HSCI 365- Quiz 4 (Equilibrium, Taste and Smell, Endocrine Central Glands)

What is the anatomy of the semicircular canals?

• Lateral- horizontal movements (shaking head “no”)

• Anterior- forward and backward movements (nodding)

• Posterior- head tilt (toward shoulders)

• Perilymph- similar to extracellular fluid, high in Na+

• Endolymph- similar to intracellular fluid, high in K+

• Embedded in gelatinous cupula 

  • Kinocilium- the 1 longest cilium 

  • (vestibular) Stereocilia- 40-70 smaller cilia

Describe the physiology of the semicircular canals (describe what happens in the endolymph, and the movement of the stereocilia)

• As the head rotates, the endolymph moves in the opposite direction, which deflects the cupular and bends the hair cell stereocilia 

• The movement direction of the stereocilia determines increased (towards the kinocilia) or decreased (away from) nerve impulses 

  • When we bend hair cells toward the kinocilium, there is an increase in action potential frequency 

  • When the hair cells bend away from the kinocilium, there is a decrease in action potential frequency 

• Stereocilia move towards the kinocilia opens cation channels

• Endolymph (K+ rich) enters the cell

• This causes depolarization, opens voltage-gated calcium channels, triggering the release of glutamate 

• Stereocilia moving away from the kinocilia closes the cation channels 

What happens to the other ear when you are turning in one direction?

• The canal that depolarizes is on the same side that you are turning and the canal on the other side is hyperpolarizing 

What happens when you turn left? Right? Tilting left? Right? Bending down? Up?

• Turning head to the left

  • Left lateral canal is depolarizing 

  • Right lateral canal is hyperpolarizing

• Turning head to the right

  • Left lateral canal is hyperpolarizing

  • Right lateral canal is depolarizing 

• Tilting head to the left 

  • Left posterior canal is depolarizing

  • Right posterior canal is hyperpolarizing

• Tilting head to the right

  • Left posterior canal is hyperpolarizing

  • Right posterior canal is depolarizing

• Bending head down 

  • Left anterior canal is depolarizing

  • Right anterior canal is depolarizing

• Bending head up

  • Left anterior canal is hyperpolarizing

  • Right anterior canal is hyperpolarizing

What are the otolith organs?

• Provide info about head position relative to gravity (static tilt)

• Detect changes in the rate of linear motion

• Utricle and Saccule are between semicircular canals and cochlea

Describe the utricle (what happens when you tilt your head? what happens in horizontal linear motion?)

• Hairs of the receptor hair cells protrude into gelatinous layer

• Movement of this layer displaces hairs and results in potentials

• Otoliths or otoconia (CaCO3 crystals) in gelatinous layer give it more inertia 

• Activation of Utricle by Head tilt

  • Tilt head- utricle hairs are bent in the direction of the tilt due to gravity exerted on gelatinous layer 

• Activation of Utricle by Horizontal linear motion

  • Horizontal linear motion- initial lag from inertia, hairs bend towards the back, hairs unbend at a constant pace, then hairs bend forward when you stop walking 

Describe the saccule

• Responds selectively to head tilting away from horizontal position and to vertically directed linear motion (like jumping or getting out of bed)

How do we maintain our sense of balance?

• Vestibular info is integrated with input from the eyes, skin, joints, and muscles

• Balance and posture

• Control external eye muscles so that the eyes remain fixed on a point despite head movement

• Perceive motion and orientation

What is Benign Paroxysmal Positional Vertigo?

• Otoliths which are normally in the utricle become dislodged and end up in the semicircular canals 

  • If calcium carbonate particles roll along hair cells going back and forth, it mimics motion → moves endolymph or rolls directly on hair cells leading to opening of ion channels 

• Treatment: Physical therapy

  • EPLEY maneuver 

What type of receptors are taste receptors?

• Chemoreceptors are packaged in taste buds in mouth and through, majority on the upper tongue surface

Describe the structure of the taste bud (what is the taste pore? can they be renewed? how is it turned to receptor potentials? how do they attach?)

• ~50 long, spindle-shaped taste receptor cells packaged with supporting cells in an arrangement like slices of an orange

• Taste pore = where the food or drink enters 

• Taste receptor cells can be regenerated and constantly renewed via basal cells 

• Modified epithelial cells with microvilli that increase surface area

• Contains integral membrane protein receptors that transduce chemicals into receptor potentials

  • Takes stimuli and converting it into action potentials

• Basal cells divide and differentiate to replace taste receptor cells

• Only chemicals in solution can attach to receptor cells 

  • Oral cavity generates enzymes to help with digestion and helps bring chemicals into solution

How do we discriminate taste?

• Binding of a tastant with a receptor cell alters the cell’s ionic channels to produce a depolarizing receptor potential

• Voltage-gated calcium channels leading to release of neurotransmitter

• Action potentials are initiated within terminal endings of afferent nerve fibers 

• Each taste receptor cell responds to only one tastant

• Each taste has a distinct signal transduction mechanism 

How do we discriminate salty?

• Stimulated by sodium influx through channels in the receptor cell membrane → cell depolarizes → triggers voltage-gated calcium channels to open → neurotransmitter release → AP to afferent nerve  

How do we discriminate sweet?

• Glucose activates G protein (gustducin) and cAMP pathway to close K+ channels 

How do we discriminate sour?

• Stimulated by acids containing H+

• H+ blocks passive K+ out of the cell → cell depolarizes 

How do we discriminate bitter?

• Associated with many poisonous substances, e.g. alkaloids like strychnine, arsenic

• Activate gustducin second-messenger pathways 

How do we discriminate umami?

• Amino acids (glutamate, others) binds GPCR and acts via gustducin second-messenger pathways 

Which taste receptors are ion channels and which receptors activate GPCR?

• Ion= salty, sour

• GPCR= sweet, bitter, umami

How do we perceive taste?

Afferent endings of cranial nerves terminate on taste buds in various regions 

• Signals are conveyed to primary gustatory cortex where taste is perceived

• Taste signals sent to hypothalamus and limbic system add effective dimensions 

Structure of the olfactory mucosa (what cells do they contain? how do odorants reach receptors?)

• Contains olfactory receptor cells (detect odors), supporting cells (secrete mucus), and basal cells (olfactory cell precursors) 

• Cilia have the receptors for binding odorants

• Odorants reach receptors by diffusion in normal breathing

• Enhanced by sniffing, wafting, etc to reach olfactory bulb 

• To be detected, odorants must be volatile, water soluble, and dissolved

Briefly describe olfactory signaling

• Odorant activates G protein, Golf, triggering cAMP intracellular reactions

• Na+ and Ca2+ influx causes depolarizing potential 

Does each cell respond to one odorant? or many?

• Each of the cells responds to more than one different odorant

• Some cells respond preferentially to a single odorant 

How do we process scent in the olfactory bulb?

• Afferent fibers from receptors synapse in the olfactory bulb

• Lined with glomeruli where receptors synapse with mitral cells

• Glomeruli file the odors

• Mitral cells refine and relay signals to the brain

• Odors elicit different patterns in several cortical areas 

• Olfactory receptors →cells they synapse on is the mitral cells (the place it occurs in is the glomeruli)

Factors that affect sense of smell

• Being human- dogs have 4B while humans have 5M

• Hunger- being hungry increases sensitivity 

• Sex- females greater olfactory sensitivities than males, sense of smell in pregnancy increases

• Smoking- decreased sensitivity with smoking

• Age- decreases with age

• State of the olfactory mucosa- the sense of smell decreases when the mucosa is congested 

Describe the smell disorders

• Head trauma- brain injury, concussion

• Neurological Disorders- Parkinson’s disease

• Aging- smell function naturally declines with age

• Genetics- predisposition to smell disorders 

What is a hormone?

• Chemical molecules that are released into the bloodstream by glands–which affects the activity of cells and tissues 

What are the two types of hydrophilic hormones? Describe their major form in plasma, receptor location, signaling mechanism, and rate of metabolism

 Peptide hormones and amines (catecholamines, indolamines) 

• Major form in plasma: free

• Receptor location: plasma membrane

• Signaling mechanism: GPCRs (cAMP, IP3, DAG, calcium), enzyme activation (tyrosine kinase, JAKs), alters activity of pre-existing intracellular proteins

• Rate of metabolism: faster (minutes), less sustained (e.g. insulin via injection)

What are the two types of lipophilic hormones? Describe their major form in plasma, receptor location, signaling mechanism, and rate of metabolism

Steroid hormones and thyroid hormones (amine)

• Major form in plasma: bound

• Receptor location: intracellular

• Signaling mechanism: directly alters gene transcription, causes formation of new intracellular proteins

• Rate of metabolism: slow (hours/days), more sustained (e.g.  birth control orally)

They are only active when unbound

Describe the processing of hydrophilic peptide hormones

• Preprohormones are synthesized in the RER

  • Preprohormone → prohormone → hormone

• Pruned to active hormones

• Packed in secretory vesicles in Golgi, stored in cytoplasm

• Secreted out of cell and picked up by the blood 

  • Rate of secretion controlled by regulating the release of stored hormone 

Describe the processing of lipophilic steroid hormones

• Cholesterol is the precursor

• Specific enzymes, hormones, and organs

• Once formed, they immediately enter the blood 

• Some need processing in peripheral tissues to be action

  • Rate of secretion controlled by synthesis

Possible fates of a hormone following its secretion

• Excreted in urine or feces

• Inactivated by metabolism

• Target cells → bind to receptor and produce a cellular response

• Activated by metabolism

• All of these influence the effective plasma concentration

What are the three factors that regulate secretion rates of hormones? Briefly describe each.

• Negative-feedback control to counteract a change in input

  • Your body wants to keep [hormones] relatively stable → for example, increase in plasma glucose concentration leads to increase in insulin → when plasma insulin increases, the inhibits further production of insulin  

• Neuroendocrine reflexes

  • Neural component and endocrine component

  • E.g. sympathetic innervation in the nervous system activates adrenal medulla which will lead to hormone secretion (epinephrine)

• Diumal rhythm

  • Some hormones have normal fluctuations throughout the day

  • E.g. cortisol: highest in the morning and decrease over the course of the day

What happens when you have too little hormone activity?

• Hyposecretion (most common)

• Increased removal from blood

• Abnormal tissue responsiveness

  • Normal range of some hormone, but there is a problem with the tissue response → non-functional receptors 

What happens when you have too much hormone secretion?

• Hypersecretion (most common)

• Decreased removal from blood

• Reduced plasma protein binding 

How are two ways that hormone receptors regulate?

• Upregulation

  • Can lead to too much hormone activity

  • Target cells start gaining receptors

• Downregulation

  • Can lead to too little hormone activity 

  • Target cells start losing receptors 

How are three ways that hormones affect hormones? Briefly describe each

• Permissiveness

  • The presence of a second hormone will allow the first hormone to do its job better

  • E.g. if epinephrine is there by itself, there is low levels of fatty acid release → if thyroid hormone is also present, epinephrine is able to do its job better → thyroid hormone upregulates the epinephrine receptors in cells 

• Synergism

  • The combo of two hormones makes the effects much greater than the sum of its effects individually

  • E.g. : FSH and testosterone together makes greater effect together, than apart

• Antagonism

  • One hormone inhibits the effect of another hormone

  • E.g. hormonal changes in pregnancy: increase in progesterone during pregnancy which blocks the uterine receptors for estrogen since estrogen helps with contractions 

What are the central endocrine glands?

hypothalamus, posterior pituitary, and anterior pituitary

Describe the posterior pituitary (hormones, relationship with hypothalamus)

• Hormones

  • Oxytocin (love hormone)

    • Helps with orgasm, bonding, helps with uterine contractions for birth, lactation, maternal behavior, social cognition, synaptic plasticity 

  • Vasopressin (antidiuretic hormone)

    • Helps with water retention, helps kidney reabsorb fluid, causes blood vessels to constrict leading to increased arterial pressure 

  • Posterior pituitary only stores these, NOT synthesize

• Hypothalamus and posterior pituitary act as a unit 

  • Neurons in hypothalamus produce vasopressin and oxytocin in the paraventricular and supraoptic nuclei → hormone travels down axon; stored in neuronal terminals in the posterior pituitary → upon neuron excitation, stored hormone is released into blood 

Describe anterior pituitary and its hormones

• Anterior pituitary- glandular epithelial tissue (adenohypophysis) → it has unique vascular link with the hypothalamus 

  • Hormones

    • Anterior pituitary synthesizes the hormones it releases

      • TSH, ACTH, FSH, LH act via GPCR’s and cAMP

      • GH, prolactin act via JAK/STAT pathway 

    • 5 types of cells that produce the 6 hormone groups: thyrotropes, corticotropes, lactotropes, somatotropes, and gonadotropes

      • “tropic”= regulates another hormone

      • Thyrotrope:Produces TSH

      • Corticotropes: Produces ACTH

      • Lactotrope: Produces prolactin (acts directly on non-endocrine tissue)

      • Somatotropes: Produces growth hormone

      • Gonadotropes: Produces hormones for the gonads

Describe the hypothalamic hormones in the anterior pituitary

• Hypothalamic hypophysiotropic hormones stimulate or inhibit secretion from anterior pituitary

• Called the hypothalamic-hypophyseal portal system

• Major hypophysiotropic hormones

  • Hypothalamus secretes hormones and regulates the anterior pituitary → anterior pituitary hormones act on other endocrine glands to secrete more hormones (EXCEPT PROLACTIN) 

  • Somatostatin= growth hormone inhibiting hormone

  • Dopamine= prolactin inhibiting hormone 

Describe the portal system for the anterior pituitary

• Regulatory hormones supplied directly to anterior pituitary

• At the hypothalamus, there are neurons that will secrete those releasing or inhibiting hormones → travel down axon → be stored in terminals until stimulated for release → there is a capillary network that connects hypothalamus to anterior pituitary → release of hormones to capillary network allows hormones to go directly to anterior pituitary → cells of the anterior pituitary then synthesize hormones into the bloodstream → enters systemic circulation 

• All of the blood that end up in the anterior pituitary first end up in the hypothalamus 

• Why is it important to have direct connection and bypass systemic circulation from the hypothalamus to the anterior pituitary?

• It’s faster acting

• Hormones will be diluted in general circulation

What. is the endocrine axis?

• There are three hormone network:

  • Hypothalamic hypophysiotropic hormone (Hormone 1)

  • Anterior pituitary tropic hormone (Hormone 2) 

  • Target endocrine gland hormone (Hormone 3) 

KNOW THE CHART OF PITUITARY VS. ANTERIOR

KNOW THE CHART OF PITUITARY VS. ANTERIOR

What is the body’s master circadian clock?

suprachiasmatic nucleus 

Describe the pineal gland (what does it interact with, environmental cues)

• Communicates with pineal gland to regulate the hormone melatonin (indoleamine)

• Synchronizing biological clock with environmental cues

  • SCN helps control natural circadian rhythm 

  • Our brain during light needs to recognize that it is light and tells pineal gland not to make melatonin

  • Ganglion cells contain melanoxin which reacts to light and tells the SCN that it is light which inhibits pineal gland from making melatonin 

  • SCN also synthesizes clock proteins that are synthesized throughout the day and then degraded – takes around 25 hours 

  • What happens when it’s out of sync?

    • Jet lag 

  • What is the biggest self-prescribed supplement?

    • Melatonin 

What. is growth?

Growth of long bones

What factors affect growth?

• Genetics

• Adequate Diet

• Freedom from chronic disease and stress

• Normal levels of growth influencing hormones 

Describe growth in children

• Fetal growth- placenta hormones, genetics, environmental factors

• Postnatal growth- growth hormone, neoplacental hormones, genetics, nutrition 

• Growth hormone is the most abundant hormone produced by anterior pituitary even in adults. What does this tell us?

• Growth hormone has metabolic effects 

  • Glucose is shunted to brain and mobilized fatty acids used for muscles

  • Maintains homeostasis in prolonged fasting or when glucose stores are exceeded

  • Increases hunger

  • Increases fat mobilization 

Describe soft tissue growth vs bone growth

• Indirect influence by stimulating insulin-like growth factor I binding to tyrosine kinase in target cells 

• Soft tissue growth

  • Cellular hypertrophy through protein synthesis (GH and IGF1)

  • Cellular hyperplasia through increased division and decreased cell death (GH and IGF1)

• Bone growth

  • Chondrocyte proliferation and hypertrophy lengthens bones (GH and IGF1)

  • Action of osteoblasts and osteoclasts thicken bones (GH and IGF1)

  • Sex hormones close growth plate 

How is protein synthesis related to growth hormones?

• Direct via GH (JAK) and indirect via IGF 1

• Increased amino acid uptake from blood (GH and IGF1) → increased ribosome and protein synthesis (GH and IGF1) → Decreased protein breakdown (GH)

What are the three ways to regulate growth hormone?

• Negative feedback loops

  • Hypothalamus-pituitary-liver axis

• GH releasing hormone

  • Stimulatory and dominant 

  • Increases cAMP

• GH inhibiting hormone

  • Inhibitory

  • Decreases cAMP

Describe growth hormone deficiency

• Onset in Childhood

  • Defects in pituitary (lack of GH), hypothalamus (lack of GHRH), GH receptors (not deficient in GH but can’t respond), or lacking IGF1

• Onset in adulthood

  • Tumors, infections, inflammation, injury, surgery, radiation, vascular issues 

Describe growth hormone excess

• Gigantism 

  • Excess GH

• Acromegaly

  • Excess GH (everything is wider) 

Describe growth hormone effect on blood glucose, fatty acids, amino acids, muscle protein, major stimuli, and primary role in metabolism

• Effect on Blood Glucose: Increase blood glucose → brain uses glucose by decreasing glucose uptake by muscles (shunted to brain) → increase gluconeogenesis 

• Effect on Blood Fatty Acids: Increase blood fatty acids → increase lipolysis

• Effect on Blood Amino Acids: Decrease blood amino acids → increase uptake in muscles to build protein 

• Effect on Muscle Protein: increase muscle protein → increase protein synthesis → decrease protein degradation

• Major Stimuli: hypoglycemia, exercise, stress, deep sleep 

• Primary Role in Metabolism: promote growth, mobilize fuel in stress sparing glucose for the brain