MCAT BIO

what is the cell

• a compartmentalized, organized, and well-oiled machine that can undergo various life processes

  • compartmentalized: split into organelles (eukaryotes)

    • prokaryotes are a soupy mix of genetic information and life-producing capacity

  • organized: each process occurs in a controlled manner (positive & negative feed backs)

  • well-oiled: processes are fluid, flows from one to the next

what is the cell theory

1. all living things are made up of cells

2. cells are the basic functional unit of life

3. cells form from pre-existing cells

4. cells carry genetic info (DNA!) that they pass onto daughter cells

what makes a virus not living?

• it breaks rules 3 and 4 of the cell theory

  • a virus cant reproduce on their own and need a cell host

  • a virus cant pass on genetic code to their daughters; but rather, must inject the code into cell hosts which are naturally programmed to run it through the cell cycle

    • the injected genetic material then either lays dormant within the cell (lysogenic) or spreads throughout the body (lytic)

why do cells only pass on DNA to daughter cells and not RNA

1. RNA is meta-stable

   • it closes in on itself by folding and is unable to be used after a while

2. RNA is unable to be passed on

   • only viruses can pass it on, not eukaryotes or prokaryotes

what are the main differences between eukaryotes and prokaryotes

• EUK (eukarya)

  • has membrane-bound organelles

  • can be single (yeast) and multi-cellular (humans)

• PRO (bacteria & archaea)

  • essentially one big organelle

  • no nucleus

  • only single celled

what is the nucleus

• control center (HQ) of the entire cell

• contained inside a semi-permeable double membrane

  • sign of importance; protection

  • has nuclear pores which allow for communication and travelling in and out of the cell

• has tightly wound DNA inside (negative charged)

  • this is wrapped around histone proteins

    • made up of amino acids (basic building blocks of proteins) that have +1 charged R groups

what is the difference between heterochromatin and euchromatin

• Heterochromatin

  • compact/tight form of DNA

• Euchromatin

  • loose/relaxed form of DNA

• Histone Acetylation

  • the act of neutralizing a positive histone protein by attaching an acetyl group to each of its terminals

  • this undoes the tightly wound DNA which needs to happen before replication of the cell

    • hetero → eu

what is the mitochondria

• the powerhouse of the cell where almost all the effective energy of the cell (ATP) is produced by the electron transport chain (ETC)

• has its own genes and is able to self-replicate

• has an outer and inner membrane (double protected)

• contains cristae

  • grooved folds of the inner membrane that increase surface area for ETC to work with

  • each groove fits more proteins for energy (cellular respiration)

    • coastline paradox

• is able to kickstart apoptosis

  • the controlled programming of cell death when something goes wrong

  • different from necrosis which is uncontrolled

what are lysosomes

• organelles that contain many hydrolytic enzymes used to break down material

  • lysozymes~ recycling centers

  • these enzymes are different from vesicles which are like boxes used to transport materials

• derived from “lysis” meaning to break

what are the smooth and rough endoplasmic reticulums (SER & RER)

• ROUGH

  • studded with ribosomes

    • factory machines for protein synthesis

    • necessary for EVERYTHING

• SMOOTH

  • lacks ribosomes

  • helps transport proteins from RER to Golgi

  • synthesizes lipids (fats/oils/waxes/etc.)

  • detoxes drugs by making them hydrophilic (attracted to water)

    • primary site for first pass metabolism which is the processes of allowing toxins to be dissolved in the blood in order to be excreted through the kidneys as urine

      • liver’s job

what is the golgi apparatus

• stack of membrane-bound “sacs”

• modify proteins to make them more efficient in their roles

  • “cellular surgery”

• packages molecules into vesicles which later merge with the cell membrane during exocytosis

what is the peroxisome

• organelle filled with hydrogen peroxide (H2O2) in order to break down material

• similar to lysosomes but it doesn’t use enzymes

• a natural antibiotic/antiviral/anti-toxin

  • H2O2 is often used as a disinfectant, antiseptic, or bleaching agent

what is the endomembrane transport

• well-oiled, fluid process of the cell:

  • mitochondria and nucleus work together to give the cell energy and instructions necessary for producing life →

  • MRNA produced from transcription in the nucleus is send to the RER →

  • RER translates MRNA into proteins and sends them through SER →

  • SER transports proteins to the golgi →

  • Golgi modifies and packages proteins into membrane-bound vesicles →

  • sacked vesicles fuse into cell membrane and proteins go through exocytosis

• Exocytosis

  • the process by which something inside the cell will leave the cell

• Endocytosis

  • the process by which something outside the cell will come into the cell

what is the difference between microfilaments, microtubules, and intermediate filaments

• microfilaments

  • made of actin whose primary job is to interact with myosin to induce muscle contraction

  • help with cell movement, contraction, and shape changes

  • make the cleavage furrow during cytokinesis

    • the separation of daughter cells during mitosis/meiosis

• microtubules

  • made of tubulin

  • involved in the synthesis of cilia and flagella

    • ex: respiratory tract and sperm cells

  • make up the centrioles and help them move to opposite sides of the cell during cell division

    • separation creates the mitotic spindle

• intermediate filaments

  • rope-like protein fibers that absorb tension and help anchor organelles

what are tissues

• organized sheets of cells

• listed in order of increasing regenerative ability:

  1. epithelial

  2. muscle

  3. connective

  4. nervous (neuron)

what are epithelial tissues

• covers the body and lines its cavities

  • cavities= holes (inner ear, nose, etc.)

• involved in absorption, secretion, transportation, and sensation

  • most organs are lined with epithelial tissue

• make up the parenchyma

  • the functional parts of any organ/gland

what are connective tissues

• create the framework for other things to rest and function on

• most cells here produce and secrete materials like collagen (strength) and elastin (flexibility) which help make up the extracellular matrix (ECM)

  • complex 3D network of proteins that provides structural support for cells and tissues

• ECM lies within connective tissues and gives it the strength and flexibility it needs to do its job

  • lots of ECM = proper connective tissue

• examples: bone/cartilage/tendons, small intestines, blood

  • even though it transports, blood is made of fluid connective tissue and not epithelial because it’s made of an ECM → plasma

    • blood vessels (arteries/veins), however, are lined with epithelial tissue

bacteria classifications

1. cocci

   • sphere shaped

     • s. aureus

   • gram neg or pos

2. bacilli

   • rod shaped

     • myobacterium tuberculosis

   • mostly gram pos

3. spirilli

   • spiral shaped

     • treponema palidum (syphillus)

   • only gram neg

what are the kinds of cell walls in prokaryotic cells

1. thick peptidoglycan layered

   • gram positive bacteria

   • stain purple or blue

     • staphylococcus pneumonae

2. thin peptidoglycan layered

   • gram negative bacteria

     • contains lipopolysaccharide (LPS) which causes much harsher infections in the body due to being immunogenic (activates and flares up the immune system)

   • stains red or pink

     • salmonella

key facts about prokaryotic cells

• have a cell wall NOT a membrane

• often have flagella that operate as motors for transportation

  • filament at the tip of the flagella rotates from the base and generates torque

• have a nucleoid region for compartmentalization

  • NOT a nucleus

• can transfer and acquire DNA through plasmids

  • small rings of DNA (separate from actual DNA) that hold information in nucleoid region

  • episomes are autonomous plasmids capable of inserting themselves directly into main bacterial DNA

• reproduce asexually

what are the ways prokaryotes can reproduce

1. Binary Fission

   • splitting into clones of themselves (SpongeBob)

2. Horizontal Gene Transfer

   • the process of bacteria acquiring new genetic material

   • Genetic Recombination is essential for HGT

     • cells break down, exchange, and rejoin DNA segments to increase genetic variation and repair damage

     • crucial for adaptation and evolution

   • Types of HGT:

     1. Transformation

        • bacteria picks up elements of another bacteria when it dies and releases its insides

     2. Transduction

        • when a virus (bacteriophage) accidentally transfers the genetic material from one bacteria to another

     3. Conjugation

        • bacteria passes on genetic material via a mating bridge which enables the acquirement of new traits like antibiotic resistance

        • bacteria with fertility factor plasmids (F+ bacteria) can form the conjugation bridge while those without (F-) cannot

          • this conjugation bridge is a “sex pilus” that allows the transfer of copied plasmids to other bacteria so an F- bacteria can become F+ and continue the cycle!

          • F+ cannot mate with F+ because it would be ineffective

            • EVERYTHING has a purpose!!

explain the life cycle of bacteria

• bacteria have lag, exponential, plateau, and death phases

  • they are born into an environment with limited resources (lag)

  • they must build up their resources (exponential), then eat through them (plateau) until there isn’t any more to consume (death)

• the rate of growth = the rate of death in this cycle

  • example of biological equilibrium

  • reason for plateau phase

what are the parts of viruses and sub-viral particles

• Protein Capsid

  • protective outer coat made of proteins

  • encloses and transports viral nucleic acid (DNA/RNA)

  • can be helical or polyhedral shaped

• Genome

  • either DNA or RNA

    • if virus has DNA, host cell does all the work and replicates, transcribes, and translates viral genome through cell cycle

    • if virus has RNA, it must bring its own enzymes:

      • RNA-dependent RNA polymerase used to help a virus make its own RNA copies for host ribosomes to make into proteins

      • Reverse transcriptase used by retroviruses to turn their RNA into DNA host can work with

  • lytic or lysogenic reproduction

• Spike Proteins

  • glycoproteins that facilitate host entry and infection through penetration

  • determine tropism: method by which a virus recognizes a host cell to infect with the specificity of a key to a lock

  • help virus evade host immune system

• SOME have a lipid envelope

  • a phospholipid bilayered membrane stolen from host cells

  • able to enter host cells through fusion

what are viruses and what are the “special” viruses

• intracellular parasites that obligate (force) a living host cell for reproduction

1. Bacteriophages

   • viruses that only target bacteria

   • can perform transduction

2. Retroviruses

   • use reverse transcriptase to change and integrate themselves into a host cell’s genome

   • famous retrovirus is HIV

3. Viroids

   • tiny viruses that infect plants

   • lack a protein coat

what is a superinfection

• a second, overlapping infection that’s often caused by

  • microorganisms resistant to treatment given to combat the first infection

  • antibiotic treatment killing off protective microflora, allowing new pathogens to strengthen

• example:

  • s. aureus is commonly caused by a post influenza infection and extremely dangerous due to immune impairment and lung damage that allows pneumonia to develop quickly

what is endocrinology

• study of the endocrine system

  • a series of glands, hormones, effectors, and pathways that mainly regulate long-distance and long-term communication within the body

  • essentially acts as a carrier pigeon: gland → circulatory system (bloodstream) → target

  • the goal is homeostasis: resisting changes to maintain a stable environment

1. glands

   • secretory tissues or organs within the body that respond to various stimuli

     • adrenal glands, pituitary glands, etc.

2. hormones

   • a molecule or protein that has the capacity to bind receptors and influence responses on the cellular/tissue/organ level

   • the thing that is released from glands into the bloodstream

     • dopamine, cortisol, insulin, etc.

3. effectors

   • structures that act in response to stimuli

     • liver responds to insulin and increases glucose uptake

4. pathways

   • complex, interconnected, signalling networks in which glands release hormones into the bloodstream to function

     • HPT axis, HPG, HPA, etc.

why does the endocrine system exist

• we are not single-celled and need a way to communicate between the furthest of cells

• the system allows us to:

  • hijack communication pathways

  • relay signals to specific places and get them there in time

  • have the signaled message stay long enough to maintain a response/effect

• the body is very needy!

  • it wants what it wants, when it wants, and in the amounts it wants it in

what is the tropic effect

• when a hormone is unable to perform a job on its own and employs a secondary messenger to regulate the response

• example:

  • the growth hormone (GH) exhibits its effects through linear growth (height) and is released from the anterior pituitary gland (APG). In order to release it, the APG is stimulated by the growth hormone releasing hormone (GHRH)

    • A → B → response

    • A is tropic, B is direct

what is the hypothalamus

• the control center (HQ) of the endocrine system

• the pituitary gland serves the hypothalamus as a henchman

  • split into two main sections: anterior and posterior

• posterior:

  • the hypothalamus produces oxytocin and ADH and sends them via long nerve fibers

• anterior:

  • the hypothalamus produces releasing and inhibiting hormones as signals

  • anterior hormones are its own!

describe the anterior pituitary gland

• front lobe of the pituitary gland that is identified as endocrine acting

  • this is because it secretes hormones directly into the bloodstream

• connects to the hypothalamus through a network of blood vessels

  • hypophyseal portal system

    • made up by the hypophyseal portal vein

    • supplies releasing and inhibiting signals from the hypothalamus and blood to the APG

• nicknamed the “master gland”

  • produces 7 key hormones (GH, FSH, LH, etc.)

describe the posterior pituitary gland

• back lobe of the pituitary gland that is identified as neuroendocrine acting

  • a.k.a neurosecretory~ essentially “one giant neuron”

• routinely shocked by the hypothalamus with nerve endings that cross over and drop electric signals

  • shocks cause hormone secretion

• only releases 2 hormones

  • oxytocin and ADH

what are the types of blood vessels and their functions

1. Veins

   • carry oxygen-poor blood toward the heart

2. Arteries

   • carry oxygen-rich blood away from the heart

3. Capillaries

   • connect veins and arteries

   • facilitate nutrient and waste exchanges

what is a portal vein

• a vein that circulates between two organ systems or tissue beds

• helps identify toxins before they enter the bloodstream

  • carries to the liver for detoxing

• contains little hormone molecules

what are the different categories for identifying hormones

1. By Effect

   • Direct

     • does the deed

       • ex: T4 accelerates cellular metabolism

   • Tropic

     • gets a guy (usually an organ) to do the deed

       • ex: TSH smacks the thyroid to make T4 accelerates cellular metabolism

   • Double-Tropic

     • gets a guy to get a guy to do the deed

       • ex: GnRH stimulates the APG into producing FSH and LH which act on endocrine gonads to produce estrogen, progesterone, and testosterone (1° sex hormones)

2. By Structure

   • Steroid Hormones

     • a derivative of cholesterol via reaction

       • ex: -one, -ol, -oid family (cortisol, progesterone)

     • mainly non polar hormones

       • allows them entrance into cell through membrane so they bind to an intracellular steroid receptor, forming a complex that travels into the nucleus and changes transcription (DNA → RNA) of DNA

         • complex is a transcription factor

   • Amino Acid Hormones

     • very polar and unable to enter through the cell membrane

       • must bind a receptor from outside, leading to a signal transduction cascade which leads to a hormonal effect

         • cascade modifies transcription in a similar way to steroid hormones

       • ex: T3, T4

   • Peptide Hormones

     • polypeptides (amino acid chains)

       • protein-derived

       • MUST be polar and MUST bind to a receptor

       • ex: insulin, ghrelin

describe the mitosis cell cycle

• a series of phases that eukaryotic cells undergo in order to reproduce

  • DNA is replicated and split, and the cell divides into 2 identical daughter cells

• mitosis only happens to somatic, diploid cells

  • somatic ~ also called autosomal; body cells with uninheritable mutations

  • diploid~ have 2 of the necessary genetic material to code for the genome (2n; n=23)

• split into 4 phases:

  1. Mitosis

     • cell is actively dividing

     • everything else is interphase (preparation for mitosis; G₁, S, G₂)

       • individual chromosomes are not visible during interphase due to DNA being in a less condensed state (loose/unwound) to get ready for replication

  2. G₁ (pre-synthetic gap)

     • growth/bulking stage where the cell size increases in preparation for replication

     • includes a checkpoint before S phase

       • ensures cell has proper amounts of, type of, and accommodations for the DNA

  3. S (synthesis)

     • cell replicates genetic material so that each daughter has identical DNA

     • after replication, each chromosome consists of 2 sister chromatids bound by a centromere

       • still 1 chromosome

     • checkpoint occurs before G₂ phase to make sure replication is correct

  4. G₂ (post-synthetic gap)

     • another bulking stage with more cell growth, copying of organelles, and protein synthesis

     • this is the time for any damaged DNA to be repaired before mitosis

       • another checkpoint

  5. G₀

     • where cells that are not dividing go to carry out functions (chill)

what are the stages of mitosis

1. Prophase

   • nuclear envelope dissolves to break the barrier between nucleus and cytoplasm

   • genetic material condenses again and chromosomes become visible

   • centrioles form and start to move away

2. Metaphase

   • chromosomes line up at the center of the cell (metaphase plate)

   • centrioles are now at opposite poles of the cell

3. Anaphase

   • centrioles begin throwing spindle fibers made of microtubules at the chromosomes, causing sister chromatids to separate from each other

4. Telophase

   • spindle apparatus disappears

   • nuclear membrane reforms

   • chromosomes uncoil

   • cleavage furrow begins to form

• Cytokinesis

  • usually begins as mitosis is ending (may have a little overlap)

  • cleavage of the cytoplasm into 2 daughter cells

what is the evolution of chromosomes during mitosis

• chromosomes are counted by centromeres so you can have 1 chromosome with 2 chromatids

  • chromatid~ 2n, single stranded

  • sister chromatids~ 2n, double stranded

1 cell with 1 chromosome, 1 chromatid → copying of DNA in synthesis of interphase →

1 cell with 1 chromosome, 2 sister chromatids → chromosome separation in anaphase of mitosis →

2 cells with 1 chromosome, 1 chromatid each after cytokinesis

describe the meiosis cell cycle

• a series of phases that non-somatic, eukaryotic cells undergo to reproduce

• occurs only in and produces haploid cells

  • gamete cells (1n; n=23)

    • sperm or egg (sex) cells

  • single stranded

  • enough to code for another genome (23 from mother (XX), 23 from father (XY))

    • 2 haploids = 1 diploid which sustains its life through mitosis

    • involves crossing over

• follows the same general formula as mitosis

what are the stages of meiosis

1. Meiosis I

   • starts with prophase I which is the same as mitosis prophase but it involves crossing over/ recombination

     • the exchange of genetic material between non-sister chromatids of homologous chromosomes by way of touching and fusing with each other

     • outside of spontaneous mutations, this process is responsible for all the genetic variation in humans

   • metaphase I is the same as mitosis metaphase

   • anaphase I is the same as mitosis anaphase but the homologous chromosomes are pulled apart

   • telophase I is the same as mitosis telophase but the end product is 2 haploid cells with their chromosomes still condensed

2. Meiosis II

   • happens right after meiosis I

   • the exact same as the mitosis cycle but with 1 single chromosome

what is the evolution of chromosomes during meiosis

• chromosomes are counted by centromeres so you can have 1 chromosome with 2 chromatids

  • chromatid~ 2n, single stranded

  • sister chromatids~ 2n, double stranded

46 double stranded chromosomes, 92 chromatid → pulling apart of homologous chromosomes

23 double stranded chromosomes, 46 chromatid after telophase I → meiosis II

23 single stranded chromosomes having 1 chromatid each as end products

what are non-disjunction errors

• problems that arise from incorrect meiosis and lead to of several diseases

  • create specific changes in sex chromosomes (23rd pair)

• typically only affect females

  • women have all the ova they will ever create at birth (frozen in time since fetuses)

• happen primarily during meiosis I when homologous chromosomes fail to separate correctly

  • leaves a haploid cell with an abnormal # of chromosomes after meiosis is completed

    • 1 extra~ trisomy

    • missing~ monosomy

what happens in cases of trisomy or monosomy of the 23rd chromosome

• Trisomy

  • when a sperm cell fertilizes an egg with a 3 pairs of the 23rd chromosome, it usually forms a zygote that cannot develop normally

    • ex: Klinefelter syndrome (XXY) is characterized by tall stature, more breast tissue resulting in a larger chest, sparse hair, small penises and testes resulting in low testosterone and low fertility

• Monosomy

  • when a sperm cell fertilizes an egg with an emply 23rd chromosome, only 22 pairs will form and the zygote will be XO

    • ex: Turner syndrome is characterized by short stature, low-functioning ovaries, broad chests, puffy hands and feet at birth, webbed necks, and infertility due to rapid loss of eggs within the ovaries

describe the male reproductive system

SEVEN UP ACRONYM:

• S

  • Seminiferous Tubules

    • specific location of meiosis where spermatozoa (sperm) are created in the testes

• E

  • Epididymus

    • where sperm are stored until matured, or gain motility

    • palpable through the skin

• V

  • Vas Deferens

    • transports sperm from epididymus to ejaculatory ducts before ejaculation occurs

• E

  • Ejaculatory Duct

    • transports sperm through prostate gland into the urethra during ejaculation

    • sperm becomes semen as it mixes with seminal fluid from the seminal vesicles, prostate gland, and cowper’s gland during ejaculation

• N

  • N/A

• U

  • Urethra

    • formed from merged ejaculatory ducts

    • transports urine and semen to outside of the body

• P

  • Penis

    • external sex organ that connects to the urethra

    • enables urination and reproduction

what is seminal fluid

• fluid that mixes with sperm to nourish it and help transport it out of the body during ejaculation

• produced by the seminal vesicles, prostate gland, and cowper’s gland

  • this also produces pre-seminal fluid (precum) to clear out the urethral pathway of urine which is a hostile (acidic) environment for incoming sperm

• semen is

  • the mix of seminal fluid and sperm

explain the onset of puberty in men

• the sex-determining region in the Y chromosome (SRY) activates in development and stimulates testes formation as well as the formation of other sex organs

  • acts as a “master switch” during gestation: pregnancy stage

• at the onset of puberty, the hypothalamus releases GnRH to stimulate the APG into releasing FSH and LH

  • FSH enters the testes and helps facilitate spermatogenesis

    • the production of semen from the primordial germ cells (diploid → haploid)

    • FSH provides the structural and nutritional needs for sperm development

  • LH enters the testes to make and release testosterone into the testes and blood

    • hormone responsible for 2° sex characteristics (body hair, voice, etc.)

    • testosterone helps mature sperm and has positive feedback on cells that facilitate spermatogenesis

describe the female reproductive system

• Ovaries

  • main reproductive organ that contains thousands of follicles

  • derived of the same tissue as testes but respond differently to hormones due to differences in development

    • SRY prevents development of female parts during pregnancy

• Follicles

  • sacs that nourish and protect ova

• Ova

  • plural of ovum

    • a single egg cell (largest in human body)

One ovum is expelled per month in response to hormonal activity. It is put into the abdominal cavity and sucked by the fimbrae of the fallopian tube

• highest point in the fallopian tube is the most common site of fertilization

explain the onset of puberty in women

• before puberty, the hypothalamus restricts the synthesis of GnRH

  • when it finally triggers, GnRH stimulates APG into releasing FSH and LH

• FSH

  • stimulates ovaries to secrete estrogen

    • forms 2° sex characteristics (body hair, breast development, etc.)

    • thickens the endometrium

      • uterine lining designed perfectly to sustain life

• LH

  • stimulates corpus luteum to secrete progesterone

    • protects and maintains the endometrium in preparation for fertilization

      • when fertilization doesn’t occur, the super thick endometrium layer (continual estrogen exposure) sheds

        • this shedding is menses: bleeding

explain the menstrual cycle

1. Follicular Phase (Days 1-13)

   • begins with menstrual shedding (flow) in response to the sudden loss of hormones from luteal phase (cycle)

     • causes stimulation of hypothalamus to release GnRH → APG → FSH & LH

   • release of FSH leads to the stimulation of follicles

     1. matures 1 egg cell in preparation for the next cycle

     2. secretes estrogen which in turn has a negative feedback effect on GnRH release from the hypothalamus

        • secreted estrogen stimulates the growth of endometrial lining, glands, and decidua

          • thick layer of mucus that lines the endometrium; reason for discharge

   • late into this phase, estrogen levels hit their peak and turn off their negative feedback effect on GnRH

     • results in a huge influx of FSH and LH release

2. Ovulation (Day 14)

   • caused by the spike in LH caused by the turning off of estrogen’s negative feedback

   • characterized by mittelshmertz

     • sharp pain in the right abdomen

     • leads to the release of mature ovum

       • ovum breaks out of the follicle it resides in, turning it into the corpus luteum: ruptured follicle

   • the corpus luteum stays behind in the ovary responding to the LH

3. Luteal Phase (Day 15-28)

   • preparation of the uterus for fertilization

   • LH stimulates the corpus luteum to secrete progesterone which:

     • leads to further development of endometrium layer

     • has a negative feedback on GnRH production

   
   

   • NO FERTILIZATION:

     • corpus luteum eventually desensitizes to LH, breaking off the chain of command

       1. sudden loss of progesterone leads to endometrium shedding → menses

       2. negative feedback turns off, restarting the cycle by releasing GnRH again → follicular phase

          • endometrium is rebuilding as it sheds! fast-healing wound to prevent infections

   
   

   • FERTILIZATION:

     • formation of a zygote which burrows into the endometrium leading to the production of β-hCG (beta human chorionic gonadotropin)

       • looks exactly like LH but the corpus luteum cant get tired of it due to shear amounts of progesterone it demands

         • happens until the placenta is matured and makes the progesterone itself until the end of pregnancy

       • β-hCG can be detected 2 weeks after implantation of the zygote

         • determination of pregnancy tests

explain the cause for the negative feedback effect estrogen has on GnRH if it leads to FSH which leads to more estrogen

• the negative effect is proportional to ovum maturity in the body

  • prevents the expulsion of more than 1 ova at the same time

• this effect is a homeostatic, fine-tuned dial

  • balance

• happens until only one egg cell is left responding to GnRH

  • perfect for fertilization or the expulsion of the egg in the next cycle

• prevents an early surge of LH which would release the egg before fully maturing

explain menopause

• ovaries become less sensitive to FSH and LH with age and eventually atrophy (shrink and lose function), leading to:

  • less production of estrogen and progesterone

  • end of menstruation

  • abundant levels of FSH and LH in the blood

    • continually trying to stimulate follicles that are no longer responding → menopause

• characterized by:

  • vaginal dryness

  • hot flashes

  • sleep problems

  • mood changes

  • risk of cardiovascular disease

what is p53

• gene modulates DNA sequences so they don’t go haywire and cause cancer

• natural tumor suppressor

  • people who do not properly inherit this gene are predisposed to cancer and usually experience several tumors of various tissues in early adulthood

describe the heart’s role in the cardiovascular system

• main player that acts as a glorified pump (among other things)

• takes in blood and shoots it back out

• main goals:

  1. transfer oxygenated blood throughout the body

  2. maintain adequate perfusion pressure

     • amount of pressure necessary to maintain blood flow to the body

     • perfusion~ process by which blood enters the place it needs to go

• the pump (heart) accomplishes these goals through pipes (vessels)

  1. Arteries~ away; most carry oxygenated blood

  2. Veins~ toward; most carry de-oxygenated blood

     • ex: pulmonary artery travels away from the heart and towards the lungs but carries de-oxygenated blood to be later oxygenated in the lungs

what are the general compartments of the heart

1. Right Atrium

   • connects to the vena cava

     • largest vein in the body

     • divides into 2 parts: superior and inferior (SVC & IVC)

       • SVC carries blood from upper body (head, neck, arms, chest)

       • IVC carries blood from lower body (abdomen, pelvis, legs)

     • carries all blood returning to the heart and lungs for re-oxygenation (venous blood)

       • this blood drains into the right atrium which then empties into the right ventricle through a valve

2. Right Ventricle

   • connects to the pulmonary artery

     • this artery carries the venous blood that’s just drained into the right ventricle to the lungs to be re-oxygenated

     • it parts into left and right pulmonary arteries to send the blood to each lung

3. Left Atrium

   • connects to the pulmonary veins (4 of them)

     • these carry oxygenated blood from the lungs into the other side of the heart

     • veins plug into the left atrium, allowing blood to be drained into the left ventricle through a valve

4. Left Ventricle

   • connects to the aorta

     • largest artery in the body

     • handles all the oxygenated blood volume that comes out of the heart through the left ventricle and transmits it to the part of the body it needs to go

• the right and left sides of the heart are separated by septa~ vertical barriers

  • interatrial septum separates the left and right atria

  • interventricular septum separates the left and right ventricles

• ventricles are more muscular/beefy than atria

  • the left ventricle is much bulkier than the right ventricle

• atria are low pressure environments, contrary to ventricles which need to generate high pressure to pump out blood through vessels

explain each valve of the heart

• valves prevent back flow of blood and open when it is time

  • act as one-way gates that are triggered by pressure changes

  • situated at ventricle and atria exits

1. Tricuspid Valve

   • a 3-leaf valve that acts as a trap door situated at the bottom of the right atrium

   • prevents back flow of blood into the right atrium as it drains into the right ventricle

   • this valve opens passively

2. Bicuspid Valve

   • a 2-leaf valve that acts as a trap door situated at the bottom of the left atrium

   • most commonly called the mitral valve

   • prevents back flow of blood into the left atrium as it drains into the left ventricle

   • this valve opens passively

3. Pulmonary Valve

   • situated at the bottom of the right ventricle

   • acts as a gate that restricts de-oxygenated blood into only flowing towards the lungs and not back flowing into the right ventricle

   • this valve swings open with pressure changes in the ventricle associated with contraction

4. Aortic Valve

   • situated at the bottom of the left ventricle

   • acts as a gate that restricts oxygenated blood into only flowing out of the heart and not back flowing into the left ventricle

   • this valve swings open with pressure changes in the ventricle associated with contraction

• the sound of the heart beat is each valve opening and closing

  • the tricuspid and bicuspid valves open and close together and are known as the atrioventricular valves because of where they are located

    • when these shut it is the first heartbeat

  • the pulmonary and aortic valves open and close together and are known as the semilunar valves because they are shaped like a half moon

    • when these shut it is the second heartbeat

explain the cardiovascular cycle

• the blood involved in this cycle DOES NOT perfuse (sustain) the heart

• this details the pulmonary cycle not the systemic cycle (blood → tissues/organs)

1. All the venous blood in the body comes back to the heart through the vena cava to be reoxygenated and empties into the right atrium

2. From the right atrium, it drains through the tricuspid valve to go into the right ventricle

3. The blood then moves through the slightly beefy right ventricle and exits through the pulmonary valve

   • valve leads to pulmonary artery which transports blood to lungs for oxygenation

4. Once blood picks up O2 at the lungs, it enters back into the heart through the pulmonary veins to be distributed to the part of the body it belongs

   • from here on out, all the blood is oxygenated to its greatest capacity unless there is a heart or blood issue

5. Blood flows into the left atrium and then drains into the very beefy left ventricle via the bicuspid or mitral valve

6. Left ventricle pumps out blood through the aortic valve which leads to the aorta

7. Oxygenated blood is distributed from the aorta to the rest of the body until it becomes de-oxygenated again

   • whole cycle restarts

explain electrical conduction in the heart

• the heart also acts as a battery

• cardiac myocites (heart muscle cells) have action potentials

  • only neurons and muscle cells are capable of this

• everything the action potential touches contracts!!

  • except SA and AV nodes

• Sinoatrial Node

  • the heart’s internal pacemaker located at the junction between atria and cardiac sinus

    • vein complex at the back of the heart (behind the right atrium)

  • made up of a bundle of cardiac myocites that fires off electrical potentials for the rest of the heart to pick up on

  • shoots off an an action potential anywhere from 60-100 BPM (beats per minute) = heart rate

  • the SA node acts solely as a messenger

• Atrial Ventricular Node

  • located at the junction between the atria and ventricles (touches all 4)

  • in charge of a roughly 0.1 second delay depending on lifestyle habits

  • this delay is of action potentials or electrical impulse from the atria to the ventricles

    • gives atria time to empty and ventricles time to fill before contraction is triggered

• Process:

  1. SA node fires action potential across both atria causing them to depolarize which leads to them “contracting” in what’s called an atrial kick

  2. Signal reaches the AV node which slows down the electrical impulse, causing a delay

  3. Action potential then swiftly travels down the interventricular septum after the delay using the Bundle of His (BOH) and wraps around the ventricle walls using the Purkinje fibers

     • ventricle walls contract

     • BOH and Purkinje fibers together make up the His-Purkinje system

• action potential travels fast across atria, then slow at the AV nodes, then super fast down the septum and around the ventricles

explain how the cardiovascular cycle and electrical conduction of the heart happen simultaneously

1. Tricuspid and bicuspid valves open passively as the heart relaxes after contracting (pulmonary and aortic valves shut)

   • as this happens, blood is entering the heart following the last pump of the ventricles and drains from the atria into the ventricles due to the agape atrioventricular valves

2. As the blood is filling up the ventricles after entering the atria, the SA node fires off action potential leading to the atrial kick

   • depolarized atria “contracts”/shocks and kicks any remaining blood down the trap doors of the atrioventricular valves

3. Action potential signal hits the AV nodes leading to the delay

   • delay gives enough time for the atrial kick to get every last drop of blood to the right and left ventricles

4. Signal then travels down the left and right BOH and is distributed through the Purkinje fibers to the ventricles

   • this causes ventricles to depolarized and contract, forcing open the semilunar valves and pushing blood out of the heart through them

   • as the semilunar valves open, the atrioventricular valves shut making first heart beat

5. Left and right ventricles repolarize, causing the heart to relax and the semilunar valves to close

   • shutting of semilunar valves produces the second heart beat

   • heart relaxation and shutting of semilunar valves opens the atrioventricular valves passively

     • cycle restarts

what does it mean that veins and arteries are umbrella terms

• Veins

  • compliant; “pushed around”

  • carry de-oxygenated blood back to the heart in systemic circulation and oxygenated blood back to the heart in pulmonary circulation

  • systemic veins are much further from the heart than the arteriole system = they have much lower pressure than arteries

  • types:

    • venules~ smallest levels of veins which receive de-oxygenated blood from capillaries

      • lead back to larger veins → vena cava

    • larger veins~ have their own valves to prevent backflow

      • ex: keeps blood going to the heart instead of gravity → legs

• Arteries

  • elastic and muscular

  • resist change by “pushing back” which generates pressure

    • arteriole system has the highest pressure in the body

  • types:

    1. large arteries~ closest to the heart; have high elastic tissue to withstand high heart pressure

    2. medium arteries~ very muscular; distribute blood to specific body organs/tissues

    3. arterioles (small)~ main source of systemic vascular resistance (SVR) which is majority of the resistance in the body

    4. capillaries (very small)~ final step of arteriole system; lead directly to venules

       • only 1 cell layer thick- red blood cells travel in a single file

         • best scenario for RBC picking up O2 and transferring it

explain systemic vascular resistance (SVR)

• SVR is the resistance that must be overcome for blood flow to circulate throughout the body

• sourced in the arterioles → medium arteries → large arteries → aorta

  • pressure translates up the arteriole system and to the aortic valve, keeping it pushed closed until the LV contracts enough to force it open (SA/AV nodes)

    • when action potential shoots down to the ventricles and depolarizes them, they contract until the pressure inside the ventricle is greater than the pressure of the SVR keeping the aortic valve closed

      • this is how blood pressure is generated in the body

• when SVR is overcome by LV, the valve shoots open and blood pumps out the aorta to the rest of the body, leaving pulmonary circulation and entering systemic circulation

what is blood pressure

• the amount of force your blood uses to get through your arteries

• needs to 2 things to generate BP:

  1. adequate blood volume outside the heart to pump against

  2. adequate blood volume inside the LV for the heart to pump against

• measured by systolic pressure / diastolic pressure~

  • normal range is 100/65 < x < 120/80

  • systolic pressure

    • peak pressure of LV contraction against aortic valve to force it open

  • diastolic pressure

    • pressure in the arteriole system when heart rests in between beats

    • lowest pressure in the aorta as the ventricle is refilling after contraction

• equation: MAP = HR · SV · SVR

  • MAP is reflective of average blood pressure (1/3 SP + 2/3 DP)

  • HR is heart rate

  • SV is stroke volume or blood volume

    • HR · SV = CO or cardiac output~ the amount of blood that exists in the heart at any given time

  • SVR is systemic vascular resistance

describe the arteriole system (systemic circulation)

1. Oxygen-rich blood leaves the LV and goes through the aorta

2. Aorta → large arteries → medium arteries → arterioles

3. Arterioles lead blood to the capillary beds where waste exchange happens

   • capillaries exchange O2 for CO2 with the cells

   • O2 and nutrients pass through capillary walls into tissues whole CO2 and waste enters blood

   • anything to large to pass through capillary walls (like proteins) is not being exchanged

4. After waste exchange, de-oxygenated blood moves to the venules from the capillaries

5. Venules → larger veins → vena cava → RA → RV → lungs

** after de-oxygenated blood leaves the capillaries and enters the venous system, it can take a secondary pathway to the vena cava via portal veins where it drops by another organ/tissue bed first

• this is the Hepatic Portal System

• these portal system veins ensure blood containing toxins and nutrients is filtered, detoxed, and metabolized (nutrients) by the liver before reaching the heart

  • portal veins are not considered “true veins” because they do not lead to the heart but the liver

describe blood composition

• blood is 55% fluid (plasma) and 45% cells:

  • erythrocytes

    • red blood cells

    • job is to carry and drop off O2; return with CO2 and drop that off

    • biconcave (side profile teaaa) which increases surface area

      • this allows them to hold more hemoglobin and improve gas exchange

    • each RBC has 250 million molecules of Hb that each hold 4 O2 molecules

      • a single RBC carries 1 billion O2 molecules

    • they lose organelles during maturation which means NO MITOCHONDRIA

      • mitochondria require O2 for energy which limits efficiency

    • unable to divide~ life span is 90-120 days

      • travel to the spleen to die after circulation

  • leukocytes

    • white blood cells

  • platelets

    • cell fragments

    • aid in coagulation

      • blood clotting, or thickening, that prevents excessive bleeding after an injury

describe how blood types work

• blood types are determined by alleles (genetics)

  • ABO Gene (3 alleles)

    • A (I_A) - equally dominant with B

    • B (I_B) - equally dominant with A

    • O (i) - recessive (need 2)

  • RH Factor (2 alleles) ~ protein found on the surface of RBC

    • Rh⁺ - dominant

      • can receive Rh⁺ or Rh^- blood

    • Rh^- - recessive (need 2)

      • Rh^- can only receive likewise blood

      • Hemolytic Disease of a baby is caused by an Rh^- mother developing anti-D antibodies against her Rh⁺ fetus during pregnancy

• a person’s immune system attacks whatever blood it doesn’t have (except O^-)

• AB⁺ is the universal recipient and O^- is the universal donor

what are the all the blood type options

1. I_AI_A ~ type A

2. I_BI_B ~ type B

3. I_AI_B ~ type AB (both show because equally dominant)

4. I_Ai ~ type A with a carrier for O

5. I_Bi ~ type B with a carrier for O

6. ii ~ type O

• each with ± for Rh

what is the interstitium

• spaces that exist outside of capillaries and act as storage sites for interstitial fluid

  • hold tons of fluid that is made of plasma (55% of blood)

  • help move nutrients/waste and anchor structures

  • exert pressure on capillary walls and vice versa

what is hydrostatic and oncotic pressure

1. hydrostatic

   • the pressure exerted by plasma on the walls of blood vessels as it travels through them

   • helps push water, O2, and nutrients out of capillaries and into surrounding tissues so cells can feed

2. oncotic

   • the sucking pressure of large proteins on red blood cells to ensure water taken by hydrostatic pressure returns to blood

   • occurs due to proteins being to large to pass through capillary walls

   • helps pull CO2 and waste back into capillaries before fluid pools and causes tissue swelling

• high hydrostatic pressure at the arterial end

• high osmotic pressure at the venous end

  • fluid balance

describe hydrostatic and oncotic pressures of the capillaries and interstitium

• P_c

  • hydrostatic pressure of the capillary

  • the force plasma exerts on capillary walls as it travels through

• π_c

  • oncotic pressure of the capillary

  • “sucking” pressure of the capillary from the interstitium

• P_i

  • hydrostatic pressure of the interstitium

  • the force interstitial fluid exerts on capillary walls

• π_i

  • oncotic pressure of the interstitium

  • “sucking” pressure of the interstitium from the capillary

• P_c and π_c both originate from the capillary while P_i and π_i originate from interstitium

• equilibrium is when P_c = P_i and π_{c =} π_i

  • fluid balance

  • this does NOT mean there is no fluid entering or exiting the capillary but that it is happening at the same rate

equation: π = iMRT

• π = oncotic pressure

  • more salt in the bloodstream = more oncotic pressure because the salt absorbs or “sucks” water from around it

• i = van’t hoff factor

• M = molarity of the substance present

• RT = constant

describe the process of fertilization

• after an LH spike, the most mature egg cell breaks from its follicle and gets released into, eventually, the fallopian tube

  • the “most mature” is the most sensitive to gonadotropins and the only egg cell responding to estrogen’s dialed down signals

  • it travels to the ampulla

    • highest point of fallopian tube where fertilization most often takes place (egg meets sperm)

• the tip of the sperm, acrosome, binds with the outside of the egg cell creating a cortical reaction

  • an explosive release of calcium in which the sperm cells expels everything it has in order to inhibit further fertilization (dangerous)

  • happens only after the acrosome passes the first 2 protective layers of the egg cell and DNA is ready to be implanted inside

    • corona radiata and zona pellucida

• the cortical reaction results in the egg cell having a depolarized membrane, or fertilization membrane

  • no longer penetrable

what is a zygote

• a single fertilized egg

  • takes about a week to travel through fallopian tube before implanting in the endometrium layer

• ectopic pregnancy

  • when a zygote fails to implant inside the uterus (typically in the fallopian tube)

    • can lead the fallopian tube to rupture causing life-threatening internal bleeding

• embryo

  • when a zygote becomes more than a single cell

how do twins happen

1. dizygotic (most common)

   • two separate fertilization events of 2 eggs by 2 sperm cells at the same time

   • leads to 2 zygotes that develop 2 organisms no more genetically alike than regular siblings

     • fraternal

2. monozygotic (chance)

   • 1 zygote splits itself in half, making 2 copies of itself

   • leads to 2 embryos that share the same genetic material

     • identical

   • characterized by the structures they share during pregnancy (di-di, mono-di, mo-mo)

• the more babies you are pregnant with = the earlier you deliver

  • biggest complication

what is the order of embryonic development

1. Fifty

   • Fertilization

2. Cats

   • Cleavage

3. Blast

   • Blastulation

4. Into a

   • Implantation

5. Gosh

   • Gastrulation

6. Darn

   • Differentiation

7. Nebula

   • Neurulation

describe the step of cleavage in embryonic development

• rapid cell division event that results in a larger number of smaller cells (unchanging volume)

• the first cleavage happens as early as 16 hours after fertilization takes place and divisions continue in increasing rates

  • zygote → 2-celled embryo → 4-celled embryo → etc.

• 2 types of cleavage:

  1. indeterminate

     • results in cells that can still form the entire organism

       • roles are not yet pre-determined

     • if separated, each clump of cells is capable of developing into a complete embryo independently

       • monozygotic twins

  2. determinate

     • cells are “pre-determined” to be a specific cell type with specific functions

     • their developmental fate is set, they have a limited capacity, and they are not independent

describe the step of blastulation in embryonic development

• after several rounds of cleavage, an embryo becomes a solid ball-like mass of cells called a morula

• the morula then undergoes a process of blastulation, meaning it forms a blastula

  • a hollow ball of cells with a fluid-filled cavity (center) and an inner mass of cells

  • essentially, a glorified morula that implants the endometrium

    • morula has no fluid center~ blastocoel

• 2 parts of a blastula:

  1. inner mass of cells

     • sits inside the fluid and later becomes the actual organism

     • much like a fetus in a fluid-filled womb

  2. outer cell mass

     • trophoblast which eventually becomes the chorion

       • chorion is the outer protective membrane that forms the placenta, while the amnion is the inner protective membrane

describe the placenta’s role

• takes over the production of progesterone to protect the endometrium and prevent spontaneous abortions

  • miscarriages

• connects fetal heart and mother’s cardiovascular system and influences her heart functions to ensure the fetus obtains adequate O2 and nutrients

  • this is why a woman’s blood pressure drops and blood volume expands the further into pregnacy

  • edema (swelling) typically occurs in the legs due to increased capillary hydrostatic pressure from taking on a lot of blood volume to maintain placenta AND account for low blood pressure

• connects to the baby via the umbilical cord

  • acts as interface, serving as the fetus’ lungs, liver, and kidneys without mixing its blood with the mother’s blood

• until the placenta matures and becomes functional, the embryo is supported by the yolk sac (enclosing pouch)

  • the allantois is an extension of the sac and aids in waste and gas exchange between the yolk sac and the embryo

describe the step of gastrulation in embryonic development

• occurs 16 days after fertilization

• invagination of the blastula occurs turning it into a gastrula

  • a process of a surface folding in on itself to form a cavity or tube

  • outward pressure forms on the outside of blastula to initiate this process

• the archenteron is the internal cavity of the gastrula and is connected to the outside of the embryo by a hole/opening called a blastopore

  • archenteron eventually becomes the lumen (inside) of the gut and the blastopore becomes the anus

• gastrulation is one of the most critical steps of development because it primes the body for organogenesis by generating the 3 primary germ layers

what are the 3 primary germ layers

1. Ectoderm

   • upper, outermost layer

   • develops

     • nervous system, adrenal medulla, epidermis and cavities (skin, hair, nails, eye lens, inner ear, epithelial of nose, mouth, anal canal)

2. Endoderm

   • innermost layer

   • inaccessible from the outside (must enter through ectoderm)

   • develops

     • GI stract, gut lining, parts of the liver & pancreas, thyroid, bladder, epithelium of digestive & respiratory tracts

3. Mesoderm

   • middle layer

   • develops

     • musculoskeletal system, circulatory system, gonads, excretory system, kidneys and their adrenal cortex, muscular and connective tissues of digestive & respiratory systems

difference between cortex and medulla

• in any sphere-like object, the cortex is the outer layer closer to the edge at all parts while the medulla is the inner layer removed from the border

• in the body,

  • cortex

    • responsible for steroid hormone production (endocrine-acting ~ APG)

    • closer to gonad tissues = comes from mesoderm

  • medulla

    • 1 big neuron (neuro-secretory ~ PPG)

    • closer to nervous tissues - comes from ectoderm

what is the difference between specification, determination, and differentiation

1. specification (freshman)

   • cells begin their path toward becoming a specific cell type

   • have unlimited potential and can reverse the process

2. determination (grad school)

   • cells commit to being a specific cell type

   • irreversible

   • can occur due to morphogens

     • chemical signals in the embryo that depend on concentration gradient for the strength of their signal (high near the source and low from far away)

       • based on how far morphogens spread out, the cell decides its fate

3. differentiation (white coat)

   • cells undergo the processes necessary to become their cell types

• stem cells are cells that have not yet differentiated and can give rise to other cells

types of stem cells

1. Totipotent

   • “whole”

   • can develop into any cell type

2. Pluripotent

   • “many”

   • can develop into numerous cell types except embryonic and placental cells

3. Multipotent

   • “several”

   • can only develop into a handful of cell types

describe the step of differentiation in embryonic development

• process by which cells start to look like their type

• critically dependent on communication of nearby cells

• inducers are cells (or tissues) that emit signals to direct the developmental fate of nearby cells

  • signalling molecules they send are morphogens which influence adjacent cells using a concentration gradient

  • foundational for tissue differentiation and organogenesis

  • relies heavily on paracrine signaling

    • **in some cases, an inducer can refer to the actual signal, or morphogens, being sent**

• responders are competent cells with the proper receptor molecules to respond to inducers/morphogens

explain the types of intercellular communication

1. Autocrine Signaling

   • cell signals itself to do something

2. Paracrine Signaling

   • cell signal stays local

3. Juxtocrine (“side-by-side”) Signaling

   • signals between touching cells; direct contact communication

4. Endocrine Signaling

   • cell signals travel far away, through the bloodstream

describe the step of neurulation in embryonic development

• occurs after gastrulation

• process where the flat ectoderm layer folds and transforms into a tube that later develops into the central nervous system

• notochord is a rod of mesodermal cells that help develop the fetus’ nervous system through signalling

• overlying ectodermal cells fold in to form horms, neural folds, and the neuro groove lowers down towards the notochord

  • all of this is a result of cell-to-cell communications

• as invagination continues, the 2 neural folds pull up and conjoin together to ft7neural tube

  • neural crest cells migrate in through here before tube closes completely

• neural folds pinch and fold into the neural tubes to make the central nervous system (brain + spine)

  • as the folds fuse into the tube, specialized cells at the borders detach and develop into the peripheral nervous system, facial structures, and melanocytes (pigment)

    • neural crest cells

  • the anterior and posterior ends of the tube remain open temporarily

    • failure to close creates defects like anencephaly or spina bifida

describe fetal circulation

• a fetus’s lungs DO NOT WORK

  • they are filled with fluid and have high pressure

• before birth, the right side of the fetus heart has greater pressure because lungs are shut

  • when lungs start functioning after birth, the left side has greater pressure because they begin supplying blood to that side and it has the job of supplying to the rest of the body

    • more blood = greater volume = greater force = greater pressure

• the placenta is where fetal blood connects to maternal blood without mixing, gets O2 and nutrients, and removes CO2 and waste

  • even though it does the job of the digestive system, lungs, liver and kidneys, a little blood still goes to these areas in order to nourish the tissues

• umbilical arteries

  • 2 arteries that carry de-oxygenated fetal blood to the placenta

• umbilical vein

  • 1 vein that carries oxygenated blood from the placenta back to the fetus

  • fetuses have a much higher affinity (desire) for oxygen than adults

• 3 shunts (redirecting passages)

  • operate simultaneously in the fetus so it is adequately nourished by O2 blood from the placenta

what are the 3 shunts of the fetal cardiovascular system (pulmonary cycle)

1. Foramen Ovale

   • means “oval hole”

   • a hole that exists in the interatrial septum to connect the right atrium to the left atrium

   • allows fetuses to bypass pulmonary circulation by shunting the blood directly to the left atrium

   • this hole closes after birth due to increased pressure in the left atrium after the first breath

2. Ductus Arteriosus

   • means “arteriol duct”

   • necessary because some blood misses the foramen ovale and continues to spill into the right ventricle from the right atrium

   • this duct diverts blood from the pulmonary artery into the aorta, bypassing the non-functional lungs

   • duct closes after birth due to increased oxygen and a drop in prostaglandins

     • hormone-like lipids that keep this duct widened and relaxed

     • in menstruation, they contract the uterus to shed the endometrium lining → cramps

     • act right when they are produced (unlike hormones)

3. Ductus Venosus

   • means “venus duct”

   • connects the umbilical cord to the IVC to bypass the liver

     • liver isn’t needed before birth because the placenta processes nutrients for the fetus

• IVC → RA → Foramen Ovale → LA → LV → Aorta

• IVC → RA → RV → Ductus Arteriosus → Aorta

O2 AND NUTRIENTS:

• Mother → Placenta → Umbilical Cord → Umbilical Vein → Ductus Venosus → IVC

CO2 AND WASTE:

• Aorta → Umbilical Arteries → Umbilical Cord → Placenta → Mother

what are teratogens

• substances that interfere with embryonic development

• drugs/medication, viruses, chemicals, alcohol, etc.

  • vitamin B9 (folate/folic acid) deficiency is teratogenic because it blocks the vitamin’s ability to aid in neural tube development, leading to defects like Spina Bifida

describe gestation

• the time from conception until birth

• measured in trimesters

  • each trimester is 12-14 weeks

  • human gestation is 40 weeks or 10 months

  • we start counting weeks after implantation, which takes place after 2 weeks after conception (bHCG is detected)

1. First Trimester

   • at 3 or 4 weeks, a baby has a heartbeat

   • at 8 weeks, an embryo becomes a fetus

     • all major organ systems have formed, but it is still immature

     • from this point on, its just growing/maturing

2. Second Trimester

   • tremendous growth

   • fetus begins moving

   • human face can be seen and eyes begin to open

   • fingers and toes elongate

     • when a fetus closes its hands, pressure of amniotic fluid creates a unique indent~ fingerprints

3. Third Trimester

   • continued rapid growth

   • lots of central nervous system (CNS) development

   • fetus has less space → little to no movement

explain birth

• NECESSARY POSITIVE FEEDBACK PATHWAY TO KNOW

• the natural signal that starts birth is unknown

  • induction occurs and uterus begins to contract

    • prostaglandins

• as the baby’s head presses against the cervix on the outlet of the vaginal canal, uterine contraction begins

  • this leads to cervical dilation which signals the hypothalamus to stimulate the PPG into releasing oxytocin which again stimulates uterine contraction

    • positive feedback loop

  • this continues happening until the end of childbirth, meaning oxytocin levels in the body are extremely high

    • newborn effect~ intense emotional bond of a mother to her child after birth

  • high oxytocin levels suddenly lower after birth, while estrogen and progesterone levels crash leaving a mother with postpartum

    • loss of placenta after birth

    • different for all women due to environmental, genetic, and hormonal factors

  • breastfeeding keeps oxytocin levels relatively high (fluctuates)

    • women who stop breastfeeding early typically have trouble bonding with their child

describe the different levels of aging

1. body breaks down

   • wrinkles, poor posture, slower

   • accumulation of “insults” to the body

     • environmental stressors, poor lifestyle choices, etc.

2. telomeres stop regenerating

   • non-coding terminals of chromosomes with repetitive nucleotide sequences that exist to protect the ends of DNA during replication

   • get shorter and shorter over time, eventually leading to cessation of cellular reproduction of that chromosome

types of cell death

• apoptosis

  • controlled

  • cell breaks into fragments in of itself to be digested by other cells

  • happens to limit the release of harmful chemicals

• necrosis

  • uncontrolled

  • cell dies due to environmental factors and explodes

  • releases a bunch of toxic compounds that can kill other cells

neurons

• cells of the nervous system capable of receiving and transmitting specific electrical impulses that the body can recognize and act on

• bundles of neurons

  • CNS: a tract

  • PNS: a nerve

    • sensory, motor, mixed, and automatic types

• parts of the neuron:

1. soma

   1. the body of the cell in which the nucleus, ribosomes, and ER are located

   2. within a tract in the CNS, somas collect into nuclei

   3. within a nerve in the PNS, somas collect into ganglia

2. dendrites

   1. finger-like structures that surround the soma and receive information from the outside

3. axon

   1. d

4. axon hillock

   1. boundary between the cell body and the axon

   2. “point of no return” that filters and integrates incoming signals as “inhibitory” and “excitatory”

5. nerve terminals

   1. signals get spat back out in the form of chemical messengers called neurotransmitters

   2. disspitate into synaptic cleft

summation

• adding up of signals to determine if they’re enough to an fire action potential

• inhibitory

  • signals that hyperpolarize membrane and move it further from firing an action potential

  • negative

• excitatory

  • signals that polarize cell membrane and move it towards firing an action potential

  • positive

saltatory conduction

• signals travelling through axon by jumping between non-insulated points on the axon (outside of myelin sheaths)

  • these points are called the Nodes of Ranvier

electrical vs chemical transmission

• electrical

  • electricity is used to pass signals down the axon within a single neuron

• chemical

  • neurotransmitters (chemicals) pass signals to subsequent neurons/muscles/glands

    • effectors

glial cells

• also known as neuroglia

• surround neurons and play supportive and structural roles for them

• can hold them in place, supply O2 and nutrients to them, insulate them from other neurons so electrical impulses are not scattered, destroy pathogens, and remove dead neurons

• types

  • astrocytes

    • nourish neurons and form the blood-brain barrier (BBB)

      • layer of cells that surround the brain blood vessels and control the transmission of solutes from blood stream into CNS

      • essentially blocking pathogens and toxins

  • ependymal cells

    • line the ventricles of the brain and produce celebrospinal fluid (CSF)

      • clear fluid (filtered plasma) that supports and cushions the brain and spine as a “shock absorber”

    • also form barrier between CSF and the interstitial fluid of the CNS

  • microglia

    • phagocytic cells that ingest and breakdown waste and pathogens in the CNS

    • “specialized macrophages”

  • mylenating cells

    • create muelin sheaths around axons as insulation points that fix all electrical signals to destination with maximum influence and more guaranteed responses (prevents scattering of voltage)

    • in CNS, these cells are called oligodendrocytes

    • in PNS, these cells are called Schwann cells

signal transmission and action potential of neurons

• every cell membrane has a voltage that almost always creates a more negative charge inside the cell than outside

• shifts in voltage across a cell membrane create action potential used for signalling of messages to the body

  • muscle contraction, hormone influence, etc.

• Vm = membrane potential

  • depolarization = raised Vm = more positive inside cell = more AP

  • hyperpolarization = lowered Vm = more negative inside cell = less AP

• resting membrane potential (RMP)

  • the net electrical potential difference that exists across a cell’s membrane, created by movement of charged molecules

  • in neurons, this potential is -70 mV

    • the two ions generating and maintaining this potential are potassium (K+) and sodium (Na+)

    • these ions keep the potential negative inside the cell by resisting its desire for neutrality

Na+/K+/ATPase

• sodium potassium pump

• maintains the neurons resting membrane potential by pumping out 3 sodium ions for every 2 potassium ions pumped in

  • NOKIA- Na outside, K inside, 1 ATP used

• a lesser concentration of Na+ is found inside the cell than inside, so ions desire to enter the cell to neutralize this imbalance → 3 ions are pumped out to maintain it

  • net positive charge (sodium > potassium)

• a greater concentration of K+ is found inside the cell than outside, so ions desire to leave the cell to neutralize this imbalance → 2 ions are pumped in to maintain it

  • net negative charge (potassium > sodium)

• 1 adenosine-triphosphate (ATP) molecule is required to generate the energy required to transport ions since both are moving against their gradient

potassium leak channels

• function to allow slight movement of K+ ions down their gradient (whichever direction that may be)

  • leaking out (NORMAL): when the cell has too much K+ inside, channels balance the sodium potassium pump

  • leaking in: restores -70 mV after hyperpolarization, helping pump when the cell becomes too negative inside

sodium leak channels

• function to allow slight movement of Na+ ions down their gradient (whichever direction that may be)

  • leaking out: when the cell has too much Na+ inside, channels balance the sodium potassium pump

  • leaking in (NORMAL): restores -70 mV after hyperpolarization, helping pump when the cell becomes too negative inside

equilibrium potential of K+ and Na+

• equilibrium between the concentration gradient that moves these ions out and the electrical gradient that moves them in → results in no net movement of the ions

• Na+ = +60 mV

• K+ = -90 mV

threshold

• the lowest magnitude of stimulus strength (electrical voltage) that will induce a response (action potential)

• membrane at axon hillock summates enough excitatory signals and depolarizes to a level between -55 mV and -40 mV

• types of summation

  • temporal summation

    • a single presynaptic terminal fires rapidly in succession at dendrites, so each new potential adds to the previous one before it fully decays, building up enough voltage at the hillock

  • spatial summation

    • multiple different presynaptic terminals fire at the same time at different locations on the neuron dendrites, combining their individual potentials together at the hillock