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Bio Component 3 > Homeostasis and the Kidney > Flashcards

Homeostasis and the Kidney Flashcards

1
Q

Define homeostasis

A

The maintenance of a constant internal environment within a living organism, irrespective of the external conditions

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2
Q

Give 3 examples of homeostatic control

A
  • Regulation of blood glucose levels
  • Regulation of solute potential
  • Regulation of core body temperature and pH
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3
Q

Homeostasis uses ____________ _________ to return the body to the set point

A

Negative feedback

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4
Q

Negative feedback uses a __________ which monitors the condition and provides input to the control ________ which evaluates the information and provides output to an _________ which makes a ________ designed to take away the deviation (return to the _____ ________)

A

Detector
Centre
Effector
Response
Set point

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5
Q

Define negative feedback

A

A receptor detects any deviation from a set point. Information is sent to a control centre which coordinates a response to return levels back to the set point

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6
Q

Give 2 examples of when the body uses positive feedback (an effector increases a change)

A
  1. Oxytocin stimulates the contraction of the uterus at the end of pregnancy. The contractions stimulate the production of more oxytocin, which increases the stimulus
  2. When the skin is cut, the first stage of clot formation is that platelets adhere to the cut surface. They secrete signalling molecules, which attract more platelets to the site
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7
Q

Name 2 functions of the kidney

A
  1. Nitrogenous excretion
  2. Osmoregulation
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8
Q

What are the 4 steps in nitrogenous excretion?

A
  1. Amine group is removed from an amino acid
  2. The removed amine group converted to ammonia
  3. With the addition of CO2, urea is formed and transported in the blood plasma to kidneys
  4. Urea is removed by the kidneys and excreted in the urine
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9
Q

Define osmoregulation

A

The control of the water content and solute composition of body fluids

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10
Q

Humans lose water by:

A
  • Urination and egestion of faeces
  • Sweating
  • Exhalation
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11
Q

What is the function of the ureter?

A

Convey urine to the bladder

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12
Q

What is the function of the urethra?

A

Carries urine to outside for elimination

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13
Q

What is the function of the sphincter?

A

A muscle that allows conscious control of urine release

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14
Q

Define ultrafiltration

A

Filtration under pressure that separates small soluble molecules from the blood plasma

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15
Q

Water and small soluble molecules are separated form the blood plasma to form filtrate in the Bowman’s capsule. To do this they are forced through:

A
  • Pores in the glomerular capillary wall
  • The basement membrane (acts as a molecular sieve)
  • Filtered between the feet of the podocytes
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16
Q

Describe ultrafiltration

A
  • High hydrostatic pressure - efferent arteriole has a narrower lumen than afferent
  • Due to this, high pressure fluid containing water and small molecules is forced out of blood in the capillaries through the pores in the capillary walls, and then through pores in the basement membrane
  • Basement membrane acts as a molecular sieve, allowing small molecules to pass through but preventing large molecules from passing through
  • The small soluble molecules are then filtered through the feet of the podocytes and glomerular filtrate is formed in the Bowman’s capsule
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17
Q

Where does selective reabsorption occur?

A

Proximal convoluted tubule

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18
Q

Define selective reabsorption

A

The process by which useful products such as glucose and salts are reabsorbed back into the blood as the filtrate flows along the nephron

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19
Q

The filtrate at the end of the proximal convoluted tubule is ________ to blood plasma

A

Isotonic

20
Q

By what mechanism are glucose and amino acids selectively reabsorbed?

A

Secondary active transport using a co-transport mechanism with Na+

21
Q

By what mechanism are most of the mineral ions selectively reabsorbed?

A

Active transport/co-transport

22
Q

By what mechanism is most of the water selectively reabsorbed?

A

By osmosis down a water potential gradient

23
Q

By what mechanism are some of the filtered proteins and urea selectively reabsorbed?

A

Diffusion

24
Q

Name 4 adaptations of the structure of the proximal convoluted tubule in relation to selective reabsorption

A
  • Large surface area (due to length and large number per kidney)
  • Cuboidal epithelial cells with microvilli to provide large surface area and nasal channels
  • Numerous mitochondria to provide ATP for active transport
  • Tight junctions to prevent seepage of reabsorbed materials back into the filtrate, and close association with peritubular capillaries
25
Q

What is the function of the loop of Henle?

A

The loop of Henle concentrates Na+ in the tissue fluid of the medulla, causing an osmotic flow of water out of the collecting ducts and distal convoluted tubules
This water can then be reabsorbed into the blood stream via the capillaries of the vasa recta. Concentrates the irks and makes it hypertonic to the blood

26
Q

The descending limb is _____________ to water

A

Permeable

27
Q

The ascending limb is ______________ to water

A

Impermeable

28
Q

Describe the hair pin counter current multiplier effect

A
  • Na+ and Cl- are actively transported out of the filtrate in the ascending limb into the tissue fluid of the medulla creating a lower water potential
  • This means that water leaves the descending limb by osmosis down a water potential gradient and can then move by osmosis into the capillaries of the vasa recta
  • The filtrate in the descending limb becomes more concentrated as it reaches the bottom of the loop of Henle due to the loss of water. Na+ and Cl- can also diffuse back into the filtrate near the bottom of the descending limb
  • As the filtrate passes up the ascending limb it becomes more dilute due to loss of ions
  • An osmotic gradient is maintained down to the bottom of the loop of Henle
29
Q

What happens in the collecting duct due to the loop of Henle creating a high Na+ concentration in the tissue fluid of the medulla?

A

Water leaves the permeable collecting ducts by osmosis to be reabsorbed into the capillaries

30
Q

What affects the permeability of collecting duct walls?

A

Antidiuretic hormone (ADH)

31
Q

How does ADH enable more concentrated urine to be formed?

A
  • ADH makes the plasma membranes of the distal convoluted tubule cells and collecting duct cells more permeable to water
  • ADH causes aquaporins to become incorporated in the plasma membranes, from within the cytosol
  • Water is reabsorbed by osmosis from filtrate into the surrounding hypertonic tissue fluid and then the blood capillaries around the DCTs and collecting ducts
  • The urine reaching the bottom of the collecting ducts has a concentration close to the concentration of the tissue fluid near the bottom of the loop which is hypertonic to general body fluids
32
Q

What detects changes in the water potential of the blood?

A

Osmoreceptors in the hypothalamus

33
Q

What is the coordinator in restoring the normal osmotic concentration?

A

Cells of the posterior lobe of the pituitary gland secrete more or less ADH

34
Q

What is the effector in restoring the normal osmotic concentration in the blood?

A

Cells of the distal convoluted tubules and collecting ducts become more or less permeable to water

35
Q

Describe what will happen if a person is dehydrated

A
  • Osmoreceptors in the hypothalamus detect a decrease in the water potential of the blood.
  • Nerve impulses are sent to the posterior pituitary gland that releases more ADH.
  • ADH travels in the bloodstream to the nephrons where it affects the cells of the collecting duct
  • More aquaporins in the plasma membrane of the collecting duct walls, making them more permeable to water
  • Water therefore leaves the filtrate in the collecting duct by osmosis into the tissue fluid of the medulla.
  • Water is then reabsorbed back into the bloodstream
  • This results in a small volume of concentrated urine.
36
Q

Describe what happens if a person is well hydrated

A
  • Osmoreceptors in the thalamus detect an increase in the water potential of the blood
  • Nerve impulses are sent to the posterior pituitary gland which release less ADH
  • Less aquaporins in the plasma membrane of the collecting duct so collecting duct walls become less permeable to water
  • Less water will leave the filtrate back into the bloodstream, producing a large volume of dilute urine
37
Q

What form of nitrogenous waste do aquatic animals excrete and why?

A

Ammonia which is highly toxic.
It is very soluble in water and can diffuse quickly across the gills of fish into the water where it is diluted to a non-toxic level

38
Q

What form of nitrogenous waste to birds, reptiles and insects excrete and why?

A

Uric acid which is almost insoluble in water
They use a lot of energy to extreme this waste but very little water is needed so these animals can survive in dry environments

39
Q

What form of nitrogenous waste do mammals excrete and why?

A

Urea
This requires a lot of water but is less toxic than ammonia so body tissues can tolerate it in higher concentrations for short periods of time

40
Q

How do desert mammals survive with very little water?

A

Water is produced from the breakdown of food during respiration in the cells (metabolic water). They may live in underground burrows which are cooler to reduce water loss by evaporation.

41
Q

Why would desert animals have a longer than average loop of Henle?

A

The longer the loop of Henle, the more opportunity to pump ions into the medulla, further increasing the concentration in the medulla. This lower water potential in the medulla enhances water reabsorption from the descending limb and collecting duct, resulting in more concentrated urine

42
Q

Name 5 causes of kidney failure

A
  • raised bood pressure
  • impact/crushing injury
  • auto-immune disease
  • diabetes
  • genetic condition
43
Q

Name 5 treatments for kidney failure

A
  • medication to control blood potassium and calcium levels
  • transplant
  • dialysis
  • reduce intake of protein in the diet to reduce urea formation
  • use of drugs to reduce blood pressure
44
Q

What is dialysis?

A

The process of removing excess water, inorganic ions and urea from the blood in people whose kidneys can no longer perform these functions naturally

45
Q

Describe how dialysis works/adaptations

A
  • The dialysate runs in counter-current flow next to the blood to be cleaned, this maintains a concentration gradient
  • Blood and dialysate are separated by a selectively permeable membrane to prevent loss of plasma proteins
  • Replacement with fresh dialysate further maintains a concentration gradient
46
Q

Why should the temperature of the dialysate be maintained at 37 degrees?

A

37 C is the internal body temperature. If blood cools down in dialysis machine then temperature shock may occur. Also increases the diffusion rate.

47
Q

What happens when someone gets a kidney transplant?

A

Functions of the failing kidneys are taken over by a single healthy kidney from a donor. It should function normally, cleaning and balancing the blood. However it may only last 9 years.
It may be rejected as antigens on the donor organ differ from antigens on the cells of the recipient. Immunosuppressants must be taken for the rest of their lives.

Bio Component 3 (8 decks)

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