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Biology > Chatper 16 - Homeostasis > Flashcards

Chatper 16 - Homeostasis Flashcards

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1
Q

What is homeostasis?

A

The maintenance of a constant internal environment despite external changes

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2
Q

What are the 2 forms of coordination between systems in animals?

A

Nervous system

Hormonal system

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3
Q

List the differences between hormonal and nervous system

A

Hormonal:
- communication by hormones
- slow
- transmission via blood stream
- effectors are target cells in tissues

Nervous:
- communication by electrical impulses
- very rapid
- Transmission via neurones
- effectors are muscles or glands

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4
Q

What is an organisms internal environment + what does it supply?

A

Tissue fluid = surrounds all cells that make up an organism

  • it supplies cells with nutrients and gases (glucose, O2) and removes waste products (CO2)
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5
Q

What is the composition of the blood + name some dissolved solutes

A

Plasma (55%): nutrients, gases, amino acids, plasma proteins, urea, vitamins and minerals

White blood cells + Platelets (4%)

Red blood cells (41%)

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6
Q

TISSUE FLUID RECAP:

How is it formed?

A
  • Ventricles contract causing a high hydrostatic pressure at the arteriole end of capillary
  • This high pressure forces water and some dissolves solutes out of capillary
  • Endothelium has pores so that leakage can occur
  • Large proteins and red blood cells are too large to leave
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7
Q

TISSUE FLUID RECAP

How does tissue fluid return to the blood?

A
  • Due to friction and water loss, the hydrostatic pressure at the venule end is lower than at the arteriole end
  • Blood also has lower water potential due to proteins left behind
  • Water returns to venule end of capillary by osmosis down its water potential gradient
  • Remaining water drains into the lymphatic system whereby a lymph eventually drains back into the blood
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8
Q

Why is homeostasis important?

A

Organisms with ability to maintain a constant internal environment can withstand greater changes in external environment so can survive a greater range of habitats

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9
Q

List the key stages of the homeostatic control system

A
  1. Input - change to the system e.g. a drop in body temp below 37 degrees
  2. Receptor - change detected in a living system e.g. hypothalamus detects the body temp to be below optimum
  3. Coordinator - operational info is stored here and used to coordinate effectors e.g. hypothalamus stimulates effectors
  4. Effector - brings about changes to system to return to optimum e.g. muscle shiver, increased metabolic rate etc
  5. Output - system returned to optimum e.g. body temp back to 37 degrees
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10
Q

What is negative feedback?

A

Usual type found in biological systems

  • when the output from the system counteracts the input so turns the system off because body is brought back to set point

E.g. a drop in body temp = a warming response so output is rise in body temp back to optimum

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11
Q

What is positive feedback?

A

When input results in an increased output resulting in an even greater deviation from optimum/ set point

E.g. giving birth

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12
Q

What type of feedback is controlling body temp an example of?

A

Negative feedback

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13
Q

What are the two responses of thermoregulation? List the effectors

A
  1. Warming response
    - blood vessels constrict (vasoconstriction)
    - muscles shiver
    - metabolic rate increases by thyroid hormones
  2. Cooling response
    - blood vessels dilate (vasodilation)
    - skin perspires (sweat gland)
    - breathing rate increases
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14
Q

Describe what happens to blood vessels when too cold

A

When too cold:
- surface blood vessels constrict and shunt vessels dilate
- this keeps blood flow lower down (further from skin)
- to prevent heat escaping by radiation

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15
Q

What is the role of hairs when cold?

A

Hair erector muscles are found around hair follicles

  • when they contract they pull hairs up on its end
  • this traps air close to skin
  • to provide insulation as air is a poor conductor of heat
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16
Q

What are endotherms? List an advantage of their mechanism

A

Endotherms = warm blooded organisms (birds and animals)

  • their body temp is controlled within (by homeostasis)
  • source of heat is from metabolic activities that take place in their bodies

✅ can survive conditions quite different from optimum point

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17
Q

What are ectotherms?

A

Ectotherms = cold blood organisms (snakes and lizards)

  • their body temp is controlled externally
  • obtain heat from environmental sources so change their behaviour to control it (sun and shade)
  • no homeostatically set point
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18
Q

What is regulating glucose concentration an example of?

A

Negative feedback

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19
Q

List the 2 factors influencing blood glucose levels

A
  1. Diet = consuming carb rich foods which get broken down into monosaccharides during digestion + absorbed into the blood. Therefore levels fluctuate depending on what and when we eat
  2. Activity level = more active we are, the more cells take up glucose from blood for respiration
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20
Q

Why is blood glucose important to regulate?

A
  • its a respiratory substrate (needed to produce ATP=energy for cells)
  • if glucose levels are too LOW = cells will be deprived of energy so wont function properly = increased water potential of blood plasma + tissue fluid causing more than normal amounts of water to move in to cells
  • if glucose levels are too HIGH = decreased water potential of blood + tissue fluid = more water than normal moves out of cells (dehydrating cells)
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21
Q

What are the 3 hormones involved in regulation of blood glucose?

A
  • Insulin
  • Glucagon
  • Adrenaline
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22
Q

Where are hormones released from?

A

Glands

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23
Q

What are the 2 types of glands and describe what they do?

A
  1. Endocrine glands
    - secrete hormones (adrenal gland = adrenaline, part of pancreas = insulin and glucagon) and releases them into bloodstream
    - goes to every organ in body but only target cells with correct complementary protein receptors respond
  2. Exocrine glands
    - secrete other products (salivary glands)
    - releases products into a duct that carries the molecule to where they are used
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24
Q

What is the role of the pancreas in blood glucose regulation?

A

Used for producing the hormones as it contains endocrine glands:
- glucagon = released by ALPHA CELLS
- insulin = released by BETA CELLS

The endocrine portion of pancreas = islets of langerhans

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25
Q

Describe the role of the liver in blood glucose regulation

A

There are target cells on liver called hepatocytes which detect the hormones and cause an output

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26
Q

Describe the system from input to output of blood glucose concentration

A

Input = a change in blood glucose concentration

Receptor = receptors on pancreas + hypothalamus detects changes in blood glucose concentration

Coordinator = pancreas produces hormone (glucagon or insulin)

Effector = hepatocytes on liver (target cells)

Output = results in either increase or decrease in blood glucose concentration

27
Q

What is insulins role in controlling blood glucose concentration?

A
  • binds to specific protein receptors on liver cells causing opening of glucose protein transporters
    OR
  • triggers insertion of more of these transporters into membrane
28
Q

What does the liver store?

A

Stores glucose in form of glycogen

  • when insulin bins to insulin receptors on liver cells (hepatocytes), internal enzymes are activated which convert glucose into glycogen for storage
29
Q

How does glucagon work?

A
  • it binds to protein receptors on liver cells which triggers glycogen stores to be broken down into glucose by enzymes

= releasing glucose which diffuses into blood to increase blood glucose concentration

30
Q

What are the following 3 important processes that occur in the liver?

Glycogenesis, glycogenolysis, gluconeogenesis

A

Glycogenesis - conversion of glucose to glycogen in liver

Glycogenolysis - hydrolysis of glycogen to glucose

Gluconeogenesis - production of glucose from non-carb sources - uses amino acids/ glycerol + fatty acids instead of glycogen (when its all gone)

31
Q

What is the role of adrenaline in controlling blood glucose concentration?

A

Used for a rapid release of glucose into blood from liver during times of ‘fight or flight’ or excitement/ stress

  • same reaction as glucagon just a whole lot faster (faster glycogenolysis)
32
Q

What is the secondary messaging system?

A

System in which hormones act on target cells to activate internal enzymes
- occurs in target cells and hormone can be either of adrenaline, glucagon or insulin

33
Q

Describe the secondary messaging system [5]

A
  1. Hormone binds to protein receptor
  2. Protein receptors changes shape which activates an enzyme called adenyl cyclase
  3. The activated adenyl cyclase converts ATP to cyclic AMP which acts as a secondary messenger
  4. The cyclic AMP activates protein kinase enzymes
  5. The protein kinase catalyses conversion of glycogen to glucose (if glucagon/ adrenaline) or glucose to glycogen (if insulin)
34
Q

What is diabetes mellitus?

A

A disease in which a person is unable to metabolise carbohydrate, especially glucose, properly.

35
Q

What is Type I diabetes?

A

Insulin dependant
- body unable to produce insulin
- may be as a result of an autoimmune response (B cells of isle of langerhans attack own cells)
- develops quickly

36
Q

What are the signs and symptoms of Type I diabetes?

A
  • high blood glucose concentration
  • presence of glucose in urine
  • need to urinate excessively
  • genital itching/ regular thrush
  • weight loss
  • blurred vision
  • tiredness
37
Q

How can Type I diabetes be controlled?

A
  • Injections of insulin (2-4 times per day)
  • dose matched to glucose intake

If you take on too MUCH insulin = low blood glucose concentration so go unconscious

Biosensors = monitor correct dose of insulin

38
Q

What is Type II diabetes?

A

Insulin independant

  • glycoprotein receptors on body cells being lost/ losing responsiveness to insulin
  • OR due to inadequate supply of insulin from pancreas
  • usually in people over 40 but also from poor diet/ obesity
39
Q

What are the signs and symptoms of Type II diabetes?

A

Less noticed so isn’t really any

40
Q

What are the controls for Type II diabetes?

A
  • regulating intake of carbohydrate in diet and matching this amount to exercise taken
  • may be supplemented by injections of insulin or by use of drugs that stimulate insulin production

Other drugs = slow down rate at which body absorbs glucose form intestine

41
Q

What is osmoregualtion?

A

The homeostatic control of the water potential of the blood plasma

  • as water is consumed it is then absorbed by large intestine via osmosis
42
Q

What is egestion and excretion?

A

Egestion = removal of undigested waste materials (faeces) that was taken in externally (food)

Excretion = process of eliminating the waste products of metabolism

43
Q

What is the function of the kidney in osmoregualtion?

A

Maintains the water potential of the blood plasma and tissue fluid surrounding cells and removes waste substances from the blood

= filters/ purifies blood forming urine

44
Q

What are the key parts of the kidney?

A

Cortex = lighter colour
Medulla = darker region
Nephron = does the filtering of the blood
Pelvis = collecting waste products from nephron

45
Q

NEPHRON of kidney

What is ultrafiltration?

A

Filtration of the blood (by the glomerulus in renal Bowermans capsule) to form glomerular filtrate

  • filters out waste products but same size as useful parts of blood so these filter through to (water, amino acids, gases, vitamins, urea)
46
Q

What is the difference between the afferent and efferent arteriole - describe function

A

Efferent - carries filtered blood away from Bowermans capsule
Afferent - carries blood to Bowermans capsule

  • Afferent arteriole is very wide into thin capillaries= very high hydrostatic pressure

LOOK AT NOTES

47
Q

What are the 3 barriers of glomerular capillaries?

A
  • capillary is made of endothelial cells + has fenestrations (pores)
  • basement membrane (netting which has little holes)
  • podocytes (gaps)

= a filtration barrier

48
Q

NEPHRON of kidney

Step 1: What is the process of ultrafiltration?

A
  1. Blood flows in through the afferent arteriole into glomerular capillaries
  2. High hydrostatic pressure in glomerular capillary due to efferent arteriole being narrower than afferent
  3. Used to overcome osmotic and capsular hydrostatic pressure coming in
  4. This forces water and dissolved substances out through fenestrations of endothelial cells, basement membrane + gaps in podocyte into Bowermans capsule
  5. Plasma proteins + cells remain
  6. Rest of blood not filtered out leaves via efferent
  7. The glomerular filtrate leaves through the proximal convoluted tubule
49
Q

NEPHRON of kidney

What is selective reabsorption?

A

Of useful molecules e.g. water and glucose, amino acids, urea

  • IN THE PROXIMAL CONVOLUTED TUBULE
50
Q

NEPHRON of kidney

What is a the lining of the proximal convoluted tubule like?

A

Made up of epithelial cells

  • contains villi/ microvilli
  • large SA due to convolutions in tubule
  • numerous mitochondria found in cells for production of ATP for active transport
51
Q

NEPHRON in kidney

Step 2: Describe the process of selective reabsorption

A

Essentially co-transport:

  • Na+ are brought in by facilitated diffusion from lumen of PCT to epithelial cells of PCT
  • this changes the shape of the carrier protein so glucose is simultaneously brought in against its concentration gradient via co-transport
  • Glucose leaves to blood via facilitated diffusion down concentration gradient
  • Na+ ions leave to blood via active transport against concentration gradient by Na+/K+ pump which requires use of ATP
  • Movement of Na+ to blood maintains the concentration gradient for Na+ to maintain uptake of glucose
52
Q

NEPHRON in kidney

What occurs after selective reabsorption?

A
  • amino acids, minerals + glucose are fully re absorbed + most water is too
  • but may still be some excess water, salt ions and urea left in filtrate

PROCESS:
- low water potential in blood vessels and high in PCT
- so water is reabsorbed into blood via osmosis

53
Q

NEPHRON in kidney

Step 3 - concentrating the urine

What is it and where does it occur?

A

In the Loop of Henle, distal convoluted tubule and collecting duct

  • urine exits the nephron through collecting duct into pelvis cavity and leaves kidney through the ureter to the bladder = excreted via urethra
54
Q

What is the function of the Loop of Henle in Step 3?

A

Acts as a counter-current multiplier

  • it creates an increasing salt concentration as you go further down the medulla
  • this maintains a water potential gradient for reabsorption of water down whole length of collecting duct
55
Q

What is the function of the collecting duct in Step 3?

A

Reabsorption of water (concentrating the urine)

  • controlled by hormones which alter the permeability of the walls.
56
Q

What is the difference between ascending and descending limb of DCT/ Loop of Henle?

A

Ascending limb has thicker walls so is impermeable to water but has carrier proteins for sodium ions.

Descending limb is permeable to water only

57
Q

Describe the process of concentrating the urine (step 3) [6]

A
  1. Na+ are actively transported out of top of ascending limb into tissue fluid
  2. This decreases the water potential of the tissue fluid (as Na+ is moving into it)
  3. As a result a water potential gradient is created. So water moves by osmosis down water potential gradient from filtrate in descending limb to tissue fluid
  4. Filtrate is most concentrated at base of Loop of Henle
  5. Na+ diffuses out into tissue fluid which makes most filtrate more dilute
  6. Most na+ diffuses out of filtrate at base where concentration gradient is steepest into tissue fluid
58
Q

What does the collecting duct then do after the urine is concentrated?

A

The water potential gradient is maintained down the whole length of the collecting duct so as much water can be reabsorbed as possible back into the blood

59
Q

APPLICATION

What is the relationship between length of loop of Henle and medulla?

A

The longer the loop into the medulla, the lower the water potential in the medulla

E.g. desert animals - need to conserve water so lose little water through urine (kangaroo rat)
- due to loads of water being reabsorbed

60
Q

What is urea?

A

When we eat protein - it is digested into amino acids and then reabsorbed into the blood in small intestine

  • amino acids then used to make protein

Our body is unable to store excess amino acids as can be toxic so they are transported to the liver where they are deaminated (removal of amine group) which is converted to ammonia + then urea

61
Q

What is ADH and where is stored?

A

ADH is a protein hormone produced by hypothalamus in brain, which is then stored in posterior pituitary gland located just below before being released

62
Q

What type of gland is the pituitary gland?

A

Its an endocrine gland so releases its hormones directly into the blood

63
Q

What causes ADH production in hypothalamus?

A

Shrinking of osmoreceptors (which detect changes in water potential of blood) in hypothalamus stimulates production of ADH in hypothalamus + secretion from posterior pituitary gland

  • when water potential in blood is low, water moves from osmoreceptor by osmosis to blood = shrinking of receptor
64
Q

Describe the hormonal control of osmoregulation [5]

A
  1. ADH in the blood
  2. ADH binds to protein receptors on cells
  3. This binding triggers vesicles containing aquaporins to move forward
  4. Vesicles fuse with cell surface membrane of collecting duct, inserting their aquaporins into the membrane
  5. This allows more movement of water out of collecting duct back into the blood (increased permeability of collecting duct)

Biology (22 decks)

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