Human Biology exam revision

define organ

groups of tissues combined together to make functional units

define organ system

made up of a complex interplay of different cell types

define homeostasis

the maintenance of a stable internal environment in the face of changing external factors

What type of tissue do you think would be at the junction of lungs and the blood? What arrangement would it be in and why?

Epithelial tissue which form the covering of all surfaces. This is likely to be in a single layer arrangement to allow for the rapid diffusion of gases.

Blood cells have a unique structure biconcave structure, what is the purpose of this?

This is to allow for an increased surface area to volume ratio, allowing for more rapid diffusion.

define anthropometry

the measurement of body size, weight and proportions.

what are the benefits and limitations of girth and body circumference

benefits: low cost, portable, quick, non-invasive

limitations: doesn't discriminate between visceral and subcutaneous fat.

what are the benefits and limitations of densitometry

benefits: high degree of accuracy

limitations: limited access, expensive, requires experience to complete, low comfort, assumptions aren't applicable to everyone (bone density, muscle density)

what are the benefits and limitations of dual-energy x-ray absorptiometry

benefits: highly accurate, quick, provides data on whole body and regions

limitations: can have high error based on hydration status, where electrodes are placed, skin temperature and different machines.

what are the limitations of bioelectrical impedance analysis (measure of total body water to provide an estimate of fat-free mass, as fat is less conductive than lean tissue)

limitations: expensive, needs a GP referral, requires training, small radiation exposure

what are the benefits and limitations of skinfold callipers

benefits: quick, cheap, portable, relatively accurate

limitations: takes practice and skill, invasive, doesn't consider fat distribution.

what is a scenario where homeostasis breaks down

glucose is usually tightly regulated, but in Type II diabetes cells stop responding to insulin signalling, causing blood glucose levels to rise.

what are the benefits and limitations of an equation to measure energy expenditure

benefits: low cost, quick

limitations: the same equation is used for everyone

what are the benefits and limitations of direct calorimetry (measures heat production)

benefits: gold standard

limitations: expensive, not always practical

what are the limitations of indirect calorimetry (measures gas exchange - oxygen uptake and CO2 production)

limitations: varies based on the food being oxidised (carbohydrates, proteins and fats require different amounts of oxygen to yield energy)

what are the benefits and limitations of accelerometers (determines activity intensity) to measure energy expenditure

benefits: more accurate than an equation

limitations: doesn't differentiate between physical activity or everyday fluctuations

what is conduction

the transfer of heat between objects of different temperatures in direct contact.

what is radiation

emission of heat energy from a surface in the form of electromagnetic waves

what is convection

the transfer of heat energy by air (or water) currents (eg: breeze, fan)

what is evaporation

liquid vaporises before reaching boiling point, taking heat away from the body.

what is endocrine signalling

production of a hormone that travels through the bloodstream to other organs (neighbourhood)

what is paracrine signalling

secretions that only act on neighbouring cells

what is autocrine signalling

signalling molecules produced by the cell that affect the cell itself.

what is the general structure of the epithelium

the epithelium lines body surfaces.

it can be squamous, cuboidal or columnar in shape and may be arranged in single or multiple layers. (eg: lung tissue = thin for gas exchange, oesophagus = thick for protection).

what is the general structure of connective tissue

connective tissue is found in between other tissue types, and provides support.

it contains fibres, cells and extracellular materials.

* loose connective tissue holds organs in place and attaches epithelial tissue to underlying structures.
* collagen is highly coiled and tightly packed, providing structure.
* dense connective tissue provides strength and elasticity
* bone is made up of organic matrix (collagen and elastin fibres for flexibility) and inorganic matrix (mineral salts and calcium for rigidity)
* blood contains plasma which supports blood cells
* adipose provides a storage area for lipids

what does nervous tissue provide

the communication network.

what is muscle tissue

tightly packed fibres capable of producing movement

what is the relationship between structure and function in terms of tissue types?

the organisation in which a tissue is put together determines how it functions within the body, but a change in function can alter structure.

what is the role of tight junctions

they fuse plasma membranes together, forming a seal.

what is the role of desmosomes

these are proteins located near tight junctions that provide structural support (resist stretch and twisting)

what is the role of gap junctions

these directly connect the cytoplasm of two cells, allowing direct cell-to-cell communication.

what do astrocytes do

provide synapse support

provide neuronal support (regulate the ionic environment, provide glucose for energy)

neurovascular coupling (controls the entry of substances into the brain)

what do microglia do

they survey the brain (detect damage or invasion)

phagocytosis

secrete inflammatory mediators (which fight infection or signal to other microglia and cells)

what does the soma do

this is where action potential initiation occurs. the soma also contains most organelles.

what does the axon do

carries products from soma to the axon terminal.

what do dendrites do

they receive input from other neurons

inotropic receptors vs metabotropic receptors

inotropic - channels that open when a neurotransmitter binds to it allowing the influx of ions.

metabotropic - binding of a neurotransmitter activates a series of proteins, resulting in a signalling cascade.

what is the process of neurotransmitter release? (3 steps)

1. when the action potential reaches the axon terminal, it opens voltage-gated calcium channels
2. calcium entry triggers vesicles containing neurotransmitters to be released into the synapse
3. neurotransmitters bind to receptors on the neighbouring dendritic spine and cause a graded potential.

what is the sympathetic division of the autonomic nervous system

this is the fight or flight response - raises blood pressure, inhibits gut motility and digestion

what is the parasympathetic division of the autonomic nervous system

this is the rest and digest response - lowers blood pressure, increases gut motility and digestion.

what is the process of the Na/K-ATPase pump (5 steps)

1. pump binds an ATP molecule and 3 intracellular Na+ ions
2. ATP is hydrolysed, which phosphorylates the pump and changes its shape
3. this new configuration has a low affinity for Na+ ions so they are released
4. 2 extracellular K+ ions are bound, phosphorylating and reverting the pump to its original configuration
5. this configuration has a low affinity for K+ so they are released.

purpose of the Na/K-ATPase pump

ionic balances are corrected by this pump.

what occurs during depolarisation

as sodium channels open, the charge in that area becomes positive, causing channels near this area to open, allowing the action potential to spread down the neuron.

following this step, voltage-gated sodium channels are inactivated so depolarisation cannot travel back along the axon towards the soma

what occurs during repolarisation

the permeability of the membrane to sodium is closed, so potassium channels open allowing potassium to rush out of the cell and restore the membrane potential.

what occurs during hyperpolarisation

ionic balances are corrected by the Na/K-ATPase pump.

in the resting membrane potential, what molecule is the membrane largely permeable to?

potassium

The site of action potential generation is the

axon hillcock

Protein synthesis in a neuron largely occurs in the

soma

What accounts for the longest delay in neuronal signalling?

Chemical transmission at the synapse

The preganglionic neurotransmitter of the sympathetic nervous system is

acetylcholine

are the 5 steps involved in generating an action potential

1. a stimulus triggers the voltage-gated sodium channels to open, allowing sodium to diffuse into the cell. if the stimulus is too small then the 'all or nothing' threshold won't be achieved, and the action potential will fail to initiate. if the stimulus triggers sufficient opening of transport channels and sodium diffusion into the cell then a full action potential is generated.
2. depolarisation
3. repolarisation
4. hyperpolarisation
5. once the membrane potential reaches its resting homeostatic concentration and chemical gradient, voltage-gated channels close, and cell awaits next stimulus.

what do you call the nervous system that is not under conscious control

autonomic

what channel allows the fastest response to a neurotransmitter

ionotropic

what is the term for an increase in resting membrane potential

depolarisation

what is the main transmitter of the parasympathetic system

acetylcholine

what is the post-ganglionic neurotransmitter of the sympathetic system

noradrenaline

what are the immune cells of the brain

microglia

what is the ion highly concentrated outside the cell

sodium

what is the term for an increase in communication between two neurons

long-term potentiation

mechano-

hearing, balance, blood pressure

photo-

vision

chemo-

taste, smell

thermo-

temperature

noci-

pain

what are the basic components of the sensory system

receptors (detect the stimulus - energy that can be converted into a signal)

neural pathway (carries the signal from the receptor to the brain)

CNS processing

merkel's receptor

sustained pressure

meissner's receptor

change in texture

ruffini receptor

skinstretch

pacinian receptor

deep pressure

how do touch receptors work

receptors are directly linked to ion channels, pressure that moves the skin forces open these channels, allowing ions to flow into the neuron and create a graded potential.

what part of the brain do touch receptors signal to

parietal lobe

what are the supporting structures of the ear

* outer and middle ear amplify sound to the cochlea
* eardrum is connected to the ossicles, which take sound vibrations from the eardrum and concentrate them onto the oval window, converting sound to mechanical energy.
* the cochlea contains a coiled section of membrane that increases in thickness along its length. the mechanical energy vibrates the liquid inside the cochlea.
* hair cells of the ear are pushed from vibrations, opening ion gates and creating a graded potential.

what does the cornea do

contributes to refractive power focussing light to the retina

what does the iris do

controls the amount of light entering the eye

what does the lens do

works with the cornea to focus light onto the retina

what does the retina do

this is a layer of photoreceptors that are responsible for turning light energy into electrical

what does the fovea do

specialised area of the retina with very high acuity

what do cones do

detect colour (only active in bright light)

what do rods do

active in dark conditions (largely black and white)

differences between compact and spongy bone

compact bone:

* is solid/dense and provides the strength of the bone
* contains yellow marrow (contains adipocytes)

spongy bone:

* lattice arrangement (lightweight but more easily fractured)
* stores red bone marrow (contains haemapoietic stem cells)

osteoclasts

bone 'eating' cells that are attracted to microfractures by chemotaxis (chemical movement).

* secrete H+ ions to acidify and break down underlying bone via an active proton pump, collagenase is secreted to break down collagen protein
* allows important minerals to be released into circulation

osteoblasts

bone 'building' cells that form the major cellular component of bones.

* secrete hydroxyapatite, which is a composition of calcium and phosphate.
* as osteoblasts secrete minerals they become immobile transitioning to osteocytes
* these then form tight junctions which isolate the bone from the extracellular fluid

functions of the bone

* provides structural support
* protects internal organs
* allows movement by providing levers for muscle attachment
* acts as a reservoir for mineral homeostasis
* provides environment for haematopoeisis

fibrous joint

no movement, bones have been fused together during development and are composed of mainly collagen

cartilaginous joint

some movement, connected entirely by cartilage

synovial join

freely moveable, features a joint cavity filled with fluid

synovial cavity

holds the synovial fluid, provides cushioning and lubrication for the joint

articular cartilage

provides a gliding surface for the synovial joint bones to move against

ligament

provides anchoring support to the synovial joint, is arranged along a number of axes to account for varying movement of the joint

bursa

small sacs of fluid that lie between bones, ligaments and joints. they provide cushioning to reduce friction and improve range of motion.

fat pad

extra cushioning to the synovial joint.

what is whole muscle

total collection of all the muscle fibres, surrounded by the epimysium

what are fascicles

bundles of muscle fibres surrounded by the perimysium

single muscle fibre

the cell unit of skeletal muscle, surrounded by the endomysium

myofibrils

bunches of myofilaments gathered within a single muscle cell

myofilaments

contains thick and thin filaments arranged into sarcomeres.

sarcomere

follows a hexagonal pattern, allowing for maximal interaction between the muscle fibres to generate force.

what are the steps involving in cross-bridge cycling

1. myosin head binds to actin filament
2. power stroke phase - myosin head pivots and pulls on the actin filament
3. ATP binds to the myosin head, detaching it from the actin filament
4. the myosin head hydrolyses the ATP molecule, resetting itself for another cycle

recruitment (mechanism of generating force)

muscle fibres are activated from small to large (graded potentials will cause greater change in smaller cells, making them more likely to reach the threshold and depolarise)

summation (mechanism of generating force)

increase in the frequency of action potentials