grade twelve biology notes

7/31/2019 Grade Twelve Biology Notes

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Grade Twelve Biology Notes

Bridget Walsh

Nervous System

Glial cells- non-conducting cells important for structural support and metabolism ofnerve cells

Neurons- conduct nerve impulses

o Sensory

afferent carry impulses from sensory preceptors located in clusterscalled ganglia outside the spinal cord

o interneurons

interpret and integrate sensory information

o motor neurons

efferent carry impulses from the central nervous system toeffectors

myelin sheath- insulation for neurons

o formed by Schwann cells

o areas between Schwann cells are called nodes of Ranvier, nerve impulses

jump from node to node

o speed of impulse along the nerve fibre is affected by myelination and

diameter of axon

dendrites- receive impulses

axon- projects nerve impulses from the cell body, is an extension of the cytoplasm

A rapid change in the chemical potential difference across the membrane of aneuron is detectable each time a nerve is excited

The difference between electrical and neural transmission

o Current travels faster along a wire than an impulse travels across a nerve

o Cytoplasmic core of a nerve cell offers great resistance to the movement of

electrical current

Julius Bernstein hypothesized that nerve impulses were and electrochemicalmessage created by the movement of ions through the nerve cell membrane

Action potential- the voltage difference across a nerve cell membrane when the

nerve is excited

Resting potential- voltage difference across a nerve cell membrane during the

resting period (-70mV)

The electrochemical event is caused by an unequal positive charge

Negative ions have little effect because they are very large and cannot pass throughthe membrane

The more rapid diffusion of potassium ions to sodium ions means exterior becomes

positive to the interior membrane

Excitation= sodium more permeable than potassium

Charge reversal results in depolarization

Refractory period- recovery time required before a neuron can produce another


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action potential

Threshold Levels: All or Nothing!

o Potential stimulus must be above critical value to produce a response

o Critical intensity= threshold level

o Threshold levels are different for different neurons

o Increasing intensity of stimuli will not produce an increased responseo Respond completely or not at all

Synaptic Transmission

o Synapses- regions between neurons or between neurons and effectors

o Neurotransmitters- chemicals released from vesicles into synapses

o Presynaptic neuron- neurons that carry impulses to the synapse

o Postsynaptic neuron- carries neurons away

Acetylcholine- is an example of a neurotransmitter. It is released from the endplates of neurons and makes postsynaptic membranes more permeable to Na+ ions,

this results in a change in gradient and thus an action potential.

Cholinesterase- is the enzyme released from postsynaptic membrane to breakdown acetylcholine and close sodium channels

EPSP and IPSP- an excitatory postsynaptic potential (EPSP) is a temporary

depolarization of postsynaptic membrane potential caused by the flow of positivelycharged ions into the postsynaptic cell. They are the opposite of inhibitory

postsynaptic potentials (IPSPs), which usually result from the flow of negative ions

into the cell. A postsynaptic potential is defined as excitatory if it makes it easier

for the neuron to fire an action potential. EPSPs can also result from a decrease inoutgoing positive charges, while IPSPs are sometimes caused by an increase in

positive charge outflow

Summation-EPSPs, like IPSPs, are graded (i.e. they have an additive effect). Whenmultiple EPSPs occur on a single patch of postsynaptic membrane, their combined

effect is the sum of the individual EPSPs. Larger EPSPs result in greater membrane

depolarization and thus increase the likelihood that the postsynaptic cell reaches thethreshold for firing an action potential.

Homeostasis: Blood Glucose regulation

Homeostasis refers to the bodys attempt to adjust to a fluctuating external

environment

All homeostatic control systems have 3 functional components: a monitor (set

point, eg. What your body temp. should be), a coordinating centre (your brain) anda regulator (your body, you start sweating thus cooling yourself)

Negative feedback mechanisms trigger a response that reverses the changed

condition

Positive feedback systems (less common) move the controlled variable even furtheraway from a steady state (eg. The birth process)

The Importance of the Endocrine System


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Hormones are chemicals that affect cells in other parts of the body, they are

classified by their activation sites

o Growth hormone or somatotropin regulate bone growth

o Insulin regulates blood sugar by increasing the permeability of cells to

glucose

o Epinephrine is produced in times of stress Hypothalamus- the region of the brain responsible for coordinating nerve and

hormone response

Pituitary gland- gland at the base of the brain that, together with the hypothalamus,functions as a control centre, coordinating the endocrine and nervous system

Steriod and Protein Hormones

o Steroid hormones- group of hormones made from cholesterol that includes

male and female sex hormones and cortisol

o Cortisol- hormone that stimulates the conversion of amino acids to glucose

by the liver

o Protein hormones- group of hormones composed of chains of amino acids

that includes insulin and growth hormones

o Steroid hormones diffuse from the capillaries into the interstilial fluid and

then into the target cell, where they combine with receptor molecules

located in the cytoplasm

o The hormone-receptor complex moves into the nucleus and binds to

chromatin activating a gene to produce a specific protein

o Protein hormones do not diffuse into the cell but combines with receptor

sites on the cell membrane, activating enzymes within the cell

Glucagon- hormone produced by the pancreas; when blood sugar levels are low,

glucagons promotes conversion of glycogen to glucose

o

Insulin and glucagon work together, insulin causes a decrease in bloodsugar level and glucagons causes an increase

Adrenal glands- located above each kidney, each gland is made up of two glands

incased in one shell

o Adrenal medulla- found at the core of the adrenal gland, produces

epinephrine and norepinephrine. Surrounded by the adrenal cortex, themedulla is regulated by the nervous system while hormones regulate the

adrenal cortex

o Norepinephrine- initiates the fight-or-flight response by increasing heart

rate and blood sugar

o The hormone- producing cells in the adrenal medulla are stimulated by

sympathetic nerves in times of stresso Adrenal cortex- outer region that produces corticoids and

mineralocorticoids

o Short term stress activates a response through the spinal cord to the adrenal

medulla

o Long term stress prompts the pituitary gland to secrete adrenocorticotropic

hormone (ACTH) to the adrenal cortex which then releases either

mineralcorticoids or glucocorticoids


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The Autonomic Nerve System

o The sutonomic nerve system is part of the peripheral nervous system, this

regulatory system works with the endocrine system

o The autonomic nerve system is a motor system regulated without conscious

control

o Made up of two distinct (opposing) units, the sympathetic nervous systemand the parasympathetic nervous system

o Sympathetic prepares the body for stress, while parasympathetic restores

normal balance

o Sympathetic nerves come from the thoracic vertebrae (ribs) and lumbar

vertebrae (small of the back)

o Parasympathetic nerves exit directly from the brain or from the spinal cord,

nerves that exit directly from the brain are called cranial nerves

o An important cranial nerve is the vagus nerve (branches to the heart,

bronchi of the lungs, liver, pancreas, and digestive tract)

o The neurotransmitters released from the sympathetic system are

acetylcholine and norepinephrine; the parasympathetic system releases onlyacetylcholine

o Pain killers:

Endorphins and enkephalins belong to a group of chemicals calledneuropeptides

Pain is interpreted by the brain by specialized cells called substantia

gelatinosa (SG), when stimulated they produce neurotransmitter thatinforms the brain of damage (pain)

When endorphins or enkephalins are present SG is prevented from

producing neurotransmitter and thus pain is decreased

Opiates target the same SG cells and prevent them from notifyingthe brain of pain

o When an initiator of stress is identified both the endocrine and nervous

system react, the somewhat slower endocrine system provides a moresustained response to the stimulus

o Stress hormones provide more blood glucose to cope with the elevated

energy requirements brought on by stress

o Epinephrine- increases by mobilizing carbohydrates and fat energy stores,

increases blood glucose and fatty acids, accelerates heart rate and the

activity of the respiratory system

o Cortisol- increases by converting proteins to glucose, elevates blood amino

acids, blood glucose and fatty acidso Glucagon- increases by converting glycogen to glucose

o Insulin- decreases by decreasing the breakdown of glycogen in the liver

Reproductive Hormones

o Male reproductive system:

Testosterone- male sex hormone produced by interstitial cells of the

testes

FSH- follicle- stimulating hormone, in males the hormone that


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increases sperm production

LH- luteinizing hormone, regulates the production of testosterone

GnRH- gonadotropin-releasing hormone- chemical messenger fromthe hypothalamus that stimulates secretion of FSH and LH from the

pituitary

o Female Reproductive System (hormonal controlthis shit is complicatedyou have to read the entire section to understand):

Gonadotropins regulate the control of hormones produced in the

ovaries: estrogen and proestrogen

FSH- in females, promotes the development of the follicles in theovary

LH- in females promotes ovulation and the formation of the corpus

luteum

Part of a complex negetive feedback loop

GnRH is released from the hypothalamus which activates the

pituitary gland (the storage site for FSH and LH)

During the follicular phase, blood carries FSH, follicle development

happens, follicles secrete estrogen

Estrogen levels rise, signaling the pituitary to turn of secretion ofFSH

Similarly high estrogen signals a release of LH , and ovulation

occurs

After ovulation the remaining follicular cells and transformed into

the corpus luteum, which secretes estrogen and proestrogen,

inhibiting the release of FSH and LH and thus the corpus luteum

deteriorates without the gonadotropic hormones, the drop in ovarianhormones signals the beginning of menstration

Kidney Structure (The Urinary System, Formation of Urine and Water Balance):

o Ureters- tubes that conduct urine from the kidneys to the bladder

o Urethra- tube that carries urine from the bladder to the exterior of the body

o Cortex- outer layer of the kidney

o Medulla- area inside the cortex

o Renal pelvis- area where the kidney joins the ureter

o Nephrons:

Slender tubules called nephrons are the functional units of the

kidney

Afferent arterioles- small branches that carry blood to the

glomerulus (branches from the renal artery, supplies the nephronwith blood)

Glomerulus- high-pressure capillary bed that is the site of filtration

(does not transfer blood to a venule)

Efferent arterioles- small branches that carry blood away from the

glomerulus to a capillary net

Peritubular capillaries- network of small blood vessels that

surround the nephron (efferent arterioles carry blood here)


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Bowmans capsule- surrounds the glomerulus, part of the nephron,

the afferent, efferent and Bowmans capsule are all part of the cortex

Fluids to be processed enter Bowmans capsule from the blood,capsule tapers into a thin tubule called the proximal tubule(connects the Bowmans capsule to the loop of Henle)

Loop of Henle- carries filtrate from the proximal tubule to the distaltubule

Distal tubule- conducts urine to the collecting duct

Urine formation depends on three functions: filtration, reabsorbtion

and secretion

Filtration:

Each nephron has an independent blood supply, bloodmoves through the afferent arteriole to the high pressure

glomerulus, dissolved solutes move from high pressure to

low pressure through the walls of the glomerulus

Reabsorption

Only 1ml of urine is formed for every 120ml filtered through

the nephron, the remaining is reabsorbed

Selective reabsorption happens both actively and passively

Reaborption occurs until the threshold level is reached aka

the max amount of material that can be moved across thenephron

pH controlled within the proximal tubule by secretion of H+

ions and reabsorption of bicarbonate, also happens in the

distal tubule

Sodium ions are actively transported out of the nephron

tubules into the intercellular space, negative ions such as Clfollow because of charge attraction, the highly concentratedsolutes in the intercellular space creates an osmotic force and

water moves from the nephron (happens in the descending

part of the loop of Henle)

Salt is permeable in the ascending loop of Henle, resulting in

diffusion out

Interstitial fluid is fluid that surrounds the body cells

Secretion

Movement of wastes from the blood into the nephron

o Regulating ADH:

Antidiuretic hormone (ADH) causes the kidneys to increase waterreabsorption

When ADH is released, more concentrated urine is produced thus

conserving water

ADH makes the upper part of the distal tubule and collecting ductpermeable to water, more water diffuses out; kidneys only control

the last 15% of the water found in the nephron

High blood osmotic pressure (dehydration) results in osmoreceptors


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located in the hypothalamus to detect the change

You experience a behavioral response (thirst), drinking then lowersthe osmotic pressure of the blood

You also release ADH through the pituitary, allowing increased

water reabsorption which prevents the osmotic pressure from

increasing further COOL RIGHT?

o Maintaining Blood pressure and volume (aldosterone):

Aldosterone is a hormone that increases Na+ reabsorption from the

distal tubule and the collecting duct

When blood pressure and or blood volume is low (dehydration,

blood loss), specialized cells within the juxtaglomerular apparatus

detect it and release renin.

Renin converts a plasma protein into angiotensin, which causes the

constriction of blood vessels and stimulates the release of

aldosterone from the adrenal gland, carried in the blood to the

kidneys, and acts on the nephron Kidney Disease

o Effects of Diabetes (insipidus and mellitus)

Mellitus

Caused by inadequate secretion of insulin from islet cells in

the pancreas

Blood sugar tends to rise

Cells in the proximal tubule have enough ATP to reabsorbabout 0.1% blood sugar, the excess sugar remains in the

nephron

Excess sugar changes the osmotic pressure, less water is ableto diffuse out

People with diabetes mellitus are often thirsty as the water

lost must be replenished

Insipidus

Destruction of ADH-producing cells of the hypothalamus or

nerve tracts

Lack of ADH regulation dramatically increased urine

production, people the diabetes insipidus must drink large

quantities of water

o Kidney Stones:

Caused by the precipitation of mineral solutes from the blood Categorized into two groups alkaline and acid stones

You pee them out, causes excruciating pain as it tears delicate tissue

o Dialysis (loss of kidney function)

Defined as the exchange of substances across a membrane

In hemodialysis a unit called a dialyzer mimics the action of the

nephron. For hemodialysis treatments a person must have a minor


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surgical operation to create access for needles and tubing

Peritoneal dialysis is done through the lining of the abdominalcavity, a catheter is inserted, a solution called dialyste is fed into the

abdominal cavity, fluid stays for 2-6 days and then drained

grade twelve biology notes

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