Homeostasis (DP IB Biology)

The role of insulin in blood glucose regulation is to lower blood glucose concentration by:

• promoting glucose uptake into cells

• converting glucose into glycogen (glycogenesis)

• increasing the rate of respiration

• converting glucose to fatty acids for fat storage.

Glucagon affects target cells as follows:

• activation of enzymes that convert glycogen into glucose (glycogenolysis)

• a decrease in the rate of respiration

• amino acids are converted to glucose (gluconeogenesis)

Diabetes is a condition in which the homeostatic control of blood glucose has failed or deteriorated.

Type 1 diabetes occurs when the pancreas fails to produce sufficient insulin. This is the result of an autoimmune response that destroys the β cells of the islets of Langerhans.

False.

Type 1 diabetes is managed with regular blood tests and insulin injections, not just diet and exercise.

Type 1 diabetes occurs when the pancreas fails to produce insulin, while type 2 diabetes occurs when body cells become resistant to insulin.

Risk factors for type 2 diabetes include:

• obesity

• lack of physical activity

• age

• ethnicity

• family history of diabetes

Type 2 diabetes is managed with:

• medication to lower blood glucose

• a low carbohydrate diet

• an exercise regime that lowers blood glucose

A peripheral thermoreceptor is a receptor in the skin that monitors external body temperature.

The role of the hypothalamus in temperature regulation includes:

• monitoring of internal body temperature via internal temperature receptors

• regulation of secretion of thyrotropin-releasing hormone

The hypothalamus and pituitary gland work together in temperature regulation as follows:

The role of thyroxin is to increase metabolic rate, increasing heat generation by cell metabolism. Altering the secretion of thyroxin therefore allows control of heat generation.

False.

White adipose tissue stores lipids which provide insulation against heat loss.

It is brown adipose tissue that generates heat energy in the absence of shivering; this is non-shivering thermogenesis

Muscle tissue contributes to thermoregulation through shivering, which raises the metabolic rate of muscle cells and releases heat energy.

False.

Birds and mammals use both behavioural and physiological mechanisms to regulate body temperature.

Vasodilation is the widening of arterioles that supply capillaries in the skin. This allow more blood to flow through skin capillaries, increasing heat loss to the environment.

Vasoconstriction is the narrowing of arterioles that supply capillaries in the skin. This allows less blood to flow through capillaries, reducing heat loss to the environment.

The role of sweat glands in thermoregulation is to secrete sweat onto the skin surface. Heat energy is lost from the body when the sweat evaporates.

Uncoupled respiration is respiration that is separated from the production of ATP, meaning that all of the energy released is in the form of heat. This process occurs in brown adipose tissue.

Hair erector muscles in thermoregulation contract to cause hairs on the skin to stand on end. This forms an insulating layer of air over the skin's surface, reducing heat loss by radiation.

Excretion is the process by which toxic waste products of metabolism are removed from the body.

Urea is a less toxic form of nitrogenous metabolic waste that can remain in the body at low concentrations but must be excreted before harmful levels build up.

False.

Nitrogenous waste comes from the breakdown of both excess dietary amino acids and nucleic acids.

Osmotic concentration is the balance of water and solutes in cells, measured in osmoles per litre (osmol L⁻¹).

Cells with a lower water potential than their surrounding environment will gain water by osmosis and the resulting internal pressure increase could cause the cell to burst.

Cells with a higher water potential than their surrounding environment will lose water by osmosis and the resulting drop in internal pressure will cause the cell to shrink.

Ultrafiltration is the process where high blood pressure in the glomerulus forces small molecules into the Bowman's capsule to form glomerular filtrate. Blood cells and large plasma proteins remain in the blood.

True.

The nephron spans all three regions of the kidney: cortex, medulla, and renal pelvis.

The glomerulus is a ball of capillaries within the Bowman's capsule that is supplied with blood by the afferent arteriole and is responsible for ultrafiltration.

Glomerular filtrate is the fluid formed in the Bowman's capsule containing small molecules including amino acids, water, glucose, urea and salts that have passed through from the blood.

False.

The basement membrane acts as a sieve, preventing the passage of large proteins while allowing small molecules through.

Podocytes are epithelial cells with foot-like projections in the Bowman's capsule that allow the passage of small molecules during ultrafiltration.

Selective reabsorption is the process where useful substances (including water, salts, glucose, and amino acids) are reabsorbed from the filtrate back into the blood as it passes along the nephron.

Most of selective reabsorption takes place in the proximal convoluted tubule.

Co-transporter proteins are specialised proteins in the proximal convoluted tubule that transport specific solutes, such as glucose, along with sodium ions across the luminal membrane. Co-transport is driven by the active transport of sodium ions out of the epithelial cells, which produces a concentration gradient of sodium ions to allow the co-transport process to occur.

False.

The ascending limb of the loop of Henle is impermeable to water.

Vasa recta is the capillary that flows alongside the loop of Henle, supplying oxygen and removing carbon dioxide while collecting reabsorbed water and ions.

Osmoregulation is the maintenance of a safe balance of water and solutes in the body, which is an example of homeostasis.

ADH (antidiuretic hormone) is a hormone released from the posterior pituitary gland that regulates the permeability of the distal convoluted tubule and collecting duct to water.

When the blood water content drops too low, it is detected by the hypothalamus in the brain, which causes the pituitary gland to secrete ADH into the blood. ADH increases the permeability of the collecting duct and distal convoluted tubule, so more water can be reabsorbed in the kidney.

Aquaporins are channel proteins that increase the permeability of cell membranes to water in the distal convoluted tubule and collecting duct.

Mitochondria release energy from respiration which is needed for active transport of sodium ions into the blood stream. This process then drives the action of the co-transporter protein which is used in the reabsorption of glucose across the membrane.

Vasodilation increases blood flow and vasoconstriction decreases blood flow in the arterioles that supply the capillary beds in different parts of the body.

False.

Blood flow to the brain remains relatively constant regardless of activity levels, with only slight increases during REM sleep.

Blood flow in the gut decreases during exercise so that more blood can be diverted to the skeletal muscles.

False.

Blood flow to the kidneys does not change significantly based on activity level, with only slight increases during sleep and rest, and slight decreases during prolonged exercise.