Module 3 - Multicellularity Flashcards
Evolution of multicellularity
Molecular clocks and fossil records are used to estimate divergence in evolution + when plants and animals diverged
Molecular clocks = used in fossil records to estimate time of divergence based on DNA sequences differences (takes certain amount of time for a base to mutate)
Mutation in genomes (1-2 bases only) can calculate time differences and common ancestors
Common Ancestor of Plants and Animal
Most likely to be a single-celled protist named Choanoflagellate (unicellular)
Evolution of Complex Multicellularity
Evolution of complex multicellular organisms has happened independently several times: fungi (2x), green-algae, red algae, brown algae and animals
Process of Multicellularity (transition)
- aggregation of cells into a cluster
- intercellular communication within the cluster
- specialisation of some cells within the cluster
- organised arrangement of cells into groups (forms tissues)
multicellularity must’ve required intercellular communication to coordinate cellular activity which allows for specialisation homeostasis, ensuring cells work in unison, ability to get signals from external cells
Types of intercellular communication
Chemical - activating nearby cells (e.g. ligands: which are local) or through bloodstream (e.g. hormones: which are systemic)
Electrical - activates very specific target by travelling long distance rapidly
Advantages of Multicellularity
- Increase in size (introduced new preys/predators)
- Cell specialisation (group of cells work in unison e.g. flagella for movement or cells dedicated to one task e.g. reproduction)
- Structural + Functionality complexity
- Creation of internal stable environment allowing exploitation of new environmental niches
- ALL LEADS UP TO ALLOWING COMPLEX TO USE ENERGY MORE EFFICIENTLY
Example of Multicellular advantage
Volvox is larger than Chlamydomonas making it less susceptible prey to Copepod (filter-feeders)
No need to switch cell types to perform tasks
Outside cells to provide movement
Outer cells create protection for inner cells
Protected inner cells for reproduction
Development of Multicellular organisms (animals)
Embryogenesis - process of multicellular complexes developing from zygotes
Zygote = single-celled
- specificity occurs from early on (plant + animals cells can be differed)
- multiple cell divisions of specialised cells occurs along a major spatial axis (radial = animals, apical/basal axes = plants)
GENE EXPRESSION DETERMINES CELL SPECIALISATION
Animal Embryogenesis
Gastrulation = cells folding inwards to form an internal cavity whilst others break off and move inside (endoderm folds inwards whilst mesoderm is inside components)
Animal germ layers:
Ectoderm - outer layer
Mesoderm - inside layer of zygote (in between ectoderm + endoderm)
Endoderm - inner layer of zygote
Tripoblastic = 3 germ layers (animal) Diploblastic = 2 germ layers (lacks mesoderm e.g. cnidarian)
Plant Embryogenesis
Plants do NOT undergo gastrulation and have no germ layers
Development is continuous from SHOOT APICAL MERISTEM and ROOT APICAL MERISTEM
3 tissues are present in plants:
Apical tissue
Basal Tissue
Radical Tissue
Requirements of Multicellularity
-Must have Barrier (to have internal environment and maintain homeostasis)
-Size limit
Too large/volume causes slow diffusion of materials
SA: Volume ratio limits cell size
When a cell increases in size, SA increases faster than volume
Ratio reduces as organism gets larger
Rate of diffusion of oxygen through water equation:
Time = (Distance^2) / 2 x 0.00001 cm2/sec
Allows all cells to be in certain proximity of external environment for diffusion (e.g. flatworms) or complexes that bring external environment into animal (e.g. hydra = hollow cavity or sponges = porous cavities)
-Must have internal transportation system
circulates extracellular fluids ensuring optimal gas exchange, waste removal, nutrient mobilisation, communication
-Communication
intercellular communication to coordinate cellular activities and respond to internal and external environment
(homeostasis, physical/chemical signals, cells working in unison, specialisation of cells)
Plant Growth Strategies (overcoming sedentary lifestyle)
-plants have continuous growth (allow to occupy new areas + responding to environmental cues)
primary growth - longitudinal (roots and shoots)
secondary growth - radial (thickness of stem)
-organ systems are suited to capture limited resources (large SA)
capturing sun (shoot system, leafs, stems, blades)
capturing water and nutrients (root system)
What is a Phytomer?
Functional unit that has continuous growth (shoot system) that consists of:
- leaf
- auxillary node
- internode
Plant Cell Wall Structure
- made up of polysaccharides, cellulose, pectin and hemicellulose
- has cellulose fibrils via hydrogen bonds (giving tensile support)
- has middle lamella which is in between cell walls, holding it together (majorly pectin)
Primary and Secondary Cell Walls
Primary: semi-rigid, selectively permeable membranes
allows for expansion which leads to
Secondary cell walls: made up of lignin (very hard and rigid), not permeable at all, unable to expand
(occurs when extra layers of cellulose is secreted from primary cell wall aka growth)
Plant Growth by Cell Expansion
- due to semi-rigid cell wall, water is able to enter (taken up by vacuole) which expands causing turgor pressure
- cell wall resists expansion
- with increased turgor pressure, this activates an enzyme to be release to soften walls and allow for expansion
Enzyme: Expansin is released where it bonds to non-covalent bonding between cellulose, hemicellulose, pectins and polysaccharides
this causes cellulose microfibrils to have ‘slippage’
allows other microfibrils to expand from ‘relaxed’ into ‘tensioned’ (cell wall would elongate)
Plant Growth by Orientated Cell Divisions
Orientated cell divisions allow for plant to control growth, determining direction of tissue growth
-longitudinal or radially
Plant Embryogenesis
- plant embryogenesis begins with a zygote and after cell divisions it divides into two daughter cells (asymmetric body)
- TWO CELL STAGE: top cell (smaller) is apical daughter cell and bottom cell is basal daughter cell
-OCTANT STAGE: more cell divisions cause apical daughter cell to become plant embryo and basal daughter cell forms suspensor (receives and gives signals/nutrients from mother)
determination stage occurs here where cells are determined their specialisations (commit to cell types before characteristics)
-HEART STAGE: changes from radial symmetry to lateral symmetry. plant embryo forms Cotyledon primordia (top sections of ‘heart’) whilst bottom area consists of tissues (epidermis, ground tissue, vasculartissue)
Differentiation occurs: cell types begin to show specialised characteristics and acquire specific functions due to gene expression
Morphogenesis occurs: groupings of cells to form tissues and organs
- TORPEDO STAGE: growth of cells (increase in cell size due to proliferation and enlargement)
- MATURE EMBRYO: through elongation of cotyledon and main axis of embryo, the ‘seed’ forms
Body Plan during Embryogenesis
Body plan is mapped our during early embryogenesis along two axis:
Apical-basal - arrangement of tissues along the shoot-root axis (lateral)
Radial - circular arrangement of tissues (dermal, ground and vascular)
Post-embryonic development
Primary growth is through the shoot apical meristem (aerial structures like phytomers)
Root apical meristem gives rise to subterrean structures (roots)
[apical meristems are formed during embryogenesis but are kept inactive until seed dispersal occurs]
Apical and Primary Meristems (Primary growth)
Shoot apical meristem (part of bottom section in embryo) gives rise to 3 other tissues (dermal, ground and vascular tissue)
Shoot apical meristem is source of cells for organ growth/development
Apical meristem continously grows due to presence of stem cells
Stem cells = undifferentiated, renewing cells
Lateral Meristems (secondary growth)
Secondary growth occurs in bark/wood parts of trees (related to thickness/wideness of plants)
Lateral meristems (cork cambium and secondary phloem) is found in older woody stems where is generates secondary growth causing secondary plant body to be formed
(stem cells are also present in lateral meristems)
-Secondary growth is occurs with vascular bundle where xylem forms wood growth
-outer layer of vascular bundle is bark (secondary phloem + cork cambium)
-relates to tree rings
(spring has more water = rings are dark and thick
summer has less water = rings are light and not as thick
winter = no water)
Plant Tissue Types
DERMAL (epidermal): forms epidermis cells (usually single cell layer)
differentiates into: stomata, trichomes (hairs), root epidermis, leaf epidermis, root hairs
GROUND: found inbetween on dermal and vascular tissues
is the bulk of plant body, ground tissues are categorised based on their cell wall structure
Parenchyma (most common): have large vacuoles and thin cell walls
Functions: photosynthesis, nutrient transport and storage
Collenchyme: elongated, thick, uneven cell walls
found in non-woody stems, growing organs and petioles
Function: mechanical support (sturdy but flexible)
Sclerenchyma: there are Fiber cells and Sclereid cells (they under go apoptosis), very thick, long circular, lignified
Fiber cells = woody/bark structural support
Sclereid cells = small bundles that are very durable (can be found in nuts), when clumped it forms gritty texture
VASCULAR: conducting/transporting tissue that forms a network throughout plant
Xylem: made up of lignified, dead cells, secondary cell walls
have Tracheids (long spindle cells with holes to allow water to move freely) and vessel elements (like pipeline for water)
Phloem: Made up of sieve tube elements and companion cells
Has Plasmodesmatas which are large holes that connect cytoplasms of sieve tubes
-causes inner cell components to be lost thus having companion cells to provide necessary nutrients/materials
Plant Cuticles
Waxy cuticle is on top of epidermis
- limits water loss and is impermeable
- protects against UV rays, pathogens and physical damage
Plant Organ: Leaf
-composed of dermal, ground and vascular tissues
-has determined growth (specific shape and size allowing for function
upper size = cuticle
lower size = stomatas)
-ground tissues in a leaf are either palisade mesophyll cells or spongy mesophyll cells (all have same function = photosynthesis)
Plant Tropism
Growth of plant towards or away from a stimulus
e.g. Heliotropism (follows path of sun like sunflowers)
Phototropism - auxin accumulates on shaded size which promotes growth causing stem to grow towards light
Gravitropism - auxin accumulates on lower side of a root which promotes growth causing root to grow against gravity
Growth is due to cell elongation and due to EXPANSIN
Auxin activates a proton pump which increases number of protons inside cell wall (increased conc)
Expansin depends on pH, thus with increased protons (more acidic), expansin is more active (disrupts microfibrils)
What is Ordovician Landscape?
Ordovician landscape is the predicted landscape of earth long ago where plants were small and always next to water bodies
Vascular plants developed 380 mya (provided structure + transport)
What is water require for in plants?
Photosynthesis, cooling of plant, transporting nutrients, structural support
Roots are the source for water
Shoots are the sink for water(where it is needed)
Macro/micronutrients that plants require
Macronutrients = Nitrogen and Phosphorus
Lack of nitrogen = required for synthesis of DNA and protein (needed for growth)
Lack of phosphorus = needed for synthesis of DNA and ATP and phospholipid production (plant becomes dark green = stress accumulation)
Micronutrient = Iron
Lack of iron = important in redox reactions + ribosomes causing plant to become yellow (affects synthesis of chlorophyll)
What is water potential?
Tendency of a solution to uptake water (pure water) across a partially permeable membrane
Water ALWAYS moves across partial permeable membrane towards a lower (NEGATIVE) water potential
Equation:
Water potential = Solute potential + Pressure potential
What is solute potential and pressure potential?
Solute potential - the greater the solute concentration, the lower water potential (water will move in)
Pressure potential - the greater the internal pressure, the higher water potential
What is turgor pressure?
Turgor pressure is the same as pressure potential
Low turgor pressure = water will move in plant by osmosis due to low solute potential
(water moves in as water is important for structure, it must maintain it’s turgor)
How is water taken up by roots?
Apoplast route - water moves through connect cell walls and intercellular spaces between cells
-rapid and unregulated route
Symplast route - water moves through cytoplasm via plasmodesmata
-slow and regulated route
Water reaches the CASPARIAN STRIP (cell wall layer, with lignin, found in between endodermis (tissue surrounding vascular bundle)
Casparian strip = diffusion barrier, enable selective uptake of solution (protects plant)
It is a protective barrier where solutes MUST go through the symplast route to get inside vascular bundle
When solution reaches vascular bundle, it is active transported out of the cell into the symplast, causing water to follow by osmosis
Water movement in xylem
Water forms a continuous stream in xylem vessels due to cohesion and adhesion
Cohesion - interaction of water molecules with each other (hydrogen bonds)
Adhesion - interaction of water molecules and xylem wall (capillary action)
Transpiration
Transpiration is the loss of water due to evaporation from leaf surface
(concentration of water vapour is less outside of plant, thus water vapour diffuses out through stomata)
Transpiration-Cohesion-Tension Mechanism
Transpiration generate surface tension in the apoplast of mesophyll cells
- this pulls water into apoplast from adjacent cells
- tension in mesophyll cells draws water out of the veins into apoplast mesophyll cells
- also causes water to enters roots by osmosis
Pressure potential in xylem
Gradient of negative pressure potential lifts water column by bulk flow
Pressure potential in xylem becomes more negative as you move up plant (roots –> outside air)
Stomata
Stomata is controlled by guard cells that become turgid when open and flaccid to close
Regulated by light, temperature, carbon dioxide and water availability
Stomata in the presence of light
Light activates photoreceptor providing protons to be pumped outside of stomata cell
Proton gradient allows potassium and chloride ions to be moved inside of cell
- Potassim diffuses in poassively
- Chloride is pumped in through the use of protons
Movements of ions decrease solute potential inside cell causing water to move in cell by osmosis
(guard cells become turgid and opens stomata)
Transport of Sugars in Plants
Translocation = movement of carbohydrates + other solutes through phloem
(some tissues can be a sink at one time but become source later on, e.g. carrot leaves are source of carbohydrates and stored in roots, then carrots become the source)
Mass Flow
Loading = sucrose + other solutes are actively transported into sieve tubes via companion cells
Sucrose accumulates in sieve tubes (decreases water potential), causing water to be drawn in by osmosis
Increase of water causes pressure potential to increase in sieve tubes
Sucrose moves down to less concentrated and into sink cells by active transport (causes increase of water potential in sieve tube) causing water to move out into xylem
Tapping the Sap
Using aphids stylet to tap into phloem of plants to get sap samples
Stylet is punctured into phloem and due to high pressure, sap flows into tube and into anus of bug
Stylet is snapped off and sap is continuously flows out
Tissue and Organ Definition
Tissue = group of similar cells that form a functional unit Organ = group of several tissues with a distinct function
Development Key Stages (animals) - Determination
First step: Determination - establishment of cells fate before development
Zygote undergoes grastulation (develop of grastula which is the primary germ cell layers)
-Ectoderm = forms external surfaces + nervous system (e.g. skin, nervous system)
-Mesoderm = internal tissues (e.g. muscles, blood vessels, connective tissue)
-Endoderm = is the alimentary canal and organs that branch off it (e.g. liver, pancreas, lining of gut, lungs)
Experiment to see when determination occurs
Trial A and B
A: early posterior tissue was taken and transplanted into another host anterior region. when embryo developed, tissue developed into anterior structures (indicating determination had not occured yet)
B: older embryo posterior tissue was used this time and when embryo developed, posterior structures grew in the place of anterior (indicates determination already occured)
Development Key Stages (animal) - Differentiation
Specialising of cells after determination (specialisation of cells occur due to specific gene expression)
Gene regulation = specification of cell fate
-essential genes (e.g. histones, ribosomes) are expressed in all genes
Development Key Stages (animal) - Morphogenesis and Growth
Process of differentiating cells are grouped and organised into different sections of body
Mechanisms occuring in morphogenesis include: Apoptosis (death of cells) Dividing Changing shape Moving Around Adhering to each other Formation of tissues/organs Breaking free of epithelial connections
Growth is the increase in size due to proliferation (many divisons) and cell enlargement
What are stem cells?
Stem cells are undifferentiated cells that can divide indefinitely (forms another stem cell and daughter cell)
They are found in regenerative tissues where new cells must be made to replace old cells (e.g. lining of gut)
(stem cells in lining of gut can differentiate into goblet cells, enterocytes (absorption) or enteroendocrine (releases hormones)
Cell Potency of stem cells
-Ability of stem cell to give arise to other types of cells
Totipotent - can give rise to ALL cell types in an organism (only found in zygote)
Pluripotent - can give rise to all cell types of body but NOT extraembryonic tissues (e.g. placenta = embryonic stem cells; iPS stem cells)
Multipotent - can give rise to specific several cell types (e.g. intestinal stem cells)
Unipotent - give rise to only one type of cell (e.g. skin cells)
iPS stem cells - induced pluripotent cells
- changing genes in a cell to make it another cell type
e. g. taking skin cells and reprogramming its genes back to undifferentiated state (expressing stem-cell key genes) then reintroduced into body to get wanted cell types
Animal Tissue Types - Nervous Tissue
Nervous Tissue
Function: gathering information from external/internal environment, processing, controlling physiology and behaviour of body
Neurons = transmits electrical signals
electrical signals can either form inhibitory or excitation electrical network
3 Types of neurons:
Sensory neurons - generates electrical signals (e.g. pain/pressure receptors on skin, stretch receptors in muscles, olfactory receptors)
Interneurons (relay neurons) - takes input from one neuron and delivers/output to another neuron
Motor neurons - receives signal from interneuron and output to muscles (effector)
Glial cells - cells found in neurons that provide nutritional/mechanical support (e.g. Schwann cells)
Animal Tissue Types - Epithelial Tissue
2D sheets of cells that line body surfaces, internal cavities and internal tubes
Function: barrier function between body and outside world and between compartments of body (e.g. Endothelia = lining of blood vessels and are mesodermal origin)
Structure:
-Apico-basally polarized
Apical side = microvilli side
Basal side - Extracellular matrix side (basal lamina)
-Tight Junctions (below microvilli)
prevent passage of small molecules between cells (must go through microvillli to enter cells)
-Adherens Junctions and Desmosomes
Function: mechanical support
Actin filaments inbetween epithelial cells with Adherens junctions/Desmosomes achoring them into the cell
-Gap junctions
connection of cytoplasm of different cells (cell communication)
-Cell-Matrix Junctions
Connecting the epithelical cell to underlying extracellular matrix (ECM protein) (basal lamina) by adhesion molecules (actin molecules joins to matrix)
Epithelia have many functions: glands (secreting enzymes)
intestine - absorption of nutrients
skin - protection
airways - beating to cilia to keep airways clear
Animal Tissue Types - Connective Tissue
Found in between other tissues, and in between organs, supporting those tissues/organs (structural, mechanical, defensive)
Connective tissue and ECM
- interlocking mesh of fibrous proteins (usually liquid but solid in bones)
- there are embedded proteins in ECM that secret elastin and collagen
Other examples:
Tendons - strong connection between muscles and bones
Bones - rigid support of body, protection of delicate
tissues
Cartilage - rubbery/flexible, shock absorbing, fraction reducing in between bones
Blood
Adipose
Animal Tissue Types - Muscle Tissue
3 Types of muscles:
Skeletal - voluntary control, muscles are connected to bones
Cardiac - wall muscles of the heart
Smooth - surrounds internal organs (peristalsis in alimentary canal)
Myosin is a motor protein responsible for contraction (movement)
Tropomyosin blocks binding site on actin (found on myosin) where calcium binds to troponin, moving tropomyosin, allowing actin binding sites can bind with myosin heads
ADP is on myson where there is no cross-bridge between myosin and actin
Pi is released on ADP and cross bridge between actin and myosin is formed
Cross bridge bends, pulling actin towards myosin causing contraction
ATP binds to myosin where it is hydrolysed into ADP + Pi breaking the cross bridge
Animal Circulatory Systems
Not all animals have circulatory systems (e.g. organisms which inner cells are close enough to external environmental) (organisms may be hollow, flat or porous)
Transportation systems are for: transportation of substances, heat and force (e.g. molluscs move by circulating inner fluids)
Systems require: muscular pump
circulating fluids
system of tubular vessels that form a circuit
Two types of circulatory systems:
Open Circulatory System - circulating fluids empty out into a body cavity
Hemolymph = fluid in circulatory system is same in body cavity
e.g. arthopods, (insects, crustaceans), molluscs
Ostia - structure where blood enters heart by
Closed Circulatory System - circulating fluid is contained within a network of vessels, circulating fluid is separated from interstitial fluid (thin layer of fluid surrounding cells) (e.g. blood plasma)
e.g. earthworms, vertebrates, octopus
Advantages: fluid flows faster (faster metabolism, relative to more active lifestyle), control of flow of fluids (direct it to where its needed), contain specialised cells only (retain some cells/large molecules)
Vertebrate Circulatory - Fish Circulatory
- Single circulatory system
- oxygenated blood goes to systemic capillaries (towards the body)
- Heart valves prevent back flow (one-way flow)
- Limitation of single circulatory system is there is low blood pressure towards body (oxygenated blood)
Bulbus arteriosus = muscular part above ventricle that helps maintain pressure in heart + continuous flow of blood
-bulbus ateriosus is very elastic thus when blood gets pumped out of ventricle, it can expand then become narrow again when ventricle is not pumping
WINDKESSEL EFFECT - dampening large influctuations (aorta is similar)
Vertebrate Circulatory - Amphibian Circulatory
Oxygenated blood can go straight to body without having to go through fine capillaries in gills
- blood can pump directly from ventricle
- high blood pressure
Limitations: mixed blood
Vertebrate Circulatory - Birds/Mammals Circulatory
Two circuits in birds/mammals which allows different pressures and no mixed blood
Two ventricles and aortas
-high pressure towards body and low pressure to heart
Vertebrate Circulatory - Semi-Aquatic Circulatory (Crocodile)
In land, high pressure from left aorta closes flap connecting to mixed blood (right aorta)
Thus blood has to go to lungs to get oxygen
Under water, pressure is not so high thus flap opens and goes through valve directly to body
-flap to lung closes
Human Circulatory System
Characteristics: four chambered heart, separate pulmonary and systemic circuits, different pressures in circuits
-organs are supplied with blood in parallel (blood travels equally to all organs so they receive enough oxygen)
(liver gets blood directly from intestine as it relates detoxification, metabolism, storage of digestive nutrients)
Human Circulatory System - Anatomy
Deoxygenated blood from body enters heart with inferior vena cava (lower body) and superior vena cava (upper body)
Enters right atrium through antrioventricular valve (tricuspid valve) and right ventricle to pulmonary atery (right pulmonary valve/semilunar valve)
Oxygenated blood returns to heart from lungs by pulmonary vein to left atrium and left ventricle (very muscular to pump blood)
Left aortic valve aka bicuspid valve
Cardiac Cycle
Spontaneous beating of pacemaker cells (sinoatrial node)
Pacemaker = cells that create rhythmic, beating of heart, controls heart rate
Action potential is spread throughout other cells (electrical signals) spreading downwards by gap-junctions causing contraction of atria
Signal activates atrioventricular node (AV node = controls top part of heart)
Signals are passed down cardiac fibres (like nerve fibres, PUNKINJE FIBRES) that causes contraction of ventricles
Diastole = at rest (lowest pressure in vessels) Systole = ventricular contractions occuring (highest pressure in vessels)
Structures of Artery, Veins and Capillaries
Arteries:
-small lumen, musclar/thick wall, elastic (can support high pressure)
Vein:
-large lumen, thinner, not as muscular, have valves
(blood flow is powered by skeletal muscles and gravity)
muscle contraction makes blood flow from one compartment to next , muscle relaxation causes valve to close ensuring blood doesn’t backflow
Capillaries:
-very thin walls (1um) thick for diffusion
Exchange in Lungs and Capillaries
Lungs:
air enters lungs and fills ALVEOLI
(alveoli are covered by network of capillaries for gas exchange)
alveoli and endothelial cells are both very thin to allow for diffusion
Capillaries:
oxygen and nutrients diffuse out of capillaries to supply cells (cells have lower concentration causing diffusion)
carbon dioxide and waste diffuses into capillaries
DEPENDENT ON WATER POTENTIAL
Water potential = osmotic potential (solute potential) + osmotic pressure (-osmotic potential/solute)
Osmotic potential is dependent on albumin (constitutes most of plasma) which is constant throughout capillary but osmotic pressure changes
Filtration = fluid leaving capillary at arterial end
Reabsorbtion = fluid taken up at venous end
Water potential is more negative in outer cells thus fluid moves out
Lymphatic System
Transportation system that drains and processes interstitial fluids
- drains excess fluids in interstitial cells and brings back to blood vasculars (major veins)
- liquids move into lymphatic capillaries due to high pressure outside ducts (large gaps which let fluids in)
Gas exchange definition
Gases in cellular respiration (oxygen/co2) moving in opposite directions
Ventilation = mass/bulk flow taking place due to convection inside body
Fick’s Law (gas exchange)
Respiratory gas exchange is controlled by physical factors
Rate of diffusion = (surface area x partial pressure gradient x diffusion coefficient) / diffusion distance
partial pressure gradient = proportional to gas concentration, gradient is relative to both ends where diffusion is occuring
What maximises gas exchange?
- large surface area, partial pressure gradient
- thin barrier (small distance)
- minimising diffusion in aqueous medium (diffusion coefficient is higher in air)
Gas exchange in water and air
Solubility of oxygen in water is low compared to carbon dioxide
- carbon dioxide is more soluble in water to oxygen (polar)
- water is more dense than air
- oxygen has a very slow diffusion rate in aqueous medium
Factors reducing oxygen solubility in water
- temperature: higher temperature decreases solubility (when aquatic animals go through metabolism/respiration, their body heats up cause water around them to heat up but harder to get oxygen as lower solubility)
- salinity
- pressure
- other organisms in water can deplete oxygen concentration too
Animals without respiratory system
Examples include: anenome, jellyfish, flatworms, corals
Gas exchange occurs through internal + external bodies by diffusion
Animal respiratory systems - Insects
Open circulatory system
Respiratory systems are made up of tracheae hat branch throughout body (internal pathways that get smaller throughout body)
-they have small openings called SPIRACLES which are passages that open to outside (similar like stomata) which can open and close for diffusion
Animal respiratory systems - Crabs (crustaceans)
Open circulatory system
Respiratory system is made up of gills which have SCAPHOGNATHITE which is a ‘boat-like’ appendage that forces water through gills in one direction
There are thin filaments with hemolymph found in gills which is where diffusion of gas occurs
Thin filaments with hemolymph flow in opposite direction as water which maximises gas exchange
Animal respiratory systems - Fish
Closed circulatory system
Fish have internal gills where water is forced through gills by the opening of mouths
Water flows through gill arches where there are thin lamallae that is covered by blood vessels (for gas exchange)
Deoxygenated bloow flows in opposite direction as water = COUNTERCURRENT FLOW
Countercurrent flow allows maximisation of gas exchange as there is gradient of oxygen concentration and opposite direction allows blood to fully become oxygenated
Countercurrent flow:
Gradient of oxygen in water is constant (water is fully oxygenated when flowing in and least when flowing out)
Water that is least dexoygenated meets with blood that is least deoxygenated but still has higher concentration causing diffusion
Animal respiratory systems - Humans
Closed cirulatory system
Respiratory system is made up of trachea
Trachea = tubules that are reinforced with rings of cartilage to prevent collapsing and lined with mucus + cilia to prevent unwanted organisms
Trachea moves down into two BRONCHI that breaks into BRONCHIOLES made up of many small ALVEOLIS
Alveoli is covered by network of blood vessels for gas exchange
Alveoli walls are covered by surfactant lipids that disrupts interactions between water so walls of alveoli do not stick together
TYPE-I PNEUMOCYTES = thin alveoli cells aiding diffusion
TYPE-II PNEUMOCYTES = produces surfactant lipids
(left lung is smaller than right to make space for heart)
Diaphragm Movement
Movement of diaphragm is controlled by phrenic nerves
Breathing in - diaphragm moves down (contracts), external intercostal muscles contracts (to elevate ribs)
Breathing out - diaphragm moves up (relaxes), internal intercostal muscles contract (to pull ribs down)
Tidal volume - usual volume of air breathed in
Inspiratory reserve volume - extra space (volume) in lungs allowing for deep breaths
Expiratory reserve volume - volume of air that can be forcefully exhaled after a normal exhale
Residual volume - volume of air that is always present in lungs after exhalation (cannot be removed)
Air in our lungs are not always fresh, it is a mixture of air
Haemoglobin and Cooperative Binding
Oxygen is carried by the 4 heme groups on haemoglobin Iron ions (Fe2+) are on heme groups where oxygen binds to
When there is 1 molecule of oxygen binded to haemoglobin, this increases the affinity of oxygen rapidly, promoting oxygen loading in alveoli (shape of heme changes allowing oxygen to bind easier)
When there is more oxygen binded, the affinity decreases (this allows oxygen to reach oxygen starved areas, e.g. muscles)
Average amount of oxygen returned to lungs is 40 mmHg (only 1 oxygen molecule was lost) due to the sigmoidal curve
Oxygen binded will only diffuse into tissue with very little partial pressure of oxygen (difference of partial pressure can be very small though)
Bohr Effect (cooperative binding)
Factors affecting the shift of the curve include:
Shifting curve to the left (increased affinity of oxygen)
- decreased co2
- decreased acidity
- decreased temperature
Shifting curve to the right (decreased affinity of oxygen)
- increased co2
- increased acidity
- increased temperature
- presence of BPG (2,3-diphosphateglycerate) (intermediate in glycolysis that is a competitive inhibitor to oxygen)
Fetal hemoglobin has higher affinity - 2 subunits of heme is gamma (adults = beta)
Myoglobin
Myoglobin are cells that are oxygen storage in muscles (have cooperative binding; greater affinity than rest)
It only have 1 oxygen binding site, causing the affinity to be very high
Unloads carbon dioxide at very low partial pressures of oxygen (holds onto oxygen until partial pressure in muscle is very low, e.g. for exercise)
Gas Exchange in Alveoli
Alveolus - 104 mmHg of oxygen and 40 mmHg of carbon dioxide
Blood Capillary - 40 mmHg of oxygen and 45 mmHg of carbon dioxide
Even though partial pressure differences are large, rate at which they diffuse is still same as carbon dioxide is more soluble than oxygen
What happens if CO2 is not diffused out?
Increased CO2 increases acidity of blood
CO2 diffuses into RBC that reacts with water to form bicarbonate ions and hydrogen ions
Hydrogen ions bind to haemoglobin (affecting pH and affinity of oxygen)
In the lungs, bicarbonate ions + hydrogen convert back into CO2 and diffuse out
Respiratory Adaptations
Marine mammals have much more haemoglobin and myoglobin where underwater their heart rate is much slower and they are able to control blood flow to necessary organs
High altitudes give shortness of breath due to partial pressures of oxygen in the environment
Higher altitudes = lower partial pressure of oxygen = lower oxygen saturation binding in body
Oxygen affinity curve shifts right (less affinity of oxygen)
After some time eat high altitudes, more haemoglobin will be produced and pH will be maintained
Chemoreceptors can detect signals to control rate of breathing
Chemoreceptors found in the medulla can detect partial pressures of CO2 and pH of blood
Peripheral receptors are found in the lining of blood vessels in heart (carotid artery, blood supply to brain) that can detect partial pressures of oxygen/CO2 and pH of blood
Signals are sent to breathing control centre where ventilation rate is controlled by phrenic nerve (diaphragm) and thoracic nerve (intercostal muscles)
Unicellular Digestion
Unicellular organisms obtain food by phagocytosis and digestion occurs in the cell when food fuses with lysosomes to form a digestive vacuole
Smaller molecules are then transported out into cytoplasm to be used
Simple Digestive Systems
Organisms with a cavity with one opening (mouth/anus) (e.g. corals, anenome, jellyfish, corals) obtain food through using tentacles where digestion occurs in the GRASTROVASCULAR CAVITY (which is also their circulatory system)
Digestion and occur by INTRACELLULAR or EXTRACELLULAR digestion
INTRACELLULAR - food molecules are taken up by digestive cells by endocytosis
EXTRACELLULAR - digested by enzymes which are secreted by gland cells (slow process)
More Complex Digestive Systems
‘Essentially’ a long hollow, muscular tube with one opening and one exit point
-more complex systems allows for wider range of diet
Digestion occurs in the lumen of the gut
Stomach for birds/invertebrates: CROP (stomach like structure which is an enlarged portion of digestive system where food is stored and digested over a long time)
GIZZARD (muscular structure in gut with stones/ridges that helps with mechanical digestion) found in: birds, earth worms, some reptiles and fish
Importance of Digestion
Developing the gut is the first step in embryogenesis (gastrulation forms gut)
Animals are heterotrophs (unable to produce their own necessary nutrients)
Necessary nutrients include: amino acids (9 esssential ones for humans), fatty acids (2 essential), vitamins (organic substances) and minerals (inorganic substances) and water
(vitamins + minerals act as co-enzymes that bind/activate to enzymes in body)
ACETYL GROUP is very important base molecule can make hormones, amino acids, heme, fatty acids (they are found in majority of proteins)
The amount which animals must eat depend on: metabolic rate (age, reproductive stage, amount of activity), body mass, environmental conditions and types of food
Metabolic rate + body mass = large size indicates you need to eat more as metabolic rate is larger HOWEVER if we measure per unit body mass, smaller animals need to eat more as the ratio between SA:V is larger thus heat is lost faster
Mammalian Digestive System
Begins with Mechanical Digestion (breaking down of foods into smaller, manageable pieces)
Enzymatic digestion - break down of foods using enzyme (leading to absorption of nutrients)
Mammalian Digestive System - Alimentary Canal
Alimentary canal consists of: Mouth Pharynx Oesophagus Stomach Small intestine (+liver and pancreas) Large intestine (+ caecum) Anus
BOLUS - ball of chewed up food mixed with saliva
Mammalian Digestive System - Mouth and Teeth
Mouth is responsible for mechanical and enzymatic digestion
Food is chewed by teeth which break down food, increasing the SA of food so it can be digested faster + easier
AMYLASE is enzyme found in saliva which hydrolyses starch in maltose
Teeth types:
Incisors - cutting food
Canines - gripping, ripping flesh, killing prey
Pre-molars = shearing food into smaller pieces
Molars - grinding
Mammalian Digestive System - Stomach
Food is transported into stomach from oesophagus by peristalsis
Stomach is very musclar which contract (churning) to digest and mix food
Stomach is very acidic (pH = 1/2) which kills all pathogens but is optimum for enzymes present (PEPSIN AND PROTEASES)
Food is reduced into CHYME which is squirted into small intestine controlled by the PYLORIC SPHINCTER (small squirts at a time)
Mammalian Digestive System - Small Intestine
Duodenum: 25 cm long + digests food further by enzymes (with the help of liver + pancreas)
Liver - produces bile (emulsifies lipids) and is stored in the gall bladder
Bile = mixture of phospholipids, acid, cholesterol (alkaline pH to neutralise acidity due to stomach)
Bile is moved into the duodenum by rhythmic contractions by gall bladder then squeezed through a small duct then large duct (hepatopancreatic duct)
Bile coats lipid droplets where the hydrophobic heads interact with the lipids causing lipid to break down into MICELLES (increased SA) then break down into fatty acids and monoglycerides by lipases
(gallstones = solidification of bile salts and cholesterol)
Pancreas - secretes digestive enzymes (lipase, amylase, protease, nucleases) + insulin (tissue of pancreas are made of CARBONADINE which is alkaline to neutralise acidity of chyme)
Enzymes are secreted into common bile duct then into intestine
Jejunum
Illeum - jejunum and illeum combined are 6m long where majority of absorption occurs
Walls of illeum are folded to increase SA with villi and microvilli
Epithelial cells of small intestine secrete more digestive enzymes (peptidases = proteins –> amino acids), maltase, sucrase, lactase
Mammalian Digestive System - Large Intestine (colon)
Some animals have a CAECUM which is a pouch which is blind ended (important for herbivores as it digests cellulose)
Colon - where re absorption of water occurs (food is slushed around to ensure maximum water is reabsorbed (too much water absorbed = diarrhoea, too little water = constipation)
Examples of specialist diets
Specialist diets = granivore (seeds), insectivore, myrmecophage (termites/ants), fungivore, frugivore, piscivore
Diets and Digestive Tracts
Carnivore - short, simple digestive tract (short small intestine and small caecum) as meat is easy to digest
Herbivore - have microbes that break down cellulose (animals do not produce cellulase)
e.g. a pouch filled with symbiotic microbes and protists that break down cellulose (contained in a pouch so microbes do not go through entire digestive system)
FOREGUT FERMENTERS:
digestion of cellulose occurs before stomach
characteristics: large stomach, (four chambered), intestines are not as long (caecum is small)
microbes break down cellulose (fibre source) and microbes can be digested as well (protein source)
e.g. kangaroos, hippopotamus
SPECIAL CASE OF FOREGUT FERMENTERS:
RUMINANTS - animals that chew their cud where they regurgitate their food and continuously chew
e.g. sheep, cow
HINDGUT FERMENTERS:
digestion of cellulose after stomach
characteristics: small stomach, long intestinal tube (caecum is large)
microbes are found in caecum and proximal colon
limitation: microbes are washed through digestive system (lost of protein source)
CAECOTROPHS - produce protein full faeces during the day which are eaten (nutrients reabsorbed in digestive tract)
normal faecal pellets are produced during the night
e.g. possums, wombats, rabbits
Cues that make the body feel hungry
External cues: sight, smell of food
thought of food
habits
emotions (stress)
Internal cues: nutrient availability (empty stomach)
low blood sugar levels
long term energy reserves (weight gain/loss)
Short term and Long term regulation of appetite
Short-Term (hours): GHRELIN
Ghrelin is a hormone that regulates appetite
When the stomach is empty, stomach cells release a peptide (prepares stomach for food + stimulates appetite)
Ghrelin levels increase before meals and decrease after meals
Ghrelin is detected by the hypothalamus where response is nervous impulses that make us hungry (stimulatory) or full (inhibitory)
High levels of ghrelin causes stomach to contract = increased secretion of gastric acid
(looking at food increases ghrelin levels in blood)
Long-term (days/week): LEPTIN
Leptin is a hormone that is produced by adipose (fat) tissues which regulates body weight for long-term
Leptin levels increase when body mass increases (supresses appetite) + leptin levels decrease when body mass decrease (increase appetite) - NEGATIVE FEEDBACK
Leptin is detected by hypothalamus which either sends:
NPY/AgRP - stimulates appetite neurons
MSH - inhibitory appetite neurons
How does body detect sweetness?
Taste buds (sensory cells) in mouth are able to detect hydroxyl groups in food In the gut, there are epithelial cells that sends signals to the brain
Artificial Sweetners
No/less calorie alternative to natural sweeteners which body CAN NOT break down (no additional energy for body)
Artificial sweeteners are a substitute in foods to reduce energy consumption
NEUROPODS - specialised small intestine epithelial cells that can detect difference between artificial and natural sweeteners
Artificial sweeteners = sucralose/ no calories (common artificial sweetener
Natural = sucrose/calories
Neuropods have different receptors for sweeteners (communicates with nervous system with different signals)
Experiment: gave rats natural sweeteners and artificial,
when given the option, rats preferred natural sweeteners
-body is evolved to seek out food with most energy value to meet energy requirements, but nowadays we have over abundance = obesity
Digestive system microbiome in humans
We have over 100 trillion microbes (bacteria, protists, fungi, viruses) mostly found in our large intestine (can be found in gut also)
Microbes produce and secrete enzymes that break down polysaccharides (that we are unable to) or microbes ferment polysaccharides –> short fatty acid chains (enhance intestinal epithelial barrier function and immune system OR are used by microbes)
Most insoluble dietary fibre are not digested by us or microbes, it is still beneficial as it helps gut moving
Microbes have mutualistic relationship which can help us decrease pathogenic invasions (if we have healthy microflora)
probiotic foods = helps increase variation of microflora (e.g. yoghurt)
Microbiota-gut-brain connection
There has been research that there is relationship between microbiota gut and brain affecting:
mood and behaviour
neurodevelopment disorders (e.g. autism, dementia)
immune system (e.g. imflammatory bowel disease)
Recent research shows relationship between specific microflora (type B2) and depression + lower quality of life
Microbiomes may be influencing mental health as different types of microbes produce different chemicals that are involved in neural pathways
TYPE B1, TYPE B2, TYPE P AND TYPE R
Homeostasis definition
maintenance of a stable internal environment despite changes in internal or external conditions
Stimulus-Reponse model
For a system to respond to a stimulus, it must:
Receptor = detects a change away from desired equilibrium
Control centre = receives and processes signals from receptors and sends signals to effectors
Effector = creates a response opposite effect of stimulus
Animal Hormones
3 main types:
Amine hormones - e.g. epinephrine (adrenaline)
Steroid hormones - e.g. testosterone (lipid soluble, cholesterol is pre-cursor)
Protein hormones - e.g. insulin (water soluble)
Hydrophilic hormones get transported out of cells by exocytosis where they can move into plasma easily, travel through blood and enters cell-surface receptors at destination
Hydrophibic hormones exits cell through diffusion and binds to a transport protein (hydrophilic) through blood and can diffuse into cell at destination (cytoplasmic receptors)
Blood glucose homeostasis
Hypoglycemia - low blood glucose (seizures, loss of consciousness)
Hyperglycemia - high blood glucose (heart disease, stroke, kidney disease, vision impairments)
BLOOD GLUCOSE LEVELS MUST BE AT 4-8 mmol/L
B-islet cells (beta) = produces insulin (pancreas)
released when blood glucose levels are high
insulin binds to insulin receptors (protein kinase) which self phospharylates and phosphates other molecules (creates a signalling pathway)
Signalling pathway increases glucose transporters and activates GLYCOGEN SYNTHASE
Glucose travels from blood stream into cells and gets converted in glycogen (storage)
a-islet cells (alpha) = produces glucagon
released when blood sugars are low
glucagon links to its receptor (g protein-linked, activates a g protein, activating effector protein) which activates GLYCOGEN PHOSPHARYLASE and inhibits glycogen synthase
Glycogen breaks down into free glucose
Chemical signals in plants
Abscisic Acid Auxins Gibberelins Brassinosteroids Cytokins Ethylene (gas)
Some hormones have overlapping functions - e.g. auxins, giberellins and brassinosteroids all promote stem growth
Some hormones work synergistically or antagonistically - e.g. abscisic acid inhibits seed germination and giberellins promote seed germination
Plant hormones regulate responses via signal pathways (focusing on auxins + gibberelin)
- transcription factor moves along DNA to promote transcription but in the absence of these hormones, repressor binds to transcription factor (inhibiting it)
- these hormones bind to their receptors forming a complex (with an F-box domain, responsible for protein-protein interactions)
- this complex can bind to repressor, stimulating a signal for protein degradation
- repressor is degraded, triggering a cellular response to hormone (transcription factor continues)
Abscisic Acid (ABA) in plants
ABA is a hormone that helps/related to guard cells
- When there is a lack of water, plant becomes dehydrated as the water potential on the outside is more negative
- change of water is sensed in plants and ABA is produced and released (made in roots and leaves)
- abscisic acid causes stomata to close as it causes ions (K+ ions) to move out of guard cells, thus water moves out too (osmosis)
(even in sunlight, ABA can close guard cells which can prevent cell damage)
long term effect - ABA can affect a set of genes that can help with stress in plants
Electrical communication in animals
Pupil response to bright light (humans)
-bright light causes pupils to constrict, reducing amount of light entering
- light detected by photoreceptors (sensory neurons), which activates a series of neurons , eventually activating constrictor muscles by motor neurons
- axons establish a negative membrane potential (inside of axon, it is more negative)
- when a neuron is fired, a small region of reversed polarity moves down axon = action potential
resting potential = -70 mV
3 sodium ions move out, 2 potassium ions move in
there is a ‘leak’ channel which allows potassium ions to diffuse out of axon, down its concentration gradient (electrochemical equilibrium)
potential threshold = -55 mV
Depolarisation = when sodium ion channels open and move inside cell (down concentration gradient) (sodium channels open in a row, causing change of charge), inside of cell becomes positive
Repolarisation = movement of potassium ions outside of cell (sodium channels close, potassium channels open) causing potassium ions to rush out
An undershoot is caused as potassium ions can still leak out when channels close
Refractory period = channels closed and returning to resting period
Myelin Sheath (myelination)
Myeline sheath is produced by schwann cells (type of glial cell) that is an insulating wrap around axon that increases rate of transmission
Node of Ranvier = gaps in between myelin sheath where channels are found
Saltatory conduction = propagation of action potentials along myelinated axons from 1 node to another (increases velocity of action potential)
At the synapse (action potential)
Action potential arrives at synaptic terminal where calcium ions rush in (can be different ions, dependent on action potential)
Vesicles with neurotransmitters increase and fuse with cell membrane, releasing neurotransmitters and released into the synaptic cleft
Neurotransmitters bind to receptor proteins at post synaptic membrane, allowing sodium ions (Na+ ions) to move into post synaptic membrane (can cause action potential)
Example of positive feedback in humans
Positive feedback and Ferguson reflex
- baby pushing against cervix activates stretch receptors
- sensory neurons are activated and send signals to tbe brain (hypothalamus)
- pituitary gland is stimulated to release oxytocin
- oxytocin causes uterus to contract
Human Reproduction
Reproduction is the union of haploid egg ad sperm forming a zygote
In mammals, it is internal fertilisation Costs (expensive) -production of gametes -production of pheremones -parental care given to offspring -cost of finding a male -competition between males
Sex Determination
Females - XX chromosome
Male - XY chromosome
On the Y chromosome, SRY gene is present causing gonads to develop into testes (produces testosterone) during embryo development
Abscence of SRY gene causes gonads to develop into ovaries (produces eggs)
Gonads and ovaries to produce androgens (testosterone), estrogen (oestrogen), and progesterone
Primary sex characteristics = sexual structures developed in embryo
Secondary sex characteristics = physical/behavioural traits that develop after gonads/ovaries are developed
Human Female Reproductive Anatomy
- females are born with ~1-2 million eggs
- puberty - 300-400k left
- adult hood - 100k
- menopause - 1000 left
Exterior layer of ovary (CORTEX) - tough epithelial cells, germ cells are present and where corpus luteum forms (from follicles)
Interior of ovary (medalla) - tissues that hold the ovary in place and supply blood to ovary (nutrients + hormones)
Ovarian Cycle
Consists of folliculogenesis and oogenesis
-when premature eggs start to develop, they become a PRIMARY OOCYTE (2n)
-around 6-12 oocytes develop (at beginning of cycle) into a follicle
follicle - contains cell wall (where gametes are formed, 1 copy only, n)
-follicle grows and develops, forming layer of cells around them called GRANULOSA CELLS and THECA CELLS (these tissues help the follicle grow)
-FSH (follicle stimulating hormone) stimulates follicle to grow further
-LH (liutenising hormone) stimulates theca cells to form ANDROGEN –> estrogen (cholesterol from blood stream) through granulosa cells
-after a week, the largest follicle will continue on, other follicles will be reabsorbed by ovary
-primary oocyte develops into a SECONDARY OOCYTE (n, first meiotic division)
-forms 1 polar body that becomes 2
-secondary oocyte forms OOTID then OVUM (overall 3 polar bodies produced, polar bodies degenerate after)
-at ovulation, follicle bursts, releasing mature egg (ovum) into fallopian tubes (caused by spike of LH)
- egg moves down fallopian tubes with help of cilia
- rest of follicle becomes CORPUS LUTEUM that secretes estrogen and progesterone (helping body for implantation and pregnancy)
- corpus luteum stays alive if implantation is successful, dies if not successful
Uterine Cycle / Menstrual Cycle
Endometrium sheds the first 4-7 days of menstrual cycle (bleeding)
-after ovulation, progesterone stimulates vascularization of endometrium (increasing blood supply, development and growth)
SPIRAL ARTERIES - small arteries in endometrium that supply blood
-after 2 weeks of no implantation, hormones signal to corpus luteum which degenerates, stopping secretion of estrogen and progesterone
= shedding of endometrium
-if egg is implanted, embryo/zygote releases human chorionic gonadotropin (HCG) which stimulates corpus luteum to keep producing hormones
Menstrual fluids consists of: blood, lining of uterus, uterine mucus
Follicular Phase
Ovulatory Phase
Luteal Phase
Role of Estrogen and Progesterone
Estrogen:
- produced by granulosa cells in follice (+ corpus luteum)
- regulates oviduct (fallopian tube), uterus, cervix, vagina and other sex organs
- prepares endometrium for implantation (vascularization and blood supply)
- promotes oestrus (mating behaviour)
Progesterone:
- produced by corpus luteum
- regulates oviduct, uterus, cervix + other sex organs
- prepares endometrium (maturing spiral arteries)
- modulates effect of estrogen + stops follicle growth
Hypothalamus and Pituitary Gland (females)
hypothalamus = control centre/link between nervous and endocrine system
-hypothalamus acts on the pituitary glands which produces a trophic hormone, activating endocrine glands to release desired hormone
-Hypothalamus secretes GONADOTROPIN RELEASING HORMONE (GnRH) into portal blood vessels to pituitary glands
(GnRH releases in pulses)
-Anterior pituitary gland produces gonadotropins (LH and FSH) which act on ovaries
Production of estrogen and progesterone causes positive feedback for the FIRST 14 DAYS OF CYCLE (continuing growth of follicle) causing peak of LH which then turns into NEGATIVE FEEDBACK
High levels of estrogen prevent FSH production + progesterone prevents FSH and LH (no more eggs are developed/released)
Endometriosis
Issue where endometrial cells grows in other parts of body (e.g. around ovaries, bladder, rectum) (affects 10% of women)
- causes abdominal pain, infertility
- endometrial tissues in other parts still respond to progesterone, developing and shedding into pelvic cavity when progesterone levels drop
Anatomy of Male Reproductive System
Penis = intromittent organ (transfers sperm during internal fertilisation)
Scrotum - contains testes (away from the body to main temperature to protect gametes)
Semen - mixture of fluids, mucus, proteins, fructose and sperm (gametes)
Prostate gland - connected to urethra where it produces mucus and alkaline fluid to neutralize the reproductive tract
Bulbourethral gland/Cowper’s gland - connected to urethra that secretes alkaline fluid to neutralise acidity + keeps urethra moist so semen can flow smoothly
Seminal Vesicle - connected to vas deferens which releases mucus and energy/nutrients for sperm
Testis - where sperm is developed and matured, stored in the epididymus
Urethra - common duct that carries both urine and semen (where bladder connects to)
Anatomy of Testis
Function: produce sperm and male sex hormones
SPERMATOGENSIS occurs in testis
Seminiferous tubules (spaghetti like structures) inside testis
Semen is produced in seminiferous tubules and stored in the epididymus
Semen exits through the VAS DEFERENS
SEMINIFEROUS TUBULES
- process of spermatogenesis occurs from the outside to inside
- sperm with flagella are released in the lumen of the tubules (centre)
Smooth muscles around seminiferous tubules allow for movement of sperm in lumen (when contracted)
Spermatogenesis
Spermatogonia - cells that undergo mitotic division to form spermatocytes (2n) –> primary spermatocytes (2n) –> secondary spermatocyte (n, first meiotic division)
Secondary meiotic division of secondary spermatocytes form spermatids (n) that differentiate and mature into spermatozoa (n)
1 spermatogonia ends up with 4 spermatozoa
(sperm begins production after puberty when GnRH signals (gonadotropin releasing hormone)
Sertoli (nurse) cells - help sperm cells develop by nourishing them (provides necessary nutrients and growth hormones)
Leydig cells - produces testosterone (found in interstitial space in between tubulues)
Production of Testosterone
Produced by LEYDIG cells from cholesterol (pre cursor; obtained from blood stream) that act by androgen receptors
Testosterone can be converted into oestradiol (estrogen) by sertoli cells to help provide nourishment to sperm cells
Testosterone can also be converted into DIHYDRO-TESTOSTERONE (DHT) (more potent androgen, contributes to secondary sex characteristics)
Structure of Mature Sperm
2um (micrometre)
-Head
Nucleus becomes compact (haploid)
Acrosome/Acrosomal vesicle = at the tip of head which contains enzymes that breaks down eggs outer coat
-Mid-piece
Helical mitochondria = allows sperm sufficient energy to swim (must get past cervical mucus = lots of energy)
Centriole (9+2 arrangement)
-Tail (flagella)
9+2 arrangement of protein fibres (microtubules)
Factors affecting sperm quality
Smoking Drugs Diet BMI Alcohol Constant exposure to heat Acute viral illness
Hypothalamo-Pituitary-Gonadal axis in males (HPG)
GnRH from hypothalamus stimulates release of LH and FH from anterior pituitary
LH - stimulates leydig cells to produce testosterone
FSH - stimulates sertoli cells to stimulate spermatogenesis
(sertoli cells produces INHIBIN that inhibits FSH production through anterior pituitary)
Testosterone positively affects accessory sex organs (e.g. seminal vesicles, prostate) and secondary sex characteristics
If testosterone levels are too high, it acts on hypothalamus (NEGATIVE FEEDBACK) thus decreasing production of LH and FSH (decreased GnRH)
Copulation and Fertilisation
- Sexual stimulation triggers nervous system causing penile erection
- Penile erection aids copulation (insertion of penis into vagina)
- Sperm is moved into ejaculatory duct by contraction of smooth muscle in vas deferens
- Semen ejaculates through contraction of muscles at the base of penis
If fertilisation occurs, HUMAN CHORIONIC GONADOTROPIN (hGC) is released by zygote (maintains corpus luteum + is detected by pregnancy kits)
Contraceptive Methods
-Physical barriers
Condoms, vasectomy
-Chemical barriers
Oral contraceptive pill, implants, IUDs (intrauterine devices)
Oral Contraceptive Pill
(contraceptive implant works the same)
Oral contraceptive pill contains synthetic progesterone and estrogen
High concentrations causes negative feedback on hypothalamus to reduce production of GnRH, LH and FSH = no eggs will develop + no ovulation
Increase of progesterone also increases cervical mucus (tougher for sperm to get through)
Continous exposure to estrogen and progesterone thins the endometrium lining (affects implantation)
MALE VERSION:
pill that contains progesterone (inhibits GnRH which decreases LH and FSH)
Endocrine Disruptors on reproductive organs
Hormonally active synthetics (and some natural) chemicals have negative effects on reproductive organs (e.g. plastic, pesticides, herbicides (DDT, dieldrin), phthalates
(DDT and dieldrin are banned now)
Bisphenol A (BPA)
-A monomer that can be polymerised into polycarbonate plastic (cheap and easy)
-Found in lining of plastics, food containers, lining of tin cans
BPA leaches from plastics when heated, aged or treated with acid/base
-BPA is a mimic of estrogen, which can act on estrogen receptors (more impact in children and babies as HPG cycle is not mature and is sensitive)
(causes fewer overall follicles developed, matured and corpus luteum. increases amount of follicles being reabsorbed)
Herbicide in male rats
-Atrazine is a chemical causes causes smaller penises as seen in male rats
