The Internal Environment (Edexcel International A Level (IAL) Biology): Flashcards

Homeostasis is the process by which physiological control systems maintain internal conditions relatively constant to allow the body to function efficiently.

Homeostasis keeps the internal environment of the body fluctuating around a specific normal level, a state known as dynamic equilibrium.

Receptors are sensory cells that detect information about the conditions inside and outside the body, allowing control systems to maintain homeostasis.

Thermoregulation is the maintenance of a constant internal body temperature using physiological mechanisms that respond to changes in the environment.

An increase in body temperature above 40 °C can cause enzymes to denature, resulting in a loss of enzyme activity.

Vasodilation increases blood flow through arterioles near the skin, bringing more blood to skin capillaries so that more heat is lost to the environment by radiation.

Sweat cools the skin by evaporation; heat energy from the body converts liquid water into vapour.

The hypothalamus monitors blood temperature and receives information from thermoreceptors, then sends impulses to effectors to initiate homeostatic responses to temperature changes.

Vasoconstriction is the narrowing of arterioles near the skin caused by muscle contraction, reducing blood flow to skin capillaries and minimising heat loss by radiation.

True.

The kidneys regulate water balance in the blood, helping maintain homeostasis.

An osmoregulatory organ is an organ that regulates the water content of the blood, essential for maintaining blood pressure and preventing cell damage due to osmosis.

Humans normally have two kidneys.

The kidneys enable the excretion of toxic waste products such as urea and substances in excess of requirements, like salts.

The fibrous capsule is the tough outer layer that surrounds the kidney and protects its inner structures.

The three main regions of the kidney are the cortex, medulla, and renal pelvis.

Each kidney contains thousands of tiny tubes called nephrons, which are the functional unit of the kidney.

The glomerulus, Bowman’s capsule, proximal convoluted tubule, and distal convoluted tubule are located in the cortex of the kidney.

A juxtamedullary nephron is a type of nephron with a long loop of Henle that extends deep into the medulla, making it very efficient at conserving water.

True.

The renal artery supplies blood to the kidney, while the ureter carries urine from the kidney to the bladder.

The afferent arteriole brings blood to the glomerulus, which then leaves via the efferent arteriole.

The removal of the amino group (-NH₂) from an excess amino acid, occurring in the liver, forming ammonia.

Because the body cannot store excess protein or amino acids, so the amino group must be removed, allowing the rest of the molecule to be used as a source of energy.

In the liver (specifically in liver cells, also called hepatocytes).

During deamination, the amino group of an amino acid combines with an extra hydrogen atom to form ammonia.

Because ammonia is highly toxic, so it is converted into less toxic urea, which can be safely transported in the blood and excreted.

By ultrafiltration in the glomerulus and Bowman's capsule; urea is a small molecule, so it is forced out of the blood into the glomerular filtrate.

True.

Urea produced in the liver is carried in the blood plasma to the kidneys, where it is filtered out and excreted in the urine.

A relatively non-toxic, nitrogen-containing waste product formed from ammonia in the liver; it is transported in the blood, filtered by the kidneys and excreted in the urine.

The reabsorption of useful substances (such as glucose, amino acids, salts and water) from the glomerular filtrate back into the blood as the filtrate passes along the nephron.

In the proximal convoluted tubule.

Glucose, amino acids, salts (ions) and most of the water.

By co-transporter proteins, which move them into the cells alongside sodium ions (an active, co-transport process).

The epithelial cells lining the proximal convoluted tubule have microvilli that increase the surface area for reabsorption.

To supply ATP for the active transport of substances such as sodium ions out of the tubule.

True.

The ascending limb is impermeable to water; ions are moved out into the medulla, but water cannot follow here, which helps set up the concentration gradient.

Sodium and chloride ions are moved out of the ascending limb into the medulla, lowering its water potential. This causes water to leave the descending limb and collecting duct by osmosis, creating a steep concentration gradient that maximises water reabsorption.

The control of the water potential of the body fluids (the blood), maintaining it within narrow limits; a key part of homeostasis.

In the hypothalamus of the brain.

A fall (decrease) in the water potential of the blood (i.e. low blood water content / high solute concentration).

The posterior pituitary gland, located just below the hypothalamus.

It increases the permeability of the collecting duct to water, so more water is reabsorbed into the blood and a small volume of concentrated urine is produced.

ADH increases water reabsorption by increasing the number of water channel proteins called aquaporins in the collecting duct cell membranes.

True.

Low blood water potential triggers ADH release, increasing water reabsorption, so a small volume of concentrated urine is produced.

A fall in water potential triggers ADH release and increased water reabsorption, which raises the water potential back towards normal; this correction then reduces further ADH release — a negative feedback loop.

A protein that controls the transcription of genes by binding to a specific region of DNA, switching genes on or off.

An activator increases the rate at which a gene is expressed, while a repressor decreases gene expression.

Because they are lipid-soluble, so they pass between the phospholipids of the membrane and enter the cell.

They enter the cell, bind to transcription factors/receptors inside it, and this complex binds to DNA to affect the transcription of genes.

They bind to receptors on the cell surface membrane, activating a second messenger (e.g. cyclic AMP) inside the cell, which triggers a cascade that can alter transcription factor activity.

A molecule (such as cyclic AMP) activated inside a cell when a peptide hormone binds to a surface receptor; it triggers a cascade of reactions that can affect gene expression.

Peptide hormones act extracellularly because they bind to receptors on the cell surface membrane rather than entering the cell.

False.

Steroid hormones are lipid-soluble and act intracellularly — they cross the membrane and bind to transcription factors inside the cell. It is peptide/protein hormones that act extracellularly via cell surface receptors.