Biological Systems (MCAT)

luteinizing hormone (LH)

in females, triggers ovulation and development of the corpus luteum

in males, stimulates Leydig cell production of testosterone

THE BODY LIKES HOMEOSTASIS

IF SOMETHING CHANGES THE BODY WILL ATTEMPT TO COMPENSATE AND CORRECT THAT CHANGE

nervous system

control and integration of other body systems

adaptive capabilities- homeostasis

cell body

part of neuron containing nucleus, soma

axon

part of neuron that sends impulse towards synapse

dendrites

parts of neuron that receive impulse

bipolar neuron- have only one dendrite

axon hillock

part of neuron that has highest concentration of voltage-gated Na+ channels

myelin sheath

part of neuron that insulates, decreasing surface area to be depolarized and increasing speed of condution

synaptic knobs

part of neuron that receives impulse and releases neurotransmitters

Nodes of Ranvier

part of neuron between myelin sheaths that concentrate the ion channels

resting membrane potential

polarized to -70mV, where the interior of cell is negatively charged

maintained by two things:

1. Na+/K+ pumps- pump 3 Na+ out, 2 K+ in
2. K+ leak channels- allows K+ to leak out

action potential

a neural impulse, a brief electrical charge that travels down an axon

depolarization (action potential)

voltage-gated Na+ channels- when membrane potential changes, they open to allow Na+ to flow into cell

they only open at threshold potential of -50 mV
bringing the cell to about +35 mV

repolarization (action potential)

voltage-gated Na+ channels inactivate after opening

voltage-gated K+ channels open slowly in response to depolarization, allowing K+ to flow out of cell

this brings cell to -90 mV, which slowly returns to -70mV

saltatory conduction

Schwann cells and oligodendrocytes wrap axons with myelin, leaving spaces for nodes of Ranvier

forces action potential to jump from node to node, speeding up conduction

refractory period

absolute refractory period- Na+ channels are inactivated when cells are too positive, K+ channels open, near Na+ equilibrium potential

relative refractory period- Na+ channels switch from inactivated to closed (deinactivated) when cells are too negative, K+ channels close as well, near K+ equilibrium potential

electrical synapse

gap junction between two cells, bidirectional flow of impulse, rare but important in cardiac muscle cells

chemical synapse

steps:

1. depolarization opens voltage-gated Ca2+ channels
2. Ca2+ influx causes exocytosis of neurotransmitters in secretory vesicles
3. neurotransmitters open ligand-gated Na+ channels on motor endplate
4. Na+ influx triggers action potential

neuromuscular junction- acetylcholine is neurotransmitter

other NTs are GABA, serotonin, dopamine, norepinephrine

1. receptor determines affect, not NT
2. neurons make only one type of NT, can respond to many

signal summation

action potential is an "all or nothing" nothing, with the only regulated step being whether the action potential will fire

excitatory postsynaptic potential- depolarize the next neuron, increases chance of action potential firing
inhibitory postsynaptic potential- polarize the next neuron, decreases chance of action potential firing

spatial summation- effect from multiple presynaptic cells is enough EPSP to fire off postsynaptic cell

temporal summation- signal presynaptic cell, if EPSP are fast enough to fire off postsynaptic cell

tetanus- too many signals building up

astrocytes

guide neuron development, regulate neurotransmitters

microglia

immune system of CNS

ependymal cells

produce and circulate cerebrospinal fluid

afferent/efferent/interneurons

afferent neurons- sensory neurons, to CNS

efferent neurons- motor/effector neurons, from CNS

interneurons- connects afferent and efferent neurons

reflexes

monosympatic reflex arc- sensory neuron directly connects to motor neuron in the spinal cord

reciprocal inhibition- to contract and reflex muscle pairs

supraspinal circuit- involves input from the brain or brainstem to process a stimuli, unlike most reflex arcs

brain subdivisions

hindbrain- medulla, pons, cerebellum
midbrain- RAS
forebrain- diencephalon, telencephalon (cerebral cortex)

medulla oblongata

controls heartbeat and breathing

pons

coordinating movement and balance

cerebellum

coordinating and smoothing out movement

reticular activating system

arousal and wakefulness

thalamus

relay point for all sensory information

hypothalamus

maintain homeostasis, basic needs, controls endocrine system through pituitary gland, hormones affect mood

spinal cord

primitive reflexes and basic behaviors like walking

white/grey matter

white matter- myelinated axons, highways

1. tract (brain)
2. tract/column (cord)
3. nerve (PNS)

grey matter- unmyelinated bodies, cities

1. nucleus (deep brain)
2. cortex (brain surface)
3. horn (cord)
4. ganglion (PNS)

think grey is more dense than white

corpus callosum

connects cerebral hemispheres

basal nuclei/ganglia

voluntary motor control

amygdala

emotion, fear

hippocampus

encoding to LTM

hemisphere

left hemisphere:

1. connected to right side of body
2. interprets right side of visual field
3. language processing (on dominant hemisphere)

right hemisphere

1. connected left side of body
2. interprets left side of visual field
3. visuospatial skills
4. emotional processing
5. music perception

occipital lobe

processes visual information

parietal lobe

contains somatosensory cortex, integrates sensory information, processes touch and taste

temporal lobe

auditory cortex, sound, emotional associations, memories

frontal lobe

higher-level processing, conscious decision making, executive functions

lobes

can be called cortices

central/peripheral nervous system

CNS- brain and spinal cord

PNS- nerves and sensory structures

somatic/autonomic

categories of PNS

somatic- voluntary control of skeletal muscle, signaled by acetylcholine, single neuron coming from CNS

autonomic- involuntary control of glands and smooth muscle (heart, stomach, bladder), signaled by acetylcholine from CNS, can excite or inhibit

para/sympathetic

categories of autonomic NS

parasympathetic- "rest and digest," decreased heart rate, respiratory rate, blood pressure, increased digestive and excretory functions

acetylcholine signal from CNS, then acetylcholine to effectors
long presynaptic neuron, short postsynaptic neuron

PARA LONG PRE

sympathetic- "fight or flight," increased HR/RR/BP, pupil dilation, deceased digestion, stimulation of adrenal medulla to release epinephrine

increased brain activity, increased glucose metabolism

4Fs = flight, fight, fright, fornicate

acetylcholine signal from CNS, then norepinephrine to effectors
short presynaptic neuron, long postsynaptic neuron

increased BP does not imply vasoconstriction

vasoconstriction- cut off blood to certain organs
vasodilation- increase blood to certain organs
happens in both systems to shift blood between GI and muscles/brain

PNS nerves

cranial nerves- carry info to/from brain stem

spinal nerves- carry info to/from spinal cord

vagus nerve- cranial nerve, part of parasympathetic NS that decreases HR and increases GI activity

dorsal root ganglion

collections of somas of the sensory neurons in the spinal cord

meninges

protective sheath of brain and spinal cord

sensory receptors

mechanoreceptors- detect mechanical movement

chemoreceptors- detect chemicals, gustation and olfaction

nociceptors- detect pain

thermoreceptors- detect changes in temperature

photoreceptors- detect EM waves, rods and cones

proprioceptors- detect body position, kinesthetic sense, muscle spindle, (Golgi tendon organs, joint capsule receptors)

gate control theory

spine contains a gate that blocks/allows pain signals

olfaction

gustation- taste buds have taste hairs, transmitted to temporal lobe

olfaction- smells detected by receptors in nasopharynx, transmitted directly to olfactory bulbs in temporal lobe

structures of the ear

pinna
auditory canal

eardrum
ossicles (malleus, incus, stapes)

oval window
cochlea (perilymph, endolymph)
organ of Corti (basilar membrane, tectorial membrane, cilia with mechanoreceptors)
semicircular canals, utricle, and saccule

round window
Eustachian tube

sensing sound

pitch- place theory describes how regions of basilar membrane that vibrate determine pitch

loudness- amplitude, generates more action potentials

transmitted to auditory cortex in temporal lobe

vestibular complex

semicircular canals (fluid shifts inside to detect balance), utricle and saccule (cilia detect acceleration), transmit to pons and cerebellum

structures of the eye

conjunctiva- mucous membrane
sclera- thick outer coat, whites

cornea
pupil
iris
lens

retina
fovea centralis
optic disk
optic nerve

anterior chamber
posterior chamber
vitreous chamber

rods and cones
bipolar cells
ganglion cells (optic nerve)

sensing light

photoreceptors are rods (best at detecting low light) and cones (best at detecting color)
opsins are proteins on photoreceptors

cones are concentrated in the fovea, cones have pigments that absorb green, red, blue, intensity of each color determines the final color perceived

photoreceptors are default on

retinal bound to opsins convert to all-trans on absorbing a photon, triggers polarization of cell by blocking Na+ channels

that stops release of glutamate to bipolar cells
ganglion cells transmit to through optic nerve

optical chasm divides the signal so left visual field goes to right brain, right visual field goes to left brain,

first hits lateral geniculate nucleus in thalamus, then goes to respective occipital lobes

signal intensity is determined by how many action potentials are sent

visual field

left visual field hits right side of retina, goes to right hemisphere

right visual field hits left side of retina, goes to left hemisphere

feature detection theory

color- trichromatic theory

form- parvocellular cells are neurons that detect shapes and boundaries

motion- magnocellular cells are neurons that detect motion

vision defects

emmetropia- normal vision
myopia- nearsightedness, needs concave lens
hyperopia- farsightedness, needs convex lens

adrenal glands

sits on top of the kidneys

adrenal medulla- releases epinephrine, sympathetic NS

adrenal cortex- releases aldosterone and cortisol (both steroid hormones), stress

endocrine glands

produce hormones

sent directly to blood

next to capillaries, no ducts

exocrine glands

produce sweat, tears, mucus, earwax, saliva, stomach acid, bile, semen, breast milk, enzymes

sent onto a body surface or cavity

all have ducts except for mucus

peptide/steroid hormones

peptide- made from amino acids, bind with cell surface receptor, which uses 2nd messenger system like cAMP, soluble in blood

fast and temporary!
ex: insulin, epinephrine

steroid- made from cholesterol, bind with intracellular receptor, with binds DNA to alter transcription, require transport proteins to move through blood

slow and more permanent!
ex: aldosterone, cortisol, ends with one/en/ol
exception: thyroid hormone is a peptide that acts like steroid

memorize hormones on pg. 317

hormone regulation

neural- hypothalamus sends action potential to releases hormone, epinephrine released from adrenal medulla

hormonal- tropic hormones release other hormones, ACTH stimulates release of cortisol from adrenal cortex

humoral- blood component release hormone, glucose triggers release of insulin, lack of glucose triggers release of glucagon

will attempt to compensate for insufficiencies

hypothalamic-pituitary control axis

anterior pituitary- adrenohypophysis, controlled indirectly by hypothalamus with tropic hormones, makes and secretes FLAT PeG

1. FSH, LH for testosterone/estrogen
2. ACTH for adrenal cortex (cortisol, aldosterone)
3. TSH for thyroid gland, stimulate metabolism
4. prolactin for milk
5. endorphins
6. growth hormone, stimulate growth

capillary cells, hormone making cells, uses portal veins

posterior pituitary- neurohypophysis, composed of neurons from hypothalamus that directly release hormones, stores and releases oxytocin and ADH (vasopressin)

neuroendocrine cells- neurons that release hormones, action potential travels down cell

thyroid gland

thyroid hormone is regulated by anterior pituitary gland

is a peptide hormone with long lasting effects

stimulate growth in children

parathyroid- releases PTH to break down bone, increases Ca2+ in blood

gonads

ovaries, testes

sex hormones are estrogen and testosterone

perfusion

flow of blood through tissue

ischemia- inadequate blood flow

hypoxia- inadequate O2 supply

arteries

away from heart, high pressure

muscular, elastic walls that regulate flow

arterioles- small arteries just before capillaries

veins

towards the heart, low pressure

muscles and organs that squish against the vessels, valves ensure unidirectional since veins are not muscular or elastic

venules- small veins just after capillaries

varicose veins- when valves fail, venous pressure builds up

capillaries

nutrient and waste exchange, walls are single cell thick

fluid pushed out due to pressure, fluid pushed back in afterwards due to osmosis

capillaries have lower pressure and lower velocity of blood flow because total cross sectional area is greater than arteries

BP drops to 0 mm Hg when it reaches vena cava

endothelial cells

inner lining of all blood vessels, type of epithelial cells

4 functions:

1. vasoconstriction- maintain BP
2. inflammation- recruit WBCs
3. angiogenesis- form new blood vessels
4. thrombosis- control blood clotting

circulation

pulmonary circulation- flow of blood from heart to the lungs and back, right side of heart pumps it

systemic circulation- flow of blood from heart to body and back, left side of heart pumps

portal systems

most blood passes through one set of capillaries before returning the heart

hepatic portal system- heart to intestine to liver to heart, transports nutrients

hypothalamic-hypophysial portal system- heart to hypothalamus to pituitary gland to heart, transports hormones

lymphatic system

retrieve water, WBCs, proteins from tissues and return to circulation

connected to circulatory system

lymph nodes- location of immune system cells, filter fluid from tissues

spleen- filters blood, removes old RBCs

thoracic duct- near the neck, where lymphatic system dumps fluid back into circulatory system

heart

superior/inferior vena cava- receives deoxygenated blood from body
right atrium- waiting room
tricuspid AV valve
right ventricle- pumps deoxygenated blood to lungs
pulmonary semilunar valve
pulmonary artery- carries deoxygenated blood to lungs

pulmonary vein- carries oxygenated blood from lungs
left atrium- waiting room
bicuspid/mitral AV valve
left ventricle- pumps oxygenated blood to body
aortic semilunar valve
aortic arch- carries oxygenated blood to body

coronary arteries

aorta branches off to supply blood to walls of heart

coronary veins carry deoxygenated blood to coronary sinus, which drains directly into right atrium

heart sounds

lub- AV valves close, systole begins
dup- semilunar valves close, diastole begins

blood pressure and cardiac cycle

systole- heart contracts, ventricles pump blood to body
systolic pressure- BP in arteries when heart contracts

diastole- heart relaxes, atria pump blood to ventricles
diastolic pressure- BP in arteries when heart relaxes

pulse pressure- difference between SP and DP

BP is directly proportional to cardiac output and peripheral resistance

cardiac output

cardiac output (L/min) = stroke volume (L/beats) x heart rate (beats/min)

stroke volume is blood pumped with each systole, affected:

1. Frank-Starling mechanism- greater venous return stretches heart, so that it contracts harder (increase venous return by not peeing)
2. change activity level for stronger heart
3. change in posture (orthostatic hypotension)

cardiac muscle cells

functional syncytium- electrical synapses, no chemical synapses

intercalated disks- connection between cardiac muscle cells, contain gap junctions

cardiac conduction system- atria signal is transmitted to ventricles after a delay, since they are separate systems not connected by gap junctions

voltage-gated Ca2+ channels- in addition to voltage-gated Na+ channels, these stay open longer for longer depolarization, greater contraction of cardiac muscle, and less tetany (twitches)

T tubules- plasma membrane dips into cytoplasm, more surface area for Ca2+ channels, also sarcoplasmic reticulum

actin-myosin fibers- contract in response to influx of Ca2+

excitation of SA node

sinoatrial (SA) node- pacemaker of the heart

Phase 4- unstable resting potential, Na+ leak channels slowly depolarize cell until threshold potential for voltage-gated Ca+ channels

Phase 0- depolarization, influx of Ca2+ from voltage-gated Ca2+ channels

Phase 3- repolarization, closure of Ca2+ channels, K+ leak channels open and K+ flows out

excitation of cardiac muscle cells

Phase 0- depolarization, influx of Na+

Phase 1- initial repolarization, closure of Na+ channels, K+ leak channels open and K+ flows out

Phase 2- plateau phase, influx of Ca2+ from voltage-gated Ca2+ channels balances K+ leak

Phase 3- repolarization, closure of Ca2+ channels, K+ leak channels keep leaking

Phase 4- resting potential, closure of K+ leak channels, maintained by Na+/K+ ATPase

cardiac conduction system

sinoatrial (SA) node- sends impulse to atria
internodal tract

atrioventricular (AV) node- delays impulse to ventricles

bundle of His (AV bundle)

Purkinje fibers- distributes electrical impulse starting at the apex of the heart and moving upwards to pump upwards

autonomic NS regulates heart

parasympathetic NS inhibits rapid automaticity- vagus nerve release acetylcholine to signal SA node to slow down

vagus tone- degree of inhibition

sympathetic NS stimulates HR- norepinephrine and epinephrine stimulate cardiac muscle cells

baroreceptors- monitor BP, high BP sends signal for vagal tone increase and sympathetic decrease

peripheral resistance

pressure gradient = cardiac output (L/min) * peripheral resistance

adrenergic tone- sympathetic NS controls peripheral resistance, increase BP

sympathetic NS can also preferentially perfuse certain tissues

local autoregulation- happens with coronary blood flow, certain metabolic wastes build up, automatically trigger high BP

components of blood

plasma (55%):

1. electrolytes- Na+, K+, Cl-, Ca2+, Mg2+
2. buffers- bicarbonate, maintain pH 7.4
3. glucose
4. albumin- maintain osmotic pressure in capillaries, mobilizes proteins/lipids in serum
5. immunoglobulins- immune system
6. fibrinogen- blood clotting
7. lipoproteins- transport lipids
8. waste- urea (breakdown of amino acids), bilirubin (breakdown of heme)

hematocrit (45%)-include red blood cells

leukocytes (1%)- white blood cells

blood forms 3 layers when centrifuged

most things in blood came from bone marrow stem cells

erythrocytes

erythropoietin- hormone made in kidney, stimulates red blood cell production in red bone marrow

RBCs are made in red bone marrow, stored and destroyed in spleen

fun facts:

1. has no organelles, no DNA
2. rely on glycolysis for ATP synthesis
3. contains hemoglobin to transport O2, also CO2
4. biconcave shape has large surface area for gas exchange

transfusion reaction

incorrect A/B/Rh antigen in blood causes clumping and destruction of RBCs

sensitization- Rh- patient must be exposed to Rh+ blood first to develop antigen, then future exposure to Rh+ blood will cause transfusion reaction

hemolytic disease of the newborn:

1. Rh- mother delivers Rh+ child, becoming sensitized to Rh+
2. future Rh+ babies at risk since Rh antibodies can cross placental barrier to destroy baby's RBCs
3. injecting mother with anti-Rh during first child can prevent sensitization

AB+ blood has all 3 antigens, universal recipient
O- has no antigens, universal donor

hemostasis

body's ability to prevent bleeding, uses platelets

platelets- thrombocytes, produced in the bone marrow, cell fragments that do not have nuclei

platelet plug- platelets aggregate at site of damage

fibrin- protein that holds the platelet plug together

thrombin- converts fibrinogen to fibrin

thrombus- blood clot

hemophilia- defect in a clotting protein, excessive bleeding

O2 transport

hemoglobin- 4 identical subunits with a heme (Fe in middle to bind O2) in each, carried on RBCs and are not in plasma!

cooperativity- when one subunit goes from tense to relaxed and binds O2, the other subunits become relaxed as well and thus have higher affinity for O2

Hill coefficient- 1 is no cooperativity, 4 is perfect cooperativity

4 factors decrease hemoglobin affinity for O2:

1. low O2 environment- cooperativity
2. low pH- Bohr effect
3. high CO2 environment
4. high temperature

% saturation = hemes with O2/total hemes

O2-hemoglobin dissociation curve show cooperativity

fetal Hb has higher affinity

oxygen debt

during physical activity, muscles do not get enough oxygen

1. anaerobic glycolysis- produce more ATP without oxygen, lactic acid is a byproduct

2. fast twitch fibers (white)- less mitochondria, use anaerobic glycolysis unlike slow twitch fibers (red)

3. creatine phosphate- supplemental energy reserve that produces more ATP, creatine is a byproduct

4. myoglobin- O2 is taken from hemoglobin and stored in myoglobin (higher O2 affinity) in muscles, can be accessed if more oxygen is needed

5. Bohr effect- oxygen saturation curve shifts down because of increased CO2/H+, allows more O2 to be dumped from hemoglobin at muscles

6. increased RR/HR- increase oxygenation

7. vasodilation- increase oxygenation

CO2 transport

CO2 + H2O

this reaction occurs within RBCs, HCO3- exits RBC by exchanging with Cl-

3 ways that CO2 is transported:

1. carbonic anhydrase- enzyme in RBCs that catalyzes rxn
2. attached to hemoglobin (not in O2 position)
3. more water soluble than O2, so in plasma

capillary exchange

things that must be exchanged in capillaries:

1. nutrients- amino acids and glucose
2. waste- liver removes wastes and secretes bile
3. lymphocytes- WBCs to attack invaders in tissue
4. water- albumin maintains oncotic pressure to keep water in blood vessels
5. inflammation- WBCs and water flow out of blood vessels to cause edema

nutrient exchange:

1. hepatic portal vein- carries amino acids and glucose from digestive tract to liver
   2.chylomicrons- lipoproteins that store fat, enter lacteals in lymphatic system, taken up by liver, converted, carries fat to adipocytes for storage

innate/natural immunity

general protection against invaders:

1. skin
2. lysozyme- enzyme in tears/saliva/blood that kills bacteria
3. stomach acidity
4. macrophages and neutrophils
5. complement system- blood proteins that nonspecifically bind to foreign cells, signal for destruction

humoral immunity

specific protection by antibodies (immunoglobulins), produced by B cells

antibody structure:

1. light and heavy chains joined by disulfide bonds
2. constant region- classes include IgG, IgA, IgM, IgD, IgE
3. variable region- specific antigen binding

antibody function:

1. epitope- small binding site on antigen
2. hapten- small molecule that is only recognized after bound to large carrier protein
3. can directly inactivate antigen, induce phagocytosis, or activate complement system

antibodies generated in one species will get recognized as a foreign substance in a different species

B cells

B cell development:

1. lymphocytes in humoral immunity derived from bone marrow stem cells
2. antibody proteins assembled by recombination to create different B cells, allows for clonal selection
3. antigen binding triggers differentiation to plasma cell or memory cell
4. plasma cells- actively secrete antibody protein into plasma
5. memory cells- become dormant, waiting for same antigen to reappear then becomes activated

primary immune response- just plasma cells on first exposure to antigen

secondary immune response- memory cells respond quickly, vaccination

T cells

T-cell development:

1. lymphocytes in cell-mediated immunity, T helpers and T killers
2. T cells are produced in bone marrow, but mature in thymus gland
3. T helpers (CD4)- activates B cells and T killer cells, communicates with hormones (lymphokines, interleukins), host of HIV
4. T killers (CD8)- destroy abnormal hosts cells (virus infected, cancer, foreign grafts)

MHC I- every cell has them, displays foreign protein on surface of cell to be detected by T killers

MHC II- only on antigen-presenting cells (macrophages and B cells), displays foreign protein after chopping it up to be detected by T helpers

T cell activation only occurs when T cell binds to both antigen and MHC molecule

leukocytes

white blood cells

3 types:

1. lymphocytes- B cells, T cells, NK cells
2. neutrophils- phagocytosis, most common
3. monocytes- phagocytosis, move to tissue through blood to become macrophages