3.4 - homeostasis + the kidney

Question 1

what’s homeostasis

Answer 1

maintenance of state of dynamic equilibrium in body despite fluctuations in internal + external conditions

Question 2

why is homeostasis important

Answer 2

to ensure optimum conditions for enzymes + cellular processes in the body

Question 3

define negative feedback

Answer 3

self-regulatory mechanisms return the internal environment to the optimum when there is a fluctuation

Question 4

define positive feedback

Answer 4

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

Question 5

what’s the set point

Answer 5

desired value or range of values determined by a coordinator

Question 6

describe receptors + effectors

Answer 6

receptors - specialised cells located in sense organs that detect specific stimulus
effectors - muscles/glands which enable a physical response to a stimulus

Question 7

describe the role of the coordinator

Answer 7

coordinated information from receptors + sends instructions to effectors

Question 8

state the components of a negative feedback system

Answer 8

• set point
• receptors
• coordinator
• effector

Question 9

what’s the mammalian kidney

Answer 9

one of a pair of organs in abdomen that has a role in osmoregulation + nitrogenous excretion

Question 10

what’s osmoregulation

Answer 10

regulation of water potential of body fluids (eg: blood, tissue fluid, lymph) by the kideny

Question 11

why is osmoregulation important

Answer 11

• prevents cells bursting or shrinking when water enters or leaves by osmosis
• cellular reactions occur in aqueous solution, water levels affect conc + rate of reactions in cells

Question 12

define excretion

Answer 12

process of removing metabolic waste from an organism

Question 13

describe how excess amino acids are excreted

Answer 13

• amino acids deaminated in liver (removal of amino group) forming ammonia
• ammonia converted to urea (less toxic)
• urea transported into blood plasma + eliminated by kidneys

Question 14

what’s the function of the renal artery

Answer 14

supplies blood to kidneys

Question 15

what’s the function of the renal vein

Answer 15

drains blood from kidneys

Question 16

what’s the function of the ureter

Answer 16

takes urine to bladder from kidneys

Question 17

what’s the function of the ureter

Answer 17

takes urine to bladder from kidneys

Question 18

what’s the function of the urethra

Answer 18

releases urine from bladder, out of body

Question 19

describe the gross structure of a mammalian kidney

Answer 19

fibrous capsule - protects kidney
cortex - outer region consists of bowman’s capsules, convoluted tubules, blood vessels
renal pyramids - cone shaped subdivisions
renal pelvis - funnel shaped dilation section of ureter
medulla - inner region consists of collecting ducts, loops of henle, blood vessels

Question 20

what’s a nephron

Answer 20

functional unit of mammalian kidney

Question 21

where are nephrons found within kidneys

Answer 21

part of nephron located in medulla + part in cortex

Question 22

describe the blood vessels associated w/ a nephron

Answer 22

wide afferent arteriole from renal artery enters renal capsule + forms glomerulus, branched knot of capillaries which combine to form narrow efferent arteriole
efferent arteriole branches to form capillary network that surrounds tubules

Question 23

define ultrafiltration

Answer 23

removal of small molecules, water + ions from blood in glomerulus of kidney at high pressure

Question 24

describe the process of ultrafiltration

Answer 24

• occurs in bowman’s capsule
• high hydrostatic pressure in glomerulus forces small molecules (e.g: urea, water, glucose, ions) out of capillary fenestrations against osmotic gradient
• basement membrane acts as filter, blood cells + large molecules (e.g: proteins) remain in capillary

Question 25

why is there a build up of pressure in glomerulus

Answer 25

afferent arteriole leading into glomerulus is wider than efferent taking blood from glomerulus

Question 26

how are you cells of bowman’s capsule adapted for ultrafiltration

Answer 26

- fenestrations between epithelial cells of capillaries - fluid can pass between + under folded membrane of podocytes

Question 27

what happens in selective re absorption

Answer 27

- useful molecules from glomerular filtrate (glucose, some water, some ion) are reabsorbed into blood - involves membrane transport proteins

Question 28

where does selective re absorption occur

Answer 28

proximal convoluted tubule

Question 29

how are cells in PCT adapted for selective reabsorption

Answer 29

- microvilli provide large SA for co-transporter proteins - many mitochondria produce ATP for active transport of glucose in intracellular spaces - folded basal membrane provides large SA - tight junctions stop reabsorbed materials leaking back into filtrate - peritubular capillaries extend into medulla enabling réabsorption of materials

Question 30

by what mechanism are amino acids + filtered glucose selectively reabsorbed into blood

Answer 30

- secondary active transport - uses co-transport mechanism involving Na+

Question 31

by what mechanism are mineral ions selectively reabsorbed into blood

Answer 31

active transport

Question 32

by what mechanism is water selectively reabsorbed into blood

Answer 32

osmosis

Question 33

how are filtered protein (+some urea) selectively reabsorbed into blood

Answer 33

via diffusion

Question 34

describe the loop of henle

Answer 34

loop consisting of descending limb (dips into medulla) + ascending limb (rises into cortex) surrounded by blood capillaries

Question 35

what’s the function of the loop of henle

Answer 35

creates low water potential in medulla, enabling reabsorption of water

Question 36

describe what happens in the loop on henle

Answer 36

- active transport of Na+ and Cl- out of ascending limb - water potential of interstitial fluid decreases - movement of water out of descending limb via osmosis (ascending limb is impermeable to water) - water potential of filtrate decreases going down descending limb, lowest in medullary region, highest at top of ascending limb - hair pin counter current mulitplier

Question 37

what’s an endocrine gland

Answer 37

gland of endocrine system that secretes hormones directly into bloodstream

Question 38

how is concentration + volume of urine controlled

Answer 38

controlled by secretion of anti-diuretic hormone (ADH)

Question 39

explain the role of the hypothalamus in osmoregulation

Answer 39

- osmoreceptors in hypothalamus detect conc of blood plasma - hypothalamus secrets ADH

Question 40

explain the role of the posterior pituitary gland in osmoregulation

Answer 40

stores + secretes ADH produces by hypothalamus

Question 41

describe how ADH affects the reabsorption of water from kidney tubules

Answer 41

- ADH causes insertion of aquaporins into plasma membranes of cells of DCT + collecting duct - increases permeability of DCT + collecting duct - more water reabsorbed - more concentrated urine produced

Question 42

describe the effects of kidney failure

Answer 42

- build up of toxic waste products (e.g urea) causes symptoms such as vomiting - fluid accumulation leads to swelling - disruption to electrolyte balance can make bones more brittle - high conc of renin may lead to hypertension - low conc of EPO can lead to anemia

Question 43

outline the potential treatments for kidney failure

Answer 43

- low protein diet - control of blood calcium + potassium levels using medication - drugs to lower blood pressure - renal dialysis - kidney transplant

Question 44

describe renal dialysis

Answer 44

- medical procedure that artificially filters blood - relies on partially permeable membrane between patients blood + dialysis fluid - 2 types: haemodialysis + peritoneal dialysis

Question 45

what’s a transplant

Answer 45

medical procedure in which an organ or tissue in an individual is replaced

Question 46

describe how animal excretory products can differ

Answer 46

- freshwater animal species excrete ammonia - reptiles, birds + insects produce uric acid - mammals excrete urea

Question 47

how does length of loop of henle differ between mammals

Answer 47

- length of loop varies depending on availability of water in mammals environment - longer loop in desert animals to allow greater time for reabsorption of water + salts