Homeostasis - Yr 2

Question 1

Homeostasis

Answer 1

The maintenance of a constant internal environment

Question 2

Control mechanism

Answer 2

A set of self-regulating stages comprising of: optimum point, receptor, coordinator, effector and feedback loop

Question 3

Ectotherm

Answer 3

An animal which gains its heat from outside their body, i.e. its environment eg reptiles

Question 4

Endotherm

Answer 4

An animal which gains its heat from metabolic activities inside its body eg birds, mammals

Question 5

Vasodilation

Answer 5

Widening the diameter of arterioles near the surface of the skin, so that warm blood passes close to its surface via capillaries

Question 6

Vasoconstriction

Answer 6

Narrowing the diameter of arterioles near the surface of the skin, so that less blood volume passes close to its surface via capillaries, retaining heat

Question 7

Hypothalamus

Answer 7

Part of the brain next to the pituitary gland; the control centre for the ANS eg controls temperature, water balance

Question 8

Second messenger model

Answer 8

The way a non-lipid-soluble hormone eg glucagon or adrenaline acts on a cell, by triggering production of an intermediary ‘second’ messenger eg cyclic AMP by activating adenyl cyclase

Question 9

Type 1 diabetes

Answer 9

Insulin dependent, due to body being unable to produce insulin. It normally begins in childhood due to an autoimmune response whereby the body’s immune system attacks the β cells of the islets of Langerhans.

Question 10

Type 2 diabetes

Answer 10

Insulin independent- due to glycoprotein receptors on body cells losing responsiveness to insulin (or it could also be due to inadequate supply from the pancreas). Usually develops in people over the age of 40 years.

Question 11

Gluconeogenesis

Answer 11

Happens in the liver - conversion of non-carbohydrates (e.g. glycerol and amino acids) into glucose; literally ‘glucose-new-manufacture’. Happens when glycogen supply is exhausted.

Question 12

Glycogenolysis

Answer 12

Happens in the liver - breakdown of glycogen to glucose – ‘breaking down glycogen’. Happens when blood glucose level is lower than normal.

Question 13

Glycogenesis

Answer 13

Happens in the liver - conversion of glucose into glycogen – ‘making glycogen’. Happens when blood glucose level is higher than normal.

Question 14

Negative feedback

Answer 14

When the feedback causes the corrective measures to be turned ‘off’, so returns the system to its original or (normal) level

Question 15

Positive feedback

Answer 15

When the feedback causes the corrective measures to be turned ‘on’, so makes the system deviate even further from its original or (normal) level

Question 16

Osmoregulation

Answer 16

The homeostatic control of the water potential of the blood.

Question 17

Nephron

Answer 17

The functional unit of the kidney – there are about one million tubular structures in each kidney.

Question 18

Fibrous capsule

Answer 18

An outer membrane which protects the kidney

Question 19

Cortex

Answer 19

A lighter coloured outer region made up of renal (Bowman’s) capsules, convoluted tubules and blood vessels

Question 20

Medulla

Answer 20

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

Question 21

Renal pelvis

Answer 21

A funnel-shaped cavity that collects urine into the ureter

Question 22

Ureter

Answer 22

A tube that carries urine to the bladder

Question 23

Renal artery

Answer 23

Supplies the kidney with blood from the heart via the aorta

Question 24

Renal vein

Answer 24

Returns blood to the heart via the vena cava

Question 25

Renal (Bowman’s) capsule

Answer 25

The closed end at the start of the nephron. It is cup-shaped and surrounds a mass of blood capillaries known as the glomerulus. The inner layer of the renal capsule is made up of specialized cells called podocytes.

Question 26

Proximal convoluted tubule

Answer 26

A series of loops surrounded by blood capillaries which are adapted to reabsorb substance into the blood by having walls made of epithelial cells which have microvilli.

Question 27

Loop of Henle

Answer 27

A long, hairpin loop that extends from the cortex into the medulla of the kidney and back again which is surrounded by blood capillaries.

Question 28

Descending limb of loop of Henle

Answer 28

Narrow, with thin walls that are highly permeable to water. The filtrate progressively loses water by osmosis at it moves down this limb.

Question 29

Ascending limb of loop of Henle

Answer 29

Wider, with thick walls that are impermeable to water. Sodium ions are actively transported out of this limb which creates a lower water potential in the region of the medulla between the two limbs.

Question 30

Distal convoluted tubule

Answer 30

A series of loops surrounded by blood capillaries. Its walls are made of epithelial cells, but it is surrounded by fewer than the proximal tubule. It makes final adjustments to the water and salts that are reabsorbed and to control the pH of the blood by selecting which ions to reabsorb. The permeability of its walls are altered under the influence of various hormones.

Question 31

Collecting duct

Answer 31

A tube into which a number of distal convoluted tubules from a number of nephrons empty. It is lined by epithelial cells and becomes increasingly wide as it empties into the pelvis of the kidney. It is permeable to water and so as the filtrate moves down it the water passes out of it by osmosis.

Question 32

Afferent arteriole

Answer 32

A tiny vessel that ultimately arises from the renal artery and supplies the nephron with blood. The afferent arteriole enters the renal capsule of the nephron where it forms the glomerulus.

Question 33

Glomerulus

Answer 33

A many-branched knot of capillaries from which fluid is forced out of the blood. They recombine to form the efferent arteriole.

Question 34

Efferent arteriole

Answer 34

A tiny vessel that leaves the renal capsule. It has a smaller diameter than the afferent arteriole and so causes an increase in blood pressure within the glomerulus. It carries blood away from the renal capsule and later branches into the blood capillaries.

Question 35

Blood capillaries

Answer 35

A concentrated network of capillaries that surround the proximal convoluted tubule, the loop of Henle and the distal convoluted tubule and from where they reabsorb mineral salts, glucose and water. They merge together into venules and then into the renal vein.

Question 36

Ultrafiltration

Answer 36

Filtration assisted by blood pressure - process by which glomerular filtrate is formed due to the afferent arteriole having a larger diameter than the efferent arteriole which causes a build up of hydrostatic pressure causing water, glucose, urea and mineral ions to be squeezed out of the capillary into the renal (Bowman’s) capsule. Blood cells and proteins cannot pass across into the renal capsule as they are too large.

Question 37

Reabsorption of water

Answer 37

Process by which all of the glucose and most other valuable molecules are reabsorbed as well as water in the proximal convoluted tubule. Sodium ions are actively transported out of cells lining the convoluted tubule into blood capillaries which carry them away. This causes sodium ions to move by facilitated diffusion down a concentration gradient from the lumen of the proximal convoluted tubule into the epithelial lining cells. It moves through via co-transport through carrier proteins, each of which carries another molecules (glucose, amino acids or chloride ions) along with the sodium ions. The molecules that have moved via co-transport then diffuse into the blood.

Question 38

Counter-current multiplier

Answer 38

When two liquids flow in opposite directions past one another, the exchange of substance between them is greater than if they flow in the same direction next to each other. The counter-current flow means that the filtrate in the collecting duct with a lower water potential meets interstitial fluid that has an even lower water potential, meaning the water potential gradient exists for the whole length of the collecting duct.

Question 39

Osmoreceptors

Answer 39

Cells in the hypothalamus of the brain detect a change in water potential

Question 40

ADH (antidiuretic hormone)

Answer 40

If a decrease in water potential is detected, more of this hormone is produced by the pituitary gland and it makes the walls of the distal convoluted tubule and collecting duct more permeable to water, meaning less water leaves the body and urine is more concentrated.