biology unit 6

homeostasis definition

Maintaining a constant internal environment within restricted limits in organisms. Homeostasis is the ability to return to the optimum point so an organism is maintained in a balanced equilibrium

importance of maintaining a core body temperature

Enzymes denature – molecules vibrate too much

which breaks the hydrogen (and other) bonds holding

their secondary and tertiary structure. Active site

changes shape; no longer complementary therefore

NO ESCs form.

importance of maintaining stable blood PH

Enzymes denature – the charges on the amino acids

are altered so the active site changes shape and

bonds may break. Active site changes shape; no

longer complementary therefore NO ESCs form.

The importance of maintaining a stable blood glucose concentration

-for water potential of blood, cells dont become hypotonic or hypertonic

-glucose is a respiratory substrate, needs to be available for adequate levels of respiration

negative feedback

when any deviation from the normal values are restored to their original level

-change away from optimum condition

-receptors detect change

-communication systems inform effector

-effector reacts to reverse change

hormones in blood glucose control

-the pancreas detects changes in the blood glucose levels, it contains endocrine cells in the islets of Langerhans which release the hormones insulin and glucagon

-adrenaline released by adrenal glands when danger anticipated

blood glucose negative feedback

-blood glucose increases, detected by beta cells in the islets of Langerhans, beta cells release insulin

-blood glucose decreases, detected by alpha cells in the islets of Langerhans, release glucagon (adrenaline has the same effect)

glycogenesis

the process of excess glucose being converted to glycogen when blood glucose is higher than normal, mainly occurs in the liver

glycogenolysis

hydrolysis of glycogen back into glucose in the liver, occurs when blood glucose levels are lower than normal

gluconeogenesis

the process of creating glucose from non-carbohydrate stores in the liver, occurs when all glycogen has been hydrolysed into glucose but your body needs more

the action of insulin

-Beta cells in islets of Langerhans detect when blood glucose too high and secrete insulin

insulin decreases blood glucose in the following ways:

• attaching to receptors on the surfaces of target cells, changes tertiary structure of the channel proteins resulting in more glucose being absorbed by FD

• more protein channels added to CSMs, more glucose absorbed from blood into the cells

• activates enzymes involved in conversion of glucose to glycogen (glycogenesis in the liver)

action of glucagon

-alpha cells in islets of Langerhans detect when blood glucose conc too low, glucagon increases it in the following ways:

• attaching to receptors on the surfaces of target cells

• when it binds it causes a protein to be activated into adenylate cyclase and convert ATP into cyclic ATP, activates the enzyme protein kinase that can hydrolyse glycogen into glucose

• activating enzymes enzymes involved in the conversion of glycerol and amino acids into glucose

second messenger model

-glucagon binds to glucagon receptors

-once bound it causes a change in shape to the enzyme adenyl cyclase, which activates it

-activated adenyl cyclase converts ATP into cyclic ATP

-activates protein kinase that can hydrolyse glycogen into glucose

action of adrenaline

increases blood glucose levels

• attaches to receptors on the surfaces of target cells, causes a protein to be activated and to convert ATP into cyclic ATP

• cyclic ATP activates an enzyme which can hydrolyse glycogen in to glucose

diabetes

when blood glucose can not be controlled

type 1 diabetes

-is due to the body being unable to produce insulin

-starts in childhood and could be the result of an autoimmune disease where beta cells are attacked

-treatment involves injections of insulin

type 2 diabetes

-due to receptors on the target cells loosing their responsiveness to insulin

-usually develops in adults due to obesity and poor diet

-controlled by regulating intake of carbohydrates, increasing exercise and sometimes insulin injections

where does osmoregulation occur

the nephrons which are in the kidneys

-osmoregulation is the control of water potential in the blood

-nephrons are long tubules surrounded by capillaries and are approx 1 million per kidney, goal is to filter blood to remove waste and selectively reabsorb back into blood

nephron structure

-efferent and afferent arterial

-renal capsule with glomerulus

-proximal convoluted tubule

-loop of henle

-distal convoluted tubule

-collecting ducts

what urine contains and does not contain

contains

• water

• dissolved salts

• urea

• other small substances

does not contain

• proteins and blood cells (too large to filter out)

• glucose (absorbed by selective reabsorption in the proximal convoluted tubule)

ultrafiltration

-blood enters through the afferent arteriole and this splits into lots of smaller capillaries which make up the glomerulus

-causes a high hydrostatic pressure of the blood

-water and other small molecules forced out of the capillaries and forms the glomerulus filtrate

-large proteins and blood cells too big to fit through capillary endothelium so remain in blood

-blood leaves via the efferent arteriole

path of water and small molecules forced out

-move out of pores in capillary endothelium

-into the basement membrane

-podocytes are final layer and are cell that wrap around capillary also have gaps

-act as filtration layers

proximal convoluted tubule adaptations

-microvilli provide a large SA for reabsorption

-lots of mitochondria to provide energy for active transport

selective reabsorption

-occurs in proximal convoluted tubule

-concentration of sodium ions in the PCT decreased as sodium ions actively transported out of the PCT cells into the capillaries (blood)

-due to the concentration gradient sodium ions diffuse down from the lumen into the cells lining the PCT, carries glucose with it through carrier proteins (co-transport)

-glucose can then diffuse from the PCT epithelial cell into the blood stream, reabsorbing all glucose

loop of henle function

-maintain a sodium ion concentration gradient to enable reabsorption of water, in the medulla by the loop of henle

-has an ascending and descending limb

loop of henle process

-mitochondria on the walls of the cell provide energy to actively transport sodium ions out of the ascending limb of the loop of henle

-accumulation of sodium ions outside the nephron in the medulla lowers the water potential

-water moves out via osmosis into the interstitial space and then into blood in capillaries (reabsorbed)

-at the base of the ascending limb some sodium ions transported by diffusion as now very dilute solution as water has moved out

distal convoluted tubule rand collecting duct

-due to all sodium ions being actively transported out of the loop of henle, when the filtrate reaches the DCT it is very dilute

-filtrate moves into the DCT and collecting duct, this section of the medulla is very concentrated

-therefore even more water diffuses out the DCT and collecting duct

-what remains is transported to form urine

factors influencing blood glucose concentration

increases following ingestion of food or drink containing carbohydrates

falls following exercise or if you haven’t eaten

what we do when water potential of blood is too high or low

-if too high the body expels water, a large volume of dilute urine produced

-if too low the body conserves water, a small volume of very concentrated urine produced

role of hypothalamus in osmoregulation

-coordinates osmoregulation, synthesizes ADH

-ADH then transported to the posterior pituitary gland where it is stored

-hypothalamus contains osmoreceptors which are sensitive to the WP of blood

-if low WP water moves out osmoreceptor cells, causing them to shrink, triggering the posterior pituitary gland to release ADH into the blood

ADH once in bloodstream

-collecting ducts have receptors specific to ADH

-cells of have vesicles containing aquaporins (protein channels for water)

-ADH attach, triggering adenylate cyclase to produce cyclic AMP, which triggers the vesicles to move to and fuse with CSM

-lots of water molecules can move in through the aquaporins by osmosis, the water can then move by osmosis into the medulla and carried away in blood

-ADH also causes the wall of the collecting duct to be more permeable to urea, now moves from the fluid in the collecting duct into the medulla, further lower medulla WP and increasing reabsorption

-less water leaves body in urine

when water potential too high

-osmoreceptors detect

-trigger PPG to release less ADH

-aquaporin returns back to vesicles, makes collecting duct walls less permeable to water

-less water reabsorbed and large volume of dilute urine produced

responses to stimuli

-a stimulus is a detectable change in the environment, these changes can be detected by cells which are called receptors

-organisms can increase their chance of survival by responding to stimuli via different response mechanisms

-taxis and kinesis are simple responses which keep organisms within the favourable conditions of their environment

taxes

-this is a simple response in which an organism will move it’s entire body towards a favourable stimulus (positive taxis) or away from an unfavourable stimulus (negative taxis)

-earthworms will show negative phototaxis as they move away from light (dark environments make them less visible to predators and avoid dehydration)

-bacteria can show positive chemotaxis, as they move towards certain chemicals to aid survival

kinesis

-when an organism changes it’s speed of movement and the rate at which it changes direction

-if an organism moves from an area of beneficial stimuli to one of harmful stimuli, it’s kinesis response will be to increase the rate at which it changes direction to return to favourable conditions quickly

-if an organism is surrounded by negative stimuli, the rate of turning decreases to keep it moving in a relatively straight line, to increase the chances of it finding a new location with favourable conditions

responses in flowers/plants

-tropisms is the term given to when plants respond (via growth) to stimuli

-tropisms can be positive or negative, growing towards or away from a stimulus, plants respond to light, gravity and water

-tropisms are controlled by specific growth factors and one key example is indoleacetic acid (IAA)

-IAA is a type of auxin and can control cell elongation in shoots and inhibit growth of cells in the roots

-made in the tip of the roots and shoots but can diffuse to other cells

phototropism in the shoots

• shoots need light for the LDR of photosynthesis, which is why plants grow and then bend towards light, this is controlled by IAA and is positive phototropism

• shoot tip cells produce IAA, which causes elongation in shoots, this IAA then diffuses to other cells, if there is unilateral (one sided) light then the IAA will diffuse to the shaded side of the shoot resulting in a higher concentration there

• the IAA causes the cells on the shaded side to elongate more, causing the plant to bend towards the light source

phototropism in the roots

-roots do not photosynthesize and do not require light and are more able to anchor the plant if they are deep in soil away from light

-in roots, high concentration of IAA inhibits cell elongation, causing root cells on the lighter side to bend more, turning down and away from the light, as IAA diffuses to shaded side

-negative phototropism

gravitropism

shoots -

• IAA will diffuse from the upper side to the lower side of a shoot (from the tip towards the pull of gravity), if a plant is vertical this causes the plant cells to elongate and the plant grows upwards, if a plant is on it’s side in a dark room (experiment) it will still cause the shoot to bend upwards

• this is negative gravitropism

roots -

• IAA diffuses to the lower side of the roots, so the upper side elongates and the root bends downwards towards gravity and anchors the plant in

• positive gravitropism

response and the nervous system

-a stimulus is a detectable change in the environment, these changes can be detected by cells called receptors, triggering a response seen below

stimulus → receptor → coordinator → effector → response

-organisms increase their chance of survival by responding to stimuli via different response mechanisms

-nervous system is made up of the PNS and CNS

• PNS includes the receptors, sensory and motor and relay neurons

• CNS brain and spinal cord

receptors

each receptor responds only to specific stimuli and this stimulation of a receptor leads to the establishment of generator potential which can cause a response

receptors include -

• Pacinian corpuscle

• rod cells

• cone cells

Pacinian corpuscle

-responds to pressure changes, these receptors occur in deep skin, mainly in fingers and feet

-it consists of a single sensory neuron wrapped with layers of tissue separated by gel

-the sensory neuron in the Pacinian corpuscle has special channel proteins in it’s plasma membrane

-these are stretch-mediated sodium ion channels, these channels will only open and allow sodium ions to enter the sensory neuron when they are stretched and deformed

-in the resting state the Na+ channels are to narrow for Na+ to diffuse into the sensory neuron, therefore resting potential is maintained

-when pressure is applied and it deforms and stretches the neuron plasma membrane, widening the channels allowing Na+ to diffuse in which leads to the establishment of a generator potential