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A level Biology > Kidney and Homeostasis ( Component 3 ) > Flashcards

Kidney and Homeostasis ( Component 3 ) Flashcards

1
Q

What does homeostasis describe ?

A

Homeostasis describes the mechanisms by which a constant internal environment is achieved, e.g. core body temperature, glucose levels, and solute potential.

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2
Q

Define homeostasis

A

The maintainance of a state of dynamic equilibrium in the body despite fluctuations in internal and external conditions.

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3
Q

Why is homeostasis important ( 3 main reasons ) ?

A

So that cells of the body can function efficiently, independently of fluctuations in the conditions of the external environment.
Cells are provided with constant conditions, even during different levels of activity of the organism.
To ensure optimum conditions for enzymes and cellular processes in the body.

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4
Q

What is the role of negative feedback ?

A

to restore conditions to their original levels

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5
Q

Define negative feedback

A

Self regulatory mechanisms that return the internal environment to the optimum when there is a fluctuation

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6
Q

What is the role of positive feedback ?

A

to enhance the size of the stimulus.

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7
Q

Define positive feedback

A

A fluctuation which triggers changes that result in an even greater deviation from the normal level

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8
Q

What is a set point ?

A

A desired value or range of values determined by a coordinator. There is a set point/norm/normal level for each condition determined by a control centre

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9
Q

How is a set point restored ?

A

Deviations from the set point are corrected by negative feedback

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10
Q

What is the role of a receptor ?

A

Receptors : specialised cells located in sense organs that detect a specific stimulus, monitor the condition and provide input to the control centre/ coordinator

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11
Q

What is the role of an effector ?

A

Muscles or glands which enable a physical response to a stimulus, makes a response designed to take away the deviation, i.e. restore the set point/norm.

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12
Q

What is the role of the coordinator ?

A

Coordinates information from the receptors and sends instructions to the effectors, evaluates the information and provides output to an effector

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13
Q

State the 4 main components of the negative feedback system

A

Set point
Receptors
Coordinator
Effectors

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14
Q

Describe the gross structure of a mammalian kidney ( fibrous capsule, cortex, renal pyramids, renal pelvis, medulla )

A

Fibrous capsule - protects kidney
Cortex - outer region consists of Bowman’s capsule, convoluted tubules, blood vessels
Renal pyramids - cone shaped subdivisions
Renal pelvis - funnel shaped dilated section of ureter
Medulla - inner region consists of collecting ducts, loop of Henle, blood vessels

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15
Q

What is a nephron ?

A

The functional unit of a mammalian kidney

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16
Q

Where are nephrons found within the kidney ?

A

Part of nephron is located in medulla other part located in cortex

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17
Q

What is the function of the renal artery ?

A

Supplies blood to kidneys

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18
Q

What is the function of the renal vein ?

A

Drains blood from kidneys

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19
Q

What is the function of the ureter ?

A

Takes urine from the kidneys to the bladder

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20
Q

What is the function of the urethra ?

A

Releases urine from body, out of bladder

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21
Q

Draw and label a diagram of a nephron ( should include : glomerulus, Bowman’s capsule, proximal and distal convoluted tubules; loop of Henlé, vasa recta, collecting duct, afferent and efferent arterioles )

A

…

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22
Q

Describe the blood vessels associated with a nephron

A

Wide afferent arteriole from renal artery enters renal capsule and forms the glomerulus, a branched knot of capillaries which combine to form narrow efferent arteriole.
Efferent arteriole branches to form capillary network that surrounds tubules

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23
Q

Define ultrafiltration

A

The removal of small molecules, water and ions from the blood in the glomerulus of the kidney at high pressure

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24
Q

Describe the process of ultrafiltration

A

Occurs in Bowman’s capsule
High hydrostatic pressure in glomerulus forces small molecules ( eg water glucose ions urea ) out of capillary fenestrations against osmotic gradient.
Basement membrane acts as filter - blood cells and large molecules ( eg proteins ) remain in capillary

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25
What key parts of the nephron are associated in ultrafiltration ?
The glomerulus, Bowman’s capsule (including podocytes) and the afferent and efferent arterioles are involved in ultrafiltration of the blood and produce glomerular filtrate in the first stage in the production of urine.
26
Why is there a build up of pressure in the glomerulus ?
Afferent arteriole leading into glomerulus is wider than the efferent arteriole taking blood from the glomerulus
27
How are cells of the Bowman's capsule adapted for ultrafiltration ?
Fenestrations between epithelial cells of capillaries Fluid can pass between and under folded membrane of podocytes
28
What are the two main functions of the mammalian kidney ?
nitrogenous excretion and water regulation
29
What is osmoregulation ?
Osmoregulation is the control of the water content and solute composition of body fluids e.g. blood, tissue fluid and lymph and excretion is the elimination of waste products of metabolism from an organism. The regulation of the water potential of body fluids by the kidney.
30
Why is osmoregulation important ?
Prevents cells bursting or shrinking when water enters or leaves by osmosis Cellular reactions occur in aqueous solution therefore water levels affect concentrations and the rate of reactions in cells
31
Define excretion
The process of removing metabolic waste from an organism
32
Describe how excess amino acids are excreted
1) Amino acids are deaminated in the liver ( removal of amino group ) to form ammonia 2) Ammonia converted to urea ( less toxic ) 3) Urea transported into the blood plasma and eliminated by kidneys. Amino acids cannot be stored and surplus amino acids, not used for the synthesis of proteins and other nitrogenous compounds are deaminated in the mammalian liver.
33
Describe the adaptations of the structure of the proximal convoluted tubule (PCT) in relation to selective reabsorption
large surface area (due to its length and large number per kidney), cuboidal epithelial cells with microvilli and basal channels provide large SA for co transporter proteins many mitochondria to provide ATP for active trasnport of glcuose into intercellular spaces folded basal membrane = large SA tight junctions preventing seepage of reabsorbed materials back into the filtrate, and close association with peritubular capillaries that extend into medulla enabling reabsorption of materials
34
What happens during selective reabsorption ?
Useful molecules from glomerlular filtrate ( glucose, ions and some water ) are reabsorbed into the blood Involves membrane transport proteins
35
Where does selective reabsorption occur ?
Proximal convulated tubule
36
Process of selective reabsorption summary
all of the filtered glucose (below the kidney threshold) and amino acids by secondary active transport * using a co-transport mechanism with Na+; * most of the mineral ions by active transport; * most of the water by osmosis; * some filtered proteins (and some urea) by diffusion
37
By what mechanism are amino acids and filtered glucose selectively reabsorped into the blood ?
Secondary active transport Uses a co transport mechanism involving Na+
38
By what mechanism are mineral ions selectively reabsorped into the blood ?
Active transport
39
By what mechanism is water selectively reabsorped into the blood ?
Osmosis
40
By what mechanism are filtered proteins and urea selectively reabsorped into the blood ?
Diffusion
41
How is the filtrate at the end of the PCT described as ?
Isotonic with blood plasma
42
Describe the loop of Henle
A loop consisting of a descending limb ( dips into medulla ) and ascending limb ( rises into cortex ) surrounded by blood capillaries
43
What is the function of the loop of Henle ?
Creates a low water potential in the medulla, enabling the reabsorption of water
44
Describe what happens in the loop of Henle
1) Active transport of Na+ and Cl- out of ascending limb 2) Water potential of interstitial fluid decreases 3) Movement of water out of descending limb via osmosis 4) Water potential of filtrate decreases going down descending limb - lowest in medullary region, highest at top of ascending limb 5) Hair pin counter current multiplier
45
Loop of Henle summary from spec
The loops of Henlé concentrate salts in the tissue fluid of the medulla and that causes an osmotic flow of water out of the collecting ducts and distal convoluted tubules. This is achieved by: * actively pumping Na+ and Cl- out of the filtrate in the ascending limb into the tissue fluid creating a low water potential * the ascending limb being impermeable to water while the descending limb is permeable; * the low water potential of the tissue fluid means that water leaves the descending limb by osmosis and is carried away by the vasa recta; * the contents of the descending limb becoming more concentrated as they reach the tip of the loop of Henlé due to the loss of water; * 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 tip of the loop of Henlé * this is called a hair-pin counter-current multiplier
46
What is an endocrine gland ?
A gland of the endocrine system that secretes hormones directly into the bloodstream
47
What is the role of the endocrine gland in secretion of ADH ?
Endocrine glands contribute towards homeostatic balance as illustrated by the role of the posterior pituitary gland in the secretion of antidiuretic hormone.
48
How is the concentration and volume of urine controlled ?
Controlled by secretion of ADH
49
Explain the role of the hypothamlamus in osmoregulation
Osmoreceptors in hypothalamus detect the concentration of the blood plasma Hypothalamus releases ADH
50
Explain the role of the posterior pituitary gland in osmoregulation
Stores and secretes the ADH produced by the hypothalamus
51
Describe how ADH affects the reabsorption of water from kidney tubules
ADH causes insertion of aquaporins into plasma membranes of cells of DCT and collecting duct Increases permeabiity of DCT and collecting duct More water reabsorbed More concentrated urine produced, lower volume
52
ADH secretion has a role in negative feedback restoring the normal osmotic concentration in the blood. Explain the roles of the detector, coordinator and effector
detectors - osmoreceptors in the hypothalamus; coordinator - posterior lobe of pituitary secreting ADH effector - distal convoluted tubules and collecting ducts of the kidneys.
53
How does ADH enable more concentrated urine to be formed ?
* 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 the filtrate into the surrounding, hypertonic, tissue fluid (and hence 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, that is, hypertonic to the general body fluids.
54
Describe the effects of kidney failure
Building of toxic waste products ( eg urea ) causes symptoms such as vomiting Fluid accumulation leads to swelling Disruption to electrolyte balance can make bones more brittle High concentrations of renin may lead to hypertension Low conc of EPO may lead to anemia
55
Outline potential treatments for kidney failure
medication to control blood potassium and calcium levels; a lower protein diet; drugs to reduce blood pressure; renal dialysis and kidney transplant.
56
Describe renal dialysis
Medical procedure that artificially filters the blood Relies on a partially permeable membrane between patient's blood and dialysis fluid - counter current flow Two types : haemodialysis and peritoneal dialysis
57
What is a transplant ?
A medical procedure in which an organ or tissue in an individual is replaced
58
What plays a part in the nitrogenous waste produced and different animals deal with its disposal in different ways ?
The mode of life and the environment in which an animal lives
59
Describe how animal excretory products can differ ( freshwater animals vs reptiles/birds/insects vs mammals )
Freshwater animal species excrete ammonia Reptiles, birds and insects produce uric acid Mammals excrete urea
60
How does the length of the loop of Henle differ between mammals ?
length of the loop of Henle varies depending on the availability of water in the mammal's environment. longer loop of henle in desert animals ( eg kangaroo rat ) to allow greater time for reabsorption of salts and water

A level Biology (10 decks)

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