The main role of the kidney is _______
Kidneys maintain the composition and volume of extracellular fluid (Extracellular fluid homeostasis)
How do you approximate the total body fluid based on a person's weight?
Total body fluid = 60% of body weight in kg. E.g. A 70 kg person has 42 L of total body fluid (0.6)70 = 42
What proportion of the total body fluid is intracellular fluid? how about extracellular fluid?
Intracellular fluid = 2/3 of the total body fluid Extracellular fluid = 1/3 of the total body fluid
What is intracellular fluid?
Intracellular fluid is the volume of all of the cells in the body. It contains fluid as well as other substances (e.g. electrolytes, proteins, etc)
Approximately how many cells are in an average body?
True or False: The concentration of intracellular fluid is similar from cell to cell and even across species
True or False: Intracellular Fluid is considered to be one compartment
What is extracellular fluid?
Extracellular fluid is the supportive environment for the cells and cellular processes that is made up of fluid and other substances( e.g. electrolytes, etc).
Extracellular fluid is made up of _____ and ____
plasma, interstitial fluid
What is plasma?
It is the non-cellular part of blood
What is interstitial fluid?
The fluid that occupies the space between cells
True or False: Plasma and interstitial fluid are constantly mixing and have the same concentration.
_____ and _____ interact across the capillary membrane. _____ and _____ interact across the cell membrane.
Plasma, interstitial fluid Interstitial fluid, intracellular fluid
All fluid intake and output (kidneys, lungs, feces, sweat, and skin) are directly from what fluid compartment? A. plasma B. Interstitial fluid C. Intracellular fluid
What are the main components of extracellular fluid? (4)
1. Sodium 2. Chloride 3. Bicarbonate 4. Calcium
What are the main components of intracellular fluid? (4)
1. Potassium 2. Phosphate 3. Magnesium 4. Proteins
True or False: Extracellular fluid has an optimal composition to sustain cellular processes.
Explain Water Balance
Water balance is part of the homeostasis that the kidneys try to achieve when managing the extracellular fluid.
Here is the example used in class:
What are the 2 input components of water balance? Which one has the highest volume?
1. Ingestion of fluids and food
2. Metabolic processes
What are the 3 output components of water balance? Which one has the highest volume?
1. Sweat and feces
2. Insensible losses (respiration, skin, etc)
For regulated substances, ingestion is ______ of insensible losses
Maintenance of ECF is achieved by regulating _____
Kidneys regulate ECF in what 4 ways?
3. Electrolyte composition (Na+, K+, Ca2+, PO43-)
4. pH (via bicarbonate)
Other than ECF, what do the kidneys regulate excretion of? (4)
- non-volatile acids
- drug metabolites
How do kidneys regulate blood pressure? (2)
1. Water and Na+ regulation
2. Renin-angiotensin system
What is the average size and weight of a kidney?
Size: 9-11 cm (fist)
Weight: 150 grams (apple)
What is a nephron?
A nephron is the most basic unit of renal structure and function
About how many nephrons are in one kidney?
What are the 2 capillary beds in nephrons?
True or False: a Glomerular capillary bed and a peritubular capillary bed are arranged in series
Glomerular filtration allows free passage of ___ and ____ into the tubule but ____, _____, and _____ remain in the blood.
Water and solutes;
larger proteins, lipids (i.e. colloids), and blood cells
What's the purpose of tubular reabsorption?
To recapture the filtered components that the kidney wishes to regulate.
True or False: Regulated substances in excess of those required to maintain a constant ECF environment are excreted
True or False: nephrons secrete substances from peritubular blood capillaries into the tubules.
True or False: in nephrons, some substances are both reabsorbed and secreted
ECF sensors regulate _____.
Tubular processing (reabsorption, secretion)
Kidneys receive ____% of the cardiac output
Renal blood flow (RBF) is about ____ L/min
Renal plasma flow (RPF) is about ______ mL/min
What is the filtration fraction? What is a normal value for filtration fraction?
In renal physiology, the filtration fraction is the ratio of the glomerular filtration rate (GFR) to the renal plasma flow (RPF). Filtration Fraction, FF = GFR/RPF The filtration fraction, therefore, represents the proportion of the fluid reaching the kidneys which passes into the renal tubules.
It is normally about 20%.
About how many liters of fluid are filtered by the kidneys per day?
What is filtrate?
Filtrate is the fluid and substances that pass from the glomerular capillaries into the tubules
About how much urine is excreted per day?
True or False: more than 99.9% of water filtered by the glomerulus is reabsorbed
For most substances, filtration and reabsorption rates are much greater than the excretion rates. What are the advantages of this? (2)
1. High filtration allows kidneys to rapidly remove waste products
2. High filtration and reabsorption allows kidneys to precisely and rapidly control the volume and composition of body fluids.
For example, the GI system has the capacity to add a large amount of unregulated material into the ECF in a short amount of time. The kidneys need a high rate of filtration and reabsorption to properly regulate the ECF to meet optimal conditions.
True or False: Kidneys produce erythropoetin (EPO).
True. Erythropoietin, also known as EPO, hematopoietin, or hemopoietin, is a glycoprotein hormone that controls erythropoiesis, or red blood cell production.
Do kidneys participate in gluconeogenesis?
Yes. Kidneys participate in gluconeogenesis (the production of glucose)
What active vitamin do kidneys produce?
Active Vitamin D (calcitriol; 1,25-dihydroxyvitamin D)
What is regulated through the renin-angiotensin axis?
What produces Renin? What does Renin do?
The kidney produces renin. Renin converts angiotensinogen into angiotensin I.
What converts angiotensin I into angiotensin II?
Angiotensin-converting enzyme (ACE)
What is the stimulus for the renin-angiotensin axis?
What does angiotensin II do?
It causes vasoconstriction which increases blood pressure
What is the rate-limiting step for the renin-angiotensin axis?
Renin (controlled by the kidneys)
In the renin-angiotensin axis, what are the 3 targets for control?
Blocking ACE from converting Angiotensin I to Angiotensin II
Blocking the angiotensin II receptors