Organisms Respond To Changes In Their Environment: - The Role Of Hormones In Osmoregulation

- Regulation of the water potential of the blood -

Osmoreceptors in the hypothalamus monitors the water potential in the blood.

If the water potential decreases in the blood, water would move out of the osmoreceptor cells by osmosis // cells decrease in volume as a result of this // signal is sent to other cells in the hypothalamus // signal then sent to the posterior pituitary gland. - this secretes the antidiuretic hormone (ADH) into the blood.

ADH makes the walls of the distal convoluted tubule and collecting duct more permeable to water.
More water is reabsorbed from these tubules into the medulla and into the blood by osmosis // small concentration of urine is produced = reduction of water loss. 

Specific protein receptors on cell surface membrane of these cells binds to ADH molecules // activation of phosphorylase (enzyme) within cell // vesicles within the cell move and fuse with the cell surface membrane.

Vesicles contain plasma membrane and have numerous water channel proteins (aquaporins) so when they fuse with the membrane the number of water channels is considerably increased - making cell-surface membrane more permeable to water. 

ADH increases permeability of collecting ducts to urea // passes out // lowering water potential of fluid around the duct.

Combining effect is more water leaves the collecting duct urea // osmosis // down a concentration gradient // re-enters the blood.

Reabsorbed water came from the blood will prevent the water potential lowering // Osmorecpetors send nerve impulses to the thirst centre of the brain encouraging the individual to seek out and drink more water.
Hypothalamus detects the rise in water potential and send fewer impulse to the pituitary gland
Pituitary gland reduces the release of ADH // permeability of the ducts return to its former state // Homeostasis and Negative Feedback.

A fall in the solute concentration of blood raises its water potential. Due to either:
1) Large volumes of water being consumed.
2) Salts used in metabolic or excreted not being replaced in the diet.


The body responds to rise in water potential:
Osmoreceptors in hypothalamus detects rise in water potential // increase frequency of the of nerve impulses to the pituitary gland to reduce its release of ADH

Less ADH // via blood // decrease in permeability of the collecting duct to water and urea

Less water is re-absorbed into the blood from the collecting duct ⇒ more dilute urine = water potential falls in the blood.

In the blood the water potential has returned to normal // osmoreceptors cause the pituitary gland to raise ADH // the levels go back to normal ⇒ Negative Feedback.

Nucleic Acids: - Inorganic Ions

- Inorganic Ions -

Inorganic ions are found in organisms in solution in the cytoplasm of cells and in body fluids, including parts of larger molecules.

They may be in areas that range from very high to very low concentration.

Functions of the ions can vary, however the specific function of a particular ion is based on the relation to it's properties.

Organisms Respond To Changes In Their Environment: - Role Of The Nephron In Osmoregulation

- Nephron filtering the blood -

1. Blood from the renal artery enters smaller arterioles in the cortex of the kidney.
2. Arterioles splits into a glomerulus // bundle of capillaries looped inside a Bowman's capsule // Ultrafiltration takes place.
3. Efferent arterioles that takes blood into each glomerulus // afferent arteriole take the filtered blood away from the glomerulus. 
4. Efferent arterioles are smaller in diameter than afferent arterioles // blood is under high pressure. 
5. High pressure forces liquid and small molecules in the blood out of the capillary and into the Bowman's capsule. 
6. Liquid and small molecules pass through 3 layers get into Bowman's capsule enter the nephron tubules - capillary wall // basement membrane and epithelium of Bowman's capsule.
7. Larger molecule - protein and blood cells can't pass through - stay in blood. Substances enter Bowman's capsule // glomerular filtrate 
8. Glomerular filtrate passes along the rest of nephron - useful substances are reabsorbed along the way. 
9. Filtrate flow through the collecting duct and passes out of the kidney along the ureter. 

Re-absorption of glucose and water by the proximal convoluted tubule

The proximal convoluted tubule is adapted to reabsorb substances: 

Its adaptations include:

- micovilli = large surface area to reasorb substances from filtrate 

- infolding of bases = large surface area to transfer reabsorbed substances back into the blood capillaries 

- high density of mitochondira to provide ATP // active transport

Process of re-absorbtion 

1. Sodium ions actively transported out of the cells lining proximal convoluted tubule into blood capillaries // sodium concentration drops 
2. Sodium ions diffuse down a concentration gradient from lumen of proximal convoluted tubule into epithelial lining cells // only through carrier proteins // facilitated diffusion. 
3. Carrier proteins are specific types to carrier other specific molecules// co-transport // molecules which have been co-transported into the cell of proximal convoluted tubule then diffuse into the blood // All glucose and other valuable minerals are reabsorbed 

Maintenance of gradient of sodium ions by the loop of Henle 

Loop of Henle = responsible for water being reabsorbed from the collecting duct // concentrating the urine so it has lower water potential than blood. 

This has 2 regions 

1. Descending limb - narrow - thin walls that are highly permeable to water. 
2. Ascending limb - wider - thick walls that impermeable to water.

1. Na+ ions are pumped out into the medulla using active transport // ascending limb impermeable therefore water does not move out lowering the water potential in the medulla, because there's a high concentration of ions. 
2. Due to there being a lower water potential in the medulla than in descending limb, water moves out the descending limb, into medulla by osmosis // filtrate is more concentrated. The water in the medulla is reabsorbed into the blood through the capillary network. 
3. Bottom of the ascending limb // Na+ ions diffuse out into the medulla, lowering the water potential further in the medulla. The ascending limb is impermeable to water, so it stays in the tubule. 
4. Water moves out of distal convoluted tubule by osmosis and is reabsorbed into the blood.
5. First three stages massively increase the ion concentration in the medulla, lowers the water potential. Water then moves out of the collecting duct by osmosis. The water in the medulla is reabsorbed into the blood through the capillary network. 

Organisms Respond To Changes In Their Environment: - Control of Blood Water Potential

- Structure Of The Nephron - 

Osmoregulation = the homeostatic control of the water potential of the blood. 

Structure of the mammalian kidney

In the mammal there are two kidneys found at the back of the abdominal cavity. 

A section through the kidney 

Fibrous Capsule = outer membrane that protects the kidney 

Cortex = lighter coloured outer region made up of renal (Bowman's) capsule, convoluted tubles and blood vessels. 

Medulla = darker coloured inner region made up of loops of Henle, collecting ducts and blood vessels 

Renal pelvis = funnel-shaped cavity that collects urine into the ureter 

Ureter = tube that carries urine to the bladder 

Rental artery = supplies the kidney with blood from the heart via the aorta

Renal vein = returns blood to the heart via the vena cava 

Structure of the nephrons 

Renal (Bowman's) capsule = closed end at the start of the nephron. It cup-shaped and surrounds a mass of blood capillaries - Glomerulus. The inner layer of the renal capsule made of specialised cells - podocytes 

Proximal convoluted tubules = series of loops surrounded by blood capillaries. It's walls made epithelial cells - have microvilli 

Loop of Henle = long hairpin loop extends from cortex into medulla of kidney and back again. Surrounded by blood capillaries 

Distal convoluted tubule = series of loops surrounded by blood capillaries. Walls are made of epithelial cell - surrounded by fewer capillaries than proximal tubule. 

Collecting duct = tube number of distal convoluted tubules from a number of nephrons empty. Lined by epithelial cells and becomes increasingly wide as it empties into the pelvis of kidney. 

Associated with each nephron there are number of blood vessels:

Afferent arteriole = tiny vessel arise from renal artery - supplies the nephron with blood // Afferent arteriole enters the renal capsule of the nephron 

Glomerulus = many-branched knots of capillaries from which fluid is forced out of the blood. Glomerulus capillaries recombine.

Efferent arterioles = tiny vessel leaves the renal capsule // smaller diameter than afferent arteriole causes an increase in blood pressure within the glomerulus. Efferent arterioles carries blood away from the renal capsule. 

Blood capillaries = concentrated network of capillaries surrounding the proximal convoluted tublue, loop of Henle mineral salts, glucose, and water. These capillaries merge to form venules, merging to form the renal vein. 

Organisms Respond To Changes In Their Environment: - Diabetes And Its Control

- Diabetes and its control - 

Types of sugar diabetes 

Type 1 - insulin dependent // body unable to produce insulin 

The body attacks its own cells - 𝛽 cells - result of autoimmune response. 

This develops quickly over a few weeks once the individual is born. Usually develops at a very young age. 

Type 2 - insulin independent // body glycoproteins receptors have lost or losing their responsiveness to insulin // body producing an insufficient amount of insulin. 

This develops in people over age of 40 - increases due to obesity and poor diet. 

Symptoms are less severe and may go unnoticed. 

90% of people have type II diabetes 

Control of diabetes 

Diabetes can be successfully treated which depends on the type of diabetes 

Type 1 diabetes = controlled by injections of insulin - cannot be taken orally as it is an enzyme and would be digested. Typcially taken 3-4 times a day. Dose of insulin would match the dose intake of glucose // glucose concentration is monitored using biosensors. 

Type 2 diabetes = controlled by regulating the intake of carbohydrates in the diet // exercise is also taken into account. Supplemented by injections of insulin by the use of drugs that stimulate insulin production. 

Organisms Respond To Changes In Their Environments: - Hormones And The Regulation Of Blood Glucose Concentration

- Hormones and their mode of action - 

Hormones differ chemically but there are characteristics which would be the same also. 

Hormones :

- Produced in glands // secrete hormones directly into blood

- Carried in blood plasma to cells which are acted on // target cells // specific receptors on their cell-surface membrane // complementary to specific hormones.
- Effective in very low concentrations // widespread // long-lasting.

 Second Messenger Model 

2 hormones are used - Adrenaline and glucagon 

1. Adrealine binds to the transmembrane protein receptor within the cell-surface membrane of the liver cell. 
2. Binding of the adrealine causes the protein to change the shape on the inside of the membrane
3. Change in shape of the protein leading to the activation of an enzyme - adenly cyclase // activated adenly cyclase converts ATP to cyclic AMP (cAMP) 
4. cAMP acts as second messenger that binds to the protein kinase enzyme, its activiated by changing its shape.
5. Active protein kinase enzyme catalyses the conversion of glycogen to glucose which moves out of the liver cell // facilitated diffusion // in to the blood through channel proteins. 

Role of the Pancrease in regulating blood glucose 

It produces enzymes - 

Protease, amylase and lipase for digestion and hormones. 

Insulin and glucagon for regulating blood glucose concentration. 

There are groups of hormone-producing cells - islets of Lnagerhans - cells of the islets of Langerhans:

- ɑ cells, larger and produce the hormone glucagon

- 𝛽 cells, smaller and produce the hormone insulin 

Role of the liver in regulating blood sugar 

There are three important processes involved with regulating blood sugar which takes place in the liver:

Glycogenesis - this is the conversion of glucose into glycogen. 

This occurs when the blood glucose concentration is higher than normal. The liver removes the glucose from the blood and converts it into glycogen. 

Glycogenolysis - this is the breakdown of glucagon into glucose.

This occurs when the blood glucose concentration is lower than normal. The liver converts glycogen into glucose which is then diffused into the blood. 

Gluconeogenesis - this is production of glucose from sources other than carbohydrates. 

This occurs when glycogen supply is exhausted. The liver produces glucose from non-carbohydrate sources - amino acids and glycerol. 

Regulation of blood glucose concentration 

Factors that influence blood glucose concentration

1. Directly from the diet = glucose is absorbed from the hydrolysis of carbohydrates 
2. From the hydrolysis of glycagon in the small intestine = glycogenolysis // stored in liver and muscle cells 
3. From gluconeogenesis 

Insulin and the 𝛽 cells of the pancreas 

when combined with receptors insulin brings about:

- Change in tertiary strucute of the glucose transport carrier proteins - changing shape and open - allows more glucose into the cells by facilitated diffusion.

- Increase in number of carrier proteins responsible for glucose transport in the cell-surface membrane. Protein from which these channels are made is part of the vesicles. // rise in insulin concentration the vesicles fusing with the cell-surface membrane increasing the number of glucose transport channels. 

- Activation of enzyme that convert glucose to glycogen and fat. 

Blood glucose is lowers through the following ways:

- Increasing the rate of absorption of glucose into the cells - muscle cells

- Increasing rate of respiration of the cells // uses more glucose // increasing the uptake from the blood

- Increasing glycogenesis in liver and muscle cells

- Increasing the rate of conversion of glucose to fat. 

The processes taking place = Negative feedback // removal of glucose reduced the secretion of insulin from 𝛽 cells. 

Glucagon and the ɑ cells of the pancreas 

ɑ cells detect the fall in blood glucose concentrations releasing the hormone glycogen directly into the blood plasma. 

Glycogen action include: 

- Attaching to specific protein receptors on cell-surface membrane of liver cells 

- Activating enzymes convert glycogen to glucose 

- Activating enzymes involved in conversion of amino acids and glycerol into glucose = glyconeogenesis 

This returns the blood glucose concentration to the optimum. 

Role of adrenaline in regulating the blood glucose level 

Adrenaline raises the blood glucose concentration by:

- Attaching to protein receptors on the cell-surface membrane of target cells 

- Activating enzymes that causes the breakdown of glycogen to glucose in the liver. 

Adrenaline is produced when there is a period of excitement or stress. 

Hormone interaction in regulating the blood glucose

Insulin and glycagon act in opposite directions = antagonistically 

These two hormones are sensitive to control of the blood glucose concentration // blood glucose concentration is not constant there are fluctuations around the optimum temperature. 

When writing about negative feedback its important to mention that the secretion of a hormone - insulin - would result in the reduction of its own secretion. 

Organisms Respond To Changes In Their Environments: - Feedback Mechanisms

- The control mechanisms -

Control of any self regulating system involves a series of stages

- Optimum point
- Receptor
- Coordination
- Effector
- Feedback mechanism

Homeostatic systems detect change and respond by negative feedback.

1) The receptor, communication system and effectors is the foundation of the homeostatic system. 

2) Receptors are there to detect when there is a change in temperature - this would be when temperature is too high or too low. Via the nervous system or hormonal system the information is passed on to the effector. 

3) The effectors are suppose to counteract the change // bring the level back to an optimum. 

4) Negative feedback = process of bring the level to an optimum temperature. 

5) Negative feedback keeps the body's temperature at an optimum which is above 0.5℃ or below 37℃.

6) However if they change is too drastic then the Negative feedback would be unable to counteract the change. This can be when there has been prolonged exposure to cold weather. 

There are multiple Negative feedback mechanisms ⇒ more control. By only having one negative feedback system ⇒ there is a slower response and less control. 

Positive feedback mechanisms can amplify a change from the normal level. 

1) some changes can trigger a positive feedback // amplifying the change. 

2) Increasing the level further away from the normal level.

3) Positive feedback rapidly activates something // Blood clot after a deep cut. 

4) Positive feedback can occur when homeostatic system breaks down e.g. Being too cold for too long.

Positive feedback is not involved in homeostasis because it does not keep the internal environment stable.

- Coordination of control mechanisms -

Control system normally have receptors and effectors allows them to have separate mechanisms that produce a positive movement towards an optimum. Allows greater degree of control of the particular factor being regulated. 

Nucleic Acids: - Water

- Water - 

Dipolar water molecule: water is made up of two atoms of hydrogen and one of oxygen. The molecule has no overall charge although oxygen has a slightly negative charge and hydrogen has a slightly positive charge.

Water and hydrogen bonding:

A positive pole of one water molecule would attract the negative pole of another water molecule, the attraction force between the opposite charges is a hydrogen bond. Each bond is weak, however together they form important forces that cause water molecules to stick together, giving water unusual properties.

Specific heat capacity:

Water molecules stick together, it takes more energy -heat- to separate them then if they did not bond to one another. Resulting in the boiling point being high (100 degrees celsius)

Without hydrogen bonding water would be a gas at temperatures on earth.

Water acts as a buffer against sudden temperatures variations - aquatic environment is a temperature stable one.

Organisms are mostly water, protects them from sudden temperature change especially in terrestrial environment.

Latent heat of vaporisation of water:

Hydrogen bonding = lots of heat energy required to evaporate 1 gram of water. - latent heat of vaporisation.

Evaporation of water in mammals is therefore a very effective means of cooling, body heat is used to evaporate the water.

Cohesion and surface tension:

Tendency of molecules sticking together = cohesion

• Hydrogen bonding = large cohesive forces, allowing it to be pulled through a tube - xylem vessel
• Water molecules meet air, tend to be pulled back into the body of water than escaping from it = surface tension.
• Water acts like a skin, strong enough to support small organisms - pond skaters

Importance of water to living organisms:

Water in metabolism -

• Used to breakdown complex molecules - hydrolysis
• Joins molecules together through the use of condensation reaction
• Chemical reactions take place in aqueous medium
• Water = major raw material in photosynthesis

Water as a solvent -

• Readily dissolves other substances - gases ie, oxygen + carbon dioxide
• Waste - ammonia + urea
• Inorganic ions + small hydrophilic molecules - amino acids, monosaccharides, + ATP
• Enzymes - reactions which takes place in a solution.

Important features of water:

• Evaporation cools and allows organisms to control their temperature.
• Not easily compressed = providing support - hydrostatic skeleton of animals// earthworm + turgor pressure in herbaceous plants
• Transparent = aquatic plants can photosynthesise // light penetrate jelly like fluid that fills the eye and reach the retina.

Nucleic Acids: - ATP

- ATP - 

ATP - Adenosine triphosphate is a nucleotide and has three phosphate groups and is key in storing energy. The bonds between the phosphate groups are unstable therefore have a low activation energy - can be easily broken. They release a considerable amount of energy. In living cells it is only the terminal phosphate that is removed

Structure of ATP:

• Adenine - nitrogen containing organic base.
• Ribose - sugar molecule with 5 carbon ring structure - backbone
• Phosphates - chain of three phosphate groups

.

Synthesis of ATP: ATP to ADP is a reversible reaction therefore energy can be used to add an inorganic phosphate to ADP to re-form ATP. This reaction is catalysed by enzyme ATP synthase. The reaction is a condensation reaction.

The synthesis ATP from ADP involves addition of phosphate molecule to ADP.

• In chlorophyll containing plant cells during photosynthesis (photophosphorylation)
• In plant and animal cells during respiration (oxidative phosphorylation)
• In plant and animal cells when phosphate groups are transferred from donor molecules to ADP (substrate level phosphorylation)

Roles of ATP:

• ATP serves as an immediate energy source of a cell
• Cells do not require large quantities of ATP
• ATP is rapidly re-formed from ADP and inorganic phosphate

ATP is required as energy-requiring processes in cells:

• Metabolic processes
• Movement
• Active transport
• Secretion
• Activation of molecules