Human Histology Module PDF

MODULE 1 UNIT 5: NERVOUS TISSUES Introduction to Histology OBJECTIVES Upon successful completion of this 1. Describe the histological features of nervous tissues. exercise, the...

MODULE 1 UNIT 5: NERVOUS TISSUES Introduction to Histology OBJECTIVES Upon successful completion of this 1. Describe the histological features of nervous tissues. exercise, the 2. Enumerate and describe the components of neural tissues. reader should be able to: T he mammalian nervous system is the most complex system in the body. It is divided into two major parts: the central nervous system (CNS) consists of the brain and spinal cord that are surrounded and protected by the cranium and vertebral bones, respectively, and the peripheral nervous system (PNS) located Engage outside of the CNS and consists of the cranial, spinal, and peripheral nerves that conduct information to (afferent or sensory) and from (efferent or motor) the CNS, and ganglia which are small groups of nerve cells outside the CNS (Fig. 5.1). FUN FACT! If we line up all the neurons in our body it would be around 600 miles long. Fig. 5.1. Main divisions of the nervous system Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distribution, uploading or posting online, or transmitting in any form or by any means, electronic or mechanical, photocopying, recording, or otherwise of any of any part of this document, without prior written permission of SLU, is strictly prohibited. 62  LABORATORY ACTIVITY 1.1: Exercise No. 5 TO DO Match the photomicrograph to the neural tissue Explore components. 4 A. Nissl bodies B. Cell body C. Dendrites D. Nucleus 3 E. Axon hillock 5 Histology of the Nervous Tissue There are two (2) types of cells: Explain 1. Nerve cells (neurons) 2. Supporting cells (neuroglia) Neurons (Fig. 5.2) - The structural and functional unit in both CNS and PNS - Diverse in size and shape - Most have lost the ability to undergo mitotic divisions - Sense and respond to stimuli and initiate movements - There are three (3) main parts: 1. Cell body - Also known as soma - Contains: ✓ nucleus and nucleolus ✓ cytoplasm, called perikaryon, containing: ‣ typical cellular organelles such as lysosomes, mitochondria, and a Golgi complex ‣ Nissl bodies - large masses of free ribosomes and RER ‣ cytoskeleton that includes intermediate filaments (neurofibrils or neurofilaments) that that provide the cell shape and support, and microtubules, which assist in moving materials between the cell body and axon ‣ lipofuscin in aging neurons - Production of neurotransmitters, maintenance of neuron structural integrity Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distribution, uploading or posting online, or transmitting in any form or by any means, electronic or mechanical, photocopying, recording, or otherwise of any of any part of this document, without prior written permission of SLU, is strictly prohibited. 63 2. Dendrites - Usually are short, tapering and highly branched neuronal processes (extensions) that emerge from the cell body of a neuron - Multiple in a neuron - Cytoplasm contains Nissl bodies, mitochondria, cytoskeleton, and other organelles - Convey impulses towards the cell body - End either in specialized sensory receptors (as in primary sensory neurons) or form synapses with neighboring neurons from which they receive stimuli 3. Axon - A long, thin, cylindrical projection from the cell body - Only one (1) in a neuron - Cytoplasm contains mitochondria, segments of SER, microtubules, and neurofibrils; but lacks Nissl bodies - Conveys impulses away from the cell body, i.e., toward another neuron, a muscle fiber, or a gland cell - Arises from cone-shaped or funnel-shaped region called the axon hillock ✓ Initial segment: closest to the axon hillock ✓ Trigger zone: junction of the axon hillock and the initial segment ✓ Axoplasm: cytoplasm of an axon ✓ Axolemma: plasma membrane of the axon ✓ Axon collaterals: side branches along the Fig. 5.2. Parts of a neuron length of an axon ✓ Axon terminals or axon telodendria: many fine processes of the end axon and its collaterals ✓ Myelin sheath: a multilayered lipid (cholesterol, phospholipids, glycolipids) and protein covering around some axons that insulates them and increases the speed of nerve impulse conduction ๏ myelinated: axons surrounded by myelin sheath ๏ unmyelinated: axons without myelin sheath ✓ Nodes of Ranvier: short intervals where the axon is not covered by a myelin sheath ✓ Synaptic end bulbs (terminal boutons): bulb-shaped structures at the tips of some axon terminals ✓ Varicosities: string of swollen bumps at the tips of some axon terminals ✓ Synaptic vesicles: many tiny membrane-enclosed sacs in both synaptic end bulbs and varicosities that store a chemical called a neurotransmitter ✓ Synapse: site of communication between two neurons or between a neuron Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distribution, uploading or posting online, or transmitting in any form or by any means, electronic or mechanical, photocopying, recording, or otherwise of any of any part of this document, without prior written permission of SLU, is strictly prohibited. 64 Classification of Neurons 1. Structural Classification a. Multipolar neurons (Fig. 5.3a) - Have numerous branched dendrites and a single icon - The most common type in the CNS - Relay motor information or form a part of integrating network with other neurons - Include all motor neurons and interneurons of the brain, cerebellum and spinal cord b. Bipolar neurons (Fig. 5.3b) - Have a single dendrite and a single axon - Are not as common - Relay special sensory information to the CNS - Are sensory neurons found in the retina of the eye, in the organs of hearing (cochlear ganglia) and equilibrium (vestibular ganglia) in the inner ear, and in the olfactory epithelium in the upper region of the nose c. Unipolar neurons (Fig. 5.3c) - Have dendrites and axon that are fused together to form a continuous process that emerges from the cell body; aka pseudounipolar neurons - were initially bipolar during embryonic development; the two neuronal processes fuse during later development and form one process - Most neurons in the adult organism - Relay sensory information from the periphery to the CNS - Are sensory neurons found in numerous sensory ganglia of cranial and spinal nerves d. Anaxonic neurons - Have many dendrites but no true axon - Do not produce action potentials but regulate electrical changes of adjacent neurons Fig. 5.3. Structural classification of neurons Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distribution, uploading or posting online, or transmitting in any form or by any means, electronic or mechanical, photocopying, recording, or otherwise of any of any part of this document, without prior written permission of SLU, is strictly prohibited. 65  Examples of sensory receptors that are dendrites of unipolar neurons. (a) A corpuscle of touch is a touch receptor that consists of a mass of dendrites enclosed by a capsule of connective tissue. (b) A type I cutaneous mechanoreceptor is a touch receptor that consists of free nerve endings (bare dendrites) that make contact with tactile epithelial cells of the stratum basale of the skin. (c) A lamellated corpuscle is a pressure receptor composed of a multilayered connective tissue capsule that encloses a dendrite. (d) A nociceptor is a pain receptor that consists of free nerve endings (bare dendrites). Thermoreceptors (which detect thermal sensations), itch receptors, and tickle receptors resemble nociceptors in that they are unipolar neurons with free nerve endings that serve as sensory receptors. 2. Functional Classification a. Sensory or afferent neurons - Either contain sensory receptors at their distal ends (dendrites) or are located just after sensory receptors that are separate cells - Receive stimuli from the receptors throughout the body - Form an action potential in its axon and the action potential is conveyed into the CNS through cranial or spinal nerves - Unipolar in structure b. Motor or efferent neurons - Convey Convey action potentials away from the CNS to effectors muscles and glands) in the periphery (PNS) through cranial or spinal nerves - Mutipolar in structure - Somatic motor nerves are under voluntary control, usually found in most skeletal muscles; autonomic motor nerves control the “involuntary” activities of glands, cardiac muscle, and most smooth muscle. c. Interneurons or association neurons - Mainly located within the CNS between sensory and motor neurons - Establish relationships among other neurons, forming complex functional networks or circuits (CNS and retina) - Most are multipolar in structure; some are anaxonic and are estimated to include 99% of the neurons in the human CNS Neuroglia or Glia - Supportive, nonneural cells that surround neurons, axons, and dendrites - Generally are smaller than neurons with dark-staining nuclei - 5x to 25x more smaller than neurons - DO NOT generate or propagate action potentials - Can multiply and divide in the mature nervous system - Physical support, insulation of the neurons and synaptic clefts, repair of injured neurons, aid in metabolic exchange - Neuroglia of the CNS - astrocytes, oligodendrocytes, microglia, and ependymal cells - Neuroglia of the PNS - Schwann cells and satellite cells Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distribution, uploading or posting online, or transmitting in any form or by any means, electronic or mechanical, photocopying, recording, or otherwise of any of any part of this document, without prior written permission of SLU, is strictly prohibited. 66 1. Astrocytes (Fig. 5.4) - The largest and most numerous of the neuroglia - Stellate (star-shaped) cells with many processes - Multiple processes form perivascular feet, together with the capillary endothelial cells’s tight junctions, form the blood-brain barrier - Provide physical support, participating in blood-brain barrier, taking part in metabolic exchange between neurons and vasculature - Two (2) types: a. Protoplasmic astrocytes - Have many short branching processes - Found in gray matter b. Fibrous astrocytes - Have many long unbranched processes - Located mainly in white matter 2. Oligodendrocytes (Fig. 5.5) - Resemble astrocytes but are smaller and contain fewer processes - Responsible for forming and maintaining the myelin sheath around CNS axons - A single oligodendrocyte myelinates several axons 3. Microglia (Fig. 5.6) - Small cells with slender processes that give off numerous spine-like projections - Originiate from blood monocytes, NOT from neural tissue precursors - Function as phagocytes (macrophage of the CNS) 4. Ependymal Cells (Fig. 5.7) - Epithelial-like cells lacking basement membrane - Cuboidal to columnar cells arranged in a single layer that possess microvilli and cilia - Line the ventricles of the brain and central canal of the spinal cord - Produce, possibly monitor, and assist in the circulation of cerebrospinal fluid; also form the blood–cerebrospinal fluid barrier Fig. 5.4. Diagram of astrocyte Fig. 5.5. Diagram of oligodendrocytes Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distribution, uploading or posting online, or transmitting in any form or by any means, electronic or mechanical, photocopying, recording, or otherwise of any of any part of this document, without prior written permission of SLU, is strictly prohibited. 67  Fig. 5.6. Diagram of Microglia Fig. 5.7. Diagram of ependymal cells Fig. 5.8. Diagram of Schwann cell Fig. 5.9. Diagram of satellite cells 5. Schwann Cells (Fig. 5.8) - Aka neurolemmocytes - Encircle PNS axons - Form the myelin sheath around large-diameter axons - Each Schwann cell myelinates a single axon; a single Schwann cell can also enclose as many as 20 or more unmyelinated axons - Participate in axon regeneration, which is more easily accomplished in the PNS than in the CNS 6. Satellite Cells (Fig. 5.9) - Flat cells surround the cell bodies of neurons of PNS ganglia - Provide structural support - Regulate the exchanges of materials between neuronal cell bodies and interstitial fluid Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distribution, uploading or posting online, or transmitting in any form or by any means, electronic or mechanical, photocopying, recording, or otherwise of any of any part of this document, without prior written permission of SLU, is strictly prohibited. 68 Central Nervous System - Consists of the brain and spinal cord - It is surrounded by: ✓ bones: brain by the skull and spinal cord by vertebral column ✓ connective tissue (meninges) layers: (Fig. 5.1) ๏ Dura mater: outermost, tough, strong, and thick layer of dense connective tissue fibers ๏ Arachnoid mater: more delicate connective tissue deeper to the dura mater ๏ Pia mater: innermost layer of delicate connective tissue containing numerous blood vessels and adheres directly to the surfaces of the brain and spinal cord ‣ Subarachnoid space is found between the arachnoid mater and pia mater. Delicate, web-like strands of collagen and elastic fibers attach the arachnoid mater to the pia mater. ✓ Cerebrospinal fluid (CSF) - A clear, colorless fluid that cushions the brain and spinal cord - Continually produced by choroid plexuses in brain ventricle - Circulates in the subarachnoid space of the brain and spinal cord; also fills up the central canal of the spinal cord - Important for homeostasis and brain metabolism - Reabsorbed into venous blood (superior sagittal sinus) via arachnoid villi Peripheral Nervous System - Consists of all nervous tissue outside the CNS - Includes nerves, ganglia, enteric plexuses, and sensory receptors Nerve is a bundle of hundreds to thousands of axons plus associated connective tissue and blood vessels that lies outside the brain and spinal cord. Twelve pairs of cranial nerves emerge from the brain and thirty-one pairs of spinal nerves emerge from the spinal cord. Each nerve follows a defined path and serves a specific region of the body. Ganglia are small masses of nervous tissue, consisting primarily of neuron cell bodies, that are located outside of the brain and spinal cord. Ganglia are closely associated with cranial and spinal nerves. Enteric plexuses are extensive networks of neuron located in the walls of organs of the gastrointestinal tract. Sensory receptor refers to a structure of the nervous system that monitors changes in the external or internal environment. Examples include touch receptors in the skin, photoreceptors in the eye, and olfactory receptors in the nose. Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distribution, uploading or posting online, or transmitting in any form or by any means, electronic or mechanical, photocopying, recording, or otherwise of any of any part of this document, without prior written permission of SLU, is strictly prohibited. 69 Myelination of Axon Peripheral Nervous System - In the peripheral nervous system, ALL axons are enveloped by highly specialized cells called Schwann cells, which provide structural and metabolic support ๏ Myelinated Nerve Fiber (Figs. 5.10 and 5.11) - Myelinated sheath: formed by Schwann cell which envelopes and spirals many times around the axon forming multiple concentric layers of Schwann cell membrane; extends from the initial segment of the axon to the terminal branches - Neurolemma (sheath of Schwann) - the outer layer of Schwann cell’s cytoplasm and nucleus, which encloses the myelin sheath - Nodes of Ranvier - constrictions at intervals along the length of a myelinated axon; are the gaps between Schwann cells that myelinate the axon - Each Schwann cell wraps one axon segment between two nodes - In larger diameter axons - Capable of a regeneration tube that guides and stimulates regrowth of the axon Fig. 5.10. Myelinated and unmyelinated axons Fig. 5.11. Neuroglia of the peripheral nervous system ๏ Unmyelinated Nerve Fiber (Figs. 5.10 and 5.11) - Enveloped only by Schwann cell cytoplasm - Do NOT show nodes of Ranvier because the Schwann cells form a continuous sheath. - Each Schwann cell can envelope numerous unmyelinated axons Central Nervous System - Myelination is similar to that in the peripheral nervous system except that the myelin sheaths are formed by cells called oligodendrocytes - Cytoplasmic extensions of one oligodendrocyte envelopes and myelinates numerous axons - A neurolemma is NOT present - Fewer nodes of Ranvier - Display little regrowth after injury Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distribution, uploading or posting online, or transmitting in any form or by any means, electronic or mechanical, photocopying, recording, or otherwise of any of any part of this document, without prior written permission of SLU, is strictly prohibited. 70 Collections of the Nervous Tissue The components of the nervous tissue are grouped together in a variety of ways. Neuronal cell bodies are often grouped together in clusters. The axons of neurons are usually grouped together in bundles. In addition, widespread regions of nervous tissue are grouped together as either gray matter or white matter. Clusters of Neuronal Cell Bodies Ganglion - A cluster of neuronal cell bodies located in the PNS - Closely associated with cranial and spinal nerves Nucleus - A cluster of neuronal cell bodies located in the CNS Bundles of Axons Nerve Fig. 5.12. Schematic diagram of an axon - A bundle of axons that is located in the PNS - Enclosed within layers of connective tissue: endoneurium, perineurium, and epineurium - Cranial nerves connect the brain to the periphery, whereas spinal nerves connect the spinal cord to the periphery Tract - A bundle of axons that is located in the CNS - Interconnect neurons in the spinal cord and brain Gray Matter and White Matter White Matter - White and glistening in a freshly dissected section of the brain or spinal cord due to myelin - Composed primarily of myelinated axons, some unmyelinated axons, and neuroglia Gray Matter - Grayish, rather than white, because the Nissl bodies impart a gray color and there is little or no myelin in these areas - Contains neuronal cell bodies, dendrites, unmyelinated axons, axon terminals, and neuroglia ๏ Blood vessels are present in both white and gray matter Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distribution, uploading or posting online, or transmitting in any form or by any means, electronic or mechanical, photocopying, recording, or otherwise of any of any part of this document, without prior written permission of SLU, is strictly prohibited. 71 Histology of the Cerebrum Gray Matter - Located peripherally - Horizontal and radial axons associated with neuronal cells in different layers give the cerebral cortex a laminated appearance - Six (6) layers: (Fig. 5.13) 1. Molecular layer - Also known as plexiform layer - Most superficial layer - Covered by pia mater - Contains neuroglial cells and horizontal cells of Cajal (small, fusiform cells) 2. External granular layer - Contains neuroglial cells and small pyramidal cells - The pyramidal cells get progressively larger in successively deeper layers of the cortex - The apical dendrites of the pyramidal cells are directed toward the periphery of the cortex, whereas their axons extend from the cell bases 3. External pyramidal layer - Is composed of medium-sized pyramidal nerve cells 4. Internal granular layer - Thin layer with small granule, pyramidal cells, and neuroglia 5. Internal pyramidal layer - Thin Contains neuroglial cells and largest pyramidal cells - A higher magnification, the large pyramidal cells have typical large vesicular nucleus with its prominent nucleolus - The most prominent cell processes are the apical dendrites of the pyramidal cells, which are directed toward the surface of the cortex - The axons of the pyramidal cells arise from the base of the cell body and pass into the white matter - The intercellular area is occupied by neuroglial cells in the cortex, small astrocytes, and blood vessels, venule and capillary 6. Multiform layer - Deepest layer adjacent to white matter - Contains intermixed cells of varying shapes and sizes White Matter - Located centrally - Consists of myelinated nerve fibers or axons Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distribution, uploading or posting online, or transmitting in any form or by any means, electronic or mechanical, photocopying, recording, or otherwise of any of any part of this document, without prior written permission of SLU, is strictly prohibited. 72  Fig. 5.13. Layers of the gray matter (cerebrum) Histology of the Cerebellum Gray Matter: outer layer - Three (3) layers: (Fig. 5.14) 1. Molecular layer - Outer layer - Contains small neuronal cell bodies and many fibers; contains scattered basket cells whose unmyelinated axons normally course horizontally 2. Purkinje layer - Middle layer - Contains large Purkinje cells arranged in a single row between the molecular cell layer and the granular cell layer 3. Granular layer - Innermost layer - With numerous small granule cells with dark-staining nuclei and a small amount of cytoplasm, larger Golgi type II cells with typical vesicular nuclei and more cytoplasm, and irregularly dispersed, clear spaces called the glomeruli that contain only synaptic complexes Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distribution, uploading or posting online, or transmitting in any form or by any means, electronic or mechanical, photocopying, recording, or otherwise of any of any part of this document, without prior written permission of SLU, is strictly prohibited. 73 White Matter: inner layer - Consists of myelinated nerve fibers or axons Fig. 5.14. Layers of the gray matter (cerebellum) Histology of the Spinal Cord Gray Matter - Located centrally - Symmetrical H-shaped or butter y-shaped - Consists of cell bodies of neurons, dendrites, unmyelinated axons, and neuroglia - Subdivided into regions called horns: 1. Posterior (dorsal) gray horns - Extend toward the back of the spinal cord - Contain interneurons and sensory neurons 2. Anterior (ventral) gray horns - Extend toward the front of the spinal cord - Contain somatic motor nuclei that provide nerve impulses for contraction of skeletal muscles and neuroglia 3. Lateral gray horns - Between the posterior and anterior gray horns - Present only in thoracic and upper lumbar segments of the spinal cord - Contain autonomic motor nuclei that regulate the activity of cardiac muscle, smooth muscle, and glands Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distribution, uploading or posting online, or transmitting in any form or by any means, electronic or mechanical, photocopying, recording, or otherwise of any of any part of this document, without prior written permission of SLU, is strictly prohibited. 74 fl - Other structures: ✓ Gray commissure: Forms the crossbar of the H that connects the 2 sides of the spinal cord ✓ Anterior (ventral) white commissure: Connects the white matter of the right and left sides of the spinal cord ✓ Central canal - Small space at the center that extends the entire length of the spinal cord Fig. 5.15. Regions of the gray matter (spinal cord) - Develops from the lumen of the embryonic neural tube - Continuous with the ventricles of the brain - Contains CSF For more information and - Lined by ependymal cells description, please refer to the Human Histology Laboratory Manual White Matter Exercise No. 5: Nervous Tissues - Located peripherally - Consists of myelinated axons grouped into tracts ✓ Sensory (ascending) tracts: conduct nerve impulses toward the brain ✓ Motor (descending) tracts: carry nerve impulses from the brain - Organized into regions called columns: 1. Anterior (ventral) white columns 2. Posterior (dorsal) white columns 3. Lateral white columns LABORATORY ACTIVITY 1.2: Exercise No. 5 Answer the following questions based on the lesson above. Elaborate 1. Differentiate myelinated from unmyelinated nerve fiber. _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ Property of and for the exclusive use of SLU. 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What is the importance of microglial cells? _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ 2. Enumerate and briefly describe the parts of a neuron. _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ END OF LABORATORY EXERCISE 4 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distribution, uploading or posting online, or transmitting in any form or by any means, electronic or mechanical, photocopying, recording, or otherwise of any of any part of this document, without prior written permission of SLU, is strictly prohibited. 76  MODULE 2 EXERCISE 6: MUSCULAR TISSUES Covering, Support and Body Movement OBJECTIVES Upon successful 1. Describe the general characteristics of muscular tissue completion of this 2. Differentiate the three histologic categories of muscular exercise, the reader should be tissues and their functions. able to: M uscle tissue is composed of cells that optimize the universal cell property of contractility. In these specialized cells, movement is generated by interaction of the proteins actin and myosin (contractile proteins). All muscle cells are of mesodermal origin and differentiate by a gradual process of cell lengthening with Engage abundant synthesis of the myofibrillar proteins actin and myosin. Certain forms of contractile cell function as single-cell contractile units: Myoepithelial cells are an important component of certain secretory glands, where they function to expel secretions from glandular acini. Pericytes are smooth muscle-like cells that surround blood vessels. Myofibroblasts are cells that have a contractile role in addition to being able to secrete collagen. This type of cell is not readily seen in normal tissues but becomes essential following tissue damage during the process of healing and repair, leading to formation of a scar. Other forms of contractile cells function by forming multicellular contractile units termed muscles. Such muscle cells can be divided into three types and can be distinguished on the basis of morphologic and functional characteristics, with the FUN FACT! structure of each adapted to its physiologic role. Skeletal muscle contains bundles of very long, multinucleated cells with cross-striations. Their contraction is quick, forceful, and usually under It takes 17 muscles in the face for us voluntary control. Cardiac muscle also has cross-striations and is to smile and 43 muscles to frown. composed of elongated, often branched cells 😊😀😃😁 attached to one another at structures called intercalated discs that are unique to cardiac muscle. Contraction is involuntary, vigorous, and rhythmic. Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distribution, uploading or posting online, or transmitting in any form or by any means, electronic or mechanical, photocopying, recording, or otherwise of any of any part of this document, without prior written permission of SLU, is strictly prohibited. 74  Smooth muscle consists of collections of fusiform cells that lack striations and have slow, involuntary contractions. Certain cell structures are given special names: ✓ sarcoplasm - cytoplasm of muscle cells ✓ sarcolemma - surrounding cell membrane or plasmalemma ✓ sarcoplasmic reticulum - smooth endoplasmic reticulum Muscle cells of all three types are surrounded by an external lamina. In all muscle cell types, contractile forces developed from the internal contractile proteins are transmitted to the external lamina via link proteins which span the muscle cell membrane. The external lamina binds individual muscle cells into a single functional mass. General Characteristics of Muscular Tissue Consists of elongated muscle cells called muscle fibers or myocytes Surrounded by connective tissue that conveys nerves, blood vessels and lymphatics throughout the muscle Specialized for contraction by the sliding interaction of myosin filaments along actin filaments (a process known as the sliding filament mechanism) Functions of Muscular Tissue Through sustained contraction or alternating contraction and relaxation, muscular tissue has four (4) key functions: Producing body movements. Walking and running, localized movements like holding a pencil, writing, or nodding the head due to muscular contractions rely on the integrated functions of skeletal muscles, bones and joints. Stabilizing body positions. Skeletal muscle contractions stabilize joints and help maintain body positions like standing or sitting. Postural muscles contract continuously when you are awake; for example, sustained contractions of your neck muscles hold your head upright when you are listening intently to your teacher talk about the muscular tissue. Storing and moving substances within the body. Storage is done by sustained contractions of ringlike bands of smooth muscle called sphincters. These sphincters prevent outflow of the contents of a hollow organ (temporary storage of urine in the urinary bladder or storage of food in the stomach). The heart pump blood through the blood vessels by the contractions of the cardiac muscle. Skeletal muscle contractions promote the flow of lymph and aid the return of blood in veins to the heart. Generating heat. Thermogenesis is the process of producing heat. Muscular tissues produce heat during contraction. Most of the heat generated by the muscle is used to maintain normal body temperature. Shivering is the involuntary contractions of skeletal muscle, which can increase the rate of heat production. Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distribution, uploading or posting online, or transmitting in any form or by any means, electronic or mechanical, photocopying, recording, or otherwise of any of any part of this document, without prior written permission of SLU, is strictly prohibited. 75  LABORATORY ACTIVITY 2.1: Exercise No. 6 TO DO Match the photomicrograph to the correct muscle type Explore A. Smooth muscle B. Skeletal muscle C. Cardiac muscle Skeletal Muscle Tissue - Usually attached to bones by tendons Explain - Long cylindrical fiber with many peripherally located nuclei; unbranched; striated with alternating light and dark bands seen by microscopy (Fig. 6.1) Fig. 6.1. Longitudinal and transverse sections of skeletal (striated) muscles of the tongue. Stain: hematoxylin and eosin. High magnification. Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distribution, uploading or posting online, or transmitting in any form or by any means, electronic or mechanical, photocopying, recording, or otherwise of any of any part of this document, without prior written permission of SLU, is strictly prohibited. 76  - Arise from the fusion of a hundred or more small mesodermal cells called myoblasts during embryonic development, thus, each mature skeletal muscle fiber has a hundred or more nuclei Part of the myoblast population does not fuse and differentiate but remains as a group of mesenchymal cells called muscle satellite cells located on the external sur face of muscle fibers inside the developing external lamina. Satellite cells proliferate and produce new muscle fibers following muscle injury. (Fig. 6.2) Fig. 6.2. Development of skeletal muscles Skeletal Muscle Fiber - Length: Very long, vary greatly in length, from a few centimeters in short muscles to 30–40 cm in the longest muscles - Diameter: Very large - 10-100 um - Structure: (Fig. 6.3) 1. Sarcolemma ๏ Transverse (T) tubules - Long, finger-like invaginations of the sarcolemma that penetrate into the sarcoplasm - Aligned with each A-I band junctions - Filled with interstitial fluid (ensures that an action potential excites all parts of the muscle fiber at essentially the same instant) 2. Nuclei - 100 or more in each skeletal muscle fiber - Found just beneath the sarcolemma 3. Sarcoplasm a. Glycogen - Large molecule composed of many glucose molecules - Can be used for ATP synthesis b. Myoglobin - A red-colored protein, found only in muscle, - Binds oxygen molecules that diffuse into muscle fibers from interstitial fluid and releases oxygen when it is needed by the mitochondria for ATP production Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distribution, uploading or posting online, or transmitting in any form or by any means, electronic or mechanical, photocopying, recording, or otherwise of any of any part of this document, without prior written permission of SLU, is strictly prohibited. 77  b. Mitochondria - Lie in rows throughout the muscle fiber, strategically close to the contractile muscle proteins that use ATP during contraction so that ATP can be produced quickly as needed c. Sarcoplasmic reticulum - A fluid-filled system of membranous sacs that encircles each myofibril - Dilated end sacs of the SR called terminal cisterns butt against the T tubule from both sides - Abundant in skeletal muscle fibers - In a relaxed muscle fiber, the sarcoplasmic reticulum stores calcium ions (Ca++ ). Release of Ca++ from the terminal cisterns of the SR triggers muscle contraction d. Myofibrils - The contractile organelles of skeletal muscle - Arranged in parallel bundles - About 2 um in diameter and extend the entire length of a muscle fiber - Containing thin and thick filaments (myofilaments) whose overlapping organization produces staining differences that cause striations For more information and description, please refer to the Human Histology Fig. 6.3. Muscle fiber Laboratory Manual Exercise No. 6: Muscular Tissue Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distribution, uploading or posting online, or transmitting in any form or by any means, electronic or mechanical, photocopying, recording, or otherwise of any of any part of this document, without prior written permission of SLU, is strictly prohibited. 78  Structure of Myofibril - Consists of a long series of sarcomeres separated by Z discs and containing thick and thin filaments that overlap in certain regions ✓ Sarcomere: the basic functional contractile unit of a myofibril ๏ Components: (Fig. 6.4) 1. Z discs Narrow, plate-shaped regions of dense material that separate one sarcomere from the next 2. A band Dark, middle part of sarcomere that extends entire length of thick filaments and includes those parts of thin filaments that overlap thick filaments 3. I band Lighter, less dense area of sarcomere that contains remainder of thin filaments but no thick filaments. A Z disc passes through center of each I band 4. H zone Narrow region in center of each A band that contains thick filaments but no thin filaments 5. M line Region in center of H zone that contains proteins that hold thick filaments together at center of sarcomere TEM X28,000 Fig. 6.4. Components of a sarcomere Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distribution, uploading or posting online, or transmitting in any form or by any means, electronic or mechanical, photocopying, recording, or otherwise of any of any part of this document, without prior written permission of SLU, is strictly prohibited. 79  Connective Tissue Components of Skeletal Muscle - Three (3) layers: (Fig. 6.5) 1. Epimysium - The outer layer, encircling the entire muscle - Consists of dense irregular connective tissue 2. Perimysium - Surrounds groups of 10 to 100 or more muscle fibers, separating them into bundles called fascicles - Consists of dense irregular collagenous connective tissue 3. Endomysium - Surrounds and separates individual muscle fibers from one another - Consists mostly of reticular fibers Muscle Proteins - Three (3) kinds of proteins 1. Contractile Proteins - Generate force during contraction Myo brils ✓ Myosin Fig. 6.5. Connective ‣ Makes up thick filament; a molecule tissue components consists of a tail and two myosin heads, which bind to myosin- binding sites on actin molecules of thin filament during muscle contraction ‣ Functions as a motor protein in all three types of muscle tissue ✓ Actin ‣ The main component of thin filament; each actin molecule has a myosin-binding site where myosin head of thick filament binds during muscle contraction. ‣ Functions as a motor protein in all three types of muscle tissue 2. Regulatory Proteins - Help switch the contraction process on and off ✓ Tropomyosin ‣ Component of thin filament; when skeletal muscle fiber is relaxed, tropomyosin covers myosin- binding sites on actin molecules, thereby preventing myosin from binding to actin ✓ Troponin ‣ Regulatory protein that is a component of thin filament; when calcium ions (Ca2+) bind to troponin, it changes shape; this conformational change moves tropomyosin away from myosin-binding sites on actin molecules, and muscle contraction subsequently begins as myosin binds to actin. Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distribution, uploading or posting online, or transmitting in any form or by any means, electronic or mechanical, photocopying, recording, or otherwise of any of any part of this document, without prior written permission of SLU, is strictly prohibited. 80 fi  3. Structural Proteins - Keep thick and thin filaments of myofibrils in proper alignment, give myofibrils elasticity and extensibility, and link myofibrils to sarcolemma and extracellular matrix ✓ Titin ‣ Connects Z disc to M line of sarcomere, thereby helping to stabilize thick filament position; can stretch and then spring back unharmed, and thus accounts for much of the elasticity and extensibility of myofibrils ✓ α-Actinin ‣ Structural protein of Z discs that attaches to actin molecules of thin filaments and to titin molecules ✓ Myomesin ‣ Forms M line of sarcomere; binds to titin molecules and connects adjacent thick filaments to one another ✓ Nebulin ‣ Wraps around entire length of each thin filament; helps anchor thin filaments to Z discs and regulates length of thin filaments during development ✓ Dystrophin ‣ Links thin filaments of sarcomere to integral membrane proteins in sarcolemma, which are attached in turn to proteins in connective tissue matrix that surrounds muscle fibers; thought to help reinforce sarcolemma and help transmit tension generated by sarcomeres to tendons Types of Skeletal Muscle Fibers - Skeletal muscle fibers are classified into three (3) main types: 1. Slow Oxidative (SO) Fibers - Fibers appear dark red because they contain large amounts of myoglobin and many blood capillaries - Contains many large mitochondria therefore SO fibers generate ATP mainly by aerobic respiration (that’s why they are called oxidative fibers) - These fibers are said to be “slow” because the ATPase in the myosin heads hydrolyzes ATP relatively slowly and the contraction cycle proceeds at a slower pace than in “fast” fibers. - SO fibers have slow speed of contraction; twitch contractions last from 100 to 200 msec, and they take longer to reach peak tension; very resistant to fatigue and capable of prolonged, sustained contractions for many hours - They are adapted for maintaining posture and for aerobic, endurance-type activities 2. Fast Oxidative-Glycolytic (FOG) Fibers - Largest and contain large amounts of myoglobin and many blood capillaries; appears dark red - Can generate ATP by aerobic respiration giving them moderately high resistance to fatigue - Can also generate ATP by anaerobic glycolysis due to high levels of intracellular glycogen level - “Fast” because the ATPase in their myosin heads hydrolyzes ATP three to five times faster than the myosin ATPase in SO fibers making their speed of contraction faster - Twitches of FOG fibers reach tension more quickly than those of SO fibers but are briefer in duration—less than 100 msec - Contribute to activities like walking and sprinting Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distribution, uploading or posting online, or transmitting in any form or by any means, electronic or mechanical, photocopying, recording, or otherwise of any of any part of this document, without prior written permission of SLU, is strictly prohibited. 81  3. Fast Glycolytic (FG) Fibers - Have low myoglobin content, few blood capillaries, few mitochondria, and appear white in color - Contain large amounts of glycogen and generate ATP mainly by glycolysis - FG fibers contract strongly and quickly due to their ability to hydrolyze ATP rapidly - Fast-twitch fibers are adopted for intense anaerobic movements of short duration; fatigues quickly Cardiac Muscle Tissue - Located in the heart and large vessels attached to the heart - Branched cylindrical fiber with one centrally located nucleus; intercalated discs join neighboring fibers; striated - Develop from mesodermal cells that migrate to and envelop the developing heart while it is still in the form of endocardial heart tubes Cardiac Muscle Fiber (Fig. 6.6) - Length: Long - 50 - 100um - Diameter: Large - 10 - 20um - Structure: ‣ Contains myosin and actin filaments arranged in sarcomeres and same bands, zones and Z discs as in skeletal muscle ‣ Contains one or two central nuclei ‣ Fibers are branched ‣ Characterized by dense junctional complexes called intercalated disks that contain gap junctions and desmosomes ‣ T tubules located at Z lines; larger than in skeletal muscle ‣ Sarcoplasmic reticulum less well developed ‣ Regulatory proteins: tropomyosin and troponin Fig. 6.6. Longitudinal and transverse section of the cardiac muscle. Stain: hematoxylin and eosin. High magnification. Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distribution, uploading or posting online, or transmitting in any form or by any means, electronic or mechanical, photocopying, recording, or otherwise of any of any part of this document, without prior written permission of SLU, is strictly prohibited. 82  Connective Tissue Components of Cardiac Muscle - Endomysium; subendocardial and sub pericardial connective tissue layers Smooth Muscle Tissue - Found in walls of hollow viscera, airways, blood vessels, iris and ciliary body of eye, arrector pili muscles of hair follicles - Fibers are fusiform in shape (thickest in middle, tapered at each end) and contain one centrally positioned nucleus; not striated (Fig. 6.7) - Develop from mesodermal cells that migrate to and envelop the developing gastrointestinal tract and viscera Fig. 6.7. Longitudinal and transverse section of the skeletal muscle in the wall of the small intestine. Stain: hematoxylin and eosin. High magnification. Smooth Muscle Fiber - Length: Intermediate - 30-200um - Diameter: Small - 3-8um - Structure: ‣ Contains myosin and actin filaments that have no regular pattern of overlap; therefore, does NOT exhibit striations ‣ Actin and myosin form lattice (criss-cross) network and insert into dense bodies in the sarcoplasm ‣ Contains one central nucleus ‣ Gap junctions couple muscle and allow ionic communication between all fibers ‣ T tubules are NOT present ‣ Short membrane invaginations, called caveolae, are often frequent at the smooth muscle cell surface ‣ Very little sarcoplasmic reticulum ‣ Regulatory proteins: myosin light-chain kinase (MLCK) and calmodulin Connective Tissue Components of Smooth Muscle - Endomysium and less-organized CT sheaths Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distribution, uploading or posting online, or transmitting in any form or by any means, electronic or mechanical, photocopying, recording, or otherwise of any of any part of this document, without prior written permission of SLU, is strictly prohibited. 83  LABORATORY ACTIVITY 2.2: Exercise No. 6 Answer the following questions based on the lesson above. Elaborate 1. Explain the structural differences among the three types of muscular tissue. _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ 2. Compare the functions and special properties of the three types of muscular tissue. _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ END OF LABORATORY EXERCISE 6 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distribution, uploading or posting online, or transmitting in any form or by any means, electronic or mechanical, photocopying, recording, or otherwise of any of any part of this document, without prior written permission of SLU, is strictly prohibited. 84  MODULE 2 EXERCISE 7: THE INTEGUMENTARY SYSTEM Covering, Support and Body Movement OBJECTIVES Upon successful completion of this Describe the histological features of the skin and its exercise, the associated structures. reader should be able to: T he skin, also known as the integument (Latin integumentum, covering) or cutaneous layer, covers the external surface of the body and is the largest organ of the body accounting for 15% to 20% of total body weight and, in adults, the skin covers an area of about 2 square meters (22 square feet). It shows Engage significant regional variation, with the thickest skin being found on the soles (4.0mm) of the feet while the thinnest is the delicate skin on the upper and lower eyelids (0.5mm). The specific functions of the skin fall into several broad categories: Protection. The skin provides a physical barrier against thermal and mechanical insults like friction and against most microorganisms. It also provides a barrier against excessive water loss and wetting. Sensory. Many types of sensory receptors allow skin to constantly monitor the environment, and various skin mechanoreceptors help regulate the body’s interactions with physical objects. Thermoregulator. A constant body temperature is normally easily maintained thanks to the skin’s insulating components (eg, the fatty layer and hair FUN FACT! on the head) and its mechanisms for accelerating heat loss (sweat production and a dense super ficial microvasculature). Some special components of skin like hair and nails provide protection against cold in the form of fur (in most Your skin constantly sheds dead cells, mammals). about 30,000 to 40,000 cells every minute! That’s nearly 9lbs. per year! Sexual signaling. The skin (pigmentation) and hair are visual indicators of health involved in attraction between the sexes in all vertebrate species. Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distribution, uploading or posting online, or transmitting in any form or by any means, electronic or mechanical, photocopying, recording, or otherwise of any of any part of this document, without prior written permission of SLU, is strictly prohibited. 85  Pheromones are produced by apocrine sweat glands and other skin gland, which are important for attraction. Metabolic. Cells of skin synthesize vitamin D3, needed in calcium metabolism and proper bone function, through the local action of UV light on the vitamins precursor. Excess electrolytes can be removed in sweat, and the subcutaneous layer stores a significant amount of energy in the form of fat. LABORATORY ACTIVITY 2.1: Exercise No. 7 TO DO Match the photomicrograph to the correct layer of the skin. Explore A. Thick Skin A. Stratum granulosum B. Stratum spinosum C. Stratum corneum D. Stratum lucidum E. Stratum basale Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distribution, uploading or posting online, or transmitting in any form or by any means, electronic or mechanical, photocopying, recording, or otherwise of any of any part of this document, without prior written permission of SLU, is strictly prohibited. 86  Skin Structure The skin has three main layers: Explain Epidermis Dermis Subcutis or hypodermis or panniculus Epidermis - Composed of keratinized stratified squamous epithelium - It contains four (4) principal types of cells (Fig. 7.1): 1. Keratinocytes (Fig. 7.2a) - Constitute about 90% of epidermal cells which are arranged in four or five layers - Produce the protein keratin (a tough, fibrous protein helps to protect the skin and underlying tissues from abrasions, heat, microbes, and chemicals. - Produce lamellar granules, which release a water-repellent sealant (minimizes entry and loss of water and inhibits entry of foreign material 2. Melanocytes (Fig. 7.2b) - Constitute about 8% of epidermal cells - Develop from the ectoderm of a developing embryo - The long, slender projections extend between the keratinocytes and transfer melanin granules to them - Melanin: a yellow-red or brown- black pigment that contributes to skin color and absorbs damaging ultraviolet (UV) light 3. Intraepidermal Macrophages (Fig. 7.2c) - Also known as Langerhans cells - Arise from the red bone marrow then migrate to the epidermis - Participate in immune responses mounted against microbes invading the skin (help other cells of the immune system recognize an invading microbe and destroy it) Fig.7.1. Location of the four principal cell types in epidermis of thick - Easily damaged by UV light skin 4. Tactile Epithelial Cells (Fig. 7.2d) - Also known as Merkel cells - Least numerous - Found in the deepest layer of the epidermis coming into contact with a tactile disc/ Merkel disc: flattened process of a sensory neuron - Detect touch sensations Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distribution, uploading or posting online, or transmitting in any form or by any means, electronic or mechanical, photocopying, recording, or otherwise of any of any part of this document, without prior written permission of SLU, is strictly prohibited. 87 Fig.7.2. Four principal cell types in the epidermis ๏ Thin Skin - Found in most regions of the body - Has four (4) strata (layers): ‣ Stratum basale ‣ Stratum spinosum ‣ Stratum granulosum ‣ Stratum corneum ๏ Thick Skin - Found in parts of the body where exposure to friction is greatest (fingertips, palms and soles) - Has five (5) strata (layers): For more information and ‣ Stratum basale description, please refer to the ‣ Stratum spinosum Human Histology Laboratory Manual ‣ Stratum granulosum Exercise No. 7: Integumentary ‣ Stratum lucidum System ‣ Stratum corneum Dermis - The second, deeper part of the skin - Important to the survival of the epidermis, and these adjacent layers form many important structural and functional relations - Composed of dense irregular connective tissue containing collagen and elastic fibers - Characteristics: ✓ It has great tensile strength, meaning it resists pulling or stretching forces ✓ It can stretch and recoil easily ✓ Thicker than the epidermis (varies from region to region in the body) - Few cells are present in the dermis and include predominantly fibroblasts, with some macrophages, and few adipocytes near its boundary with the subcutaneous layer - Blood vessels, nerves, glands, and hair follicles (epithelial invaginations of the epidermis) are embedded in the dermal layer - Can be divided into thin superficial papillary region and thick deeper reticular region Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distribution, uploading or posting online, or transmitting in any form or by any means, electronic or mechanical, photocopying, recording, or otherwise of any of any part of this document, without prior written permission of SLU, is strictly prohibited. 88 Hypodermis - A superficial fascial sheath with interspersed adipose tissue. - It is a layer directly below the dermis and serves to connect the skin to the underlying fascia (fibrous tissues) of bones and muscles. ✓ The fascia reduces the friction between the dermis and deeper musculature. ✓ Adipose tissue participates in thermoregulatory mechanisms as well as disperses forces generated from direct impact. - Laboratory emphasis: ✓ When viewed under the microscope using H&E stain (Fig. 7.3), the hypodermis is the lightest layer visible and consists mainly of adipose tissue. ✓ Dense connective tissue strands may extend from the dermis deep into the hypodermis and anchor the skin to underlying structures. HOW TO LOCATE THE HYPODERMIS IN A STAINED SLIDE? Since hypodermis is generally composed of adipose tissue and some connective tissues, try to locate first “adipose cells” and check the border between the dermis and hypodermis. The hypodermis is the lightest stained layer with an abundance of adipose cells. Fig.7.3. Thin skin, Human, (H&E) (Epi: epidermis, D: dermis, H: hypodermis Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distribution, uploading or posting online, or transmitting in any form or by any means, electronic or mechanical, photocopying, recording, or otherwise of any of any part of this document, without prior written permission of SLU, is strictly prohibited. 89  Fig.7.4. Hair showing the different parts Accessory Structures of the Skin - Include hair, skin glands, and nails - Develop from embryonic epidermis Hair (Pili) (Fig. 7.4) - Function is limited: ✓ Hair on the head guards the scalp from injury and the sun’s rays; Decreases heat loss from the scalp ✓ Eyebrows and eyelashes protect the eyes from foreign particles, just like the hair in the nostrils and in the external ear canal ✓ Hairs also function in sensing light touch (touch receptors associated with hair follicles are activated whenever a hair is moved. Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distribution, uploading or posting online, or transmitting in any form or by any means, electronic or mechanical, photocopying, recording, or otherwise of any of any part of this document, without prior written permission of SLU, is strictly prohibited. 90  Skin Glands (Fig. 7.4) SEBACEOUS (OIL) ECCRINE SWEAT APOCRINE SWEAT CERUMINOUS FEATURE GLANDS GLANDS GLANDS GLANDS Largely in lips, Throughout skin of Skin of axillae, glans penis, labia most regions of groin, areolae, minora, and tarsal the body, bearded regions Exernal auditory Distribution glands; small in especially skin of of the face, canal trunk and limbs; forehead, palms, clitoris, and labia absent in palms and soles minora and soles Mostly in deep dermis Mostly in deep Location of (sometimes in dermis and upper Subcutaneous Dermis secretory portion upper subcutaneous layer subcutaneous layer layer) Surface of external auditory Termination of Most connected Surface of canal or into Hair follicles excretory duct to hair follicle epidermis ducts of sebaceous glands Perspiration, Perspiration, which consists of Sebum (mixture of which consists of water, ions (Na+, triglycerides, the same Cl-), urea, uric Cerumen, a waxy Secretion cholesterol, components as acid, ammonia, material proteins, and eccrine sweat amino acids, inorganic salts glands plus lipids glucose, and and proteins lactic acid Impede entrance Prevents hairs of foreign bodies Regulation of from drying out, and insects into body Stimulated during prevent water loss external ear temperature, emotional stress Functions from skin, keep canal, waste removal, and sexual skin soft, inhibit waterproof stimulated during excitement growth of some canal, prevent emotional stress bacteria microbes from entering cells Relatively inactive during childhood; Onset of function Soon after birth Puberty Soon after birth activated during puberty Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distribution, uploading or posting online, or transmitting in any form or by any means, electronic or mechanical, photocopying, recording, or otherwise of any of any part of this document, without prior written permission of SLU, is strictly prohibited. 91  Nails - Plates of tightly packed, hard, dead, keratinized epidermal cells that form a clear, solid covering over the dorsal surfaces of the distal portions of the digits - Parts: (Figs. 7.5 and 7.6) 1. Nail body - Visible portion of of the nail - Comparable to the stratum corneum of the epidermis, with the exception that its flattened, keratinized cells fill with a harder type of keratin and cells are not shed - Below is a region of epithelium and a deeper layer of dermis 2. Free edge - Part of the nail body and may extend past the distal end of the digit - White in color because there are no capillaries underneath. - Underneath is the hyponychium: a thickened region of stratum corneum which secures the nail to the fingertip 3. Nail root - Portion of the nail that is buried in a fold of skin - A whitish, crescent-shape area of the proximal end of the nail body called the lunula can be seen ๏ Nail bed - The skin below the nail plate that extends from the lunula to the hyponychium - Epidermis lacks a stratum granulosum ๏ Eponychium (cuticle) - A narrow band of epidermis that extends from and adheres to the margin of the nail wall - Occupies the proximal border of the nail and consists of stratum corneum ๏ Nail matrix - Portion of the epithelium proximal to the nail root - Divides mitotically to produce new nail cells - Growth rate is determined by the rate of mitosis in matrix cells, influenced by factors like person’s age, health and nutritional status - Growth also varies according to the season, time of day, and environmental temperature ✓ The average growth in the length of fingernails is about 1mm (0.04 in) per week. ✓ Toenails grow slower compared to fingernails. ✓ The longer the digit, the faster the nail grows Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distribution, uploading or posting online, or transmitting in any form or by any means, electronic or mechanical, photocopying, recording, or otherwise of any of any part of this document, without prior written permission of SLU, is strictly prohibited. 92  - Functions: ✓ Protect the distal end of the digits ✓ Provide support and counter pressure to the palmar surface of the fingers to enhance touch perception and manipulation ✓ Allow us to grasp and manipulate small objects, and they can be used to scratch and groom the body in various ways Fig.7.5. Nail showing the different parts Fig.7.6. Fingernail, monkey (H&E). E - eponychium; N - nail plate; H - hyponychium; DP - distal phalanx Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distribution, uploading or posting online, or transmitting in any form or by any means, electronic or mechanical, photocopying, recording, or otherwise of any of any part of this document, without prior written permission of SLU, is strictly prohibited. 93  LABORATORY ACTIVITY 2.2: Exercise No. 7 Answer the following questions based on the lesson above. Elaborate 1. Describe the layers of the epidermis and the cells that compose them. _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ 2. Contrast the locations and functions of sebaceous glands, sudoriferous glands, and ceruminous glands. _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ 3. Enumerate the functions of the skin. _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ END OF LABORATORY EXERCISE 7 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distribution, uploading or posting online, or transmitting in any form or by any means, electronic or mechanical, photocopying, recording, or otherwise of any of any part of this document, without prior written permission of SLU, is strictly prohibited. 94  MODULE 3 EXERCISE 8: THE ENDOCRINE SYSTEM Regulation & Integration of the Body OBJECTIVES Upon successful Describe the histological features of the major organs that completion of this comprise the endocrine system and relate these to their exercise, the reader should be functions. able to: T he endocrine system is responsible for the production and secretion of chemical messengers known as hormones. These hormones maybe distributed throughout the body by the bloodstream, where they will act on a specific target organs or affect a wide range of organs and tissues. Other hormones Engage act locally, arriving at their site of action through a specialized microcirculation. Together with the nervous system, hormones coordinate and integrate the functions of all the physiological systems. Responses of the endocrine system are slower than responses of the nervous system; although some although some hormones act within seconds, most take several minutes or more to cause a response. The effects of nervous system activation are generally briefer than those of the endocrine system. The nervous system acts on specific muscles and glands. The influence of the endocrine system is much broader; it helps regulate virtually all types of body cells. As a general rule, endocrine glands are composed of islands of secretory epithelial cells with intervening support tissue, rich in blood and lymphatic capillaries. The secretory cells discharge hormone into the interstitial spaces and it is rapidly absorbed into the circulatory system. Recall in Exercise No. 3 that the body contains two FUN FACT! kinds of glands: exocrine glands and endocrine glands. Exocrine glands secrete their products into ducts that carry the secretions into body cavities, into the lumen of an organ, or to outer surface of the Stress kicks the body. Endocrine glands secrete their products into endocrine system into the interstitial fluid surrounding the secretory cells. From the interstitial fluid, hormones diffuse into blood high gear. capillaries and blood carry them to target cells throughout the body. Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distribution, uploading or posting online, or transmitting in any form or by any means, electronic or mechanical, photocopying, recording, or otherwise of any of any part of this document, without prior written permission of SLU, is strictly prohibited. 88 Reflecting their active hormone synthesis, cells of the endocrine system have prominent nuclei and abundant mitochondria, endoplasmic reticulum, Golgi bodies and secretory vesicles. The nature of the secretory vesicles varies according to the hormone secreted. There are four main groups of chemicals which can act as hormones: Protein and glycoprotein molecules, e.g. insulin, growth hormone, parathyroid hormone (PTH). Small peptide molecules, e.g. vasopressin, products of enteroendocrine cells. Amino acid derivatives, e.g. thyroxine, adrenaline and noradrenaline. Steroids derived from cholesterol, e.g. adrenal cortical hormones, ovarian and testicular hormones. Endocrine cells produce hormones based on amino acids, peptides and proteins often have characteristic membrane-bound secretory vacuoles with electron-dense central cores (dense core granules). The endocrine system can be divided into three parts: The major endocrine organs in which the sole or major function of the organ is the synthesis, storage, and secretion of hormones (e.g. thyroid and adrenal glands) Endocrine components within other solid organs, like the endocrine components of the pancreas, ovary, testis and kidney, in the form of clusters of endocrine cells within other tissues The diffuse endocrine system, scattered individual hormone cells (or small clumps), usually within an extensive epithelium (GIT and RT). The major function of these cells is probably paracrine (i.e. acting on adjacent non-endocrine cells, rather than entering the bloodstream and producing systemic effects). LABORATORY ACTIVITY 3.1: Exercise No. 8 TO DO Match the photomicrograph to the correct structure of the pituitary Explore gland. A. Neurohypophysis A. Pars tuberalis B. Adenohypophysis B. Pars distalis C. Pars intermedia Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distribution, uploading or posting online, or transmitting in any form or by any means, electronic or mechanical, photocopying, recording, or otherwise of any of any part of this document, without prior written permission of SLU, is strictly prohibited. 89  A. Chromophobes A. Pars nervosa B. Chromophils B. Infundibulum A. Herring bodies B. Pituicytes Match the photomicrograph to the correct structure of the adrenal gland. A. Cortex B. Medulla C. Glomerulosa D. Capsule E. Fasciculata F. Reticularis Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distribution, uploading or posting online, or transmitting in any form or by any means, electronic or mechanical, photocopying, recording, or otherwise of any of any part of this document, without prior written permission of SLU, is strictly prohibited. 90  Match the photomicrograph to the correct Match the photomicrograph to the correct structure of the thyroid gland. structure of the parathyroid gland.