WEEK 9: 9.2 Blood Flow to the Kidneys; The Nephron; Urine formation, concentration & hormone influences

Question 1

What are the 4 steps in blood flow through the kidney?

Answer 1

1. O2 rich blood arrives via renal artery
2. renal artery divides into segmental arteries in the renal sinus
3. segmental arteries branch into interlobar arteries, which run within renal columns
4. interlobar arteries branch into smaller vessels, culminating in afferent arterioles that supply each nephron

Question 2

How does blood flow around the nephron in 3 steps?

Answer 2

after entering the glomerulus via the afferent arteriole,
5. the efferent arteriole carried blood from the glomerulus to the peritubular capillaries
6. peritubular capillaries surround the renal tubule and collect water/solutes absorbed by the nephron, as well as deliver other solutes to the nephron for secretion
7. peritubular capillaries drain into cortical veins carry filtered blood back to the inferior vena cava

Question 3

What are nephrons?

Answer 3

functional units of the kidney

Question 4

what are the two types of nephrons?

Answer 4

cortical and juxtamedullary nephrons

Question 5

What are cortical nephrons?

Answer 5

• located within the renal cortex
• excreting waste products into urine

Question 6

What are juxtamedullary nephrons?

Answer 6

• long nephron loops extending into renal medulla
• producing concentrated urine

Question 7

What are the 3 main sections of the nephron?

Answer 7

Renal corpuscle
Renal tubule
Collecting system

Question 8

What occurs in the renal corpuscle?

Answer 8

Water and dissolved solutes are pushed out of blood and into renal tubule
site of blood filtration

Question 9

What occurs in renal tubule?

Answer 9

components of the filtrate are altered via secretion and absorption
filtrate modification

Question 10

What occurs in the collecting system?

Answer 10

urine empties into the collecting system and is transported to minor calyces

Question 11

Describe the physiological process of filtration in the kidney?

Answer 11

It only occurs in the renal corpuscle
solutes within blood pass through filtration membrane into the nephron

Question 12

Describe the physiological process of reabsorption in the kidney?

Answer 12

• transport of water/solutes from filtrate into the peritubular fluid (into bloodstream)

Question 13

Describe the physiological process of secretion in the kidney

Answer 13

To transport solutes from peritubular fluid into tubular fluid (filtrate)

Question 14

What structures does the renal corpuscle consist of?

Answer 14

glomerulus (capillary network)
glomerular capsule

Question 15

What are the two types of arterioles in the glomurulus?

Answer 15

Afferent - going in
efferent - going out

Question 16

why are efferent arterioles of a smaller diameter?

Answer 16

this increases glomerular pressure by establishing a pressure gradient, which enhances filtration as blood pressure forces water/solutes out of the capillaries into the capsule space and renal tubule

Question 17

What structure allows the filtration of blood from the glomerulus into the glomerular capsule?

Answer 17

Filtration membrane

Question 18

How is glomerular filtration at the renal corpuscle enhanced?

Answer 18

• thinness of the filtration membrane
• large surface area of glomerular capillaries
• high glomerular BP due to different in size of efferent arteriole

Question 19

What is the glomerular filtration rate?

Answer 19

a GFR of 60 = kidneys working at 60%
roughly equates to kidney function
the formula is based on creatinine levels, age and gender

Question 20

What 3 things is the filtration membrane composed of?

Answer 20

fenestrated epithelium (contains large intercellular pores) - stops cells and platelets
basement membrane (interwoven mesh fibres) - stops large proteins
filtration slits between pedicels - stops medium sized proteins

Question 21

What is the filtration membrane?

Answer 21

a barrier controlling what components of blood can enter nephron/stay outside

Question 22

What gets through the filtration membrane?

Answer 22

Water
Small proteins
Amino acids, glucose, salts
Waste solutes

Question 23

What can’t get through the filtration membrane?

Answer 23

medium-large proteins
cells
platelets

Question 24

What is a podocyte?

Answer 24

a specialised cell in the kidney, found in the glomerulus, that contain long foot like extensions called pedicels, which help form the filtration barrier in the glomerulus and allow water/small molecules to pass into the bowman’s capsule, while preventing larger molecules like protein and blood cells from being filtered out of the blood

Question 25

Where do filterable and nonfilterable components go once they enter the glomerulus?

Answer 25

filterable components ---> capsular space nonfilterable components exit the glomerulus via the efferent arteriole

Question 26

What are the two types of barriers in the basement membrane, and what are their functions?

Answer 26

physical barrier: to large plasma proteins charge barrier: repels negatively charged molecules

Question 27

What are mesangial cells?

Answer 27

specialised cells in kidney that provide structural support, regulate blood flow and clear waste in the glomerulus

Question 28

Where are mesangial cells located?

Answer 28

between adjacent capillaries

Question 29

What is the function of mesangial cells?

Answer 29

they contract and relax to control capillary diameter and blood flow rate they also phagocytose to keep glomerular filter free of debris and produce the intercellular matrix

Question 30

What are the 3 components of the renal tubule?

Answer 30

proximal convoluted tubule nephron loop (loop of henle) distal convoluted tubule (DCT)

Question 31

What is the PCT?

Answer 31

marks the beginning of the renal tubule reabsorbs essential substances from the filtrate back into blood like ions, glucose, small proteins cells have microvilli to aid reabsorption

Question 32

What is nephron loop (loop of henle)?

Answer 32

Increase the volume of hypertonic urine middle segment of renal tubule contains descending and ascending portions descending reabsorbs water ascending reabsorbs Na+ and Cl-

Question 33

What is distal convoluted tubule?

Answer 33

last segment of renal tubule adjusts filtrate composition via reabsorption and secretion, engages in finetuning

Question 34

What does the collecting duct do?

Answer 34

Filtrate is carried through osmotic gradient in the renal medulla water may or may not be reabsorbed depending on hydration status

Question 35

What does the papillary duct do?

Answer 35

Collect filtrate from multiple collecting ducts and delivers it to a minor calyx

Question 36

describe the structure of the PCT

Answer 36

consists of microvilli mitochondria for active transport centrally located nucleus acidophilic cytoplasm

Question 37

What is the function of the loop of henle?

Answer 37

It creates a concentration gradient in the medulla to concentrate urine, and retain water

Question 38

What is the descending limb of the loop of henle permeable to?

Answer 38

Water only (no solutes)

Question 39

What happens in the descending limb of the loop of henle?

Answer 39

Water leaves the tubule via osmosis due to salty surounding medulla, concentrating the filtrate

Question 40

What is the ascending limb of the loop of henle permeable to?

Answer 40

Solutes like sodium, chloride and potassium, but not water

Question 41

What happens in the ascending limb of the loop of henle?

Answer 41

active transport of salts into the medulla, making it more salty to create a gradient

Question 42

What does ADH do in the collecting duct?

Answer 42

make the duct more permeable to water, allowing reabsorption of water into the salty medulla

Question 43

What role does the vasa recta play?

Answer 43

Maintain the concentration gradient by reabsorbing water and recycling urea and salts

Question 44

What is the effect of the salty medulla on urine concentration?

Answer 44

It pulls water out of the collecting duct, concentrating the urine.

Question 45

What are the key functions of the DCT

Answer 45

Na is reabsorbed, while K+ is secreted Bicarbonate ions are reabsorbed for further acidification of urine ADH/vasopressin acts on DCT cells to make cells more permeable to water

Question 46

How is Na content controlled?

Answer 46

It is controlled by the hormone aldosterone, which is secreted from the adrenal cortex when stimulated by angiotensin II

Question 47

What does aldosterone do?

Answer 47

increases reabsorption of Na+ and secretion of K+

Question 48

What does the increased blood Na+ concentration result in?

Answer 48

Increased blood volume and blood pressure

Question 49

What is the function of collecting tubules and ducts?

Answer 49

concentrate urine by passive reabsortion of water into medulla

Question 50

Describe the structure of collecting tubules/ducts

Answer 50

cuboidal -> columnar cells

Question 51

What does the juxtaglomerular apparatus do?

Answer 51

It regulates systemic blood pressure using RAAS and provides feedback to regulate filtration

Question 52

What are the two components of the JGA?

Answer 52

JG cells (produce renin) -> aldosterone release from adrenal cortex -> increase Na resorption in DCT Macula densa -> monitor Na+ level in filtrate and decreased sodium results in increased renin secretion

Question 53

What do diuretics do? provide examples

Answer 53

increase excretion of Na and H2O , and include caffeine, alcohol, medications

Question 54

What is hypohydration?

Answer 54

a state of water deficit and can be due to high temp, excess sweating as well as diuretics

Question 55

What are 3 metabolic waste products?

Answer 55

1. urea - abundant waste product and by product of AA breakdown 2. creatinine 3. uric acid - by product of recycling nitrogenous bases of RNA

Question 56

Describe the negative homeostatic mechanism of ADH when there is a water deficit in the body

Answer 56

Water deficit ---> increased extracellular osmolarity --> increased ADH secretion from posterior pituitary --> increased plasma ADH -> increased H2O permeability in distal tubules and collecting ducts ---> increased H2O reabsorption --> less H2O excreted

Question 57

When ADH levels are low, urine will be what?

Answer 57

More dilute urine

Question 58

When ADH levels are higher, urine will be what?

Answer 58

more concentrated, as water will move into the concentrated interstitial space.