Physiology Exam 3 Lecture 10C [Renal Anatomy and Glomerular Filtration: Cabeza]

Role of the Kidney

Purify the blood

General way Kidneys do their function

Step one: Remove all dissolved material from plasma

Step two: Only take up what you want

Step three: Return the plasma with the good stuff

Body fluids

Total body water: 60% of body weight

Intracellular Water: 40% of body weight

Extracellular water: 20% of body weight

- Interstitial water= 15% body weight

- Plasma = 5% of body weight

Any fluid intake and output is from the

Plasma

The interstitial fluid must then equilibrate with the plasma and then the intracellular fluid must equilibrate with the interstitial fluid

Major corporeal fluid intake

GI (30 min to equilibrium)

Major corporeal fluid removal

Kidneys, lungs, and skin

The major cation in the plasma is

Na+

The major anion in the plasma

Cl

and

Bicarbonate

Major cation in the interstitial fluid

Na

Major anion in the interstitial fluid

Cl

and

Bicarbonate

Plasma has a lot of proteins and interstitial fluid

does not

Intracellular fluids major cation

K+

Intracellular fluids major anion

Phosphate

Hyponatremia

Plasma Na less than 135 mEq/L

- Increase in ICF volume - cell swelling

- Over-hydration/lack of Na+/vomiting/excessive sweating

Hypernatremia

Plasma Na over 145 mEq/L

- Decreased ICF volume - cells shrinking

- Drinking seawater-soy sauce/ inadequate water intake/excessive loss of water

Hypokalemia

Plasma K less than 3.5 mEq/L

- Cell hyperpolarization

- Excessive alcohol.diarrhea/diarrhea/diuretics/ excessive sweating

Hyperkalemia

Plasma K+ over 6 mEq/L

- Cells excitability increased - especially heart

- Kidney disease/diuretics/high intake of K in foods

Note:

Not normally a problem with working kidneys

SUMMARY: Body water is mainly

inside cells

SUMMARY: Extracellular water is in the

interstitial space of in plasma

SUMMARY: Major changes to body water are the result of

water ingestion, urine production, sweating, and breathing

SUMMARY: The major cation/anion in intracellular water is

K+/PO4

SUMMARY: The major cation/anion in extracellular water (plasma, interstitial fluid) is

Na/Cl

SUMMARY: Changes to extracellular Na and K

can be very dangerous

Kidneys work at high

arterial pressures

Renal artery

Branch off the aorta coming into the kidney

Renal vein

Blood flow back to the vena cava from the kidney

ureter

From each kidney: travels down the abdomen to the urinary bladder.

Derek Note:

Just your friendly little Piss carrier

Urinary bladder

Stores piss

When its time to empty the urinary bladder

Empties through the urethra

Kidneys are located within

the rib cage which offers some protection

From the Pyramid into the kidney we call it the

Medulla

All the pyramids collect into

the renal papilla which lead to a urine draining area and exits through the renal pelvis and down the ureter

The business end of the kidneys

The Nephron

Two kinds of nephrons

Cortical nephrons

- 80% of all nephrons

Juxtamedullary nephrons

- 20% of all nephrons

Juxtamedullary nephron

Long loop that connects into the collecting duct

Cortical nephron

Short loop that connect into the collecting duct

Parts of the nephron (general)

Glomerulus

- Afferent arteriole

- Efferent arteriol

Bowman's capsule

Proximal convoluted tubule (PCT)

Loop of Henle

Distal tubule

Collecting duct

Parts of the nephron

Loop of henle's job

Make urine dilute

Juxtaglomerular apparatus role

Feedback auto-regulation of glomerular filtration rate

Bowman's capsule/glomerulus =

glomerular filtration

SUMMARY: The renal system works at higher

arterial pressures than most other organs

SUMMARY: The functional unit of the kidneys are the

nephrons

SUMMARY: Two types of nephrons

Cortical nephrons: Have short loop of henle and make up 80% of the nephrons

Juxtamedullary nephrons: Have long loop of henle and make up 20% of the nephrons

SUMMARY: The different part of the nephron do very different jobs and have a complicated spatial position:

1. Bowman's capsule

2. Proximal convoluted tubule

3. Loop of Henle

4. Distal convoluted tubule

5. Collecting ducts

SUMMARY: The juxtaglomerular apparatus sits between

the distal convoluted tubule and the glomerulus

Basic function of the kidneys

Glomerular filtration:

- 5% of our plasma is filtered into the proximal tubule every minute by glomerular filtration. At this rate we would lose our entire blood volume in 20 minutes

Tubular reabsorption

- Substances that we need back such as water, glucose, amino acids, peptides, essential ions or minerals are almost entirely reabsorbed from the proximal tubule back into the blood

Tubular secretions

- Excretory products such as urea and protons to maintain acid-base balance are secreted into the ducts for elimination in urine

Glomerular filtrations begins the process of

renal reulation

Important materials from the filtrate are

reabsorbed

Some wastes or excress materials are

secreted

Water balance is

critically regulated by the kidney

Filtration of the plasma takes place at

Bowmans capsule

Reabsorption primarily takes place at the

proximal convoluted tubule

- Amino acids, glucose, fatty acids, etc

Regulation of excess materials primarily is dealt with at the

distal convoluted tubule

- Potassium secretion and some sodium reabsorption

TIP: Almost all the regulation (excluding the glomerular apparatus) takes place at the

distal end

Water balance requires the concerted actions of the

loop of Henle, the distal convoluted tubule, and the collecting ducts

- Highly regulated process at the distal convoluted tubule and the collecting ducts

We filter 125mL/min of blood volume into nephrons. Since plasma volume is only 2.8L, we would lose our entire blood volume in 22 minutes.

We are saved by our bodies ability to

reabsorb essentially everything that is important to us

Substance reabsorption rates (%): Water

Reabsorbed: 99

Excreted: 1

Substance reabsorption rates: Sodium

Reabsorbed: 99.5

Excreted: 0.5

Substance reabsorption rates: Glucose

Reabsorbed: 100

Substance reabsorption rates: Urea

Reabsorbed: 50

Excreted: 50

Substance reabsorption rates: phenol

Reabsorbed: 0

Excreted 100

SUMMARY: The renal system basically accomplished 4 main functions

1. Glomerular filtration

2. Reabsorption of needed materials

3. Excretion of unwanted materials

4. Regulation of water balance (homeostasis)

SUMMARY: Bowman's capsule is responsible for the

glomerular filtration

SUMMARY: the proximal convoluted tubule is primarily responsible for the

reabsorption of needed materials

SUMMARY: The distal convoluted tubule regulates the

secretion of K and the uptake of Na

SUMMARY: The loop of Henle, the distal convoluted tubules and the collecting ducts work in concert to regulate

water balance

SUMMARY: Actions at the distal convoluted tubule and the collecting ducts are

highly regulated

The Filtration of the blood plasma occurs at the

Bowman's capsule/glomerulus

The juxtaglomerular apparatus helps to

regulate how the glomerulus works

- Are we filtering to much or not enough plasma

The Glomerular capillaries are operating under _______ and are still only one cell thick

high pressure

The endothelial layer of the glomerular capillaries has a lot of finestra that are basically holes that allow for

the leakiness properties of these capillaries

In order to give the capillaries strength they are surrounded by a specialized cell called a

podocyte

Podocyte

foot structures in contact with capillary endothelium to create a regulated filtration barrier

Three primary filtration layers of the glomerular capillaries

1. Fenestrated endothelium: Provides pores that line the capillary

2. Glomerular Basement membrane

3. Filtration slits between podocyte foot structures

The glomerular basement membrane has what kind of charge

Negative

Derek Note:

- Like my attitude while I do this at 8:30pm when I'd rather be asleep

The negative change of the basement membrane allows for

repelling of negative charged proteins and forcing them to be retained in the plasma

- Makes the kidney not have to deal with these proteins (they keep their asses in the plasma like good little boys)

Fenestrated endothelium is very

leaky and acts like a sieve

Glomerular basement membrane is very

negatively charged and prevents proteins from going through

Filtration slits are controlled by the

podocytes and determine filtration rate by changing the filtration constant

Glomerular Filtration Rate

Glomerular Filtration Rate: Kf

Filtration coeffiecient

Glomerular Filtration Rate: PGC

Glomerular capillary hydrostatic pressure

Glomerular Filtration Rate:PBS

Bowman's space hydrostatic pressure

Glomerular Filtration Rate: πGC

Glomerular capillary oncotic pressure

Glomerular filtration rate: Why is there no oncotic pressure of Bowmans capsule (interstitial fluid)

because of that negative basement membrane not allowing for any proteins to get in.

Change GFR by

Changing the permeability (podocyte slits)

Change the pressure

Small changes in MAP

do not lead to large changes in GFR because of the myogenic regulation of the blood vessels entering the glomerulus

SUMMARY: Glomerular filtration takes place in

Bowman's capsule

SUMMARY: The glomerulus consists of three barriers

1. fenestrated glomerular capillaries (very leaky)

2. Glomerular basement membrane - highly negatively charged to prevent proteins from leaving the capillary

3. Podocytes- maintain capillary stability and control the filtration slits that primarily regulate the filtration coefficient

SUMMARY: The primary pressures for glomerular filtration are

capillary hydrostatic pressure

Bowman's capsule hydrostatic pressure

Capillary oncotic pressure

SUMMARY: Most of the hydrostatic and oncotic pressure

Do not vary much (under physiological conditions) and so the filtration coefficient is the main factor determining rate of filtration

The distal tubule interacts with the arterioles

To form a network of cells that create a feedback system

Monitors nephron function to allow compensation through changes in afferent and efferent arteriole pressures

Three cell types of the network of cells that create the feedback system from the distal tubule and arterioles

Mesangial cells

Macula densa

Granular cells

Mesangial cells have 4 major functions at the glomerulus

1. Physically support the capillaries

2. Adjust contractions based on blood pressure

3. Remove proteins adhering to glomerular filter

4. Provide part of immune responses at the glomerulus

Macula densa cells primarily

respond to changes in the level of Na+ in the distal tubule

High Na: Too high GFR

Low Na: Too low GFR

NOTE:

These cells are a physical part of the distal tubule

Granular cells release

Renin to control blood pressure (MAP)

If the salt load is high = GFR high and thus

Macula densa cells scerete ATP and adenosine that signal to P2X receptors on the afferent arterioles causing constriction of the vessel, reducing blood flow, decreasing capillary pressure and thus GFR

If salt load is low = GFR low and thus

Macula densa secrete Nitric Oxide (vasodilator). Causes vasodilation and thus increase GFR

Just gotta know this figure