MCAT Biology

Class 4 - 20/06/24:

Viruses, bacteria, reproduction of bacteria

• Viruses: intracellular parasite

• Virus structure: made up of a capsid(coat) with a nucleic acid genome inside(Can’t have both DNA and RNA)

• Basic Steps: attachment(adsorption) - specific attachment but not infected yet; and injection - penetration - from bacterium to host

• Lytic Cycle: transcribe and translate viral genome; replicate; lysis of host

  • Early genes - hydrolase and capsid

  • Hydrolase: destroy host cell genome

    • Replicate genome

    • Lysis of host and release of viral particles

• Lysogenic Cycle: integrate viral genome into host then induce with normal host activity and excision and lytic cycle happens

  • Transduction - insertion of new DNA that was not present before

• Productive Cycle: does not destroy the host cell

• RNA Viral Genomes: can be both positive and negative types of RNA viruses

  • (+) RNA requires translation of RNA to protein - RNA dependant and RNA polymerases make the proteins

  • (-) RNA need a copy of RNA pol., and translate the now + RNA to proteins that negative

• Prions - do not follow central dogma because they are self-replicating proteins

  • No DNA/RNA

  • no membranes

  • no organelles

  • very small

  • extremely stable

• Prion categories = normal and mutagenic - mutant can lead to cell death

  • Mutant = Bad prions - come from a mutation in a prion, can be inherited, or by ingesting a bad prion → bad ones can make good ones bad too

• Viroids: circular RNA, no capsid, must be co-infected, no protein code - block translation

  • two different mechanisms make viroids -

    • one by taking negative RNA, translating it to positive RNA to form many +RNA to form viroid copies

    • One by taking -RNA and wrap +RNA to form a viroid copy

• Bacteria:

  • Can have three different shapes:

    • Round = coccus

    • Rod = bacilli

    • Spiral = spirillum

    • can have a flagella to move it or cilia

    • Bacteria have a cell wall and a cell membrane

  • gram + = stain dark and have a cell membrane covered by thick peptidoglycan(2 layers)- easier to get in

  • gram - = stain light and have an inner membrane covered by a cell wall covered by an outer cell membrane peptidoglycan(3 layers) - harder to get in

  • Temperature-dependent bacteria:

    • mesophiles → 30*C

    • Thermophiles → 100*C

    • psychrophiles → 0*C

  • Oxygen uses in Bacteria:

    • Obligate aerobe = use it and need it

    • Facultative anaerobe = can use it and survives

    • Tolerant anaerobe = doesn’t need it but can tolerate

    • Obligate anaerobe = can’t use it and can die due to O2

  • Energy/Nutrients of Bacteria

    • Photoauto = uses light and makes it on its own

    • Chemoauto = use chemicals by self

    • Photohetero = carnivorous plants

    • Chemohetero = need other energy sources

• Reproduction - use of binary fission to duplicate identical copies

• Binary Fission - growth follows an exponential growth pattern

• Conjugation(genetic Diversity) - helps to provide genetic diversity, rather than increase population size

  • horizontal gene transfer - donor-to-recipient transfer with direct contact

  • F- is the donor(male) and F+ is the female recipient - gives an F plasmid, not a genome

Class 5 - 27/06/24:

Cell Biology, colligative properties, membranes, mitosis, cancer

• Cell Biology and organelles → Eukaryotes

  • Nucleus and Nucleolus - DNA; makes ribosomes

  • Ribosomes - make Proteins(RNA to amino acids)

  • Rough ER - Makes post-translational protein modifications, proteins for the cell to use

  • Smooth ER - production/metabolism to fats and steroids

  • Golgi apparatus - prepares to ship/modify/sort proteins/lipids for in-cell and outside use

  • Lysosomes - break down foreign particles, eliminate toxins

  • Peroxisomes - eliminate H2O2, oxidative reactions of reactive O2 species

• ALL transcription in the nucleus, and ALL translation in the cytosol

  • Secreted, transmembrane, lysosomal proteins are made in the Rough ER → resident proteins

• Start in the nucleus(transcription, mRNA processes) → goes to the cytosol(begin all translation) → some proteins finish translation in the Rough ER → signal sequence tells the 3 proteins made by the Rough ER

• Components of the cell membrane

  • Phospholipids - the membrane bilayer

  • Cholesterol - stabilizes membrane and keeps it fluid

  • Proteins

  • Carbohydrates

• Colligative properties depend on the number to solute but not their identity

  • Freezing point, boiling point, vapour pressure, osmotic pressure

• Electrolytes: free ions in a solution that come by dissolving ionic substances

  • ex. NaCl → Na + cl-

• Van’t Hoff factor: the number of ions produced per molecule of an electrolyte when dissolved in water

  • ex. NaCl = 2 → 2 ions are produced per NaCl molecule

• Freezing Point depression:

  • The freezing point of 1 KG H2O is OºC

  • FP depression Tf = -kf x i x m

    • kf water = 1.9℃

    • i = Van’t Hoff factor

    • m = # of moles

• Vapour pressure depression:

  • need to raise the temperature to boil and evaporate molecules in a liquid

• Boiling Point elevation:

  • BP Elevation Tb = kb x i x m

    • kb water = 0.5℃

• Osmotic pressure elevation: we care about the number of particles(that change osmolarity)

  • Osmotic pressure = particle [C]

  • TT = i x M x R x T

    • M = molarity

    • R = gas constant

    • T = temperature

• Diffusion: particles moving down a gradient → high [C] to low [C]

• Osmosis: movement of water → water moves from high [C] to low [C]

  • Hypertonic = more particles than…

  • Hypotonic = fewer particles than…

  • Isotonic = the same amount of particles than…

• Pressure is required to resist the movement of water by osmosis

  • osmotic pressure = particle [C]

    • ex. put a RBC(which is 0.9% NaCl into a beaker with 20% NaCl → water wants to leave the cell to equalize it, but the cell will shrivel → hypertonic

    • ex. put the same RBC into a beaker with 1% NaCl, very close to the RBC, some water leaves but not a lot → isotonic

• Passive transport: no energy is needed and relies on the concentration gradient for movement

  • Simple diffusion and facilitated diffusion

    • Simple → works well for small hydrophobic molecules, ex. steroids, CO2, O2, lipids

    • Facilitated → still moves down a gradient and uses small hydrophilic molecules ex. glucose, amino acids, ions, H2O → need helper protein

• Helper Proteins: pores, channels, porters

  • Pores: limits things in/out by size only

  • Channels: highly specific → Na/K channels

  • Porter: can undergo a conformational change to move molecules → The shapeshifters

• Active transport: requires E and can move molecules without the need for concentration gradients

  • Primary: use ATP

    • Na/K pumps(every 2K for 3 Na)

    • K leak channels → can go by the concentration gradient

    • These maintain osmotic balance, establish e-gradient, set up gradient for secondary transport

• Secondary: uses ATP indirectly and relies on the setup of the primary

• G-Protein: adenylyl cyclase → makes cAMP → activates cAMP-dep kinases → phosphorylates enzymes and changes enzyme activity in cells

  • cAMP is a secondary messenger, signal amplification, fast and temporary

• Phospholipase C → breaks phosphoinositol biphosphate → breaks into IP3 and DAG → DAG activates kinase and changes enzyme activity

• Cytoskeleton:

  • Microtubules: made of a and b tubulin and are large in diameter and are used for mitotic spindle, intracellular transport, and cilia/flagella

    • Cilia/flagella → 9 microtubules surrounding 2 lone tubules

  • Microfilament: made of actin protein, smaller in diameter, and used for muscle contraction, pseudopod formation, cytokinesis

  • Intermediate filament: several different protein types, medium in diameter, and used in many structural roles

• Cell Junctions:

  • desmosomes = general adhesive junctions

  • tight junctions: seal lumens and separate environments

  • Lumen also has gap junction → cell-to-cell communication

• Cell Cycle: Interphase to mitosis(PMAT)

  • Sister chromatids: absolutely identical → same order, genes, alleles

  • Homologous chromosomes: same genes, same order, but can have different alleles

  • Interphase: cell growth and synthesis of DNA

    • G1 = cell growth, normal cell activities,

    • S = synthesis of DNA and DNA replication

    • G2 = growth and prepare for mitosis

  • Mitosis = PMAT → ends with two identical daughter cells similar to the parent

    • Prophase: condenses DNA, forms mitotic spindle, nuclear membrane breaks down

    • Metaphase: chromosomes align on the center

    • Anaphase: the sister chromatids separate and travel to the ends of the two poles and begin cytokinesis

    • Telophase: reverse prophase(DNA un-condenses and nuclear membrane forms again) - cytokinesis finishes

• Cancer: mutation to DNA, starts from a single cell with mutations, goes through the cell cycle rapidly and out of control, spreads to other tissue → Metatsis

  • Two types of Cancer genes: oncogenes and tumour suppressors

• Proto-oncogenes: genes are normally present in the cell and code for proteins that regulate the cell cycle →

  • Active types: fetal development, growth, and healing

  • Inactive types: when healing or growth is not required

• Oncogenes: the mutated version of proto-oncogenes that are permanently on(always active and dividing)

• Tumour suppressor genes: code for proteins that stop the cell cycle, and monitor the genome of cells in the cell cycle, if DNA damaged they initiate repair mechanisms, if DNA cannot be repaired then they initiate cell death(apoptosis)

  • If they lose their function to save or get rid of mutations, cancers can come from those mutations that were not ‘killed’ off by apoptosis

Class 6 - 01/07/24:

Genetics, Hardy-Weinberg, and Evolution

• Meiosis - making of 4 cells that differ from the parent cell and each other → unique cells

  • Crossing over happens of DNA → leads to diversity

    • Non-disjunction - failure to separate DNA during meiosis

• Genetics - the study of genes

  • Allele - the genes found on a chromosome

  • Trait - the characteristic that appears from the alleles

    • Polymorphic - several types of one trait

    • polygenic - several genes that determine a trait

• Classical Dominance: homozygous dominant/recessive, heterozygous

  • Genotype: combination of alleles

  • Phenotype: physical characteristics

• Incomplete: display a blend of the parental phenotypes

  • ex. red flower RR x white flower WW = pink flower RW

• Co-dominance: both alleles are expressed independently and at the same time

  • Ex. Blood types → I^A I^B i

• Epistasis: dominance between two different genes - one gene can mask or modify the expression of another gene, for example, Albinism

• Test-cross: where one of an unknown genotype is crossed with another of a homozygous recessive genotype

• Backcross - F1 x P

• Mendel’s Laws

  • Law of segregation - alleles separate during gamete formation

  • Law of independent assortment - one allele is independent of another allele

• Single-gene crosses - 4 types

  • Homozygote 1 x Homozygote 1

  • Homozygous dominant x homozygous recessive

  • heterozygote x homozygote dom/rec

  • heterozygoye x heterozygote

• Rules of Probability

  • A AND B - multiply the probabilities

  • A OR B - add individual probabilities

• Linked Genes: genes found close together on the chromosome

  • Dihybrid crosses = crosses between two traits

    • F1xF1 = 9:3:3:1 → unlinked

    • F1xHomozygous recessive Parent = 1:1:1:1 → unlinked

      • When the actual ratio differs from this, they will be linked genes as they don’t follow the expected ratios

• Recombination: genes that do not assort independently

  • recombination frequency = # recombinants/total offspring x 100

    • Tells us the map units(mu) distance between genes on the chromosome

      • 1 mu = 1 cM(Centimorgan)

• Hardy Weinberg: tells us that allele frequencies within a population do not change from generation to generation

  • p + q = 1 → allele frequency where p = dominant allele and q = recessive allele

  • pp + 2pg + qq = 1 → genotype frequency where 2pq is the heterozygous allele

• 5 Conditions where Hardy-Weinberg hold:

  • No mutation

  • No natural selection

  • No migration

  • Total random mating

  • Large population size

Class 7 - 10/07/2024:

Nervous System, Auditory, and Optical systems

• Neuron Structure

  • Specialized cells of the nervous system

    • Have a soma(central), dendrites, axon, axon terminus

    • Dendrites receive signals

    • Axon sends off signals

      • Axon has myelin covering it

        • Speeds and protects the axon

  • Types of Neurons:

    • Multipolar - connects and receives from many neurons

    • Bipolar - depends on the direction of the synapse - two-sided

    • Unipolar - soma is attached to one node only

• Resting Potentials

  • at -70mV

  • sodium/potassium pump out one net positive ion, creating a Na/K gradient

  • many + ions lost via K leakage channels

  • The result is that the cell is more negative inside than outside

• Action Potentials

  • When the cell reaches positive levels to send a signal across the neuron - All or None event

    • Depolarization - cell becomes more positive

    • Hyper polarization - when the cell becomes more negative

    • Repolarization - return to rest

    • Equilibrium potential - when there is no driving force on the ion, neither +/-

• At -70mV → resting potential

• At -55 → threshold - Na+ channels open

• Depolarization upto +35mV - Na+ channels inactivate and K+ fully open

• Hyperpolarization to -90mV - Na+ and K+ close

• Repolarization to -70mV by Na/K pumps

  • This happens in a matter of 2-3 msec

• Nerve Impulse: by a synapse from neuron-neuron or neuron-organ junction

• Refractory Periods

  • Absolute: not able to fire a second action potential due to Na channels being inactive and the cell is too positive at the moment

  • Relative refractory period: there is a small chance of firing a second AP since Na channels are closed and the cell is too negative

• Electrical Synapse - relatively rare but important in muscle cells

  • Require:

    • Physical connections - gap junctions

    • Always excitatory - AP in post-synapse

    • Bi-directional - either pre/post synapse

    • Unregulated

• Chemical Synapse - more common - transport of neurotransmitters

  • One neuron can only make one type of NT but can respond to many

  • NT in the synaptic cleft can be re-uptaken or broken down

  • Response of the post-synapse depends on the receptors, not the NT

  • Need more than one vesicle of NT to make a change to post-synapse

• EPSPs and IPSPs

  • EPSP = excitatory post-synaptic potential → Many accumulate to make an action potential - help reach the threshold

  • IPSP = inhibitory post-synaptic potential → Many accumulate to prevent an AP from reaching a threshold

  • EPSP and IPSP can cancel each other out

• Summation

  • Spatial: The add-up of inputs from multiple sources

  • Temporal: the add-up of frequent impulses from a single source

• General System Functions

  • Sensory Input - PNS

    • Info coming into the CNS

    • carried on the sensory neurons → afferent → towards CNS

  • Integration - CNS

    • decision making

    • interneurons - entirely contained within the CNS

  • Motor Output - PNS

    • commands sent out to the body

    • Carried on the motor neurons → efferent → exit CNS

• Reflexes

  • rapid integration to avoid potential injury

    • Patellar tendon stretch reflex

• CNS Anatomy

  • Telencephalon: cerebrum

    • Cerebral hemispheres - left and right - connected by the corpus callosum

    • Cerebral cortex - divided into 4 lobes

      • Frontal - complex processes and voluntary movement

      • Parietal - general sensations - touch, temperature, taste

      • Temporal lobe - sound and audition and olfactory, STM, language

      • Occipital lobe - Visual sensations

• Diencephalon:

  • Epithalamus: Pineal gland and secretion of melatonin - links to the limbic system

  • Thalamus: sensory - all sensory (except olfactory)

  • Hypothalamus: sends hormones to the pituitary - primary link to endocrine - homeostasis and behaviour/emotions

• Hindbrain:

  • cerebellum - movement and balance

  • Medulla - controls vital autonomic functions and relays info between other areas - respiratory centers located here

  • pons - the role is posture and balance

• Spinal Cord: connects brain and body and is protected by the CSF

• Limbic System: works for emotion and memory

• White Matter vs Grey Matter:

  • White: myelinated axons - cell-to-cell communication

    • CNS to brain = Tract

    • CNS to cord = tract/column

    • PNS = nerve

  • Grey: non-myelinated axons - decision-making

    • CNS to deep brain = nucleus

    • CNS to brain surface = cortex(conscious mind)

    • CNS to cord = horn

    • PNS = ganglion

• PNS

  • all nerves and sensory systems outside of the CNS

• Somatic vs Autonomic

  • Somatic = voluntary control of the skeletal muscles

    • uses Ach only, excitatory only, single neuron effector

  • Autonomic = involuntary control of glands and smooth muscle

    • uses Ach and Norepinephrine, can be excitatory or inhibitory, a chain of two effectors

• Parasympathetic vs. Sympathetic

  • Para = rest and digest

    • decrease HR, breathing, BP

    • Increase Digestion

    • release Ach to organs either inhibit(heart rate down) or excite(increase digest)

  • Symp = fight or flight

    • Fight, flight, fright, sex

    • increase body activity

    • decrease digestion

    • increase blood flow to skeletal muscles

    • release norepinephrine at the organ level

• Sensory receptors - 5 Classes:

  • Mechanoreceptors: by physical shape changes, touch

  • Chemoreceptors: by chemicals, pH, O2, taste buds

  • Thermoreceptors: stimulated by temperature, hot or cold

  • Nociceptors: stimulated by pain, free nerve endings, chemicals, heat

  • Photoreceptors: by light, rods and cones

• General Sensory Processing

  • Absolute threshold: the minimum stimulus required to trigger a receptor

  • Difference threshold: how much a stimulus must change to detect it

  • Sensory adaption: receptor stops responding to constant stimulus

    • pain receptors do not adapt

• Bottom-up processing:

  • from the environment to the brain → sensory receptors take in the info, send it to the brain, and the brain uses the info

• Top-down processing:

  • from inside to environment → The brain applies prior knowledge to identify the environment

• Visual System

• Cone cells: colour vision, stimulated in light only - three kinds: red, green, blue

  • Cone like a triangle; like a prism; prism makes rainbow - colour!

    • in the Fovea centralis only

• Rod cells: susceptible to light and work in low light conditions

  • Concentrated in the retina

• Auditory System

• Sound waves → auricle → external auditory canal → tympanic membrane→ malleus → incus → stapes → oval window → perilymph → endolymph → basilar membrane - auditory hair cells → tectorial membrane → Neurotransmitters stimulate bipolar auditory neurons → brain → perception

Class 8 - 20/07/24:

Endocrine system, Cardiovascular system, Immune system

• Endocrine system: hormones → through the bloodstream → no ducts

• Exocrine system: hormones by way of ducts → into the intestinal lumen

• Peptide hormones: made from amino acids, the receptor is on the cell surface, 2nd messengers, fast effects but temporary

• Steroid hormones: made from cholesterol, intracellular binding, binds to DNA and modifies transcription, effects are slower but last longer

• Mechanisms to control hormone release: neural, hormonal, humoral(in the blood)

• Hypothalamus - pituitary: The hypothalamus controls neurally and humoral while the pituitary has divided control

  • Anterior pituitary: made of gland tissue, secretes six major hormones: FLAT PIG

    • FSH, LH, ACTH, TSH, Prolactin, Endorphins, growth hormone

      • Has hormones making cells and many veins

  • Posterior Pituitary: made of nervous tissue, stores and secretes two hormones - Oxytocin and ADH(vasopressin)

    • Many neurons and capillaries

• Blood vessels: Veins and arteries

  • Veins: lower pressure, blood moves back to the heart - more rigid and made of collagen

  • Arteries: higher pressure, moves blood away from the heart - more elastic and can control dilation/constriction

  • Capillaries - smallest in size but largest SA → can exchange products like O2

  • The inner layer of blood vessels is endothelial cells

• The heart - 4 chambers:

• Blood carries from the aorta to the body → vena cava carries blood back to the heart from the body → into the right atrium → to the right ventricle → to the pulmonary artery to the lungs(deox) → blood comes back from the lungs into the pulmonary veins(oxy) → into left atrium → into left ventricle → to the aorta

• Systole: ventricular contraction - empty

• Diastole: ventricular filling

  • Lub Dub:

    • Lub: close AV valves and begin systole

    • Dub close SL valves and begin diastole

  • systole/diastole = Blood Pressure

  • BP is directly proportional to CO and peripheral resistance

• CO = cardiac output = stoke volume x HR

  • volume pumped per minute x beats per minute

  • Stroke volume = change in blood volume, activity level, posture

• Peripheral resistance = how hard it is to move blood through the vessels

  • Vasoconstriction and Vasodilation

    • Constrict = smaller diameter, lower flow, higher resistance, higher BP

    • Dilate = larger diameter, higher flow, lower resistance, lower BP

• Tetany - tetanic contraction = involuntary muscle contraction from overstimulated neurons and low Ca levels

• Cardiac cell potential: slow opening of CA+ channels, fast depolarization to 20+, then potassium channels open and repolarization back - unstable resting potential due to NA leakages

• Cardiac Conduction: SA node → AV node → HIS Bundle → Purkinje Fibers

• Blood composition: 54% plasma, 45% RBC, 1% leukocytes/WBC

• Oxygen Dissociation Curve: oxygen is 3% dissolved in plasma and 97% dissolved in Hb → The higher the O2 levels, the higher the Hb saturation, and the more it is exchanged to tissues

• Immunity:

  • Antigen: a foreign protein that can trigger an immune response

  • Antibody: a specific marker for anti-gen

  • Pathogen: disease-causing organism

• B cells - humoral immunity - make antibodies

  • Produce and secrete antibodies into the blood - when stimulated, will clone into thousands of B cells to enhance antibody production - rearrange antibody genes(DNA) to generate antibody diversity

• T cells - kill virus-infected cells, and tumour cells, and control the immune response(helper T cells)

  • T = thymus(develop in childhood)

• MHC 1 → found on all cells, allows the display of cell contents

• MHC 2 → macrophages and B cells, allows cells to display eaten stuff on the cell surface

• Classes of Antibodies:

  • IgM = blood and B cell surface - initial immune response

  • IgG = blood - ongoing immune response

  • IgD = B cell surface - with IgM, antigen on B cells

  • IgA = secretions(saliva, mucus, tears, breast milk, etc) - protect newborns

  • IgE = blood - allergic reactions

• Autoimmunity: uneliminated B and T cells(that did not undergo apoptosis) that get released into the body and go by attacking normal body proteins leading to an autoimmune reaction and other inflammation responses.

Class 9 - 27/07/24:

• Excretory organs:

  • Colon - eliminates solid waste - material not absorbed into the blood

  • Liver - eliminates hydrophobic water - material too hydrophobic to be dissolved into the plasma

  • Kidney: eliminates hydrophilic waste - material eaten and absorbed into the blood and dissolved into the plasma

• Kidney -> ureter -> bladder -> internal sphincter -> external sphincter -> urethra

  • The kidney has the ureter that connects to the renal pelvis, to the medulla and medullary pyramids, to the nephrons -> outer side of the kidney is the cortex

• 3 processes to produce urine: 

  • filtration(moving a substance across a membrane using pressure

  • Reabsorption(move a substance from the filtrate to the blood(glucose, amino acids, water) -> glomerular filtration 

  • Secretion: move a substance from the blood to the filtrate(drugs, toxins, creatine)

• Nephron Structure: 

  • Afferent arterioles come into the glomerulus leading to the PCT(mostly reabsorption and secretion), then to the loop of Henle - descending is permeable to H2O and the ascending is permeable to salt - DCT is specialized for absorption and reabsorption then the collecting duct(regulated H2O reabsorption)

• Urine and Blood flow are opposites

• Renin-Angiotensin system: 

  • Angiotensinogen -> angiotensin 1 -> angiotensin 2 -> increases release of aldosterone and leads to systemic vasoconstriction

• Juxtaglomerular apparatus(JGA): contact point between afferent arteriole and distal convoluted tubule

  • Afferent = baroreceptor

  • Distal = chemoreceptor

• ANP - blood pressure regulation:

  • High BP -> arteria of heart stretch -> right atrium releases atrial natriuretic peptide(ANP) -> vasodilation and inhibits renin release

• Accessory Digestive Organs: Liver and gallbladder

  • Liver = produces bile(amphipathic) → attack lipids(fats)

  • Gallbladder → stores the bile

  • Pancreas: Endocrine role = insulin and glucagon and Exocrine role = digestive enzymes, proteases, lipases, amylases, nucleases, and bicarbonate(pH control)

• Alimentary Canal: Contains mucosa(epithelium), submucosa(connective tissue), serosa, and circular and longitudinal muscle

  • peristalsis → movement in one direction only

• Regions of the alimentary canal:

  • Mouth = grind food and begin starch digestion by amylase and lingual lipase(fats) and use of lysozyme to kill bacteria

  • Esophagus = tube from mouth to stomach by the movement of peristalsis and starts off as voluntary(skeletal) to involuntary(smooth) → also has the cardiac sphincter. that prevents the movement of acid reflux

  • Stomach = storage tank for food and grinds food down more by gastric glands - parietal cells make HCL and Cheif cells make pepsinogen to make pepsin(by HCl) - the G cells in the stomach secrete gastrin and activate gastric glands(negative feedback loop)

  • Small Intestine: all digestion and absorption happens here in three regions - duodenum to jejunum to ileum - food brushes up against the microvilli to absorb nutrients - enterokinase(activates trypsin for pancreatic enzymes) and brush border enzymes(to break up peptides) as well as enterogastrone(reduce stomach mobility and empty food), CCK(bile release), and secretin(if pH too low, release bicarbonate by pancreas)

  • Large Intestine: absorbs water and feces only - has bacteria, internal and external anal sphincters - bacteria break up remaining stuff and make/absorbs vitamins A, K, D, C

Class 10 - 01/08/24:

Musculoskeletal System and Respiratory System

• Skeletal muscle overview: voluntary function, on the bones, multinucleate and striated appearance

• Hierarchy:

  • protein filament - actin and myosin → they do not shorten

  • Sarcomere - a unit of contraction → Shortening happens here → Depolarization

    • 1 sarcomere is one Z line to the next Z line

    • Actin, thin filaments are held by the Z-line

    • The myosin, thick filaments, is centred in each sarcomere but doesn’t reach the Z-line

    • The I band (isotropic) are the regions with full actin or ½ actin

    • The A band(anisotropic) are the regions where there are both actin and myosin - it is both dark and light - ends at the ends of the myosin

    • H zone is the light zone where there is only myosin and no overlap with actin

    • The M line is the middle of the sarcomere

  • Myofibril

    • Covered by sarcoplasmic reticulum(holds Ca)

    • T-tubules - the plasma membrane goes in deep to help action potential travel to the interior of the cell

  • Muscle cell - myofiber

  • Fascicle

  • Whole muscle

• Sliding Filament Theory:

  • Myosin binds to actin (cross bridge formation)→ needs calcium

  • myosin pulls actin towards the center of the sarcomere - power stroke → myosin returns to low-E state

  • Myosin release actin → needs ATP but doesn’t break it down

  • Myosin resets to high-E → ATP hydrolysis

• When you run out of ATP, you can’t relax

• Excitation-contraction coupling:

  • Excitation - depolarize, open voltage-gated Ca channels

  • Troponin binds Ca and changes shape, lifts tropomyosin off myosin binding sites, and myosin binds to actin

  • Contraction occurs

• Motor Neuron - a neuron and all the muscle cells it controls

  • Contraction of the motor unit is all or none

  • Contraction of the whole muscle is graded

• Large vs. Small:

  • Large is 1000s of m/n

  • Small is 10-20 m/n

• Gross motor control - a few large motor units

• Fine motor control - many many small motor units

• Muscle Energy:

  • Fastest source of E = Creatine (substrate-level phosphorylation)→ reversible process

  • Medium source of E = Glycolysis(fermentation) - 2 ATP per glucose and lactic acid

  • Slowest source of E = aerobic respiration → 30 ATP, H2O, CO2 → store O2(myoglobin)

• Oxygen Debt - extra O2 needed after exercise

  • replenish O2 stores in myoglobin

  • convert lactic acid into something useful → back into pyruvate

• How to repay O2 debt? Bohr effect → pH and temp changes after O2 is used, then Hb is changed - rather than holding lots of O2, gives more of it back to tissues

• Skeletal Muscle Types:

• Slow Twitch- more myoglobin, more blood vessels, slow contraction, higher mitochondria, higher fatigue resistance, the low force generated

• Fast Twitch IIA: medium level of myoglobin and blood vessels, faster contraction, medium mitochondria levels, medium resistance to fatigue, medium force generated

• Fast Twitch 11B: low myoglobin levels, lesser capillary network, fast contraction and higher force, lower mitochondria, lower fatigue resistance

  • Fast twitch makes more glycolytic enzymes - more glycolysis

• Cardiac and Smooth Muscle

  • Cardiac = auto, involuntary, only in the heart(vessels have smooth muscle) - uninucleate - striated appearance → The filaments overlap(the difference is that some of the calcium for contraction comes from the extracellular environment)

  • Smooth muscle = involuntary, neural, mechanical, hormonally stimulated; located in the walls of hollow organs; uninucleated; non-striated but has bundles of actin and myosin and still needs calcium

• 4 different tissues:

  • Muscle

  • Neural

  • Epithelial

    • The first three are mostly cells(living)

  • Connective - mostly non-living

• Connective tissue: cells in a matrix

  • matrix is made of fibres and glop(ground substance)

    • Fibers are made of collagen and elastic fibres

    • glop is the glue that holds everything

      • Liquid or solid → Blood plasma or bone → in between is cartilage

  • osteoblasts - form new bone - can still divide and make the matrix

  • osteoclasts - break down bone

  • -cyte cells: the mature cells - don’t divide

• Bone helps:

  • Support and movement

  • Store minerals - calcium and phosphate

  • Protection

  • blood cell formation

• Osteoporosis - bone creation is slower than its removal → Weak and brittle bones

• Long Bone Anatomy:

  • Shaft = Diaphysis

  • Ends = Epiphysis - holds spongy bone that makes RBC

  • Core = medullary cavity = yellow bone marrow(fat)

  • Surrounding the core is a compact bone

  • Epiphyseal plate = growth plate

    • ossification greater than cell division

• Compact bone:

  • Osteons → have a central canal → central canal holds blood vessels → central canal made of rings that hold osteocytes

• Bone Turnover:

  • PTH and Calcitonin

    • PTH - increases blood calcium by dissolving bones, increases Ca absorption in intestines and kidneys

    • Calcitonin - builds bone back, and decreases intestinal and kidney absorption

  • Vitamin D(calcitriol) - increases PTH effects and absorption in kidneys

  • osteoclasts - dissolve bone - eat bone, not like bone cells

• Respiratory System:

  • Gas exchange and pH regulation

  • Ventilation = move in the air and out

  • Respiration = gas exchange (External and Internal)

• Conduction zone = ventilation only

  • Air drawn in by the nose → nasal cavity → warmed up and filtered here → tissue is respiratory epithelium(mucus cells and cilia) → air to pharynx(naso, oro and laryngo pharynx) → air to larynx and travels down to trachea → separates to R/L primary bronchi → travels to secondary Bronchi in lobes → travels to tertiary bronchi → travels to terminal bronchioles to reach the respiratory bronchioles

    • The larynx is all cartilage → keeps airways open and separates air and food(epiglottis) and helps produce sound

    • Trachea: a muscle lined with cartilage rings and connective tissue membrane → The muscle can contract and pull the rings together → increases the speed of airflow(ex. coughing)

    • Primary bronchi → cartilage rings → cilia cells

    • Secondary bronchi → oddly shaped cartilage rings, some smooth muscles → short cells, no cilia

    • Tertiary bronchi → all smooth muscle, no cartilage → no cilia, short cells

• Respiratory zone = Gas exchange

  • Air travels from respiratory bronchioles to alveolar ducts → enters alveolar sac and gas exchanges occur in the alveoli by the capillary network surrounding the sac → O2 is released into the blood and CO2 is picked up → CO2 travels back outside the lungs

    • Alveolar cells:

      • Type 1 = walls of alveoli

      • Type 2 = secrete surfactant → makes breathing easier and reduces tension/friction

• The Lungs: there are two of them → The right lobe has 2 parts and the left lobe has 3

  • lungs stick to the chest cavity due to surface tension and slight negative pleural pressure(Inhale) → pressure wants to go positive, hence, becomes like environment(exhale)

  • Inspiration: Active → contraction of the diaphragm

  • Relaxed expiration: Passive → Diaphragm contracts

  • Forced expiration: Active → Abdominal muscles contract

  

• Skin: has 3 layers

  • Epidermis: epithelial tissue

  • Dermis: connective tissue

  • Hypodermis: fat

• Thermoregulation:

  • Cold = no sweat, shivering, vasoconstriction

  • Hot = sweat, no shivers, vasodilation

Class 11 - 15/08/24:

Reproductive System

• Primary Sex Organs - testes and ovaries → make gametes(sperm or egg)

• accessory sex organs - any organ or structure that has a role in development and reproduction that is not directly involved in the production of gametes

• Male System:

  • Scrotum = suspends testes outside the body

    • Sperm viability needs high testosterone levels and slightly lower cooler levels than body temp

  • The testes: make sperm and testosterone(androgen) - higher in males

    • testes filled with seminiferous tubules with sustentacular cells(Sertoli cells) that sustain sperm development - secrete nutrients and ABP(androgen binding protein) → spermatogonia - cells that WILL become sperm(not yet)

      • The hormone FSH in males stimulates Sertoli cells and spermatogonia

    • Interstitial cells make testosterone - Leydig cells(surround seminiferous tubules) - stimulated by LH

  • Spermatogenesis - from puberty to death

    • Spermatogonia - can divide into many more spermatogonia(mitosis)

    • Then, activation to the Primary Spermatocyte(not yet meiosis)

    • Secondary spermatocytes after meiosis 1(haploid now and onward)

    • Spermatid forms after meiosis 2

    • Goes off to finish up and makes sperm

      • 1 Spermatogonium makes 4 spermatids

  • Epididymis(6M long) - Sperm storage and secrete nutrients and give sperm their swimming ability(2-3 weeks to travel through here)

  • Vas deferens - long muscular duct and peristalsis for ejaculation and crosses body wall and enters body cavity(vasectomy happens here and can be undone(sometimes))

  • Urethra(shared pathway) - carries urine and semen(the fluid component, not sperm)

  • Accessory glands - sperm prefer basic environment - seminal vesicles, prostate, bulbourethral glands(alkaline mucus because urethra is also acidic(due to urine))

  • The penis: functions to inject sperm into the female tract

• Sexual function:

  • Arousal by parasympathetic control, reception by dilating erectile arteries, and lubrication by activation of bulbourethral glands

  • Orgasm is sympathetic control → emission by mixing sperm and semen in the urethra(contract vas deferens and accessory glands) → ejaculation by reflexive contractions

  • Resolution → sympathetic control and constrict erectile arteries

• Sex Development:

  • Male = Wolffian, XY, testes, testosterone, Wolffian ducts(WOLFGANG(by SKZ(boy group, get it?)), woof woof)

  • Female = Mullerian, XX, testes, Mullerian inhibiting factor(MIF) - making Mullerian ducts

• Female External and Internal Genitalia

  • External = Labia, skin folds that enclose openings

    • Vaginal and urethral opening

  • greater vestibular glands: secrete alkaline mucus on arousal

  • Mammary glands: to produce milk for infants

  • Vagina = birth canal - muscular, stretchy, and acidic(to fight bacteria)

  • Cervix = opening to uteru, when non-fertile → closed and sticky and acidic; when fertile → open, dilated, thin, watery, alkaline mucus

  • Uterus = pregnancy develops here

    • Endometrium - layer which sheds every month and fertilizes the egg

    • Myometrium - the muscle part of the uterus → cells here can divide

    • Uterine tubes(fallopian) = connect the uterus and ovary - path for an egg to the uterus → covered with ciliated cells to push the egg down(fertilization happens here) → then the clump of cells move to the uterus(usually) → ectopic pregnancies - in the fallopian tube → tubal ligation happens here too(tie the tubes, usually can’t be reversed)

  • The Ovary and Oogenesis: The ovary make eggs(ova) and estrogen and progesterone

    • Oogenesis: not continuous unlike the male system

      • Prenatal → Oogonia undergo mitosis and make more oogonia(200k-400K) and made into primary oocytes by activation(females don’t make more eggs after birth) - > Stop

      • Then from puberty(up to menopause), take 5-6 primary oocytes and make secondary oocytes and polar body by meiosis 1 → usually 1 successful → the secondary oocyte is the one ovulated

      • If the oocyte is fertilized, undergoes meiosis 2, makes ovum and secondary polar body

    • Eggs are the only cells that can be seen with the naked eye(microscope)

    • From one oogonium, we get 1 ovum(and 2 polar bodies( the first polar body can divide, making a total of 3 polar bodies).

• Ovarian Cycle:

  • hypothalamus → GNRH → anterior pituitary → LH and FSH → progesterone and estrogen(-feedback) → uterus

  • Ovarian Cycle - 1-13 days of follicular phase → build a follicle(oocyte and support cells(granulosa cells, fluid)); triggered by FSH to build it and secretes estrogen

  • Ovulation(day 14) - oocyte and some cells(corpus luteum left behind) released from the ovary and triggered by a surge of LH

  • Luteal Phase(15-28 days) - form corpus luteum from follicle remains, triggered by LH surge, and secretes estrogen and progesterone

• Uterine cycle:

  • Estrogen Establishes Endometrium

  • Progestogen Protects Endometrium

  • menstruation(1-5 days) - shed off old endometrium(low Es and Pro)

  • Proliferative stage(6-14 days) - rebuild endometrium - low pro and rising est

  • Secretory phase(15-28) - enhance endometrium, stable est and high prog

• Fertilization = when a sperm implants into the oocyte → only 1 can get through it → egg can block polyspermy(only letting 1 in) → egg depolarizes to repel other sperm or slow block that causes the egg surface to harden

• Cleavage → dikaryon(one cell, 2 nuclei) → need to finish meiosis first and kick out second polar body → makes zygote → 24 hours turns into 2 cells stage → then morula which is a ball of cells into a blastula(hollow ball of cells) → a larger cell cluster that implants into the uterus in 4-5 days

  • The outer shell of the blastula is trophoblast that secretes hCG to maintain the corpus luteum → will become the placenta in 3 months and takes over hormone secretion and hCG falls - pregnancy tests for hCG level but only works before the first trimester —> the inner part of the cell is the embryo and turns into the umbilical cord and amniotic sack

  • The stem cells → can become many other cells and make more stem cells → found in blastocysts → embryonic stem cells

  • Embryonic stem cells → Determination(determines its path to which cell it wants to be) → Differentiation (physical change into a new cell type) → Pluripotent cells that can become any type of cell in the body but not the placenta

  • Stem cells in other parts of the body(adult cells) → ex. blood cell type in blood → but these cells can only become one type of cell(blood cells only and restricted)

  • Totipotent cells from zygote→ can be any body cell or the placenta

• Embryonic Stages:

  • First 8 weeks → fertilization through 8 weeks → medically pregnant is 10 weeks here

  • Gastrulation → about 4 weeks to form 3 primary germ layers → endoderm(inner linings), mesoderm(organs, blood vessels, non-gland organs), ectoderm(nervous system, nails, skin)

  • Neurulation and organogenesis 4- 8 weeks → form all other body organs and structures → nothing new formed after this

  • Functional beating heart at 3 weeks!

  • Week 12 - ID the sex of the baby

  • Week 16 - Baby movements

  • week 24 - eyelids infuse and sound and light

  • Week 28 - testes descend in males

  • Week 33 - lung release surfactant

  • Week 38 - full term

• Labor - 3 triggers

  • The placenta deteriorates, the uterus stretches, baby’s head stretches the cervix(ideal position)

  • Baby’s head stimulus hypothalamus releases oxytocin from post. pituitary, uterus contracts majorly → + feedback

    • Baby’s gain 1 pound a week during the last weeks of pregnancy

• Baby changes:

  • close lung bypass - a hole between the Right and Left aorta and vessel connects the pulmonary artery to the aorta

  • Liver bypass

  • close umbilical vessel → close the arteries first after being born and veins close second

  • Baby stops making fetal hemoglobin → regular hemoglobin(mother) and baby’s hemoglobin has a higher affinity to O2 than mother’s → high affinity is then removed to go to regular hemoglobin

• Mom’s Changes → more hormonal in nature → deliver placenta → drop in estrogen and progesterone → now prolactin is secreted(increase) to make milk, baby nurses, and makes more milk(NOT + Feedback). Baby nursing also causes oxytocin to rise