3.6 Organisms respond to changes in their internal and external environments

Homeostasis

The maintenance of a constant internal environment

importance of homeostasis in temperature

Increased temperature, increases rate of reaction by increasing kinetic energy so substrates are more likely to collide with enzymes more. However, if temperature goes too high then enzymes denature as hydrogen bonds break and the 3D shape changes. Optimum is 37 degrees.

importance of homeostasis in pH

Fluctuation of blood pH causes enzymes and proteins to denature as hydrogen bonds will break and the active site shape will change.

pH

pH\=-log[H+]. Based on the concentration of hydrogen ions.

negative feedback

Deviations from the norm trigger responses that restore the system to its original level.

positive feedback

Deviations from the norm are not corrected and the deviations may be made larger, it is usually harmful as it tends to produce unstable conditions and extreme states e.g. oxytocin during labour causing contractions, hypothermia

Control of blood glucose

TOO HIGH: pancreas produces hormone insulin which allows glucose to move from the blood into the liver cells and is stored as glycogen

TO LOW: pancreas produced glucagon which causes glycogen to be turned into glucose and released into the blood

role of liver in blood glucose control

receives all glucose absorbed into the blood from the intestines via the hepatic portal vein. Responsible for adding glucose by glycogenolysis and gluconeogenesis. Responsible for removing glucose by glycogenesis.

Glycogenolysis

breakdown of glycogen to glucose - GLUCAGON

Gluconeogenesis

The formation of glucose from noncarbohydrate sources, such as amino acids. - GLUCAGON

Glycogenesis

formation of glycogen from glucose - INSULIN

role of pancreas in blood glucose control

\-Release of insulin from beta cells in islets of Langerhans when glucose is high in the blood

\-Release of glucagon from alpha cells in islets of Langerhans when glucose is low in the blood

Insulin

lowers blood glucose levels by binding to hepatocytes on muscles and liver which increase permeability of membranes to glucose to remove it from the blood by increasing channel proteins - GLUT 4

Glucogan

increases blood glucose levels by binding to hepatocytes of liver and activates enzyme for glycogenolysis and gluconeogenesis.

glucose transporter - GLUT 4

Channel proteins that allow glucose to be transported across the cell membrane by facilitated diffusion. GLUT 4 is stored in vesicles which moves to the membrane when insulin binds allows glucose to enter cells.

Negative feedback of increased glucose concentration

Hyperglycaemia, beta cells secrete insulin, insulin binds to hepatocytes, causes GLUT 4 to move, activates enzymes for glycogenesis and synthesis of lipids from glucose

Negative feedback of decreased glucose concentration

Hypoglycaemia, alpha cells secrete glucagon, glucagon binds to hepatocytes, activates enzymes for glycogenolysis and gluconeogenesis.

Adrenaline

secreted by adrenal glands when glucose concentration is low, stressed or exercising. Binds to hepatocytes and activates glycogenolysis and inhibits glycogenesis. Activates glucagon and inhibits insulin.

second messenger

To activate glycogenolysis, adenylate cyclase needs to be activated, then converts ATP into cAMP which activates protein kinase which causes a cascade of reactions for glycogenolysis

diabetes

Metabolic disorder where blood glucose concentration cannot be controlled, caused by a lack of insulin or loss of responsiveness to insulin.

Type 1 diabetes

Diabetes of a form that usually develops during childhood, autoimmune response where the immune system attacks beta cells so cannot secrete insulin

type 2 diabetes

Usually occurs later in life, loss of responsiveness in the hepatocytes to insulin or less production from beta cells - obesity/ poor diet, age, lack of exercise

diabetes treatment

insulin injections, education, exercise, healthy diet

glucose in urine

• colorimetry

• serial dilution of known concentrations and calibration curve

nephron structure

Glomerular capsule, proximal tubule, loop of henle, distal tubule, collecting duct

Ultrafiltration

The process where liquid and small molecules are forced from the blood out of the capillaries of the glomerulus, under high pressure (WANE) , into the Bowman's capsule.

Layers filtrate pass through to get to Bowman's capsule

capillary endothelium that has pores called fenestrae, basement membrane, epithelium of the bowman's capsule that has podocytes and pedicels to increase SA and rate of diffusion

Selective reabsorption

useful substances such as all sugar, some mineral ions, and water are reabsorbed back into the blood from the filtrate in the PCT (has microvilli). Active transport using symport for sodium and glucose into cells from filtrate, Facilitated diffusion for glucose and sodium-potassium pump from cell to blood, osmosis for water.

maintaining a gradient of sodium ions in the medulla by the loop of Henle

Sodium ions actively pumped out of ascending limb to create low water potential in medulla as ascending limb is impermeable to water so it stays. Therefore water moves out of the descending limb due to low water potential into the medulla and is reabsorbed into the blood. Sodium ions also diffuse out of bottom of loop of Henle.

role of the DCT and collecting duct

Water moves out of the DCT by osmosis e to low water potential in medulla and is reabsorbed into the blood. Low water potential in medulla also causes water to leave collecting duct via osmosis and it is also reabsorbed into the blood.

Osmoregulation

Osmoreceptors in the hypothalamus monitor water potential of the blood. Decrease in water potential causes water to leave the osmoreceptors, decreasing their volume which sends a signal to the pituitary gland that releases ADH.

ADH

ADH binds to target cell receptors in the DCT and collecting ducts membranes and cause metabolic changes. Causes aquaporins in the membranes to form which allows water to pass through via osmosis so it can reabsorbed into the blood by osmosis, less urine produced to prevent water loss.

negative tropism

growth away from a stimulus to increase survival

positive tropism

Growth towards a stimulus to increase survival

Phototropism

A growth response to light

Hydrotropism

a plants growth response to water

Gravitropism

a plant's growth response to gravity

Auxin

a natural plant hormone that respond to stimuli and has a variety of effects, including cell elongation, root formation, secondary growth, and fruit growth.

IAA

Indoleacetic acid is an auxin - a plant growth factor which is produced in small quantities and made in roots and shoots. When light hits it unevenly distributes via diffusion and active transport and softens cell walls by affecting hydrogen bonds in cellulose. It causes elongation of shoot cells but inhibits elongation in root cells.

taxis

directed movement in response to a stimulus

kinesis

non-directional movement in response to a stimulus

Orthokinesis

change in speed of movement

Klinokinesis

a change in the rate of turning

coordinator

controls response

Effector

bring about response

response

a reaction to a stimulus

sensory neurons

carry impulses from the receptor to the central nervous system

motor neurons

carry impulses from the CNS to effectors

Relay neurone

carry impulse between sensory and motor neurons

human receptor cells

sensitive to a particular stimulus acts as transducers as convert energy of stimulus into electrical energy and initiate an impulse

Reflex action

automatic, involuntary responses to stimuli that is innate

local chemical mediator

excreted from cells and target the cells next to where they are produced.

Prostoglandins

inflammatory response - blood pressure regulation and clotting

Histamine

inflammatory response to injury and infection, increases permeability of capillaries

resting potential

The potential difference between the inside (negative) and outside (positive) of a neuron's cell membrane

generator potential

stimulus detected and alters the potential difference as membrane becomes more permeable to ions.

action potential

if the generator potential exceeds threshold level then a action potential is reached and electrical impulse is sent - all or nothing.

Panician corpuscle

mechanoreceptors sensitive to changes in pressure or touch in the skin, tendons, muscles and joints. Pressure acts as stimulus and causes stretch-mediated sodium channels to open and causes a change in charge.

Photoreceptors in the eyes

photoreceptors in retina detect light as it enters via pupil and controlled by iris, bipolar neuron and optic nerve

Thrichromatic Theory of Color Vision

there are 3 different types of cones, each most sensitive to a different range of wavelengths (blue, green, red)

Rod cells

peripheral parts in retina, respond to low light intensities, numerous rods make a single bipolar neuron. High retinal convergence which lowers visual acuity

Stimulation of rod cells

light bleaches rhodopsin and products trigger a generator potential which triggers action potential if it exceeds threshold level

cone cells

located in fovea, operate best in bright light; enable high-acuity, color vision as each bipolar cell is stimulated by a single cone cell \= low retinal convergence

stimulation of cone cells

light bleaches iodopsin and products trigger a generator potential which triggers action potential if it exceeds threshold level

resting potential

• negatively charged inside compared to outside -70mv

• SOPI pump, uses active transport to move 3 NA+ out and 2 K+ in

• potassium ion channels allow facilitated diffusion of K+ out

stages of action potential

1. depolarisation as gated sodium channels open and it diffuses in

2. repolarisation as sodium channels close and potassium channels open

3. hyperpolarisation when resting potential is beginning to be reached again the potassium gates slowly close and ion exchange is complete

refractory period

the time following an action potential during which a new action potential cannot be initiated. Absolute - no new action potential and relative - only action potential if big stimulus.

Wave of depolarisation

Action potentials travel across neurons in a wave. The depolarisation in one region triggers depolarisation in the next as Na+ that diffused through ion channels diffuse sideways to stimulate the next channels

all or nothing principle

Once the threshold is reached an action potential will fire with the same change in voltage no matter the size of the stimulus, but will fire more frequently. If threshold level is not reached it will not fire.

speed of nerve transmission - myelin

myelin sheath produced by schwann cells insulate the axon and speed up transmission by nodes of ranvier as the action potential can jump causing saltatory conduction.

speed of nervous transmission - diameter

greater the diameter, faster the speed of conductance as leads to less leakage of ions so can maintain membrane potential

speed of nervous transmission - temperature

the higher the temperature, the more kinetic energy so the faster the impulse. Active transport and SOPI pump rely on enzymes so requires an optimum temperature.

synapse with ACH

1. action potential reaches presynaptic neuron
2. increases permeability to calcium
3. calcium ions diffuse in from tissue fluid
4. calcium causes vesicles to migrate towards presynaptic membrane
5. vesicles fuse with membrane to release ACH (exocytosis)
6. ACH released into cholinergic synapse and diffuse across
7. ACH diffuses and binds to postsynaptic cholinergic receptors
8. triggers sodium gated channels to open
9. ACH broken down by acetylcholinesterase into acetic acid and choline
10. products diffuse back to presynaptic neuron to resynthesis ACH using ATP from mitochondria

neuromuscular junction

1. Specialised cholinergic synapse between motor neuron and a muscle cell

2. ACH binds to nicotinic receptors

3. This stimulates ion channels in the sarcolemma to open, allowing sodium ions to diffuse in which depolarises the sarcolemma, generating an action potential that passes down the T-tubules towards the centre of the muscle fibre

4. These action potentials cause voltage-gated calcium ion channel proteins in the membranes of the sarcoplasmic reticulum to open

5. Calcium ions diffuse out of the sarcoplasmic reticulum (SR) and into the sarcoplasm surrounding the myofibrils

6. Calcium ions bind to troponin molecules, stimulating them to change shape

7. This causes the troponin and tropomyosin proteins to change position on actin and exposes the myosin-binding sites

8. The process of muscle contraction (known as the sliding filament model) can now begin as the myosin-actin cross bridge can form

Unidirectionality of synapses

one direction as neurotransmitters are made in the presynaptic and receptors are on the postsynaptic

Summation

combines different sources of information before responding

spatial summation

The sum of multiple synapses firing at different locations at one time to exceed threshold level and trigger an action potential

temporal summation

2 or more impulses arrive in quick succession from the same synapse to exceed threshold and trigger an action potential

excitatory neurotransmitters

Cause depolarization of postsynaptic membranes and promotes action potentials

inhibitory neurotransmitters

hyperpolarize the postsynaptic neuron preventing action potential as makes it more negative

Control of heartbeat

1. SAN produces impulse to stimulate atrial systole

2. Non conductive tissue delays impulse

3. Impulse stimulates AVN

4. Impulse travels down bundle of his

5. Bundle of his splits into left and right ventricles

6. Impulse from purkinje fibres causes ventricular systole

modification of heart rate

1. cardiovascular centre in medulla

2. Cardio-acceleratory centre or cardio-inhibitory centre

3. increase - sympathetic, decrease - parasympathetic

4. increased frequency - release noradrenaline, decreased frequency - release acetylcholine

Chemoreceptors

sensitive to chemical changes, carbon dioxide in the blood affects pH levels so they increased heart rate.

Baroreceptors

sensitive to changes in blood pressure, sends impulses to cardio centres to either increase or decrease.

smooth muscle

involuntary muscle found in internal organs

cardiac muscle

Involuntary muscle tissue found only in the heart, myogenic so has own inherit rhythm.

skeletal muscle

voluntary muscle used to move

Sarcolemma

muscle cell membrane

T tubules

tubular infoldings of the sarcolemma which penetrate through the cell and spread electrical impulses

sarcoplasmic reticulum

Organelle of the muscle fiber that stores calcium for contraction

muscle fibres

multinucleate, lots of mitochondria, myofibrils

Myofibrils

organelles made of protein - bundles of thick and thin myofilaments that slide past each other to contract

Myofilaments

thin (actin) and thick (myosin)

sliding filament theory

When sarcomeres shorten (contract), the thick and thin filaments do not change length, but rather slide past each other and the thin filaments move toward the center of the sarcomere from both ends. As this happens, the H zones and I bands narrow, regions of overlap widen, and the Z lines move closer together, shortening the sarcomere.

I band of sarcomere

contains only thin actin filaments

A band of sarcomere

contains all of the thick myosin filaments plus any overlapping think actin filaments

M line of sarcomere

center of sarcomere

z-line of sarcomere

end of actin

H zone of sarcomere

central myosin only

myosin heads

Bind to specific sites on actin molecules to form cross bridges