Unit 4 - Homeostasis

Grade 12 Bio

What does a feedback system consist of?

• sensor (affector)

• control centre

• effector

Sensor

• part of a feedback system

• detects changes and sends signals to the control system

Control Centre

• part of a feedback system

• sets the range of values a variable (ex: concentration of ions or any other substance in the body) to maintain

• receives signals from sensors and sends signals to the effector

Effector

• part of a feedback system

• receives signals from the control centre and responds to them by changing the variable (ex: concentration of sumn)

• can be: muscle, gland, organs

Positive Feedback

• a feedback system that enhances, strengthens and increases the change in the original variable (like concentration)

Negative Feedback

• a feedback system that works against the change in the original variable (like concentration) in order to bring it back within normal range

What is the function of the nervous system?

regulates body functions to maintain homeostasis despite fluctuations caused by changes in internal and external environments

Central Nervous System

• consists of the brain and spinal chord

• integrates and processes information sent by the nerves

Peripheral Nervous System

• contains the somatic and autonomic systems

neurons

• basic structural unit of the nervous system

• organized into tissues called nerves

glial cells

• supports neurons

  • nourishes them

  • removes waste

  • defends them against infections

• also functions as structural support cells

What are the different parts of a neuron?

• dendrites

• cell body

• axon (myelinated or unmyelinated)

• branching ends

Dendrites

• numerous branches extending from the cell body

• receives impulses from other neurons or sensory receptors and relays the impulse to the cell body

Why are dendrites so highly branched and large in number?

• To increase surface area

  • allows for more information to be received (more area to receive it)

Cell Body of a Neuron

• receives inputs from dendrites

• if the inputs are large enough, relays it to the axon

• contains the nucleus and the cell’s metabolic reactions

Axon

• receives input from the cell body and initiates an impulse away from the cell body to the branching ends

• can be myelinated or unmyelinated

Axon Terminal

• ends of the axon that branch out

• releases chemicals in order to communicate with adjacent neurons, glands, or muscles into the space between itself and the dendrites/receptors of the target

Myelin Sheath

• made up of Schwann cells surrounding the axon

• protects the axon and increases the rate of transmission

• gives the white sheen color of the axon

Sensory Neurons

• receives an impulse from and created by sensory receptors like the skin that have received stimuli

• transmits this impulse to the the rest of the central nervous system through interneurons

• Receptor→CNS

Interneurons

• neurons that are in between sensory and motor neurons that act as the middle man

• processes incoming sensory information and relays outgoing motor information

• CNS→CNS

Motor neuron

• CNS→Effector

• transmits motor information from the central nervous system to glands, muscles, and other organs that respond to nerve impulses

Reflex Arc

• a simple connection of neurons that allows for a fast reaction

• creates an involuntary response to stimulus, a “reflex”

• brain centers for voluntary control are not activated until after the response

Nerve Impulses

• an electrical signal used to communicate other neurons, glands, and muscles

• changes the charge across a cell’s plasma membrane

Membrane Potential

• a charge separation across the membrane of a neuron

• at rest, the charge outside is positive while the charge inside is negative

Why does the membrane potential exist?

• large, negative proteins are located within the neuron cell

• The sodium potassium pump moves sodium and potassium across the cell membrane in different proportions using ATP (both are positively charged, but for every 3 Na+ moved outside of the cell only 2 K+ is moved inside, making the outside more positive than inside)

Depolarization

• when a cell becomes less polar (less difference in charge across the cell)

Action Potential

• causes depolarization

• triggered when the threshold potential is reached (-55 for humans)

• travels down an axon

Describe step 1 of an action potential

• Name: depolarization

• Action potential is triggered when the threshold potential is reached (-55 mv)

• all or none phenomenon, either action potential is initiated or not, no in between

Describe step 2 of an action potential

• Name: rising phase

• Sodium Ion pumps are opened

• Sodium Ions move down their concertation gradient into the axon

• this balances out the charge inside and outside, causing depolarization

How are action potentials different when the strength of the stimulus changes?

• the size does not change but the frequency increases

When the action potential reaches the end of the axon, it causes an influx of. .

Ca2+ ions

Neurotransmitter

• chemicals

• travels across the synapse to bind to the receptors of the next neuron or effector, transferring the signal from the neuron it came from

Synapse

• the connection/bond between two neurons

excitatory effect

• caused by a neurotransmitter binding to the receptors on the postsynaptic membrane

• the receptor proteins trigger ion channels to open (like Na channels) to allow positive ions (like Na) to flow through to the inside of the membrane (making it less positive within), depolarizing the membrane and continue the action potential through that neuron

inhibitory effect

• caused by neurotransmitters binding to the receptors on the postsynaptic membrane

• causes the potassium channels on the membrane to open so that positive potassium ions inside the membrane can move out of the neuron, resulting in hyperpolarization (an increase in the difference in charges inside vs outside the neuron, inside more negative, outside more positive)

Dopamine

• a neurotransmitter hormone that affects brain synapses in control of body movements

• linked to sensations of pleasure such as eating

What are the effects of having abnormal levels of dopamine in the body?

• Excessive: schizophrenia

• Deficiency: Parkinson’s disease (progressive disorder, destroys neurons, causing tremors, slurred speech and loss of motor control)

Serotonin

• Neurotransmitter hormone in control of mood regulation

• Regulates temperature and sensory perception

What are the effects of having abnormal levels of serotonin in the body?

• Deficiency: depression

• Excess: can cause seizures, diarrhea, shivering, muscle rigidity, fever and death if not treated

Endorphins

• neurotransmitter hormone that acts as a natural pain killer in the synapses of the brain

• involved in mood control

What can abnormal levels of endorphins cause?

• Deficiency: can cause an increased risk of alcoholism

• Excess: doesn’t cause any health complications but can cause compulsory behavior when it is an addiction

Norepinephrine

• a neurotransmitter hormone that complements the actions of epinephrine

• readies the body to respond to danger or other stressful situations

What can abnormal levels of norepinephrine cause?

• Excess: high blood pressure, anxiety, insomnia

• Deficiency: hunger cravings and exhaustion

What are the different parts of the hindbrain?

• cerebellum

• medulla oblongata

• pons

What functions is the hindbrain associated with?

• coordination

• homeostasis

What function is the midbrain associated with?

• processing sensory input

What are the different parts of the forebrain?

• thalamus

• hypothalamus

• cerebrum

What functions is the forebrain associated with?

• thought

• emotions

• learning

Cerebellum

• located in the hindbrain

• walnut shaped “little brain”

• controls the unconscious coordination of posture, reflexes, and body movements as well as fine voluntary motor skills (ex: writing, hitting a tennis ball, riding a bicycle)

Medulla Oblongata

• located in the hindbrain, sits at the brain stem, connects the brain to the spinal chord

• coordinates reflexes and many involuntary body processes that maintain homeostasis( ex: heart rate, blood vessel contraction & dilation, coughing, swallowing,

Pons

• located in the hindbrain in front of the medulla in the brainstem

• serves as a relay channel for the neurons on the right and left hemispheres of the cerebrum

thalamus

• located at the base of the forebrain

• provides connections to different parts of the brain, mainly between the forebrain, hindbrain, and between areas of the sensory system (except for smell)

hypothalamus

• part of the forebrain, below the thalamus

• regulates the body’s internal environment

• regulates certain aspects of behavior

• the link between the endocrine and nervous system

• contains neurons that control blood pressure, heartrate, body temperature and basic drives (ex:hunger and exhaustion)

Cerebrum

• largest part of the brain, part of the forebrain

• divided into right and left cerebral hemispheres

• contains the centers for intellect, learning, memory and language

• interprets and controls the response to sensory information

midbrain

• found above the pons in the brainstem

• processes information from sensory neurons in the eyes, ears and nose

• relays that information to the hindbrain and forebrain

• helps with eye movement and control of skeletal muscles

Endocrine system

• consists of hormones (chemical messengers) and the glands that secrete them

• facilitates cellular communication and control

• slower but more long lasting effect compared to the nervous system

What are the glands that function exclusively as endocrine glands?

• pituitary glands

• adrenal glands

• thyroid glands

• parathyroid glands

What are the tissues/organs that secrete endocrine hormones that have other functions beyond the endocrine system?

• hypothalamus (also involved with the nervous system)

• pancreas

• testes

• ovaries

Target Cells

• the cells targeted by hormones which contain different protein receptors that allow different hormones to bind

• hormone & receptor fit like puzzle pieces

What is the pathway of water-soluble hormones?

• Polar, and therefore cannot pass directly through the plasma membrane

• uses the bloodstream to travel

• binds to a protein receptor on the target cell, which activates other processes within the cell using ATP that reach the necessary outcome

What is the pathway of non-soluble hormones?

• Non-polar, therefore diffuses through the plasma membrane

• does not require capillaries to travel

• enters the nucleus directly and binds to a receptor protein inside to create a hormone-receptor complex

• the hormone-receptor complex activates a gene on DNA and therefore the synthesis of a specific mRNA molecule

Why are hormones that are not water soluble stronger/more effective than those that are?

• Because their non-polarity allows them to diffuse through the lipid bilayer of the plasma membrane and interact with DNA directly

• Water soluble hormones cannot enter the nucleus because of the non-polar lipid bilayer, and therefore are unable to interact with DNA directly

Pituitary Gland

• Has two lobes: posterior (back) and anterior (front) pituitary glands

• Vasculated because the hormones it secretes are water soluble and therefore need to be transported through the bloodstream to reach target cells

Anterior Pituitary Gland

• Front lobe of the pituitary gland

• Secretes:

  • follicle stimulating hormone (FSH)

  • luteinizing hormone (LH)

  • human growth hormone (hGH)

  • prolactin (PRL)

  • adrenocorticotropic hormone (ACTH)

  • thyroid stimulating hormone (TSH)

Posterior Pituitary Gland

• Back of the pituitary gland

• Secretes

  • oxytocin

  • antidiuretic hormone (ADH)

Human Growth Hormone (hGH)

• secreted by the anterior pituitary gland

• affects almost every tissue in the body, but targets the liver, muscle cells and bone cells directly

• The liver releases growth factors (chemicals) that help it increase:

  • cell division & growth

  • protein synthesis

  • breakdown of lipids from fat

Hyposecretion of hGH

• results in dwarfism

Hypersecretion of hGH

• as an adult can lead to acromegaly (no increase in height but widening of bone and muscle tissue, can cause fatigue and headaches or overly large organs, looks primal, hard to diagnose without physical changes)

• in early childhood can cause gigantism

Thyroid Gland

• produces and secretes thyroxine (T4)

• requires iodine to make hormones

• The hormones it secretes regulates metabolic rate

• located in the throat

• contains parathyroid glands in its back

Thyroxine (T4)

• produced by the thyroid

• increases the rate at which the body metabolizes fats, carbohydrates and proteins for energy

• targets the cells in the:

  • heart

  • skeletal muscles

  • kidney

  • liver

• to increase cellular respiration

Hypothyroidism

• condition of the body in which there is a deficiency of thyroxine

• can result in cretinism in children

• creates fatigue and weight gain in adults due to a slow metabolism

Hyperthyroidism

• condition of the body in which there is too much thyroxine being produced

• can result in Grave’s disease in which the immune system attacks the thyroid gland

• Symptoms include anxiety, weight loss and insomnia

• Can be treated with medication or the removal of part of the thyroid gland

What kind of feedback loop does thyroxine follow and what are its steps?

• Negative feedback loop

• 1) Hypothalamus sends releasing hormones to the anterior pituitary gland

• 2) The anterior pituitary gland secretes TSH in response

• 3) TSH stimulates the thyroid to produce T4

• 4) The T4 inhibits the hypothalamus and anterior pituitary gland from continuing the cycle

What happens if there isn’t enough iodine for the thyroid gland to use?

• Thyroxine will not be made, and there will be nothing to inhibit the secretion of TSH

• constant simulation of the thyroid gland cause it to enlarge, creating a goitre

Goitre

• a large bump on the neck caused by the enlargement of the thyroid gland in response to constant TSH simulation with no iodine to produce T4

Parathyroid glands

• small glands in he back of the thyroid gland

• secretes parathyroid hormone (PTH)

• works with the thyroid gland to regulate calcium levels

What are the two hormones released for calcium regulation and where are they secreted from?

• Calcitonin from the thyroid gland

• parathyroid hormone (PTH) from the parathyroid gland

What kind of feedback loop regulates calcium levels in blood?

• Negative feedback loop

How does the endocrine system re-establish homeostasis when Ca levels are elevated?

1) Thyroid gland secretes calcitonin

2) Calcitonin inhibits osteoclasts (stopping bone reabsorption) and stimulates osteoblasts (to use up the extra Ca to make more bone, amplifies excretion by kidney

How does the endocrine system re-establish homeostasis when Ca levels are low?

1) Parathyroid gland secretes PTH

2) PTH inhibits osteoblasts (stopping bone building) and stimulates osteoclasts (increasing bone reabsorption to put more Ca in the bloodstream), inhibits kidney excretion and enables kidney reabsorption of Ca from urine which enables vitamin D, which stimulates increased small intestine reabsorption by making the necessary protein D9K for it (more vitamin D, more D9K made = more protein to carry away Ca for reabsorbtion

Osteoblast

• cell that builds new bone tissue and adds onto existing bone tissue

Osteoclast

• cell that breaks down existing old or damaged bone tissue to create Ca that will be added to the bloodstream

Hypocalcemia

• The condition of the body in which there is a deficiency of Ca

• Symptoms:

  • Dry skin

  • muscle cramps

  • brittle nails

  • coarser hair

  • depression

  • irritability

  • restlessness

  • hallucinations

Hypercalcemia

• The condition of the body in which there is too much calcium

• Symptoms:

  • can be a symptom of cancer

  • thirst & frequent urination due to kidney being overworked to filter excess Ca

  • stomach pain

  • vomiting

  • constipation

  • fast beating & fluttering heart

  • bone and joint weakness if caused by too much bone reabsorption

Adrenal glands

• pair of glans located on top of each kidney (one per kidney)

• involved in regulating stress response and blood sugar levels

• made of two parts:

  • adrenal cortex (outer layer)

  • adrenal medulla (inner layer)

• each layer functions independently as an organ and produces different hormones

Adrenal Medulla

• inner layer of the adrenal gland

• responds to short term stress ( creates the fight or flight response)

• secretes:

  • epinephrin

  • norepinephrine

In response to a stressor, what happens in short term stress response?

• The sympathetic system carries a signal from the hypothalamus to the adrenal medulla

• Epinephrine and norepinephrine is released, causing:

  • elevated heartrate

  • elevated breathing rate

  • elevated blood pressure

  • elevated blood flow to the heart and muscles

  • elevates rate of conversion from glycogen to glucose in the liver

What is the difference between epinephrine and norepinephrine?

• epinephrine has more of an effect on the heart

• norepinephrine has more of an effect on blood vessels

adrenal cortex

• outer layer of the adrenal gland

• produces hormones that respond to long term stress

• secretes:

  • glucocorticoids (genre of hormones)

  • mineralocorticoids (genre of hormones)

Glucocorticoids

• a group of hormones that respond to long term stress by increasing blood sugar

• ex: cortisol

Mineralocorticoids

• group of hormones that respond to long term stress by increasing blood pressure

• ex: aldosterone

Cortisol

• a glucocorticoid

• promotes the breakdown of fats and proteins to increase glucose levels

• also an anti-inflammatory

• immune system suppressant

• controlled by a negative feedback loop

  • high levels can impair thinking, damage the heart and cause an early death

Explain the steps of cortisol secretion

• Hypothalamus secretes a releasing hormone

• this hormone stimulates the anterior pituitary gland

• the anterior pituitary gland releases adrenocorticotropic hormone (ACTH)

• ACTH targets the adrenal cortex, which secretes cortisol

Aldosterone

• main mineralocorticoid

• stimulates the kidneys to increase absorption of sodium in the blood, which raises blood pressure

What happens if the adrenal cortex is damaged?

• Addison’s disease can result, which includes

  • low glucocorticoid and mineralocorticoid production

    • which causes low blood sugar (hypoglycemia), sodium and potassium imbalances, and weight loss

  • Needs to be treated within a few days or it can be fatal

Pancreas

• Functions both in the digestive and endocrine system

• Has over 2000 clusters of endocrine cells named Islets of Langerhans scattered throughout

• These cells secrete:

  • insulin (secreted by beta cells)

  • glucagon (secreted by alpha cells)

Insulin

• lowers blood glucose levels by making target cells more permeable to glucose

• secreted by beta cells on the Islets of Langerhans in the pancreas

Glucagon

• increases blood glucose levels by stimulating the liver to convert glycogen into glucose

• secreted by alpha cells on the Islets of Langerhans in the pancreas

What are the two major types of diabetes?

• Type 1: diagnosed in childhood, the immune system attacks and destroys the beta cells in the pancreas that produces insulin, requires daily injections of insulin

• Type 2: diagnosed in adulthood and overweight people have a higher chance of developing it, caused by insulin receptors in the body no longer responding to insulin

gonad

• organs that produce sex hormones and reproductive cells: sperm for male and egg for female