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Biology > Homeostasis > Flashcards

Homeostasis Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

What is homeostasis?

A
  • the maintenance of a relatively constant internal environment for the cells within the body
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2
Q

What factors are controlled by homeostasis?

A
  • core body temp.
  • metabolic wastes; carbon dioxide and urea
  • blood pH
  • blood glucose conc.
  • water potential of blood
  • oxygen and carbon dioxide conc.
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3
Q

What two systems control homeostasis?

A
  • Endocrine system
  • Nervous system
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4
Q

What are four features of tissue fluid that influence cell activities?

A
  • temperature:
    low temperatures slow down metabolic reactions
    high temperatures denatures enzymes and proteins
  • water potential:
    if w.p decreases, water moves out of cell, so metabolic reactions slow/stop
    if w.p increases water may enter cell by osmosis and cause it to burst
  • conc. of glucose in blood:
    low glucose; respiration slows down
    high glucose; can cause water to move out of cell
  • pH:
    controls enzyme activity
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5
Q

What is negative feedback?

A
  • a process in which some change in parameter (e.g blood glucose conc.) brings about a process which returns it to normal
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6
Q

Describe negative feedback mechanism:

A

stimuli –> receptor –> CNS/brain –> effector –> response

e.g; thermoregulation
stimuli: increase in core body temp.
response: vasodilation/sweating to reduce body temp.

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7
Q

What is positive feedback?

A
  • when a change in parameter brings about a process that further moves the change in its initial direction
    e.g; if something increases, it will increase more
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8
Q

What is excretion?

A
  • the removal of toxic/waste products of metabolism from the body
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9
Q

What are two excretory products?

A
  • Carbon dioxide
  • Urea
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10
Q

What is deamination?

A
  • the breakdown of excess amino acids in the liver by the removal of an amine group
  • amino acid –> keto acid + ammonia
  • ammonia will be converted into urea
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11
Q

What happens to a keto acid?

A
  • it is respired or converted into glucose, glycogen or fat and can enter Krebs cycle
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12
Q

Why is ammonia converted into urea?

A
  • ammonia is:
  • very soluble
  • highly toxic
  • increases pH in cytoplasm
  • can interrupt respiration and cell signaling
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13
Q

How is ammonia converted into urea?

A

2NH3 + CO2 –> CO(NH2)2 + H2O
ammonia + carbon dioxide –> urea + water
- urea is less soluble and less toxic than ammonia

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14
Q

What are the main components of the excretory system?

A
  • inferior vena cava + aorta
  • kidneys
  • renal vein + artery
  • ureter
  • bladder
  • urethra
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15
Q

What are the main components of a Kidney?

A
  • Fibrous capsule
  • Cortex
  • Medulla
  • Nephron
  • Branches of renal vein + artery
  • Pelvis
  • Ureter
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16
Q

What are the components of a Nephron?

A
  • Bowman’s capsule + glomerulus
  • Proximal convoluted tubule
  • Loop of Henlé
  • Distal convoluted tubule
  • Collecting duct
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17
Q

What parts of the nephron are located in the cortex?

A
  • Bowmans capsule + glomerulus
  • PCT
  • DCT
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18
Q

Which parts of the nephron are located in the medulla?

A
  • loop of Henlé
  • collecting duct
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19
Q

What is the process of ultrafiltration?

A
  • occurs in Bowman’s capsule
  • blood flows from renal artery in AFFERENT arteriole
  • small molecules (amino acids, glucose, water, urea) are filtered out of the blood capillaries of glomerulus
  • into the Bowman’s capsule to form glomerular filtrate
  • large molecules such as plasma proteins cannot pass through basement membrane
20
Q

What are the afferent and efferent arterioles?

A

Afferent: leads towards the glomerulus
Efferent: leads away from the glomerulus

21
Q

How many layers are between the capillaries and the lumen of the Bowman’s capsule?

A
  • Three layers;
  • endothelium of capillary
  • basement membrane
  • Bowman’s capsule epithelium (consists of podocytes)
22
Q

Factors that effect water potential in the Bowman’s capsule + glomerulus:

A

Pressure:
- afferent arteriole wider than efferent, so blood pressure in glomerulus is HIGH
- so w.p in glomerulus higher
- so water moves by osmosis into the Bowman’s capsule

Solute Concentration:
- since plasma proteins, RBC, WBC’s and platelets cannot enter through basement membrane
- solute concentration in glomerulus is HIGH
- so water moves by osmosis into the glomerulus

  • Pressure outweighs solute concentration, so net movement of water is out of glomerulus, into the Bowman’s capsule
23
Q

What is selective reabsorption?

A
  • movement of certain substances from the filtrate in the nephrons back into the blood
24
Q

What substances are reabsorbed in the PCT?

A
  • ALL glucose, by active transport
  • amino acids, inorganic ions, vitamins
  • water moves into blood by osmosis
  • urea
25
Q

What is the process of selective reabsorption in the PCT?

A
  • basal membranes in PCT have sodium-potassium pumps
  • Na+ is pumped out of the PCT cells, using ATP, into the blood
  • by active transport
  • so Na+ diffuses back into PCT from lumen since concentration gradient forms
  • glucose, amino acids and Na+ move into the PCT through a co-transport mechanism
  • through carrier/transport protein
  • glucose and amino acids can diffuse back into the blood
  • ALL glucose reabsorbed into blood
  • SOME water and urea reabsorbed
26
Q

What are the adaptations of the PCT for selective reabsorption?

A
  • Many microvilli; increases SA
  • Many co-transporter proteins in luminal membrane; each co-transporter moves a specific solute (e.g; glucose)
  • Many mitochondria; provide energy for sodium-potassium pumps in basal membranes
  • Cells tightly packed together; no fluid can pass between cells
  • folded basal membrane for many sodium pumps
27
Q

What is reabsorbed in the loop of Henlé?

A
  • salts are reabsorbed at ascending limb FIRST
  • water potential in loop gets higher so;
  • water reabsorbed at descending limb by osmosis
28
Q

What is reabsorbed at the DCT and collecting duct?

A
  • the first part of the DCT functions like the loop of Henle, whereas the second part of the DCT functions like the collecting duct
  • in the collecting duct, sodium ions are actively pumped OUT the tubule to blood
  • potassium ions are actively transported IN the tubule
29
Q

What is osmoregulation?

A
  • the control of water potential of blood and tissue fluid
  • by controlling water concentration or ion content
30
Q

What happens if the water potential of the blood is LOW?

A
  • osmoreceptors in hypothalamus are stimulated
  • nerve impulse sent to posterior pituitary gland
  • ADH released
  • ADH binds to receptors on membrane of collecting duct
  • enzyme cascade signaled by cAMP
  • vesicles with aquaporins move towards membrane
  • number of aquaporins on luminal membrane of collecting duct INCREASE
  • collecting ducts become more permeable to water
  • filtrate flows along CD and water moves into blood
  • concentrated urine produced
  • flows of the kidney through ureter and into bladder
31
Q

What happens if the water potential of the blood is too HIGH?

A
  • Osmoreceptors in the hypothalamus are not stimulated
  • No nerve impulses are sent to the posterior pituitary gland
  • No ADH released
  • Aquaporins are moved out of the luminal membranes of the collecting duct cells via vesicles
  • Collecting duct cells are no longer permeable to water
  • The filtrate flows along collecting duct but loses no water and is very dilute
  • A large volume of dilute urine is produced
  • This flows from the kidneys, through the ureters and into the bladder
  • w.p in blood decreases
32
Q

Describe the action of ADH on the kidney:

A
  • affects collecting duct
  • binds to receptors on cell surface membrane of collecting duct
  • activates series of enzyme controlled reactions
  • final enzyme produced is phosphorylase
  • aquaporins/vesicles move to cell surface on luminal side
  • aquaporins fuse with cell surface membrane
  • cells become more permeable to water
  • water moves out of lumen
  • down water potential gradient
  • into bloodstream
33
Q

What do a-cells secrete?

A

Glucagon

34
Q

What do B-cells secrete?

A

Insulin

35
Q

What happens when there is an increase in blood glucose?

A
  • glucose enters B-cells by facilitated diffusion
  • these cells respire and produce ATP
  • potassium channels close
  • voltage-gated calcium channels open
  • Insulin secreted by exocytosis
  • insulin binds to receptors on liver, muscle and adipose tissue
  • permeability of target cells to glucose increases
  • insulin activates glucokinase enzyme
  • which phosphorylates glucose to keep it inside target cells
  • glycogen synthase
  • catalyses glycogenesis
36
Q

How is blood glucose regulated?

A

To decrease:
- glycogenesis
- increased uptake of glucose by cells
- increased use of glucose in respiration

To increase:
- glycogenolysis

37
Q

What three enzymes does insulin activate?

A
  • glucose kinase; phosphorylates glucose to keep it inside target cells

For glycogenesis; synthesis of glycogen by addition of glucose monomers
- phosphofructosekinase
- glycogen synthase

38
Q

What happens if there is a decrease in blood glucose?

A
  • Pancreatic a-cells secrete glucagon
  • Glucagon binds to liver cell receptors
  • Conformational change to receptor activates G protein
  • G protein activates adenylyl cyclase
  • Adenylyl cyclase uses ATP to make cAMP
  • cAMP binds to protein kinase A enzymes
  • protein kinase A activate phosphorylase kinase enzymes
  • phosphorylase kinase activates glycogen phosphorylase enzymes
  • Glycogenolysis occurs
  • blood glucose conc. increases
39
Q

How is the concentration of glucose measured in urine?

A
  • glucose presence in urine may indicate diabetes
  • test strips
  • contain glucose oxidase and peroxidase

reactions:
by glucose oxidase
- glucose + oxygen —-> gluconic acid + hydrogen peroxide

by peroxidase
- hydrogen peroxide + chromogen (colourless) —-> oxidized chromogen (coloured) + water

40
Q

How is glucose measured in the blood?

A
  • biosensors
  • a device that uses biological material such as an enzyme to measure the concentration of a chemical compound
  • uses glucose oxidase immobilized on a recognition layer
41
Q

Describe the structure of a guard cell:

A
  • thick cell wall facing stoma and thick waxy cuticle
  • cellulose microfibrils arranged in bands around cell
  • cell walls have no plasmodesmata
  • folded cell surface membrane and contains many channel proteins
  • cytoplasm contains chloroplasts + mitochondria
  • chloroplast have thylakoids, few grana
  • many cristae in mitochondria
  • several small vacuoles
  • nucleus
42
Q

What causes stomata to open and why do they need to open?

A

what
- increase light intensity
- low CO2 conc. in leaf

why
- to gain CO2 for photosynthesis
- allow O2 out

  • allow transpiration stream to occur which
  • brings water/mineral ions in
  • for photosynthesis/turgidity
43
Q

What causes stomata to close and why do thy need to close?

A

what
- in darkness
- in low humidity/high temperature/water stress/high wind

why
- CO2 not needed for photosynthesis
- to maintain cell turgidity/prevent water loss

44
Q

Explain the mechanism by which guard cells open stomata:

A
  • proton pumps in cell surface membrane
  • actively pump H+ out of cell
  • lower H+ conc inside
  • K+ channels open
  • K+ moves into cell by facilitated diffusion
  • Cl- ions enter cell
  • water potential of cell decreases
  • water moves in by osmosis
  • aquaporins
  • volume of guard cell increases and becomes more turgid
45
Q

Describe the role of abscisic acid (ABA) in stomata closure:

A
  • ABA is a stress hormone
  • plant secretes ABA in high temp./dry conditions
  • ABA binds to receptors
  • on cell surface membrane of guard cells
  • inhibits proton pumps
  • high H+ conc. in cell
  • ABA stimulates Ca2+ into cell
  • allowing K+ to diffuse out of cell
  • water potential in cell increases
  • water moves out by osmosis
  • volume of guard cells decrease and they become flaccid
  • quick response
46
Q

Explain the reabsorption of water in loop of Henlé:

A
  • sodium ions are reabsorbed in the descending limb/less Na in filtrate
  • this is done by Na+ being actively pumped from filtrate into tissue fluid in medulla (then passes to blood)
  • this increases the water potential of the filtrate
  • so more water is reabsorbed by osmosis
  • decreases volume of urine

Biology (9 decks)

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