Anatomy & Physiology II: Unit 1 Lecture Exam 1 PDF

Anatomy & Physiology II: Lecture Exam \# 1 Chapters 17 & 18 **[Chapter 17: The Special Senses ]** **An Introduction to the Special Senses** Special Senses - Olfaction (smell) - Gustation (taste) - Vision - Equilibrium (balance) - Hearing **17-1 Olfaction, the Sense of Smell, Invol...

Anatomy & Physiology II: Lecture Exam \# 1 Chapters 17 & 18 **[Chapter 17: The Special Senses ]** **An Introduction to the Special Senses** Special Senses - Olfaction (smell) - Gustation (taste) - Vision - Equilibrium (balance) - Hearing **17-1 Olfaction, the Sense of Smell, Involves Olfactory Receptors Responding to Airborne Chemical Stimuli.** **[Olfaction:]** sense of smell. **Anatomy of the Olfactory Organs** **[Olfactory organs:]** located in nasal cavity on either side or nasal septum. - Made up of two layers... - Olfactory epithelium. - Lamina propria. Olfactory epithelium contains... - **[Olfactory sensory neurons:]** highly modified nerve cells that detect dissolved chemicals as they interact with odorant-binding proteins. - Supporting cells. - Basal epithelial cells (stem cells). Lamina propria contains... - Areolar tissue, blood vessels, and nerves. - **[Olfactory glands:]** secretions form mucus. **Olfactory Receptors and the Physiology of Olfaction** Olfactory reception begins with binding of odorant to G-protein-coupled receptor and creates **[generator potential]** (depolarization). **Olfactory Pathways** - Afferent fibers leave olfactory epithelium... - Collect into 20 or more bundles. - Penetrate cribriform plate of ethmoid. - Reach olfactory bulbs of cerebrum where first synapse occurs. - Axons leaving olfactory bulb... - Travel along olfactory tract to **[olfactory cortex] (in the temporal lobe)**, hypothalamus, and limbic system. - Olfactory information is the only type of sensory information to reach cerebral cortex directly. - All other sensations are relayed from thalamus. **Olfactory Discrimination** We can distinguish thousands of chemical stimuli. - Dogs have 72 times more olfactory receptor surface area than humans do. - Thus, their sense of smell is more than 10,000 times better than ours. - Olfactory receptors are replaced frequently, BUT total number of neurons declines with age. **17-2 Gustation, the Sense of Taste, Involves Gustatory Receptors Responding to Dissolved Chemical Stimuli.** **[Gustation (taste):]** provides information about food and liquids consumed. **Anatomy of Papillae and Taste Buds** Gustatory epithelial cells (taste receptors) are found in taste buds. - Distributed on superior surface of tongue and portions of pharynx and larynx. - Associated with epithelial projections (lingual papillae) on surface of tongue. **Types of Lingual Papillae** - **[Filiform papillae:]** do not contain taste buds. *Looks like a flame.* - **[Fungiform papillae:]** contains about 5 taste buds. *Looks like a mushroom.* - **[Vallate (Circumvallate) papillae:]** contain as many as 100 taste buds each. - **[Foliate papillae:]** have taste buds. **[Taste buds:]** contain basal epithelial cells (stem cells). **Gustatory Receptors** - **[Gustatory epithelial cells ]** - Extend microvilli through **[taste pore]**. - Replaced about every 10 days. - Innervated by cranial nerves that synapse in solitary nucleus of medulla oblongata, - Travels to thalamus and gustatory complex of insula. **Gustatory Discrimination and Physiology of Gustation** **There are four primary taste sensations.** - **[Sweet ]** - **[Salty ]** - **[Sour ]** - **[Bitter ]** There are two additional taste sensations. - **[Umami:]** pleasant, savory taste imparted by glutamate. - Characteristic of broths. - **[Water:]** detected by water receptors in pharynx. **17-3 Internal Eye Structures Contribute to Vision, while Accessory Eye Structures Provide Protection.** \*\*\* We rely more on vision than any other special sense. \*\*\* **Accessory Structures of the Eye** Accessory structures of the eye provide protection, lubrication, and support and include... - Eyelids - Superficial epithelium of the eye - Lacrimal apparatus **The Eyelids** **[Eyelids (palpebrae):]** continuation of skin. - Blinking keeps surface of eye lubricated and clean. - **[Palpebral fissure:]** gap that separates upper and lower eyelids. Eyelids are connected at... - Medial angle, also called, *medial canthus*. - Lateral angle, also called, *lateral canthus*. **[Eyelashes:]** robust hairs. - Help prevent foreign matter from reaching eye. **[Tarsal glands:]** secrete lipid-rich product that helps keep eyelids from sticking together. **[Lacrimal caruncle:]** mass of soft tissue at medial angle of eye. - Contains glands that produce thick secretions. **The Superficial Epithelium of the Eye** **[Conjunctiva:]** mucous membrane covered by an epithelium. **[Conjunctivitis (pinkeye):]** inflammation of conjunctiva. - **[Palpebral conjunctiva:]** covers inner surface of eye. - **[Bulbar conjunctiva:]** covers anterior surface if eye, extends to edges of cornea. **[Cornea:]** transparent part of fibrous outer layer that extends from the bulbar conjunctiva. **The Lacrimal Apparatus** **[Lacrimal apparatus:]** produces, distributes, and removes tears. **[Lacrimal gland:]** tear gland. - Produces tears that cover conjunctiva. - Secretions contain **[lysozyme:]** antibacterial enzyme. **[Fornix:]** pocket where palpebral conjunctiva joins bulbar conjunctiva. - Receives 10-12 ducts from lacrimal gland. **Tears** - Collect in lacrimal lake at medial angle of eye and pass through... - Lacrimal puncta (pores), - Lacrimal canaliculi (canals), - Lacrimal sac, - Nasolacrimal duct, - Nasal cavity. **Anatomy of the Eyeball** Layers of the wall of the eyeball \*\*\* layers are also called tunics. \*\*\* - Outer fibrous layer. - Intermediate vascular layer (uvea). - Deep inner layer (retina). **[Orbital fat:]** cushions and insulates each eye. **[Eyeball ]** - Hollow. - Filled with fluid. - Two interior cavities... - Small **[anterior cavity]** - **[Aqueous humor ]** - Large **[posterior cavity]** - **[Vitreous body ]** **The Fibrous Layer** The fibrous layer is the outermost layer of the eyeball. - **[Sclera:]** white of the eye. - **[Cornea:]** transparent portion. - **[Corneoscleral junction (corneal limbus):]** border between cornea and sclera. **The Vascular Layer** The uvea is the vascular layer of the eyeball. - **[Iris:]** colored part of the eye, contains blood vessels, melanocytes, and two layers of smooth muscle called pupillary muscles. - **[Pupillary muscles:]** change diameter of pupil. - **[Pupil:]** central opening of iris. - **[Ciliary body:]** attaches to iris and extends posteriorly to ora serrata. - Contains ciliary muscle and ciliary processes. - **[Ora serrata:]** serrated anterior edge of neural layer of retina. - **[Ciliary zonule (suspensory ligament):]** attaches lens to ciliary processes. - **[Choroid:]** vascular layer that separates fibrous and inner layers posterior to ora serrata. - Capillaries deliver oxygen and nutrients to retina. **Vascular Layer Functions** - Provides route for blood vessels and lymphatics that supply tissues of eye. - Regulates amount of light entering eye. - Secretes and reabsorbs aqueous humor that circulates within chamber of eye. - Controls shape of lens, which is essential for focusing. **The Inner Layer** Inner layer (retina) consists of a thin layer called the pigmented layer and a thicker covering called the neural layer. **[Pigmented layer:]** absorbs light that passes through neural layer. **[Neural layer:]** contains supporting cells and neurons - Outermost part contains **[photoreceptors]**. - Rods and cones. **Photoreceptors** - **[Rods]** (black/white/gray) - Do not discriminate colors. - Highly sensitive to light. - **[Cones]** (colors) - Provide color vision. - Densely clustered in **[macula]**. - Especially at **[fovea centralis (fovea)]**. - At center of macula, - Site of sharpest color vision. - Visual axis is the line from an object to the fovea. - **[Bipolar cells:]** synapse with rods and cones. - **[Ganglion cells:]** synapse with bipolar cells. **The Neural Layer: The Optic Disc** **[Optic disc:]** origin of optic nerve. - Circular region just medial to fovea. - No photoreceptors (blind spot). **The Chambers of the Eye** Ciliary body and lens divide interior of eye into... - **[Large posterior cavity ]** - **[Small anterior cavity ]** - Divided by iris into anterior and posterior chambers. **[Aqueous humor:]** fluid that circulates within anterior cavity. - Also diffuses through posterior cavity. - Enters scleral venous sinus (canal of Schlemm) at corneoscleral junction. - Reenters circulation at veins in sclera. - **[Intra-ocular pressure:]** fluid pressure in aqueous humor, helps retain eye shape. - **[Glaucoma:]** elevated intra-ocular pressure. **[Vitreous body:]** gelatinous mass in posterior cavity. - Helps stabilize shape of eye. - **[Vitreous humor:]** fluid portion of vitreous body. **Lens** **[Lens:]** held in place by ciliary zonule, also called, *suspensory ligaments*. - **[Cataracts:]** loss of transparency or cloudiness in lens. - **[Senile cataracts:]** most common form; natural consequence of aging. **[Lens fibers:]** enucleate cells in interior of lens. - Filled with **[crystallins]**, which provide clarity and focusing power. **17-4 The Focusing of Light on the Retina Leads to the Formation of a Visual Image.** **An Introduction to Light** Light energy is a form of radiant energy that travels in waves. **Wavelength and Color: visible spectrum acronym: ROY G BIV (red, orange, yellow, green blue, indigo, violet)** R: red (740-625nm) longest visible wavelength V: violet (435-380nm) shortest visible wavelength Visible light is also described as being made up of photons, small energy packets with characteristic wavelengths. Photons of red light carry the least energy and have the longest wavelength, whereas photons of violet carry the most energy and have the shortest wavelength. **Refraction and Focusing of Light** Light is **[refracted (bent)]** as it passes through cornea and lens. - **[Focal point:]** specific point of intersection of light rays on retina. - **[Focal distance:]** distance between center of lens and focal point. **[Astigmatism:]** condition where light passing through cornea and lens is not refracted properly, visual image is distorted. **[Accommodation:]** automatic adjustment of eye to provide clear vision. - Lens becomes rounder to focus on [nearby] objects. - Flatter lens allows focus on [distant] objects. **Image Formation and Reversal** Image arriving at retina is miniaturized, upside down, and reversed from left and right and the brain compensates for this. **Visual Acuity** **[Visual acuity:]** clarity of vision. - Standard rating is 20/20. This means a person can see at 20 feet what should normally be seen at 20 feet. 20/15 is better than normal vision, while 20/30 is slightly worse. A person is legally blind when their vision with assistance is 20/200 or worse (person needs to be at 20 feet to see what can normally be seen at 200 feet). **[Scotoma:]** abnormal, permanent blind spot. - May result from compression of optic nerve, damage to photoreceptors, or central damage. **[Emmetropia:]** normal vision. **[Myopia:]** nearsightedness. **[Hyperopia:]** farsightedness. **[Photorefractive keratectomy (PRK):]** computer-guided laser shapes the cornea to exact specifications. - LASIK is a variation of PRK. **17-5 Photoreceptors Transduce Light into Electrical Signals that are then Processed in the Visual Cortex.** **Physiology of Vision** The rods and cones of the retina are called photoreceptors because they detect photons, the basic units of visible light. **Anatomy of Photoreceptors: Rods and Cones** **[Rods:]** detect pressure or absence of photons. **[Cones:]** provide information about wavelengths of photons. Both rods and cones have... - Inner segment containing major organelles. - Outer segment with membranous discs that contain visual pigments. **Physiology of Photoreceptors** **[Visual pigments:]** absorb pigments. - First step in photoreception. - Derivatives of rhodopsin. - Opsin (protein) plus retinal (pigment). - Retinal is synthesized from vitamin A. **[Color vision:]** provided by blue cones, green cones, and red cones. - Each type has a different form of opsin. **[Color blindness:]** inability to distinguish certain colors. **Steps in Photoreception** - Absorption of a photon changes retinal from 11-cis to 11-trans form. - This activates opsin. - Opsin activates transducin (G-protein). - Which activates phosphodiesterase (PDE). - PDE reduces levels of cyclic GMP - Chemically gated sodium ion channels close. - Dark current is reduced. - Rate of neurotransmitter release declines. **Bleaching and Regeneration of Visual Pigments** **[Bleaching ]** - After absorbing a photon, rhodopsin splits into retinal and opsin. - 11-trans retinal is converted back to 11-cis retinal. - Requires ATP. - Retinal then recombines with opsin. **Synthesis and Recycling of Visual Pigments** **[Night blindness (nyctalopia):]** results from deficiency of vitamin A. **Light and Dark Adaption of Visual Pigments** **[Dark-adapted state:]** visual pigments are fully receptive to stimulation. **[Light-adapted state:]** rates of bleaching and reassembly of visual pigments are balanced. **[Retinitis pigmentosa (RP):]** inherited disease characterized by progressive retinal degeneration. **The Visual Pathways** - Begin at photoreceptors, - End at visual cortex of cerebral hemispheres. - Messages must cross two synapses before moving toward brain. - Photoreceptor to bipolar cell, - Bipolar cell to ganglion cell. **Processing by the Retina** **Ganglion Cells** **[Ganglion cells:]** monitor specific portions of field of vision. **[M cells:]** ganglion cells that monitor rods. - Relatively large. - Provide information about... - General form of an object. - Motion. - Shadows in dim lighting. **[P cells:]** ganglion cells that monitor cones. - Smaller and more numerous than M cells. - In fovea, ratio of cones to ganglion cells is 1:1. - Provide information about... - Edges. - Fine detail. - Color. **[On-center neurons:]** excited by light arriving in center of receptive field. - Inhibited when light strikes edges. **[Off-center neurons:]** excited by light at edges. - Inhibited by light in central zone. **Central Processing of Visual Information** - Axons from ganglion cells converge on optic disc. - Penetrate wall of eye. - Proceed toward diencephalon as optic nerve (II). - Two optic nerves reach diencephalon after partial crossover at **[optic chiasm]**. - Information travels to visual cortex in occipital lobe. - **[Optic radiation:]** bundle of projection fibers linking lateral geniculates with visual cortex. **The Field of Vision** **[Field of vision:]** combined visual images from left and right eyes. - **[Depth perception:]** obtained by comparing relative positions of objects between images received from both eyes. **Brainstem and Visual Processing** **[Circadian rhythm:]** daily pattern of activity tied to day-night cycle. - Established from visual information. - Affects metabolic rate, blood pressure, etc. **17-6 Equilibrium Sensations Monitor Head Position and Movement, while Hearing Involves the Detection and Interpretation of Sound Waves.** **Anatomy of the Ear** The ear is divided into three anatomical regions... - External ear - Middle ear - Internal ear **The External Ear** **[Auricle (pinna):]** surrounds and protects external acoustic meatus (EAM). - Provides directional sensitivity. **[Tympanic membrane (eardrum):]** thin, semitransparent sheet at the end of EAM that separates the external ear from the middle ear. **[Ceruminous glands:]** integumentary gland along EAM that secrete **[cerumen]** (ear wax). - Helps keep out foreign objects and insects. - Slows growth of microorganisms. **The Middle Ear** **[Middle ear (tympanic cavity) ]** - Air-filled chamber. - Communicates with nasopharynx through auditory tube. - Permits equalization of pressure on either side of tympanic membrane. - Contains 3 tiny ear bones called auditory ossicles. - **[Malleus (hammer)]** - **[Incus (anvil)]** - **[Stapes (stirrup) ]** When sound waves vibrate tympanic membrane, auditory ossicles conduct vibrations to internal ear. **Muscles of the Middle Ear** - Two small muscles protect the ear from very loud noises. - **[Tensor tympani ]** - Pulls on malleus and stiffens tympanic membrane. - **[Stapedius ]** - Reduces movement of stapes at oval window. **The Internal Ear** **[Labyrinth:]** winding passageway. **[Bony labyrinth]** surrounds and protects **[membranous labyrinth]**. - Perilymph flows between the two labyrinths. - Endolymph is within membranous labyrinth. Bony labyrinth can be subdivided into... - Vestibule - Semicircular canals - Cochlea **[Vestibule:]** encloses saccule and utricle. - Receptors detect gravity and linear acceleration. **[Semicircular canals:]** contains three semicircular ducts. - Receptors stimulated by rotation of head. **[Cochlea:]** contains cochlear duct of membranous labyrinth. - Receptors provide sense of hearing. **[Round window:]** thin, membranous partition that separates perilymph from air spaces of middle ear. **[Oval window:]** connected to base of stapes by collagen fibers. **Equilibrium** **[Equilibrium:]** state of physical balance. **The Vestibular Complex and Physiology of Equilibrium** - Sensations provided by receptors of vestibular complex (vestibule and semicircular canals). - **[Hair cells:]** sensory receptors of internal ear. - Provide information about direction and strength of mechanical stimuli. **The Semicircular Ducts: Rotational Movements** **[Anterior, posterior, and lateral semicircular ducts:]** continuous with utricle. - Each duct contains an expanded region (ampulla). - With gelatinous **[ampullary cupula]**. - **[Ampullary crest]** contains hair cells. - Each hair cell in vestibular complex has... - 80-100 stereocilia (resembles long microvilli). - A single large kinocilium. **The Utricle and Saccule: Position and Acceleration** - Hair cells provide sensations of position and linear movement. - Connected with **[endolymphatic duct]**, which ends in **[endolymphatic sac]**. **[Maculae:]** oval structures where hair cells cluster. - **[Macula of utricle:]** sense horizontal movement. - **[Macula of saccule:]** senses vertical movement. **[Otoliths (ear stones):]** densely packed calcium carbonate crystals on surface of gelatinous mass. **Pathways for Equilibrium Sensations** Sensory neurons in **[vestibular ganglia]**. - Monitor hair cells of vestibular complex. - Fibers from ganglia form **[vestibular nerve]** of vestibulocochlear nerve (VIII). - Synapse within **[vestibular nuclei]** at boundary between pons and medulla oblongata. There are four functions of vestibular nuclei... - Integrate sensory information about balance and equilibrium from both sides of head. - Relay information from vestibular complex to cerebellum. - Relay information from vestibular complex to cerebral cortex. - Providing conscious sense of head position. - **Send commands to motor nuclei in brainstem and spinal cord.** **Reflexive Motor Commands from Vestibular Nuclei** - Distribute to motor nuclei for cranial nerves involved with eye, head, and neck movements. - Instructions descending in vestibulospinal tracts of spinal cord. - Adjust peripheral muscle tone. - Complement reflexive movements of head and neck. **Automatic Movements of Eyes** - Directed by superior colliculi of midbrain in response to sensations of motion. - Attempt to keep gaze focused on a specific point. - If spinning rapidly, eyes make jerky movements. - **[Nystagmus:]** trouble controlling eye movements when body is stationary. - Caused by damage to brainstem or internal ear **Hearing** - Sound waves are converted into mechanical movements by vibration of tympanic membrane. - Auditory ossicles conduct vibrations to internal ear. - Vibrations are converted to pressure waves in fluid. - Detected by hair cells in cochlear duct. - Information is sent to auditory cortex of brain. **An Introduction to Sound** **[Pressure wave:]** sine wave (S-shaped curve). - Consists of a region where air molecules are crowded together, - And adjacent zone where they are farther apart. **[Wavelength:]** distance between two adjacent wave crests. **[Frequency:]** number of waves (cycles) that pass a fixed reference point in a given time. - Measured in **[hertz (Hz):]** number of cycles per second. **[Pitch:]** our sensory response to frequency. **[Amplitude:]** height of a sound wave. **[Intensity:]** amount of energy in a sound wave, determines how loud it seems. - Measured in **[decibels]**. **Anatomy of the Cochlear Duct** **[Cochlear duct (scala media)]** lies between **[scala vestibuli (vestibular duct)]** and **[scala tympani (tympanic duct)]**. - Hair cells lie in **[spiral organ (organ of Corti).]** - Rests on **[basilar membrane]**. - Separates cochlear duct from scala tympani. - Hair cells lack kinocilia. - Stereocilia contact overlying **[tectorial membrane]**. **Auditory Discrimination** - Range from softest to loudest tolerable sound represents trillion-fold increase in power. - Young children have greatest hearing range. - With age, damage accumulates... - Tympanic membrane gets less flexible. - Articulations between ossicles stiffen. - Round window may begin to ossify. **The Physiology of Hearing** There are six basic steps in process of hearing... - Sound waves arrive at tympanic membrane. - Movement of tympanic membrane displaces auditory ossicles. - Movement of stapes at oval window produces pressure waves in perilymph in perilymph of scala vestibuli. - Pressure waves distort basilar membrane on their way to round window of scala tympani. - Vibration of basilar membrane causes hair cells to vibrate against tectorial membrane. - Information about stimulation is relayed to CNS over cochlear nerve. - Spiral ganglion contains cell bodies of bipolar sensory neurons that monitor cochlear hair cells. **Auditory Pathways** - Afferent fibers of sensory neurons in spiral ganglion form cochlear nerve. - Axons enter medulla oblongata and synapse at cochlear nucleus. - Information ascends to... - Superior olivary nuclei of pons. - Inferior colliculi of midbrain. - Midbrain coordinates unconscious motor responses. - Ascending auditory sensations synapse in medial geniculate body of thalamus. - Projection fibers deliver information to auditory cortex of temporal lobe. Chapter 18: The Endocrine System **An Introduction to the Endocrine System** Endocrine cells and tissues produce about 30 different **[hormones]** (chemical messengers). - Hormones control and coordinate body processes. 18-1 Homeostasis is preserved through intercellular communication by the nervous and endocrine systems. **Mechanisms of Intercellular Communication** There are several mechanisms of intercellular communication... **[Direct communication:]** exchange of ions and molecules between adjacent cells across gap junctions between **two cells of the same type.** - Highly specialized and relatively rare. **[Paracrine communication:]** chemical signals transfer information from **cell to cell within a single tissue.** **[Autocrine communication:]** messages affect the **same cells that secrete them.** - **[Autocrine:]** the chemicals involved in autocrine communication. - Ex: *prostaglandins secreted by smooth muscle cells cause the same cells to contract.* **[Endocrine communication:]** cells release hormones that are transported in bloodstream. - Alters metabolic activities of many organs. **[Target cells:]** have receptors needed to bind and "read" hormonal messages. **[Hormones:]** chemical messengers. - Change types, quantities, or activities of enzymes and structural proteins in target cells. - Can alter metabolic activities of multiple tissues and organs at the same time. - Affect long-term processes like growth and development. **[Synaptic communication:]** neurons release neurotransmitters at a synapse. - Leads to action potentials that are propagated along axons. - Allows for high-speed "messages" to reach specific destinations. - Ideal for crisis management. **Comparisons of Endocrine and Nervous Communication** **BOTH** endocrine and nervous systems... - Rely on release of chemicals that bind to specific receptors on target cells. - Share chemical messengers such as, norepinephrine and epinephrine. - Regulated mainly by negative feedback. - Function to preserve homeostasis by coordinating and regulating activities. The endocrine system includes all endocrine cells and tissues that produce hormones or paracrines. - Endocrine cells release secretions into extracellular fluid. - Unlike exocrine cells. - Endocrine organs are scattered throughout body. 18-2 The endocrine systemphysiological procoesses by releasing bloodborne hormones that bind to receptors on remote target organs. **[Classes of Hormones]** There are 3 classes of homrones: amino acid derivatives, peptide hormones, and lipid derivatives. **[1.Amino Acid Derivatives (Biogenic Amines)]** - Small molecules structurally related to amino acids. Amino acid derivative hormones can either be synthesized from tyrosine or tryptophan. **Derivatives of [tyrosine]** - Thyroid hormones. - Catecholamines (epinephrine, norepinephrine, and dopamine). **Derivatives of [tryptophan]** - Serotonin and melatonin. **[2. Peptide Hormones]** - Chains of amino acids. - Most are synthesized as **[prohormones]**. - Inactive molecules converted to active hormones before or after they are secreted. We can divide peptide hormones into 2 groups: glycoproteins and short polypeptides/small proteins. **Glycoproteins** - Proteins more than 200 amino acids long that have carbohydrate side chains Ex. *TSH, LH, FSH.* **Short Polypeptides** - ADH and OXT are each 9 amino acids long. **Small Proteins** - Insulin (51 amino acids). - GH (191 amino acids). - PRL (198 amino acids). Includes all hormones secreted by hypothalamus, heart, thymus, digestive tract, pancreas, posterior lobe of the pituitary gland, etc. **[3.Lipid Derivatives]** There are 2 groups of lipid derivatives: eicosanoids and steroid hormones. **Eicosanoids** **[Eicosanoids:]** a signaling molecule, derived from **[arachidonic acid]**, a 20-carbon fatty acid. Eicosanoids include... - Leukotrienes. - **[Prostaglandins:]** coordinate local cellular activities. - Thromboxanes. - Prostacyclins. **Steroid Hormones** **[Steroid hormones:]** derived from cholesterol. - Bound to specific transport proteins in the plasma. - Remain in circulation longer than peptide hormones. Steroid hormones include... - Androgens from testes in males. - Estrogens and progesterone from ovaries in females. - Corticosteroids from adrenal cortex. - Calcitriol from kidneys. **Transport and Inactivation of Hormones** Hormones may circulate freely, or travel bound to special carrier proteins. - Free hormones remain functional for less than an hour and are inactivated when they... - Diffuse out of bloodstream and bind to receptors on target cells. - Absorbed and broken down by liver or kidneys. - Broken down by enzymes in blood or interstitial fluids. - Thyroid and steroid hormones. - Remain functional much longer. - More than 99 percent become attached to special transport proteins in blood. - Equilibrium state exists between free and bound forms. - Bloodstream contains a substantial reserve of bound hormones. **Mechanisms of Hormone Action** Binding of a hormone may... - Alter genetic activity. - Alter rate of protein synthesis. - Change membrane permeability. To affect a target cell, a hormone must FIRST interact with an appropriate receptor... **[Hormone receptor:]** protein molecule to which a particular molecule binds strongly. - Different tissues have different combinations of receptors. - Presence or absence of a specific receptor determines hormonal sensitivity of a cell. The presence or absence of a hormone can also affect the nature and number of hormone receptor proteins. **[Down-regulation:]** presence of a hormone triggers a [decrease] in the number of hormone receptors. - When levels of a particular hormone are **[HIGH]**, cells become **[LESS]** sensitive to it. **[Up-regulation:]** absence of a hormone triggers an [increase] in the number of hormone receptors. - When levels of a particular hormone are **[LOW]**, cells become **[MORE]** sensitive to it. Hormone receptors are either located on the plasma membrane (extracellular response) or within target cells (intracellular response). These different types of receptors respond with different mechanisms. **Extracellular Receptors** - Catecholamines and peptide hormones are... - Not lipid soluble. - Unable to penetrate plasma membrane. - Bind to receptor proteins on outer surface of plasma membrane (extracellular receptors). **Intracellular Receptors** - Steroid and thyroid hormones are... - Lipid soluble. - Diffuse across plasma membrane and bind to receptors inside cell (intracellular receptors). **Hormones and Extracellular Receptors: Second Messengers** **[First messenger:]** hormone that binds to extracellular receptor. - Promotes release of second messenger in cell. **[Second messenger:]** intermediary molecule that appears due to hormone--receptor interaction. - May act as enzyme activator, inhibitor, or cofactor. - Results in change in rates of metabolic reactions. - Example: cAMP, cGMP, Ca^2+^. **Process of Amplification** - When a small number of hormone molecules binds to extracellular receptors, thousands of second messengers may appear. - Magnifies effect of hormone on target cell. **G-proteins and cAMP** **[G-protein:]** enzyme complex coupled to membrane receptor. - Protein binds GTP. - Involved in link between first messenger and second messenger. The steps involved in increasing cAMP level, which accelerates metabolic activity of cell... 1. Activated G protein activates **adenylate cyclase**. 2. Adenylate cyclase converts ATP to **cyclic AMP (cAMP)**. 3. cAMP functions as a second messenger. 4. Generally, cAMP activates kinases that phosphorylate proteins. Increase in cAMP level is usually short-lived. - **Phosphodiesterase (PDE)** converts cAMP to AMP. **G-proteins and Ca^2+^** 1. G protein activates **phospholipase C** (**PLC**). 2. Triggers receptor cascade beginning with production of **diacylglycerol** (**DAG**) and **inositol** **triphosphate** (**IP~3~**) from phospholipids. 3. IP**~3~** diffuses into cytoplasm and triggers release of Ca^2+^ from intracellular reserves. 4. Calcium ion channels open due to activation of **protein kinase C** (**PKC**), and Ca^2+^ enters cell. 5. Ca^2+^ binds to **calmodulin**, activating enzymes. **Hormones and Intracellular Receptors** - Steroid hormones can alter rate of DNA transcription in nucleus. - Alterations in synthesis of enzymes or structural proteins. - Directly affect activity and structure of target cell. - Thyroid hormones bind to receptors within nucleus and on mitochondria. - Activate genes or change rate of transcription. - Increase rates of ATP production. **Control of Hormone Secretion** Hormone secretion is [mainly controlled] by **negative feedback**. - Stimulus triggers production of hormone that reduces intensity of the stimulus. - May only involve one hormone. - Can be triggered by... - **[Humoral stimuli]** (change in extracellular fluid) - **[Hormonal stimuli]** (arrival or removal of hormone) - **[Neural stimuli]** (neurotransmitters) **[Humoral stimuli:]** control hormone secretion by heart, pancreas, parathyroid gland, and digestive tract. **[Hormonal stimuli:]** may involve one or more intermediary steps. - Two or more hormones involved. **[Neural stimuli:]** hypothalamus provides highest level of control. 18-3 The anterior lobe of the pituitary gland produces and releases hormones under hypothalamic control, while the posterior lobe releases hypothalamic hormones. **[PITUITARY GLAND (Hypophysis)]** - Lies within sella turcica. - Sellar diaphragm isolates pituitary gland from cranial cavity. - Hangs inferior to **[hypothalamus]**. - Connected by infundibulum. - Releases nine important peptide hormones. - Bind to extracellular receptors. - Use cAMP as second messenger. **[HYPOTHALAMUS]** - Regulates functions of the pituitary gland. - Synthesizes ADH and OXT and transports them to posterior pituitary gland for release. - Secretes **[regulatory hormones]** that control secretory activity of anterior pituitary gland. - Contains autonomic centers that exert direct control over adrenal medulla. The hypothalamus divides into two lobes: **[the anterior lobe (*adenohypophysis*)]** and the **[posterior lobe (*neurohypophysis*)]**. **The Anterior Lobe of the Pituitary Gland** - Also called **[adenohypophysis] because it is made from epithelial glandular tissue** - Hormones "turn on" endocrine glands or support functions of other organs. **Portal Vessels** - Blood vessels that link two capillary networks that are not primarily for delivery of oxygen and removing wastes. - Entire complex is called a portal system. **[Hypothalamic-Hypophyseal portal system:]** ensures that regulatory hormones from the hypothalamus reach cells in anterior pituitary before entering general circulation. **Hypothalamic Control of Anterior Lobe** Two classes of hypothalamic regulatory hormones: releasing hormones and inhibiting hormones. **[Releasing hormones (RH):]** stimulate synthesis and secretion of one or more hormones at anterior lobe. **[Inhibiting hormones (IH):]** prevent synthesis and secretion of hormones from anterior lobe. Rate of secretion is controlled by negative feedback. **Hormones of Anterior Pituitary Lobe** - **[Thyroid-stimulating hormone (TSH)]** - **[Adrenocorticotropic hormone (ACTH)]** - Released due to **[corticotropin-releasing hormone (CRH)]** - **[Prolactin (PRL)]** - Release inhibited by **[prolactin-inhibiting hormone (PIH)]** - Release stimulated by **[prolactin-releasing hormone (PRH)]** - **[Growth hormone (GH)]**, or somatotropin - Gonadotropins - **[Follicle-stimulating hormone (FSH)]** - **[Luteinizing hormone (LH)]** - In females, it induces ovulation and stimulates secretion of estrogens and progesterone. - In males, it stimulates production of androgens. - Production of FSH and LH is stimulated by **[gonadotropin-releasing hormone (GnRH)]** - **[Hypogonadism:]** caused by low production of gonadotropins. **[Growth hormone (GH)]** stimulates... - Liver cells to release **[somatomedins]** that stimulate tissue growth. - Somatomedins cause skeletal muscle fibers and other cells to increase uptake of amino acids. - Stem cells in epithelia and connective tissues to divide. - Breakdown of triglycerides in adipocytes, which leads to **[glucose-sparing effect]**. - Breakdown of glycogen by liver cells causing **[diabetogenic effect]**. Production of growth hormone is regulated by... - **[Growth hormone--releasing hormone (GH--RH)]** - **[Growth hormone--inhibiting hormone (GH--IH)]** **Pars Intermedia** - Secretes **[melanocyte-stimulating hormone (MSH)]** - Stimulates melanin production. Virtually nonfunctional in adults except in... - Pregnant women - Those with certain diseases **Posterior Lobe of the Pituitary Gland** - Also called **[neurohypophysis] because it is made of neural tissue** - Contains unmyelinated axons/terminals of hypothalamic neurons storing neurohormones in vesicles. - Hypothalamus manufactures two neurohormones: - **[Antidiuretic hormone (ADH)]** - **Helps regulate fluid balance by acting on the kidney and by initiating thirst** - **[Oxytocin (OXT)]** - Stimulates contraction of uterus during labor. - Promotes ejection of milk after delivery. 18-4 The thyroid gland synthesizes thyroid hormones that affect rate the rate of metabolism. **[THYROID GLAND]** - Lies inferior to thyroid cartilage of larynx. - Consists of two **lobes** connected by narrow **isthmus**. - **Thyroid** **follicles** - Hollow spheres lined by cuboidal epithelium. - Surrounded by capillaries. - Cells absorb **iodide ions** (**I^--^**) from blood. - **Follicle** **cavity** contains viscous colloid. - **C** (**clear**) **cells**, or parafollicular cells **Thyroglobulin** - Globular protein synthesized by follicle cells. - Secreted into colloid of thyroid follicles. - Contains the amino acid, **[tyrosine]** - The building block of thyroid hormones. **Thyroid hormones** - **[Thyroxine (T4)]**, or tetraiodothyronine - Contains four iodine atoms. - **[Triiodothyronine (T3)]** - Contains three iodine atoms. **Thyroid-binding globulins (TBGs)** - Proteins that bind about 75 percent of T4 and 70 percent of T3 entering the bloodstream. - Transthyretin and albumin - Bind most of the remaining thyroid hormones. - About 0.3 percent of T3 and 0.03 percent of T4 remain unbound and free to diffuse into tissues. **Thyroid-stimulating hormone (TSH)** - Absence causes thyroid follicles to become inactive. - Neither synthesis nor secretion occurs. - Binds to plasma membrane receptors. - Activates key enzymes in thyroid hormone production. Thyroid hormones affect almost every cell in body. - Enter target cells by transport system - Bind to receptors - In cytoplasm - On surfaces of mitochondria - In nucleus - In children, essential to normal development of skeletal, muscular, and nervous systems. Thyroid hormones activate genes involved in glycolysis and ATP production. - Results in **[calorigenic effect]**. - Increased energy consumption and heat generation of cells. - Responsible for strong, immediate, and short-lived increase in rate of cellular metabolism. **[C cells:]** produce calcitonin (CT). - Helps regulate concentrations of Ca2+ in body fluids. - Stimulates Ca2+ excretion by kidneys. - Prevents Ca2+ absorption by digestive tract. **Effects of thyroid hormones** - Elevate oxygen and energy consumption; in children, may cause rise in body temperature. - Increase heart rate and force of contraction. - Increase sensitivity to sympathetic stimulation. - Maintain normal sensitivity of respiratory centers to oxygen and carbon dioxide concentrations. - Stimulate red blood cell formation. - Stimulate activity in other endocrine tissues. - Accelerate turnover of minerals in bone. 18-5 The four parathyroid glands secrete parathyroid hormone, which increases the blood calcium ion level. **[PARATHYROID GLANDS ]** - Two pairs. - Embedded in posterior surface of thyroid gland. - Altogether, the four glands weigh 1.6 g. Parathyroid hormone (PTH), or parathormone - Secreted by parathyroid (principal) cells in response to low concentrations of Ca2+ in blood. - **Antagonist for calcitonin**. Major effects of parathyroid hormone - Stimulates osteoclasts. - Accelerates mineral turnover and Ca2+ release. - Enhances reabsorption of Ca2+ by kidneys, reducing urinary losses. - Stimulates formation and secretion of calcitriol by kidneys. **[ADRENAL GLANDS]** 18-6 The paired adrenal glands secrete several hormones that affect electrolyte balance and stress responses. - Lie along superior border of each kidney. **Superficial adrenal cortex** - Stores lipids, especially cholesterol and fatty acids. - Manufactures steroid hormones (**corticosteroids**). **Inner adrenal medulla** - Secretory activities controlled by sympathetic division of ANS. - Produces epinephrine and norepinephrine (**catecholamines**). **Adrenal cortex** - Subdivided into three zones... - Outer zona glomerulosa - Middle zona fasciculata - Inner zona reticularis **Zona glomerulosa (SALT)** - Outer region of adrenal cortex - Produces mineralocorticoids. Ex. *aldosterone* - Stimulates conservation of sodium ions and elimination of potassium ions - Increases sensitivity of salt receptors in taste buds - Secreted in response to... - Drop in blood Na+, blood volume, or blood pressure - Rise in blood K+ concentration **Zona fasciculata (SUGAR)** - Produces glucocorticoids. Ex. *cortisol, corticosterone, and cortisone* - Secretion is regulated by negative feedback Glucocorticoids have inhibitory effect on production of... - Corticotropin-releasing hormone (CRH) in hypothalamus - ACTH in anterior pituitary - Effects of glucocorticoids - Accelerate glucose synthesis and glycogen formation, especially in liver - Have anti-inflammatory effects - Inhibit activities of white blood cells and other components of immune system **Zona reticularis (SEX)** - Branching network of endocrine cells - Forms narrow band bordering each adrenal medulla - Produces small quantities of androgens under stimulation by ACTH - Some are converted to estrogens in bloodstream - Stimulate development of pubic hair before puberty **Adrenal medulla (ADRENALINE)** - Contains two types of secretory cells... - One produces epinephrine (E). - 75--80 percent of medullary secretion. - The other produces norepinephrine (NE). - 20--25 percent of medullary secretion. Results of activation of adrenal medulla - In skeletal muscles, E and NE trigger mobilization of glycogen reserves. - And accelerate breakdown of glucose. - In adipose tissue, stored fats are broken down into fatty acids. - In the liver, glycogen molecules are broken down. - In the heart, stimulation of β1 receptors speeds and strengthens cardiac muscle contraction. 18-7 The pineal gland secretes melatonin, which affects the circadian rhythm. - Lies in posterior portion of roof of third ventricle. - Contains [ **pinealocytes**]. - Synthesize hormone **[melatonin]**. **Functions of melatonin** - Influence circadian rhythms. - Inhibit reproductive functions. - Protect against damage by free radicals. **[PANCREAS]** 18-8 The pancreas is both an exocrine organ and an endocrine gland that produces hormones affecting the blood glucose level. - Large gland. - Lies in loop between inferior border of stomach and proximal portion of small intestine. - Mostly retroperitoneal. - Contains exocrine and endocrine cells. **Exocrine Pancreas** - Consists of clusters of gland cells called pancreatic acini and their attached ducts. - Takes up roughly 99 percent of pancreatic volume. - Gland and duct cells secrete alkaline, enzyme-rich fluid. - Passes through a network of ducts to lumen of digestive tract. **Endocrine Pancreas** - Consists of cells that form clusters known as **[pancreatic islets (*islets of Langerhans*)]**. - **[Alpha (α) cells]** produce **glucagon**. - **[Beta (β) cells]** produce **insulin**. - **[Delta (δ) cells]** produce peptide hormone identical to GH--IH (somatostatin). - **[Pancreatic polypeptide cells (PP cells)]** produce pancreatic polypeptide (PP). When blood glucose level increases... - Beta cells secrete insulin. - Stimulating transport of glucose into target cells. When blood glucose level decreases... - Alpha cells secrete glucagon. - Stimulating glycogen breakdown and glucose release by liver. **Insulin** - Released by beta cells. - Effects on target cells... - Accelerating glucose uptake. - Accelerating glucose use and enhancing ATP production. - Stimulating glycogen formation. - Stimulating amino acid absorption and protein synthesis. - Stimulating triglyceride formation in adipocytes. **Glucagon** - Released by alpha cells. - Mobilizes energy reserves. - Effects on target cells... - Stimulating breakdown of glycogen in skeletal muscle fibers and liver cells. - Stimulating breakdown of triglycerides in adipocytes. - Stimulating production and release of glucose in liver cells (gluconeogenesis). **[Hyperglycemia:]** abnormally high glucose levels in the blood. **[Diabetes mellitus:]** characterized by high glucose concentrations that overwhelm reabsorption capabilities of kidneys. - Glucose appears in urine. **[Polyuria:]** urine volume becomes excessive. **Type 1 diabetes mellitus** - Characterized by inadequate insulin production by pancreatic beta cells. - Patients require daily injections or continuous infusion of insulin. - Approximately 5 percent of cases. - Usually develops in children and young adults. **Type 2 diabetes mellitus** - **\*\*\* Most common form \*\*\*** - Usually, normal amounts of insulin are produced, at least initially. - **[Insulin resistance:]** tissues do not respond properly. - Associated with obesity. - Weight loss can be an effective treatment. Complications of untreated or poorly managed diabetes mellitus include... - Kidney degeneration. - Retinal damage (diabetic retinopathy). - May lead to blindness. - Early heart attacks (3--5 times more likely). - Peripheral nerve problems (diabetic neuropathies). - Peripheral tissue damage due to reduced blood flow. - Tissue death, ulceration, infection, and amputation. **[OTHER ENDOCRINE ORGANS]** 18-9 Many organs have secondary endocrine functions. **Organs with secondary endocrine functions** - Intestines (digestive system) - Kidneys (urinary system) - Heart (cardiovascular system) - Thymus (lymphatic system) - Gonads (reproductive system) **Intestines** - Release hormones that coordinate digestive activities. **Kidneys** - Release the hormones **[calcitriol]** and **[erythropoietin (EPO)]**. - Release the enzyme **[renin]**. - Renin converts **[angiotensinogen]** to **[angiotensin I]**. - In the lungs, **[angiotensin-converting enzyme]** converts angiotensin I to **[angiotensin II]**. **Heart** - Produces **[natriuretic peptides (ANP and BNP)]**. - When blood volume becomes excessive. - Actions opposes those of angiotensin II. - Resulting in reduction in blood volume and blood pressure. **Thymus** - Produces **[thymosin]** (blend of several hormones). - Promotes development and maturation of lymphocytes. **Testes** - **[Interstitial endocrine cells:]** produce androgens. - **[Testosterone]** is an important androgen. - **[Nurse cells (Sertoli cells):]** support differentiation and physical maturation of sperm. - Secrete inhibin for negative feedback. **Ovaries** - Produce **[estrogens]**. - Principal estrogen is **[estradiol]**. - After ovulation, follicle cells. - Reorganize into corpus luteum. - Release estrogens and progesterone. **Adipose tissue** - Produces **[leptin]**. - Provides feedback control of appetite. - Maintains normal levels of GnRH and gonadotropin synthesis. 18-10 Hormones interact over our lifetime to produce coordinated physiological responses. When a cell receives instructions from two hormones at the same time, four outcomes are possible. **[Antagonistic effect:]** result depends on balance between two hormones. **[Synergistic effect:]** additive effect. **[Permissive effect:]** one hormone is needed for another to produce effect. **[Integrative effect:]** hormones produce different but complementary results. **Hormones important to growth** - Growth hormone - Thyroid hormones - Insulin - Parathyroid hormone and calcitriol - Reproductive hormones **Growth hormone (GH)** - In children... - Supports muscular and skeletal development. - In adults... - Maintains normal blood glucose concentrations. - Mobilizes lipid reserves. **Thyroid hormones** - If absent during fetal development or for first year after birth... - Nervous system fails to develop normally. - Developmental delay results. - If T4 concentrations decline before puberty... - Normal skeletal development does not continue **Insulin** - Allows passage of glucose and amino acids across plasma membranes. - Important for growing cells. **Parathyroid hormone (PTH) and calcitriol** - Promote absorption of calcium salts from bloodstream for deposition in bone. - Inadequate levels result in weak, flexible bones. **Reproductive hormones** Androgens in males, estrogens in females. - Stimulate cell growth and differentiation in target tissues. - Produce gender-related differences in. - Skeletal proportions. - Secondary sex characteristics. **[Stress:]** any condition that threatens homeostasis. **[General adaptation syndrome (GAS), *stress response*:]** how body responds to stress-causing factors. - Divided into three phases... - Alarm phase - Resistance phase - Exhaustion phase **Alarm phase** - Immediate response to stress. - Directed by sympathetic division of ANS. - Energy reserves (mainly glucose) are mobilized. - Body prepares "fight or flight" responses. - **Epinephrine is dominant hormone**. **Resistance phase** - Occurs if stress lasts longer than a few hours. - May last for weeks or months. - Lipids and amino acids are mobilized for energy. - Glucose is conserved for use by nervous tissue. - **Glucocorticoids are dominant hormones**. **Exhaustion Phase** - Begins when homeostatic regulation breaks down. - Drop in K+ levels due to aldosterone produced in resistance phase. - Failure of one or more organ systems will be fatal. **Hormone changes** - Can affect behavior, intellectual capabilities, memory, learning, and emotional states. **Few functional changes occur with age** - Reproductive hormones decline in concentration. - Some endocrine tissues become less responsive to stimulation.