multicellularity Flashcards
1
Q
Molecular clock
A
-DNA sequences mutate overtime by mutation -By comparing DNA sequences of similar species, we can infer the sequence of the common ancestor - the rate of mutation can be use to find out when the ancestor wasn’t extinct
2
Q
The transition form unicellular to multicellular
A
Occur through several steps -Aggregation of cell into cluster -Intercellular communication within the cluster -Specialization of cell within the cluster -Organization of cell into groups (tissue) * This evolution has occur independently for at least 6 times
3
Q
What does cell multicellularity enable
A
- Increase in size - Cell specialization - Increase structural and functional complexity - Creation of a stable environment - Exploitations of new environmental niche
4
Q
Embryogenesis in plant and animal
A
- Multi-cellular organism develop form a zygotes as a result of embryogenesis - During embryogenesis, specific cell type are produced
5
Q
What determine cell specialization
A
- the expression of gene
6
Q
What is triploblastic and diploblastic
A
Triploblastic have 3 germ layer: ectoderm, mesoderm and endoderm (most animal are triploblastic) Diploblastic only have two germ cell layer
7
Q
cell specialization in plant
A
- The basic body of the plant forms in early embryogenesis - Cell specialization occur along the apical-basal and radial axes -plant cell does not have germ layer - development in plant is an ongoing process. they make new organ as they growth
8
Q
Requirement of multicellularity
A
- A barrier to maintain their internal environment and keep it stable - Use of diffusion or transport system for gaseous exchange - intracellular communication by electrical or chemical messenger
9
Q
Plant grow strategy
A
-having organs system that cover a large area in order to collect limited resources +shoot system to capture sunlight +root system to absorb water and mineral - Growing continuously to obtain more resources in a larger area +primary growth: longitude +secondary growth: radial - continuous growth is related to phytomer
10
Q
Plant cell wall
A
- provide semi-rigid structure - provide a barrier to counter infection - also grow as the plant cell grow - made up of polysaccharide, cellulose hemicellulose and pectin - pectin is a major component of middle lamella - cellulose fibril form via hydrogen bond (high tensile strength)
11
Q
How does plant cell expand
A
-water enter the cell, causing the vacuole to grow bigger and form turgor pressure - expansin weaken non-covalent bond in the plant cell wall, allowing it to expand
12
Q
Key step in plant embryogenesis
A
- Zygote under asymmetrical division form two cell stage - oriental division into octant stage - more oriental division and cell expansion for heart stage - further elongation into a mature embryo
13
Q
Process in embryogenesis
A
- Determination: commitment to a particular cell fate before characteristic become apparent -differentiation: cell acquire different characteristic due to gene expression -morphogenesis: formation of tissue and organ by specialise cell -Growth: increase in plant and organ size by cell expansion
14
Q
Apical meristem
A
- formed during embryogenesis but are kept inactive until seed dispersal - associated with only primary growth - have self-renewing stem cell which acts as a source of cell for organ and three tissue formation
15
Q
Secondary growth
A
- increase thickness by bark production - controlled by lateral meristem called cambium - stem cell is involve
16
Q
Different plant tissue type
A
-Dermal: form a single layer know as an epidermis -cuticle: a waxy layer which control water loss, gas exchange and protection form the environment -Ground: locate between the dermal and vascular system ( the bulk of the plant body) - Vascular system: transporting tissue that form a network in the plant( xylem water, phloem mineral and nutrient)
17
Q
Tropism
A
-Growth toward or away from a stimuli - controlled by auxin
18
Q
How does Auxin working
A
- it bind with proton pump into the cell, pumping proton into the cell -low pH activate expansin causing cell to growth
19
Q
Basic transport need of plant
A
Plant must acquire water and mineral in the soil via the roots Water for photosynthesis, structural support, transport and cooling Micro and macronutrient for synthesis of organic compound
20
Q
Water potential
A
-The tendency of a solution to take up water through a semi-permeable membrane -Move from high water potential to low Total water potetial= solute putential+pressure potential -plant cell turgor is equal to pressure potential
21
Q
Water uptake by root cell
A
-Water and dissolved mineral move through cell by 2 pathway -Apoplast: move through the cell wall and intracellular space (rapid and unregulated) -Symplast: move through cytoplasm and plasmodesmata (slow and regulated) -The apoplast pathway is stoped at endodermis due to Casparian strip
22
Q
Movement in xylem
A
-Xylem is composed of long tubular vessel and vessel element -Transpiration occurs in the leaves, generate surface tension -This cause water to be drawn out from veins causing tension in the xylem -Cohesion of water cause it to be passively drawn up the xylem -Tension also cause water to enter xylem via osmosis
23
Q
Control of osmosis through light
A
-light activate photoreceptor -signal cascade activate proton pump -H+ pump out of the cell -K+ enter the cell down the electrochemical gradient -the gradient is maintained by H+, Cl- pump -Decrease in water potential cause water to enter the cell -It become turgid, guard cell bend and reveal the stoma
24
Q
Transport of sugar in cell
A
-The movement of carbohydrate through cell is called translocation -Tissue can be sink (consumer) or source(producer) at different time
25
Phloem sieve tube element
-Phloem is comprised of sieve tube element (living cell) -Sieve tube element has a cell wall, plasmodesmata but no nucleus, cytosol or Golgi body -Sieve tube element is maintained by a companion cell
26
Mass Flow Hypothesis
-Sucrose and other solute are actively transported into sieve tube element by companion cell -This cause water potential to lower and water in adjacent tissue move in via osmosis -Increase in pressure cause the mass to move away -Active transport take sucrose into the sink, causing water potential to increase -Water leaves via osmosis, the pressure in normalise
27
Establishment of germ cell layer
- At the gastrula stage, cell partition into germ layer - Ectoderm gives rise to the external surface and nervous system - Mesoderm gives rise to internal tissue and connective tissue -endoderm gives rise to cell that line the alimentary canal of different organ -Cell fate is determine at later stage
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Morphogenesis
-Morphogenesis is how cell organize and arrange themselves for the final body. This is achieved by: - Dividing - Dying(apoptosis) - Changing shape - Moving around - Adhering to each other - Forming tissue - Break free of epithelial connection
29
Stem cell help on the maintenance of the body
- In regenerative tissue, cell die and need to be replaced - New cell come form stem cell, undifferentiated cell that can divide continuously - When stem cell divide, one daughter cell become specialise while the other remains a stem cell
30
Cell potency
The ability of a cell giving rise to another cell is called potency -Totipotent: produce all kind of cell -Pluripotent: produce all but extraembryonic tissue like placenta -Multipotent: can produce several types of cell -Unipotent: can only produce one type of cell
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induced Polipotent stem cell
- Skin cell can be extracted and revert back into an iPS cell -It can then be used to produce other tissue - use for therapeutic purpose
32
Tissue type in animal
-There are four main tissue type in animal -Nervous tissue -Epithelial tissue -Connective tissue -Muscular tissue
33
Connective tissue
-support and connect other tissue -consist of a few cells that contribute to an extra-cellular matrix -ECM is an interlocking mesh of fibrous protein and some ground within some ground material usually liquid but can be solid such as bone -Have a wide range of functions: form connection with muscle and bone, rigid support for delicate tissue, transport, energy storage, flexibility, shock-absorbing and friction-reducing
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Epithelial tissue
- a two-dimensional sheet of cell that covers the body surface, internal cavities and internal tubes - Provide a barrier role for the body to the outside world and between organs
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Epithelial cell are?
-apical basally polarise contain cell to cell junction: -tight junction that prevent passage of small molecule - adherence junction and desmosome for mechanical supports -Gap junction allow cell to cell communication
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Nervous tissue
- Gather info about the external and internal world -Process info -control physiology and behavior of the body
37
Neuron
-There is three primary types of neuron: sensory, interneuron and motor -each neuron have: dendrite (tiny projections), Soma (body), axon (to conduct electrical signal) and form synapse with tissue or other neurons -Neuron integrate signal form another neuron which can be inhibitory to excitatory - When a threshold is reached, an action potential is generated and travel down the axon -the electrical signal passed through synapse to the target cell
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Organs
-Organs are composed of all four type of tissue - there are 11 organ system in the body -organ system work together
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Muscle tissue
There are three types of muscle tissue
- Skeletal muscle that binds to the skeleton and under voluntary control
- cardiac muscle form wall of the heart - smooth muscle surrounds internal organ
- Muscle contraction is caused by an ATP dependant motor called myosin pulling on Actin filament
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The surface area to volume problem
- The surface area to volume is too low
- distance to the internal environment is too great for diffusion
41
why does some animal lack a circulatory system?
- all cell has a short distance to the environment because the animal is:
- small
- flat
- porous
- hollow
42
Two types of circulatory system in animal
Open Circulatory system
- circulatory fluid empties into the body cavity
- fluid in the circulatory system is the same as those in the body cavity (hemolymph)
- used by anthropoid and majority of mollusc Closed circulatory system
- circulatory fluid contained in a network of vessel
- circulatory fluid is separate from interstitial fluid - the circulatory fluid is called plasma
- Used by: earthworm, vertebrate and cephalopod mollusc
43
Single circuit and dual circuit
-In fish, blood is pump through the lung and the entire body in a single circuit (low blood pressure) - in other animals, deoxygenated blood is pumped to the lung and return to the heart before it is pumped through the entire body again (high blood pressure)
44
Characteristic of Human circulatory system
- 4 chambered heart
- pulmonary and systematic circuit is separated
- different pressure in the pulmonary and systematic circuit
- organs are supplied in parallel
- liver receives blood directly from the intestine
45
Structure of a human heart
46
Cardiac cycle
- spontaneous beating of pacemaker cell
- electrical signal spread downward by the gap junction causes contraction of atria
- signal cause the activation of atrioventricular nodes
- the signal is passed down modified cardiac fibre
- cause coordinated contraction of the ventricle
47
Arteries, vein and capillary
* Arteries are thick, elastic and muscular ( able to support blood leaving the heart at high pressure)
* Vein have valves that ensure one-way blood flow of blood returning to the heart at low pressure (power by muscle contraction and gravity)
* capillaries have a thin cell wall to facilitate diffusion
*
48
Gas exchange in the lung
* Air enters the lung and fill the alveoli
* alveoli is cover by a network of capillaries
* incoming blood has low conc of O2 which diffuse in and high conc of CO2 which diffuse out
*
49
Exchange in the capillary
* Exchange occurs due to concentration gradient
* O2 and nutrient diffuse into cell which is at a lower conc
* CO2 and nitrous waste diffuse into the capillary due to high conc in the cell
50
Water potential in circulatory system
* Water potential = Pressure potential + Osmotic potential
* Water potential drop from arterial to the venous end
* fluid leave at the arterial end (filtration) and is reabsorbed at the venous end(reabsorption)
51
What is gaseous exchange?
* Movement of O2 and CO2 in opposite directions
* Cellular respiration
* Respiratory gases: O2 and CO2
Respiratory gas exchange is controlled by physical factors
Rate of diffusion =( surface area x partial pressure gradient x diffusion coefficient)/ diffusion distance
52
Enhancing diffusion maximises gas exchange
* Large surface areas
* Maximise the partial pressure gradient
* Minimise the diffusion that takes place in an aqueous medium
* Thin barrier (minimise diffusion distance)
53
Water air as gas exchange medium
* Air is a mixture of gases approximately 78% nitrogen, 21% oxygen, and only a small proportion of CO2 (currently about 500 ppm)
* Solubility of O2 in water is low compared to that of CO2
* CO2 is approximately 20 x more soluble in water than oxygen
* Very slow rates of O2 diffusion through aqueous medium
- There are many factors in water that can affect the diffusion rate: temperature, salinity and pressure
54
Diversity in gas exchange surfaces
- Body surface: gas diffuses into the cell through the surface area
- Trachea: gas enter the trachea and diffuse into tissue cell
- External gills
- Internal gills: one-way airflow ( have lamella on gill filaments). Some fish have counter-current airflow which maintain a gradient of O2 saturation over the full length of the exchange surface which lead to a higher per cent of oxygen saturation in the blood
- Lung: two-way airflow
55
The Human Lung
* The human respiratory system includes nasal passages, mouth, trachea which is supported by cartilage rings, lung and diaphragm
* In the lung, trachea supply air for the bronchi which supply air to smaller vessel know as bronchiole and cluster of alveoli
* Surfactant coat the alveoli. it lowers surface tension so alveoli don’t collapse
56
Lung Ventilation
* Gas exchange is tidal
* Tidal volume is the normal amount of air exchanged when breathing at rest.
* Expiratory reserve volume is additional air that can be forcefully exhaled
* residue volume: the amount of air left after maximum exhalation
* Inspiratory reserve volume: the additional capacity of the lung that allows for the deepest breath
57
Protein carriers in blood
* In mammalian blood, O2 is carried in the blood by haemoglobin
* each haemoglobin is made up of 4 heme group. Each heme group contain a fe2+ ion
* At low pO2, only one oxygen is attached to the haemoglobin
* When oxygen is bound to it, the hemoglobin affinity for oxygen increase
* when three oxygen is bonded to it, the affinity increase further to reach 100% binding
58
Usage of oxygen in the blood
* Deoxygenated blood PO2 is at 40 mm Hg while fully oxygenated blood leaves the aorta at 100 mm Hg
* 25% is used during rest or light exercise
* 75% is held by the hemoglobin and can be released to tissue with low PO2
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Factors that can influence the haemoglobin dissociation curve
* High CO2
* Increased acidity
* BPG (2,3 bisphosphoglycerate)
60
Muscles oxygen storing molecule
* Myoglobin
* binds ONE oxygen per myoglobin increased O2 affinity (greedy) compared to haemoglobin
* binds oxygen at lower partial pressure (concentration)
61
How is CO2 transported in blood
62
Respiratory adaptions: How do marine mammals hold their breath for so long during underwater dives?
* Increased concentrations of haemoglobin
* Increased concentration of myoglobin (10x more than in humans)
* Reduce their heart rate
* Reduce blood flow to extremities and organs
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Cell communication and breathing
* Chemoreceptors (chemical receptors)
* Medulla (pCO2/pH)
* Carotid bodies (mainly pO2, but also pCO2/pH)
* Aortic bodies (pCO2/pH and pO2)
* Signal sent to breathing control centre
* Ventilation rate adjusted via phrenic nerve (diaphragm) and thoracic nerve (intercostal muscles)
64
Diversity of digestive systems
* Unicellular protists have intracellular digestion
* Simple digestive systems: A cavity with one opening (called mouth). Food is digested by a combination of Extracellular digestion (digestive enzymes secreted) and Intracellular digestion (endocytosis)
* Complex digestive system: Digestion occurs in the lumen of the gut
* Crop – enlarged portion of the digestive system (in invertebrates and birds) that temporally store food
* Gizzard – mechanical digestion with grit or stones (in birds, earthworms, some fish, some reptiles)
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What is the energy source for animals?
* Animals are heterotrophs so food is the source of their energy: Carbohydrates, Lipids, Proteins
* Animals require other essential nutrients to be healthy and be able to reproduce:
• amino acids (9 in humans)
* • fatty acids (2 in humans)
* • Vitamins (organic substances)
* • Minerals (inorganic substances)
* • water
* Animals use the chemical groups present in their food to make other molecules required
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Specialisations in diet
* Carnivore
* Omnivore
* Herbivore
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How much do animals need to eat?
It depends on several factors:
* Metabolic rate (varies with age, reproductive stage, activity)
* Body mass and environmental conditions
* Types of food
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Metabolic rate and body mass
* Size plays a big role in metabolic rate
* energy per unit body mass SMALL animals need more food
* Small animals have a larger surface area to volume ratio than larger animals
* More energy expended by small animals generating heat
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Role of the digestive system
* Digestive systems break down large molecules into smaller molecules• Molecules must be small enough to be transported across a membrane in the gut
* • Types of digestion: Mechanical digestion and Enzymatic digestion
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Mammalian digestive system
* Mouth/buccal cavity (incl. salivary glands)
* Pharynx
* Oesophagus
* Stomach
* Small intestine (incl pancreas, liver)
* Large intestine (incl. caecum
) • anus
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Mouth or buccal cavity
* Mechanical digestion (teeth and jaws)
* Increases the surface area of food
* Mixes it with saliva
* Saliva contains the enzyme amylase
* An enzyme that hydrolyses starch -\> maltose (a disaccharide, sugar)
72
Mammalian teeth
* Incisors (cutting food into bite-size pieces)
* Canines (gripping, killing prey and ripping flesh)
* Pre-molars – shearing
* Molars – grinding
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Stomach
* Mechanical digestion
* Muscular walls cause stomach churning
* Storage vessel
* Enzymatic digestion
* Acidic (HCl, pH 1-2)
* Enzymes: mostly pepsin and other proteases
* Food reduced to chyme in the stomach
sphincter controls the movement of objects in and out of the stomach
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The small intestine
* Pyloric sphincter controls the release of chyme into the small intestine
* Small intestine is a muscular tube with 3 parts: duodenum, jejunum and ileum
* Enzymatic digestion occurs in the duodenum
* nutrient absorption occurs in the jejunum and ileum
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Liver and pancreas
* Liver and pancreas secrete digestive fluids into the duodenum
• Liver Produces bile (emulsifies lipids) a mixture of acids, salts, phospholipids, cholesterol
* • Bile concentrated and stored in gallbladder
* Solidification of the bile salts and cholesterol would lead to the creation of gall stone
* Pancreas Secretes digestive enzymes including lipases, amylases, proteases, and nucleases
76
absorption of nutrient in the small intestine
* The small intestine has a large surface area to maximise absorption by having intestinal fold, villus and microvillus
* Approx. 90% of the absorption of nutrients occurs in the jejunum and ileum
* Absorption of nutrients into bloodstream (diffusion and facilitated diffusion, active transport, secondary active transport) in the jejunum and ileum
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Large intestine or colon (and caecum)
Caecum
• Blind ended sac
• Cellulose digestion (prominent in herbivores)
Large intestine
* Water absorption
* Formation of faeces
78
Diet of Animal
Generalist can make use of a variety of different resources
specialist has a limited diet
79
Adaptation of carnivorous digestive system
Protein is easy to digest
* short, simple digestive tracts
* Short intestine, small caecum
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Herbivores and digesting cellulose
* Plant cell walls made of cellulose
* Most abundant carbohydrate on the planet
Their digestive system are
* long, complex digestive tracts, with a large caecum
* Most animals do not produce cellulase
* Symbiotic bacteria and protists live in their digestive tracts and digest cellulose
* Two types of vertebrate herbivores (based on where the CELLULOSE is digested) • Foregut fermenters • Hindgut fermenters
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Foregut fermenters
* Digestion of cellulose occurs before the stomach in the fore stomach
* larger stomach
ruminants
* Regurgitate their food and chew it to reduce the size of food particles
* Food are fermented in the Large foreguts which have four chambers rumen, reticulum, omasum, and true stomach
83
Hindgut fermenters
* Digestion of cellulose occurs after stomach
* Digestion of cellulose occurs after stomach
* e.g. horse, koala, wombat, pig, rabbit
* Bacteria (only) present in the caecum and proximal colon therefore these parts of the digestive tract are prominent. They are not washed away during digestion
Some hindgut fermenter are Caecotrophy
* Specialisation of eating your own faeces (e.g. ringtail possum)
* Two types of faeces produced • Protein rich (caecotrophs)
* Normal faecal pellets
* Protein in the faeces is recovered in the second pass through the digestive tract
84
Homeostasis
* In a multicellular organism, cell depend on their immediate environment: interstitial fluid
* Many factors must be maintained within the physiological range: temperature, pH, osmotic potential, gas level and conc of mineral
* Homeostasis is the maintenance of a relatively stable internal environment despite changes in internal and external factors
85
Stimulus respond model
For a system to respond to a stimulus it requires three thing
* A receptor that detects the change from the desire equilibrium value and send a signal to the control centre
* A control centre that receive and process information and communicate with an effector
* An effector that respond to the change (to correct it or amplify its effect)
These cell can communicate through electrical signal or chemical signals
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Hormone group
* amine hormone
* steroid hormone
* protein hormone
87
Hydrophilic vs lipophilic protein
Hydrophilic
* secreted from the cell via exocytosis
* bind to surface membrane receptor
lipophilic
* diffuse through membrane
* bind to hydrophilic transporter protein
* diffuse through the target cell membrane and bind with intracellular receptor
88
Importance of blood glucose in the body
* Blood glucose must be kept at 4-8mmol/L
* Low blood sugar level cause hypoglycemia which leads to seizure and loss of conscious
* High blood level cause hyperglycemia which leads to damage cell and increases the risk of heart disease, stroke, kidney disease and vision impairment
89
Role of pancreas in glucose control
* high glucose level in the blood is detected by B-islet which secrete insulin
* Low glucose blood level is detected by A-islet which secrete glucagon
90
Insulin
* Insulin binds to insulin receptor in the liver cell
* The binding lead to two effects: an increase in glucose transporter in the membrane and the activation of glycogen synthase ( which convert glucose into glycogen)
* blood sugar level goes down
91
Glucagon
* glucagon bind to glucagon receptor on the liver cell
* This cause the activation of glycogen phosphorylase and inhibition of glycogen synthase
* this lead to the breakdown of glycogen into glucose
* blood sugar level is increase
92
Cellular communication in plant
* They also respond to external and internal cue similar to animal
93
Plant hormone
* 6 class of hormone
* Each hormone have any different role
* Some hormone have an overlapping function (Auxin, Gilbereline)
* Some hormone work synergistically, other antagonistically
* Plant hormone can be synthesized in different part through the plant
94
Auxin/Glibereline pathway
* In the absence of hormone, cellular are kept inactive by a repressor
* Hormone bind to a receptor, allowing it to enter the nucleus
* the complex bind to the repressor, leading to the degradation of it
* This trigger a cellular response for the hormone
95
Role of ABA
* On a hot windy day, plant become dehydrated because the water potential of the air becomes very negative
* This change in water potential is detected and cause the synthesis of ABA in leaves
* This causes the movement of K+ out of the cell and water
* the stomata close despite it being a sunny day. reduced water loss
96
Pupil respond to bright light
* Light is detected by photoreceptor which activates a series of neuron. eventually, lead to the activation of constrictor muscles that close up the pupil
97
Resting potential
The resting potential is established by two channels:
* The Na/K pump that moves 3 Na out for every 2K they take in(active transport)
* A leak channel that allows K to move out of the cell, down its concentration gradient
* an electrochemical equilibrium is reach with high conc of NA outside and K inside with a potenrial of -60mV
98
Depolarisation
* the arrival of an action potential causes the region to be slightly depolarised. leading to the open of some NA voltage-gated channel
* The influx of NA cause more channel to open, furthering depolarisation
* When a threshold is reached, the positive feedback loop ensures the creation of an action potential
99
Repolarisation
* When the membrane reaches 40mV, Na channel close and K channel open
* K ion leaves the cell, reducing membrane potential. it even undershoot resting potential a bit.
* The voltage-gated channel close and remain inactive for a while. This is known as a refractory period and prevent the ap to travel back
* The NA/K pump and K leak restore the resting potential
100
Faster ap method
* Invertebrate, glial cell warp around the axon, creating insulated section. this is known as myelination
* Unmyelinated gap is known as node of Ranvier
* This allow signal to jump form gap to gap. up to 20 time faster know as saltatory conduction
101
What happens at the synapse
* Action potential arrive
* voltage-gated Ca2+ channel open
* Increase in Ca2+ lead to exocytosis of synaptic vesicle
* neurotransmitter bind to a receptor of the targeted cell
* allow the inflow of Na+ which generate an action potential
102
Ferguson loop
* Baby pushing against the cervix activate stretches of receptor neuron
* sensory neuron sends a signal to the brain(hypothalamus)
* pituitary gland is stimulated to release oxytocin
* oxytocin causes the uterus to contract
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stimuli that make your body feel hungry
External cues
* smell and/or sight of food
* thought of food • habits
* Emotions
Internal cues
* Nutrient availability (empty stomach)
* Low blood sugar
* Long term energy reserves (weight loss/gain)
104
Hormones regulation of appetite
* There are multiple brain areas and signals involved • Short-term (hours) ghrelin
* Long-term (days/weeks) leptin
105
Ghrelin
Ghrelin is a short-term signal that regulates appetite
• When stomach is empty ghrelin is released by stomach cells
* stimulates appetite
* prepares the stomach for food
Ghrelin levels fluctuate
* levels rise before meals
* levels decrease after meals
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Control of Grelin
The hypothalamus is the control centre for hunger
* Receptors for ghrelin in the hypothalamus
* The response is nervous impulses that make us feel either hungry or full (satiated).
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Leptin
regulates body weight on a longer time scale
• Adipose (fat) tissue produces leptin
* Leptin is a peptide hormone
* Leptin levels increase when fat mass increases Resulting in suppression of appetite
* Leptin levels decrease when fat mass decreases Resulting in increased appetite
Leptin is detected by the hypothalamus leading to two different sets of neurons • stimulate appetite (NPY/AgPR) • reduce appetite (MSH )
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How does the body sense something is sweet
In the mouth:
• “Taste buds” are sensory cells in the mouth, mostly on the tongue
• These cells fire neurons that are connected to the brain
In the gut:
• Special epithelial cells that send signals to the brain
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Artificial sweeteners
* Body “tastes” them as sweet
* Have no (or less) calories measure of usable energy define
* Substituted in foods to reduced energy consumption
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distinguish between sugar and artificial sweeteners
* Specialised small intestinal epithelial cell called neuropods in mice guts can distinguish between sugar (calories) and an artificial sweetener (no calories)
* Neuropods are electrically excitable cells that communicate with nerves
* Send different signal to the brain depending on whether sugar or a sweetener has been consumed
* Sucralose is a common artificial sweetener
* Digestive enzymes cannot break it down
* Sugar and sucralose detected by different receptors in the membranes of the neuropods
* Communicate with the nervous system with different signals
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Digestive system microbiome in humans
* Human gut microbiome – more than 100 trillion microbes (including bacterial, protists, fungi and viruses)
* Mostly found in our large intestine
* Humans ingest many polysaccharides that are indigestible by human digestive enzymes
* Some microbes produce (and secrete) enzymes that can degrade the polysaccharides humans can’t
* Some microbes ferment (anaerobic respiration) certain polysaccharides and produce short-chain fatty acids
* Most insoluble dietary fibre not digested by us or the microbes
113
Significance of sexual reproduction
* Union of haploid eggs and sperm
* In mammals this union occurs through internal fertilisation (i.e. delivery of the sperm close to the egg by a penis to the egg)
* Produces offspring that are genetically different to their parents
* Generates variation within populations
* Sexual reproduction is expensive for animals
114
Sex determination in humans
* Chromosomal • XY, XX (and variations XO, XXY)
* The gene controlling maleness is on the Y chromosome • SRY (sex determining region on the Y chromosome)
* In early embryo development there are bipotential gonads.
* Embryos producing the SRY protein develop testes that produce sperm (i.e. if they possess the Y chromosome)
* In the absence of SRY protein (i.e. no Y chromosome) the embryos develops ovaries that produce eggs.
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The gonads (ovaries and testes) production of sex hormone
The gonads (ovaries and testes) produce 3 major steroid sex hormones
The precursor of the steroid sex hormones is cholesterol
* Androgens (principally testosterone)
* Oestrogens (principally oestradiol)
* Progesterone
* Both males and females produce all these hormones, but at different concentrations.
116
Human Female reproductive anatomy
* Consist of: Labia majora, Labia minora, vagina, cervix, uterus, oviduct and the ovary
* Egg are mature in and release by the ovary
* Egg are then taken by the oviduct to the uterus. fertilisation occurs in the upper region of the oviduct
* The blastocyst implant itself in the endometrium where embryonic development occur
* The neck of uterus is the cervix which remain close and dilates during childbirth
Sperm is deposited in the vagina during copulation. it is also a birth cannal
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Ovarian cycle
* Once every month between puberty and menopause, 6-12 primary oocytes began to mature. they have a layer of cell (follicle) surrounding it
* The follicle nourish the development of oocyte and release oestrogen
* After 1 week, usually, only one oocyte continues to develop
* At ovulation, the follicle rupture, releasing the oocytes
* The follicle then forms the corpus luteum which release oestrogen and progestogen
* If fertilisation doesn't occur, the corpus luteum degenerate
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Folliculogenesis
* Development of the follicle (follicle includes egg, fluid-filled sac, theca cells, granulosa cells)
* Granulosa cells nourish the egg
* Theca cells
* Within the follicle occurs the oocyte development of oogenesis
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Oogenesis
* Primary oocytes are dormant until puberty
* Meiosis occurs to produce the mature egg (ovum) with one set of chromosomes
* Asymmetric division means that the egg gets most of the cytoplasm during the meiotic divisions
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Uterine cycle
* Uterus lining is called the endometrium
* For the first 4-7 days of the cycle the lining is sloughed off (bleeding, menstruation)
* After ovulation progesterone produced by the corpus luteum stimulates vascularization of the endometrium (increase in blood supply)
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Ovarian hormones
Oestrogen
* Produced by the granulosa cells in the follicle • Acts via oestrogen receptors
* Regulates oviduct (Fallopian tube), uterus, cervix, vagina and other sex organs
* Prepares endometrium for implantation (increases vascularization, blood supply)
• Promotes oestrus (or mating) behaviour
Progesterone
* Produced by the corpus luteum
* Acts via progesterone receptors
* Regulates oviduct, uterus, cervix, vagina, other sex organs • Prepares endometrium for implantation (by maturing spiral arteries)
* Modulates effects of oestrogen, STOPS follicle growth
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Hormonal control of reproduction in human females
* Co-ordination of ovarian and uterine (menstrual) cycles by the same hormones transported by blood
* Preparation of the uterus for a foetus every month
* Co-ordination involves several endocrine organs that work together
* Regulation of reproduction occurs by hormonal control and feedback loops
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Hypothalamus and Pituitary gland
Major control centre of homeostasis is the hypothalamus
* The hypothalamus is the link between the nervous and endocrine systems
* Pituitary gland - separated from the hypothalamus by a stalk containing the portal blood vessels, underneath the brain • Anterior • Posterior
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Hypothalamo-Pituitary-Gonadal axis (HPG axis) act together in the hormonal control of reproduction
* The hypothalamus secretes gonadotrophin-releasing hormone (GnRH) that acts on anterior pituitary
* GnRH release is in pulses (scientists still finding out what controls the amplitude and frequency of the pulses)
* Anterior pituitary produces the gonadotrophins
* Follicle-stimulating hormone (FSH)
* Luteinising hormone (LH
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Anterior pituitary hormones in the HPG axis (gonadotrophins)
Follicle stimulating hormone (FSH)
• Stimulates folliculogenesis
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• Acts on granulosa cells to stimulate conversion of androgens to oestrogens
Luteinising Hormone (LH)
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* Stimulates theca cells to produce androgens
* A surge in LH stimulates ovulation
* Stimulates formation of corpus luteum
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Menstrual cycle:
During menstruation, the anterior pituitary gland secretes FSH and LH
- Concentrations of FSH and LH increase over the next few days à control activity of ovaries – responsible for ovulation
- In the ovary, one follicle becomes the ‘dominant’ one
- the presence of FSH and LH stimulates cells surrounding the follicle to secrete oestrogen
- the production of oestrogen induces a negative feedback and decreases the production and concentration of FSH and LH
- Oestrogen stimulates the endometrium to grow, thicken and develop numerous blood capillaries
- There is a surge of LH secretion and a slight increase in FSH secretion. The high concentration of LH causes the follicle to burst and shed the gamete into the oviduct. The remnants of the follicle collapse and forms the corpus luteum (yellow body)
Corpus luteum secretes:
progesterone: inhibits the anterior pituitary gland from secreting FSH and LH à no more follicles develop and some oestrogen
- they maintains the uterus lining so that it’s ready to receive an embryo if fertilisation occurs
- Low stimulation of the corpus luteum causes it to degenerate. As a result, less oestrogen and progesterone is secreted and their concentrations decrease
endometrium is not maintained so menstruation begins
releases inhibition of anterior pituitary gland cause FSH gets secreted à another cycle begins!
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Reproductive anatomy of males
* Penis (contain gland penis)
* Urethra
* Erectile tissue
* Cowper’s gland
* Prostate gland
* Ejaculatory duct
* Seminal vesicle
* Male sex organs produce sperm and deliver sperm to the female reproductive tract.
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Anatomy of the testis
* Spermatogenesis occurs from puberty
* Sperm produced in the seminiferous tubules
* Sperm stored in the epididymis
* Vas deferens transports sperm from epididymis to urethra (via ejaculatory ducts)
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Seminiferous tubules
* Spermatogenesis occurs from the outside to the inside in seminiferous tubules
* Sperm with flagella are released in the lumen of the seminiferous tubules
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Testis: structure and function
1. Sperm production (spermatogenesis)
* occurs in seminiferous tubules
* controlled by Sertoli (nurse) cells
• Sertoli cells can convert testosterone to oestradiol to facilitate spermatogenesis
2. Hormone production
* Testosterone produced in Leydig cells (interstitial space in between tubules)
* steroid, androgen
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Testosterone production
* Produced by Leydig cells
* Steroid hormone
* Acts via androgen receptor in cells
* Can be converted to oestradiol in Sertoli cells to aid spermatogenesis or to dihydrotestosterone DHT (more potent androgen)
* Stimulates accessory sex organs (e.g. prostate gland and seminal vesicles)
* Modulates secondary sex characteristics (e.g. courtship, aggression, deep voice, increased muscle mass, body hair)
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Spermatogenesis
* Male germ cell undertakes mitosis division, growing to primary spermatocyte
* Meiosis then occur, forming secondary spermatocytes and into spermatids.
* Spermatid mature into spermatozoa and continue to grow
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Structure of mature sperm
Specialised cell for motility (with 3 parts)
1. Head
• Acrosome containing enzymes to digest the eggs outer coating
2. Mid-piece
• Lots of mitochondria (to power the journey through the female reproductive tract)
3. Tail (flagella)
• (9+2 microtubule arrangement)
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What factors can affect the quality (count, motility, morphology) of male sperm
* Diet
* Smoking
* Drugs, including steroids and recreational drugs
* BMI (body mass index)
* Alcohol consumption
* Exposure to heat (saunas, working in hot temperatures)
* Acute viral illness
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Hypothalamo-Pituitary-Gonadal axis (HPG axis) in male
* GnRH from hypothalamus stimulates release of LH and FSH from anterior pituitary
* LH stimulates Leydig cells to produce testosterone
* FSH stimulates spermatogenesis by acting on Sertoli cells
* Testosterone positively affects accessory sex organs (e.g. seminal vesicles, prostrate) and secondary sex characteristics
* Negative feedback regulates testosterone and spermatogenesis.
* Testosterone inhibits GnRH and LH secretion, inhibin produced by Sertoli cells inhibits FSH secretion
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Copulation and Fertilisation
* Sexual stimulation triggers the nervous system and the result is penile erection
* Penile erection aids copulation
* Sperm is moved to ejaculatory ducts by contraction of smooth muscle in vas deferens
* Semen ejaculated by contractions of muscles at base of penis (orgasm)
* Copulation in mammals results in internal fertilization
* Fertilisation, fusion of egg and sperm to form a zygote, produces a hormone
* Human chorionic gonadotropin (hCG)
* Stimulates corpus luteum to continue producing progesterone and oestrogen
* Pregnancy kits detect hCG
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Contraceptive methods
* Fertility can be controlled by humans
* Variety of methods
* physical barriers e.g. condoms, diaphragm, tubal ligation
* Chemical e.g. contraceptive implants, Intrauterine devices (IUDs), oral contraceptive pill
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How does the oral contraceptive pill work?
* Combined oral contraceptive contains synthetic progesterone and oestrogen
* Works by suppressing GnRH, FSH and LH
* Prevents follicle growth and ovulation
* Increases cervical mucus thickness to stop sperm
* Continual exposure to progestin and oestrogen thins endometrial lining, hampers implantation
* Approximately one-third of women using contraception use the oral contraceptive pill
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