4U BIOLOGY: HOMEOSTASIS

 Process by which a constant internal environment is maintained, despite a fluctuating external environment

Homeostasis

An alternate term for homeostasis.

Dynamic equilibrium

What is a threshold level?

Tolerable range at which homeostasis can be maintained

3 main components of homeostatic control mechanisms

• Sensor (Monitor)

• Coordinating Centre (Integrator)

• Effector (Regulator)

What is negative feedback?

Balancing action occurs in response to a change in environment

NEGATIVE FEEDBACK: Order the following. Sensor, effector, stimulus, integrator, response

Stimulus, sensor, integrator, effector, response

What type of homeostatic response amplifies conditions away from the baseline state?

Positive feedback

ECTOTHERM: Definition, Examples

• An organism whose activity is regulated by/fluctuates based on the environment 

• Invertebrates, (most) fish, amphibians

ENDOTHERM: Definition, Examples

An organism that maintains its own constant body temperature

Part of brain responsible for nerve and hormone function

• Hypothalamus 

STEROID HORMONES: Makeup, Function, Examples

• Cholesterol (Fat-soluble) 

• Binds to receptor INSIDE TARGET CELL to cause changes

• Sex hormones, cortisol

PROTEIN HORMONES: Makeup, Function, Examples

• Amino acid chains (Water-soluble) 

• Binds to receptors on CELL SURFACE 

• E.g insulin, growth hormones 

Which pituitary lobe STORES hormones produced by the hypothalamus? Which ones?

• Posterior Pituitary Gland 

• Antidiuretic Hormone (ADH), Oxytocin

Which pituitary gland produces and releases ITS OWN HORMONES?

Anterior pituitary gland

3 Glands that affect metabolism:

• Thyroid Gland 

• Parathyroid Gland 

• Anterior Pituitary Gland

Ratio of T3 to T4 secreted by the thyroid gland.

35:65

Glucose is stored as ______ in the liver/muscle cells ?

Glycogen

What are Islets of Langerhans?

Cells in the pancreas that produce hormones.

(T/F) Beta islet cells produce glucagon.

False. Beta islet cells produce insulin.

What is the human body’s ‘metabolic bank’?

Liver

What is the relationship between insulin and glucagon?

They are antagonistic hormones

What causes Type I Diabetes? Type II?

1. Early degeneration of beta cells (Typically childhood)

2. Decreased production/use of insulin

Why does diabetes cause excess urination?

High concentration of glucose in kidneys draws water out of blood

Where are the adrenal glands located?

On top of the kidneys

What is the adrenal medulla?

inner layer of the adrenal glands

Name of the outer layer of adrenal glands

Name of the outer layer of adrenal glands

• Adrenal cortex

What regulates short-term stress responses (Fight or flight)? What hormones are produced

• Adrenal Medulla 

• Epinephrine/adrenaline and norepinephrine/noradrenaline

3 steps of Short-term stress response: 

1. Hypothalamus triggered by stressor 

2. Nerve signal is carried from hypothalamus to adrenal medulla 

   1. Signal triggers release of epinephrine and norepinephrine, which targets adrenoreceptors

What hormones are produced during long-term stress response? What part of the body regulates its release?

• Cortisol

• Adrenal cortex

5 Steps of long-term stress response? 

1. Hypothalamus releases CRH(Corticotropin Releasing Hormone) 

2. CRH triggers release of ACTH from anterior pituitary

3. ACTH triggers release of cortisol from from the adrenal cortex

4. Release of cortisol triggers an increase in blood glucose levels, breaks down proteins + fats 

5. Immune system is suppressed, inflammation reduced

What hormones help with sperm production? Where are they produced? 

• Androsterone and testosterone 

• Produced in the testes

What controls the production of hormones/sperm? 

• Hypothalamus

• Pituitary gland

What does the hypothalamus secrete at puberty? What is the function of this hormone?

• (GnRH) gonadotropin-releasing hormone 

• Stimulates ant. pituitary gland to produce and store gonadotropic hormones FSH and LH

What does testosterone inhibit? How? 

• LH production

• Deactivates the hypothalamus

What are the female sex hormones?

• Estrogen

• Progesterone

Groups of cells in the ovaries are called? 

• Follicles

Relationship between FSH + LH and estrogen and progesterone

• FSH and LH regulate control of estrogen and progesterone 

• Estrogen and progesterone control FSH and LH

Hormone released when a fertilized egg implants in the uterine lining? What is its function? 

• Human Chorionic Gonadotropin (hCG) 

• Maintains endometrial lining because corpus luteum secretes estrogen and progesterone

Function of synthetic estrogen and progesterone in the birth control pill? 

• Suppresses release of FSH, stopping follicle maturation + uterine lining from thickening + LH (preventing ovulation)

(TRH) Thyroid Releasing Hormone: Function, Target, What secretes it?

• Stimulates thyroid to produce thyroxine

• Thyroid gland 

• Anterior pituitary 

(hGH) Human Growth Hormone: Function, Target, What secretes it?

• Whole body

• Anterior pituitary

(TSH) Thyroid Stimulating Hormone: Function, Target, What secretes it?

• Stimulates thyroid to produce thyroxine

• Thyroid gland 

• Anterior pituitary

Thyroxine/T4: Function, Target, What secretes it?

• Increases basic metabolic rate/blood sugar 

• All body cells 

• Thyroid

Calcitonin: Function, Target, What secretes it?

• Decreases Ca in blood, Adds Ca to bones

• Blood/Bones 

• Thyroid

(PTH) Parathyroid Hormone: Function, Target, What secretes it? 

• Increases Ca level + Decreases PO4 in blood, removes from bones.

• Bones + Kidney tubules 

• Parathyroid

Insulin: Function, Target, What secretes it?

• Causes muscle/liver cells to become permeable to glucose 

• Muscle, fat, liver

• Beta islet cells (Pancreas)

Glucagon: Function, Target, What secretes it? 

• Catalyses breakdown of glycogen into glucose in liver, which is released into blood.

Cortisol: Function, Target, What secretes it?

• Stimulates breakdown of protein, releases amino acids that are converted to glucose by liver, raises blood sugar

• Liver, fat, muscle 

• Adrenal cortex

Progesterone: Function, Target, What secretes it?

• Prepares uterine lining for implantation of egg

• Prevents menstruation during pregnancy

EXCITATORY SYNAPSE

• The binding of a neurotransmitter to postsynaptic neuron OPENS Na+ gated channels

• Na+ Diffuses INTO postsynaptic neuron

• Depolarization occurs, less stimulus required to achieve action potential because of an increase in charge

INHIBITORY SYNAPSE

• Binding of neurotransitter to postsynaptic neuron opens K+ gated channels

• Inside of neuron becomes MORE negative, hypolarizing the membrane and making it difficult to reach action potential

Which nerves comprise the Central Nervous System(CNS)

• Nerves of brain 

• Spinal cord

2 Types of nerves in the Peripheral Nervous System(PNS) 

• Somatic

• Autonomic

2 Types of cells in Nerve Tissue 

• Neurons 

• Glial cells

In which direction do neural impulses travel?

• Dendrite to axon

What is a myelin sheath? 

• Fatty protein that surrounds + insulates SOME axons 

• Formed by Schwann(Glial) cells

Name for spaces between segments of myelin sheath? 

• Nodes of Ranvier

What type of neuron is pictured below? Function? Location?

• Sensory/Afferent neurons 

• Sense + Relay information from environment and organs to CNS 

• Clusters found outside spinal cord

What type of neuron is pictured below? Function? Location?

• Interneurons/Association neurons 

• Interpret stimuli, connect incoming (afferent) to outgoing (efferent) neurons

What type of neuron is pictured below? Function?

• Motor/Efferent neuron 

• Relays information to effectors (Muscles, organs, glands)

(NEURAL PATHWAY) Put the following in order:

Sensory (afferent) neurons, motor (efferent) neurons, Sensory receptors, Interneurons(brain/spinal cord), effectors(gland, muscle, etc.)

Sensory receptors → Sensory (afferent) neurons → interneurons (brain and/or spinal cord) → motor neurons (efferent) → effector (gland, muscle, etc)

What creates electrochemical messages sent by neurons? 

• Movement of ions across neural membrane

• Under direction of voltage-gated ion channels

What’s resting potential? Where are high concentrations of K+ and Na+ ions found during resting potential? What's the approximate potential difference of a resting nerve membrane?

• (Electrical potential inside neuron) - (outside neuron)

• High K+ INSIDE cell

• High NA+ OUTSIDE cell

• State at which there is no net movement of K+

• -70 mV

What is a voltage-gated channel?

• A membrane channel that opens and closes depending on the voltage surrounding them 

What is the action potential? What is the AP value when a nerve is excited? 

• Action potential

• +40mV

Which gated channels are closed @ resting potential?

• Na+ Channels

After K+ diffuses outside the cell during resting potential, why are K+ ions attracted back into the cell? 

• Inside of cell has negative proteins.

What does it mean when a membrane is POLARIZED?

• Uneven distribution of + charged ions inside/outside of nerve cell creates an electrochemical charge

Process of depolarization

• Stimulus disturbs plasma membrane on dendrite, Na+ channels OPEN 

• Na+ diffuses into neuron, more Na+ channels open as concentration of Na+ gets higher (At around -50 mV, the rest of the channels open)

• When stimuli is above THRESHOLD level, a response is produced.

• Na+ rush into the cell, potential becomes very positive (Peak of action potential) 

• Neuron is DEPOLARIZED

Process of Repolarization

• At approx. +40 mV, Na+ channels close, K+ channels open. 

• K+ ions flow out of cell, inside becomes more negative

What is the refractory/hyperpolarization period? What restores resting potential? Purpose?

• When the rapid release of K+ ions causes membrane potential to dip LOWER than RESTING potential

• Sodium-Potassium pump transports 3 Na+ out, 2K+ in 

• Ensures action potential moves along the neuron membrane in the correct direction (Nerves cannot be activated until resting potential is restored).

What is a synapse? How does it work?

• The point of communication between two neurons/a neuron and effector.

• Impulse travels down axon > NTs released from PRESYNAPTIC NEURON > NTs diffuse across SYNAPTIC CLEFT > POSTSYNAPTIC neuron is depolarized.

Sacs that contain neurotransmitters found in the end plates of terminal axons.

• Synaptic vesicles

During excitatory synaptic transmission, the action potential arrives at the presynaptic neuron, causing voltage-gated _________ channels to open. __________ ions then diffuse into the cell, causing synaptic vesicles to release neurotransmitters via ___________. These neurotransmitters cross the _______ cleft through __________ and bind to _________ channels on postsynaptic membrane. Na+ rushes into postsynaptic neuron, depolarizes membrane potential to threshold and action potential fires

Calcium, Calcium, Exocytosis, synaptic cleft, diffusion, sodium