Organisms respond to changes in their internal and external environments

What is the primary role of the kidneys in relation to water?

The kidneys control osmoregulation, which involves managing the water potential of the blood by reabsorbing water into the blood and removing it in urine.

Where does the process of creating a low water potential in the kidney medulla begin?

The process begins at the loop of Henle.

What is the function of the ascending limb of the loop of Henle?

It actively transports salts such as sodium and chloride ions out into the surrounding medulla, contributing to a lower water potential.

What happens to water in the descending limb of the loop of Henle?

Water is reabsorbed from the filtrate into the blood by osmosis because the descending limb is permeable to water.

What hormone regulates the permeability of the distal convoluted tubule and collecting duct to water?

The hormone ADH (antidiuretic hormone) regulates the membrane permeability to water.

How do osmoreceptors function in the kidney's response to water potential changes?

Osmoreceptors in the hypothalamus detect changes in water potential and signal the pituitary gland to release more or less ADH accordingly.

What is the effect of increased ADH levels on urine concentration?

Increased ADH levels lead to more reabsorption of water, resulting in more concentrated urine.

What is the counter-current multiplier effect in the loop of Henle?

It allows for a greater exchange of substances by having two fluids flow in opposite directions, enhancing the concentration gradient.

What are aquaporins and their role in osmoregulation?

Aquaporins are channel proteins that increase the permeability of cell membranes to water, facilitating its reabsorption in the collecting ducts.

What are the consequences of low water potential in the blood?

It triggers a series of events where more ADH is released, increasing water reabsorption and resulting in decreased urine volume and higher concentration.

What happens when there is high water potential in the blood?

It leads to less ADH release, making the collecting ducts less permeable to water, resulting in increased urine volume and lower concentration.

What are the two main roles of the kidneys in the body?

Osmoregulation and excretion.

What is osmoregulation?

Maintaining the water potential of blood by removing excess water or retaining water.

What is excretion in the context of kidney function?

Removing nitrogenous waste in the form of urea from the blood.

Describe the process of urine formation in the kidneys.

The kidneys filter blood to remove urea and dilute it with water to form urine, which is sent to the bladder via the ureter.

What is a nephron?

A fine tube structure in the kidney that carries out filtration and reabsorption.

What is the cortex and its role?

The outer layer full of the filtration parts of the nephrons and filters the blood

What is the medulla and its role?

The inner layer which contains the tubes carrying filtered wastes to the centre (pelvis) of the kidney. Contains the loop of henle and the collecting duct parts of the nephrons

What is the function of the glomerulus?

To filter blood using blood pressure, forcing fluid out into the Bowman's capsule.

What does the Bowman's capsule do?

It is a cup-shaped sack that surrounds the glomerulus and collects the filtrate.

Where does ultrafiltration occur

In the Glomerulus

What are the 3 vessels associated with the kidney

Ureter, renal artery and renal vein

What are the 3 regions of the kidney

Renal cortex, medulla, renal pelvis

Explain how the glomerulus is able to perform its function

• Blood enters the glomerulus through the afferent arteriole

• has a greater diameter than the efferent arteriole

• creates a build up of high hydrostatic pressure

• forces plasma out the blood through walls of capillaries

• capillaries have fenestrations

• allowing ultrafiltration to occur

Describe how ultrafiltration produces glomerular filtrate

• high hydrostatic pressure

• causes small molecules e.g. glucose and water

• to pass through fenestrations of the capillary endothelium walls

• basement membrane acts as a filter

• but proteins are too large to pass through so stay behind

What is selective reabsorption in the kidneys?

The process that ensures necessary molecules like glucose and amino acids are reabsorbed back into the bloodstream.

What structures in the kidney are responsible for adjusting water reabsorption?

The proximal convoluted tubule (PCT) and the distal convoluted tubule (DCT) manage the reabsorption of water and other substances.

What prevents large molecules such as proteins from entering the glomerular filtrate?

The filtration system, including podocytes and the basement membrane, restricts their passage.

What is the renal pelvis?

The part of the kidney where all the collecting ducts come together and connect to the ureter.

What is the role of the ureter?

To transport urine from the kidney to the bladder for excretion.

What happens in the proximal convoluted tubule (PCT)?

Approximately 85% of the filtrate, including all glucose and amino acids, is reabsorbed into the blood.

What structures aid in maximizing reabsorption in the PCT?

Folded membranes, numerous membrane proteins, ribosomes, and mitochondria.

What is the function of the loop of Henle?

To make final adjustments to water and salts reabsorption and control blood pH.

What is adrenaline?

A hormone from the adrenal glands that prepares the body for stress or emergencies.

The second messenger model

Describes how non-lipid-soluble hormones trigger an internal intermediary messenger.

Role of secondary messengers

To amplify the hormone's original signal within the cell.

Can protein hormones cross membranes?

No; they are not lipid-soluble and cannot diffuse through the plasma membrane.

Examples of protein hormones

Glucagon and Adrenaline.

Glycogenolysis in liver cells

Activated via the second messenger model.

Step 1 of the Glycogenolysis Pathway

A hormone, such as glucagon or adrenaline, acts as a first messenger and binds to a specific receptor on the liver cell membrane.

Step 2 of the Glycogenolysis Pathway

The binding of the hormone activates a G protein, which then activates the enzyme adenylyl cyclase.

Step 3 of the Glycogenolysis Pathway

Active adenylyl cyclase converts ATP into cyclic AMP (cAMP).

Step 4 of the Glycogenolysis Pathway

cAMP acts as a second messenger that initiates the activation of protein kinases.

Step 5 of the Glycogenolysis Pathway

The activated protein kinases catalyze the enzymic breakdown of glycogen into glucose.

Step 1 of adrenaline's action on liver cells

Adrenaline binds to specific receptors on the cell surface membrane of liver cells.

Step 2 of adrenaline's action on liver cells

The binding of adrenaline causes the activation of the enzyme adenylyl cyclase.

Step 3 of adrenaline's action on liver cells

Activated adenylyl cyclase converts ATP into cyclic AMP (cAMP).

Step 4 of adrenaline's action on liver cells

Cyclic AMP (cAMP) acts as a second messenger, which then activates protein kinase enzymes.

Step 5 of adrenaline's action on liver cells

Protein kinases catalyze a chain of reactions that leads to glycogenolysis, the breakdown of glycogen into glucose.

Step 6 of adrenaline's action on liver cells

Glucose is released from the liver cells, which increases blood glucose levels.

What triggers the release of adrenaline from the adrenal glands?

Adrenaline is released when there is a low concentration of blood glucose, during stress, or exercise.

What process does adrenaline activate to increase blood glucose levels?

Adrenaline activates glycogenolysis.

What effect does adrenaline have on glycogenesis?

Adrenaline inhibits glycogenesis, which is the conversion of glucose into glycogen.

How does adrenaline influence insulin and glucagon secretion?

Adrenaline activates glucagon secretion and inhibits insulin secretion from the pancreas.

What is the role of adrenaline during exercise?

Adrenaline stimulates the breakdown of glycogen stores in muscles to provide glucose for respiration.

What is the primary purpose of increased glucose availability due to adrenaline?

It prepares the body for a flight or fight response.

What are the main hormones secreted by the pancreas?

Insulin and glucagon.

What type of cells in the islets of Langerhans secrete glucagon?

Alpha cells.

What type of cells in the islets of Langerhans secrete insulin?

Beta cells.

What happens when blood glucose concentration is too high?

Beta cells release insulin, promoting glucose uptake and lowering blood glucose levels.

What is the role of insulin in blood glucose regulation?

Insulin stimulates the uptake of glucose into cells and promotes glycogenesis in the liver.

What occurs when blood glucose concentration is too low?

Alpha cells secrete glucagon, which enhances the release of glucose into the blood.

What is glycogenesis?

The conversion of glucose to glycogen stimulated by insulin.

What is glycogenolysis?

The conversion of glycogen to glucose stimulated by glucagon.

How does insulin increase the permeability of cells to glucose?

Insulin binding promotes the addition of glucose transporter proteins to the cell surface.

What is the effect of glucagon on insulin secretion?

Glucagon secretion increases when insulin secretion decreases, particularly when blood glucose is low.

What is the normal range for blood glucose concentration in mmol dm-3?

4-8 mmol dm-3.

What happens if blood glucose concentration is too low?

Cells may not have enough glucose for respiration, particularly affecting brain cells.

What are the effects of high blood glucose levels?

It disrupts the water potential of blood and can cause water to move in and out of cells, including red blood cells.

What causes blood glucose concentration to increase in the body?

Carbohydrates are broken down into monosaccharides, glycogen is broken down in the liver, and other substances like lactate, amino acids, glycerol, and fatty acids are converted into glucose.

What causes blood glucose concentration to decrease?

Increased respiration during exercise, the liver converting excess glucose into glycogen, and alcohol consumption which inhibits glucose production by the liver.

What role does the pancreas play in blood glucose regulation?

It secretes hormones insulin and glucagon that regulate blood glucose levels.

Where are the receptors for blood glucose regulation hormones located?

In the islets of Langerhans in the pancreas.

What types of cells are the target cells for insulin and glucagon?

Liver, muscle, and fat cells, which have specific receptors for these hormones.

What is Glucagon and where is it produced?

A hormone produced by A cells at the islets of Langerhans in the pancreas that increases blood glucose levels by initiating the breakdown of glycogen to glucose.

What is Gluconeogenesis?

The conversion of non-carbohydrates (e.g. glycerol and amino acids) into glucose, occurring in the liver when glycogen supply is exhausted.

What is Glycogenesis?

The conversion of glucose into glycogen, occurring in the liver when blood glucose levels are higher than normal.

What is Glycogenolysis?

The breakdown of glycogen to glucose, occurring in the liver when blood glucose levels are lower than normal.

What is the difference between a cholinergic synapse and a neuromuscular junction?

Cholinergic synapses occur between neurones or between neurones and glands and can be either excitatory or inhibitory, while neuromuscular junctions are between motor neurones and muscles and are excitatory only.

What neurotransmitter is primarily involved in neuromuscular junctions?

Acetylcholine (ACh) is the neurotransmitter that binds to receptors on the postsynaptic membrane at neuromuscular junctions.

What role does acetylcholinesterase play in neuromuscular junctions?

Acetylcholinesterase breaks down acetylcholine in the synaptic cleft, preventing continuous stimulation of the muscle cell.

How does nicotine affect synaptic transmission?

Nicotine mimics acetylcholine and binds to cholinergic receptors, resulting in more activated receptors in the brain.

What is the effect of amphetamines on neurotransmitter release?

Amphetamines stimulate the release of dopamine from presynaptic neurones into the synaptic cleft, increasing the number of activated receptors.

What is a consequence of nerve gases on synaptic function?

Nerve gases inhibit acetylcholinesterase, leading to loss of muscle control due to prolonged action of acetylcholine.

How do opioids affect neurotransmitter release?

Opioids block Ca2+ ion channels in presynaptic neurones, reducing exocytosis of neurotransmitters.

What is the function of curare in relation to neurotransmitter receptors?

Curare blocks cholinergic receptors at neuromuscular junctions, reducing the number of receptors that can be activated.

What structure is responsible for triggering an action potential in muscle cells?

The sarcolemma is responsible for triggering an action potential when acetylcholine binds to its receptors.

What structural feature of the postsynaptic membrane aids in neuromuscular transmission?

The postsynaptic membrane has folds forming clefts that store acetylcholinesterase for breaking down acetylcholine.

What are behavioural temperature adaptations?

Changes in an animal's behavior in response to environmental temperature to regulate their body temperature.

Give an example of a behavioural adaptation for cooling off.

Seeking shade or cooling off with water.

What do some organisms do to increase or decrease heat loss?

They can increase or reduce their surface area.

What is one way animals can warm up in cold conditions?

Huddling for warmth.

What happens to the A bands during muscle contraction at the sarcomere level?

A bands stay the same length because the myosin filament doesn't shorten.

What happens to the I bands and H zones when a sarcomere contracts?

I bands and H zones get shorter because the actin filaments are pulled over the myosin filament.

What occurs to the Z lines when the sarcomere contracts?

The Z lines get closer together because the sarcomere gets shorter overall.

What is the sliding filament model in relation to muscle contraction?

Muscles contract due to the shortening of each sarcomere through the sliding of myosin and actin filaments over one another.

Describe the relationship between sarcomere contraction and muscle relaxation.

When sarcomeres return to their original length, the muscle relaxes.

What is homeostasis in mammals?

The process of maintaining the internal environment within restricted limits.

What type of feedback system is involved in homeostasis?

Negative feedback system.

What happens when a condition increases above the optimum level?

Receptors detect the increase and effectors cause changes to return to the optimum level.