Anatomy and Physiology PDF

Structural Classification of Neurons There are 3 types of neurons, based on differences in size, shape, and structure: Multipolar neurons: have many dendrites and one axon arising from their cell bodies; most neurons with cell bodies in CNS (interneurons and motor neurons) are...

Structural Classification of Neurons There are 3 types of neurons, based on differences in size, shape, and structure: Multipolar neurons: have many dendrites and one axon arising from their cell bodies; most neurons with cell bodies in CNS (interneurons and motor neurons) are multipolar. Loading… Bipolar neurons have 2 processes extending from the cell body, a dendrite and an axon; found in some of the special senses, such as the eyes, nose, and ears. Unipolar neurons have only 1 process extending from the cell body; outside the cell body, it soon splits into 2 parts that function as 1 axon; the peripheral process has dendrites near a peripheral body part, and the central process runs into the CNS; the cell bodies are found in ganglia outside the CNS; these are sensory neurons. © McGraw Hill, LLC 11 Figure 9.4: Structural Classification of Neurons & Part A: Multipolar neurons consist of one axon with several dendrites protruding from the cell body. Part B : Bipolar neurons consist of one axon and one dendrite. The dendrite extends to form several minute branches. Part C: Unipolar neurons consist of only one axon on either side of a round cell body devoid of dendrites. One section of the axon is labeled the peripheral process (extending to the peripheral nervous system). The other section of the axon is labeled the central process (extending to the central nervous system). © McGraw Hill, LLC 12  important for exam Functional Classification of Neurons Sensory (afferent) neurons: conduct impulses from peripheral receptors to the CNS; usually unipolar, although some are bipolar. Interneurons (association or internuncial neurons): multipolar neurons lying within the CNS that form links between other neurons; the cell bodies of some interneurons aggregate in specialized masses called nuclei. Motor (efferent) neurons: multipolar neurons that conduct impulses from the CNS to peripheral effectors (muscles or glands). © McGraw Hill, LLC 13 Figure 9.5: Functional Classification of Neurons The nervous system is divided into two, the central nervous system (CNS) and the peripheral nervous system (PNS). Signals (information) are received by the sensory receptors in the PNS which leads to the sensory neuron. It is noted that the sensory (afferent) neurons transfer sensory information to neurons in the CNS. The information is transferred to the interneuron in the CNS which leads to the next interneuron. © McGraw Hill, LLC 14 Figure 9.5: Functional Classification of Neurons From the second interneuron, the information is released to the motor neuron. It is noted that the interneurons transfer information from one part of the CNS to another. From the motor neurons of the CNS, information is released to the effector muscle or gland of the PNS. It is noted that the motor (efferent) neurons transfer instructions from the CNS to the effectors. © McGraw Hill, LLC 15  9.4: Neuroglia Neuroglia (glial cells, “nerve glue”) are cells that support neurons. Functions: fill spaces, structurally support, protect, and insulate neurons Do not generate or conduct nerve impulses - only thereto support 4 types in CNS, 2 types in PNS Central nervous system neuroglia: Microglia: small cells that function as phagocytes for bacterial cells and cellular debris and produce scar tissue in sites of injury Oligodendrocytes: form the myelin sheath around axons in the brain and spinal cord Ependymal cells produce cerebrospinal fluid in CNS. © McGraw Hill, LLC 16  Types of Neuroglia Astrocytes: lie between blood vessels and neurons; functions: Structural support Regulation of nutrient and ion concentrations Formation of the blood-brain barrier, which protects brain tissue from chemical fluctuation and prevents entry of many substances Peripheral nervous system neuroglia: Schwann cells: produce the myelin sheath around PNS axons Satellite cells: provide protective coating around cell bodies of neurons in the PNS © McGraw Hill, LLC 17 Figure 9.6: Neuroglia of the Central Nervous System Four types of neuroglia are found in the CNS namely the microglial cell, oligodendrocyte, astrocyte, and ependymal cell. A microglial cell consists of a round structure with filaments and branches protruding from it. Oligodendrocyte is a round structure extending from the Schwann cells of two neurons. Astrocytes are structures that consist of a round head with branches extending to the capillaries and neighboring neurons. The fluid-filled cavity of the brain or spinal cord is enclosed by a line of ependymal cells. © McGraw Hill, LLC 18  Figure 9.7: Satellite Cells and Schwann Cells of the PNS Several rod-shaped Schwann cells are present on the axon. Schwann cells produce the myelin sheath that surrounds the axons of peripheral nerves. From one of the axons protrudes the round structure of the neuron cell body. The neuron cell body is enclosed by a lining of satellite cells. Satellite cells provide a protective coat around the cell bodies of peripheral neurons. © McGraw Hill, LLC 19  Membrane Potential and Distribution of Ions Membrane Potential: the charge inside a cell Resting Membrane Potential: the charge in a cell when it is at rest; this is about -70 mV in neurons Charge inside a neuron results from unequal distribution of ions inside and outside of cells There is a greater concentration of sodium ions on the outside the cells than inside, and a greater concentration of potassium ions inside the cells than outside. Many large negatively charged ions and proteins are found on the inside of cells. © McGraw Hill, LLC 22 Figure 9.8: Resting Membrane Potential The voltmeter is attached to the intracellular fluid of the cytosol and the extracellular fluid. A channel is located on the cell membrane of the cell. ATP molecules from the cell reach the extracellular fluid via the channel. ADP from the extracellular fluid enters the cell via the channel. Protein particles are present inside the cell. Inside and outside the cell are several chloride ions, potassium ions, and sodium ions. Potassium ions are high in number inside the cell while chloride and sodium ions are high in number outside the cell. The voltmeter reads 70 volts. © McGraw Hill, LLC 23  big exam question Stimulation and the Action Potential A neuron remains at rest until stimulated. A stimulus can change resting potential in either direction. An excitatory stimulus opens chemically-gated channels; ions flow into cell due to concentration gradient, causing inside of neuron to become less negative. Threshold stimulus: a stimulus strong enough to cause so many ions to enter neuron, that potential changes from -70 to -55 mV (the threshold potential). Upon reaching threshold potential, voltage-gated channels open, changing charge to about +30 mV; this begins an action potential. g Change from negative to positive charge inside neuron is called depolarization, since now, inside and outside are both positive. © McGraw Hill, LLC 24  big exam question Stimulation and the Action Potential Reaching an action potential is all-or-none response: Action potential either occurs or does not. & An action potential occurs when the charge reaches -55 mV. Action potentials of a neuron are all of the same strength. * When an action potential is reached, cell responds by returning to resting of Potassium potential (-70 mV) by process of repolarization. opening mannels - * Repolarization returns the polarized state and is accomplished by outward flow of potassium ions through potassium channels. At end of repolarization, a slight overshoot called hyperpolarization occurs, in which potential dips below -70 mV. + Finally, the Nat/k Pump moves Nat back out of cell, and Nat back into cell. © McGraw Hill, LLC 25  Figure 9.9: Ion Channels and the Action Potential moresodium inside Potassium outside 55mU mainly sodium Flowe sodiumis coming inside positive making Inside 70mV back to · resting Potential © McGraw Hill, LLC 26  Important test question Figure 9.10: A Recording of an Action Potential The horizontal x-axis shows milliseconds from 0 to 8 in increments of 1. The vertical y-axis shows membrane potential in millivolts from minus 80 to 40 in irregular increments. A line in the graph represents the membrane potential. The membrane potential begins as a resting potential and increases to reach a peak at (2.5, 30) during depolarization. The membrane potential then decreases during repolarization. It then reaches the point (3.2, minus 70) which is marked as hyperpolarization. The line then extends quite steadily where the resting potential is re-established. © McGraw Hill, LLC 27  9.6: Impulse Conduction An action potential at the trigger zone causes an electrical current to flow to adjacent regions of the axon’s membrane. This spreads by a local current flowing down the fiber that stimulates the next region and continues down the axon to the axon terminal. This process is called impulse conduction. Refractory period: period during and after an action potential, during which a threshold stimulus will not cause another action potential: Limits frequency of action potentials Ensures the impulse is only transmitted in one direction – down the axon © McGraw Hill, LLC 28  : - A series of action The Process of Impulse Conduction Potential occurs along the axon TABLE 9.1 Impulse Conduction 1. Neuron membrane Neuron membrane maintains potential restingresting potential. zomu - 1. 2 Threshold stimulus is received. 1. 3 Sodium channels in the trigger zone of the axon open. Inside + 30mv 1. & Sodium ions diffuse inward, depolarizing the axon membrane. 1. S Potassium channels in the axon membrane open. 6 1. Potassium ions diffuse outward, repolarizing the axon membrane. out 7 1. The resulting action potential causes a local electric current that stimulates the adjacent portions of the axon membrane. © McGraw Hill, LLC 30  Types of Impulse Conduction Continuous conduction: Occurs in unmyelinated axons no node of ranvier - Conduct impulses sequentially over the entire length of their membrane slower - Saltatory conduction: Fat > - Occurs in myelinated axons The myelin sheath insulates axons from ion movement across the cell membrane Impulses “jump” from one Node of Ranvier to the next, since sodium and potassium channels occur only at the nodes Speed of impulse conduction is proportional to axon diameter: Thick, myelinated motor axons conduct at 120 m/s Thin, unmyelinated sensory axons conduct at 0.5 m/s © McGraw Hill, LLC 31  Figure 9.12: Saltatory Conduction in a Myelinated Axon © McGraw Hill, LLC 32  9.7: The Synapse A synapse is a junction between 2 communicating neurons. The small gap between the neurons is called the synaptic cleft; the impulse must be conveyed across the cleft. The neuron sending the impulse is the presynaptic neuron. The neuron receiving the impulse is the postsynaptic neuron. Neural communication across the cleft is called synaptic transmission. Communication is accomplished by a chemical called a neurotransmitter, which is stored in synaptic vesicles and released from an expansion at the distal end of the presynaptic neuron, called the synaptic knob. Neurotransmitters are released in response to a nerve impulse reaching the synaptic knob; they diffuse across the cleft and bind to receptors on the membrane of the postsynaptic neuron. © McGraw Hill, LLC 33  Important for exam 9.8: Synaptic Transmission Excitatory and Inhibitory Actions: Excitatory Neurotransmitters: Increase entry of ions into postsynaptic neuron Bring membrane closer to threshold, making action potential more likely Inhibitory Neurotransmitters: Increase flow of (i ions into neuron or flow of kT ions out of the neuron Makes charge inside the neuron more negative, making action potential less likely The postsynaptic neuron may have many presynaptic neurons influencing it, so it sums the excitatory & inhibitory inputs from all of these neurons to derive its response. © McGraw Hill, LLC 37 Figure 9.16: Excitatory versus Inhibitory Stimulus In both graphs, the horizontal and vertical graphs are not labeled. The horizontal axes are devoid of units. The vertical axes read units of -80, -70, and -55 (from the origin). The graphs show the two types of stimulus excitatory and inhibitory generated due to the neurotransmitter. Part A: Excitatory cells spread the network activity in and out of the network. As a result, a line begins at -70, extends steadily, increases diagonally to reach a peak, and curves. Part B: Inhibitory cells provide recurrent feedback. It is regulated by the rate of synaptic activity. As a result, a line begins at -70, extends steadily, decreases diagonally with a slight curve, reaches a peak, and ends at a point. © McGraw Hill, LLC 38  Neurotransmitters More than 100 neurotransmitters are produced in synaptic knobs and stored in synaptic vesicles. Neurotransmitters include acetylcholine, monoamines, amino acids, neuropeptides. The action of the neurotransmitter depends on type of receptors in a specific synapse. Some neurons produce one type of neurotransmitter, while others produce two or three. © McGraw Hill, LLC 39  Important Some Neurotransmitters & Their Actions TABLE 9.2 Some Neurotransmitters and Representative Actions Neurotransmitter Locatio Major Actions n Acetylcholine CNS Controls skeletal muscle actions. PNS Stimulates skeletal muscle contraction at neuromuscular junctions; may excite or inhibit autonomic nervous system actions, depending on receptors. Monoamines Norepinephrine CNS Creates a sense of feeling good; low levels may lead to depression. PNS May excite or inhibit autonomic nervous system actions, depending on receptors. Dopamine CNS Creates a sense of feeling good; deficiency in some brain areas is associated with Parkinson disease. PNS Limited actions in autonomic nervous system; may excite or inhibit, depending on receptors. Serotonin CNS Primarily inhibitory; leads to sleepiness; action is blocked by LSD, enhanced by selective serotonin reuptake inhibitor drugs (SSRIs). © McGraw Hill, LLC 40  Histamine CNS Release in hypothalamus promotes alertness. Some Neurotransmitters & Their Actions TABLE 9.2 Some Neurotransmitters and Representative Actions Neurotransmitter Locatio Major Actions n Amino acids GABA CNS Generally inhibitory. Glutamic acid CNS Generally excitatory. Neuropeptides Substance P PNS Excitatory; pain perception. Endorphins, CNS Generally inhibitory; reduce pain by inhibiting substance P release. enkephalins Gases Nitric oxide PNS Vasodilation. CNS May play a role in memory. © McGraw Hill, LLC 41  Events Leading to Release of a Neurotransmitter TABLE 9.3 Events Leading to the Release of a Neurotransmitter 1. Action Potential Action potentialPasses passes along along an anaxon and over axon theover and surface of itssurface the of Its synaptic knob synaptic knob. 1. 2 Synaptic knob membrane becomes more permeable to calcium ions, and they diffuse inward. 1. 3 In the presence of calcium ions, synaptic vesicles fuse to synaptic knob membrane. 1. A Synaptic vesicles release their neurotransmitter into synaptic cleft. © McGraw Hill, LLC 42  Facilitation, Convergence, and Divergence Facilitation: An increase in the release of neurotransmitter in response to one impulse, which occurs in an excitatory presynaptic neuron upon repeated stimulation; this response increases the likelihood that the postsynaptic neuron will reach threshold Convergence: The transmission of nerve impulses to a single neuron within a pool from two or more fibers; this makes it possible for the neuron to summate impulses from different sources Divergence: The transmission of nerve impulses from a neuron in a pool to several output fibers; this serves to amplify an impulse © McGraw Hill, LLC 45 Figure 9.17: Impulse Processing: Convergence and Divergence Part A: Impulses from neurons 1 and 2 together lead to neuron 3. Part B: Impulses from neuron 4 reaches neurons 5 and 6 separately. © McGraw Hill, LLC 46  9.12: Meninges The brain and spinal cord are surrounded by 3 membranes called meninges that lie between the skull bones & vertebrae and the soft CNS tissues. The meninges consist of the dura mater, arachnoid mater, and pia mater. Dura mater: Outermost layer of meninges Made up of tough, dense connective tissue, and is very thick Contains many blood vessels Forms the internal periosteum of the skull bones In some areas, the dura mater forms partitions between lobes of the brain, and in others, it forms dural sinuses. The sheath around the spinal cord is separated from the vertebrae by an epidural space. © McGraw Hill, LLC 56  Meninges Arachnoid mater: The middle layer of meninges Thin, weblike layer that lacks blood vessels Between the arachnoid and pia mater is the subarachnoid space, which contains cerebrospinal fluid (CSF) Pia mater: The innermost layer of the meninges Thin layer, which contains many blood vessels and nerves Attached to the surface of the brain and spinal cord and follows their contours © McGraw Hill, LLC 57 Figure 9.22: The Meninges of the Brain Part A shows the posterior view of the head. The view shows the scalp and cranium, cerebrum & cerebellum, vertebra, spinal cord, & the layer of meninges forming the outer layer of the brain stem. Part B shows the layers present in the meninges. The illustration shows the outer skin followed by the subcutaneous tissue, bone of the skull, & dural sinus. The meninges is comprised of three layers namely the dura mater, arachnoid mater, and pia mater. The Dura mater is the outermost layer, the pia mater is the innermost layer & the arachnoid mater is the middle layer. The space between the arachnoid mater and the pia mater is the subarachnoid space. Outside the pia mater are the cerebrum which is composed of grey matter and white matter (neurons). © McGraw Hill, LLC 58 Figure 9.23: The Meninges of the Spinal Cord Part A shows the structure of the dura mater which encloses the spinal cord. The parts located in the illustration are the Spinal cord, Pia mater, Subarachnoid space filled with cerebrospinal fluid, Arachnoid mater, Dura mater, Anterior root, Posterior root, Spinal nerve, Posterior root ganglion, & Thoracic vertebra. Part B shows a segment of the vertebra with meninges covering it. The parts located in the illustration are the Pia mater, Subarachnoid space filled with cerebrospinal fluid, Arachnoid mater, Dura mater, Spinal nerve, Posterior root ganglion, Central canal, Subarachnoid space, Epidural space, Posterior root, Spinal cord, Anterior root, and Body of vertebra. © McGraw Hill, LLC 59  9.13: Spinal Cord Spinal cord: Begins at the base of the brain at the foramen magnum Extends as a thin cord to the level of the intervertebral disc between the 1st and 2nd lumbar vertebrae Cervical enlargement: A thickened area near top of spinal cord Provides nerves to upper limbs Lumbar enlargement: A thickened region near the bottom of the spinal cord Gives rise to nerves that serve the lower limbs. Cauda equina (horse’s tail): Structure formed where spinal cord tapers to a point inferiorly Consists of spinal nerves in the lumbar & sacral areas © McGraw Hill, LLC 60 Figure 9.24: Lateral View of Spinal Cord The illustration shows the midsagittal section of the brain which shows the various parts of the brain. The base of the brain consists of the foramen magnum. The brain stem extends to form the cervical enlargement, the spinal cord, the vertebral canal, lumbar enlargement, and cauda equina at the tail of the spinal cord © McGraw Hill, LLC 61  Structure of the Spinal Cord Spinal cord consists of 31 segments, each of which connects to a pair of spinal nerves. Two deep grooves (anterior median fissure and posterior median sulcus) divide the cord into right and left halves. White matter, made up of bundles of myelinated nerve fibers (nerve tracts), surrounds a butterfly-shaped core of gray matter housing interneurons and neuron cell bodies. Cell bodies of sensory neurons that enter the spinal cord are found in the posterior root ganglia outside the spinal cord. The upper and lower wings of gray matter form the posterior and anterior horns; between them is the lateral horn. The gray matter divides the white matter into three regions: anterior, lateral and posterior funiculi (columns), each consisting of longitudinal bundles of axons called tracts. A central canal in the middle of the gray matter contains cerebrospinal fluid. © McGraw Hill, LLC 62 Figure 9.25: A Cross Section of the Spinal Cord Part A: A cross-section of the spinal cord shows the white matter and gray matter. The illustration shows the following parts: Butterfly-shaped structure of the gray matter which is comprised of posterior horn, lateral horn, and anterior horn; gray commissure at the center of the mirror structures of gray matter, posterior median sulcus; a white matter which is composed of the posterior funiculus, lateral funiculus, and anterior funiculus; dorsal root of the spinal nerve; dorsal root of the ganglion; posterior of the spinal nerve; ventral root of the spinal nerve; anterior median fissure, and central canal. Part B shows the micrograph of the cross-section of the spinal cord. The gray matter, white matter, dorsal root of the spinal nerve, dorsal root of the ganglion, and posterior of the spinal nerve are visible. © McGraw Hill, LLC (b): Ed Reschke/Photolibrary/Getty Images 63  Functions of the Spinal Cord Major functions: transmit impulses to and from the brain, and to house spinal reflexes Ascending tracts carry sensory information to the brain; descending tracts carry motor information from brain to muscles or glands The names that identify nerve tracts identify the origin and termination of the fibers in the tract: Spinothalamic tracts: carry sensory information from the spinal cord to the thalamus Corticospinal tracts (pyramidal tracts): carry motor impulses from the cerebral cortex to the spinal cord; pass through pyramid-shaped areas in the medulla oblongata Extrapyramidal tracts: descending tracts involved with balance and posture Spinal reflexes: controlled by reflex arcs that pass through the spinal cord © McGraw Hill, LLC 64  Figure 9.26: Ascending Tracts The ascending tract begins from the skin. Impulses from the temperature receptors or pain receptors are originated in the skin. The impulses reach the sensory fibers of the spinal cord where the cross-over happens. The transverse section of the spinal cord is located. The impulse reaches the brainstem which follows the order of the medulla oblongata, pons, spinothalamic tract, and midbrain, and finally reaches the thalamus in the frontal section of the cerebrum. © McGraw Hill, LLC 65  Figure 9.27: Descending Tracts The descending tract begins from the motor cortex in the frontal section of the cerebrum. The impulses begin at the cerebrum and reach the corticospinal tract followed by the brainstem in the order of midbrain, pons, and medulla oblongata where the motor fibers cross-over takes place. The impulse then reaches the spinal cord and is directed to the skeletal muscle. © McGraw Hill, LLC 66  9.14: The Brain The brain is the largest, most complex portion of the nervous system, containing 100 billion multipolar neurons, and many neuroglia to support the neurons. Structure is reversed from that of spinal cord; gray matter outside and white matter inside. The 4 main parts of the brain: Cerebrum: largest portion; associated with higher mental functions, and sensory & motor functions Diencephalon: processes sensory input and controls many homeostatic processes Cerebellum: coordinates muscular activity Brainstem: coordinates and regulates visceral activities and connects different parts of the nervous system © McGraw Hill, LLC 67 Figure 9.28a: Midsagittal Section of the Brain (Diagram) The illustration of the midsagittal section of the brain shows the following parts: The outer hard layer of the skull; dura mater; gyrus and sulcus of the brain; cerebrum; diencephalon which is comprised of the thalamus, pineal gland, hypothalamus, and posterior pituitary gland; brainstem which is comprised of the midbrain, pons, and medulla oblongata, corpus callosum which bridges the hemispheres of the brain, cerebellum at the base of the brain, and spinal cord which extends from the brain stem. © McGraw Hill, LLC 68  Structure of the Cerebrum The Cerebrum is the largest portion of the mature brain. Consists of 2 cerebral hemispheres, which are mirror images Corpus callosum: flat bundle of nerve fibers that connects the hemispheres. The surface of the brain is marked by these features: Gyri (singular is gyrus): ridges Sulci (singular is sulcus): grooves Fissures (longitudinal and transverse): deep grooves © McGraw Hill, LLC 70  Structure of the Cerebrum Four lobes of the cerebrum are named according to the bones they underlie: frontal, parietal, temporal, and occipital lobes. The fifth lobe is the insula; it lies deep in the lateral sulcus. A thin layer of gray matter, the cerebral cortex, lies on the outside of the cerebrum, and contains 75% of the neuron cell bodies in the nervous system. -mylinated Beneath the cortex lies a mass of white matter made up of myelinated nerve fibers connecting the cell bodies of the cerebral cortex with the rest of the nervous system. © McGraw Hill, LLC 71  Figure 9.29a: Lateral View of the Human Brain (Diagram) The brain is comprised of four major lobes namely the frontal lobe, temporal lobe, parietal lobe, and occipital lobe. Between the frontal and temporal lobes is the insula. Sensory areas: which interpret impulses that arrive from all sensory receptors in body. Motor areas: contain pyramidal cells, impulses travel from pyramidal cells down corticospinal tracts in spinal cord before reaching skeletal muscle. Frontal eye field: controls voluntary movements of eyes & learned movement patterns such as writing. © McGraw Hill, LLC 72  Functions of the Cerebrum The cerebrum provides higher brain functions: Interpretation of sensory input Initiating voluntary muscular movements Stores information for memory Integrates information for reasoning Intelligence Personality © McGraw Hill, LLC 73  Functional Areas of the Cerebral Cortex The functional areas of the brain overlap, but the cortex can generally be divided into sensory, association, and motor areas. The sensory areas are located in several areas of the cerebrum; they interpret sensory input, producing feelings or sensations: Cutaneous senses: anterior parietal lobe Visual area: posterior occipital lobe Auditory area: posterior temporal lobe Taste area: base of central sulcus and insula Smell area: deep in temporal lobe Sensory fibers from the PNS cross over in the spinal cord or the brainstem; this results in sensory impulses from the right side of the body being interpreted by centers in the left cerebral hemisphere. © McGraw Hill, LLC 74  Functional Areas of the Cerebral Cortex Association areas of the brain analyze and interpret sensory impulses, and function in reasoning, judgment, emotions, verbalizing ideas, and storing memory: Association areas of the frontal lobe control a number of higher intellectual processes (planning, problem solving). Association areas of the parietal lobe function in understanding speech and choosing the proper words. Association areas in occipital lobe help analyze visual patterns and combine visual images with other sensory information. Association areas next to sensory areas are important for analyzing the sensory input. A general interpretive area is found at the junction of the parietal, temporal, and occipital lobes, and plays a primary role in complex thought processing and integration. Not all association areas are bilateral; Wernicke’s area of the temporal lobe is g usually on the left side only; it helps with understanding of written and spoken exam language. question © McGraw Hill, LLC 75  Functional Areas of the Cerebral Cortex The primary motor areas lie in the posterior frontal lobes, anterior to the central sulcus. This region includes the pyramidal cells that are also called upper motor neurons; they synapse with lower motor neurons that exit the spinal cord and reach the skeletal muscles. There is also crossover in the brainstem in motor systems, so that the right cerebral hemisphere controls muscles on the left side of the body. Broca’s motor speech area is in the frontal lobe, usually on the left side; controls muscle movements for speech. Frontal eye field in the frontal lobe controls voluntary eye movements. © McGraw Hill, LLC 76  The Basal Nuclei The basal nuclei are masses of gray matter (nuclei) located deep within the cerebral hemispheres. Basal nuclei are also called basal ganglia. Consist of the caudate nucleus, the putamen, and the globus pallidus Produce the inhibitory neurotransmitter, dopamine Relay motor impulses from the cerebrum and help control motor activities by interacting with the motor cortex, thalamus, and cerebellum Help facilitate voluntary movement Altered activity of these nuclei neurons produces the signs of Parkinson disease and Huntington disease. © McGraw Hill, LLC 78  11.2: Hormone Action Structurally, there are 2 types of hormones: Steroids or steroid-like substances, which are derived from cholesterol Nonsteroids: amines, peptides, proteins, or glycoproteins, which are produced from amino acids © McGraw Hill, LLC 9  need to know Types of Hormones TABLE 11.2 Types of Hormones Type of Compound Formed From Examples Steroids Cholesterol Estrogen, testosterone, aldosterone, cortisol Amines Amino acids Norepinephrine, epinephrine, thyroid hormones Peptides Amino acids Antidiuretic hormone, oxytocin, thyrotropin-releasing hormone Polypeptides and proteins Amino acids Parathyroid hormone, growth hormone, prolactin Glycoproteins Protein and Follicle-stimulating hormone, carbohydrate luteinizing hormone, thyroid- stimulating hormone © McGraw Hill, LLC 10  Steroid Hormones Characteristics of steroid hormones: Lipid-soluble, so they can pass through cell membranes Carried in the bloodstream weakly bound to plasma proteins, which prevents rapid degradation Loading… Protein receptors for steroid hormones are located inside the target cell The hormone-receptor complex binds with the DNA and activates specific genes that, in turn, direct the synthesis of specific proteins The new protein may function as an enzyme, transport protein, or hormone receptor; it carries out the effects of the steroid hormone © McGraw Hill, LLC 11  Figure 11.3: Steroid Hormone Action © McGraw Hill, LLC 12  receptorhas topresent - The be it Nonsteroid Hormones - Characteristics of nonsteroid hormones: Water-soluble; cannot penetrate the phospholipid bilayer of cell membranes Nonsteroid hormones combine with receptors in target cell membranes; the receptors have a binding site and an activity site The hormone is called the first messenger The chemicals in the cell that respond to binding of the hormone, and cause changes in the cell, are called second messengers The cascade of biological activity through the cell membrane to the inside, beginning with the binding of the hormone, is called signal transduction The hormone-receptor complex generally activates a G protein, which then activates the enzyme adenylate cyclase that is bound to the inside of the cell membrane Adenylate cyclase breaks down ATP to cAMP, which activates protein kinases Protein kinases phosphorylate other proteins, activating them; this carries out the effects of the hormone © McGraw Hill, LLC 13 Figure 11.4: Nonsteroid Hormone Action © McGraw Hill, LLC 14  11.4: Pituitary Gland The pituitary gland (hypophysis) is attached to the hypothalamus by a stalk called the infundibulum: Anterior pituitary (anterior lobe): Consists mostly of glandular epithelial tissue Arranged around blood vessels and enclosed in a capsule of collagenous connective tissue Posterior pituitary (posterior lobe): Part of the nervous system Consists of axons of neurons of the hypothalamus © McGraw Hill, LLC 22 Figure 11.7: The Pituitary Gland and Hypothalamus The pituitary gland is located at the base of the brain, where a pituitary stalk (infundibulum) attaches it to the hypothalamus. The gland is about 1 cm in diameter & consists of an anterior & posterior lobe. The pituitary gland is attached to the hypothalamus and lies in the sella turcica of the sphenoid bone. © McGraw Hill, LLC 23  Control of the Pituitary Gland by the Hypothalamus The hypothalamus controls the activity of the pituitary gland. Anterior pituitary control: Releasing and inhibiting hormones from the hypothalamus control the secretion from the anterior pituitary These hormones are carried in the bloodstream along the pituitary stalk directly to the anterior pituitary by hypophyseal portal veins Specific anterior pituitary cells are then stimulated to release or stop releasing their hormone Posterior pituitary control: The posterior pituitary stores hormones made by the hypothalamus The posterior pituitary releases these hormones into the blood in response to nerve impulses from the hypothalamus © McGraw Hill, LLC 24  Figure 11.8: Secretion of Pituitary Hormones ) Releasing hormones from neurons in the hypothalamus stimulates secretory cells of the anterior lobe of the pituitary gland to secrete anterior pituitary hormones. (b) Other neurons in the hypothalamus release their hormones directly into capillaries of the posterior lobe of the pituitary gland as posterior pituitary hormones. © McGraw Hill, LLC 25  Anterior Pituitary Hormones Growth Hormone (GH): Stimulates body cells to grow and reproduce Speeds the rate at which cells use carbohydrates and fats Growth hormone-releasing hormone (GHRH) from the hypothalamus increases the amount of GH secreted, GH inhibiting hormone (GHIH, somatostatin) inhibits its secretion Nutritional status also affects the release of GH; more is released when glucose is low, or when certain amino acids increase GH imbalances: Pituitary dwarfism: Due to GH deficiency during childhood Gigantism: Due to GH oversecretion during childhood Acromegaly: Due to GH oversecretion in adulthood © McGraw Hill, LLC 26  Anterior Pituitary Hormones Prolactin (PRL): Promotes milk production following the birth of an infant Controlled by prolactin releasing factor (PRF) and prolactin inhibiting hormone (PIH) from the hypothalamus There is no known normal physiological role in males Thyroid-stimulating hormone (Thyrotropin or TSH): Controls the secretion of hormones from the thyroid gland Thyrotropin-releasing hormone (TRH) from the hypothalamus stimulates the release of TSH As blood concentration of thyroid hormones increases, secretions of TRH and TSH decrease © McGraw Hill, LLC 27 Figure 11.9: The TRH-TSH-Thyroid Hormone Pathway Thyrotropin-releasing hormone (TRH) from the hypothalamus stimulates the anterior pituitary gland to release thyroid-stimulating hormone (TSH), which stimulates the thyroid gland to release thyroid hormones. These thyroid hormones reduce the secretion of TSH and TRH by negative feedback + = stimulation - = inhibition © McGraw Hill, LLC 28  Anterior Pituitary Hormones Adrenocorticotropic hormone (ACTH): Controls the secretion of certain hormones from the adrenal cortex Regulated by corticotropin-releasing hormone (CRH) from the hypothalamus Loading… Stress can also increase release of CRH, which increases ACTH secretion Gonadotropins (FSH and LH): Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) affect the gonads: testes in the male and ovaries in the female In males, LH is also known as interstitial-cell stimulating hormone (ICSH). © McGraw Hill, LLC 29  Posterior Pituitary Hormones Neurons in the hypothalamus produce antidiuretic hormone (ADH) and oxytocin (OT), which are stored in the posterior pituitary Impulses from the hypothalamus release the hormones from the posterior pituitary gland These hormones travel down the axons of the hypothalamus to their storage area in the posterior pituitary gland Even though these 2 hormones are synthesized in the hypothalamus, they are called posterior pituitary hormones, because they are released into the blood there © McGraw Hill, LLC 30 Figure 11.10: Histology of the Anterior and Posterior Pituitary Histology of (a) anterior pituitary composed of epithelial tissue and (b) posterior pituitary composed of nervous tissue. The posterior pituitary consists mostly of axons and neuroglia, unlike the anterior pituitary which is composed primarily of glandular epithelial cells. Neuroglia support the axons which originate from neurons in the hypothalamus. The secretions of these neurons function not as neurotransmitters, but as hormones. © McGraw Hill, LLC 31  Posterior Pituitary Hormones 2 Antidiuretic hormone (ADH or vasopressin): Causes the kidneys to conserve water, and reduces amount of water excreted in the urine The hypothalamus regulates the secretion of ADH, based on the amount of water in body fluids Osmoreceptors detect changes in osmotic pressure in body fluids, and adjust amount of ADH secretion At high level, also causes vasoconstriction of blood vessels, which helps to maintain blood pressure in conditions of dehydration Diabetes insipidus is a condition resulting from insufficient ADH © McGraw Hill, LLC 32  Posterior Pituitary Hormones Oxytocin (OT): Plays a role in childbirth by contracting muscles in the uterine wall, and in milk ejection by forcing milk into ducts from the milk glands during breastfeeding Stretching of the uterine and vaginal tissues in the latter stages of pregnancy stimulates release of oxytocin Suckling of an infant at the breast stimulates release of oxytocin after childbirth Release is controlled through positive feedback © McGraw Hill, LLC 33  Hormones of the Pituitary Gland 1 TABLE 11.3 Hormones of the Pituitary Gland Hormone Action Source of Control Anterior Lobe Growth hormone Stimulates an increase in the size Secretion stimulated by growth (GH) and division rate of body cells; hormone-releasing hormone from the enhances movement of amino hypothalamus. Secretion inhibited by acids across membranes growth hormone inhibiting hormone from hypothalamus Prolactin (PRL) Sustains milk production after Secretion inhibited by prolactin- birth inhibiting hormone (dopamine) from the hypothalamus. Secretion stimulated by numerous prolactin-releasing factors, including thyrotropin-releasing hormone (TRH) from the hypothalamus Thyroid-stimulating Controls secretion of hormones Thyrotropin-releasing hormone (TRH) hormone (TSH) from thyroid gland from hypothalamus Adrenocorticotropic Controls secretion of certain Corticotropin-releasing hormone (CRH) hormone (ACTH) hormones from adrenal cortex from hypothalamus © McGraw Hill, LLC 34  Hormones of the Pituitary Gland 2 TABLE 11.3 Hormones of the Pituitary Gland Hormone Action Source of Control Follicle-stimulating In females, responsible for the development Gonadotropin-releasing hormone (FSH) of egg-containing follicles in ovaries and hormone from hypothalamus stimulates follicular cells to secrete estrogen; in males, stimulates production of sperm cells Luteinizing Promotes secretion of sex hormones; plays Gonadotropin-releasing hormone (LH) a role in releasing an egg cell in females hormone from hypothalamus Posterior Lobe* Antidiuretic Causes kidneys to conserve water; in high Hypothalamus in response to hormone (ADH) concentration constricts blood vessels changes in water concentration in body fluids Oxytocin (OT) Contracts smooth muscle in the uterine Hypothalamus in response to wall; contracts myoepithelial cells stretching of uterine and associated with milk-secreting glands vaginal walls and stimulation of *These hormones are synthesized in the hypothalamus, as explained in the text. breasts © McGraw Hill, LLC 35  11.5: Thyroid Gland The thyroid gland is located below the larynx and consists of two broad lobes connected by an isthmus Two hormones of the thyroid gland help control caloric intake, and one helps regulate blood calcium level and bone growth Structure of the thyroid gland: The thyroid consists of secretory units called follicles, filled with hormone-storing colloid Follicular cells secrete hormones that can be stored in the colloid or released into the blood © McGraw Hill, LLC 36  Figure 11.11: Structure of the Thyroid Gland (a) The thyroid gland consists of two lobes connected anteriorly by an isthmus. (b) Illustration of thyroid follicles (c) micrograph of thyroid tissue. Follicular cells secrete the thyroid hormones; thyroxine and triiodothyronine. Extrafollicular cells secrete calcitonin. © McGraw Hill, LLC (c) Jose Luis Calvo/Shutterstock 37  Hormones of the Thyroid Gland Follicular cells produce 2 iodine-containing hormones, thyroxine is the more potent hormone These two hormones have similar actions; they regulate metabolism of carbohydrates, lipids and proteins They also increase the rate at which cells release energy from carbohydrates, enhance protein synthesis, and stimulate the breakdown and mobilization of lipids Thyroid hormone level is the major factor in determining the basal metabolic rate (BMR), the caloric intake necessary to maintain life These hormones are essential for normal growth and development and nervous system maturation The hypothalamus and pituitary gland control release of thyroid hormones Iodine is needed by the follicular cells to make thyroid hormones © McGraw Hill, LLC 38  Hormones of the Thyroid Gland Extrafollicular (parafollicular) cells of the thyroid secrete calcitonin, a hormone which lowers blood levels of calcium and phosphate ions when they are too high Calcitonin increases calcium deposition in bones, by inhibiting the bone-resorbing activity of osteoclasts It also increases calcium and phosphate excretion by the kidneys into urine Calcitonin secretion is regulated by the blood concentration of calcium; when calcium is high, calcitonin is secreted © McGraw Hill, LLC 39  Thyroid Disorders Hypothyroidism: Underactivity of the thyroid gland Causes low metabolic rate, fatigue and weight gain in adults In infants, causes cretinism: poor growth and bone formation, abnormal mental development, sluggishness Hyperthyroidism: Overactivity of the thyroid gland Causes high metabolic rate, restlessness, overeating in adults May lead to eye protrusion (exophthalmia) Depending on cause of disease, either hypothyroidism or hyperthyroidism may lead to formation of a goiter, an enlarged thyroid that appears as a bulge in the neck © McGraw Hill, LLC 40  Hormones of the Thyroid Gland TABLE 11.4 Hormones of the Thyroid Gland Hormone Action Source of Control Increases rate of energy release Thyroid-stimulating hormone from carbohydrates; increases from the anterior pituitary gland rate of protein synthesis; accelerates growth; necessary for normal nervous system maturation Same as above, but five times Thyroid-stimulating hormone more potent than thyroxine from the anterior pituitary gland Calcitonin Lowers blood calcium and Blood calcium concentration phosphate ion concentrations by inhibiting release of these ions from bones and by increasing excretion of these ions by kidneys © McGraw Hill, LLC 41  11.6: Parathyroid Glands 4 tiny parathyroid glands are located on posterior of thyroid gland Structure of the Glands: Parathyroid glands consist of tightly packed secretory cells covered by a thin capsule of connective tissue; secretory cells are associated with capillaries Parathyroid Hormone (PTH): PTH increases blood calcium ion concentration and decreases phosphate ion concentration PTH stimulates bone resorption by osteoclasts, which releases calcium into the blood PTH also stimulates the kidneys to conserve calcium PTH causes activation of vitamin D by kidneys, which causes increased absorption of calcium in the intestines A negative feedback mechanism involving blood calcium level regulates release of PTH © McGraw Hill, LLC 42  Figure 11.12: The Parathyroid Glands The parathyroid glands are embedded in the posterior surface of the thyroid gland. A thin capsule of connective tissue covers each small, yellowish-brown parathyroid gland. The body of the glands consists of many tightly packed secretory cells closely associated with capillary networks. © McGraw Hill, LLC 43  Figure 11.13: Effects of Parathyroid Hormone © McGraw Hill, LLC 44  Calcium Regulation and Parathyroid Disorders Calcitonin and PTH maintain proper blood calcium concentration Calcitonin and PTH exert opposite effects in regulating calcium ion levels in the blood Calcitonin decreases blood calcium when it is too high PTH increases blood calcium when it is too low Parathyroid hormone disorders: Hypoparathyroidism: deficiency of PTH, due to surgical removal or injury to glands, which results in a decrease in blood calcium Hyperparathyroidism: excess of PTH, perhaps due to parathyroid tumor, which results in an increase in blood calcium © McGraw Hill, LLC 45  11.7: Adrenal Glands The adrenal glands sit on top of the kidneys, enclosed in a layer of adipose and connective tissues Structure of the Glands: The pyramid-shaped glands consist of an inner adrenal medulla and an outer adrenal cortex The adrenal medulla consists of modified postganglionic neurons that are connected to the sympathetic nervous system The adrenal cortex comprises most of the adrenal glands, and consists of epithelial cells in three layers: an outer layer (zona glomerulosa), middle layer (zona fasciculata), and an inner layer (zona reticularis) © McGraw Hill, LLC 46  Figure 11.14: Structure of the Adrenal Glands © McGraw Hill, LLC 47  Hormones of the Adrenal Medulla The adrenal medulla secretes epinephrine and norepinephrine into the bloodstream These two hormones are similar in structure and function Adrenal medulla secretes 80% epinephrine and 20% norepinephrine Effects resemble those of the sympathetic neurotransmitters of the same name, except that they last up to 10 times longer when they are secreted as hormones They are used in times of stress and for “fight-or-flight” responses Effects: increase heart rate, blood pressure and blood glucose, dilate airways, decrease digestive activities Release of medullary hormones is regulated by nerve impulses from the central nervous system through the sympathetic division of the autonomic nervous system © McGraw Hill, LLC 48  Effects of Epinephrine & Norepinephrine TABLE 11.5 Comparative Effects of Epinephrine and Norepinephrine Structure or function affected Epinephrine Norepinephrine Heart Increases rate Increases rate Increases force of contraction Increases force of contraction Blood vessels Vasodilation, especially Vasoconstriction in skin and viscera shifts important in skeletal muscle at blood flow to other areas, such as exercising onset of fight-or-flight response skeletal muscle Systemic blood pressure Some increase due to increased Some increase due to increased cardiac cardiac output output and vasoconstriction (offset in some areas, such as exercising skeletal muscle, by local vasodilation due to other factors) Airways Dilation Some dilation Reticular formation of Activated Little effect brainstem Liver Promotes breakdown of Little effect on blood glucose level glycogen to glucose, increasing blood sugar concentration Metabolic rate Increases Increases © McGraw Hill, LLC 49  Hormones of the Adrenal Cortex The cells of the adrenal cortex produce over 30 steroids, some of which are hormones that are vital to survival Most important hormones are aldosterone, cortisol, and the sex hormones Aldosterone: Aldosterone, a mineralocorticoid, is secreted by cells of the outer zone; helps regulate mineral/electrolyte balance Causes the kidneys to conserve sodium ions and thus water, and to excrete potassium ions in the urine Aldosterone is secreted in response to decreasing blood volume and blood pressure; these changes are detected by the kidney © McGraw Hill, LLC 50  Cortisol Characteristics of Cortisol: Cortisol is a glucocorticoid; regulates glucose metabolism Produced by cells of the middle layer of the adrenal cortex Functions of cortisol: Inhibits protein synthesis, which increases blood amino acids Promotes fatty acid release from adipose tissue, increasing use of fatty acids for energy and decreasing use of glucose Causes liver cells to produce glucose from noncarbohydrates, to increase blood glucose A negative feedback mechanism involving CRH from the hypothalamus and ACTH from the anterior pituitary controls the release of cortisol Stress, injury, or disease can also trigger increased release of cortisol © McGraw Hill, LLC 51  Figure 11.15: Negative Feedback and Cortisol Secretion © McGraw Hill, LLC 52  Adrenal Sex Hormones and Disorders of the Adrenal Cortex Adrenal sex hormones: Sex hormones, produced in the inner zone, are mostly male hormones (adrenal androgens), but can be converted to female hormones in the skin, liver, and adipose tissues These hormones supplement those released by the gonads and may stimulate early development of reproductive organs Disorders of hormones of the adrenal cortex: Addison disease: hyposecretion of glucocorticoids and mineralocorticoids Cushing syndrome: hypersecretion of adrenal cortical hormones © McGraw Hill, LLC 53  Hormones of the Adrenal Cortex TABLE 11.6 Hormones of the Adrenal Cortex Hormone Action Factor Regulating Secretion Aldosterone Helps regulate concentration of Blood sodium and potassium extracellular electrolytes by concentrations conserving sodium ions and excreting potassium ions Cortisol Decreases protein synthesis, Corticotropin-releasing hormone increases fatty acid release, and from the hypothalamus and stimulates glucose synthesis from adrenocorticotropic hormone noncarbohydrates (ACTH) from the anterior pituitary Adrenal androgens Supplement sex hormones from Adrenocorticotropic hormone the gonads; may be converted to (ACTH) from the anterior estrogens in females pituitary plus unknown factors © McGraw Hill, LLC 54  11.8: Pancreas The pancreas secretes hormones as an endocrine gland, and digestive juice into the digestive tract as an exocrine gland Pancreatic hormones control level of blood glucose Structure of the gland: The pancreas is an elongated organ posterior to the stomach Its endocrine portions are the pancreatic islets (islets of Langerhans), that include 2 cell types: alpha cells that secrete glucagon, and beta cells that secrete insulin Pancreatic duct joins the pancreas to the duodenum, for digestive juice to enter duodenum of the small intestine © McGraw Hill, LLC 55 Figure 11.16: Structure of the Pancreas The hormone-secreting cells of the pancreas are grouped in clusters, or islets, that are near blood vessels. Other pancreatic cells secrete digestive enzymes into ducts leading to the small intestine. © McGraw Hill, LLC 56  Figure 11.17: Light Micrograph of a Pancreatic Islet Light micrograph of a pancreatic islet © McGraw Hill, LLC Victor P. Eroschenko 57  Hormones of the Pancreatic Islets Glucagon: Increases the blood level of glucose, by stimulating the breakdown of glycogen and the conversion of noncarbohydrates into glucose by the liver The release of glucagon is controlled by negative feedback Low blood glucose level stimulates the secretion of glucagon Insulin: Decreases the blood level of glucose by stimulating the liver to form glycogen, promotes facilitated diffusion of glucose into cells, increases protein synthesis, and stimulates adipose cells to store fat The release of insulin is controlled by negative feedback High blood glucose stimulates the release of insulin Insulin and glucagon coordinate to maintain a relatively stable blood glucose concentration © McGraw Hill, LLC 58  Figure 11.18: Control of Blood Glucose by Insulin and Glucagon Insulin and glucagon function together to help maintain a relatively stable blood glucose concentration after a meal and between meals. Negative feedback responding to the blood glucose concentration controls the levels of both hormones. © McGraw Hill, LLC 59  Diabetes Mellitus A metabolic disease due to lack of insulin or the inability of cells to recognize insulin High blood glucose harms eyes, heart, kidneys, peripheral nerves Causes disturbances in metabolism of carbohydrates, fats, proteins Glucose entry into body cells is impaired Symptoms: hyperglycemia, glycosuria, polydipsia, polyphagia, acidosis Type 1 diabetes mellitus (insulin-dependent diabetes mellitus, IDDM) is an autoimmune disorder, in which beta cells are destroyed, so insulin production decreases or stops Type 2 diabetes mellitus (noninsulin-dependent diabetes mellitus, NIDDM) occurs when insulin is produced but is not recognized by cells © McGraw Hill, LLC 60  Other Endocrine Tissues and Organs Reproductive Organs: The ovaries produce estrogen and progesterone The placenta produces estrogen, progesterone, and gonadotropin The testes produce testosterone Digestive Organs: The digestive glands secrete hormones associated with the stomach and small intestine for the processes of digestion Fat Cells of Adipose Tissue: Secrete leptin, a hormone that helps regulate food intake and energy balance When fat stores increase, leptin level increases and appetite is suppressed Heart: Secretes atrial natriuretic peptide, which affects sodium and water excretion by the kidneys Kidneys: Secrete erythropoietin for blood cell production © McGraw Hill, LLC 62  Responses to Stress Responses to stress are designed to maintain homeostasis Responses to stress involve a set of reactions called the stress response or general adaptation syndrome The stress response has 2 stages: the “alarm” stage and the “resistance” stage: The alarm stage involves the immediate "fight or flight" responses of the sympathetic nervous system; it is activated by the hypothalamus: Increases blood glucose and fatty acids Increases heart rate, breathing rate, blood pressure Increases epinephrine secretion from adrenal medulla Dilates air passages Sends more blood to skeletal muscles, and less to skin and digestive organs © McGraw Hill, LLC 64  Responses to Stress In the longer-lasting resistance stage, CRH from the hypothalamus travels to the anterior pituitary, and increases ACTH secretion, which increases cortisol secretion from the adrenal cortex Actions of cortisol from the adrenal cortex: Increases blood amino acids, fatty acid release, and glucose formation from noncarbohydrates Long term stress can be harmful: Decreases lymphocytes, which lowers resistance to infections and some cancers Increases risk of high blood pressure, atherosclerosis, and GI ulcers © McGraw Hill, LLC 65 Figure 11.19: The Stress Response © McGraw Hill, LLC 66  12.1: Introduction to the Blood Blood: a type of connective tissue with a fluid matrix (plasma) Blood, heart, and blood vessels make up the circulatory system Blood transports substances throughout the body, helps to maintain homeostasis and distributes heat Blood transports nutrients and oxygen to the body cells, and removes metabolic wastes and carbon dioxide The blood contains red blood cells (for respiratory gas transport), white blood cells (for fighting infection), platelets (for stoppage of bleeding), and plasma (the liquid matrix) Red blood cells, white blood cells, and platelets are called the formed elements of the blood; they are produced in the red bone marrow © McGraw Hill, LLC 2 Figure 12.1: Composition of the Blood Loading… Blood is a complex mixture of formed elements in a liquid extracellular matrix, called plasma. Note that water and proteins account for 99% of the plasma. © McGraw Hill, LLC 3  12.2: Formed Elements Red Blood Cells (Erythrocytes, RBCs): Biconcave disks; this shape makes the RBCs flexible as they travel through blood vessels, puts oxygen in close proximity to the hemoglobin, and increases surface area for gas exchange Red blood cells discard their nuclei and most organelles during development, and so cannot reproduce or produce proteins RBCs contain one-third hemoglobin Hemoglobin transports oxygen and some carbon dioxide through the blood When oxygen combines with hemoglobin, it forms oxyhemoglobin, which gives blood its bright red color When oxygen is released, deoxyhemoglobin is darker in color Produce ATP by glycolysis, and do not contain mitochondria, so they do not use the oxygen they are transporting to the cells © McGraw Hill, LLC 6 Figure 12.4: Structure of a Hemoglobin Molecule The structure of the hemoglobin molecule includes four polypeptide chains (the globular portion), each with a heme pigment, and in the center of each heme is an iron that binds to oxygen. When oxygen is bound to hemoglobin, resulting in oxyhemoglobin, the color of blood is bright red, and when the oxygen is released, the resulting deoxyhemoglobin makes blood a darker red. (a) Structure of hemoglobin molecule (b) Chemical structure of the heme © McGraw Hill, LLC portion that include iron 8  Red Blood Cell Production and Its Control Red blood cell (RBC) production is called erythropoiesis In the embryo and fetus, RBC production occurs in the yolk sac, liver, and spleen; after birth, it occurs in the red bone marrow (hematopoiesis) RBCs are produced from hematopoietic stem cells (or hemocytoblasts); they go through several stages of development before becoming mature RBCs Average life span of a RBC is 120 days Total number of RBCs remains relatively constant, due to a negative feedback mechanism utilizing the hormone erythropoietin, released from the kidneys and liver in response to detection of low oxygen levels Excessive increase in red blood cells is called polycythemia, which causes viscous, slow moving blood and oxygen deficiency © McGraw Hill, LLC 10  Figure 12.5: Hematopoiesis: A Light Micrograph of a Hematopoietic Stem Cell and Development of Blood Cells in the Red Bone Marrow Loading… A hematopoietic stem cell (arrow) In red bone marrow. (b) The development of RBCs from hematopoietic stem cells (blood forming cells) also called hemocytoblasts. As the RBCs develop, they synthesize hemoglobin. When there is enough hemoglobin, most of the organelles are ejected forming a reticulocyte that still contains some rough endoplasmic reticulum (RER). The young RBC enters circulation, ejects its remaining RER & becomes a mature erythrocyte. It takes 3-5 days for development from a hemocytoblast to a mature RBC. © McGraw Hill, LLC (a): Alvin Telser/McGraw Hill 11  Figure 12.6: Erythropoietin and Red Blood Cell Production The hormone erythropoietin controls the rate of RBC formation through negative feedback. The kidneys, and to a less extent the liver, release erythropoietin in response to prolonged oxygen deficiency. This drop in the blood oxygen level triggers the release of erythropoietin, which travels via the blood to the red bone marrow and stimulated RBC production. © McGraw Hill, LLC 12  Dietary Factors Affecting RBC Production Vitamins and folic acid are needed for DNA synthesis, so they are necessary for the reproduction of all body cells, especially in hematopoietic tissue Iron is needed for hemoglobin synthesis; most of the iron comes from recycling old red blood cells A deficiency in red blood cells or quantity of hemoglobin results in anemia, which reduces oxygen-carrying capacity of the blood © McGraw Hill, LLC 13  Types of Anemia TABLE 12.1 Types of Anemia Primary Cause Due to Results in Decreased RBC Hemorrhage Hemorrhagic anemia number Bacterial infections or blood transfusion Hemolytic anemia incompatibilities destroy RBCs Deficiency of intrinsic factor from Pernicious anemia stomach causes inadequate vitamin B12 absorption Destruction of bone marrow by radiation, Aplastic anemia certain medications, cancer, viruses, and certain poisons Decreased Dietary malnourishment, heavy Iron-deficiency hemoglobin menstruation, persistent bleeding ulcer anemia concentration Abnormal Variant in a gene resulting in abnormal Sickle cell anemia hemoglobin © McGraw Hill, LLC hemoglobin structure 14  Breakdown of Red Blood Cells With age, red blood cells become increasingly fragile and are damaged by passing through narrow capillaries Macrophages in the liver and spleen phagocytize damaged red blood cells (RBCs) Hemoglobin from the decomposed red blood cells is converted into heme and globin Heme is decomposed into iron and the pigment biliverdin, which is converted into bilirubin; both pigments are excreted in bile The globin is broken down into amino acids and reused Most of iron is stored in the liver, but can recycle back to red bone marrow to synthesize new RBCs © McGraw Hill, LLC 15  Figure 12.7: The Life Cycle of a Red Blood Cell 1. Nutrients are absorbed by the small intestine. 2. Blood transports absorbed nutrients. 3. Nutrients and erythropoietin are used by the red bone marrow to produce red blood cells. 4. Red blood cells circulate in the bloodstream for about 120 days. 5. Macrophages in liver (and spleen) phagocytize and break down old red blood cells. 6. Hemoglobin is broken down into globin and heme. Globin is further degraded into amino acids that may be reused. 7. Heme is further broken down into iron, which is either stored, or recycled to produce hemoglobin and myoglobin. The pigment is converted to biliverdin. 8. Most biliverdin is converted into bilirubin. These pigments become part of tile or bilirubin derivatives are carried by the blood to © McGraw Hill, LLC the kidneys to be eliminated in urine. 16  White Blood Cells White blood cells (WBCs, leukocytes) help defend the body against disease They are formed from hemocytoblasts (hematopoietic stem cells) in red bone marrow WBCs can leave the bloodstream to fight infection, by squeezing between cells of wall of small blood vessels; this is called diapedesis. Outside circulation, WBCs move by amoeboid motion, and are chemically attracted to damaged tissues, called positive chemotaxis Hormones that stimulate WBC production fall into two categories, interleukins and colony-stimulating factors (CSFs) 5 types of WBCs are in circulating blood, and are distinguished by size, granular appearance of the cytoplasm, shape of the nucleus, and staining characteristics © McGraw Hill, LLC 17  Figure 12.8: Diapedesis by a Leukocyte Leukocytes squeeze between the endothelial cells of a capillary wall and enter the tissue space outside the blood vessel, using a type of movement called diapedesis. © McGraw Hill, LLC 18  Types of White Blood Cells and Their Functions Granulocytes: Have granular cytoplasm, short life-span (about 12 hours): Neutrophils have fine, purple-staining cytoplasmic granules and a nucleus with 2 to 5 lobes; they comprise 50 to 70% of leukocytes; strong phagocytes (they aggressively kill bacteria by creating a respiratory burst, a toxic chemical cloud of oxidizing agents such as hydrogen peroxide and bleach, around the bacteria. Eosinophils have coarse granules that stain deep red, a bilobed nucleus, and make up 1 to 3% of circulating leukocytes; kill certain parasites (tapeworms) and moderate inflammation Basophils have fewer granules than eosinophils; granules stain blue; they account for 10,500 WBCs/µL of blood) occurs during an acute infection, smoking, or leukemia Leukopenia (