, though it is possible and we will expand on that in MSS (reflex arcs can also be used and you’ll explore that in neuro). Dermatomes and sensory innervation is particularly useful because you can check sensation more easily; you’ll hear this a lot in future lectures. It should be noted as in all things anatomical, there can be substantial variation in dermatomes and myotomes between individuals, depending on region. Dermatomes (Fig. 10) in particular are helpful because there are easy external landmarks for them such as the thumb for C6, nipple for T4, umbilicus for T10, and big toe/dorsomedial foot for L5. Therefore, any issue affecting the spinal nerve (or peripheral nerve from that level) can be localized using dermatomes. In reality dermatomes are not cleanly demarcated but fuzzy gradients due to fiber overlap. Block: Foundations | PROFFITT [14 of 27] INTRODUCTION TO ANATOMY Figure 10: Hypothesized dermatome map based on studies of spinal nerve lesions. Note that in reality these dermatomes have substantial overlap and have varying levels of reliability. Use anatomical landmarks to find territories dominated by particular dermatomes such as the thumb for C6, the nipple for T4, and the umbilicus for T10 Moore et al., 2015 When learning dermatomes and the nerves that supply these regions, it should be noted that dermatomes do not directly match peripheral nerve territories (Fig. 11). This is because a single dermatome can be found across multiple peripheral nerves (due to plexus and branching of spinal nerves into different terminal branches). Therefore, you will learn basic dermatomes as well as key landmarks for specific peripheral nerves. Specific injury patterns can damage certain peripheral nerves more than others due to position, such as vulnerability of the ulnar nerve to elbow fracture. In such a case, you would observe numbness in the sensory region of the ulnar nerve (medial hand), which corresponds to the C8 dermatome since the C8 spinal nerve contributes to the ulnar nerve. Block: Foundations | PROFFITT [15 of 27] INTRODUCTION TO ANATOMY Figure 11: Example of how peripheral nerve territories differ from dermatome maps. Note that the C6 dermatome contains sensory fibers from the median nerve, radial nerve, and lateral cutaneous nerve of the forearm. This is because the C6 spinal nerve branches to contribute to multiple peripheral nerves in the brachial plexus. Moore et al., 2015 Lastly, I will note that spinal nerve segmentation applies to supply to internal structures as well. This innervation pattern is complicated and will be explored in later blocks, though we will discuss some basic principles below. For now, I want you to understand that nerve supply to organs is also segmental, and this means that if organs are impacted by a problem your patient may experience pain that can be vaguely referred to a particular area of the body wall (Fig. 12). This phenomenon, referred pain, is due to cross-talk between sensory neurons from organs and sensory neurons from the external body. A general pattern you may observe is that structures that are lower in the body, such as the colon, refer pain more inferiorly than more superior structures such as the heart and the gallbladder. This is a handy tool in your diagnostic toolkit when working with your patient. We will discuss this division in innervation between the body wall and the organs below. Figure 12: Referred pain map. For now, just note general patterns in segmentation (more superior structures refer pain more superiorly). Moore et al., 2015 LO 7 The nervous system is complicated (Fig. 13), but a few key distinctions should be introduced now to help you understand its function (as well as some clinical features such as where we feel pain from organs). The first of these is that the central nervous system (brain and spinal cord-CNS) is housed within the skull and vertebral column, and sends out processes (nerves) to the periphery. The central Block: Foundations | PROFFITT [16 of 27] INTRODUCTION TO ANATOMY nervous system consists of multiple tracts of neurons that deliver and process information to (e.g. motor controls) and from (e.g. sensation) the periphery. Nerves in the periphery are collectively referred to as the peripheral nervous system (PNS). These nerves consist of afferent fibers (bringing information into the CNS) and efferent fibers (sending information out of the CNS). These nerves can either innervate muscles, bones, and the body wall (somatic PNS) or visceral structures such as organs (visceral PNS). Figure 13: Summary of the somatic and visceral peripheral nervous system, showing connection to the brain. Moore et al., 2015 The types of information carried, as well as whether we are conscious of it or not, is determined by this division between somatic and visceral divisions: Somatic o Motor innervation (efferent) = conscious and/or reflexive control of muscle o Sensory innervation (afferent) = sensation such as pain, touch, proprioception. This type of information is conscious and localized Visceral o Motor innervation (efferent) = the two autonomic systems that interact to govern homeostasis Block: Foundations | PROFFITT [17 of 27] INTRODUCTION TO ANATOMY ▪ Parasympathetic (rest + digest) = derived from cranial nerves and spinal nerves in lower back (sacrum), promotes response such as vasodilation in gut, lower heart rate, etc. ▪ Sympathetic (fight or flight) = derived from spinal nerves in the thorax and lumbar areas of the back, promotes response such as vasoconstriction in gut, sweating, etc. o Sensory innervation (afferent) = sensation that is unconscious for control of autonomic reflexes, OR noxious stimuli (e.g. ischemia) that can be experienced as pain (often diffuse-compare a stomach ache to stubbing your toe). Pain location can often tell you what organ is affected. In organs above the pelvis, pain fibers travel along the same pathway as sympathetics. LO 8 Figure 14: Summary of the circulatory system including systemic (A) and pulmonary (B) circulations. (C) displays a more complete summary, including odd arrangements that allow for filtration such as in the kidney and liver. In the liver we have a portal system, where veins subdivide into capillaries for a functional purpose prior to reforming into large veins once again. The main portal system in humans is within the abdomen and liver; smaller portal systems exist to facilitate hormone transport. Moore et al., 2015 Block: Foundations | PROFFITT [18 of 27] INTRODUCTION TO ANATOMY The circulatory system delivers blood to different regions of the body to facilitate gas and nutrient exchange, as well as provide a pathway for immune molecules (Fig. 14). The circulatory system is divided into two circulations: a pulmonary circulation between the heart and lungs, and a systemic circulation between the heart and the rest of the body. These two circulations enable efficient gas exchange and nutrient delivery, allowing us to maintain a high level of metabolic activity. The circulatory system contains three types of vessels; arteries, capillaries, and veins. In gross anatomy, we will primarily focus on arteries and veins (Fig. 15). Structurally, arteries are built to maintain high pressure and deliver blood away from the heart, including relatively thick smooth muscle and elastic fibers. This arrangement gives arteries a bulbous appearance and a “springy” feeling in lab; they typically appear more robust than veins. Veins are built to facilitate draining blood and delivery back to the heart under low pressure following the recombination of capillaries, typically including valves, superficial and deep collateral flow to allow muscles to assist in blood return, and rarely have thick smooth muscle except in larger vessels. In lab, this means that veins will often appear depressed or floppy, and will often be dark colored due to clotted blood following embalming. A helpful mnemonic to remember the function of each vessel: arteries away; veins drain. This Figure 15: Structural differences between veins and arteries. Note the thickness of the arteries in particular; this difference will be obvious in lab. Moore et al., 2015 is true irrespective of the oxygen content of the blood (in systemic arteries carry O2 rich, CO2 poor blood, in pulmonary O2 poor, CO2 rich blood). Block: Foundations | PROFFITT [19 of 27] INTRODUCTION TO ANATOMY Blood vessels usually exist in parallel (Fig. 16), with arteries paralleled by veins (the technical term for this is accompanying veins or venae comitantes). Veins and arteries typically share a fascial sheath that encloses them in wrapping; nerves can very commonly be associated with Figure 15: Schematic showing how veins accompany arteries in fascial sheaths. Note that in this case the accompanying vein forms a plexus around the artery, rather than a single trunk. Moore et al., 2015 these vascular bundles protected by fascia and fat, forming neurovascular bundles. As one moves from the largest veins (e.g., superior/inferior vena cava; iliac veins, femoral/popliteal veins, subclavian and axillary veins) to smaller veins, it is common for veins to form an interconnected network that surround the arteries called a venous plexus. LO 9 Blood supply and drainage follows several functional arrangements that are clinically useful. The first of these is that arteries and veins form interconnections known as anastomoses (singular, anastomosis). These are particularly prevalent in areas of high mobility or functional importance where blood vessels can become constricted or where prevention of blockage or enhancement of bloodflow is critical (e.g., brain, gut, nose, shoulder, elbow, knee, hand, foot). These anastomoses provide enhanced bloodflow or detours around blockages, ensuring critical bloodflow is maintained. Anastamosis is particularly critical in clinical settings because it can be used to ensure bloodflow when an artery must be subjected to a clinical intervention. For example, surgical procedures Figure 16: Schematic of anastomosis surrounding the shoulder blade. Note that the interconnections provide detours for bloodflow in case one vessel is compressed. Moore et al., 2015 Block: Foundations | PROFFITT [20 of 27] INTRODUCTION TO ANATOMY that require clamping of the axillary artery can still maintain bloodflow to the distal upper limb because of the anastamotic network of vessels surrounding the shoulder blade (Fig. 17). Sometimes, small anastomoses between vessels can become pathologically and dangerously enlarged due to diseases affecting bloodflow, especially in the venous drainage. Figure 17: Summary figure of lymphatic drainage in the body at a gross level (A), and micro level from capillary to afferent vessel, to node, to efferent vessel, to node/duct (B). Note that lymphatic drainage often roughly parallels venous drainage. Moore et al., 2015 Another key concept is understanding the patterns of venous drainage, both in terms of overall territories drained as well as superficial vs. deep drainage patterns (Fig. 18). Veins typically drain vascular territories through deep veins that are assisted by muscular contraction, and superficial veins that act as key drainage routes that are interconnected with deep vessels through smaller communicating veins. Venous access to the circulatory system can occur via superficial veins (e.g., great saphenous vein) or through deep veins that are more superficial or accessible, visualized with ultrasound. Furthermore, maintenance of healthy veins and flow between superficial and deep vessels is critical to bloodflow and avoiding clotting or venous disorders. Lastly, venous drainage patterns can affect the transport of infection, cancer, and drugs. Lymphatics will not often be visualizable in gross lab, but it is key to understand the lymphoid system (Fig. 18). For now, I want you to understand why we care about lymphatics: lymphatics reabsorb much of the extracellular fluid and material not reabsorbed by capillaries, preventing edema (swelling due to excess fluid). Furthermore, the lymphatic system is a key component of the immune system protecting us against pathogens in the drained fluid. and also absorbs dietary fat. Because of its critical function as fluid transport, infection and cancer can travel Block: Foundations | PROFFITT [21 of 27] INTRODUCTION TO ANATOMY along lymphatic drainage routes much as they can with veins. Therefore, in anatomy it is critical to have a general appreciation for general patterns of lymphatic drainage. A particularly relevant example is the spread of prostate or cervical cancer via venous systems to the vertebral column, or the spread of breast cancer to axillary lymph nodes and ultimately the venous system. LO 10 Fascia is connective tissue underneath the skin that protects and supports muscles and organs. Between the skin and the deeper structures (muscle, viscera, bone) there are two main layers of fascia: superficial fascia (including fat and loose connective tissue), and deep fascia, which is devoid of fat and is typically composed of tendinous dense regular connective tissue (Fig. 19). The deep fascia directly overlies muscles and can vary widely in thickness, from very thick and stout (over muscles of abdomen and limbs) to nearly obsolete (over the facial muscles). There are other fascial layers that you will observe in cases where extra strength is needed, such as the abdominal wall (these layers can derive muscle tendons). You will also observe fascial coverings of organs deep to the body wall and bones to protect and lubricate organs. These coverings typically have specific names depending on the organ they cover (e.g., pericardium, pleura, meninges, see Concept LO 8 below). Layers between fascial planes can be separated and used to access structures for clinical procedures. These layers are not easily appreciated on embalmed donor bodies. Figure 19: Example of fascial layers from the abdominal cavity. Note that in this case there are multiple layers of deep fascia (not always true, see the muscular compartment example below). Moore et al., 2015 LO 11 Deep to the body wall are true 3D spaces that contain organs and other visceral structures (Fig. 20). These spaces protect, lubricate, and assist in the function of viscera. For example, the thoracic cavity protects the lungs, but also changes shape with the action of muscles to drive respiration. Voluntarily increasing pressure within the abdominal cavity is essential to assisting the abdominal and pelvic organs in actions such as eliminating waste and giving birth. Block: Foundations | PROFFITT [22 of 27] INTRODUCTION TO ANATOMY Figure 20: Illustration of the three major compartments of the trunk. Cavities are separated via muscles (e.g., diaphragm at inferior ribcage) or fascia (e.g., inferior border of peritoneal sac near pelvic inlet). Moore et al., 2015 The primary cavities of the body are the thoracic cavity, abdominal cavity, and pelvic cavity. The cranial cavity within the skull is another. Each of these cavities has bony and (in most cases) muscular components forming a wall. Within that wall, there are additional fascial coverings (bursae, meninges) that shield the organs within. Clinical Correlations: Fluid Buildup in Anatomical Spaces Anatomical spaces can act as reservoirs for pathological fluid buildup. Fluid build up can interfere with normal organ function (such as air buildup in the thoracic cavity in the case of pneumothorax) or determine routes of infection (drainage of pus into the space between the rectum and uterus due to gravity). Spaces can also be used for clinical purposes, such as pumping fluid into the abdomen to remove waste products through diffusion with peritoneal dialysis. Synovial bursae are closed sacs of connective tissue that contain lubricating serous fluid (Fig. 21). They are found in areas subject to friction. Bursae are found covering tendons and within joints, facilitating joint and tendon movement. Bursae are also found covering organs such as the heart, lungs, and abdominal viscera. The layer of the bursae that touches the body wall is referred to as the parietal layer, whereas the layer that touches the organ itself is known as the visceral layer. Block: Foundations | PROFFITT [23 of 27] INTRODUCTION TO ANATOMY Figure 21: Illustration of bursae surrounding a tendon (A) and an analogy for the anatomy of bursae surrounding organs (bursa is the balloon, organ is the fist). Moore et al., 2015 The serous fluid-filled layer between parietal and visceral layers of bursae are typically collapsed or nearly so. Pathological fluid buildup between layers can separate these layers, creating a true 3D space. These are known as potential spaces-which typically exist due to pathology or clinical intervention. Potential spaces are not limited to bursae-they exist wherever there are layers of tissue that can be separated (for example, the subdural space between layers of meninges covering the brain). Realized potential spaces are usually a problem, as they interfere with the lubricating/protecting function of bursae, or put pressure on vulnerable organs, nerves, and vessels. Furthermore, like with venous and lymphatic drainage potential spaces can act as a route of infection spread and cancer metastasis. LO 12 Anatomical systems do not exist in isolation, they are integrated with other systems into multilayered and multifunctional regions. These multifunctional organizations can be used to chunk anatomical knowledge and improve learning through organization. To gain practice in examining how different systems interact, let’s focus on two examples: a myofascial compartment-somatic (Fig. 22) and the small intestine-visceral (Fig. 23). Block: Foundations | PROFFITT [24 of 27] INTRODUCTION TO ANATOMY Figure 22: Transverse section of the leg (section between knee and ankle) displaying three myofascial compartments (1 anterior, 1 posterior, 1 lateral). Note the location of muscles, vessels, and nerves, including superficial nerves and vessels just under the skin. Moore et al., 2015 In the somatic system, systems are typically in layers of muscle and fascia. Within the limbs, myofascial compartments are layers of muscle encircled by connective tissue, that often contain neurovasculature (arteries, veins, nerves). These compartments are typically multilayered from superficial to deep, for example in the posterior compartment of the leg (Fig. 22), you can observe several layers of muscle. Deep to several of these muscles close to the bone there are several deep vessels and nerves. Typically, nerves and vessels that supply muscles are deep to those muscles. Exceptions are often clinically relevant, because critical neurovasculature can become damaged more easily. Superficial to the compartments are layers of superficial fascia and adipose tissue, that often support superficial vessels (especially veins) and superficial nerves (detecting sensation from the skin). Critically, many muscles in compartments are innervated by a small number of nerves and often share common functional roles, so you can learn anatomy by compartment rather than memorize things separately. That way, you only have to learn the main role of the region, and the exceptions. Innervation and bloodflow are excellent ways to organize knowledge. Block: Foundations | PROFFITT [25 of 27] INTRODUCTION TO ANATOMY Figure 23: Schematic of the small intestine. Note the relationship between connective tissue suspending the organ, which transmits critical vasculature and nerve. Additional nerves and vasculature run along the surface of the organ, to integrate with internal layers of muscle, neurovasculature, and lymphatics. Moore et al., 2015. Visceral organs also have integration of multiple systems, as can be observed in the small intestine (Fig. 23). For example, the intestine is suspended from the body wall by a sheet of connective tissue containing fat and critical neurovasculature. These vessels supply (artery) or drain (vein) the organ, whereas the nerves either modulate the activity of the organ (autonomic or visceral motor) or detect conscious/unconscious stimuli from the organ (visceral sensation). Organs can be more difficult to organize than somatic structures, but their blood supply and nervous supply is typically segmental (e.g., many structures of the superior abdomen, or foregut, all receive bloodflow primarily form the celiac trunk of the aorta. Therefore, you can group structures into broad regions based on this supply, or organize them by their containing cavity (e.g. thoracic, abdominal, pelvic). The system of organization into compartments or segments/watersheds supplied by particular nerves and vessels is critical to first-level diagnostic thinking because your patient will present differently based on the anatomy affected. Patients will come in reporting pain, or a particular disfunction. Therefore, it is important to consider how these organizational schemes can help you differentially diagnose issues that may arise in the clinic. LO 13 Block: Foundations | PROFFITT [26 of 27] INTRODUCTION TO ANATOMY Figure 24: Schematic of anatomical variation of the artery that feeds the gallbladder. Critical to account for this variation during gall bladder surgery so as to not ligate the artery incorrectly. Moore et al., 2015. The anatomy that you will engage with in your donor bodies and in your patients will inevitably vary from the textbook diagrams. Variation is the currency of biological evolution and humans are no exception. Some variations are clinically relevant (e.g. Fig. 24), because they can alter your clinical algorithm or chosen course of action. We will present some of the most common variations, but learning anatomy by creating associations between structures (e.g., this arterial branch has X destination and goes with Y nerve) will help you adapt when you see a new variant. Block: Foundations | PROFFITT [27 of 27]