Regulation and reproduction

Question 1

What is membrane potential?

Answer 1

• electric charge difference
  
  • across membrane

Question 2

What is resting potential?

Answer 2

• imbalance of positive and negative charges across membrane (-70mV)
• no signal
• inside negative, outside positive

Question 3

What causes resting potential?

Answer 3

• inside
  
  • K+
  • protein anions (-)
• outside
  
  • Na+
  • Cl-
• sodium-potassium pumps (ATP needed)
  
  • for every 3Na+, 2K+ are pumped
    
    • more Na+ on the outside
• leakages
  
  • voltage gated channels = open at certain electrical potential value
    
    • closed are leaky
      
      • more K+ leaks outside

Question 4

How do voltage-gated channels work?

Answer 4

• Na+
  
  • open at threshold potential (depolarisation)
  • Na+ in
  • close at action potential
• K+
  
  • open at action potential (repolarisation)
  • K+ out
  • close after reaching resting potential again

Question 5

How is action potential propagated?

Answer 5

• ion movement depolarises one part
  - Na+ inside move from depolarised part to not yet depolarised
  - Na+ outside move the opposite direction
  - difference = -50mV (threshold potential reached)
• impulse initiated at one terminal
  
  • passed at other terminal

Question 6

What is axon hillock?

Answer 6

• junction between cell body and axon
  
  • plasma membrane composition changes
    
    • voltage-gated channels
• initiates electric impulse
  
  • small amounts of Na+ accumulate there

Question 7

What is depolarisation?

Answer 7

• Na+ in axon hillock
• charge grows inside neurone
  
  • plasma membrane depolarisation
• threshold potential is reached (-55mV)
  
  • voltage-gated channels open
    
    • Na+ inside
      
      • more Na+ channels open = positive feedback
    • charge changes to 40mV = action potential

Question 8

What is repolarisation?

Answer 8

• at action potential
  
  • Na+ closes — K+ open
  • K+ outside
    
    • charge drops
    • K+ and Na+ at wrong sides

Question 9

What is hyperpolarisation?

Answer 9

• K+ channels close
  
  • slow
• potential inside drops further than resting state

Question 10

What happens at the absolute refractory period?

Answer 10

• after action potential
  
  • Na+ channels can’t open
• no action potential
  
  • prevents backflow

Question 11

What happens at relative refractory period?

Answer 11

• hyperpolarisation
  
  • harder to reach threshold potential
  • stronger stimulus needed (more Na+)

Question 12

How is action potential propagated forward?

Answer 12

• depolarisation
  
  • opens channels in next part of axon
    
    • signal goes forward
• local currents
  
  • Na+ inside the cell (depolarised part) move to the polarised part
  • Na+ outside the cell (polarised) moves to depolarised part
    
    • this prevents signal from going backwards
    • reduces concentration gradient (easier to reach -55mV)

Question 13

What is myelin?

Answer 13

• coats nerve fibres
• phospholipid bilayer
  
  • Schwann cells deposit myelin
    
    • 20 or more layers
• gap: node of Ranvier
• saltatory conduction
  
  • impulse jumps from node to node
    
    • quicker

Question 14

What is a synapse?

Answer 14

• space between the axon terminals of one nerve and dendrites of the other
  
  • or muscles and glands
• fluid-filled gap = synaptic cleft (20nm)

Question 15

How does a signal move?

Answer 15

• neurotransmitters send signals across synapses
  
  • from signal to receiver cell
    
    • receptors on post-synaptic cell
  • diffusion

Question 16

What are the steps of synaptic transmission?

Answer 16

1. impulse propagated along pre-synaptic neuron
   
   • reaches axon terminal
2. depolarisation of membrane
   
   • voltage-gated channels of Ca2+ open
     
     • Ca2+ inside
3. Ca2+ influx causes vesicles with neurotransmitters to move
   
   • fuse with membrane
4. neurotransmitter is released to synaptic cleft
   
   • exocytosis
5. neurotransmitters bind to post-synaptic receptors
6. Na+ channels open
   
   • Na+ into the cell
     
     • threshold potential
7. neurotransmitter degraded by enzyme or back into pre-synaptic membrane by a transporter or reuptake pump

Question 17

How are neurotransmitters in axon terminal?

Answer 17

• produced in cell body
  
  • in vesicles
    
    • transported to axon terminal

Question 18

What happens after synaptic transmission?

Answer 18

• vesicles fuse with pre-synaptic membrane
  
  • enlarged
• neurotransmitter reuptake
  
  • endocytosis

Question 19

What is a motor neurone?

Answer 19

• from central nervous system (CNS) to muscles
  - elongated axon
• connected to muscle
  
  • neuromuscular junction
    
    • chemical synapse
      
      • neurotransmitter: acetylcholine (cholinergic)

Question 20

How is acetylcholine produced?

Answer 20

• pre-synaptic cell
  
  • combining choline (diet) with acetyl group (aerobic respiration)

Question 21

How does cholinergic synapse work?

Answer 21

• acetylcholine is released after Ca2+ influx
• ACh binds to Na+ channel receptors
  
  • threshold potential
  • shortly bounded: only 1 action potential
• acetylcholinesterase (in synaptic cleft) breaks ACh down into choline and acetate
• choline is reabsorbed by pre-synaptic neuron
  
  • back into ACh

Question 22

How is knowledge about synaptic transmission applied?

Answer 22

• neuronal and mental diseases
  
  • Selective Serotonin Reuptake Inhibitor (SSRI) = antidepressants
• neuroactive toxins
  
  • neonicotinoids (pesticide)

Question 23

What are neonicotinoids?

Answer 23

• similar to nicotine
• binds acetylcholine receptors
  
  • insects
• acetylcholinesterase doesn’t break it down
  
  • irreversible
  • paralysis and death
• not toxic to humans
  
  • more cholinergic synapses in CNS of insects
  • bind less strongly to receptors
• imidacloprid = commonly used pesticide
• harmful for honeybees

Question 24

What are hormones?

Answer 24

• chemical messengers
  
  • produced by endocrine glands
• homeostasic regulation
• modification of activity of tissues
• transported by blood
• slower but long lasting effects

Question 25

What are the differences between nervous and endocrine system?

Answer 25

• nerve impulse vs chemical messenger
• neurons vs blood
• fast vs slow
• carried to specific cells vs throughout body
• muscles / glands vs range of organs affected

Question 26

What are different types of hormones?

Answer 26

~ steroids
- receptors in nucleus
- action by transcription regulation
- affect gene expression
- slow
> peptides
- receptors in plasma membrane
- act by signalling cascade
- affect chemical processes and gene expression
- fast
> proteins, glycoproteins, amines or tyrosine derivatives

Question 27

How do steroid hormones work?

Answer 27

• cross through plasma and nuclear membrane
  
  • bind to receptors
  • ex. sex hormones
• form receptor-hormone complex
  
  • serves as transcription factor (promotion or inhibition)
• produced from cholesterol
• calciferol: intestinal cell membrane
  
  • complex affects expression of calcium transport protein calbindin
    
    • absorption of calcium
• cortisol binds in cytoplasm and enters nucleus
  
  • in liver cell: gluconeogenesis
    
    • conversion of fats and proteins into glucose
  • decreases expression of insulin receptor
    
    • in pancreas

Question 28

How do peptide hormones work?

Answer 28

• bind to membrane receptors
  
  • triggers cascade reaction, edited by second messengers
• hydrophilic so cannot pass the membrane

Question 29

What is an example of second messengers?

Answer 29

• water soluble — spread signal fast
  
  • Ca2+ and cyclic AMP (cAMP)

Question 30

How does epinephrine signalling work?

Answer 30

• epinephrine mediates “fight or flight” (first messenger)
  
  • supply of glucose (energy) needed
  • in liver binds to G-protein couple receptor
    
    • activation of G-protein
      
      • uses GTP as energy to activate enzyme adenylyl cyclase
        
        • ATP —> cAMP
  • cAMP (cyclic adenosine monophosphate) activates protein kinase enzymes
    
    • glycogen breakdown and inhibit glycogen synthesis

Question 31

What are the endocrine glands?

Answer 31

• pituitary
• pineal
• hypothalamus
• thyroid
• parathyroid
• thymus
• mammary
• adrenal

Question 32

What is the role of hypothalamus?

Answer 32

• combines nervous and endocrine system
  
  • control of pituitary gland
• secretion of releasing factors
  
  • stimulate anterior pituitary gland
    
    • carried by portal vein
• negative feedback
  
  • blood solute high
  • osmoreceptors in hypothalamus react
    
    • ADH secretion
  • blood solute low
    
    • ADH reduced

Question 33

What is the role of pituitary gland?

Answer 33

• anterior pituitary
  
  • growths, reproduction, homeostasis
    
    • FSH and LH
• posterior pituitary
  
  • oxytocin and ADH
• hormones synthesised in neurosecretory cell in hypothalamus
  
  • the end of axons
    
    • impulse stimulates secretion

Question 34

What is thyroxin and its function?

Answer 34

• hormone
• regulates metabolic rate (especially in liver, muscle and brain) and helps control body temp
  
  • as the body cools, more thyroxine is produced
• secreted by thyroid gland (neck)
  
  • 4 atoms of iodine
    
    • deficiency of iodine = no synthesis of thyroxin

Question 35

How is temperature controlled by thyroxin?

Answer 35

• hypothalamus controls blood temperature
  
  • decrease = signal to thyroid
• metabolic rate in cells increases
  
  • more heat

Question 36

What are the results of thyroxin deficiency?

Answer 36

• thyroxine is a hormone regulating metabolism
• deficiency => less metabolism
  
  • less ATP
    
    • imparted muscle work —> fatigue
    • imparted neural work —> dizziness, forgetfulness, depression, imparted brain development
  • less heat —> feeling cold
  • less sugars and lipids used for cellular respiration —> body fat accumulation
• iodine deficiency (hypothyroidism = underactive thyroid)
  
  • cause of thyroxin deficiency
  • enlargement of thyroid = goiter

Question 37

How is milk produced and ejected in mammals?

Answer 37

• in mammary glands
• prolactin
  
  • anterior pituitary
  • development of mammary glands
  • milk production
  • oestrogen and progesterone increases prolactin
    
    • inhibits effect of prolactin on milk production
    • at labour production begins (no oestrogen and progesterone)
• oxytocin
  
  • release of milk
  • nursing by infant stimulates prolactin and oxytocin
  • contraction of surrounding cells
    
    • ejection of milk
  • positive feedback

Question 38

How are growth hormones used by athletes?

Answer 38

• produced in anterior pituitary
  
  • targets liver cells
• release of insulin-like growth factor
  
  • stimulates bone and cartilage growth
  • increase muscle mass
• short burst of strength
• banned

Question 39

What is melatonin’s function?

Answer 39

• feeling of drowsiness, drops body temp
• pineal gland
• controls circadian rhythms
  
  • depend on suprachiasmic nuclei (SCN) in hypothalamus
    
    • control secretion of melatonin by pineal gland
    • information about light from retina
• concentration decreases at dawn

Question 40

What are the causes of jet lag?

Answer 40

• three or more time zones
• difficulty in remaining awake and sleeping through night
  
  • fatigue, irritation, headaches
• melatonin can be taken

Question 41

What glands exist in pancreas?

Answer 41

• exocrine
  
  • digestive enzymes
  • alkaline solution
• endocrine
  
  • hormones

Question 42

How is blood glucose level controlled?

Answer 42

• in pancreas
  
  • regions of endocrine tissue: islets of Langerhans
• set point: 5mmol/L
• alpha cells
  
  • glucagon
  • blood glucose levels fall
    
    • stimulation of glycogen breakdown into glucose
      
      • released into blood
• beta cells
  
  • insulin
  • blood glucose levels increase
    
    • stimulation uptake of glucose by tissues
      
      • skeletal muscle, liver
    • insulin broken down by cells it acts upon = ongoing secretion

Question 43

What are the types of diabetes?

Answer 43

• type I
  
  • early onset
    
    • autoimmune (destruction of beta)
  • no insulin
  • skinny complexion
• type II
  
  • insulin signal not received by cells (insulin resistant)
  • old
  • associated with obesity
    
    • disturbance of glucose homeostasis
  • bad diet, no exercise

Question 44

What are the treatments for diabetes?

Answer 44

• type I (defects in B cells of pancreas)
  
  • insulin injections
    
    • before meal
  • implanted devices
  • stem cells maybe
• type II (insulin resistance)
  
  • adjusting diet, exercise

Question 45

What is leptin?

Answer 45

• produced by adipose tissue
  
  • glucose uptake
• excess of energetic substrates present
• appetite control centre in hypothalamus
• feeling of satiety
• in mice with recessive on alleles no leptin
  
  • obesity
  • objection of leptin decreased mass

Question 46

Why isn’t leptin used to treat obesity?

Answer 46

• skin irritation and swelling
• short-lived protein
• rare cases of “low leptin” obesity
  
  • loss of leptin sensibility is more probable

Question 47

What are the functions of reproductive system?

Answer 47

• gamete production
  
  • storage
  • nourishment
  • transport
• fertilisation
• pregnancy

Question 48

What did Harvey do in his experiment?

Answer 48

• “soil and seed” theory by Aristotle
  
  • sperm = seed that develops in woman’s uterus with menstrual blood
• dissection of deer’s uterus
  
  • no foetus shown
  • hypothesis: foetus development is independent from sex

Question 49

What are the steps of oogenesis?

Answer 49

1. before birth
   
   • oogonia formation
   • meiosis arrested at prophase I
     - primary oocyte (follicle)
2. after puberty
   
   • each month —> oocyte completes meiosis I and starts prophase II
     - first polar body
     - secondary oocyte (released at each cycle)
     - secondary follicle —> mature follicle
3. fertilisation
   
   • meiosis II completed
     - ovum
     - maturation of gamete

Question 50

What happens to the follicle after releasing of an oocyte?

Answer 50

• degenerating follicle = corpus luteum —> corpus albicans

Question 51

Where does spermatogenesis occur?

Answer 51

• in testes
  
  • narrow tubes = seminiferous tubules
    
    • outer layer = germinal epithelium
      
      • sperm production begins
      • more mature = closer to lumen
    • on the wall —> Sertoli cells (large nurse)
  • small cells in the gaps = interstitial cells (Leydig cells)

Question 52

What are the steps of spermatogenesis?

Answer 52

1. mitosis (puberty)
   
   • spermatogonium —> primary spermatocyte
2. meiosis I
   
   • primary spermatocyte —> 2 secondary spermatocytes
3. meiosis II
   
   • secondary spermatocytes —> 2 spermatids
4. maturation
   
   • spermatozoa = sperm

Question 53

How is sex of the embryo determined?

Answer 53

• starting as females
  
  • reproductive hormones: oestrogen and progesterone
    
    • from ovaries and placenta
• SRY (sex-determining region Y) gene on Y chromosome
  
  • encoding for TDF (testicle-determining factor)
  • TDF triggers development of gonads into testes
  • testes produce testosterone
• testosterone : oestrogen ratio high
  
  • further development of male parts

Question 54

How does testosterone work in male development?

Answer 54

• pre-natal
  
  • gonads —> testes
  • male reproductive organs
• puberty
  
  • production of sperm (primary sexual characteristic)
  • secondary sexual characteristics
    
    • enlargement of penis
    • pubic hair
    • deepening of voice

Question 55

What causes pre- and post-natal development of females?

Answer 55

• prenatal
  
  • oestrogen and progesterone
    
    • both sexes
    • ratio testosterone : oestrogen matters
    • female genitalia development during foetal development
• puberty
  
  • enlargement of breasts
  • pubic hair
  • underarm hair

Question 56

What are the stages of menstrual cycle?

Answer 56

follicular —> ovulation —> luteal —> menstruation

Question 57

What happens during follicular phase?

Answer 57

• follicles developing into ovary
  
  • most developed breaks open —> into oviduct
    
    • rest degenerate
• uterus walls (endometrium) thicken and repair

Question 58

What happens during luteal phase?

Answer 58

• wall of follicle releasing egg —> corpus luteum
• endometrium prepares for embryo
  
  • if no, menstruation starts
  • corpus luteum breaks down

Question 59

What hormones control menstrual cycle?

Answer 59

• pituitary protein hormones
  
  • FSH (follicle stimulating)
  • LH (luteinising hormone)
• ovarian hormones
  
  • oestrogen
  • progesterone

Question 60

What are the roles of different hormones in menstrual cycle?

Answer 60

• FSH
  
  • peak at the end of mentruation
  • development of follicles (with oocyte and follicular fluid)
  • secretion of oestrogen by follicle wall
• oestrogen
  
  • peak at the end of follicular phase
  • repair and thickening of endometrium
  • increases FSH receptors —> follicles more receptive to FSH —> more oestrogen (positive feedback)
  • high levels —> inhibition of FSH (negative feedback)
    
    • LH secretion
• LH
  
  • sharp peak at the end of follicular phase
  • completion in meiosis of oocyte
  • partial digestion of follicle wall = opening at ovulation
  • development of follicle wall into corpus luteum
    
    • secretes oestrogen (positive feedback) and progesterone
• progesterone
  
  • rise at start of luteal phase
    
    • drops back at the end
  • thickening and maintaining endometrium
  • inhibits FSH and LH (negative feedback)

Question 61

What are different fertilisation types?

Answer 61

• internal (terrestrial animals)
  
  • gametes would dry
    
    • close proximity
• external
  
  • bringing egg into proximity with sperm
  • risks: predation, temperature, pH
    
    • aquatic animals

Question 62

What happens the first stage of fertilisation?

Answer 62

• acrosome reaction
  
  • corona radiata = layer of cells closest to zona pellucida
  • zona pellucida = coat of glycoproteins around egg
  • acrosome = membrane-bound sac of enzymes
    
    • in sperm head
    • digest zona pellucida and corona radiata (+ flagella action)

Question 63

What happens at stage 2 of fertilisation?

Answer 63

• membrane on the tip of sperm
  
  • proteins that bind to egg membrane
• first one to get through binds
  
  • fusion of membranes
  • sperm nucleus enters = fertilisation

Question 64

What is the cortical reaction?

Answer 64

• sperm activates egg
  
  • cortical granules = vesicles near egg membrane
    
    • contents released by exocytosis
      
      • digestion of binding proteins
        
        • no more binding
        • zona pellucida hard
          > prevention of polyspermy

Question 65

What happens at stage 3 and 4 of fertilisation?

Answer 65

• fusion of plasma membrane of oocyte and sperm
  
  • sperm DNA into oocyte
• meiosis II completed
  
  • mature ovum + polar body

Question 66

What happens at stage 5 of fertilisation?

Answer 66

• male and female pronuclei
  
  • chromosomal material decondenses
    
    • in ovum after meiosis
• no distinction in nuclei
• DNA replication in pronuclei

Question 67

What happens at stage 6 of fertilisation?

Answer 67

• membranes of pronuclei breakdown
  
  • chromosomes condense
  • mitosis
    
    • uses centrioles from sperm

Question 68

What happens during early embryonic division?

Answer 68

• no size change
  
  • mitosis (identical cells)
  • morula formed
  • 4 days after fertilisation
• unqualified division = formation of blastocyst
  
  • 5 days after

Question 69

What is a blastocyst?

Answer 69

• unequal mitotic division + migration of cells (making hollow ball = blastocyst)
• 7 days —> blastocysts in uterus (125 cells)
  
  • moved by cilia in oviduct wall
  • zona pellucida breaks down
• blastocyst needs external source of food
  
  • sinks into endometrium = implantation
  • exchanging materials with mothers blood
    
    • placenta formation

Question 70

What is hCG?

Answer 70

• human Chorionic Gonadotropin (hCG)
  
  • produced by early embryo and placenta
  • maintains corpus luteum for first week —> progesterone necessary for endometrial activity
    
    • later placenta starts producing progesterone
    • corpus luteum degrades

Question 71

What is placenta?

Answer 71

• made out of foetal tissue
  
  • contact with maternal tissue
  • placental villus (foetal tissue)
    
    • increase with progression of pregnancy (foetus needs food)
    • maternal blood in inter-villus
      
      • small distance between maternal foetal blood
        
        • placental barrier = cells between
          
          • selectively permeable
• foetus also develops amniotic sac
  
  • support for foetus

Question 72

What are the hormones released by placenta?

Answer 72

• oestrogen and progesterone
  
  • sustaining pregnancy
    
    • no corpus luteum
• danger of miscarriage in the switch

Question 73

What happens at the end of childbirth?

Answer 73

• progesterone inhibits oxytocin and contractions of myometrium
• foetal signal to placenta —> no progesterone
  
  • oxytocin
• oxytocin —> contraction of muscle fibres —> stretch receptor signal to pituitary gland to increase oxytocin —> more contractions
  
  • positive feedback
• cervix dilates
  
  • uterine contraction burst amniotic sac (water breaking)
• uterine contractions push baby

Question 74

How does child labour work?

Answer 74

• head close to cervix
• amniotic fluid released
  
  • baby into vagina
• baby pushed out
• umbilical cord cut, breathing
  
  • placenta expelled

Question 75

What are the steps of in vitro fertilisation?

Answer 75

• step 1: down-regulation
  
  • drug each day –> pituitary stops secretion of FSH and LH
    
    • no oestrogen and progesterone
  • suspension of cycle
• intramuscular injections of FSH and LH daily for 10 days
  
  • follicle development
    
    • higher concentration, more follicles = superovulation
• injection hCG to stimulate maturation
• micropipette on ultrasound scanner to take eggs
  
  • incubated
• embryo placed in uterus
  
  • extra progesterone as tablet in vagina (uterus lining maintained)