Intro to Kidneys & Body Fluid

Question 1

How much of our body weight is made up of water?

Answer 1

Total body water: 60% body weight

Question 2

How much of our body weight is composed of intracellular water?

Answer 2

Intracellular water: 40% body weight (ICF compartment)

Question 3

How much of our body weight contributes to ECF?

Answer 3

Extracellular water: 20% body weight (ECF compartment)

Question 4

How does water move between ICF and ECF?

Answer 4

Osmosis determines movement of water between ICF and ECF

Question 5

Describe the water content of a 70kg average man

Answer 5

A 70kg man,
60% water by weight: total body water is 42 L
40% body weight will be intracellular (ICFV = 28L)
20% extracellular (ECFV = 14L)

Question 6

What are the 2 components of ECFV?

Answer 6

The ECFV consists of two sub-compartments:

• Plasma (3L)
• Interstitial fluid (11L)

Question 7

How do substances move between plasma and Interstitial fluid?

Answer 7

Starling forces from capillary filtration determine fluid and solute movement between plasma and interstitial fluid

Question 8

What is osmolarity?

Answer 8

Total concentration of osmotically active solutes

Question 9

How is movement between ICF and ECF regulated?

Answer 9

Solute composition of ECF and ICF differs, but osmolarity must be kept the same to avoid excessive shifts of water between ECF and ICF

Question 10

What determines ECF osmolarity?

Answer 10

Sodium is the principal electrolyte of the ECF, therefore sodium (with associated anions) is the major determinant of ECF osmolarity

Question 11

What is the significance of body fluids?

Answer 11

Cell structure + function
- Large shifts between ECFV / ICFV disrupts tissue
structure + function

Tissue perfusion

• Depends on balance between circulating volume
  (plasma) + interstitial volume

Question 12

What 2 key processes determine salt and water balance?

Answer 12

Osmoregulation and volume regulation

Question 13

What is osmoregulation?

Answer 13

The maintainance of osmotic equilibrium between ICFV and ECFV

Question 14

What is meant by volume regulation?

Answer 14

Maintaining adequate ECFV to support plasma volume

Question 15

How is plasma osmolarity estimated?

Answer 15

2[Na] + 2[K] + [glucose] + [urea] (all in mmol L-1)

Question 16

How is osmolarity of a solution changed?

Answer 16

1. Add/remove solute

2. Add/remove water

Question 17

How does the body achieve osmoregulation?

Answer 17

The body accomplishes osmoregulation by adding or removing water not sodium

Question 18

Explain the effect of increasing plasma osmolarity

Answer 18

Plasma osmolarity rises – more water needed

Kidneys respond by producing small volume of concentrated urine (water retention)

Question 19

What is the effect of decreasing plasma osmolarity?

Answer 19

Plasma osmolarity falls – too much water

Kidneys respond by producing large volume of dilute urine (water excretion)

Question 20

What is volume regulation referring to?

Answer 20

Refers specifically to the control of the circulating (plasma) volume

Question 21

How does the body achieve volume regulation?

Answer 21

Changes detected by stretch / pressure receptors in CVS

A fall in blood volume is opposed by Na retention; water follows osmotically, restoring volume

Question 22

What is the main function of the kidneys?

Answer 22

Kidney function is homeostasis

Urine is a by-product of kidney function

Question 23

What is the significance of the urinary tract?

Answer 23

The urinary tract is important for temporary storage and then to remove the urine from the body

Question 24

List the functions of the kidneys

Answer 24

• Osmoregulation
• Volume regulation
• Acid-base balance
• Regulating electrolyte balance (eg k+, Ca2+, phosphate)
• Removal of metabolic waste products from blood
• Removal of foreign chemicals in the blood (e.g. drugs)
• Regulation of rbc production (erythropoietin)

Question 25

What is a nephron?

Answer 25

Basic unit of structure in the kidney

Question 26

Outline the structural features of nephrons

Answer 26

Consists of special blood vessels and elaborate tubules (tiny tubes) Microscopic, structures 1.25 million per kidney Where urine production begins

Question 27

What major structures does each nephron consist of?

Answer 27

- Blood vessels - The glomerulus - Bowman capsule - The renal tubule

Question 28

Which major vessels supply the kidneys?

Answer 28

Common Iliac artery | Inferior vena cava

Question 29

Outline the blood vessels allowing perfusion through kidneys

Answer 29

``` Renal. A ↓ Segmental. A ↓ Interlobular. A ↓ Arcuate . A ↓ Interlobular. A ↓ Afferent arterioles ↓ Nephrons ↓ Venules ↓ Interlobular. V ↓ Arcuate. V ↓ Interlobular. V ↓ Renal Vein ```

Question 30

How is the kidney supplied with blood?

Answer 30

The whole kidney is supplied by the renal artery which subdivides many times into fine arterioles supplying each nephron, the afferent arteriole

Question 31

How is renal blood drainage carried out?

Answer 31

Drained by the renal vein, which is supplied by venules coming away from each nephron, joining together into larger veins which merge into the renal vein

Question 32

What is between the arterioles and venules?

Answer 32

Complex capillary networks

Question 33

What is the process of urine formation

Answer 33

1. Glomerular Filtration 2. Tubular Reabsorption 3. Tubular Secretion 4. Excretion of water + solutes in urine

Question 34

What is glomerular filtration?

Answer 34

(GFR) - first step in urine production | => amount of filtrate kidneys produce each minute (125 ml/min)

Question 35

What affect does renal failure have on GFR?

Answer 35

GFR is reduced in renal failure

Question 36

Explain how glomerular filtration occurs

Answer 36

Hydrostatic pressure forces fluids + solutes through glomerular capillary membrane Small molecules pass readily- large (proteins) and cells can't pass => leads to plasma ultrafiltrate in Bowman’s capsule

Question 37

What is reabsorption?

Answer 37

Many substances are filtered and then reabsorbed from the tubular lumen into the peritubular capillaries

Question 38

What is the significance of Tubular secretion?

Answer 38

- Disposing substances not already in filtrate - Eliminating undesirable substances e.g. urea + uric acid - Ridding the body of excess K+ ions - Controlling blood pH

Question 39

How is excretion of fluid and solutes regulated?

Answer 39

[ ] of any solute present in urine is given by the amount filtered out of plasma - amount reabsorbed + amount secreted

Question 40

How is water and sodium balance maintained?

Answer 40

1. Changes in water intake/excretion 2. Changes in body fluid osmolarity 3. Sensors (e.g. sensory cells in hypothalamus) detect new ECF osmolarity 4. Effectors (kidneys) adjust amount of water excreted / retained 5. Change in renal water excretion => Intake = output

Question 41

What is the effect of intake / output mismatch?

Answer 41

Mismatch of intake and output will cause a change in osmolarity Shift of water between ICFV and ECFV

Question 42

What can cause water restriction?

Answer 42

Loss of water (sweat, breathing). Thirsty, but no water is available to drink

Question 43

What is the physiological response to water restriction?

Answer 43

Plasma osmolality rises | Response is increased secretion of hormone, ADH

Question 44

What is the effect of ADH on water restriction?

Answer 44

Results in - Decreased urine volume - Increased urine osmolality

Question 45

What is the effect of increased water intake?

Answer 45

Increase in water absorption through GIT - Plasma osmolality falls - Response is reduced secretion of ADH

Question 46

What does reduced ADH cause?

Answer 46

Results in - Urine volume increases - Urine osmolality decreases

Question 47

What is the normal plasma osmolality?

Answer 47

Plasma osmolality is maintained (~280 - 300 mOsmol/Kg) in face of changes in water intake by retaining or by excreting water

Question 48

How is plasma osmolality maintained?

Answer 48

Done by ADH system, kidneys & behavioural thirst response

Question 49

What determines ECF volume?

Answer 49

ECF volume is determined by the amount of sodium in this compartment

Question 50

How is ECFV maintained?

Answer 50

Sodium intake and excretion must be balanced to maintain constant ECF volume Main volume sensors are in the cardiovascular system

Question 51

What is the physiological response to low blood volume?

Answer 51

A fall in blood volume is opposed by hormonal signals promoting sodium retention; water follows osmotically, restoring volume

Question 52

How is sodium balance maintained?

Answer 52

The maintenance of sodium balance is based (mainly) on the control of the ECFV Intake ~ output

Question 53

What hormone systems contribute to Na balance?

Answer 53

Sodium retaining: - RAAS Sodium Eliminating: - ANP

Question 54

Explain how the hormone systems respond to a decreased ECFV

Answer 54

1. Low ECFV / ↓Na excretion 2. ↓ANP 3. ↑RAAS