Nervous, Integumentary, and Endocrine Systems

BIOL 252

How does the nervous circuit work? How are the Central and Peripheral Nervous Systems involved?

Nervous Circuit: Input → Processing → Output

• 1) Sensory receptors — ex: visual/chemo receptors

  • Input delivered via affectors

• 2) Integrations in the brain and spinal cord (decisions made)

• 3) Motor receptors — ex: skeletal muscles

  • Output delivered via effectors

CNS vs. PNS

• CNS: control center

  • Brain/Spinal Cord

  • Reflexes require spinal cord

  • No nerves

  • We sense in the cerebral cortex (cognitive functioning)

• PNS: inputs and outputs

  • Nerves

  • Sensory receptors only send messages/motor receives them

What are Nissl Bodies? How are they related to, and what are gray and white matter?

• Gray matter is enriched with cell bodies

  • Rich with rough ERs and ribosomes

  • Neurons make lots of proteins

  • Contain lots of organelles

  • More dense

  • Appear darker in Nissl stains

• White matter is lighter in Nissl stains and less dense

What systems make up the Peripheral Nervous System?

• Sensory (Afferent)

  • Somatic (skin, skeletal muscle and joints)

  • Visceral (internal organs)

• Motor (Efferent)

  • Somatic (skeletal muscles — ex: diaphragm)

  • Autonomic (smooth and cardiac muscles)

Autonomic = Motor, Visceral = Sensory

What is myelin sheath?

• Whitish, fatty segmented sheath around most (not all) long axons

  • Dendrites/soma not myelinated

  • Formed by Schwann Cells (PNS) and Oligodendrocytes (CNS)

  • Concentric layers of membrane

• Increases the speed of nerve impulse transmission

What are the 6 types of microglia? What distinguished neuroglia from neurons?

Neuroglia support and nourish neurons — they do not transmit information, serving supportive roles in the nervous tissue.

1. Astrocytes

   • Support and brace neurons

   • Control the chemical environment by secreting and absorbing ions

   • Also aid in structural anchoring, facilitation of nutritional transport, formation of the blood brain barrier, and repairing damaged brain tissue

2. Oligodendrocytes

   • Insulators of the thick neurons of the CNS

   • One can insulate many neurons

3. Ependymal cells

   • Circulate the cerebrospinal fluid

   • Involved in CSF formation and monitoring its composition

4. Microglia

   • Macro/phagocytic functions

   • Capable of removing a blood clot from the brain

   • Ingest disease-causing organisms, dead neurons, and other cellular debris

   • Secrete inflammation-stimulating chemicals

5. Schwann Cells

   • Form myelination in the PNS

   • Play a role in repairing damaged axons

6. Satellite Cells

   • Support neuron cell bodies and regulate the extracellular environment.

     
     

What is the Blood Brain Barrier? What cells are involved in its formation?

• Found between the capillaries in the brain and the extracellular fluid in the brain

• Regulates what gets into the brain

• Protects the cerebrospinal fluid and what goes from the CSF to the ECF

• Made up of epithelial cells (endothelial cells) which line the capillary

• Junctions between cells are blocked via tight junctions

• Astrocytes and pericytes induce the formation of the BBB by regulating tight junctions (signal to make more, for example)

What is the Cerebrospinal Fluid? What neuroglia are associated with it and how? What would happen if they weren’t working?

• The CSF lines the brains and fills the ventricles, serving as a cushion (shock absorption)

• Ependymal cells are ciliated epithelial cells which line the central cavities of the brain and spinal column

• They form a permeable barrier between the CSF and the nervous tissue

• Their beating cilia help circulate the CSF

• Without this dynamic movement of the CSF, it would fail to drain and accumulate, causing the brain to enlarge, pressure to increase, and tissues to die

  • Drainage problem = hydrocephalus, occurs in youth, when the skull bones aren’t and medical intervention may work

Define the following terms: soma, Nissl bodies, dendrites, axon, axon hillock, axolemma, axon terminal/synaptic knob

• Soma- The cell body of the neuron, which contains the nucleus and organelles.

• Nissl bodies- Dark-staining clusters containing the ribosomes and rough endoplasmic reticulum of the neuron.

• Dendrites- Short, forked branches that extend from the neuron’s cell body which receive input from other neurons.

• Axon- Long singular branch that carries neuronal signals away from the cell body in the form of action potentials.

• Axon hillock- The first part of the axon where the cell body tapers into the thin axon.

• Axolemma - The plasma membrane which envelops the axon.

• Axon terminal/synaptic knob- The ending part of the axon where the axon tapers into thin branches, which communicates with the next (target) cell.

What are the concentration and electrical (electrochemical) gradients across the neuronal membrane? Why is this gradient importent?

• Ion channels allow ions to move down the membrane, driven by the electrochemical gradient (high to low)

• K+:

  • There is a high concentration of K+ in the cytosol than in the ECF

  • K+ leaves the cell via K+ leak channels due to the chemical gradient

  • As K+ leaves, an electrical gradient starts to pick up, driving K+ into the cell

  • A negative electrical membrane potential counteracts the K+ outflow (reverse potential, net flow = 0)

• Na+:

  • Found in higher concentrations in the ECF compared to the cytosol

  • Assuming full permeability, the reverse potential of Na+ would be positive (to counteract increasing positivity of inside cell)

What is resting membrane potential? What creates this potential?

• ~ -70 mV

• Na+ and K+ equilibrium at rest

• The impact of Na+ on membrane potential is much lower than K+ because the membrane is much less permeable to Na+

• RMP is mainly dependent on the K+ electrochemical gradient, which is negative

• Sodium-Potassium Pump

  • The Na+/K+ pump restores the chemical gradients and maintains the resting membrane potential

  • Pumps (more) sodium out, and potassium in — against their concentration gradients via primary active transport

What are membrane channels? What are some different types of ion channels?

• Channels: transmembrane proteins that allow certain substances to cross the membrane and pass into/out of the cell

• Types:

  • Leak Channels

    • Specific to an ion/a few ions

    • Ions move down the concentration gradient via (facilitated) diffusion

  • Chemically/Ligand- Gated Channels

    • Open in response to a ligand via conformational change

    • Can be ion-specific or not

    • Ex: Ach receptor at the neural-muscular junctions - permeable to both Na+ and K+

  • Voltage-Gated Channels

    • Open/close depending on the charge of the environment

    • Ion selective

    • Open and close at different speed

  • Mechanically-Gated Channels

    • Found in some sensory receptors

    • Ex: Hair cells in the ear

What does it mean that the membrane is polarized? What is depolarization vs. hyperpolarization? How can we depolarize or hyperpolarize a cell?

• Membrane: polarized = negatively charged

  • Depolarization: making the cell less polarized ( → positive)

    • Depolarize by a stimulus (ex: a chemical stimulus)

    • Sodium channels opening leads to depolarization

  • Hyperpolarization: making the cell more polarized ( → negative)

    • K+ ions flow out of the the cell and/or anions (Cl-) flow into the cell

What is a graded potential and how is one generated in a cell? How would increasing the ion or ligand concentration impact it? How do graded potentials spread and do they die out?

• Graded potential: short-range change in a membrane potential upon a stimulus

  • Ligand channels will close

  • Depolarization

• Increased Na+ concentration or increased # of ligand molecules → greater local potential

  • Graded potential increased with a stronger stimulus

• Graded potentials spread locally, as cations move towards a negative charge

  • The site next to the original depolarization will depolarize, creating another graded potential

  • Can move in either direction

  • Dies out eventually (Na+/K+ pump is still working)

How are actions potentials different from graded/local potentials? Where in the body can they be propagated and why only there?

• Action potentials, unlike graded potentials:

  • Are not/do not proportional to the stimulus size, act locally, or attenuate with distance (all or nothing)

  • They spread in one direction (unidirectional)

  • Take place in neurons and muscle cells

    • Only at the axon in neurons — voltage-gated channels are found mainly on the axon and axon hillock (not enough in the soma)

    • Ions flow into the soma, but there are no(t enough) voltage-gated channels

Define the following processes: simple diffusion, facilitated diffusion, channel-mediated diffusion, carrier-mediated diffusion, primary active transport, secondary active transport

• Simple diffusion- Occurs with non-polar solutes, which pass directly through the phospholipid bilayer membrane.

• Facilitated diffusion- Occurs with charged or polar solutes, which require a membrane protein to pass through the phospholipid bilayer.

• Channel-mediated diffusion - Protein channels with hydrophilic amino acids in the interior allow charged and polar solutes to pass through. These are usually specific to solutes.

• Carrier-mediated diffusion- Carrier proteins bind to specific solutes and carry them into/out of the cell. The protein changes shape when bound to the solute, which allows movement through the membrane.

• Primary active transport- Involves a protein pump, which binds a solute and transports from low to high concentration. The hydrolysis of ATP provides the energy to run this transport.

• Secondary active transport - The cell uses ATP to create a concentration gradient by pumping one substance across the cell membrane. The cell then uses the potential energy from the gradient to power the active transport of another substance.

What is the difference between a uniporter, an antiporter, and a symporter?

• Uniporter- A type of carrier protein which transports a single solute.

• Antiporter- A type of carrier protein which moves two different solutes in opposite directions (one in, one out).

• Symporter- A type of carrier protein which moves two solutes in the same direction.

What voltage-gated channels are involved in action potential propagation? What are the steps of action potential propagation?

• Voltage-gated channels respond to threshold (-55 mv) → changed voltage = conformational change

• Sodium Voltage-Gated Channels (two gates):

  • Activation Gate: interior of membrane protein, fast gate

    • Closed at resting state, opens upon depolarization

  • Inactivation Gate: cytosol-end of membrane protein, slow gate

    • Open at resting state and slow to close upon depolarization

  • Both gates must be open for Na+ to flow

• Potassium Voltage-Gated Channel:

  • Slow gate

  • Closed at resting state, slowly opens upon depolarization

• Steps:

  • 1) Na+ inactivation gates open, activation gates closed (resting membrane potential)

    • Stimulus causes local potential, membrane potential approaches threshold

  • 2) Na+ activation gates open (depolarization)

    • Na+ inactivation start to close and K+ gates start to open

  • 3) Na+ inactivation gates close and K+ gates open (repolarization)

    • Na+ activation gate closes upon return to -55 mVs

  • 4) Na+ activation gates close, K+ gates open (hyperpolarization)

    • K+ gates slow to close → undershoot

    • We return to RMP by letting astrocytes collect K+ ions from the ECF

Why do action potentials not die out as they progress? Why are they unidirectional?

• A single action potential does not move through the cell

• The formation of an AP in one site generates an AP in the next site (new ions flow into next voltage-gated channels)

• Refractory Periods:

  • Absolute Refractory Period:

    • Na+ channels have not yet reset to their resting positions

    • A new AP CANNOT be generated

    • Channels unresponsive (inactivation gate closed)

  • Relative Refractory Period:

    • Some Na+ channels have reset to their resting positions

    • Na+ inactivation gates start to reopen at -55 mV, but very slowly

    • Requires a very strong stimulus to fire

  • The refractory period is responsible for unidirectional flow

How does myelin provide faster propagation? What is saltatory conduction? What happens if we don’t have myelin? How is size important in AP conduction?

• Myelin Sheath → saltatory conduction = regeneration of APs at each Node of Ranvier

  • Ions are faster because there is less attraction to the ions on the other side of the membrane ( - charge further away)

  • Thicker myelin = faster conduction

  • Unmyelinated axons experience, on the other hand, continuous conduction

• Multiple Sclerosis:

  • Autoimmune disorder in which immune cells attack oligodendrocytes in the CNS, causing myelin degradation

  • Slows APs (doesn’t completely destroy propagation)

• Size:

  • The larger the diameter of the axon, the lower the resistance, and the faster the impulse

  • Important neurons are wider and heavily myelinated

What is the cerebral cortex and how/what does it control? What are the functional areas of the cortex?

• The cerebral cortex is responsible for higher mental functions (learning, memory, personality, cognition, language, and conscience) and important in sensation and movement.

• It is contralateral, meaning each hemisphere is responsible for the opposite side of the body

• Conscious behavior involves the entire cortex, but there are certain functional areas

  • Motor areas control voluntary movement

  • Sensory areas involve conscious awareness of sensation

  • Multimodal association areas integrate diverse information

How do the cortex’s motor areas function? How is the body represented in them?

• Primary Motor Cortex: allows conscious control of voluntary movements (somatic, not visceral)

  • Located on the precentral gyrus (anterior to the central sulcus)

• Premotor Cortex/Motor Association Area:

  • Controls learned, repetitious, or patterned motor skills

  • Coordinates simultaneous or sequential actions

  • Involved in the planning of movemennts

  • Learning = forming/solidifying neural connections (synaptic plasticity)

• Somatotopy:

  • The entire body is represented spatially in the primary motor cortex

  • Primary motor cortex is composed of neurons that eventually control different skeletal muscles

  • The skeletal muscles of the body can be mapped according to the location of their stimulating neurons

  • The motor homunculus reflects the relative space body parts occupy on the primary motor cortex

    • Disproportionate amount of tissue for some body parts

How do the cortex’s sensory areas function? How is the body represented in them?

• Primary Somatosensory Cortex:

  • Receives information from the skin, joints, skeletal muscles (stretch receptors)

• Somatosensory Association Area:

  • Processes and analyzes sensory inputs coming from the primary sensory cortex

  • Integrates sensory information

  • Forms comprehensive understanding of the stimulus

  • Determines size, texture, and relationship or parts

  • Damage = confusing objects (perception and recognition degraded)

• Somatotopy:

  • The sensory homunculus reflects the relative space body parts occupy on the primary somatosensory cortex

What/where are the auditory and visual areas in the brain?

• Auditory Areas

  • Primary Auditory Cortex

    • Receives information related to pitch, rhythm, and loudness

    • The anatomy of our ears senses these characteristics for us

  • Auditory Association Area

    • Stores memories of sounds and permits perception of sounds

    • Tells us what the sound is beyond its qualities

    • Ex: Distinguishing laughing and crying

  • Both located in temporal lobe - association area slightly inferior and posterior

• Visual Areas

  • Visual Cortex: colors and general shape

    • Damage may cause blindness

  • Visual Association Area: face and object recognition, perception

    • Damage may cause things like visual agnosia

What is the prefrontal cortex? What happens if we cut its connections to other brain regions?

• PFC = most complicated region in the cerebral cortex (very developed)

• Responsible for intellect, learning, and personality (decision-making, motivation, etc.)

• Associated with working (short term) memory and emotions

• Connected to many other brain regions

• Phineas Gage:

  • PFC damage, other vital parts of the brain (medulla oblongata, brainstem, etc.) remained intact

  • Changes in personality, motivation, aggression, etc.

• Frontal Lobotomies:

  • Surgery to cure mental illness and change personality

  • Amygdala goes to the PFC, they cut the PFC through the eyes

  • Worked in theory, they became completely apathic

  • Rosemary Kennedy was famously lobotomized, regressed completely

What areas make up our language center? How are they connected to other parts of the brain, and what is the pathway we use when analyzing and saying words? What are some disorders that can occur if there’s damage?

• Broca’s Area:

  • Controls muscles involved in speech

  • Part of premotor cortex

  • Designs a speech plan, executed (sent directly to) the primary motor cortex

  • Present in one hemisphere, usually the left

  • Damage: Broca’s Aphasia

    • Unable to produce coherent speech

    • Intact speech muscles, damaged planning

    • Know what they want to say and understand questions

    • May or may not be able to write/sing

    • “Nonfluent Aphasia”

• Wernicke’s Area:

  • Permits recognition/comprehension of spoken and written language

  • Receives inputs from the visual and auditory cortices

  • Works with other regions to interpret, sends signals to the Broca’s Area

  • Present in one hemisphere, typically on left/same side as Broca’s

  • Damage: Wernicke’s Aphasia

    • Unable to comprehend languages

    • Fluent speaking, may not make sense in context

    • “Fluent Aphasia”

• Primary Motor Cortex:

  • Damage: Apraxia/Dyspraxia:

    • Damage to primary motor cortex neurons

    • Broca’s/Wernicke’s intact

    • Muscles intact, plan intact, neurons disrupted

    • Hard to distinguish from Broca’s

    • Speech therapy may work

• Pathway of Language:

  • Visual (photo)receptors → sensory neurons → visual cortex → visual association area → Wernicke’s area → Broca’s area → primary motor cortex → motor neurons → speech muscles

What does it mean that the hemispheres of the brain are lateralized? What connects the hemispheres and what happens if it’s severed?

• Relationship between two hemispheres, connected via the corpus callosum (bundle of nerve fibers connecting the hemispheres of the brain, largest commissural tract)

  • A person with a severed corpus callosum is still alive, but some traits are compromised → new pathways must be found

• Each hemisphere has abilities not shared with its partner (ex: Broca’s/Wernickes

• When you are right-handed, the region controlling the muscles involved in writing is more developed in your left hemisphere

What are the basal nuclei and what do they control?

• Basal nuclei = gray matter, clusters of cell bodies, embedded within the white matter

• Determine the onset and cessation of intentional movements

• Contribute to a better motor plan with the premotor cortex (voluntary movements)

• Coordinate control of antagonistic muscle pairs (ex: biceps/triceps)

  • Muscles can only pull, movements are a tug of war

  • Both muscles contracting at once → tremors)

What are the types of white matter tracts in the brain?

• Commissural: Connect the right and left cerebral hemispheres (ex: the corpus callosum)

• Projection: Connect the brain from the top to bottom.

• Association: Connect different areas of the same hemisphere.

What is the diencephalon composed of? What do each of them do?

• Thalamus:

  • Sensory relay center of the brain

  • Sensual afferent impulses converge and synapse in the thalamus

  • Impulses of similar function are sorted out, edited, and relayed as a group

  • Almost all inputs ascending to the cerebral cortex pass through the thalamus (not smell)

• Epithalamus (biological clock)

• Hypothalamus:

  • Visceral control center of our body

  • Link between the nervous and endocrine systems

  • Controls drives (thirst, hunger, sex, etc.)

  • Regulation of body temperature

  • Regulation of the autonomic nervous system

What components make of the brainstem? What are their functions?

• Brainstem = structural framework, hosting ascending and descending neural fibers

  • Holds nuclei responsible for our built-in, automatic system

• Midbrain:

  • Various nuclei

  • Substantia Nigra:

    • Nuclei in the midbrain which release dopamine to the basal nuclei and inhibit them visa IPSPs

    • If the cells of the Substantia nigra degrade, there would be overactivation of the basal nuclei and coordination would be impacted

      • Parkinson’s Disease, loss of angonistic muscle control

• Pons:

  • Respiratory center

  • Controls rate and depth of respiration

  • Conscious breathing = cerebral cortex — if we wait too long the ponds and medulla will override via the hypothalamus

• Medulla Oblongata:

  • ANS reflex center

  • Cardiovascular, respiratory, and digestive

What does the cerebellum control and how?

• Cerebellum = two hemisphere of gray matter found at the cortex and nuclei, with white matter in between

• Controls the “autopilot” of the brain, comparing the cerebral movement plan with the current state of the body and then sends a better plan

• Sensory receptors (equilibrium, visual, and proprioceptors) send inputs to the cerebellum

• Cerebellum sends EPSPs and IPSPs to the premotor cortex to adjust the plan, and signals down the SC

What region is most involved in memory? What types of memory do we have?

• Memory:

  • Working memory (immediate): short term; e.g. a phone number

  • Declarative memory: data from our past experience

  • Non-declarative memory: skills, motor, and emotional (playing the piano and riding a bike)

• Region/Cells:

  • No exact memory region (synapses and connections on the other hand)

  • The hippocampus is responsible for creating a new declarative memory (loads STM to LTM)

    • Damage: cannot form new memories

  • Aniston Cells: certain areas fire in response to certain faces

What is the autonomic nervous system and what are its two divisions? How are they antagonistically controlled?

• ANS = motor neurons that make adjustments (fine tuning) to ensure optimal support for body activities, which operates via subconscious control

• Divisions:

  • Parasympathetic: “rest and digest” — keeps body energy low

  • Sympathetic: “flight or flight” — prepares the body for emergency or vigorous activity

• Antagonistic Control:

  • Most internal organs are innervated by both divisions of the ANS, which exhibit antagonistic control

  • Ex: Heart Rate — an increase in sympathetic stimulation causes HR to increase whereas an increase in parasympathetic control causes a decrease (always getting some degree of sympathetic control to keep our heart beating)

What components make up the Integumentary system? What are the functions of the skin?

• Components:

  • Skin

  • Sweat glands

  • Oil glands

  • Hairs

  • Nails

• Functions of the Skin:

  • Protection → not losing water, protects from toxins/infectious organs

  • Body temperature regulation

  • Sensory reception → touch/pain

  • Metabolism

  • Excretion (sweat glands)

What layers make up the cutaneous membrane? What is the purpose of the hypodermis?

• Outermost layer: Epidermis

• Dermis

• Subcutaneous tissue: Hypodermis (fat cells)

  • Anchors the skin to the muscles

  • Shock absorber → bones and muscles don’t take full hit

  • Heat insulator

  • Gaining fat = more fat in cells/more fat cells

What is the structure of the Epidermis? What cell types exist in it?

• Stratified Squamous (flat cell) Epithelium

• Cell Types:

  • Keratinocytes

    • Majority of cells

    • Produce keratin, a fibrous protein which is a family member of the intermediate filaments

    • Formed by stem cells near basal layer, slowly start to die as they approach

    • Water can diffuse across cells, but blocked by lamellated granules (lipid secretion) near dead cells → less diffusion and nutrients for dead cells

    • Acts as physical barrier

  • Melanocytes

    • In the stratum basale

    • Produce and secrete melanin, a polymer of tyrosine residues that absorbs UV light and protects our body from DNA damage

    • Melanin accumulates in the keratinocytes

    • Protects the body from UV-light

    • Amount of melanocytes is the same in everyone, amount of melanin differs

    • Tanning tells you that you have increased your changes of getting your DNA damaged

      • *However, some UV light is necessary = Cholesterol → Vitamin D → Calcium Absorption

  • Merkel Cells — Sensory cells

  • Langerhans’ Cells — Defense system, phagocytotic

What is the structure and purpose of the Dermis?

• Two layers: papillary and reticular

  • Dermal Papilla = fingerprints

  • Papillary = highly vascular, many capillaries

    • Heat loos (conduction from capillaries around the epidermis)

• Provides a support for the epidermis

• Hosts skin appendages

• Regulates body temperature

• Houses hairs, glands, etc.

What are sweat glands?

• Eccrine sweat glands

• Main function is the regulation of body temperature — getting rid of water

What is the endocrine system? How does it differ from the nervous system? What parts of the body are included in the endocrine system?

• Endocrine System: body’s second greatest controlling system, composed of endocrine glands

  • Act by means of hormones, synthesized in the glands and secreted into the blood → body tissues

  • Responses are slow and long (up to weeks)

  • Amplitude = strength

• Nervous System:

  • Acts via electrochemical signals (potentials)

  • Fast and short responses

  • Strength = frequency (fixed amplitude)

• Glands (one cell → whole organs)

  • Control system = Hypothalamus

  • Only endocrine glands = Pituitary gland, Pineal gland (biological clock), Thyroid gland, Parathyroid gland, Thymus gland (immune system), Adrenal glands

  • Glands w/ other functions = Pancreas, Testis, Ovary

What types of hormones exist? What types of transport are there? How do hormones interact with their targets?

• Hormones:

  • Amino-acid based: amines, peptide, and protein hormones (water soluble, receptor on membrane)

  • Steroids: synthesized from cholesterol (lipid soluble, receptor in cell)

• Transport:

  • Circulate the blood in two forms

  • Unbound: water soluble hormones (short duration)

  • Bound: steroids and thyroid hormone are attached to binding proteins (prolonged effect)

• Interactions are specified via receptors exhibited by different cells

  • The response of the target cell is target cell dependent (doesn’t work the same in every cell)

  • Another hormone, another cell, another response

• When a hormone is secreted, it circulates the whole body

How do hydrophobic and hydrophilic hormones differ in their interactions with cells?

• Hydrophobic (lipid-soluble) = intracellular receptors

  • Lipid soluble and thyroid hormone interact with receptors in the cytoplasm or on the nuclear membrane (passive diffusion in)

  • Regulates transcription

  • mRNA translated into proteins, bringing about a cellular effect

  • Receptor-hormone complex may act as transcription factor

• Hydrophilic (water-soluble) = second messengers

  • Following hormone-receptor binding, ATP will be converted into cAMP that will initiate a cascade of events leading to many cellular events

  • Enzyme cascades

  • Ex: glucagon (glucose secretion), based on conformational change and enxyme activation

What are the functions of the posterior pituitary gland? What hormones are associated with it

• The posterior pituitary gland is not a real gland, it is an extension of the hypothalamus and a hormone storage area

• Hypothalamic neurons extend their axons to the posterior pituitary

• Neurohormones are produced in the hypothalamic neurons and stored at the axon terminals within the posterior pituitary

  • Secretes when hypothalamus sends APs

• Stores and secretes two polypeptide hormones:

  • Antidiuretic hormone (ADH):

    • Helps to avoid dehydration

    • Osmoreceptors in the hypothalamus (thirst center) monitor the solute concentration of the blood

    • With high solutes, ADH preserves water, by regulating urine production in the kidney

    • With low solutes, ADH is not released, thus causing water loss

  • Oxytocin (“love hormone”):

    • Stimulates contraction of the smooth muscles of the uterus, involved in birth

    • Synthetic and natural oxytocic drugs are used to induce or hasten labor

    • Triggers milk ejection (“letdown” reflex) in women producing milk

      • Milk made by prolactin

What does the anterior pituitary gland do?

• Is a real gland (synthesizes and secretes)

• Synthesizes and secretes hormones in response to hypothalamic control and other inputs

  • Hypothalamus directs

  • Hormones secreted affect target cells and target glands

• Neurohormones reach the anterior lobe via the hypophyseal portal system (capillaries)

What are the two regions of the adrenal glands? What families of hormones are secreted from the first? How are some of these hormones helpful in responding to a stressor?

• Adrenal Cortex

  • Mineralocorticoids: regulate the concentration of minerals, such as sodium and potassium ions, in the body – they also regulate extracellular fluid volume, and help maintain blood pressure and acid-base homeostasis

  • Glucocorticoids: help mediate the body’s response to stress through blood glucose regulation – they also conduct gluconeogenesis in the liver, and oversee the release of amino acids from muscle tissue and fatty acids from adipose tissue

    • Aiding in stress response: by releasing amino acids into the blood, more amino acids are available for the liver in gluconeogenesis, which synthesizes enzymes to help convert amino acids and fats into glucose. This energy is crucial during response to a stressor.

    • While this loss may be detrimental if continued in the long-term, in the short-term, energy is more necessary. amino acids can be resynthesized to prevent loss of muscle proteins in the long run, but when dealing with an acute stressor, this energy is necessary to overcome the stressor and survive.

  • Androgenic steroids: promote muscle growth, develop male characteristics, and increase RBC production

How does the adrenal cortex work with the anterior pituitary and the hypothalamus to mediate a stress response? (Pathway)

• Hypothalamus: releases CRH (corticosteroid-releasing hormone)

• → Anterior Pituitary: releases ACTH (adrenocorticotropic hormone)

• → Adrenal Cortex: releases cortisol

  • Negative feedback on hypothalamus and anterior pituitary

  • Responses:

    • Immune system: inflammatory response

    • Liver: gluconeogenesis

    • Muscle tissue: protein catabolism (breaks down proteins for energy)

    • Adipose tissue: lipolysis

What is Cushing's syndrome?

• Excess of cortisol in the blood causes lipolysis (release of fat) in the upper/lower limbs, which is then deposited in the trunk and face

What is the thyroid gland, what it it’s structure, and what hormones does it synthesize?

• The thyroid gland is made up of two connected, highly vascular lobes located on each side of the trachea

  • Inferior to the larynx

• Contains follicles composed of epithelial cells, surrounding a colloid

  • Colloid = highly viscous, gel-like pool

  • Colloids store the synthesized hormones and are also essential in the biosynthesis of hormones (the intermediate of the hormone enters the colloid, where it finishes synthesis)

• Thyroid Hormone:

  • Important, not essential (will survive if absent)

  • TH is a major metabolic hormone

    • Metabolism = sums of energy-related pathways

      • Catabolism: breaking down of macromolecules (proteins → amino acids)

      • Anabolism: building up of macromolecules (making polypeptides)

  • Once synthesized, TH can be stored for months in the gland

  • Acts as a steroid hormone because it’s so small - binds to nuclear receptors

  • Consists of two related iodine-containing compounds:

    • T4: two tyrosine molecules + four bound iodine atoms — main thyroid gland product (can be converted to T3)

    • T3: two tyrosine molecules + three bound iodine atoms — function thyroid hormone

What does TH regulate and how? How do we avoid overheating?

• TH affects nearly every tissue in the body, with varied responses between target tissues (based on receptors)

  • Metabolism is primarily affected in certain tissues (heart, blood, liver, etc.)

    • Heat production → heat up body by increasing metabolism (energy released via heat)

      • Na+/K+ pump works hardest, releases most heat

  • Growth Maturation in other tissues (anabolism in the bone, hair, nervous tissues, muscles, etc.)

• Regulation of TH and body temp:

  • Exposure to cold:

    • Thermoreceptors in the skin detect, hypothalamus acts as thermostat

    • Cold temp → synthesis and secretion of hypothalamis TRH

    • TRH induces TSH secretion from the anterior pituitary (via pituitary portal)

    • → Secretion of TH and proliferation of follicle cells (increased size and number → increased production)

    • Effect: Increased metabolic rate and heat production

  • Overheating:

    • Negative feedback loop

    • Production of T3 and T4 will inhibit TRH and TSH production

    • Hormones can’t perfectly regulate size of effect like the nervous system

    • If solution (heating) is not adequate (still cold), the inputs (TRH → TSH) will continue

What happens if we under/oversecrete TH?

• Hypothyroidism:

  • Reduced/no secretion of TH — damaged pathway, lack of iodine, broken receptors, inadequate TSH stimulation

  • Decreased - not complete - rate of metablism

  • Low body temperature, reduced heart rate, drowsiness

  • Solution: Run blood tests

    • Not immediate iodine supplements, can make Hashimoto’s Disease (autoimmune and major cause of hypothyroidism) worse

• Hyperthyroidism:

  • Abnormally increased secretion of TH

  • Increased metabolic rate

  • High body temperature, rapid heart rate, high blood pressure, sweating

  • Goiter

What is a goiter and what can cause it?

• Excess proliferation of cells causes enlargement of the thyroid gland

  • Elevated levels of an antibody TSI, which mimics TSH and stimulates the thyroid gland (Grave’s Disease = elevated TSI, negative feedback will not stop TSI production)

• May be caused by chronic hyperthyroidism

• Lack of iodine (hypothyroidism) can also lead to goiter

  • T3/T4 are not produced, and no negative feedback goes to TRH and TSH, so the thyroid gland continues to proliferate

  • Factory expands but isn’t making any output

How does the pancreas function, both in the endocrine system and outside of it? What are the two major cell types in the pancreas?

• The pancreas is not just an endocrine gland, but also functions as an exocrine gland (has both)

• Located behind the stomach

• Most of the cells produce an enzyme-rich juice used for digestion, which leaves via a duct (exocrine product)

• Pancreatic islets produce hormones (endocrine products)

• The islets contain two major cell types:

  • Alpha cells produce glucagon

  • Beta cells produce insulin

How do glucagon and insulin regulate blood glucose levels? Why is glucose important? Where is it stored and in what form?

• Glucose supplies the brain and body with energy, and is stored in the liver and skeletal muscles

• Glucagon: Acts to INCREASE glucose levels in the blood

  • Glycogen is the main storage form of glucose, composed of thousands of glucose molecules covalently bonded to a core protein

  • Glycogen accumulates in the liver and muscles

  • Glucagon acts by breaking down glycogen, blocking glucose from entering the cells, and releasing glucose from the livers → increasing glucose in the blood

• Insulin: Acts to LOWER glucose levels in the blood

  • Insulin opens glucose transporters, increasing glucose levels in the cells

  • Promotes the formation of glycogen in the liver and muscles

What is Diabetes Mellitus? What are its two types and how are they treated/prevented?

• Diabetes Mellitus: Characterized by high blood-glucose levels

  • Type I: Loss of beta cells

    • Usually an autoimmune disorder

    • Common in young people

    • Loss of beta cells = no secretion of insulin

    • May develop from Type II due to high glucose damages

    • Treatment: Supply insulin (injection, taken from yeast) and change lifestyle

  • Type II: Insulin resistance

    • Impaired function of any of the components responding to insulin (such as receptors)

    • Common in adults 40+ (epidemic starting earlier)

    • Secondary effects: obesity; damage to blood cells, nerves, retina, and kidney

    • Side effects in the liver, blood, and cardiovascular systems

    • Insulin in the system, but the body doesn’t respond

    • Treatment: Weight control, physical exercise, and nutrition (cannot be fully prevented, but genetic/lifestyle risk can be reduced)