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Biology > Topic 17 - Homeostasis > Flashcards

Topic 17 - Homeostasis Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

What is homeostasis?

A

Physiological control systems that maintain the internal environment within restricted limits.

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2
Q

What is an endotherm?

A

Warm-blooded

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3
Q

What is an ectotherm?

A

Cold-blooded

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4
Q

Characteristics of a hormone.

A
  • Produced by endocrine gland.
  • Carried in blood plasma to the target cell.
  • Binds to receptors on target cell –> complementary shaped to the hormone, ‘acts’ on the target cell.
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5
Q

How does injecting a small amount of adrenaline into the body cause a rapid increase in blood glucose concentration? (Second-messenger Systems)

A

1) Adrenaline binds to complementary receptor on target cells in plasma membrane.
2) Adenylate cyclase becomes activated.
3) Hydrolyses ADP into cAMP which activates protein kinase. Hydrolyses glycogen to glucose (glycogenesis).
4) Repeated multiple times.

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6
Q

What are the 3 sources of blood glucose?

A

1) Glycogenolysis.
2) Gluconeogenesis.
3) Food

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7
Q

Can glucose diffuse across the phospholipid bilayer?

A

No, glucose is too big - goes via facilitated diffusion/active transport, not simple diffusion.

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8
Q

What are the three roles of the pancreas?

A

1) Endocrine gland = insulin, glucagon
2) Exocrine gland = digestive enzymes
3) Detects blood glucose concentration

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9
Q

What happens when there is a rise in glucose concentration?

A

1) Beta cells from pancreas (Islet of Langerhans) detect blood glucose rise and secrete insulin.
2) Insulin travels in blood then undergoes glycogenesis which causes glucose levels to return back to optimum level.

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10
Q

What happens when insulin binds to receptor (in muscle/liver)?

A

1) Insulin binds to receptor on outside of cell.
2) Releases a chemical signal.
3) Vesicle (with glucose channel proteins) move to plasma membrane, fuses, and adds carrier proteins to it.

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11
Q

What are the short and long term consequences of blood glucose concentration?

A

SHORT = tiredness (glucose is a respiratory substance –> less respiration –> less ATP).

LONG = cells would take on water –> swell and burst –> death.
Nerve cells can die, potential organ failure and stunted growth (less mitosis).

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12
Q

What happens when there is a fall in blood glucose concentration?

A

1) Alpha cells from Islets of Langerhans detect blood glucose decrease and secrete glucagon.
2) Travels in blood, reaching target cell, works by 2nd messenger system, causing glycogenolysis.
3) Gluconeogenesis synthesises glucose from amino acids and glycerol.
4) Blood glucose levels increase.

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13
Q

What are the actions of glucagon?`

A

Binds to complementary receptor, activates adenylate cyclase, hydrolyses ATP to cAMP, which activates protein kinase. Glycogen hydrolysed into glucose.

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14
Q

What are the actions of adrenaline?

A

Activates enzymes involved in conversion of glycogen –> glucose = glycogenolysis.

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15
Q

Type 1 Diabetes:
What is it?
How is it treated?

A

Type 1 people do not produce any insulin. After a meal, blood glucose is high and glucose can’t enter respiring cells.
- Usually begins in childhood.
- Autoimmune response.
- Beta cells in islets of Langerhans attacked.

Treated: Injections of insulin 2-4x a day, allows glucose to enter cells.
Cannot be taken orally as it will be denatured in the stomach.

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16
Q

What is hyperglycaemic?

A

Blood glucose concentration remains high.

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17
Q

What is hypoglycaemic?

A

Blood glucose concentration falls too low.

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18
Q

Type 2 diabetes:
What is it?
How is it treated?

A

Type 2 people’s glycoprotein receptors on body cells lose sensitivity to insulin.
- Usually occurs later in life (>40s) but also common in obese people.
- Develops slowly.
- Insulin resistance.

Treated: Combination of exercise and diet.

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19
Q

What is the collecting duct?

A

Tube into which a number of distal convoluted tubules empty.

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20
Q

What is the Loop of Henle?

A

Long, hairpin loop that extends from cortex into medulla of kidney and back. Surrounded by blood capillaries.

21
Q

What is the efferent arteriole?

A

Tiny vessel that leaves the capsule, has a smaller diameter than afferent arteriole. Causes an increase in blood pressure in glomerulus.

22
Q

What is the afferent arteriole?

A

Tiny vessel that arises from renal artery and supplies nephron with blood.

23
Q

What is the Renal (Bowman’s) Capsule?

A

Closed end at the start of nephron. Cup-shaped, surrounds a mass of blood capillaries named glomerulus. Inner layer is made up of specialised cells named podocytes.

24
Q

What is the distal convoluted tubule?

A

Series of loops surrounded by blood capillaries. Walls are made from epithelial cells, but surrounded by fewer capillaries than proximal tube.

25
Q

What is the proximal convoluted tubule?

A

Series of loops surrounded by blood capillaries, walls are made of epithelial cells which have microvilli.

26
Q

What is the glomerulus?

A

Many-branched knot of capillaries from which fluid is forced out of the blood.

27
Q

What is the blood capillaries?

A

Concentrated network of capillaries surrounding the PCT, loop of Henle, and DCT. Reabsorbs mineral salts, glucose, and water, then form the renal vein.

28
Q

What are 5 molecules that can move out of the glomerular capillaries into the glomerular filtrate?

A

Hormones, glucose, salts, oxygen, carbon dioxide, urea etc.

29
Q

What are 3 things that cannot move out the glomerular capillaries? Why?

A

Blood protein, red blood cells, platelets etc.
They are too big.

30
Q

What are 5 factors that resist the movement of small molecules out of the glomerular capillaries and into the glomerular fitrate?

A
  • Presence of capillary endothelial cells.
  • Connective tissue.
  • Epithelial cells of renal capsule.
  • Hydrostatic pressure of fluid in renal capsule space.
  • Osmotic pressure of glomerular filtrate.
31
Q

What are 2 structures that aid the movement of small molecules into glomerular filtrate?

A
  • Endothelium has gaps that lets small molecules through.
  • Podocytes allow us to strain molecules through.
32
Q

What is the basement membrane?

A

Smallest holes so decides what can and can’t get out. Made of collagen.

33
Q

A person with a damaged basement membrane in the renal capsule has large proteins in their urine. Why?

A

Basement membrane has smallest holes, so if damaged, larger molecules can filter through.

34
Q

Pododycte

A

Foot-like processes

35
Q

Reabsorption in the proximal convoluted tubule

A
  • Glomerular filtrate formed in Bowman’s capsule. This contains water, glucose, urea, mineral ions, amino acids, vitamins.
  • Useful substances are then reabsorbed back into capillaries e.g. water and glucose.
  • 99% of water is reabsorbed, 85% absorbed back into blood in the proximal convoluted tubule.
36
Q

What are the adaptations of the epithelial cells for reabsorption in the proximal convoluted tubule?

A
  • Sodium potassium pump for active transport.
  • Mitochondrion provide ATP for active transport.
  • Microvilli increase surface area for more reabsorption.
  • Microvilli one cell thick so short diffusion pathway.
  • Transport protein for facilitated diffusion.
37
Q

What do the reabsorbed substances have to move across before reaching the blood plasma?

A

Tubule –> epithelial cells –> interstitial (tissue) fluid –> capillary endothelial cell –> blood plasma.

38
Q

How are substances reabsorbed in the proximal convoluted tubule?

A

1) Active transport of 3 sodium ions out epithelial cells, lining the PCT, into tissue fluid, into blood.
2) Lowers concentration of sodium ions inside cell.
3) Sodium ions diffuse down concentration gradient, through number of different co-transport proteins in cell-surface membrane of epithelial cells of PCT - facilitated diffusion.
4) Each type of co-transport protein transports sodium ions and either glucose or amino acids or chloride ions or vitamins together into epithelial cell.
5) They diffuse down their concentration gradient via facilitated diffusion (channel proteins) into the capillaries.
6) Diffusion of soluble substances into epithelial cell lowers water potential, so water moves into epithelial cell of PCT, into tissue fluid, before diffusing across endothelial cell and into capillary via osmosis.

39
Q

Why is glucose often present in the urine of an undiagnosed diabetic?

A

Higher glucose concentration in blood. Only place where glucose can be reabsorbed, cant all be reabsorbed.

Forces more glucose molecules through basement membrane.

40
Q

High blood pressure leads to an accumulation of tissue fluid. Explain how.

A
  • High blood pressure = high hydrostatic pressure.
  • Increases outward pressure from end of capillary.
  • More tissue fluid formed.
41
Q

Explain the role of the loop of Henle.

A
  • Extends into medulla of kidney.
  • Responsible for water being absorbed from collecting duct, concentrating urine.
  • Two parts: ascending limb and descending limb.
  • Walls of ascending limb thicker than wall of descending limb.
  • Fluid in descending limb flows in opposite direction to fluid in ascending limb, maintains a concentration gradient.
  • The longer the loop, the more water reabsorbed.
  • Descending limb is narrow, with thin walls that are highly permeable to water, but not to mineral ions.
  • Ascending limb starts narrow, but then widens. Has thick walls that are impermeable to water but permeable to mineral ions.
  • Two limbs work together as a counter-current multiplier.
42
Q

Filtrate entering the loop of Henle has the same water potential as the blood. Explain why.

A

In capsule, water potential is higher.
PCT –> water reabsorbed into blood by osmosis, equilibrium reached.

43
Q

What is the hypothalamus?

A

Region of brain which acts as control centre for autonomic nervous system and regulates blood water potential.

44
Q

What are osmoreceptors?

A

Cells within hypothalamus that detect changes in blood water potential.

45
Q

What is the pituitary gland?

A

Endocrine gland situated at base of brain. 2 parts = anterior (front) and posterior (back).

46
Q

What is the antidiuretic hormone (ADH)

A

Hormone produced by hypothalamus and secreted by posterior pituitary gland.

47
Q

What happens when the water potential in the blood increases?

A

1) Detected by osmoreceptors in hypothalamus.
2) Pituitary gland releases less ADH.
3) Walls of DCT and collecting duct become less permeable to water.
4) Concentration of urine decreases = drink less.
5) WP lowers.

48
Q

What happens when the water potential in the blood decreases?

A

1) Detected by osmoreceptors in hypothalamus.
2) Hypothalamus makes more ADH.
3) ADH to blood via pituitary gland.
4) To get cells in DCT and CD to respond.
5) Walls of collecting duct/CT allows more water from filtrate -> blood.
6) Concentration of urine increases so drink more.

49
Q

What does ADH do?

A

1) ADH bonds to specific protein receptors on surface of cells in DCT and CD.
2) Leads to activation of the enzyme phosphorylase.
3) Causes vesicles containing water channel proteins (aquaporins) to move and fuse to the cell surface membrane.
4) Increases cell membranes permeability to water.
5) ADH increases permeability of collecting duct to urea.
6) Urea passes out of collecting duct, further lowers water potential of fluid around duct, causing water to move out via osmosis.

Biology (28 decks)

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